Wafer Resistivity Detection via Optical Interference for Laser Processing
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Solution Overview
Problem
Existing methods for forming modified layers in semiconductor wafers face challenges due to changes in focal point position and increased laser beam absorption caused by impurity doping, leading to improper layer formation and requiring pre-processing of outer circumferential regions, as well as cumbersome wafer sorting based on resistivity measurements.
Innovation Solution
A method that estimates resistivity using an interference waveform acquired by irradiating a plate-shaped workpiece with light, allowing determination of resistivity without processing, by associating resistivity with the maximum value of the interference waveform and selecting appropriate processing conditions based on stored resistivity information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser beam is used to form modified layers in a doped wafer, then chip division can be achieved, but the focal point position changes and laser beam absorption increases due to impurity doping
Solution Approach 1:
The patent applies preliminary action by measuring the resistivity of the wafer before laser processing to determine the appropriate processing conditions. This advance measurement allows the system to pre-determine optimal focal point positions and laser parameters that compensate for the effects of impurity doping, ensuring accurate modified layer formation despite variations in wafer composition.
Solution Approach 2:
The patent employs parameter changes by adjusting laser processing parameters (such as focal point position, power, and pulse duration) based on the measured resistivity values. By dynamically changing these parameters according to the specific wafer characteristics, the system maintains manufacturing precision while achieving effective chip division across wafers with varying impurity levels.
2Measurement precision
If resistivity is measured using a resistivity meter, then wafer electrical properties can be determined, but wafers need to be sorted out and management becomes cumbersome
Solution Approach 1:
The patent merges the resistivity measurement function with the laser processing system by integrating a light source and detector directly into the processing apparatus. This combination eliminates the need for separate resistivity measurement equipment and manual sorting operations, as the system can determine appropriate processing conditions directly from the optical measurement data during the processing workflow.
Solution Approach 2:
The system applies self-service by automatically determining processing conditions based on real-time optical measurement of the wafer. The integrated system performs both measurement and processing control without requiring external sorting equipment or manual intervention, thereby simplifying wafer management while maintaining measurement precision.
3Manufacturing precision
If outer circumferential surplus region is processed in advance, then proper processing conditions can be established, but additional processing steps are required
Solution Approach 1:
The patent extracts the essential information needed for determining processing conditions from the wafer's optical properties rather than requiring physical processing of reference regions. By using optical measurement to directly obtain resistivity-related data, the system eliminates the need for separate preliminary processing steps on outer circumferential regions while maintaining the ability to establish accurate processing conditions.
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 determination of resistivity corresponding to processability without processing the workpiece, facilitating accurate and efficient formation of modified layers by adjusting laser beam parameters.
Implementation Method 1
acquiring an interference waveform between light reflected by the first surface and light that has been transmitted through the first surface and been reflected by the second surface
Implementation Method 2
acquiring an interference waveform between light reflected by the first surface and light that has been transmitted through the first surface and been reflected by the second surface
Implementation Method 3
light that has been transmitted through the first surface
Data Source
AI summary
A detection method of resistivity is a detection method of resistivity in which resistivity of a plate-shaped workpiece having a back surface and a front surface on a side opposite to the back surface is detected. The detection method includes an interference waveform acquisition step of irradiating the back surface of the plate-shaped workpiece with light from a light source and acquiring an interference waveform between light reflected by the back surface and light that has been transmitted through the back surface and been reflected by the front surface, and an estimation step of estimating the resistivity of the plate-shaped workpiece on the basis of the interference waveform acquired in the interference waveform acquisition step.