Crystallic defect inspection

Abstract

The invention discloses a wafer inspection system employing reflective bright field microscopy. The wafer inspection system may be fitted with polarization optical elements and mirrors to detect polarization change defects, such as microtubes, in semiconductor wafers. The polarization altering defects may be located within a bulk of the semiconductor wafer and may be imaged as bright features on a darker background. The system may also be used for conventional bright field inspection of non-polarization change defects such as contaminants and inclusions.

Description

Background Technology

[0001] Silicon carbide (SiC) is a semiconductor single crystal with excellent thermal conductivity, high saturated electron mobility, and high voltage breakdown resistance. It is suitable for fabricating high-frequency, high-power, high-temperature, and radiation-resistant electronic devices. During the production of SiC wafers for semiconductor applications, the crystal is subjected to internal and external stresses, leading to the growth of defects or dislocations within the atomic lattice. One such defect is called a micropipe defect.

[0002] Micropipes, also known as micropores, microtubes, capillary defects, or pinhole defects, are crystallographic defects in single-crystal substrates. Another type of defect, called a screw dislocation, is a common dislocation that transforms a continuous atomic plane within a crystal lattice into a helical shape. Micropipes can form once a screw dislocation propagates through the bulk of the sample during wafer growth. Micropores are generally considered "fatal defects" and the presence of high-density micropipes within SiC wafers can, for example, lead to significant losses in device yield during device fabrication processes using SiC wafers. Summary of the Invention

[0003] This document describes an apparatus and method for imaging microtubes and other polarization-altering defects in semiconductor wafers. According to some implementations, one or more polarizers and mirrors can be added to a bright-field microscope to transform the microscope into an inspection tool for detecting polarization-altering defects. For example, a first polarizer can prepare radiation incident on the semiconductor wafer in a first polarization state (e.g., circularly polarized radiation). The radiation in the first polarization state can pass through the semiconductor wafer and be reflected back by a mirror and pass through the wafer again. Polarization-altering defects in the semiconductor wafer can cause a localized change in the polarization of the radiation as it passes through the semiconductor wafer, by an amount different from that of a defect-free region of the semiconductor wafer. The radiation reflected back from the semiconductor wafer can be analyzed by either the first or second polarizer to detect the presence of polarization-altering defects in the microscope's field of view.

[0004] Some implementations relate to systems for detecting polarization-altering defects in semiconductor wafers. Such systems may include: an illumination source for emitting radiation; an objective lens for focusing the radiation from the illumination source onto the semiconductor wafer; a mirror arranged to reflect radiation emitted from the semiconductor wafer back through the semiconductor wafer as reflected radiation; an imaging array for recording an image of at least a portion of the semiconductor wafer produced by at least a portion of the reflected radiation returning through the semiconductor wafer; and a linear polarizer positioned between the semiconductor wafer and the imaging array. The linear polarizer may be oriented to: block a first portion of reflected radiation traveling through the semiconductor wafer that does not include a first region of polarization-altering defects; and transmit at least a portion of a second portion of reflected radiation traveling through the semiconductor wafer that includes a second region of polarization-altering defects.

[0005] Some implementations involve methods for detecting polarization-altering defects in semiconductor wafers. Such methods may include the following actions: irradiating a region of the semiconductor wafer having radiation in a first polarization state with radiation from an irradiation source; reflecting the radiation that has passed through the semiconductor wafer back towards the semiconductor wafer as reflected radiation using a mirror; collecting a portion of the reflected radiation with an objective lens to form an image of the region of the semiconductor wafer; blocking a first portion of the reflected radiation traveling through the region of the semiconductor wafer that does not include the first region of polarization-altering defects using a linear polarizer; transmitting at least a portion of a second portion of the reflected radiation traveling through the region of the semiconductor wafer that includes a second region of polarization-altering defects using a linear polarizer; and detecting an image of the region of the semiconductor wafer generated by the at least portion of the second portion of the reflected radiation transmitted by the linear polarizer using an imaging array.

[0006] Some implementations involve kits for converting a wafer inspection system into a system for detecting polarization-altering defects in semiconductor wafers. Such kits may include: at least one linear polarizer mounted in the forward optical path of the wafer inspection system, the forward optical path extending between an illumination source and the semiconductor wafer, wherein the illumination source is arranged to illuminate an area of ​​the semiconductor wafer for inspection; at least one waveplate mounted in the forward optical path between the linear polarizer and the semiconductor wafer; and a mirror mounted in the wafer inspection system at a position such that radiation from the illumination source traveling along the forward optical path and passing through the semiconductor wafer is reflected back by the mirror, through the semiconductor wafer, and toward an objective lens of the wafer inspection system.

[0007] Some implementations involve methods for detecting polarization-altering defects in semiconductor wafers using a kit that adapts a wafer inspection system for detecting polarization-altering defects in semiconductor wafers. Such methods may include: mounting a linear polarizer in the forward optical path of the wafer inspection system, the forward optical path extending between an illumination source and the semiconductor wafer, wherein the illumination source is arranged to illuminate the semiconductor wafer for inspection; mounting a waveplate in the forward optical path between the linear polarizer and the semiconductor wafer; and mounting a mirror in the wafer inspection system at a position such that radiation from the illumination source traveling along the forward optical path and passing through the semiconductor wafer is reflected back from the mirror, passes through the semiconductor wafer, and faces the objective lens of the wafer inspection system.

[0008] It should be understood that all combinations of the foregoing concepts, as well as the additional concepts discussed in more detail below (provided that such concepts are not inconsistent with each other), are contemplated as part of the inventive subject matter disclosed herein. In particular, all combinations of the claimed subject matter appearing at the end of this disclosure are contemplated as part of the inventive subject matter disclosed herein. It should also be understood that terms expressly adopted herein and which may also appear in any disclosure incorporated by reference shall be given the meaning most consistent with the specific concepts disclosed herein. Attached Figure Description

[0009] Those skilled in the art will understand that the accompanying drawings are primarily for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily drawn to scale; in some cases, various aspects of the inventive subject matter disclosed herein may be exaggerated or enlarged in the drawings to facilitate understanding of different features. In the drawings, similar reference characters generally refer to similar features (e.g., elements that are functionally similar and / or structurally similar).

[0010] Figure 1 An example wafer inspection system is depicted, in which a device for inspecting polarization-altering defects can be installed.

[0011] Figure 2 Describes the use of wafer inspection systems (such as...) Figure 1 An example arrangement of optical elements adapted to a system that can also detect polarization-change defects.

[0012] Figure 3 Showing Figure 2 How can an adapted wafer inspection system detect polarization-altering defects (such as microtubes) in semiconductor wafers?

[0013] Figure 4A These are images of SiC wafers obtained using reflective bright-field microscopy without polarization-sensitive imaging.

[0014] Figure 4B It was obtained using a compatible wafer inspection system. Figure 4A Microscopic images of silicon carbide (SiC) wafers. The images include bright features indicating the presence of microtube defects.

[0015] Figure 5 Describes the use of wafer inspection systems (such as...) Figure 1 Another example arrangement of optical elements (the system) adapted to a device that can also detect polarization change defects.

[0016] Figure 6A Describes the use of wafer inspection systems (such as...) Figure 1 Another example arrangement of optical elements (the system) adapted to a device that can also detect polarization change defects.

[0017] Figure 6B Describes the use of wafer inspection systems (such as...) Figure 1 Another example arrangement of optical elements (the system) adapted to a device that can also detect polarization change defects.

[0018] Figure 6C Describes the use of wafer inspection systems (such as...) Figure 1 Another example arrangement of optical elements (the system) adapted to a device that can also detect polarization change defects.

[0019] Figure 7 Describes the use of wafer inspection systems (such as...) Figure 1 Another example arrangement of optical elements (the system) adapted to a device that can also detect polarization change defects.

[0020] Figure 8 Describes the use of wafer inspection systems (such as...) Figure 1 Another example arrangement of optical elements (the system) adapted to a device that can also detect polarization change defects.

[0021] Figure 9 An example arrangement of optical elements in a wafer inspection system adapted to detect polarization-altering defects is depicted.

[0022] Figure 10 This demonstrates how a wafer inspection system can be adapted to use a linear polarizer without a quarter-wave plate to detect polarization-altering defects.

[0023] Figure 11 It describes the ability to perform wafer inspection in systems such as Figure 1 An example of a wafer chuck used in a system.

[0024] Figure 12 It describes the ability to perform wafer inspection in systems such as Figure 1 Details of the wafer chucks and adapters used in the system.

[0025] Figure 13 Depicts what can be used to load semiconductor wafers onto Figure 12 The wafer clamping end effector is used to unload semiconductor wafers onto and from the wafer chuck and adapter.

[0026] Figure 14 Depicting in Figure 12 Semiconductor wafers in the loading position on the wafer chuck and adapter.

[0027] Figure 15 Another example of an adapter is depicted. Detailed Implementation

[0028] Semiconductor wafers are frequently inspected for defects to control the yield of processes incorporating such wafers. The most typical method for inspecting semiconductor wafers for defects is using reflective bright-field microscopy (e.g., using a microscope system with coaxial illumination). In reflective bright-field microscopy, defects and contaminants in or on the wafer typically appear as dark spots against a bright background. In bulk semiconductor wafers, defects such as microvias or slip lines are difficult (if not impossible) to distinguish from other types of defects that may be present in the wafer (such as inclusions, pinholes, and contaminants) when inspected using typical reflective bright-field microscopy, because all of these defects and contaminants appear as dark spots, and there is no clear difference between them in the observed image.

[0029] The inventors have recognized and understood that the ability to optically detect polarization-altering defects (such as micropipes) in wafer inspection systems (such as microscopes or wafer inspection tools) can be a valuable functionality when inspecting semiconductor wafers (such as SiC wafers). As discussed above, SiC wafers are prone to forming micropipe defects during manufacturing. The ability to detect and identify these defects from other types of defects and contaminants can improve device yields in manufacturing facilities by rejecting SiC wafers with micropipe defect densities exceeding a threshold level. Furthermore, wafers that might otherwise be rejected due to the inability to identify micropipe defects from surface contaminants, for example, using conventional bright-field microscopy, can be cleaned and used instead of wasted. Other semiconductor wafers that can be inspected for polarization-altering defects and benefit from the devices described herein include, but are not limited to, gallium arsenide (GaAs), gallium nitride (GaN), silicon (Si), silicon germanium (SiGe), indium phosphide (InP), and gallium phosphide (GaP).

[0030] 1. Overview of Wafer Inspection Tools

[0031] The inventors have devised a method to convert a wafer inspection system with optical elements for bright-field microscopy into a wafer inspection system that can detect microtubes and other polarization-altering defects in or on semiconductor wafers, in addition to detecting other defects or contaminants by conventional bright-field microscopy. Figure 1 An example of a wafer inspection system 100 is depicted, which can detect defects and contaminants using conventional reflective bright-field microscopy and can be further adapted to detect micropipes and other polarization-altering defects in or on a semiconductor wafer. Adaptation of this system can further enable the detection of contaminants (such as carbon inclusions) within the bulk of a semiconductor wafer 150.

