Nondestructive testing and manufacturing metrology system and method

Abstract

Nondestructive testing and manufacturing metrology systems and methods are disclosed. A sample is measured or detected by a non-destructive system and method. A plurality of light pulses are emitted from the light source. The light pulses are separated into pump pulses and probe pulses. The first probe pulse reaches the surface of the sample after a first duration after the first pump pulse reaches the surface. A second pump pulse reaches the surface after a duration after the first probe pulse. When the second pump pulse reflects out of the sample, the second pump pulse may be altered by an acoustic wave generated by the first probe pulse. The reflected second pump pulse may be analyzed to determine a characteristic of the sample.

Description

[0001] This application is a divisional application based on the Chinese invention patent application with application date of May 22, 2020, application number 2020800379793, and invention name “Non-destructive testing and manufacturing metrology system and method”. Background Art

[0002] Inspecting and measuring materials or products to help ensure the quality of those products is a useful step in manufacturing. This is also true for semiconductor wafers or similar products that include microscopic elements that are not easy to measure. Metrology systems have previously been used to measure such wafers. It would be advantageous to improve those metrology systems, including power consumption, throughput, and performance.

[0003] It is with respect to these and other general considerations that the aspects disclosed herein have been made.In addition, although relatively specific problems may be discussed, it should be understood that these examples should not be limited to solving specific problems identified elsewhere in the background or in this disclosure. Summary of the invention

[0004] Examples of the present disclosure describe systems and methods for measuring, detecting, and manufacturing semiconductors, metal films, and other samples that require microscopic measurement techniques. In one aspect, the technology relates to a method for characterizing a sample through photoacoustic metrology by switching functions associated with a pump beam and a probe beam, wherein a first pump pulse generates a first acoustic wave in the sample. The method includes generating a second acoustic wave by directing a first probe pulse to the surface of the sample after a first duration from the first pump pulse, wherein the first probe pulse reflects off the sample. The method also includes directing a second pump pulse to the surface of the sample after a second duration after the first probe pulse reflects off the surface of the sample, wherein the second pump pulse reflects off the sample and is changed by the second acoustic wave. The method also includes determining a first characteristic of the sample using the reflected second pump pulse.

[0005] In one example, the first duration is less than the second duration. In another example, the method further includes determining a second characteristic of the sample at a first depth based on the first detection pulse, wherein the first characteristic is at a second depth and the second depth is greater than the first depth. In yet another example, the method further includes changing the delay based on adjusting the delay stage. In yet another example, the second pump pulse has a first polarization and the first detection pulse has a second polarization. In yet another example, the method includes directing a third pump pulse and a third detection pulse to a location on the sample that is different from the location to which the first pump pulse and the second detection pulse are directed. In another example, the third pump pulse is a secondary pump pulse separated from the first pump pulse, and the third detection pulse is a secondary detection pulse separated from the first detection pulse.

[0006] In another aspect, the technology relates to a method for characterizing a sample by photoacoustic metrology by switching functions associated with a pump beam and a probe beam. The method includes directing a first pump pulse toward a surface of the sample, wherein the first pump pulse generates a first acoustic wave in the body of the sample, and directing a first probe pulse toward the surface of the sample, wherein the first probe pulse generates a second acoustic wave in the body of the sample. The method also includes directing a second pump pulse toward the surface of the sample, wherein when the second pump pulse is reflected from the surface of the sample, the second pump pulse is altered by the second acoustic wave to produce a reflected second pump pulse. The method also includes determining a first characteristic of the sample at a first depth based on the detected reflected second pump pulse.

[0007] In one example, the method also includes detecting the reflected first probe pulse, and determining a second characteristic of the sample at the second depth based on the detected reflected first probe pulse. In another example, the duration between the first pump pulse reaching the surface and the first probe pulse reaching the surface is less than the duration between the first probe pulse reaching the surface and the second pump pulse reaching the surface. In yet another example, the first depth is greater than the second depth. In another example, the first probe pulse passes through a variable delay stage and the method includes further operations. For example, the method also includes increasing the length of the variable delay stage; after increasing the length of the variable delay stage, directing a third pump pulse to the surface, wherein the third pump pulse generates a third acoustic wave in the sample; directing the second probe pulse through the variable delay stage and toward the surface of the sample, wherein: when the second probe pulse is reflected from the surface of the sample, the second probe pulse is changed by the third acoustic wave to produce a reflected second probe pulse; the second probe pulse generates a fourth acoustic wave in the body of the sample. The method may also include detecting the reflected second probe pulse; and determining a third characteristic of the sample at a third depth based on the detected reflected second probe pulse, wherein the third depth is greater than the second depth.

[0008] In another example, the method further includes directing a fourth pump pulse toward a surface of the sample, wherein when the fourth pump pulse is reflected from the surface of the sample, the fourth pump pulse is altered by a fourth acoustic wave to produce a reflected fourth pump pulse; and determining a fourth characteristic of the sample at a fourth depth based on the detected reflected fourth pump pulse, the fourth depth being less than the first depth. In yet another example, the first probe pulse has a first polarization and the second pump pulse has a second polarization. In yet another example, the first pump pulse and the second pump pulse are parts of a pump beam.

[0009] In another aspect, the technology relates to a system for characterizing a sample by photoacoustic metrology by switching functions associated with a pump beam and a probe beam, wherein a first pump pulse generates a first acoustic wave in the sample. The system includes means for generating a second acoustic wave by directing a first probe pulse to a surface of the sample after a first duration from the first pump pulse, wherein the first probe pulse reflects off the sample; means for directing a second pump pulse to the surface of the sample after a second duration after the first probe pulse reflects off the surface of the sample, wherein the second pump pulse reflects off the sample and is altered by the second acoustic wave; and means for determining a first characteristic of the sample using the reflected second pump pulse.

[0010] In one example, the first duration is less than the second duration. In another example, the second pump pulse has a first polarization and the first probe pulse has a second polarization. In yet another example, the system also includes means for generating a second characteristic of the sample using the reflected first probe pulse. In yet another example, the first characteristic corresponds to a first depth and the second characteristic corresponds to a second depth, the first depth being greater than the second depth.

[0011] In another aspect, the technology relates to a method, the method comprising emitting a light pulse from a light source; separating the light pulse into a pump pulse and a probe pulse; separating the probe pulse into a primary probe pulse and a secondary probe pulse; and directing the pump pulse to a measurement point on a sample. The method also comprises directing the primary probe pulse and the secondary probe pulse to the measurement point on the sample such that: the primary probe pulse arrives at the measurement point after at least a portion of the pump pulse arrives at the measurement point; and the secondary probe pulse arrives at the measurement point after the primary probe pulse arrives at the measurement point. In one example, the method also comprises detecting the primary probe pulse after the primary probe pulse has been reflected from the measurement point; and detecting the secondary probe pulse after the secondary probe pulse has been reflected from the measurement point. In another example, the method also comprises analyzing the detected primary probe pulse and the secondary probe pulse; based on the analysis of the detected primary probe pulse and the secondary probe pulse, approving the sample for an additional manufacturing step; and performing one or more of the additional manufacturing steps based on the approval of the sample. In yet another example, the method also comprises separating the pump pulse into the primary pump pulse and the secondary pump pulse. In yet another example, directing the pump pulse to the measurement point includes directing a primary pump pulse and a secondary pump pulse to the measurement point.In yet another example, the primary pump pulse arrives at the measurement point before the primary probe pulse, and the secondary pump pulse arrives at the measurement point before the secondary probe pulse.

[0012] In another example, the method further includes modulating the pump pulse before separating the pump pulse. In yet another example, the primary pump pulse has a polarization different from a polarization of the secondary pump pulse. In yet another example, the method further includes modulating the probe pulse before separating the probe pulse. In yet another example, the primary probe pulse is directed toward the measurement point at a first azimuth angle and the secondary probe pulse is directed toward the measurement point at a second azimuth angle. In another example, the primary probe pulse arrives at the measurement point less than 9 nanoseconds after the pump pulse arrives at the measurement point; and the secondary probe pulse arrives at the measurement point at least 9 nanoseconds after the pump pulse arrives at the measurement point.

[0013] In another aspect, the technology relates to a system comprising: a light source configured to emit light pulses; a first beam splitter positioned to separate the light pulses into a pump pulse and a probe pulse; and a second beam splitter positioned in a beam path of the probe pulse to separate the probe pulse into a primary probe pulse and a secondary probe pulse. The system also comprises at least one mirror positioned in the beam path of the secondary probe pulse so that the beam path length of the secondary probe pulse is longer than the beam path length of the primary probe pulse; and one or more focusing optics positioned to direct the pump pulse, the primary probe pulse, and the secondary probe pulse to a measurement point on a sample. In one example, the system also comprises an optical modulator positioned in the beam path of the probe pulse and between the first beam splitter and the second beam splitter, wherein the probe beam optical modulator is configured to modulate the probe pulse. In another example, the system further includes one or more detectors, wherein the one or more detectors are positioned to receive the primary detection pulse and the secondary detection pulse after the primary detection pulse and the secondary detection pulse have been reflected off the sample. In yet another example, the system also includes a pump beam optical modulator, which is positioned in the beam path of the pump pulse, wherein the pump beam optical modulator is configured to modulate the pump pulse. In yet another example, the system further includes a third beam splitter, which is positioned in the beam path of the pump pulse to separate the pump pulse into a primary pump pulse and a secondary pump pulse. In yet another example, the system further includes a half-wave plate, which is positioned between the third beam splitter and the focusing optical devices, in at least one of the beam paths of the primary pump pulse or the secondary pump pulse.

[0014] In another example, the system further comprises an adjustable delay stage positioned between the first beam splitter and the second beam splitter and configured to increase a beam path length of the probe pulse, wherein the adjustable delay stage comprises at least three reflectors. In yet another example, the difference between the beam path length of the pump pulse and the beam path length of the secondary probe pulse is configured to cause the secondary probe pulse to arrive at the measurement point at least 9 nanoseconds after the pump pulse arrives at the measurement point. In yet another example, the difference between the beam path length of the pump pulse and the beam path length of the primary probe pulse is configured to cause the primary probe pulse to arrive at the measurement point less than 9 nanoseconds after the pump pulse arrives at the measurement point.

[0015] In another aspect, the technology relates to a method for manufacturing. The method includes emitting a light pulse from a light source; separating the light pulse into a pump pulse and a probe pulse; separating the pump pulse into a primary pump pulse and a secondary pump pulse; and separating the probe pulse into a primary probe pulse and a secondary probe pulse. The method also includes directing the primary pump pulse and the primary probe pulse to a first measurement point on a sample; and directing the secondary pump pulse and the secondary probe pulse to a second measurement point on the sample. In one example, the method also includes detecting the primary probe pulse after the primary probe pulse has been reflected from the first measurement point; and detecting the secondary probe pulse after the secondary probe pulse has been reflected from the second measurement point. In another example, the method also includes analyzing the detected primary probe pulse and the secondary probe pulse; based on the analysis of the detected primary probe pulse and the secondary probe pulse, approving the sample for an additional manufacturing step; and performing one or more of the additional manufacturing steps based on the approval of the sample. In yet another example, the method further includes analyzing a first signal corresponding to the detected primary probe pulse; determining a thickness of a layer of the sample at a first measurement point based on the analysis of the first signal; analyzing a second signal corresponding to the detected secondary probe pulse; and determining a thickness of the layer of the sample at a second measurement point based on the analysis of the second signal. In yet another example, the primary pump pulse has a polarization different from a polarization of the secondary pump pulse. In yet another example, the primary probe pulse has a polarization different from a polarization of the secondary probe pulse.

[0016] In another example, the primary probe pulse has the same polarization as the secondary pump pulse. In yet another example, the method further includes modulating the pump pulse using a first optical modulator before separating the pump pulse; and modulating the probe pulse using a second optical modulator before separating the probe pulse, wherein the pump pulse is modulated at a different frequency than the probe pulse. In yet another example, directing the primary pump pulse and the primary probe pulse to the first measurement point includes directing at least one of the primary pump pulse or the primary probe pulse through one or more optical fibers. In yet another example, directing the secondary pump pulse and the secondary probe pulse to the second measurement point includes directing at least one of the secondary pump pulse or the secondary probe pulse through one or more optical fibers. In another example, the light source is a laser.

[0017] In another aspect, the technology relates to a system comprising: a light source configured to emit light pulses; a first beam splitter positioned to separate the light pulses into a pump pulse and a probe pulse; a second beam splitter positioned in a beam path of the probe pulse to separate the probe pulse into a primary probe pulse and a secondary probe pulse; and a third beam splitter positioned in a beam path of the pump pulse to separate the pump pulse into a primary pump pulse and a secondary pump pulse. The system also comprises one or more focusing optics positioned to: direct the primary pump pulse and the primary probe pulse to a first measurement point on a sample; and direct the secondary pump pulse and the secondary probe pulse to a second measurement point on the sample. In one example, the system further comprises one or more detectors, wherein the one or more detectors are positioned to receive the primary probe pulse and the secondary probe pulse after the primary probe pulse and the secondary probe pulse have been reflected off the sample. In another example, the system further includes at least one processor; and a memory operatively connected to the at least one processor, the memory storing instructions that, when executed by the at least one processor, cause the system to perform a set of operations. The set of operations includes analyzing a first signal from the one or more detectors, the first signal corresponding to the reflected primary detection pulse; determining a thickness of a layer of the sample at a first measurement point based on the analysis of the first signal; analyzing a second signal from the one or more detectors, the second signal corresponding to the reflected secondary detection pulse; and determining a thickness of a layer of the sample at a second measurement point based on the analysis of the second signal.

[0018] In another example, the primary pump pulse has a polarization different from the polarization of the secondary pump pulse. In yet another example, the primary probe pulse has a polarization different from the polarization of the secondary probe pulse. In yet another example, the primary probe pulse has the same polarization as the secondary pump pulse. In yet another example, the system further includes a first optical fiber positioned to receive the secondary pump pulse, the first optical fiber configured to guide the secondary pump pulse to a second measurement point; and a second optical fiber positioned to receive the secondary probe pulse, the second optical fiber configured to guide the secondary probe pulse to a second measurement point. In another example, the system further includes a first optical modulator positioned between the first beam splitter and the third beam splitter, the first optical modulator configured to modulate the pump pulse. In yet another example, the system further includes a second optical modulator positioned between the first beam splitter and the second beam splitter, the second optical modulator configured to modulate the probe pulse at a frequency different from the pump pulse.

