A method and system for measuring the depth of a semiconductor high-aspect-ratio microstructure

Abstract

The application discloses a semiconductor high-depth-width micro-size structure depth measurement method and system, and relates to the technical field of semiconductors. The method comprises the following steps: dividing the field of view area of a measurement system, and determining the positional relationship between a to-be-measured area and an auxiliary area; based on the positional relationship between the to-be-measured area and the auxiliary area, the efficiency is improved by monitoring the light intensity fluctuation in the scanning process and automatically adjusting the step length. Meanwhile, the state value is introduced in the method for adjusting the step length, the segmentation and matching of multiple local coherent signals are realized, the accuracy of the peak position is ensured, the scanning step length adjustment condition is recorded after the collection is completed, the local coherent peak of the continuous section of the adjustment state value is identified, and the improved gravity algorithm is used to calculate the peak position of the local coherent peak and the corresponding depth value. The application can effectively reduce the image collection amount without reducing the accuracy, and can eliminate the influence of the multi-peak ambiguity of the interference signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a semiconductor high aspect ratio micro-size structure depth measurement method and system. BACKGROUND

[0002] High aspect ratio (HAR) structures in micro-nano scale provide a breakthrough for three-dimensional heterogeneous integration in semiconductor technology, allowing researchers to integrate multiple structures in limited space and effectively realize micro-nano functional structures. However, the small line diameter and height directionality of HAR structures pose challenges to the efficiency and accuracy of their vertical depth measurement. White light scanning interference technology is suitable for HAR structure depth measurement scenarios due to its non-contact and sub-nanometer longitudinal precision. The wide spectrum of the white light source determines the localization of the coherent fringe signal, especially during long-distance scanning, where a significant portion of the defocused signal collection does not have interference fringes. Therefore, although white light scanning interference technology shows reliable accuracy in HAR structure measurement, this consistent step size pattern limits the measurement efficiency.

[0003] To address the time-consuming problem of white light scanning interference technology due to redundant information, researchers have added additional devices to the original interference system to assist in obtaining coherent peak positions, which drives the motion system to fine scan near the target surface. However, this method increases the complexity of the measurement system, making it more difficult to integrate and implement. Considering this, some researchers have integrated an auto-focusing algorithm into the optical system, using software-level algorithms to search for the best interference fringe area. However, these methods still cannot balance stability and efficiency well. In terms of signal formation, HAR structures are susceptible to numerical aperture limitations and stray reflected light interference, resulting in white light scanning interference systems obtaining signals containing two coherent peaks. In addition, the common film structure in the semiconductor field also affects the number of coherent peaks in the interference signal. This abnormal multi-peak signal significantly interferes with the envelope extraction and coherent peak positioning of the interference signal. SUMMARY

[0004] The purpose of the present application is to provide a semiconductor high aspect ratio micro-size structure depth measurement method and system that can effectively reduce image acquisition while eliminating the influence of multi-peak ambiguity of interference signals without compromising accuracy.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] A semiconductor high aspect ratio micro-size structure depth measurement method, comprising:

[0007] Divide the field of view area of the measurement system to determine the positional relationship between the to-be-measured area and the auxiliary area;

[0008] Based on the position relationship between the to-be-measured region and the auxiliary region, a micro-displacement structure is driven to perform scanning collection with an initial setting step to obtain an initial adjacent frame microscopic interferogram; the initial adjacent frame microscopic interferogram is the first two interferograms collected by data collection;

[0009] The displacement structure is continuously driven to perform scanning collection, and an adjacent frame light intensity fluctuation evaluation function is calculated according to the (n-1)th interferogram and the nth interferogram; wherein n=[3, N]; N is the total number of interferograms;

[0010] Whether the scanning step is adjusted is judged according to the light intensity fluctuation evaluation function and a set light intensity fluctuation threshold value, and scanning step adjustment conditions are recorded after collection is completed;

[0011] Based on the scanning step adjustment conditions, a local coherence peak of a continuous section of adjustment state values is identified;

[0012] The peak position and the corresponding depth value of the local coherence peak are calculated by using an improved barycentric algorithm.

