VTFET Wrap-Around Contact Formation
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Solution Overview
Problem
Current VTFET device fabrication processes result in significant erosion of top source and drain epitaxial material and limited contact area, leading to increased resistance due to the small contact area formed during the contact trench etch.
Innovation Solution
The implementation of a wrap-around contact design for top source and drain contacts, achieved through a method involving multiple interlayer dielectric layers, sacrificial caps, and selective etching to form non-merged top source and drain structures with a diamond-shaped design, which minimizes epitaxy erosion and enhances contact area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a contact trench etch is used to form top source and drain contacts, then the contact area is reduced, but the manufacturing process is simpler
Solution Approach 1:
The contact formation process is segmented into multiple steps: first forming top source and drain regions separately in trenches, then forming a wrap-around contact structure that contacts both regions. This segmentation allows the contact to achieve larger area by wrapping around rather than using a single planar contact trench
Solution Approach 2:
The contact structure transitions from a two-dimensional planar contact trench to a three-dimensional wrap-around contact that extends vertically and laterally. The contact wraps around the top source and drain regions, utilizing the vertical dimension to increase contact area without proportionally increasing lateral footprint
2Productivity
If a standard contact trench etch is performed, then the process is faster, but significant erosion of top source and drain epitaxial material occurs
Solution Approach 1:
A sacrificial cap layer is introduced as an intermediary protective layer during the contact trench etch process. This sacrificial cap prevents direct contact between the etch chemistry and the top source and drain epitaxial material, thereby preventing erosion while allowing the etch to proceed at standard speeds
Solution Approach 2:
The sacrificial cap is formed preliminarily before the contact trench etch to provide protection. By preparing this protective layer in advance, the subsequent etch process can proceed quickly without causing material erosion, and the sacrificial cap is later removed to complete the contact formation
Data Source
AI summary
Improved top source and drain contact designs for VTFET devices are provided. In one aspect, a method of forming a VTFET device includes: depositing a first ILD over a VTFET structure having fins patterned in a substrate, bottom source and drains at a base of the fins, bottom spacers on the bottom source and drains and gates alongside the fins; patterning trenches in the first ILD; forming top spacers lining the trenches; forming top source and drains in the trenches at the tops of the fins; forming sacrificial caps covering the top source and drains; depositing a second ILD onto the first ILD; patterning contact trenches in the second ILD, exposing the sacrificial caps; removing the sacrificial caps through the contact trenches; and forming top source and drain contacts in the contact trenches that wrap around the top source and drains. A VTFET device is also provided.