Via-First Metal Gate Contact Structure for Wider Process Windows
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Solution Overview
Problem
The narrow process window in semiconductor fabrication processes for forming reliable contacts to metal gate layers and adjacent source, drain, and/or body regions, particularly due to aggressive scaling and complex patterning techniques, leads to device degradation and failure.
Innovation Solution
A via-first metal gate contact process is employed, where a gate via is formed on the metal gate before connecting the metal contact layer, increasing the process window and reducing leakage current by providing greater isolation between the metal contact layer and neighboring gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional contact formation processes are used with aggressive scaling, then device dimensions are reduced and production efficiency is improved, but the process window becomes too narrow leading to device degradation and failure
Solution Approach 1:
The contact formation process is divided into multiple sequential steps: forming mandrels, depositing first dielectric layer, forming contact holes, depositing metal contact layer, depositing second dielectric layer, and forming openings. This segmentation allows each step to be optimized independently, maintaining a sufficient process window while achieving scaled dimensions.
Solution Approach 2:
Mandrels are formed in the first dielectric layer before the metal contact layer is deposited. This preliminary action defines the contact footprint early in the process, enabling subsequent steps to be performed with appropriate alignment margins and maintaining process robustness through scaling.
2Ease of manufacture
If direct contact between metal contact layer and metal gate layer is formed, then manufacturing steps are reduced, but leakage current increases due to insufficient isolation from neighboring gates
Solution Approach 1:
A second dielectric layer is deposited over the metal contact layer and filled with conductive material to form an intermediary structure. This second dielectric layer provides additional isolation from neighboring metal gate layers, preventing leakage current while the conductive material ensures proper electrical connection. This intermediary approach maintains manufacturing efficiency by using standard deposition and etching processes.
Solution Approach 2:
The isolation structure is extended into the vertical dimension by depositing a second dielectric layer above the metal contact layer. This vertical dimension provides additional isolation distance from neighboring gates, effectively reducing leakage current without adding lateral complexity or requiring additional lateral process steps.
3Manufacturing precision
If overlay control requirements are increased for accurate alignment, then contact precision is improved, but the process becomes more complex and difficult to control
Solution Approach 1:
Mandrels are formed in the first dielectric layer before metal layer deposition, establishing the contact footprint early. This preliminary definition of the contact area provides a stable reference for subsequent alignment steps, reducing the cumulative effect of overlay errors through the process while maintaining manufacturing precision.
Solution Approach 2:
The patterning process is segmented into multiple steps: forming mandrels, forming contact holes through the first dielectric layer, and forming openings through the second dielectric layer. Each patterning step works from a previously established reference, distributing the overlay control requirements across multiple steps rather than requiring single-step precision, thereby reducing overall process complexity.
Data Source
AI summary
A method and structure for forming a via-first metal gate contact includes depositing a first dielectric layer over a substrate having a gate structure with a metal gate layer. An opening is formed within the first dielectric layer to expose a portion of the substrate, and a first metal layer is deposited within the opening. A second dielectric layer is deposited over the first dielectric layer and over the first metal layer. The first and second dielectric layers are etched to form a gate via opening. The gate via opening exposes the metal gate layer. A portion of the second dielectric layer is removed to form a contact opening that exposes the first metal layer. The gate via and contact openings merge to form a composite opening. A second metal layer is deposited within the composite opening, thus connecting the metal gate layer to the first metal layer.