Detection system and method with multi-wavelength light source

Abstract

The invention relates to a detection system and method with a multi-wavelength light source. A method includes positioning a substrate in an optical path of a multi-wavelength light source; generating a first detection result by exposing a first region of the substrate to first light having a first wavelength band selected by the multi-wavelength light source; and generating a second detection result by exposing a second region of the substrate to second light having a second wavelength band selected by the multi-wavelength light source. A system includes a multi-wavelength light source comprising: a light source; and a wavelength selector located in an optical path of the light generated by the light source. The system further includes a spectrometer operable to measure a spectrum of the first light selected by the wavelength selector; a mask stage operable to position the mask in the optical path; and a controller operable to adjust at least one parameter of the multi-wavelength light source in response to the spectrum of the first light.

Description

Technical Field

[0001] The present application relates to a detection system and method with a multi-wavelength light source. Background Art

[0002] The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs, each with smaller and more complex circuits than the previous generation. Over the course of IC evolution, functional density (i.e., the number of interconnected devices per unit chip area) has generally increased, while geometry size (i.e., the smallest component (or line) that can be created using a manufacturing process) has decreased. This shrinking process generally provides benefits by increasing production efficiency and reducing associated costs. This shrinking has also increased the complexity of processing and manufacturing ICs. Summary of the invention

[0003] According to one aspect of the present application, a method is provided, comprising: positioning a substrate in the light path of a multi-wavelength light source; generating a first detection result by exposing a first area of ​​the substrate to a first light, the first light having a first wavelength band, the first light being selected by the multi-wavelength light source; and generating a second detection result by exposing a second area of ​​the substrate to a second light, the second light having a second wavelength band that does not overlap with the first wavelength band, the second light being selected by the multi-wavelength light source.

[0004] In some implementations, the method further includes generating the first light and the second light by an acousto-optic modulator of the multi-wavelength light source.

[0005] In some implementations, the method further includes: further including: selecting the first light by a wavelength selector.

[0006] In some implementations, selecting includes positioning, by an actuator, an opening of the wavelength selector in a path of the first light.

[0007] In some implementations, selecting includes adjusting a size of the opening based on digital data generated by a spectrometer that receives the first light.

[0008] In some implementations, positioning includes moving the opening via a piezoelectric transducer.

[0009] In some implementations, the first region and the second region have different materials from each other.

[0010] According to one aspect of the present application, a method is provided, comprising: generating a first detection result by exposing a first area of ​​a substrate to first light of a first wavelength; generating a second detection result by exposing a second area of ​​the substrate to second light of a second wavelength; generating at least one parameter of an optical system based on the first detection result and the second detection result; depositing a plurality of particles on the first area and the second area; determining a defect sensitivity of an inspection system by exposing the plurality of particles to the first light and the second light; and performing inspection based on at least one parameter of the optical system in response to the defect sensitivity exceeding a threshold value.

[0011] In some implementations, generating at least one parameter includes generating a radio frequency signal, the radio frequency signal driving an acousto-optic modulator of a light source, and the light source generates the first light and the second light.

[0012] In some implementations, performing the inspection includes inspecting a mask.

[0013] In some implementations, depositing the plurality of particles includes spraying the plurality of nanoscale particles onto the first region and the second region.

[0014] In some implementations, the method further includes generating the first light and the second light by a nonlinear light source, the first light being zero-order light, and the second light being first-order light.

[0015] In some implementations, the method further includes: generating the first light by a first single wavelength light source; and generating the second light by a second single wavelength light source, the second single wavelength light source being different from the first single wavelength light source.

[0016] In some implementations, the method further includes: before generating the first detection result, detecting a spectrum of the first light using a spectrometer.

[0017] According to one aspect of the present application, a system is provided, comprising: a multi-wavelength light source, comprising: a light source; and a wavelength selector located in an optical path of light generated by the light source; a spectrometer operable to measure a spectrum of a first light selected by the wavelength selector; a mask stage operable to position a mask in the optical path; and a controller operable to adjust at least one parameter of the multi-wavelength light source in response to the spectrum of the first light.

[0018] In some implementations, the multi-wavelength light source further includes an acousto-optic modulator, wherein the acousto-optic modulator is located between the light source and the wavelength selector.

[0019] In some implementations, the light source includes a plurality of single wavelength light sources.

[0020] In some implementations, the wavelength selector includes an opening having a certain opening size.

[0021] In some implementations, the wavelength selector includes a piezoelectric transducer operable to adjust the position of the opening.

[0022] In some implementations, the wavelength selector can be operated to pass one light beam while blocking other light beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] When with Figure 1 When read together, various aspects of the present disclosure can be best understood through the following detailed description. It should be noted that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, for clarity of discussion, the size of various features may be arbitrarily increased or reduced.

[0024] Figure 1 is a schematic diagram of a system operable to inspect a substrate in accordance with an embodiment of the present disclosure.

[0025] Figure 2 and Figure 3 is an illustration of a system for inspecting a substrate according to various aspects of the present disclosure.

[0026] Figures 4A-4E is an illustration of a system for generating a selected single light for inspection and for verifying the selection thereof, according to various embodiments.

[0027] Figure 5 is a flow chart of a method of performing sensitivity verification according to various embodiments.

[0028] Fig. 6A and Figure 6B is a diagram illustrating a sensitivity verification operation according to various embodiments.

[0029] Figures 7A-7C is a schematic diagram depicting a calibration substrate according to various embodiments.

[0030] Figures 8A-9B is a diagram of a system for inspecting a substrate according to various embodiments.

[0031] Fig.10 is a block diagram of a controller according to various embodiments. DETAILED DESCRIPTION

[0032] The following disclosure provides many different embodiments or examples for implementing the different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming a first feature on or above a second feature may include an embodiment in which the first feature and the second feature are directly in contact, and may also include an embodiment in which additional features may be formed between the first feature and the second feature so that the first feature and the second feature may not be in direct contact. In addition, the present disclosure may repeat reference numbers and / or letters in various examples. This repetition is for the purpose of simplicity and clarity, and does not itself dictate the relationship between the various embodiments and / or configurations discussed.

[0033] Additionally, spatially relative terms such as "below," "beneath," "below," "above," "upper," etc. may be used herein to describe the relationship of one element or feature relative to another (one or more) element or (one or more) feature as shown in the figures. These spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly.

[0034] For the convenience of description, terms such as "about", "substantially", "substantially", etc. may be used herein. Those skilled in the art will be able to understand and deduce the meaning of these terms.

[0035] Semiconductor manufacturing generally involves forming electronic circuits by performing multiple depositions, etches, cleans, anneals, and / or implants of material layers, thereby forming a stacked structure including many semiconductor devices and interconnections therebetween.

[0036] In many instances, etching is performed based on a pattern. The pattern may first be transferred to a resist layer by reflecting light from a mask having a pattern thereon. Defects in the mask may be transferred along with the pattern, which may result in improper etching and failure of the semiconductor device. Therefore, an inspection of the mask is typically performed before the mask is used in semiconductor processing. For example, after the mask is manufactured, a "golden" digital image of a mask without defects may be captured. Then, before the mask is used, another digital image may be captured and compared to the golden digital image to determine if there are (one or more) defects. In response to the presence of (one or more) defects, the mask may be cleaned, repaired, reworked, or replaced before semiconductor processing begins.

[0037] When inspecting a mask, a single wavelength light source directs light to the mask, which reflects the light back to the detector. However, a single wavelength of light may not be sufficient to inspect new generation node masks and support complex mask pattern designs. To meet different mask pattern spacings, the tunable wavelength light source function is conducive to improved resolution. Another problem is that the sensitivity (capture rate) may not be uniform as the inspection frequency increases. Defect signals of different wavelengths have different responses, which may increase the risk of missed or false detections.

[0038] In an embodiment of the present disclosure, a tunable wavelength light source is implemented. The tunable wavelength light source may include an acousto-optic modulator (AOM) that generates light of multiple wavelengths and a slit for selecting a single wavelength from the multiple wavelengths generated by the AOM. In some embodiments, the tunable wavelength light source has a multi-wavelength nonlinear light source instead of a single wavelength light source. In some embodiments, the tunable wavelength light source includes a switchable light source level instead of a single wavelength light source. The switchable light source level may include multiple single wavelength light sources instead of the multi-wavelength nonlinear light source.

[0039] In some embodiments, two spectrometers are included to perform real-time spectral variation monitoring. Based on feedback from the spectrometers, a laser intensity feedback control loop for checking light energy stability can be implemented, and a wavelength feedback control loop with an AOM and a spectrometer can be implemented to improve wavelength accuracy in real time. An optical path stabilizer can be included to select optical path pointing and / or position control. A locally selected wavelength can be included as an inspection light to overcome insufficient resolution or contrast.

