Backside Contact Etch Sequencing for Short-Free GAA Transistors
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Solution Overview
Problem
The deployment of gate-all-around (GAA) or nanoribbon transistors and backside contacts faces challenges such as contact shorts due to the difficulty in forming effective backside contacts without interfering with the gate structure, which hinders the advancement of transistor density and performance.
Innovation Solution
Performing backside contact etch before cavity spacer formation, allowing a portion of the spacer material to contact the backside contact metal and eliminate shorts between the backside contact metal and the gate structure, thereby reducing resistance and improving device structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside contact etch is performed after cavity spacer formation, then the gate structure can be formed, but contact shorts between backside contact metal and gate structure occur
Solution Approach 1:
The backside contact etch is performed before cavity spacer formation, establishing the backside contact metal position in advance. This preliminary action prevents the backside contact metal from interfering with subsequent gate structure formation and eliminates contact shorts, as the etch pattern is defined before the spacer material is deposited to form the gate structure.
2Reliability
If backside contact etch is performed before cavity spacer formation, then contact shorts are eliminated, but process timing is extended
Solution Approach 1:
The backside contact etch process is merged with the existing cavity formation process sequence. By performing the backside contact etch before cavity spacer formation, the process utilizes existing process windows and equipment, avoiding the need for separate dedicated etch steps and minimizing overall process time extension.
3Reliability
If backside contacts are formed to reduce resistance, then power delivery is improved, but interference with gate structure formation occurs
Solution Approach 1:
The backside contact metal is formed in advance before the gate structure is created. This preliminary formation allows the backside contact etch pattern to be established without interfering with subsequent gate structure formation, as the spacer material deposited later defines the gate structure boundaries and prevents interference.
Solution Approach 2:
The cavity spacer material acts as an intermediary between the backside contact metal and the gate structure. This spacer material, formed after the backside contact etch, provides physical separation and prevents the gate structure from interfering with the backside contact metal, while still allowing the backside contact to achieve low resistance connection.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Devices, transistor structures, systems, and techniques are described herein related to backside contacts for field effect transistors formed using a backside contact etch prior to cavity spacer formation. A transistor includes semiconductor structures such as nanoribbons extending between a source and a drain. A spacer material is between a gate and the source/drain as cavity spacer fill. The spacer material is also between a portion of a backside contact and a portion of the source/drain, to eliminate a short between the backside contact and the gate.