SOI Oxide Stripping With Center-to-Edge Spin Etching
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Solution Overview
Problem
Conventional methods for removing oxide films from silicon-on-insulator (SOI) structures, such as immersion stripping and wafer spinning, often result in non-uniform oxide removal and hydrogen fluoride (HF) undercuts, which degrade the dielectric layer and cause defects during epitaxial deposition.
Innovation Solution
A center-to-edge spin etch process is employed, where the etchant solution is dispersed near the center of the SOI structure during the first phase and then directed towards the edge in a second phase, reducing HF undercuts and preserving the backside oxide, thereby improving the uniformity and quality of the epitaxial layer deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional immersion stripping or wafer spinning methods are used to remove oxide films, then oxide removal is achieved, but hydrogen fluoride undercuts form that degrade the dielectric layer and cause defects
Solution Approach 1:
The oxide removal process is segmented into two distinct phases: a first phase targeting the center region and a second phase targeting the edge region. This segmentation allows different etching conditions to be applied to different areas, preventing HF undercuts while effectively removing oxide including terrace oxide, thus resolving the contradiction between oxide removal uniformity and HF undercut formation
Solution Approach 2:
The center region etching is performed as a preliminary action before edge region etching. This preliminary etching of the center region modifies the oxide thickness distribution, which prevents HF undercut formation during subsequent edge etching, thereby achieving uniform oxide removal without harmful undercuts
2Reliability
If masking is used to protect the backside oxide during oxide removal, then backside oxide protection is achieved, but damage occurs to the top silicon layer during wafer tape adhesion and removal
Solution Approach 1:
The harmful masking step is extracted and eliminated from the process. Instead of using masks that require adhesion and removal operations that damage the top silicon layer, the invention uses a two-phase spin etching method that inherently protects the backside oxide through process design, thus maintaining backside oxide protection while eliminating top layer damage
Solution Approach 2:
The etching parameters are changed by controlling the spin speed and etchant distribution pattern during two phases. By adjusting these parameters, the etching is selectively applied to remove terrace oxide while preserving the backside oxide without requiring physical masks, thereby protecting both the backside oxide and top silicon layer integrity
3Productivity
If conventional spin etching with etchant distributed at the wafer center is used, then oxide removal is achieved, but terrace oxide at the edge remains and HF undercuts are formed
Solution Approach 1:
The etching process is made dynamic by transitioning from a static center-only etching approach to a two-phase dynamic process where the etching target transitions from center to edge. This dynamic approach ensures complete terrace oxide removal while controlling HF undercut formation, achieving both high productivity and precision
Solution Approach 2:
The center region etching serves as a preliminary action that modifies the oxide distribution, creating conditions that enable complete terrace oxide removal in the subsequent edge etching phase, thus achieving complete oxide removal without HF undercuts
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 method effectively removes the terrace oxide while minimizing HF undercuts and maintaining the protective backside oxide, leading to improved thickness uniformity and reduced defectivity of the epitaxial silicon layer, enhancing the overall quality of the SOI structure.
Implementation Method 1
A center-to-edge spin etch process is employed, where the etchant solution is dispersed near the center of the SOI structure during the first phase and then directed towards the edge in a second phase
Data Source
Figure 1A~1C
Figure 2
Figure 3~4
AI summary
Methods for removing an oxide film from a silicon-on-insulator structure are disclosed. The oxide may be stripped from a SOI structure before deposition of an epitaxial silicon thickening layer. The oxide film may be removed by dispensing an etching solution toward a center region of the SOI structure and dispensing an etching solution to an edge region of the structure.