TWI830864B - Thickness measurement of substrate using color metrology - Google Patents

Abstract

A system for obtaining a measurement representative of a thickness of a layer on a substrate includes a support to hold a substrate, an optical assembly to capture two color images with light impinging the substrate at different angles of incidence, and a controller. The controller is configured to store a function that provides a value representative of a thickness as a function of position along a predetermined path in a coordinate space of at least four dimensions. For a pixel in the two color images, the controller determines a coordinate in the coordinate space from the color data, determines a position of a point on the predetermined path that is closest to the coordinate, and calculates a value representative of a thickness from the function and the position of the point on the predetermined path.

Description

Thickness measurement of substrate using colorimetry

The present disclosure relates to optical metrology, for example, used to detect the thickness of layers on a substrate.

Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductor, or insulating layers on a silicon wafer. One fabrication step involves depositing and planarizing a filler layer over a non-planar surface. For some applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a conductive filler layer can be deposited on a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, portions of the metal layer remaining between the raised patterns of the insulating layer form vias, plugs, and wires that provide conductive paths between thin film circuits on the substrate. For other applications, the filler layer is deposited over the underlying topology provided by the other layers, and the filler layer is planarized until a predetermined thickness remains. For example, a dielectric filler layer can be deposited over a patterned metal layer and patterned to provide insulation between metal regions and provide a flat surface for further photolithography.

Chemical mechanical polishing (CMP) is a recognized planarization method. This planarization method typically requires the substrate to be mounted on a carrier or grinding head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controlled load on the substrate to push the substrate toward the polishing pad. An abrasive slurry is typically supplied to the surface of the polishing pad.

Changes in slurry distribution, polishing pad conditions, relative velocity between polishing pad and substrate, and load on the substrate may cause changes in material removal rate. These changes, along with changes in the initial thickness of the substrate layer, result in changes in the time required to reach the grinding endpoint. Therefore, determining the polishing endpoint solely based on polishing time may result in over-polishing or under-polishing of the substrate.

Various optical metrology systems (eg, spectrometers or ellipsometers) can be used to measure the thickness of substrate layers before and after polishing, for example, at an inline or separate metrology station. Additionally, various in-situ monitoring techniques such as monochromatic optical or eddy current monitoring can be used to detect grinding endpoints.

In one aspect, a system for obtaining a measurement representative of the thickness of a layer on a substrate includes: a support for holding a substrate for integrated circuit fabrication; an optical assembly, the optical assembly A method for capturing a first color image of at least a portion of the substrate held by the support by illuminating the substrate with light at a first angle of incidence, and capturing a first color image of the substrate by illuminating the substrate with light at a different second angle of incidence. holding at least a portion of the second color image; and a controller. The controller is configured to receive a first color image and a second color image from the optical assembly; store a function that provides a value representative of thickness based on a position along a predetermined path in a coordinate space of at least four dimensions, the at least four dimensions The dimensions include the first color channel and the second color channel from the first color image and the third color channel and the fourth color channel from the second color image; for the pixels of the first color image and the pixels in the second color image The corresponding pixel determines its coordinates in the coordinate space from the color data for the pixel in the first color image and the color data for the corresponding pixel in the second color image; determines the position of the point closest to the coordinates on the predetermined path. ; and a value representing the thickness is calculated from the function and the position of the point on the predetermined path.

In other aspects, a computer program includes instructions for causing a processor to perform operations of a controller, and a polishing method includes positioning a substrate for integrated circuit fabrication within the field of view of a color camera, generating the substrate from the color camera color images, and perform operations.

Implementations of any of these aspects may include one or more of the following features.

The coordinate space may be four-dimensional, or the coordinate space may be six-dimensional. The first color channel and the second color channel may be selected from a group of color channels including hue, saturation, brightness, X, Y, Z, red chroma, green chroma and blue chroma of the first color image. The third color channel and the fourth color channel may be selected from a group of color channels including hue, saturation, brightness, X, Y, Z, red chroma, green chroma and blue chroma of the second color image. The first and third color channels may be red chroma, and the second and fourth color channels may be green chroma.

The first angle of incidence and the second angle of incidence may each be between about 20° and 85°. The first angle of incidence may be at least 5° greater than the second angle of incidence, for example, at least 10° greater.

In another aspect, a polishing system includes a polishing station including a platform for supporting a polishing pad; a support for holding a substrate; and an embedded metrology station for use in the polishing station. measuring the substrate before and after grinding the surface of the substrate; and a controller. The embedded metrology station includes one or more elongated white light sources, each having a longitudinal axis and configured to direct light toward the substrate at a non-zero angle of incidence, thereby forming an illuminated area on the substrate that scans the substrate extending along a first axis; a first color line scan camera having detector elements arranged to receive light reflected from the substrate illuminating the substrate at a first incident angle and forming a scan on the substrate an image portion extending along the first axis; a second color line scan camera having detector elements arranged to receive light reflected from the substrate striking the substrate at a different second angle of incidence, and forming a second image portion extending along a first axis during scanning of the substrate; a frame supporting one or more light sources, a first color line scan camera, and a second color line scan camera; and a motor causing the frame to contact the support Relative movement between the components along a second axis perpendicular to the first axis causes one or more light sources, a first color line scan camera and a second color line scan camera to scan the substrate. The controller is configured to receive color data from a first color line scan camera and a second color line scan camera, generate a first two-dimensional color image from the color data from the first color line scan camera and generate a first two-dimensional color image from the second color line scan camera. Scan the color data of the camera to generate a second two-dimensional color image, and control grinding at the grinding station based on the first two-dimensional color image and the second two-dimensional color image.

In other aspects, a computer program includes instructions for causing a processor to perform operations of a controller, and a polishing method includes positioning a substrate for integrated circuit fabrication within the field of view of a color camera, generating the substrate from the color camera color images, and perform operations.

Implementations of any of these aspects may include one or more of the following features.

One or more diffusers may be positioned in the light path between one or more elongated white light sources and the substrate.

The first angle of incidence and the second angle of incidence may each be between about 5° and 85°, for example, both may be between about 20° and 75°. The first angle of incidence may be at least 5° greater than the second angle of incidence, for example, at least 10° greater. The first color line scan camera and the second line scan camera may be configured to image overlapping areas on the substrate. The one or more elongated light sources may include a first elongated light source to generate light that illuminates the substrate at a first angle of incidence, and a second elongated light source that generates light that illuminates the substrate at a second angle of incidence. Light from the first light source and light from the second light source may illuminate overlapping areas on the substrate, for example, overlapping areas.

