JP2010503862A - Polarization imaging - Google Patents

Abstract

  In systems and methods for inspecting various defects on a substrate, polarizing filters are used to improve the contrast of polarization-dependent defects such as defocus and exposure defects, while pits, voids, cracks, chipping And the same sensitivity to polarization independent defects such as particles.

Description

(Cross-reference of related applications)
This application is filed on September 12, 2006 under the 35th US Code 119 (e) (1), with the name “Polarization Imaging” and agent serial number Claims priority to US Provisional Patent Application No. 60 / 844,297, which is A126.199.101, the teachings of which are incorporated herein by reference.

(Field of Invention)
The present invention generally relates to inspection and metrology tools for use in quality assurance and yield improvement in semiconductor device manufacturing processes.

  In the lithographic semiconductor device fabrication process, it is essential that the stepper accurately focus the reticle image onto the semiconductor substrate or wafer. When the image of the reticle is out of focus (also known as defocus), the resulting semiconductor device structure can be inappropriate in size and shape. For example, the perimeter of the resulting structure is relatively scattered, obscure, has a rounded or undercut surface, and often has the desired linear geometry. May not. This defocus condition often results in malfunction and / or inoperability in the semiconductor device in question. Thus, defocus measurements allow semiconductor device manufacturers to allow the stepper to always focus the reticle image on the wafer, thereby allowing a larger and more profitable yield from the manufacturing process It is an important means for

  Another problem common to the formation of semiconductor devices is exposure defects. If the exposure of the photoresist layer to light is outside the range of acceptable light doses, features to be formed on the semiconductor substrate may be formed incorrectly. It is therefore important to identify the exposure defects in which they exist.

  In addition to inspection of substrate or wafer exposure or defocus defects, inspection for substrate or wafer process or material related defects, commonly referred to as “macro” defects, is also important. Macro defects are often defined as chippings, cracks, scratches, pits, delaminations, and / or particles that appear on the substrate and have dimensions of about 0.5 u to 10 u. Such defects can easily cause defects in the semiconductor device and significantly reduce the yield of the manufacturer of the device. It should be noted that the size of the macro defect may be larger or smaller than the size range described above, and the above size is merely a definition of the nominal size of such a defect.

  Traditionally, macro defects have been inspected using a dedicated inspection system, but the presence of exposure or defocus defects has not been easily or reliably identified. Exposure and defocus defects typically use an optical critical dimension (OCD) technique in any of a number of precision metrology tools, such as ellipsometers, reflectometers, and scatterometers. Identified. It is desirable to combine the ability to identify the presence of exposure and defocus defects with the ability to inspect macro defects on the substrate, and it is desirable that the same optical system be used for both functions.

  One embodiment of an inspection system for identifying defects on a substrate includes a light source that directs light onto the substrate to be inspected. The first polarizing filter or polarizer is located between the light source and the substrate. The second polarizing filter or analyzer is located between the substrate and an optical sensor that receives light reflected from the substrate. The polarizer and analyzer are angled relative to each other so that the image intensity of the image captured by the optical sensor is at least partially correlated with the presence of polarization-dependent defects on the substrate under test. Be placed. Polarization dependent defects include, among other things, defocus and exposure defects. It is also possible to identify defects that are not defocused or exposed defects and have a major dimension that is approximately below the wavelength of the incident light.

  The light source can be of any useful type, including but not limited to broadband incandescent light or a laser. Any of these light sources can be stroboscopic and can be positioned to direct light onto the surface of the substrate at any useful angle of incidence, including a right angle of incidence. The lasers can be fixed, monochrome, or arranged to output light at a plurality of different nominal wavelengths.

  When using strobe illumination, the strobe flashes continuously, at least partially correlated to the speed at which the substrate moves relative to the inspection system. This ensures that the inspection system can capture an image of the substrate at an appropriate location.

  The photosensor or imaging device can be a monochrome charge coupled device (CCD). In some cases, the light sensor may be a Bayer-type or a three-chip design color imaging device. In yet other cases, one or more light sources and / or color filters can be used with a monochrome light sensor to obtain color data from the substrate. Both area scanning light sensors and line scanning light sensors can be used.

  In addition to defocus and exposure defects, other types of defects can be identified. These other defects include pits, voids, chipping, cracks, particles, and scratches.

  The inspection system according to the present invention is operated by first placing a light source to direct light onto the substrate. The first polarizing filter is installed between the light source and the substrate, and the optical sensor is installed so as to receive the light reflected from the substrate. The second polarizing filter is installed between the substrate and the optical sensor, and the first and second polarizing filters are installed at a relative angle selected from each other. The inspection system is then used to capture images of the substrate and comparative data is generated from these images to identify the presence of exposure and / or defocus defects on the substrate, if any. Arranging the polarizing filter to capture the required image comprises rotating the first and second polarizing filters together to a desired inspection angle while maintaining a selected relative angle between the filters. Can be accompanied.

