Method and system for improving second harmonic representation precision based on spatial light regulation and control technology

Abstract

The invention relates to a method and system for improving second harmonic representation precision based on a spatial light regulation and control technology, and the method comprises the steps: adding a spatial light modulator in an incident light path of an SHG measurement platform, and correcting the inclination phase difference of an incident light beam; a light path adjuster is added in a detection light path of the SHG measurement platform, and multi-dimensional path adjustment is carried out on a detection light beam; according to the signal characteristics detected by the detector in the detection light path of the SHG measurement platform, the control parameters of the spatial light modulator, the light path adjuster and the sample table are regulated and controlled, the SHG signal receiving efficiency of the detector is improved, and the SHG characterization precision is further improved. According to the invention, it is ensured that the detected SHG signal is received efficiently, and the SHG characterization precision is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor detection technology, and in particular to a method and system for improving second harmonic characterization accuracy based on spatial light control technology. Background Art

[0002] Second harmonic generation (SHG), as a non-destructive and non-invasive detection technology, has been widely used in the semiconductor field. This technology can detect the electric field at the semiconductor interface without direct contact with the sample surface. SHG can be used to detect the surface flatness and impurities of semiconductor materials with central inversion symmetry. It can also characterize the number density and polarity of charges in dielectric films. By measuring the variation of SHG intensity with the polarization state of the incident light, the orientation information of the crystal can be obtained.

[0003] Since spatial light beams will produce dynamic tilt phase differences during atmospheric propagation, this will have a great impact on the beam effect, which will inevitably lead to a reduction in the efficiency of wafer detection of SHG signals. In addition, since the detection optical path has fewer control dimensions and only stays in the coarse adjustment stage, when using SHG to characterize defects in semiconductor wafers, the quality of the focused light spot will be reduced during the transmission of the incident fundamental frequency light, and the detector's receiving efficiency will be low, which will have an adverse effect on the SHG detection signal carrying defect information, ultimately leading to a reduction in the characterization accuracy of semiconductor wafers. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to disclose a method and system for improving the accuracy of second harmonic characterization based on spatial light control technology; solve the problem of low efficiency in detecting SHG signals and improve the accuracy of SHG characterization.

[0005] This invention discloses a method for improving the accuracy of second harmonic characterization based on spatial light control technology, comprising:

[0006] Step S1: adding a spatial light modulator to the incident light path of the SHG measurement platform to correct the tilt phase difference of the incident light beam;

[0007] Step S2: adding an optical path adjuster to the detection optical path of the SHG measurement platform to perform multi-dimensional path adjustment on the detection beam;

[0008] Step S3: According to the signal characteristics detected by the detector in the detection optical path of the SHG measurement platform, the control parameters of the spatial light modulator, the optical path adjuster and the sample stage are adjusted to improve the efficiency of the detector in receiving SHG signals and further improve the SHG characterization accuracy.

[0009] Furthermore, in step S3, the SPGD algorithm is used to precisely control the control parameters of the spatial light modulator, the optical path adjuster and the sample stage to correct the tilt phase difference of the incident light beam and compensate for the mechanical error of the detection optical path; the SPGD algorithm applies random perturbations to the control parameters in the performance evaluation function and completes the gradient estimation based on the change in the evaluation function after the perturbation.

[0010] Furthermore, the spatial light modulator is located between the polarizer and the objective lens in the incident light path, and has three control parameters: x-axis direction, y-axis direction and piston phase in a coordinate system based on the light modulator to adjust the tilt phase difference of the light beam.

[0011] Furthermore, the spatial light modulator is a transmissive spatial light modulator; the model of the spatial light modulator is determined according to the transmittance of the incident light beam working band and the modulation efficiency requirements; and the effective working area of ​​the spatial light modulator is more than 3 times the cross-section of the fundamental frequency light.

