An Automatic Test and Sorting Method for the MTF Value of a Chip

Abstract

The present invention relates to the technical field of physical analysis, and particularly relates to an automatic test and sorting method for the MTF value of a chip, which includes: obtaining MTF charts under each light source brightness in several cyclic tests of the chip to be tested, determining the comprehensive reliability of each MTF chart, combining the curves in the MTF charts under adjacent different light source brightnesses in the same cyclic test to determine the light source brightness suitability factor of each MTF chart, and then combining the curves in the MTF charts in different cyclic tests under the same light source brightness to determine the excellence of each light source brightness, so as to determine the optimal MTF value of the chip to be tested for sorting the chip to be tested. The present invention ensures the accuracy of sorting the chip to be tested by selecting the optimal light source brightness during the test of the chip to be tested.

Description

Technical Field

[0001] The present invention relates to the technical field of physical analysis, and particularly relates to an automatic test and sorting method for the MTF value of a chip. Background Art

[0002] MTF (Modulation Transfer Function), namely the modulation transfer function, is a term in the field of optical engineering and is used to evaluate the performance of a lens (optical system). It describes the ability of an optical system to transfer different spatial frequency components and reflects the degree to which the system preserves image details. The MTF value ranges from 0 to 1, and the higher the value, the stronger the ability of the optical system to preserve image details and the higher the imaging quality. Therefore, the chips can be sorted by obtaining the MTF value of the chip to be tested and setting a qualified threshold.

[0003] Existing problems: In preparing the automatic test environment for the MTF value of a chip, the selection of the light source brightness is one of the key factors affecting the test accuracy. The sensitivity (ISO value) of different chips is different, so different light source brightnesses are required in the automatic test environment for the MTF value of different chips. An inappropriate light source brightness will make the obtained MTF value inaccurate, thus affecting the sorting of chips. Summary of the Invention

[0004] The present invention provides an automatic test and sorting method for the MTF value of a chip to solve the existing problems.

[0005] The automatic test and sorting method for the MTF value of a chip of the present invention adopts the following technical solutions:

[0006] An embodiment of the present invention provides an automatic test and sorting method for the MTF value of a chip, and the method includes the following steps:

[0007] Obtain MTF charts for each light source brightness in several cyclic tests of the chip to be tested under different light source brightnesses; the MTF charts include curves of 30 lines in the tangential direction, curves of 30 lines in the radial direction, curves of 10 lines in the tangential direction, and curves of 10 lines in the radial direction; the horizontal axis of the MTF chart represents the distance from the monitoring point to the optical center of the lens, and the vertical axis represents the contrast;

[0008] Determine the reliability of each curve according to the peaks and valleys on each curve in each MTF chart;

[0009] Determine the comprehensive reliability of each MTF chart according to the reliability of each curve in each MTF chart and the difference between curves of the same-sized lines in different directions;

[0010] Determine the light source brightness suitability factor for each MTF chart based on the comprehensive reliability of each MTF chart and the curves in the MTF charts under different light source brightnesses adjacent to each other in the same cycle test;

[0011] Determine the excellence of each light source brightness based on the light source brightness suitability factor of each MTF chart and the curves in the MTF charts under different cycle tests with the same light source brightness;

[0012] Determine the optimal MTF value of the chip to be tested according to the excellence of each light source brightness; sort the chips to be tested according to the optimal MTF value of the chips to be tested.

[0013] Further, the specific steps included in determining the reliability of each curve are as follows:

[0014] Denote any curve in any MTF chart as curve A;

[0015] Divide curve A into several curve segments using the peak and valley in curve A;

[0016] Calculate the difference between the maximum contrast and the minimum contrast in the th curve segment of curve A, and denote the ratio of the difference to the size of the horizontal axis range where the th curve segment of curve A is located as the first ratio;

[0017] Calculate the product of the reciprocal of the median in the horizontal axis range where the th curve segment of curve A is located and the first ratio, and take it as the first product of the th curve segment of curve A;

[0018] Determine the reliability of curve A according to the first product of each curve segment of curve A and all the contrasts in curve A.

[0019] Further, the specific steps included in determining the reliability of curve A are as follows:

[0020] Calculate the product of the sum value of the first products of all the curve segments of curve A and the variance of all the contrasts in curve A, and denote it as the second product;

[0021] Take the product of the inverse proportional normalization value of the second product and the mean value of all the contrasts in curve A as the reliability of curve A.

[0022] Further, the specific steps included in determining the comprehensive reliability of each MTF chart are as follows:

[0023] Denote the two curves of the 30 - line in the tangential and radial directions in any MTF chart as curve A1 and curve A2 respectively;

[0024] Calculate the normalized value of the absolute value of the difference between the ordinates corresponding to the same abscissa of curve A1 and curve A2 as the difference value corresponding to each abscissa, and form a difference curve with the difference values corresponding to all abscissas;

[0025] On the difference curve, divide several curve segments with difference values greater than a preset first threshold, and record them as abnormal curve segments;

[0026] Denote the mean value of the reliabilities of curve A1 and curve A2 as the first mean value;

[0027] Determine the comprehensive reliability of curve A1 and curve A2 according to the first mean value and each abnormal curve segment on the difference curve;

[0028] In any one of the MTF charts, obtain the comprehensive reliability of the two curves of the 10-line in the tangential and radial directions according to the acquisition method of the comprehensive reliability of the two curves of the 30-line in the tangential and radial directions, and take the mean value of the comprehensive reliability of the two curves of the 30-line in the tangential and radial directions and the comprehensive reliability of the two curves of the 10-line in the tangential and radial directions as the comprehensive reliability of any one MTF chart.

