WO2022267687A1 - 一种基于白光干涉的微纳深沟槽结构快速测量方法 - Google Patents

一种基于白光干涉的微纳深沟槽结构快速测量方法 Download PDF

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WO2022267687A1
WO2022267687A1 PCT/CN2022/089613 CN2022089613W WO2022267687A1 WO 2022267687 A1 WO2022267687 A1 WO 2022267687A1 CN 2022089613 W CN2022089613 W CN 2022089613W WO 2022267687 A1 WO2022267687 A1 WO 2022267687A1
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groove
interferograms
sample
interface
interferogram
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PCT/CN2022/089613
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English (en)
French (fr)
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张可欣
梁宜勇
李国忠
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浙江大学
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Priority to US18/082,552 priority Critical patent/US11733034B2/en
Publication of WO2022267687A1 publication Critical patent/WO2022267687A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/22—Measuring arrangements characterised by the use of optical techniques for measuring depth
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02083—Interferometers characterised by particular signal processing and presentation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/0209—Low-coherence interferometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N2021/0106—General arrangement of respective parts

Definitions

  • the invention relates to a groove structure measurement method in the field of integrated circuit (IC) and microelectromechanical system (MEMS) device measurement, in particular to a fast measurement method for micro-nano deep groove structure based on white light interference.
  • IC integrated circuit
  • MEMS microelectromechanical system
  • the contact type is a stylus optical profiler
  • optical measurement is a non-contact measurement technology.
  • optical measurement techniques optical probe method, scanning tunneling microscope method, laser focusing method and interference microscopy method are included.
  • the probe method is prone to broken needles and damage to sensitive components.
  • contact measurement is gradually reducing the size of the probe, as the surface structure of the sample to be tested becomes more and more complex, there will still be some areas that cannot be detected. detected.
  • the main principle of the scanning tunneling microscope is based on the tunneling effect of quantum mechanics.
  • the measurement object of the scanning tunneling microscope is mainly micron or nanoscale samples, and it is a point measurement, point by point, line by line, surface by surface, which usually takes a long time and has low efficiency. It also needs to find the measurement area on the measured sample. Takes a long time.
  • the basic principle of the laser focusing method is to feed back the focus information generated by the laser unit to the differential photoelectric device through reflection, and then control the vertical movement of the focusing probe through computer processing to obtain the surface topography of the measured sample. , and the working range is on the order of microns.
  • micro-interference structure is used for measurement. Since the light in the micro-interference optical path is converging light, it will be limited by the depth of field of the microscope lens in the actual process, and due to the convergence of the beam, if the focal plane is detected Interfering light is generated above the bottom surface of the grooved sample. The use of parallel light interference will increase the depth range of the sample. In theory, no matter how deep the sample is, it can be vertically incident on the bottom of the sample and exit vertically. In the prior art, the micron-level trench structure is mostly aimed at, and this patent mainly focuses on the simulation and reconstruction of the submillimeter-level trench structure.
  • the algorithm of the invention uses contrast information as an evaluation index to perform effective reconstruction of a set of scanning interferograms. The information is extracted, the image is processed and then 3D reconstruction is performed, the effect obtained is better than the result obtained by directly using the center of gravity method, and the time will also be reduced.
  • the present invention proposes a rapid measurement method for micro-nano deep groove structures based on white light interference, which utilizes the characteristics of high detection depth and small error obtained by parallel light white light interference, and combines parallel light white light interference with The combination of accelerated methods enables three-dimensional topography measurement of submillimeter-structured grooves.
  • the present invention comprises the following steps:
  • a white light interference system including a light source, a beam splitter, a CCD camera and a plane mirror; the white light generated by the light source is incident into the beam splitter for transmission and reflection, and the transmitted light of the beam splitter is reflected by the plane mirror and then incident back into the beam splitter, and then incident back into the beam splitter.
  • the transmitted light of the mirror is reflected in the beam splitter, and the reflected beam is incident into the CCD camera as the first beam;
  • the reflected light of the mirror is transmitted in the beam splitter, and the transmitted beam is used as the second beam and enters the CCD camera; the interference between the first beam and the second beam is detected by the CCD camera, and the CCD camera detects and collects the groove Interferogram;
  • the CCD camera collects multiple sets of groove interferograms and records each groove in each group. The number corresponding to the interferogram;
  • the interface reconstruction images corresponding to all groups of groove interferograms of the groove samples are stitched together to obtain the three-dimensional structure reconstruction images of the groove samples, and the depth and width of the groove samples are measured according to the three-dimensional structure reconstruction images.