[0012] Furthermore, the optical path adjuster is located between the filter and the detector in the detection optical path; it includes first, second, third and fourth reflectors; after the detection light beam passes through the filter, it is reflected by the first, second, third and fourth reflectors in sequence and then detected by the detector; the first, second, third and fourth reflectors all have two control parameters in the x-axis direction and the y-axis direction in a coordinate system based on the reflector, which are used for multi-dimensional path adjustment of the detection light beam.

[0013] Furthermore, the iterative formula of the SPGD algorithm is:

[0014]

[0015] Where U (n) (s x ,s y ,s p ,v x ,v y ,v h ,l 1x ,l 1y ,l 2x ,l 2y ,l 3x ,l 3y ,l 4x ,l 4y ) is the control variable of the nth iteration, where (s x ,s y ,s p ) represent the x-axis direction control parameter, y-axis direction control parameter and piston phase control parameter of the spatial light modulator respectively; (v x ,v y ,v h) are the control parameters of the x-axis direction, y-axis direction, and z-axis direction of the sample stage respectively; (l 1x ,l 1y ,l 2x ,l 2y ,l 3x ,l 3y ,l 4x ,l 4y ) are the x-axis control parameters and y-axis control parameters of the four controllable mirrors respectively; r is the iteration weight, δJ (n) is the change of performance evaluation function before and after disturbance, J( n ) is the system performance evaluation function value before and after disturbance, δU (n) are statistically independent random disturbances.

[0016] Furthermore, the detector is a single-photon detector under the beam wavelength band, and the evaluation function is the average value of the detector reading E(t) over a period of time t0;

[0017] Furthermore, the detector is a spectrometer, and the evaluation function is the maximum value of the spectrum at the detection moment.

[0018] Furthermore, the iterative process during the SPGD algorithm control includes:

[0019] 1) Generate the pseudo-random code vector of the nth iteration and convert it into a random perturbation δU (n) , the random disturbances satisfy the mean of zero and the variance is equal;

[0020] 2) Apply the forward random disturbance and the reverse random disturbance to the driver of each parameter adjustment in turn, and obtain the evaluation function value of the forward disturbance of the nth iteration And the evaluation function value of negative perturbation

[0021] 3) Calculate the change of the evaluation function of the nth iteration based on the evaluation function values ​​of positive disturbance and negative disturbance

[0022] 4) The change of the evaluation function and the random disturbance δU of the nth step iteration (n) and the control variable U (n) Substitute into the iterative formula of the SPGD algorithm to obtain the control variable U of the n+1th step iteration (n+1) ;

[0023] Repeat the above iterative process until the set maximum number of iterations N is reached and then stop the iterative update.

[0024] The present invention also discloses a second harmonic characterization optical system for realizing the above-mentioned method for improving the second harmonic characterization accuracy based on spatial light control technology, comprising: an incident light path unit, a detection light path unit, a sample stage and a control unit; wherein,

[0025] The incident light path unit is generated by emitting the fundamental frequency light to the fundamental frequency light beam that meets the test conditions, and sequentially comprises a laser, a polarizer, a spatial light modulator and a first objective lens;

[0026] The fundamental frequency light beam that meets the test conditions output by the first objective lens irradiates the wafer to be tested on the sample stage;

[0027] The detection optical path unit, which follows the detection light beam reflected from the wafer to be tested to detect the second harmonic light beam carrying defect information, comprises a second objective lens, an analyzer, a filter, an optical path adjuster and a detector in sequence; the detector detects the second harmonic light beam carrying defect information;

[0028] The control unit runs the SPGD algorithm based on the detected second harmonic beam to precisely adjust the control parameters of the spatial light modulator, optical path adjuster, and sample stage, correct the tilt phase difference of the incident beam and compensate for the mechanical error of the detection optical path, thereby improving the efficiency of the detector in receiving SHG signals.

