Silicon Carbide Substrate Surface Roughness Control for Epitaxial Defect Reduction
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Solution Overview
Problem
Silicon carbide substrates with high back surface roughness lead to uneven temperature distribution and increased warping during epitaxial film growth, resulting in defects and reduced yield in semiconductor devices.
Innovation Solution
A silicon carbide substrate with controlled surface roughness, where the front surface has an average roughness of not greater than 0.5 nm and a standard deviation of not greater than 0.2 nm, and the back surface has an average roughness of not smaller than 0.3 nm and not greater than 10 nm, and a standard deviation of not greater than 3 nm, to ensure uniform contact and prevent defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the back surface roughness is increased to improve contact state during heating treatment, then the temperature distribution uniformity is improved, but the film quality of the epitaxial film deteriorates due to crystal defect development
Solution Approach 1:
The patent applies local quality by differentiating the surface roughness requirements between the front surface and back surface of the silicon carbide substrate. The front surface is polished to an average roughness of 0.1 nm or less to prevent crystal defect development, while the back surface is controlled to 1 nm or less to ensure uniform heating contact. This localized differentiation of surface quality resolves the contradiction between temperature uniformity and film quality.
2Productivity
If the substrate size is increased to improve productivity, then the manufacturing efficiency is improved, but the warping of the substrate increases leading to defects in epitaxial film formation
Solution Approach 1:
The patent applies parameter changes by strictly controlling the surface roughness parameters of the substrate to prevent warping in large-sized substrates. The back surface roughness is controlled to an average of 1 nm or less, and the front surface to 0.1 nm or less. By changing and controlling these surface roughness parameters, the substrate maintains dimensional stability even when scaled to 6 inches or larger, thereby improving productivity without increasing warping-related defects.
3Manufacturing precision
If the front surface roughness is reduced to improve epitaxial film quality, then the film quality is improved, but the manufacturing complexity increases due to additional polishing steps
Solution Approach 1:
The patent applies preliminary action by performing precise polishing of both the front and back surfaces of the silicon carbide substrate before the epitaxial film formation step. The back surface is polished to an average roughness of 1 nm or less, and the front surface to 0.1 nm or less, in advance of the epitaxial growth process. This preliminary surface preparation eliminates the need for additional in-situ polishing steps during device fabrication, thereby improving film quality without significantly increasing overall manufacturing complexity.
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
This approach results in improved film quality, reduced defect probability, and lower manufacturing costs by suppressing warping and ensuring uniform epitaxial layer growth, thereby enhancing the yield and performance of semiconductor devices.
Implementation Method 1
Since such silicon carbide is higher in thermal conductivity than a nitride semiconductor such as gallium nitride (GaN), a substrate composed of silicon carbide is expected as a material for a power device
Implementation Method 2
during heating treatment in a step of growing an epitaxial film on a front surface of the substrate, a state of contact between a susceptor on which the substrate is carried and the back surface of the substrate varies and consequently temperature distribution is produced in the substrate
Data Source
AI summary
A substrate capable of achieving a lowered probability of defects produced in a step of forming an epitaxial film or a semiconductor element, a semiconductor device including the substrate, and a method of manufacturing a semiconductor device are provided. A substrate is a substrate having a front surface and a back surface, in which at least a part of the front surface is composed of single crystal silicon carbide, the substrate having an average value of surface roughness Ra at the front surface not greater than 0.5 nm, a standard deviation σ of that surface roughness Ra not greater than 0.2 nm, an average value of surface roughness Ra at the back surface not smaller than 0.3 nm and not greater than 10 nm, standard deviation σ of that surface roughness Ra not greater than 3 nm, and a diameter D of the front surface not smaller than 110 mm.