[0032] Figure 1An example wafer inspection system 100 includes an inspection instrument 110, which includes an inspection head 120, a wafer chuck 140 for holding a semiconductor wafer 150, and a positioning stage 130. The inspection head 120 (which may be referred to as an "inspection microscope") further includes optical and electronic components for illuminating the semiconductor wafer 150 and for obtaining microscopic images of features on and around the semiconductor wafer 150. For example, the inspection head 120 may include at least one objective lens 125, an imaging optics element 128, and an imaging array 124 (e.g., a CMOS or CCD imager) on a rotatable head 122 to obtain and record different magnified images of features on and around the semiconductor wafer 150. The inspection head 120 may further include an illumination source 121, a beam splitter 127, and an illumination optics element 126 to provide illumination radiation incident on the semiconductor wafer 150. Radiation from the illumination source 121 can be folded into the imaging optical path (in the beam splitter 127) by the beam splitter 127. Figure 1 (Vertically extended in the middle). When the irradiation wavelength transmitted through the semiconductor wafer 150 is selected, the inspection head can form a bright-field micrograph of features on the surface of the semiconductor wafer 150 or within the bulk of the semiconductor wafer 150.

[0033] Irradiation source 121 can be broadband (e.g., white light from a halogen bulb or bright LED adapted to emit white light). In some cases, irradiation source 121 may include one or more narrowband sources (e.g., narrowband LEDs). Broadband irradiation source 121 can emit radiation across a wavelength bandwidth of at least 100 nm to 200 nm or greater (e.g., simultaneously emitting wavelengths from 450 nm to 550 nm). Narrowband irradiation source 121 can emit radiation within wavelength bandwidths that are, in some cases, no wider than 90 nm, in some cases, no wider than 50 nm, or in some cases, even no wider than 20 nm. Radiation from irradiation source 121 used in inspection head 120 can have wavelengths from approximately or exactly 400 nm to approximately or exactly 10 μm, or in some cases, any subrange thereof. For SiC wafers, irradiation source 121 can emit radiation with wavelengths in a band between 500 nm and 1.5 μm. For Si wafers, the irradiation source 121 can emit radiation with wavelengths in the band between 1.5 μm and 5 μm. In some cases, the irradiation source 121 can emit radiation with wavelengths in the band between 350 nm and 400 nm (near-ultraviolet wavelengths). In other cases, the irradiation source 121 can emit radiation with wavelengths in the band between 400 nm and 700 nm (visible wavelengths). In still other cases, the irradiation source 121 can emit radiation with wavelengths in the band between 700 nm and 3000 nm (near-infrared and short-wavelength infrared wavelengths). In some implementations at longer wavelengths, image acquisition can be based on passive illumination (e.g., thermal radiation emitted from the object).

[0034] In some implementations, multiple illumination sources 121 emitting at different wavelengths can be mounted in an inspection head 120 and rotated or moved into position under the control of a controller 112 to provide radiation for inspecting the semiconductor wafer 150. For example, a first illumination source 121 may emit radiation that reflects from the surface of the semiconductor wafer 150 and does not propagate through it. This first illumination source 121 can be used to inspect the wafer for surface defects and / or contaminants via reflective bright-field microscopy. A second illumination source 121 may emit radiation that can propagate through the semiconductor wafer 150. This second illumination source 121 can be used to detect defects and / or contaminants in bulk semiconductor wafer 150 via bright-field microscopy and additionally or alternatively via polarization-sensitive microscopy, as further described below.

[0035] The wafer chuck 140 and the semiconductor wafer 150 can be positioned in two dimensions (e.g., by positioning stage 130) via the positioning stage 130. Figure 1The positioning stage 130 is driven to scan the semiconductor wafer 150 in the x and y directions (as indicated in the image) to inspect different regions of the semiconductor wafer 150. In some implementations, the positioning stage 130 is driven to scan the semiconductor wafer in the x and y directions, allowing imaging and analysis of at least several small areas across most of the wafer surface (e.g., 90% or more of the surface) to assess the wafer's suitability for semiconductor processing. For example, multiple sample images (each dimension of the inspection head's field of view) can be acquired at random locations across the semiconductor wafer 150, and an average defect density can be calculated for the wafer to determine whether it should be rejected for semiconductor processing. The dimensions of the wafer chuck 140 can be determined to hold large semiconductor wafers (e.g., wafers with a diameter of 150 mm, 200 mm, 300 mm, and even larger).

[0036] According to some implementations, the inspection head 120 can move vertically (±z direction) to adjust the focal length of the inspected area for the imaging optics. In some implementations, autofocus is achieved by the controller 112 based on analysis of the image acquired by the imaging array 124. Autofocus can be used to compensate for bending or warping in the semiconductor wafer 150 during wafer inspection. For example, autofocus can track height variations of up to 200 micrometers in the semiconductor wafer 150 caused by bending or warping as the wafer moves laterally under the inspection head 120. The wafer inspection system 100 can be marketed as a wafer inspection tool for semiconductor manufacturing facilities or semiconductor foundries. In some cases, the wafer inspection system 100 can be implemented as a desktop microscope.

[0037] The inspection instrument 110 or some of its components may be operated manually in some cases (e.g., as in a conventionally manually operated microscope) or automated under the control of the controller 112. When automated, the positioning stage 130 includes one or more actuators (e.g., stepper motors, piezoelectric positioners, etc.) configured to move the wafer chuck 140 in at least two dimensions in response to control signals issued by the controller 112. Changes in the objective lens 125 may also be automated by the controller 112 (e.g., by commanding the rotation of the rotatable head 122). The autofocusing of the inspection head 120 may also be controlled by the controller 112. Other aspects that may be controlled by the controller 112 include, but are not limited to, the selection and brightness of the illumination source 121, the setting of the apertures in the illumination optics 126 and the imaging optics 128, the selection of optical filters, and the orientation of the polarization optics (which will be described below in conjunction with imaging polarization-varying defects).

[0038] The controller 112 may be communicatively coupled to at least the positioning stage 130 and may be further communicatively coupled to the inspection head 120. The controller 112 may be adapted with machine-readable instructions (which may be stored in memory 115) to operate the wafer inspection system 100. In some cases, the controller 112 may control the inspection head 120 to obtain digital images of different regions of the semiconductor wafer 150 as the wafer 150 is moved to different positions by the positioning stage 130.

[0039] Controller 112 can be implemented in different ways. In one example, controller 112 includes a microprocessor. However, controller 112 may include a combination of components selected from the following list: microprocessor, microcontroller, programmable logic unit (PLU), field-programmable gate array (FPGA), application integrated circuit (ASIC), digital signal processor (DSP), and digital logic chip. One, none, or more of a particular type of component from the list may be present in the combination (e.g., one PLU and three FPGAs).

[0040] Figure 2 Describes a way, Figure 1 The wafer inspection system 100 can be adapted with optical components in this way to detect polarization change defects in or on a semiconductor wafer 150. The example shown is for SiC wafers, but the optical arrangement will work for other types of semiconductor wafers 150.

[0041] To adapt to the wafer inspection system 100, several optical components, such as... Figure 2 The following is depicted added to the examination head 120. In the example shown, a linear polarizer 210 and a waveplate 220 (such as a quarter-wave plate or a custom waveplate) are placed between the examination head 120 and the semiconductor wafer 150 (e.g., between the objective lens 125 and the semiconductor wafer 150). Additionally, a mirror 230 is placed outside the semiconductor wafer 150 on the opposite side (or back surface) from the examination head 120, such that radiation from the illumination source 121 in the examination head 120 passes through the semiconductor wafer 150 and is reflected back by the mirror 230 to travel back through the semiconductor wafer 150 and return to the examination head 120. The returned radiation will again pass through the quarter-wave plate 220 and the linear polarizer 210, and then reach the examination head 120 and the imaging array 124 for image recording.

[0042] Linear polarizer 210 can be an absorbing polarizer (transmitted light is linearly polarized along the polarization axis of the polarizer, and absorbed light is not polarized along that axis). For example, such polarizers can be made of stretched polyvinyl alcohol (PVA). Other polarizers can also be used to generate linearly polarized light, such as polarization beam splitters, reflective polarizers, and birefringent (double-refractive) polarizers. An example linear polarizer is a high-performance glass linear polarizer (e.g., part number 47-216) available from Edmund Optics, Barrington, New Jersey.

[0043] The quarter-wave plate 220 can be formed of a birefringent material (e.g., a birefringent crystal such as calcite or a birefringent polymer film) with a thickness selected for the designed wavelength of light. This thickness is chosen such that a linearly polarized component is phase-blocked by 90 degrees relative to a second orthogonally linearly polarized component of the radiation at the designed wavelength as it passes through the quarter-wave plate. The quarter-wave plate can be a multi-order quarter-wave plate, a zero-order quarter-wave plate, or a pseudo-true zero-order quarter-wave plate. An example quarter-wave plate is a pseudo-true zero-order quarter-wave plate (e.g., part number WPQ10M-633) available from Thorlabs in Newton, New Jersey.

[0044] Mirror 230 preferably has sufficient optical quality and is large in size. The flatness of the mirror can be less than one wavelength deviation within the mirror area. The diameter of the mirror can be up to 150 mm in some cases, up to 200 mm in others, and even up to 300 mm in still others. Mirror 230 can be a coated metal mirror or a multilayer dielectric mirror. In some implementations, mirror 230 includes a semiconductor wafer that has been coated to achieve high reflectivity (e.g., at least 85% reflectivity for radiation from illumination source 121). The coated wafer can be clamped in wafer chuck 140 to a flat chuck surface to provide a flat reflective surface for mirror 230.

[0045] In some implementations, mirror 230 may be smaller than semiconductor wafer 150 in diameter or area. In such implementations, semiconductor wafer 150 may be moved (e.g., displaced and / or rotated) relative to mirror 230 to allow inspection of the entire area of ​​semiconductor wafer 150.

[0046] Figure 2The adapted system operates significantly differently from a conventional bright-field microscope. In a conventional bright-field microscope, radiation from the examination head 120 is typically focused by the objective lens 125 onto the proximal side of the semiconductor wafer 150 facing the examination head (sometimes referred to as the front surface or process surface), and is reflected back from the front surface to the examination head 120 for imaging and image recording. Defects such as contaminants on the surface of the semiconductor wafer 150 scatter radiation beyond the collection angle of the objective lens 125, and thus appear as dark features against a brighter background.

[0047] Through such Figure 2 The depiction includes a linear polarizer 210, a quarter-wave plate 220, and a mirror 230. Furthermore, by using radiation that can be transmitted twice through a semiconductor wafer 150 having sufficient transmittance for image detection, polarization-changing defects, such as microtubes in, at, or extending to the surface of the semiconductor wafer 150, can be detected. Figure 3 It demonstrates how defects can be detected.

[0048] 2. Polarization-sensitive detection of polarization-altering defects

[0049] For the purpose of explaining polarization-sensitive detection of polarization-changing defects, a simplification was made. Figure 3 The accompanying figure does not show the focusing performed by the objective lens 125 in the wafer inspection system 100. The figure also separates the forward optical path 302 (left side of the figure) and the reflected optical path 304 (right side of the figure), which may or may not be separated in the implemented wafer inspection system 100. Figure 2 In the example system, the forward optical path 302 and the reflected optical path 304 at least partially overlap spatially. In this example, the forward optical path 302 and the reflected optical path 304 pass collinearly through the polarization component and the semiconductor wafer 150, and are separated elsewhere in the inspection head 120. In some implementations, the forward optical path 302 may be incident on the mirror 230 at an angle greater than 0 degrees relative to the normal direction of the mirror surface, such that the reflected optical path 304 is oriented at a non-zero angle relative to the forward optical path 302. As used herein, the optical path is defined by the central axis of the optical beam as it travels through the inspection instrument 110.

