Silicon Layer Stops Dislocation Propagation in MOS Stressors
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Solution Overview
Problem
Conventional stressor formation processes in MOS devices suffer from stress relaxation due to impurity implantation, leading to reduced channel stress and increased leakage currents, as silicon and germanium atoms are dislocated from lattice locations, causing dislocation propagation towards source/drain junctions.
Innovation Solution
A semiconductor structure is formed with a silicon layer over a silicon-containing compound layer, where the silicon layer comprises substantially pure silicon and has a lower silicon concentration than the compound layers, and a doped region with a higher impurity concentration is created above the silicon layer to prevent dislocation propagation, thereby maintaining channel stress and reducing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If SiGe stressors are grown to apply high compressive stress to the channel region, then channel stress is improved, but stress relaxation occurs due to subsequent impurity implantation causing dislocation propagation
Solution Approach 1:
A silicon sacrificial layer is introduced as an intermediary between the SiGe stressor layers. This intermediate silicon layer acts as a barrier that stops dislocation propagation from the SiGe layers, preventing stress relaxation while maintaining the high compressive stress in the channel region. The silicon layer is positioned at a critical interface where dislocations would otherwise propagate toward the channel.
Solution Approach 2:
The stressor structure is segmented into multiple layers: bottom SiGe layer, intermediate silicon sacrificial layer, and top SiGe layer. This segmentation allows each layer to serve a specific function - the SiGe layers provide compressive stress while the intermediate silicon layer prevents dislocation propagation, resolving the contradiction between achieving high stress and maintaining stress stability.
2Ease of operation
If impurity implantation is performed to dope source/drain regions, then device functionality is improved, but leakage currents increase due to dislocation propagation toward source/drain junctions
Solution Approach 1:
The intermediate silicon sacrificial layer serves as a barrier that stops dislocation propagation before dislocations can reach the source/drain junctions. This prevents the harmful effect of increased leakage currents while allowing the necessary impurity implantation to proceed for device functionality.
3Stress or pressure
If high concentration of germanium is used in SiGe stressors to increase stress, then channel stress is improved, but stress relaxation becomes more significant due to increased dislocation propagation
Solution Approach 1:
The intermediate silicon layer acts as a barrier that prevents dislocation propagation, allowing high germanium concentration to be used in the SiGe layers to generate high compressive stress without suffering from the associated stress relaxation problem. The silicon layer blocks the harmful dislocations while preserving the beneficial stress.
Solution Approach 2:
The stressor structure uses a composite material approach, combining SiGe layers (for high stress) with an intermediate silicon layer (for dislocation blocking). This composite structure allows the system to achieve both high stress and high stress stability by leveraging the complementary properties of different materials.
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 approach significantly reduces stress relaxation and leakage currents by blocking dislocation propagation, maintaining higher channel stress and improving device performance.
Implementation Method 1
a silicon layer on the first silicon-containing compound layer, wherein the silicon layer comprises substantially pure silicon... blocking dislocation propagation
Data Source
AI summary
A composite semiconductor structure and method of forming the same are provided. The composite semiconductor structure includes a first silicon-containing compound layer comprising an element selected from the group consisting essentially of germanium and carbon; a silicon layer on the first silicon-containing compound layer, wherein the silicon layer comprises substantially pure silicon; and a second silicon-containing compound layer comprising the element on the silicon layer. The first and the second silicon-containing compound layers have substantially lower silicon concentrations than the silicon layer. The composite semiconductor structure may be formed as source/drain regions of metal-oxide-semiconductor (MOS) devices.