Plasma Smoothing of 3D Silicon Features Without Shape Loss
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Solution Overview
Problem
Existing methods for reducing surface roughness on non-planar surfaces of silicon substrates, such as microneedles and trenches, are inadequate as they either damage the 3D structures or fail to effectively smooth the surface without causing structural harm.
Innovation Solution
A plasma-based method involving sequential plasma deposition and etch steps using specific gas mixtures and pressures, with controlled RF bias, to smooth non-planar silicon surfaces while preserving their topographic dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If CMP or self-planarizing films are used to reduce surface roughness, then surface smoothness is improved, but the 3D structures are damaged
Solution Approach 1:
The patent replaces the mechanical CMP process with a plasma-based chemical process. The plasma treatment uses reactive species to chemically modify and smooth the surface without mechanical contact, thereby achieving surface smoothing while preserving the integrity of 3D structures like microneedles and trenches.
Solution Approach 2:
The patent employs controlled plasma processing parameters including specific gas compositions (oxygen, fluorocarbon gases), pressure ranges (100 mTorr or greater), and RF bias power levels (less than 100 W) to achieve surface smoothing. By carefully controlling these parameters, the process smooths surfaces without removing excessive material or damaging structural features.
2Productivity
If conventional plasma etching is used, then material removal is efficient, but surface roughness increases
Solution Approach 1:
The patent employs alternating deposition and etching cycles rather than continuous etching. The process alternates between depositing conformal layers using fluorocarbon gases and removing material through plasma etching. This periodic action allows the surface to be smoothed incrementally over multiple cycles while maintaining overall productivity, as each cycle removes a small amount of material uniformly across the surface.
Solution Approach 2:
The patent uses composite gas mixtures combining oxygen and fluorocarbon gases in specific proportions. This composite approach allows simultaneous achievement of surface smoothing and controlled material removal, as the fluorocarbon component provides conformal deposition that fills in surface irregularities while the oxygen component enables subsequent etching of the deposited material.
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 significantly reduces surface roughness by a factor of ten or more, maintaining the original shape and functionality of features like microneedles and trenches.
Implementation Method 1
a plasma deposition step using oxygen and at least one fluorocarbon gas at a total process pressure of 100 mTorr or greater, with no RF bias or with an RF bias power of less than 100 W
Implementation Method 2
a plasma etch step using oxygen, at least one fluorocarbon etchant gas, and SF6 at a total process pressure of 100 mTorr or greater, with no RF bias or with an RF bias power of less than 100 W
Data Source
AI summary
Surface roughness on a non-planar surface of a silicon substrate with upstanding and/or recessed features can be reduced. A first sequence of plasma processing steps and a second sequence of plasma processing steps can be performed on the silicon substrate to reduce the surface roughness of the upstanding and/or recessed features while retaining these features. The first sequence of plasma processing steps includes i) a plasma deposition step using oxygen and at least one fluorocarbon gas followed by ii) a plasma etch step using oxygen, at least one fluorocarbon etchant gas, and SF6. The second sequence of plasma processing steps includes i) an isotropic plasma etch step using oxygen and at least one fluorine containing etchant gas followed by ii) a plasma etch step using at least one fluorine containing or chlorine containing etchant gas.