[0050] Adapted to, for example Figure 3The wafer inspection system 100 for the optical components shown can detect polarization change defects 350 as follows: Radiation 310 from a source is incident on a linear polarizer 210 to prepare radiation 310 in a first polarization state 315. The first radiation can be selected to have a wavelength or wavelength range that is transmitted through a semiconductor wafer 150 having high transmittance (e.g., at least 60% transmittance). Radiation 310 may or may not be polarized. Radiation 310 before the linear polarizer 210 can be referred to as "first radiation," and radiation after the linear polarizer 210 can be referred to as "second radiation" because the second radiation can be in a different polarization state than the first radiation 310.

[0051] Radiation in the first polarization state 315 can pass through the quarter-wave plate 220 and be converted to a second polarization state 320. The second polarization state 320 can be circular or elliptical, for example, depending on the orientation of the linear polarizer 210 relative to the quarter-wave plate 220. When the polarization axis of the linear polarizer 210 is oriented at a 45-degree angle to the fast axis of the quarter-wave plate 220, the second polarization state 320 is right-handed or left-handed circularly polarized. Radiation in the second polarization state 320 can be referred to as second radiation.

[0052] The radiation in the second polarization state 320 can then pass through the semiconductor wafer 150 and exit as radiation in the third polarization state 325 for regions 352 of the semiconductor wafer 150 where there is no polarization change defect 350. The radiation in the third polarization state 325 can be referred to as third radiation. The third polarization state 325 can be different from the second polarization state 320 (e.g., if the semiconductor wafer 150 has a certain degree of birefringence), or it can be the same as the second polarization state 320.

[0053] Radiation passing through region 354 of semiconductor wafer 150 containing polarization-changing defect 350 and interacting with polarization-changing defect 350 can have its polarization changed to a fourth polarization state 321, which is different from the third polarization state 325. For example, the third polarization state 325 can be right circular polarization, and the fourth polarization state 321 can be right elliptic polarization. Other polarization states are also possible for these two different polarization states. In general, polarization-changing defect 350 will cause the polarization of radiation interacting with defect 350 and passing through semiconductor wafer 150 to change locally relative to the polarization of radiation passing through region of semiconductor wafer 150 without polarization defect 350. Radiation in the fourth polarization state 321 can be referred to as fourth radiation.

[0054] Radiation emitted from semiconductor wafer 150 is reflected by mirror 230, resulting in a fifth polarization state 330 (left circular or left elliptical polarization in this example) and a sixth polarization state 323 (left elliptical polarization in this example). The phase reversal after reflection from the mirror reverses the cycloidity of the circular or elliptical polarization. The reflected radiation travels back through semiconductor wafer 150 and any polarization-changing defects 350 therein, resulting in radiation in a seventh polarization state 335 (e.g., left circular or left elliptical polarization) and an eighth polarization state 327 (e.g., left elliptical polarization). Because the radiation passes through the polarization-changing defect 350 a second time, the radiation in the eighth polarization state 327 further alters its polarization from that of the radiation in the seventh polarization state 335. The radiation in the fifth polarization state 330 can be referred to as the fifth radiation. The radiation in the sixth polarization state 323 can be referred to as the sixth radiation. The radiation in the seventh polarization state 335 can be referred to as the seventh radiation. The radiation in the eighth polarization state 327 can be referred to as the eighth radiation.

[0055] Radiation in the seventh polarization state 335 and the eighth polarization state 327 can then pass back through the same quarter-wave plate 220 (or, in some implementations, a different quarter-wave plate 220), which, according to this example, converts the radiation back into the predominantly linearly polarized radiation in the ninth polarization state 340. Due to the polarization-changing defect 350, radiation in the sixth polarization state 323 is converted, for example, from the elliptically polarized state 329 emitted from the quarter-wave plate 220. Due to the phase reversal after reflection at mirror 230, radiation in the ninth polarization state 340 can be linearly polarized in an orientation orthogonal to the linear polarization of the first polarization state 315. Therefore, most of the radiation in the ninth polarization state 340 is blocked by the linear polarizer 210 (or, if the reflected light path 304 is separated from the forward light path 302, a different linear polarizer). The amount of radiation blocked in the ninth polarization state 340 depends at least in part on the extinction ratio of the linear polarizer 210. The amount of radiation blocked in the ninth polarization state 340 can also depend on whether the semiconductor wafer 150 is birefringent and whether the quarter-wave plate 220 is aligned with the linear polarizer 210.

[0056] In some implementations, one or both of the quarter-wave plate 220 and the linear polarizer 210 can be mounted on a rotary mount to allow for fine adjustments to the rotational alignment of the two components in the system relative to each other and relative to the semiconductor wafer 150. Such fine adjustments can be used to reduce background radiation (which may be caused by incomplete blocking of light that has not passed through the polarization-changing defect 350). The rotation of these polarizing components is about the central axis of the forward optical path 302 (e.g., in the xy plane).

[0057] Radiation in the tenth polarization state 329, whose polarization has been altered by polarization-changing defect 350, can be elliptically, circularly, or even linearly polarized after quarter-wave plate 220. If linearly polarized, the linear polarization differs from that of the ninth polarization state. Therefore, at least a portion of the radiation 360 in the tenth polarization state 329 passes through linear polarizer 210. As used herein, “portion” means a part of the whole (e.g., between 0% and 100% of the whole).

[0058] A portion of the radiation 360 passing through the linear polarizer 210 can produce an image with bright features against a dark background. These bright features represent polarization-changing defects 350 (such as microtubes) in, on, or extending from the surface of the semiconductor wafer 150. In effect, the objective lens 125 is used to focus the radiation 310 at a location on the semiconductor wafer 150 (e.g., within the bulk of the wafer or at or near the surface of the semiconductor wafer) and to form an image using the radiation collected from the semiconductor wafer 150. The depth of focus (DOF) of the objective lens 125 can range from approximately or exactly 10 micrometers to approximately or exactly 40 micrometers. The object location for imaging can be at the surface of the semiconductor wafer 150 or within the bulk of the semiconductor wafer 150. In some cases, the depth of focus (DOF) of the objective lens 125 can range from approximately or exactly 1 micrometer to approximately or exactly 5 micrometers. In some cases, the depth of focus (DOF) of the objective lens 125 can range from approximately or exactly 5 micrometers to approximately or exactly 10 micrometers. In some cases, the depth of focus (DOF) of objective lens 125 can be in the range of approximately or exactly 10 micrometers to approximately or exactly 20 micrometers. In some cases, the depth of focus (DOF) of objective lens 125 can be in the range of approximately or exactly 20 micrometers to approximately or exactly 30 micrometers. In some cases, the depth of focus (DOF) of objective lens 125 can be in the range of approximately or exactly 30 micrometers to approximately or exactly 70 micrometers. In some cases, the depth of focus (DOF) of objective lens 125 can be in the range of approximately or exactly 70 micrometers to approximately or exactly 100 micrometers.

[0059] In some implementations, the linear polarizer 210 may be oriented at an angle other than 45 degrees relative to the fast axis of the quarter-wave plate. For example, if the wafer exhibits birefringence, an orientation other than 45 degrees may be possible. Alternatively, an orientation other than 45 degrees may be selected to provide simultaneous imaging of polarization-changing defects and non-polarization-changing defects, as further described below. The value of the orientation of the polarization axis of the linear polarizer 210 relative to the fast axis of the quarter-wave plate 220 can range from approximately or exactly 5° to approximately or exactly 85°, or any subrange therein (e.g., from 35° to 55°, 45° ± 4°, 45° ± 2°, from 25° to 65°, etc.).

[0060] In some cases, a more general-purpose waveplate or retarder can be used instead of or replace a quarter-wave plate, having a relative phase delay of less than or greater than a quarter wave between orthogonal polarization components. A waveplate with a relative phase delay of less than or greater than a quarter wave can be used on wafers exhibiting birefringence. A waveplate for this purpose can delay the phase of one orthogonal polarization component relative to the phase of another orthogonal polarization component of the light wave passing through the waveplate by an angle of less than or greater than 90 degrees. Such waveplates can be custom-made. The delay angle can range from approximately or exactly 5 degrees to approximately or exactly 89 degrees, or from approximately or exactly 91 degrees to approximately or exactly 175 degrees. In such cases, the waveplate can be mounted with its fast axis at a fixed angle relative to the linear polarizer 210 and is not rotatable relative to the linear polarizer 210. In some cases, the waveplate can be rotatable relative to the linear polarizer 210.

[0061] Figure 4A This is an image of a SiC wafer obtained using bright-field reflection microscopy without polarization-sensitive imaging. Defects and contaminants appear as darker features against a brighter background in bright-field microscopy. Some features 410 and 420 are marked for comparison with... Figure 4B The images are compared.

[0062] Figure 4B This includes polarization-sensitive microscopic images of regions of a SiC semiconductor wafer 150 obtained using a wafer inspection system 100, which is adapted with optical components to detect polarization-altering defects 350, as described above. The polarization-altering defects 350 appear as bright features 410 (which may be referred to as "comets") against a darker background. For example, the pixel intensity level of the bright feature 410 may be at least 20%, at least 50%, or at least 100% higher than the average pixel intensity level of the background. In some systems, the image intensity may be inverted, causing the polarization-altering defects 350 to appear as dark features against a brighter background. For example, the pixel intensity level of the polarization-altering defects 350 may be at least 20%, at least 50%, or at least 80% lower than the average pixel intensity level of the background. Three of the more prominent bright features 410 are marked in the image, although many other bright features are visible, thus indicating the presence of multiple polarization-altering defects 350 (such as microtubes).

[0063] Computer image processing can be applied to images (e.g.) Figure 4BThe process is performed on an image to determine the number of polarization-altering defects 350 per unit area of ​​the semiconductor wafer 150 used for wafer screening. For example, a bright feature 410 with a local intensity peak above a threshold and a full width at half maximum (FWHM) radius or FWHM diameter below a threshold can be counted as a defect to determine the number of polarization-altering defects 350 within the field of view (FOV) of the recorded image. A bright feature 410 with a wider radius or diameter and a lower peak value cannot be counted as a polarization-altering defect. Several images can be obtained for different regions of the semiconductor wafer 150 and processed to determine the average defect density of the wafer. Wafers with a defect density exceeding a threshold can be rejected for further semiconductor processing.

[0064] exist Figure 4B Dark features 420 against a lighter background are also visible in the polarization-sensitive microscopy image. Dark features 420 are associated with additional defects (such as carbon inclusions and contaminants) in or on the semiconductor wafer 150. Dark features 420 are visible because the optics are configured not to block all radiation returning from the quarter-wave plate 220 in the ninth polarization state 340. For example, the quarter-wave plate 220 can be oriented to produce impure circularly polarized radiation, such that the ninth polarization state 340 is linearly polarized in an orientation orthogonal to the transmission axis of the linear polarizer 210. Thus, a bright-field microscopy image of the same area of ​​the semiconductor wafer 150 is obtained, and this image is superimposed on the polarization-sensitive microscopy image. Such imaging can allow the simultaneous detection of polarization-changing defects 350 (such as microtubes) and non-polarization-changing defects (such as contaminants and inclusions) without altering the optics in the inspection head 120 of the system. In some implementations, wafer screening can be based on a combination of polarization-changing defects 350 and non-polarization defects.