  The comparison data is obtained by first generating a difference image for each captured image and then averaging the respective pixel intensity differences of the difference image over all of the difference images to obtain an average image intensity for each difference image. be able to. The average image intensity of each captured image is evaluated against a predetermined threshold to determine the presence of at least one of exposure and defocus defects on the substrate, if any.

  Calibration of the output of the photosensor for at least one of known levels of exposure and defocus defects in the substrate is used to determine the appropriate defocus and exposure defect levels. In one embodiment, calibration involves capturing a plurality of images of the calibration substrate, each image undergoing a known degree of defocus and exposure defects. As described above, a difference image is generated for each captured image, and the pixel intensity difference of the difference image is averaged over the entire difference image to obtain an average image intensity. For each captured image with a known degree of defocus and exposure defects, an average image intensity value is recorded. Whether the user selects any recorded average image intensity value indicative of a particular degree or magnitude of defocus and / or exposure defect as a threshold or interpolates between the recorded values Or, simply, the recorded value can be used as a starting point for product specific modifiers to be applied. It is solely up to the user of the inspection system to define a suitable threshold for defocus and / or exposure defects.

  The step of generating a difference image can involve averaging a plurality of captured images pixel by pixel to obtain an average image. This average image is then subtracted from each captured image on a pixel-by-pixel basis to form a difference image that can be thought of as an array of pixel intensity values or as an array of pixel intensity value differences.

  Inspection of substrate defocus and / or exposure defects can be performed simultaneously with inspection of other defects such as pits, voids, chipping, cracks, particles, and scratches. Alternatively, inspection of each of these types of defects can be performed continuously or in a time-shifted manner, i.e., at a considerable distance from one another.

  In another embodiment of the present invention, an image analysis method such as a Spatial Pattern Recognition (SPR) method can be used to analyze the difference image and identify the boundaries of the layers on the substrate. . A layer boundary as described above is part of a layer that is an intentional part of the substrate, or is associated with a remaining part that is not an intentional part of the substrate, i.e. one type or another type of contamination. Note that there may be layers that can be things.

  In accordance with the present invention, in a system and method for inspecting various defects on a substrate, a polarizing filter is used to improve the contrast of polarization-dependent defects such as defocus and exposure defects, while The same sensitivity can be maintained for polarization independent defects such as voids, cracks, chipping and particles.

1 is a schematic diagram of one embodiment of an imaging system of the present invention having a nominal incident angle other than 90 °. FIG. 1 is a schematic diagram of one embodiment of an imaging system of the present invention having a nominal incident angle of substantially 90 °. FIG. It is the figure which showed the related component of the reflected light reflected from the board | substrate in vector format. Figure 6 is a chart showing the relevant components of the reflected light before passing through a properly placed analyzer. Figure 6 is a chart showing the relevant components of reflected light after passing through a properly positioned analyzer. 5 is a flowchart illustrating a method for setting an inspection system for inspection. 5 is a flowchart illustrating a method for inspecting a substrate.

  In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. In the drawings, like reference numerals designate substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be used and structural, logical, and electrical changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and equivalents thereof.

  The present invention relates to a method and apparatus for determining the presence of exposure and defocus lithographic defects in a semiconductor substrate by measuring the change in polarization of light reflected from the surface of the substrate. For simplicity of the following description, the term “defocus” is used herein to mean exposure and defocus defects, but a given substrate has one defect, the other It should be understood that it may be subject to defects or both. Furthermore, the term “defocus” has any characteristic consequences similar to exposure and / or defocus defects, and any defects and desirable of the substrate under inspection that can be identified or characterized by the inspection system of the present invention. Should be interpreted broadly to include no features. In general, defocus defects are polarization dependent features, ie, defocus defects cause a change in the polarization state of the light reflected therefrom, but those skilled in the art will appreciate other aspects of defocus defects. It will be understood that this may affect the nature and extent of the change in polarization.

  As used herein, the term “substrate” should be construed to include any material or structure that can be inspected by the inspection system of the present invention. Specifically, the term “substrate” includes, but is not limited to, a full wafer, an unpatterned wafer, a patterned wafer, a partially patterned wafer, a fully or partially patterned divided wafer, and a patterned wafer. Any structure including cut wafers in any form and on any support mechanism, including non-divided wafers, film frames, JEDEC trays, Auer boats, dies in gels or waffle packs, multi-chip modules often referred to as MCMs, etc. , In the form, or material of a semiconductor wafer. The terms “substrate” and “wafer” can be used interchangeably herein.

  The term “macro defect” as used herein includes all unintentional features that appear on a substrate that is essentially polarization independent. As described above, macro defects are conventionally described as chipping, cracks, pits, particles, scratches, and the like. Note that in some cases the size of the macro defect may approach the wavelength of the incident radiation used for inspection purposes. In these cases, macro defects may affect the polarization state of light reflected therefrom.