[0019] In another aspect, the technology relates to a method comprising directing a pump pulse to a measurement point of a sample, wherein the measurement point of the sample comprises a pillar protruding from a surface of the sample, the pillar having a first layer of a first material and a second layer of a second material; directing a probe pulse to the measurement point of the sample; detecting the probe pulse after it has been reflected from the measurement point on the sample; analyzing a characteristic of the detected probe pulse to determine an internal depth of the first layer; measuring an external height of the pillar at the measurement point; and determining a difference between the measured height of the pillar and the internal depth of the first layer to determine a thickness of the second layer above the surface of the sample. In one example, the measuring of the external height of the pillar is performed using an optical interferometry system. In another example, the measuring of the external height of the pillar is performed using a mechanical measurement system. In yet another example, the measuring of the external height of the pillar is performed using a sonar measurement system. In yet another example, measurement of the external height of a pillar includes: emitting a first electromagnetic wave pulse toward a surface of a sample; detecting the first electromagnetic wave pulse after the first electromagnetic wave pulse has been reflected from the surface of the sample; determining a first distance based on a time between emitting the first electromagnetic wave and detecting the first electromagnetic wave; emitting a second electromagnetic wave pulse toward a top of the pillar; detecting the second electromagnetic wave pulse after the second electromagnetic wave pulse has been reflected from the top of the pillar; determining a second distance to the top of the pillar based on a time between emitting the second electromagnetic wave and detecting the second electromagnetic wave; and determining a difference between the first distance and the second distance to determine the external height of the pillar above the surface.

[0020] In another example, the measurement of the external height of the pillar includes: transmitting a first pressure wave toward the surface of the sample; detecting the first pressure wave after it has been reflected from the surface of the sample; determining a first distance based on a time between transmitting the first pressure wave and detecting the first pressure wave; transmitting a second pressure wave toward the top of the pillar; detecting the second pressure wave after it has been reflected from the top of the pillar; determining a second distance to the top of the pillar based on a time between transmitting the second pressure wave and detecting the second pressure wave; and determining a difference between the first distance and the second distance to determine the external height of the pillar above the surface. In yet another example, the first material is tin-silver (SnAg) and the second material is copper (Cu).

[0021] The present invention is provided to introduce a series of concepts in a simplified form, which will be further described in the following detailed description. The present invention is not intended to identify the key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Additional aspects, features and / or advantages of the examples will be listed in part in the description below, and in part will be apparent from the description, or can be learned by practicing the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Non-limiting and non-exhaustive examples are described with reference to the following figures.

[0023] Figure 1A A portion of an exemplary metrology system for testing a sample is depicted.

[0024] Figure 1B Depicted Figure 1A A schematic diagram of an exemplary metering system is depicted.

[0025] Figure 2A Another exemplary metering system for testing a sample is depicted.

[0026] Figure 2B Another exemplary metering system for testing a sample is depicted.

[0027] Figure 2C A portion of an exemplary metrology system for testing a sample is depicted.

[0028] Figure 3A Another exemplary metering system for testing a sample is depicted.

[0029] Figure 3B Another exemplary metering system for testing a sample is depicted.

[0030] Figure 4 An example of a suitable operating environment for analyzing signals is depicted.

[0031] Figure 5 A portion of an exemplary metrology system for inspecting a sample having pillars is depicted.

[0032] Figure 6 Exemplary methods for detecting samples are depicted.

[0033] Figure 7 Another exemplary method for detecting a sample is depicted.

[0034] Figure 8 Another exemplary method for detecting a sample having pillars is depicted.

[0035] Fig.9A Schematic diagram of a photoacoustic metrology system with a single sensor for measuring pump pulse intensity and probe pulse intensity.

[0036] Fig. 9B Schematic diagram of a photoacoustic metrology system with two sensors for measuring the pump pulse intensity and the probe pulse intensity.

[0037] Fig. 10A Schematic diagram relating the various delay stage settings shown in FIG. 2 a to the measurement depth in the sample.

[0038] Fig. 10B is a diagram showing various delay stage settings.

[0039] Fig.11 The standard timing sequence of photoacoustic pump / probe pulses is shown.

[0040] Fig.12 The timing sequencing of photoacoustic pump / probe pulses according to an embodiment of the present invention is shown.

[0041] Fig.13 An exemplary method for controlling a photoacoustic metrology system is shown.

[0042] FIG. 14A to FIG. 14B An exemplary method for characterizing a sample by photoacoustic metrology is depicted.

[0043] Fig.15 Describes the basis FIG. 14A to FIG. 14B Pulse patterns for the exemplary method depicted. DETAILED DESCRIPTION

[0044] Metrology systems can be used to measure microscopic features of samples such as semiconductor wafers. Metrology systems typically use lasers to generate a beam of light consisting of a series of light pulses. For example, an optical pump pulse and an optical probe pulse can be generated. The pump pulse is directed to a measurement point on the sample and when the pump pulse reaches the sample, an acoustic wave is generated that travels through the body of the sample internally. When the acoustic wave encounters a layer change of the sample or the edge of the sample, the acoustic wave is reflected back toward the surface of the sample. After the pump pulse reaches the sample, a probe pulse is directed to a measurement point on the sample. When the probe pulse reaches the measurement point, if the acoustic wave has reached the surface after reflecting from the layer change of the sample or the edge of the sample, the probe pulse is affected by the acoustic wave. Therefore, analyzing the probe pulse after it is reflected from the measurement point provides information about the sample, such as the thickness of the sample. For example, the time delay between the pump pulse and the probe pulse affected by the acoustic wave indicates the duration of the acoustic wave traveling through the body of the sample. Based on the known speed of sound of the sample material or a specific layer in the sample, the thickness of the sample or layer can be determined from the time the sound travels.

[0045] However, in metrology systems, the delay between the pump pulse and the probe pulse is difficult to increase. For example, in some metrology systems, a single laser pulse is separated into a pump pulse and a probe pulse. In such systems, delaying the probe pulse after the pump pulse is challenging, and the maximum thickness that can be measured is limited by the maximum delay between the pump pulse and the probe pulse. The present technology provides improvements that allow the delay between the pump pulse and the probe pulse to be increased, even if both the pump pulse and the probe pulse are generated from the same laser pulse. Thus, an increased thickness can be measured.

[0046] In addition, the present technology also provides better performance of the metrology system. The improved performance allows for reduced detection or measurement time and increased accuracy of the measurement. For example, the present technology can utilize or recycle light that was previously blocked or wasted in the metrology system. By utilizing previously blocked light, additional measurements can be completed with a single laser pulse. For example, in some examples, multiple measurements of a single measurement point can be achieved with a single laser pulse. Therefore, additional measurements can be completed faster because multiple measurements can be performed with each light pulse emitted from the laser.

[0047] Figure 1AA portion of an exemplary metrology system 100 for measuring or detecting a sample 131 having a first layer 131A and a second layer 131B is depicted. In the system 100, a pump pulse travels along a pump beam path 104 and is directed to a measurement point 132. When the pump pulse reaches the measurement point 132, an acoustic wave 120 is generated that travels internally into the body of the sample 131. The acoustic wave 120 travels through the sample 131 until it reaches the boundary between the first layer 131A and the second layer 131B. At the boundary, a portion of the acoustic wave 120 is reflected back toward the surface of the sample 131, as depicted by the reflected acoustic wave 120R. In addition, a portion of the acoustic wave 120 continues across the boundary into the second layer 131B. When the acoustic wave 120 reaches the edge of the sample 131, it is reflected back toward the surface of the sample 131. After the pump pulse reaches the measurement point 132, a probe pulse travels along a probe beam path 106 to the measurement point 132. The probe pulse reflects from the measurement point 132 and continues along the probe beam path 106 until it reaches the detector 153. The probe pulse is affected by the reflected acoustic wave 120R if the reflected acoustic wave 120R has reached the surface of the sample 131 at about the same time as the probe pulse reaches the measurement point 132. When the reflected probe pulse is detected, the effect of the reflected acoustic wave 120R on the probe pulse can be identified in the signal generated by the detector 153.

[0048] Based on the time between the pump pulse arriving at the measurement point 132 and the probe pulse arriving at the measurement point 132, the thickness (T1) of the first layer 131A and the thickness (T2) of the second layer 131B can be determined based on the speed of sound of the sound wave 120. For example, the first layer 131A can be made of aluminum, and the speed of sound in aluminum is about 64.1 angstroms / picoseconds. In such an example, where the effects of the acoustic wave 120 are seen in a probe pulse that arrives at the measurement point 132 approximately 9,300 picoseconds after the pump pulse, it can be determined that the first layer 131A has a thickness (T1) of approximately 29.8 microns. Similar measurements and determinations can be made to determine the thickness (T2) of the second layer 131B and / or the total thickness (T1+T2) of the sample 131.

[0049] Because the thickness determination is based on the delay between the pump pulse and the probe pulse, increasing this delay allows for the measurement of samples with increased thickness. In situations where the pump pulse and the probe pulse are generated from the same laser pulse, creating or extending the delay is a challenge. The present system 100 provides improvements that allow for increasing the delay between the pump pulse and the probe pulse by incorporating an extended delay stage in the probe beam path.

[0050] Additional details regarding metering system 100 are described in Figure 1B, which depicts a schematic diagram of a metrology system 100. In the system 100, a light source 101, such as a laser, emits light pulses along a beam path 102. A first beam splitter 103 is located in the beam path 102. The first beam splitter 103 separates the light pulses emitted from the light source 101 into pump pulses along a pump beam path 104 and probe pulses along a probe beam path 106. As used herein, a beam splitter is an optical device that can separate an incident light beam or pulse into two or more light beams. In examples, these beam splitters can be plate beam splitters or cube beam splitters, such as cube polarizers.

[0051] The pump pulse follows the pump beam path 104 and reaches the pump beam optical modulator 105. The pump beam optical modulator 105 modulates the pump pulse. In some examples, the pump beam optical modulator 105 modulates the pump pulse. The frequency at which the pump pulse is modulated may be in the range of several megahertz (MHz), such as approximately 5 MHz or 5.5 MHz. Other frequencies may also be utilized. The modulated pump pulse then continues along the pump beam path 104 and reaches a pump beam splitter 107 located after the pump beam optical modulator 105 in the pump beam path 104. The pump beam splitter 107 splits the modulated pump pulse. A portion of the pump pulse continues along the pump beam path 104, and the remainder of the pump pulse is routed along a wasted or blocked pump light path 108 into a wasted or blocked pump beam dump 109 (also referred to as a photon dwelling point). As such, extra light from the pump pulse is wasted. A beam dump as used herein is an optical element used to absorb light, such as a blocked pump pulse.

[0052] The unobstructed portion of the pump pulse continues along the pump beam path 104 into the pump beam delay stage 111. The pump beam delay stage 111 extends the length of the pump beam path 104 and thus increases the time for the pump pulse to reach the measurement point. However, in some examples, the pump beam delay stage 111 may be omitted. The pump beam delay stage 111 includes a first pump beam delay mirror 113, a second pump beam delay mirror 115, a pump beam delay reflector 117, and a third pump beam delay mirror 119. The first pump beam delay mirror 113 directs the pump pulse to the second pump beam delay mirror 115. The second pump beam delay mirror 115 directs the pump pulse to the pump beam delay reflector 117. The pump beam delay reflector 117 directs the pump pulse back to the second pump beam delay mirror 115, which directs the pump pulse to the third pump beam delay mirror 119. The third pump beam delay mirror 119 directs the pump pulses to the pump beam directing mirror 121. The pump beam directing mirror 121 directs the pump pulses to the directing mirror 123, which directs the pump pulses to the plurality of focusing optical devices 125. Some elements of the pump beam delay stage 111 may also be adjustable. For example, the position of the pump beam delay reflector 117 may be adjusted to be closer to or farther away from the second pump beam delay mirror 115. For example, the pump beam delay reflector 117 may be located on a platform controlled by a motor, servo and / or piezoelectric controller, among other possible controllers. Moving the pump beam delay reflector 117 closer to the second pump beam delay mirror 115 shortens the total path length of the pump beam pulses, and thus increases the delay between the pump beam pulses and the probe beam pulses. In contrast, moving the pump beam delay reflector 117 farther away from the second pump beam delay mirror 115 lengthens the total path length of the pump beam pulses, and thus shortens the delay between the pump beam pulses and the probe beam pulses.

[0053] The focusing optics 125 include a focusing mirror 127, a focusing lens 129 and a height detection system 133. The focusing optics 125 are positioned to direct and focus the probe pulse onto a measurement point 132 of the sample 131. Figure 1B In the depicted example, the pump pulse continues from the directional mirror 123 along the pump beam path 104 until the pump pulse reaches the focusing mirror 127. The focusing mirror 127 directs the pump pulse through a focusing lens 129 which focuses the pump pulse to a measurement point 132.

[0054] The pump pulse arrives at the measurement point 132, generating an acoustic wave 120 that travels through the body of the sample 131. The pump pulse also reflects from the measurement point 132 and the reflected pump pulse may be captured by a detector 153 or a beam dump (not shown). In some examples, the reflected pump beam may be filtered out by the detector 153 or before reaching the detector 153, because the reflected pump pulse is typically not analyzed.

[0055] Returning to the first beam splitter 103 discussed above, the first beam splitter 103 also separates the light pulses from the light source 101 into probe pulses that follow the probe beam path 106. The probe pulses travel along the probe beam path 106 and are directed by the probe beam steering mirror 135. The probe beam steering mirror 135 directs the probe pulses to an extended probe beam delay stage 137.

[0056] The extended probe beam delay stage 137 is configured to extend the length of the probe beam path 106 and thus create a delay between the time when the pump pulse arrives at the measurement point 132 and the time when the probe pulse arrives at the measurement point 132. The extended probe beam delay stage 137 creates an unusually long extension of the probe beam path 106, which provides the metrology system 100 with the ability to measure greater depths or thicknesses than previously possible. The extended probe beam delay stage 137 includes a first probe beam delay mirror 139 that directs the probe pulse to a first probe beam delay reflector 141A. The first probe beam delay reflector 141A directs the probe pulse to a second probe beam delay reflector 141B, which directs the probe pulse to a third probe beam delay reflector 141C, which directs the probe pulse to a fourth probe beam delay reflector 141D. From the fourth probe beam delay reflector 141D, the probe pulse returns through the plurality of probe beam delay reflectors 141. For example, the fourth detection beam delay reflector 141D guides the detection pulse back to the third detection beam delay reflector 141C, which reflects the detection pulse to the second detection beam delay reflector 141B, which reflects the detection pulse to the first detection beam delay reflector 141A. Then, the first detection beam delay reflector 141A reflects the detection pulse to the second detection beam delay mirror 143.

[0057] The extended probe beam delay stage 137 may also be adjustable. For example, the first probe beam delay reflector 141A and the second probe beam delay reflector 141B may be located on a platform controlled by a motor, servo and / or piezoelectric controller, as well as other possible controllers. Thus, the first probe beam delay reflector 141A and the third probe beam delay reflector 141C may be moved closer to the second probe beam delay reflector 141B and the fourth probe beam delay reflector 141D. Moving the respective probe beam delay reflectors 141 closer to or further away from each other reduces or increases the total path length of the probe pulse, which reduces or increases the delay between the pump pulse and the probe pulse. Therefore, if a specific delay time is desired, the delay time may be achieved by adjusting the relative position of the probe beam delay reflector 141. In one example, the delay may be configured from zero picoseconds to 9,300 picoseconds.

[0058] In the depicted example, the extended probe beam delay stage 137 includes four probe beam delay reflectors 141 to produce an eight-pass delay stage. In other examples, the extended probe beam delay stage 137 may include more than four probe beam delay reflectors 141. For example, the extended probe beam delay stage 137 may include eight probe beam delay reflectors 141 to produce a sixteen-pass delay stage.

