High-sensitivity image-based reflectance measurement

Abstract

A method for performing imaging reflectance measurements includes: illuminating a measurement region on a sample with an input beam having a first peak wavelength; and obtaining multiple images of the measurement region using portions of the input beam reflected from the sample. A reflectance intensity value is determined for each pixel of multiple pixels in each of these images. The reflectance intensity values ​​are used to determine parameters associated with a specific structure.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to US 16 / 831,575, filed March 26, 2020. The disclosure of US 16 / 831,575 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 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 using a first input beam having a first peak wavelength; receiving a portion of the first input beam reflected from the sample at an imaging sensor; obtaining a plurality of first images of the measurement region using the portion of the first input beam reflected from the sample and received at the imaging sensor, each of the plurality of first images including a plurality of pixels, wherein a first corresponding pixel includes a single pixel from each of the plurality of first images and associated with approximately the same portion of the measurement region in each of the plurality of first images; determining a first reflection intensity value for each pixel of the plurality of pixels in each of the plurality of first images; determining a first representative reflection intensity value for each of the first corresponding pixels based on the first reflection intensity value of each of the first corresponding pixels; and determining a first parameter associated with a structure on the surface of the sample within the measurement region, the first corresponding pixel being associated with the structure, based at least in part on the first representative reflection intensity value of each of the first corresponding pixels in the plurality of first images. The method further includes: illuminating the measurement region on the sample using a second input beam having a second peak wavelength different from the first peak wavelength; receiving a portion of the second input beam reflected from the sample at the imaging sensor; obtaining a plurality of second images of the measurement region using the portion of the second input beam reflected from the sample and received at the imaging sensor, each of the plurality of second images comprising a plurality of pixels, wherein a second corresponding pixel comprises a single pixel from each of the plurality of second images and associated with approximately the same portion of the measurement region in each of the plurality of second images; determining a second reflection intensity value for each of the plurality of pixels in each of the plurality of second images; determining a second representative reflection intensity value for each of the second corresponding pixels based on the second reflection intensity value of each of the second corresponding pixels; and determining a second parameter associated with a structure on the surface of the sample within the measurement region, the second corresponding pixel being associated with the structure, based at least in part on the second representative reflection intensity value of each of the second corresponding pixels in the plurality of second images.

[0008] In one embodiment, the method further includes: illuminating the measurement region on the sample with one or more additional input beams, and performing the corresponding steps of: receiving portions of the one or more additional input beams; using portions of the one or more additional input beams to obtain multiple additional images of the measurement region; determining additional reflection intensity values; and determining additional parameters associated with the structure on the surface of the sample. In another embodiment, the method further includes: comparing the first parameter with the second parameter to identify the measurement sensitivity of the first peak wavelength and the second peak wavelength.

[0009] In another embodiment, the first parameter is determined using the average of the first reflection intensity values ​​of each pixel in the first corresponding pixel, and the second parameter is determined using the average of the second reflection intensity values ​​of each pixel in the second corresponding pixel.

[0010] In another embodiment, the first and second parameters associated with the structure are film thickness or a critical dimension.

[0011] In some embodiments, each of the plurality of first images and each of the plurality of second images is obtained using approximately the same exposure time. In other embodiments, each of the plurality of first images is obtained using approximately the same first exposure time, and each of the plurality of second images is obtained using approximately the same second exposure time, which is different from the first exposure time.

[0012] According to another embodiment, a method for performing an imaging reflectance measurement includes: illuminating a measurement region on a sample using a first input beam having a first peak wavelength; receiving a portion of the first input beam reflected from the sample at an imaging sensor; obtaining a plurality of first images of the measurement region using the portion of the first input beam reflected from the sample and received at the imaging sensor, each of the plurality of first images including a plurality of pixels, wherein a first corresponding pixel includes a single pixel from each of the plurality of first images and associated with approximately the same portion of the measurement region in each of the plurality of first images; determining a first reflection intensity value for each of the plurality of pixels in each of the plurality of first images; and determining a first parameter associated with a structure on the surface of the sample within the measurement region, the first corresponding pixel being associated with the structure, based at least in part on the first reflection intensity value of each of the first corresponding pixels in the plurality of first images.

