Stepped Semiconductor Contact Structure for Lower Contact Resistance
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Solution Overview
Problem
As semiconductor devices miniaturize, the decreasing cross-sectional area of the conductive channel and contact area between the channel and the metal silicide layer lead to increased contact resistance, hindering performance and functionality.
Innovation Solution
A contact structure is developed with an interlayer dielectric layer, a contact hole having a larger first portion and a smaller second portion extending into a doped region, and a contact layer comprising first and second layers on the bottom surfaces of these portions, increasing the contact area between the conductive channel and the epitaxial layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the feature size of the semiconductor device is reduced to increase integration density, then the performance and functionality of the chip improves, but the contact area between the conductive channel and the metal silicide layer decreases, causing contact resistance to increase
Solution Approach 1:
The contact structure is divided into multiple segments: the contact hole is segmented into a first portion (in interlayer dielectric) and a second portion (in doped region), and the contact layer is segmented into a first contact layer and a second contact layer. This segmentation allows each portion to be optimized independently, with the second contact layer providing additional contact area in the doped region to compensate for the reduced overall contact area due to miniaturization.
Solution Approach 2:
The contact hole transitions from a simple vertical structure to a multi-dimensional structure with different cross-sectional areas at different depths. The first portion has a larger cross-sectional area than the second portion, creating a tapered or stepped geometry that increases the contact area at the bottom where it matters most, without increasing the opening size at the top.
2Reliability
If the contact hole diameter is increased to increase contact area, then the contact resistance decreases, but the device feature size increases, reducing integration density
Solution Approach 1:
The contact hole exhibits asymmetric geometry with different cross-sectional areas at different depths. The first portion (in interlayer dielectric) has a larger cross-sectional area than the second portion (in doped region). This asymmetric design allows the contact area at the critical bottom interface to be maximized while keeping the opening size at the top minimized, thereby reducing contact resistance without increasing device footprint.
3Reliability
If a metal silicide layer is formed on the epitaxial layer to reduce contact resistance, then the contact resistance between the conductive channel and the epitaxial layer decreases, but the contact area further decreases due to miniaturization
Solution Approach 1:
The contact structure implements a nested configuration where the second contact layer is positioned within the contact hole at the bottom, surrounded by the first contact layer. This nested arrangement maximizes the contact area at the bottom interface between the contact layer and the doped region, compensating for the reduced contact area due to miniaturization, while maintaining the low contact resistance provided by the metal silicide material.
Data Source
AI summary
A semiconductor device includes an epitaxial layer and a doped region located in the epitaxial layer. A contact structure of the semiconductor device includes: an interlayer dielectric layer, arranged on the epitaxial layer; a contact hole, including a first portion extending through the interlayer dielectric layer and a second portion extending into the doped region, where a size of the first portion is greater than a size of the second portion, the second portion is open on a bottom surface of the first portion, and a bottom surface of the second portion is arranged in the doped region; a contact layer, including a first contact layer arranged on the bottom surface of the first portion and a second contact layer arranged on the bottom surface of the second portion; and a conductive channel, arranged in the contact hole and contacting the contact layer.