[0059] Once the probe pulse reaches the second probe beam delay mirror 143 from the extended probe beam delay stage 137, the second probe beam delay mirror 143 directs the probe pulse along the probe beam path 106 to an optional probe beam optical modulator 146. The probe beam optical modulator 146 modulates the probe pulse at a frequency different from that of the pump beam light that has been modulated. For example, the probe beam optical modulator 146 can modulate the probe pulse at a frequency that is an order of magnitude different from the modulation frequency of the pump beam. In some examples, the probe beam optical modulator 146 can be omitted. The modulated probe pulse then reaches the probe beam splitter 147. The probe beam splitter 147 splits the probe pulse, which allows a portion of the probe pulse to continue along the probe beam path 106 and another portion of the probe pulse to be directed along the wasted or obstructed probe light path 110 into the wasted or obstructed probe beam dump 149. Thus, the other portion of the probe pulse that is directed along the wasted or obstructed probe light path 110 is effectively wasted.

[0060] Portions of the probe light pulse continue along the probe beam path 106 and pass through a half-wave plate 150. The half-wave plate 150 changes the polarization of the primary probe pulse, such as by rotating the polarization of the primary probe pulse by 90 degrees. Leaving the half-wave plate 150, the probe pulse continues along the probe beam path 106 and reaches a probe beam steering mirror 151. In some examples of the metrology system 100, the half-wave plate 150 and the probe beam splitter 147 may be omitted. In such examples, the probe pulse may travel directly from the extended probe beam delay stage 137 to the probe beam steering mirror 151.

[0061] The detection beam directing mirror 151 directs the detection pulse to the directing mirror 123, which directs the detection pulse to the focusing optical device 125. The focusing optical device 125 focuses the detection pulse onto the measurement point 132 of the sample 131. For example, the focusing mirror 127 directs the detection pulse through the focusing lens 129, which focuses the detection pulse onto the measurement point 132. The detection pulse is then reflected off the surface of the sample 131 to the detector 153. The detector 153 detects the detection pulse after the detection pulse has been reflected from the measurement point 132. The detector 153 can convert the reflected detection pulse into an electrical signal, which can be in a digital format or an analog format. The detector 153 transmits the signal to the signal processing and analysis system 154, where the signal is analyzed. The signal processing and analysis system 154 is capable of determining the thickness of the sample 131 based on the electrical signal received from the detector 153. Additional details regarding a suitable operating environment for the signal processing and analysis system 154 are referred to below. Figure 4 Further detailed discussion.

[0062] By utilizing Figure 1A and Figure 1B The exemplary metrology system 100 depicted can achieve increased thickness measurements as the delay between the pump pulse and the probe pulse increases. Figure 1B In the depicted example, the exemplary metrology system 100 is capable of achieving a delay of at least 9,300 picoseconds between the pump pulse and the pulsed probe beam. With such a delay, a thickness of approximately 30 microns can be measured. Table 1 below identifies the thickness measurement capabilities of the exemplary metrology system 100 based on different types of materials.

[0063]

[0064] Table 1

[0065] More specifically, Table 1 includes a list of material types that can form a layer in the sample in Column 1. The second column includes the corresponding sound speeds for the materials listed in Column 1. The third column then provides a potential thickness measurement for a delay of 9,300 picoseconds between the arrival of the pump pulse at measurement point 132 and the arrival of the probe pulse at measurement point 132.

[0066] Figure 2A Another exemplary metering system 200A for measuring or detecting a sample is depicted. The system 200A collects or recovers samples in other metering systems (such as Figure 1B The probe beam light is wasted or blocked in the metrology system 100 depicted. For example, as described above with reference to Figure 1B As discussed, the detection beam splitter 147 splits the detection pulse so that a portion of the detection pulse follows the wasted or blocked detection light path 110 and is extinguished by the wasted or blocked detection beam dump 149 . Figure 2A The depicted exemplary metrology system 200A harvests wasted light to allow multiple measurements to be performed with a single pulse of light from a light source.

[0067] Similar to the exemplary metering system 100 discussed above, Figure 2A The depicted exemplary metrology system 200A includes a light source 201, such as a laser, that emits light pulses that travel along a beam path 202. A first beam splitter 203 is located in the beam path 202. The first beam splitter 203 separates the light pulses emitted from the light source 201 into pump pulses that follow a pump beam path 204 and pump pulses that follow a probe beam path 206.

[0068] The pump pulse follows the pump beam path 204 and reaches the pump beam optical modulator 205. The pump beam optical modulator 205 modulates the pump pulse. In some examples, the pump beam optical modulator 205 modulates the pump pulse. The frequency at which the pump pulse is modulated may be in the range of several megahertz (MHz), such as a frequency of about 5 MHz or 5.5 MHz. Other frequencies may also be utilized. The modulated pump pulse then continues along the pump beam path 204 and reaches the pump beam splitter 207 located after the pump beam optical modulator 205 in the pump beam path 204. The pump beam splitter 207 splits the modulated pump pulse. A portion of the pump pulse continues along the pump beam path 204, and the remainder of the pump pulse is routed along the wasted or blocked pump light 208 into the wasted or blocked pump beam dump 209 (also referred to as a photon dwelling point). As such, extra light from the pump pulse is wasted.

[0069] The unwasted portion of the pump pulse continues along the pump beam path 204 into the pump beam delay stage 211. The pump beam delay stage 211 extends the length of the pump beam path 204 and thus increases the time for the pump pulse to reach the measurement point. However, in some examples, the pump beam delay stage 211 may be omitted. The pump beam delay stage 211 includes a first pump beam delay mirror 213, a second pump beam delay mirror 215, a pump beam delay reflector 217, and a third pump beam delay mirror 219. The first pump beam delay mirror 213 directs the pump pulse to the second pump beam delay mirror 215. The second pump beam delay mirror 215 directs the pump pulse to the pump beam delay reflector 217. The pump beam delay reflector 217 directs the pump pulse back to the second pump beam delay mirror 215, which directs the pump pulse to the third pump beam delay mirror 219. The third pump beam delay mirror 219 directs the pump pulses to the pump beam directing mirror 221. The pump beam directing mirror 221 directs the pump pulses to the directing mirror 223, which directs the pump pulses to the plurality of focusing optical devices 225. Some elements of the pump beam delay stage 211 may also be adjustable. For example, the position of the pump beam delay reflector 217 may be adjusted to be closer to or farther away from the second pump beam delay mirror 215. For example, the pump beam delay reflector 217 may be located on a platform controlled by a motor, servo and / or piezoelectric controller, among other possible controllers. Moving the pump beam delay reflector 217 closer to the second pump beam delay mirror 215 shortens the total path length of the pump beam pulses, and thus increases the delay between the pump beam pulses and the probe beam pulses. In contrast, moving the pump beam delay reflector 217 farther away from the second pump beam delay mirror 215 lengthens the total path length of the pump beam pulses, and thus shortens the delay between the pump beam pulses and the probe beam pulses.

[0070] The focusing optics 225 include a focusing mirror 227, a focusing lens 229 and a height detection system 233. The focusing optics 225 are positioned to direct and focus the probe pulse onto a measurement point 232 of the sample 231. Figure 2A In the depicted example, the pump pulse continues from the directional mirror 223 along the pump beam path 204 until the pump pulse reaches the focusing mirror 227. The focusing mirror 227 directs the pump pulse through a focusing lens 229 which focuses the pump pulse to a measurement point 232.

[0071] The pump pulse arrives at the measurement point 232, generating an acoustic wave that travels through the body of the sample 231. The pump pulse also reflects from the measurement point 232 and the reflected pump pulse may be captured by a detector 253 or a beam dump (not shown). In some examples, the reflected pump beam may be filtered out by the detector 253 or before reaching the detector 253, because the reflected pump pulse is typically not analyzed.

[0072] Returning to the first beam splitter 203 discussed above, the first beam splitter 203 also separates the light pulses from the light source 201 into probe pulses that follow the probe beam path 206. The probe pulses travel along the probe beam path 206 and are guided by the probe beam steering mirror 235. The probe beam steering mirror 235 guides the probe pulses to the probe beam delay stage 237. The probe beam delay stage 237 is shorter than the probe beam delay stage 237. Figure 1B The depicted extended probe beam delay stage 137 is simpler. The probe beam delay stage 237 includes only two probe beam delay reflectors 241. As such, the total path length of the pump beam cannot be adjusted or extended to have Figure 1B The depicted extended probe beam delay stage 137 is the extent of what is possible. However, in some examples, the extended probe beam delay stage 137 may be utilized in place of the probe beam delay stage 237 .

[0073] When the detection pulse reaches the detection beam delay stage 237, the first detection beam delay mirror 239 guides the detection pulse to the first detection beam delay reflector 241. The first detection beam delay reflector 241A guides the detection pulse to the second detection beam delay reflector 241B, which reflects the detection pulse back to the first detection beam delay reflector 241A. Then, the first detection beam delay reflector 241A reflects the detection pulse to the second detection beam delay mirror 243.

[0074] and Figure 1B Similar to the depicted extended probe beam delay stage 137, the probe beam delay stage 237 may also be adjustable. For example, a first probe beam delay reflector 241A on a platform controlled by a motor, servo and / or piezoelectric controller. Thus, the first probe beam delay reflector 241A may be moved closer to the second probe beam delay reflector 241B. Moving the respective probe beam delay reflectors 241 closer to or further away from each other reduces or increases the total path length of the probe pulse, which reduces or increases the delay between the pump pulse and the probe pulse. Therefore, if a specific delay time is desired, the delay time may be achieved by adjusting the relative position of the probe beam delay reflector 241. In one example, the delay may be configured from zero picoseconds to approximately 4,700 picoseconds.

[0075] Once the probe pulse reaches the second probe beam delay mirror 243 from the probe beam delay stage 237, the second probe beam delay mirror 243 directs the probe pulse along the probe beam path 206 to the probe beam optical modulator 246. The probe beam optical modulator 246 modulates the probe pulse at a frequency different from the modulated pump beam light. For example, the probe beam optical modulator 246 can modulate the probe pulse at a frequency that is different from the modulation frequency of the pump beam. For example, the probe beam can be modulated at about 0.5 MHz. The modulation frequency of the pump beam and the modulation of the probe beam can be represented by a pump-probe modulation ratio. In some examples, the pump-probe modulation ratio can be about 10:1. In other examples, the probe beam can be modulated at a higher frequency than the pump beam. In such examples, the pump-probe modulation ratio can be 1:10. Other pump-probe modulation ratios can also be used, such as 20:1, 5:1, 2:1, 1:2, 1:5, and 1:20, and ranges between these pump-probe modulation ratios. In some examples, the pump-to-probe modulation ratio is at least 10:1 or less than 1:10.

[0076] By modulating the probe pulse and the pump pulse with different frequencies, the light from the pump pulse can be more easily distinguished from the light from the probe pulse. For example, for a sample with a rough surface, the light from the pump pulse can be scattered when reflected from the surface of the sample. The photons from the pump pulse can then reach the detector 153 after reflecting from the sample. However, the light from the pump pulse can cause errors in the final measurement because only the probe pulse is intended to be analyzed. For example, the pump beam light can produce excessive noise in the signal generated from the detector 153. In order to reduce the undesirable effects of the pump pulse photons, the detector 153 can be configured to demodulate the detected light to distinguish the pump pulse light from the probe pulse light. In this way, the accuracy can be improved by separating out any detected pump pulse light to better analyze only the probe pulse light.

[0077] The modulated detection pulse then reaches detection beam splitter 247. Detection beam splitter 247 separates the detection pulse into a primary detection pulse that travels along primary detection beam path 210 and a secondary detection pulse that travels along secondary detection beam path 212. The primary detection pulse is similar to Figure 1B The probe pulse is depicted, and along with Figure 1B 2. The primary probe pulse travels along a path similar to that depicted. For example, the primary probe pulse travels along the primary probe beam path 210 and passes through the half-wave plate 261. The half-wave plate 261 changes the polarization of the primary probe pulse, such as by rotating the polarization of the primary probe pulse by 90 degrees. The primary probe pulse is then directed by the probe beam steering mirror 251. The probe beam steering mirror 251 directs the probe pulse to the steering mirror 223, which directs the probe pulse to the focusing optical device 225.

[0078] However, in system 200A, secondary probe pulses are acquired and utilized, whereas in systems such as Figure 1B In the exemplary metrology system 100 depicted, this light is wasted or blocked. For example, the secondary probe pulse travels along the secondary probe beam path 212, where the secondary probe pulse is directed by the secondary probe beam directing mirror 255 to another secondary probe beam directing mirror 257. The secondary probe beam directing mirror 257 directs the secondary probe pulse to another secondary probe beam directing mirror 259. The secondary probe beam directing mirror 259 directs the secondary probe pulse to a beam path that is then substantially the same as the beam path of the primary probe pulse. For example, the secondary probe pulse is directed by the probe beam directing mirror 251 to the directing mirror 223, which directs the secondary probe pulse to the focusing optics 225. Due to the additional reflective elements in the secondary probe beam path 212, such as the secondary probe beam directing mirrors 255, 257, 259, the total path length of the secondary probe pulse is greater than the total path length of the primary probe pulse. As such, the secondary probe pulse reaches the focusing optics 225 after the primary probe pulse and ultimately reaches the sample 231.

[0079] Focusing optics 225 focuses the primary and secondary probe pulses onto measurement point 232 of sample 231. For example, focusing mirror 227 directs the primary and secondary probe pulses through focusing lens 229, which focuses the primary and secondary probe pulses onto measurement point 232. The primary and secondary probe pulses are then reflected off the surface of sample 231 to detector 253. Detector 253 detects the primary and secondary probe pulses after they have been reflected from measurement point 232. Detector 253 may convert the reflected primary and secondary probe pulses into electrical signals, which may be in digital format or analog format. Detector 253 transmits the signals to signal processing and analysis system 254, where the signals are analyzed. Signal processing and analysis system 254 is capable of determining the thickness of sample 231 based on the signals received from detector 253. Additional details regarding a suitable operating environment for signal processing and analysis system 254 are referenced below. Figure 4 Further detailed discussion.

[0080] Utilizing a secondary probe pulse in addition to a primary probe pulse allows multiple measurements to occur as well as measuring deeper thicknesses. For example, because the secondary probe pulse arrives at the measurement point after the primary probe pulse, the two pump pulses can be analyzed separately. Thus, two thickness measurements can be made from a single light pulse from light source 201, whereas in previous systems, only one measurement could be made from the single light pulse. Such improvements increase the rate at which samples can be measured or detected. In addition, because the path length of the secondary probe pulse is greater than the path length of the primary probe pulse, the delay between the secondary probe pulse and the pump pulse is also greater. For similar reasons as described above, the increase in the delay between the secondary probe pulse and the pump pulse allows for increased thickness measurements.

