High sensitivity image-based reflectometry

Abstract

A method for performing imaging reflectometry includes determining representative reflection intensity values using a plurality of images of a measurement region including a particular structure and / or using a plurality of pixels each associated with the particular structure within the measurement region. Parameters associated with the particular structure are determined using the representative reflection intensity values.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to US 16 / 831,643, filed March 26, 2020. The disclosure of US 16 / 831,643 is incorporated herein by reference in its entirety for all purposes. Technical Field

[0003] The embodiments described herein generally relate to imaging reflectometers, and more specifically to methods for improving the sensitivity of image-based reflectance measurements. Background Technology

[0004] Imaging reflectance measurements can be used to measure critical dimensions (CD) of small features and film thickness. Systems performing these measurements typically utilize either spot scanning or line scanning mechanisms. In spot scanning mechanisms, the spectrum at each point is recorded by a spectrometer, which generally comprises a grating or prism to distribute the spectrum onto a line sensor. In line scanning mechanisms, each row of the area sensor records an image of the scan line, and each column records the spectrum. These mechanisms provide flexibility for handling large samples or samples with large measurement fields.

[0005] There is a need for imaging reflectance measurement systems and methods with improved measurement sensitivity. Summary of the Invention

[0006] The embodiments described herein provide improved sensitivity for image-based reflectance measurements. Based on the resulting contrast, image-based reflectance measurements can be used to identify different properties or features of a sample. The ability of image-based reflectance measurements to distinguish between similar properties or features depends on the signal-to-noise ratio. Increasing the number of electrons in each pixel of an image sensor can increase the signal, but each pixel has a full-well capacity, which limits the amount of charge a pixel can retain before reaching saturation. To overcome this limitation, some embodiments described herein increase the reflectivity signal by combining measurements from pixels associated with a specific structure on the sample and / or by combining reflectance measurements from pixels associated with a specific structure in multiple images. This effectively increases the number of electrons without exceeding the full-well capacity.

[0007] For example, according to a particular embodiment, a method for performing an imaging reflectance measurement includes: illuminating a measurement region on a sample with an input beam; receiving a portion of the input beam reflected from the sample at an imaging sensor; obtaining a plurality of images of the measurement region using the portion of the input beam reflected from the sample and received at the imaging sensor, each of the plurality of images including a plurality of pixels, wherein a corresponding pixel includes a single pixel from each of the plurality of images and associated with approximately the same portion of the measurement region in each of the plurality of images; determining a reflectance intensity value for each pixel of the plurality of pixels in each of the plurality of images; determining a representative reflectance intensity value for each pixel of the corresponding pixels based on the reflectance intensity value of each pixel of the corresponding pixels; and determining, at least in part, a parameter associated with a structure on the surface of the sample within the measurement region, the corresponding pixel being associated with the structure, based on the representative reflectance intensity value of each of the corresponding pixels in the plurality of images.

[0008] In one embodiment, the representative reflectance value of each of the corresponding pixels is based on the average of the reflectance values ​​of each of the corresponding pixels.

[0009] In another embodiment, the method further includes: determining a composite image of the measurement area, wherein each pixel of the composite image is determined based on the representative reflectance value of each of the corresponding pixels.

[0010] In another embodiment, the parameter associated with the structure is film thickness or a critical dimension.

[0011] In some implementations, each of the plurality of images is obtained using approximately the same integration time length, or each of the plurality of images is obtained using a different integration time length.

[0012] In another embodiment, the portion of the input beam is reflected from the surface of the sample.

[0013] In yet another embodiment, the structure includes multiple structures.

[0014] According to another embodiment, a method for performing imaging reflectance measurement includes: illuminating a measurement region on a sample using an input beam, the measurement region including a first sub-region and a second sub-region, each first sub-region including a similar structure on the surface of the sample, and each second sub-region including a similar structure on the surface of the sample that is different from the similar structure in the first sub-region; receiving a portion of the input beam reflected from the sample at an imaging sensor; acquiring an image of the measurement region using the imaging sensor, the image including a plurality of pixels; identifying a first portion of the plurality of pixels associated with the first sub-region and a second portion of the plurality of pixels associated with the second sub-region; determining a first reflectance intensity value for each pixel of the first portion of the plurality of pixels associated with the first sub-region; determining a first representative reflectance intensity value based on the first reflectance intensity value of each pixel of the first portion of the plurality of pixels associated with the first sub-region; and determining a parameter associated with the similar structure in the first sub-region based at least in part on the first representative reflectance intensity value.

