Neutral-Charge Liner for Uniform Wet Etching in Small-CD Features
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Solution Overview
Problem
The challenge in semiconductor fabrication is achieving uniform wet etching across features with different critical dimensions (CD) due to surface charge-induced CD-dependent etching, which results in uneven etch rates and material removal.
Innovation Solution
A thin liner layer with a neutral surface charge is formed within features before etching, or the etch solution is adjusted to ensure wall surfaces exhibit a neutral charge, preventing surface charge-induced CD-dependent etching and achieving uniform etching rates across all areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a wet etch process is utilized to remove material from within features having different critical dimensions, then material removal is achieved, but the etch rate differs across features of different CD resulting in uneven material removal
Solution Approach 1:
The patent adjusts the pH of the etch solution to a specific range (pH 2-4) to minimize surface charge effects on the wall surfaces. By changing this chemical parameter, the electrostatic attraction/repulsion between charged walls and reactive ions is reduced, leading to more uniform etch rates across features of different critical dimensions while maintaining effective material removal
Solution Approach 2:
The patent introduces a liner layer (such as silicon nitride, silicon oxynitride, or silicon carbon nitride) as an intermediary between the wall surface and the etch solution. This liner layer has neutral surface charge characteristics that prevent electrostatic interactions with reactive ions, thereby eliminating the CD-dependent etching effect and ensuring uniform etching across all feature sizes
2Reliability
If the wall surface exhibits positive or negative surface charge in the presence of etch solution, then electrostatic forces change the local concentration of reactive ions, but this results in surface charge induced CD-dependent etching
Solution Approach 1:
The patent changes the pH parameter of the etch solution to a neutral range (pH 2-4) where the wall surface charge is minimized. This parameter adjustment reduces electrostatic forces between the wall surface and reactive ions, preventing the harmful CD-dependent etching while maintaining reliable etch process control
Solution Approach 2:
The patent converts the harmful surface charge effect into a beneficial neutral surface charge by selecting specific wall materials (such as silicon nitride, silicon oxynitride, or silicon carbon nitride) that exhibit neutral charge characteristics at the optimized pH. This transforms the previously harmful electrostatic interactions into a neutral state that promotes uniform etching
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 ensures uniform etching rates within features and on planar areas, preventing uneven material removal and enhancing the precision of semiconductor fabrication processes.
Implementation Method 1
electrostatic forces between the charged wall surface and the reactive ions in the etch solution may change the local concentration of the anions/cations within the features
Implementation Method 2
The chemical solution (otherwise referred to herein as an etch solution) often contains a solvent and etchant chemical(s) designed to react with materials on the substrate surface and promote dissolution of the reaction products
Data Source
AI summary
Embodiments of a wet etch process and methods are disclosed herein to provide uniform wet etching of material formed within features (e.g., trenches, holes, slits, etc.), and on more planar areas of a patterned substrate, when a critical dimension (CD) of the features is relatively small compared to the more planar areas of the patterned substrate. In the present disclosure, uniform wet etching is provided by ensuring that wall surfaces adjacent to the material being etched exhibit a neutral surface charge when exposed to the etch solution used to etch the material.