[0081] In some examples, the primary probe beam path length and the secondary probe beam path length may be substantially the same. In such examples, the primary probe pulse and the secondary probe pulse may be combined and arrive at measurement point 132 substantially simultaneously. Such examples may increase the amplitude of the final probe pulse that arrives at measurement point 132 and is detected by detector 153. By increasing the amplitude of the probe pulse, the signal-to-noise ratio of the signal from detector 153 representing the detected probe pulse may be higher, thereby producing a potentially more accurate result or a result with a higher confidence.

[0082] Figure 2B Another exemplary metering system 200B is depicted. System 200B is similar to Figure 2A The depicted system 200A differs in that it also collects and utilizes previously wasted or blocked light from the pump pulse. Figure 1B As described, when a pump pulse is split by the pump beam optical modulator 105 in the system 100 , a portion of the pump pulse is wasted and directed along a wasted or blocked pump light path 108 to a wasted or blocked pump beam dump 109 . Figure 2B The system 200B in collects and utilizes the wasted pump beam light to generate a secondary pump pulse. The secondary pump pulse is then directed to the measurement point 232 so that it arrives at the measurement point 232 after the primary pump pulse. Combined with the primary and secondary probe pulses, the primary and secondary pump pulses allow two pump-probe beam pairs and therefore allow two separate measurements to be made with a single light pulse from the light source 201.

[0083] More specifically, in Figure 2B In the depicted exemplary system 200B, a light source 201 emits light pulses that travel along a beam path 202. A first beam splitter 203 is located in the beam path 202, and the first beam splitter 203 separates the light pulses emitted from the light source 201 into pump pulses that follow a pump beam path 204 and probe pulses that follow a probe beam path 206. The probe pulses follow the same beam path as described above with respect to FIG. Figure 2A The same beam path as described above. However, the pump pulses are directed and utilized in a different way.

[0084] Leaving the first beam splitter 203, the pump pulse follows a pump beam path 204. The pump pulse follows the pump beam path 204 and reaches a pump beam optical modulator 205. The pump beam optical modulator 205 modulates the pump pulse. In some examples, the pump beam optical modulator 205 modulates the pump pulse. The frequency at which the pump pulse is modulated may be in the range of several megahertz (MHz), such as approximately 5 MHz or 5.5 MHz. Other frequencies may also be utilized. The modulated pump pulse then continues to follow the pump beam path 204 and reaches a pump beam splitter 207 located after the pump beam optical modulator 205 in the pump beam path 204. The pump beam splitter 207 separates the modulated pump pulse into a primary pump pulse that follows a primary pump beam path 214 and a secondary pump pulse that follows a secondary pump beam path 216. The primary pump beam path 214 is coupled to the secondary pump beam path 216 in the embodiment of the present invention. Figure 2A The pump beam paths in the depicted system 200A are substantially the same. However, the secondary pump beam path 216 in the system 200B is different from the beam path in the system 200A.

[0085] The secondary pump pulse travels along the secondary pump beam path 216 to a secondary pump beam steering mirror 263, which directs the secondary pump pulse through a half-wave plate 265. The half-wave plate 265 changes the polarization of the secondary pump pulse, such as by rotating the polarization of the secondary pump pulse by 90 degrees. Once the secondary pump pulse passes through the half-wave plate 265, another secondary pump beam steering mirror 267 directs the secondary pump pulse back onto substantially the same trajectory as the primary pump beam path 214. That is, the secondary pump beam steering mirror 267 directs the secondary pump pulse to a steering mirror 223, which directs the secondary pump pulse to a focusing optic 225 along a similar trajectory as the primary pump pulse.

[0086] Focusing optics 225 focus the primary pump pulse and the secondary pump pulse onto a measurement point 232 of a sample 231. Because the secondary pump beam path 216 is longer than the primary pump beam path 214, the secondary pump pulse arrives at the measurement point 232 after the primary pump pulse.

[0087] In some examples of system 200B, the optical elements in the corresponding beam paths are arranged so that the primary pump pulse arrives at the measurement point 232 first, the primary detection pulse arrives thereafter, the secondary pump pulse arrives thereafter, and the secondary detection pulse arrives last. That is, the order in which the pump pulses and the detection pulses arrive at the measurement point 232 is as follows: (1) primary pump pulse, (2) primary detection pulse, (3) secondary pump pulse, and (4) secondary detection pulse. This ordering of pulse timing is achieved by the arrangement of optical elements in system 200B. For example, the position of the reflector and the adjustment of the delay stage can be used to change the beam path length of each pulse in the corresponding pulses. In order to achieve the above ordering, the total beam path length of the primary pump pulse is the shortest. The beam path length of the primary detection pulse is longer than the beam path length of the primary pump pulse, but shorter than the beam path length of the secondary pump pulse. The beam path length of the secondary pump pulse is shorter than the beam path length of the secondary detection pulse.

[0088] In such examples, the primary pump pulse causes a first acoustic wave to propagate through the body of the sample. Then, when the primary probe pulse is reflected from the measurement point 232, the primary probe pulse is changed by the first acoustic wave. The reflected primary probe pulse is detected by the detector 253 and the signal from the detector can be analyzed to determine the first thickness of the layer of the sample at the measurement point 232. Then, the secondary pump pulse causes a second acoustic wave to propagate through the body of the sample. Then, when the secondary probe pulse is reflected from the measurement point 232, the secondary probe pulse is changed by the first acoustic wave. The reflected secondary probe pulse is detected by the detector 253 and the signal from the detector can be analyzed to determine the second thickness of the layer of the sample at the measurement point 232. The detector 253 transmits the signal to the signal processing and analysis system 254, where the signal is analyzed. The signal processing and analysis system 254 can determine the thickness of the sample 231 based on the signal received from the detector 253. In some examples, depending on the thickness to be measured, the secondary probe pulse can arrive at the measurement point 232 before the primary probe pulse arrives at the measurement point 232. Additional details regarding a suitable operating environment for the signal processing and analysis system 254 are provided below in reference Figure 4 Further detailed discussion.

[0089] The delay between the primary pump pulse and the primary probe pulse determines in part the amount of the first thickness that can be measured using the primary pump-probe pulse pair. Similarly, the delay between the secondary pump pulse and the secondary probe pulse determines in part the amount of the first thickness that can be measured using the secondary pump-probe pulse pair. In some cases, the delay between the primary pump pulse and the primary probe pulse can be substantially the same as the delay between the secondary pump pulse and the secondary probe pulse. In such instances, the measurement made by the primary pump-probe pulse pair is repeated by the secondary pump-probe pulse pair. Such repeated measurements can allow for a higher confidence in the results of the final analysis. In other cases, the delay between the primary pump pulse and the primary probe pulse can be different from the delay between the secondary pump pulse and the secondary probe pulse. In such instances, the first pump-probe pulse pair can be used to measure the first thickness, and the second pump-probe pulse pair can be used to measure a second thickness that is different from the first thickness.

[0090] Figure 2C A portion of an exemplary metrology system 200C for measuring or detecting a sample 231 is depicted. More specifically, Figure 2C A top view of sample 231 is depicted. In the depicted example, primary probe beam path 210 arrives at measurement point 232 at a first azimuth angle and secondary probe beam path 212 arrives at measurement point 232 at a second azimuth angle. Due to the different azimuth angles of primary probe beam path 210 and secondary probe beam path 212, first detector 253 and second detector 379 may be required. For example, a primary probe pulse travels along primary probe beam path 210, reflects off measurement point 232, and is detected by first detector 253. A secondary pulse travels along secondary probe beam path 212, reflects off measurement point 232, and is detected by detector 379.

[0091] Angle 210 is defined between primary detection beam path 210 and secondary detection beam path 212. exist Figure 2C In the depicted example, the primary detection beam path 210 and the secondary detection beam path 212 are orthogonal to each other, and therefore the angle In other examples, the primary detection beam path 210 and the secondary detection beam path 212 need not be orthogonal to each other. For example, in some examples, the angle Between about 45 degrees to about 135 degrees, 45 degrees to 90 degrees, 90 degrees to about 135 degrees, 60 degrees to 120 degrees, and 80 degrees to 100 degrees. The azimuth angle can be selected based on the angle that provides the maximum reflectivity from the measurement point on the sample. In order to achieve different azimuth angles for the primary probe beam path 210 and the secondary probe beam path 212, two sets of focusing optics can be used. In addition or alternatively, fiber optic elements can be integrated into the metrology system to guide the probe pulses to the measurement point 232. For example, the first optical fiber 270 can guide the primary pump pulses to the measurement point 232 and the second optical fiber 272 can guide the secondary pump pulses to the measurement point 232. In some examples, the pump beam can also be guided through one or more optical fibers. For example, the primary pump beam can be guided through the first optical fiber 270 or another optical fiber adjacent to the first optical fiber 270. The secondary pump beam can be guided through the second optical fiber 272 or another optical fiber adjacent to the second optical fiber 272.

[0092] Figure 3A Another exemplary metering system 300A is depicted. Similar to the Figure 2B In the system 200B, Figure 3A The system 300A in the embodiment collects previously wasted or blocked pump beam light and probe light to make multiple measurements with a single light pulse. However, the system 300A is configured to measure two different locations of the sample with a single light pulse. To this end, the system 300A is configured so that the primary pump pulse and the primary probe pulse are directed to a first measurement point 332 on the sample 331, and the secondary pump pulse and the secondary probe pulse are directed to a second measurement point 334 on the sample 331.

[0093] exist Figure 3A In the depicted exemplary system 300A, a light source 301 emits light pulses that travel along a beam path 302. A first beam splitter 303 is located in the beam path 302, and the first beam splitter 303 separates the light pulses emitted from the light source 301 into pump pulses that follow a pump beam path 304 and probe pulses that follow a probe beam path 306. Leaving the first beam splitter 303, the pump pulses follow the pump beam path 304 and arrive at a pump beam optical modulator 305. The pump beam optical modulator 305 modulates the pump pulses. In some examples, the pump beam optical modulator 305 modulates the pump pulses. The frequency at which the pump pulses are modulated may be in the range of several megahertz (MHz), such as approximately 5 MHz or 5.5 MHz. Other frequencies may also be utilized. The modulated pump pulses then continue along the pump beam path 304 and arrive at a pump beam splitter 307 located in the pump beam path 304 after the pump beam optical modulator 305. The pump beam splitter 307 separates the modulated pump pulses into primary pump pulses following a primary pump beam path 314 and secondary pump pulses following a secondary pump beam path 316 .

[0094] The primary pump pulse enters the pump beam delay stage 311. The pump beam delay stage 311 extends the length of the pump beam path 304 and thus increases the time for the pump pulse to reach the first measurement point 332. However, in some examples, the pump beam delay stage 311 may be omitted. The pump beam delay stage 311 includes a first pump beam delay mirror 313, a second pump beam delay mirror 315, a pump beam delay reflector 317, and a third pump beam delay mirror 319. The first pump beam delay mirror 313 directs the primary pump pulse to the second pump beam delay mirror 315. The second pump beam delay mirror 315 directs the primary pump pulse to the pump beam delay reflector 317. The pump beam delay reflector 317 directs the primary pump pulse back to the second pump beam delay mirror 315, which directs the primary pump pulse to the third pump beam delay mirror 319. The third pump beam delay mirror 319 directs the primary pump pulse to the pump beam directing mirror 321. The pump beam directing mirror 321 directs the primary pump pulse to the directing mirror 323. Some elements of the pump beam delay stage 311 may also be adjustable. For example, the position of the pump beam delay reflector 317 may be adjusted to be closer to or farther away from the second pump beam delay mirror 315. For example, the pump beam delay reflector 317 may be located on a platform controlled by a motor, servo and / or piezoelectric controller, as well as other possible controllers. Moving the pump beam delay reflector 317 closer to the second pump beam delay mirror 315 shortens the total path length of the primary pump beam pulse, and thus increases the delay between the primary pump beam pulse and the probe beam pulse. In contrast, moving the pump beam delay reflector 317 farther away from the second pump beam delay mirror 315 lengthens the total path length of the primary pump beam pulse, and thus shortens the delay between the primary pump beam pulse and the probe beam pulse.

[0095] The directional mirror 323 directs the primary pump pulse to a first set of focusing optics 325. The first set of focusing optics 325 includes a focusing mirror 327, a focusing lens 329, and a height detection system 333. The focusing optics 325 are positioned to direct and focus the primary pump pulse onto a first measurement point 332 of the sample 331. Figure 3A In the depicted example, the pump pulse continues from the directional mirror 323 to the focusing mirror 127. The focusing mirror 127 directs the primary pump pulse through the focusing lens 129, which focuses the pump pulse to the first measurement point 332.

[0096] The primary pump pulse arrives at the first measurement point 332, where it generates an acoustic wave that travels through the body of the sample 131. The pump pulse also reflects from the measurement point 332 and the reflected pump pulse may be captured by a detector 353 or a beam dump (not shown). In some examples, because the reflected primary pump pulse is typically not analyzed, the reflected pump pulse may be filtered out by the detector 353 or before reaching the detector 353. For example, a lock-in detection method may be implemented.

[0097] From the pump beam splitter 307, the secondary pump pulse follows the secondary pump beam path 316. The secondary pump pulse is reflected by the secondary pump beam steering mirror 363 through the half wave plate 365. The half wave plate 365 changes the polarization of the secondary pump pulse, such as by rotating the polarization of the secondary pump pulse by 90 degrees. Once the secondary pump pulse passes through the half wave plate 365, another secondary pump beam steering mirror 367 directs the secondary pump pulse to the secondary pump beam steering mirror 369. Thus, as in Figure 2B Unlike the depicted system 200B, the secondary pump pulses in system 300A are not routed to the same beam path as the primary pump pulses. Instead, the secondary pump pulses in system 300A are routed to a secondary beam directing mirror 369, which directs the secondary pump pulses to a second set of focusing optics 371. The second set of focusing optics 371 directs the secondary pump pulses to a second measurement point 334 of the sample 331.

[0098] The second set of focusing optics 371 is similar to the first set of focusing optics 325, except that the second set of focusing optics 371 directs the secondary pump pulse to the second measurement point 334 of the sample 331 instead of the first measurement point 332 of the sample 331. More specifically, the second set of focusing optics 371 includes a second focusing mirror 373, a second focusing lens 329, and a second height detection system 377. The secondary pump pulse is directed by the second focusing mirror 373 through the second focusing lens 375, which focuses the second pump pulse to the second measurement point 334 on the sample 331.

[0099] Returning to the first beam splitter 303 discussed above, the first beam splitter 303 also separates the light pulses from the light source 301 into probe pulses that follow a probe beam path 306. The probe pulses travel along the probe beam path 306 and are directed by a probe beam steering mirror 335. The probe beam steering mirror 335 directs the probe pulses to a probe beam delay stage 337. The probe beam delay stage 337 is similar to that described above and as FIG. 2A to FIG. 2B The depicted probe beam delay stage 237 is substantially the same. However, in some examples, a Figure 1BThe depicted extended probe beam delay stage 137 replaces the probe beam delay stage 337 .

