Semiconductor Recess Fabrication for Flat Bottoms
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Solution Overview
Problem
The formation of a 'Σ' shaped recess in semiconductor devices often results in a cuspate bottom, which hinders the growth of high-quality SiGe, essential for enhancing channel mobility in PMOS devices.
Innovation Solution
A method involving the formation of a 'U' shaped recess, treated with a surfactant to prevent oxide formation on sidewalls, followed by orientation selective wet etching using an etchant with an oxide stop layer to prevent etching of the recess bottom, ensuring a flat 'Σ' shape is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If orientation selective wet etching is performed on a U-shaped recess to form a Σ-shaped recess, then the channel mobility for PMOS devices is enhanced through compressive stress, but the recess bottom becomes cuspate-shaped which hinders high-quality SiGe growth
Solution Approach 1:
A thin oxide layer is formed on the recess bottom before the orientation selective wet etching process. This preliminary oxide layer serves as a protective mask that prevents the etchant from attacking the bottom surface, thereby maintaining flatness while allowing the sidewalls to be etched into the desired Σ-shape for stress enhancement
Solution Approach 2:
The oxide layer acts as an intermediary protective layer between the etchant and the recess bottom. It selectively protects the bottom surface during etching while allowing the etching process to proceed on the sidewalls, thus mediating between the need for shape modification and bottom flatness preservation
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 prevents the occurrence of a cuspate bottom, allowing for high-quality SiGe epitaxial growth and improved channel mobility in PMOS devices.
Implementation Method 1
treating the U-shaped recess with a surfactant, wherein an amount of surfactant adsorbed on sidewalls of the U-shaped recess is larger than an amount adsorbed on a bottom of the U-shaped recess
Implementation Method 2
performing orientation selective wet etching on the sidewalls of the U-shaped recess with an etchant using the oxide as an etching stop layer
Data Source
AI summary
A method of fabricating a semiconductor device for improving the performance of “Σ” shaped embedded source/drain regions is disclosed. A “U” shaped recess is formed in a Si substrate. The recess is treated with a surfactant, the amount of surfactant adsorbed on the recess sidewalls being greater than that on the recess bottom. An oxide is formed on the bottom. The presence of surfactant on the sidewalls, prevents oxide from forming thereon. The surfactant on the sidewalls is then removed and an orientation selective wet etching process is performed on the sidewalls. The oxide protects the Si at the bottom is from being etched.