[0029] The present invention can achieve one of the following beneficial effects:

[0030] The present invention discloses a method and system for improving the accuracy of second harmonic characterization based on spatial light control technology. The method and system utilize a spatial light modulator to correct the tilt phase difference and shape the beam (for example, converting a Gaussian beam into a flat-top beam), and precisely control the system beam direction in real time to ensure that during the process of collecting the SHG signal of the wafer sample, the incident light can be focused on the wafer surface with high power density. In addition, by adding an optical path adjuster and applying SPGD algorithm drive control, the optical path system at the receiving end can be precisely controlled, thereby enhancing the detector's ability to receive signals, ensuring efficient reception of the detected SHG signal, and improving the SHG characterization accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0032] Figure 1 Schematic diagram of the structure of the SHG measurement platform in an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of an SHG characterization platform with a spatial light modulator in an embodiment of the present invention;

[0034] Figure 3Schematic diagram of a second harmonic characterization optical system in an embodiment of the present invention;

[0035] Figure numerals: 1-laser, 2-polarizer, 3-objective lens, 4-fundamental frequency light that meets the test conditions, 5-objective lens, 6-polarizer, 7-filter, 8-second harmonic beam carrying defect information, 9-detector, 10-wafer, 11-sample stage, 12-spatial light modulator, 13-optical path adjuster (including the first, second, third and fourth mirrors). DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, which constitute a part of this application and are used to illustrate the principles of the present invention together with the embodiments of the present invention.

[0037] like Figure 1 Figure 2 shows the structure of the SHG measurement platform. Fundamental frequency light is emitted from a laser and polarized by a polarizer to a specific polarization state. After being focused by an objective lens, the fundamental frequency light that meets the test requirements is incident on the wafer. The fundamental frequency light interacts with defects in the wafer to produce SHG. The beam reflected from the wafer is collimated by the objective lens and then passes through an analyzer to produce probe light with a specific polarization state. After the fundamental frequency light is filtered out by a filter, the SHG light carrying wafer defect information is received by a detector. Furthermore, by controlling the movement of the sample stage, defects at different locations on the wafer can be detected. Instruments in the incident light path work in conjunction with those in the detection light path to obtain SHG signals at different incident angles, enabling further quantitative analysis of defect information.

[0038] Since spatial light beams will produce dynamic tilt phase differences during atmospheric propagation, this will have a great impact on the beam effect, which will inevitably lead to a reduction in the efficiency of wafer detection of SHG signals. In addition, since the detection optical path has fewer control dimensions and only stays in the coarse adjustment stage, when using SHG to characterize defects in semiconductor wafers, the quality of the focused light spot will be reduced during the transmission of the incident fundamental frequency light, and the detector's receiving efficiency will be low, which will have an adverse effect on the SHG detection signal carrying defect information, ultimately leading to a reduction in the characterization accuracy of semiconductor wafers.

[0039] One embodiment of the present invention discloses a method for improving the accuracy of second harmonic characterization based on spatial light control technology, comprising:

[0040] Step S1, adding a spatial light modulator in the incident light path of the SHG measurement platform to correct the tilt phase difference of the incident light beam;

[0041] The tilt phase difference of the light beam is precisely controlled by the spatial light modulator to ensure that the incident fundamental frequency light can be focused on the wafer surface with high quality and high power density;

[0042] Step S2: adding an optical path adjuster to the detection optical path of the SHG measurement platform to perform multi-dimensional path adjustment on the detection beam;

[0043] By adjusting the detection beam's path in multiple dimensions, the mechanical error of the detection light path can be compensated.

[0044] Step S3: According to the signal characteristics detected by the detector in the detection optical path of the SHG measurement platform, the control parameters of the spatial light modulator, the optical path adjuster and the sample stage are adjusted to improve the efficiency of the detector in receiving SHG signals and further improve the SHG characterization accuracy.

[0045] Specifically, in step S3, the SPGD algorithm (stochastic parallel gradient descent algorithm) is used to precisely control the control parameters of the spatial light modulator, optical path adjuster and sample stage to correct the tilt phase difference of the incident light beam and compensate for the mechanical error of the detection optical path; the SPGD algorithm applies random perturbations to the control parameters in the performance evaluation function, and then completes the gradient estimation based on the change in the evaluation function after the perturbation, thereby improving the efficiency of the detector in receiving SHG signals.