[0013] Optionally, the auxiliary region is a peripheral surrounding region of the to-be-measured region, and based on a field of view region, a general interference signal considering the influence of thin film interference and high aspect ratio structure characteristics is established according to the following mathematical model equation in combination with the basic theory of partially coherent light interference:

[0014]

[0015] Wherein, S i (z, NA) represents a region factor; Ω=∑ i＝1,2,3 S i (z, NA), represents a region factor and participating in the formation of the local interference region signal; the background light I bg is equal to the sum of the reference light intensity I ref and the test light intensity I surf ; z is the height of the to-be-measured topography; c is the speed of light; Δν and represent the spectral width and average frequency of the wide spectrum light source respectively, and NA represents the numerical aperture; when NA decreases or z position moves up, the multi-peak characteristics of I(z) decay with the decrease of S i (z, NA), and then degenerate into a single peak interference signal to be solved;

[0016] Due to the limitation of experimental environment and optical system, the formed interference fringes present a band-shaped straight line color fringe moving on the surface at the same height, based on the mathematical model equation, the Gaussian envelope term in the expression I(z) is maximum at the equal optical path z=0, and rapidly decays with the increase of the coherence distance, therefore, the point coordinates in the field of view plane region satisfy the condition:

[0017] max{d(∑1(x1,y1),∑2(x2,y2))} = FWHM

[0018] min{d(∑2(x2,y2),T(x,y))} = l max

[0019] where ∑1(x1,y1),∑2(x2,y2) are points on curves ∑1,∑2 respectively, the maximum Euclidean distance between the curves equals the full width at half maximum FWHM of the Gaussian envelope curve of the interference signal; T(x,y) is a point in the region T to be measured, the minimum Euclidean distance from the point on curve ∑2 to the region T equals the maximum coherence length l of the broadband light source max .

[0020] Optionally, the setting calculation formula of the light intensity fluctuation threshold is:

[0021] η = k std [I2(T1) - I1(T1)]

[0022] where std(·) is a mean square deviation function, after calculating the light intensity fluctuation evaluation function of the initial adjacent frames of microinterferograms I1, I2 on the auxiliary region T1, multiply by the coefficient k as the threshold η; k takes 1.1-1.4.

[0023] Optionally, the expression of the light intensity fluctuation evaluation function is:

[0024] ψ i = std [I i (T1) - I i-1 (T1)], i = 2···N

[0025] where std(·) is a mean square deviation function, T1 represents an auxiliary region, I i represents the i-th interferogram, I i-1 represents the i-1-th interferogram, and N is the total number of interferograms.

[0026] Optionally, the light intensity fluctuation threshold is set according to the light intensity fluctuation evaluation function to determine whether to adjust the scanning step, and the specific process comprises:

[0027] Comparing the light intensity fluctuation evaluation function with the set light intensity fluctuation threshold: when the light intensity fluctuation evaluation function is less than the set light intensity fluctuation threshold, the scanning step is not adjusted, and the micro-displacement structure is kept at the initial setting step; when the light intensity fluctuation evaluation function is greater than or equal to the set light intensity fluctuation threshold, the scanning step is adjusted to a small step, and scanning is performed with the updated small step; the small step is a set value smaller than the initial setting step.

[0028] Optionally, the recording process of the scanning step adjustment is:

[0029] When the step length of the micro displacement structure is adjusted during the scanning process, the monitoring state is recorded in the form of 0 value, and when the step length of the micro displacement structure is not adjusted, the monitoring state is recorded as a random value in (0, 1).

[0030] Optionally, the calculation formula of the improved barycenter method is:

[0031] P = ∑ m M(m)·m / ∑ m M(m)

[0032] M(m) = [I(m) - I(m-1)] 2 ,m = 2···N s

[0033] Wherein, N s Indicates the length of the local coherent peak signal segment, M(m) indicates the square of the light intensity difference value between adjacent frames, I(m) indicates the mth interference graph, and P indicates the depth value corresponding to the peak position of the local coherent peak.

