Gas Chopped DRIE Sidewall Roughness Control
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Solution Overview
Problem
Current high aspect ratio anisotropic etching techniques face challenges in achieving smooth sidewalls for nanostructures due to radiation damage, undercutting, and contamination, particularly in the sub-50 nm regime, where gas chopping processes result in sidewall roughness and scalloping.
Innovation Solution
A method of radical reduced, gas chopped deep reactive ion etching is employed, using a combination of an etchant and a passivator, with controlled radical concentrations, where a hydrogen source acts as a getter to reduce radical concentrations, and CF2 radicals are generated to enhance anisotropy and smoothness, achieving sidewall roughness of less than 10 nm RMS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If gas chopping process is used for high aspect ratio anisotropic etching, then etching anisotropy is improved, but sidewall roughness and scalloping increase
Solution Approach 1:
The patent employs gas chopping with periodic switching between etchant and passivator supply to achieve anisotropic etching. The periodic nature of the process allows control over the balance between vertical etching and sidewall passivation, improving anisotropy while managing sidewall quality through optimized cycle parameters.
Solution Approach 2:
The patent modifies process parameters including gas flow rates, pressure, RF power, and temperature to control radical concentrations. By adjusting these parameters, the process achieves smooth sidewalls with reduced roughness while maintaining high aspect ratio etching anisotropy, resolving the contradiction between anisotropy and sidewall smoothness.
2Productivity
If high energy ion bombardment is used for anisotropic etching, then etching rate and anisotropy are improved, but radiation damage and substrate damage increase
Solution Approach 1:
The patent optimizes RF power, pressure, and gas composition to control ion energy and radical concentration. By carefully balancing these parameters, the process achieves high etching rates with reduced ion bombardment damage, minimizing radiation effects while maintaining productivity.
Solution Approach 2:
The patent introduces a passivator gas that acts as an intermediary, providing protective species that reduce the direct impact of high energy ions on the substrate. The passivator forms protective layers that mitigate radiation damage while allowing continued anisotropic etching.
3Stability of the object's composition
If fluorocarbon plasma is used for sidewall passivation, then anisotropy control is improved, but sidewall roughness increases due to deposition and etching cycles
Solution Approach 1:
The patent uses periodic switching between fluorocarbon passivation and etching steps. By optimizing the duration and frequency of these periodic cycles, the process achieves good anisotropy control while minimizing the accumulation of roughness and scalloping effects from repeated deposition and removal cycles.
Solution Approach 2:
The patent adjusts gas flow rates, pressure, and RF power to control the deposition and etching rates during fluorocarbon plasma processing. By balancing these parameters, the process achieves effective sidewall passivation for anisotropy while minimizing surface roughness through optimized deposition thickness and removal rates.
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 method enables the production of smooth sidewalls with reduced roughness, allowing for the transfer of sub-50 nm features with high aspect ratios, improving the control of anisotropy and etching rates, and minimizing radiation damage, thereby enhancing the fabrication of nanostructures.
Implementation Method 1
ionizing at least some of the etchant and passivator
Implementation Method 2
ionizing at least some of the etchant and passivator
Implementation Method 3
controlling a concentration of radicals produced by the ionizing of the etchant
Implementation Method 4
hydrogen source acts as a getter to reduce radical concentrations
Implementation Method 5
CF2 radicals are generated to enhance anisotropy and smoothness
Implementation Method 6
enhancing the control of anisotropy and etching rates
Data Source
AI summary
A method for silicon micromachining techniques based on high aspect ratio reactive ion etching with gas chopping has been developed capable of producing essentially scallop-free, smooth, sidewall surfaces. The method uses precisely controlled, alternated (or chopped) gas flow of the etching and deposition gas precursors to produce a controllable sidewall passivation capable of high anisotropy. The dynamic control of sidewall passivation is achieved by carefully controlling fluorine radical presence with moderator gasses, such as CH4 and controlling the passivation rate and stoichiometry using a CF2 source. In this manner, sidewall polymer deposition thicknesses are very well controlled, reducing sidewall ripples to very small levels. By combining inductively coupled plasmas with controlled fluorocarbon chemistry, good control of vertical structures with very low sidewall roughness may be produced. Results show silicon features with an aspect ratio of 20:1 for 10 nm features with applicability to nano-applications in the sub-50 nm regime. By comparison, previous traditional gas chopping techniques have produced rippled or scalloped sidewalls in a range of 50 to 100 nm roughness.