  • Described step 2) specifically is:
  • the step 3) calculates the contrast of each group of groove grayscale interferograms, which is specifically set by the following formula:
  • J is the contrast of the groove gray-scale interferogram
  • Imax is the maximum gray value of the groove gray-scale interferogram
  • Imin is the minimum gray value of the groove gray-scale interferogram.
  • step 5 it is judged whether all sub-regions are interface regions according to the preset difference threshold and the maximum contrast ratio, specifically:
  • the absolute value is taken as the contrast difference of the current sub-region. If the contrast difference of the current sub-region is less than or equal to the preset difference threshold, the current sub-region is an interface region. If If the contrast difference of the current sub-region is greater than the preset difference threshold, the current sub-region is not an interface region.
  • the position of the groove sample or the plane mirror where clear interference fringes appear is specifically the upper surface of the groove sample, the bottom of the groove and the upper surface of the boss in the groove, wherein the upper surface of the boss and the upper surface of the groove sample Surface or groove bottom parallel.
  • the optical path of the present invention is simpler, and the method combined with the algorithm is used to detect the submillimeter level groove structure, the width can reach hundreds of microns, and the depth can be several millimeters.
  • the present invention can accelerate the process of collecting the groove interferogram by quickly skipping the groove interferogram.
  • the present invention has less reconstruction time and has an acceleration effect. Compared with the traditional algorithm, the reconstruction time of the three-dimensional structure is reduced, and the effect is better than the traditional center of gravity method. reconstruction effect.
  • the present invention proposes a method for firstly reconstructing the local area, and then splicing the local reconstruction results according to the image segmentation results to obtain the three-dimensional reconstruction result of the whole sample. This method plays an important role in improving the effect and speed of image reconstruction.
  • the invention can use the combination of white light interference and acceleration algorithm to detect the appearance of submillimeter-level high-aspect-ratio structural grooves, and the depth of the detection structure can reach millimeter level.
  • Fig. 1 is the overall flowchart of the present invention.
  • Fig. 2 is an optical path diagram of the white light interference system.
  • FIG. 3 is a schematic diagram of a trench structure with vertical sidewalls.
  • Fig. 4 is a schematic diagram of a trench sample structure with inclined sidewalls.
  • Figure 5 is a comparison of the interferograms of grooves with different depths.
  • FIG. 6 is a diagram of a contrast comparison process.
  • Fig. 7 is a comparison diagram between the result obtained by using the interpolation center of gravity method and the three-dimensional structure reconstruction diagram of the present invention.
  • the trench samples described in the present invention are typically, but not limited to, microelectronics and power semiconductor devices, for example. Since the grooved sample used in the present invention has only the upper surface and the grooved bottom of the grooved sample, the grooved sample with two surfaces is taken as an example in the following step description.
  • the present invention comprises the following steps:
  • a white light interference system including a light source, a beam splitter, a CCD camera, and a plane mirror; the white light generated by the light source is incident on the beam splitter for transmission and reflection, and the transmitted light of the beam splitter is reflected by the plane mirror and then incident back into the beam splitter In the mirror, the transmitted light that is incident back to the beam splitter is reflected in the beam splitter, and the reflected beam is used as the first beam and enters the CCD camera; the reflected light of the beam splitter is incident back into the beam splitter after being reflected by the groove, and the The reflected light back to the beam splitter is transmitted in the beam splitter, and the transmitted beam is used as the second beam and enters the CCD camera; the interference between the first beam and the second beam is detected by the CCD camera, and the CCD camera detects and collects Groove interferogram; where the light source is a wide-spectrum light source with a wavelength range of 380nm-780nm, that is
  • the CCD camera collects two sets of groove interferograms and records each groove in each group. The number corresponding to the interferogram;
  • Step 2) is specifically:
  • the size of the groove sample is 5mm*5mm
  • the upper part of the side wall inclined groove is 1mm*5mm
  • the lower part is 0.8mm*5mm
  • the depth is 0.1 mm
  • the lengths of the reference arm and the measuring arm of the measurement optical path corresponding to the groove sample are both 60 mm.
  • the position of the grooved sample or plane mirror along the optical axis record the positions of all grooved samples or plane mirrors with clear interference fringes in the CCD camera and the times of clear interference fringes, among which the grooved samples with clear interference fringes or The position of the plane mirror is recorded as the interface position;
  • the position of the groove sample or the plane mirror with clear interference fringes is specifically the upper surface of the groove sample, the bottom of the groove and the upper surface of the boss in the groove, wherein the upper surface of the boss Parallel to the upper surface of the grooved sample or the bottom of the groove. In this embodiment, it is the upper surface of the groove sample and the bottom of the groove, so the number of clear interference fringes is twice.
