Pressure control system for the cavity of a light source

Abstract

To provide systems for controlling the pressure in a cavity of a light source.SOLUTION: One system includes a barometric pressure sensor configured for measuring the pressure in a cavity of a light source. The system also includes one or more gas flow elements configured for controlling the amount of one or more gases in the cavity. In addition, the system includes a control subsystem configured for comparing the measured pressure to a predetermined range of values of the pressure and, when the measured pressure is outside of the predetermined range, altering a parameter of at least one of the one or more gas flow elements based on results of the comparison.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention generally relates to a method and system for controlling pressure in a cavity of a light source.

Background Art

[0002] The following description and examples are not admitted to be prior art for the reasons included in this item.

[0003] Manufacturing semiconductor devices such as logic devices and memory devices typically involves processing a substrate such as a semiconductor wafer using many semiconductor manufacturing processes to form various features and multiple heights of the semiconductor device. For example, lithography is a semiconductor manufacturing process that includes transferring a pattern from a reticle to a resist disposed on a semiconductor wafer. Further examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices.

[0004] Inspection processes are used at various stages during semiconductor manufacturing processes to detect defects in wafers and other substrates, and to drive higher yields and associated higher profit margins in the manufacturing process. Inspection has always been an important part of the manufacturing of semiconductor devices such as integrated circuits (ICs). However, as the dimensions of semiconductor devices become smaller, inspection has become even more important for the normal manufacturing of acceptable semiconductor devices because smaller defects can cause device failures.

[0005] There are several variations that can negatively impact the inspection results and limit their usefulness. For example, variations in the processes used to form the wafers can cause changes in the wafers (e.g., from wafer to wafer and / or across the entire wafer) that, although not necessarily causing wafer defects, can be detected as such by the inspection. Variations in the inspection process or inspection tool can also negatively impact the inspection results. For example, inspection tool parameters can drift over time and can negatively impact the inspection results. Specifically, when the parameters of the inspection tool shift unexpectedly, the inspection tool may detect abnormal counts of wafer defects, many of which are not actual defects. If the shift in the inspection tool parameters goes undetected and affects the inspection results, the inspection results are not useful for changing the processes performed on the inspection samples and / or are used in an undesirable manner, unless it is clear from the inspection results that the tool has drifted.

[0006] Much energy and time have been spent attempting to minimize and / or compensate for variations related to non-defects in inspection samples and inspection tool parameters in order to minimize the impact of such variations on the inspection results. Further, because many inspection processes and inspection tools operate at or near their maximum performance limits, variations in parameters that may not have been important in the past are now having a significant negative impact on the inspection results. One such parameter that the inventors have discovered can have a significant negative impact on the inspection results is the change in air pressure around and / or within the inspection tool laser. However, it is not thought that current methods for stabilizing air pressure with lasers are being utilized. Specifically, the state-of-the-art methods are methods that either use optical adjustments inside the laser to compensate for air pressure changes or methods that do not perform any compensation at all.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, there are several problems with the currently used inspection stabilization process and inspection stabilization system. For example, as described above, the variations in several parameters identified by the inventor as potential problems are not considered to be monitored or controlled in any way. Furthermore, the currently used method for compensating for air pressure changes has a relatively slow reaction time and is not sufficient due to the compensation range and the overall complexity of the compensation algorithm. Moreover, there is no single parameter used in the feedback loop for responding to air pressure changes.

[0009] Therefore, it is advantageous to develop a system and / or method for controlling the pressure in the cavity of a light source that does not have one or more of the above problems.

Means for Solving the Problems

[0010] The following description of various embodiments is not to be construed as limiting the subject matter of the invention of the appended claims.

[0011] One embodiment relates to a system configured to control the pressure in a cavity of a light source. The system includes a barometric pressure sensor configured to measure the pressure in the cavity of the light source. The system also includes one or more gas flow elements configured to control the amount of one or more gases in the cavity. Further, the system includes a control subsystem configured to compare the measured pressure to a predetermined range of pressure values and, if the measured pressure is outside of the predetermined range, change at least one parameter of one or more of the gas flow elements based on the result of the comparison. The system may be further configured as described herein.

[0012] Another embodiment relates to a computer-implemented method for controlling the pressure in a cavity of a light source. The method includes measuring the pressure in the cavity of the light source and controlling the amount of one or more gases in the cavity using one or more gas flow elements. The method includes comparing the measured pressure to a predetermined range of pressure values. If the measured pressure is outside of the predetermined range, the method further includes changing at least one parameter of one or more of the gas flow elements based on the result of the comparison.

[0013] Each step in the above method may be performed as further described herein. Further, the above method may include other methods described herein. Further, the above method may be performed by any of the systems described herein.

[0014] A further embodiment relates to a non - transitory computer - readable medium storing program instructions executable by a computer system for performing a computer - implemented method for controlling the pressure of a cavity of a light source. The computer - implemented method includes the steps of the above - described method. The computer - readable medium may be further configured as described herein. The steps of the computer - implemented method may be performed as further described herein. Additionally, a computer - implemented method for which the program instructions are executable may include other steps among the other methods described herein.

Brief Description of the Drawings

[0015] Other objects and advantages of the present invention will become apparent from reading the following detailed description and with reference to the following attached drawings.

Figure 1

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Figure 7

[0016] The present invention is capable of various modifications and alternative forms, and specific embodiments thereof are shown by way of examples in the drawings and are set forth in detail herein. However, the drawings and the detailed description are not intended to limit the present invention to the specific forms disclosed, but on the contrary, are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

Embodiments for Carrying Out the Invention

[0017] Referring to the drawings, the drawings are not drawn to a uniform scale. Specifically, the scale of some of the components in the drawings is greatly exaggerated to emphasize the features of the components. Also, the drawings are not drawn at the same scale. Components shown in one or more drawings that may be similarly configured are denoted by the same reference numerals. Unless otherwise described herein, all components described and drawn may optionally include commercially available components.

