Wafer Test Key Scatterometry for In-Process Crack Detection
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Solution Overview
Problem
Current methods for detecting cracks in wafers are limited to post-manufacturing failure analysis, which is non-real-time and results in wafer scrapping.
Innovation Solution
A real-time test method using an optical scatterometer to analyze the optical characteristics of a test key on the wafer, comparing the data to a standard sample without cracks, and determining the presence of cracks based on a tolerance threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If failure analysis is performed on fully fabricated wafers to examine cracks, then crack detection is possible, but the wafer must be scrapped and real-time monitoring is not achieved
Solution Approach 1:
The patent implements a test key structure with fins in the frame area that enables preliminary crack detection during manufacturing processes. The optical scatterometer measures light scattering from the test key fins to detect cracks in real-time, allowing intervention before the wafer is fully fabricated and scrapped. This preliminary action transforms post-manufacturing failure analysis into in-process quality control.
2Measurement precision
If failure analysis is performed on fully fabricated wafers to examine cracks, then crack detection is possible, but wafer scrapping occurs
Solution Approach 1:
The test key structure enables preliminary detection of cracks during manufacturing, allowing defective wafers to be identified and removed before full fabrication. This prevents the loss of entire wafers that would otherwise be scrapped after failure analysis, significantly reducing material waste while maintaining quality control.
Solution Approach 2:
The patent extracts the testing function from the final product area by placing a dedicated test key structure in the frame area. This separate test structure can be measured independently using optical scatterometry without affecting the chip areas, allowing quality verification while preserving functional wafer areas.
3Productivity
If optical scatterometer is used to measure test key in frame area, then real-time non-destructive testing is achieved, but additional test structure is required
Solution Approach 1:
The test key structure serves multiple functions: it acts as both a structural element in the frame area and an optical test target for crack detection. The same test key fins that define the frame structure also serve as the measurement target for the optical scatterometer, eliminating the need for completely separate test structures and reducing overall complexity.
Solution Approach 2:
The test key fins are designed with the same pitch and space parameters as the minimum features in the chip areas. This copying of geometric parameters ensures that the test key responds to cracks in the same manner as the functional areas, providing representative quality data without requiring a completely different test structure design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables real-time, non-destructive monitoring of crack conditions in wafers, preventing defective wafers from progressing and reducing scrap rates.
Implementation Method 1
data of an optical characteristic of a test key of the wafer is acquired using an optical scatterometer
Data Source
AI summary
A test method for a wafer is provided. First, data of an optical characteristic of a test key of the wafer is acquired using an optical scatterometer. The wafer has chip areas and a frame area surrounding and separating the chip areas. The test key is disposed in the frame area. Then, the data is compared with corresponding data of a standard sample without a crack, and a difference between the data and the corresponding date is obtained. It is determined that a crack is formed in the test key and a crack condition in the chip areas does not meet a criterion of the wafer when the difference is larger than a tolerance. It is determined that the crack condition in the chip areas meets the criterion of the wafer when the difference is smaller than or equal to the tolerance.