Silicon Carbide Plasma Etching Defect Reduction
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Solution Overview
Problem
Silicon carbide is difficult to etch effectively due to surface imperfections and defects formed during previous process steps, leading to high defect formation rates in etched features, especially when using SF6/O2, SF6/O2/He, or SF6/O2/Ar process gases.
Innovation Solution
A method of plasma etching silicon carbide using an initial plasma etch with a gas mixture of oxygen and a fluorine-rich gas like CF4 or SF6 at a volume ratio of less than 50%, followed by a bulk plasma etch with different conditions, which significantly reduces defect density and process time, and can be performed using an inductively coupled plasma with optimized pressure and bias power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a standard bulk plasma etch process is used on lapped silicon carbide, then etching can proceed, but heavy defect formation is observed with greater than 50% of vias containing defects
Solution Approach 1:
The etch process is divided into three distinct stages: a breakthrough step to remove surface contaminants and initiate etching, a transition step to optimize plasma conditions, and a bulk etch step for deep via formation. This segmentation allows each stage to be optimized independently, preventing defect formation during critical transition phases while maintaining high productivity in the bulk etch stage.
Solution Approach 2:
The breakthrough step performs preliminary action by removing lapping residues, photoresist contaminants, and surface oxides before the bulk etch begins. This preliminary cleaning action prevents these contaminants from causing defects during subsequent etching, ensuring high-quality via formation without sacrificing overall process speed.
2Reliability
If an argon plasma breakthrough step is used to remove seed layer residues, then some residues are cleared, but it is insufficient to remove all residues and prevent defects in lapped silicon carbide
Solution Approach 1:
The breakthrough step uses a specific gas composition (CHF3/CF4 mixture with precise ratios), pressure (5-15 mTorr), and power settings optimized for removing lapping residues and photoresist. The transition step then adjusts parameters to optimize plasma density and ion flux for the bulk etch. These parameter changes ensure complete residue removal while maintaining a manageable process sequence.
Solution Approach 2:
The patent uses a composite gas mixture of CHF3 and CF4 in the breakthrough step, combining the oxygen-containing groups from CHF3 for effective photoresist removal with the fluorine content from CF4 for silicon carbide etching. This composite approach achieves superior residue removal compared to single-gas processes without significantly increasing complexity.
3Productivity
If the fluorine rich gas volume ratio is increased to enhance etching speed, then productivity improves, but defect formation increases due to preferential etching of lapping damage
Solution Approach 1:
The process dynamically adjusts gas composition and flow rates between stages. The breakthrough step uses higher CHF3 content for aggressive contaminant removal, then the transition step adjusts the mix to optimize conditions for the bulk etch. This dynamic adjustment allows high etch rates in the bulk stage while preventing preferential etching of lapping damage that would occur with consistently high fluorine content throughout.
Solution Approach 2:
The etch process applies periodic action through distinct time-separated stages with different gas compositions and parameters. The breakthrough step operates with one gas composition for a defined time, then the transition step modifies parameters, and finally the bulk etch proceeds with optimized settings. This periodic structure allows aggressive etching when needed while preventing defect formation during critical phases.
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 a substantial reduction in defect density and etching time, with enhanced etch depths and reduced columnar growths, effectively addressing the challenge of defect-prone etching in silicon carbide surfaces, particularly lapped surfaces.
Implementation Method 1
performing an initial plasma etch of the masked surface using a first set of process conditions, wherein the plasma is produced using an etchant gas mixture
Implementation Method 2
the plasma is produced using an etchant gas mixture which includes (i) oxygen and (ii) at least one fluorine rich gas... CF4 and/or SF6
Data Source
Figure 1(a)~1(b)
Figure 2a~2d
Figure 3a~3e
AI summary
According to the invention there is provided a method of plasma etching a silicon carbide workpiece including the steps of: forming a mask on a surface of the silicon carbide workpiece; performing an initial plasma etch on the masked surface using a first set of process conditions, wherein the plasma is produced using an etchant gas mixture which includes i) oxygen and ii) at least one fluorine rich gas which is present in the etchant gas mixture at a volume ratio of less than 50%; and subsequently performing a bulk plasma etch process using a second set of process conditions which differ from the first set of process conditions.