[0029] Further, the specific steps included in determining the comprehensive reliability of curve A1 and curve A2 are as follows:

[0030] On the difference curve, calculate the normalized value of the size of the horizontal axis range where the th abnormal curve segment is located and the product of the maximum difference value in the th abnormal curve segment as the third product, calculate the product of the reciprocal of the median value within the horizontal axis range where the th abnormal curve segment is located and the third product as the fourth product of the th abnormal curve segment, and take the product of the inverse proportional normalized value of the sum of the fourth products of all abnormal curve segments and the first mean value as the comprehensive reliability of curve A1 and curve A2.

[0031] Further, the specific steps included in determining the light source brightness suitability factor of each MTF chart are as follows:

[0032] In any one cycle test, sort all types of light source brightnesses from small to large, and obtain the MTF charts of the chip under test for each light source brightness in sequence according to the sorting to form an MTF chart sequence;

[0033] In the MTF chart sequence, calculate the Pearson correlation coefficient between the curves of the 30-line in the tangential direction of the th and the th MTF charts as the first correlation coefficient, and calculate the Zhang and the Pearson correlation coefficient between the curves of the 30th line in the radial direction in the Zhang MTF chart, as the second correlation coefficient, calculate the normalized value of the sum of the first correlation coefficient and the second correlation coefficient, as the first sum value, calculate the Zhang and the Absolute value of the difference in the comprehensive reliability of the two curves of the 30th line in the tangential and radial directions in the Zhang MTF chart, as the first difference, the ratio of the first sum value to the first difference, as the Zhang and the Curve similarity of the 30th line in the tangential and radial directions in the Zhang MTF chart ;

[0034] According to the acquisition method of, obtain the Curve similarity of the 10th line in the tangential and radial directions in the Zhang MTF chart between the Zhang and the Zhang MTF chart, the the Curve similarity of the 10th line in the tangential and radial directions in the Zhang MTF chart between the Zhang and the Zhang MTF chart, the and the Curve similarity of the 30th line in the tangential and radial directions in the Zhang MTF chart between the Zhang and the Zhang MTF chart; ;

[0035] Take , , and the mean value of, as the second mean value, multiply the second mean value by the comprehensive reliability of the Zhang MTF chart in the MTF chart sequence, as the light source brightness suitability factor of the Zhang MTF chart in the MTF chart sequence.

[0036] Furthermore, the determination of the excellence of each light source brightness includes the following specific steps:

[0037] In all cyclic tests, obtain all MTF charts corresponding to the th light source brightness, as the reference MTF charts;

[0038] According to the trend changes of each curve in each reference MTF chart, determine the credibility of each data point on each curve in each reference MTF chart;

[0039] Denote the curves of the 30th line in the tangential direction in any two reference MTF charts as curve A4 and curve A5 respectively;

[0040] Use the DTW algorithm to match curve A4 and curve A5, obtaining several matching pairs and the DTW distance of each matching pair;

[0041] Calculate the mean of the credibility of two data points in the th matching pair between curve A4 and curve A5 as the third mean, and multiply the third mean by the DTW distance of the th matching pair between curve A4 and curve A5 as the fifth product of the th matching pair between curve A4 and curve A5. Take the sum of the fifth products of all matching pairs between curve A4 and curve A5 as the initial inconsistency between curve A4 and curve A5;

[0042] For any two reference MTF charts, obtain the initial inconsistency of the curve of the 30th line in the tangential direction in the same way as the acquisition method, and obtain the initial inconsistency of the curve of the 30th line in the radial direction , the initial inconsistency of the curve of the 10th line in the tangential direction and the initial inconsistency of the curve of the 10th line in the radial direction . Take the inverse proportional normalization value of the sum of , , and as the overall curve shape consistency of any two reference MTF charts;

[0043] Denote the mean of the overall curve shape consistency of all any two reference MTF charts as the fourth mean, and denote the mean of the light source brightness suitability factors corresponding to all reference MTF charts as the fifth mean. Take the product of the fourth mean and the fifth mean as the goodness of the rd light source brightness.

[0044] Furthermore, the specific steps for determining the credibility of each data point on each curve in each reference MTF chart are as follows:

[0045] Denote any curve in any reference MTF chart as curve A3;

[0046] Divide curve A3 into several curve segments based on the peaks and valleys in curve A3, and denote the curve segments with the starting point as the valley or the ending point as the peak as the rising trend curve segments;

[0047] Calculate the difference between the maximum contrast and the minimum contrast in the th rising trend curve segment of curve A3, and denote the ratio of the difference to the size of the horizontal axis range where the th rising trend curve segment of curve A3 is located as the second ratio. Calculate the The product of the reciprocal of the median within the horizontal axis range where the th rising trend curve segment is located and the second ratio is used as the th data untrustworthiness of the rising trend curve segment ;

[0048] Take as the credibility of each data point in the th rising trend curve segment of curve A3; where is a linear normalization function;

[0049] Set the credibility of each data point on curve A3 that is not in the rising trend curve segment to a preset second threshold.

[0050] Furthermore, the specific steps for determining the optimal MTF value of the chip to be tested are as follows:

[0051] Among the excellences of all light source brightnesses, use the light source brightness corresponding to the maximum excellence as the optimal light source brightness of the chip to be tested;

[0052] Obtain the MTF values at a preset specific spatial frequency in all MTF charts of the chip to be tested under the optimal light source brightness, and use the average value of the MTF values at the preset specific spatial frequency in all the MTF charts as the optimal MTF value of the chip to be tested.