[0100] exist Figure 3A In the depicted exemplary system 300A, when a probe pulse reaches the probe beam delay stage 337, the first probe beam delay mirror 339 directs the probe pulse to the first probe beam delay reflector 341. The first probe beam delay reflector 341A directs the probe pulse to the second probe beam delay reflector 341B, which reflects the probe pulse back to the first probe beam delay reflector 341A. The first probe beam delay reflector 341A then reflects the probe pulse to the second probe beam delay mirror 343.

[0101] Similar to FIG. 2A to FIG. 2B The probe beam delay stage 237 depicted, the probe beam delay stage 337 may also be adjustable. For example, a first probe beam delay reflector 341A on a platform controlled by a motor, servo and / or piezoelectric controller. Thus, the first probe beam delay reflector 341A can be moved closer to the second probe beam delay reflector 341B. Moving the respective probe beam delay reflectors 341 closer to or further away from each other reduces or increases the total path length of the probe pulse, which reduces or increases the delay between the pump pulse and the probe pulse. Therefore, if a specific delay time is desired, the delay time can be achieved by adjusting the relative position of the probe beam delay reflector 341. In one example, the delay can be configured from zero picoseconds to approximately 4,700 picoseconds.

[0102] Once the probe pulse reaches the second probe beam delay mirror 343 from the probe beam delay stage 337, the second probe beam delay mirror 343 guides the probe pulse to the probe beam optical modulator 346 along the probe beam path 306. The probe beam optical modulator 346 can modulate the probe pulse at a frequency different from the modulation of the pump pulse. For example, the probe pulse can be modulated at a frequency of 0.5 MHz. Other frequencies can also be used. For example, a modulation frequency that satisfies the pump-to-probe modulation ratio discussed above can be used. The modulated probe pulse then reaches the probe beam splitter 347. The probe beam splitter 347 separates the probe pulse into a primary probe pulse that travels along the primary probe beam path 310 and a secondary probe pulse that travels along the secondary probe beam path 312.

[0103] The primary probe pulse travels along primary probe beam path 310 and passes through half-wave plate 361. Half-wave plate 361 changes the polarization of the primary probe pulse, such as by rotating the polarization of the primary probe pulse by 90 degrees. The primary probe pulse is then directed by probe beam directing mirror 351 to directing mirror 323, which directs the primary probe pulse to a first set of focusing optics 325. First set of focusing optics 325 directs the primary probe pulse to a first measurement point 332 on sample 331. The primary probe pulse reflects off first measurement point 332 of sample 331, and the reflected primary probe pulse is detected by first detector 353. First detector 353 generates one or more signals based on the detected reflected primary probe pulse. Signal processing and analysis system 354 is capable of determining the thickness of sample 331 at first measurement point 332 based on the signals received from detector 353. Additional details regarding a suitable operating environment for signal processing and analysis system 354 are provided below with reference to Figure 4 Further detailed discussion.

[0104] The secondary probe pulse travels from the probe beam splitter 347 along the secondary probe beam path 312 to the secondary probe beam directing mirror 355. The secondary probe beam directing mirror 355 directs the secondary pump pulse to the secondary probe beam directing mirror 357, which directs the secondary pump pulse to the secondary beam directing mirror 369. The secondary beam directing mirror 369 directs the secondary probe pulse to the second set of focusing optics 371. The second set of focusing optics 371 directs the secondary probe pulse to the second measurement point 334 on the sample 331. The secondary probe pulse reflects off the second measurement point 334, and the reflected secondary probe pulse is detected by the second detector 379. The second detector 379 generates one or more signals based on the detected reflected primary probe pulse. The signal processing and analysis system 354 can determine the thickness of the sample 331 at the second measurement point 334 based on the signals received from the detector 379. In some examples, the first detector 353 and the second detector 379 can be part of a single housing or a single detector. For example, instead of having two detectors, a single large detector may be implemented.

[0105] Thus, the primary pump pulse and the primary probe pulse are directed to first measurement point 332, and the secondary pump pulse and the secondary probe pulse are directed to second measurement point 334. In some cases, the primary pump pulse may arrive at first measurement point 332 at about the same time that the secondary pump pulse arrives at second measurement point 334. In such instances, the primary pump pulse beam path length and the secondary pump pulse beam path length are substantially the same. In other examples, the primary pump pulse may arrive at first measurement point 332 at a different time than the secondary pump pulse arrives at second measurement point 334.

[0106] However, the primary probe pulse arrives after the primary pump pulse at the first measurement point 332. Similarly, the secondary probe pulse arrives after the secondary pump pulse at the second measurement point 334. Therefore, the primary probe pulse has a longer beam path length than the primary pump pulse, and the secondary probe pulse has a longer beam path length than the secondary pump pulse.

[0107] Figure 3B Another exemplary metering system 300B is depicted. Metering system 300B is similar to Figure 3B The metrology system 300A, metrology system 300B depicted also has the ability to measure two different measurement points on a sample using a single light pulse. However, system 300B is able to perform such measurements using a single set of focusing optics, while system 300A includes two sets of focusing optics. In the depicted example, differentiation is achieved by positioning the secondary beam directing mirror 369 so that the secondary pump pulse and the secondary probe pulse are directed to the focusing mirror 327 in the focusing optics 325. The primary pump pulse and the primary probe pulse are also directed to the focusing mirror 327. The incident angle of the primary pump pulse and the primary probe pulse entering the focusing mirror 327 is different from the incident angle of the secondary pump pulse and the secondary probe pulse entering the focusing mirror. Therefore, the primary pump pulse and the primary probe pulse are directed to the first measurement point 332, and the secondary pump pulse and the secondary probe pulse are directed to the second measurement point 334.

[0108] Many elements in system 300B are substantially similar to elements in system 300A. For example, system 300B includes a light source 301 that emits light pulses. The light pulses from light source 301 are separated by a beam splitter 303 into pump pulses along a pump beam path 304 and probe pulses along a probe beam path 306. The pump pulses are modulated by a pump beam optical modulator 305, and the modulated pump pulses are separated by a pump beam splitter 307 into primary pump pulses along a primary pump beam path 314 and secondary pump pulses along a secondary pump beam path 316.

[0109] The primary pump pulse travels through the pump beam delay stage 311 and is directed by the pump beam directing mirror 321 to a directing mirror 323, which directs the primary pump pulse to a focusing optic 325. The focusing optic 325 directs the primary pump pulse to a first measurement point 332 on a sample 331. For example, a focusing mirror 327 directs the primary pump pulse through a focusing lens 329, which focuses the primary pump pulse onto the first measurement point 332 of the sample.

[0110] The secondary pump pulse is guided by the secondary pump beam steering mirror 363 through the half-wave plate 365, and then guided by the secondary pump beam steering mirror 367 to the secondary beam steering mirror 369. The secondary beam steering mirror 369 guides the secondary pump pulse to the focusing optics 325. The focusing optics 325 guides the secondary pump pulse to the second measurement point 334 on the sample 331. For example, the focusing mirror 327 guides the secondary pump pulse through the focusing lens 329, which focuses the secondary pump pulse onto the second measurement point 334 of the sample 331.

[0111] Returning to first beam splitter 303, the probe pulse travels along probe beam path 306 and is directed by probe beam steering mirror 335 to probe beam delay stage 337. The probe pulse travels through probe beam delay stage 337 to probe beam modulator 346. The modulated probe pulse is separated by probe beam splitter 347 into a primary probe pulse that follows primary probe beam path 310 and a secondary probe pulse that follows secondary probe beam path 312. The primary probe pulse travels through half-wave plate 361 and is directed by probe beam steering mirror 351 to steering mirror 323, which directs the primary probe pulse to focusing optics 325. Focusing optics 325 directs the primary probe pulse to first measurement point 332 on sample 331. The primary probe pulse reflects off first measurement point 332 and travels to first detector 353, where first detector 353 detects the reflected primary probe beam. First detector 353 generates one or more signals based on the detected reflected primary probe pulse. The signal processing and analysis system 354 is capable of determining the thickness of the sample 331 at the first measurement point 332 based on the signal received from the first detector 353. Additional details regarding a suitable operating environment for the signal processing and analysis system 354 are provided below with reference to Figure 4 Further detailed discussion.

[0112] The secondary probe pulse travels along a secondary probe beam path 312, where the secondary probe beam path is guided by a secondary probe beam steering mirror 355, which directs the secondary probe beam to a secondary probe beam steering mirror 357. Secondary probe beam steering mirror 357 directs the secondary probe pulse to a secondary beam steering mirror 369, which directs the secondary probe pulse to a second measurement point 334 on sample 331. The secondary probe pulse reflects off the second measurement point 334 and travels to a second detector 379, where the second detector 379 detects the reflected secondary probe pulse. The second detector 379 generates one or more signals based on the detected reflected primary probe pulse. The signal processing and analysis system 354 is capable of determining the thickness of the sample 331 at the second measurement point 334 based on the signals received from the second detector 379.

[0113] In some examples, the diameter of focusing lens 329 can be larger than the diameter of the focusing lens in other examples described above to accommodate both the primary pump pulse and the primary probe pulse and the secondary pump pulse and the secondary probe pulse. In other examples, focusing lens 329 can alternatively be two focusing lenses, such as a first focusing lens for the primary pump pulse and the primary probe pulse and a second focusing lens for the secondary pump pulse and the secondary probe pulse.

[0114] The foregoing examples are generally discussed in terms of a single light pulse from a light source traveling through an exemplary metrology system. In implementations, multiple light pulses are emitted by the light source and each of the light pulses is directed in the same manner by the optical elements of the exemplary system. Other methods for generating light pulses may also be implemented. As used herein, the beam path length of a corresponding pulse from the light source to a corresponding measurement point is measured. For example, in Figure 3B In the exemplary system 300B of FIG. 3 , the beam path length of the primary probe beam is measured from the light source 301 to the first measurement point 332 . Then, the beam path length of the secondary probe beam is measured from the light source 301 to the second measurement point 334 .

[0115] In addition, a greater or lesser number of optical elements may be included in the examples described above, and these optical components may be configured to achieve substantially the same functions. For example, an additional delay stage may be included in the secondary pump beam path or the secondary detection beam path. Including such a delay stage in the secondary detection beam path allows for an additional increase in the delay between the corresponding pump pulse and the detection pulse. Similarly, an additional delay stage may also be included in the secondary pump beam path. The half-wave plate described above may also be omitted in some examples or located in a different beam path. For example, a half-wave plate that is typically located in the primary detection beam path as described above may alternatively be placed in the secondary detection beam path. The half-wave plate located in the secondary pump beam path as described above may also alternatively be located in the primary pump beam path.

[0116] Figure 4An example of a suitable operating environment 400 is shown in which one or more of the examples of the present signal processing and analysis systems, such as the signal processing and analysis systems 154, 254, and / or 354, may be implemented. The operating environment may be directly incorporated into the system disclosed herein, or may be incorporated into a computer system that is separate from the metering system described herein but is used to control the metering system described herein. This is merely one example of a suitable operating environment and is not intended to provide any limitation on the scope of use or functionality. Other computing systems, environments, and / or configurations that may be applicable include, but are not limited to, imaging systems, personal computers, server computers, handheld or laptop devices, multiprocessor systems, microprocessor-based systems, programmable consumer electronics such as smart phones, network PCs, minicomputers, mainframe computers, tablet computers, distributed computing environments including any of the above systems or devices, and the like.

[0117] In its most basic configuration, operating environment 400 typically includes at least one processing unit 402 and memory 404. Depending on the exact configuration and type of computing device, memory 404 (which stores, among other things, instructions for executing the image acquisition and processing methods disclosed herein) may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.), or some combination of the two. Figure 4 406. In addition, the environment 400 may also include storage devices (removable 408 and / or non-removable 410), including but not limited to disks or optical disks or tapes. Similarly, the environment 400 may also have input devices 414 such as a touch screen, keyboard, mouse, pen, voice input, etc., and / or output devices 416 such as a display, speaker, printer, etc. One or more communication connections 412 may also be included in the environment, such as LAN, WAN, point-to-point, Bluetooth, RF, etc.

[0118] The operating environment 400 typically includes at least some form of computer-readable media. Computer-readable media can be any available media that can be accessed by the processing unit 402 or other devices that include the operating environment. For example, the operating environment may include at least one processor and a memory operatively connected to the at least one processor. The memory stores instructions that, when executed by the at least one processor, cause the system to perform a set of operations, such as those described herein, including those described below with reference to Figures 6 to 8 The method operation discussed.

[0119] By way of example and not limitation, computer-readable media may include computer storage media and communication media. Computer storage media include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer-readable instructions, data structures, program modules or other data. Computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical storage, cassettes, tapes, disk storage devices or other magnetic storage devices, solid-state memory or any other tangible medium that can be used to store desired information. Communication media specifically embodies computer-readable instructions, data structures, program modules or other data in modulated data signals (such as carrier waves or other transmission mechanisms), and includes any information delivery medium. The term "modulated data signal" refers to a signal in which one or more of its characteristics are set or changed in some way so that information is encoded in the signal. By way of example and not limitation, communication media include wired media such as wired networks or direct wired connections, and wireless media such as sound, RF, infrared and other wireless media. Any combination of the above should also be included in the scope of computer-readable media. A computer-readable device is a hardware device that incorporates a computer storage medium.

[0120] Operating environment 400 can be a single computer that operates in a networked environment using a logical connection to one or more remote computers. The remote computer can be a personal computer, a server, a router, a network PC, a peer device or other public network node, and typically includes many or all of the elements described above and other elements that are not mentioned in this way. The logical connection can include any method supported by an available communication medium. Such networked environments are common in offices, enterprise-wide computer networks, intranets and the Internet.

[0121] In some embodiments, the components described herein include such modules or instructions that can be executed by the computer system 400, which can be stored on computer storage media and other tangible media and transmitted in communication media. Computer storage media include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information such as computer readable instructions, data structures, program modules or other data. Combinations of any of the above should also be included in the scope of readable media. In some embodiments, the computer system 400 is part of a network that stores data in a remote storage medium for use by the computer system 400.

[0122] Figure 5A portion of an exemplary metrology system 500 for measuring or detecting a sample 531 having a pillar 580 is depicted. The pillar 580 protrudes from a surface 533 of the sample, and the pillar may have a first layer 582 made of a first material and a second layer 584 made of a second material. In some examples, the first material may be tin-silver (SnAg), and the second material may be copper (Cu) or nickel (Ni). Other materials may also be implemented and analyzed using the techniques described herein. The metrology system 500 is used to measure the thickness of the layer within the pillar 580.

[0123] The metering system 500 may include the same as described above with reference to FIGS. Figure 4 Many of the same components as the metrology systems discussed above. Thus, a pump pulse can be generated and directed along the pump beam path 504 to the measurement point 532, and a probe pulse can be directed along the probe beam path 106 to the measurement point 532. When the pump pulse reaches the measurement point 532, an acoustic wave is generated that enters the body of the pillar 580. The acoustic wave propagates through the first layer 582 and is at least partially reflected at the transition between the first layer 582 and the second layer 584. The probe pulse is changed by the reflected acoustic wave, and the reflected probe beam is detected by the detector 553. The thickness of the first layer 582 or the determination of the internal depth D1 can then be determined by analyzing the detected probe pulse (or a signal representing the detected probe pulse).

