Focusing method using axial chromatic aberration and optical detection architecture using the same

Abstract

The application discloses a focusing method using axial chromatic aberration and an optical detection architecture using the method. Different waveband light rays are imaged by an optical system to sample surfaces of different depths, that is, for any specific depth of a sample surface, different waveband light rays are imaged by the optical imaging system to show different degrees of focusing. The degree of focusing can be calculated by an algorithm to obtain a quantitative index, and different color light corresponds to its respective quantitative index at each sample depth. A quantitative index ratio lookup table of different color light is previously established, when the optical detection equipment is detected on the production line, each detection point only needs to obtain an image and distinguish the first waveband image data and the second waveband image data, and obtain the respective quantitative index value corresponding to the focusing degree analysis, match the corresponding position parameter in the quantitative index ratio lookup table according to the ratio of the two values, and then obtain the adjustment basis of the focal plane position of the optical detection equipment, thereby improving the detection efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical inspection technique, and more particularly, to a focusing method using axial chromatic aberration and an optical inspection architecture using the same. BACKGROUND

[0002] With the improvement of semiconductor manufacturing technology, more transistors are contained in the unit area of an integrated circuit (IC) chip, providing efficient operation with multi-tasking and low power consumption. In the pursuit of production capacity, the principle of high-volume manufacturing (HVM) highlights the importance of time cost. Among various stages of semiconductor manufacturing, corresponding detection procedures need to be deployed to ensure the production quality of the production line and prevent defective products from flowing into subsequent processes, causing waste. However, these detection procedures often increase unnecessary time costs.

[0003] The surface of a semiconductor element is detected by an optical inspection system to determine whether it has defects, due to the depth of field limitation of the lens assembly used in each optical inspection system. The depth of field range provides the axial resolution of the optical inspection system, and the range outside the depth of field cannot provide a clear image for detection and analysis. Under the process scale of today's semiconductor manufacturing, the working distance range (depth of field) of the lens carried by the optical inspection system is about microns. Therefore, when the height difference of the surface topography on the chip or the detection height error caused by the translation of the detection conveyor belt between different dies is greater than the depth of field, the optical inspection system often needs to find and adjust the focal plane to allow the surface of the detection point on the chip to fall within the depth of field range of the optical inspection system.

[0004] The optical inspection system traditionally uses a sequential moving method to find the focal plane, that is, the optical inspection system individually scans each detection point of the device under test in the axial direction. Each scan must rely on mechanical action to change the distance between the lens (objective lens) and the device under test to determine whether the focal plane position of the detection point is in focus. The time-consuming mechanical repetitive motion procedure cannot meet the requirement of fast detection under high-volume manufacturing (HVM). The high time cost of the automatic optical inspection architecture needs to be broken through in terms of technology. SUMMARY

[0005] One of the purposes of the present application is to save the detection time required for optical inspection and improve the detection efficiency.

[0006] Another purpose of the present application is to make the optical inspection system suitable for detection in high-volume manufacturing (HVM) production lines.

[0007] To achieve the above object, the present application provides a focusing method using axial chromatic aberration. The method is based on a pre-established quantization index ratio lookup table. In a detection procedure, a detector is used to focus on a detection point in a first axial direction. The method comprises the following steps: the detector is used to obtain a detection image in a working interval of the detection point. The detection image is divided into a first band image data and a second band image data of different wave bands. Quantization index values corresponding to the first band image data and the second band image data are obtained respectively. A ratio between the two quantization index values is obtained according to the quantization index values of the first band image data and the second band image data. A position parameter is searched in the quantization index ratio lookup table according to the ratio. The focal plane position of the detector is adjusted according to the position parameter. The quantization index ratio lookup table is obtained by the following steps: in the detection procedure, a reference focal plane position in the working interval and a plurality of identification intervals divided from the working interval are used. In each identification interval, the detector is used to obtain a quantization index ratio corresponding to the different wave bands and a difference degree information between the current focal plane position of the detector and the reference focal plane position based on the image obtained by the detector. The difference degree information is used as the position parameter.

