Polysilicon Etching Composition for Low-Residue Selective Removal
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Solution Overview
Problem
Current methods for etching polysilicon in semiconductor devices, such as using tetramethylammonium hydroxide (TMAH), are inefficient and can contaminate surfaces with residual alkali metal ions, and exhibit differential etch rates for n-doped and p-doped polysilicon, which is undesirable for applications with multiple polysilicon surfaces.
Innovation Solution
A composition comprising choline hydroxide, an oxidizing agent like periodic acid, and optionally a surfactant, which reduces etching selectivity based on silicon crystal orientation, minimizing residual silicon residues and achieving high selectivity of polysilicon over silicon nitride and silicon oxide, allowing for controlled removal rates and surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TMAH is used for polysilicon etching, then etching capability is achieved, but surface contamination with alkali metal ions occurs
Solution Approach 1:
The patent changes the chemical composition parameters of the etching solution by using choline hydroxide instead of TMAH or KOH, and by adding oxidizing agents like periodic acid. This parameter change maintains etching capability while eliminating alkali metal ion contamination, achieving both productivity and purity requirements
Solution Approach 2:
The patent employs a disposable-like approach by using a single-bath solution that combines etching and cleaning functions. The etchant is designed to be consumed and discarded after use, ensuring no persistent contamination, similar to the concept of disposable objects that eliminate long-term harmful effects
2Productivity
If TMAH or KOH is used for polysilicon etching, then etching rate is achieved, but differential etching of n-doped and p-doped polysilicon occurs
Solution Approach 1:
The patent changes the chemical mechanism of etching by introducing oxidizing agents (periodic acid, iodate, persulfate) to the choline hydroxide solution. This parameter change transforms the etching process from one that is sensitive to doping type to one that etches all polysilicon uniformly, maintaining high etching rates while achieving manufacturing precision through consistent removal of n-doped and p-doped polysilicon
3Productivity
If conventional etchants are used, then polysilicon removal is achieved, but high selectivity over silicon nitride and silicon oxide is not obtained
Solution Approach 1:
The patent achieves high selectivity (>1000:1) by changing the chemical parameters of the etching solution - specifically using choline hydroxide combined with oxidizing agents at controlled concentrations and temperatures. This parameter optimization enables rapid polysilicon removal while maintaining exceptional selectivity against silicon nitride and silicon oxide, resolving the contradiction between productivity and reliability
Solution Approach 2:
The patent employs strong oxidizing agents (periodic acid, iodate, persulfate) to accelerate the etching of polysilicon. These oxidants enhance the etching rate and selectivity by preferentially oxidizing polysilicon over silicon nitride and silicon oxide, achieving both high productivity and high reliability in the etching process
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 composition enables efficient and selective etching of polysilicon with high selectivity (>1000:1) and controlled removal rates, avoiding the use of neurotoxic TMAH and alkali metal hydroxides, while reducing surface roughness and residual contamination.
Implementation Method 1
Typical methods of removal of polysilicon include dry etching and wet etching methods. In the case of anisotropic wet etching, bases such as tetramethylammonium hydroxide (TMAH) and alkali metal hydroxides have been used.
Implementation Method 2
The compositions comprise choline hydroxide, an oxidizing agent such as periodic acid
Data Source
AI summary
The invention provides compositions useful in the etching of polysilicon in the presence of silicon oxide and silicon nitride. The compositions comprise choline hydroxide, an oxidizing agent such as periodic acid, and optionally a surfactant, and are useful in the etching of polysilicon in general, and in particular in both the operation of polysilicon trim as well as polysilicon exhume. The utilization of an added oxidizing agent was found to reduce selectivity of silicon etching based on the silicon crystal orientation, which was found to reduce roughness and the presence of residual silicon residues, such as silicon (111) residues after the etching step.