Dual Layer Hardmask for PMOS Gate Spacer Protection
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Solution Overview
Problem
Forming a uniform thin hard mask in integrated circuits with silicon-germanium epitaxial source/drain regions while maintaining lateral separation from the gate and avoiding damage to underlying silicon nitride gate offset spacers has been problematic.
Innovation Solution
A dual layer hard mask is formed with a first layer of carbon-containing silicon nitride using a hydrocarbon reagent and a second layer of chlorine-containing silicon nitride using a chlorinated silane reagent, which is then removed using a wet etch process that selectively removes the second layer at a faster rate than the first layer, ensuring the integrity of the gate offset spacers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin hard mask is formed to maintain lateral separation between SiGe epitaxial source/drain and gate, then lateral separation control is improved, but the hard mask becomes difficult to remove without damaging underlying gate offset spacers
Solution Approach 1:
The hard mask is divided into two distinct layers: a first layer of carbon-containing silicon nitride and a second layer of chlorine-containing silicon nitride. This segmentation allows each layer to have different etch selectivity, enabling the second layer to be removed rapidly while the first layer remains to protect the gate offset spacers.
Solution Approach 2:
Different chemical compositions are introduced at different locations within the hard mask structure. The first layer contains carbon from hydrocarbon reagents, while the second layer contains chlorine from chlorinated silane reagents. This local quality differentiation creates distinct etch rates in different regions of the hard mask, solving the removal difficulty.
2Manufacturing precision
If a uniform thin hard mask is formed, then lateral separation uniformity is improved, but the hard mask cannot be selectively removed without damaging gate offset spacers
Solution Approach 1:
The hard mask is segmented into two layers with different chemical compositions and etch selectivities. The first layer provides uniform coverage and protection, while the second layer enables selective removal, thus maintaining both uniformity and gate offset spacer integrity during the removal process.
Solution Approach 2:
The hard mask is formed as a composite structure combining carbon-containing silicon nitride and chlorine-containing silicon nitride. This composite material approach allows the hard mask to exhibit both uniform physical properties for lateral separation control and differential chemical properties for selective removal without damaging underlying structures.
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 dual layer hard mask achieves uniformity and lateral separation between SiGe epitaxial source/drain regions and the gate, while effectively removing the hard mask without damaging the underlying gate offset spacers, ensuring precise fabrication of PMOS transistors in integrated circuits.
Implementation Method 1
the hard mask is removed using a wet etch which removes the second layer at a rate at least three times faster than the first layer
Implementation Method 2
A first layer of the hard mask is carbon-containing silicon nitride formed using a hydrocarbon reagent
Implementation Method 3
A second layer of the hard mask is chlorine-containing silicon nitride formed on the first layer using a chlorinated silane reagent
Data Source
AI summary
An integrated circuit containing PMOS transistors may be formed by forming a dual layer hard mask. A first layer of the hard mask is carbon-containing silicon nitride formed using a hydrocarbon reagent. A second layer of the hard mask is chlorine-containing silicon nitride formed on the first layer using a chlorinated silane reagent. After SiGe epitaxial source/drain regions are formed, the hard mask is removed using a wet etch which removes the second layer at a rate at least three times faster than the first layer.