[0008] In an embodiment of the present application, the denominator of the ratio is the quantization index value corresponding to the second band image data, and the numerator of the ratio is the quantization index value corresponding to the first band image data. The first band image data is based on light of a first wavelength, and the second band image data is based on light of a second wavelength. The second wavelength is longer than the first wavelength.

[0009] In an embodiment of the present application, when the ratio is not equal to an expected value, the focal plane position of the detector is adjusted towards the corresponding focal plane position of the quantization index ratio lookup table corresponding to the quantization index value of 1 in the step of adjusting the focal plane position of the detector, taking the expected value as 1.

[0010] In an embodiment of the present application, the second wavelength is red light, and the first wavelength is blue light.

[0011] In an embodiment of the present application, when the ratio is less than the quantization index value corresponding to the reference focal plane position, the control direction of the detector in the first axial direction is lowered in the step of adjusting the focal plane position of the detector. When the ratio is greater than the quantization index value corresponding to the reference focal plane position, the control direction of the detector in the first axial direction is raised in the step of adjusting the focal plane position of the detector.

[0012] To achieve the above object, the present application provides an optical inspection apparatus for inspecting a device under test, comprising an objective lens assembly, a light source assembly, a guiding assembly, an adjusting assembly, a sensor assembly, and a control host. The guiding assembly is coupled to the objective lens assembly at a lower end and coupled to the light source assembly at a side. The guiding assembly guides the illumination light generated by the light source assembly toward the objective lens assembly, and guides the reflected light from the device under test to an upper end of the guiding assembly. The adjusting assembly is coupled to the upper end of the guiding assembly to receive the reflected light and to pass the reflected light, and is used to adjust the position of a focal plane formed by the objective lens assembly. The sensor assembly is coupled to the upper end of the adjusting assembly to receive the reflected light and to generate image data. The control host is coupled to the adjusting assembly and the sensor assembly to receive the image data generated by the sensor assembly and to control the adjusting assembly to adjust the position of the focal plane. The control host is used to perform the focusing method as described above. The control host controls the adjusting assembly to adjust the position of the focal plane according to a quantization index ratio lookup table stored in the control host and the image data generated by the sensor assembly.

[0013] In an embodiment of the present application, the guiding assembly guides the illumination light generated by the light source assembly and the reflected light by a half mirror.

[0014] In an embodiment of the present application, the light source assembly is used to provide two different wave bands of illumination light at the same time. One wave band can be red light, and the other wave band can be blue light.

[0015] Accordingly, the present application uses the characteristics of axial chromatic aberration to break the symmetry of the quantization index by two kinds of light waves, and then extracts the key information required for matching focusing. By using the different differences in the quantization index values corresponding to the defocusing or focusing states of different wave bands, the matching relationship in the preset stage can be applied to the data in actual detection, so that the detection machine can perform the focusing program only by shooting one image under the operation of the matching focusing mechanism, which eliminates the long and time-consuming sequential scanning, and can be applied to the defect detection of HVM production lines, with significant efficiency improvement. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a focusing diagram of the optical inspection system in sequential detection;

[0017] Figure 2 is a graph of the relationship between the quantization index M and the focal plane position P at a detection point;

[0018] Figure 3 is a flowchart of the focusing method according to an embodiment of the present application;

[0019] Figure 4 is a focusing diagram of light rays of different wave bands in the axial direction;

[0020] Figure 5It is a graph showing the relationship between the quantization index M and the quantization index ratio r of light of different wavelengths at a detection point and the focal plane position P;

[0021] Figure 6 This is a schematic diagram of an optical inspection device according to an embodiment of the present invention. Detailed Implementation

[0022] To fully understand the purpose, features, and effects of the present invention, the present invention will now be described in detail with reference to the following specific embodiments and accompanying drawings:

[0023] In this application, the terms "a" or "an" are used to describe units, components, structures, devices, modules, systems, parts, or regions, etc. This is used merely for ease of explanation and to provide a general meaning for the scope of this invention. Therefore, unless it is clearly intended otherwise, this description should be understood to include one or at least one, and the singular also includes the plural.

[0024] In this application, the terms "comprising," "including," "having," or any other similar terms are not limited to the elements listed herein, but may include other elements not expressly listed but which are typically inherent in the unit, component, structure, device, module, system, part, or region.