[0015] In one embodiment, at least some of the first sub-regions are not adjacent to other first sub-regions within the first sub-region of the measurement area.

[0016] In another embodiment, the similar structures in the first sub-region have similar surface patterns, and the similar structures in the second sub-region have different surface patterns.

[0017] In another embodiment, the method further includes: determining a second reflection intensity value for each pixel of the second portion of the plurality of pixels associated with the second sub-region; determining a second representative reflection intensity value based on the second reflection intensity value of each pixel in the second portion of the plurality of pixels associated with the second sub-region; and determining a parameter associated with the similar structure in the second sub-region based on the second representative reflection intensity value.

[0018] In yet another embodiment, the similar structures in the first sub-region each include a plurality of structures.

[0019] Further aspects, advantages, and features will be apparent from the claims, description, and drawings. Attached Figure Description

[0020] The various embodiments described herein (both in terms of structure and operation) and their features and advantages can be best understood by referring to the following detailed description and accompanying drawings.

[0021] In the picture:

[0022] Figure 1 This is a simplified cross-sectional view of an imaging reflectometer.

[0023] Figure 2 This is a simplified cross-sectional view of a multi-wavelength light source.

[0024] Figure 3 This is a simplified cross-sectional view of an imaging reflectometer system configured to provide area reflectance measurements and point reflectance measurements.

[0025] Figure 4 It is a flowchart that outlines the method used to measure the reflectivity of a sample.

[0026] Figure 5A These are images showing measurement areas on samples with different types of structures, according to embodiments. Figure 5B It is a graph illustrating the measurement noise from a single pixel and the measurement noise from multiple pixels, according to the implementation method.

[0027] Figure 6 Multiple images according to an embodiment are shown, each of which includes a measurement area.

[0028] Figure 7 It is an image that emphasizes similar structures within the measurement area according to the implementation method.

[0029] Figure 8-9 It is a flowchart illustrating a method for performing imaging reflectance measurements according to some implementation methods.

[0030] It will be understood that, for the sake of simplicity and clarity, the elements shown in the figures are not necessarily drawn to scale. For example, some elements may be enlarged relative to other elements for clarity. Furthermore, where appropriate, reference numerals may be repeated in the figures to indicate corresponding or similar elements. Detailed Implementation

[0031] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments described herein. However, it should be understood that various embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the features described.

[0032] Various embodiments will be described in detail, with one or more examples of these embodiments illustrated in the figures. Each example is provided by way of explanation and is not intended to be limiting. Furthermore, features illustrated or described as part of one embodiment may be used in other embodiments or in combination with other embodiments to produce further embodiments. This specification is intended to include these modifications and variations.

[0033] The term "sample" or "sample" as used herein includes, but is not limited to, semiconductor wafers, semiconductor workpieces, photolithographic masks, and other workpieces such as memory disks. Depending on some embodiments that may be combined with other embodiments described herein, the system and method are configured for or applied to reflectance measurement applications.

[0034] The embodiments described herein generally relate to improving the sensitivity of imaging reflectance measurements. In some embodiments, the reflectance signal is increased by combining measurements from pixels associated with a specific structure on the sample. This specific structure may include multiple structures on the sample, which may be adjacent to each other or may not be adjacent to each other. In other embodiments, the reflectance signal is increased by combining reflectance measurements from pixels associated with a specific structure in multiple images.

[0035] Figure 1 This is a simplified cross-sectional view of an imaging reflectometer 100 according to one embodiment. The imaging reflectometer 100 shown in this example can be used to implement the methods described herein. However, the imaging reflectometer 100 is shown only as an example, and other imaging reflectometers can perform the methods described. By way of example only, the methods can be performed using an imaging reflectometer configured to obtain an image of a portion (rather than the entire sample) and / or an imaging reflectometer using a single-wavelength or multi-wavelength light source.

