SiGe Etching Formulation for Silicon Selectivity and Faster Stabilization
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Solution Overview
Problem
Existing etching compositions for silicon-germanium (SiGe) in microelectronic devices face challenges such as reduced selectivity between SiGe and silicon as the germanium content decreases, requiring longer times to achieve stable etch rates, and excessive etching of other materials like silicon nitride and silicon oxide due to high hydrofluoric acid concentrations.
Innovation Solution
Incorporating additional acids like formic acid, sulfuric acid, or lactic acid into etching compositions containing hydrogen fluoride (HF) and hydrogen peroxide, which improve the selectivity and etch rate of SiGe relative to silicon, while reducing the etch rate of silicon nitride and silicon oxide, and accelerating the time to reach 90% of the maximum etch rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high concentration of hydrofluoric acid is used in etching composition, then etch rate of silicon-germanium is improved, but etching of other materials like silicon nitride and silicon oxide increases excessively
Solution Approach 1:
The patent modifies the chemical composition parameters of the etching solution by adding formic acid and sulfuric acid to the existing HF/H2O2/acetic acid system. This parameter change allows the etch rate of SiGe to be maintained or improved while the selectivity against silicon nitride and silicon oxide is enhanced, thereby reducing excessive etching of these materials.
Solution Approach 2:
The patent creates a composite etching composition by combining multiple acids (hydrofluoric acid, formic acid, sulfuric acid, acetic acid, and hydrogen peroxide) in specific proportions. This composite formulation works synergistically to achieve high SiGe etch rate while providing better selectivity and reducing damage to other materials compared to using high concentration HF alone.
2Manufacturing precision
If germanium content in sacrificial SiGe material is reduced, then match for silicon features is improved, but selectivity for etching SiGe relative to silicon diminishes
Solution Approach 1:
The patent changes the chemical parameters of the etching system by introducing formic acid and sulfuric acid, which modifies the etching mechanism to maintain high selectivity between SiGe and silicon even when germanium content is low. This allows the use of SiGe with minimal germanium that better matches silicon features while preserving etching selectivity.
3Reliability
If standard three-part etching composition is used, then good etching rate for SiGe with high selectivity to silicon is achieved, but long time is required to achieve stable etch rate after H2O2 addition
Solution Approach 1:
The patent incorporates formic acid and sulfuric acid into the etching composition in advance, before the etching process begins. These pre-added acids prepare the chemical environment to accelerate the formation of stable etch conditions, reducing the induction period typically observed when hydrogen peroxide is added to the etching system.
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 modified etching compositions enhance the selectivity and etch rate of SiGe, decrease the etch rate of silicon and other materials, and significantly reduce the time required to achieve a stable etch rate, making them more efficient for complex microelectronic device structures.
Implementation Method 1
aqueous etching composition comprising: from 0.1 to 10 parts by weight hydrofluoric acid, from 10 to 35 parts by weight hydrogen peroxide, from 5 to 50 parts by weight acetic acid, from 2 to 40 parts by weight formic acid, from 0.1 to 10 parts by weight sulfuric acid, and from more than 10 to 20 parts by weight lactic acid
Implementation Method 2
contacting the surface with the aqueous silicon germanium selective etching composition for time and at a temperature effective to selectively remove silicon-germanium relative to the silicon
Data Source
AI summary
Compositions useful for the selective removal by etching of silicon-germanium-containing materials relative to silicon-containing materials, from a microelectronic device having features containing these materials at a surface, the compositions containing hydrofluoric acid, acetic acid, hydrogen peroxide, and at least one additional acid that will improve performance as measured by one or more of an etching rate or selectivity and are tunable to achieve the required Si:Ge removal selectivity and etch rates.