Selective SiGe Etching for RF Epitaxial Silicon Leakage Control
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Solution Overview
Problem
Conventional silicon substrates used in RF device fabrication suffer from harmonic distortion and low resistivity, leading to heat dissipation issues and current leakage, particularly with the use of SiGe layers, which can impair device performance.
Innovation Solution
A selective etching process using a reactive chemistry combination of sulfur hexafluoride (SF6), nitrogen (N2), and boron chloride (BCl3) is employed to remove SiGe interfacial layers while forming an etch passivation film on doped epitaxial silicon, optimizing etching and passivation rates to enhance thermal and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SiGe interfacial layer is used between silicon substrate and epitaxial silicon, then misfit dislocation is reduced, but current leakage occurs due to narrow gap nature of SiGe material
Solution Approach 1:
The patent removes the SiGe interfacial layer completely from the structure after it has served its purpose of reducing misfit dislocations during fabrication. This extraction eliminates the harmful current leakage effect while preserving the beneficial dislocation reduction that occurred during the manufacturing process.
Solution Approach 2:
The SiGe layer is temporarily introduced during the fabrication process to reduce misfit dislocations, then systematically removed in a controlled manner. This preliminary action allows the structure to benefit from dislocation reduction without retaining the harmful conducting properties of SiGe in the final device.
2Ease of manufacture
If conventional silicon substrate is used for RF device fabrication, then cost is reduced and manufacturing capacity is increased, but harmonic distortion and low resistivity occur
Solution Approach 1:
The patent introduces a silicon-on-insulator (SOI) structure as an intermediary layer between the conventional silicon substrate and the epitaxial silicon layer. This mediator provides high resistivity and reduces harmonic distortion while allowing the use of low-cost conventional silicon substrates for manufacturing.
3Adaptability or versatility
If SiGe layer is used instead of buried oxide layer, then RFSOI wafer shortage is addressed, but harmonic distortion occurs due to silicon substrate
Solution Approach 1:
The patent removes the SiGe layer that was previously used as a substitute for buried oxide, and instead implements a proper SOI structure with oxide layer. This extraction eliminates the harmonic distortion problem while maintaining wafer availability through alternative manufacturing approaches.
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 process effectively reduces harmonic distortion and current leakage, improving the thermal and electrical performance of RF devices by selectively removing SiGe layers and forming a protective passivation film, thereby enhancing device reliability and efficiency.
Implementation Method 1
A selective etching process using a reactive chemistry combination of sulfur hexafluoride (SF6), nitrogen (N2), and boron chloride (BCl3) is employed to remove SiGe interfacial layers while forming an etch passivation film on doped epitaxial silicon
Implementation Method 2
The reactive chemistry combination is chosen in a manner that the reactive chemistry combination reacts differently to the interfacial layer and the active layer
Data Source
AI summary
The present disclosure relates to a fabricating procedure of a radio frequency device, in which a precursor wafer including active layers, SiGe layers, and a silicon handle substrate is firstly provided. Each active layer is formed from doped epitaxial silicon and underneath a corresponding SiGe layer. The silicon handle substrate is over each SiGe layer. Next, the silicon handle substrate is removed completely, and the SiGe layer is removed completely. An etch passivation film is then formed over each active layer. Herein, removing each SiGe layer and forming the etch passivation film over each active layer utilizes a same reactive chemistry combination, which reacts differently to the SiGe layer and the active layer. The reactive chemistry combination is capable of producing a variable performance, which is an etching performance of the SiGe layer or a forming performance of the etch passivation film over the active layer.