  With reference to FIG. 1, one embodiment of an imaging system 8 includes an illuminator 10, a polarizer 12, an analyzer 14, and an optical sensor 16. The illuminator 10 directs light onto the polarizer 12 along the optical path P, but substantially transmits only light having a predetermined polarization angle. The light transmitted by the polarizer 12 then enters the substrate S. In one embodiment, the substrate S is a silicon wafer or a portion thereof having a structure formed thereon. In some embodiments, these structures form one or more semiconductor devices on the substrate S. Other mechanisms and structures can also be formed on the substrate S.

  As can be seen from FIG. 1, the optical path P is an incident angle that is not perpendicular to the substrate S. In some embodiments, the illuminator 10, the polarizer 12, the analyzer 14, and the optical sensor 16, and other related optical elements such as an objective lens, change the angle of incidence of light on the substrate S. Can be attached as possible. Types of attachment mechanisms useful for changing the angle of incidence of light in the system 8 are known to those skilled in the art and can include a mounting plate to which the optical elements of the system 8 are mounted, which can include one or more mounting plates. It can be rotated by a rotating means that can be an actuator. The angle of incidence can be essentially fixed (as shown) or can be changed for each product setting. Further, in some embodiments, the angle of incidence can be changed during inspection as needed.

  The illuminator 10 includes any wideband white light, a laser with a fixed wavelength output, a laser arranged to output multiple wavelengths, or a plurality of lasers arranged to direct light along the optical path P It can be of a useful type. The intensity required for the illuminator may vary depending on the intended use of the system 8. Some applications require high intensity illumination, and conversely, other applications require relatively low intensity illumination. The illuminator 10 can be arranged to provide a substantially constant output, or it can be arranged to strobe to freeze the movement of the substrate S in the system 8, thereby providing a substrate. S images can be captured quickly.

  The light incident on the substrate S is reflected therefrom, and this reflected light is incident on the analyzer 14. The analyzer is a polarization optical element similar to the polarizer 12, and has a predetermined polarization angle. Only the light it has is allowed to pass. The light that has passed through the analyzer 14 is incident on the optical sensor 16, which captures an image of the substrate S. The optical sensor 16, in one embodiment, is a two-dimensional electronic optical sensor such as a charge coupled device (CCD), but is a line scan or time delay integration (TDI) imaging device, or a CMOS optical sensor array. Any device that can form a two-dimensional array of pixel intensity values in grayscale or color units, such as

  In one embodiment, the light sensor 16 is a monochrome light sensor, and each pixel of the two-dimensional pixel array of the light sensor exhibits a grayscale value from 0 to 256, and based on these pixels, an image of the substrate S Represents. When a monochrome light sensor is used, one or more color filters 18 are installed in the optical path P between the illuminator 10 and the light sensor 16 so that only light within the wavelength range corresponding to the color filters is received. Can be passed.

  In another embodiment, the light sensor can be a Bayer-type color light sensor or a three-chip color sensor with separate light sensors, each sensor dedicated to a separate color, eg, one sensor is red For light, one sensor is dedicated to blue light and one sensor is dedicated to green light.

Those skilled in the art will recognize that the basic elements of the system 8 described herein may be in conjunction with or separate from other optical elements including, but not limited to, optical filters, lenses, mirrors, retarders, and modulators. It will be understood that it can be used. One inspection system that can be adapted to carry out the present invention is marketed by Rudolph Technologies (Flanders, New Jersey) under the trade name WaferView ^™ . Furthermore, it should be understood that the system 8 can be arranged to perform a plurality of functions, which are performed simultaneously or at intervals in time. For example, the system 8 can be adapted to perform defocus defect inspection as well as macro defect inspection. In addition, the system 8 can inspect for macro defects and then inspect for defocus defects or vice versa, or perform both inspections simultaneously.

  The color filter 18 can be used in the system 8 as schematically shown in FIG. One or more color filters 18 are disposed between the polarizer 12 and the substrate S, between the substrate S and the analyzer 14, between the illuminator 10 and the polarizer 12, or between the analyzer 14 and the light. It can be installed between the sensor 16. In one embodiment, the color filter 18 may be a type of filter wheel known in the prior art, and one of the group of color filters has the color filter 18 selectively located throughout the optical path P. Thus, it is attached to a rotating wheel installed in the optical path P. In another embodiment, a removable filter holder can be installed in the optical path P so that different color filters can be installed in the optical path P. In yet another embodiment, a fixed color filter can be installed in the optical path P. It should be understood that any filter medium or mechanism suitable for selectively passing a predetermined wavelength or wavelength range can be used as a color filter.