[0040] Various benefits are associated with these embodiments. Resolution limitations due to single wavelength light sources may be overcome. Spectral monitoring is improved due to the inclusion of one or more spectrometers in the system. Energy control accuracy is improved by wavelength tuning and calibration due to the inclusion of (one or more) spectrometers. Sensitivity is improved due to enhanced defect signal response from operating at different selectable wavelengths. Switchable multi-wavelength detection techniques may be implemented for output wavelengths ranging from visible light to ultraviolet (UV), mid-ultraviolet (MUV), deep ultraviolet (DUV), and extreme ultraviolet (EUV) domains.

[0041] Figure 1 is a schematic diagram of a system 10 operable to inspect a substrate in accordance with an embodiment of the present disclosure.

[0042] The system 10 includes a multi-wavelength light source 100, one or more spectrometers 110, 140, an acousto-optic modulator (AOM) 120, a multi-function structure 130, an imaging device calibration device 150, a mask inspection device 160, and an image post-processing and defect classification device 170. There are one or more feedback control loops between the various components of the system 10, which are beneficial to improve the quality of mask inspection. To simplify the description, Figure 1 Some components may be omitted from the illustration of system 10. In some embodiments, Figure 1 Some components depicted in the drawings may be omitted (eg, may be optional).

[0043] The multi-wavelength light source 100 is operable to generate one or more light sources including different wavelengths. In some embodiments, the tunable multi-wavelength inspection light source comprises a nonlinear light source system or a switchable light source stage. Figure 2 The nonlinear light source system 20 according to various embodiments is described in more detail. Figure 3 The switchable light source stage 30 according to various embodiments is described in more detail.

[0044] Nonlinear interactions can be generated by various mixing processes, such as acousto-optic (AO), second harmonic generation (SHG), third harmonic generation (THG), higher harmonic generation (HHG), difference frequency generation (DFG), sum frequency generation (SFG), optical parametric oscillation (OPO), optical parametric generation (OPG), etc. The nonlinear light source system can be operated to perform the following functions: adjust the oscillator cavity length, switch different gain media in the oscillator, have nonlinear crystals for harmonic generation, such as β-barium borate (BBO), lithium triborate (LBO), cesium lithium borate (CLBO), bismuth borate (BiBO), potassium titanyl phosphate (KPT), etc.

[0045] In some embodiments, the multi-wavelength light source 100 includes an inspection light source that includes one or more laser sources. The laser source(s) have a laser wavelength that may be a single wavelength or include multiple wavelengths and may include one or more of a fundamental frequency laser or a harmonic generator.

[0046] The output of the multi-wavelength light source 100 can be received by the first spectrometer 110. Spectrometry is included to monitor the wavelength modulation results to determine whether the target laser wavelength is at a selected wavelength. For example, the first spectrometer 110 can detect abnormal laser amplification and / or prevent wrong wavelengths. The first spectrometer 110 can include one or more of a grating, a slit and a preamplifier, an imaging device (e.g., a CMOS, CCD, or TDI), and / or a photodiode. The first spectrometer 110 can analyze the spectral distribution and intensity of the light output by the multi-wavelength light source 100, which can be used in a laser intensity control loop to select the light intensity. In the detection system 10, in order to improve the accuracy of the modulation results, two spectrometer devices can be installed in two positions, such as Figure 1 The first spectrometer 110 is located at the exit of the multi-wavelength light source 100 (eg, a nonlinear laser system) to determine whether the wavelength distribution of the incident light is within the selected measurement spectrum.

[0047] A second spectrometer 140 may be placed below the mask stage to capture the target (mask) wavelength distribution in the selected measurement spectrum. The second spectrometer 140 may be similar to the first spectrometer 110 in most respects, but may be positioned after the multifunctional structure or device 130. The inclusion of two spectral measurement devices 110, 140 facilitates the AOM 120 to improve tuning to the selected wavelength based on known (e.g., historical or stored) background information and effectively reduce optical noise by moving the slit. Figures 4A-4C The moving slit 470 according to various embodiments is described in more detail.

[0048] The acousto-optic modulator (AOM) 120 can perform acousto-optic modulation, which is Figures 4A-4C 120 is shown in more detail. To realize a multi-wavelength light source, an AOM is a device that can operate to modulate an original wavelength to a new wavelength within a certain range. AOM 120 may include a frequency modulator so that a tunable laser wavelength can be generated via RF signal modulation. The stability of the RF signal can be monitored by AOM 120 or an external monitoring device.

[0049] Embodiments of the present disclosure include an AOM, (one or more) spectrometers, and one or more control loops. Acousto-optic modulation can be performed by an AOM 120, which operates based on the acousto-optic effect to provide diffraction and frequency shifting for incident light. A periodic RF signal can be input to the piezoelectric transducer of the AOM 120, whereby the acoustic waves affect the expansion and compression of the refractive index change. The interaction of phonons and photons can achieve sum frequency generation (SFG) or difference frequency generation (DFG) based on conservation of momentum and conservation of energy in a nonlinear system. The use of an AOM 120 to modulate the wavelength improves the simplicity of the system. For example, the AOM 120 can be easily retrofitted into an existing system as an in-situ component, thereby immediately providing a choice of optical wavelengths for mask inspection, which is beneficial for different mask pattern sizes (e.g., pitch and spacing) and improves defect signal detection.

[0050] The multifunctional structure or device 130 may include one or more of an optical path stabilizer, a speckle reducer, and a homogenizer. In some embodiments, the multifunctional device 130 includes one or more of (one or more) diffusers, (one or more) homogenizers, (one or more) wave plates, (one or more) lenses, and (one or more) reflectors for light quality improvement. The multifunctional device 130 is operable to perform optical path pointing and / or position correction of the AOM 120.

[0051] An optical path stabilizer (OPS) can be a system that improves the stability and consistency of the optical path length in an optical system, which is beneficial for high-resolution systems such as those used for EUV mask inspection. An optical path stabilizer can compensate for environmental factors or equipment-induced vibrations that may cause optical path variations or disturbances, which is beneficial for providing consistent and high-quality output. An OPS can use various techniques to stabilize the optical path, such as moving mirrors or lenses, or using acousto-optic devices.

[0052] Speckle may refer to a particle-like interference pattern that occurs when coherent light (such as laser light) reflects from or passes through a rough surface. In system 10, speckle may introduce noise or false indications, thereby increasing the difficulty of correctly analyzing semiconductor masks. Speckle reduction techniques may include software algorithms, introducing controlled randomness to the optical setup, or using multiple wavelengths or illumination angles. In some embodiments, techniques for reducing speckle noise include spatial filtering, temporal filtering, polarization filtering, etc.

[0053] Homogenizers can be used to improve the uniformity of a light source’s intensity distribution across its profile, which is beneficial for inspection, as uneven illumination can introduce artifacts or shadows that can lead to incorrect analysis. Homogenizers can be made of or include a series of lenses, prisms, or other optical elements that evenly distribute light. Homogenizers can use a variety of techniques to produce a uniform light distribution, such as diffusion, scattering, and diffraction. In the context of EUV mask inspection systems, homogenizers can improve uniform illumination of the mask, making it easier to identify defects or irregularities.

[0054] The second spectrometer 140 is located after the multi-function device 130 and is operable to feed back spectrum information to the AOM 120 , feed back laser power information to the multi-wavelength light source 100 , detect abnormal wavelengths, and the like.

[0055] The imaging device calibration apparatus 150 is operable to calibrate or select parameters of an imaging device, which may include a charge coupled device (CCD) imaging device or a complementary metal oxide semiconductor (CMOS) imaging device. Both the CCD imaging device and the CMOS imaging device may be time delay integration (TDI) imaging devices. In some embodiments, the imaging device calibration apparatus 150 includes a controller (e.g., a microcontroller unit or "MCU"), a processor, a multi-processor, etc. The imaging device calibration apparatus 150 may communicate data with the optical sensor to select its parameters. In some embodiments, the system 10 includes a controller 180 and the imaging device calibration apparatus 150 is included in the controller 180. Reference Fig.10 The controller 1000 according to various embodiments is described in more detail.

[0056] Various parameters of CCD, CMOS, TDI CCD and TDI CMOS sensors can be controlled in real time by, for example, an MCU (e.g., controller 180). The gain of the sensor can control the degree to which the signal from each pixel is amplified. Increasing the gain can increase the sensitivity of the sensor, but it can also increase noise. The offset of the sensor controls the black level of the image. Increasing the offset can reduce the noise in the image, but it can also make it more difficult to detect small defects in the mask. The integration time can refer to the amount of time the sensor is exposed to light. Increasing the integration time can improve the signal-to-noise ratio (SNR) of the image, but it can also make the sensor more susceptible to motion blur. The sensor can be triggered to start and stop integration in real time, which is beneficial for synchronizing the sensor with a mask scanner or other equipment in the inspection system.