[0018] The embodiments described herein generally relate to the stabilization of the air pressure of an improved laser or other light source performance. The embodiments described herein improve light sources such as lasers from the viewpoints of reliability, stability, and extended lifespan. A plurality of embodiments are generally configured to control the air pressure inside a laser or other light source housing and to be unaffected by variations in air pressure changes.

[0019] Currently, some inspection tools in use always perform optimization during the operation of an infrared (IR) engine in the background to compensate for air pressure changes by optimizing the temperature of an etalon using a thermoelectric cooler (TEC) (e.g., TEC model XXXX commercially available from Thorlabs, Newton, New Jersey). According to the data collected by the inventors, it has been observed that the laser pressure drop corresponds to changes in air pressure due to nearby inclement weather. The pressure drop is related to the TEC adjustment. The inventors also observed that after the pressure began to rise and the laser strengthened or weakened due to misalignment, the TEC also rose in a better direction. Since the etalon operating setpoint is unstable, the laser environment compensation control exceeds its range. The TEC setpoint may need to be adjusted because it may be very close to the critical temperature (e.g., 20 °C). The setpoint can be adjusted by performing infrared (IR) optimization.

[0020] If the etalon operating setpoint is unstable, or if the laser environment compensation control is unstable in other respects, it may affect the image generated on the sample using light from the laser. For example, the instability of the laser may cause high-frequency intensity oscillations in the sample image. The intensity vibrations may appear as vertical banding in the sample image and may cause a change in the sensitivity of the inspection. Specifically, high-frequency intensity oscillations may result in defects of a smaller minimum size that can be detected more greatly (meaning that the sensitivity of the inspection is lower). Therefore, due to air pressure changes, the number of defects in the inspection results decreases, and the air pressure changes correlate with the number of defects in the inspection results. What the inventors propose in this specification is not to adjust the temperature of the etalon to compensate for air pressure changes, but to stabilize the pressure inside the laser head (or other light source) so that the laser (or other light source) is less affected by air pressure changes.

[0021] One embodiment relates to a system configured to control the pressure in a cavity of a light source. In one embodiment, the light source is a laser configured to generate single-wavelength light. In another embodiment, the light source is a laser configured to generate narrow-band light. "Narrow-band light" is defined throughout this specification as light having one or more wavelengths spanning a wavelength band of less than 10 nm (e.g., from 190 nm to 200 nm). For example, the embodiments described herein are particularly advantageous for single-mode (or single-wavelength) narrow-band, CW lasers. The light generated by such lasers may be infrared (IR), visible, ultraviolet (UV), or deep ultraviolet (DUV) light. The embodiments described herein may be used with multi-mode lasers, although the effect of wavelength dependence on ambient pressure is not particularly essential for such lasers. However, in certain applications where the wavelength stability of the output light is important, multi-mode lasers, pulsed lasers, or mode-locked lasers may also be beneficial. These embodiments may be utilized to stabilize the pressure in diodes and fiber lasers. Thus, generally, the embodiments described herein may be used to control the pressure of a light source where wavelength stability is important and the wavelength stability depends on the variation in the pressure of the light source. Some of the embodiments are specifically described herein with respect to lasers, but none of the embodiments are limited to laser light sources.

[0022] The embodiments described herein provide pressure control that is different from that implemented with some gas lasers such as excimer lasers and argon lasers. For example, some gas lasers have a cavity containing a gaseous active medium that is emitted by the laser after light is generated. In such lasers, the pressure of the active medium may be controlled in the cavity in which it is contained (e.g., for gain control of the active medium). However, that pressure is not the pressure controlled by the embodiments described herein. Specifically, the pressure controlled by the embodiments described herein is the atmospheric pressure (air pressure) within the cavity of the light source. Thus, the pressure of the gaseous active medium of the laser may be different from the air pressure within the light source. In such an embodiment, the gaseous active medium may be contained in a cavity within the light source, and the pressure within the cavity may be controlled. However, such pressure control does not affect, control, or otherwise modify the air pressure outside the cavity except within the light source (which may include the air pressure of one or more other cavities of the light source). Similarly, when the embodiments described herein are used to control the air pressure of such a cavity of a light source, the air pressure control is designed not to change the pressure of any gaseous active medium within the light source. Thus, the pressure controlled by the embodiments described herein does not include the pressure of the active medium of the light source. Further, the embodiments described herein may be configured to control the air pressure of gas lasers, solid-state lasers, and any other light source described herein.

[0023] In one embodiment, the cavity is a harmonic generation cavity of a light source. For example, the harmonic generation cavity may be a second harmonic generation (SHG) cavity, a third harmonic generation (THG) cavity, a fourth harmonic generation (FHG) cavity, or the like. In another embodiment, the cavity is an infrared cavity of the light source. In an additional embodiment, the cavity is the main cavity of the light source. For example, as shown in FIG. 1, a light source 100 configured as a laser head may include a main cavity 102 and a cavity 104. Cavity 104 may be a harmonic generation cavity, an infrared cavity, or another type of cavity described herein. The cavity may also include some arrangements of one or more cavities that contain one or more cavities inside another cavity, such as an infrared cavity or a harmonic generation cavity that is inside the main cavity as shown in FIG. 1.

[0024] As used herein, the term "cavity" is generally defined as an enclosure (or partial enclosure) formed by several housing elements in which light is generated by a light source. The "cavity" described herein is generally not empty and may contain any components (not shown) required to generate light within the cavity and emit light outside the light source (e.g., via a window in the cavity and a window in the housing of the light source) for use in a system such as an inspection system. Thus, the configurations and elements included in the cavities described herein may vary for each light source, and the embodiments described herein are not limited to the type or configuration of the cavities in which they are used. Any specific cavity described herein is merely an example of a light source and the type of its cavity that may particularly benefit from the pressure control described herein.

