Line Scan Knife-Edge Height Sensor for Semiconductor Inspection and Metrology

Abstract

Embodiments of the present application relate to a line scanning knife-edge height sensor for semiconductor inspection and metrology. The knife-edge mirror is positioned at the focus of the light reflected from the wafer so that the reflective film on the knife-edge mirror is configured to block at least some of the light reflected from the wafer. When the light reflected from the wafer is underfocused or overfocused, the portion of light blocked changes. At least one sensor receives the light reflected from the wafer. A reading from the at least one sensor can be used to determine whether the light is underfocused or overfocused. The height of an irradiated area on the surface of the wafer can be determined using this reading from the at least one sensor.

Description

[0001] Information about divisional applications

[0002] This application is a divisional application of the invention patent application with the application date of December 17, 2015, application number "201580065602.8", and invention name "Line scanning knife edge height sensor for semiconductor inspection and measurement".

[0003] CROSS REFERENCE TO RELATED APPLICATIONS

[0004] This application claims priority to provisional patent application filed on December 17, 2014 and assigned as US Application No. 62 / 092,836, the disclosure of which is hereby incorporated by reference. Technical Field

[0005] The present invention relates to semiconductor wafer inspection and metrology. Background Art

[0006] The semiconductor industry requires three-dimensional ("3D") inspection and / or metrology processes for silicon wafers. For example, such inspection can be used to test through-silicon vias ("TSVs") and bump structures or particle shapes (e.g., size and height). Typical techniques used for inspection or metrology include: (1) triangulation; (2) geometric shadowgraphy; (3) various confocal microscopy techniques; and (4) white light (or broadband light) interferometry. Triangulation and geometric shadowgraphy techniques are not sufficiently accurate for modern back-end-of-line ("BEOL") applications. Confocal microscopy and interferometry techniques are generally unable to meet throughput requirements.

[0007] White light interferometry is known as a high-resolution method for 3D inspection and metrology and has been used in the semiconductor industry. There are two types of such devices on the market: (1) scanning white light interferometers ("SWI"); and (2) spectral white light interferometers. In a SWI device, a sample (e.g., a wafer under inspection) or inspection optics is scanned for a distance in a direction perpendicular to the wafer surface (e.g., the z direction). Multiple frames at a specific z value are taken to determine the height measurement of a specific xy location on the wafer surface. Such SWI devices are robust but typically slow. In addition, this technique requires moving the sample into the field of view and holding the sample steady before making a measurement, which also limits speed. Likewise, the throughput of current spectral white light interferometers is also slow for the semiconductor industry.

[0008] In semiconductor inspection and metrology processes, an autofocus mechanism is used for an optical probe (OP). In this technique, a chopper is used to test whether the focus is at a preset position, before a preset position, or after a preset position. The light passes through the chopper to a dual-element photodetector. The dual-element photodetector and the chopper are electronically connected to a lock-in amplifier. When the light is focused, there is a zero phase shift between the reference signal from the chopper and the signals from the two channels of the dual-element photodetector. If the light is underfocused or overfocused, the phase of one element is shifted negatively or positively, respectively, and the phase of the other element is shifted in the opposite direction relative to the reference signal. Under a 100x objective, this method can perform detection and servo loops to control the focus better than 20nm. However, the throughput of the chopper technique is slow.

[0009] When the target structure height is reduced to less than 10μm, existing triangulation and geometric shadowing techniques generally do not provide the accuracy and precision required for 3D inspection. Confocal and interferometry methods generally do not provide the throughput required for 3D inspection or are too expensive. Therefore, there is a need for an inspection and metrology technology that can provide better accuracy, cost and throughput. Summary of the invention

[0010] In a first embodiment, a system is provided. The system includes: a light source configured to provide light; a stage configured to hold a wafer to receive the light from the light source; a knife-edge mirror; and a sensor configured to receive the light reflected from the wafer. The knife-edge mirror is configured to receive the light reflected from the wafer. The knife-edge mirror includes a reflective film and an anti-reflective film, both of which are disposed on the knife-edge mirror, thereby forming a boundary between the reflective film and the anti-reflective film. The knife-edge mirror is positioned at a focus of the light reflected from the wafer, so that the reflective film is configured to block at least some of the light reflected from the wafer. The knife-edge mirror is configured so that the portion of the light blocked by the knife-edge mirror is different when the light reflected from the wafer is underfocused or overfocused. The sensor detects whether the light reflected from the wafer is underfocused or overfocused.

[0011] The system may include an objective lens configured to illuminate the wafer with light from the light source and to combine light reflected from the wafer.

