Wafer Chip Strength Measurement With Defect-Based Traceability
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Solution Overview
Problem
Current methods for determining the flexural strength of semiconductor chips rely on dummy wafers, making it difficult to trace the processing properties of actual device chips, especially for those used in vehicles, where traceability is crucial.
Innovation Solution
A method and apparatus for measuring the flexural strength of device chips by fracturing defective chips and assessing chipping, reverse side roughness, and side surface roughness of acceptable chips, allowing for the recording of these properties for traceability purposes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the flexural strength of device chips is measured by fracturing them, then the measurement accuracy is improved, but the traceability of acceptable devices is lost because they cannot be fractured
Solution Approach 1:
The wafer is divided into defective device chips and acceptable device chips based on inspection results. Defective chips are selected for flexural strength measurement through fracturing, while acceptable chips are preserved intact. This segmentation allows measurement on a subset (defective chips) without compromising the integrity of the main product (acceptable chips), thereby resolving the contradiction between measurement accuracy and traceability.
Solution Approach 2:
Defective device chips serve as intermediaries for measuring the flexural strength properties that would otherwise need to be measured on acceptable chips. By measuring defective chips (which have the same mechanical properties as acceptable chips from the same wafer), the invention obtains traceable measurement data without fracturing acceptable devices, thus maintaining both measurement accuracy and traceability.
2Measurement precision
If all device chips are measured for flexural strength by fracturing, then the measurement completeness is improved, but the productivity is reduced due to the need to handle and process all chips
Solution Approach 1:
Instead of measuring all device chips for flexural strength, the invention applies partial action by measuring only a subset (defective chips) that provides sufficient statistical representation of the wafer's mechanical properties. This reduces the number of fracturing operations from 100% to a small percentage of chips, significantly improving productivity while maintaining measurement completeness through proper sampling.
Solution Approach 2:
Electrical property inspection is performed preliminarily on all chips before selecting which chips will undergo flexural strength measurement. This preliminary sorting identifies defective chips that can be used for measurement, allowing the system to prepare measurement samples in advance and avoid unnecessary fracturing of acceptable chips, thereby improving overall processing efficiency.
3Productivity
If dummy wafers are used for measuring flexural strength, then the productivity is improved by avoiding handling of actual device chips, but the reliability of traceability is worsened because dummy wafer properties cannot represent actual device chips
Solution Approach 1:
The actual device chips (specifically defective ones) serve themselves as the measurement subjects rather than using separate dummy wafers. By utilizing the defective chips that would otherwise be discarded or handled separately, the system obtains authentic mechanical property data from the actual product material, ensuring traceability while maintaining productivity through efficient use of available resources.
Solution Approach 2:
The invention changes the selection criterion for measurement from 'dummy wafer material' to 'defective device chips from actual wafer'. This parameter change in sample selection ensures that the measured chips have identical manufacturing history, material composition, and processing conditions as the acceptable device chips, thereby guaranteeing traceability while maintaining the efficiency of dedicated measurement operations.
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 reliable measurement and storage of flexural strength and other properties for device chips, enhancing traceability and ensuring that acceptable devices are handled with accurate attribute information without being fractured.
Implementation Method 1
The flexural strength of a chip is measured by a three-point bending test. Since the three-point bending test is a test where an indenter is pressed against a chip to destroy the chip
Implementation Method 2
a chip observing mechanism for measuring one or more of chipping, reverse side roughness, or side surface roughness of the device chip
Data Source
AI summary
There is provided a method of processing a wafer having devices formed in respective areas on a face side thereof that are demarcated by a plurality of crossing projected dicing lines on the face side. The method of processing a wafer includes a wafer unit forming step of forming a wafer unit having a wafer, a tape, and an annular frame, a dividing step of dividing the wafer along the projected dicing lines into a plurality of device chips, a pick-up step of picking up one at a time of the device chips from the wafer unit, and a measuring step of measuring the device chip picked up in the pick-up step. The method also includes a distinguishing step, before the pick-up step, of inspecting properties of the devices to distinguish acceptable devices and defective devices among the devices and storing distinguished results.