[0025] The system includes a barometric pressure sensor configured to measure the pressure of the cavity of a light source. For example, as shown in FIG. 1, the system may include a barometric pressure sensor 106 configured to measure the pressure in the cavity 104 of the light source 100. This barometric pressure sensor and any other types of barometric pressure sensors described herein may include a commercially available suitable barometric pressure sensor that is well known in the art. An example of a commercially available suitable barometric pressure sensor is the pressure transmitter GE Druck PMP5073 commercially available from Cole-Parmer of Vernon Hills, Illinois. The barometric pressure sensor 106 and its various configurations and other barometric pressure sensors are further described.

[0026] The system also includes one or more gas flow elements configured to control the amount of one or more gases in the cavity. Multiple configurations suitable for the one or more gas flow elements are further described herein. Generally, the gas flow element may include any gas flow element that allows one or more gases to flow into and / or out of the cavity whose barometric pressure is being controlled. The one or more gas flow elements may also include one or more elements that can be used to create a specific pressure (positive or negative pressure) in the cavity of the light source in response to control signals, control values, control commands, etc. from the control subsystem further described herein. The one or more gases may include any suitable gas, and a particularly suitable example is clean dry air (CDA).

[0027] The system further includes a control subsystem configured to compare the measured pressure with a predetermined range of pressure values and, if the measured pressure is outside the predetermined range, change at least one parameter of one or more gas flow elements based on the result of the comparison. Multiple suitable configurations of the control subsystem are further described herein. The control subsystem may include only mechanical components, only computer components, or different types of components. Also, the control subsystem may be digital or analog. The predetermined range of pressure values may be determined by the user and, in some cases, may include one pressure value, but often includes at least some range of pressure values. Depending on how much the pressure is controlled by the components of the system and / or how much the pressure needs to be controlled to ensure relatively stable performance of the light source and the system it is included in, the range of values may be relatively small or relatively large.

[0028] The parameters of at least one gas flow element changed by the control subsystem may include appropriate parameters that cause a pressure change in the cavity of the light source. Some examples of these are further described herein and may vary depending on the configuration of the gas flow element. The change in the parameters of at least one gas flow element may be determined in an appropriate manner (e.g., experimentally or theoretically) using an appropriate type of control loop, algorithm, method, function, etc. In one embodiment, the control subsystem is configured to change parameters using a proportional-integral-derivative (PID) control loop. For such a control loop, the control subsystem may include a current amplifier and a controller (not shown) between a barometric pressure sensor and a gas flow element such as a valve for setting appropriate PID gains for the control loop. Also, the control subsystem may be configured to perform a calibration process on the barometric pressure sensor and the gas flow element. The calibration process may be performed in an appropriate well-known manner.

[0029] In one embodiment, one or more gas flow elements include a first gas flow conduit connected to a cavity and a clean dry air source. Such a gas flow element also includes a second gas flow conduit connected to the cavity and an exhaust device. The first gas flow conduit, the second gas flow conduit, the clean dry air source, and the exhaust device are configured to generate a positive pressure in the cavity. For example, as shown in FIG. 1, the gas flow element may include a gas flow conduit 108 connected to a cavity 104 and a clean dry air source 110, and may also include a gas flow conduit 112 connected to the cavity 104 and an exhaust device 114. The gas flow conduit 108 may be configured to provide a flow of clean dry air entering the cavity 104 from the clean dry air source 110, and the gas flow conduit 112 may be configured to provide a flow of clean dry air exiting the cavity. Although the gas flow conduit is depicted as physically contacting the cavity itself, the gas flow conduit may be connected to the cavity without being physically connected to the cavity itself. For example, the gas flow conduit may be physically contacted and connected to the housing of a light source, and thereby connected to the cavity (e.g., through an opening made in the light source housing), and by allowing gas to flow into and out of the housing, the conduit and the internal gas flow may generate a positive pressure within the cavity. Thus, the gas flow conduit may be connected to the cavity without physically contacting the cavity through the gas flow entering and exiting the gas flow conduit.

[0030] The gas flow entering and exiting the gas flow conduit may vary depending on the cavity and gas flow elements and may have appropriate parameters. In a non-limiting example described for illustrative purposes only, the incoming clean dry air flow may have a volumetric flow rate of about 1.5 liters per minute (LPM) and a pressure of about 50 psig, and the outgoing clean dry air flow may have a volumetric flow rate of about 0.5 liters per minute and an unregulated pressure. The laser head may be purged with clean dry air to slightly raise the pressure within the head to about 1 atm. In this way, the pressure inside the laser head may be set higher than 1 atm. Note that the above absolute values and any other absolute values described herein are for illustrative and descriptive purposes only and do not limit the invention to specific absolute values. For example, the appropriate absolute values of the parameters described herein may vary for each type of light source and may further vary for each light source unit (of the same type from the same manufacturer). Additionally, the pressure generated in the cavity of the light source may be above or below atmospheric pressure as long as it is stable through the controls described herein (e.g., when a sub-atmospheric pressure is created by generating a vacuum in the cavity via one or more gas removal components such as a pump). The first gas flow conduit, the second gas flow conduit, and any other conduits described herein may have well-known appropriate configurations (e.g., tubes or pipes made of appropriate materials with appropriate dimensions and other flow characteristics).

[0031] In such an embodiment, the one or more gas flow elements may further include a purge conduit connected to the cavity and a proportional valve connected to the purge conduit, and the parameter changed by the control subsystem is the parameter of the proportional valve. For example, as shown in FIG. 1, it may include a purge conduit 116 connected to the cavity 104 and a proportional valve 118 connected to the purge conduit. The purge flow through the purge conduit may vary according to the cavity and gas flow control and may have appropriate parameters. In a non-limiting example described only for illustrative purposes, the exiting purge flow may have a volumetric flow rate of about 0.5 liters per minute and a pressure of about 16 psia. The purge conduit may be configured to purge gas from the cavity to the atmosphere. The purge conduit may be further configured as described herein with respect to other gas flow conduits. The proportional valve may include a suitable proportional valve well-known in the art.

