Wafer Polishing Thickness Mapping for Uniform Laser Dicing
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Solution Overview
Problem
Inappropriate processing by a laser beam during wafer division can result in insufficient division and damage to device chips, due to uneven wafer thickness after grinding mark removal by the polishing apparatus.
Innovation Solution
A polishing apparatus equipped with a chuck table, a rotatable polishing unit, a vertical feeding mechanism, a parallel feeding mechanism, a thickness measuring unit, and a controller that forms mapping data of the wafer's thickness to ensure uniformity before laser processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If polishing is performed to remove grinding marks, then surface smoothness is improved, but wafer thickness uniformity deteriorates
Solution Approach 1:
The patent measures wafer thickness at multiple positions before laser processing and creates a thickness distribution map in advance. This preliminary measurement allows the system to identify thickness variations caused by polishing and adjust laser processing parameters accordingly, preventing damage to areas with non-uniform thickness.
Solution Approach 2:
The patent implements a feedback mechanism where thickness measurement data from multiple wafer positions is used to adjust laser processing parameters. The system continuously monitors thickness uniformity and modifies processing conditions based on the measured thickness distribution, ensuring consistent laser processing despite polishing-induced thickness variations.
2Productivity
If laser processing is applied to divide the wafer, then device chip division is achieved, but damage to device chips occurs due to non-uniform thickness
Solution Approach 1:
The patent applies different laser processing parameters to different regions of the wafer based on local thickness characteristics. By dividing the wafer into multiple measurement positions and creating a thickness distribution map, the system tailors laser processing conditions to each specific area, ensuring safe processing for thin regions while maintaining efficiency for uniform regions.
Solution Approach 2:
The patent dynamically adjusts laser processing parameters such as power, speed, and focal position based on measured wafer thickness at each position. This parameter adaptation allows the system to maintain optimal processing conditions across the entire wafer surface, preventing damage to device chips while preserving division efficiency.
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
The apparatus ensures that only wafers with uniform thickness are subjected to laser processing, preventing damage to device chips and ensuring reliable division into individual chips.
Implementation Method 1
a diffraction grating that spectrally disperses the return light branched by the light branching section by wavelength
Implementation Method 2
an image sensor that detects intensity of the light spectrally dispersed by wavelength by the diffraction grating and that generates a spectral interference waveform
Data Source
AI summary
A polishing apparatus includes a polishing unit that rotatably supports a polishing pad for polishing a wafer held on a holding surface of a chuck table and that has a spindle formed with a through-hole extending from one end of the spindle to the other end of the spindle in an axis of the spindle. A thickness measuring unit is disposed at one end of the through-hole of the spindle that measures a thickness of the wafer. A controller obtains information regarding the thickness of the wafer measured by the thickness measuring unit at a position defined by a variation in a distance between a rotational center of the rotating wafer fed by a parallel feeding mechanism, a center of the other end of the through-hole facing the wafer, and a rotational angle of the chuck table, and forms mapping data regarding the thickness of the wafer.