[0012] The system may include a processor in electrical communication with the sensor.The processor may be configured to determine a height of an irradiated area on a surface of the wafer relative to a normal plane of the wafer.

[0013] The sensor may include two photodiodes. When the light reflected from the wafer is under-focused or over-focused, the two photodiodes may receive different amounts of the light reflected from the wafer.

[0014] The sensor may include a dual-unit photodiode and a prism configured to refract two halves of the light reflected from the wafer onto the dual-unit photodiode.

[0015] The system may include diffractive optics configured to shape the light into lines for projection onto the wafer.The sensor may include a photodiode array.

[0016] The knife-edge mirror may be positioned at a non-perpendicular angle relative to the light reflected from the wafer. The sensor may include two photodiodes. The system may further include a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror. The second sensor may include two photodiodes.

[0017] The knife-edge mirror may be positioned at a non-perpendicular angle relative to the light reflected from the wafer. The sensor may include a dual-unit photodiode. The system may further include a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror. The second sensor may include a second dual-unit photodiode.

[0018] The knife-edge mirror may be positioned at a non-perpendicular angle relative to the light reflected from the wafer. The sensor may include a dual-unit photodiode. The system may further include: a diffractive optical device configured to shape the light into a line for projection onto the wafer; a prism configured to refract two halves of the light reflected from the wafer onto the dual-unit photodiode; a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror; and a second prism configured to refract two halves of the light reflected from the wafer reflected by the knife-edge mirror onto the second dual-unit photodiode. The second sensor may include a second dual-unit photodiode.

[0019] The knife-edge mirror may be positioned at a non-perpendicular angle relative to the light reflected from the wafer. The second sensor may include two photodiode arrays. The system may further include: a diffractive optical device configured to shape the light into a line projected onto the wafer; and a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror. The second sensor may include two photodiode arrays.

[0020] The stage may be configured such that the wafer is scanned relative to the light from the light source.

[0021] In a second embodiment, a method is provided. The method includes reflecting light from a surface of a wafer; passing the light through a knife-edge mirror; receiving the light from the knife-edge mirror with at least one sensor; and using a reading from the at least one sensor to determine whether the light is under-focused or over-focused. The knife-edge mirror includes a reflective film and an anti-reflective film, both of which are disposed on the knife-edge mirror, thereby forming a boundary between the reflective film and the anti-reflective film. The knife-edge mirror is positioned at a focal point of the light reflected from the wafer such that the reflective film is configured to block at least some of the light reflected from the wafer and such that the portion of the light blocked by the knife-edge mirror is different when the light reflected from the wafer is under-focused or over-focused.

[0022] The method may further include determining a height of an irradiated area on the surface of the wafer relative to a normal plane of the wafer. The method may further include determining that a defect exists on the wafer.

[0023] The wafer may be scanned relative to the light.

[0024] The method may further include: splitting the light from the knife-edge mirror into two quantities; and determining whether the quantities are equal.

[0025] The light projected onto the wafer may be shaped into a line.

[0026] A portion of the light may be reflected from the knife-edge mirror to a second sensor. Readings from the second sensor may be used to determine whether the light is under-focus or over-focus. The method may also further include: splitting the light reflected from the knife-edge mirror into two quantities; and determining whether the quantities are equal. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] For a more complete understanding of the nature and purpose of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0028] Figure 1 is an embodiment according to the present invention using two photodiodes;

[0029] Figures 2 to 4 Respectively indicate when the light is focused, underfocused, and overfocused Figure 1 The photodiode readings;

[0030] Figure 5 is a schematic diagram of light passing through a knife-edge mirror according to an embodiment of the present invention;

[0031] Figure 6 is an embodiment according to the present invention using a dual-unit photodiode;

[0032] Figures 7 to 9Respectively indicate when the light is focused, underfocused, and overfocused Figure 6 Readings of dual-cell photodiodes;

[0033] Fig.10 is an embodiment using a photodiode array according to the present invention;

[0034] Figures 11 to 13 Respectively indicate when the light is focused, underfocused, and overfocused Fig.10 The photodiode array readings;

[0035] Fig.14 is another schematic diagram of light passing through a knife-edge mirror according to an embodiment of the present invention;

[0036] Fig.15 is an embodiment according to the present invention using four photodiodes;

[0037] Figures 16 to 18 Respectively indicate when the light is focused, underfocused, and overfocused Fig.15 The photodiode readings;

[0038] Fig.19 is an embodiment according to the present invention using two dual-unit photodiodes;