[0025] In this application, the ordinal terms such as "first" or "second" are used to distinguish or refer to elements, structures, parts, or regions that are related to the same or similar entities, and do not necessarily imply a spatial order of these elements, structures, parts, or regions. It should be understood that in certain situations or configurations, ordinal terms may be used interchangeably without affecting the implementation of the invention.

[0026] Figure 1 This is a schematic diagram of the focusing process of an optical inspection system during sequential inspection. The inspection unit 300 of the optical inspection system is positioned above the support 100, and the device under test 200 is supported on the support 100.

[0027] like Figure 1 As shown, the testing machine 300 has a degree of freedom along the first axis X, allowing it to move up and down. The first axis X is parallel to the optical axis of the testing machine 300, thereby allowing the focal plane of the testing machine 300 to move within a working range W. This working range W is set to cover all the undulations in the surface topography of the device under test 200. This working range W can also be maintained by fixing the testing machine 300 stationary while the support 100 moves up and down along the first axis X. The following description will use the operating mode where the testing machine 300 can move freely while the support 100 remains stationary as an example.

[0028] The microscopic function of the inspection machine 300 has its corresponding recognition interval (depth of field) under the matching of a proper objective lens. Within the working interval W of the inspection machine 300, this recognition interval also moves up and down, changing its position on the first axis X. The working interval W is to enable the inspection machine 300 to find the proper focal plane position on the surface of the device under test 200 (optimal resolution, and the corresponding high definition), and to take the image at this position as the basis for subsequent analysis.

[0029] Therefore, the inspection machine 300 can form multiple segments of normal resolution recognition intervals in the working interval W, and the length of each segment corresponds to the depth of field that the inspection machine 300 can provide. For ease of illustration, Figure 1 only four segments of recognition intervals are shown, namely the first recognition interval d1, the second recognition interval d2, the third recognition interval d3, and the fourth recognition interval d4. After the inspection machine 300 obtains the images of the four segments of recognition intervals, subsequent analysis of these images is performed, and the optimal image is evaluated by an algorithm, which is then used as the basis for subsequent analysis.

[0030] To further illustrate, Figure 1 the device under test 200 has a first part 210 and a second part 220, and the surface topography of the first part 210 is lower than that of the second part 220. First, assume that each detection point is assigned to only one detection site. When the detection point is at the first part 210, the inspection machine 300 must be moved to a first position on the first axis X, which allows the first recognition interval d1 (the depth of field range of the inspection machine 300) to fall on the position shown in Figure 1 , and then the first image is obtained. Next, the inspection machine 300 is moved to a second position on the first axis X, which allows the second recognition interval d2 to fall on the position shown in Figure 1 , and then the second image is obtained. Next, the inspection machine 300 is moved to a third position on the first axis X, which allows the third recognition interval d3 to fall on the position shown in Figure 1 , and then the third image is obtained. Next, the inspection machine 300 is moved to a fourth position on the first axis X, which allows the fourth recognition interval d4 to fall on the position shown in Figure 1 , and then the fourth image is obtained. Finally, the first to fourth images are analyzed to determine which one is the optimal detection image (optimal definition) at the detection point of the first part 210. The optimal detection image will be used as the basis for the optical detection system to determine the defects of the device under test. Each recognition interval has a corresponding in-focus focal plane position, and within a certain range (i.e., the recognition interval) above and below the focal plane position based on the depth of field range, a clear image is formed.

[0031] In Figure 1In the example sequential detection, a relatively long time is required for each detection point to obtain the respective detection image in the first axial direction (e.g., the aforementioned recognition intervals d1-d4) on the production line, so as to select the optimal detection image corresponding to each detection point.

[0032] The focusing methods of general optical systems are classified into active focusing and passive focusing. The active focusing is to actively emit a specific light wave to a measured object, and receive the light wave reflected from the measured object, so as to determine the distance between the measured object and the optical system, and then achieve the focusing purpose. For example, infrared ranging and ultrasonic ranging. The passive focusing is to analyze the obtained image data of the measured object, so as to determine the focusing position, and then achieve the focusing purpose. The focusing method adopted in the semiconductor process of the present embodiment belongs to passive focusing.