[0032] As further shown in FIG. 1, the system includes a control subsystem 120 coupled to a pneumatic sensor 106 and a proportional valve 118. The control subsystem may include suitable components such as elements further described herein that can receive pressure measurements from the pneumatic sensor, and based on the measured pressure, when the measured pressure deviates from a predetermined range, send a control signal (e.g., a control voltage between 0 and 5V) to the proportional valve 118. In this way, the pressure inside the light source is adjusted to stabilize at a set value. For example, the basic principle of the system operation shown in FIG. 1 is that the control subsystem opens and closes the proportional valve based on a control signal determined from the pressure measured by the pneumatic sensor. In such an embodiment, the pneumatic sensor measures the pressure inside the light source (or in the cavity of the light source), and through a control loop, the control subsystem adjusts the proportional valve connected upstream of a clean dry air exhaust device (not shown). When the control loop closes the valve, the pressure rises, and when the control loop opens the valve, the pressure drops. Also, the opening and closing of the valve may each include only a partial opening and closing of the valve. Such operation of the proportional valve enables substantially accurate control of the pressure inside the laser head and is substantially unaffected by possible changes in pneumatic pressure. Specifically, due to the substantially stable pressure inside the light source, during operation, the light source is substantially unaffected by the action of pneumatic pressure. Thus, since the proportional valve can be used to adjust the exhaust flow of clean dry air, the pressure of the light source or the cavity of the light source can be controlled. As a result, the internal pressure of the cavity 104 can be maintained at a stable set value (e.g., about 1 atmosphere).

[0033] In another embodiment, the pneumatic sensor is disposed at a location outside the cavity and the light source and is coupled to a purge conduit. For example, as shown in FIG. 1, the pneumatic sensor 106 may be outside the light source and the cavity located therein and is coupled to the purge conduit 116. The pneumatic sensor may be coupled to the purge conduit in a well-known stable manner.

[0034] Light sources such as lasers can have several cavities and require a pressure return to prevent air leakage between them and contamination of deep ultraviolet components. In some embodiments, the system includes an additional barometric pressure sensor configured to measure the pressure in an additional cavity of the light source and one or more additional gas flow elements configured to control the amount of one or more gases in the additional cavity, and the control subsystem is configured to compare the pressure measured in the additional cavity with a predetermined range of pressure values for the additional cavity, and when the pressure measured in the additional cavity is outside the predetermined range of pressure values for the additional cavity, based on the result of comparing the pressure measured in the additional cavity, at least one parameter of the one or more additional gas flow elements is configured to be changed. For example, as shown in FIG. 1, the system may include an additional barometric pressure sensor 122 configured to measure the pressure in an additional cavity of the light source (e.g., the main cavity 102). The additional gas flow element(s) may include a purge conduit 124 connected to the main cavity 102 and a proportional valve 126 connected to the purge conduit. The purge flow through the purge conduit 124 may have appropriate parameters but may vary based on cavity and gas flow control. In one non-limiting example described for illustrative purposes only, the exiting purge flow may have a volumetric flow rate of about 0.5 liters per minute and a pressure of about 15 psia. The purge conduit may be configured to purge gas from the cavity to the atmosphere.

[0035] Furthermore, as shown in FIG. 1, the system includes a control subsystem 128 coupled to a pneumatic sensor 122 and a proportional valve 126. This control subsystem can receive a measured pressure value from the pneumatic sensor and, based on that measured value, can send a control signal (e.g., a control voltage between 0 and 5 V) to the proportional valve 126 if the measured value is outside a predetermined range, and may include suitable elements as further described herein. For example, the basic principle of system operation as shown in FIG. 1 is that the control subsystem opens and closes (at least partially) the proportional valve based on a control signal determined from the pressure measured by the pneumatic sensor 122. As a result, the internal pressure of the main cavity 102 can be maintained at a stable set value (e.g., about 1 atm). The pneumatic sensor 122, purge conduit 124, proportional valve 126, and control subsystem 128 may each be further configured as described herein for the pneumatic sensor 106, purge conduit 116, proportional valve 118, and control subsystem 120, respectively.

[0036] In such an embodiment, the cavity is the harmonic generation cavity of the light source, and the additional cavity is the main cavity of the light source. For example, as shown in FIG. 1, cavity 104 may be the harmonic generation cavity or other types of cavities described herein, and the additional cavity may be main cavity 102. Further, rather than controlling the pressure of cavity 104 and any main cavity 102 as described above, the system may be configured to control only the pressure of the main cavity, which may be sufficient for the embodiments described herein. In such a case, the system shown in FIG. 1 may be modified to not include the barometric pressure sensor 106, purge conduit 116, proportional valve 118, and control subsystem 120. In such an example, the first gas flow conduit 108 and the second gas flow conduit 112 may each be connected to main cavity 102 rather than cavity 104 as described above. The first gas flow conduit and the second gas flow conduit may be connected to the main cavity as described above and configured to purge the laser head with clean dry air to slightly raise the pressure inside the head above 1 atm. In another option, the first conduit and the second conduit configured to generate the pressure inside the cavity may not be connected to the cavity itself, but may be connected only to the laser head. By raising or lowering the pressure in the laser head, the pressure of one or more cavities may also be raised or lowered to a corresponding (or predictable) extent.