[0057] In addition to these parameters, some sensors may allow real-time control of other characteristics, such as the number of TDI levels or the shift frequency. The parameters that can be controlled or selected in real time may vary depending on the sensor and MCU.

[0058] The following are examples of how real-time control or selection of sensor parameters can be used in semiconductor mask inspection. The gain of the sensor can be adjusted to compensate for changes in lighting conditions. The offset of the sensor can be adjusted to compensate for changes in background noise levels. The integration time of the sensor can be adjusted to improve the signal-to-noise ratio of different mask features. The sensor can be triggered to start and stop integration at selected points during the mask scan process, which is beneficial for synchronizing the sensor with a mask scanner or capturing images of selected areas on the mask.

[0059] CCD, CMOS, TDI CCD and / or TDI CMOS sensors can include various features that are beneficial for semiconductor mask inspection. For example, a CCD sensor can have features such as pixel size, well depth, and read noise. Smaller sizes of each pixel on the sensor may be beneficial for obtaining higher resolution images, but may also result in more noise. Well depth may refer to the maximum number of photoelectrons a pixel can hold before it saturates, which is beneficial for low light imaging and imaging of high contrast scenes. Read noise may refer to the amount of noise introduced into the image during the readout process. Reducing read noise may be beneficial for low light imaging and imaging scenes with high dynamic range.

[0060] For CMOS sensors, pixel size, fill factor, and dark current can be characteristics that are beneficial for semiconductor mask inspection. As mentioned earlier, smaller pixels can achieve higher resolution images, but may also result in more noise. Fill factor can refer to the percentage of pixel area that is sensitive to light. The higher the fill factor, the higher the sensitivity of the sensor. Dark current refers to the amount of current that flows through a CMOS sensor even when exposed to light. Reduced dark current can be beneficial for low light imaging and high dynamic range imaging scenarios.

[0061] In a TDI CCD sensor, advantageous properties may include the number of stages and the shift frequency. The number of stages is associated with the number of times an image charge packet moves along the rows of the CCD sensor. A higher number of stages may produce an image with a higher signal-to-noise ratio (SNR). The shift frequency may refer to the frequency at which the image charge packet is shifted along the rows of the CCD sensor. Matching the shift frequency to the speed of the imaged object (e.g., a mask) may help improve the image quality.

[0062] In a TDI CMOS sensor, the number of stages, shift frequency, and rolling shutter can be features that can be advantageous for mask inspection in one or more ways. A CMOS sensor can use a rolling shutter, which refers to a sensor that reads one row at a time. A rolling shutter can cause image distortion when the imaged object (e.g., a mask) moves. A TDI CMOS sensor can include a global shutter that reads the entire sensor at once. This can be advantageous in reducing or eliminating image distortion, but can increase the cost and / or complexity of the CMOS sensor.

[0063] In the context of semiconductor mask inspection, the following characteristics may be particularly beneficial: pixel size, well depth, read noise, TDI number of levels, shift frequency, rolling shutter, and integration time. The pixel size can be selected small enough to resolve features on the mask. The well depth can be selected high enough to avoid saturating the pixel when imaging bright features on the mask. The read noise can be selected low enough to avoid masking small defects on the mask. The number of levels can be selected high enough to achieve a selected SNR. The shift frequency can be selected to match the speed of the mask scanner. A global shutter can be selected to avoid image distortion. Semiconductor mask inspection can be performed in low light conditions, so sensors with long integration times can be advantageously selected.

[0064] The mask inspection system 160 may include one or more components of the system 10, such as the multi-wavelength light source 100, the AOM 120, the multi-function device 130, and a controller for selecting parameters of one or more components. Figure 1. For example, the mask inspection system 160 may include an imaging device or system. The imaging system may capture an image of the mask through its sensor, which may be a CCD sensor or a CMOS sensor. The mask inspection system 160 may include a reflective imaging system in which EUV light is reflected from the mask onto the sensor. The mask inspection system 160 may include a stage operable to move the mask relative to the illumination and imaging system. This allows the entire mask to be inspected. The mask inspection system 160 may include an image processing system operable to analyze the image of the mask and detect defects. This may be performed by various image processing algorithms. Reference Figures 8A-9B The mask inspection systems 80 , 90 according to various embodiments are described in further detail.

[0065] The working principle of the mask inspection system 160 may include placing the mask on a workbench and illuminating the mask with light from the multi-wavelength light source 100. The reflected light is then captured by the imaging system and analyzed by the image processing system. The image processing system detects any defects in the mask and may optionally generate a report that the operator uses to determine whether the mask is acceptable. In addition to the above items, the mask inspection system 160 may also include a contamination control system having various contamination control devices or devices, such as a HEPA (High Efficiency Particulate Arrestment) filter. The mask inspection system 160 may include a temperature control system that is operable to maintain the mask at a substantially constant temperature during inspection. This is because changes in temperature can cause the mask to expand or contract, resulting in image defects. The mask inspection system 160 may include a vibration control system that may include a vibration isolation table that is conducive to reducing vibration.

[0066] The image post-processing and defect classification device 170 (or simply referred to as "processing device 170") is operable to process the image of the mask captured by the mask inspection system 160, and determine the type and / or number and / or location of (one or more) defects based on the processed image. In some embodiments, the processing device 170 is included in the mask inspection system 160. In some embodiments, the processing device 170 is included in the controller described previously, or is another controller separate from the controller described previously.

[0067] The processing device 170 can use various image processing algorithms to detect defects, which may include one or more of thresholding, edge detection, template matching, machine learning, etc. Thresholding can include converting the image into a binary image, where each pixel is black or white. It is then determined whether the pixel is defective or non-defective based on the intensity of the pixel. Edge detection algorithms can be used to detect the edges of objects in the image. Defects in the mask may cause changes in the edges of the object. By detecting these changes, the edge detection algorithm can be used to identify defects. Template matching algorithms can be used to detect defects by comparing the image to a reference image of a non-defective mask. Any difference between the two images is identified as a defect. Machine learning algorithms can be trained to detect defects in masks. These algorithms can be trained on image data sets of defective and non-defective masks. After training, the algorithm can be used to identify defects in new images.

[0068] The selected image processing algorithm(s) used in the mask inspection system may depend on the type of defects being inspected. For example, a mask inspection system for EUV masks may use different algorithms than mask inspection systems for other types of masks. The types of defects in the mask may include one or more of pinhole defects, bridging defects, particle defects, and the like. A pinhole defect is a small hole in the mask, which can be detected using threshold processing or template matching algorithms. A bridging defect is a small bridge of material connecting two features on the mask, which can be detected using edge detection or machine learning algorithms. Particle defects are small particles deposited on the mask, which can be detected using threshold processing or machine learning algorithms. In some embodiments, template matching can be used for any of the defects just described.

[0069] Figure 2 and Figure 3 is an illustration of a system for inspecting a substrate according to various aspects of the present disclosure.

[0070] exist Figure 2 In the embodiment, the system 20 may include a multi-wavelength light source 200 that generates a single light having multiple wavelengths, where the wavelengths may be represented as ω1+ω2+…+ω n , where "n" is an integer greater than 1. The multi-wavelength light source 200 may be a tunable multi-wavelength inspection light source including a nonlinear light source. The nonlinear light source may generate single wavelength light, and one or more lenses may be positioned so that the paths of the single wavelength light travel in parallel and are incident on the wavelength selector 210.

[0071] The nonlinear interaction can be generated by one or more mixing processes, such as acousto-optic (AO), second harmonic generation (SHG), third harmonic generation (THG), higher harmonic generation (HHG), difference frequency generation (DFG), sum frequency generation (SFG), optical parametric oscillation (OPO), optical parametric generation (OPG), etc. The multi-wavelength light source 200 can be operated to adjust the oscillator cavity length, switch different gain media in the oscillator and / or use nonlinear crystals to generate harmonics, such as BBO, LBO, CLBO, BiBO, KPT, etc. In some embodiments, the multi-wavelength light source 200 includes a single laser capable of operating to generate three or more single wavelength lights, a first lens, an AOM, and a second lens. Reference Figures 4A-4C A multi-wavelength light source including an AOM is described in more detail.