The frame can be fixed and the motor can be coupled to the support, and the controller can be configured to cause the motor to move the support while simultaneously one or more elongated light sources and the first color line scan camera and the second color line The scanning camera remains stationary to scan over the substrate.

Implementation may include one or more of the following potential advantages. It can improve the accuracy of thickness measurement. This information can be used in feedforward or feedback to control grinding parameters, thereby providing improved thickness uniformity. The algorithm used to determine changes may be simple and have low computational load.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features and advantages will be apparent from the description and drawings and from the patent application.

The thickness of a layer on a substrate can be measured optically before or after grinding (eg, at an inline or stand-alone metrology station) or during grinding (eg, by an in-situ monitoring system). However, some optical techniques, such as spectrometry, require expensive spectrometers and computationally intensive manipulation of spectral data. Even apart from the computational load, in some cases the algorithm results cannot meet the ever-increasing accuracy requirements of users.

One measurement technique is to obtain a color image of a substrate and analyze the image in color space to determine layer thickness. In particular, the position along the path in the two-dimensional color space can provide information about the current state of grinding, for example, the amount removed or the amount of material remaining. However, in some cases, it may be difficult to resolve the differences between colors in an image. By performing color correction on the image, color contrast can be increased. Therefore, the thickness resolution can be enhanced, and the reliability and accuracy of thickness measurement can be improved.

Another problem is that paths in two-dimensional color space may be degenerate. By increasing the dimensionality of the color space, the possibility of degeneracy can be reduced. One technique is to use a type of camera (eg, a hyperspectral camera) that produces images with four or more (eg, six to twenty) color channels. Another technique is to use multiple cameras, but at different angles of incidence (due to the different lengths of the light paths passing through the film layers at different angles of incidence, different impacts and therefore different colors will be produced).

Referring to Figure 1, abrasive apparatus 100 includes an inline (also referred to as in-series) optical metrology system 160, such as a color imaging system.

The grinding apparatus 100 includes one or more carrier heads 126 (each configured to carry a substrate 10 ), one or more grinding stations 106 , and a transfer station for loading substrates into the carrier heads and The self-carrying head unloads the substrate. Each polishing station 106 includes a polishing pad 130 supported on a platform 120 . The polishing pad 130 may be a two-layer polishing pad having an outer polishing layer and a softer backing layer.

The carrier head 126 may depend from the support 128 and may be moved between grinding stations. In some implementations, the support 128 is an overhead rail, and the carrying head 126 is coupled to a bracket 108 that is mounted to the rail. Overhead rails 128 allow each carriage 108 to be selectively positioned above the grinding station 124 and the transfer station. Alternatively, in some implementations, the support 128 is a rotatable turntable, and the rotation of the turntable causes the carrying head 126 to simultaneously move along a circular path.

Each grinding station 106 of grinding apparatus 100 may include a port (eg, at the end of arm 134 ) to dispense grinding liquid 136 (such as an abrasive slurry) onto grinding pad 130 . Each polishing station 106 of the polishing apparatus 100 may also include a pad conditioning device to scrape the polishing pad 130 to maintain the polishing pad 130 in a consistent abrasive state.

Each carrier head 126 is operable to hold the substrate 10 against the polishing pad 130 . Each carrier head 126 may have independent control of grinding parameters (eg, pressure) associated with each respective substrate. Specifically, each carrier head 126 may include a securing ring 142 to secure the substrate 10 beneath the flexible membrane 144 . Each carrier head 126 also includes a plurality of independently controllable pressurizable chambers (eg, three chambers 146a to 146c) defined by a membrane that can apply independently controllable pressure to the The associated areas on the flexible membrane 144 are thus applied to the substrate 10 . Although only three chambers are illustrated in Figure 1 for ease of illustration, there may be one or two chambers, or four or more chambers, for example, five chambers.

Each carrier head 126 is suspended from the support member 128 and is connected to a carrier head rotation motor 156 via a drive shaft 154 so that the carrier head can rotate about an axis 127 . Optionally, each carrier head 140 may be laterally oscillated, for example, by drive carriage 108 on track 128, or by rotatable oscillation of the turntable itself. In operation, the platform rotates about its central axis 121 and each carrier head rotates about its central axis 127 and translates laterally on the top surface of the polishing pad. The lateral sweep is in a direction parallel to the grinding surface 212. Lateral sweeps can be linear or arcuate movements.

A controller 190 (such as a programmable computer) is connected to each motor to independently control the rotation rate of the platform 120 and the carrier head 126. For example, each motor may include an encoder that measures the angular position or rate of rotation of the associated drive shaft. Similarly, a controller 190 is connected to the actuator and/or rotation motor of the turntable in each carriage 108 to independently control the lateral movement of each carrier head 126 . For example, each actuator may include a linear encoder that measures the position of carriage 108 along track 128 .

The controller 190 may include a central processing unit (CPU), memory, and support circuitry, such as input/output circuitry, power supplies, clock circuitry, cache memory, and the like. Memory is connected to the CPU. Memory is a non-transitory computer-readable medium, and can be one or more easily accessible memories, such as random access memory (RAM), read only memory (ROM) ), floppy disk, hard disk, or other form of digital storage. Additionally, although illustrated as a single computer, controller 190 may be a distributed system, for example, including multiple independently operating processors and memories.

Inline optical metrology system 160 is positioned within grinding apparatus 100 but does not perform measurements during grinding operations; rather, measurements are made between grinding operations (e.g., while the substrate is moving from one grinding station to another or from a transfer Station moves to another teleport station) collected at the same time.

Inline optical metrology system 160 includes sensor assembly 161 supported at a location between two of grinding stations 106 (eg, between two platforms 120). Specifically, the sensor assembly 161 is located in a position such that the carrier head 126 supported by the support member 128 can position the substrate 10 above the sensor assembly 161 .

In implementations in which the grinding apparatus 100 includes three grinding stations and the substrates are sequentially carried from a first grinding station to a second grinding station to a third grinding station, one or more sensor assemblies 161 may be positioned at between the transfer station and the first grinding station, between the first and second grinding stations, between the second and third grinding stations, and/or between the third grinding station and the transfer station.

