2-D Semiconductor Source/Drain Contacts With Graded Metal Composition
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Solution Overview
Problem
The challenge of forming reliable semiconductor devices at smaller sizes is exacerbated by the complexity of fabrication processes as feature sizes continue to decrease, leading to issues such as thermal damage and poor adhesion of metal layers, which affect device performance and contact resistance.
Innovation Solution
A method involving a two-step deposition process is employed, where a first metal layer with a low melting point is deposited, followed by a second metal layer with a high melting point, allowing the second layer to re-melt the first layer and form a conformal coating, thereby improving adhesion and reducing thermal damage, resulting in better crystallinity and lower contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single metal layer is deposited for source/drain contacts, then the fabrication process is simple, but adhesion is poor and contact resistance is high
Solution Approach 1:
The source/drain contact structure is segmented into multiple metal layers (first metal layer and second metal layer) with different properties. The first metal layer provides good adhesion to the semiconductor substrate, while the second metal layer provides low contact resistance and structural stability, resolving the contradiction between simple fabrication and reliable contact performance
Solution Approach 2:
The contact structure uses composite materials comprising different metal layers with complementary properties. The first metal layer (e.g., tungsten) provides strong adhesion, while the second metal layer (e.g., cobalt or nickel) provides low resistance, creating a composite structure that achieves both good adhesion and low contact resistance
2Reliability
If high temperature processing is used to improve adhesion, then adhesion improves, but thermal damage occurs to the semiconductor structure
Solution Approach 1:
The patent changes the physical parameters of the metal layers by selecting materials with different melting points. The first metal layer has a higher melting point and can withstand processing temperatures without damage, while the second metal layer has lower melting point and can be deposited at controlled temperatures to avoid thermal damage to the semiconductor structure, achieving good adhesion without excessive heat
Solution Approach 2:
The first metal layer acts as an intermediary between the semiconductor substrate and the second metal layer. It provides a thermally stable interface that prevents direct thermal damage to the semiconductor structure during subsequent processing, while still achieving good adhesion for the overall contact structure
3Productivity
If feature sizes are reduced to increase functional density, then production efficiency improves, but fabrication complexity and difficulty increase
Solution Approach 1:
The contact structure is segmented into multiple layers that can be independently optimized for different functions. This segmentation allows each layer to be tailored for specific performance requirements (adhesion, resistance, thermal stability), enabling reliable contacts at reduced feature sizes without proportionally increasing overall fabrication complexity
Solution Approach 2:
Different regions of the contact structure have different local qualities - the first metal layer has high melting point and strong adhesion properties, while the second metal layer has low resistance properties. This local differentiation of material properties allows the structure to maintain reliability at smaller dimensions while managing fabrication complexity through targeted material selection
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 performance of semiconductor devices by achieving lower contact resistance and improved adhesion of source/drain contacts, maintaining device integrity and functionality at smaller scales.
Implementation Method 1
the second metal layer has a higher melting point than the first metal layer, during the second deposition process, the first metal layer is re-melted, and the melted first metal layer is conformally coated on the second metal layer
Data Source
AI summary
A device includes a substrate, a 2-D semiconductor material layer over the substrate, a first conductive contact in contact with a first region of the 2-D semiconductor material layer, a second conductive contact in contact with a second region of the 2-D semiconductor material layer spaced apart from the first region of the 2-D semiconductor material layer, a gate structure over the 2-D semiconductor material layer and laterally between the first conductive contact and the second conductive contact. The first conductive contact is a mixture of a first metal and a second metal, and the first metal has a higher atomic concentration in an outer portion of the first conductive contact than in an inner portion of the first conductive contact.