[0072] In some embodiments, nonlinear crystals are used in multi-wavelength light sources to generate multiple wavelengths of light through a process known as nonlinear optical frequency conversion. Nonlinear optical frequency conversion is the process of converting light from a single wavelength to another wavelength by interacting with a nonlinear crystal. The wavelength conversion that occurs can be selected based on the type of nonlinear crystal included and the characteristics of the incident light. For example, nonlinear crystals can be used to generate a multi-wavelength light source through optical parametric oscillation (OPO). OPO is a nonlinear optical process that generates two output beams from a single input beam, which can be referred to as a signal beam and an idler beam. The wavelengths of the signal beam and the idler beam are selected by the characteristics of the nonlinear crystal and the wavelength of the input beam. An example of an OPO multi-wavelength light source is a YAG:OPO laser. A YAG:OPO laser is a type of OPO laser that includes an yttrium aluminum garnet (YAG) crystal as a nonlinear crystal. A YAG:OPO laser can generate light in a variety of wavelength ranges from ultraviolet to infrared.

[0073] Another way to generate a multi-wavelength light source using nonlinear crystals is through a process known as supercontinuum generation. Supercontinuum generation is a nonlinear optical process that produces a broad spectrum of light from a single input beam. The spectrum of the generated light can be selected based on the properties of the nonlinear crystal and the input beam parameters. An example of a multi-wavelength light source for supercontinuum generation is a titanium sapphire laser. A titanium sapphire laser is a supercontinuum laser that uses a titanium sapphire crystal as the nonlinear crystal. A titanium sapphire laser can generate a very broad spectrum of light from the ultraviolet to the infrared.

[0074] In some embodiments, the multi-wavelength light source 200 is or includes a white light source that includes one or more nonlinear crystals. The white light source may include a nonlinear crystal that doubles the frequency of the laser beam. For example, a potassium dihydrogen phosphate (KDP) crystal may be used to double the frequency of a green laser beam to produce a white light source.

[0075] The system 20 includes a wavelength selector 210 that receives a single light from the multi-wavelength light source 200. The wavelength selector 210 is operable to select one of a plurality of lights, each carrying a single wavelength or a narrow band of wavelengths centered around a single wavelength. Figures 4A-4C The wavelength selector 470 according to various embodiments is described in more detail. In short, the wavelength selector 210 may include a movable slit disposed after the second lens of the multi-wavelength light source 200 to select one of a plurality of lights as a light source for inspection.

[0076] System 20 includes a mask inspection system 260 that receives the light selected from wavelength selector 210. Mask inspection system 260 can be similar in most aspects to reference system 210. Figure 1 The mask inspection system 260 is similar to the mask inspection system 160 described above. In short, the mask inspection system 260 positions the mask in the path of the selected light so that a reflection of the mask is produced by the selected light. The reflected image is captured by the imaging sensor, and the image can be processed to determine whether there are defects in the mask, as described in reference to Figure 1 described.

[0077] exist Figure 3 In the embodiment, the system 30 includes a light source 300 , which includes a plurality of single wavelength light sources 302 , 304 , . . . , 306 . Figure 3 Three single wavelength light sources 302, 304, 306 are shown in FIG. The light source 300 may include Figure 3 The three single wavelength light sources 302, 304, 306 shown may be fewer or more light sources. Each of the single wavelength light sources 302, 304, 306 may generate a single light having a selected wavelength or a single light having a selected narrow band wavelength centered on the selected wavelength. For example, the first single wavelength light source 302 may generate a single light having a first wavelength ω1, the second single wavelength light source 304 may generate a single light having a second wavelength ω2, and the nth single wavelength light source 306 may generate an nth wavelength ω n A single light, "n" is an integer greater than 1.

[0078] System 30 includes a wavelength selector 310 that can be similar in most respects to reference Figure 2 The wavelength selector 210 described is similar. The wavelength selector 310 is operable to select one of the single lights generated by the light source 300 to be incident on the mask being inspected.

[0079] Figures 4A-4E is a diagram of a system 40 for generating a selected single light for inspection and for verifying its selection, according to various embodiments. The system 40 may be referred to as a multi-wavelength light source 40 based on an AOM.

[0080] exist Figure 4A , the system 40 includes a light source 400, a first lens 410, an AOM 430, a second lens 450, and a wavelength selector 470. Figure 4A Also depicted is a spectrometer 480 that can verify the wavelength of light selected by the wavelength selector 470.

[0081] The light source 400 is operable to generate light 402 having a single wavelength ω, such as a laser, and may be a laser light source 400. The output wavelength range of the light source 400 may be in a wavelength domain, such as a visible light domain, a UV domain, a MUV domain, a DUV domain, an EUV domain, etc. The light source 400 may include a visible domain laser, such as a helium-neon laser, an argon laser, a krypton laser, etc. In some embodiments, the light source 400 includes an excimer laser, a helium-cadmium laser, a nitrogen molecular laser, an argon fluoride laser, a krypton fluoride laser, a free electron laser, etc.

[0082] In microscopic inspection systems, diffraction is related to the wavelength of the incident light. The wavelength-resolution relationship can be expressed as: resolution ∝λ / NA, where "NA" is the numerical aperture. For a microscopic inspection system in operation, the basic resolution is improved due to contrast enhancement, which allows resolution beyond simple optical designs. When the wavelength changes, the resolution also changes accordingly. This means that the signal response to defects also changes accordingly. When the wavelength is reduced, the resolution increases. In this way, defect sensitivity verification can be performed. Sensitivity verification can include line spacing patterns, hole patterns, diagonal line patterns, brightness / darkness patterns, and other complex patterns.

[0083] In a limited modulation wavelength region (e.g., about a few nanometers), optical chromatic aberration tolerance (e.g., central wavelength ±10%) can be compensated in addition to certain optical elements. However, these potential disadvantages can be addressed at the system level, such as by serial optical switches. Optical-related calibrations can include focus, astigmatism, flare, polarization, alignment, etc. Lenses mounted with actuators and combined with optical path and beam size correction systems can improve position accuracy and provide appropriate divergence or convergence angles in use. Imaging devices (e.g., CCD or CMOS sensors) can also perform calibrations such as shading calibration and gain calibration.

[0084] The first lens 410 is operable to direct and / or focus the light 402 onto the AOM 430. The light leaving the first lens 410 may be referred to as directed light 420. The first lens 410 may be or include an aspheric lens, which may be made of fused quartz or other materials that reduce aberrations and improve production efficiency. Fused quartz may be used due to its low coefficient of thermal expansion and high resistance to laser-induced damage. Aspheric lenses may be beneficial in correcting spherical aberrations, thereby providing a more focused point, which is beneficial in mask inspection where defects may be very small. High numerical aperture (NA) lenses may be used to improve resolution. The first lens 410 may include one or more coatings applied thereto to reduce reflections and improve transmittance at the selected laser wavelength used. In some embodiments, the coating includes an anti-reflective coating. In some embodiments, the first lens 410 includes a collimating lens. The system 40 may also include an optional polarizer or additional optical element before or after the first lens 410.

[0085] The system 40 includes an AOM 430. The AOM 430 may include an acousto-optic material, which may be a transparent crystal, such as tellurium dioxide (TeO2) or quartz, selected based on acousto-optic properties (e.g., efficiency and transparency at a selected wavelength). The AOM 430 may include an ultrasonic transducer that is attached to the acousto-optic material and generates acoustic waves when an electrical signal is applied to the acousto-optic material. In some embodiments, the ultrasonic transducer may be a piezoelectric transducer. The AOM 430 may include a radio frequency (RF) driver that generates an RF signal that drives the ultrasonic transducer. The frequency and amplitude of the RF signal may control the characteristics of the acoustic wave, and thus control the modulation of the light 420.

[0086] In operation, an RF driver can send an electrical signal to an ultrasonic transducer, which then generates an acoustic wave that propagates through an acousto-optic material or "crystal." As the acoustic wave passes through the crystal, it can cause periodic changes in the refractive index of the acousto-optic material, thereby forming a dynamic diffraction grating. A collimated light beam 420 (e.g., from a laser 400) is directed into the crystal, encountering the dynamic diffraction grating. Depending on the characteristics of the acoustic wave (e.g., frequency and amplitude), the incident light beam will diffract. A first-order diffracted light beam can be used for modulation, but higher-order light beams can also be used in some embodiments. By selecting the frequency and amplitude of the RF signal, the angle and intensity of the diffracted light can be selected, thereby achieving real-time modulation. This reference Figure 4C Describe in more detail.

[0087] exist Figure 4A, AOM 430 outputs three lights 442, 444, 446 having different wavelengths. The first light 442 has the same wavelength as the light 420 incident on the AOM 430. The second light 444 has a second wavelength ω-Ω. The third light 446 has a third wavelength ω+Ω. In the foregoing description, "Ω" refers to the RF frequency of the electrical signal applied by the RF driver. The second wavelength ω-Ω can be referred to as a -1st order wavelength, and the third wavelength ω+Ω can be referred to as a +1st order wavelength.