  • the direction along the optical axis is the direction parallel to the beam direction at the grooved sample or plane mirror;
  • the groove interferograms within the required range above and below the interface position and the current interface position are used as a set of groove interferograms of the groove sample, so as to obtain two sets of groove interferograms of the groove sample and each groove in each group
  • the number corresponding to the interferogram; among them, the number of groups of groove samples is the same as the number of clear interference fringes. Since the spectral range of visible light is 380-780nm, it is recommended to be within 3um in theory. In practice, the required range is 2um.
  • the preset step size is within 200nm, which is determined according to the actual spectral width used. In specific implementation, the preset step size is 80nm.
  • step 3 the contrast of each group of groove grayscale interferograms is calculated, which is specifically set by the following formula:
  • J is the contrast of the groove gray-scale interferogram
  • Imax is the maximum gray value of the groove gray-scale interferogram
  • Imin is the minimum gray value of the groove gray-scale interferogram.
  • the direction of the fringe development is the direction of the fringe extension
  • obtain each sub-region of the three-dimensional reconstruction map of the local structure and calculate each sub-region
  • the contrast ratio of each sub-region is judged according to the preset difference threshold and the maximum contrast whether it is an interface region.
  • the preset difference threshold is 0.1. If it is an interface area, record the coordinate parameters of the current sub-area, otherwise, do not record; obtain the coordinate parameters of all interface areas; extract the interface reconstruction map in the local structure 3D reconstruction map according to the coordinate parameters of all interface areas ;
  • a in Figure 6 is the equal optical path interferogram on the upper surface of the deep groove.
  • the contrast of the two sub-regions framed in the figure is different, and the sub-region on the left is similar to the overall contrast value of the 3D reconstruction image of the local structure. , and the contrast value of the sub-region on the right will decrease significantly compared with the contrast value of the whole image because it is far away from the equi-path position.
  • Figure 6b is the equal optical path interferogram of the lower surface of the deep groove.
  • the contrast values in the two sub-regions are completely opposite, that is, the right sub-region is at the equal optical path position, so the contrast of the right sub-region is the same as that of the entire picture.
  • the contrast difference is small, and the contrast of the left sub-region is far away from the position of equal optical path, so the contrast difference between the contrast and the whole picture is relatively large.
  • step 5 it is judged whether all sub-regions are interface regions according to the preset difference threshold and the maximum contrast, specifically:
  • the absolute value is taken as the contrast difference of the current sub-region. If the contrast difference of the current sub-region is less than or equal to the preset difference threshold, the current sub-region is an interface region. If If the contrast difference of the current sub-region is greater than the preset difference threshold, the current sub-region is not an interface region.
  • steps 3)-5) for the remaining groups of groove interferograms of the groove sample to obtain the interface reconstruction diagram corresponding to all groups of groove interferograms of the groove sample; in the white light interferometry system, the different spectral widths used Broad-spectrum light source, the interference distance to produce clear fringes near the equal optical path position is different. When the optical path is smaller than the interference distance, clear interference fringes will be produced. When the optical path is greater than the interference distance, there will be no interference fringes.
  • the groove depth is within the interference distance, the groove is a shallow groove, and the upper surface and the lower surface will be included in a groove interferogram If the groove depth is greater than the interference distance, the groove is a deep groove, and the interference fringes of the upper surface and the lower surface will not be included in a groove interferogram.
  • a of Fig. 5 is a reconstructed image of the interface of the shallow trench, where the depth of the shallow trench sample used is 100 nm.
  • Figure 5b and Figure 5c are reconstruction images of the interface of deep grooves, in which the depth of the deep groove sample used is 300um, and Figure b is the reconstruction image of the interface collected at the position of equal optical path on the upper surface, Figure c is the reconstruction image of the interface collected at the equal optical path position of the lower surface. You can see the difference in contrast in different areas of the image.
  • the interface reconstruction images corresponding to all groups of groove interferograms of the groove samples are stitched together to obtain the three-dimensional structure reconstruction images of the groove samples, and the depth and width of the groove samples are measured according to the three-dimensional structure reconstruction images.
  • the present invention uses Virtuallab Fusion to simulate and collect the groove samples to obtain 4000 groove interferograms, and uses Python to perform three-dimensional reconstruction on the collected 4000 groove interferograms.
  • the result map obtained by the inventive method the reconstruction time required by the direct use of the center of gravity method in the existing method is 1.54s
  • (a) in Figure 7 is the three-dimensional structure reconstruction map obtained by the interpolation center of gravity method in the existing method, using this The reconstruction time required by the inventive method is 0.04s.