[0124] The metrology system 500 may also include an external height measurement system 590. The external height measurement system 590 measures the external height H of the pillar 580. The external height measurement system 590 may be an optical interferometry system, such as a scanning white light interferometer (SWLI) system. In such examples, interferometry may be used to measure the external height H of the pillar 580. In other examples, the external height measurement system 590 may be a mechanical measurement system, an acoustic or sonar measurement system, and / or an optical measurement system. After measuring the external height H of the pillar 580 and the internal depth D1 of the first layer 582, the thickness D2 or height of the second layer 584 above the surface 533 of the sample 531 may be determined. For example, the internal depth D1 may be subtracted from the external height H to determine the thickness D2 of the second layer 584 above the surface 533. Although the system 500 is described as specifically including the pillar 580, the system 500 may be used with any protruding structure having multiple material layers other than the pillar.

[0125] Figure 6 An exemplary method 600 for measuring or detecting a sample is depicted. At operation 602, a light pulse is emitted from a light source such as a laser. At operation 604, the light pulse is separated into a pump pulse and a probe pulse. The pump pulse and the probe pulse may be separated by a beam splitter such as a laser. Figure 1B , FIG. 2A to FIG. 2B and FIG. 3A to FIG. 3BThe optical pulses are separated by the beam splitter discussed in . In some examples, the pump beam and / or the probe beam may be modulated. The probe beam may be modulated at a frequency different from the pump beam. In other examples, only the pump beam may be modulated. At operation 606, the probe pulse is separated into a primary probe pulse and a secondary probe pulse. At operation 608, the pump pulse is directed to a measurement point on the sample. The pump pulse may be directed by a plurality of optical components such as a set of focusing optical devices. At operation 610, the primary probe pulse and the secondary probe pulse are directed to a measurement point on the sample. The pump beam may have a polarization different from a polarization of at least one of the primary probe pulse and the secondary probe pulse. In some examples, when each respective probe pulse arrives at the measurement point, the primary probe pulse may have a polarization different from a polarization of the secondary probe pulse. In addition, directing the primary probe pulse and the secondary probe pulse to the measurement point may include directing the primary probe pulse to the measurement point at a first azimuth angle and directing the secondary probe pulse to the measurement point at a second azimuth angle.

[0126] The timing of the respective pulses may be configured such that the pump pulse arrives at the measurement point before the primary probe pulse and the secondary probe pulse. Then, the primary probe pulse may arrive at the measurement point after the pump pulse, and the secondary probe pulse arrives at the measurement point after the primary pump pulse. Such timing may be achieved by positioning the optical components such that the beam path length of the pump pulse is shorter than the beam path length of the primary probe pulse, which is shorter than the beam path length of the secondary probe pulse. In some examples, the primary probe pulse arrives at the measurement point less than 9 nanoseconds after the pump pulse arrives at the measurement point, and the secondary probe pulse arrives at the measurement point at least 9 nanoseconds after the pump pulse arrives at the measurement point. For example, the secondary probe pulse may arrive at the measurement point a few nanoseconds after the primary probe pulse.

[0127] At operation 612, the reflected primary and secondary probe pulses are detected. For example, as described above, when the primary and secondary probe pulses arrive at the measurement point, they reflect off the sample. The reflected probe pulses then arrive at a detector, which detects the reflected probe pulses. Detecting the primary and secondary probe pulses may also include generating one or more signals representing the reflected primary and secondary probe pulses. For example, the detector may convert light in the probe pulses into electrical signals that may be processed and analyzed. At operation 614, a thickness of the sample at the measurement point is generated based on analyzing at least one of the detected primary probe pulses and / or the detected secondary probe pulses. For example, a signal representing the detected primary probe pulse and a signal representing the detected secondary probe pulse may be analyzed to determine the effect of the acoustic waves generated by the pump pulse on either or both of the detected pump pulses. Based on the delay between the pump pulse and the primary and secondary probe pulses, the thickness of the sample may be determined and generated. The generated thickness may be for one or more layers within the sample.

[0128] In some examples, the pump beam may also be separated into a primary pump beam and a secondary pump beam. The primary pump beam and the secondary pump beam are directed to the measurement point. In such examples, the primary pump beam may arrive at the measurement point before the primary probe beam, and the secondary pump beam may arrive at the measurement point after the primary probe beam. Then, the secondary probe beam arrives at the measurement point after the secondary pump beam.

[0129] At operation 616, it may be decided whether to approve the sample based on the thickness measurement results of the system. For example, the sample is intended to be manufactured to have a layer with a specific thickness within a specific tolerance. The acceptable tolerance or range may be predetermined. For example, the manufacturer of the sample may specify a tolerance or range of thickness of a component or layer of the sample. In some examples, the tolerance or range may be based on the minimum or maximum thickness required for the operability of the sample. If one or more thicknesses generated in operation 614 fall within the expected thickness and tolerance, the sample may be approved in operation 616. If one or more thicknesses generated in operation 614 do not fall within the expected thickness and tolerance, the sample may be rejected in operation 616. In some examples, the thickness may not be explicitly generated, and the sample may be approved based on the analysis of the detected primary and secondary detection pulses. In addition, in some examples, the methods disclosed herein may be used to analyze individual chips of a wafer, and each individual chip may be rejected or approved in operation 616 instead of the entire wafer.

[0130] If the sample is approved in operation 616, the method 600 proceeds to operation 618, in which additional manufacturing steps are performed. In an example where the sample is a wafer, the additional manufacturing steps include operations such as back grinding the wafer. The manufacturing steps may also include cleaning and other finishing operations of the sample, including packaging operations. In some examples, the additional manufacturing steps may include additional tests, such as electrical tests of semiconductor devices or chips on the wafer. For example, electrical tests may be performed on each chip on the wafer to determine whether the chip is normal or working as expected. The chips may be virtually classified into virtual boxes based on the test results of the chips. Chips that fail the test may be marked as bad or faulty and placed in a faulty virtual box for the faulty chip. Conversely, chips that pass the test may be marked as good or qualified and placed in a qualified virtual box. After the test, the wafer may be thinned and then cut into individual chips. The chips that have been marked as passing the test are packaged into devices or applications such as memory cards or storage devices and other computer chips. The percentage of chips approved from the test is generally referred to as the yield rate. Once the chip has been packaged, the chip may be further tested to help ensure that the bond from the chip to the rest of the package or device has been properly formed and that performance is still within acceptable limits. The approved packaged device may then be further incorporated into a computing device. For example, where the chip from the wafer is packaged into a memory device, the memory device may be installed or incorporated into a computing device such as a laptop or mobile phone.

[0131] If the sample is not approved in operation 616, the method 600 proceeds to operation 620, where the sample is rejected and may be discarded. In some cases, the rejected sample may be salvageable or recyclable. By measuring or testing the sample before performing additional manufacturing steps such as back grinding and cleaning, the additional manufacturing steps are only performed on samples that are acceptable or within tolerance. Therefore, resources are not wasted finishing samples that are unacceptable or out of tolerance.

[0132] Figure 7 Another exemplary method 700 for measuring or detecting a sample is depicted. The method 700 allows two different measurement points to be measured using a single light pulse emitted from a light source. At operation 702, a light pulse is emitted from a light source such as a laser. At operation 604, the light pulse is separated into a pump pulse and a probe pulse. The pump pulse and the probe pulse may be separated by a beam splitter such as a laser. Figure 1B , FIG. 2A to FIG. 2B and FIG. 3A to FIG. 3B The optical pulses may be separated by a beam splitter as discussed in . In some examples, the pump pulses and / or the probe pulses may be modulated. The pump pulses may be modulated by a first optical modulator, and the probe pulses may be modulated by a second optical modulator. The probe beam may be modulated at a different frequency than the pump beam. In other examples, only the pump beam or only the probe beam may be modulated.

[0133] At operation 706, the pump pulse is separated into a primary pump pulse and a secondary pump pulse. At operation 708, the probe pulse is separated into a primary probe pulse and a secondary probe pulse. At operation 710, the primary pump pulse and the primary probe pulse are directed to a first measurement point on the sample. Directing the primary pump pulse and the primary probe pulse to the first measurement point may also include directing at least one of the primary pump pulse or the primary probe pulse through one or more optical fibers. At operation 712, the secondary pump pulse and the secondary probe pulse are directed to a second measurement point on the sample. Directing the secondary pump pulse and the secondary probe pulse to the first measurement point may also include directing at least one of the secondary pump pulse or the secondary probe pulse through one or more optical fibers.

[0134] When the primary pulse arrives at the first measurement point, the primary pump pulse may have a different polarization than the primary probe pulse, and when the secondary pulse arrives at the second measurement point, the secondary pump pulse may have a different polarization than the secondary probe beam. In some examples, when the pulse arrives at the sample, the primary pump pulse has a different polarization than the polarization of the secondary pump pulse, and the primary probe pulse has a different polarization than the polarization of the secondary probe pulse. In such examples, when the pulse arrives at the sample, the primary probe pulse may have the same polarization as the secondary pump pulse.

[0135] The timing of the respective pulses may be configured such that the primary pump pulse arrives at the first measurement point before the primary probe pulse. Similarly, the secondary pump pulse may arrive at the second measurement point before the secondary probe pulse. Such timing may be achieved by making the beam path length of the primary pump pulse shorter than the beam path length of the primary probe pulse. The beam path length of the secondary pump pulse is also shorter than the beam path length of the secondary probe pulse.

[0136] At operation 714, a primary probe pulse is detected after the primary probe pulse has been reflected from the first measurement point, and a secondary probe pulse is detected after the secondary probe pulse has been reflected from the second measurement point. The reflected primary probe pulse may be detected by a first detector, and the reflected secondary probe pulse may be detected by a second detector. Detecting the primary probe pulse and the secondary probe pulse may also include generating one or more signals representing the reflected primary probe pulse and the secondary probe pulse. For example, the detector may convert light in the probe pulse into an electrical signal that may be processed and analyzed.

[0137] At operation 716, a thickness of the sample at a first measurement point is generated based on analyzing the detected primary detection pulse. For example, a signal representing the detected primary detection pulse may be analyzed to determine the effect of the acoustic waves generated by the primary pump pulse on the primary detection pulse. Based on the delay between the primary pump pulse and the primary detection pulse, the thickness of the sample at the first measurement point is determined and generated. The generated thickness may be for one or more layers within the sample at the first measurement point. Also at operation 716, a thickness of the sample at a second measurement point is generated based on analyzing the detected secondary detection pulse. For example, a signal representing the detected secondary detection pulse may be analyzed to determine the effect of the acoustic waves generated by the secondary pump pulse on the secondary detection pulse. Based on the delay between the secondary pump pulse and the secondary detection pulse, the thickness of the sample at the second measurement point is determined and generated. The generated thickness may be for one or more layers within the sample at the second measurement point.

[0138] At operation 718, a decision may be made to approve the sample based on the thickness measurements of the system. For example, the sample is intended to be manufactured with a layer having a certain thickness within a certain predetermined tolerance. If one or more thicknesses generated in operation 716 fall within the expected thickness and tolerance, the sample may be approved in operation 718. If one or more thicknesses generated in operation 716 do not fall within the expected thickness and tolerance, the sample may be rejected in operation 718. In some examples, the thickness may not be explicitly generated, and the sample may be approved based on an analysis of the detected primary and secondary detection pulses.

[0139] If the sample is approved in operation 718, the method 700 proceeds to operation 720, in which additional manufacturing steps are performed. In an example where the sample is a wafer, the additional manufacturing steps include operations such as backgrinding the wafer. The manufacturing steps may also include cleaning and other finishing operations of the sample, including packaging operations. If the sample is not approved in operation 718, the method 700 proceeds to operation 722, in which the sample is rejected and the sample may be discarded. In some cases, the rejected sample may be salvageable or recyclable. By measuring or testing the sample before performing additional manufacturing steps such as backgrinding and cleaning, the additional manufacturing steps are performed only on samples that are acceptable or within tolerance. Therefore, resources are not wasted finishing samples that are unacceptable or out of tolerance.

[0140] Figure 8Another exemplary method 800 for measuring or detecting a sample is depicted. More specifically, the exemplary method 800 determines different depths of a measurement point having a pillar. At operation 802, a pump pulse is directed to a measurement point of a sample, the measurement point of the sample including a pillar protruding from a surface of the sample. The pillar may have a first layer made of a first material and a second layer made of a second material. For example, the first material may be tin-silver (SnAg), and the second material may be copper (Cu) or nickel (Ni). At operation 804, a probe beam is directed to the measurement point of the sample. At operation 806, the probe beam is detected after the probe beam has been reflected from the measurement point on the sample. At operation 808, characteristics of the detected probe beam are analyzed to determine an internal depth of the first layer.

[0141] At operation 810, the external height of the pillar is measured at the measurement point. The external height of the pillar can be measured in a variety of ways. For example, an optical interferometry system such as a scanning white light interferometer (SWLI) system can be used to measure the external height of the pillar. A confocal microscope or other measurement system can also be used. The measurement of the height of the pillar can also be performed using a mechanical measurement system or a sonar measurement system. Measuring the external height of the pillar can be performed by the same equipment that performs the internal depth measurement of the first layer. For example, an optical interferometry system can be incorporated into the optical interferometry system described above in Figures 1 to 3. Figure 5 In one of the exemplary metrology systems discussed in . In other examples, measuring the exterior height of the pillars can be performed by a different device than the device that performs the interior depth measurement of the first layer. For example, the depth measurement of the first layer can be performed before or after measuring the exterior pillar height. The sample can be passed between two different devices to perform two different measurements.

[0142] Various types of optical measurement systems can be used to determine the external height of the pillar. In such examples, measuring the external height of the pillar can include emitting a first electromagnetic wave pulse toward the surface of the sample. The first electromagnetic wave pulse is detected after it has been reflected from the surface of the sample, and a first distance is determined based on the time between emitting the first electromagnetic wave and detecting the first electromagnetic wave. A second electromagnetic wave pulse can also be emitted toward the top of the pillar. The second electromagnetic wave pulse is detected after it has been reflected from the top of the pillar, and a second distance to the top of the pillar is determined based on the time between emitting the second electromagnetic wave and detecting the second electromagnetic wave. Then, the difference between the first distance and the second distance can be determined, which results in the external height of the pillar above the surface of the sample.

[0143] Various types of acoustic measurement systems can also be used to determine the external height of the pillar. For example, a first pressure wave can be emitted toward the surface of the sample. The first pressure wave is detected after it has reflected from the surface of the sample, and a first distance is determined based on the time between emitting the first pressure wave and detecting the first pressure wave. A second pressure wave can also be emitted toward the top of the pillar. The second pressure wave is detected after it has reflected from the top of the pillar, and a second distance to the top of the pillar is determined based on the time between emitting the second pressure wave and detecting the second pressure wave. The difference between the first distance and the second distance can then be determined, which results in the external height of the pillar above the surface.