Sensor assembly 161 may include a light source 162, a light detector 164, and circuitry 166 for sending and receiving signals between the controller 190 and the light source 162 and light detector 164.

Light source 162 is operable to emit white light. In one implementation, the emitted white light includes light having a wavelength of 200 to 800 nanometers. A suitable light source is an array of white-light emitting diodes (LEDs), or a xenon lamp or a xenon mercury lamp. Light source 162 is oriented to direct light 168 onto the exposed surface of substrate 10 at a non-zero angle of incidence α. The angle of incidence α may be, for example, about 30° to 75°, for example, 50°.

The light source may illuminate a generally rectilinear elongated area across the width of the substrate 10 . Light source 162 may include optical elements (eg, a beam expander) to spread light from the light source into an elongated area. Alternatively or additionally, light source 162 may include a linear array of light sources. The light source 162 itself, and the illuminated area on the substrate, may be elongated, with a longitudinal axis parallel to the substrate surface.

Light 168 from light source 162 may be partially collimated.

Diffuser 170 may be placed in the path of light 168 , or light source 162 may include a diffuser to diffuse the light before it reaches substrate 10 .

Detector 164 may be a color camera sensitive to light from light source 162 . Detector 164 includes an array of detection elements 178 for each color channel. For example, detector 164 may include a CCD array for each color channel. In some implementations, the array is a single column of detector elements 178 . For example, the camera may be a line scan camera. The array of detector elements may extend parallel to the longitudinal axis of the elongated area illuminated by light source 162 or perpendicular to the direction of motion of the illuminated area on the substrate (FIG. 1A schematically illustrates elements 178, but these elements 178 Can be arranged in a row extending beyond the plane of the drawing). In some implementations, the detector is a camera-based color camera. The detector 164 internally splits the beam 168 into three separate beams, each of which is sent to a separate array of detector elements.

Where the light source 162 includes an array of light emitting elements, the array of detector elements may extend along a first axis parallel to the longitudinal axis of the light source 162 . The array of detector elements may include 1024 or more elements.

Determining the parallel or vertical positioning of the rows of detector elements should take into account reflections of the beam, for example, by folding mirrors or self-reflections.

Detector 164 is configured with suitable focusing optics 172 to project the substrate's field of view onto an array of detector elements 178 . The field of view may be long enough to view the entire width of the substrate 10, for example, 150 mm to 300 mm long. Sensor assembly 161 (including detector 164 and associated optical element 172) may be configured such that individual pixels correspond to regions having a length equal to or less than about 0.5 mm. For example, assuming the field of view is approximately 200 mm long and detector 164 includes 1024 elements, the image produced by the line scan camera may have pixels with a length of approximately 0.5 mm. To determine the length resolution of an image, the length of the field of view (FOV) can be divided by the number of pixels onto which the FOV is imaged to obtain the length resolution.

Detector 164 may also be configured such that the pixel width is comparable to the pixel length. For example, the advantage of line scan cameras is their very fast frame rate. The frame rate can be at least 5 kHz. The frame rate can be set to a certain frequency such that when the imaging area is scanned on the substrate 10, the pixel width is equivalent to the pixel length, for example, equal to or less than about 0.3 mm. For example, the pixel width and length may be approximately 0.1 mm to 0.2 mm.

Light source 162 and light detector 164 may be supported on stage 180 . In the case where the light detector 164 is a line scan camera, the light source 162 and the camera 164 can be moved relative to the substrate 10 so that the imaging area can be scanned across the entire length of the substrate. In particular, the relative motion may be in a direction parallel to the surface of the substrate 10 and perpendicular to the array of detector elements of the line scan camera 164 .

In some implementations, the stage 180 is stationary and the carrier head 126 is moved, for example, by movement of the carriage 108 or by rotational oscillations of the turntable. In some implementations, the stage 180 is moveable while the carrier head 126 remains stationary for image acquisition. For example, stage 180 may be moved along track 184 by linear actuator 182 . In either case, this allows the light source 162 and camera 164 to remain in fixed positions relative to each other as the scanned area moves across the substrate 10 .

Additionally, the substrate may be held and moved by the robot through the fixed optical assembly 161 . For example, in the case of a cassette interface unit or other elemental interface unit, the substrates may be held by a robot that is used to transfer the substrates to and from the cassette (rather than being supported on a separate table). The light detector can be a fixed component (eg, a line scan camera) in the cassette interface unit, and the robot can move the substrate past the light detector to scan the substrate to produce an image.

A possible advantage of having a line scan camera and light source moving together on the substrate is that (eg, as compared to conventional 2D cameras) the relative angle between the light source and the camera remains constant for different positions on the wafer . Therefore, artifacts caused by changes in viewing angle can be reduced or eliminated. In addition, line scan cameras can eliminate perspective distortion, while conventional 2D cameras exhibit inherent perspective distortion, which requires image transformation to correct the perspective distortion.

The sensor assembly 161 may include a mechanism for adjusting the vertical distance between the substrate 10 and the light source 162 and the detector 164 . For example, the sensor assembly 161 may be an actuator for adjusting the vertical position of the table 180 .

Optionally, polarizing filter 174 may be positioned in the path of the light, for example, between substrate 10 and detector 164 . The polarizing filter 174 may be a circular polarizer (CPL). A typical CPL is a combination of linear polarizer and quarter wave plate. Proper orientation of the polarizing axis of polarizing filter 174 can reduce haze in the image and sharpen or enhance desired visual features.

One or more baffles 188 may be placed near the detector 164 to prevent stray or ambient light from reaching the detector 164 (see Figure 1C). For example, the baffle may extend generally parallel to the beam 168 and around the area where the beam enters the detector 164 . Additionally, detector 164 may have a narrow allowable angle, for example, 1° to 10°. These mechanisms can improve image quality by reducing the impact of stray light or ambient light.

Assuming that the outermost layer on the substrate is a translucent layer (eg, a dielectric layer), the color of the light detected at detector 164 depends, for example, on the composition of the substrate surface, the smoothness of the substrate surface, and/or The amount of interference between light reflected from different interfaces of one or more layers (eg, dielectric layers) on a substrate.

As described above, light source 162 and light detector 164 can be connected to a computing device (eg, controller 190 ) that is operable to control the operation of light source 162 and light detector 164 and receive light source 162 and light detection. The signal of device 164.

