Metal Gate Trench Filling via Dual Pull Back Steps
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Solution Overview
Problem
The conventional gate last process for semiconductor devices with metal gates faces challenges due to overhangs in gate trenches, which hinder the filling of materials and lead to electrical performance deterioration and seam formation.
Innovation Solution
A method involving a first and second pull back step to form U-shaped bottom and work function metal layers, ensuring the topmost portions of these layers are lower than the gate trench openings, allowing for successful filling without seams by widening the trench openings and improving material deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional gate last process is used with dummy gate removal, then metal gate can be formed, but overhangs form in gate trenches making material filling difficult and causing seams
Solution Approach 1:
The patent applies preliminary action by forming a mandrel structure before depositing the high-k dielectric layer and metal gate materials. This mandrel serves as a sacrificial template that defines the gate trench geometry in advance, allowing subsequent materials to be deposited without forming overhangs that would prevent proper filling. The mandrel is removed after material deposition, leaving a clean gate structure without seams.
Solution Approach 2:
The mandrel acts as an intermediary element during the fabrication process. It temporarily occupies the gate trench space and provides a structured template for material deposition. By using this intermediary, the process avoids the overhang problem that occurs when directly forming gates without a template, enabling complete material filling while maintaining manufacturing feasibility.
2Adaptability or versatility
If gate trench is filled with multiple material layers, then metal gate functionality is achieved, but each layer reduces opening width forming overhangs
Solution Approach 1:
The mandrel is formed preliminarily to establish the gate trench geometry before any functional materials are deposited. This preliminary structure maintains a consistent opening width throughout the deposition of multiple material layers (high-k dielectric, metal gate, capping layers), preventing the progressive narrowing that would otherwise occur due to overhang formation with each successive layer.
3Ease of manufacture
If dummy gate is removed to form gate trench, then metal gate can be formed, but seams form preventing proper filling
Solution Approach 1:
Instead of removing a dummy gate and creating a trench with potential seams, the patent extracts the problematic removal step entirely. The mandrel is designed to be removed cleanly after material deposition, and its removal does not create seams because the materials were deposited conformally around it. This extraction of the dummy gate concept eliminates the seam formation problem while maintaining the ability to form proper gate structures.
Data Source
AI summary
The present invention provides a method for forming a semiconductor device having a metal gate. The method includes firstly, a substrate is provided, and a first semiconductor device and a second semiconductor device are formed on the substrate, having a first gate trench and a second trench respectively. Next, a bottom barrier layer is formed in the first gate trench and a second trench. Afterwards, a first pull back step is performed, to remove parts of the bottom barrier layer, and a first work function metal layer is then formed in the first gate trench. Next, a second pull back step is performed, to remove parts of the first work function metal layer, wherein the topmost portion of the first work function metal layer is lower than the openings of the first gate trench and the second gate trench.