Gate Dielectric Etching Sequence for Work Function Metal Alignment
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Solution Overview
Problem
Existing semiconductor manufacturing processes face challenges in achieving precise control over the etching of gate dielectric layers and work function metals, leading to potential adverse effects on device performance due to misalignment or excessive etching.
Innovation Solution
A multi-step plasma etching process using chlorine- and bromine-containing gases is employed to selectively etch gate dielectric layers while forming a protective layer over work function metals, ensuring precise control over the etching process and minimizing the height difference between the top surfaces of these layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching is used to etch gate dielectric layers, then etching can be performed, but precise control over etching depth and selectivity is difficult to achieve, leading to potential misalignment or excessive etching
Solution Approach 1:
The etching process is divided into multiple sequential steps, each with specific gas compositions and process parameters. The first step uses a chlorine-containing gas to etch the gate dielectric layer, followed by a second step using a bromine-containing gas to etch the work function metal layer. This segmentation allows precise control over etching depth and selectivity for each layer independently.
Solution Approach 2:
A protective layer is formed over the work function metal layer before the etching process begins. This protective layer is selectively removed during the etching sequence, allowing controlled exposure of the work function metal layer for precise etching in the second step while protecting it during the first step.
2Productivity
If higher plasma density is used to increase etching efficiency, then productivity improves, but control over selective etching of different materials becomes more difficult
Solution Approach 1:
The process uses different gas compositions (chlorine-containing vs. bromine-containing gases) and different process parameters for each etching step. The first etching step uses chlorine-containing gas at specific flow rates and power settings to etch the gate dielectric layer, while the second step uses bromine-containing gas with adjusted parameters to etch the work function metal layer, maintaining selectivity and precision.
Solution Approach 2:
The multi-step etching process is performed in continuous sequence without breaking vacuum or exposing the substrate to ambient conditions between steps. Each step builds upon the previous step, with the protective layer being selectively removed and the work function metal layer being etched in a continuous, controlled manner to achieve precise final dimensions.
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 process effectively reduces the distance between the top surfaces of the work function metal and gate dielectric to less than 1 nm, reducing the likelihood of contact between the gate contact and the gate dielectric, thereby enhancing semiconductor device performance.
Implementation Method 1
three processes compete with each other during plasma etching; physical bombardment by ions
Implementation Method 2
three processes compete with each other during plasma etching; chemical etching by radicals and ions
Implementation Method 3
three processes compete with each other during plasma etching; surface passivation by the deposition of passivating films
Implementation Method 4
plasma assisted etching operates in the milliTorr range and above
Data Source
AI summary
A method includes forming a gate structure across a channel region from a top view, the gate structure comprising a work function metal and a gate dielectric layer wrapping around the work function metal, the gate dielectric layer having a U-shaped cross-sectional profile; performing a first plasma etching process, by using a chlorine-containing reactant, on the gate structure; performing a second plasma etching process, by using a bromine-containing, reactant on the gate structure.