  • Figure 7(a) is the three-dimensional structure reconstruction diagram obtained by the inventive method. It can be seen that the present invention not only significantly improves the reconstruction speed, but also greatly improves the reconstruction effect. improvement.

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Abstract

本发明公开了一种基于白光干涉的微纳深沟槽结构快速测量方法。本发明包括：搭建白光干涉***，利用白光干涉***测量沟槽的结构，CCD相机采集获得多组沟槽干涉图及各组中每张沟槽干涉图对应的编号；对沟槽样品的各组沟槽干涉图进行处理后，获得各组沟槽干涉图的最大对比度与局部结构三维重建图；提取各组沟槽干涉图对应的局部结构三维重建图中的分界面重建图；将所有组沟槽干涉图对应的分界面重建图进行拼接后获得沟槽样品的三维结构重建图，根据三维结构重建图测量沟槽样品的深度和宽度。本发明光路更为简洁，方法能对亚毫米级别的沟槽结构进行探测，宽度达到几百微米，深度达到几毫米，测量速度得到很大提升。

Description

一种基于白光干涉的微纳深沟槽结构快速测量方法 技术领域
本发明涉及了集成电路(IC)和微机电***(MEMS)器件测量领域的一种沟槽结构测量方法，具体涉及了一种基于白光干涉的微纳深沟槽结构快速测量方法。
背景技术
现有对沟槽结构进行探测的技术中，主要有以下几种方式：分为接触式和非接触式方法。接触式是触针式光学轮廓仪，光学测量属于非接触式的测量技术。在光学测量技术中，包含光学探针法、扫描隧道显微镜法、激光聚焦法和干涉显微法。其中，探针法容易对出现断针现象，且容易对敏感元件造成破坏，接触式测量虽然在逐步缩小探针尺寸，但是随着待测样品表面结构越来越复杂，仍会有一部分区域无法探测到。扫描隧道显微镜主要原理是依据量子力学的隧道效应，粒子运动到高于粒子能量的壁垒也是有一定概率穿过壁垒的。扫描隧道显微镜的测量对象主要是微米或纳米级的样品，且是点式测量，逐点、逐线、逐面扫描，通常耗费时间长，效率较低，在被测样品上找到测量区域也需要耗费较长时间。激光聚焦法基本原理为，将由激光单元发生的计光经过反射将焦点信息反馈到差分光电器，然后通过计算机处理，控制聚焦式测头垂直方向的上下移动，以获得被测样品的表面形貌，工作区间约为微米量级。
对于白光干涉测量技术，使用显微干涉结构进行测量，由于显微干涉光路中光是汇聚光，所以在实际过程中会收到显微镜头景深的限制，且由于光束的汇聚，如果焦面在探测沟槽样品底面之上，会产生干扰光。使用平行光干涉会增加样品的深度范围，理论上无论样品深度为多少都可以垂直入射到样品底部并垂直出射。现有技术中，多针对微米级别的沟槽结构，本专利主要针对亚毫米级别的沟槽结构进行仿真重建。
同时，如果直接使用传统的重心法与差值重心法对深度较宽的结构进行三维重建，会引入很多干扰，本专利发明的算法利用对比度信息作为评价指标，对一组扫描干涉图中的有效信息进行提取，对图像做处理之后再进行三维重建，得到的效果优于直接使用重心法得到的结果，同时时间也会减少。
发明内容
为了解决背景技术中存在的问题，本发明提出了一种基于白光干涉的微纳深沟槽结构快速测量方法，利用平行光白光干涉探测深度高，所得误差小的特点，将平行光白光干涉与加速方法相结合实现对亚毫米结构的沟槽进行三维形 貌测量。
本发明的技术方案如下：
本发明包括以下步骤：