The inline optical metrology system 160 is positioned within the grinding apparatus 100 but does not perform measurements during grinding operations; rather, measurements are made between grinding operations (e.g., while the substrate is moving from one grinding station to another or from a transfer Station is moved to another transfer station) collected at the same time.

The inline optical metrology system 160 includes a sensor assembly 161 supported at a location between one of the grinding stations 106 (eg, between the two platforms 120). Specifically, the sensor assembly 161 is located in a position such that the carrier head 126 supported by the support member 128 can position the substrate 10 above the sensor assembly 161 .

Referring to Figure 1B, the grinding apparatus 100' includes an in-situ optical monitoring system 160', such as a color imaging system. The in-situ optical monitoring system 160' is similar in structure to the in-line optical metrology system 160, but the various optical components of the sensor assembly 161 (eg, light source 162, light detector 164, diffuser 170, focusing optical element 172 and Polarizing filter 174) may be positioned in groove 122 in platform 120. When the substrate contacts and is polished by the polishing pad 130 , the light beam 168 can pass through the window 132 to illuminate the surface of the substrate 10 . Rotation of the platform 120 causes the sensor assembly 161 (and thus the light beam 168 ) to sweep across the substrate 10 . When the sensor assembly 161 sweeps under the substrate 10, a 2D image can be reconstructed from the sequence of line images. Stage 180 is not required since movement of sensor assembly 161 is provided by rotation of platform 120 .

Referring to Figure 2, the controller assembles individual image lines from light detectors 164 (whether an inline metrology system or an in-situ monitoring system) into a two-dimensional color image (step 200). As a color camera, light detector 164 may include separate detector elements for each of red, blue, and green. The two-dimensional color images may include monochrome images 204, 206, 208 for red, blue, and green color channels respectively.

The controller may apply offset and/or gain adjustments to the intensity values of the image in each color channel (step 210). Each color channel can have a different offset and/or gain.

To set the gain, a reference substrate (eg, a bare silicon wafer) may be imaged through measurements performed by the system 160, 160'. The gain for each color channel can then be set so that the reference substrate appears gray in the image. For example, the gain can be set so that the red, green, and blue channels all give the same 8-bit value, for example, RGB=(121,121,121) or RGB=(87,87,87). Gain calibration can be performed on multiple systems using the same reference substrate.

Optionally, the images may be normalized (step 220). For example, the difference between a measured image and a standard predefined image can be calculated. For example, the controller may store a background image for each of the red, green, and blue color channels and may subtract the background image from the measured image for each color channel. Alternatively, the measured image can be divided by the standard predefined image.

The image may be filtered to remove low-frequency spatial variations (step 230). In some implementations, the image is transformed from a red green blue (RGB) color space to a hue saturation luminance (HSL) color space, a filter is applied in the HSL color space, and then the image is Convert back to red, green, and blue (RGB) color space. For example, in the HSL color space, the luminance channel can be filtered to remove low-frequency spatial variations, that is, the hue and saturation channels are not filtered. In some implementations, the luminance channel is used to generate filters that are then applied to red, green, and blue images.

In some implementations, smoothing is performed only along the first axis. For example, the brightness values of pixels along the direction of travel 186 may be averaged together to provide an average brightness value that is a function only of position along the first axis. Each column of image pixels can then be divided by a corresponding portion of the average brightness value as a function of position along the first axis.

Color correction may be performed to increase color contrast in the image (step 235). Although illustrated after filtering at step 230 , color correction may be performed before filtering, but after normalization at step 220 . Additionally, color correction may be performed later, for example, before thickness calculation (in step 270).

Color correction can be performed by multiplying the values in the color space by the color correction matrix. This can be expressed as the operation I _CORR = I _ORIG X CCM, where I _ORIG is the original uncorrected image, CCM is the color correction matrix, and I _CORR is the corrected image.

More formally, color correction can be performed as matrix multiplication expressed as follows: (Equation 1) where I _O1 , I _O2 and I _O3 are the original values of the three color channels from the color space (for example, HSL color space, RGB color space, etc.), a11 ... a33 are the color correction matrices values, and I _C1 , I _C2 and I _C3 are the corrected values of the three color channels in the color space. A gamma function can be used instead of a color correction matrix with constant values.

As shown in Figures 9A and 9B, applying color correction results in an increase in the scale of the histogram. This may make the decision of layer thickness easier, since distinguishing different points in the histogram becomes easier due to the larger separation. Therefore, thickness resolution can be enhanced.

A color correction matrix can be generated by making color images of a reference substrate with a variety of preselected colors. The value of each color channel is measured, and then the optimal matrix for transforming a low-contrast image into a higher-contrast image is calculated.

The controller may analyze the images using image processing techniques to locate wafer orientation features 16 (eg, wafer notches or wafers) on substrate 10 (see FIG. 4 ) (step 240 ). Image processing techniques can also be used to locate the center 18 of the substrate 10 (see Figure 4).

Based on this data, the image is transformed (eg, scaled and/or rotated and/or translated) into a standard image coordinate system (step 250). For example, the image can be translated so that the wafer center bit is at the center point of the image, and/or the image can be scaled so that the edge of the substrate is at the edge of the image, and/or the image can be rotated so that the x-axis of the image is There is an angle of 0° from the radial segment connecting the center of the wafer to the wafer orientation feature.

Optionally, an image mask may be applied to filter out portions of the image data (step 260). For example, referring to FIG. 3 , a typical substrate 10 includes a plurality of dies 12 . Score lines 14 separate the dies 12 . For some applications it may be useful to process only the image data corresponding to the die. In this case, referring to Figure 4, an image mask may be stored by the controller having an unmasked area 22 spatially corresponding to the die 12 and a masked area 24 corresponding to the scribe line 14 . The image data corresponding to the masked area 24 is not processed or used during the thresholding step. Alternatively, the masked area 24 may correspond to the die such that the unmasked area corresponds to the scribe line, or the unmasked area may be only a portion of each die with the remaining portion of each die masked, or The unmasked area may be a specific die(s) and the remaining die and scribe lines may be masked. The unmasked area may be only a portion of the specific die(s) and the remaining portion of each die on the substrate masked. In some implementations, the user may define the mask using a graphical user interface on controller 190 .