[0053] Furthermore, the specific steps for sorting the chip to be tested are as follows:

[0054] When the optimal MTF value is greater than the preset qualified threshold, determine that the chip to be tested meets the standard;

[0055] When the optimal MTF value is less than or equal to the preset qualified threshold, determine that the chip to be tested does not meet the standard.

[0056] The beneficial effects of the technical solution of the present invention are:

[0057] In an embodiment of the present invention, several cyclic tests of the chip to be tested are performed under different light source brightnesses, and MTF charts under each light source brightness are obtained. The comprehensive reliability of each MTF chart is determined. Thus, by analyzing the changes in the curves in the MTF chart and the differences in the curves at the same spatial frequency, it is judged whether the MTF chart is reliable, which is used as a basic parameter for selecting the optimal light source brightness. Combining the curves in the MTF charts under adjacent different light source brightnesses in the same cyclic test, the light source brightness suitability factor of each MTF chart is determined. Thus, by analyzing the similarity of the curves in the MTF charts under different light source brightnesses, the accuracy of selecting the optimal light source brightness is ensured. Then, combining the curves in the MTF charts in different cyclic tests under the same light source brightness, the goodness of each light source brightness is determined. Thus, by analyzing the shape consistency of the curves in the MTF charts in different cyclic tests under the same light source brightness, the accuracy of selecting the optimal light source brightness is further ensured. Finally, according to the optimal light source brightness, the optimal MTF value of the chip to be tested is determined, which is used to sort the chip to be tested. Thus, the present invention ensures the accuracy of sorting the chip to be tested by selecting the optimal light source brightness during the test process. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for describing the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0059] Figure 1 is a flowchart of the steps of an automatic test and sorting method for the MTF value of a chip according to the present invention;

[0060] Figure 2 is a schematic diagram of the test card and the moving distance from the optical center of the lens;

[0061] Figure 3 is an MTF chart. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation manners, structures, features, and effects of an automatic test and sorting method for the MTF value of a chip according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs.

[0064] The following specifically describes the specific solution of an automatic test and sorting method for the MTF value of a chip provided by the present invention in conjunction with the accompanying drawings.

[0065] Please refer to Figure 1 , which shows a flowchart of the steps of an automatic test and sorting method for the MTF value of a chip provided by an embodiment of the present invention. The method includes the following steps:

[0066] Step S001: Obtain MTF charts for each light source brightness in several cyclic tests of the chip to be tested under different light source brightnesses; the MTF charts include curves of 30 lines in the tangential direction, curves of 30 lines in the radial direction, curves of 10 lines in the tangential direction, and curves of 10 lines in the radial direction; the horizontal axis of the MTF chart represents the distance of the monitoring point from the optical center of the lens, and the vertical axis represents the contrast ratio.

[0067] The purpose of this embodiment is to obtain the optimal MTF value from the MTF charts of the chip under different light source brightnesses to ensure the accuracy of chip sorting.

[0068] Set up a stable test environment, including a light source, the chip to be tested, an imaging device, etc. Under the condition that other conditions remain unchanged, for the same chip to be tested, preset several different light source brightnesses, and sequentially obtain the MTF charts for each light source brightness from small to large as a cyclic test, and obtain the MTF charts of the chip to be tested for each light source brightness in several cyclic tests.

[0069] It should be noted that: in this embodiment, the range of the light source brightness is 50 to 300 lumens (lm), and a test is performed every 10 lumens. The number of cycles of the cyclic test is 10, and this is used as an example for description.

[0070] The specific process of obtaining the MTF chart is as follows: In this embodiment, a test card with 30 lines and 10 lines is used to obtain the contrast ratio of the image formation every 5 millimeters (mm) from the center of the image to the edge, that is, in the direction from the center of the image to the edge, the center of the image, 5 mm, 10 mm, 15 mm, and 20 mm away from the center of the image are used as monitoring points respectively to obtain the contrast ratio of the image formation at each monitoring point. The schematic diagram of the moving distance of the test card from the optical center of the lens is as Figure 2 shown. The MTF chart is as Figure 3 shown.

[0071] It should be noted that: Figure 2The thin line of 30 lines is used to test the resolution, and the thick line of 10 lines is used to test the contrast. V2 is the tangential line (the line perpendicular to the center of the screen towards the edge), which is represented as a dashed line (U1 and U3) on the MTF chart. V1 is the radial line (the line parallel to the center of the screen towards the edge), which is represented as a solid line (U2 and U4) on the MTF chart. Among them, the radial and tangential directions can help understand the imaging performance of the optical system in different directions. Therefore, each MTF chart contains a curve of 30 lines in the tangential direction, a curve of 30 lines in the radial direction, a curve of 10 lines in the tangential direction, and a curve of 10 lines in the radial direction, as Figure 3 shown, where Figure 3 the four curves in Figure 3 from top to bottom are the curve represented by the dashed line U1 for 10 lines in the tangential direction, the curve represented by the solid line U2 for 10 lines in the radial direction, the curve represented by the dashed line U3 for 30 lines in the tangential direction, and the curve represented by the solid line U4 for 30 lines in the radial direction. Figure 2 The horizontal axis of the MTF chart in Figure 3 represents the distance of the monitoring point from the optical center of the lens, with the unit of millimeter (mm), and the vertical axis represents the contrast, with the unit of percentage (%). Among them,

[0072] Step S002: Determine the reliability of each curve according to the peaks and valleys on each curve in each MTF chart.

[0073] In the MTF chart, the higher the contrast of the curve, the more accurately the imaging chip can capture the details of the pattern. And the smoother the curve, the more uniform the change in the imaging performance of the optical system during the process of moving away from the optical center of the lens, without obvious performance fluctuations or mutations. This indicates that the contrast transfer ability of the system when processing different detail sizes is relatively stable, which is beneficial to providing consistent image quality. A smooth curve may also mean that less noise and errors are introduced during the testing process, making the data more reliable.

