Three-dimensional imaging for semiconductor wafer inspection

Patent metadata

Field	Value
Publication number	US-10887580-B2
Application number	US-201715683077-A
Country	US
Kind code	B2
Filing date	Aug 22, 2017
Priority date	Oct 7, 2016
Publication date	Jan 5, 2021
Grant date	Jan 5, 2021

Abstract

Methods and systems for improved detection and classification of defects of interest (DOI) on semiconductor wafers based on three-dimensional images are described herein. Three dimensional imaging of volumes of thick, layered structures enables accurate defect detection and estimation of defect location in three dimensions at high throughput. A series of images are acquired at a number of different wafer depths. A three dimensional image of a thick semiconductor structure is generated from the series of images. Defects are identified and classified based on an analysis of the three dimensional image of the thick semiconductor structure. In some examples, the three-dimensional image stack is visualized by contour plots or cross-sectional plots to identify a characteristic defect response. In some examples, the three-dimensional image is processed algorithmically to identify and classify defects. In another aspect, the location of a defect is estimated in three dimensions based on the three dimensional image.

First claim

What is claimed is:

1. A system comprising:
an optical subsystem comprising:
an illumination subsystem that provides an amount of illumination light to a vertically stacked structure disposed on a substrate, the illumination subsystem comprising an illumination source, an illumination aperture subsystem and an illumination polarization subsystem;
a collection subsystem that collects light from the vertically stacked structure in response to the amount of illumination light provided by the illumination subsystem, the collection subsystem comprising a collection aperture subsystem, wherein the optical subsystem generates a focused optical image at each of a plurality of focus planes located at a plurality of different depths of the vertically stacked structure;

a detector configured to detect the light collected at each of the plurality of different depths and generate a plurality of output signals indicative of the amount of light collected at each of the plurality of different depths; and
a computing system configured to:
receive the plurality of output signals;
communicate control commands to any of the illumination source, the illumination aperture subsystem, the collection aperture subsystem, and the illumination polarization subsystem that cause any of the illumination source to change a spectral range of the illumination light, the illumination aperture to change a shape of the illumination light provided to the substrate, the illumination polarization subsystem to change a polarization of illumination light provided to the substrate, and the collection aperture subsystem to change a shape of collected light at the detector to achieve a performance objective, wherein the performance objective is a minimization of a response of the vertically stacked structure in the three dimensional image, an enhancement of a defect signal in the three dimensional image, a minimization of wafer noise or one or more nuisance signals in the three dimensional image, a discrimination of the defect signal from wafer noise or the one or more nuisance signals in the three dimensional image, an improvement of an accuracy of an estimated physical location of the defect estimated from the three dimensional image, or any combination thereof;
generate a three dimensional image of an inspected volume spanned by the plurality of different depths of the vertically stacked structure based on the plurality of output signals;
determine the presence of a defect within the inspected volume based on the three dimensional image; and
classify the defect as a defect of interest based on the three dimensional image, wherein the determining and classifying of the defect involves generating a two dimensional cross-section of the three dimensional image and determining whether a measured signal visible in the two dimensional cross-section exceeds a predetermined threshold value.

2. The system of claim 1 , wherein the computing system is further configured to:
determine a location of the defect in three dimensions within the inspected volume of the vertically stacked structure.

3. The system of claim 2 , wherein the determining of the location of the defect involves generating a two dimensional cross-section of the three dimensional image, and wherein the location of the defect is based on a depth associated with a value of the measured signal visible in the two-dimensional cross-section.

4. The system of claim 1 , wherein the generating of the three dimensional image of the inspected volume involves aligning a plurality of images in two lateral dimensions each associated with different depths based on one or more alignment marks visible in each of the plurality of images.

5. The system of claim 1 , wherein the computing system is further configured to:
filter the three dimensional image of the inspected volume, wherein the determining and classifying of the defect within the inspected volume is based on the filtered three dimensional image.

6. The system of claim 1 , wherein the determining and classifying of the defect involves a model-based analysis of the three dimensional image or a library-based analysis of the three dimensional image.

7. The system of claim 2 , wherein the determining of the location of the defect involves a model-based analysis of the three dimensional image or a library-based analysis of the three dimensional image.

8. The system of claim 1 , wherein the classifying of the defect involves any of a three dimensional filter, a clustering algorithm, and a deep learning algorithm.

9. The system of claim 1 , the collection subsystem further comprising a Fourier filter subsystem and a collection polarization subsystem, wherein the computing system is further configured to communicate control commands to any of the Fourier filter subsystem and the collection polarization subsystem that cause any of the Fourier filter subsystem to change a spatial frequency content of the collected light and the collection polarization subsystem to select a polarization of collected light at the detector to achieve the performance objective.

10. The system of claim 1 , wherein the illumination subsystem is further configured to provide the amount of illumination light at a plurality of incidence angles, a plurality of illumination wavelengths, or both, wherein the collection subsystem further configured to collect light from the vertically stacked structure at the plurality of incidence angles, the plurality of illumination wavelengths, or both, wherein the detector is further configured to detect light collected at each of the plurality of incidence angles, each of the plurality of illumination wavelengths, or both, and generate a plurality of output signals indicative of the amount of light collected at each of the plurality of incidence angles, each of the plurality of illumination wavelengths, or both, and the computing system is further configured to generate an image of the inspected volume having more than three dimensions based on the plurality of output signals.

11. The system of claim 1 , wherein the vertically stacked structure is a three dimensional NAND memory device.

12. The system of claim 1 , wherein an illumination source of the illumination subsystem is a broadband laser sustained plasma light source.

13. The system of claim 1 , wherein the illumination light includes wavelengths between 260 nanometers and 950 nanometers.

14. The system of claim 1 , further comprising:
a wafer positioning system configured to scan the substrate in a scanning motion in two dimensions parallel to a substantially flat surface of the substrate at a plurality of different positions in a direction normal to the substantially flat surface, the wafer positioning system further configured to fix a position of the substrate in the two dimensions parallel to the substantially flat surface and move the substrate in the direction normal to the substantially flat surface.

15. A method comprising:
providing an amount of illumination light to a vertically stacked structure disposed on a substrate, the amount of illumination light generated by an illumination source;
collecting light from the vertically stacked structure in response to the amount of illumination light, wherein the providing of the amount of illumination light and the collecting of light in response to the amount of illumination light generates a focused optical image at each of a plurality of focus planes located at a plurality of different depths of the vertically stacked structure;
communicating control commands to any of an illumination source, an illumination aperture subsystem, a collection ap

Assignees

• Kla Tencor Corp

Inventors

• Kolchin Pavel
• Danen Robert M
• Measor Philip

Classifications

• G06F18/24

  Classification techniques · CPC title

• G06V10/141

  Control of illumination · CPC title

• G06T2207/10148

  Varying focus · CPC title

• G01N2021/8861

  Determining coordinates of flaws · CPC title

• G06T2207/20221

  Image fusion; Image merging · CPC title