1)搭建白光干涉***，包括光源、分光镜、CCD相机和平面镜；光源产生白光入射到分光镜中发生透射和反射，分光镜的透射光通过平面镜的反射后入射回分光镜中，入射回分光镜的透射光在分光镜中产生反射，反射后的光束作为第一光束并入射至CCD相机中；分光镜的反射光通过沟槽样品的沟槽的反射后入射回分光镜中，入射回分光镜的反射光在分光镜中产生透射，透射后的光束作为第二光束并入射至CCD相机中；第一束光与第二束光产生干涉被CCD相机所探测，CCD相机探测采集获得沟槽干涉图；
2)利用白光干涉***测量沟槽的结构，记录CCD相机中出现清晰干涉条纹的次数，根据出现清晰干涉条纹的次数，CCD相机采集获得多组沟槽干涉图并记录各组中每张沟槽干涉图对应的编号；
3)对沟槽样品的每组沟槽干涉图进行灰度处理后获得对应的沟槽灰度干涉图，计算当前组沟槽灰度干涉图的对比度，记录当前组沟槽灰度干涉图的最大对比度；
4)根据当前组沟槽干涉图和当前组中每张沟槽干涉图对应的编号，利用重心法或差值重心法对当前组沟槽干涉图进行局部三维重建，获得当前组沟槽干涉图对应的局部结构三维重建图；
5)沿与沟槽干涉图中的条纹展开方向相垂直的方向对局部结构三维重建图进行区域划分，获得局部结构三维重建图得各个子区域，计算各个子区域的对比度，根据预设差值阈值和最大对比度判断各个子区域是否是分界面区域，如果是分界面区域，则记录当前子区域的坐标参数，否则，则不记录；获得所有分界面区域的坐标参数；根据所有分界面区域的坐标参数提取局部结构三维重建图中的分界面重建图；
6)对沟槽样品的剩余组沟槽干涉图重复步骤3)-5)，获得沟槽样品所有组沟槽干涉图对应的分界面重建图；
7)将沟槽样品所有组沟槽干涉图对应的分界面重建图进行拼接后获得沟槽样品的三维结构重建图，根据三维结构重建图测量沟槽样品的深度和宽度。
所述步骤2)具体为：
2.1)将沟槽样品沿沟槽长度方向倾斜放置，调整沟槽样品的倾斜角度以及白光干涉***中的平面镜与分光镜之间或者沟槽样品与分光镜之间的沿光轴的距离，直至CCD相机所采集的图像上产生条纹，固定沟槽样品的倾斜角度、沟槽 样品和平面镜；
2.2)沿光轴方向移动沟槽样品或平面镜的位置，记录CCD相机中所有出现清晰干涉条纹时的沟槽样品或平面镜的位置以及出现清晰干涉条纹的次数，其中出现清晰干涉条纹的沟槽样品或平面镜的位置记为分界面位置；
2.3)再次沿光轴方向移动沟槽样品或平面镜的位置，利用CCD相机在预设步长下采集沟槽干涉图并依次对每张沟槽干涉图进行编号，选取所有分界面位置的上下所需范围内以及所有分界面位置的沟槽干涉图，将一个分界面位置的上下所需范围内以及当前分界面位置的沟槽干涉图作为沟槽样品的一组沟槽干涉图，从而获得沟槽样品的多组沟槽干涉图及各组中每张沟槽干涉图对应的编号。
所述步骤3)中计算每组沟槽灰度干涉图的对比度，具体通过以下公式进行设置：
Figure PCTCN2022089613-appb-000001
其中，J为沟槽灰度干涉图的对比度，Imax为沟槽灰度干涉图的最大灰度值，Imin为沟槽灰度干涉图的最小灰度值。
所述步骤5)中根据预设差值阈值和最大对比度判断所有子区域是否是分界面区域，具体为：
将每个子区域的对比度与最大对比度作差后取绝对值作为当前子区域的对比度差值，如果当前子区域的对比度差值小于等于预设差值阈值，则当前子区域是分界面区域，如果当前子区域的对比度差值大于预设差值阈值，则当前子区域不是分界面区域。
所述出现清晰干涉条纹的沟槽样品或平面镜的位置具体为沟槽样品上表面、沟槽底部和沟槽中的凸台的上表面，其中，所述凸台的上表面与沟槽样品上表面或沟槽底部平行。
本发明的有益效果是：
本发明光路相比于现为干涉结构的光路更为简洁，且使用与算法相结合的方法对亚毫米级别的沟槽结构进行探测，宽度可以达到几百微米，深度可以得到几毫米。
本发明在采集沟槽干涉图上，可以通过快速略过实现采集沟槽干涉图过程中的加速。
本发明在沟槽三维形貌重建过程中，本发明的重建时间较少，有加速作用， 对三维结构的重建时间相比于传统算法有缩减，并且效果相比于传统的重心法具有更好的重建效果。
本发明在沟槽三维形貌重建过程中，提出了一种先局部重建，再根据图像分割结果进行局部重建结果拼接从而得到整体样品的三维重建结果的方法。这一方法对图像重建的效果和速度的提升都有重要作用。