[0034] The application also provides a semiconductor high-depth-width-ratio micro-size structure depth measurement system for applying the method, which comprises a light source, an aperture, a beam expansion collimation module, a beam splitter, an imaging lens group, a camera, an absorbing plate, a micro displacement structure and an interference objective lens; a wide-spectrum light beam is emitted by the light source, exits after the size of the light beam is controlled by the aperture with the function of size adjustment, is modulated into a uniformly distributed light beam after passing through the beam expansion collimation module, enters the beam splitter, and the projected beam splitter light is directly irradiated on the absorbing plate and is absorbed, and the reflected measurement beam splitter light enters the interference objective lens; the interference objective lens is a Michelson structure, and is clamped and positioned by the micro displacement structure and is driven by the micro displacement structure; the measurement light beam carries the topographic information of the object to be measured under the action of the interference objective lens, returns to the light path system, and is finally collected by the camera target surface after passing through the imaging lens group to obtain an interference light intensity graph.

[0035] According to the specific embodiments provided by the application, the following technical effects are disclosed:

[0036] The application discloses a semiconductor high-depth-width-ratio micro-size structure depth measurement method and system, and the method comprises the following steps: dividing a field of view area of a measurement system to determine the positional relationship between a to-be-measured area and an auxiliary area; based on the positional relationship between the to-be-measured area and the auxiliary area, the efficiency is improved by monitoring the light intensity fluctuation in the scanning process and automatically adjusting the step length. Meanwhile, the state value is introduced in the method for adjusting the step length, the segmentation and matching of multiple local coherent signals are realized, the accuracy of the peak position is ensured, the scanning step length adjustment condition is recorded after the collection is completed, the local coherent peak of the continuous section of the adjustment state value is identified, and the improved gravity algorithm is used to calculate the peak position of the local coherent peak and the corresponding depth value. The application can effectively reduce the image collection amount without reducing the accuracy, and the multi-peak ambiguity influence of the interference signal is eliminated. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0038] Figure 1 It is a flowchart of the semiconductor high-depth-width-ratio micro-size structure depth measurement method of the present application.

[0039] Figure 2 It is a light beam propagation schematic diagram of the HAR structure in the embodiment.

[0040] Figure 3 It is a to-be-measured area and a monitoring area position division schematic diagram in the embodiment.

[0041] Figure 4 It is a variable-speed scanning method schematic diagram for optimizing the sampling frequency in the embodiment.

[0042] Figure 5 It is a multiple local coherent peak identification method schematic diagram in the embodiment. Part (a) is an interframe light intensity variance fluctuation distribution schematic diagram obtained by uniform step scanning, part (b) is a step length monitoring state value schematic diagram in the variable-speed process, and part (c) is an interference light intensity signal schematic diagram of a certain pixel point.

[0043] Figure 6 It is a schematic diagram of an optical path system used in the embodiment.

[0044] Figure 7Fig. 1 is a schematic diagram of three-dimensional reconstruction results of different algorithms in the embodiment; wherein, (a) is a schematic diagram of the reconstruction result of the method of the application, (b) is a schematic diagram of the reconstruction result of the improved barycentric method, (c) is a schematic diagram of the Fourier transform method, (d) is a schematic diagram of the wavelet transform method, and (e) is a schematic diagram of the cross-sectional morphology corresponding to different algorithms.

[0045] Reference signs:

[0046] 1, light source; 2, diaphragm; 3, beam expansion and collimation module; 4, beam splitting plate; 5, imaging lens group; 6, camera; 7, absorption plate; 8, micro displacement structure; 9, interference objective lens; 10, object to be measured. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0048] The purpose of the application is to provide a semiconductor high aspect ratio micro-size structure depth measurement method and system, which can effectively reduce image acquisition without reducing accuracy, and eliminate the influence of multi-peak ambiguity of interference signals.

[0049] In order to make the above-mentioned purposes, characteristics and advantages of the application more obvious and easy to understand, the application will be further described in detail below with reference to the drawings and specific embodiments.

[0050] As shown in Figure 1 The application provides a semiconductor high aspect ratio micro-size structure depth measurement method, which comprises the following steps:

[0051] Step 100: dividing the field of view area of the measurement system to determine the positional relationship between the to-be-measured area and the auxiliary area.

[0052] Step 200: based on the positional relationship between the to-be-measured area and the auxiliary area, driving the micro displacement structure to scan and collect at an initial setting step length to obtain initial adjacent frame microscopic interference graphs; the initial adjacent frame microscopic interference graphs are the first two interference graphs collected by data collection.

[0053] Step 300: continuing to drive the displacement structure to scan and collect, and calculating the light intensity fluctuation evaluation function of adjacent frames according to the (n-1)th interference graph and the nth interference graph; wherein, n=[3, N]; N is the total number of interference graphs.