[0039] Figures 20 to 22 Respectively indicate when the light is focused, underfocused, and overfocused Fig.19 Readings of dual-cell photodiodes;

[0040] Fig.23 is an embodiment according to the present invention using four photodiode arrays;

[0041] Figures 24 to 26 Respectively indicate when the light is focused, underfocused, and overfocused Fig.23 The photodiode array readings;

[0042] Fig. 27 is an embodiment according to the present invention using two photodiode arrays;

[0043] Figures 28 to 30 Respectively indicate when the light is focused, underfocused, and overfocused Fig. 27 The photodiode array readings;

[0044] Fig.31 is another embodiment according to the present invention using two photodiode arrays;

[0045] Fig.32 is a schematic diagram showing the reshaping of an image in a photodiode array;

[0046] Figures 33 to 35 Respectively indicate when the light is focused, underfocused, and overfocused Fig.31The photodiode array readings; and

[0047] Fig.36 is a flow chart of a method according to the present invention. DETAILED DESCRIPTION

[0048] Although the claimed subject matter will be described in terms of certain embodiments, other embodiments including embodiments that do not provide all of the advantages and features set forth herein are also within the scope of the present invention. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the present invention. Therefore, the scope of the present invention is defined solely by reference to the appended claims.

[0049] Embodiments of the systems and methods disclosed herein use a phase shift characteristic relative to focus shift to improve throughput. A knife-edge mirror (KEM) is used to determine whether the light is in focus, underfocus, or overfocus. Although more signals can be used, only 2 to 4 signals per xy point are required to determine the height of the reflection point on the wafer. This design is more robust and less expensive than the prior art, and can be faster than white light interferometry. Especially for 3D inspection and metrology, embodiments of the systems and methods disclosed herein provide better throughput, cost, and accuracy than the prior art. For example, when using a line scan scheme, the throughput can be increased by several orders of magnitude compared to chopper technology.

[0050] Figure 1 1 is an embodiment using two photodiodes 115, 116. System 100 has a light source 101, which is configured to provide light 102 having a wavelength spectrum range. In some embodiments, light source 101 can be configured to provide white light (i.e., broadband light in the visible spectrum) or light that is partially or completely outside the visible spectrum. In an exemplary embodiment, light source 101 provides light 102 including a wavelength (λ) from 400 nm to 800 nm.

[0051] A laser light source may be used for light source 101, which may provide higher brightness than spectroscopic methods such as white light interferometry and color confocal microscopy. Laser light sources such as diode lasers improve the lifetime, stability, and thermal control of the light source. For example, light source 101 may be a visible diode laser.

[0052] Light 102 is projected toward light source pinhole 103 and beam splitter 104, and beam splitter 104 splits light 102 into two quantities, such as Figure 1 Next, light 102 is projected through objective lens 105, which may be a high-magnification objective lens. Some or all of light 102 passes through objective lens 105 and reaches at least a portion of the sample at illumination point 107. For example, the sample may be a wafer 106. The spot size of light 102 at illumination point 107 may be diffraction limited.

[0053] Wafer 106 is disposed on stage 117, which is configured to position wafer 106 to receive light 102. Stage 117 can be fixed or can be scanned along the x-direction, y-direction, and / or z-direction. In one example, wafer 106 can be clamped to stage 117, such as by mechanical and / or electrostatic clamping. For example, stage 117 can translate wafer 106 along a plane perpendicular to the axis of light 102 or objective lens 105 (e.g., xy plane).

[0054] The reflected light 108 from the wafer 106 is projected through the objective lens 105 and the KEM 109. The KEM 109 includes a reflective film 110 and an anti-reflective film 111 disposed on the KEM 109. There is a boundary between the reflective film 110 and the anti-reflective film 111. For example, half of the KEM 109 may be coated with the anti-reflective film 111 and half of the KEM 109 may be coated with the reflective film 110. The boundary of the reflective film 110 and the anti-reflective film 111 is a straight line and can be used as a knife edge in a Foucault test.

[0055] When the surface of the wafer 106 is in its normal z position, the boundary between the reflective film 110 and the anti-reflective film 111 of the KEM 109 is aligned at the focus of the reflected light 108, in the middle of the focused spot. As in the Foucault test, the KEM 109 provides a uniformly transmitted beam when the reflected light 108 passes through the KEM 109. This provides a balanced signal at both the photodiodes 115, 116.