本发明能够使用白光干涉与加速算法相结合对亚毫米级别高深宽比结构沟槽进行形貌检测，探测结构的深度可达到毫米级别。
附图说明
图1是为本发明的整体流程图。
图2是白光干涉***的光路图。
图3是侧壁垂直的沟槽结构示意图。
图4是侧壁倾斜的沟槽样品结构示意图。
图5是不同深度沟槽干涉图对比。
图6是对比度比较过程图。
图7是使用插值重心法重建获得结果图与本发明的三维结构重建图的对比图。
具体实施方式
下面结合附图及具体实例对本发明作进一步详细说明。
本发明所述的沟槽样品通常例如为微电子和功率半导体器件，但不限于此。由于本发明所使用的沟槽样品仅有沟槽样品上表面和沟槽底部，所以下面的步骤说明中以具有两个表面的沟槽样品为例。
如图1所示，本发明包括以下步骤：
1)搭建白光干涉***，如图2所示，包括光源、分光镜、CCD相机和平面镜；光源产生白光入射到分光镜中发生透射和反射，分光镜的透射光通过平面镜的反射后入射回分光镜中，入射回分光镜的透射光在分光镜中产生反射，反射后的光束作为第一光束并入射至CCD相机中；分光镜的反射光通过沟槽的反射后入射回分光镜中，入射回分光镜的反射光在分光镜中产生透射，透射后的光束作为第二光束并入射至CCD相机中；第一束光与第二束光产生干涉被CCD相机所探测，CCD相机探测采集获得沟槽干涉图；其中，光源为宽光谱光源，波长范围为380nm-780nm，即可见光光谱范围，在其内选取任意光谱宽度的宽光谱光源即可，分光镜与平面镜光路为参考臂，分光镜与沟槽样品光路为测量臂。
2)利用白光干涉***测量沟槽的结构，记录CCD相机中出现清晰干涉条纹 的次数，根据出现清晰干涉条纹的次数，CCD相机采集获得两组沟槽干涉图并记录各组中每张沟槽干涉图对应的编号；
步骤2)具体为：
2.1)将沟槽样品沿沟槽长度方向倾斜放置，调整沟槽样品的倾斜角度以及白光干涉***中的平面镜与分光镜之间或者沟槽样品与分光镜之间的距离，直至CCD相机所采集的图像上产生清晰的条纹，固定沟槽样品的倾斜角度、沟槽样品和平面镜；侧壁垂直的沟槽结构示意图如图3所示，沟槽样品的尺寸为5mm*5mm，沟槽宽度为0.2mm，深度为2mm，该沟槽样品对应的测量光路的参考臂和测量臂的长度为15mm。侧壁倾斜的沟槽样品结构示意图如图4所示，沟槽样品的尺寸为5mm*5mm，侧壁倾斜沟槽上部分尺寸为1mm*5mm，下部分尺寸为0.8mm*5mm，深度为0.1mm，该沟槽样品对应的测量光路的参考臂和测量臂的长度均为60mm。
2.2)沿光轴方向移动沟槽样品或平面镜的位置，记录CCD相机中所有出现清晰干涉条纹的沟槽样品或平面镜的位置以及出现清晰干涉条纹的次数，其中出现清晰干涉条纹的沟槽样品或平面镜的位置记为分界面位置；出现清晰干涉条纹的沟槽样品或平面镜的位置具体为沟槽样品上表面、沟槽底部和沟槽中的凸台的上表面，其中，凸台的上表面与沟槽样品上表面或沟槽底部平行。本实施例中为沟槽样品上表面和沟槽底部，因此出现清晰干涉条纹的次数为两次。沿光轴方向为与沟槽样品或平面镜处的光束方向平行的方向；
2.3)再次沿光轴方向移动沟槽样品或平面镜的位置，利用CCD相机在预设步长下采集沟槽干涉图并依次对每张沟槽干涉图进行编号，其中不在分界面位置的上下所需范围内的区域为快速采集区域，仅需要获得该区域中的所有沟槽干涉图的编号，选取所有分界面位置的上下所需范围内以及所有分界面位置的沟槽干涉图，将一个分界面位置的上下所需范围内以及当前分界面位置的沟槽干涉图作为沟槽样品的一组沟槽干涉图，从而获得沟槽样品的两组沟槽干涉图及各组中每张沟槽干涉图对应的编号；其中，沟槽样品的的组数与出现清晰干涉条纹的次数相同，由于可见光光谱范围是380-780nm，理论上建议3um以内，具体实施中，所需范围为2um。预设步长为200nm以内，根据实际采用的光谱宽度确定，具体实施中，预设步长为80nm。
3)对沟槽样品的每组沟槽干涉图进行灰度处理后获得对应的沟槽灰度干涉图，计算每组沟槽灰度干涉图的对比度，记录当前组沟槽灰度干涉图的最大对比度；
