SiGe Stressor Segmentation for Short Channel Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional stressor formation processes for MOS devices, particularly PMOS devices, face challenges in achieving effective compressive stress due to non-conformal formation of SiGe stressors, leading to reduced thickness on sidewalls and inadequate barrier effectiveness against p-type impurity diffusion, which adversely affects short channel characteristics.
Innovation Solution
A semiconductor structure with a SiGe stressor comprising three regions: a first region doped with a high p-type impurity concentration, a second region with a substantially lower p-type impurity concentration, and a third region also doped with a high p-type impurity concentration, where the second region acts as a diffusion barrier and the third region enhances stress application, while maintaining a high germanium concentration to apply compressive stress to the channel region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high boron concentration is used in SiGe stressors to reduce sheet resistance, then electrical conductivity is improved, but lattice constant is reduced and strain is relaxed, and boron laterally diffuses into channel regions, degrading short channel characteristics
Solution Approach 1:
The SiGe stressor is divided into three distinct regions along the vertical direction: a first region with high p-type impurity concentration, a second region with low p-type impurity concentration, and a third region with high p-type impurity concentration. This segmentation allows each region to perform different functions - the high concentration regions provide electrical conductivity while the low concentration middle region acts as a diffusion barrier, preventing lateral impurity diffusion into the channel region.
Solution Approach 2:
Different regions of the SiGe stressor are assigned different impurity concentrations based on their specific functional requirements. The first and third regions have high p-type impurity concentration for electrical conductivity, while the second region has low p-type impurity concentration to serve as a diffusion barrier. This local differentiation of quality optimizes both electrical performance and stress preservation.
2Reliability
If conventional SiGe stressor formation is used to apply compressive stress to the channel region, then carrier mobility is improved, but p-type impurities diffuse laterally into the channel region, degrading device performance
Solution Approach 1:
The SiGe stressor is segmented into three vertical regions with different impurity concentrations. The middle region with low impurity concentration serves as a diffusion barrier that prevents p-type impurities from diffusing laterally into the channel region, while the outer regions with high impurity concentration maintain electrical conductivity. This segmentation preserves the compressive stress benefit while eliminating the harmful lateral diffusion.
Solution Approach 2:
The second region with low p-type impurity concentration acts as an intermediary layer between the high concentration source regions and the channel region. This intermediate layer with low impurity concentration serves as a diffusion barrier, mediating the interaction between the doped stressor regions and the channel to prevent harmful impurity diffusion while maintaining the stress application function.
3Reliability
If SiGe layers are formed with adequate thickness on sidewalls to improve barrier effectiveness, then lateral impurity diffusion is reduced, but formation becomes more difficult due to non-conformal growth
Solution Approach 1:
The stressor structure is segmented into three vertically distinct regions with different impurity concentrations. This segmentation allows the middle low-concentration region to function as an effective diffusion barrier even with moderate thickness, as its primary function is to block lateral diffusion rather than provide mechanical strength. This makes the formation process more achievable compared to requiring uniformly thick high-concentration layers throughout.
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 improves short channel characteristics by reducing lateral impurity diffusion and preserving channel stress, thereby enhancing the performance of MOS devices without sacrificing compressive stress effectiveness.
Implementation Method 1
Since SiGe has a greater lattice constant than silicon has, it applies a compressive stress to the channel region
Implementation Method 2
the second region acts as a diffusion barrier and the third region enhances stress application
Data Source
AI summary
A semiconductor structure includes a first compound layer including an element, and a first impurity having a first impurity concentration; and a second compound layer including the element and a second impurity of a same conductivity type as the first impurity, wherein the second impurity has a second impurity concentration, and wherein the second compound layer is on the first compound layer. The semiconductor structure further includes a third compound layer including the element and a third impurity of a same conductivity type as the first impurity, wherein the third impurity has a third impurity concentration, and wherein the third compound layer is on the second compound layer, and wherein the second impurity concentration is substantially lower than the first and the third impurity concentrations.