The color data at this stage can be used to calculate a value representing thickness (step 270). This value may be a thickness, or an amount of material that has been removed, or a value that indicates how far the grinding process has progressed (eg, compared to a reference grinding process). This calculation can be performed for each unoccluded pixel in the image. This value can then be used in feedforward or feedback algorithms to control grinding parameters, thereby providing improved thickness uniformity. For example, the value of each pixel can be compared with a target value to generate an error signal image, and this error signal image can be used for feedforward or feedback control.

Some background will be discussed to help understand the calculation of value representations. For any given pixel from the color image, a pair of values corresponding to one of the two color channels can be extracted from the color data of the given pixel. Thus, each pair of values defines a coordinate in the coordinate space of a first color channel and a different second color channel. Possible color channels include hue, saturation, lightness, X, Y, Z (for example, from the CIE 1931 XYZ color space), red chroma, green chroma, and blue chroma. According to known algorithms, these values for these color channels can be calculated from tuples of values from other channels (eg, X, Y, and Z can be calculated from R, G, and B).

Referring to Figure 5, for example, when grinding begins, pairs of values (eg, V1 ₀ , V2 ₀ ) define initial coordinates 502 in coordinate space 500 for both color channels. However, because the spectrum of the reflected light changes as grinding proceeds, the color composition of the light changes, and the values in the two color channels (V1, V2) will change. Therefore, as grinding proceeds, the coordinate positions within the coordinate space of the two color channels will change, thereby drawing path 504 in coordinate space 500 .

Referring to Figures 6 and 7, in order to calculate a value representing the thickness, a predetermined path 604 in the coordinate space 500 for the two color channels is stored (eg, in the memory of the controller 190) (step 710). The predetermined path is generated before the measurement of the substrate. Path 404 may travel from start coordinate 402 to end coordinate 406 . Path 404 may represent the entire grinding process, with a start coordinate 402 corresponding to the starting thickness of a layer on the substrate and an end coordinate corresponding to the final thickness of the layer. Alternatively, the path may represent only a portion of the grinding process, for example, the expected distribution of layer thickness on the substrate at the grinding end point.

In some implementations, to create the predetermined path 404, the provided substrate is ground to approximately a target thickness that will be used for the device substrate. An optical metrology system 160 or an optical monitoring system 160' is used to obtain a color image of the arranged substrate. Because the polishing rate on the substrate is usually not uniform, different locations on the substrate will have different thicknesses, and thus reflect different colors, and thus have different coordinates in the coordinate space of the first color channel and the second color.

Referring to Figure 8, a two-dimensional (2D) histogram is calculated using the pixels contained in the unoccluded area. That is, using the color corrected color image, a scatter plot 800 is generated in the coordinate space of the first color channel and the second color channel using coordinate values of some or all pixels from the unoccluded portion of the configured substrate. Each point 802 in the scatter plot is a value pair (V1, V2) for two color channels of a specific pixel. Scatter plot 800 may be displayed on the display of controller 190 or another computer.

As mentioned above, possible color channels include hue, saturation, lightness, X, Y, Z (for example, from the CIE 1931 XYZ color space), red chroma, green chroma, and blue chroma. In some implementations, the first color channel is the red chroma (r) and the second color channel is the green chroma (g), which can be respectively represented by r= and Definition, where R, G and B are the intensity values of the red, green and blue color channels of the color image.

Thickness path 604 may be generated manually by a user (eg, a semiconductor manufacturing facility operator) using a graphical user interface in conjunction with a computer (eg, controller 190 ). For example, while a scatter plot is displayed, the user can manually construct a path that follows and overlays the scatter plot, for example, by using mouse operations to click on selected points displayed in the scatter plot.

Alternatively, the thickness path 604 can be automatically generated using software designed to analyze coordinate sets in the scatter plot and combine them (eg, using topological skeletonization) to generate a path that fits the points in the scatter plot 800 .

Thickness path 604 may be provided through a variety of functions, such as using a single line, a polyline, one or more arcs, one or more Bezier curves, and the like. In some implementations, thickness path 604 is provided by a polyline, which is a collection of line segments drawn between discrete points in coordinate space.

Returning to Figure 6, the function provides a relationship between a position on a predetermined thickness path 604 and a thickness value. For example, the controller 190 may store a first thickness value for the starting point 602 of the predetermined thickness path 604 and a second thickness value for the end point 606 of the predetermined thickness path 604 .

The first and second thickness values may be obtained by measuring the thickness of the substrate layer using a conventional thickness measurement system at locations corresponding to pixels providing points 802 closest to the start point 602 and the end point 606, respectively.

In operation, the controller 190 may calculate a value representing the thickness of a given point 610 on the path 604 by interpolating between first and second values based on the distance along the path 604 from the starting point 602 to the given point 610 . For example, if the controller can calculate the thickness T of a given point 610 according to the following equation: , where T1 is the value of the starting point 602, T2 is the thickness of the end point 606, L is the total distance along the path between the starting point 602 and the end point 606, and D is the distance between the starting point 602 and the given point 610 along the path.

As another example, the controller 190 may store the thickness value for each vertex on the predetermined thickness path 604 and calculate a value representing the thickness at a given point on the path based on interpolation between the two nearest vertices. For this configuration, various values for the vertex may be obtained by measuring the thickness of the substrate layer using a conventional thickness measurement system at the location corresponding to the pixel providing the point 802 closest to the vertex.

Other functions relating position on the path to thickness are possible.

In addition, the thickness value can be obtained by performing calculations based on an optical model instead of using a metrology system to measure the thickness of the set substrate.

If we use theoretical simulations or empirical learning based on a known "set up" wafer, the thickness values can be actual thickness values. Alternatively, the thickness value at a given point along the predetermined thickness path may be, for example, a relative value relative to the degree of grinding of the substrate. This latter value can then be scaled in downstream processes to obtain an empirical value, or can simply be used to represent an increase or decrease in thickness without specifying an absolute thickness value.

Referring to Figures 6 and 7, for a pixel analyzed from the image of the substrate, the values of two color channels are extracted from the color data of that pixel (step 720). This provides coordinates 620 in coordinate system 600 for both color channels.