  In some embodiments, it is desirable to separate the output of the photosensor 16 for a predetermined color channel, but a “color channel” is defined as a predetermined wavelength or wavelength range. Color channel separation is a color that directly incorporates the ability to distinguish between each color channel, as suggested above, by using color filters, or as done by 3-chip and Bayer photosensors. This can be accomplished by using an optical sensor or by using an illuminator 10 that outputs light in a preselected wavelength range. It should be understood that some substrates S can have partial or total transparency for a particular wavelength range or color. By way of example only, a given substrate S can transmit or destructively disturb most of all blue incident light having a wavelength centered around 475 nm, but is incident on the substrate S. Most of the red light having a wavelength centered at about 700 nm can be reflected.

  In this embodiment, it can then be useful to be able to use the signal output by the photosensor 16 resulting from the incidence of red light on the photosensor 16. The use of data for each color channel depends on what features are being examined in the tests being performed by the system 8. In some embodiments, certain semiconductor substrates (also known as products) tend to have features that reflect light in a known manner, thus making inspection system 8 particularly suitable for a given product. Can be set to optimize product inspection.

  FIG. 2 is a diagram illustrating another embodiment of the present invention, in which the inspection system 30 has an optical path through a deflector 36, a filter 40 (optional), and a beam splitter 42 in a rectangular array. An illuminator 32 that guides light onto the substrate S along P is included. The light reflected from the substrate S onto the path P is guided by the beam splitter 42 to the optical sensor 34 through the filter 40 (optional) and the analyzer 38. Systems 8 and 30 are substantially similar except for the presence of the beam splitter and the difference in incidence angle. In the present embodiment, the optical path P is substantially perpendicular to the substrate S.

  It was observed that the defocus defect changes the reflectivity of the substrate S because the defocus defect changes the geometry of the structure formed on the substrate S. Other factors that change the reflectivity of the substrate S are the properties of the other film layers and the wavelength, polarization, and angle of the light incident on the substrate. By using an inspection system (e.g., system 8 or 30) according to various embodiments of the present invention, it is possible to distinguish between changes in reflectivity due to defocus defects and to make the distinction in a quick and reliable manner. Is possible.

  In general, light from the illuminators 10 and 32 is polarized at a predetermined angle P by the polarizers 12 and 36 and is incident on the substrate S at a specific angle θ. Upon reflection, the substrate S changes the polarization state of the incident light in relation to its many features, particularly defocus. Information on the defocus defect in the substrate S can be obtained by this change in polarization. The reflected light passes through the analyzer 14 and enters the optical sensor 16. When the analyzer 14 is arranged as described in detail herein below, the data obtained from the optical sensor 16 can provide information regarding changes in both the amplitude and polarization of the reflected light, and in particular the substrate S. Helps to include information about the presence of the above defocus defects.

  In one embodiment, light incident on the substrate S is linearly polarized by the polarizers 12, 36. It provides the simplest solution to the immediate inspection problem. In other embodiments, the incident light is polarized elliptically or circularly as required. By setting the analyzers 14, 38 at an angle A relative to the polarizers 12, 36, the light reaching the photosensors 16, 34 can be adjusted. The angle between the polarizers 12, 36 and the analyzers 14, 38 is given by PA.

Referring now to FIG. 3, in general, when light is reflected from the substrate S, a portion of the incident light (E _P ) is reflected differently than other portions of the incident light. A portion of the incident light _EP is reflected from polarization independent features on the surface of the substrate S without any significant change in its polarization, as indicated by E ₁ and E ₂ in FIG. Some examples of such features that can be found on the semiconductor substrate S include, but are not limited to, light and dark within the substrate S, such as chipping, cracks, scratches, pits, voids, and particles. The defect that appears is mentioned. Another portion (E ₃ ) of the reflected incident light is reflected from the polarization dependent features formed on the substrate S, arranged to change the polarity of the incident light.

Some examples of polarization dependent features or structures found on the semiconductor substrate S include, but are not limited to, line structures, conductors, interconnects, vias, and streets. Yet another portion of the incident light reflected from the surface of the substrate S is reflected by features or structures that change the polarization of the reflected light and are also subject to defocus defects. This light (E ₄ ) has a polarization state different from that of E ₃ . Structures that reflect light E ₄ are structurally similar to the nominal structure from which light E ₃ is reflected, except for the fact that they suffer from defocus defects and their magnitude affects the intensity of light E _4. Can be similar or identical.

Referring to FIG. 4, it can be seen that there is almost no contrast in the intensity between the reflected light E ₃ and E ₄ for the light that has not passed through the analyzers 14, 38. As is apparent, it is difficult to identify defocus defects under these circumstances. However, the reflected light _{E 1, E 2, E 3} , and _{E 4,} and suitably passed through an analyzer 14, 38 arranged, an optical signal _{E'1, E'2, E'3} , and _E'4 , The contrast level between the optical signals E ′ ₃ and E ′ ₄ is sufficient to obtain useful information regarding the presence of defocus defects. Please refer to FIG.