[0065] Figure 4A The defect marker in the text corresponds to Figure 4B The location of the same defect in the images. Based on image comparison, it is impossible to distinguish them. Figure 4A Which defects in the bright-field images are potentially device failure-induced microtubules, and which are not? (Combined with...) Figure 2 and Figure 3 The described adapter optics transform the wafer inspection system 100 into a tool capable of detecting polarization-altering defects in SiC semiconductor wafers and other wafers. Such polarization-altering defects can include, but are not limited to, microtube defects, screw dislocations, slip lines, slip planes, and defects that generate localized internal stress and strain, resulting in stress-induced birefringence. The spatial range of polarization-altering defects can be from the micrometer scale to the millimeter scale (e.g., from approximately or exactly 5 μm to approximately or exactly 5 mm). In some cases, smaller defects (e.g., as small as 1 μm or 250 nanometers) can be detected.

[0066] 3. Implementation method of additional system

[0067] Figure 5 Another arrangement of optical components for adapting a wafer inspection system 100 to detect polarization-altering defects is depicted. In this implementation, a linear polarizer 210 and a quarter-wave plate 220 are positioned above the objective lens 125 of the inspection head 120. For example, the linear polarizer 210 and the quarter-wave plate 220 may be located between the illumination source 121 of the inspection head 120 and the objective lens 125. In this arrangement, the linear polarizer 210 and the quarter-wave plate 220 may be located in a portion of the optical path of the inspection head 120, where the illumination beam from the illumination source 121 is collimated. Positioning the linear polarizer 210 and the quarter-wave plate 220 in the collimated portion of the illumination beam provides better contrast and image quality compared to positioning the linear polarizer 210 and the quarter-wave plate 220 behind the objective lens 125, where the illumination beam is not collimated.

[0068] As noted above, the accompanying drawings are not drawn to scale and are generally intended to illustrate the arrangement of optical components in the wafer inspection system 100. For example, the semiconductor wafer 150 will typically be thinner than the mirror 230 and the wafer chuck 140. The relative distances between the different components may vary. Figure 2 , Figure 3 , Figure 5 The figures depicted are significantly different from those in the accompanying drawings and other figures mentioned below.

[0069] Figure 6A Another arrangement of optical components for adapting a wafer inspection system 100 to detect polarization-altering defects is depicted. Inspection instrument 110 and... Figure 2The similarity of the inspection instruments lies in the fact that the linear polarizer 210 and the quarter-wave plate 220 are located between the objective lens 125 and the semiconductor wafer 150. One or both of the linear polarizer 210 and the quarter-wave plate 220 can be mounted on an adjustable mount 630. The adjustable mount may include a rotation mount (e.g., to adjust the angle of the polarization axis of the linear polarizer 210 relative to the fast axis of the quarter-wave plate 220). The adjustable mount may additionally or alternatively include a tilt adjustment (e.g., to adjust the angle between the planar surface of the linear polarizer 210 or the quarter-wave plate 220 and the optical axis of the light passing through the linear polarizer 210 or the quarter-wave plate 220), such that Fresnel reflections from the surfaces of the linear polarizer 210 and / or the quarter-wave plate 220 deflect the light passing through the linear polarizer 210 or the quarter-wave plate 220. A first portion of the forward optical path 302 from the illumination source 121 is offset from a first portion of the reflected optical path 304 including the imaging array 124. The folding mirror 620 and beam splitter 127 can be used to align the second portion of the forward optical path 302 with the second portion of the reflected optical path 304. Radiation from the reflected optical path 304 can transmit an image (e.g., Figure 4A The images are formed onto the imaging array 124 for recording and / or analysis.

[0070] The linear polarizer 210 and the quarter-wave plate 220 can be located at different positions in the forward optical path 302 and in the reflected optical path 304 in some implementations of the inspection instrument 110. Figure 6B In this configuration, a linear polarizer 210 is located between the objective lens 125 and the semiconductor wafer 150, while a quarter-wave plate 220 is located between the wafer 150 and the mirror 230. Generally, the linear polarizer 210 can be located anywhere between the illumination source 121 and the semiconductor wafer 150, and the quarter-wave plate 220 can be located anywhere in the forward optical path between the linear polarizer 210 and the mirror 230. If either or both of the linear polarizer 210 and the quarter-wave plate 220 are located in a portion of the forward optical path 302 that is not collinear with the reflected optical path 304, then a second linear polarizer and / or a quarter-wave plate can be placed in a portion of the reflected optical path 304 that is not collinear with the forward optical path 302.

[0071] Figure 6C Another arrangement of the polarization components in the inspection instrument 110 is depicted. In this arrangement, a linear polarizer 210 is located between the illumination source 121 and the objective lens 125. A quarter-wave plate 220 is located between the objective lens 125 and the semiconductor wafer 150. In another implementation, the quarter-wave plate 220 may be located between the semiconductor wafer 150 and the mirror 230.

[0072] Figure 7Another implementation of the inspection instrument 110 is depicted. In this implementation, a circular polarizer 710 is used instead of a linear polarizer 210 separate from the quarter-wave plate 220. The circular polarizer 710 may include a linear polarizer combined with and / or mounted together with the quarter-wave plate as a single optical component. An example of a circular polarizer is a left-handed circular polarizer (part number CP1L633) available from Thorlabs in Newton, New Jersey, although a right-handed circular polarizer may also be used. The circular polarizer 710 can receive random or unpolarized radiation and output circularly polarized radiation. In some implementations, an ellipsoidal polarizer may be used instead of the circular polarizer 710 or the linear polarizer 210 separate from the quarter-wave plate 220. The ellipsoidal polarizer may include a linear polarizer combined with the quarter-wave plate as a single optical component, wherein the linear polarizer is aligned with the quarter-wave plate to produce ellipsoidal polarization.

[0073] The advantage of mounting the linear polarizer 210 and the quarter-wave plate 220 as separate components in the inspection instrument 110 is that the polarization state of the output from the quarter-wave plate 220 in the forward optical path 302 can be adjusted. For example, one or both of the linear polarizer 210 and the quarter-wave plate 220 can be mounted on a rotary mount to adjust the ellipticity (e.g., from a circle to a certain amount of ellipticity) and orientation (e.g., the orientation of the major axis of the ellipsoidally polarized radiation or the orientation of the linearly polarized radiation in the system relative to the crystallographic axis of the semiconductor wafer). For wafers that may exhibit birefringence, it may be beneficial (in terms of the resulting image contrast and imaging quality) to illuminate the wafer with ellipsoidally polarized radiation oriented at a specific angle instead of circularly polarized radiation. The orientation and ellipticity of the ellipsoidally polarized radiation can be empirically set by rotating the quarter-wave plate 220 to increase or maximize the contrast of the detected images of the semiconductor wafer 150 and the polarization-altering defect 350.

[0074] The circular polarizer 710 can be positioned between the irradiation source 121 and the objective lens 125 in the inspection instrument 110, such as... Figure 7 As shown. In other implementations, the circular polarizer 710 can be located between the objective lens 125 and the semiconductor wafer 150.

[0075] There are several ways to reduce unwanted Fresnel reflections from polarizing optical components (linear polarizers, quarter-wave plates, circular polarizers) and other optical components added to the inspection instrument 110. Fresnel reflections can occur at the interface between two materials (e.g., glass and air) with two different refractive index values. One way to reduce unwanted reflections is to coat the optical components with an anti-reflective (AR) coating on their surfaces in the optical path. Alternatively, the optical components in any of the above systems can be positioned relative to the incident beam (an example of which is shown in the image). Figure 8The beam (as depicted) is oriented at angle α to direct any unwanted Fresnel reflections away from the reflecting light path 304 so that unwanted Fresnel reflections are not collected and / or imaged onto the imaging array 124. The tilt angle α relative to the light path can, for example, range from approximately or exactly 1 degree to approximately or exactly 40 degrees. In some cases, the tilt angle can be less than 1 degree, less than 2 degrees, less than 3 degrees, less than 4 degrees, less than 5 degrees, less than 10 degrees, or less than 20 degrees. Small (e.g., less than 2 degrees) or no tilt angle α can be used for quarter-wave plate 220 (e.g., to avoid elliptical polarization when circular polarization is required). Larger tilt angles can be used for linear polarizer 210.

[0076] exist Figure 9 Another implementation of the inspection instrument 110 is described. In this implementation, a forward optical path 302 is incident on the semiconductor wafer 150 at a first angle, and a reflected optical path 304 exits from the semiconductor wafer 150 relative to the forward optical path 302 at an angle β greater than zero degrees. The forward optical path 302 also passes through the semiconductor wafer 150 at an angle greater than zero degrees relative to the reflected optical path 304 returning through the semiconductor wafer. The forward optical path 302 and the reflected optical path 304 are separate, although the forward optical beam may spatially overlap with the reflected optical beam at the semiconductor wafer 150. The angle β can range from approximately or exactly 0.2 degrees to approximately or exactly 30 degrees.

[0077] Illumination system 910 is located at the beginning of forward optical path 302. Illumination system 910 may include an illumination source and illumination optics to form an illumination beam traveling along forward optical path 302. The illumination beam may be collimated or focused onto semiconductor wafer 150. In this example, a first linear polarizer 210 is located along forward optical path 302 to generate linearly polarized radiation.

[0078] Imaging system 920 is located at the end of reflected light path 304 to acquire images of defects in or on semiconductor wafer 150. Imaging system 920 may include an imaging array, objective lens, and other imaging optics to form images of defects in or on semiconductor wafer onto the imaging array. Second linear polarizer 211 may be located along reflected light path 304. The polarization axis of second polarizer 211 may be oriented approximately parallel to the polarization axis of first polarizer 210.

[0079] A single quarter-wave plate 220 can be placed in the inspection instrument at a position that intercepts both the forward optical path 302 and the reflected optical path 304. However, two quarter-wave plates (e.g., one of each of the forward optical path 302 and the reflected optical path 304) can be used in other implementations. In some cases, the angle β can be very small (e.g., less than 10 degrees), such that the forward illumination beam traveling along the forward optical path 302 and the returning beam traveling along the reflected optical path 304 significantly overlap in the semiconductor wafer 150.

[0080] 4. Alternative detection method for birefringence polarization alteration defects

[0081] Depending on the implementation, a quarter-wave plate may not be used in the inspection instrument 110. For example, the quarter-wave plate 220 may be removed from the aforementioned system. When the quarter-wave plate 220 is not used, two linear polarizers 210 may be installed in the system (one in the forward optical path 302 and one in the reflected optical path 304) and oriented so that their polarization axes are orthogonal to each other. Figure 10 This describes how such an implementation can detect polarization-changing defects exhibiting birefringence when the semiconductor wafer 150 exhibits no or negligible birefringence. Radiation from the irradiation source can be linearly polarized by a first linear polarizer 210a to produce radiation in a first polarization state 315. Throughout the inspection apparatus, the irradiation radiation should remain in the first polarization state 315 unless (a) it encounters a polarization-changing defect 350, or (b) the semiconductor wafer 150 is birefringent and the linear polarization is not aligned with the eigenaxis of the birefringent semiconductor wafer 150. Figure 10 In the demonstration, the bulk semiconductor wafer 150 was not birefringent.