[0036] exist Figure 1 In this example, light from source module 102 is transferred to homogenizer 108 via light guide 106. Light 116 from homogenizer 108 passes through illumination pupil 114 and is guided to beam splitter 120. A portion 138 of light 116 is reflected by beam splitter 120 toward reference sensor 134, while a portion 122 of light passes through beam splitter 120 and continues along the optical path toward sample 130.

[0037] A portion 122 of the light 116 passing through the beam splitter 120 is imaged onto the sample 130 by the large image field lens 126. Light reflected from the sample 130 is guided by at least a portion of the lens 126 and reflected by the beam splitter 120 toward the imaging sensor 158.

[0038] The imaging reflectometer 100 may include a plurality of other lenses (e.g., 110, 112, 118, 136) that shape and / or guide light along an optical path to illuminate sample 130, reference sensor 134, guide light to other lenses (e.g., 120, 140, 144), and guide light reflected from the sample to imaging sensor 158. For example, in some embodiments, light may pass through one or more polarizers (e.g., polarizers 110, 154). These polarizers may be inserted in the illumination path and / or imaging path to provide enhanced sensitivity to scalation changes and / or film thickness on the pattern structure of sample 130 when the pattern is not circularly symmetrical. Waveplates may also be inserted to change the phase of polarized light. The waveplates and / or polarizers may be at a fixed angle to provide polarized reflectance measurements or may be rotated to provide elliptically polarized measurements. It should be understood that the imaging reflectometer according to the embodiments described herein may not include… Figure 1 The example shows all optical elements and / or may include other optical elements not included in this example.

[0039] In this example, source module 102 provides a multi-wavelength light source capable of sequentially generating different beams, each beam having a narrow wavelength range. In some embodiments, a multi-wavelength light source is provided by multiple light sources that can be activated individually. Each of the light sources generates a beam, and at least some of the beams have different nominal wavelengths.

[0040] In other embodiments, a multi-wavelength light source is provided by adjusting the source power sent to source module 102 to generate beams with different nominal wavelengths. The power of each wavelength can be independently controlled to optimize the dynamic range of reflections measured at each wavelength.

[0041] In other embodiments, a multi-wavelength light source is provided using a broadband light source and a set of bandpass filters. The broadband light source can be used in conjunction with the bandpass filters to produce a beam of light at a selected nominal wavelength.

[0042] In other embodiments, source module 102 may include multiple light sources, a broadband light source, and a set of bandpass filters.

[0043] In one embodiment, the large image field lens 126 has a measurement field size (or illumination area) slightly larger than the size of the sample 130, allowing the entire sample image to be acquired by the imaging sensor 158 without scanning light or moving the platform 132. For example, the large image field lens 126 may have a measurement field size of 300 mm or larger for measuring semiconductor wafers with a diameter of 300 mm. The large image field lens 126 may be a telecentric lens, such that light rays traveling from the large image field lens 126 to the sample 130 are approximately parallel to the optical axis, which is substantially perpendicular to the surface of the sample 130. This provides substantially normal illumination over the entire sample 130 or across the entire measurement area. Because the illumination angle is approximately the same, this reduces measurement errors. Telecentric imaging allows light to reflect at substantially the same angle across the entire image field to reach the imaging sensor. In one embodiment, for example, the light illuminating sample 130 may have a telecentricity error of less than 0.3 degrees in the wavelength range of about 350 nm to about 1200 nm, and in some embodiments, it may have a telecentricity error of less than 1% in the wavelength range of about 350 nm to about 1100 nm. As used herein, telecentricity error is a measure of the angular deviation of light rays incident on and reflected from the wafer surface relative to the normal (or optical axis).

[0044] In some embodiments, the large-field lens 126 has a field size smaller than the diameter of the sample 130. In this case, the region (or measurement area) is imaged, and the optics and / or platform 132 can be moved and / or the optical module can be scanned to image adjacent fields. Depending on the application, the size of the measurement area can be approximately the same as the field of the die or stepper. Known techniques can be used to stitch adjacent images to provide multi-field images or full-sample images.