[0088] The system 40 includes a second lens 450 through which the three lights 442, 444, 446 pass before reaching the wavelength selector 470. The second lens 450 can be similar to the first lens 410 in many respects. The second lens 450 can be a collimating lens that can operate to make the light beams with an angle offset parallel. That is, after passing through the second lens 450, the three lights 442, 444, 446 with an angle offset become parallel lights 462, 464, 466 that are parallel to each other, respectively. The parallel lights 462, 464, 466 emitted from the second lens 450 are incident on the wavelength selector 470.

[0089] The system 40 includes a wavelength selector 470. The wavelength selector 470 includes a moving slit 472 controlled by a motion controller 474. Inserting the moving slit 472 after the AOM 430 allows the slit 472 to operate as a color filter to select wavelengths that are beneficial for inspection. The opening distance "d" or size of the moving slit 472 can be associated with wavelength accuracy. The movement of the moving slit 472 can be driven by a high precision control motor or piezoelectric transducer (PZT) 474, which can select the "d" width and position of the slit. When "d" is smaller, higher purified wavelengths can be selected and the energy output is reduced. When "d" is increased, greater energy output can be achieved while including more wavelengths outside the selected band in the output light used for inspection. Figure 4A In the example shown, the third light 466 is selected by the wavelength selector 470, while the first light 462 and the second light 464 are blocked by the wavelength selector 470. Figure 4D and Figure 4E Wavelength selectors according to various embodiments are described in more detail.

[0090] Spectrometer or spectrum measurement system 480 is optionally and / or selectively positioned in the optical path of parallel light 462, 464, 466. Spectrometer 480 may be a reference Figure 1 An embodiment of the second spectrometer 140 is described. Figure 4AIn the example of FIG. 4 , the spectrometer 480 in operation detects the amplitude and wavelength of the third light 466 passing through the moving slit 472. The spectrometer 480 can generate digital data representing the amplitude and wavelength of the light detected by the spectrometer 480. One representation of the digital data is Figure 4A 490 is depicted in FIG. In some embodiments, the digital data is in another data format, such as an array, a table, or other suitable data format. The digital data can be stored in a memory, a database, and / or a local memory of a controller of the spectrometer 480.

[0091] The control loop may link the spectrum measurement system 480, the AOM 430, and the moving slit 472. When the output spectrum measurement result is out of range or abnormal, the control loop may trigger a wavelength calibration to adjust one or more of the following items: the position and / or opening size of the moving slit 472, the RF frequency and amplitude of the AOM 430 (e.g., the RF power may be controlled to be below the saturation level), and energy stability.

[0092] exist Figure 4B In some instances, when the opening distance "d" is too large to allow high amplitude signals at other wavelengths outside the selected frequency band to enter the spectrometer 480, the system 40 may be forced to stop based on an operating state error or error. Figure 4B In the example shown, the movable slit 472 is positioned so that the first light 462 and the second light 464 pass through and the third light 466 is blocked. Figure 4A , which allows two lights 462, 464 to pass through instead of just one light. In this way, the spectrometer 480 detects multiple amplitude peaks at a narrow band around the wavelengths of the first light 462 and the second light 464. In response to detecting more than one peak, the spectrometer 480 or a controller in data communication therewith can trigger a forced stop of the system 40.

[0093] Figure 4C The operation of AOM 430 is depicted. In some embodiments, the operation of AOM 430 can be such that the output separation angle θ between the zero-order wavelength and the first-order wavelength is expressed as θ=λ*Ω / V, where Ω refers to the RF frequency of the RF driver, λ refers to the laser wavelength of light 420, and V refers to the speed of sound. Then, the frequency of the output lasers 462, 464, 466 is in the range of ω+ / -Ω, where ω refers to the frequency of the input laser 402. In some embodiments, such as for EUV or optical mask inspection tools, for AOM 430, the RF frequency can be in the sub-GHz to multiple-GHz range, corresponding to an operating range of approximately sub-nanometer to multiple-nanometers.

[0094] Figure 4D and Figure 4Eis a view showing a wavelength selector 470 according to various embodiments.

[0095] exist Figure 4D , the wavelength selector 470 includes two plates 471, 473, which are separated by an opening 472 having a dimension "d" in the vertical direction Z. One or more actuators 474, 476 can be connected to the respective plates 471, 473 to control the movement of the plates 471, 473 along the vertical direction Z. That is, the plates 471, 473 are operable to move independently of each other under the control of the actuators 474, 476, which can be high-precision control motors or piezoelectric transducers (PZT), as previously described with reference to Figure 4A In some embodiments, actuators 474, 476 are substantially the same or of the same type (e.g., both are PZTs). In some embodiments, actuators 474, 476 are different from one another. For example, actuator 476 may be a low precision control motor and actuator 474 may be a PZT, or another suitable combination of actuators 474, 476. Figure 4D In the wavelength selector 470, the size "d" of the opening 472 and the position of the opening 472 along the Z-axis direction can be controlled, which can be beneficial for selecting a single wavelength of light with high precision and rejecting other wavelengths of light to obtain enhanced signal energy.

[0096] exist Figure 4E , the wavelength selector 470 includes a single plate 471 having an opening 472 therein, rather than two plates 471, 473. The opening 472 may be completely embedded within the single plate 471 such that the dimension "d" of the opening 472 is fixed or constant in the vertical direction Z. In such an embodiment, a single actuator 474 may be included that controls the position of the opening 472 without controlling the dimension "d" of the opening 472. Figure 4E The control of the wavelength selector 470 depicted in FIG. 4 can be compared to that of FIG. Figure 4D However, due to Figure 4D The wavelength selector 470 has a variable dimension "d" instead of Figure 4E of fixed size “d” and therefore can provide slightly better signal energy performance.

[0097] Figure 5 is a flow chart of a method of performing sensitivity verification according to various embodiments. Fig. 6A and Figure 6B FIG. 7 is a plan view of a substrate according to various embodiments. FIG. Figure 5 The actions shown can be based on the reference Figure 1-4E and Figure 6A-107 shows a flow chart of a method 70 for performing sensitivity verification according to one or more aspects of the present disclosure. Method 70 is an example and is not intended to limit the present disclosure to what is explicitly shown in method 70. Additional actions may be provided before, during, and after method 70, and some of the actions described may be replaced, eliminated, or moved for additional embodiments of the method. For example, method 70 may be used to inspect masks, wafers, etc. For simplicity, not all actions are described in detail herein. Figure 1 -4 and Figure 6B-10 The actions of method 70 are described with reference to the elements of system 10. Many actions may be referred to as Fig.10 For example, the controller 1000 may execute instructions to perform the actions of the method 70. It should be understood that the method 70 is not limited to being performed by the system 10 and / or the controller 1000, and may be performed by a system and / or controller that is different from the system 10 and / or the controller 1000 in other embodiments in one or more aspects.

[0098] exist Figure 5 In the method 50, the method 50 begins at act 500, where an exposure test is performed on two or more wavelengths of light. Figures 4A-4E In the example of FIG4 , a first exposure test may be performed on first light 462, a second exposure test may be performed on second light 464, and a third exposure test may be performed on third light 466. In some embodiments, each of the first exposure test, the second exposure test, and the third exposure test may include multiple operations, such as power and intensity measurements, wavelength measurements, focus and / or alignment measurements, optional pulse duration and / or timing measurements, aberration measurements, system checks, etc.

[0099] Power and intensity measurements may include operating a power meter to measure the initial output power of the selected light. A beam profiler may be operated to confirm that the laser beam has a substantially uniform intensity across its profile. Wavelength calibration may include measuring the wavelength by a wavelength meter or spectrometer to measure the operating wavelength of the laser. Focusing and alignment may include coarse alignment, in which the laser is aligned with the optical path so that the beam passes through any lens, beam expander, or other optical component along the optical path. Fine alignment may be performed using a micrometer stage or other fine-tuning mechanism to more accurately align the laser. Focus measurements may include operating a focal plane array or similar device to focus the laser beam at a target plane where the mask will be placed. Pulse duration and timing measurements may include measuring the pulse duration by an autocorrelator or other time domain measurement device to determine the laser pulse duration. Aberration measurements may include checking aberrations by a wavefront sensing device to identify any optical aberrations, such as astigmatism or spherical aberration.