[0054] Step 400: judging whether to adjust the scanning step length according to the light intensity fluctuation evaluation function and the set light intensity fluctuation threshold value, and recording the scanning step length adjustment condition after the acquisition is completed.

[0055] Step 500: identifying the local coherence peak of the continuous segment of the adjustment state value based on the scanning step length adjustment condition.

[0056] Step 600: calculating the peak position and the corresponding depth value of the local coherence peak by using the improved barycenter algorithm.

[0057] As a specific embodiment, the above steps are described in detail:

[0058] HAR structure plays an important role in the manufacturing and design of semiconductor devices such as microelectronic devices. With the continuous reduction of the size of semiconductor devices, especially in the process nodes of micro-nanometer level, the depth value measurement of HAR structure is facing challenges. White light scanning interference technology shows certain advantages in the measurement of HAR structure, especially its non-contact, nanometer-level resolution and large-range measurement characteristics, making it a tool for measuring and characterizing complex microstructures in the semiconductor field. However, this technology relies on scanning each position and collecting a large number of interference images. In order to ensure the accuracy of the measurement, a more detailed scanning step length is required when measuring large-size or complex three-dimensional structures, which limits the measurement efficiency of white light scanning interference technology. In addition, under the influence of thin film multi-beam interference and numerical aperture, the interference signal at a single pixel is usually superimposed by the scattered reflection light around the measured point, making the coherent signal present multiple interference peaks, which makes the application effect of the existing peak positioning algorithm worse. Therefore, the present application mainly embodies a white light automatic variable-speed scanning interference system and a processing method for multi-peak ambiguous interference signals. The purpose is to improve the measurement efficiency and accuracy of HAR structure measurement of white light scanning interference technology. Specifically, the improved barycenter method is selected as the peak positioning algorithm of the local coherence peak in the method of the present application. In the specific implementation case experiment, different period and line diameter groove and hole structures are taken as the objects.

[0059] The specific application method is shown in the method flow shown in Figure 1 .

[0060] Due to the relatively large focusing spot size, when WLSI measures the bottom plane of HAR microstructure, the scattered reflection signal from the non-focal plane will interfere with the collected interference signal. As shown in the test beam propagation process of the white light interference system in Figure 2 , the bottom signal of the HAR structure collected on the CCD target surface collects the reflection light of the film surface layer and the bottom layer via light propagation. This microstructure film and high aspect ratio feature make the final superimposed interference signal appear multiple coherent peaks, which further affects the solution of the expected height information.

[0061] Based on this, combined with the basic theory of partially coherent light interference, the mathematical model equation of multi-peak interference signal considering the influence of film layer and HAR structure characteristics is established as follows:

[0062]

[0063] Where, S i (z,NA) represents the area factor, the area factor participating in the formation of local interference area signal and Ω = ∑ i＝1,2,3 S i (z,NA), the background light I bg is equal to the sum of the reference light path light intensity I ref and the test light path light intensity I surf . Z is the surface height to be measured, c is the speed of light, Δν and respectively represent the spectral width and average frequency of the broadband light source. Different from the conventional partially coherent light field distribution, the formula defines the area factor S i (z,NA), which represents the weight of the multi-layer surface in the interference signal formation process. This term is mainly related to the numerical aperture NA and the scanning longitudinal position z. When NA decreases or z position moves up (i.e. the surface layer is measured), the multi-peak characteristics of I(z) decay with the decrease of S i (z,NA), and then degenerate into single-peak interference signal which can be directly calculated by algorithm.

[0064] Further, considering that the light intensity value distribution near the peak of the wide light interference signal presents oscillation, the peripheral area of the measured area is divided into a surrounding area for monitoring the equal path distance position in the scanning process. And the light intensity fluctuation in the area is selected to realize the local interference signal judgment and fine adjustment of sampling. The detailed parameter basis of setting the monitoring area is shown in Figure 3 . The purple area is the HAR structure scale information to be obtained, and the area surrounded by the two yellow dashed lines is the monitoring area for evaluating the light intensity fluctuation. The height distribution of HAR structure on the wafer is non-continuous step type, and the interference fringes on the surface of the same height present band straight line color fringes moving. As can be seen from the mathematical model, the Gaussian envelope term is maximum at equal path distance z=0, and rapidly decays with the increase of coherence distance.