[0013] In one embodiment, the first parameter is determined using the average of the first reflection intensity values ​​of each of the first corresponding pixels.

[0014] In another embodiment, the first parameter associated with the structure is the film thickness or a critical dimension.

[0015] In another embodiment, the method further includes: illuminating the measurement region on the sample using a second input beam having a second peak wavelength different from the first peak wavelength; receiving a portion of the second input beam reflected from the sample at the imaging sensor; obtaining a plurality of second images of the measurement region using the portion of the second input beam reflected from the sample and received at the imaging sensor, each of the plurality of second images comprising a plurality of pixels, wherein a second corresponding pixel comprises a single pixel from each of the plurality of second images and associated with approximately the same portion of the measurement region in each of the plurality of images; determining a second reflection intensity value for each of the plurality of pixels in each of the plurality of second images; and determining a second parameter associated with a structure on the surface of the sample within the measurement region, the second corresponding pixel being associated with the structure, based at least in part on the second reflection intensity value of each of the second corresponding pixels in the plurality of second images. Each of the plurality of first images and each of the plurality of second images may be obtained using approximately the same exposure time. Each of the plurality of first images may be obtained using approximately the same first exposure time, and each of the plurality of second images may be obtained using approximately the same second exposure time, which differs from the first exposure time. The method may further include: irradiating the measurement region on the sample with one or more additional input beams, and performing the corresponding steps of: receiving portions of the one or more additional input beams; using portions of the one or more additional input beams to obtain a plurality of additional images of the measurement region; determining additional reflection intensity values; and determining additional parameters associated with the structure on the surface of the sample.

[0016] Further aspects, advantages, and features will be apparent from the claims, description, and drawings. Attached Figure Description

[0017] 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, in which:

[0018] Figure 1 This is a simplified cross-sectional view of an imaging reflectometer.

[0019] Figure 2 This is a simplified cross-sectional view of a multi-wavelength light source.

[0020] Figure 3 This is a simplified cross-sectional view of an imaging reflectometer system configured to provide area reflectance measurements and point reflectance measurements.

[0021] Figure 4 It is a flowchart that outlines the method used to measure the reflectivity of a sample.

[0022] 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.

[0023] Figure 6 Multiple images according to an embodiment are shown, each of which includes a measurement area.

[0024] Figure 7 It is a timing diagram illustrating the synchronization between illumination and imaging according to the implementation method.

[0025] Figures 8A-8B It is a flowchart illustrating a method for performing imaging reflectance measurements according to some implementation methods.

[0026] 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

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The implementations described herein generally relate to improving the sensitivity of imaging reflectance measurements. In some implementations, reflectance signals are increased by combining reflectance measurements from pixels in multiple images associated with one or more specific structures.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] In other embodiments, source module 102 may include multiple light sources, a broadband light source, and a set of bandpass filters.

[0039] 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).

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 sample is imaged.

[0045] In one embodiment, multiple wavelength sources sequentially generate different input beams from the input beam and / or sequentially generate combinations of multiple input beams. This can be used with imaging sensors (e.g., Figure 1The imaging sensor 158 shown sequentially generates these 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 can 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 can have sufficient output power to enable high-speed measurements (or measurements at or near the readout speed of the imaging sensor).

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 1It has a low telecentricity error similar to that of imaging reflectometers.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] Figures 5A-5B The 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.

[0061] 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.

[0062] Figure 6 Multiple images 602a, 602b, ..., 602n according to embodiments are shown, each including a measurement region 604. It should be understood that some embodiments may include additional measurement regions. Each of the measurement regions generally includes structures having similar features or characteristics. Figure 6 In the example, the x-axis and y-axis represent the two-dimensional positions within images 602a, 602b, ..., 602n, while the z-axis represents time. Although not shown in this example due to the stacking arrangement of images 602a, 602b, ..., 602n, the measurement region 604 is located in the same region in each image (or the measurement region 604 includes the same x and y pixels in each image). Furthermore, the measurement region 604 in each image includes the same features on the sample.

[0063] 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 602a, 602b, ..., 602n 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 604 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 that structure using only those pixels associated with a given structure within the measurement area 604. The second average reflectance intensity value can be used to determine parameters associated with that structure (e.g., CD or film thickness).

[0064] 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.