[0074] Preferably, in an embodiment of the present invention, the method for obtaining the reliability of each curve in each MTF chart includes:

[0075] Denote any one curve in any one MTF chart as curve A.

[0076] Use the peak-valley detection algorithm to obtain the peaks and valleys in curve A, and divide curve A into several curve segments based on the peaks and valleys in curve A. Among them, the peak-valley detection algorithm is a well-known technology, and the specific method will not be introduced here.

[0077] Calculate the The difference between the maximum contrast and the minimum contrast in the -th curve segment of curve A, and the ratio of this difference to the size of the horizontal axis range where the -th curve segment of curve A is located is denoted as the first ratio. Calculate the product of the reciprocal of the median within the horizontal axis range where the -th curve segment of curve A is located and the first ratio, and take it as the first product of the

[0078] -th curve segment of curve A. Calculate the product of the sum value of the first products of all curve segments of curve A and the variance of all contrasts in curve A, and denote it as the second product. Take the product of the inverse proportional normalization value of the second product and the mean value of all contrasts in curve A as the reliability of curve A.

[0079]

[0080] In the formula, is the reliability of curve A, is the mean value of all contrasts in curve A. The larger is, the more accurately the details of the pattern can be captured. is the variance of all contrasts in curve A. The smaller is, the greater the overall smoothness of curve A, and the more reliable curve A is. is the number of curve segments into which curve A is divided. is the -th curve segment of curve A, which is the difference between the maximum contrast and the minimum contrast. represents the size of the horizontal axis range where the -th curve segment of curve A is located. is the first ratio. The larger is, the greater the contrast change that occurs under a smaller distance change, that is, a large contrast mutation occurs locally in the area where the -th curve segment of curve A is located. is the median within the horizontal axis range where the -th curve segment of curve A is located. The smaller is, the closer it is to the optical center of the lens. Usually, the imaging quality in the center area of the lens is the highest, and the imaging quality in the center area directly reflects the basic performance of the lens. That is, the imaging quality analysis closer to the lens center is more important. Therefore, take as the weight of is the first product of the -th curve segment of curve A. The larger is, the smaller the local smoothness of curve A. is the exponential function with the natural constant as the base. In this embodiment, is used to present the inverse proportional relationship and normalization processing of the second product. The implementer can set the inverse proportional function and normalization function according to the actual situation. Therefore, represents the comprehensive smoothness of curve A. The larger its value, the smoother it is. Therefore, the larger, the more reliable curve A is.

[0081] Step S003: Determine the comprehensive reliability of each MTF chart according to the reliability of each curve in each MTF chart and the differences of curves of the same-sized lines in different directions.

[0082] Since 30 lines usually represent higher spatial frequencies, that is, the details of the image, while 10 lines represent lower spatial frequencies, that is, the larger features of the image. At the same spatial frequency, when the curves in different directions are more consistent, it means that the lens shows similar capabilities in processing details in different directions, which means that the image maintains good contrast and detail retention capabilities throughout the field of view.

[0083] Preferably, in an embodiment of the present invention, the method for obtaining the comprehensive reliability of each MTF chart includes:

[0084] The two curves of 30 lines in the tangential and radial directions in any one MTF chart are respectively denoted as curve A1 and curve A2.

[0085] Calculate the normalized value of the absolute value of the difference between the ordinates corresponding to each same abscissa of curve A1 and curve A2 as the difference value corresponding to each abscissa, and form a difference curve with the difference values corresponding to all abscissas.

[0086] Among them, for the normalized value of the absolute value of the difference, in this embodiment, a linear normalization function is used to normalize the absolute value of the difference to between 0 and 1.

[0087] A preset first threshold is 0.2, and this is used as an example for description.

[0088] On the difference curve, divide several curve segments with difference values greater than the preset first threshold, and denote them as abnormal curve segments.

[0089] Denote the mean value of the reliabilities of curve A1 and curve A2 as the first mean value.

[0090] On the difference curve, calculate the normalized value of the horizontal axis range size where the th abnormal curve segment is located and the product of the maximum difference value in the The product of the reciprocal of the median within the horizontal axis range where the abnormal curve segment is located and the third product is used as the fourth product of the th abnormal curve segment. The product of the inverse proportional normalization value of the sum of the fourth products of all abnormal curve segments and the first mean value is used as the comprehensive reliability of curve A1 and curve A2.

[0091] It should be noted that: The calculation formula for the comprehensive reliability of curve A1 and curve A2 is:

[0092]

[0093] In the formula, is the comprehensive reliability of curve A1 and curve A2, and are the reliabilities of curve A1 and curve A2 respectively, is the first mean value, is the number of abnormal curve segments in the difference curve, is the th median within the horizontal axis range where the abnormal curve segment is located, is the th horizontal axis range size where the abnormal curve segment is located, is the horizontal axis range size where the difference curve is located. In this embodiment, is 's normalization value, is the th maximum difference value in the abnormal curve segment, is the third product. The larger the third product, it indicates that within a larger distance range, the imaging performance of the 30-line in the radial and tangential directions is more inconsistent, and the data is less reliable. At is the weight, The smaller it is, it indicates that it is closer to the optical center of the lens, and the center of the lens is usually the area with the highest imaging quality. The imaging quality in the central area directly reflects the basic performance of the lens, that is, the imaging quality analysis closer to the center of the lens is more important. is the th fourth product of the abnormal curve segment, obtaining the adjustment coefficient of the reliability, so as to obtain the comprehensive reliability of the 30-line curve in the radial and tangential directions. is the exponential function with the natural constant as the base. In this embodiment, is used to present 's inverse proportional relationship and normalization processing. The implementer can set the inverse proportional function and normalization function according to the actual situation.