[0065] Based on this, the point coordinates in the plane area should satisfy the condition:

[0066] max{d(∑1(x1,y1),∑2(x2,y2))}=FWHM

[0067] min{d(∑2(x2,y2),T(x,y))}=l max

[0068] Wherein, ∑1(x1,y1),∑2(x2,y2) are points on curve ∑1,∑2 respectively, the maximum Euclidean distance between curves equals to the full width at half maximum (FWHM) of the Gaussian envelope curve of interference signal. T(x,y) is a point in the region T, the minimum Euclidean distance from the points on curve ∑2 to the region T equals to the maximum coherence length l of the broadband light source max . The first distance condition in the formula maximizes the light intensity fluctuation near the interference peak into the region T1 to capture the light intensity fluctuation. The second distance condition maximizes the exclusion of redundant information of defocus region. When the interference fringes enter the region T1 to trigger the monitoring state, the region T just enters the coherence range and at the same time reduces the PZT step distance to obtain refined sampling data. When the interference fringes leave the region T1 to release the monitoring state, the region T leaves the coherence range and adjusts the large step sampling frequency of the PZT to reduce the data redundancy.

[0069] Further, the trigger condition of the region T1 is set as follows: first, start running with a set PZT initial step size, and collect the initial two images I1, I2. The light intensity fluctuation evaluation function ψ is established by the mean square deviation of the light intensity in the region T1 i , and its expression is:

[0070] ψ i =std[I i (T1)-I i-1 (T1)],i=2···N

[0071] Wherein, std(·) is the mean square deviation function, and after calculating the light intensity fluctuation evaluation function ψ2 corresponding to I1, I2, multiply by the coefficient k as the threshold η. The value of k is between 1.1 and 1.4, and k is too small means that noise, stray light and other interference factors are easy to cause the monitoring of the region T1 to be misjudged and collect useless interference information, and k is too large means that the region T1 is not easy to be triggered to monitor and thus miss part of the information of the coherence region.

[0072] Further, after the threshold is determined, the PZT continues to acquire the image I3, calculates ψ3 and compares it with the threshold η, and when ψ3 is less than η, the PZT keeps the original large step, and when ψ3 is greater than or equal to η, the PZT reduces the step size for refined scanning at the next position. In this way, the white light variable step scanning interference measurement process is completed until the Nth step is completed.

[0073] Based on the established mathematical model, there is not only a light intensity maximum value at one equal optical path in the interference signal obtained after the PZT scanning is completed, and part of the reflected light will be received at the local edge of the measured region by the light beam with a larger aperture angle. The part of the surface reflected interference beam produces redundant local interference peaks in the signal, which further affects the accuracy of solving the equal optical path position.

[0074] Furthermore, in order to correctly separate the desired local interference region signal from the multi-coherence peak signal, a monitoring state value is introduced in the step adjustment link to mark the coherence peak position. Figure 4 As shown, the sampling rhythm is optimized by using a variable-step scanning interferometer system. Interference signal areas are finely sampled, while out-of-focus areas are monitored using only sparse sampling to monitor light intensity fluctuations in area T1. When the PZT step size is adjusted during scanning, a monitoring state is recorded as a value of 0. When the PZT step size is not adjusted, the monitoring state is recorded as a random value within the range (0, 1).

[0075] Based on this, in order to verify the effectiveness of this setting, Figure 5 Part (a) shows the light intensity fluctuation value of area T1 during the traditional constant step scanning process. Every time the area to be measured T enters the coherence range, the ψ on T1 i The value will increase rapidly and determine the value of the monitoring status.

[0076] Correspondingly, when the variable step size scanning method is adopted, we get Figure 5 The monitoring state value of part (b) is plotted on the Figure 5 In this case, the invention method designs an algorithm for extracting continuous values ​​to realize the identification of continuous segments of monitoring status values, and realizes the matching and positioning of multiple local coherence peaks according to the length and distribution of continuous segments. Figure 5 In the continuous segments ①②③④ in part (c), area T1 monitors four local interference signals, and it can be determined that segments ①②③④ correspond to the thin film surface interference, thin film bottom layer interference, thin film multi-beam interference and structure bottom interference, respectively.