[0065] 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).

[0066] Figure 7 This is a timing diagram illustrating the synchronization between illumination and imaging according to an embodiment. This timing diagram can be compared, for example, with... Figure 2 The multi-wavelength light source shown and such Figure 1 The imaging sensors shown are used together. In this timing diagram, the control of different illumination sources and imaging sensors is plotted as a function of time. Each illumination source (source 1, source 2, ..., source 6) provides illumination for a period of time, which is plotted by a curve that initially rises, then levels off, and finally falls. This represents the source being turned on, stabilizing, and then turned off. It should be understood that... Figure 7 Provided only as an example, and any method of making the source pass through and any number of irradiation sources can be used.

[0067] An illumination source (source 1, source 2, ..., source 6) illuminates the sample and directs the reflected portion of the illumination toward an imaging sensor, where an image is acquired. Each source can provide an input beam with a narrow wavelength range from about 0.1 nm or less to about 50 nm or greater. By way of example only, in one embodiment, source 1 can provide a peak wavelength of about 350 nm, source 2 can provide a peak wavelength of about 430 nm, source 3 can provide a peak wavelength of about 530 nm, source 4 can provide a peak wavelength of about 590 nm, source 5 can provide a peak wavelength of about 730 nm, and source 6 can provide a peak wavelength of about 940 nm.

[0068] Figure 7 The timing diagram shown also illustrates the control of the imaging sensor. During each period of source on-time or illumination provision (labeled as the integration time), the imaging sensor acquires multiple images. Each image is represented by a rectangle in the diagram, and in this example, the imaging sensor acquires eight images during each integration time. Each image comprises multiple pixels. Each pixel corresponds to reflected illumination from a specific portion of the measurement area.

[0069] In this example, exposure time is the length of time the sensor is exposed to illumination, and frame rate is the reciprocal of the time between the start of exposure for one image and the start of exposure for the next image (or the end of exposure for one image and the end of exposure for the next image). The timing diagram also shows a channel guard band, which is the length of time between turning off one illumination source and turning on the next illumination source.

[0070] According to some implementations, depending on the number of illumination sources or the number of illumination sources used for a specific measurement, multiple first images can be obtained using a first wavelength (e.g., source 1), multiple second images can be obtained using a second peak wavelength (e.g., source 2), and so on. A reflection intensity value can be determined for each pixel of each image, and parameters (e.g., thickness, CD, etc.) can be determined based on these reflection intensity values. Parameters obtained at each peak wavelength can be compared to identify the peak wavelength (or wavelength) that provides optimal measurement sensitivity. Settings such as exposure time, frame rate, integration time, channel guard band, illumination intensity, conduction duration, and others can also be varied and may differ for different illumination sources.

[0071] Figure 8AThis is a flowchart illustrating a method for performing an imaging reflectance measurement according to an embodiment. The method includes: illuminating a measurement region (802) on a sample using a first input beam having a first peak wavelength, and receiving a portion of the first input beam reflected from the sample at an imaging sensor (804). The measurement region may be a region smaller than the sample. The first input beam may be a broadband beam or a beam having a narrow wavelength range. The imaging sensor may include one or more digital cameras.

[0072] The method further includes: obtaining a plurality of first images of a measurement region using a portion of the first input beam reflected from the sample and received at an imaging sensor, each of the plurality of first images comprising a plurality of pixels, wherein a first corresponding pixel comprises a single pixel (806) from each of the plurality of first images and associated with approximately the same portion of the measurement region in each of the plurality of first images. These corresponding pixels may each have the same x, y pixel positions, or these corresponding pixels may comprise image information from the same portion of the sample.

[0073] A first reflection intensity value (808) is determined for each pixel in each of the plurality of first images, and a first parameter (810) is determined based at least in part on the first reflection intensity value of each first corresponding pixel in the plurality of first images that is associated with a structure on the surface of the sample within the measurement area. The parameter associated with the structure may be film thickness and / or CD value.

[0074] Can Figure 8A The method provided can be used as a standalone method to determine the first parameter, or the method can be combined with... Figure 8B The methods provided are used in combination to identify the optimal peak wavelength for illumination. Figure 8B The method includes: illuminating a measurement area on the sample (812) with a second input beam having a second peak wavelength different from the first peak wavelength, and receiving a portion of the second input beam reflected from the sample at an imaging sensor (814).