[0046] The schematic diagram of the SHG measurement platform using the above-mentioned method of improving the second harmonic characterization accuracy based on spatial light control technology is shown in the figure. Figure 2 shown.

[0047] Specifically, the spatial light modulator is located between the polarizer and the objective lens in the incident light path, and has three control parameters: x-axis direction, y-axis direction and piston phase, so as to adjust the tilt phase difference of the light beam.

[0048] Preferably, the spatial light modulator is a transmissive spatial light modulator; the model of the spatial light modulator is determined according to the transmittance of the incident light beam working band and the modulation efficiency requirements; and the effective working area of ​​the spatial light modulator is more than 3 times the cross-section of the fundamental frequency light.

[0049] Specifically, the optical path adjuster is located between the filter and the detector in the detection optical path; it includes a first, second, third and fourth reflectors; the first, second, third and fourth reflectors constitute a multi-dimensional detection path, and the detection light beam passes through the filter and is reflected by the first, second, third and fourth reflectors in sequence before being detected by the detector; the first, second, third and fourth reflectors all have two control parameters in the x-axis direction and the y-axis direction in a coordinate system based on the reflector, which are used for multi-dimensional path adjustment of the detection light beam.

[0050] In a more preferred solution, a filter may be further added between the optical path adjuster and the detector to filter out optical interference signals introduced during the path adjustment process.

[0051] In step S3, the control parameters of the spatial light modulator, the optical path adjuster, and the sample stage are output as analog voltage signals. Multiple control parameters are involved in the iterative process, and the iterative formula of the SPGD algorithm is expressed as:

[0052]

[0053] Where U (n) (s x ,s y ,s p ,v x ,v y ,v h ,l 1x ,l 1y ,l 2x ,l 2y ,l 3x ,l 3y ,l 4x ,l 4y ) is the control variable of the nth iteration, where (s x ,s y ,s p ) represent the x-axis direction control parameter, y-axis direction control parameter and piston phase control parameter in the coordinate system based on the spatial light modulator; (v x ,v y ,v h ) are the x-axis direction control parameters, y-axis direction control parameters, and z-axis direction control parameters in the sample stage coordinate system; (l 1x ,l 1y ,l 2x ,l 2y ,l 3x ,l 3y ,l 4x ,l 4y ) are the x-axis control parameters and y-axis control parameters of the four controllable reflectors respectively; r is the iteration weight, and when the system performance index needs to be optimized to the maximum value, r is a positive value; δJ (n) is the change of performance evaluation function before and after disturbance, J (n) is the system performance evaluation function value before and after disturbance, δU (n) are statistically independent random disturbances.

[0054] Preferably, the signal received by the detector is used as an evaluation function, and different evaluation functions can be selected for different detector types.

[0055] When the detector is a single-photon detector in the beam band, the evaluation function is the average value of the detector reading E(t) over a period of time t0;

[0056] When the detector is a spectrometer, the evaluation function is the maximum value of the spectrum at the detection moment J=Max(S(λ)); wherein S(λ) is the spectrum value of the light beam with wavelength λ.

[0057] Specifically, the iterative process during the SPGD algorithm control includes:

[0058] 1) Generate the pseudo-random code vector of the nth iteration and convert it into a random perturbation δU (n) , the random disturbances satisfy the mean of zero and the variance is equal;

[0059] Among them, the initial control variable U( 0 ) is a preset value.

[0060] 2) Apply the forward random disturbance and the reverse random disturbance to the driver of each parameter adjustment in turn, and obtain the evaluation function value of the forward disturbance of the nth iteration And the evaluation function value of negative perturbation

[0061] Evaluation function value of positive perturbation

[0062] Evaluation function value of negative disturbance

[0063] 3) Calculate the change of the evaluation function of the nth iteration based on the evaluation function values ​​of positive disturbance and negative disturbance

[0064] 4) The change of the evaluation function and the random disturbance δU of the nth step iteration (n) and the control variable U( n ) is introduced into the iterative formula of the SPGD algorithm to obtain the control variable U( n+1 );

[0065] Repeat the above iterative process until the set maximum number of iterations N is reached and then stop the iterative update.