[0045] Imaging sensor 158 may be a region imaging sensor, comprising one or more digital cameras for capturing light 142 reflected from sample 130 and passing through imaging pupil 150. Imaging sensor 158 provides an image of sample 130 based on the received light 142. In some embodiments, imaging sensor 158 may include a single camera configured to image the entire surface of sample 130. In other embodiments, imaging sensor 158 may include multiple cameras, each imaging adjacent or slightly overlapping fields (or measurement areas) on sample 130. Adjacent images can be stitched together using known techniques. Image resolution can be increased by using a higher resolution imaging sensor or by using multiple imaging sensors, each imaging a smaller field.

[0046] The imaging reflectometer 100 includes an illumination path providing light to a sample 130 and an imaging path providing light to an imaging sensor 158. This allows for independent control of the illumination numerical aperture (NA) and the imaging NA. By way of example only, if the imaging sensor 158 has an array size of 5120 pixels by 5120 pixels and the imaging NA is approximately 0.004, then the pixel size on the sample 130 is approximately 60 μm for a 300 mm wafer, which provides approximately 55 μm Rayleigh resolution at a wavelength of 365 nm and approximately 153 μm Rayleigh resolution at a wavelength of 1 μm. Generally, the illumination NA is larger than the imaging NA to correct for residual color telecentricity errors and to provide tolerance to tilt and bending of the sample 130. In some embodiments, the illumination NA can range from approximately 0.005 to approximately 0.5, and the imaging NA can range from approximately 0.003 to approximately 0.2.

[0047] Reference sensor 134 may include one or more digital cameras for capturing light 138 reflected from beam splitter 120. Reference sensor 134 may have a lower resolution than imaging sensor 158. Reference sensor 134 can be used to monitor the uniformity and stability of light 138 and provide real-time calibration of reflection measurements performed by imaging sensor 158. Measurements at reference sensor 134 can be used to adjust the characteristics of the light source (e.g., output power) to provide spatial and temporal corrections.

[0048] Figure 2 This is a simplified cross-sectional view of a multi-wavelength light source according to one embodiment. This multi-wavelength light source can be used, for example, as... Figure 1 This is part of the source module 102 in the imaging reflectometer 100. The multi-wavelength light source includes multiple light sources 202 and multiple optical fibers 206. Each light source 202 may each include one or more light-emitting diodes (LEDs) and / or laser diodes (LDs). Each light source 202 is optically coupled to a homogenizer 208 via one of the optical fibers 206. Each of the light sources 202 generates a beam, and at least some of the beams may have different nominal wavelengths. Light from the homogenizer 208 can be directed to a large image field lens and used as... Figure 1 The ground is used to image the sample.

[0049] In one embodiment, a multi-wavelength light source sequentially generates different input beams from the input beam and / or sequentially generates a combination of multiple input beams. This can be used with an imaging sensor (e.g., Figure 1The imaging sensor 158 shown sequentially generates beams at the same frame rate switching rate to achieve an image of the same field on the sample at each wavelength. In some embodiments, the sensor's frame rate may be faster than the wavelength switching rate. A faster switching rate allows averaging of multiple images at each wavelength to achieve a higher signal-to-noise ratio. The output power of each of the light sources 202 can be independently controlled and adjusted so that the sensor signal is close to saturation at each wavelength to maximize the signal-to-noise ratio. Each of the light sources 202 may have sufficient output power to enable high-speed measurements (or measurements at or near the readout speed of the imaging sensor).

[0050] In some implementations, optical throughput can be increased by inserting a diffuser between optical fiber 206 and homogenizer 208. Multiple light sources 202 can be combined using other components such as dichroic beam splitters, and light sources 202 can be coupled to homogenizer 208 using other components such as free-space optical repeaters.

[0051] In some implementations, a bandpass filter can be inserted between each of the light sources 202 and the corresponding optical fiber 206 of these light sources to narrow the bandwidth of each wavelength. A narrower bandwidth can provide better sensitivity for measurements of thick film stacks or dense patterns on the surface of a sample. The bandpass filter can also improve measurement accuracy by accurately defining the measurement wavelength to eliminate wavelength drift of the LED.

[0052] Imaging sensors (e.g.) Figure 1 The imaging sensor 158 shown can have a high readout rate (e.g., 50 to 1000 frames per second (FPS) or greater, and up to 100 million pixels per frame or greater). As an example, at a readout rate of 100 FPS, the imaging sensor can be able to perform 6000 reflectance measurements per minute. Measurements can be performed at the same or different wavelengths. Obtaining multiple measurements at the same wavelength can enhance the signal-to-noise ratio and improve measurement sensitivity.