[0075] The method further includes: using a portion of the second input beam reflected from the sample and received at the imaging sensor to obtain a plurality of second images of the measurement region, each of the plurality of second images including a plurality of pixels, wherein a second corresponding pixel includes a single pixel from each of the plurality of second images and associated with approximately the same portion of the measurement region in each of the plurality of second images (816).

[0076] A second reflection intensity value (818) is determined for each pixel in each of the plurality of second images, and a second parameter (820) is determined based at least in part on the second reflection intensity value of each second corresponding pixel in the plurality of second images associated with a structure on the surface of the sample within the measurement region. The first parameter may be determined using the average of the first reflection intensity values ​​of each pixel in the first corresponding pixel, and the second parameter is determined using the average of the second reflection intensity values ​​of each pixel in the second corresponding pixel. The first parameter and the second parameter may be compared to identify the measurement sensitivity of the first peak wavelength and the second peak wavelength.

[0077] In some implementations, a first representative reflection intensity value for each of the first corresponding pixels can be determined based on a first reflection intensity value for each pixel in the first corresponding pixel. The first representative reflection intensity value can, for example, be the average of the reflection intensity values ​​of each pixel in the first corresponding pixel. A first parameter can be determined at least partially based on the first representative reflection intensity value. A second representative reflection intensity value for each of the second corresponding pixels can be determined based on a second reflection intensity value for each pixel in the second corresponding pixel. The second representative reflection intensity value can, for example, be the average of the reflection intensity values ​​of each pixel in the second corresponding pixel. A second parameter can be determined at least partially based on the second representative reflection intensity value.

[0078] Some implementations include illuminating a measurement area on a sample using one or more additional input beams, and performing the following corresponding steps: receiving the portion of the one or more additional input beams reflected from the sample at an imaging sensor; using the portion of the one or more additional input beams reflected from the sample and received at the imaging sensor to obtain multiple additional images of the measurement area; determining additional reflection intensity values; and determining additional parameters associated with structures on the surface of the sample. Each of the one or more additional input beams may have a peak wavelength different from any of the other peak wavelengths.

[0079] It should be understood that Figures 8A-8B 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, Figures 8A-8B 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.

[0080] 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: The surface of the sample is irradiated with a first input beam having a first peak wavelength; The portion of the first input beam reflected from the sample is received at the imaging sensor; A plurality of first images of the sample are obtained using the portion of the first input beam reflected from the sample and received at the imaging sensor, each of the plurality of first images comprising a plurality of pixels, wherein a first corresponding pixel comprises a single pixel from each of the plurality of first images and associated with the same portion of the sample in each of the plurality of first images; A first reflection intensity value is determined for each pixel of the plurality of pixels within the measurement area of ​​each of the plurality of first images; A single value is determined as the first representative reflection intensity of each of the first corresponding pixels in the measurement area based on the first reflection intensity value of each pixel in the measurement area. The first parameter associated with the measurement region is determined at least in part based on the first representative reflection intensity of each of the first corresponding pixels associated with the measurement region; The surface of the sample is irradiated with a second input beam having a second peak wavelength different from the first peak wavelength; The portion of the second input beam reflected from the sample is received at the imaging sensor; A plurality of second images of the sample are obtained using the portion of the second input beam reflected from the sample and received at the imaging sensor, each of the plurality of second images comprising a plurality of pixels, wherein a second corresponding pixel comprises a single pixel from each of the plurality of second images that is associated with the same portion of the sample in each of the plurality of second images; A second reflection intensity value is determined for each pixel of the plurality of pixels in the measurement area for each of the plurality of second images; A single value is determined as the second representative reflection intensity of each of the second corresponding pixels in the measurement area based on the second reflection intensity value of each pixel in the measurement area. and The second parameter associated with the measurement region is determined at least in part based on the second representative reflection intensity of each of the second corresponding pixels associated with the measurement region.

2. The method of claim 1, further comprising: The sample surface is irradiated with one or more additional input beams, and the following corresponding steps are performed: receiving portions of the one or more additional input beams; using the portions of the one or more additional input beams to obtain multiple additional images of the sample; determining additional reflection intensity values; and determining additional parameters associated with the measurement area.

