Source/Drain Contact Structure With Inlaid Hard Mask Alignment
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Solution Overview
Problem
The formation of source/drain contact openings in densely packed semiconductor devices requires high overlay precision and high-aspect-ratio etching, leading to reduced process windows and increased contact resistance due to the tapering of contact openings and smaller landing areas.
Innovation Solution
Replacing the top portion of the source/drain contact cut feature with a hard mask layer, allowing selective etching of the interlayer dielectric layer, which eliminates the need for high-aspect-ratio etching and improves the landing area by inlaying the hard mask into the ILD layer rather than depositing it over the top surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-aspect-ratio etching is used to form contact openings through thick dielectric layers, then contact openings can reach densely packed source/drain features, but process windows are reduced and contact resistance increases due to tapering
Solution Approach 1:
The contact formation process is divided into two separate etching operations: first forming a contact cut opening through the first dielectric layer to expose the source/drain feature, then forming the final contact opening through the second dielectric layer. This segmentation allows each etching step to work with thinner dielectric layers, reducing aspect ratio and tapering effects, thereby improving both precision and reducing contact resistance
Solution Approach 2:
The contact cut opening is formed in advance through the first dielectric layer before the second dielectric layer is deposited. This preliminary action creates a pre-formed pathway that guides subsequent processing, allowing the second etching step to focus only on removing the second dielectric layer rather than etching through the entire combined thickness, thus reducing the effective aspect ratio
2Ease of manufacture
If conventional contact formation is used with densely spaced source/drain features, then manufacturing is simplified, but overlay precision requirements become extremely demanding
Solution Approach 1:
The contact cut feature structure itself serves as the alignment reference for forming the contact opening. The contact opening is formed aligned to the contact cut feature, which was previously formed aligned to the source/drain features. This self-aligned approach eliminates the need for additional overlay steps, allowing densely packed features to be manufactured with standard overlay capabilities while maintaining high precision
Data Source
AI summary
A method according to the present disclosure includes receiving a workpiece that includes a gate structure, a first gate spacer feature, a second gate spacer feature, a gate-top dielectric feature over the gate structure, the first gate spacer feature and the second gate spacer feature, a first source/drain feature over a first source/drain region, a second source/drain feature over a second source/drain region, a first dielectric layer over the first source/drain feature, and a second dielectric layer over the second source/drain feature. The method further includes replacing a top portion of the first dielectric layer with a first hard mask layer, forming a second hard mask layer over the first hard mask layer while the second dielectric layer is exposed, etching the second dielectric layer to form a source/drain contact opening and to expose the second source/drain feature, and forming a source/drain contact over the second source/drain feature.