[0100] Fig. 6A An example of a wavelength exposure test according to act 500 according to various embodiments is depicted. The wavelength exposure test may be performed via a calibration substrate 60, which may be a calibration mask 60, a calibration wafer 60, or the like. Fig. 6A A calibration mask 60 is depicted that includes four different material layers or multilayers 600, 610, 620, 630. In some embodiments, layer 600 can be a substrate. For example, layer 600 can be glass or include glass, such as fused silica or ultra-low expansion (ULE) glass. Multilayer 610 can be a reflective multilayer stack that includes alternating layers of two or more different materials, such as silicon and molybdenum. Layer 620 can be an absorption layer that can absorb any light that is not reflected, and can include tantalum, boron nitride, etc. Layer 630 can be a capping layer, which can be a thin layer of material such as ruthenium or silicon, which is deposited on top of the absorption layer to protect the calibration mask 60 from contamination and / or oxidation. Fewer or additional layers can be included in the calibration mask 60, such as adhesion layers, buffer layers, anti-reflective coating (ARC) layers, etch stop layers, etc.

[0101] One or more of the layers 600, 610, 620, 630 may have an exposed surface. Since the characteristic sizes of the layers 600, 610, 620, 630 are different from each other, each exposed surface may be illuminated by light of a respective different wavelength. For example, the layer 630 may be exposed to a first light 662 having a first wavelength ω-Ω, the layer 620 may be exposed to a second light 664 having a second wavelength ω+Ω, and the layer 600 may be exposed to a third light 666 having a third wavelength ω+Ω". The third wavelength ω+Ω" may exceed the second wavelength ω+Ω, and the second wavelength ω+Ω may exceed the first wavelength ω-Ω. During the exposure test, the light 662, 664, 666 is directed to the calibration mask 60. The reflection of the light 662, 664, 666 may be measured using one or more of the previously described measurements. For example, power and intensity, beam profile, wavelength, focus and alignment, etc. may be measured based on the reflection of the light 662, 664, 666.

[0102] Act 510 follows act 500 and includes measuring a resolution of the mask inspection system. In some embodiments, the resolution is measured by a modulation transfer function (MTF) operation, Fourier transform analysis, a combination thereof, or the like.

[0103] In MTF, a test target may be provided, which may be a high resolution test target with a selected spatial frequency. For example, the test target may be an MTF target with a sinusoidal pattern or a bar pattern. The test target is imaged by an optical system, which may have an imaging setup that is similar in most respects to actual operating conditions. The image is acquired by a high resolution detector, taking into account potential sources of noise or aberrations. Software may be operated to analyze the acquired image, such as to measure the effect of the system in reproducing various spatial frequencies in the test target. The MTF may be plotted as a curve depicting contrast (e.g., in percent) as a function of spatial frequency. The point at which the contrast drops below a selected threshold (e.g., 10%) may be considered the resolution limit. Based on the MTF results, adjustments may be optionally made to the optical system to improve its performance.

[0104] In Fourier transform analysis, a test pattern having selected, finely spaced features can be imaged. For nanometer-scale resolution, the test pattern can have features on the order of a selected resolution (e.g., a few nanometers). (One or more) high-quality images of the test pattern can be captured by a high-resolution detector, which can include taking multiple shots and averaging the shots to improve the signal-to-noise ratio. A 2D Fourier transform can be performed on the acquired image to convert it to the frequency domain, which can reveal the spatial frequency components present in the image. The Fourier transformed image can be examined to identify the highest spatial frequencies that are clearly represented, which can correspond to the finest details that the system can resolve. In some embodiments, an inverse Fourier transform can be applied to reconstruct the image using only high-order frequencies to verify the system's ability to resolve these frequencies. Based on Fourier analysis, the system can be fine-tuned to achieve a selected resolution.

[0105] Action 520 follows action 510 and includes performing a surface quality sanity check or sanity test. The sanity check can be performed on the calibration substrate and can be or include one or more of the following: visual inspection, atomic force microscopy, scanning electron microscopy, reflectivity measurement, X-ray reflectometry, interferometry, etc. A sanity check can be performed to determine whether there are obvious defects on the calibration substrate, such as scratches, dust or other particles. In some embodiments, the sanity check can determine whether the reflectivity and / or flatness on the calibration substrate is substantially uniform. In response to a sanity check failure, the calibration substrate can be repaired, reworked, or replaced. In response to a sanity check passing, the calibration substrate can be used for subsequent actions 530 and 540.

[0106] Action 530 follows action 520 and includes performing optical calibration. Optical calibration may include calibrating the optical system (including the laser source, one or more lenses, AOM, etc.) for one or more of the following: focus, astigmatism, flare, shading, polarization, beam size, gain, etc. The calibration may be based on the measurement data generated in actions 500 and 510.

[0107] Act 540 follows act 520 and includes performing defect sensitivity verification. Figure 6B An example of defect sensitivity verification is depicted in FIG. When performing defect sensitivity verification, particles 640 can be deposited on a calibration substrate, acting as "defects" to be detected by the optical system. Particles 640 can be nanoscale particles. Deposition of particles 640 can be performed by spraying or other suitable deposition methods. Particles 640 can be deposited on exposed surfaces of layers 600, 610, 620, 630. In Figure 6B In the embodiment, particles 640 are deposited on the exposed surfaces of layers 600 , 620 , 630 .

[0108] After depositing the particles 640, a verification can be performed to determine whether the particles 640 can be detected by the light 662, 664, 666 that has been calibrated in act 530. The detection of the particles 640 can include determining a count of the particles 640. In response to determining that the particles 640 can be correctly detected, the method 50 can proceed to act 550. In response to determining that the particles 640 are not correctly detected, acts 510, 520, 530, and 540 can be repeated to recalibrate the optical system and / or repair, rework, or replace the calibration substrate.

[0109] Action 550 follows action 540. In response to the defect sensitivity verification passing, appropriate parameters of the optical system may be recorded (taped out). For example, the light source wavelength, AOM frequency, slit opening size, lens positioning / angle, etc. associated with passing the defect sensitivity verification may be stored for subsequent use in mask inspection operations.

[0110] Figures 7A-7C is a schematic diagram depicting a substrate 70 according to various embodiments. The substrate 70 may be a calibration mask, a calibration wafer, a production mask, a production wafer, or the like.

[0111] like Fig. 7A As shown, and in method 50, substrate 70 may include at least two different regions 700, 710, 720, 730, which may be exposed via two or more different wavelengths ω+Ω", ω+Ω, ω-Ω. Fig. 7AThe substrate 70 shown includes four regions 700, 710, 720, and 730. The first region 700 is selected to be exposed to a first light having a first wavelength ω+Ω". The second region 710 and the third region 720 are selected to be exposed to a second light having a second wavelength ω+Ω, which may be shorter than the first wavelength ω+Ω". The fourth region 730 may be selected to be exposed to a third light having a third wavelength ω-Ω, which may be shorter than the second wavelength ω+Ω. For example, the first wavelength ω+Ω" may be a second-order modulation of the fundamental wavelength ω, while the second wavelength ω+Ω and the third wavelength ω-Ω may be first-order modulations of the fundamental wavelength ω.

[0112] In some embodiments, substrate 70 is a production mask or a production wafer. That is, after inspection, substrate 70 will be used directly in semiconductor processing operations to reflect light carrying a pattern in photolithography as a production mask, or undergo processing (e.g., deposition, etching, annealing, epitaxial growth, etc.) that will produce an integrated circuit (IC) chip. Figure 1-6B The described system 10 is operable to inspect different regions of the substrate 70 via light of different wavelengths. For example, the first region 700 and the second region 710 may have different types of pattern designs from each other, such as bars, stripes, lines, dots, polygons, etc. In another example, the first region 700 and the third region 720 may have different depths from each other, such as in reference to FIG. Fig. 6A and Figure 6B In yet another example, the third region 720 and the fourth region 730 may have different materials from each other, such as Fig. 6A and Figure 6B As described. Fig. 7A As shown, two or more regions, such as the second region 710 and the third region 720, may be inspected using light having the same wavelength.

[0113] The arrangement of regions 700, 710, 720, 730 may correspond to different circuit functional regions, different material regions, different depths, or other appropriate arrangement methods. Regions 700, 710, 720, 730 may have the same or different sizes from each other. Regions 700, 710, 720, 730 may be arranged in a regular pattern or may not be arranged in a regular pattern, such as Fig. 7A shown.

[0114] Figure 7BA substrate 70 having three regions 700, 710, 720 is depicted, which are to be exposed to light having two different wavelengths ω+Ω, ω-Ω. The three regions 700, 710, 720 are arranged along a first horizontal direction (e.g., an X-axis direction) and extend along a second horizontal direction (e.g., a Y-axis direction) orthogonal to the first horizontal direction. The second region 710 is located between the first region 700 and the third region 720. The first region 700, the second region 710, and the third region 720 may have differences in the type of pattern design, depth, material, etc., as described in reference to FIG. Fig. 7A As described.