[0056] The focal point 118 of the reflected light 108 relative to the KEM 109 can be preferably seen at Figure 1 When the boundary of the reflective film 110 and the anti-reflective film 111 of the KEM 109 is located in the middle of the focus 118 (Airy disk), the reflective film 110 shears the reflected light 108 in such a way that the transmitted light beam has a uniform intensity distribution across the beam.

[0057] The reflected light 108 passing through the KEM 109 is split into two quantities on both sides by a prism 112 with a high reflective coating, and each component beam is projected to one of the photodiodes 115, 116 through one of the optional lenses 113, 114. Ideally, the prism 112 is placed at the pupil plane via a relay lens when necessary. Lenses 113, 114 are not necessary in this embodiment, and the reflected light 108 can be projected directly from the prism 112 to one of the photodiodes 115, 116. The photodiodes 115, 116 can provide the same performance in terms of photoelectronic efficiency, time response, and electronic amplification gain.

[0058] Figures 2 to 4 Respectively indicate when the light is focused, underfocused, and overfocused Figure 1The light 102 illuminates the wafer 106 at the illumination point 107. If the KEM 109 is located at the focus of the reflected light 108, the light beam emerging from the KEM 109 is uniform and then the two photodiodes 115, 116 will provide balanced signals, such as Figure 2 However, the illumination point 107 on the wafer 106 may vary across the surface of the wafer 106 or otherwise be at different heights. For example, there may be a bump, scratch, unfilled via, or defect on or in the wafer 106. This changes the focus of the reflected light 108 relative to the KEM 109.

[0059] If the height of the surface of the wafer is increased relative to the normal setting in the z-direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, such as Figure 3 In this example, the two photodiodes 115, 116 will provide unbalanced signals because the KEM 109 acts as a barrier, allowing more light to exit to the photodiode 116 and less light to exit to the photodiode 115. The light beam exiting the KEM 109 is therefore non-uniform.

[0060] If the height of the surface of the wafer is set lower relative to the normal in the z-direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, such as Figure 4 In this example, the two photodiodes 115 and 116 will follow the same mechanism to Figure 3 The defocused example in the opposite way provides an unbalanced signal.

[0061] The system 100 can discern whether a detected feature on the wafer 106 is above or below the normal plane of the wafer 106 from the signals of the two photodiodes 115, 116. Which of the photodiodes 115, 116 receives more or less light can be used to determine whether the reflected light 108 is under-focused or over-focused. Thus, if the photodiodes 115, 116 do not receive equal amounts of reflected light 108, it can be determined that the detected feature on the wafer 106 is above or below the normal plane of the wafer 106.

[0062] Figure 5 is a schematic diagram of light passing through the KEM 109 based on the illumination point. The reflective film 110 (R=1) is configured to block about half of the reflected light 108 from the wafer by placing the boundary through the middle of the Airy disk, regardless of whether the reflected light 108 is focused, underfocused, or overfocused. The only difference is that the intensity uniformity changes when the reflected light 108 is focused, underfocused, or overfocused. The anti-reflective film 111 (T=1) is configured to allow a portion of the reflected light 108 to pass through. In an example, Figure 5Half of the Airy disk formed by the beam spot of the reflected light 108 (shown in dotted lines) will be blocked by the reflective film 110.

[0063] Figure 6 is an embodiment using a dual-unit photodiode 203. A dual-unit photodiode (e.g., dual-unit photodiode 203) has two active photodiode regions that can measure the uniformity of a light beam. In system 200, prism 201 refracts both halves of reflected light 108 onto dual-unit photodiode 203. This can be done with optional lens 202. When wafer 106 is focused, dual-unit photodiode 203 will be balanced.

[0064] Figures 7 to 9 Respectively indicate when the light is focused, underfocused, and overfocused Figure 6 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the KEM 109 is located at the focus of the reflected light 108, the dual-unit photodiode 203 will provide a balanced signal because the light beam emitted from the KEM 109 is uniform, such as Figure 7 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Figure 8 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig. 9 System 200 can discern whether a detected feature on wafer 106 is above or below the normal plane of wafer 106 based on the signal of dual-cell photodiode 203 .

[0065] Fig.10 303 is an embodiment using a photodiode array (PDA) 303. System 300 uses a light source slit 304 to shape light 102 into a line rather than a point. This light source slit 304 may have a first dimension (e.g., a "length" of the light source slit 304, which may be the y direction) that is substantially larger than a second dimension (e.g., a "width" of the light source slit 304, which may be the z direction). In certain exemplary embodiments, the length of the light source slit 304 may be 1 mm to 5 mm. For example, in an embodiment, the length of the light source slit 304 is 3 mm. Other lengths are possible. The width of the light source slit 304 is typically sufficiently small that the light source slit 304 may be considered one-dimensional. For example, the width of the light source slit 304 may be similar to the diameter of a point beam in a conventional interferometer. For example, in some embodiments, the size of the light source slit 304 may be 5 μm to 30 μm.