[0077] Furthermore, in order to ensure that the computer can select the corresponding local interference signal to solve the peak position when reconstructing the surface and bottom layer of the HAR structure, it is necessary to distinguish the different surfaces to be measured within T. The microscopic image collected by the scanning interferometer system is significantly affected by stray light and noise. If the surface and bottom layer areas of the HAR structure are directly binarized and then morphologically processed, the final effect is not ideal. Therefore, the maximum light intensity ratio between area ① and area ④ in the signal of each point in T can be calculated, and then binarized to obtain a clear edge contour. In the inventive method, the local coherence peaks of different areas are selected according to the top and bottom of the structure, and then the improved center of gravity method is used to quickly and effectively determine the equal optical path position P. The calculation process is shown in the following formula:

[0078] P=∑ m M(m)·m / ∑ m M(m)

[0079] M(m)=[I(m)-I(m-1)] 2 ,m=2···N s

[0080] where N s represents the length of local coherent peak signal segment, M(m) represents the square of light intensity difference between adjacent frames, which is brought into the center of gravity algorithm to eliminate the influence of background light intensity.

[0081] Comparative Example 1:

[0082] In order to verify the performance of the application method in the actual measurement scene and show its superiority, the applicant conducts experimental verification. The measurement light path is shown in Figure 6 A white light vertical scanning interferometry system is built in the comparative example, and a matching software with variable step function is developed. The system uses a Michelson type 5 times microscopic interferometer, and a white light LED lamp is selected as the wide spectrum light source. The light beam is collected by a color camera with a resolution of 2592x1944 after propagating through the optical system. The scanning process of the objective lens in the vertical direction is driven by a PZT controller with a minimum resolution step of 14 nm. The object to be measured is placed on a horizontal displacement table driven by a two-axis ball screw. Unless otherwise specified in the example, the collected interference images are obtained at a scanning step of 20 nm.

[0083] The measurement area of the comparative experiment in this group is a groove structure with a width of 9 μm and a period of 27 μm on a wafer. The reference measurement depth value is 35.2264 μm obtained by the artificial calibration method. Then, the interference data is collected in the same experimental environment by variable step scanning, where the coarse scanning large step is set to 320 nm and the fine scanning small step is set to 20 nm. The height difference between the upper and lower surfaces of the topography reconstructed by the method is used as the variable step scanning measurement depth result 35.2458 μm, which deviates from the artificial calibration result by only 0.0551%, and the number of collected image frames is 24.4% of the uniform step scanning method. The example results show that the application method can greatly improve the measurement efficiency under the premise of ensuring accuracy.

[0084] Comparative Example 2:

[0085] In order to demonstrate the applicability of the application method to different deep groove sizes and deep hole units, comparative example 2 is performed. The measurement object properties and measurement results in this group of experiments are shown in Table 1. The measurement depth becomes shallower as the structure size decreases, which is consistent with the error of deep silicon etching process. And the data in Table 1 shows that the proposed method achieves stable topography reconstruction results in different periods, different widths and deep hole structures, and the average compression of the number of collected image frames is 75.27%, which improves the measurement efficiency by about 4 times on this group of microstructure samples.

[0086] Table 1 Measurement object properties and measurement results

[0087]

[0088] Comparative Example 3

[0089] In Comparative Example 3, a set of algorithms for interference signal processing are compared. In order to verify the processing effect on multi-peak signals, the three-dimensional topography reconstruction of the sample under test is performed by the proposed method, the improved center of gravity method (Ai), the Fourier transform method (FT) and the wavelet transform method (WT), respectively. The reconstructed groove structure is shown in Figure 7 , wherein Figure 7 The same range of color bars is used in parts (a) to (d), and different colors correspond to different height values. From the three-dimensional overall view, the longitudinal scale of the topography reconstructed by the proposed method is the largest and closest to the reference value, and the depth results obtained by the other three algorithms are shallower. The cross-sectional profile along the diagonal of the three-dimensional topography is obtained in part (e) of Figure 7 , the result of directly processing the multi-peak signal by the Ai algorithm produces a significant error in the topography, and the FT and WT solving results result in a significant lack of depth due to the interference of the oxide film layer.

