Bonded Wafer Handle Substrate Polishing to Prevent Void Defects
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Solution Overview
Problem
The generation of void defects in the bonding step of bonded wafers leads to film peeling, reducing yield and quality, despite existing techniques to control surface roughness of polycrystalline silicon layers.
Innovation Solution
A production method for a handle wafer involving forming a protective oxide film on a polycrystalline silicon layer, followed by polishing to inhibit impurity adhesion and etching, resulting in a polished surface with reduced roughness and pit defects, using methods like SC-1 cleaning or ozone passivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polycrystalline silicon layer is formed on the handle wafer to trap carriers for high-frequency operation, then the RF performance is improved, but void defects are generated during bonding causing film peeling and reduced yield
Solution Approach 1:
The invention applies different surface quality requirements to different regions of the polycrystalline silicon layer. The bonding surface is polished to extreme smoothness (Ra≤1nm) to prevent void defects, while other regions maintain the carrier-trapping polycrystalline structure. This local differentiation resolves the contradiction between RF performance and bonding yield.
Solution Approach 2:
The invention performs preliminary polishing of the polycrystalline silicon layer before bonding to eliminate surface roughness that would cause void defects. By pre-treating the surface to Ra≤1nm, the subsequent bonding process achieves high yield without void formation, while the underlying polycrystalline structure remains intact for RF operation.
2Manufacturing precision
If the surface roughness of the polycrystalline silicon layer is controlled to be 1 nm or less to inhibit void defects, then bonding quality is improved, but the complexity of the manufacturing process increases
Solution Approach 1:
The invention introduces an intermediary oxide film between the monocrystalline handle wafer and the polycrystalline silicon layer. This oxide film serves as a buffer that allows the polycrystalline layer to be formed with relaxed surface requirements, then selectively removed or polished only where needed, simplifying the overall process while achieving the required Ra≤1nm bonding surface.
3Reliability
If further measures are taken beyond controlling surface roughness to improve bonded wafer quality, then void defect prevention is enhanced, but the production time and cost increase
Solution Approach 1:
The invention integrates the surface polishing step into the continuous manufacturing flow, performing it immediately after polycrystalline silicon deposition and before bonding. This continuous approach eliminates the need for separate intermediate handling and storage steps, achieving enhanced quality (Ra≤1nm) without significant time penalty.
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
Inhibits void defects by preventing impurity-induced erosion, ensuring a high-quality bonded wafer with reduced surface roughness and pit formation, enhancing production efficiency and yield.
Implementation Method 1
forming an oxide film on the handle wafer body
Implementation Method 2
the protective oxide film may be formed through SC-1 cleaning
Implementation Method 3
the protective oxide film may be formed through ozone passivation
Implementation Method 4
polishing to remove the protective oxide film and polishing the polycrystalline silicon layer
Data Source
AI summary
A producing method of a handle wafer for a bonded wafer produced by bonding an active wafer and the handle wafer through an insulation film includes: preparing a handle wafer body made from a monocrystalline silicon wafer; forming an oxide film on the handle wafer body; depositing a polycrystalline silicon layer on the oxide film; forming a protective oxide film on a surface of the polycrystalline silicon layer; and polishing to remove the protective oxide film and polishing the polycrystalline silicon layer.