[0066] In this embodiment, a spatial light modulator is used to correct the tilt phase difference and shape the beam (for example, a Gaussian beam is converted into a flat-top beam), and the system beam direction is precisely controlled in real time to ensure that during the collection of the SHG signal of the wafer sample, the incident light can be focused on the wafer surface with a high power density. In addition, by adding a reflector and applying the SPGD algorithm to drive the control, the optical path system at the receiving end is precisely controlled, so that the detector's ability to receive signals is enhanced, ensuring efficient reception of the detected SHG signal and improving the SHG characterization accuracy.

[0067] This embodiment also discloses a second harmonic characterization optical system based on the above-mentioned spatial light control technology to improve the second harmonic characterization accuracy method. Figure 3 As shown, it includes: an incident light path unit, a detection light path unit, a sample stage and a control unit; wherein,

[0068] The incident light path unit is generated by emitting the fundamental frequency light to the fundamental frequency light beam that meets the test conditions, and sequentially comprises a laser, a polarizer, a spatial light modulator and a first objective lens;

[0069] The fundamental frequency light beam that meets the test conditions output by the objective lens irradiates the wafer to be tested on the sample stage;

[0070] The detection optical path unit, which follows the detection light beam reflected from the wafer to be tested to detect the second harmonic light beam carrying defect information, comprises a second objective lens, an analyzer, a filter, an optical path adjuster and a detector in sequence; the detector detects the second harmonic light beam carrying defect information;

[0071] The control unit runs the SPGD algorithm based on the detected second harmonic beam to precisely adjust the control parameters of the spatial light modulator, optical path adjuster, and sample stage, correct the tilt phase difference of the incident beam and compensate for the mechanical error of the detection optical path, thereby improving the efficiency of the detector in receiving SHG signals.

[0072] The specific technical details and beneficial effects in this solution are the same as those in the previous solution in the embodiment. Please refer to them for details and I will not go into details here.

[0073] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for improving the accuracy of second harmonic characterization based on spatial light control technology, characterized in that: include: Step S1: adding a spatial light modulator to the incident light path of the SHG measurement platform to correct the tilt phase difference of the incident light beam; Step S2: adding an optical path adjuster to the detection optical path of the SHG measurement platform to perform multi-dimensional path adjustment on the detection beam; Step S3: According to the signal characteristics detected by the detector in the detection optical path of the SHG measurement platform, the control parameters of the spatial light modulator, the optical path adjuster and the sample stage are adjusted to improve the efficiency of the detector in receiving SHG signals and further improve the SHG characterization accuracy.

2. The method for improving the accuracy of second harmonic characterization based on spatial light control technology according to claim 1, characterized in that: In step S3, the SPGD algorithm is used to precisely adjust the control parameters of the spatial light modulator, optical path adjuster and sample stage to correct the tilt phase difference of the incident light beam and compensate for the mechanical error of the detection optical path; the SPGD algorithm applies random perturbations to the control parameters in the performance evaluation function and completes the gradient estimation based on the change in the evaluation function after the perturbation.

3. The method for improving the accuracy of second harmonic characterization based on spatial light control technology according to claim 2, characterized in that: The spatial light modulator is located between the polarizer and the objective lens in the incident light path and has three control parameters, namely, the x-axis direction, the y-axis direction and the piston phase, in a coordinate system based on the light modulator to adjust the tilt phase difference of the light beam.

4. The method for improving second harmonic characterization accuracy based on spatial light control technology according to claim 3, characterized in that: The spatial light modulator is a transmissive spatial light modulator; the model of the spatial light modulator is determined according to the transmittance of the incident light beam working band and the modulation efficiency requirements; and the effective working area of ​​the spatial light modulator is more than 3 times the cross-section of the fundamental frequency light.