[0090] In addition, the time consumed for three-dimensional topography reconstruction of the local area is compared in the example, and all image signal processing processes are run on a desktop computer with a 2.50GHz i5-12400F CPU in Matlab software. The proposed method takes a total of 2.20s from image input to reconstruction completion, which is only slightly longer than the 1.28s of the Ai method, while the FT and WT algorithms take 3.78s and 372.33s respectively due to the frequency domain transformation. The reason why the proposed method takes slightly longer than the Ai method is that it has an additional region segmentation process, but this process is the key to solving the error recovery topography of the Ai algorithm. Therefore, overall, the proposed method not only reduces most of the time in variable-speed scanning interferometry, but also has the advantage of short time consumption in algorithm processing, and most importantly, it realizes the accurate measurement result of white light scanning interferometry.

[0091] The above selects a certain measurement object as an example to introduce in detail the white light automatic variable-speed scanning interferometry system and the processing method of multi-peak ambiguous interference signals of the present application. In the content of the present application, a piezoelectric ceramic driver is used as a mechanical mechanism for generating micro-displacement, and an LED light source is used as a wide-spectrum light source for illumination. This specific interferometry system is to help relevant industry personnel better understand the idea and execution process of the method of the present application.

[0092] At the same time, for specific application measurement objects and algorithm processing processes, such as setting the to-be-measured region and the auxiliary detection region to other shapes or dividing them according to other distance limits, using an existing peak positioning algorithm for the improved center of gravity method of the local coherent signal, the method or application based on the above similar target should be considered within the scope covered by the present application method, and these changes should be within the protection scope of the claims of the present application.

[0093] The various embodiments described in this specification are presented for the purpose of illustrating the principles of the present application and its best mode of operation. Each of the embodiments described in this specification are presented for the purpose of illustrating the various aspects of the present application, and the embodiments are not intended to limit the scope of the application.

[0094] The principles and operation of the present application are explained further with reference to the accompanying drawings. While the present application has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and in some instances some features of the present application will be employed without a corresponding use of other features. Accordingly, it is intended that the specification and depicted embodiments are as example only, and do not limit the scope of the present application. Changes can be made in the product by one having ordinary skill in the art without departing from the spirit of the application in its broader aspect. The appended claims are intended to cover and embrace all such changes and modifications.

Claims

1. A method for measuring the depth of a semiconductor microstructure with a high aspect ratio, characterized in that: include: Divide the field of view of the measurement system and determine the positional relationship between the area to be measured and the auxiliary area; Based on the positional relationship between the area to be measured and the auxiliary area, the micro-displacement structure is driven to scan and collect data with an initially set step size to obtain an initial adjacent frame microscopic interferogram; the initial adjacent frame microscopic interferogram is the first two interferograms obtained through data collection; Continue to drive the micro-displacement structure to perform scanning acquisition, and calculate the light intensity fluctuation evaluation function of adjacent frames based on the n-1th interference pattern and the nth interference pattern; where n = [3, N]; N is the total number of interference patterns; Determine whether to adjust the scanning step length according to the light intensity fluctuation evaluation function and the set light intensity fluctuation threshold, and record the scanning step length adjustment after the acquisition is completed; Based on the scanning step size adjustment, identifying a local coherence peak of a continuous segment of the adjustment state value; The improved centroid algorithm is used to calculate the peak position of the local coherence peak and the corresponding depth value.

2. The method for measuring the depth of a semiconductor high aspect ratio micro-scale structure according to claim 1, wherein: The auxiliary area is the peripheral surrounding area of ​​the area to be measured. Based on the field of view area and combined with the basic theory of partially coherent light interference, the following mathematical model equation is established for the general interference signal under the influence of thin film interference and high aspect ratio structural characteristics: Among them, S i (z,NA) represents the regional factor; Ω = ∑ i＝1,2,3 S i (z, NA), represents the regional factors and background light I involved in the formation of local interference region signal; bg Equal to the reference light path intensity I ref And the test light path intensity I surf and; z is the height of the surface to be measured; c is the speed of light; Δν and They represent the spectral width and average frequency of the broadband light source, respectively, and NA represents the numerical aperture. When NA decreases or the z position moves up, the multi-peak characteristics of I(z) decrease with the increase of S i The signal decays with the decrease of (z, NA) and then degenerates into a single-peak interference signal to be solved; Due to the limitations of the experimental environment and optical system, the interference fringes formed appear as strip-shaped straight color fringes moving on the surface at the same height. Based on the mathematical model equation, the Gaussian envelope term in the expression I(z) It is maximum at the equal optical path z = 0 and decays rapidly with the increase of coherence distance. Therefore, the coordinates of points in the field of view plane satisfy the conditions: max{d(∑1(x1,y1),∑2(x2,y2))}=FWHM Where ∑1(x1,y1) and ∑2(x2,y2) are points on curves ∑1 and ∑2 respectively. The maximum Euclidean distance between the curves is equal to the full width at half maximum (FWHM) of the Gaussian envelope curve of the interference signal. T(x,y) is a point in the measured area T. The minimum Euclidean distance from a point on curve ∑2 to area T is equal to the maximum coherence length l of the broadband light source. max .

