Variable Faraday Shield for Plasma Etching Roughness Control
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Solution Overview
Problem
Current plasma processing technologies face challenges in controlling substrate roughness due to ion erosion and sputtering in RIE and ICP systems, with existing Faraday shields either failing to eliminate or fully control sputtering, particularly in RIE reactors, and lacking flexibility in achieving desired surface roughness for various applications.
Innovation Solution
A variable Faraday shield with a combination of metallic and dielectric layers, allowing controlled exposure of the substrate holder, clamping ring, or electrode to plasma, enabling adjustable sputtering from complete elimination to maximum, achieved through varying the polarized surface area and using Teflon or other dielectric materials for plasma confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a Faraday shield is used to eliminate ion erosion and sputtering, then substrate holder protection is improved, but control over roughness formation is lost
Solution Approach 1:
The patent applies the dynamics principle by making the Faraday shield movable rather than fixed. The shield can be positioned at different distances from the substrate holder, allowing dynamic adjustment of the plasma shielding effect. This enables the system to transition between complete protection (shield close to holder) and controlled sputtering (shield farther away), resolving the contradiction between protection and control.
Solution Approach 2:
The patent changes the physical parameter of shield-to-substrate-holder distance to control the degree of plasma exposure. By varying this distance parameter, the system can adjust the level of ion erosion and sputtering, enabling controlled roughness formation while still providing protection when needed. This parameter change allows the system to achieve both protection and adaptability.
2Manufacturing precision
If sputtering is eliminated to achieve smooth surfaces, then manufacturing precision is improved, but the ability to create controlled roughness for functional properties is lost
Solution Approach 1:
The movable shield enables dynamic control over sputtering intensity, allowing the system to switch between producing smooth surfaces (shield positioned for maximum protection) and creating controlled roughness (shield positioned to allow controlled sputtering). This dynamic capability provides both manufacturing precision and functional adaptability.
Solution Approach 2:
By changing the shield position parameter, the system controls the degree of sputtering to achieve desired surface roughness levels. This parameter control enables the production of surfaces with specific functional properties (wetting, adhesion, optical characteristics) while maintaining the ability to produce smooth surfaces when required.
3Device complexity
If a fixed Faraday shield configuration is used, then device complexity is reduced, but control over capacitive coupling and sputtering is insufficient
Solution Approach 1:
The patent introduces a movable shield mechanism that, while adding some complexity, provides significant control over capacitive coupling and sputtering. The movement capability allows the system to adjust plasma exposure dynamically, achieving adaptability that outweighs the moderate increase in device complexity.
Solution Approach 2:
The movable shield serves multiple functions: it acts as a Faraday shield for plasma protection, a controllable aperture for plasma exposure, and a means to adjust capacitive coupling. This multi-functionality justifies the added complexity by providing comprehensive control over plasma processing parameters.
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 variable Faraday shield allows precise control of substrate roughness, reducing roughness from 1.2-1.4 µm to below 0.05 µm, depending on shielding coverage, effectively managing micro masking and etching quality across different materials and processes.
Implementation Method 1
Radio Frequency (RF) capacitive coupling is reduced by the use of Faraday shields, also called electrostatic shields
Implementation Method 2
RF capacitive coupling is reduced by the use of Faraday shields
Implementation Method 3
By means of the proposed use of Teflon or other dielectric layer between the top metallic layer and the substrate holder/electrode/ clamping ring or their combinations the plasma is confined only in the processing area
Implementation Method 4
These high-energy ions, are damaging the substrate holder (in the area not covered by the substrate) resulting in sputtering of the clamping ring of the substrate or of the substrate holder material
Implementation Method 5
high-energy ions (with energy ranging from several electron volts to several hundreds of electron volts) are accelerated along the electric field lines toward the substrate
Implementation Method 6
allowing for pulsed plasma processing with very little reflected power
Data Source
Figure 1a~1b
Figure 2a~2g
Figure 3a~3e
AI summary
A grounded, static, electrostatic shield design with variable shielding for the substrate holder, a clamping ring, or an electrode or their combination in a Reactive Ion Etching (RIE) or an Inductively Coupled Plasma (ICP), or other low pressure Plasma Etching system is proposed. The advantage of this type of shield is that it controls the capacitive coupling, and with it the erosion of the substrate holder due to sputtering from plasma ions. The shield, and therefore the amount of sputtering, can be freely adjusted in order to have controllable micro masking on the substrate to be plasma treated, allowing full control of roughness formation on the substrate.