Cobalt Mask Passivation for Selective Gate Etching
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Solution Overview
Problem
Cobalt, a promising candidate for interconnects due to its low resistivity, poses processing challenges such as easy oxidation, which reduces etch selectivity in relation to other interconnect and gate materials, especially at small feature sizes like the 5 nm Node.
Innovation Solution
A method involving a fluorine-containing gas mixture is used to form a passivation layer on a cobalt mask layer, allowing for selective etching of gate materials with a removal rate ratio of 6:1 or greater, thereby enhancing etch selectivity and preventing oxidation-induced degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cobalt is used as interconnect material to achieve low resistivity, then electrical performance is improved, but etch selectivity deteriorates due to easy oxidation
Solution Approach 1:
A silicon-containing passivation layer is introduced as an intermediary between the cobalt mask layer and the etching environment. This passivation layer acts as a protective mediator that prevents direct oxidation of cobalt while allowing the etching process to proceed selectively on exposed gate material surfaces. The passivation layer is formed by exposing cobalt to a silicon-containing gas mixture, creating a protective barrier that resolves the contradiction between maintaining cobalt's low resistivity and preventing its oxidation-induced etch selectivity loss.
2Productivity
If conventional etching is used on cobalt mask layer, then etching speed is maintained, but etch selectivity between cobalt and gate material deteriorates
Solution Approach 1:
The invention applies local quality by creating different surface conditions in different regions. The silicon-containing gas mixture selectively forms a passivation layer on the cobalt mask layer surfaces, while leaving the gate material surfaces exposed and reactive. This local differentiation of surface properties (passivated cobalt vs. exposed gate material) enables high etch selectivity without compromising overall etching speed, as the etching process rapidly removes exposed gate material while the passivated cobalt remains protected.
3Productivity
If feature size is reduced to sub-ten nanometer nodes, then circuit density is improved, but processing precision deteriorates due to oxidation challenges
Solution Approach 1:
The invention applies preliminary action by forming the silicon-containing passivation layer on the cobalt mask layer before the main etching process. This pre-protection step ensures that cobalt surfaces are already passivated against oxidation before exposure to the etching environment, preventing oxidation-induced dimensional errors and profile degradation. The preliminary passivation enables accurate feature formation at sub-ten nanometer nodes by eliminating oxidation-related processing variability.
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
The method provides highly selective and reliable etching of cobalt relative to other transistor gate materials, maintaining interconnect performance by preventing oxidation and ensuring accurate feature formation in sub-ten nanometer gate materials.
Implementation Method 1
exposing a cobalt mask layer to a fluorine-containing gas mixture in a first mode to form a passivation layer on the cobalt mask layer
Implementation Method 2
exposing the portion of the gate material to an etching gas mixture in a second mode to etch the portion of the gate material
Data Source
AI summary
Implementations described herein generally relate to an etching process for etching materials with high selectivity. In one implementation, a method of etching a gate material to form features in the gate material is provided. The method includes (a) exposing a cobalt mask layer to a fluorine-containing gas mixture in a first mode to form a passivation film on the cobalt mask layer. The cobalt mask layer exposes a portion of a gate material disposed on a substrate. The method further comprises (b) exposing the portion of the gate material to an etching gas mixture in a second mode to etch the portion of the gate material. The portion of the gate material is etched through openings defined in the cobalt mask layer and the portion of the gate material is etched at a greater rate than the cobalt mask layer having the passivation layer disposed thereon.