Strained Source/Drain Bi-Layer Structure for Leakage Reduction
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Solution Overview
Problem
Conventional methods for creating strained barrier layers in semiconductor devices face limitations such as poor device performance, severe SiGe loss, and relaxation of strained layers, particularly at advanced technology nodes like the 32 nm node, due to inadequate strain application and complexity in customizing strains for different MOS devices.
Innovation Solution
A bi-layer or tri-layer source/drain structure is implemented, where a trench is etched in the source/drain region, a strained layer is deposited, and a capping layer is added, with a lightly doped region between the substrate and the strained layer, to enhance strain retention and device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a strained barrier layer is formed on a MOS device, then strain is applied to improve device performance, but the thickness is limited due to subsequent gap filling difficulty
Solution Approach 1:
The source/drain structure is segmented into multiple regions: a first source/drain region with a first doped concentration and a second source/drain region with a second doped concentration. This segmentation allows each region to be optimized independently for strain application and gap filling, resolving the contradiction between applying sufficient strain and maintaining manufacturability.
Solution Approach 2:
Different doped concentrations are applied to different source/drain regions to create local quality variations. The first source/drain region has a first doped concentration optimized for strain, while the second source/drain region has a second doped concentration optimized for gap filling, allowing each region to fulfill its specific function without compromising the other.
2Stress or pressure
If the thickness of the strained barrier layer is increased to apply more strain, then strain effect is enhanced, but gap filling becomes more difficult
Solution Approach 1:
The source/drain structure is divided into first and second source/drain regions with different doped concentrations. The first region can be made thicker to provide enhanced strain effect, while the second region is optimized for easy gap filling, thus resolving the contradiction between strain effect and manufacturability.
Solution Approach 2:
The doped concentration parameter is changed between the first source/drain region and the second source/drain region. By varying this parameter, the structure achieves both high strain effect in the first region and easy gap filling in the second region, eliminating the need to compromise between these conflicting requirements.
3Length of moving object
If conventional scaling techniques are used, then device size is reduced, but device performance deteriorates due to poor junction leakage and severe SiGe loss
Solution Approach 1:
Different doped concentrations are applied to different source/drain regions to create local quality variations. This allows the first source/drain region to be optimized for strain retention and the second source/drain region to be optimized for reducing junction leakage, thereby maintaining high device performance at scaled dimensions.
Solution Approach 2:
The source/drain structure uses a composite approach with two differently doped regions, creating a composite structure that combines the benefits of high strain retention and low junction leakage, enabling continued performance improvement as devices are scaled down.
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 junction leakage, resistivity, and strain retention, resulting in higher device gain and lower sheet resistivity, with a marked reduction in junction leakage by one to two orders of magnitude compared to standard processes.
Implementation Method 1
a strained layer is deposited within the source/drain region
Implementation Method 2
a lightly doped region between the substrate and the strained layer
Data Source
AI summary
A semiconductor device and method of manufacture thereof wherein a PMOS source/drain region of a transistor within the substrate includes a first strained layer in the PMOS source/drain region and a first capping layer in contact with the first strained layer. Further, the semiconductor device and method provide for an NMOS source/drain region of a transistor within the substrate including a second strained layer in the NMOS source/drain region and a second capping layer in contact with the second strained layer.