[0082] Irradiation radiation interacting with the polarization-changing defect 350 will change its polarization from linear polarization to a second polarization state 321 as it travels along the forward optical path 302 through the semiconductor wafer 150. The second polarization state 321 can be elliptical or circular (with right-handed or left-handed rotation), depending on the characteristics and length of the polarization-changing defect 350. After reflection from mirror 230, the rotation of the elliptical or circular polarization will reverse. Irradiation radiation interacting with the polarization-changing defect 350 will further change its polarization to a third polarization state 323 as it travels back along the reflected optical path 304 through the semiconductor wafer 150.

[0083] The returned radiation is then incident on the second linear polarizer 210b. The second linear polarizer 210b can be oriented such that its polarization axis is orthogonal to the polarization axis of the first linear polarizer 210a and / or to the polarization of the returned optical beam having a first polarization state 315. In this orientation, the second linear polarizer 210b will block most of the returned radiation, except for at least a portion of the radiation 360 that interacts with the polarization-changing defect 350. This portion of the radiation 360 passing through the second linear polarizer 210b can then be used to form an image of the polarization-changing defect 350 on an imaging array.

[0084] If the semiconductor wafer 150 is birefringent, detection of the birefringent polarization-changing defect 350 can still occur, provided that the birefringence of the defect 350 differs from that of the semiconductor wafer 150, and that the intrinsic axis of at least one of the defect 350 and the semiconductor wafer 150 is not aligned with the polarization axis of the first linear polarizer 210a. The resulting image can produce a bright polarization-changing defect 350 against a darker background, or a dark polarization-changing defect 350 against a brighter background, depending on the relative amounts of the defect 350 and the semiconductor wafer 150. For example, if the semiconductor wafer 150 exhibits more birefringence than the polarization-changing defect 350, and the first linear polarizer 210a is not aligned with the intrinsic axis of either the polarization-changing defect 350 or the semiconductor wafer 150, then more light passing through the defect-free region of the semiconductor wafer 150 will change its polarization state more than the light passing through the polarization-changing defect 350. Therefore, more light passing through the defect-free region of the semiconductor wafer 150 will pass through the second linear polarizer 210b, causing the polarization-changing defect 350 to appear as a darker feature against a brighter background. If the first linear polarizer 210a is rotated so that its polarization axis is aligned with the intrinsic axis of the semiconductor wafer 150, the light passing through the defect-free region of the semiconductor wafer 150 will not change its polarization state and will be blocked by the second linear polarizer 210b. In this case, the polarization-changing defect 350 will appear as a brighter feature against a darker background.

[0085] In a further implementation, only one linear polarizer 210b can be used in the inspection instrument 110. For example, the illumination source 121 can output linearly polarized light, making the first linear polarizer 210a unnecessary. The second linear polarizer 210b can be oriented such that its polarization axis is orthogonal to the linear polarization output by the illumination source 121.

[0086] 5. Wafer chucks and adapters

[0087] Figure 11An example of a wafer chuck 140 is depicted, which can be used to hold a semiconductor wafer 150 in the inspection instrument 110 of the wafer inspection system 100 described in any of the foregoing implementations. The wafer chuck 140 can be mounted on the positioning stage 130 (e.g., in the wafer inspection system 100) within the wafer inspection system 100. Figure 1 As shown, the wafer is scanned laterally relative to the inspection head 120. Laterally scanning the semiconductor wafer 150 (e.g., in the x and y directions) allows for the inspection of the entire wafer.

[0088] The wafer chuck 140 includes a body 141, which may be made of a metal (such as stainless steel, aluminum, aluminum alloy, titanium, and / or titanium alloy). The body 141 may have a recess 142 in which a mirror 230 is mounted. The wafer chuck 140 includes a flange 144 above the recess that supports a semiconductor wafer 150 above the mirror 230, with the back side of the semiconductor wafer not in contact with the mirror. The gap or distance between the surface of the mirror 230 and the back side of the semiconductor wafer 150 can range from approximately or exactly 20 micrometers to approximately or exactly 2 millimeters, or any subrange within these two values. In some implementations, the semiconductor wafer 150 may contact the mirror 230, and there may be no gap. The wafer chuck 140 may include vacuum features or mechanical features (such as clasps or jaws) to hold the semiconductor wafer 150 to the wafer chuck 140. Vacuum features may include a vacuum cavity 147 and a vacuum port 149 fluidly coupled to the vacuum cavity 147. Vacuum can be applied to wafer chuck 140 via vacuum port 149.

[0089] The vacuum feature may further include orifices 145 located on the flange 144 of the wafer chuck 140, such that the orifices 145 are distributed around a peripheral region of the semiconductor wafer 150. For example, the peripheral region may be limited to an annular ring at the edge of the semiconductor wafer 150, extending inward from the edge of the semiconductor wafer by no more than 8 mm, for example. Three to 24 orifices 145 may be formed on the wafer chuck 140 within this annular ring. The vacuum at the orifices 145 can pull the peripheral region of the semiconductor wafer 150 into contact with the wafer chuck 140 or an O-ring disposed at the orifice 145 to secure the semiconductor wafer 150 to the wafer chuck 140. In some implementations, O-rings may be located at each orifice 145 to help provide a vacuum seal at each orifice 145. The O-rings may be made of… Silicone resin or another polymer is formed. By contacting the semiconductor wafer 150 only at a few locations on the back side of the wafer and supporting the semiconductor wafer 150 above the mirror 230, contamination of the semiconductor wafer can be avoided or minimized.

[0090] Figure 12This is a perspective view of an example implementation of a wafer chuck 140, which includes an adapter 1210 to adapt the wafer chuck for use in any of the inspection systems described above. In this example, the adapter 1210, which is annular in shape, is mounted to the body 141 of the wafer chuck 140. Adapters with other peripheral shapes (square, pentagonal, hexagonal, polygonal, etc.) can be used in other implementations. The adapter 1210 provides a flange 144 to raise the semiconductor wafer above a mirror 230, which can be mounted inside or below the adapter 1210. In some cases, a backlight can be mounted behind the wafer (e.g., inside the wafer chuck 140) instead of a mirror for back-side illumination of the wafer. In some implementations of the system, back-side illumination can be used to detect defects (polarized and non-polarized).

[0091] Adapter 1210 may be formed of metal and its dimensions are determined to hold a specific wafer size (e.g., a 150mm diameter wafer, a 200mm diameter wafer, etc.). Several screws 1230 secure adapter 1210 to the body 141 of wafer chuck 140 and allow easy interchangeability of different sized adapters for different wafer sizes. Adapter 1210 may be semi-annular in shape, having at least one cutout 1220. Cutout 1220 provides an entry point for wafer loading / unloading tools (such as wafer clamping end effectors) to enter the central area of ​​the adapter, which in Figure 13 The aperture 145 used to hold the wafer can be located along the inner edge of the adapter 1210 (e.g., within 8 mm of the inner edge of the annular ring).

[0092] If mirror 230 is smaller in area than semiconductor wafer 150, adapter 1210 can be mounted on a rotary mount and / or translation stage. Semiconductor wafer 150 can then be moved (e.g., rotated and / or displaced) relative to mirror 230 to allow inspection of the entire semiconductor wafer. The rotary mount and / or translation stage supporting adapter 1210 can be automated and communicatively coupled to and controlled by controller 112.

[0093] Figure 13 The end effector 1300 can be used to clamp a semiconductor wafer (e.g., from a carrier) and load the wafer onto a vacuum chuck 140. The end effector 1300 can be formed of metal and has a long, wide, and thin arm 1310 that can reach below or above the semiconductor wafer. The arm 1310 may have multiple apertures 1345 for applying a vacuum to clamp the semiconductor wafer at multiple locations. Figure 13The example wafer clamping end effector 1300 is designed to clamp wafers d1 with a diameter of 150 mm and d2 with a diameter of 200 mm. Other types of end effectors can be used in other implementations (which can use mechanical clamping of the wafer instead of vacuum).

[0094] Figure 14 The end effector 1300 is shown in the loaded position, with the semiconductor wafer 150 positioned on the wafer chuck 140. The semiconductor wafer 150 is shown in a semi-transparent view, allowing the end effector 1300 to be seen beneath it. After loading, a vacuum is applied to the wafer chuck 140 to clamp the semiconductor wafer 150 via adapter 1210, and the vacuum is released from the end effector 1300. The wafer clamping end effector 1300 can then be removed from beneath the wafer to allow for wafer inspection. After inspection, the end effector 1300 is removed from beneath the wafer to re-clamp the wafer and then move it back to the wafer carrier. The loading and unloading of the semiconductor wafer 150 by the end effector 1300 can be fully automated using robotic devices that can be mechanically coupled to the end effector 1300 within the wafer inspection system 100 and operate under the control of controller 112.

[0095] Figure 15 Another implementation of an adapter 1510 for a wafer chuck is shown. The adapter 1510 is circular in shape and includes a raised feature 1520 surrounding at least a portion of the adapter's periphery. The raised feature 1520 can be used to support a semiconductor wafer 150 (not shown) over a surface 1550 of the adapter 1510. The raised feature 1520 may include a vacuum recess 1525 to which a vacuum can be applied to secure and hold the semiconductor wafer 150 to the raised feature 1520 when a wafer is loaded onto the raised feature 1520 and a vacuum is applied to the vacuum recess 1525. The surface 1550 of the adapter may be reflective, or a mirror may be mounted to the surface. An opening 1540 may be present in the raised feature 1520 to allow an end effector to enter and exit for loading and unloading wafers onto and from the adapter 1510. The adapter 1510 may be formed and / or comprised of: metal (e.g., aluminum, titanium, stainless steel) or a metal alloy comprising at least one of these materials.

[0096] 6. Kit Implementation Method

[0097] Components for adapting the wafer inspection system 100 (such as a semiconductor inspection tool or a conventional microscope) to a device that can also detect polarization-altering defects can be provided as a conversion kit. For example, at least one circular polarizer 710, an elliptical polarizer, or a pair of linear polarizers 210 and a quarter-wave plate 220 can be provided for insertion into the forward optical path 302 of the inspection system 100 at a location that also intercepts the reflected optical path 304. Alternatively, replicas of each polarizing component can be provided; one copy to be inserted into the forward optical path 302 and one copy to be inserted into the reflected optical path 304. One or more swivel mounts can be provided in the kit to mount one or more of the linear polarizer 210 and the quarter-wave plate 220 (e.g., to allow the user to adjust the angle between the polarization axis of the linear polarizer 210 and the fast axis of the quarter-wave plate 220). A mirror 230 can also be provided for mounting on the wafer chuck 140 or sample holding stage of the system. In some cases, at least one adapter 1210 can be included in the kit to raise the wafer above the mirror 230. Adapter 1210 can be configured to hold a mirror within adapter 1210 and secure mirror 230 to wafer chuck 140 or sample stage. For example, adapter 1210 may include holes for screws 1230 that allow the adapter to be attached to wafer chuck 140 or a sample stage of a conventional microscope. In some cases, a replacement wafer chuck 140 or sample stage may be provided, comprising a mounted mirror and at least one adapter for supporting a semiconductor wafer above mirror 230.

[0098] Various configurations of the above-described inspection apparatus and the methods associated with it are possible, some of which are listed below.