In one embodiment, the angle PA between the polarizer 12 and the analyzer 14 is determined experimentally. Referring now to FIG. 6, a test substrate S is placed in the system 8 for inspection (step 50), and the illuminator 10 (in one embodiment a strobe illuminator) is set to a predetermined illumination level ( Step 52), the illumination level is preferably set near its maximum intensity output, but can be any suitable intensity. Light E _P from the illuminator or light source 10 is directed onto the substrate S through the polarizer 12. Next, the polarizer 12 is set to the angle P (step 54).

In one embodiment, the polarizer 12 is oriented at an angle substantially perpendicular to any linear structure present on the substrate S. Of course, if the substrate S is a semiconductor wafer on which a semiconductor device is formed (in any finished state), such a structure is generally, but not necessarily, marked linear features. Have Reflected light _{(E 1, E 2, E} 3, and _{E 4)} passes through the analyzer 14, the optical signal _E'1 on the optical sensor 16, _{E'2, E'3,} and _E'4 obtain. If there is no distinguishable orientation relative to the linear structure on the substrate S, or if no linear structure is formed on the substrate S, any angle P can be selected for the polarizer 12. .

  Next, as described in US Pat. Nos. 6,324,298, 6,487,307, and 6,826,298 (which are co-owned and referenced herein) The analyzer 14 is rotated to an angle A (step 56) so that sufficient illumination reaches the optical sensor 16 (step 56), and the macroscopic or polarization independent defect of the substrate S. Enable inspection. Quality sufficient to satisfy the end user of the system 8, not only when the illumination allows inspection of the substrate S for defects, but also no serious errors such as misjudgments and oversight of defects occur during the inspection. Note that the analyzer 14 is considered to be at the correct angle A when testing with a signal-to-noise ratio. The signal to noise ratio of the system 8 is determined by analyzing the output of the optical sensor 16 in a known manner.

Knowing the angles P and A at which the polarizer and the analyzer are located, the polarizer and the analyzer are kept in the above-mentioned manner while maintaining the relative angle (PA) between the polarizer and the analyzer substantially constant. Are rotated together through a series of inspection angles to a desired angular position relative to the substrate S that provides the necessary contrast between the optical signals E ′ ₃ and E ′ ₄ (step 58). During rotation of the polarizer 12 and analyzer 14, the incident intensity of light on the photosensor 16 is recorded. The light intensity at the optical sensor 16 is recorded for each inspection angle or position through which the polarizer 12 and analyzer 14 are rotated. In one embodiment, the polarizer and analyzer 14 are rotated in a substantially continuous manner, and the position of the polarizer and analyzer, and the light intensity present in the light sensor 16, finely increases the rotation of the polarizer and analyzer. Is recorded. Analysis of the data obtained during rotation of the polarizer and analyzer is performed to identify the optimal inspection angle or position of the polarizer and analyzer with respect to the contrast between the reflected light E ′ ₃ and E ′ ₄ .

  The process of identifying the optimal settings for angles P and A can be done manually, and the user of system 8 rotates polarizer 12 and analyzer 14 over a selected range of angles while photosensor 16 Records the image data, which is processed by a suitable type of computer C to determine the optimum angle PA. Alternatively and preferably, the polarizer 12 and the analyzer 14 can be controlled by the above-described computer from their optimal optical sensor 16 at various angles PA, while their rotation can be controlled. Automated so that data can be recorded. Automation of polarizers and analyzers is known to those skilled in the art. As suggested above, the process of determining the optimum angle PA between the polarizer and the analyzer requires multiple iterations both before and after the steps described immediately below. There is. For example, once all of the calibration / setting process is complete, it may be useful to run the entire calibration / setting process multiple times to determine if the resulting system settings are optimal.

  As described with reference to FIG. 6, once the system 8 is properly set up, it can inspect for defocus defects and other defects as required. However, first, the system 8 must be calibrated. Calibration is preferably performed using a Focus Exposure Matrix (FEM) wafer. An FEM is a substrate on which a plurality of patterns or structures are formed, each having a different focal position and exposure time. FEMs are typically made as part of the calibration process for photolithography equipment used in semiconductor device manufacturing. FEM incorporates structural changes in the pattern or structure formed on the substrate S caused by changes in focus position and exposure. The defocus and exposure data obtained from the FEM are used as a comparator during the inspection of the substrate S. It should be noted that the pattern formed on the FEM may be different from that formed on the substrate S under test, but is preferably the same.

  Since the method of obtaining defocus data is substantially the same for calibration purposes and inspection purposes, the method of obtaining defocus data for calibration purposes will be described as part of the inspection process. Differences between the calibration procedure and the inspection procedure are noted as necessary.