[0033] The focusing method of passive focusing is generally based on an existing algorithm, and then calculates the corresponding sharpness evaluation function value of each image in the focusing process. Finally, the position corresponding to the maximum sharpness evaluation function value is determined as the sharpest imaging position. Accordingly, the focusing method is to further estimate the image data by the algorithm to obtain the evaluation function value of each detection point at different positions in the axial direction (for reference Figure 1 ), and then find the image data with the maximum evaluation function value. The position (for reference Figure 1 ) corresponding to the image data, i.e., the position of the detection machine 300 in the first axial direction X, is the position of the detection machine in the detection point that can make the imaging sharpest. That is, the recognition interval (depth of field) provided by the detection machine 300 at this time can cover the surface topography of the measured object at this detection point.

[0034] The basis of the existing algorithm includes gray scale function and frequency domain function. These functions are selectively used to generate the sharpness evaluation function value of each detection point in the axial direction corresponding to each recognition interval. These functions are applicable to the focusing method described in the subsequent embodiments of the present application.

[0035] The following is an introduction to several algorithms. One algorithm based on the gray scale function, such as the Tenengrad gradient function, uses Sobel operators to extract the gradient values in the horizontal and vertical directions of the image data. The Sobel operator is a kind of existing discrete differentiation operator.

[0036] The approximate gradient at (x, y) satisfies:

[0037]

[0038] In equation (1): G(x,y) represents the approximate gradient value at (x,y); G x (x,y) represents the gradient value extracted in the horizontal direction using the Sobel operator; G y (x,y) represents the gradient value extracted in the vertical direction using the Sobel operator; G x (x,y), G y (x,y) represent the convolutions of the recorded image f(x,y) with different Sobel operators, and their calculation relationships are as follows:

[0039] G x (x,y)=f(x,y)*S1 (2)

[0040] G y (x,y)=f(x,y)*S2 (3)

[0041] In equations (2) and (3), S1 and S2 are Sobel operand templates.

[0042] Finally, the Tenengrad function can be evaluated as follows:

[0043] F = ∑ x ∑ y G 2 (x,y),|G(x,y)|>T (4)

[0044] In equation (4), T is the threshold value for edge detection, and the sensitivity of the evaluation function can be changed by adjusting the value of T.

[0045] Therefore, in Figure 1 Within the example working range W, each identification range can obtain a corresponding image data, and then the corresponding value can be obtained through the Tenengrad gradient function. The best value is selected from these values, and the identification range corresponding to this value is the optimal working distance of the detector 300 for this detection point.

[0046] Another algorithm based on grayscale functions, such as the Laplacian gradient function, is essentially the same as the Tenengrad gradient function, mainly replacing the Sobel operator with the Laplacian operator. The Laplacian gradient function is a function that calculates the grayscale values ​​of the target point and its four surrounding points. It first calculates the sum of the grayscale differences between the target point and its four surrounding points, and then performs a sum-of-squares operation.

[0047] The formula for calculating the Laplacian gradient function is as follows:

[0048] F = Σ x Σy [4f(x,y)-f(x,y+1)-f(x,y-1)-f(x+1,y)-f(x-1,y)] 2 (5)

[0049] Accordingly, in the working interval W of the example, each recognition interval can obtain a corresponding image data, and then the corresponding value can be obtained through the Laplacian gradient function, and the best value can be selected from the values, and the recognition interval corresponding to the value is the best working distance of the detection machine 300 for the detection point. Figure 1

[0050] Another algorithm based on the gray scale function, such as the Brenner function, is to calculate the gray scale difference between the two pixels separated by two units in the horizontal direction as the basis for judging the image sharpness.

[0051] The calculation formula based on the Brenner function is as follows:

[0052] F = ∑ x ∑ y [f(x+2,y)-f(x,y)] 2 (6)

[0053] Accordingly, in the working interval W of the example, each recognition interval can obtain a corresponding image data, and then the corresponding value can be obtained through the Brenner function, and the best value can be selected from the values, and the recognition interval corresponding to the value is the best working distance of the detection machine 300 for the detection point. Figure 1

[0054] In the use of the foregoing example algorithm or other algorithms for evaluating image sharpness (focus or not), the evaluation results can be used to evaluate which image of the detection machine 300 is in focus (the detection surface can fall within the depth of field) based on the evaluation results, and the image in focus is used as the basis for subsequent defect judgment of the device to be tested at this detection point.