[0053] Figure 3 This is a simplified cross-sectional view of an imaging reflectometer system 300 according to one embodiment, configured to provide area reflectance measurement and point reflectance measurement. In this example, light from the source module 302 passes through the illumination pupil 314 and is guided toward a large image field lens 326. The large image field lens 326 may have a field size (or illumination area) that enables area reflectance measurement without scanning light or moving platform 332. The large image field lens 326 may be a telecentric lens, such that light rays traveling from the large image field lens 326 toward the sample are substantially parallel to the optical axis and have the same characteristics as described above. Figure 1 It has a low telecentricity error similar to that of imaging reflectometers.

[0054] In this example, the imaging reflectometer system 300 also includes a point reflectometer 376. The point reflectometer 376 can be a high-sensitivity reflectometer for performing point reflectance measurements. The point reflectometer 376 can be mounted on a robotic arm 372, which allows the point reflectometer 376 to be moved to any position above the sample for point measurements and / or moved outside the field of view of the large image field lens 326 during area measurements. For example, the robotic arm can be an R-θ robotic arm. Alternatively, the platform 332 can be an xy-scanning platform that positions the sample below the large image field lens 326 or the point reflectometer 376.

[0055] In some implementations, the large image field lens 326 can be used to perform full-sample or large-area image reflectance measurements. Using area measurements, specific points on the sample can be identified for further measurements, and the point reflectometer 376 can be used to perform point reflectance measurements at those specific points. The wavelength range of the point reflectometer 376 can be greater than the wavelength range of the large image field lens 326.

[0056] Figure 3 This is a simplified cross-sectional view of the imaging reflectometer system 300, and for simplicity, many parts and components are not shown. For example, this figure does not show the beam splitter, reference sensor, imaging sensor, imaging pupil, and / or several other components individually. It should be understood that the imaging reflectometer system 300 may include these and other components, for example, regarding... Figure 1 And / or those components described in other conventional reflectometer systems.

[0057] Figure 4 This is a flowchart outlining a method for measuring the reflectivity of a sample using an imaging reflectometer, which includes a large image field lens, according to an embodiment. The method includes sequentially generating multiple input beams (402) at a first switching rate. In some embodiments, each of the multiple input beams is generated by a different light source, and at least some of the multiple input beams may have a nominal wavelength different from the other input beams. In other embodiments, at least some of the multiple input beams are generated by a broadband light source, and the wavelength of each of the multiple input beams is defined using a set of bandpass filters.

[0058] Each of the multiple input beams is guided through an illumination pupil (404) having a first NA. The illumination pupil may be arranged along a first optical path. In some embodiments, each of the multiple input beams may be separated, and a first portion of each of the multiple input beams may be guided along the first optical path to a reference sensor, and a second portion of each of the multiple input beams may be allowed to continue along the first optical path.

[0059] At least a portion of each of the multichannel input beams utilizes a large image field lens to provide substantially telecentric illumination over the imaged sample (406). A portion of each of the multichannel input beams may also be provided to a reference sensor for monitoring the uniformity and stability of the input beams. In some embodiments, the measurement field of the large image field lens may be larger than the imaged sample to provide full-sample measurement.

[0060] The reflected portion of the substantially telecentric illumination from the sample is received at a large image field lens and guided through an imaging pupil with a second NA, which is smaller than the first NA (408) of the illumination pupil. A beam splitter can be used to guide the reflected portion through the imaging pupil.

[0061] At the imaging sensor module, the reflected portion is received and corresponding image information is generated, wherein the image information is generated at a frame rate that is the same as or faster than the first switching rate (410). The image information can be calibrated or normalized based on information from the reference sensor.

[0062] In some implementations, images obtained using the methods described herein can be processed to identify process deviations. The images can be processed based on known deviation identification techniques. For example, reflectance measured at multiple wavelengths can be compared to modeled reflectance or a known good sample. Patterns measured at different locations on the sample can also be compared to identify variations and / or anomalies. Measured variations can be quantified by calculating the root mean square (RMS) difference at multiple wavelengths. Measurement sensitivity can be enhanced by selecting one or more wavelengths with the highest sensitivity based on the measurement data. Multi-wavelength reflectance can be processed by nonlinear regression of a theoretical model to derive the CD of film thickness and / or pattern.