步骤3)中计算每组沟槽灰度干涉图的对比度，具体通过以下公式进行设置：
Figure PCTCN2022089613-appb-000002
其中，J为沟槽灰度干涉图的对比度，Imax为沟槽灰度干涉图的最大灰度值，Imin为沟槽灰度干涉图的最小灰度值。
4)根据当前组沟槽干涉图和当前组中每张沟槽干涉图对应的编号，利用重心法或差值重心法对当前组沟槽干涉图进行局部三维重建，获得当前组沟槽干涉图对应的局部结构三维重建图；
5)沿与沟槽干涉图中的条纹展开方向相垂直的方向对局部结构三维重建图进行区域划分，条纹展开方向为条纹延伸方向，获得局部结构三维重建图得各个子区域，计算各个子区域的对比度，根据预设差值阈值和最大对比度判断各个子区域是否是分界面区域，具体实施中，预设差值阈值为0.1。如果是分界面区域，则记录当前子区域的坐标参数，否则，则不记录；获得所有分界面区域的坐标参数；根据所有分界面区域的坐标参数提取局部结构三维重建图中的分界面重建图；
如图6所示，图6的a为深沟槽上表面等光程干涉图，图中框出的两个子区域对比度是不同的，左边的子区域与局部结构三维重建图整体的对比度值近似，而右边的子区域由于远离等光程位置，对比度值相比于整张图片的对比度值会显著下降。图6的b为深沟槽下表面等光程干涉图，两个子区域中对比度值是完全相反的，即右边的子区域是等光程位置，所以右边的子区域的对比度与整张图片的对比度差值较小，左边的子区域的对比度由于远离等光程位置，对比度与整张图片的对比度差值较大。
步骤5)中根据预设差值阈值和最大对比度判断所有子区域是否是分界面区域，具体为：
将每个子区域的对比度与最大对比度作差后取绝对值作为当前子区域的对比度差值，如果当前子区域的对比度差值小于等于预设差值阈值，则当前子区域是分界面区域，如果当前子区域的对比度差值大于预设差值阈值，则当前子区域不是分界面区域。
6)对沟槽样品的剩余组沟槽干涉图重复步骤3)-5)，获得沟槽样品所有组沟槽干涉图对应的分界面重建图；在白光干涉***中，使用的不同光谱宽度的宽光谱光源，在等光程位置附近产生清晰条纹的干涉距离是不同的，当光程小于干涉距离时，会产生清晰的干涉条纹。当光程大于干涉距离时，则不会有干涉条纹，如果沟槽深度在干涉距离之内，则该沟槽为浅沟槽，则在一张沟槽干涉 图中会包含上表面和下表面的干涉条纹；如果沟槽深度大于干涉距离，则该沟槽为深沟槽，则不会在一张沟槽干涉图中同时包含上表面和下表面的干涉条纹。
如图5所示，图5的a为浅沟槽的分界面重建图，其中使用的浅沟槽样品的深度为100nm。图5的b和图5的c均为深沟槽分界面重建图，其中使用的深沟槽样品的深度为300um，图b为处于上表面等光程位置采集到的分界面重建图，图c为处于下表面等光程位置采集到的分界面重建图。可以看出图像中不同区域的对比度差异。
7)将沟槽样品所有组沟槽干涉图对应的分界面重建图进行拼接后获得沟槽样品的三维结构重建图，根据三维结构重建图测量沟槽样品的深度和宽度。
在具体实施中，本发明使用Virtuallab Fusion对沟槽样品进行仿真模拟采集获得4000张沟槽干涉图，使用Python对采集获得4000张沟槽干涉图进行三维重建，图7为使用现有方法和本发明方法所得到的结果图，现有方法中直接使用重心法所需的重建时间是1.54s，图7的(a)为现有方法中的插值重心法重建获得的三维结构重建图，使用本发明方法所需的重建时间是0.04s，图7的(a)为本发明方法重建获得的三维结构重建图，可以看出本发明不仅在重建速度上有显著的提升，在重建效果也有很大的提高。

Claims (5)

  1. 一种基于白光干涉的微纳深沟槽结构快速测量方法，其特征在于，包括以下步骤：