3. The method of claim 1, further comprising: The first parameter is compared with the second parameter to identify the measurement sensitivity of the first peak wavelength and the second peak wavelength.

4. The method of claim 1, wherein the first parameter is determined using the average of the first representative reflection intensity of each of the first corresponding pixels in the measurement area, and the second parameter is determined using the average of the second representative reflection intensity of each of the second corresponding pixels in the measurement area.

5. The method of claim 1, wherein the first parameter and the second parameter associated with the measurement area are film thickness.

6. The method of claim 1, wherein the first parameter and the second parameter associated with the measurement area are critical scales (CD).

7. The method of claim 1, wherein each of the plurality of first images and each of the plurality of second images is obtained using the same exposure time.

8. The method of claim 1, wherein each of the plurality of first images is obtained using the same first exposure time, and each of the plurality of second images is obtained using the same second exposure time, the second exposure time being different from the first exposure time.

9. The method of claim 1, wherein each of the plurality of first images is obtained using the same first illumination intensity, and each of the plurality of second images is obtained using the same second illumination intensity, the second illumination intensity being different from the first illumination intensity.

10. A method for performing an imaging reflectance measurement, the method comprising: The surface of the sample is irradiated with a first input beam having a first peak wavelength; The portion of the first input beam reflected from the sample is received at the imaging sensor; A plurality of first images of the sample are obtained using the portion of the first input beam reflected from the sample and received at the imaging sensor, each of the plurality of first images comprising a plurality of pixels, wherein a first corresponding pixel comprises a single pixel from each of the plurality of first images associated with the same portion of the sample in each of the plurality of first images; A first reflection intensity value is determined for each pixel of the plurality of pixels within the measurement area of ​​each of the plurality of first images; A single value is determined as the first representative reflection intensity of each of the first corresponding pixels in the measurement area based on the first reflection intensity value of each pixel in the measurement area. and The first parameter associated with the measurement region is determined at least in part based on the first representative reflection intensity of each of the first corresponding pixels associated with the measurement region.

11. The method of claim 10, wherein the first parameter is determined using the average of the first representative reflection intensity of each of the first corresponding pixels in the measurement area.

12. The method of claim 10, wherein the first parameter associated with the measurement region is the film thickness.

13. The method of claim 10, wherein the first parameter associated with the measurement area is a critical scale (CD).

14. The method of claim 10, further comprising: The surface of the sample is irradiated with a second input beam having a second peak wavelength different from the first peak wavelength; The portion of the second input beam reflected from the sample is received at the imaging sensor; Multiple second images of the sample are obtained using the portion of the second input beam reflected from the sample and received at the imaging sensor, each of the multiple second images comprising multiple pixels, wherein a second corresponding pixel comprises a single pixel from each of the multiple second images and associated with the same portion of the sample in each of the multiple second images; A second reflection intensity value is determined for each pixel of the plurality of pixels in the measurement area within each of the plurality of second images; A single value is determined as the second representative reflection intensity of each of the second corresponding pixels in the measurement area based on the second reflection intensity value of each pixel in the measurement area. The second parameter associated with the measurement region is determined at least in part based on the second representative reflection intensity of each of the second corresponding pixels associated with the measurement region; as well as The first parameter is compared with the second parameter to identify the measurement sensitivity of the first peak wavelength and the second peak wavelength.

15. The method of claim 14, wherein each of the plurality of first images and each of the plurality of second images are obtained using the same exposure time.

16. The method of claim 14, wherein each of the plurality of first images is obtained using the same first exposure time, and each of the plurality of second images is obtained using the same second exposure time, the second exposure time being different from the first exposure time.

17. The method of claim 14, further comprising: The sample surface is irradiated with one or more additional input beams, and the following corresponding steps are performed: receiving portions of the one or more additional input beams; using the portions of the one or more additional input beams to obtain multiple additional images of the sample; determining additional reflection intensity values; and determining additional parameters associated with the measurement area.

18. The method of claim 14, wherein each of the plurality of first images is obtained using the same first illumination intensity, and each of the plurality of second images is obtained using the same second illumination intensity, the second illumination intensity being different from the first illumination intensity.

Images