SiC Epitaxial Wafer Surface Composition for Gate Oxide Reliability
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Solution Overview
Problem
SiC wafers exhibit significant variations in device characteristics, particularly in power devices, due to unevenness in the surface composition affecting the lifetime of the gate insulating film, leading to defective chips and reduced yield.
Innovation Solution
A SiC wafer with an epitaxial layer having a controlled surface composition ratio of C—Si at 50 atm% or less, achieved through a carbon-rich treatment, to stabilize the gate insulating film and reduce characteristic variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional epitaxial growth is performed without carbon-rich treatment, then the growth process is simple, but the surface composition is uneven causing significant variations in device characteristics and gate insulating film lifetime
Solution Approach 1:
The patent applies carbon-rich treatment by changing the chemical composition parameters of the epitaxial layer surface, specifically increasing the carbon concentration to achieve a carbon-rich state. This parameter change stabilizes the surface composition and prevents unevenness, thereby improving both the reliability of the gate insulating film and the uniformity of device characteristics across the wafer surface.
Solution Approach 2:
The patent creates a localized carbon-rich region at the surface of the epitaxial layer through carbon-rich treatment. This local quality change ensures that the surface composition is uniformly carbon-rich across the entire wafer, which stabilizes the gate insulating film lifetime and reduces variations in device characteristics without affecting the bulk properties of the epitaxial layer.
2Reliability
If carbon-rich treatment is applied to control surface composition, then device characteristic variations are reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent performs carbon-rich treatment during the epitaxial growth process itself, before subsequent manufacturing steps. This preliminary action ensures that the surface composition is controlled and uniform from the beginning, preventing variations in device characteristics. By integrating the carbon-rich treatment into the existing epitaxial growth process, the additional complexity is minimized while achieving the desired reliability improvement.
3Productivity
If the epitaxial layer surface is not made carbon-rich, then the manufacturing process is simpler, but there are more defective chips and lower yield
Solution Approach 1:
The patent changes the surface composition parameters of the epitaxial layer by applying carbon-rich treatment, which stabilizes the gate insulating film and reduces device failures. This parameter change directly improves the wafer yield by reducing the number of defective chips, while the treatment can be integrated into the existing manufacturing process to minimize the impact on process simplicity.
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 carbon-rich treatment enhances the reliability of SiC wafers by extending the dielectric breakdown lifetime and uniformizing device characteristics, thereby improving yield and reducing defective chips.
Implementation Method 1
silicon atoms are evaporated from a surface of a silicon carbide epitaxial layer, whereby a silicon carbide surface is made to be carbon atoms with 95 at % or more
Data Source
AI summary
A SiC wafer including a SiC substrate, a buffer layer made of SiC and formed on the SiC single crystal substrate, and an epitaxial layer formed on the buffer layer and containing SiC is provided. The epitaxial layer is single crystal and a composition ratio of C—Si bonds to the sum of bonds containing carbon (C—Si, C—C, C—O, C═O, and O—C—O) of an upper surface of the epitaxial layer is 50 atm % or less.