Shallow Trench Isolation Pad Oxide Regrowth
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Solution Overview
Problem
The existing shallow trench isolation (STI) process, particularly in forming silicon-germanium heterojunction bipolar transistors, faces issues with electrical leakage and crystal defects due to damage to the pad oxide layer and underlying silicon during etching steps, leading to junction spiking and device failure.
Innovation Solution
A method involving a dry etch-back process with high selectivity to form inner sidewalls using a heavily N-doped silicon dioxide layer, followed by thermal oxidation to grow a second pad oxide layer, which protects the silicon and enables filling with isolation dielectric material, reducing damage and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet etching is used to remove inner sidewalls, then the inner sidewalls can be removed effectively, but the pad oxide layer and underlying silicon are damaged causing electrical leakage
Solution Approach 1:
A new pad oxide layer is grown by thermal oxidation before removing the inner sidewalls. This preliminary action creates a protective barrier that prevents the wet etching process from damaging the underlying silicon and causing electrical leakage, while still allowing effective removal of the inner sidewalls.
Solution Approach 2:
The thermal oxidation process creates a cushioning pad oxide layer that absorbs the harmful effects of the subsequent wet etching process. This cushioning layer protects the critical silicon substrate from direct exposure to the etchant, preventing junction spiking and electrical leakage while enabling complete inner sidewall removal.
2Manufacturing precision
If dry etching is used to form inner sidewalls, then precise sidewall formation is achieved, but damages occur to the pad oxide layer and silicon during etching steps
Solution Approach 1:
The pad oxide layer is regrown by thermal oxidation before the wet etching step. This preliminary protective action ensures that the silicon substrate is shielded from damage during the inner sidewall removal process, eliminating the harmful effects of etching while maintaining the precision benefits of the earlier dry etching step for inner sidewall formation.
3Device complexity
If multiple etching steps are performed, then inner sidewalls can be formed and removed, but crystal defects and junction spiking occur
Solution Approach 1:
Thermal oxidation is performed as a preliminary action between the inner sidewall formation and removal steps. This intermediate protective step prevents crystal defects and junction spiking that would otherwise occur during the subsequent wet etching process, allowing the multi-step etching process to proceed without compromising device reliability.
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 significantly reduces junction spiking and electrical leakage by maintaining the integrity of the pad oxide layer and silicon, ensuring high-quality thermal oxidation and minimizing damage during subsequent etching processes.
Implementation Method 1
etching the second oxide layer by using a dry etch-back process to form inner sidewalls in the one or more trenches
Implementation Method 2
growing a silicon dioxide layer, which serves as a second pad oxide layer, over a surface of each of the one or more trenches by thermal oxidation of the exposed underlying silicon
Data Source
AI summary
A method of filling shallow trenches is disclosed. The method includes: successively forming a first oxide layer and a second oxide layer over the surface of a silicon substrate where shallow trenches are formed in; etching the second oxide layer to form inner sidewalls with an etchant which has a high etching selectivity ratio of the second oxide layer to the first oxide layer; growing a high-quality pad oxide layer by thermal oxidation after the inner sidewalls are removed; and filling the trenches with an isolation dielectric material. By using this method, the risk of occurrence of junction spiking and electrical leakage during a subsequent process of forming a metal silicide can be reduced.