[0094] In any MTF chart, obtain the comprehensive reliability of the two curves of the 10-line under tangential and radial directions according to the method of obtaining the comprehensive reliability of the two curves of the 30-line under tangential and radial directions, and take the mean value of the comprehensive reliability of the two curves of the 30-line under tangential and radial directions and the comprehensive reliability of the two curves of the 10-line under tangential and radial directions as the comprehensive reliability of any MTF chart.

[0095] Step S004: Determine the light source brightness suitability factor of each MTF chart according to the comprehensive reliability of each MTF chart and the curves in the MTF chart under different light source brightnesses adjacent in the same cycle test.

[0096] Preferably, in an embodiment of the present invention, the method for obtaining the light source brightness suitability factor of each MTF chart includes:

[0097] In any cycle test, sort all light source brightnesses from small to large, and obtain the MTF charts of the chip under test under each light source brightness in sequence according to the sorting to form an MTF chart sequence.

[0098] Since the dynamic range of the imaging system is limited, it defines the ratio between the brightest and darkest signals that the system can handle. Within the normal brightness range, the dynamic range of the system can fully cope with the change of brightness, so the change of the MTF chart is small. While in the case of too low or too high brightness, the system may be close to the limit of its dynamic range, and at this time, the change of brightness may cause a significant change in the MTF chart. Therefore, in the MTF chart sequence, when a certain MTF chart is more similar to its adjacent MTF chart, it means that the light source brightness corresponding to this certain MTF chart is more suitable for the chip under test.

[0099] In the MTF chart sequence, calculate the Pearson correlation coefficient between the curves of the 30-line under the tangential direction of the th and the th MTF charts as the first correlation coefficient, calculate the Pearson correlation coefficient between the curves of the 30-line under the radial direction of the th and the th MTF charts as the second correlation coefficient, calculate the normalized value of the sum of the first correlation coefficient and the second correlation coefficient as the first sum value, calculate the absolute value of the difference between the comprehensive reliabilities of the two curves of the 30-line under the tangential and radial directions of the th and the th MTF charts as the first difference value, and take the ratio of the first sum value to the first difference value as the similarity of the curves of the 30-line under the tangential and radial directions of the th and the th MTF charts .

[0100] It should be noted that: The -th and the -th MTF charts have a curve similarity of the 30 - line in the tangential and radial directions, and the calculation formula is as follows:

[0101]

[0102] In the formula, is the Pearson correlation coefficient between the curves of the 30 - line in the tangential direction of the -th and the -th MTF charts in the MTF chart sequence, and it is also the first correlation coefficient. is the Pearson correlation coefficient between the curves of the 30 - line in the radial direction of the -th and the -th MTF charts in the MTF chart sequence, and it is also the second correlation coefficient. Among them, the Pearson correlation coefficient is a well - known technology, and the Pearson correlation coefficient ranges from - 1 to 1. The closer it is to 1, the more consistent the change trends of the two curves are, indicating that the performance of the optical system is relatively stable under these two lighting conditions. Therefore, the light source brightness corresponding to the -th MTF chart is more suitable for the chip to be measured. is a linear normalization function. and are the comprehensive reliabilities of the two curves of the 30 - line in the tangential and radial directions of the -th and the -th MTF charts respectively. is an absolute - value function. The smaller it is, the more similar the comprehensive reliabilities of the curves of the 30 - line in the radial and tangential directions of the two MTF charts are. Therefore, The larger it is, the more similar the curves of the 30 - line in the radial and tangential directions between the two MTF charts are.

[0103] In the MTF chart sequence, in the above - mentioned manner, obtain the curve similarity of the 10 - line in the tangential and radial directions of the -th and the -th MTF charts, the curve similarity of the 10 - line in the tangential and radial directions of the -th and the -th MTF charts, and the curve similarity of the 30 - line in the tangential and radial directions of the -th and the -th MTF charts.

[0104] It should be noted that: The first and the last MTF charts in the MTF chart sequence are not analyzed. They are in the lowest and highest test light source brightness, which are extreme states and not used for the selection of appropriate light source brightness.

[0105] Take the mean value of , , and as the second mean value, and multiply the second mean value by the comprehensive reliability of the th MTF chart in the MTF chart sequence, and use the product as the light source brightness suitability factor of the th MTF chart in the MTF chart sequence.

[0106] It should be noted that: The greater the comprehensive reliability, the more reliable the th MTF chart. And the greater the second mean value, the more similar the th MTF chart is to its adjacent MTF images. Therefore, the greater the light source brightness suitability factor, the more suitable the light source brightness corresponding to the th MTF chart is for the chip under test.

[0107] Step S005: Determine the excellence of each light source brightness according to the light source brightness suitability factor of each MTF chart and the curves in the MTF charts in different cycle tests under the same light source brightness.

[0108] Since the brightness of the light source is directly affected by the supply voltage and current. Any slight power fluctuation may cause the fluctuation of the light source brightness, and the dust in the environment will affect the propagation and distribution of light, and the change of dust will also cause the brightness fluctuation.

[0109] Therefore, under a certain light source brightness, the credibility of a single test is relatively low. Therefore, in this embodiment, the optimal light source brightness is determined through the analysis of the MTF charts under multiple tests with the same light source brightness.