[0099] (1) A system for detecting polarization-changing defects in a semiconductor wafer, the system comprising: an irradiation source for emitting radiation; an objective lens for focusing radiation from the irradiation source onto the semiconductor wafer; a mirror arranged to reflect radiation emitted from the semiconductor wafer back through the semiconductor wafer as reflected radiation; an imaging array for recording an image of at least a portion of the semiconductor wafer generated by at least a portion of the reflected radiation returning through the semiconductor wafer; and a linear polarizer located between the semiconductor wafer and the imaging array, wherein the linear polarizer is oriented to: block a first portion of reflected radiation traveling through the semiconductor wafer that does not include a first region of polarization-changing defects; and transmit at least a portion of a second portion of reflected radiation traveling through the semiconductor wafer that includes a second region of polarization-changing defects.

[0100] (2) The system according to configuration (1), wherein the linear polarizer includes an absorbing polarizer.

[0101] (3) The system according to configuration (1) or (2) further includes a waveplate located between the linear polarizer and the semiconductor wafer, wherein the waveplate includes a birefringent crystal.

[0102] (4) The system according to configuration (3), wherein the linear polarizer and the waveplate are located between the irradiation source and the objective lens.

[0103] (5) The system according to configuration (3) or (4), wherein the polarization axis of the linear polarizer is oriented at an angle of 35 to 55 degrees relative to the fast axis of the waveplate.

[0104] (6) The system according to any one of configurations (3) to (5) further includes a rotatable mount for holding at least one of the linear polarizer and the waveplate, such that the angle between the fast axis of the waveplate and the polarization axis of the linear polarizer can be adjusted.

[0105] (7) The system according to configuration (1) or (2) further includes a wave plate, wherein the linear polarizer and the wave plate are located between the objective lens and the mirror.

[0106] (8) The system according to configuration (7) further includes a rotatable mount for holding at least one of the linear polarizer and the waveplate, such that the angle between the fast axis of the waveplate and the polarization axis of the linear polarizer can be adjusted.

[0107] (9) The system according to configuration (1) or (2) further includes a quarter-wave plate combined with a first linear polarizer to form a circular polarizer.

[0108] (10) The system according to configuration (9), wherein a circular polarizer is located in the system to intercept the forward optical path from the irradiation source to the mirror, and further intercepts the reflected optical path from the mirror to the imaging array.

[0109] (11) The system according to configuration (1) or (2) further includes a waveplate combined with a linear polarizer to form an ellipsoidal polarizer. (12) The system according to configuration (11) wherein the ellipsoidal polarizer is located in the system to intercept the forward optical path extending from the irradiation source to the mirror, and further intercepts the reflected optical path extending from the mirror to the imaging array.

[0110] (13) The system according to configuration (11) or (12) further includes a rotatable mount for holding the ellipsoidal polarizer so that the angle between the major axis of the ellipsoidal polarized radiation output from the ellipsoidal polarizer and the crystallographic axis of the semiconductor wafer can be adjusted.

[0111] (14) According to any one of the configurations (1) to (13) of the system, wherein the imaging array denotes the second portion of the reflected radiation transmitted by the linear polarizer as a bright feature at a darker background level, wherein:

[0112] Bright features indicate polarization-altering defects;

[0113] Bright features have a higher intensity level compared to the background level; and

[0114] The background level is generated by the first part of the reflected radiation blocked by the linear polarizer.

[0115] (15) The system according to configuration (14), wherein the linear polarizer is oriented such that bright-field images of non-polarization-changing defects in the first and second regions of the semiconductor wafer are recorded simultaneously with bright features.

[0116] (16) The system according to any one of configurations (1) to (15) further includes a wafer chuck or an adapter for the wafer chuck for holding the semiconductor wafer and the mirror.

[0117] (17) The system according to configuration (16) wherein the semiconductor wafer is supported above the mirror in a wafer chuck or adapter such that the back side of the semiconductor wafer does not contact the surface of the mirror.

[0118] (18) The system according to any one of configurations (1) to (17), wherein the polarization-changing defect includes a microtube.

[0119] (19) The system according to any one of configurations (1) to (18), wherein the irradiation source emits unpolarized radiation having a radiation bandwidth in the range of 350 nm to 3000 nm.

[0120] (20) The system according to any one of configurations (1) to (19) is configured to detect polarization change defects in a semiconductor wafer comprising silicon carbide.

[0121] (21) The system according to any one of configurations (1) to (20), wherein the system defines: a forward optical path extending from an irradiation source to a mirror, along which radiation travels from the irradiation source to the mirror; and a reflected optical path extending from the mirror to an imaging array, along which reflected radiation travels from the mirror to the imaging array, wherein the forward optical path and the reflected optical path pass collinearly through a semiconductor wafer.

[0122] (22) A method for detecting polarization-changing defects in a semiconductor wafer, the method comprising: irradiating a region of the semiconductor wafer having radiation in a first polarization state with radiation from an irradiation source; reflecting the radiation that has passed through the semiconductor wafer as reflected radiation toward the semiconductor wafer with a mirror; collecting a portion of the reflected radiation with an objective lens to form an image of the region of the semiconductor wafer; blocking a first portion of the reflected radiation traveling through the region of the semiconductor wafer that does not include the first region of the polarization-changing defect with a linear polarizer; transmitting at least a portion of a second portion of the reflected radiation traveling through the region of the semiconductor wafer that includes the second region of the polarization-changing defect with a linear polarizer; and detecting an image of the region of the semiconductor wafer generated by the at least portion of the second portion of the reflected radiation transmitted by the linear polarizer with an imaging array.

[0123] (23) The method according to (22) further includes converting radiation from the irradiation source into circularly polarized radiation with a circular polarizer for the first polarization state.

[0124] (24) The method according to (22) further includes converting radiation from the irradiation source into elliptically polarized radiation with an elliptically polarized plate for the first polarization state.

[0125] (25) The method of (24) further includes converting elliptically polarized radiation into circularly polarized radiation using a semiconductor wafer. (26) The method of (24) or (25) wherein the elliptically polarizer comprises a linearly polarizing plate and a waveplate.

[0126] (27) The method according to any one of (22) to (26) further includes converting radiation from the irradiation source into linearly polarized radiation with a linear polarizer for a first polarization state.

[0127] (28) The method according to any one of (22) to (27), wherein the detected image includes forming a bright feature on a background, wherein: the bright feature is formed by a portion of a second portion of reflected radiation transmitted by a linear polarizer; the bright feature represents a polarization change defect and has a higher intensity level than the intensity level of the background; and the background in the image is generated by a first portion of the reflected radiation blocked by a linear polarizer.

[0128] (29) According to the method of (28), the detection image further includes forming a dark feature in the image representing a non-polarization change defect, the dark feature having an intensity level lower than the intensity level of the background.

[0129] (30) A kit for converting a wafer inspection system into a system for detecting polarization-altering defects in a semiconductor wafer, the kit comprising: at least one linear polarizer for mounting in the forward optical path of the wafer inspection system extending between an irradiation source and a semiconductor wafer, wherein the irradiation source is arranged to irradiate an area of ​​the semiconductor wafer for inspection; at least one waveplate for mounting in the forward optical path between the linear polarizer and the semiconductor wafer; and a mirror for mounting in the wafer inspection system at a position such that radiation from the irradiation source traveling along the forward optical path and passing through the semiconductor wafer is reflected back from the mirror through the semiconductor wafer and toward an objective lens of the wafer inspection system.

[0130] (31) According to the kit described in configuration (30), the linear polarizer in at least one of the linear polarizers includes an absorbing polarizer.

[0131] (32) According to the kit described in configuration (30) or (31), the waveplate in at least one of the waveplates comprises a birefringent crystal.

[0132] (33) According to any one of the configurations (30) to (32) of the kit, wherein at least one of the waveplates comprises a quarter-waveplate.

[0133] (34) According to the kit described in configuration (30), wherein at least one linear polarizer and at least one waveplate are mounted together as a single unit for generating circular polarization from unpolarized light.

[0134] (35) According to the kit described in configuration (30), wherein at least one linear polarizer and at least one waveplate are mounted together as a single unit for generating elliptical polarization from unpolarized light.

[0135] (36) The kit according to any one of configurations (30) to (35), wherein: at least one linear polarizer is a single linear polarizer; at least one waveplate is a single waveplate; the single linear polarizer is configured to be located in the wafer inspection system such that it intercepts a segment of the reflected light path extending from the semiconductor wafer through the objective lens and reaching the imaging array of the wafer inspection system; and the single waveplate is also configured to be located in the wafer inspection system such that it intercepts the reflected light path.

[0136] (37) The kit according to any one of configurations (30) to (36) further includes a rotary mount for holding and allowing rotational adjustment of at least one of: a linear polarizer in at least one linear polarizer; and a waveplate in at least one waveplate in a wafer inspection system.

[0137] (38) The kit according to any one of configurations (30) to (37) further includes an adapter for a wafer chuck for holding a semiconductor wafer between an objective lens and a mirror.

[0138] (39) The kit according to configuration (38), wherein the adapter is configured to hold the semiconductor wafer only at the peripheral region of the semiconductor wafer, the peripheral region comprising an annular ring extending inward from the edge of the semiconductor wafer by no more than 8 mm.

[0139] (40) The kit according to configuration (38) or (39), wherein the mirror is mounted to the adapter or adjacent to the adapter.

[0140] (41) The kit according to any one of configurations (38) to (40), wherein the adapter has at least a partial annular shape and is configured to keep the semiconductor wafer away from the mirror at a distance such that the semiconductor wafer does not contact the mirror.

[0141] (42) The kit according to any one of configurations (38) to (41), wherein the size of the adapter is determined to hold a semiconductor wafer having a diameter of at least 150 mm.

[0142] (43) The kit according to any one of configurations (38) to (42), wherein the adapter has a cutout to allow the wafer clamping end effector to enter the central area of ​​the adapter for loading and unloading the semiconductor wafer.

[0143] (44) The kit according to any one of configurations (30) to (43), wherein the polarization-changing defect includes microtubes.

[0144] (45) The kit according to any one of configurations (30) to (44), wherein the kit is adapted to a wafer inspection system to detect polarization change defects in a silicon carbide semiconductor wafer.

[0145] (46) A method for detecting polarization-altering defects in a semiconductor wafer using a kit that adapts a wafer inspection system to detect polarization-altering defects in a semiconductor wafer, the method comprising: mounting a linear polarizer in the forward optical path of the wafer inspection system, the forward optical path extending between an irradiation source and a semiconductor wafer, wherein the irradiation source is arranged to irradiate the semiconductor wafer for inspection; mounting a waveplate in the forward optical path between the linear polarizer and the semiconductor wafer; and mounting a mirror in the wafer inspection system at a position such that radiation from the irradiation source traveling along the forward optical path and passing through the semiconductor wafer is reflected back from the mirror through the semiconductor wafer and toward an objective lens of the wafer inspection system.

[0146] (47) The method according to (46) further includes: irradiating a region of a semiconductor wafer having radiation in a first polarization state with radiation from an irradiation source; reflecting the radiation that has passed through the semiconductor wafer back toward the semiconductor wafer as reflected radiation with a mirror; collecting a portion of the reflected radiation with an objective lens to form an image of the region of the semiconductor wafer; blocking a first portion of the reflected radiation that does not include a first region of polarization-changing defects traveling through the region of the semiconductor wafer with a linear polarizer; transmitting at least a portion of a second portion of the reflected radiation that includes a second region of polarization-changing defects traveling through the region of the semiconductor wafer with a linear polarizer; and detecting an image of the region of the semiconductor wafer generated by at least a portion of the second portion of the reflected radiation transmitted by the linear polarizer with an imaging array.

