Bonded SOI Wafer Defect Evaluation via Coordinate Mapping
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Solution Overview
Problem
The existing methods for manufacturing bonded SOI wafers face challenges in detecting surface defects that cause void defects, leading to reduced manufacturing yield and increased void occurrence ratios, as current defect inspection methods are not sensitive enough to identify only defects that result in voids during the bonding process.
Innovation Solution
Inspecting surface defects on both the mirror-polished silicon single crystal substrate before and after polycrystalline silicon layer deposition, and determining substrates with defects at the same position as defective products, thereby selectively identifying and avoiding substrates that would cause voids in the bonded SOI wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper limit of the quantity standard for surface defects is lowered to reduce void occurrence ratio, then the void defect occurrence ratio is reduced, but the manufacturing yield of substrates to be bonded degrades
Solution Approach 1:
The defect inspection process is segmented into two distinct stages: first inspecting the silicon single crystal substrate before polycrystalline silicon layer formation, and second inspecting the polycrystalline silicon layer after deposition. This segmentation allows for tracking defects through the manufacturing process and identifying which defects persist to cause voids, enabling more precise quality control without excessive rejection of good substrates.
Solution Approach 2:
The first defect inspection is performed preliminarily, before the polycrystalline silicon layer is deposited on the substrate. This preliminary inspection establishes a baseline defect map that can be compared against the second inspection after layer formation, allowing identification of defects that persist through the process and are likely to cause voids, versus defects that are introduced or healed during manufacturing.
2Productivity
If current defect inspection methods are used, then manufacturing yield is maintained, but sensitivity to detect defects causing voids is insufficient
Solution Approach 1:
The invention implements a feedback mechanism where defect data from the first inspection (before polycrystalline silicon layer deposition) is stored and compared with defect data from the second inspection (after deposition). This feedback loop allows the system to learn which defects persist through the manufacturing process and are correlated with void formation, enabling more accurate prediction of which substrates will produce voids without requiring overly stringent inspection criteria that would reduce yield.
Data Source
Figure 1A~2(b)
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Figure 5~6
AI summary
The present invention provides a method for evaluating surface defects of a substrate to be bonded, including the steps of: preparing a mirror-polished silicon single crystal substrate; inspecting surface defects on the mirror-polished silicon single crystal substrate; depositing a polycrystalline silicon layer on a surface of the silicon single crystal substrate subjected to the defect inspection; performing mirror edge polishing to the silicon single crystal substrate having the polycrystalline silicon layer deposited thereon; polishing a surface of the polycrystalline silicon layer; inspecting surface defects on the polished polycrystalline silicon layer; and comparing coordinates of defects detected at the step of inspecting the surface defects on the silicon single crystal substrate with counterparts detected at the step of inspecting the surface defects on the polycrystalline silicone layer and determining quality of the silicon single crystal substrate having the polycrystalline silicon layer as a substrate to be bonded on the basis of presence/absence of defects present at the same position. Consequently, there is provided the method for evaluating surface defects of a substrate to be bonded which enables rationally avoiding a reduction in manufacturing yield of the substrates to be bonded and decreasing a void defect occurrence ratio after bonding.