[0066] Diffractive optics (not illustrated) may also be included to shape the light 102 into a line rather than a point before the light 102 is incident on the beam splitter 104 or the light source slit 304. The illumination line 305 is incident on the wafer 106. The KEM 109 is aligned so that its edge is parallel to the line of reflected light 108. The border of the KEM 109 is aligned to block half of the imaged line of the illumination line 305, regardless of whether the wafer 106 is focused, underfocused, or overfocused. However, when the wafer 106 is focused, the intensity distribution of the line in the pupil plane will be uniform. The spot size of the illumination line 305 may be diffraction limited.

[0067] The prism 301 refracts the reflected light 108 of both halves through the lens 302 onto the PDA 303. The lens 302 may be required to provide spatial resolution along the illumination line 305 on the wafer 106. The PDA (e.g., PDA 303) has an array of multiple regions that can detect light beams. When the wafer 106 is focused, the PDA 303 will be balanced. If the wafer 106 has different heights at points on the illumination line 305 relative to the normal plane of the wafer 106, the focus corresponding to the point will shift, thereby generating an unbalanced signal at the corresponding pixel on the PDA 303. The height can be extracted from the signal from the PDA 303 based on the unbalanced intensity of two or more photodiodes in the PDA 303 (e.g., in a pixel-to-pixel manner). The PDA 303 may be, for example, two conventional PDAs aligned side by side or another type of PDA with 2×n pixels (e.g., a PDA with 2 rows). The number of pixels in the PDA 303 may vary.

[0068] Figures 11 to 13 Respectively indicate when the light is focused, underfocused, and overfocused Fig.10 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the focus of the reflected light 108 is located at the KEM 109, then the PDA 303 will provide a balanced signal, such as Fig.11 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Fig.12 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig.13 The system 300 can discern whether the detected feature on the wafer 106 is above or below the normal plane of the wafer 106 based on the signal of the PDA 303.

[0069] Fig.14 is another schematic diagram of light passing through KEM 109 based on an irradiation line, which can be used with Figure 5 Same mechanism. Reflective film 110 (R=1) is configured to block half of the reflected light 108 (shown in dashed lines) from the wafer, regardless of whether the reflected light 108 is focused, under-focused, or over-focused. Anti-reflective film 111 (T=1) is configured to allow the rest of the reflected light 108 to pass through. When the beam is focused, the focused spot has a finite size (Airy disk) rather than an infinitely small geometric point. The boundary of KEM 109 always reflects half of the beam and transmits half of the beam. When the focus changes, the only difference is that the uniformity changes when the beam exits KEM 109.

[0070] Fig.15 405. In the system 400, the KEM 109 is tilted at an angle so that the portion of the light beam emitted from the R=1 range (i.e., from the reflective film 110) is delivered to the photodiodes 404, 405 through the prism 401 and one of the optional lenses 402, 403. The KEM 109 can be tilted to be at a non-perpendicular angle relative to the reflected light 108 (e.g., the axis of the reflected light 108). The lenses 402, 403 are not necessary, and the reflected light 108 can be projected directly from the prism 401 to one of the photodiodes 404, 405. The signals of the photodiodes 404, 405 provide redundant and complementary measurements that can be used to improve accuracy and precision. For example, the photodiodes 115, 116, 404, 405 can provide multiple measurements so that the final result can be an average of the multiple measurements. Therefore, in the presence of systematic errors, the systematic errors can be separated into symmetric and asymmetric parts, and the asymmetric parts can be averaged in the final calculation.

[0071] Figures 16 to 18 Respectively indicate when the light is focused, underfocused, and overfocused Fig.15 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the focus of the reflected light 108 is located at the KEM 109, the photodiodes 115, 116, 404, 405 will provide a balanced signal, such as Fig.16 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Fig.17 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig.18System 400 can discern whether a detected feature on wafer 106 is above or below the normal plane of wafer 106 based on the signals of photodiodes 115 , 116 , 404 , 405 .

[0072] Fig.19 is an embodiment using two dual-unit photodiodes 203, 503. In system 500, KEM 109 is tilted so that the beam portion emitted from the R=1 range (i.e., from the reflective film 110) is delivered to prism 501, which refracts the two halves of the beam portion onto dual-unit photodiode 503. This can be done by optional lens 502. When the wafer 106 is focused, the dual-unit photodiode 503 will be balanced. The signals of the dual-unit photodiodes 203, 503 provide redundant and complementary measurements that can be used to improve accuracy and precision.