[0110] Preferably, in an embodiment of the present invention, the method for obtaining the excellence of each light source brightness includes:

[0111] In all cycle tests, obtain all the MTF charts corresponding to the th light source brightness (i.e., the th MTF chart in each cycle test) as the reference MTF charts, and obtain multiple reference MTF charts.

[0112] Since in the MTF curve graph, theoretically the curve should show a downward trend as it moves away from the center of the lens, and as it gets farther and farther from the center, the speed of the curve decline will accelerate because of the reduction of contrast caused by aberration and diffraction effects in the edge region.

[0113] Therefore, in the MTF chart, if there is a curve segment in an upward trend on a curve, the upward-trending curve segment may be caused by measurement errors, data processing errors, or other unexpected factors. The data in the upward segment is usually considered untrustworthy because it does not conform to the normal behavior of the optical system.

[0114] Denote any curve in any reference MTF chart as curve A3. Obtain the curve segments of curve A3 divided according to peaks and valleys. Denote the curve segments with the starting point at a valley or the ending point at a peak as upward-trending curve segments.

[0115] Calculate the difference between the maximum contrast and the minimum contrast in the th upward-trending curve segment of curve A3. Denote the ratio of this difference to the size of the horizontal axis range where the th upward-trending curve segment of curve A3 is located as the second ratio. Calculate the product of the reciprocal of the median within the horizontal axis range where the th upward-trending curve segment of curve A3 is located and the second ratio, and take it as the data untrustworthiness of the th upward-trending curve segment of curve A3. .

[0116] It should be noted that: the smaller the median within the horizontal axis range where the th upward-trending curve segment of curve A3 is located, the closer the th upward-trending curve segment is to the lens center, and the more untrustworthy the data in the th upward-trending curve segment. And the larger the second ratio, the greater the increase in contrast appears under a smaller distance change, that is, the more untrustworthy the data in the th upward-trending curve segment. Therefore, the larger , the more untrustworthy the data in the th upward-trending curve segment.

[0117] Take as the credibility of each data point in the th upward-trending curve segment of curve A3.

[0118] Among them, is a linear normalization function used to normalize to between 0 and 1.

[0119] Obtain the credibility of each data point in each upward-trending curve segment of curve A3 in the above manner.

[0120] Preset the second threshold as 1 and describe it by taking this as an example.

[0121] Set the credibility of each data point on curve A3 that is not in the rising trend curve segment to a preset second threshold, thereby obtaining the credibility of each data point on curve A3.

[0122] Since the overall shape of the curve in the MTF chart represents the imaging performance of the optical system.

[0123] Denote the curves of the 30 lines in the tangential direction in any two reference MTF charts as curve A4 and curve A5 respectively.

[0124] Use the DTW algorithm to match curve A4 and curve A5, obtaining a number of matching pairs and the DTW distance of each matching pair.

[0125] It should be noted that: The DTW algorithm is a well-known technology. The smaller the DTW distance, the more similar the two curves are. Each matching pair includes a data point in curve A4 and a data point in curve A5. The DTW distance of each matching pair is represented by the Euclidean distance between the two data points in each matching pair.

[0126] Calculate the mean value of the credibility of the two data points in the th matching pair between curve A4 and curve A5 as the third mean value, and take the product of the third mean value and the DTW distance of the th matching pair between curve A4 and curve A5 as the fifth product of the th matching pair between curve A4 and curve A5. Take the sum value of the fifth products of all matching pairs between curve A4 and curve A5 as the initial inconsistency between curve A4 and curve A5.

[0127] For any two reference MTF charts, obtain the initial inconsistency of the curve of the 30 lines in the radial direction in the same way as the acquisition method of the initial inconsistency of the curve of the 30 lines in the tangential direction , the initial inconsistency of the curve of the 10 lines in the tangential direction and the initial inconsistency of the curve of the 10 lines in the radial direction . Take , , and 's sum value 's inverse proportional normalization value as the overall shape consistency of the curves of this arbitrary two reference MTF charts.

[0128] It should be noted that: 's inverse proportional normalization value is represented by . Among them, the larger the third mean value, the The DTW distance of a matching pair is more reliable. That is, when analyzing the overall shape consistency of the curve, focus on the data that conforms to the expected downward trend to obtain a reliable DTW distance. The larger the DTW distance, the more inconsistent the shapes of the two curves. Therefore, use The inverse proportional normalization value of

[0129] As the overall shape consistency of the curve. In all cyclic tests, for the th MTF chart (reference MTF chart) in each cyclic test, that is, the specific acquisition process of the excellence of the corresponding

[0130] th light source brightness is as follows: Denote the mean value of the overall shape consistency of the curves of all arbitrarily selected two reference MTF charts as the fourth mean value, denote the mean value of the light source brightness suitability factors corresponding to all reference MTF charts as the fifth mean value, and take the product of the fourth mean value and the fifth mean value as the excellence of the

[0131] th light source brightness. It should be noted that: the larger the fourth mean value, the more consistent the overall shapes of the curves of the MTF charts in all sub-tests under the th light source brightness, that is, the th light source brightness has better stability in repeated tests. The larger the fifth mean value, the more suitable the

[0132] th light source brightness is for the chip to be tested. Therefore, the greater the excellence, the more suitable the light source brightness is for the chip to be tested.

[0133] Preferably, in an embodiment of the present invention, the acquisition method for sorting the chip to be tested includes:

[0134] Obtain the excellence of each light source brightness in the above manner, and take the light source brightness corresponding to the maximum excellence as the optimal light source brightness of the chip to be tested in this embodiment.

[0135] Obtain the MTF charts of the chip to be tested in multiple cyclic tests under the optimal light source brightness, obtain the MTF value of the chip to be tested at a preset specific spatial frequency from each MTF chart, and take the mean value of the MTF values of the chip to be tested at the preset specific spatial frequency in all MTF charts under the optimal light source brightness as the optimal MTF value of the chip to be tested.