[0055] Among them, the aforementioned method for finding the focus surface must obtain the image of each recognition interval in the working interval W of the detection machine 300 during detection, in order to complete the sampling data required at each detection point for subsequent determination of the focus surface. However, the optical detection technology disclosed in the embodiment can only obtain a single image data at each detection point of the detection machine 300, and the detection machine 300 can be determined to be moved to where at this detection point, that is, the focus recognition interval of the detection machine 300 at this detection point can be directly determined, and the focusing action is completed.

[0056] Please refer to Figure 1 ​​and Figure 2 , Figure 2 This is a graph showing the relationship between the quantization index M and the focal plane position P at a detection point. Figure 2 The algorithm uses the Brenner function to evaluate image sharpness (focus), and its curve exhibits a Lorentzian distribution. Other algorithms, however, produce curves with different patterns, such as a Gaussian distribution.

[0057] At a detection point, as the detection machine 300 captures images of various focal plane positions (with corresponding recognition intervals) along the first axis X, the image of each focal plane position, after evaluation by the algorithm, yields the corresponding figure of merit value, which represents the degree of focus. Figure 2 In the example of using the Brenner function as an algorithm to evaluate image sharpness (whether it is in focus), a higher quantization index indicates a higher degree of focus.

[0058] Figure 2 In this process, the more focal plane positions are allocated, the smoother the fitted curve will be. Figure 2 This example uses a relatively large number of focal plane positions. Figure 1 (Examples only, 4 examples) Figure 2 The horizontal coordinates D10, D30, and D50 refer to the positions of the focal planes along the first axis X. Figure 2 The best image sharpness can be obtained at the focal plane position D30. The focal plane position D30 is the target position that the inspection machine 300 needs to be moved to at this inspection point.

[0059] Next, please refer to Figure 3 The following is a flowchart of a focusing method according to an embodiment of the present invention. In the embodiment disclosed in the present invention, the focusing method at each detection point is as follows: Step S100—Acquire a detection image within a working range. Next, Step S200—Divide the detection image into a first band image data and a second band image data with two different wavebands, and obtain a quantization index value corresponding to each of the first band image data and the second band image data in terms of sharpness analysis. Next, Step S300—Obtain a ratio between the quantization index values ​​of the first band image data and the second band image data, and find a matching position parameter in the quantization index ratio lookup table according to the ratio. Next, Step S400—Adjust the focal plane position of the detection machine according to the position parameter.

[0060] In step S200, the quantization index corresponding to each aspect of sharpness refers to the sharpness evaluation function value obtained by estimating the image data using the aforementioned existing algorithm. In step S300, the matching is defined as the calculated ratio being exactly a specific ratio in the quantization index ratio lookup table, or the calculated ratio falling between two specific ratios in the quantization index ratio lookup table. The latter situation can be estimated by proportionally estimating the corresponding positional parameters; for example, interpolation can be used for estimation.

[0061] The quantization index ratio lookup table refers to pre-built comparison data. Based on this pre-built data, the detection machine can quickly match the target position to be adjusted. Furthermore, in the detection process, for each detection point, the detection machine can use only one image capture for focal plane position determination. This is because there is a quantifiable correspondence between each quantization index ratio and the correct focal plane position. Embodiments of this invention achieve a highly efficient detection process through this correspondence. In other words, the quantization index ratio corresponds to the current focal plane position of the detection machine. Accordingly, multiple identification intervals are assigned their respective quantization index ratios. The degree of difference between the quantization index ratio calculated from the current focal plane position of the detection machine and the quantization index ratio calculated from the reference focal plane position corresponds to the degree of difference between the current focal plane position of the detection machine and the reference focal plane position in real space.

