Dummy Gate Formation Using Lateral Recess Hardmask
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Solution Overview
Problem
Current methods for forming dummy gates in semiconductor devices face challenges such as increased aspect ratio difficulties due to taller hardmasks required for spacer pull down, which can lead to epitaxial nodule growth issues during the replacement metal gate process, and are limited by the fin height.
Innovation Solution
A novel method involving the lateral recess of a silicon nitride hardmask layer underneath an oxide hardmask layer to create a protective hat for the spacer, preventing further pull down and increasing the process window by decoupling the fin height from the spacer etch process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a taller hardmask is used for spacer pull down, then the spacer can be etched deeper, but the aspect ratio increases causing epitaxial nodule growth issues
Solution Approach 1:
The hardmask is divided into two separate layers: a first hardmask layer (silicon nitride) and a second hardmask layer (oxide). The first hardmask layer provides the necessary height for spacer pull down, while the second hardmask layer caps the top surface to prevent epitaxial nodule growth. This segmentation allows each layer to fulfill its specific function independently, resolving the contradiction between achieving deep spacer etch and preventing defects.
2Length of moving object
If the fin height is increased, then the device performance improves, but the spacer pull down process becomes more difficult
Solution Approach 1:
By segmenting the hardmask into two layers with the second layer capping the first, the process can accommodate taller fins without requiring an excessively tall single hardmask layer. The capped structure provides a stable platform for spacer formation and etching, making the spacer pull down process easier even with increased fin height.
Solution Approach 2:
The dual-layer hardmask structure combines silicon nitride (first layer) and oxide (second layer) materials. This composite structure provides both the height needed for spacer pull down and the protective capping function, enabling the process to handle taller fins effectively while maintaining ease of manufacture.
3Manufacturing precision
If the hardmask height is increased to support spacer pull down, then the spacer etch process is improved, but the dummy gate stack aspect ratio increases
Solution Approach 1:
The hardmask is segmented into two functional layers: the first layer (silicon nitride) provides the height necessary for effective spacer pull down and etching, while the second layer (oxide) caps the structure to prevent further spacer pull down and reduce the effective aspect ratio of the dummy gate stack. This segmentation allows the spacer etch process to be improved while keeping the overall structure more manageable.
Data Source
AI summary
Forming a dummy gate on a semiconductor device is disclosed. A first sacrificial layer is formed on a fin, and a second sacrificial layer is formed on the first sacrificial layer. A first hardmask layer is formed on the second sacrificial layer, and a second hardmask layer is formed on the first hardmask layer and patterned. The first hardmask layer is laterally recessed in a lateral direction under the second hardmask layer. The first and second sacrificial layers are etched to a corresponding width of the first hardmask layer. A spacer layer is formed on the fin, the first sacrificial layer, second sacrificial layer, the first hardmask layer and the second hardmask layer. The spacer layer is etched until it remains on a sidewall of the first sacrificial layer, the second sacrificial layer and the first hardmask layer, wherein the first and second sacrificial layers form the dummy gate.