[0037] The control subsystem may be configured to control the pressure of the main cavity as further described herein (e.g., using a PID control loop). If the system includes elements used to individually control the pressures of separate cavities of the light source, the elements used to control the pressure of one cavity may or may not have a different configuration than the elements used to control the pressure of another cavity (e.g., depending on the cavity configuration and sensitivity to the pressure of the generated light). The control subsystem shown in FIG. 1 includes two different control subsystems, each configured to control the pressure of only one of a plurality of cavities, but the control subsystem included in the system may include only one control subsystem configured to control the pressure of one or more of the plurality of cavities. The pressures created and maintained in separate cavities of the light source may or may not be different. For example, the stable pressure created in both cavities shown in FIG. 1 may be about 1 atm. However, the stable pressure created in one of the plurality of cavities may be higher or lower than the pressure created in another one of the plurality of cavities. In such an embodiment, if the first cavity is more responsive to contamination, the pressure within that cavity is higher than that of the second cavity, reducing the inflow of contamination from the second cavity to the first cavity. The higher pressure in the first cavity may be selected as the minimum pressure value that reduces the contamination flowing into the cavity to a negligible amount, thereby making it possible to keep the pressure difference within the light source at a minimum value, making the control and stability of the pressures of both cavities easier, more reliable, and more stable.

[0038] In such further embodiments, the pressure sensor, at least one of the one or more gas flow elements, and the control subsystem are included in a backpressure regulator connected to the purge conduit, and the parameter changed by the control subsystem is a parameter of the backpressure regulator. For example, as shown in FIG. 2, the purge conduit 200 may be connected to the cavity 104. The backpressure regulator 202 may be connected to the purge conduit. Depending on which cavity (one or more) of the light source has its pressure controlled, the system shown in FIG. 2 may include one or more backpressure regulators. For example, as shown in FIG. 2, the system may include a purge conduit 204 connected to the main cavity 102 and a backpressure regulator 206 connected to the purge conduit. The purge conduit and other elements shown in FIG. 2 may be further configured as described above. The backpressure regulators may have similar or different configurations, and an appropriate example is shown in FIG. 3.

[0039] One embodiment of a backpressure regulator that may be used in the embodiments described herein is shown in FIG. 3. However, FIG. 3 is included herein only to show the general elements of the backpressure regulator, and does not show their functions and how they are utilized in the systems described herein. The backpressure regulator actually included in the system in practice may be selected from many commercially available regulators available, based on the exact configuration of the light source and system in which it is included.

[0040] As shown in FIG. 3, the back pressure regulator 300 may include some housing 302 in which various elements of the regulator are included and are supported in a desired positional relationship with other elements. The back pressure regulator may include a conduit 304 connectable to the purge conduit shown in FIG. 2, such that the gas in the purge conduit can flow through the back pressure regulator, for example, in the direction indicated by the arrow in conduit 304. The back pressure regulator further includes a valve body 306 connected to conduit 304, and conduit 304 operates as a negative feedback mechanism for the back pressure regulator. The valve body is connected to a diaphragm 308 via a diaphragm assembly 312, and the diaphragm functions as a pneumatic sensor for the back pressure regulator. Thus, in embodiments including a back pressure regulator, the diaphragm may function as a pneumatic sensor configured to measure the pressure in the cavity of the light source (via the connection to the cavity of the diaphragm via the purge conduit and the valve body).

[0041] The diaphragm may be connected to a spring 310 via a diaphragm assembly 312, and the diaphragm can transmit the suction pressure to the spring. The spring may act as a control subsystem of the back pressure regulator as described herein. The spring may be connected to an adjustment screw 316 via a plate 318 that restricts the other end of the spring within an opening 320. The adjustment screw functions as a setting position adjustment part of the back pressure regulator. For example, a user or a system may be configured to set a desired pressure in the cavity of the light source via adjustment screw 316. The spring keeps the back pressure regulator in a normally closed position. For example, by the spring pressing down the diaphragm assembly, the valve body is positioned. Thus, the back pressure regulator reaches a certain back pressure setting and can start adjusting the pressure. The upstream pressure (in the embodiments described herein, the pressure within the cavity) is sensed under the diaphragm.

[0042] The backpressure regulator is designed to adjust the position of the spring via a valve body and maintain a specific backpressure (in the cavity). For example, when the upstream pressure is higher than the spring setting, the spring setting is controlled to compress the spring, and as a result, the valve body is lifted and the valve opens (by the amount required), and the pressure decreases. On the contrary, when the upstream pressure is lower than the spring setting, the spring extends due to the spring setting, and as a result, the valve body is pushed down, closing the valve body (by the amount required), and the upstream pressure increases. Therefore, in the backpressure regulator, the predetermined range of the valve can be set via an adjustment screw, the spring functions as the control subsystem described herein, and the valve body functions as at least one gas flow element that controls the amount of one or more gases in the cavity.

[0043] Examples of commercially available backpressure regulators that may be suitable for use in the embodiments described herein include those commercially available from CIRCOR Instrumentation located in Spartanburg, South Carolina. Further, as a suitable example for use in the embodiments described herein, a spring-loaded backpressure regulator is shown in FIG. 3, but other types of backpressure regulators, including dome-loaded, aeroloaded, vented, non-vented, may also be suitable for use in the embodiments described herein, but are not limited thereto.

[0044] The backpressure regulator can provide several advantages in the embodiments described herein. For example, a properly sized backpressure regulator can achieve nearly accurate control, reliable performance, relatively fast response, relatively low noise, and minimal maintenance. The backpressure regulator is also advantageous because it does not require an external power source to operate the valve. Another advantage of the backpressure regulator is that it does not require a separate measurement element or feedback controller. The design of the backpressure regulator is relatively simple, achieving relatively low cost, high reliability, easy maintenance, and providing further advantages. Further, the backpressure regulator communicates directly with the controlled variable and provides a substantially fast response.

[0045] As described above, the pressure sensor and the gas flow element(s) may be positioned outside the light source (to the extent possible). However, for example, the pressure sensor and / or one or more gas flow elements may be positioned inside the light source and be part of the light source using firmware that controls the operation of the gas flow element(s) via a servo loop. For example, in another embodiment, the pressure sensor is disposed inside the cavity of the light source. In an additional embodiment, at least one of the pressure sensor and one or more gas flow elements is disposed inside the cavity of the light source. In such an embodiment, the control subsystem includes firmware configured to control the operation of the servo loop. Such an embodiment is shown in FIG. 4.

