SiGe Bipolar Device Boron Penetration Protection
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Solution Overview
Problem
Boron penetration through the gate oxide into the underlying silicon is a significant issue in semiconductor devices, particularly when bipolar transistors and CMOS transistors are fabricated on the same chip, leading to decreased threshold voltages and performance degradation due to hydrogen diffusion from conventional nitride films during heat treatments.
Innovation Solution
A protective layer with a hydrogen weight percent less than about 9% is used, which is selective to silicon germanium (SiGe) deposition, preventing SiGe formation on the layer and reducing boron penetration by inhibiting hydrogen diffusion, thereby maintaining threshold voltages in non-bipolar regions during the fabrication of bipolar devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nitride film is used as protective layer during bipolar transistor fabrication, then the CMOS region is protected from fabrication processes, but hydrogen diffuses from the nitride film into the gate oxide causing boron penetration and threshold voltage drop
Solution Approach 1:
The patent changes the chemical composition parameters of the protective layer by using silicon oxynitride with specific oxygen and nitrogen ratios instead of conventional silicon nitride. This parameter change reduces hydrogen content in the protective layer, thereby preventing hydrogen diffusion into the gate oxide and subsequent boron penetration, while maintaining the protective function during bipolar transistor fabrication.
Solution Approach 2:
The patent employs a composite protective layer structure consisting of silicon oxynitride combining properties of both oxide and nitride materials. This composite material provides protection against fabrication processes while having reduced hydrogen content compared to conventional nitride films, thus preventing boron penetration without sacrificing protective capabilities.
2Productivity
If gate oxide thickness is reduced below 3.0 nm to improve device performance, then device optimization is achieved, but boron penetration becomes more acute and threshold voltage control becomes difficult
Solution Approach 1:
The patent applies preliminary anti-action by using the modified protective layer (silicon oxynitride with reduced hydrogen content) to prevent boron penetration before the threshold voltage degradation can occur. This proactive measure counteracts the increased susceptibility to boron penetration that arises from reduced gate oxide thickness, thereby maintaining threshold voltage control in optimized devices.
3Reliability
If polysilicon and nitride stack is deposited over CMOS region to protect it, then protection is provided, but hydrogen diffusion occurs during heat treatments causing weaker bonds in gate oxide
Solution Approach 1:
The patent changes the compositional parameters of the protective layer to reduce hydrogen content. By using silicon oxynitride with controlled oxygen and nitrogen ratios, the protective layer maintains its protective function during heat treatments while containing less hydrogen that could diffuse into the gate oxide and create weak bonds, thereby preserving gate oxide strength.
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 solution effectively reduces boron penetration, maintaining desired threshold voltages and improving device performance by using a protective layer with low hydrogen content, specifically silicon oxynitride, that is resistant to hydrofluoric etching and selective to SiGe deposition, resulting in a significant improvement in threshold voltage stability.
Implementation Method 1
During the actual nitride deposition step and subsequent heat treatments, hydrogen can diffuse from the nitride film down through the PMOS poly gate and into the gate oxide
Implementation Method 2
The protective layer has a weight percent of hydrogen that is less than about 9% and is selective to silicon germanium (SiGe) deposition, such that SiGe does not form on the protective layer
Data Source
AI summary
The invention, in one aspect, provides a method of manufacturing a semiconductor device. This aspect includes forming gate electrodes in a non-bipolar transistor region of a semiconductor substrate, placing a polysilicon layer over the gate electrodes in the non-bipolar transistor region and over the semiconductor substrate within a bipolar transistor region. A protective layer is formed over the polysilicon layer. The protective layer has a weight percent of hydrogen that is less than about 9% and is selective to silicon germanium (SiGe), such that SiGe does not form on the protective layer. This aspect further includes forming emitters for bipolar transistors in the bipolar transistor region, including forming a SiGe layer under a portion of the polysilicon layer.