Extended Side Contacts for Transistors With Lower Contact Resistance
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Solution Overview
Problem
In the manufacturing of integrated circuits, contact plugs face challenges in achieving optimal adhesion and reducing contact resistance between source/drain contact plugs and underlying conductive features, which affects the performance of transistors like FinFETs.
Innovation Solution
The formation of a contact plug with both top and side contacts to the underlying conductive features, where the upper source/drain contact plug is intentionally vertically offset to etch a portion of the first inter-layer dielectric and the sidewall of the lower source/drain contact plug, enhancing adhesion and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contact plugs are formed using conventional processes with metal layers and barrier layers, then the contact structure is complete, but adhesion between contact plugs and underlying conductive features is insufficient and contact resistance is high
Solution Approach 1:
The contact plug structure is segmented into multiple portions (first contact plug portion and second contact plug portion) with different configurations. The first portion has lateral extent greater than vertical extent for stability, while the second portion has vertical extent greater than lateral extent for reaching deeper conductive features, optimizing both adhesion and electrical connection.
Solution Approach 2:
Different portions of the contact plug structure are given different geometric qualities tailored to their specific functions. The lower portion uses a wider, more stable configuration for adhesion, while the upper portion uses a narrower, deeper configuration for reaching target conductive features, allowing each region to optimize its local performance.
2Reliability
If contact plugs are formed using conventional processes with metal layers and barrier layers, then the contact structure is complete, but contact resistance between contact plugs and source/drain regions is high
Solution Approach 1:
The contact structure is divided into segments that can be formed through separate etching and filling operations. This segmentation allows for optimized formation of each portion's geometry and material composition, enabling better electrical coupling while maintaining manufacturing feasibility through standardized process steps.
Solution Approach 2:
The contact plug transitions from a conventional single-dimension vertical structure to a multi-dimensional structure where the second contact plug portion extends vertically deeper than laterally, creating a tapered or extended geometry that reaches source/drain regions more effectively, thereby reducing contact resistance through improved dimensional access.
3Reliability
If the upper contact plug is vertically offset to etch portions of the inter-layer dielectric and sidewall of the lower contact plug, then adhesion is enhanced and contact resistance is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The etching process is designed to preliminarily remove portions of the inter-layer dielectric and sidewall of the lower contact plug before filling with conductive material. This preliminary action creates the desired vertical offset and surface area for enhanced adhesion, while the offset itself is pre-planned and pre-executed as part of the contact formation sequence, making the overall process more controllable despite increased complexity.
Solution Approach 2:
The etching process acts as an intermediary step that mediates between the lower contact plug structure and the upper contact plug formation. By selectively removing material to create the vertical offset and expose sidewalls, the etching process enables enhanced adhesion and electrical coupling without requiring direct modification of both contact plugs simultaneously, thus managing process complexity through staged intervention.
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 improves the adhesion between the upper and lower source/drain contact plugs, thereby reducing contact resistance and enhancing the performance of transistors by ensuring better electrical coupling.
Implementation Method 1
performing an etching process to etch the second inter-layer dielectric, the etch stop layer, and an upper portion of the first inter-layer dielectric to form an opening
Implementation Method 2
performing an anneal process to react the metal layer with the source/drain regions
Implementation Method 3
performing a Chemical Mechanical Polish (CMP) process to remove excess metal
Data Source
AI summary
A method includes forming a source/drain region for a transistor, forming a first inter-layer dielectric over the source/drain region, and forming a lower source/drain contact plug over and electrically coupling to the source/drain region. The lower source/drain contact plug extends into the first inter-layer dielectric. The method further includes depositing an etch stop layer over the first inter-layer dielectric and the lower source/drain contact plug, depositing a second inter-layer dielectric over the etch stop layer, and performing an etching process to etch the second inter-layer dielectric, the etch stop layer, and an upper portion of the first inter-layer dielectric to form an opening, with a top surface and a sidewall of the lower source/drain contact plug being exposed to the opening, and forming an upper source/drain contact plug in the opening.