[0062] Figure 4 This diagram illustrates the focal points of light rays at different wavelengths along the optical axis. When capturing a color image, the optical system L images the object under test at the focal plane position P onto the image sensor at the rear. Each pixel of the image sensor is typically sensed through three channels: red, green, and blue light, to form the color representation of each pixel. When the light incident on the image sensor is separated into different wavelengths for separate observation, each wavelength has its own corresponding focal plane position (i.e., the collimated focal plane) due to the axial chromatic aberration of the optical system L. In other words, when the inspection machine captures an image at a predetermined position and the image is viewed separately as image data in different wavelengths, the image data in different wavelengths will have different levels of sharpness.

[0063] like Figure 4 As shown in the example, along axis X1, when the optical system L is fixed, the focal planes of blue light B and red light R are located above and below the focal plane of green light G, respectively. That is, when green light G is in focus, the image data of red light R and blue light B, after being processed by the algorithm, will show a quantization index that is out of focus (low sharpness). Using the Brenner function as an example of the algorithm for evaluating image focus, the quantization index values ​​of red light R and blue light B image data are lower than the quantization index value of green light G image data because they are not in focus.

[0064] Next, please refer to Figure 1 and Figure 5 , Figure 5 This is a graph showing the relationship between the quantization index M and the quantization index ratio r of light of different wavelengths at a detection point and the focal plane position P. Figure 5 The example illustrates the relationship between blue light (B) and red light (R) in terms of quantization index M, quantization index ratio r, and focal plane position P. The focal plane position P on the horizontal axis refers to the working range W of the detector 300 along the first axis X (refer to...). Figure 1 The focal plane position that can be adjusted.

[0065] It is understood that blue light (B) and red light (R) will have different quantization index values ​​at the same focal plane position P. Therefore, at different positions within the working range W, the ratio of the quantization indexes of blue light (B) and red light (R) will exhibit different values ​​(each position corresponds to a quantization index ratio). A pre-determined focal plane position for accurate focusing can be established within the working range W. For example, a reference test object can be placed at this focal plane position, allowing the inspection machine to capture an image of the reference test object, which remains in a fixed position, in each recognition interval. After image acquisition at the pre-determined focal plane position, the quantization index ratio of blue light (B) to red light (R) corresponding to this position is used as a reference ratio to define the required quantization index ratio for accurate focusing. Since the working range W is divided into multiple recognition intervals, each recognition interval can be defined with a corresponding quantization index ratio. The difference between this ratio and the reference ratio can then be used as the basis for determining how much the inspection machine 300 should be adjusted along the first axis X.

[0066] For example, in the preset stage, assuming that the reference ratio is defined as 1, the quantization index ratio can be defined as a preset distance that needs to be increased or decreased by 0.1 (or other values) per difference. The preset distance is determined by how far the current focal plane position of the detector 300 is from the in-focus focal plane position in the preset stage (not the detection procedure running on the production line). That is, the aforementioned position parameter. Accordingly, in the detection stage (the detector 300 takes pictures in the working interval W at each detection point), assuming that the actual detection obtains a quantization index ratio of 1.2, it means that the detector 300 needs to be increased or decreased by 2 times the preset distance from the current position. Therefore, when a quantization index ratio lookup table of the focal plane position in a given working interval W corresponding to each quantization index ratio is established in advance, the actual measured quantization index ratio can be used to find the matching focal plane position in the quantization index ratio lookup table (and obtain the difference between the quantization index ratio and the reference ratio) during subsequent detection, and the corresponding position parameter can be obtained. The position parameter represents the degree of the detector 300 from the in-focus position in the first axial direction X, and the detector 300 can be adjusted accordingly to complete focusing. The reference ratio defined as 1 is an expected value, and the size of the expected value can be defined by the user in other embodiments.

[0067] In the example of blue light B and red light R, when the measured quantization index ratio (such as r=0.96, 0.88, 0.8) is less than the reference ratio, it means that the control direction of the detector 300 should be lowered in the first axial direction X. On the other hand, when the measured quantization index ratio (such as r=1.19, 1.12, 1.04) is greater than the reference ratio, it means that the control direction of the detector 300 should be raised in the first axial direction X. The distance parameter of how much to raise or lower is determined according to the quantization index ratio lookup table, that is, according to the pre-established matching data (the relationship between the difference in quantization index ratio and the position).

