Phase Shift Mask Hard Mask for CD Resolution
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Solution Overview
Problem
Conventional phase shift masks suffer from significant critical dimension loss and rounding of auxiliary features due to etching bias between main and auxiliary features, limiting optical proximity correction and pattern resolution in semiconductor photolithography.
Innovation Solution
A phase shift mask with a hard mask layer formed between the phase shift layer and the opaque layer, where the hard mask layer has etching selectivity with respect to the phase shift layer, reducing etching bias and preventing critical dimension shrinkage of auxiliary features, while maintaining compatibility with existing photomask manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional phase shift mask is used, then phase shifting function is achieved, but significant critical dimension loss and rounding of auxiliary features occur due to etching bias
Solution Approach 1:
A hard mask layer is introduced as an intermediary between the phase shift layer and the opaque layer. This hard mask layer serves as a protective mediator that prevents direct etching of the phase shift layer, thereby eliminating etching bias and preventing critical dimension loss and rounding of auxiliary features during the etching process.
2Manufacturing precision
If hard mask layer is added to prevent etching bias, then pattern fidelity is improved, but device complexity increases
Solution Approach 1:
The hard mask layer is formed with the same material composition as the phase shift layer (MoSiNx), creating a homogeneous structure. This allows the hard mask layer to be formed using the same deposition process as the phase shift layer, integrating the additional functional layer without adding significant process complexity or requiring additional material deposition steps.
3Ease of manufacture
If conventional etching process is used, then manufacturing simplicity is maintained, but etching bias causes critical dimension shrinkage
Solution Approach 1:
The hard mask layer is formed preliminary to the etching process, specifically positioned between the phase shift layer and the opaque layer. This preliminary protective layer is prepared in advance to prevent etching bias during the subsequent etching process, allowing the use of conventional etching processes while achieving high precision.
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 solution effectively enhances the fidelity of transferred patterns by preventing critical dimension loss and improving optical proximity correction, ensuring accurate and effective optical proximity correction without impacting the photomask making cycle time.
Implementation Method 1
Phases of wavefronts of light passing through a photomask pattern of the phase shift mask are intentionally phase shifted in selected portions to selectively produce destructive interference
Implementation Method 2
selectively produce destructive interference, thereby reducing undesired light exposures of a photosensitive layer due to diffraction of light passing through the patterned photomask
Implementation Method 3
The diffraction or optical fringing and interference of light cause undesired light exposure on the photosensitive layer
Implementation Method 4
the phase shift layer has an etching selectivity with respect to the hard mask layer
Data Source
AI summary
A phase shift mask blank includes a transparent substrate, a phase shift layer, a first hard mask layer and an opaque layer. The transparent substrate is disposed on the transparent substrate. The first hard mask layer is disposed on the phase shift layer. The phase shift layer has an etching selectivity with respect to the first hard mask layer. The opaque layer is disposed on the first hard mask layer.