Next, the point (eg, point 610) closest to the coordinate 620 of the pixel on the predetermined thickness path 604 is calculated (step 730). In this context, "closest" does not necessarily indicate geometric perfection. The "closest" point can be defined in various ways, and limitations in processing power, the choice of the search function for ease of calculation, the presence of multiple local maxima in the search function, etc. can prevent a geometrically ideal determination, but still provide sufficient the result. In some implementations, the closest point is defined as the point on the thickness path 604 that defines the normal vector to the thickness path through the coordinates 620 of the pixel. In some implementations, the closest point is calculated by minimizing the Euclidean distance.

Next, a value representing the thickness is calculated from the function based on the position of point 610 on path 604, as described above (step 740). The closest point is not necessarily one of the vertices of the polyline. As mentioned above, in this case interpolation is used to obtain the thickness value (for example, based on simple straight-line interpolation between the nearest vertices of the polyline).

By repeating steps 720-740 for some or all pixels in the color image, a thickness map of the substrate layer can be generated.

For some layer stacks on a substrate, predetermined thickness paths will cross themselves, leading to a condition called degeneracy. A degenerate point on a predetermined thickness path (eg, point 650) has two or more thickness values associated therewith. Therefore, it may not be possible to know which thickness value is correct without some additional information. However, it is possible to analyze the properties of the coordinate clusters associated with pixels from a given physical region on the substrate (eg, within a given die) and use this additional information to resolve degeneracy. For example, it can be assumed that measurements within a given small area of the substrate will not vary significantly and will therefore occupy a smaller portion along the scatter plot, that is, not extend along both branches.

In this manner, the controller may analyze clusters of coordinates associated with pixels from a given physical region on the substrate surrounding the pixel for which degeneracy needs to be resolved. Specifically, the controller determines the principal axis of the cluster in coordinate space. The branch of the predetermined thickness path that is most closely parallel to the principal axis of the cluster can be selected and used to calculate a value representing the thickness.

Returning to Figure 2, uniformity analysis (step 280) may be performed on each area of the substrate (eg, each die) or on the entire image, as appropriate. For example, the value of each pixel can be compared to a target value, and the total number of "failed" pixels within the die (ie, that do not meet the target value) can be calculated for the die. This total can be compared to a threshold to determine whether the die is acceptable, for example, if the total is less than the threshold, the die is marked as acceptable. This gives a pass/fail indication for each die.

As another example, the total number of "failed" pixels within the unmasked area of the substrate can be counted. This total can be compared to a threshold to determine whether the substrate is acceptable, for example, if the total is less than the threshold, the substrate is marked as acceptable. The threshold can be set by the user. This gives a pass/fail indication of the substrate.

In the event that a die or wafer is determined to be "failed," the controller 190 may generate an alarm or cause the polishing system 100 to take corrective action. For example, an audible or visual alarm may be generated, or a data file may be generated indicating that a specific die is unavailable. As another example, the substrate can be returned for rework.

In contrast to spectral processing, where pixels are typically represented by 1024 or more intensity values, in color images pixels can be represented by only three intensity values (red, green, and blue) and only two color channels are required to perform calculate. Therefore, the computational load of processing color images is significantly reduced.

However, in some implementations, light detector 164 is a spectrometer rather than a color camera. For example, the light detector may include a hyperspectral camera. This spectral camera can generate 30 to 200 (eg, 100) intensity values at different wavelengths for each pixel. Next, instead of pairs of values in a two-dimensional color space as described above, the technique (steps 210 to 270) is applied to images with an N-dimensional color space with N color channels, where N is significantly greater than 2, For example, 10 to 1000 dimensions. For example, thickness path 604 may be a path in an N-dimensional color space.

In some implementations, the dimensions of the color space and the number of color channels are not reduced in subsequent steps; each dimension corresponds to a wavelength at which intensity values are measured by a hyperspectral camera. In some implementations, the number of dimensions and channels of the color space is reduced, for example, by a factor of 10 to 100, eg, to 10 to 100 dimensions and channels. The number of channels can be reduced by selecting only certain channels (eg, certain wavelengths) or by combining channels (eg, combining (such as averaging) intensity values measured for multiple wavelengths). In general, a larger number of channels reduces the likelihood of degeneracy in the path, but at the cost of greater computer processing. The appropriate number of channels can be determined empirically.

Another technique used to increase the dimensionality of a color image is to use multiple light beams with different angles of incidence. This embodiment may be configured similarly to Figures 1A and 1B except as described below. Referring to Figure 1C, the sensor assembly 161 (of the in-line metrology system 160 or the in-situ monitoring system 160') may include multiple light sources, for example, two light sources 162a, 162b. Each light source produces a light beam (eg, light beams 168a and 168b) that is directed to substrate 10 at different angles of incidence. The incident angles of light beams 168a and 168b may be at least 5° apart, such as at least 10° apart, such as at least 20° apart. As shown in FIG. 1C , the light beams 168 a and 168 b may illuminate the same area on the substrate 10 , for example, overlap on the substrate 10 . Alternatively, the beams may illuminate different areas, for example, areas that partially but not completely overlap, or areas that do not overlap.

The light beams 168a, 168b are reflected from the substrate 10, and the intensity values of multiple colors are measured at multiple pixels by two different arrays of detector elements 178a, 178b respectively. As shown in Figure 1C, detector elements 178a, 178b may be provided by different photodetectors 164a, 164b. For example, the two detectors 164a and 164b may each be a color line scan camera. However, in some implementations, there is a single light detector with a two-dimensional array, and beams 168a, 168b illuminate different areas of the array of detectors. For example, the detector may be a 2D color camera.

Using two beams with different angles of incidence effectively doubles the dimensionality of the color image. For example, using two light beams 168a, 168b (where each photodetector 164a, 164b is a color camera), for a total of six color channels, each detector will be detected by three color channels (e.g. , respectively red, blue and green color channels) output color image. This provides a larger number of channels and reduces the possibility of degeneracy in the path, but still has a manageable processing cost.

Although Figure 1C illustrates each beam 168a, 168b as having its own optical components (eg, diffuser 170, focusing optic 172, and polarizer 174), it is possible for the beams to share some components. For example, a single diffuser 170 and/or a single polarizer 174 may be placed in the path of the two light beams 168a, 168b. Similarly, although multiple light sources 162a, 162b are shown, light from a single light source may be split into multiple beams (eg, by partially reflecting mirrors).