[0136] It should be noted that: In this embodiment, the average value of the contrast of the two curves of 30 lines in the radial and tangential directions at a distance of 5 mm from the optical center of the lens in each MTF chart is used as the MTF value of the chip under test at a preset specific spatial frequency in each MTF chart. That is, the preset specific spatial frequency is 30 lines, and it includes two directions of radial and tangential. The selected horizontal axis coordinate is 5 mm from the optical center of the lens. This is taken as an example for description.

[0137] Set the qualified threshold of the MTF value according to the product quality requirements of the chip under test. In this embodiment, the preset qualified threshold is 0.8. This is taken as an example for description.

[0138] Compare the optimal MTF value of the chip under test with the preset qualified threshold to determine whether it meets the standard. When the optimal MTF value is greater than the preset qualified threshold, it is determined that the chip under test meets the standard. When the optimal MTF value is less than or equal to the preset qualified threshold, it is determined that the chip under test does not meet the standard.

[0139] Classify the qualified chips into the qualified category, and classify the unqualified chips into the unqualified category.

[0140] It should be noted that: In this embodiment, when the denominator in the formula is 0, the denominator is set to 1. This is taken as an example for description to ensure that the formula holds.

[0141] So far, the present invention is completed.

[0142] In summary, in the embodiment of the present invention, several MTF charts of the chip under test under different light source brightnesses in a number of cyclic tests are obtained, the comprehensive reliability of each MTF chart is determined, the light source brightness suitability factor of each MTF chart is determined by combining the curves in the MTF charts under adjacent different light source brightnesses in the same cyclic test, and then the excellence of each light source brightness is determined by combining the curves in the MTF charts in different cyclic tests under the same light source brightness, so as to determine the optimal MTF value of the chip under test for sorting the chip under test. The present invention ensures the accuracy of sorting the chip under test by selecting the optimal light source brightness during the test process.

[0143] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An automatic test and sorting method for the MTF value of a chip, characterized in that, The method includes the following steps: Obtain MTF charts for each light source brightness in several cyclic tests of the chip under test; the MTF charts include curves of 30 lines in the tangential direction, curves of 30 lines in the radial direction, curves of 10 lines in the tangential direction, and curves of 10 lines in the radial direction; the horizontal axis of the MTF chart represents the distance of the monitoring point from the optical center of the lens, and the vertical axis represents the contrast; Determine the reliability of each curve based on the peaks and valleys on each curve in each MTF chart; Determine the comprehensive reliability of each MTF chart based on the reliability of each curve in each MTF chart and the differences between curves of the same-sized lines in different directions; Determine the light source brightness suitability factor of each MTF chart based on the comprehensive reliability of each MTF chart and the curves in MTF charts under adjacent different light source brightnesses in the same cyclic test; Determine the excellence of each light source brightness based on the light source brightness suitability factor of each MTF chart and the curves in MTF charts in different cyclic tests under the same light source brightness; Determine the optimal MTF value of the chip under test based on the excellence of each light source brightness; sort the chips under test according to the optimal MTF value of the chip under test.

2. The automatic test and sorting method for the MTF value of a chip according to claim 1, characterized in that, The specific steps included in determining the reliability of each curve are as follows: Denote any one curve in any one MTF chart as curve A; Divide curve A into several curve segments using the peak and valley in curve A; Calculate the difference between the maximum contrast and the minimum contrast in the th curve segment of curve A, and denote the ratio of the difference to the size of the horizontal axis range where the th curve segment of curve A is located as the first ratio; Calculate the product of the reciprocal of the median within the horizontal axis range where the th curve segment of curve A is located and the first ratio, and use it as the first product of the th curve segment of curve A; Determine the reliability of curve A based on the first product of each curve segment of curve A and all the contrasts in curve A.

3. The automatic test and sorting method for the MTF value of a chip according to claim 2, wherein The specific steps included in determining the reliability of curve A are as follows: Calculate the product of the sum of the first products of all curve segments of curve A and the variance of all the contrasts in curve A, and denote it as the second product; Take the product of the inverse normalization value of the second product and the mean of all the contrasts in curve A as the reliability of curve A.

4. The automatic test and sorting method for the MTF value of a chip according to claim 1, wherein, The specific steps included in determining the comprehensive reliability of each MTF chart are as follows: Denote the two curves of 30 lines in the tangential and radial directions in any one MTF chart as curve A1 and curve A2 respectively; Calculate the normalized value of the absolute value of the difference between the ordinates corresponding to each same abscissa of curve A1 and curve A2 as the difference value corresponding to each abscissa, and form a difference curve with the difference values corresponding to all abscissas; On the difference curve, divide several curve segments with difference values greater than a preset first threshold into abnormal curve segments; Denote the mean of the reliabilities of curve A1 and curve A2 as the first mean; Determine the comprehensive reliability of curve A1 and curve A2 based on the first mean and each abnormal curve segment on the difference curve; In any one of the MTF charts, obtain the comprehensive reliability of the two curves of the 10-line in the tangential and radial directions according to the method of obtaining the comprehensive reliability of the two curves of the 30-line in the tangential and radial directions, and use the mean value of the comprehensive reliability of the two curves of the 30-line in the tangential and radial directions and the comprehensive reliability of the two curves of the 10-line in the tangential and radial directions as the comprehensive reliability of any one of the MTF charts.

