Silicon Carbide Substrate Full Super Junction Manufacturing
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Solution Overview
Problem
The challenge in manufacturing high-voltage silicon carbide semiconductor devices is the difficulty in forming a full super junction (SJ) structure due to the limitations of existing trench etching and epitaxial growth processes, which result in increased ON resistance and reduced breakdown voltage, especially as the thickness of the drift layer increases.
Innovation Solution
A method involving a combination of trench embedding epitaxial and multi-stage epitaxial processes to form a drift layer with a full SJ structure by alternately stacking embedded-trench parallel pn layers and multi-stage epi parallel pn layers, allowing for a thicker drift layer with reduced trench widths and improved epitaxial growth efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the drift layer is increased to achieve high-voltage capability, then the breakdown voltage is improved, but the ON resistance increases and the trench etching and epitaxial growth become difficult
Solution Approach 1:
The drift layer is divided into multiple segments (first drift layer, second drift layer, third drift layer) with different structures. The first and third drift layers have SJ structure formed by trench embedding epitaxial process, while the second drift layer has SJ structure formed by multi-stage epitaxial process. This segmentation allows each layer to be optimized for its specific function, enabling the formation of full SJ structure across the entire drift layer thickness.
2Ease of manufacture
If the trench embedding epitaxial process is used to form deep trenches for thick drift layers, then the SJ structure can be formed, but the trench etching becomes difficult and the oxide film thickness must be increased causing stress
Solution Approach 1:
The drift layer formation process is segmented into three separate epitaxial growth stages, each forming a partial parallel pn layer. This segmentation reduces the required trench depth for each etching step, making the trench etching process more controllable and reducing the need for excessively thick oxide films, thereby reducing stress on the substrate.
Solution Approach 2:
The n-type drift layer is formed first by epitaxial growth before trench formation. This preliminary action establishes the base structure upon which the SJ structure is subsequently built, allowing for better process control and reduced complexity in the overall manufacturing process.
3Ease of manufacture
If the trench embedding epitaxial process is used for thick drift layers, then the SJ structure can be formed, but the epitaxial growth period becomes longer and voids occur
Solution Approach 1:
The epitaxial growth process is divided into three separate stages, each forming a partial parallel pn layer with thickness of several micrometers. This segmentation significantly reduces the epitaxial growth period for each stage compared to forming the entire drift layer in one stage, and prevents void formation by maintaining manageable trench aspect ratios throughout the process.
4Ease of manufacture
If the multi-stage epitaxial process is used to increase drift layer thickness in stages, then the SJ structure can be formed, but the ion implantation must be repeatedly performed increasing process complexity
Solution Approach 1:
The drift layer is formed in three separate epitaxial growth stages, with each stage forming a partial parallel pn layer. This segmentation eliminates the need for repeated ion implantation processes required in conventional multi-stage epitaxial methods, as the SJ structure is formed through controlled epitaxial growth and trench embedding in each stage, thereby reducing process 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 enables the formation of a silicon carbide semiconductor device with a full SJ structure across the entire drift layer thickness, reducing ON resistance and enhancing breakdown voltage, while simplifying the manufacturing process and improving device characteristics.
Implementation Method 1
performing a first stacking process of forming a first partial parallel pn layer on the starting substrate by a trench embedding epitaxial process
Implementation Method 2
an ion implantation for selectively forming the p-type regions is repeatedly performed for each stage of epitaxial growth performed
Implementation Method 3
both forming the trenches by etching (hereinafter, trench etching) and completely embedding the trenches with the epitaxial layer are difficult. The deeper is the trench, the more difficult it is to form, by dry etching, a favorable trench-shape
Data Source
AI summary
A method of manufacturing a silicon carbide substrate having a parallel pn layer. The method includes preparing a starting substrate containing silicon carbide, forming a first partial parallel pn layer on the starting substrate by a trench embedding epitaxial process, stacking a second partial parallel pn layer by a multi-stage epitaxial process on the first partial parallel pn layer, and stacking a third partial parallel pn layer on the second partial parallel pn layer by another trench embedding epitaxial process. Each of the first, second and third partial parallel pn layers is formed to include a plurality of first-conductivity-type regions and a plurality of second-conductivity-type regions alternately disposed in parallel to a main surface of the silicon carbide substrate. The first-conductivity-type regions of the first and third partial parallel pn layers face each other in a depth direction of the silicon carbide substrate, and the second-conductivity-type regions partial parallel pn layers face each other in the depth direction.