3. The method for measuring the depth of a semiconductor high aspect ratio micro-scale structure according to claim 1, wherein: The calculation formula for setting the light intensity fluctuation threshold is: η=k·std[I2(T1)-I1(T1)] Wherein, std(·) is the mean square error function. After calculating the light intensity fluctuation evaluation function of the initial adjacent frame microscopic interference patterns I1 and I2 in the auxiliary area T1, it is multiplied by the coefficient k as the threshold η; k is set to 1.1 to 1.

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4. The method for measuring the depth of a semiconductor high aspect ratio micro-scale structure according to claim 1, wherein: The expression of the light intensity fluctuation evaluation function is: ψ i =std[I i (T1)-I i-1 (T1)],i=2···N Where std(·) is the mean square error function, T1 represents the auxiliary area, I i represents the i-th interference pattern, I i-1 represents the i-1th interference pattern, and N is the total number of interference patterns.

5. The method for measuring the depth of a semiconductor high aspect ratio micro-scale structure according to claim 1, wherein: The light intensity fluctuation threshold is set according to the light intensity fluctuation evaluation function to determine whether to adjust the scanning step length. The specific process includes: The light intensity fluctuation evaluation function is compared with the set light intensity fluctuation threshold: when the light intensity fluctuation evaluation function is less than the set light intensity fluctuation threshold, the scanning step length is not adjusted, and the micro-displacement structure maintains the initial set step length; when the light intensity fluctuation evaluation function is greater than or equal to the set light intensity fluctuation threshold, the scanning step length is adjusted to a small step length, and scanning is performed with the updated small step length; the small step length is a set value that is smaller than the initial set step length.

6. The method for measuring the depth of a semiconductor high aspect ratio micro-scale structure according to claim 1, wherein: The recording process of the scanning step adjustment is as follows: When the step size of the micro-displacement structure is adjusted during the scanning process, the monitoring state is recorded as a value of 0, and when the step size of the micro-displacement structure is not adjusted, the monitoring state is recorded as a random value within (0,1).

7. The method for measuring the depth of a semiconductor high aspect ratio micro-scale structure according to claim 1, wherein: The calculation formula of the improved center of gravity algorithm is: P=∑ m M(m)·m / ∑ m M(m) M(m)=[I(m)-I(m-1)] 2 ,m=2···N s Among them, N s represents the length of the local coherence peak signal segment, M(m) represents the square of the light intensity difference between adjacent frames, I(m) represents the mth interference pattern, and P represents the depth value corresponding to the peak position of the local coherence peak.

8. A semiconductor high aspect ratio micro-scale structure depth measurement system, used for applying the method according to any one of claims 1 to 7, characterized in that: include: Light source, aperture, beam expansion and collimation module, beam splitter, imaging lens assembly, camera, absorption plate, micro-displacement structure and interference objective lens; A broad-spectrum light beam is emitted by the light source, which is then emitted after the size of the beam is controlled by an aperture with an adjustable size function. After passing through the formed beam expansion and collimation module, it is modulated into a uniformly distributed light beam. After entering the beam splitter plate, the projected split light is directly irradiated on the absorption plate and absorbed. The reflected measurement split light enters the interference objective lens, which is a Michelson structure and is clamped by a micro-displacement structure to achieve positioning and micro-displacement drive. Under the action of the interference objective lens, the measurement beam carries the morphological information of the object to be measured and returns to the optical path system. Finally, after passing through the imaging lens group, the interference light intensity map is collected by the camera target surface.

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