5. The method for improving second harmonic characterization accuracy based on spatial light control technology according to claim 2, characterized in that: The optical path adjuster is located between the filter and the detector in the detection optical path; it includes first, second, third and fourth reflectors; after the detection light beam passes through the filter, it is reflected by the first, second, third and fourth reflectors in sequence and then detected by the detector; the first, second, third and fourth reflectors all have two control parameters in the x-axis direction and the y-axis direction in a coordinate system based on the reflector, which are used for multi-dimensional path adjustment of the detection light beam.

6. The method for improving second harmonic characterization accuracy based on spatial light control technology according to claim 2, characterized in that: The iterative formula of the SPGD algorithm is: Where U (n) (s x ,s y ,s p ,v x ,v y ,v h ,l 1x ,l 1y ,l 2x ,l 2y ,l 3x ,l 3y ,l 4x ,l 4y ) is the control variable of the nth iteration, where (s x ,s y ,s p ) represent the x-axis direction control parameter, y-axis direction control parameter and piston phase control parameter of the spatial light modulator respectively; (v x ,v y ,v h ) are the control parameters of the x-axis direction, y-axis direction, and z-axis direction of the sample stage respectively; (l 1x ,l 1y ,l 2x ,l 2y ,l 3x ,l 3y ,l 4x ,l 4y ) are the x-axis control parameters and y-axis control parameters of the four controllable mirrors respectively; r is the iteration weight, δJ (n) is the change of performance evaluation function before and after disturbance, J( n ) is the system performance evaluation function value before and after disturbance, δU (n) are statistically independent random disturbances.

7. The method for improving second harmonic characterization accuracy based on spatial light manipulation technology according to claim 6, characterized in that: The detector is a single-photon detector under the beam band, and the evaluation function is the average value of the detector reading E(t) over a period of time t0; 8. The method for improving second harmonic characterization accuracy based on spatial light control technology according to claim 6, characterized in that: The detector is a spectrometer, and the evaluation function is the maximum value of the spectrum at the detection moment.

9. The method for improving second harmonic characterization accuracy based on spatial light manipulation technology according to claim 2, characterized in that: The iterative process when the SPGD algorithm is controlling includes: 1) Generate the pseudo-random code vector of the nth iteration and convert it into a random perturbation δU (n) , the random disturbances satisfy the mean of zero and the variance is equal; 2) Apply the forward random disturbance and the reverse random disturbance to the driver of each parameter adjustment in turn, and obtain the evaluation function value of the forward disturbance of the nth iteration And the evaluation function value of negative perturbation 3) Calculate the change of the evaluation function of the nth iteration based on the evaluation function values ​​of positive disturbance and negative disturbance 4) The change of the evaluation function and the random disturbance δU of the nth step iteration (n) and the control variable U( n ) is introduced into the iterative formula of the SPGD algorithm to obtain the control variable U( n+1 ); Repeat the above iterative process until the set maximum number of iterations N is reached and then stop the iterative update.

10. A second harmonic characterization optical system for implementing the method for improving second harmonic characterization accuracy based on spatial light manipulation technology as described in any one of claims 1 to 9, characterized in that: include: Incident light path unit, detection light path unit, sample stage and control unit; wherein, The incident light path unit is generated by emitting the fundamental frequency light to the fundamental frequency light beam that meets the test conditions, and sequentially comprises a laser, a polarizer, a spatial light modulator and a first objective lens; The fundamental frequency light beam that meets the test conditions output by the first objective lens irradiates the wafer to be tested on the sample stage; The detection optical path unit, which follows the detection light beam reflected from the wafer to be tested to detect the second harmonic light beam carrying defect information, comprises a second objective lens, an analyzer, a filter, an optical path adjuster and a detector in sequence; the detector detects the second harmonic light beam carrying defect information; The control unit runs the SPGD algorithm based on the detected second harmonic beam to precisely adjust the control parameters of the spatial light modulator, optical path adjuster, and sample stage, correct the tilt phase difference of the incident beam and compensate for the mechanical error of the detection optical path, thereby improving the efficiency of the detector in receiving SHG signals.

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