[0115] Figure 7C A substrate 70 having three regions 700, 710, 720 is depicted, which are to be exposed to light having three different wavelengths ω+Ω", ω+Ω, ω-Ω. Fig. 7A and Figure 7B As described, the three regions 700, 710, 720 may differ in type of pattern design, depth, material, etc.

[0116] It should be understood that the substrate 70 may include Figures 7A-7C , which are to be exposed to light having fewer or more wavelengths than those depicted in . For example, substrate 70 may include five or more regions that are to be exposed to light having five different wavelengths, such as a fundamental / dominant wavelength, two first-order modulation wavelengths, and two second-order modulation wavelengths. In some embodiments, more than five wavelengths may be used.

[0117] Figures 8A-9B is a diagram of a system for inspecting a substrate according to various embodiments. Fig. 8A and Fig.9A The system is depicted during a calibration operation prior to a checking operation. Figure 8B and Fig. 9B Depicted is the system during inspection operation.

[0118] exist Fig. 8A 8, system 80 includes a light source 800, a first lens 810, a beam steering assembly or system 820, a filter assembly 830, a spectrometer 840, and a stage 82. System 80 is operable to calibrate light source 800 and first lens 810 and inspect a mask 84 (or other substrate) located on stage 82.

[0119] The light source 800 may be Figure 1-4E The light source 800 is similar to the multi-wavelength light source described above. The light source 800 is operable to generate light beams of different wavelengths and select one of the light beams as the light beam 85 to be output to the first lens 810.

[0120] The first lens 810 may be an objective lens. The first lens 810 is operable to focus the light 86 to a focal plane associated with the substrate 84 on the stage 82. In some embodiments, the first lens 810 includes a different type of lens instead of an objective lens. The focused light 86 may be generated by another focusing component (e.g., by one or more of a concave mirror, a zone plate, a reflective parabolic mirror, etc.) that may assist in inspection.

[0121] The Spectrometer 840 can be similar in most respects to the reference Figure 1-4E In system 80, spectrometer 840 is positioned below stage 82. In operation, stage 82 can be positioned out of the optical path of light 86 during a calibration or verification phase so that spectrometer 840 receives light 87. Spectrometer 840 can generate wavelength amplitude / intensity data 850 based on light 87.

[0122] When the incident laser 85 passes through the first lens 810, which may be an objective lens, its beam size becomes larger outside the focal plane, such as Fig. 8A As shown. The system 80 includes a beam steering assembly 820 after the first lens 810 and receiving the light 86. The light 86 that has left the first lens 810 has an expanded beam size outside the focal plane. The beam steering assembly 820 beneficially collects the light 86 and directs the light 86 toward the spectrometer 840 as light 87. The light 87 leaves the beam steering assembly 820. In some embodiments, the beam steering assembly 820 includes a second lens 822, followed by a reflector 824, and followed by a third lens 826. The second lens 822 is operable to collect the light 86. The reflector 824 is operable to bend the light 86, for example, 90 degrees. The third lens 826 can also focus the light 86 as light 87 onto the focal plane of the detector of the spectrometer 840. When calculating the target intensity (e.g., on the mask surface), the transmittance of (one or more) lenses 810, 822, 826 and the filter assembly 830 and the reflectance of the reflector 824 can be considered.

[0123] In some embodiments, the intensity of light 87 leaving the beam steering assembly 820 is high enough to damage or harm the spectrometer 840. The system 80 includes a filter assembly 830 positioned after the beam steering assembly 820. The filter assembly 830 is positioned between the light 87 and the spectrometer 840, which is conducive to reducing the intensity of the light 87 before reaching the spectrometer 840. In some embodiments, the filter assembly 830 is an optical attenuator or includes an optical attenuator, such as a fixed attenuator or a variable attenuator. The filter assembly 830 may include one or more neutral density filters, rotating neutral density filters, variable optical attenuators (VOAs), beam splitters, polarizers, holes and / or pinholes, liquid crystal variable attenuators, combinations thereof, and the like. The filter assembly 830 may protect the detector of the spectrometer 840, which may be a delicate device that is easily damaged by exposure to excessive light. The optical attenuator may be used to reduce the intensity of the incident light beam to a level that is safe for the detector. The filter assembly 830 may improve the accuracy of the measurement. In some embodiments, reducing the intensity of the incident light beam can be beneficial to improve the accuracy of the measurements made by the spectrometer 840. This is because the response of some detectors can be non-linear, which can result in measurement errors if the intensity of the incident light beam is too high. The filter assembly 830 can increase the dynamic range of the measurements captured by the spectrometer 840. The dynamic range of a spectrometer is the range of light intensities that can be accurately measured. An optical attenuator can be used to extend the dynamic range of the spectrometer 840 by reducing the intensity of high intensity light beams so that they can be accurately measured.

[0124] exist Fig. 8A 86, the operation of the light source 800, the first lens 810, the beam steering assembly 820, and the filter assembly 830 may be calibrated and / or verified when the workbench 82 is in a first position outside the path of the light 86.

[0125] exist Figure 8B 86. Thus, information associated with light 86 may not be present in wavelength amplitude / intensity data 852 generated by spectrometer 840. Light 86 may be directed to various locations on substrate 84 via the movement of stage 82 in order to perform inspection of substrate 84. Substrate 84 may be similar in most respects to reference substrate 84. Figures 7A-7C The inspection of substrate 70 may be similar to that described above. That is, system 80 may inspect a calibration mask, a calibration wafer, a production mask, or a production wafer. Inspection of substrate 70 may be similar in most respects to that described above. Figure 1-7C In some embodiments, one or more parameters of light source 800 and first lens 810 are adjusted in response to the results of inspecting substrate 84 via light 86 .

[0126] During inspection of a production mask or a production wafer, the system 80 may direct a first light 86 having a first wavelength onto a first area of ​​the substrate 84, and then may direct a second light 86 having a second wavelength different from the first wavelength onto a second area. The first light 86 and the second light 86 may be selected by a wavelength selector, as shown in FIG. Figure 1-4E Additional light 86 of different wavelength(s) may again be directed to other areas of substrate 84 at the selection of the wavelength selector. System 80 may be based on, for example, a reference Figure 1 The described imaging system, such as a CCD or CMOS imaging device, senses the first light, the second light, and the additional light 86 to determine the presence of one or more defects in the first region, the second region, and / or other regions of the substrate 84 .

[0127] Fig.9A and 9B A system 90 is depicted according to various embodiments. The system 90 is similar in many respects to the reference Fig. 8A and 8B The described system 80 is similar, and like reference numerals refer to like elements. In the system 90, a compact beam collection device 920 is included, which facilitates installation into a limited space. The beam collection device 920 collects a portion of the light 86 and then reflects it into the collector lens 926 to collect the light intensity and spectral intensity into the spectrometer 840 via the optical fiber 930. The beam collection device 920 prevents the light 86 from returning via the optical path, which may destroy or damage the optical device or degrade the inspection results. The laser stability and power of the light source 800 can also be controlled by the system 90.

[0128] exist Fig.9A 9, stage 82 is in a first position such that light 86 is incident on low reflectivity mirror 924, which overlaps a portion of light 86 and reflects portion 97 of light 86 toward collector lens 926. Portion 97 of light 86 is directed into optical fiber 930 via collector lens 926. Since only portion 97 of light 86 is collected and reflected by low reflectivity mirror 924, the intensity of portion 97 of light 86 that reaches spectrometer 840 is sufficiently low that filter assembly 830 may be omitted in system 90.

[0129] exist Fig. 9B 8, stage 82 is in the second position, wherein substrate 84 is located in the optical path of light 86. Therefore, light 86 is reflected and / or absorbed by substrate 84 and is no longer partially transmitted to spectrometer 840 via mirror 924, lens 926, and optical fiber 930. In some embodiments, one or more parameters of light source 800 and first lens 810 are adjusted in response to the result of inspecting substrate 84 via light 86.

[0130] Fig.10 is a schematic diagram of a controller 1000 according to various embodiments. The controller 1000 may be a reference Figure 1 The controller 1000 may perform the following steps: Figure 1-9B Controller 1000 is described with reference to system 10 and method 50. Controller 1000 is also operable to perform the operations of systems 20, 30, 40, 80, 90.

[0131] exist Fig.10 In the embodiment of the present invention, the controller or control system 1000 includes a processor 1002, a memory 1000, a data interface 1010, and a network interface 1012. To simplify the description, some elements of the controller 1000 may be omitted from the view. For example, the controller 1000 may include a power supply (e.g., a voltage regulator), an analog-to-digital converter (ADC), a digital-to-analog converter (DAC), a pulse width modulation (PWM) controller, a clock and timing circuit, etc.

[0132] Control system 1000 generates output control signals for controlling the operation of one or more components of system 10. Control system 1000 may receive input signals from one or more components of system 10.