[0068] In the embodiments of the present application, the denominator of the aforementioned ratio is the quantization index value corresponding to the second waveband image data, and the numerator of the ratio is the quantization index value corresponding to the first waveband image data. The first waveband image data is based on light with a first wavelength, and the second waveband image data is based on light with a second wavelength. The second wavelength can be configured to be longer than the first wavelength, for example, the aforementioned second wavelength is red light, and the first wavelength is blue light.

[0069] In the embodiment of the present application, the characteristics of axial chromatic aberration are applied to break the symmetry of quantization index by two light waves, and then the key information required for matching focus is extracted. The different difference amount (r value) of quantization index value corresponding to defocus or focus state by different wave bands is used, and then the matching relationship in the preset stage (the establishment stage of quantization index ratio lookup table) is applied to the data in actual detection. The detection machine can operate under the matching focus mechanism, and only one image needs to be taken to perform the focusing program, and then the second image for subsequent detection and analysis is taken after focusing (but if the first image is determined to be in focus, this image can be directly used for detection and analysis without taking the second image). Compared with the prior art which needs to take multiple images to complete the focusing program, the focusing method applying axial chromatic aberration disclosed in the embodiment has significantly improved efficiency.

[0070] Among them, the focusing method applying axial chromatic aberration disclosed in the embodiment can be applied to the detection machine with variable focal length element (with zoom mechanism), and to the detection machine with traditional mechanical focus shifting. The foregoing embodiment is explained by the detection machine with traditional mechanical focus shifting. In the case of the detection machine with zoom mechanism, the detection machine adjusts the focal length to complete the focusing according to the matched position parameters (that is, the difference degree of focal position is changed to the adjustment range of focal length).

[0071] Figure 6 The optical detection device according to an embodiment of the present application is shown in the schematic diagram. The optical detection device under the optical detection architecture of the embodiment includes: an objective lens assembly 310, a light source assembly 320, a guide assembly 330, an adjustment assembly 340, a sensor assembly 350, and a control host 400.

[0072] The lower end of the guide assembly 330 is coupled to the objective lens assembly 310, and the side of the guide assembly 330 is coupled to the light source assembly 320. The guide assembly 330 can guide the illumination light generated by the light source assembly 320 through the half mirror 331, so that the illumination light transmits through the objective lens assembly 310 and is emitted outward, and then can be illuminated to the device under test 200 carried on the carrier seat 100. In addition, the guide assembly 330 can guide the reflected light from the device under test 200 to the upper end of the guide assembly 330 through the penetration characteristics of the half mirror 331.

[0073] The upper end of the guide assembly 330 is coupled to an adjustment assembly 340. The adjustment assembly 340 can allow the reflected light to pass through. The adjustment assembly 340 can be an adjustable refractive member controlled by the control host 400, or a mechanical moving member (e.g. moving in the aforementioned first axial direction) controlled by the control host 400, to provide the adjustment function of the focal plane position of the optical detection device. An image sensor is disposed in the sensor assembly 350, coupled to the upper end of the adjustment assembly to receive the reflected light and generate image data through the image sensor.

[0074] The control host 400 is coupled to the adjustment assembly 340 and the sensor assembly 350 to receive the image data generated by the sensor assembly 350, and control the adjustment assembly 340 to adjust the focal plane position formed by the objective lens assembly 310. The control host 400 can also be coupled to the light source assembly 320 to control the light source. The light source assembly 320 can be used to provide two phase-different wave bands of illumination light at the same time. For example, one wave band can be red light, and the other wave band can be blue light.

[0075] In summary, the present application uses the axial chromatic aberration characteristics to obtain the key information required for matching focusing, uses the different difference amounts in the quantization index values when different wave bands of light correspond to out-of-focus or in-focus states, and then applies the matching relationship in the preset stage to the data in the actual detection, so that the detection machine only needs to take one image in the actual detection process to perform the focusing process, greatly improving the detection efficiency, and thus being suitable for detection in high-volume production (HVM) production lines.

[0076] The preferred embodiments of the present application are disclosed in the foregoing description, which should be considered as merely illustrative of the principles of the application. It is understood that variations and modifications will occur to those skilled in the art upon reading this description. Therefore, the scope of the application should be determined not with reference to the description, but with reference to the claims that follow.

