Plasma Etching Residue Removal via Low Pressure and Heat
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Solution Overview
Problem
Existing methods for plasma etching in semiconductor and MEMS industries face challenges in removing polymer residues from narrow trenches and undercuts with high aspect ratios, as reactive particles or wet etching solutions struggle to penetrate and rinse effectively, leading to residue accumulation that can impair device functionality.
Innovation Solution
A method involving a two-step process where the first step creates a structured surface through etching, followed by a second step at low ambient pressure (<60 Pa) and elevated substrate temperature (>150°C) to facilitate deep penetration of reactive particles for residue removal, without the need for ion incidence, using gases like O2, H2, N2, or ammonia to enhance residue incineration and reduce SiO2 formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching methods are used to create structured surfaces, then anisotropic etching can be achieved, but polymer residues remain in narrow trenches and undercuts that cannot be effectively removed
Solution Approach 1:
The patent changes the pressure parameter from conventional high pressure to low pressure (below 60 Pa, preferably 1-50 Pa), and changes the substrate temperature parameter to elevated temperatures (above 150°C, preferably 200-400°C). These parameter changes enable free radicals to penetrate deeply into narrow structures and effectively remove polymer residues through enhanced diffusion and reduced recombination.
Solution Approach 2:
The patent replaces the mechanical ion bombardment system with a chemical free radical system. Instead of using ion incidence to remove residues, the patent uses free radicals generated in low pressure plasma that can chemically react with and remove polymer residues through diffusion into narrow trenches and undercuts without requiring ion incidence.
2Object-generated harmful factors
If wet etching solutions are used to remove residues, then chemical cleaning can be achieved, but penetration into narrow trenches with high aspect ratios is insufficient
Solution Approach 1:
The patent uses low pressure plasma as a gas-phase cleaning medium that can penetrate deeply into narrow trenches. The low pressure condition enables the cleaning agents (free radicals) to overcome capillary forces and reach deep into high aspect ratio structures, unlike liquid wet etching solutions that are hindered by capillary action.
Solution Approach 2:
By changing the pressure parameter to low pressure (below 60 Pa), the mean free path of reactive particles increases, enabling them to penetrate deeply into narrow trenches and undercuts. The elevated temperature parameter (above 150°C) further enhances penetration by reducing the viscosity and surface tension of the plasma medium.
3Object-generated harmful factors
If O2 plasma stripping is used to remove residues, then polymer removal can be achieved, but penetration into narrow structures is limited due to low mean free path length
Solution Approach 1:
The patent changes the pressure parameter from conventional high pressure (where mean free path is short) to low pressure (below 60 Pa), which increases the mean free path of reactive particles. This enables O2 plasma stripping to effectively penetrate into narrow trenches and undercuts, overcoming the limitation of short mean free path length in conventional conditions.
4Manufacturing precision
If ion incidence plasma etching is used, then anisotropic etching is achieved, but residues in inaccessible areas cannot be removed
Solution Approach 1:
The patent replaces the ion incidence mechanism with a free radical diffusion mechanism. Free radicals can reach inaccessible areas through diffusion and chemical reaction, whereas ions require direct line-of-sight incidence. This substitution enables removal of residues from areas that are inaccessible to ion bombardment, such as deep undercuts and caverns.
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 approach allows for effective removal of polymer residues from complex structures, ensuring functional micromechanical components like sensors and microphones by enabling deeper penetration of reactive particles and reducing the complexity of the manufacturing process, regardless of the substrate's geometric conditions.
Implementation Method 1
a method for removing residues from a structured surface of a substrate, during which an ambient pressure for the substrate is set to be lower than 60 Pa, and a substrate temperature of the substrate is set to be higher than 150° C.
Implementation Method 2
residues are removed from the substrate... using free radicals in the plasma
Implementation Method 3
Both these methods have in common the fact that it is difficult in general to adequately penetrate into narrow trenches with these media under these process conditions. This is due to the low mean free path length in stripping processes in the typical Torr pressure range
Implementation Method 4
an ambient pressure for the substrate, which is preferably lower than 60 Pa, and a substrate temperature, which is preferably higher than 150° C., are set during the second method step
Data Source
AI summary
A method is described for manufacturing a micromechanical structure, in which a structured surface is created in a substrate by an etching method in a first method step, and residues are at least partially removed from the structured surface in a second method step. In the second method step, an ambient pressure for the substrate which is lower than 60 Pa is set and a substrate temperature which is higher than 150° C. is set.