  During inspection, a substrate S of the type to be inspected is obtained and placed in a known manner on a wafer support or top plate (not shown) that moves the substrate S relative to the optical elements of the inspection system 8. . The substrate S (product or FEM) is inspected piecewise in some embodiments. In one embodiment where the substrate S is a wafer with semiconductor devices formed thereon, the inspection of the substrate S is performed on a die level basis, i.e., images of individual dies on the substrate S are sensor 16. And these images are processed as described below.

  In other embodiments, the inspection is performed on a visual field basis. The optical elements of system 8 are arranged to capture an image of the field of view, and the size of the field of view may be different from that of individual dies or individual stepper shots. If the field of view of system 8 is smaller than the individual dies, the multiple fields of view are stitched together to form a composite image of the individual dies. A composite image of all stepper shots can be formed using the same stitching technique. It should be understood that the formation of a composite image by stitching images is a technique known in the art.

  In other embodiments where the field of view is larger than an individual die or larger than a stepper shot, the resulting image can be cut out to show one or more dies or stepper shots. In general, the die formed by the first stepper shot is acceptable, while the die formed by the second stepper shot may be defective, so multiple stepper shots may result in multiple die. It is useful not to crop a large image to include. Image cropping is a technique known to those skilled in the art.

  In yet another embodiment, inspection of the substrate S is accomplished by first capturing an image of the entire substrate S. If the substrate S is relatively small, it can be captured using the system 8 operating on the area scanning principle. If the substrate is larger than the field of view of the area scanning system 8, multiple images of the substrate S can be obtained and spliced together as suggested above. The stitching can be used with line scan type and area scan type inspection systems 8, as will be readily understood by those skilled in the art.

  Once the appropriate polarizer / analyzer angle PA is obtained as described above, images of individual dies on the substrate S are captured by the optical sensor 16 (step 60). Please refer to FIG. The calibration and inspection process described below is described as being performed on a die basis, but it should be understood that other criteria may be used. The imaged die on the substrate S can be selected by a user who determines that the die is substantially free of chipping, cracks, pits, color changes, particles, etc. for model formation. This determination is entirely up to the user of the system 8 and can vary greatly depending on the nature and application of the product on the substrate S. For example, a user inspecting a substrate S on which a semiconductor device intended for use in a pacemaker is placed may impose very stringent standards regarding the number of defects on a die used to form a model. There is. Conversely, a user inspecting a substrate S on which the same semiconductor device is formed, intended for use with cheap and substantially disposable consumer goods, can detect defects in the die used to form the model. There is a possibility that a large number can be easily tolerated.

  In short, it is up to the user of the system 8 to define what is a “good” die for the purpose of forming a model. It is assumed that all “good” dies on the substrate S are obtained for the purpose of modeling, which is generally a statistically significant number of “good” dies. This is the case with only dies, and this number is generally less than the total number of “good” dies and is about 10-15. At least dies with random and relatively inconspicuous defects to be selected as small random defects that do not exceed a reasonable number will be inspected if a statistically significant sample of such dies is sampled. It will be appreciated that large non-random defects are more likely to distort the inspection process, although less likely to have a major impact.

  Useful models can also be obtained using automated methods. For example, the computer C controlling the system 8 can randomly select a statistically significant number of dies and capture their images. These images are then used to form a model for use in examining the individual images that formed the model. If the selected die is found to be defective under the criteria selected by the user, the defective image is replaced with another randomly selected die image. This process is repeated until a suitable model is formed. A model formed manually or automatically changes over time if it remains unchanged, i.e. does not change over time, or as inspection proceeds, a new good die is added to the model. Note that there may be cases.

  The term “model” may have different meanings depending on the person skilled in the art and should be clarified when used herein. The term “golden die” or “golden reference” refers to an image whose constituent pixels are the intensity values obtained by summing the corresponding pixel values of multiple dies and obtaining the average of those values. Have Thus, the golden die is simply an image of the average die. The term “model” is broader than the terms “golden die” or “golden reference” and in some cases does not incorporate or use golden die or golden reference information.

  The golden die is used for defocus inspection in one embodiment (step 62). Similarly, the golden die can form at least part of the model reference used for macro defect inspection. However, in general, the model used for macro defect inspection moves beyond a simple golden die by defining a pixel intensity threshold for each pixel in the image. In the inspection of macro defects, if the pixel intensity values are found out of the range defined by the threshold during evaluation, those pixels are considered defective. The threshold itself can be as simple as the standard deviation calculated from the golden die, but is usually applied to the various features, variations and characteristics of the substrate S and the products formed thereon. May include weight factors, taking into account user-defined standards.

