Carbon-Doped SOI Layer for Threshold Stability
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Solution Overview
Problem
Current semiconductor devices with MISFETs on SOI substrates face challenges in improving overall characteristics, particularly in controlling threshold values and reducing parasitic channel formation, which affects leakage current, speed, and power consumption.
Innovation Solution
The solution involves forming a semiconductor device with a field effect transistor on an SOI substrate, where a p-type or n-type impurity region is ion-implanted below the BOX layer, and carbon is ion-implanted into the semiconductor layer to enhance the characteristics, and interstitial atoms are introduced to suppress impurity diffusion, thereby improving threshold control and reducing fluctuations in transistor characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron is introduced into the end part of the channel region to prevent parasitic channel, then the parasitic channel formation is suppressed, but the concentration of boron in the end part increases which may cause threshold variation
Solution Approach 1:
Carbon is introduced as an intermediary substance that forms a diffusion barrier layer between the boron-containing end part and the channel region. This carbon layer mediates the interaction by blocking boron diffusion into the channel, thus preventing parasitic channel formation while maintaining stable threshold voltage without requiring high boron concentration in the end part.
Solution Approach 2:
The invention applies local quality by creating a carbon-doped region specifically in the end part of the channel region where it is most needed. The carbon concentration is locally optimized to provide sufficient diffusion blocking without affecting the overall device characteristics, allowing different regions to have different functional properties.
2Manufacturing precision
If carbon is introduced into the silicon layer to suppress impurity diffusion, then the threshold value controllability is improved, but the activation rate of impurities is reduced
Solution Approach 1:
Carbon is introduced only in the end part of the silicon layer adjacent to the gate electrode, not throughout the entire channel region. This localized carbon doping provides diffusion blocking where needed while leaving the rest of the channel region free for proper impurity activation and electrical characteristics.
Solution Approach 2:
The silicon layer is segmented into different functional regions: the end part containing carbon for diffusion suppression, and the rest of the channel region optimized for electrical performance. This segmentation allows each region to fulfill its specific function without compromising the other.
3Manufacturing precision
If ion implantation is used to introduce impurities below the BOX layer, then the threshold value controllability is improved, but the process complexity increases
Solution Approach 1:
The invention combines multiple functions into a single ion implantation step: introducing carbon for diffusion blocking, creating the end part structure, and establishing the threshold voltage characteristics. By merging these functions into one process step, the overall manufacturing complexity is reduced despite the advanced functionality achieved.
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 approach enhances the semiconductor device's performance by improving threshold value controllability, reducing parasitic channel formation, and minimizing fluctuations in transistor characteristics, leading to better leakage current, speed, and power consumption characteristics.
Implementation Method 1
carbon is ion-implanted into the semiconductor layer
Implementation Method 2
interstitial atoms are introduced to suppress impurity diffusion
Data Source
AI summary
A semiconductor device having an n channel MISFET formed on an SOI substrate including a support substrate, an insulating layer formed on the support substrate and a silicon layer formed on the insulating layer has the following structure. An impurity region for threshold adjustment is provided in the support substrate of a gate electrode so that the silicon layer contains carbon. The threshold value can be adjusted by the semiconductor region for threshold adjustment in this manner. Further, by providing the silicon layer containing carbon, even when the impurity of the semiconductor region for threshold adjustment is diffused to the silicon layer across the insulating layer, the impurity is inactivated by the carbon implanted into the silicon layer. As a result, the fluctuation of the transistor characteristics, for example, the fluctuation of the threshold voltage of the MISFET can be reduced.