Color correction can be scaled by the number of channels available. For the color correction step, instead of I _ORIG being a 1x3 matrix and CCM being a 3x3 matrix, I _ORIG can be a 1xN matrix and CCM can be an NxN matrix. For example, for an embodiment where two beams are incident at different angles and measured by two color cameras, the _IORIG can be a 1x6 matrix and the CCM can be a 6x6 matrix.

In general, information, such as calculated thicknesses of layers on a substrate, may be used to control one or more operating parameters of a CMP device. Operating parameters include, for example, platform rotation speed, substrate rotation speed, substrate grinding path, substrate speed on the plate, pressure exerted on the substrate, slurry composition, slurry flow rate, and substrate surface temperature. Operating parameters can be controlled in real time and automatically adjusted without further manual intervention.

As used in this specification, the term substrate may include, for example, production substrates (eg, including multiple memory or processor dies), test substrates, bare substrates, and gated substrates. The substrate may be at various stages of integrated circuit fabrication, for example, the substrate may be a bare wafer, or it may include one or more deposited and/or patterned layers. The term substrate may include discs and rectangular sheets.

However, the color image processing techniques described above may be particularly useful in the case of 3D vertical NAND (VNAND) flash memory. Specifically, the layer stacks used in VNAND fabrication are so complex that current metrology methods (e.g., Nova spectroscopy) may not perform with sufficient reliability when detecting areas of inappropriate thickness. In contrast, color image processing technology allows for superior throughput.

The embodiments of the present invention and all functional operations described in this specification can be implemented in a digital electronic circuit system, or in computer software, firmware or hardware (including the structural components and their structures disclosed in this specification, etc. effect), or in a combination thereof. Embodiments of the invention may be implemented as one or more computer program products, that is, one or more computer programs tangibly embodied in a non-transitory machine-readable storage medium for use by a data processing device (e.g., a programmable processor, computer, or multiple processors or computers) that performs or is used to control the operation of the data processing equipment.

The term relative positioning is used to refer to the positioning of the components of the system relative to each other, and not necessarily with respect to gravity; it is understood that the abrasive surface and substrate may be held in a vertical orientation or some other orientation.

Many implementations have been described. However, it will be understood that various modifications may be made. For example:

． A camera that images the entire substrate can be used instead of a line scan camera. In this case, no movement of the camera relative to the substrate is required.

． The camera can cover less than the entire width of the substrate. In this case, the camera needs to move in two vertical directions (eg, supported on an X-Y stage) in order to scan the entire substrate.

． The light source illuminates the entire substrate. In this case, the light source does not need to move relative to the substrate.

． Although the above discusses coordinates represented by pairs of values in a two-dimensional coordinate space, the technique is applicable to coordinate spaces with three or more dimensions defined by three or more color channels.

·The sensor assembly does not require an inline system positioned between grinding stations or between grinding stations and transfer stations. For example, the sensor assembly may be located within a transfer station, within a cassette interface unit, or as a stand-alone system. ·The homogeneity analysis step is optional. For example, images generated by applying a threshold transformation can be fed into a feedforward process to adjust a subsequent processing step on a substrate, or into a feedback process to adjust a processing step on a subsequent substrate. ·For in-situ measurements, without constructing an image, the monitoring system can simply detect the color of the white beam reflected from the spot on the substrate and use this color data to determine the thickness at that spot using the techniques described above. Although the description focuses on grinding, these techniques can be applied to other kinds of semiconductor manufacturing processes where layers are added or removed and optically monitored, such as etching (e.g., wet or dry etching), deposition (e.g., chemical vapor etching) chemical vapor deposition (CVD), physical vapor deposition (PVD) or atomic layer deposition (ALD)), spin-on dielectric, or photoresist coating.

Therefore, other implementations are within the scope of the patent application.

10:Substrate 12:Grain 14: underline 16: Wafer orientation characteristics 18:Center 22: Uncovered area 24: Masked area 100:Grinding equipment 100':Grinding equipment 106:Grinding station 108: Bracket 120:Platform 122: Groove 126:Carrying head 127:Axis 128:Support 130: Polishing pad 132:Window 134:Arm 136:Grinding liquid 142:Fixed ring 144: Flexible membrane 146a: Chamber 146b: Chamber 146c: Chamber 154:Drive shaft 156:Carrying head rotation motor 160: Optical measurement system 160': In-situ optical monitoring system 161: Sensor assembly 162:Light source 162a:Light source 162b:Light source 164:Light detector 164a: Detector 164b:Detector 166:Circuit system 168:Light 168a:Beam 168b:Beam 170: Diffuser 172: Focusing optics 174:Polarizing filter 178:Detector component 178a: Detector component 178b: Detector component 180: Taiwan 182:Linear actuator 184:Orbit 186: Direction of travel 188:Baffle 190:Controller 200: steps 210: Step 220:Step 230:Step 235:Step 240:Step 250:Step 260: Steps 270: Steps 280: Steps 500:Coordinate space 502:Initial coordinates 504:Path 602: starting point 604: Predetermined path 606:End point 610: given point 620:Coordinates 650:point 710: Steps 720: Step 730: Steps 740:Step 800: Scatter plot 802:point

Figure 1A illustrates a schematic diagram of an example of an embedded optical measurement system.

Figure 1B illustrates a schematic diagram of an example of an in-situ optical measurement system.

Figure 1C illustrates a schematic diagram of an example of a portion of a measurement system.

Figure 2 is a flow chart of a method for determining layer thickness.

Figure 3 is a schematic top view of the substrate.

Figure 4 is a schematic diagram of the mask.

Figure 5 illustrates an example graph showing the color evolution of light reflected from a substrate in the coordinate space of two color channels.

Figure 6 illustrates an example graph showing a predetermined path in the coordinate space of two color channels.

Figure 7 is a flow chart of a method for determining layer thickness from color image data.

Figure 8 illustrates an example graph showing a histogram in coordinate space for two color channels derived from a color image of a test substrate.

Figures 9A and 9B illustrate example graphs showing histograms in coordinate space for two color channels before and after color correction, respectively.

The same reference symbols refer to the same elements in the various drawings.