[0073] Figures 20 to 22 Respectively indicate when the light is focused, underfocused, and overfocused Fig.19 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the focus of the reflected light 108 is located at the KEM 109, the dual-unit photodiode 203, 503 will provide a balanced signal, such as Fig. 20 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Fig.21 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig. 22 The system 500 can discern whether the detected feature on the wafer 106 is above or below the normal plane of the wafer 106 based on the signal of the dual unit photodiodes 203, 503.

[0074] Fig.23 604, 605, 609, 610. The system 600 uses the light source slit 304 to shape the light 102 into a line rather than a point. Diffractive optics (not illustrated) may also be included to shape the light 102 into a line rather than a point before the light 102 is incident on the beam splitter 104 or the light source slit 304. The illumination line 305 is incident on the wafer 106. The KEM 109 is aligned so that its edge is parallel to the line of reflected light 108.

[0075] The prism 601 refracts the two halves of the reflected light 108 onto two PDAs 604, 605. Lenses 602, 603 are positioned between the prism 601 and the PDAs 604, 605 to provide spatial resolution along the illumination line 305. When the wafer 106 is focused, the PDAs 604, 605 will be balanced. If the wafer 106 has different heights at points on the illumination line 305 relative to the normal plane of the wafer 106, the focus corresponding to the points will shift, thereby producing different balanced signals at corresponding pixels on the PDAs 604, 605. The signals from the PDAs 604, 605 can be extracted (e.g., in a pixel-to-pixel manner) based on the unbalanced intensity signals from the two photodiodes in each of the PDAs 604, 605.

[0076] In system 600, KEM 109 is tilted so that the beam portion emitted from the R=1 range (i.e., from reflective film 110) is delivered to prism 606, which refracts the two halves of the beam portion onto PDAs 609, 610. Lenses 607, 608 provide spatial resolution along the illumination line 305. When the wafer 106 is focused, the PDAs 609, 610 will be balanced. The signals of PDAs 609, 610 provide redundant and complementary measurements that can be used to improve accuracy and precision.

[0077] Figures 24 to 26 Respectively indicate when the light is focused, underfocused, and overfocused Fig.23 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the focus of the reflected light 108 is located at the KEM 109, then the PDA 604, 605, 609, 610 will provide a balanced signal, such as Fig.24 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Fig.25 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig.26 The system 600 can discern whether the detected feature on the wafer 106 is above or below the normal plane of the wafer 106 based on the signals of the PDAs 604 , 605 , 609 , 610 .

[0078] Fig. 27is an embodiment using two PDAs 303, 703. In system 700, KEM 109 is tilted so that the beam portion emitted from the R=1 range (i.e., from the reflective film 110) is delivered to prism 701, which refracts the two halves of the beam portion through lens 702 onto PDA 703 to provide spatial resolution along the illumination line 305. When the wafer 106 is focused, PDA 703 will be balanced. The signal of PDA 703 provides redundant measurements that can be used to improve accuracy and precision.

[0079] Figures 28 to 30 Respectively indicate when the light is focused, underfocused, and overfocused Fig. 27 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the focus of the reflected light 108 is located at the KEM 109, then the PDA 303, 703 will provide a balanced signal, such as Fig.28 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Fig.29 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig.30 The system 700 can discern whether the detected feature on the wafer 106 is above or below the normal plane of the wafer 106 based on the signal of the PDA 303, 703.

[0080] Fig.31 is another embodiment using two PDAs 803, 806. The reflected light 108 is delivered to a prism 801 which refracts the two halves of the beam through a lens 802 onto a PDA 803 to provide spatial resolution along the illumination line 305. When the wafer 106 is focused, the PDA 803 will be balanced.

[0081] In system 800, KEM 109 is tilted so that the beam portion emitted from the R=1 range (i.e., from reflective film 110) is delivered to prism 804, which refracts the two halves of the beam portion onto PDA 806. This can be done through optional lens 805. When wafer 106 is focused, PDA 806 will be balanced. The signal of PDA 806 provides redundant and complementary measurements that can be used to improve accuracy and precision.

[0082] PDA 803, 806 can be configured as Fig.32 The image of the line emitted from the KEM can be further reshaped by beam splicing technology, so that the left and right halves of the line image are as follows Fig.32The difference between the left and right halves of the image line can be detected simultaneously using the same PDA 807. Therefore, the actions of the two PDAs 808, 809 can be performed by a single PDA 807. This can provide more accurate results.

