Strain Compensation in Transistor Channels Using Epitaxial Layers
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Solution Overview
Problem
As transistors in integrated circuits become smaller, it becomes increasingly difficult to provide uniaxial transistor channel stress through the source and drain regions, and existing methods struggle to maintain strain in the channel region effectively, leading to inefficiencies and defects.
Innovation Solution
The use of channel structures with interlayered compressive and tensile epitaxial layers, grown within aspect ratio trapping (ART) trenches, which limit epitaxial-induced defects and allow for significant height retention of strain in the channel, enabling efficient operation and improved switching performance without relying on source and drain region stressors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistors are made smaller to increase integration, then circuit density improves, but the ability to provide uniaxial channel stress through source and drain regions deteriorates
Solution Approach 1:
The channel structure is segmented into multiple epitaxial layers with different lattice constants (first layer with lattice constant a1, second layer with a2, third layer with a3). These layers are grown within ART trenches to provide independent strain control, allowing the channel to maintain uniaxial stress even as transistor dimensions shrink and source/drain stressors become less effective.
Solution Approach 2:
The invention transitions from providing stress through the source and drain regions (one-dimensional approach) to providing stress through the channel structure itself via multiple epitaxial layers (multi-dimensional approach). The alternating compressive and tensile layers create a strain profile distributed through the channel's vertical dimension, enabling effective stress provision in scaled transistors.
2Productivity
If epitaxial layers are grown to provide channel strain, then switching performance improves, but epitaxial-induced defects increase
Solution Approach 1:
Different regions of the channel structure are assigned different local qualities: the first epitaxial layer provides compressive strain, the second layer provides tensile strain, and the third layer provides opposite strain to the second. This local differentiation of strain characteristics allows the channel to maintain high switching performance while the alternating strain profile prevents defect propagation that would occur in uniformly strained structures.
Solution Approach 2:
The channel is constructed as a composite structure with multiple epitaxial layers having different lattice constants and strain characteristics. This composite approach combines materials with contrasting properties (compressive vs. tensile strain) to achieve overall strain compensation, enabling high-performance switching while minimizing the accumulation of epitaxial-induced defects.
3Productivity
If channel height is increased to improve device performance, then switching efficiency improves, but maintaining strain in the channel becomes more difficult
Solution Approach 1:
The epitaxial layers are arranged in a periodic alternating pattern of compressive and tensile strain (first layer compressive, second layer tensile, third layer compressive opposite to second). This periodic strain distribution creates a self-balancing structure where the strain in each layer is compensated by the opposite strain in adjacent layers, enabling strain retention throughout the channel height without relaxation.
Solution Approach 2:
The alternating compressive and tensile epitaxial layers act as counterbalancing elements. The compressive strain in one layer is counterbalanced by tensile strain in the adjacent layer, creating a strain-compensated structure that maintains mechanical equilibrium. This anti-weight approach allows the channel to achieve significant height while retaining strain, as each layer's strain is offset by its neighbor.
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 results in defect-free channels that operate more efficiently, allowing for larger channel heights and improved switching performance, while maintaining strain, thus enhancing the performance of transistors in integrated circuits.
Implementation Method 1
a first epitaxial layer, on the substrate, including a first epitaxial material having a first lattice constant; a second epitaxial layer, on the first layer, including a second epitaxial material having a second lattice constant; a third epitaxial layer, on the second layer, including a third epitaxial material having a third lattice constant
Implementation Method 2
the second and third epitaxial layers are oppositely strained such that the second and third epitaxial layers compensate for one another
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An embodiment includes a device comprising: a first epitaxial layer, coupled to a substrate, having a first lattice constant; a second epitaxial layer, on the first layer, having a second lattice constant; a third epitaxial layer, contacting an upper surface of the second layer, having a third lattice constant unequal to the second lattice constant; and an epitaxial device layer, on the third layer, including a channel region; wherein (a) the first layer is relaxed and includes defects, (b) the second layer is compressive strained and the third layer is tensile strained, and (c) the first, second, third, and device layers are all included in a trench. Other embodiments are described herein.