[0147] (48) The method according to (47) further includes converting radiation from the irradiation source into circularly polarized radiation with a linear polarizer and a waveplate for a first polarization state.

[0148] (49) According to the method described in (48), the wave plate is a quarter-wave plate formed of a birefringent crystal.

[0149] (50) The method according to (47) further includes converting radiation from the irradiation source into elliptically polarized radiation for a first polarization state using a linear polarizer and a waveplate.

[0150] (51) The method according to (50) further includes using a semiconductor wafer to convert elliptically polarized radiation into circularly polarized radiation incident on a mirror.

[0151] (52) The method according to any one of (46) to (51), wherein the linear polarizer is an absorbing polarizer.

[0152] (53) The method according to any one of (47) to (52), wherein the detected image includes forming a bright feature on a background, wherein: the bright feature is formed by a portion of a second portion of reflected radiation transmitted by a linear polarizer; the bright feature represents a polarization change defect and has a higher intensity level than the intensity level of the background; and the background in the image is generated by a first portion of the reflected radiation blocked by a linear polarizer.

[0153] (54) According to the method of (53), the detection image further includes forming a dark feature in the image representing a non-polarization change defect, the dark feature having an intensity level lower than the intensity level of the background.

[0154] (55) The method according to any one of (46) to (54), wherein mounting the mirror comprises mounting the mirror on a wafer chuck that holds the semiconductor wafer.

[0155] (56) The method according to (55), wherein mounting the mirror further comprises mounting an adapter to a wafer chuck, wherein the adapter has at least a partial annular shape and is configured to keep the semiconductor wafer away from the mirror at a distance such that the semiconductor wafer does not contact the mirror.

[0156] (57) The method according to (56), wherein the size of the adapter is determined to hold a semiconductor wafer having a diameter of at least 150 mm.

[0157] (58) The method according to any one of (55) to (57), wherein the adapter has a notch to allow the wafer clamping end effector to enter the central region of the adapter for loading and unloading the semiconductor wafer.

[0158] 7. Conclusion

[0159] Although various embodiments of the invention have been described and illustrated herein, those skilled in the art will readily conceive of various other means and / or structures for performing the functions described herein and / or obtaining these results and / or one or more of these advantages, and each such variation and / or modification is considered to be within the scope of the embodiments of the invention described herein. More generally, those skilled in the art will readily understand that all parameters, dimensions, materials, and configurations described herein are exemplary, and actual parameters, dimensions, materials, and / or configurations will depend on one or more specific applications using the teachings of this invention. Those skilled in the art will recognize or be able to determine many equivalents of the specific embodiments of the invention described herein using only conventional experiments. Therefore, it should be understood that the foregoing embodiments are presented by way of example only, and that embodiments of the invention may be practiced in ways different from those specifically described and claimed within the scope of the appended claims and their equivalents. The embodiments of the invention disclosed herein relate to each individual feature, system, article of manufacture, material, kit, and / or method described herein. Furthermore, any combination of two or more such features, systems, articles, materials, kits and / or methods is included within the scope of this disclosure if such features, systems, articles, materials, kits and / or methods do not contradict each other.

[0160] Various inventive concepts can be implemented as one or more methods, with at least one instance provided. Actions performed as part of a method can be ordered in any suitable manner. Thus, embodiments can be constructed in which actions are performed in a different order than those shown, which may include performing several actions simultaneously, even if the actions are shown as consecutive actions in the illustrative embodiments.

[0161] All definitions defined and used herein should be understood as controls over the general meaning of dictionary definitions, definitions incorporated by reference in other documents, and / or the terms defined.

[0162] Unless explicitly stated otherwise, the indefinite articles “a” and “an” as used herein in the specification and claims shall be understood to mean “at least one”.

[0163] As used herein, the phrase “and / or” in the specification and claims should be understood to mean “any one or both” of the elements so combined, i.e., elements that exist together in some cases and separately in others. Multiple elements listed with “and / or” should be understood in the same way, i.e., “one or more” of the elements so combined. Other elements may optionally be present, whether related to or unrelated to those specifically identified by the “and / or” clause. Thus, as a non-limiting example, the reference to “A and / or B” when used in conjunction with open-ended language (such as “comprising”) may mean: in one embodiment, only A (optionally including elements other than B); in another embodiment, only B (optionally including elements other than A); in yet another embodiment, both A and B (optionally including other elements); and so on.

[0164] As used herein in the specification and claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when items in a list are separated, “or” or “and / or” should be interpreted as inclusive, i.e., including multiple elements or at least one element in the list of elements, but also including more than one element, as well as optional additional items not listed. Terms that are clearly indicated only in reverse, such as “only one of…” or “exact one of…” or, when used in a claim, “consisting of…” will refer to multiple elements or exactly one element in the list of elements. In general, when preceded by an exclusive term, such as “any one,” “one of…,” “only one of…,” or “exact one of…,” the term “or” as used herein should be interpreted only as indicating an exclusive substitution (i.e., “one or the other, not both”). When used in a claim, “consisting substantially of…” should have the ordinary meaning as used in the field of patent law.

[0165] As used herein in the specification and claims, the phrase "at least one" relating to a list having one or more elements should be understood to mean at least one element selected from any one or more elements in the element list, but not necessarily including at least one of every element specifically listed in the element list, and does not exclude any combination of elements in the element list. This definition also allows for the optional presence of elements other than those specifically identified in the element list referred to by the phrase "at least one," whether related to or unrelated to those specifically identified elements. Thus, as a non-limiting example, "at least one of A and B" (or equivalently "at least one of A or B" or equivalently "at least one of A and / or B") can mean: in one embodiment, at least one, optionally including more than one A, without B (and optionally including elements other than B); in another embodiment, at least one, optionally including more than one B, without A (and optionally including elements other than A); in yet another embodiment, at least one, optionally including more than one A, and at least one, optionally including more than one B (and optionally including other elements); etc.

[0166] In the claims and the foregoing description, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “accommodating,” “constituting,” “composed of,” etc., should be understood as open-ended, meaning that they include but are not limited to. As described in Section 2111.03 of the U.S. Patent Examination Procedure Manual, only the transitional phrases “composed of” and “substantially composed of” should be closed or semi-closed transitional phrases, respectively.

[0167] This invention also includes the following:

[0168] 1. A system for detecting polarization change defects in a semiconductor wafer, the system comprising:

[0169] An irradiation source, used to emit radiation;

[0170] An objective lens, used to focus the radiation from the irradiation source onto the semiconductor wafer;

[0171] A mirror is arranged to reflect the radiation emitted from the semiconductor wafer back through the semiconductor wafer as reflected radiation;

[0172] An imaging array for recording an image of at least a portion of the semiconductor wafer produced by at least a portion of the reflected radiation returning through the semiconductor wafer; and

[0173] A linear polarizer is located between the semiconductor wafer and the imaging array, wherein the linear polarizer is oriented as follows:

[0174] A first portion of the reflected radiation, excluding the first region of the polarization-changing defect, that blocks travel through the semiconductor wafer; and

[0175] At least a portion of the second portion of the reflected radiation that travels through the second region of the semiconductor wafer, including the polarization-changing defect, is transmitted through the semiconductor wafer.

[0176] 2. The system according to claim 1, wherein the linear polarizer includes an absorbing polarizer.

[0177] 3. The system according to claim 1, further comprising a waveplate located between the linear polarizer and the semiconductor wafer, wherein the waveplate comprises a birefringent crystal.

[0178] 4. The system according to item 3, wherein the linear polarizer and the waveplate are located between the illumination source and the objective lens.

[0179] 5. The system according to item 3, wherein the polarization axis of the linear polarizer is oriented at an angle of 35 to 55 degrees relative to the fast axis of the waveplate.

[0180] 6. The system according to claim 3, further comprising a rotatable mount for holding at least one of the linear polarizer and the waveplate, such that the angle between the fast axis of the waveplate and the polarization axis of the linear polarizer can be adjusted.

[0181] 7. The system of claim 1, further comprising a waveplate, wherein the linear polarizer and the waveplate are located between the objective lens and the mirror.

[0182] 8. The system according to claim 7, further comprising a rotatable mount for holding at least one of the linear polarizer and the waveplate, such that the angle between the fast axis of the waveplate and the polarization axis of the linear polarizer can be adjusted.

[0183] 9. The system according to claim 1, further comprising a quarter-wave plate combined with a first linear polarizer to form a circular polarizer.

[0184] 10. The system according to claim 9, wherein the circular polarizer is located in the system to intercept the forward optical path extending from the irradiation source to the mirror, and further intercepts the reflected optical path extending from the mirror to the imaging array.

[0185] 11. The system according to claim 1, further comprising a waveplate combined with the linear polarizer to form an elliptic polarizer.

[0186] 12. The system according to claim 11, wherein the elliptic polarizer is located in the system to intercept the forward optical path extending from the irradiation source to the mirror, and further intercepts the reflected optical path extending from the mirror to the imaging array.

[0187] 13. The system according to claim 11, further comprising a rotatable mount for holding the ellipsoidal polarizer such that the angle between the major axis of the ellipsoidal polarized radiation output from the ellipsoidal polarizer and the crystallographic axis of the semiconductor wafer can be adjusted.

[0188] 14. The system according to claim 1, wherein the imaging array records the second portion of the reflected radiation transmitted by the linear polarizer as a bright feature at a darker background level, wherein:

[0189] The bright feature indicates the polarization change defect;

[0190] The bright feature has a higher intensity level compared to the background level; and

[0191] The background level is generated by the first portion of the reflected radiation blocked by the linear polarizer.

[0192] 15. The system according to claim 14, wherein the linear polarizer is oriented such that bright-field images of non-polarization-changing defects in the first and second regions of the semiconductor wafer are recorded simultaneously with the bright features.

[0193] 16. The system according to claim 1, further comprising a wafer chuck or an adapter for the wafer chuck for holding the semiconductor wafer and the mirror.

[0194] 17. The system of claim 16, wherein the semiconductor wafer is supported above the mirror in the wafer chuck or adapter such that the back side of the semiconductor wafer does not contact the surface of the mirror.

[0195] 18. The system according to claim 1, wherein the polarization alteration defect comprises a microtube.

[0196] 19. The system according to claim 1, wherein the irradiation source emits unpolarized radiation having a radiation bandwidth in the range of 350 nm to 3000 nm.

[0197] 20. The system according to claim 1, configured to detect the polarization change defect in the semiconductor wafer comprising silicon carbide.

[0198] 21. The system according to claim 1, wherein the system is defined as follows:

[0199] The radiation travels along the forward optical path from the irradiation source to the mirror, extending from the irradiation source to the mirror; and

[0200] A reflected light path extends from the mirror to the imaging array, the reflected radiation travels along the reflected light path from the mirror to the imaging array, wherein the forward light path and the reflected light path are collinear through the semiconductor wafer.

[0201] 22. A method for detecting polarization change defects in a semiconductor wafer, the method comprising:

[0202] Irradiate a region of a semiconductor wafer that has radiation in a first polarization state with radiation from an irradiation source.

