Trench Sidewall Protection for Selective Epitaxial Growth
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Solution Overview
Problem
The use of hydrofluoric acid (HF) precleaning in semiconductor manufacturing can cause unwanted expansion of trench openings in dielectric layers, leading to undesired semiconductor material formation during epitaxial growth, as it attacks the patterned dielectric layer and enlarges the areas where additional material is deposited.
Innovation Solution
A protective guard layer, resistant to HF, such as silicon nitride or silicon oxynitride, is applied to the trench sidewalls to prevent erosion during precleaning, ensuring the integrity of the trench pattern and confining epitaxial semiconductor material deposition to the desired regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HF precleaning is used to clean the substrate before epitaxial growth, then cleaning effectiveness is improved, but trench sidewall expansion occurs leading to loss of manufacturing precision
Solution Approach 1:
A protective layer is introduced as an intermediary between the HF precleaning solution and the trench sidewalls. This protective layer is selectively removed after precleaning, allowing the trench pattern to be restored to its original dimensions. The protective layer acts as a temporary mediator that enables effective cleaning while preventing harmful sidewall expansion.
Solution Approach 2:
The protective layer is applied before the HF precleaning step to preemptively counteract the harmful expansion effect. By having the protective layer in place beforehand, the trench sidewalls are shielded from the etching action of HF, preventing the unwanted widening that would otherwise occur during the necessary cleaning process.
2Device complexity
If no protective layer is used during precleaning, then process complexity is reduced, but unwanted semiconductor material formation occurs during epitaxial growth
Solution Approach 1:
The protective layer is applied in advance of the epitaxial growth step, specifically before the HF precleaning that would otherwise cause sidewall expansion. This preliminary action ensures that when epitaxial growth occurs, the trench pattern remains intact and material deposition is confined to the intended regions, preventing unwanted semiconductor material formation.
Solution Approach 2:
The protective layer serves as a temporary intermediary structure that maintains trench pattern integrity throughout the precleaning and epitaxial growth processes. After these critical steps are completed, the protective layer is selectively removed, having fulfilled its mediating role in preventing both sidewall expansion and unwanted material formation.
3Area of stationary object
If trench sidewalls are allowed to expand during precleaning, then cleaning coverage is improved, but epitaxial material deposits in undesired areas
Solution Approach 1:
The protective layer acts as a mediator that allows thorough cleaning of the trench bottom and sidewalls while preventing the trench pattern from expanding. By shielding the trench sidewalls during HF precleaning, the protective layer ensures that cleaning coverage is achieved without the unwanted side effect of sidewall expansion that would lead to material deposition in undesired areas.
Solution Approach 2:
The protective layer provides localized protection specifically to the trench sidewall regions that are susceptible to HF etching. This localized quality control ensures that only the areas requiring cleaning are exposed to HF, while the trench pattern boundaries are selectively protected, thereby maintaining precise control over where epitaxial material will eventually deposit.
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 protective guard layer effectively prevents excessive trench widening, allowing precise control over semiconductor material formation, ensuring that additional material is deposited only in intended areas and maintaining the integrity of the patterned trenches.
Implementation Method 1
forming a protective layer on sidewalls of the trench... subjecting the substrate to a precleaning operation... wherein the protective layer prevents expansion of the sidewalls of the trench as a result of the precleaning operation
Implementation Method 2
forming epitaxial semiconductor material within the trench and over the exposed one or more semiconductor structures
Data Source
AI summary
A method of forming a semiconductor device includes forming an insulator layer over a substrate; opening a trench in the insulator layer so as to expose one or more semiconductor structures formed on the substrate; forming a protective layer on sidewalls of the trench; subjecting the substrate to a precleaning operation in preparation for epitaxial semiconductor formation, wherein the protective layer prevents expansion of the sidewalls of the trench as a result of the precleaning operation; and forming epitaxial semiconductor material within the trench and over the exposed one or more semiconductor structures.