5. The automatic test and sorting method for the MTF value of a chip according to claim 4, wherein The specific steps included in determining the comprehensive reliability of curve A1 and curve A2 are as follows: On the difference curve, calculate the product of the normalized value of the horizontal axis range where the th abnormal curve segment is located and the maximum difference value in the th abnormal curve segment as the third product. Calculate the product of the reciprocal of the median within the horizontal axis range where the th abnormal curve segment is located and the third product as the fourth product of the th abnormal curve segment. Take the product of the inverse proportional normalization value of the sum of the fourth products of all abnormal curve segments and the first mean value as the comprehensive reliability of curve A1 and curve A2.

6. The automatic test and sorting method for the MTF value of a chip according to claim 4, characterized in that The specific steps included in determining the light source brightness suitability factor for each MTF chart are as follows: In any one cycle test, sort all types of light source brightnesses from small to large, and sequentially obtain the MTF charts of the chip under test for each light source brightness according to the sorting to form a sequence of MTF charts; In the MTF chart sequence, calculate the Pearson correlation coefficient between the curves of the 30 lines in the tangential direction in the th and th MTF charts as the first correlation coefficient. Calculate the Pearson correlation coefficient between the curves of the 30 lines in the radial direction in the th and th MTF charts as the second correlation coefficient. Calculate the normalized value of the sum of the first correlation coefficient and the second correlation coefficient as the first sum value. Calculate the absolute value of the difference in the comprehensive reliability of the two curves of the 30 lines in the tangential and radial directions in the th and th MTF charts as the first difference. Take the ratio of the first sum value to the first difference as the th and th MTF charts for the curve similarity of the 30 lines in the tangential and radial directions ; According to the acquisition method, obtain the th similarity of the 10-line curves in the tangential and radial directions in the th and the th MTF charts; the similarity of the 10-line curves in the tangential and radial directions in the th and the th MTF charts; as well as the similarity of the 30-line curves in the tangential and radial directions in the th and the th MTF charts ; Take , , and 's mean value as the second mean value, and multiply the second mean value by the comprehensive reliability of the th MTF chart in the MTF chart sequence, and use the product as the light source brightness suitability factor of the th MTF chart in the MTF chart sequence.

7. The automatic test and sorting method for the MTF value of a chip according to claim 1, characterized in that The specific steps included in determining the goodness of each light source brightness are as follows: In all cyclic tests, obtain all MTF charts corresponding to the brightness of the th light source as the reference MTF charts; According to the trend changes of each curve in each reference MTF chart, determine the credibility of each data point on each curve in each reference MTF chart; Denote the curves of the 30-line in the tangential direction in any two reference MTF charts as curve A4 and curve A5 respectively; Use the DTW algorithm to match curve A4 and curve A5 to obtain a number of matching pairs and the DTW distance of each matching pair; Calculate the mean of the credibility of the two data points in the th matching pair between curve A4 and curve A5 as the third mean, and multiply the third mean by the DTW distance of the th matching pair between curve A4 and curve A5 as the fifth product of the th matching pair between curve A4 and curve A5. Take the sum of the fifth products of all matching pairs between curve A4 and curve A5 as the initial inconsistency between curve A4 and curve A5; For any two reference MTF charts, obtain the initial inconsistency of the curve of the 30 lines in the tangential direction in the same way as described above, and obtain the initial inconsistency of the curve of the 30 lines in the radial direction , the initial inconsistency of the curve of the 10 lines in the tangential direction and the initial inconsistency of the curve of the 10 lines in the radial direction . Then, take , , and , and use the inverse proportional normalization value of their sum as the overall shape consistency of the curves of the two reference MTF charts. Denote the mean of the overall shape consistency of the curves of all pairs of reference MTF charts as the fourth mean, denote the mean of the light source brightness suitability factors corresponding to all reference MTF charts as the fifth mean, and take the product of the fourth mean and the fifth mean as the goodness of the light source brightness of the 8. The automatic test and sorting method for the MTF value of a chip according to claim 7, characterized in that The specific steps included in determining the credibility of each data point on each curve in each reference MTF chart are as follows: Denote any one curve in any one reference MTF chart as curve A3; Divide curve A3 into several curve segments with the peak value and trough value in curve A3, and denote the curve segments with the starting point as the trough or the ending point as the peak as the upward trend curve segments; Calculate the difference between the maximum contrast and the minimum contrast in the th rising trend curve segment of curve A3, and record the ratio of the difference to the size of the horizontal axis range where the th rising trend curve segment of curve A3 is located as the second ratio. Calculate the product of the reciprocal of the median within the horizontal axis range where the th rising trend curve segment of curve A3 is located and the second ratio, and use it as the data untrustworthiness of the th rising trend curve segment of curve A3 ; Take as the credibility of each data point in the th rising trend curve segment of curve A3; where is a linear normalization function; Set the credibility of each data point on curve A3 that is not in the upward trend curve segment to a preset second threshold.

9. The automatic test and sorting method for the MTF value of a chip according to claim 1, characterized in that The specific steps included in determining the optimal MTF value of the chip under test are as follows: Among the goodness of all light source brightnesses, use the light source brightness corresponding to the maximum goodness as the optimal light source brightness of the chip under test; Obtain the MTF values at the preset specific spatial frequency in all MTF charts of the chip under test at the optimal light source brightness, and use the mean value of the MTF values at the preset specific spatial frequency in all MTF charts as the optimal MTF value of the chip under test.

10. The automatic test and sorting method for the MTF value of a chip according to claim 1, characterized in that, The specific steps included in sorting the chip under test are as follows: When the optimal MTF value is greater than the preset qualified threshold, determine that the chip under test meets the standard; When the optimal MTF value is less than or equal to the preset qualified threshold, determine that the chip under test does not meet the standard.

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