[0083] Figures 33 to 35 Respectively indicate when the light is focused, underfocused, and overfocused Fig.31 The height difference on the surface of the wafer 106 causes the focus of the reflected light 108 to change. If the focus of the reflected light 108 is located at the KEM 109, then the PDA 803, 806 will provide a balanced signal, such as Fig.33 If the height of the surface of the wafer is increased relative to the normal setting in the z direction, the focus of the reflected light 108 exceeds the KEM 109, which makes the reflected light 108 out of focus, as shown in FIG. Fig.34 If the height of the surface of the wafer is set lower relative to the normal in the z direction, the focus of the reflected light 108 is in front of the KEM 109, which makes the reflected light 108 overfocused, as shown in FIG. Fig.35 The system 800 can discern whether the detected feature on the wafer 106 is above or below the normal plane of the wafer 106 based on the signals of the PDAs 803, 806.

[0084] Fig.36 is a flow chart of a method. In 900, light is reflected from a surface of a wafer (e.g., wafer 106). In 901, the reflected light passes through a KEM. In 902, the reflected light from the KEM is received by at least one sensor. In 903, a reading from the at least one sensor is used to determine whether the light is underfocus or overfocus. The resulting determination of underfocus or overfocus can be used to determine the height of the surface of the wafer or to determine whether there are defects on the surface of the wafer.

[0085] Some or all of the sensors disclosed herein (e.g., photodiodes, dual-unit photodiodes, PDAs) may be electronically connected to a controller. The controller may include a processor, an electronic storage device in electronic communication with the processor, and a communication port in electronic communication with the processor. The processor may receive readings from the sensors, for example, through an electronic connection. Using the readings from the sensors, the processor may be configured to determine the height of an illuminated area (e.g., a point or line) of the wafer surface or determine whether a defect is on or in the wafer surface.

[0086] In the embodiments disclosed herein, the wafer can be scanned relative to the light in the x-direction and / or y-direction using a stage. This can provide surface topography information about an area of ​​the surface of the wafer. For example, this area can be a desired point for a block image, full wafer inspection, or bump height inspection.

[0087] It should be noted that the embodiments disclosed herein may determine the surface height profile of the wafer without scanning in the z-direction, but the stage may be capable of moving in the z-direction for other purposes.

[0088]

[00136] It may be desirable to calibrate embodiments of the systems disclosed herein. Calibration may include determining a relative signal difference (eg, a ratio of a pixel difference to a pixel sum) in relation to a known height difference.

[0089] The power supplied to the laser light source may be controlled, for example, by modulation or pulsing which may enable gating. In one example, during operation of the embodiments disclosed herein, the optics may be held steady or otherwise fixed, and the wafer may be moved in a direction perpendicular to the illumination line in synchronization with a PDA readout timer. Gating techniques (e.g., due to modulating the laser and synchronizing the laser with a PDA reader) may provide further spatial improvements because gating may reduce blurring caused by motion of a stage (e.g., stage 117).

[0090] Embodiments of the systems disclosed herein can be used for inspection or metrology of wafers. The height of the wafer surface or the presence or absence of defects on or on the wafer surface can be used as feedback during semiconductor manufacturing.

[0091] A number of design parameters of embodiments of the systems disclosed herein can be optimized. For example, height sensitivity related to depth of field is inversely proportional to the square of the objective numerical aperture (NA). Relatively high NAs can be tuned, but many applications require NAs greater than 0.25. High NA objectives typically provide a smaller field of view, which results in higher spatial (x and y) resolution and slower operation.

[0092] Although the invention has been described with respect to one or more specific embodiments, it will be understood that other embodiments of the invention may be made without departing from the scope of the invention. Therefore, it is considered that the invention is limited only by the appended claims and reasonable interpretations thereof.

Claims

1. A system for semiconductor wafer inspection and metrology, comprising: a light source configured to provide light; a stage configured to hold a wafer to receive the light from the light source; a knife-edge mirror configured to receive light reflected from the wafer, wherein the knife-edge mirror includes a reflective film and an anti-reflective film, both of which are disposed on the knife-edge mirror, thereby forming a boundary between the reflective film and the anti-reflective film, wherein the anti-reflective film is configured to allow a portion of the light reflected from the wafer to pass through the knife-edge mirror, wherein the boundary between the reflective film and the anti-reflective film is aligned at a focus of the light reflected from the wafer when the surface of the wafer is in a normal z-direction, wherein the z-direction is perpendicular to the surface of the wafer; and a sensor configured to receive the light reflected from the wafer, Wherein the system is configured to determine, based on readings from the sensor, whether the light reflected from the wafer is under-focused or over-focused relative to the knife-edge mirror and use the determination to determine a height of an illuminated area on the surface of the wafer.

