Two-Step Cleaning for Silicon Germanium Substrates
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Solution Overview
Problem
Conventional cleaning processes for semiconductor substrates with silicon and silicon germanium layers result in uneven etching rates, native oxide layer formation, and subsequent epitaxial growth issues, leading to unreliable semiconductor device performance.
Innovation Solution
A method involving a two-step cleaning process using a first solution to remove native oxide layers and a second solution with a high water-to-ammonium hydroxide ratio to achieve balanced etching rates and prevent excessive silicon germanium layer loss, ensuring uniform cleaning results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SC1 cleaning solution is used to clean the substrate, then cleaning effectiveness is improved, but silicon germanium layer loss increases due to excessive etching
Solution Approach 1:
The cleaning process is divided into multiple sequential steps: first using NH4OH-based solution to remove organic contaminants, then using HF-based solution to remove native oxide layers, and finally using a diluted SC1 solution with reduced H2O2 concentration to perform gentle cleaning. This segmentation allows each step to target specific contaminants while minimizing damage to the silicon germanium layer.
Solution Approach 2:
The concentration of hydrogen peroxide in the cleaning solution is reduced from the conventional SC1 ratio (1:4:20) to a diluted version (1:4:100 or higher water content), significantly lowering the etching rate on silicon germanium while maintaining cleaning effectiveness. Additionally, the cleaning process is performed at controlled temperatures and for optimized durations to prevent excessive material loss.
2Manufacturing precision
If etching process is performed to expose silicon and silicon germanium layers, then pattern formation is improved, but native oxide layer formation increases over time
Solution Approach 1:
The cleaning process is performed immediately after the etching process to prevent extensive native oxide formation. The multi-step cleaning protocol is designed to quickly and effectively remove oxide layers as they form, with the HF-based step specifically targeting oxide removal. This preliminary and prompt cleaning action prevents oxide layers from becoming too thick and difficult to remove.
Solution Approach 2:
The NH4OH-based cleaning solution serves as an intermediary step between etching and final cleaning, removing organic contaminants and preparing the surface for subsequent oxide removal. The HF-based solution then acts as a specialized intermediary to selectively remove oxide layers without significantly etching the silicon germanium layer, thanks to the low H2O2 concentration.
3Reliability
If hydrogen peroxide is used in cleaning solution, then cleaning capability is improved, but new oxide layer formation occurs on silicon layers
Solution Approach 1:
The cleaning process uses periodic alternation between different cleaning solutions: first NH4OH-based solution for organic contaminant removal, then HF-based solution for oxide removal, and finally a diluted SC1 solution with low H2O2 concentration for gentle final cleaning. This periodic use of different chemical mechanisms allows effective cleaning while minimizing oxide formation by limiting hydrogen peroxide exposure time and concentration.
Solution Approach 2:
Different regions of the cleaning process use different chemical compositions tailored to specific needs: the initial NH4OH step targets organic contaminants, the HF step targets oxide layers, and the final diluted SC1 step provides gentle overall cleaning. This localized application of different cleaning chemistries ensures that hydrogen peroxide is only used when necessary and at minimal concentrations, reducing unwanted oxide formation while maintaining cleaning effectiveness.
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 method ensures uniform etching and minimizes silicon germanium layer loss, allowing for reliable semiconductor device fabrication with consistent performance.
Implementation Method 1
performing a first cleaning sub-process, wherein the first cleaning sub-process comprises using a first cleaning solution to remove a native oxide layer from the semiconductor substrate
Implementation Method 2
using an etching solution that etches silicon and silicon germanium with similar etching rates
Implementation Method 3
The effectiveness (i.e., cleaning efficiency) of the cleaning process that uses SC1 varies in accordance with the thickness of the native oxide layer that forms between the etching and cleaning processes
Data Source
AI summary
A method for cleaning a substrate on which a silicon layer and a silicon germanium layer are formed and exposed, and method for fabricating a semiconductor device using the cleaning method are disclosed. The cleaning method comprises preparing a semiconductor substrate on which a silicon layer and a silicon germanium layer are formed and exposed; and performing a first cleaning sub-process that uses a first cleaning solution to remove a native oxide layer from the semiconductor substrate. The cleaning method further comprises performing a second cleaning sub-process on the semiconductor substrate after performing the first cleaning sub-process, wherein the second cleaning sub-process comprises using a second cleaning solution. In addition, the second cleaning solution comprises ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2), and deionized water (H2O), and the second cleaning solution comprises at least 200 times more deionized water (H2O) than ammonium hydroxide (NH4OH) by volume.