    1)搭建白光干涉***，包括光源、分光镜、CCD相机和平面镜；光源产生白光入射到分光镜中发生透射和反射，分光镜的透射光通过平面镜的反射后入射回分光镜中，入射回分光镜的透射光在分光镜中产生反射，反射后的光束作为第一光束并入射至CCD相机中；分光镜的反射光通过沟槽样品的沟槽的反射后入射回分光镜中，入射回分光镜的反射光在分光镜中产生透射，透射后的光束作为第二光束并入射至CCD相机中；第一束光与第二束光产生干涉被CCD相机所探测，CCD相机探测采集获得沟槽干涉图；
    2)利用白光干涉***测量沟槽的结构，记录CCD相机中出现清晰干涉条纹的次数，根据出现清晰干涉条纹的次数，CCD相机采集获得多组沟槽干涉图并记录各组中每张沟槽干涉图对应的编号；
    3)对沟槽样品的每组沟槽干涉图进行灰度处理后获得对应的沟槽灰度干涉图，计算当前组沟槽灰度干涉图的对比度，记录当前组沟槽灰度干涉图的最大对比度；
    4)根据当前组沟槽干涉图和当前组中每张沟槽干涉图对应的编号，利用重心法或差值重心法对当前组沟槽干涉图进行局部三维重建，获得当前组沟槽干涉图对应的局部结构三维重建图；
    5)沿与沟槽干涉图中的条纹展开方向相垂直的方向对局部结构三维重建图进行区域划分，获得局部结构三维重建图得各个子区域，计算各个子区域的对比度，根据预设差值阈值和最大对比度判断各个子区域是否是分界面区域，如果是分界面区域，则记录当前子区域的坐标参数，否则，则不记录；获得所有分界面区域的坐标参数；根据所有分界面区域的坐标参数提取局部结构三维重建图中的分界面重建图；
    6)对沟槽样品的剩余组沟槽干涉图重复步骤3)-5)，获得沟槽样品所有组沟槽干涉图对应的分界面重建图；
    7)将沟槽样品所有组沟槽干涉图对应的分界面重建图进行拼接后获得沟槽样品的三维结构重建图，根据三维结构重建图测量沟槽样品的深度和宽度。
  2. 根据权利要求1所述的一种基于白光干涉的微纳深沟槽结构快速测量方法，其特征在于，所述步骤2)具体为：
    2.1)将沟槽样品沿沟槽长度方向倾斜放置，调整沟槽样品的倾斜角度以及白 光干涉***中的平面镜与分光镜之间或者沟槽样品与分光镜之间的沿光轴的距离，直至CCD相机所采集的图像上产生条纹，固定沟槽样品的倾斜角度、沟槽样品和平面镜；
    2.2)沿光轴方向移动沟槽样品或平面镜的位置，记录CCD相机中所有出现清晰干涉条纹时的沟槽样品或平面镜的位置以及出现清晰干涉条纹的次数，其中出现清晰干涉条纹的沟槽样品或平面镜的位置记为分界面位置；
    2.3)再次沿光轴方向移动沟槽样品或平面镜的位置，利用CCD相机在预设步长下采集沟槽干涉图并依次对每张沟槽干涉图进行编号，选取所有分界面位置的上下所需范围内以及所有分界面位置的沟槽干涉图，将一个分界面位置的上下所需范围内以及当前分界面位置的沟槽干涉图作为沟槽样品的一组沟槽干涉图，从而获得沟槽样品的多组沟槽干涉图及各组中每张沟槽干涉图对应的编号。
  3. 根据权利要求1所述的一种基于白光干涉的微纳深沟槽结构快速测量方法，其特征在于，所述步骤3)中计算每组沟槽灰度干涉图的对比度，具体通过以下公式进行设置：
    Figure PCTCN2022089613-appb-100001
    其中，J为沟槽灰度干涉图的对比度，Imax为沟槽灰度干涉图的最大灰度值，Imin为沟槽灰度干涉图的最小灰度值。
  4. 根据权利要求1所述的一种基于白光干涉的微纳深沟槽结构快速测量方法，其特征在于，所述步骤5)中根据预设差值阈值和最大对比度判断所有子区域是否是分界面区域，具体为：
    将每个子区域的对比度与最大对比度作差后取绝对值作为当前子区域的对比度差值，如果当前子区域的对比度差值小于等于预设差值阈值，则当前子区域是分界面区域，如果当前子区域的对比度差值大于预设差值阈值，则当前子区域不是分界面区域。
  5. 根据权利要求2所述的一种基于白光干涉的微纳深沟槽结构快速测量方法，其特征在于，所述出现清晰干涉条纹的沟槽样品或平面镜的位置具体为沟槽样品上表面、沟槽底部和沟槽中的凸台的上表面，其中，所述凸台的上表面与沟槽样品上表面或沟槽底部平行。
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