2. The system of claim 1, further comprising an objective lens configured to illuminate the wafer with light from the light source and to combine the light reflected from the wafer.

3. The system of claim 1, further comprising a processor in electrical communication with the sensor, wherein the processor is configured to determine a height of an irradiated area on a surface of the wafer relative to a normal plane of the wafer.

4. The system of claim 1, wherein the sensor comprises two photodiodes, wherein the two photodiodes receive different amounts of the light reflected from the wafer when the light reflected from the wafer is under-focused or over-focused.

5. The system of claim 1, wherein the sensor comprises a dual-unit photodiode, and the system further comprises a prism configured to refract both halves of the light reflected from the wafer onto the dual-unit photodiode.

6. The system of claim 1, further comprising diffractive optics configured to shape the light into lines projected onto the wafer, and wherein the sensor comprises a photodiode array.

7. The system of claim 1 , wherein the knife-edge mirror is positioned at a non-perpendicular angle relative to the light reflected from the wafer, wherein the sensor comprises two photodiodes, and further comprising a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror, wherein the second sensors each comprise two photodiodes.

8. The system of claim 1 , wherein the knife-edge mirror is positioned at a non-perpendicular angle relative to the light reflected from the wafer, wherein the sensor comprises a dual-unit photodiode, and the system further comprises a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror, wherein the second sensor comprises a second dual-unit photodiode.

9. The system of claim 1, wherein the knife-edge mirror is positioned at a non-perpendicular angle relative to the light reflected from the wafer, wherein the sensor comprises a dual-cell photodiode, and the system further comprises: a diffractive optic configured to shape the light into a line projected onto the wafer; a prism configured to refract both halves of the light reflected from the wafer onto the dual-unit photodiode; a second sensor configured to receive the light reflected from the wafer reflected by the knife-edge mirror, wherein the second sensor comprises a second dual-cell photodiode; and A second prism is configured to refract both halves of the light reflected from the wafer reflected by the knife-edge mirror onto the second dual-unit photodiode.

10. The system of claim 1, wherein the knife-edge mirror is positioned at a non-perpendicular angle relative to the light reflected from the wafer, wherein the sensor comprises two photodiode arrays, and the system further comprises: a diffractive optic configured to shape the light into a line projected onto the wafer; and A second sensor is configured to receive the light reflected from the wafer reflected by the knife-edge mirror, wherein the second sensor includes two photodiode arrays.

11. The system of claim 1 , wherein the stage is configured such that the wafer is scanned relative to the light from the light source.

12. A method for semiconductor wafer inspection and metrology, comprising: causing light to reflect from a surface of the wafer; passing the light through a knife-edge mirror, wherein the knife-edge mirror includes a reflective film and an anti-reflective film, both of which are disposed on the knife-edge mirror, thereby forming a boundary between the reflective film and the anti-reflective film, wherein when the surface of the wafer is in a normal z-direction, the boundary between the reflective film and the anti-reflective film is aligned at a focus of the light reflected from the wafer, wherein the z-direction is perpendicular to the surface of the wafer, and the anti-reflective film is configured to allow a portion of the light reflected from the wafer to pass through the knife-edge mirror; receiving light from the knife-edge mirror with at least one sensor; and Readings from the at least one sensor are used to determine whether the light is under-focused or over-focused relative to the knife-edge mirror and the determination is used to determine a height of an illuminated area on the surface of the wafer.

13. The method of claim 12, further comprising determining a height of an irradiated area on the surface of the wafer relative to a normal plane of the wafer.

14. The method of claim 12, further comprising determining that a defect exists on the wafer.

15. The method of claim 12, further comprising scanning the wafer relative to the light.

16. The method of claim 12, further comprising: splitting the light from the knife-edge mirror into two quantities; and It is determined whether the amounts are equal.

17. The method of claim 12, further comprising shaping the light projected onto the wafer into a line.

18. The method of claim 12, further comprising reflecting a portion of the light from the knife-edge mirror to a second sensor.

19. The method of claim 18, further comprising using readings from the second sensor to determine whether the light is under-focus or over-focus.

20. The method of claim 19, further comprising: splitting the light reflected from the knife-edge mirror into two quantities; and It is determined whether the amounts are equal.

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