[0046] As shown in FIG. 4, the pressure sensor 400 may be positioned within the cavity 104 of the light source. In this way, the pressure sensor is inside the light source rather than outside as shown by the pressure sensor 106 in FIG. 1. Although the pressure sensor is shown inside the cavity 104, the pressure sensor may be positioned in the main cavity 102 or simply within the housing of the light source (i.e., inside the light source but outside the cavity it houses). The pressure sensor 400 may be configured as described herein in other respects.

[0047] In the present embodiment, the proportional valve 402 is also shown as being located inside the cavity 104, i.e., inside the light source. However, the proportional valve 402 may be positioned outside the light source (as shown by the proportional valve 118 in FIG. 1). On the other hand, the barometric pressure sensor is disposed inside the cavity or the light source. As shown in FIG. 4, the proportional valve 402 may be inside the cavity 104 or simply inside the housing of the light source (i.e., inside the light source but outside the cavity housed therein). As shown in FIG. 4, regardless of whether it is the pressure in the cavity of the light source or the pressure inside the light source but outside the cavity within the light source, since the barometric pressure sensor can simply measure the barometric pressure of the atmosphere in which it is disposed, when the barometric pressure sensor is located inside the cavity of the light source or is disposed inside the light source but outside the cavity housed therein, the barometric pressure sensor does not necessarily have to be connected to a purge conduit or other conduits. However, as shown in FIG. 4, the proportional valve 402 may be connected to the purge conduit 404. Thus, as described above, the proportional valve can change the pressure in the cavity or the housing by controlling the gas flow through the purge conduit.

[0048] As further shown in FIG. 4, control subsystem 406 may include firmware 408 and a servo loop 410. The firmware and the servo loop may have a configuration well known in the art suitable for changing parameters of at least one gas flow element in response thereto after comparing the measured pressure with a predetermined range of pressure values. As shown in FIG. 4, the barometric pressure sensor 400 and the proportional valve 402 are disposed inside the cavity 104, while the control subsystem 406 is disposed outside the cavity and the light source 100. Alternatively, the control subsystem 404 and any elements included therein may be located inside the light source but outside the cavity contained therein, or in one of the plurality of cavities themselves. Further, although FIG. 4 shows one barometric pressure sensor and a proportional valve inside the cavity 104, another barometric pressure sensor and a proportional valve outside the light source and connected to the main cavity 102, all of the barometric pressure sensors and proportional valves shown in FIG. 4 may be positioned in their respective cavities. Specifically, one or more barometric valves 122, proportional valves 126, and control subsystem 128 may be positioned inside the main cavity 102 or inside the light source but outside the cavity contained therein, as described above, and these components may be configured to control the pressure of the main cavity or simply the light source itself.

[0049] The embodiments described herein have several advantages over other methods for controlling the operation of a light source as described herein. For example, the embodiments described herein provide a compensation range that is larger than previously used compensation ranges. Further, the embodiments described herein provide a faster response time. Also, in the embodiments described herein, complex compensation algorithms are not required, reducing the overall complexity of the laser system. Further, the embodiments described herein enable the manufacture of lasers with higher reliability and longer life at high power in any type of laser, which is extremely important for the types of systems described herein in which the light sources described herein are used.

[0050] In one embodiment, the system also includes an illumination subsystem configured to direct light generated by a light source towards a sample, a detection subsystem configured to detect light from the sample, and a computer subsystem configured to detect a defect of the sample based on an output responsive to the detection light generated by the detection subsystem. For example, the light source may be included in an illumination subsystem as described below. The detection subsystem and the computer subsystem may be further configured as described below.

[0051] In such an embodiment, the sample is a wafer. The wafer may include wafers well-known in semiconductor technology. Some embodiments described herein may relate to one or more wafers, but the embodiments are not limited to the samples in which they are used. For example, the embodiments described herein may be used for samples such as reticles, flat plates, personal computer (PC) substrates, and other semiconductor samples.

[0052] One configuration that may be used for the embodiments of the system described herein is shown in FIG. 5. The system includes an optical (light-based) subsystem 500, and the optical subsystem 500 includes at least one illumination subsystem that includes a detection subsystem including a light source and a detector. The light source is configured to generate light directed towards the sample. The detector is configured to detect light from the sample and generate an output in response to the detected light. The embodiment of the system shown in FIG. 5 may also be configured to perform light-based processing, inspection processing, and measurement processing as further described herein.

[0053] The illumination subsystem includes at least one light source, the pressure of which is controlled as further described herein. For example, as shown in FIG. 5, the illumination subsystem includes a light source 504. The light source 504 is configured as described and shown in FIGS. 1, 2, and 4 and may be coupled to other elements. In one embodiment, the illumination subsystem may be configured to direct the light generated by the light source to the sample at one or more angles of incidence, which may include one or more oblique angles and / or one or more right angles. For example, as shown in FIG. 5, the light from the light source 504 is directed through an optical element 506 and then through a lens 508 to reach a beam splitter 510, and the beam splitter 510 directs the light to the sample 502 at a right angle of incidence. The angle of incidence may include a suitable angle of incidence and may vary, for example, depending on the characteristics of the sample and the processing performed on the sample.

[0054] The illumination subsystem may be configured to direct light to the sample at different angles of incidence and different numbers of times. For example, the optical subsystem may be configured to change one or more characteristics of one or more elements of the illumination subsystem such that the light is directed to the sample at an angle of incidence different from that shown in FIG. 5. In such an embodiment, the optical subsystem may be configured to move the light source 504, the optical element 506, and the lens 508 such that the light is directed to the sample at different angles of incidence.

[0055] In some examples, the optical subsystem may be configured to direct light at the sample at one or more angles of incidence simultaneously. For example, the illumination subsystem may include one or more illumination channels, and one of the illumination channels may include a light source 504, an optical element 506, and a lens 508 as shown in FIG. 5, and another illumination channel (not shown) may include similar elements. The similar elements may be differently or similarly configured, or may include at least one light source and, optionally, one or more other components as further described herein. When such light is directed at the sample simultaneously with other light, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed at the sample at different angles of incidence may be different, and as a result, the light generated from different angles of incidence in the illumination of the sample is distinguishable from each other by the detector.