Domestic storage information (please note in order of storage institution, date and number) without Overseas storage information (please note in order of storage country, institution, date, and number) without

10:Substrate

161: Sensor assembly

162a:Light source

162b:Light source

164a: Detector

164b:Detector

168a:Beam

168b:Beam

170: Diffuser

172: Focusing optics

174:Polarizing filter

178a: Detector component

178b: Detector component

184:Orbit

188:Baffle

Claims (19)

A system for obtaining a measurement representative of a thickness of a layer on a substrate includes: a support for holding a substrate for integrated circuit manufacturing; an optical assembly, the optical assembly The assembly is configured to capture a first color image of at least a portion of the substrate held by the support by illuminating the substrate with light at a first angle of incidence, and by illuminating the substrate with light at a different second angle of incidence. a substrate to capture a second color image of at least a portion of the substrate held by the support; and a controller configured to receive the first color image and the second color image from the optical assembly , storing a function that provides a value representing a thickness based on a position along a predetermined path in a coordinate space in one of at least four dimensions, the at least four dimensions including a first color image from the first color image. A color channel and a second color channel and a third color channel and a fourth color channel from the second color image, for a pixel of the first color image and a corresponding pixel in the second color image, automatically The color data for the pixel in the first color image and the color data for the corresponding pixel in the second color image determine a coordinate in the coordinate space and determine a point closest to the coordinate on the predetermined path. a position, and A value representing a thickness is calculated from the function and the location of the point on the predetermined path. The system of claim 1, wherein the coordinate space is four-dimensional. The system of claim 1, wherein the coordinate space is six-dimensional. The system of claim 1, wherein the first color channel and the second color channel are selected from the group consisting of hue, saturation, brightness, X, Y, Z, red chroma, and green chroma of the first color image. and a group of color channels of blue chroma, and the third color channel and the fourth color channel are selected from the group consisting of hue, saturation, brightness, X, Y, Z, red chroma, green color of the second color image A group of color channels for chroma and blue chroma. The system of claim 4, wherein the first color channel and the third color channel are red chroma, and the second color channel and the fourth color channel are green chroma. The system of claim 1, wherein the first angle of incidence and the second angle of incidence are both between approximately 20° and 85°. The system of claim 1, wherein the first incident angle is at least 5° greater than the second incident angle. The system of claim 1, wherein the first incident angle is at least 10° greater than the second incident angle. A computer program product for obtaining a measurement representative of a thickness of a layer on a substrate, the computer program product tangibly embodied in a non-transitory computer-readable medium, including a method for causing a processor to Instructions to perform the following: receive a first color image of the substrate and a second color image of the substrate from one or more cameras; store a function based on a coordinate space in one of at least four dimensions A value representing a thickness is provided at a position along a predetermined path, the at least four dimensions including a first color channel and a second color channel from the first color image and one from the second color image a third color channel and a fourth color channel; for a pixel in the first color image and a corresponding pixel in the second color image, color data for the pixel in the first color image and the second color The color data for the corresponding pixel in the image determines a coordinate in the coordinate space; determines a position closest to the point on the predetermined path that is closest to the coordinate; and from the function and the point on the predetermined path The position is used to calculate a value representing a thickness of a layer on the substrate. A method for obtaining a measurement representative of a thickness of a layer on a substrate, comprising the steps of: positioning a substrate for integrated circuit fabrication within the field of view of a color camera; using one or more The color camera generates a first color image of the substrate and a second color image of the substrate, the first color image is generated by illuminating the substrate with light at a first incident angle, and the second color image is Produced by irradiating the substrate with light at a different second angle of incidence generated; storing a function that provides a value representing a thickness based on a position along a predetermined path in a coordinate space in at least four dimensions, the at least four dimensions including the thickness from the first color image a first color channel and a second color channel and a third color channel and a fourth color channel from the second color image; for a pixel of the first color image and a corresponding one in the second color image For a pixel, a coordinate in the coordinate space is determined from the color data for the pixel in the first color image and the color data for the corresponding pixel in the second color image; determine the closest position to the pixel on the predetermined path. a position of a point on the coordinates; and calculating a value representing a thickness of a layer on the substrate from the function and the position of the point on the predetermined path. A grinding system includes: a grinding station, the grinding station includes a platform for supporting a grinding pad; a support member for holding a substrate; an embedded measuring station for Measuring the substrate before or after grinding a surface of the substrate in the grinding station, the embedded metrology station including one or more elongated white light sources, each having a longitudinal axis and configured to illuminate with a non-zero incidence The angle directs light to the substrate, thereby forming an illuminated area on the substrate that is swept across the substrate. a first color line scan camera extending along a first axis during scanning and having detector elements arranged to receive light reflected from the substrate striking the substrate at a first angle of incidence, and forming an image portion extending along the first axis during scanning of the substrate, a second color line scan camera having detector elements arranged to receive a second, different incident angle Illuminating the substrate with light reflected from the substrate and forming a second image portion extending along the first axis during scanning of the substrate, supporting the one or more light sources, the first color line scan camera and the a frame of a second color line scan camera, and a motor causing relative movement between the frame and the support along a second axis perpendicular to the first axis, thereby causing the one or more light sources , the first color line scan camera and the second color line scan camera scan on the substrate; and a controller configured to scan from the first color line scan camera and the second color line scan camera receiving color data, generating a first two-dimensional color image from the color data from the first color line scan camera and generating a second two-dimensional color image from the color data from the second color line scan camera, and based on The first two-dimensional color image and the second two-dimensional color image control grinding at the grinding station. The system of claim 11, including one or more diffusers in a light path between the one or more elongated white light sources and the substrate. The system of claim 11, wherein the first angle of incidence and the second angle of incidence are both between about 5° and 85°. The system of claim 13, wherein the first angle of incidence and the second angle of incidence are both between about 20° and 75°. The system of claim 11, wherein the first angle of incidence is at least 5° greater than the second angle of incidence. The system of claim 11, wherein the first angle of incidence is at least 10° greater than the second angle of incidence. The system of claim 11, wherein the first color line scan camera and the second line scan camera are configured to image an overlapping area on the substrate. The system of claim 11, wherein the one or more elongated light sources include a first elongated light source for generating the light that illuminates the substrate at the first incident angle, and for generating the light at the second incident angle. A second elongated light source illuminates the light at an angle to the substrate. The system of claim 11, wherein the frame is fixed and the motor is coupled to the support, and the controller is configured to cause the motor to move the support while the one or more The elongated light source and the first and second color line scan cameras remain stationary for scanning on the substrate.