Epitaxial Wafer Scratch Removal for Yield Improvement
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Solution Overview
Problem
During the epitaxial growth of silicon wafers, scratches occur in the boundary area between the chamfered surface and the susceptor, leading to particle generation during device processing, which reduces yield due to particle deposition on the front surface.
Innovation Solution
A method for manufacturing epitaxial wafers that involves growing an epitaxial film using a vapor-phase epitaxial method and subsequently removing scratches with a depth of 0.5 μm or greater and length of 1 μm or greater from the boundary area by polishing or etching the rear surface, preventing particle generation and increasing device yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a circular susceptor with SiC front surface is used to evenly heat and supply source gas on the entire wafer front surface, then the epitaxial film can be evenly grown, but scratches are caused in the boundary area of the silicon wafer due to friction and thermal expansion difference
Solution Approach 1:
A susceptor front surface made of silicon oxide or silicon oxynitride is introduced as an intermediary layer between the silicon wafer and the heating mechanism. This intermediary material has a coefficient of thermal expansion closer to silicon than SiC, reducing thermal stress and friction-induced scratching while still enabling effective heat transfer for uniform epitaxial film growth.
Solution Approach 2:
The material composition of the susceptor front surface is changed from SiC to silicon oxide or silicon oxynitride. This parameter change modifies the coefficient of thermal expansion to be closer to that of silicon, thereby reducing the thermal expansion difference that causes scratching during high-temperature epitaxial growth.
2Ease of operation
If the boundary area is used as the wafer supporting position on the susceptor, then the wafer can be securely held, but particles are generated from scratched portions during device process, reducing yield
Solution Approach 1:
The silicon oxide or silicon oxynitride front surface acts as a protective intermediary that prevents direct damaging contact between the susceptor and wafer boundary area. This intermediary layer reduces friction and thermal stress, preventing scratch formation that would otherwise generate particles during subsequent device processing steps.
Solution Approach 2:
The invention converts the potentially harmful interaction between the susceptor and wafer boundary area into a beneficial low-friction contact. By using silicon oxide or silicon oxynitride, the material that would normally cause scratching is transformed into a protective layer that actually protects the wafer while maintaining necessary mechanical contact for secure holding.
3Temperature
If SiC is used as susceptor material due to its hardness, then the susceptor can withstand high temperature, but the hardness difference causes scratches on the softer silicon wafer surface
Solution Approach 1:
The susceptor front surface material is changed from SiC to silicon oxide or silicon oxynitride. This parameter change maintains high-temperature resistance while adjusting the hardness to be closer to silicon, eliminating the hardness difference that causes scratching during epitaxial growth.
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 method effectively removes scratches from the epitaxial wafers, preventing particle deposition on the front surface during device processing and enhancing yield by ensuring a scratch-free boundary area, thus improving the quality of devices.
Implementation Method 1
growing an epitaxial film on a front surface of a semiconductor wafer in a vapor-phase epitaxial method
Implementation Method 2
when being heated by a heater provided external to the reactor
Implementation Method 3
the susceptor has a higher coefficient of thermal expansion than the silicon wafer, as the coefficient of thermal expansion of SiC is 4.8×10−6/k and that of silicon is 2.5×10−6/k
Data Source
AI summary
An epitaxial wafer is provided capable of eliminating particles in a device process, particles being generated from a scratch in a boundary area between a rear surface and a chamfered surface of a wafer. The scratch in the boundary area between the rear surface and the chamfered surface is removed in a scratch removal process. Thus, no particles exist caused by a scratch, at a time of immersion in an etching solution in the device process, and thus a device yield is increased.