[0056] In another example, the illumination subsystem may include only one light source (e.g., the light source 504 shown in FIG. 5), and the light from the light source may be separated into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. Then, the light in each different optical path may be directed at the sample. The plurality of illumination channels may be configured to direct light at the sample simultaneously or at different timings (e.g., when irradiating the sample in sequence using different illumination channels). In another example, the same illumination channel may be configured to direct light at samples with different characteristics at different timings. For example, in some examples, the optical element 506 may be configured as a spectral filter, and the characteristics of the spectral filter may be changed in various different ways (e.g., by replacing the spectral filter), and different wavelengths of light may be directed at the sample a different number of times. The illumination subsystem may have other suitable configurations known in the art for directing light with different or the same characteristics at the sample at different or the same angles of incidence, either sequentially or simultaneously.

[0057] The light source 504 may be a suitable laser in the art configured to generate light of a suitable wavelength well-known in the art. Further, the laser may be configured to generate monochromatic light or substantially monochromatic light. Thus, the laser may be a narrow-band laser. The light source may further include a multi-color light source that generates light of a plurality of individual wavelengths or wavelength bands.

[0058] The light from the optical element 506 may be focused by the lens 508 onto the beam splitter 510. The lens 508 is shown in FIG. 5 as a single refractive optical element, but in practice, the lens 508 may include several refractive elements and / or refractive optical elements that combine the light from the optical elements and focus it onto the sample. The illumination subsystem shown in FIG. 5 and described herein may include other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarizing elements, spectral filters, spatial filters, refractive optical elements, apodizers, beam splitters, apertures (any number of each), etc., and may include suitable optical elements well-known in the art. Further, the system may be configured to change one or more elements of the illumination subsystem based on the type of illumination used.

[0059] The optical subsystem may also include a scan subsystem configured to scan the light over the sample. For example, the optical subsystem may include a stage 512 on which the sample 502 is placed. The scan subsystem may include a suitable mechanical assembly and / or robotic assembly (including the stage 512) configured to move the sample so that the light can be scanned over the sample. Additionally, or alternatively, the optical subsystem may be configured such that one or more optical elements of the optical subsystem perform the scanning of the light over the sample. The light may be scanned over the sample in a suitable manner.

[0060] The detection subsystem may include one or more detection channels. At least one of the detection channels includes a detector configured to detect light from the sample by illuminating the sample and configured to generate an output in response to the detected light. For example, the detection subsystem shown in FIG. 5 includes two detection channels, one formed by detectors 514, element 516, and detector 518, and the other formed by detectors 520, element 522, and detector 524. As shown in FIG. 5, the two detection channels are configured to collect and detect light at different collection angles. In some examples, one detection channel is configured to detect specularly reflected light, and the other detection channel is configured to detect light from the sample that is non-specularly reflected (e.g., scattered light, diffracted light, etc.). However, two or more detection channels may be configured to detect the same type of light from the sample (e.g., specularly reflected light). Although FIG. 5 shows an embodiment of a detection subsystem that includes two detection channels, the detection subsystem may include a different number of detection channels (e.g., only one detection channel, or two or more detection channels). Although each collector is shown in FIG. 5 as a single refractive optical element, each collector may include one or more refractive optical elements and / or one or more reflective optical elements.

[0061] One or more detection channels may include suitable detectors well-known in the art such as photomultiplier tubes (PMTs), charge-coupled devices (CCDs), time-delay integration (TDI) cameras, etc. The detectors may also include non-imaging detectors or imaging detectors. If the detector is a non-imaging detector, each detector may be configured to detect a particular characteristic of light, such as intensity, but not to detect characteristics such as a function of position within the imaging plane. Therefore, the output generated by each detector included in each detection channel may be a signal or data, but not an image signal or image data. In such a case, a computer subsystem, such as computer subsystem 526 of the system, may be configured to generate an image of the sample from the non-imaging output of the detector. However, in another example, the detector may be configured as an imaging detector configured to generate an image signal or image data. Thus, the system may be configured in several ways to generate the outputs and / or images described herein.

[0062] Note that FIG. 5 is provided herein to illustrate the configuration of an illumination and detection subsystem that may be included in an embodiment of the system described herein. Of course, the configuration of the illumination and detection subsystem described herein may be modified to optimize the performance of the system, as is typically done when designing a commercial system. Further, the systems described herein may be implemented using existing optical systems, such as the 29XX, 39XX, "Voyager (trademark)", "Puma (trademark)" series of tools commercially available from KLA Corp. located in Milpitas, California (e.g., by adding the functionality described herein to an existing optical system). For some such systems, the methods described herein may be provided as any functionality of the system (e.g., in addition to other functions of the system). Alternatively, the systems described herein may be designed "from scratch" to provide a completely new system.

[0063] The computer subsystem 526 of the system may be connected in a suitable manner (e.g., via one or more transmission media that may include "wired" and / or "wireless" transmission media) to the detectors of the detection subsystem, so that the computer subsystem can receive the output, images, etc. generated by the detectors during the scanning of the sample. The computer subsystem 526 may be configured to perform some functions using the output, images, etc. of the detectors described herein and other functions further described herein. This computer subsystem may be configured as further described herein.

[0064] This computer subsystem (similar to other computer subsystems described herein) may be referred to as a computer system herein. Each computer subsystem or system described herein may take various forms, including personal computer systems, image computers, mainframe computer systems, workstations, network appliances, Internet appliances, and other devices. In general, the term "computer system" may be broadly defined to encompass any device having one or more processors that execute instructions from a storage medium. Also, a computer subsystem or system may include any suitable processor well known in the art, such as a parallel processor. Further, a computer system or system may include a computer platform with high-speed processing and high-speed software, either as a stand-alone or networked tool.