[0144] At operation 812, a height of a second layer above the surface of the sample may be determined. The height of the second layer may be determined based on a difference between the measured height of the pillars and the depth of the first layer. For example, the height of the second layer may be determined by subtracting the inner depth of the first layer from the outer height of the pillars.

[0145] At operation 814, a decision may be made as to whether to approve the sample based on the measurements made in performing method 800. For example, the sample is intended to be manufactured to include layers having specific thicknesses within certain predetermined tolerances. If one or more thicknesses generated during performance of method 800 fall within the expected thicknesses and tolerances, the sample may be approved in operation 814. If one or more thicknesses generated during performance of method 800 do not fall within the expected thicknesses and tolerances, the sample may be rejected in operation 814. For example, if the interior depth of a first layer or the thickness of a second layer is required to be within predetermined tolerances, and the measurements indicate that the first layer and / or the second layer do not have characteristics that fall within these tolerances, the sample may be rejected in operation 814, or at least the measured struts may be rejected.

[0146] If the sample is approved in operation 814, method 800 proceeds to operation 816, in which additional manufacturing steps are performed. In an example where the sample is a wafer, the additional manufacturing steps include operations such as backgrinding the wafer. The manufacturing steps may also include cleaning and other finishing operations of the sample, including packaging operations. If the sample is not approved in operation 814, method 800 proceeds to operation 818, in which the sample is rejected and the sample may be discarded. In some cases, the rejected sample may be salvageable or recyclable. By measuring or testing the sample before performing additional manufacturing steps such as backgrinding and cleaning, the additional manufacturing steps are only performed on samples that are acceptable or within tolerance. Therefore, resources are not wasted on finishing samples that are unacceptable or out of tolerance. Although method 800 is described as being applied to pillars, method 800 can be used with any protruding structure having multiple material layers.

[0147] As described above, in single laser photoacoustic techniques, a mechanical delay stage is used to generate a delay between a series of laser pulses used for measurement. Since there is a direct correlation between the linear range of the delay stage and the depth that can be measured in the sample, a longer delay stage is beneficial for measuring a larger depth. However, since the delay stage works by forcing one set of pulses (the probe pulses) to travel a greater distance than the second set of pulses (the pump pulses), the speed of light imposes size limitations on the opto-mechanical delay stage. Longer delays can be proportional to the physical size of the delay stage, and the physical form of the metrology system can limit how much delay the delay stage can produce. However, the physical constraints of the measurement equipment generally prevent the physical size of the delay stage from increasing. Aspects of the present technology can also provide methods and systems for expanding the capabilities of the delay stage without increasing the size of the delay stage.

[0148] Fig.9A An exemplary photoacoustic opaque film thickness metrology system 900 is shown. System 900 is presented in simplified form, and system 900 shares several components of the systems described above. As such, only a rough description of the physical aspects of system 900 will be provided here. Photoacoustic system 900 includes a laser 90 that outputs short light pulses that can be emitted at a rate of about 60 MHz. The emitted pulses are separated into two beams by a beam splitter 903. The first beam is directed through an electro-optic modulator (EOM) 905. This first pulsed beam (also referred to as a "pump" pulse) is directed to a focusing optical device 929, which directs the pump pulse onto the surface of a sample 931. Sample 931 may include a substrate having an opaque film formed thereon.

[0149] Beam splitter 903 directs a second pulsed beam (referred to as a "probe" pulse) through a delay stage 937 and another EOM 946, and then directs the probe pulse through focusing optics 929 onto the surface of substrate 931. The pump pulse and the probe pulse may substantially coincide with each other on the surface of sample 931.

[0150] Fig.9A The use of steering mirrors to form the optical paths of the pump and probe beams is shown. Other devices such as optical fibers may be used to define the optical path from the laser 901 to the sample 931 in addition to the optical path in the delay stage. It is also noted that the optical system shown in FIG9 is simplified and certain aspects of the optical system, such as various optical elements, lenses, filters, apertures, etc., are omitted for clarity.

[0151] Fig. 9B Shows Fig.9A Another embodiment of the system 900 is shown in FIG. 9 , in which two completely independent sensors 953 ′ and 953 ″ are used instead of a single sensor 953. It should be understood that as Fig.9AThe single sensor 953 shown may be arranged to independently and simultaneously measure the intensity of both the pump pulses and the probe pulses originating from the laser 901 . Fig. 9B It is shown that sensors 953' and 953" can be arranged independently of each other.

[0152] One difference between pre-existing optical systems arranged for performing photoacoustic thin film measurements and the system 900 of the present technique is that in the present system 900, both the pump beam and the probe beam are incident on one or more sensors, schematically shown as sensors 953, when returning from the surface of the sample 931. The sensors 953 may include one or more sensors for measuring the intensity of the pump beam and the probe beam and / or the deflection of the pump beam and the probe beam. The sensors 953 may include one or more position sensitive detectors (PSDs) associated with each of the pump beam and the probe beam.

[0153] As described above, photoacoustic film measurement begins by inducing acoustic waves in the sample 931 using a pump beam pulse from the laser 12. Fig. 10A In FIG. 1 , a laser pulse 1000 is incident on the surface of a sample 1031. The laser pulse that causes the acoustic wave is called a pump pulse. The acoustic wave (dashed line 1002) moves through the sample 1031 and interacts with structures within the sample 1031. In the event that the acoustic wave 1002 intersects an object or structure within the sample 1031, a portion of the acoustic wave will be reflected back toward the surface of the sample 1031. Subsequently, a second laser pulse 1000 will be directed to the sample 1031 at a time delay associated with a specific distance below the surface of the sample 1031. In the event that the reflected acoustic wave 1002 reaches the surface of the sample 1031 while the second laser pulse 1000 is incident on the surface, the second laser pulse 1000 will be modified by changes in the surface of the sample. These changes may include changes in the intensity of the second laser pulse 1000 reflected from the sample 1031 to the sensor or a deflection in the position of the reflected laser pulse 100 incident on the sensor.

[0154] A time delay is generated between the pump pulse and the probe pulse of the laser using an opto-mechanical delay stage 937 in which the light is caused to travel different distances. In operation, a single laser pulse from the laser 901 is separated by the beam splitter 903. The resulting discrete laser pulses remain substantially synchronized, even though they do not travel along different branches of the optical path of the system 900. Assuming the optical paths are the same length, the discrete pulses will be incident on the sample 931 at the same time. In the case where the delay stage 937 extends the optical path of the laser pulse therethrough, the additional time required for the laser pulse to move through the delay stage 937 will produce a delay between the pump pulse and the probe pulse.

[0155] Fig. 10B The delay stage 937 position shown may be associated with the depth at which the measurement is made in the sample 931. The '0' position of the delay stage 937 may be associated with examining a structure of the sample 931 at position '0', such as a film interface, e.g. Fig. 10A Extending the delay stage 937 path length (e.g., in Fig. 10B Moving the reflector 9411 between the positions 0, 1, 2, 3, ..., n as shown allows the sensor 953 to identify Fig. 10A Structure at positions 0, 1, 2, 3, ..., n shown. This is possible because the longer delay stage positions allow more time for the acoustic wave 1002 to travel down into the sample 931 and back to the surface.

[0156] One challenge associated with using an opto-mechanical delay stage is that extremely long delay stages may be required to obtain measurements deeper into the sample 931. This is simply because the speed at which the laser pulse moves through the delay stage is much greater than the speed at which the acoustic wave 1002 moves through the sample 931. Light moves at about 3×10^8 m / s, while acoustic waves move through the sample at about 5000 m / s.

[0157] Fig.11 It is shown how the probe beam delay can be modified using the delay-only stage 937 to control the delay between the pump pulse and the probe pulse. Fig.11 The pump pulse 41 in FIG. 1 travels through the EOM 905, and the probe pulse 43 passes through the delay stage 937. Modifying the optical path length using the delay stage 937 can control the time t1 between the incidence of the pump pulse 41 and the incidence of the probe pulse 43 from synchronization to an arbitrary delay limited by the adjustability of the delay stage 937. Fig. 10A and Fig. 10B , at delay stage position '0', the pump pulse and the probe pulse are incident on the sample nearly simultaneously, and at delay stage position 'n', the pump pulse and the probe pulse have reached their maximum separation. Due to limitations of standard operating methods of photoacoustic measurement systems, the time delay between the incidence of the probe pulse and the incidence of the subsequent pump pulse is basically not used.

[0158] One benefit of using an optical arrangement such as that used by system 900 is that pump pulses and probe pulses are interchangeable. After all, both pulses originate from the same laser 1000. For our purposes, the significant difference between pulses following either branch of the optical path through system 900 is that delay stage 937 adds length to the optical path of the pulses passing through EOM 946. From a practical standpoint, it does not matter which beam is used for probe and which is used for pumping, as either will suffice.

[0159] Sensor 953 measures the intensity and / or deflection of both sets of laser pulses, with the result that either set can be used as a probe beam or a pump beam. This has the beneficial effect of allowing the "loss" time mentioned in the previous paragraph to be added to the delay t1. By switching between pump and probe laser pulses as needed, longer delays between pump and probe can be achieved, and structures located deeper within sample 931 can therefore be evaluated. Note that sensor 953 can be separated based on polarization to ensure that there is little, if any, crosstalk between the pump and probe pulses incident on sensor 931.

[0160] In one example, a train of laser pulses is incident on the sample 931 at a substantially constant frequency. The frequency can be varied and is selected so that the period between pulses will allow measurements to be made at a desired depth within the sample 931. Return Figure 11 to Figure 12 , the period between each pump pulse is represented by arrow t0. The delay stage 937 is manipulated to create the delay t1 indicated. The delay t1 is a function of the length of the optical path of the delay stage 937. All structures (e.g., layer / film interfaces or voids) within the shallower portion of the sample 931 are measured. Thereafter, the pump beam and probe beam are nominally switched, and all structures within the deeper portion of the sample 931 are measured. Note that "switching" is not a physical process, and at least this means that the data from the sensor 953 is obtained "relative to" a specific probe / pump arrangement.

[0161] In another embodiment, such as Fig. 9B As shown, two separate sensors 953' and 953" are provided to allow simultaneous measurement of both the probe beam and the pump beam. In this embodiment, sensors 953' and 953" generate signals that can be as follows: Fig.11 As shown or Fig.12 Continuous data flow for the evaluation shown.

[0162] The concepts of "shallow" and "deep" relate to the extent to which the delay stage can be modified to extend or shorten the delay between the pump pulse and the probe pulse, where "shallow" the probe pulse travels through the delay stage and where "deep" the probe pulse does not travel through the delay stage. In the case where the probe pulse travels through the delay stage 937, the delay between the pump pulse and the probe pulse is limited to a depth that is a function of the length of the delay stage 937 and the speed of sound of the acoustic wave in the sample 931. Shallow means that the delay is relatively short and is limited by the extension of the delay stage 937, while deep means that the delay also includes a portion of the laser 901 period t2 that is not addressable by adjusting the delay stage 937. It is noted that in the case of providing pump pulses at a relatively low frequency, the time periods t1 and t2 may not add up to the amount of time t0. In the case where the total delay t1 that can be achieved by the delay stage 937 is greater than the period t0 of the laser 901 or is about half of the period t0 of the laser 901, all or most of the period of the laser 901 can be used to extend the delay. Careful selection of the laser 901 frequency and control of the delay stage length can provide significantly longer delays and allow deeper structures to be measured with very little modification to the system 900. The measurement depth of the system 900 may not extend beyond the position corresponding to the maximum delay. Moving beyond this maximum is possible but requires ignoring or preventing selected probe pulses and / or pump pulses from reaching the sample 931.

[0163] Fig.13 An exemplary method 1300 for controlling a photoacoustic metrology system is depicted. At operation 1302, a pump laser pulse is directed to the surface of a sample. The pump laser pulse travels along a first optical path and may pass through a delay stage before reaching the surface of the sample. In some examples, the pump laser pulse may include a series of laser pulses directed to the surface of the sample at a fixed rate or period. At operation 1304, a probe laser pulse is directed to the surface of the sample through a second optical path, which may include a variable delay stage. The probe laser pulse may include a series of laser pulses directed to the surface of the sample at a fixed rate. At operation 1306, the length of the delay stage is modified, which allows for measurement of at least one characteristic of the sample at a specific or selected depth or depth range. The modification of the delay stage causes the pump pulse or the probe pulse to be directed to the surface of the sample at a variable rate or variable delay period relative to the other pulse. For example, wherein the probe pulse may be variably delayed to produce a variable delay period relative to the pump laser pulse.

[0164] At operation 1308, the intensity and / or deflection of the probe beam and / or the pump beam are measured. For example, in some examples, the intensity and deflection of both the probe beam and the pump beam are measured. The measurement may include using at least one of a first optical sensor and a second optical sensor positioned to receive the first laser pulse and the second laser pulse. The measurement may also include measuring or determining the time it takes for a photoacoustic wave emitted by one of the first laser pulse and the second laser pulse to return to the surface of the sample. The measurement may be performed over a range of delays, where each of the delays is related to a vertical position within the sample. Based on the measurements performed in operation 1308, at least one characteristic of the sample is determined in operation 1310. For example, the thickness of a feature, such as the thickness of an opaque film on the sample, may be determined.

[0165] FIG. 14A to FIG. 14B An exemplary method 400 for characterizing a sample by photoacoustic metrology is depicted. Specifically, the method 400 swaps or switches functions associated with a pump beam and a probe beam. At operation 1402, a first pump pulse from the pump beam is directed to a surface of the sample. The first pump pulse generates a first acoustic wave in the sample. At operation 1404, a first probe pulse from the probe beam is directed to the surface of the sample so that the first probe pulse arrives at the surface of the sample at a first duration after the first pump pulse arrives at the surface of the sample. As discussed herein, the first duration can be controlled or changed by changing the length of the delay stage. However, the first duration is limited by the length of the delay stage. Therefore, the maximum duration of the first duration can be based on the maximum length of the delay stage. The first probe pulse generates a second acoustic wave in the sample. When the first probe pulse reflects off the sample, the first probe pulse can also be affected by the first acoustic wave. At operation 1406, the reflected first probe pulse can be detected by a detector.

[0166] At operation 1408, a second pump pulse is directed to the surface of the sample such that the second pump pulse arrives at the surface of the sample a second duration after the first probe pulse arrives at the surface of the sample. Figure 11 to Figure 12, the second duration (e.g., the time between the first probe pulse and the second pump pulse) is based at least in part on the pulse frequency of the laser generating the pulses. For example, the second duration may be equal to the difference between the pulse frequency of the laser (e.g., the period between pulses) and the first duration (e.g., the time between the first pump pulse and the first probe pulse). Thus, the second duration may be significantly longer than the first duration, which allows measurements to be made at depths of the sample that were previously unavailable. When the second pump pulse is reflected from the surface of the sample, the second pump pulse is affected by the second acoustic wave. The second pump pulse also generates a third acoustic wave in the sample. At operation 1410, the reflected second pump pulse is detected by a detector. To distinguish the second pump pulse from the first probe pulse, the first detector may be used to detect the first probe pulse, and the second detector may be used to detect the second pump pulse. Alternatively or in addition, the first probe pulse may have a first polarization or a first modulation, and the second pump pulse may have a second polarization or a second modulation, so that the first probe pulse can be distinguished from the second pump pulse. In such examples, the first probe pulse and the second pump pulse may be detected by the same detector.