[0077] Reference Signs

[0078] 100 carrier

[0079] 200 device under test

[0080] 210 first region

[0081] 220 second region

[0082] 300 detection machine

[0083] d1 first recognition interval

[0084] d2 second recognition interval

[0085] d3 third recognition interval

[0086] d4 fourth recognition interval

[0087] D10 focal position

[0088] D30 focal position

[0089] D40 focal position

[0090] M quantization index

[0091] P focal position

[0092] R red light

[0093] G green light

[0094] B blue light

[0095] L optical system

[0096] r ratio of quantization indices

[0097] X first axis direction

[0098] S100-S400 steps

Claims

1. An axial chromatic focusing method based on a pre-constructed quantization index ratio lookup table, for a detection machine to focus on a detection point in a first axial direction in a detection procedure, comprising: acquiring a detection image of the detection machine in a working interval of the detection point; dividing the detection image into a first waveband image data and a second waveband image data of two different wavebands, and acquiring a quantization index value corresponding to each of the first waveband image data and the second waveband image data in sharpness analysis; acquiring a ratio between two values according to the quantization index value of each of the first waveband image data and the second waveband image data, and searching for a position parameter in the quantization index ratio lookup table according to the ratio; and adjusting a focal plane position of the detection machine according to the position parameter, wherein the quantization index ratio lookup table refers to, other than in the detection procedure, acquiring a quantization index ratio corresponding to the two different wavebands and a difference degree information between a current focal plane position of the detection machine and a reference focal plane position in each of a plurality of identification intervals based on image acquisition of the detection machine in the working interval and a plurality of identification intervals divided from the working interval, and the difference degree information is used as the position parameter.

2. The focusing method of claim 1, wherein, The denominator of the ratio is the quantization index value corresponding to the second waveband image data, and the numerator of the ratio is the quantization index value corresponding to the first waveband image data, the first waveband image data is based on light of a first wavelength, and the second waveband image data is based on light of a second wavelength.

3. The focusing method of claim 2, wherein, The second wavelength is longer than the first wavelength.

4. The focusing method of claim 3, wherein, When the ratio is not equal to 1, in the step of adjusting the focal plane position of the detection machine, the focal plane position of the detection machine is adjusted in the direction of the corresponding focal plane position of the quantization index ratio lookup table where the quantization index ratio is 1.

5. The focusing method of claim 3, wherein, The second wavelength is red light, and the first wavelength is blue light.

6. The focusing method of claim 5, wherein, When the ratio is less than the quantization index ratio corresponding to the reference focal plane position, in the step of adjusting the focal plane position of the detection machine, the control direction of the detection machine is lowered in the first axial direction; and when the ratio is greater than the quantization index ratio corresponding to the reference focal plane position, in the step of adjusting the focal plane position of the detection machine, the control direction of the detection machine is raised in the first axial direction.

7. An optical detection device for detecting a device under test, comprising: an objective lens assembly; a light source assembly; a guide assembly coupled to the objective lens assembly at a lower end and coupled to the light source assembly at a side, the guide assembly guiding illumination light generated by the light source assembly toward the objective lens assembly, and the guide assembly guiding reflected light from the device under test to an upper end of the guide assembly; an adjustment assembly coupled to the upper end of the guide assembly to receive and pass the reflected light and for adjusting a focal plane position formed by the objective lens assembly; a sensor assembly coupled to an upper end of the adjusting assembly to receive the reflected light and generate image data; and a control host coupled to the adjusting assembly and the sensor assembly to receive the image data generated by the sensor assembly and control the adjusting assembly to adjust the focal plane position, wherein the control host is configured to perform the method of focusing using axial chromatic aberration as claimed in any one of claims 1 to 6, the control host controls the adjusting assembly to adjust the focal plane position according to an internal stored quantized index ratio lookup table and the image data generated by the sensor assembly.

8. The optical detection device of claim 7, wherein, the guiding assembly guides the illumination light generated by the light source assembly and the reflected light through a half mirror.

9. The optical detection device of claim 8, wherein, the light source assembly is configured to provide illumination light of two different wave bands at the same time, one wave band is red light and the other wave band is blue light.

Images