[0065] If the system includes one or more computer subsystems, as further described herein, different computer subsystems may be interconnected with each other, and images, data, information, instructions, etc. can be transmitted between the computer subsystems. For example, computer subsystem 526 may be connected to computer subsystem(s) 528 (as shown by the dashed line in FIG. 5) by a suitable transmission medium that may include suitable wired and / or wireless transmission media well known in the art. Such two or more computer subsystems may also be effectively connected by a shared computer-readable recording medium (not shown).

[0066] The computer subsystem(s) may be configured to detect defects in a sample by applying a defect detection method to the output generated by the detector(s). Detecting defects in the sample may be performed in a suitable manner well known in the art using a suitable defect detection method and / or algorithm (e.g., applying a defect detection threshold to the output and determining whether an output having a value above the threshold corresponds to a defect or a possible defect).

[0067] As described above, the computer subsystem may detect defects in the sample using the output generated by the detector(s). Thus, the system described herein may be configured as an inspection system. In another embodiment, the system described herein may be configured as a measurement or defect review system. Specifically, the embodiments of the system described herein and shown in FIG. 5 may modify one or more parameters to provide different imaging capabilities depending on the use for which it is employed. In such an example, the optical subsystem shown in FIG. 5 may be configured to have a higher resolution when used for measurement rather than inspection. In other words, the embodiments of the subsystem shown in FIG. 5 describe some general and various configurations for the optical subsystem that can be adapted in several ways that will be apparent to those skilled in the art to manufacture systems having different imaging capabilities suitable for different uses.

[0068] Each embodiment of the system may be further configured based on other embodiments described herein. Also, the embodiments described herein may be further configured as described in Germanenko et al. U.S. Patent No. 9,116,445, issued August 25, 2015, which is incorporated herein by reference in its entirety.

[0069] Other embodiments relate to a computer-implemented method for controlling the pressure of a cavity of a light source. The method includes measuring the pressure of the cavity of the light source, as shown in step 600 of FIG. 6. The method also includes controlling the amount of one or more gases in the cavity having one or more gas flow elements, as shown in step 602 of FIG. 6. Further, the method includes comparing the measured pressure to a predetermined range of pressure values, as shown in step 604 of FIG. 6. If the measured pressure is outside the predetermined range, the method includes changing at least one parameter of at least one of the one or more gas flow elements based on the result of the comparison, as shown in step 606 of FIG. 6. Each step of the method may be further performed as described herein. The method may include other steps implemented by the systems described herein. The steps of the method may be performed by the systems described herein and may be configured based on any of the embodiments described herein.

[0070] Further embodiments relate to a non-transitory computer-readable medium storing program instructions executable on a computer system for performing a computer-implemented method for controlling the pressure of a cavity of a light source. One such embodiment is shown in FIG. 7. Specifically, as shown in FIG. 7, the non-transitory computer-readable medium 700 includes program instructions 702 executable on a computer system 704. The computer-implemented method may include any of the steps of the methods described herein.

[0071] The program instructions 702 for executing the method as described in this specification may be based on a computer-readable medium 700. The computer-readable medium may be a storage medium such as a magnetic disk or an optical disk, a magnetic tape, or other suitable non-transitory computer-readable media well-known in the art.

[0072] The program instructions may be executed in various ways, including, in particular, procedure-based techniques, component-based techniques, and / or object-oriented techniques. For example, the program instructions may be executed using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), Streaming SIMD Extension instructions (SSE), or other technologies and methods as needed.

[0073] The computer system 704 may be configured based on any of the embodiments described in this specification.

[0074] In view of the description herein, further modifications and alternative embodiments of various aspects of the present invention will become apparent to those skilled in the art. For example, a method and system for controlling the pressure of the cavity of a light source are provided. Accordingly, the description herein is to be construed as illustrative only and is intended to teach those skilled in the art a general way of implementing the present invention. The forms of the invention depicted and described herein are to be understood as the preferred embodiments at the time of filing. The components and materials may be replaced with those exemplified and described herein, the components may be interchanged, the order of the steps may be reversed, and certain features of the invention may be utilized independently, all of which will be apparent to those skilled in the art who have obtained the benefits of the description of the present invention. Modifications may be made to the components described herein without departing from the spirit and scope of the invention as claimed below.

Claims

1. A system configured to control the pressure within a cavity containing a gaseous active medium for generating light from a laser light source, a barometric pressure sensor configured to measure the pressure within the cavity of the laser light source, one or more gas flow elements configured to control the amount of one or more gases within the cavity, a control subsystem configured to compare the measured pressure to a predetermined range of values for the pressure and, when the measured pressure is outside the predetermined range, change at least one parameter related to the gas flow of the one or more gas flow elements based on the result of the comparison, an illumination subsystem configured to direct light generated by the laser light source towards a sample, a detection subsystem configured to detect light from the sample, a computer subsystem configured to detect a defect on the sample based on an output responsive to the detection light generated by the detection subsystem, comprising, further, an additional cavity surrounding the cavity, an additional barometric pressure sensor configured to measure the pressure within the additional cavity, one or more additional gas flow elements configured to control the amount of one or more gases within the additional cavity, wherein the control subsystem compares the pressure within the additional cavity measured by the additional barometric pressure sensor to a predetermined range and, when the measured pressure within the additional cavity is outside the predetermined range, changes at least one parameter related to the gas flow of the one or more additional gas flow elements based on the result of the comparison.

2. The system according to claim 1, wherein the sample is a wafer.

3. The system according to claim 1, wherein the laser light source is a laser that generates single-wavelength light.

4. The system according to claim 1, wherein the laser light source is a laser configured to generate narrow-band light.

5. The system according to claim 1, wherein the cavity is a harmonic generation cavity of the laser light source.

6. The system according to claim 1, wherein the cavity is an infrared cavity of the laser light source.

7. The system according to claim 1, wherein the additional cavity is the main cavity of the laser light source.

Images