[0063] It should be understood that the imaging reflectometer described herein can be configured as a stand-alone metrology tool or integrated with other metrology or process tools. As an example, the imaging reflectometer described herein can be integrated with a process tool and positioned outside a window separating the imaging reflectometer from the process chamber. In some embodiments, a large image field lens positioned outside the window illuminates the sample positioned inside the process chamber. The large image field lens can be configured to illuminate all or part of the sample (e.g., the size of the measurement area can be approximately the same as the field of the wafer or stepper). This allows reflectance measurements to be performed during processing and / or immediately after processing, while the sample is inside the vacuum chamber. This can shorten control loops, improve process control, and avoid material damage caused by the atmospheric environment.

[0064] Figures 5A-5BThe embodiments illustrate how the signal-to-noise ratio can be increased by combining measurements from different pixels in an image. Figure 5A In the diagram, the outline of the measurement region 504 within image 502 is drawn as a square. For the purposes of this example, it is assumed that the measurement region 504 corresponds to a 200-pixel area of ​​image 502 (or imaging sensor). Points 506 within the measurement region 504 are indicated by arrows, and each point 506 corresponds to a single pixel.

[0065] In the experiment, approximately 100 images were captured, and within each image, the reflectance intensity value from point 506 was compared to the average reflectance intensity value from 40,000 pixels within a 200-pixel by 200-pixel measurement area 504. The results are shown in... Figure 5B In this study, the measured reflection intensity value 508 from a single point 506 has much more noise than the average reflection intensity value 510 from 40,000 pixels within the measurement area 504.

[0066] Figure 6 This is an image emphasizing similar structures within measurement region 604 according to one embodiment. In this image, some structures on the surface of the sample have similar features. For example, the structures within sub-regions 620a, 620b, 620c, 620d, and 620e each have similar structures. Sub-region 620a is a single, continuous region comprising numerous small structures, some of which appear to have slightly different patterns, but all of these small structures are clustered together within the same portion of measurement region 604. Sub-region 620b comprises four adjacent but separate sub-regions extending over a larger structure and appearing unpatterned, while sub-region 620e comprises three non-adjacent and appearing unpatterned regions. Sub-regions 620b and 620c also have similar structures.

[0067] The signal-to-noise ratio of reflectance intensity values ​​can be increased by combining measurements from pixels within each sub-region. For example, a representative reflectance intensity value can be determined based on the reflectance intensity values ​​of pixels within sub-region 620a. This representative reflectance intensity value can be used to determine parameters associated with similar structures in sub-region 620a. The representative reflectance intensity value can be an average, sum, or similar value, and the parameter can be CD or film thickness. The same process can be performed using the reflectance intensity values ​​of pixels within each of the other sub-regions. Similarly, parameters associated with each of the other sub-regions 620b, 620c, 620d, and 620e can be determined in a similar manner.

[0068] Figure 7Multiple images 702a, 702b, ..., 702n according to an embodiment are shown, each including a measurement region 704. In this example, the x-axis and y-axis represent two-dimensional positions within images 702a, 702b, ..., 702n, while the z-axis represents time. Although not shown in this example due to the stacking arrangement of images 702a, 702b, ..., 702n, the measurement region 704 is located in the same region in each image (or the measurement region 704 includes the same x and y pixels in each image). Furthermore, the measurement region 704 in each image includes the same features on the sample.

[0069] Such as about Figure 5B As explained, the signal-to-noise ratio (SNR) can be increased by determining the average reflectance intensity value from each of the pixels within the measurement area. Similarly, the SNR can be increased by using multiple images 702a, 702b, ..., 702n to determine a first average reflectance intensity value for each x, y pixel location. That is, the first average reflectance intensity value can be determined for each x, y pixel location in the measurement area 704 using pixels at the same x, y location in each image. Then, using the first average reflectance intensity value for each pixel, a second average reflectance intensity value can be determined for a given structure using only those pixels associated with that structure within the measurement area 704. The second average reflectance intensity value can be used to determine parameters associated with that structure (e.g., CD or film thickness).