  The model used for defect inspection can be formed in a myriad of ways, and if it is based at all on the golden die, it is also not based, and the only requirement for the macro defect inspection model results It should be understood that the test results in satisfying the user of the system 8. If a macro defect inspection is performed, a model suitable for such inspection can be obtained at approximately the same time as the golden die is generated (step 64). As indicated by arrow 65, golden die information may be used in some cases to form the model. Once the model is formed, the captured image is then compared with the model to identify defects (step 72).

  Using the golden die image obtained in the previous step, the background of the image captured during the defocus defect inspection is removed, resulting in an image referred to as the difference image (step 66). The difference image is composed of the difference between each corresponding pixel value of the golden die image and the image of the die under inspection. The pixel intensity values that form the difference image can be positive, negative, or zero and are summed and averaged over all of the difference images (step 68). The resulting average value is then compared with a similar average obtained by inspection of the FEM to determine if the average value exceeds a predetermined threshold set by the user of the system. In some embodiments, the average value of the FEM-derived difference image is directly compared to the average value of the inspection-derived difference image to determine if there is an unacceptable level of defocus defect in the die. Is also possible.

As will be appreciated by those skilled in the art, the polarizer 12 and the analyzer 14 are angled with respect to each other so as to prevent the passage of substantially all light or allow the passage of substantially all light. Can be placed. In one embodiment of the invention, the polarizer 12 and the analyzer 14 are arranged at an angle to each other so as to block the passage of substantially all light E ₁ and E ₂ . In the present embodiment and when the substrate S does not affect the polarization state of the reflected light, the optical sensor 16 does not register substantially any image. However, the features that change polarity are generally present on the substrate S and generally there is at least some defocus defect so that the light E ₃ and E ₄ are incident on the photosensor 16.

  The angular position of the polarizer 12 with respect to the analyzer 14 is most dependent on the nature of the substrate S to be inspected, but other factors are used including, but not limited to, the nature of the light source 12 and the physical properties of the optical system You can also In one embodiment, the polarization angle of the polarizer 12 is about 45 ° with respect to the linear structure present on the substrate S to be inspected. Thus, it should be appreciated that in some embodiments, the polarization angle of the analyzer 14 may vary depending on the nature of the substrate being examined.

  In some embodiments, multiple scan inspections are used to determine the presence of a defect on the substrate S. In one embodiment, the first pass is performed by the polarizer 12 and the analyzer 14 in a setting that passes insufficient light for macro defect inspection. This first pass is merely intended to determine whether a defocus or exposure defect is present in the imaging region of the substrate, generally one or more dies or stepper shots. The second pass involves finding macro defects such as chipping, cracks, particles, voids, and scratches, with polarizers 12 and arranged arranged so that a greater amount of light can pass through them. Performed by the analyzer 14.

  In another embodiment, the system 8 can be used to detect a change in the thickness of a thin film on the substrate, or its presence. In some cases, unnecessary residual film remains on all or part of the substrate S after the processing step. When properly positioned, the differential image of the substrate 8 identifies the location and size of the remaining film.

  While particular embodiments of the present invention have been illustrated and described herein, those skilled in the art will recognize that any mechanism intended to accomplish the same purpose can be substituted for the particular embodiment shown. It will be understood. Many adaptations of the invention will be apparent to those skilled in the art. This application is therefore intended to cover any adaptations or variations of the present invention. It is expressly intended that this invention be limited only by the following claims and equivalents thereof.

  The present invention uses polarization filters in systems and methods for inspecting various defects on a substrate to improve the contrast of polarization-dependent defects such as defocus and exposure defects, while pits, voids, and the like. By maintaining the same sensitivity to polarization-independent defects such as cracks, chipping, and particles, it is useful for ensuring quality and improving yield in the manufacturing process of semiconductor devices.

8 Imaging System 10 Illuminator 12 Polarizer 14 Analyzer 16 Optical Sensor 18 Color Filter P Optical Path S Substrate

Claims (33)