[0203] The radiation that has passed through the semiconductor wafer is reflected back towards the semiconductor wafer as reflected radiation using a mirror;

[0204] A portion of the reflected radiation is collected using an objective lens to form an image of the region on the semiconductor wafer;

[0205] A linear polarizer is used to block a first portion of the reflected radiation traveling through the region of the semiconductor wafer that does not include the first region of the polarization-changing defect;

[0206] At least a portion of the second portion of the reflected radiation transmitted through the region of the semiconductor wafer, including the second region of the polarization-changing defect, via the linear polarizer; and

[0207] An image of the region of the semiconductor wafer is generated by detecting at least a portion of the second portion of the reflected radiation transmitted by the linear polarizer using an imaging array.

[0208] 23. The method according to item 22, further comprising:

[0209] For the first polarization state, a circular polarizer is used to convert the radiation from the irradiation source into circularly polarized radiation.

[0210] 24. The method according to item 22, further comprising:

[0211] For the first polarization state, an ellipsoidal polarizer is used to convert the radiation from the irradiation source into ellipsoidally polarized radiation.

[0212] 25. The method according to item 24, further comprising:

[0213] The semiconductor wafer is used to convert the elliptically polarized radiation into circularly polarized radiation.

[0214] 26. The method according to item 24, wherein the elliptic polarizer comprises the linear polarizer and the waveplate.

[0215] 27. The method according to item 22, further comprising:

[0216] The radiation from the irradiation source is converted into linearly polarized radiation using the linear polarizer for the first polarization state.

[0217] 28. The method according to item 22, wherein detecting the image includes forming a bright feature on the background, wherein:

[0218] The bright feature is formed by a portion of the second portion of the reflected radiation transmitted by the linear polarizer;

[0219] The bright feature represents the polarization-altering defect and has a higher intensity level compared to the background; and

[0220] The background in the image is generated by the first portion of the reflected radiation being blocked by the linear polarizer.

[0221] 29. The method of claim 28, wherein detecting the image further comprises forming a dark feature in the image representing a non-polarization change defect, the dark feature having an intensity level lower than the intensity level of the background.

[0222] 30. A kit for converting a wafer inspection system into a system for detecting polarization-change defects in semiconductor wafers, the kit comprising:

[0223] At least one linear polarizer is used to be mounted in the forward optical path of the wafer inspection system, the forward optical path extending between an irradiation source and the semiconductor wafer, wherein the irradiation source is arranged to irradiate a region of the semiconductor wafer for inspection of the semiconductor wafer.

[0224] At least one waveplate, configured to be mounted in the forward optical path between the linear polarizer and the semiconductor wafer; and

[0225] A mirror is used to mount the wafer inspection system in a position such that radiation from the irradiation source traveling along the forward optical path and passing through the semiconductor wafer is reflected back from the mirror through the semiconductor wafer and toward the objective lens of the wafer inspection system.

[0226] 31. The kit according to item 30, wherein the linear polarizer in the at least one linear polarizer includes an absorbing polarizer.

[0227] 32. The kit according to item 30, wherein the waveplate in the at least one waveplate comprises a birefringent crystal.

[0228] 33. The kit according to item 30, wherein the waveplate in the at least one waveplate comprises a quarter-waveplate.

[0229] 34. The kit according to item 30, wherein the linear polarizer in the at least one linear polarizer and the waveplate in the at least one waveplate are mounted together as a single unit for generating circular polarization from unpolarized light.

[0230] 35. The kit according to item 30, wherein the linear polarizer in the at least one linear polarizer and the waveplate in the at least one waveplate are mounted together as a single unit for generating elliptical polarization from unpolarized light.

[0231] 36. The kit according to item 30, wherein:

[0232] The at least one linear polarizer is a single linear polarizer;

[0233] The at least one waveplate is a single waveplate;

[0234] The single linear polarizer is configured to be located in the wafer inspection system such that it intercepts a segment of reflected light extending from the semiconductor wafer through the objective lens and reaching the imaging array of the wafer inspection system; and

[0235] The single waveplate is also configured to be located in the wafer inspection system such that it intercepts the reflected light path.

[0236] 37. The kit according to item 30, further comprising a swivel mount for retaining and allowing rotational adjustment of at least one of the following:

[0237] The linear polarizer in the at least one linear polarizer; and

[0238] The waveplate in the at least one waveplate of the wafer inspection system.

[0239] 38. The kit according to item 30, further comprising an adapter for a wafer chuck for holding the semiconductor wafer between the objective lens and the mirror.

[0240] 39. The kit according to item 38, wherein the adapter is configured to hold the semiconductor wafer only at a peripheral region of the semiconductor wafer, the peripheral region comprising an annular ring extending inward from the edge of the semiconductor wafer by no more than 8 mm.

[0241] 40. The kit according to item 38, wherein the mirror is mounted to or adjacent to the adapter.

[0242] 41. The kit according to item 38, wherein the adapter has at least a partial annular shape and is configured to keep the semiconductor wafer away from the mirror at a distance such that the semiconductor wafer does not contact the mirror.

[0243] 42. The kit according to item 41, wherein the size of the adapter is determined to hold a semiconductor wafer having a diameter of at least 150 mm.

[0244] 43. The kit according to item 41, wherein the adapter has a notch to allow the wafer clamping end effector to enter the central region of the adapter for loading and unloading the semiconductor wafer.

[0245] 44. The kit according to item 30, wherein the polarization alteration defect comprises a microtube.

[0246] 45. The kit according to claim 30, wherein the kit is adapted to the wafer inspection system to detect the polarization change defect in a silicon carbide semiconductor wafer.

[0247] 46. ​​A method for detecting polarization-altering defects in a semiconductor wafer using a kit, the kit adapting a wafer inspection system to detect polarization-altering defects in the semiconductor wafer, the method comprising:

[0248] A linear polarizer is installed in the forward optical path of the wafer inspection system, the forward optical path extending between an irradiation source and the semiconductor wafer, wherein the irradiation source is arranged to irradiate the semiconductor wafer for inspection.

[0249] The waveplate is installed in the forward optical path between the linear polarizer and the semiconductor wafer; and

[0250] The mirror is mounted in such a position in the wafer inspection system that radiation from the irradiation source traveling along the forward optical path and passing through the semiconductor wafer is reflected back from the mirror, passes through the semiconductor wafer, and faces the objective lens of the wafer inspection system.

[0251] 47. The method according to item 46, further comprising:

[0252] The region of the semiconductor wafer having radiation in a first polarization state is irradiated by radiation from the irradiation source.

[0253] The mirror reflects the radiation that has passed through the semiconductor wafer back towards the semiconductor wafer as reflected radiation.

[0254] The objective lens is used to collect a portion of the reflected radiation to form an image of the region of the semiconductor wafer;

[0255] The linear polarizer blocks a first portion of reflected radiation traveling through the region of the semiconductor wafer that does not include the first region of the polarization-changing defect; and

[0256] At least a portion of the second portion of the reflected radiation transmitted through the region of the semiconductor wafer, including the second region of the polarization-changing defect, via the linear polarizer; and

[0257] An image of the region of the semiconductor wafer is generated by detecting at least a portion of the second portion of the reflected radiation transmitted by the linear polarizer using an imaging array.

[0258] 48. The method according to item 47, further comprising:

[0259] The radiation from the irradiation source is converted into circularly polarized radiation using the linear polarizer and the waveplate for the first polarization state.

[0260] 49. The method according to item 48, wherein the waveplate is a quarter-wave plate formed of a birefringent crystal.

[0261] 50. The method according to item 47, further comprising:

[0262] The radiation from the irradiation source is converted into elliptically polarized radiation using the linear polarizer and the waveplate for the first polarization state.

[0263] 51. The method according to item 50, further comprising:

[0264] The semiconductor wafer is used to convert the elliptically polarized radiation into circularly polarized radiation incident on the mirror.

[0265] 52. The method according to item 50, wherein the linear polarizer is an absorbing polarizer.

[0266] 53. The method according to item 47, wherein detecting the image includes forming a bright feature on the background, wherein:

[0267] The bright feature is formed by a portion of the second portion of the reflected radiation transmitted by the linear polarizer;

[0268] The bright feature represents the polarization-altering defect and has a higher intensity level compared to the background; and

[0269] The background in the image is generated by the first portion of the reflected radiation being blocked by the linear polarizer.

[0270] 54. The method according to claim 53, wherein detecting the image further comprises forming a dark feature in the image representing a non-polarization change defect, the dark feature having an intensity level lower than the intensity level of the background.

[0271] 55. The method according to claim 46, wherein mounting the mirror comprises mounting the mirror on a wafer chuck holding the semiconductor wafer.

[0272] 56. The method of claim 55, wherein mounting the mirror further comprises mounting an adapter to the wafer chuck, wherein the adapter has at least a partial annular shape and is configured to keep the semiconductor wafer away from the mirror at a distance such that the semiconductor wafer does not contact the mirror.

[0273] 57. The method according to item 55, wherein the size of the adapter is determined to hold a semiconductor wafer having a diameter of at least 150 mm.

[0274] 58. The method of claim 55, wherein the adapter has a notch to allow a wafer clamping end effector to enter the central region of the adapter for loading and unloading the semiconductor wafer.

Claims

1. A system for detecting polarization change defects in a semiconductor wafer, the system comprising: An irradiation source, used to emit radiation; An objective lens, used to focus the radiation from the irradiation source onto the semiconductor wafer; A mirror is arranged to reflect the radiation emitted from the semiconductor wafer back through the semiconductor wafer as reflected radiation; An imaging array for recording an image of at least a portion of the semiconductor wafer produced by at least a portion of the reflected radiation returning through the semiconductor wafer; as well as A linear polarizer is located between the semiconductor wafer and the imaging array, wherein the linear polarizer is oriented as follows: A first portion of the reflected radiation, excluding the first region of the polarization-changing defect, is blocked from traveling through the semiconductor wafer; as well as At least a portion of the second portion of the reflected radiation that travels through the second region of the semiconductor wafer, including the polarization-changing defect, is transmitted through the semiconductor wafer.

2. The system according to claim 1, wherein the linear polarizer includes an absorbing polarizer.

3. The system of claim 1, further comprising a waveplate located between the linear polarizer and the semiconductor wafer, wherein the waveplate comprises a birefringent crystal.

4. The system of claim 3, wherein the linear polarizer and the waveplate are located between the irradiation source and the objective lens.

5. The system of claim 3, wherein the polarization axis of the linear polarizer is oriented at an angle of 35 to 55 degrees relative to the fast axis of the waveplate.

6. The system of claim 3, further comprising a rotatable mount for holding at least one of the linear polarizer and the waveplate, such that the angle between the fast axis of the waveplate and the polarization axis of the linear polarizer can be adjusted.

7. The system of claim 1, further comprising a waveplate, wherein the linear polarizer and the waveplate are located between the objective lens and the mirror.

8. The system of claim 7, further comprising a rotatable mount for holding at least one of the linear polarizer and the waveplate, such that the angle between the fast axis of the waveplate and the polarization axis of the linear polarizer can be adjusted.

9. The system of claim 1, further comprising a quarter-wave plate combined with a first linear polarizer to form a circular polarizer.

10. The system of claim 9, wherein the circular polarizer is located in the system to intercept the forward optical path extending from the irradiation source to the mirror, and further intercepts the reflected optical path extending from the mirror to the imaging array.

Images