[0070] It should be understood that while an average reflectance value was used in the previous examples, other parameters or statistical methods may be used to determine representative reflectance values. For example, a median reflectance value, the sum of reflectance values, or other parameters or statistical methods may be used in conjunction with the embodiments described herein.

[0071] Furthermore, while pixels at the same x, y position in each image can be used to determine the first average reflectance value for each x, y pixel location, in some embodiments, multiple pixels at approximately the same x, y position in each image can also be used. Multiple pixels at approximately the same x, y position include pixels in each image associated with approximately the same portion of the measurement area (i.e., pixels not located at the same x, y position but including image information from the same portion of the sample).

[0072] Figure 8This is a flowchart illustrating a method for performing an imaging reflectance measurement according to one embodiment. The method includes: illuminating a measurement region (802) on a sample with an input beam, and receiving a portion of the input beam reflected from the sample at an imaging sensor (804). The measurement region may be a region smaller than the sample. The input beam may be a broadband beam or a beam having a narrow wavelength range (e.g., from about 0.1 nm or less to about 50 nm or greater). The imaging sensor may include one or more digital cameras.

[0073] The method further includes: obtaining multiple images of the measurement region using a portion of the input beam reflected from the sample and received at an imaging sensor, each of the multiple images comprising multiple pixels, wherein a corresponding pixel comprises a single pixel from each of the multiple images and associated with approximately the same portion of the measurement region in each of the multiple images (806). Corresponding pixels may each have the same x, y pixel position, or corresponding pixels may include image information from the same portion of the sample.

[0074] The reflectance intensity value of each pixel in each of the plurality of images is determined (808), and a representative reflectance intensity value is determined for each pixel in the corresponding image based on the reflectance intensity value of each pixel in the corresponding image (810). The representative reflectance intensity value of each pixel in the corresponding image may be, for example, based on the average or sum of the reflectance intensity values ​​of each pixel in the corresponding image.

[0075] The method further includes determining parameters associated with a structure on the surface of a sample within the measurement area, based at least in part on representative reflectance intensity values ​​of corresponding pixels in a plurality of images, the corresponding pixels being associated with the structure (812). The parameters associated with the structure may include CD and / or film thickness.

[0076] Figure 9 This is a flowchart illustrating a method for performing imaging reflectance measurement according to another embodiment. The method includes illuminating a measurement region on a sample using an input beam. The measurement region includes a first sub-region and a second sub-region. Each first sub-region includes a similar structure on the surface of the sample, and each second sub-region includes a similar structure on the surface of the sample that differs from the structure in the first sub-region (902). The first and second sub-regions are regions smaller than the measurement region (or having fewer pixels than the measurement region). The first and second sub-regions may each include a single region, a single region having a similar patterned structure, multiple regions each having a similar patterned structure, or multiple regions each having a similar structure. Multiple regions may be adjacent to or separated from each other within the measurement region.

[0077] The method further includes: receiving a portion of the input beam reflected from the sample at an imaging sensor (904), and obtaining an image of the measurement area using the imaging sensor, the image comprising a plurality of pixels (906).

[0078] The method further includes: identifying a first portion of the plurality of pixels associated with a first sub-region and a second portion of the plurality of pixels associated with a second sub-region (908). Pixels associated with the first and second sub-regions can be identified based on reflectance intensity values. For example, similar reflectance intensity values ​​can be grouped within a sub-region. Alternatively, pixels associated with the first and second sub-regions can be identified based on x and y positions within the image.

[0079] A first reflection intensity value is determined for each pixel of the first portion of the plurality of pixels associated with the first sub-region (910), a first representative reflection intensity value is determined based on the first reflection intensity value of each pixel in the first portion of the plurality of pixels associated with the first sub-region (912), and a parameter associated with a similar structure in the first sub-region is determined based at least in part on the first representative reflection intensity value (914).

[0080] It should be understood that Figure 8-9 The specific steps illustrated provide a particular method for measuring reflectivity according to some embodiments. Other sequences of steps can also be performed according to alternative embodiments. For example, the steps outlined above can be performed in a different order in alternative embodiments. Furthermore, Figure 8-9 The individual steps illustrated may also include multiple sub-steps that can be performed using various sequences. Furthermore, additional steps may be added or removed depending on the specific application.

