SiC Plasma Etching for Tapered Trenches With Rounded Corners
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Solution Overview
Problem
Current methods for fabricating compound semiconductor devices, such as SiC devices, face challenges in achieving high volume production at a low cost due to the need for multiple processing steps. Additionally, existing plasma etching techniques for creating tapered trenches in SiC often require thermally activated etching, which has limitations and risks.
Innovation Solution
A plasma etching method that uses a gas mixture comprising chlorine-containing components, inert gases, and passivation material precursors to anisotropically etch a silicon carbide substrate, producing a tapered feature with sidewalls inclined at an angle of less than 85° to the horizontal. This method allows for the control of the taper and rounding of corners, combining the advantages of U-shaped and V-shaped trenches in a single etching step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching methods are used to create tapered trenches in SiC, then the etching process can be performed, but micro-trenching occurs at the corners leading to field bunching and reduced breakdown voltage
Solution Approach 1:
The patent applies dynamics by continuously adjusting the etch rate during the plasma etching process. The etch rate is modulated to be higher at the beginning to quickly reach the desired depth, then reduced towards the end to prevent micro-trenching at the corners. This dynamic control of etch rate allows formation of tapered trenches with rounded corners, eliminating field bunching while maintaining the desired trench profile.
Solution Approach 2:
The patent employs periodic action through multiple etching cycles with varying parameters. The process alternates between high etch rate phases and low etch rate phases, and between etching and passivation steps. This periodic modulation allows precise control over the trench profile, creating the desired tapered shape with rounded corners while avoiding micro-trenching defects.
2Reliability
If thermally activated etching is used to create V-shaped trenches with {0338} plane sidewalls, then channel mobility is improved, but the process requires thermal annealing which reduces throughput and has additional risks
Solution Approach 1:
The patent extracts the thermal annealing step from the process by achieving the desired {0338} plane sidewall orientation through plasma etching alone. By removing the thermal processing step, the method eliminates the associated throughput reduction and process risks while maintaining the channel mobility benefits of the {0338} plane orientation.
Solution Approach 2:
The patent substitutes the thermal field (thermal annealing) with a plasma field to achieve the same crystallographic plane exposure. Instead of using heat to activate etching and reveal the {0338} plane, the method uses controlled plasma chemistry and dynamics to directly etch along the desired crystal planes, achieving the same result through a different physical mechanism.
3Reliability
If multiple processing steps are used to fabricate compound semiconductor devices, then device quality can be maintained, but the fabrication cost increases and high volume production becomes challenging
Solution Approach 1:
The patent merges multiple processing steps into a single plasma etching process. By combining trench formation, sidewall angle control, corner rounding, and crystal plane orientation into one integrated plasma process, the method eliminates several sequential steps that would otherwise be required. This consolidation maintains device quality while enabling high volume production through improved throughput.
Solution Approach 2:
The patent achieves multi-functionality by designing a plasma etching process that simultaneously performs multiple functions: creating the trench profile, controlling sidewall angles, rounding corners, and exposing specific crystal planes. This universal process replaces several specialized steps, reducing overall process complexity and enabling scalable high volume manufacturing.
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 achieves high substrate-to-mask selectivity, allowing selectivities of up to 9:1, and enables the formation of features with both tapered sidewalls and rounded corners, which can enhance breakdown voltage and reduce field bunching.
Implementation Method 1
The plasma etch step comprises generating a plasma from an etchant gas mixture
Implementation Method 2
performing a plasma etch step to anisotropically etch the substrate through the opening to produce a tapered feature
Implementation Method 3
The anisotropic etching of the substrate comprises deposition of a passivation material on at least the opening such that the tapered feature comprises at least two sidewalls
Data Source
AI summary
A silicon carbide substrate is etched to form a tapered feature. The plasma etch step includes generating a plasma from an etchant gas mixture comprising at least one chlorine-containing component, at least one inert gas component and at least one passivation material precursor. The anisotropic etching of the substrate comprises deposition of a passivation material.