Doped Backside Contact Placeholder for Nanosheet CMOS Integration
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Solution Overview
Problem
As nanosheet devices scale down, forming separate backside contacts with sufficient surface contact to the source/drain becomes increasingly challenging due to interference and spatial constraints, making it difficult to achieve effective doping and contact formation.
Innovation Solution
The implementation of a microelectronic structure with doped source/drain transistors and a placeholder on the backside surface, where the placeholder is doped with the same material as one of the source/drain, allowing for selective removal and minimizing damage to the source/drain, enabling the formation of backside contacts without using a Si placeholder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If devices are scaled down and fitted closer together to increase device density, then the number of devices per area increases, but separate backside contacts cannot be formed with sufficient surface contact
Solution Approach 1:
A placeholder structure is introduced as an intermediary element between the source/drain region and the backside contact. This placeholder provides a larger surface area for contact formation while the source/drain can be selectively removed from beneath it, enabling sufficient contact surface area even when devices are closely spaced.
Solution Approach 2:
The solution moves the contact formation problem to another dimension by using a placeholder that extends beyond the immediate source/drain footprint. This allows contact to be established in a different spatial relationship, providing sufficient surface area without requiring lateral expansion that would increase device spacing.
2Ease of manufacture
If standard doping processes are used on source/drains, then source/drain regions are formed, but placeholder removal damages the underlying source/drain
Solution Approach 1:
Different dopant materials are used in different locations: the source/drain regions are doped with first dopant material while the placeholder is doped with second dopant material. This local differentiation allows selective removal of the placeholder through doping-specific etching processes without affecting the source/drain regions.
Solution Approach 2:
The etching selectivity is achieved by changing the dopant material parameter between the source/drain and placeholder regions. This parameter change enables the placeholder to be removed under conditions that leave the source/drain intact, protecting source/drain integrity during placeholder removal.
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 allows for the successful formation of backside contacts with minimal damage to the source/drain, improving contact quality and reliability in densely packed nanosheet transistor arrays.
Implementation Method 1
A placeholder is located on a backside surface of the second source/drain and the placeholder is doped with a third material. The third material is the same as the first material.
Implementation Method 2
A placeholder doped with a specific material, such as SiGe:B, is used on the backside surface of source/drains to facilitate the formation of backside contacts without damaging the underlying source/drains, allowing for selective removal and connection to the nanosheet transistors.
Data Source
AI summary
A microelectronic structure includes a first nanosheet transistor that includes a first source/drain and a second source/drain. The first source/drain and the second source/drain are doped with a first material. A second nanosheet transistor that includes a third source/drain and fourth source/drain. The third source/drain and the fourth source/drain are doped with a second material. The first material and the second material are different. A placeholder is located on a backside surface of the second source/drain and the placeholder is doped with a third material. The third material is the same as the first material.