[0081] While specific embodiments have been described above, other and additional embodiments can be designed without departing from the basic scope of these embodiments. For example, features of one or more embodiments of the invention can be combined with one or more features of other embodiments without departing from the scope of the invention. Therefore, this specification and drawings should be viewed in an illustrative rather than restrictive sense. Consequently, the scope of the invention should not be determined by reference to the foregoing description, but rather by reference to the entire scope of the appended claims and their equivalents.

Claims

1. A method for performing an imaging reflectance measurement, the method comprising: Irradiate the measurement area on the sample with the input beam; The portion of the input beam reflected from the sample is received at the imaging sensor; Multiple images of the measurement region are obtained using the portion of the input beam reflected from the sample and received at the imaging sensor, each of the multiple images comprising multiple pixels, wherein a corresponding pixel comprises a single pixel from each of the multiple images and associated with the same portion of the measurement region in each of the multiple images; Determine a reflection intensity value for each pixel of the plurality of pixels in each of the plurality of images; Based on the reflection intensity value of each pixel in the corresponding pixel, a representative reflection intensity value is determined for each pixel in the corresponding pixel; and Parameters associated with a structure on the surface of the sample within the measurement area are determined, at least in part, based on the representative reflectance intensity value of each of the corresponding pixels in the plurality of images, wherein the corresponding pixel is associated with the structure.

2. The method of claim 1, wherein the representative reflection intensity value of each of the corresponding pixels is based on the average of the reflection intensity values ​​of each pixel of the corresponding pixel.

3. The method of claim 1, further comprising: A composite image of the measurement area is determined, wherein each pixel of the composite image is determined based on the representative reflectance value of each of the corresponding pixels.

4. The method of claim 1, wherein the parameter associated with the structure is film thickness.

5. The method of claim 1, wherein the parameter associated with the structure is a critical scale (CD).

6. The method of claim 1, wherein each of the plurality of images is obtained using the same integration time length.

7. The method of claim 1, wherein each of the plurality of images is obtained using a different integration time length.

8. The method of claim 1, wherein the portion of the input beam is reflected from the surface of the sample.

9. The method of claim 1, wherein the structure comprises a plurality of structures.

10. A method for performing an imaging reflectance measurement, the method comprising: The measurement area on the sample is irradiated with an input beam. The measurement area includes a first sub-region and a second sub-region. Each first sub-region includes a similar structure on the surface of the sample, and each second sub-region includes a similar structure on the surface of the sample that is different from the similar structure in the first sub-region. The portion of the input beam reflected from the sample is received at the imaging sensor; The imaging sensor is used to obtain an image of the measurement area, the image comprising multiple pixels; Identify a first portion of the plurality of pixels associated with the first sub-region and a second portion of the plurality of pixels associated with the second sub-region; A first reflection intensity value is determined for each pixel of the first portion of the plurality of pixels associated with the first sub-region; A first representative reflection intensity value is determined based on the first reflection intensity value of each pixel in the first portion of the plurality of pixels associated with the first sub-region; and The parameters associated with the similar structure in the first sub-region are determined at least in part based on the first representative reflection intensity value.

11. The method of claim 10, wherein the first representative reflection intensity value is based on the average of the first reflection intensity values ​​of each pixel in the first portion of the plurality of pixels.

12. The method of claim 10, wherein at least some of the first sub-regions are not adjacent to other first sub-regions within the measurement area.

13. The method of claim 10, wherein the parameter associated with the similar structure in the first sub-region is the film thickness.

14. The method of claim 10, wherein the parameter associated with the similar structure in the first sub-region is a critical scale (CD).

15. The method of claim 10, wherein the similar structures in the first sub-region have similar surface patterns, and the similar structures in the second sub-region have different surface patterns.

16. The method of claim 10, further comprising: A second reflection intensity value is determined for each pixel of the second portion of the plurality of pixels associated with the second sub-region; A second representative reflection intensity value is determined based on the second reflection intensity value of each pixel in the second portion of the plurality of pixels associated with the second sub-region; and The parameters associated with the similar structure in the second sub-region are determined based on the second representative reflection intensity value.

17. The method of claim 10, wherein each of the similar structures in the first sub-region comprises a plurality of structures.

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