An inspection system for identifying defects on a substrate,
A light source arranged to direct light onto the substrate;
A first polarizing filter disposed between the light source and the substrate;
A photosensor arranged to receive light reflected from the substrate;
A second polarizing filter disposed between the substrate and the photosensor;
With
The first and second polarizing filters are angled relative to each other such that the image intensity of the image captured by the photosensor is at least partially correlated with the presence of polarization-dependent defects on the substrate. Inspection system, characterized by being attached to.   The inspection system according to claim 1, wherein the light source is a strobe light source.   The inspection system according to claim 1, wherein the light source is selected from the group consisting of a laser and a white light source.   The inspection system according to claim 3, wherein the laser light source is a monochrome laser.   The inspection system according to claim 3, wherein the laser light source is a plurality of lasers each having a different nominal wavelength output.   The inspection system according to claim 1, wherein the optical sensor is a color optical sensor.   The inspection system according to claim 6, wherein the color light sensor is selected from the group consisting of a monochrome light sensor, a Bayer color light sensor, and a 3-chip color light sensor having a color filter associated therewith.   The inspection system according to claim 1, further comprising at least one light color filter disposed between the light source and the light sensor.   The inspection system of claim 1, wherein the optical sensor captures an image of sufficient quality to allow identification of a defect selected from the group consisting of pits, voids, chipping, cracks, particles, and scratches. .   The inspection system according to claim 1, wherein the optical sensor is selected from the group consisting of an area scanning optical sensor and a line scanning optical sensor.   The inspection system of claim 1, wherein the light source is a strobe that illuminates the substrate at a speed that is at least partially correlated to the speed at which the substrate moves relative to the inspection system.   The inspection system according to claim 1, wherein the polarization-dependent defect is selected from the group consisting of a defocus defect and an exposure defect. An inspection system for identifying defects on a substrate,
A light source arranged to direct light onto the substrate;
A first polarizing filter disposed between the light source and the substrate;
A photosensor arranged to receive light reflected from the substrate;
A second polarizing filter disposed between the substrate and the photosensor;
With
The first and second polarizing filters are angled with respect to each other so that at least a first type and a second type of defect can be simultaneously identified using an image captured by the photosensor. Inspection system characterized by being arranged.   The inspection system of claim 13, wherein the identified first type of defect is at least one of the group consisting of a defocus defect and an exposure defect.   14. The identified second type of defect, if any, is at least one of the group consisting of pits, voids, chippings, cracks, particles, and scratches on the substrate. Inspection system.   The inspection system according to claim 13, wherein the light source is a strobe light source.   The inspection system of claim 13, wherein the light source is selected from the group consisting of a laser and a white light source.   The inspection system according to claim 17, wherein the laser light source is a monochrome laser.   The inspection system of claim 17, wherein the laser light source is a plurality of lasers each having a different nominal wavelength output.   The inspection system according to claim 13, wherein the optical sensor is a color optical sensor.   21. The inspection system of claim 20, wherein the color light sensor is selected from the group consisting of a monochrome light sensor having a color filter associated therewith, a Bayer color light sensor, and a 3-chip color light sensor.   The inspection system according to claim 13, further comprising at least one light color filter disposed between the light source and the light sensor.   The inspection system according to claim 13, wherein the optical sensor is selected from the group consisting of an area scanning optical sensor and a line scanning optical sensor.   The inspection system of claim 13, wherein the light source is a strobe that illuminates the substrate at a speed that is at least partially correlated to the speed at which the substrate moves. A method for inspecting substrate exposure and defocus defects,
A light source disposed to direct light onto the substrate, a first polarizing filter disposed between the light source and the substrate, and an optical sensor disposed to receive light reflected from the substrate Providing an inspection system comprising: a second polarizing filter disposed between the substrate and the photosensor;
Placing the first and second polarizing filters at a selected relative angle relative to each other;
Capturing an image of the substrate;
Generating comparison data from the image to identify the presence of at least one of exposure and defocus defects on the substrate;
A method for inspecting a substrate, comprising:   26. A method for inspecting a substrate according to claim 25, further comprising rotating the first and second polarizing filters together to an inspection angle while maintaining the selected relative angle between the filters. Processing the image comprises:
Generating a difference image for each captured image;
Averaging the respective pixel intensity differences of the difference image over all of the difference images to obtain an average image intensity for each difference image;
Evaluating the average image intensity of each captured image against a predetermined threshold to determine the presence of at least one of exposure and defocus defects on the substrate, if any. 26. A method for inspecting a substrate according to 25.   26. The method of inspecting a substrate of claim 25, comprising calibrating the output of the photosensor for at least one of a known level of exposure and defocus defects in the substrate. The step of calibrating comprises:
Capturing images of a plurality of calibration substrates, each image experiencing a known degree of defocus and exposure defects;
Generating a difference image for each captured image;
Averaging the pixel intensity differences of the difference image across all of the difference images to obtain an average image intensity;
29. A method of inspecting a substrate according to claim 28, comprising: recording the average image intensity value for each captured image having a known degree of defocus and exposure defects.   The step of generating the difference image includes a step of averaging a plurality of captured images in units of pixels to obtain an average image, and subtracting the average image from each captured image in units of pixels to obtain a difference image. 28. A method for inspecting a substrate according to claim 27.   26. The method of inspecting a substrate of claim 25, further comprising, for each captured image, inspecting a defect selected from the group consisting of pits, voids, chippings, cracks, particles, and scratches.   32. Inspecting a defect selected from the group consisting of the pits, voids, chipping, cracks, particles, and scratches is performed substantially simultaneously with inspection of at least one of the exposure and defocus defects. A method for inspecting a substrate described in 1.   32. The method of inspecting a substrate of claim 30, further comprising inspecting the difference image to identify layer boundaries therein.

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