[0133] The control system 1000 includes a processor 1002 and a non-transitory computer-readable storage medium 1004 encoded with (i.e., storing) a computer program code 1006 (i.e., a set of executable instructions). The computer-readable storage medium 1004 is also encoded with instructions 1007 for interfacing with components of the system 10. The processor 1002 is electrically coupled to the computer-readable storage medium 1004 via a bus 1008. The processor 1002 is also electrically coupled to an I / O interface via the bus 1008. A network interface 1012 is also electrically connected to the processor 1002 via the bus 1008. The network interface 1012 is connected to a network 1014, enabling the processor 1002 and the computer-readable storage medium 1004 to be connected to external elements via the bus. The processor 1002 is configured to execute the computer program code 1006 encoded in the computer-readable storage medium 1004 so that the control system 1000 can be used to perform part or all of the operations described with respect to the system 10.

[0134] In some embodiments, processor 1002 is a central processing unit (CPU), a multiprocessor, a distributed processing system, an application specific integrated circuit (ASIC), and / or a suitable processing unit.

[0135] In some embodiments, the computer-readable storage medium 1004 is an electrical, magnetic, optical, electromagnetic, infrared, and / or semiconductor system (or device or apparatus). For example, the computer-readable storage medium 1004 includes a semiconductor or solid-state memory, a magnetic tape, a removable computer floppy disk, a random access memory (RAM), a read-only memory (ROM), a hard disk, and / or an optical disk. In some embodiments using optical disks, the computer-readable storage medium 1004 includes a compact disk read-only memory (CD-ROM), a compact disk read / write (CD-R / W), and / or a digital video disk (DVD).

[0136] In some embodiments, the storage medium 1004 stores computer program code 1006 configured to cause the control system 1000 to perform operations as described with respect to the system 10 and the method 50. In some embodiments, the storage medium 1004 also stores information required to perform operations as described with respect to the system 10 and the method 50, such as a set of executable instructions for performing operations as described with respect to the system 10 and the method 50.

[0137] In some embodiments, storage medium 1004 stores instructions 1007 for interfacing with system 10. Instructions 1007 enable processor 1002 to generate operating instructions readable by elements of system 10 to effectively implement operations as described with respect to system 10 and method 50.

[0138] Control system 1000 includes I / O interface 1010. I / O interface 1010 is coupled to external circuits. In some embodiments, I / O interface 1010 includes a keyboard, a keypad, a mouse, a trackball, a trackpad, and / or cursor direction keys for transmitting information and commands to processor 1002.

[0139] The control system 1000 also includes a network interface 1012 coupled to the processor 1002. The network interface 1012 allows the control system 1000 to communicate with a network 1014 to which one or more other computer systems are connected. The network interface 1012 includes: a wireless network interface, such as BLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA; or a wired network interface, such as ETHERNET, USB, or IEEE-1394.

[0140] The control system 1000 may be configured to receive information related to the spectrometers 110, 140 and the imaging device calibration apparatus 150 via the I / O interface 1010. The information is transmitted to the processor 1002 via the bus 1008 and then stored in the computer readable medium 1004 as parameters 1016. The control system 1000 may be configured to receive information related to the threshold value via the I / O interface 1010. In some embodiments, the threshold value is received from an operator. The information is stored in the computer readable medium 1004 as threshold value parameters 1018. For example, the threshold value parameters 1018 may be related to the reference value 1016. Figures 4A-4C 1018. In one example, the amplitude of the light at the selected wavelength may be compared to the threshold parameter 1018, and a determination may be made whether to adjust one or more parameters of the light source 400, the lenses 410, 450, the AOM 430, the wavelength selector 470, etc. In another example, the defect sensitivity measured in act 540 of method 50 may be compared to the threshold parameter 1018, and based on the comparison result (e.g., the defect sensitivity exceeds the threshold), appropriate parameters of the optical system may be selected in act 550.

[0141] During operation, in some embodiments, the processor 1002 executes a set of instructions to determine whether the amplitude of the light has exceeded or fallen below a threshold value. Based on the above determination, the processor 1002 generates a control signal to instruct one or more components of the system 10 to adjust its parameters. In some embodiments, the control signal is transmitted using the I / O interface 1010. In some embodiments, the control signal is transmitted using the network interface 1012.

[0142] The parameters adjusted via the control signal may include parameter(s) associated with the light source 200. For example, when the nonlinear light source 200 has a tunable wavelength, the wavelength may be modulated based on the type of the nonlinear light source 200.

[0143] Embodiments may provide advantages. Including a tunable or selectable light source with multiple wavelengths improves the calibration and / or inspection performance of different regions of a substrate such as a mask or wafer. Different regions may have different patterns, different depths, different materials, etc. Each region may be exposed to light of a wavelength that is favorable for detecting defects, which reduces missed defect signals and false defect detections.

[0144] According to at least one embodiment, a method includes: positioning a substrate in a light path of a multi-wavelength light source; generating a first detection result by exposing a first area of ​​the substrate to a first light, the first light having a first wavelength band, the first light being selected by the multi-wavelength light source; and generating a second detection result by exposing a second area of ​​the substrate to a second light, the second light having a second wavelength band that does not overlap with the first wavelength band, the second light being selected by the multi-wavelength light source.

[0145] According to at least one embodiment, a method includes: generating a first detection result by exposing a first area of ​​a substrate to first light of a first wavelength; generating a second detection result by exposing a second area of ​​the substrate to second light of a second wavelength; generating at least one parameter of an optical system based on the first detection result and the second detection result; depositing a plurality of particles on the first area and the second area; determining a defect sensitivity of an inspection system by exposing the plurality of particles to the first light and the second light; and, in response to the defect sensitivity exceeding a threshold, performing inspection based on the at least one parameter of the optical system.

[0146] According to at least one embodiment, a system includes a multi-wavelength light source, the multi-wavelength light source including: a light source; and a wavelength selector located in an optical path of light generated by the light source. The system also includes: a spectrometer operable to measure a spectrum of a first light selected by the wavelength selector; a mask stage operable to position a mask in the optical path; and a controller operable to adjust at least one parameter of the multi-wavelength light source in response to the spectrum of the first light.

[0147] The features of several embodiments have been summarized above so that those skilled in the art can better understand the detailed description that follows. Those skilled in the art should understand that they can easily use this disclosure as a basis for designing or modifying other processes and structures to perform the same purposes and / or achieve the same advantages as the embodiments described herein. Those skilled in the art should also be aware that such equivalent structures do not depart from the spirit and scope of the present disclosure, and that they can make various modifications, substitutions, and changes to this document without departing from the spirit and scope of the present disclosure.

Claims

1. A method comprising: positioning a substrate in a light path of a multi-wavelength light source; generating a first detection result by exposing a first area of ​​the substrate to a first light having a first wavelength band, the first light being selected by the multi-wavelength light source; as well as A second detection result is generated by exposing a second area of ​​the substrate to a second light having a second wavelength band that does not overlap with the first wavelength band, the second light being selected by the multi-wavelength light source.

2. The method according to claim 1, further comprising: The first light and the second light are generated by an acousto-optic modulator of the multi-wavelength light source.

3. The method according to claim 1, further comprising: The first light is selected by a wavelength selector.

4. The method according to claim 3, wherein: The selecting includes positioning an opening of the wavelength selector in a path of the first light by an actuator.

5. The method according to claim 4, wherein: The selecting includes adjusting a size of the opening based on digital data generated by a spectrometer that receives the first light.

6. The method according to claim 4, wherein: The positioning includes moving the opening via a piezoelectric transducer.

7. The method according to claim 1, wherein: The first region and the second region have different materials from each other.

8. A method comprising: generating a first detection result by exposing a first region of the substrate to first light of a first wavelength; generating a second detection result by exposing a second region of the substrate to second light of a second wavelength; generating at least one parameter of the optical system based on the first detection result and the second detection result; depositing a plurality of particles on the first region and the second region; determining a defect sensitivity of an inspection system by exposing the plurality of particles to the first light and the second light; as well as In response to the defect sensitivity exceeding a threshold, an inspection is performed based on at least one parameter of the optical system.

9. The method according to claim 8, wherein: Generating the at least one parameter includes generating a radio frequency signal, wherein the radio frequency signal drives an acousto-optic modulator of a light source, and the light source generates the first light and the second light.

10. A system comprising: Multi-wavelength light sources, including: Light source; and a wavelength selector located in the optical path of light generated by the light source; a spectrometer operable to measure a spectrum of the first light selected by the wavelength selector; a mask stage operable to position a mask in the optical path; and A controller is operable to adjust at least one parameter of the multi-wavelength light source in response to the spectrum of the first light.

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