Self-Aligned Contact Gate Conductor Isolation
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Solution Overview
Problem
Conventional self-aligned contact methods for CMOS devices reduce metal gate volume, increasing gate resistance, while thick metal gates reduce parasitic capacitance but introduce electrical shorts.
Innovation Solution
A partial dielectric cap is formed on the gate conductor, extending less than its width, with a self-aligned contact adjacent to the sidewall spacer, electrically isolated from the gate conductor by the cap and spacer, allowing the full height of the metal gate to remain un-recessed outside the contact area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the metal gate is recessed to form an insulator cap, then electrical shorts between the SAC and metal gate are prevented, but the metal gate volume is reduced and gate resistance increases
Solution Approach 1:
The patent applies local quality by forming the dielectric cap only in the region where electrical isolation is needed (adjacent to the self-aligned contact), while leaving the rest of the metal gate intact. This localized approach provides electrical isolation precisely where required without unnecessarily reducing the overall metal gate volume, thus maintaining low gate resistance while preventing electrical shorts.
2Reliability
If a full dielectric cap is formed on the gate conductor, then electrical isolation is maximized, but the metal gate volume is significantly reduced
Solution Approach 1:
Instead of forming a full dielectric cap across the entire gate conductor, the patent forms the dielectric cap only in the specific region adjacent to the self-aligned contact where electrical isolation is needed. This localized approach provides sufficient electrical isolation to prevent shorts while preserving the majority of the metal gate volume to maintain low gate resistance.
Solution Approach 2:
The patent applies partial action by forming the dielectric cap only where necessary for electrical isolation, rather than across the entire gate conductor. This partial cap provides the minimum required isolation function without the excessive material removal that would occur with a full cap, thus optimizing the balance between electrical isolation and gate volume preservation.
Data Source
AI summary
A method for fabricating self-aligned contacts includes forming a liner over a gate structure having a gate conductor and one sidewall spacer and etching an exposed gate conductor to form a recess extending less than a width of the gate conductor. A dielectric layer is conformally deposited to fill the recess between the liner and the one sidewall spacer to form a partial dielectric cap formed on the gate conductor. A self-aligned contact is formed adjacent to the one sidewall spacer of the gate structure that is electrically isolated from the gate conductor by the partial dielectric cap and the at least one sidewall spacer.