[0167] At operation 1412, one or more characteristics of the sample are determined based on the detected pulses. For example, a first characteristic of the sample may be determined based on the reflected second pump pulse detected in operation 1410. The first characteristic of the sample may be for a first depth in the sample. The first depth of the sample corresponds to a second duration. A second characteristic may also be determined based on the reflected first probe pulse detected in operation 1406. The second characteristic may be for a second depth in the sample. For example, the first characteristic may be a thickness of a first feature or layer of the sample, and the second characteristic may be a thickness of a second feature or layer of the sample. In examples where the first duration (e.g., the time between the first pump pulse and the first probe pulse) is less than the second duration (e.g., the time between the first probe pulse and the second pump pulse), the second depth is less than the first depth. Thus, compared to existing systems, characteristics of the sample may be determined based on the detected probe pulse and / or the detected pump pulse.

[0168] Method 1400 may continue to operation 1414, where the length of the delay phase is changed. Changing the length of the delay phase causes the time between the pump pulse and the probe pulse to change. After changing the length of the delay phase, at operation 1416, the third pump pulse is directed toward the surface of the sample to generate another acoustic wave (e.g., a fourth acoustic wave) in the sample. Then, at operation 1418, a second probe pulse is directed to the surface of the sample. The second probe pulse arrives at the surface of the sample at a third duration after the previous third pump pulse. Depending on whether the delay phase is extended or shortened in operation 1414, the third duration may be longer or shorter than the first duration. If the delay phase is extended, the third duration is longer than the first duration. If the delay phase is shortened, the third duration is shorter than the first duration. When the second probe pulse is reflected from the surface of the sample, the second pulse is affected by the fourth acoustic wave. The second probe pulse may also generate another acoustic wave (e.g., a fifth acoustic wave) in the sample. The reflected second probe pulse may then be detected in operation 1420.

[0169] At operation 1422, a fourth pump pulse is directed to the surface of the sample. The fourth pump pulse arrives at the surface of the sample at a fourth duration after the second probe pulse arrives at the surface of the sample. The fourth duration may be based on the pulse frequency of the laser generating the pulses and the length of the delay phase after the change in operation 1414. For example, if the delay phase is extended in operation 1414 and the pulse repetition frequency of the laser remains constant, the fourth duration may be less than the second duration (e.g., the time between the first probe pulse and the second pump pulse). When the fourth pump pulse is reflected from the surface of the sample, the fourth pump pulse is affected by the acoustic wave (e.g., the fifth acoustic wave) generated by the second probe pulse. At operation 1424, the reflected fourth pump pulse is detected by a detector.

[0170] At operation 1426, additional characteristics of the sample may be determined based on the detected one or more pulses. The characteristic may be a feature of the sample or a thickness of a layer. For example, a third characteristic corresponding to a third depth may be determined based on the detected second probe pulse. A fourth characteristic corresponding to a fourth depth may be determined based on the detected fourth pump pulse. The third depth may be less than or greater than the second depth depending on whether the delay phase is extended or shortened in operation 1414. Similarly, the fourth depth may be less than or greater than the first depth depending on whether the delay phase is extended or shortened and whether the pulse rate of the laser is kept constant or varied in operation 1414.

[0171] At operation 1428, a decision may be made as to whether to approve the sample based on the characteristics determined or measured at operation 1426 and / or operation 1412. For example, the sample is intended to be manufactured to have a layer of a specific thickness within a specific tolerance. The acceptable tolerance or range may be predetermined. For example, the manufacturer of the sample may specify a tolerance or range for the thickness of a component or layer of the sample. In some examples, the tolerance or range may be based on the minimum or maximum thickness required for the operability of the sample. If the characteristics determined in operation 1426 and / or operation 1412 fall within the expected thickness and tolerance, the sample may be approved in operation 1428. If the characteristics determined in operation 1426 and / or operation 1412 do not fall within the expected thickness and tolerance, the sample may be rejected in operation 1428.

[0172] If the sample is approved in operation 1428, method 1400 proceeds to operation 1430, in which additional manufacturing steps are performed. In an example where the sample is a wafer, the additional manufacturing steps include operations such as back grinding the wafer. The manufacturing steps may also include cleaning and other finishing operations of the sample, including packaging operations. In some examples, the additional manufacturing steps may include additional tests, such as electrical tests of semiconductor devices or chips on the wafer. For example, electrical tests may be performed on each chip on the wafer to determine whether the chip is normal or working as expected. The chips may be virtually classified into virtual boxes based on the test results of the chips. Chips that fail the test may be marked as bad or faulty and placed in a faulty virtual box for faulty chips. Conversely, chips that pass the test may be marked as good or qualified and placed in a qualified virtual box. After the test, the wafer may be thinned and then cut into individual chips. The chips that have been marked as passing the test are packaged into devices or applications such as memory cards or storage devices and other computer chips. The percentage of chips approved from the test is generally referred to as the yield rate. Once the chip has been packaged, the chip may be further tested to help ensure that the bond from the chip to the rest of the package or device has been properly formed and that performance is still within acceptable limits. The approved packaged device may then be further incorporated into a computing device. For example, where the chip from the wafer is packaged into a memory device, the memory device may be installed or incorporated into a computing device such as a laptop or mobile phone.

[0173] If the sample is not approved in operation 1428, the method 1400 proceeds to operation 1432, where the sample is rejected and may be discarded. In some cases, the rejected sample may be salvageable or recyclable. By measuring or inspecting the sample before performing additional manufacturing steps such as back grinding and cleaning, the additional manufacturing steps are only performed on samples that are acceptable or within tolerance. Therefore, resources are not wasted finishing samples that are unacceptable or out of tolerance.

[0174] Fig.15Describes the basis FIG. 14A to FIG. 14B , and as described above. First, a first pump pulse 1501 is directed to the surface of the sample. Then, a first probe pulse 1502 is generated at a first duration (t1) after the first pump pulse 1501. A second pump pulse 1503 is generated based on the pulse frequency of the laser and directed to the surface of the sample. The period between laser pulses is represented as duration (t0). At a second duration (t2) after the first probe pulse 1501, the second pump pulse 1503 is directed to the surface of the sample.

[0175] At some point after the second pump pulse 1503 is directed to the surface of the sample, the delay phase changes. In the depicted exemplary pulse pattern, the delay phase is extended, which increases the path length of the probe pulse. After the delay phase is extended, the third pump pulse 1504 is directed to the surface of the sample. Then, at a third duration (t3) after the third pump pulse 1504, the second probe pulse 1505 is directed to the surface of the sample. In the depicted example, the third duration (t3) is greater than the first duration (t1) because the delay phase is extended. A fourth pump pulse 1506 is generated based on the pulse frequency of the laser that has been kept constant in this example and directed to the surface of the sample. Therefore, a fourth pump pulse 1506 is generated at a duration (t0) corresponding to the period between laser pulses after the third pump pulse 1504. The generation of the fourth pump pulse 1506 occurs at a fourth duration (t4) after the second probe pulse 1505. Due to the increase in the length of the delay phase, the fourth duration (t4) is shorter than the second duration (t2).

[0176] It should be understood from the above that the pump beam and the probe beam can be interchanged with each other to allow measurements at greater depths without having to physically change the size of the photoacoustic measurement device. For example, the initial separation of the laser beam results in two laser pulses that reach the surface of the sample. Although one of these pulses is traditionally considered a "pump" pulse and the other is considered a "probe" pulse, both pulses can be analyzed and generate acoustic waves in the body of the sample. Therefore, when the two pulses are detected and analyzed, the effect of the acoustic waves generated by either of these pulses can be analyzed and used to determine the characteristics of the sample. Such analysis allows the determination of characteristics at a depth range that is greater than the depth range corresponding to the delay between the pump pulse and the probe pulse alone. In some examples, the measurement of the first laser pulse and the second laser pulse can be performed in a substantially continuous manner so that a series of two pulses is detected and recorded. During the emission of this series of pulses, the delay between the first pulse and the second pulse can be varied (e.g., by extending or shortening the delay phase) to provide a variety of detected data for analysis. Through lock-in detection techniques, the first pulse can be identified or distinguished from the second pulse. The data can then be analyzed to determine the effect of the acoustic waves generated by any previous pulses on the particular pulse being analyzed.

[0177] The embodiments described herein can be implemented and executed using software, hardware, or a combination of software and hardware. Although specific devices are described as performing specific functions throughout this disclosure, it will be appreciated by those skilled in the art that these devices are provided for illustrative purposes, and other devices can be used to perform the functions disclosed herein without departing from the scope of this disclosure. In addition, some aspects of this disclosure are described above with reference to the block diagram and / or operational diagrams of the systems and methods of various aspects of this disclosure. The functions, operations, and / or actions mentioned in the frame may not occur in the order shown in any corresponding flow chart. For example, according to the functions involved and the specific implementation, the two frames shown in succession can actually be implemented or executed substantially simultaneously or in reverse order.

[0178] The present disclosure describes some embodiments of the present technology with reference to the accompanying drawings, wherein only some embodiments of possible embodiments are shown. However, other aspects can be embodied in a variety of different forms, and should not be construed as being limited to the embodiments described herein. On the contrary, these embodiments are provided to make the present disclosure thorough and complete, and the scope of possible embodiments is fully conveyed to those skilled in the art. In addition, as used herein and in the claims, the phrase "at least one of element A, element B, or element C" is intended to convey any of the following: element A, element B, element C, element A and B, element A and C, element B and C, and element A, B and C. In addition, those skilled in the art will understand that terms such as "about" or "substantially" convey the degree of measurement techniques used herein. In the case where those skilled in the art may not be able to clearly define or understand such terms, the term "about" should mean plus or minus ten percent.

[0179] Although specific embodiments are described herein, the scope of the present technology is not limited to those specific embodiments. In addition, although different examples and embodiments can be described separately, such embodiments and examples can be combined with each other when implementing the technology described herein. Those skilled in the art will recognize other embodiments or improvements within the scope and essence of the present technology. Therefore, the specific structures, actions or media disclosed are only exemplary embodiments. The scope of the present technology is limited by the following claims and any equivalents thereof.

Claims

1. A method comprising: generating pump pulses and probe pulses from light; dividing the pump pulse into a first pump pulse and a second pump pulse; generating a difference between a beam path length of the first pump pulse and a beam path length of the second pump pulse; directing the first pump pulse and the second pump pulse to a measurement point on a sample; directing the probe pulse to the measurement point on the sample; as well as The probe pulse reflected from the measurement point is detected.

2. The method according to claim 1, wherein: The first pump pulse arrives at the measurement point before the second pump pulse arrives at the measurement point; and The probe pulse arrives at the measurement point after both the first pump pulse and the second pump pulse arrive at the measurement point. 3 . The method of claim 1 , further comprising determining a characteristic of the sample based on the detected probe pulse. 4 . The method of claim 1 , further comprising modulating the pump pulses prior to separating the pump pulses.

5. The method of claim 1, further comprising generating different characteristics in the first pump pulse and the second pump pulse.

6. The method according to claim 5, wherein: Generating different characteristics in the first pump pulse and the second pump pulse includes producing a different polarization state in the first pump pulse than in the second pump pulse.

7. The method according to claim 1, further comprising: dividing the detection pulse into a first detection pulse and a second detection pulse; Wherein, directing the detection pulse to the measurement point of the sample includes directing the first detection pulse and the second detection pulse to the measurement point so that: the second detection pulse arrives at the measurement point after the first detection pulse arrives at the measurement point; and The second detection pulse arrives at the measurement point after both the first pump pulse and the second pump pulse arrive at the measurement point.

8. The method according to claim 7, wherein: The first probe pulse arrives at the measuring point after the first pump pulse arrives at the measuring point and before the second pump pulse arrives at the measuring point.

9. The method of claim 7, further comprising modulating the detection pulses prior to separating the detection pulses.

10. The method according to claim 7, wherein: The first detection pulse is directed toward the measurement point at a first azimuth angle, and the second detection pulse is directed toward the measurement point at a second azimuth angle.

11. The method of claim 1 , further comprising adjusting a beam path length of the probe pulse to produce a desired delay between arrival of the probe pulse at the measurement point and arrival of the first and second pump pulses at the measurement point.

12. A system comprising: a light source configured to emit light pulses; a first beam splitter configured to split the optical pulse into a pump pulse and a probe pulse; a second beam splitter disposed in a beam path of the pump pulse to split the pump pulse into a first pump pulse and a second pump pulse; at least one reflector disposed in a beam path of the second pump pulse so that a beam path length of the second pump pulse is longer than a beam path length of the first pump pulse; one or more focusing optics arranged to direct the first pump pulse, the second pump pulse and the probe pulse to a measurement point on a sample; as well as A detector is arranged to receive the detection pulse reflected from the measurement point.

13. The system of claim 12, wherein: The first pump pulse arrives at the measurement point before the second pump pulse arrives at the measurement point; and The probe pulse arrives at the measurement point after both the first pump pulse and the second pump pulse arrive at the measurement point.

14. The system of claim 12, further comprising: at least one processor; as well as a memory operatively connected to the at least one processor, the memory storing instructions that, when executed by the at least one processor, cause the system to perform a set of operations comprising: A characteristic of the sample is determined based on a signal from the detector in response to the reflected probe pulse.

15. The system of claim 12, further comprising an optical modulator disposed in a beam path of the pump pulses before the second beam splitter, wherein the optical modulator is configured to modulate the pump pulses.

16. The system of claim 12, further comprising one or more optical devices for generating different characteristics in the first pump pulse and the second pump pulse.

17. The system of claim 16, wherein: The one or more optical devices include a half-wave plate disposed between the second beam splitter and the focusing optics in at least one of the beam paths of the first pump pulse and the second pump pulse.

18. The system of claim 12, further comprising a third beam splitter disposed in a beam path of the probe pulse to split the probe pulse into a first probe pulse and a second probe pulse, wherein: The one or more focusing optics are arranged to direct the first and second probe pulses to the measurement point on the sample such that: the second detection pulse arrives at the measurement point after the first detection pulse arrives at the measurement point; and The second detection pulse arrives at the measurement point after both the first pump pulse and the second pump pulse arrive at the measurement point.

19. The system of claim 18, wherein: The first probe pulse arrives at the measuring point after the first pump pulse arrives at the measuring point and before the second pump pulse arrives at the measuring point.

20. The system of claim 18, further comprising an optical modulator disposed in the beam path of the probe pulse between the first beam splitters, wherein: The optical modulator is configured to modulate the probe pulse.

21. The system according to claim 12 further includes an adjustable delay platform, which is arranged between the first beam splitter and the focusing optical device, and is configured to increase the beam path length of the detection pulse to produce a desired delay between the detection pulse arriving at the measurement point and the first pump pulse and the second pump pulse arriving at the measurement point.

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