Phase Shift Mask With Shielding Layer For SRAFs
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Solution Overview
Problem
As semiconductor technology advances, particularly in dynamic random access memory (DRAM) with 38 nanometer nodes, the critical dimension approaches the physical limitations of optical exposure properties, making it challenging to maximize the process window under current exposure machine and mask conditions.
Innovation Solution
A phase shift mask with a phase shift layer and a shielding layer is developed, where the phase shift layer has a transmission higher than 6% and a 180-degree phase shift, and the shielding layer covers the sub-resolution assist feature, preventing it from being imaged on the semiconductor substrate after exposure and development processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the critical dimension is reduced to 38 nanometers, then the technology node is downsized, but the critical dimension approaches the physical limitation of optical properties making it difficult to maximize the process window
Solution Approach 1:
The mask pattern is segmented into main patterns and sub-resolution assist features (SRAFs). The SRAFs are auxiliary structures with dimensions below the resolution limit that cannot be imaged on the substrate. By segmenting the pattern and adding these non-imaged SRAFs, the optical contrast and process window for the main patterns are improved without sacrificing the downsized critical dimension.
2Reliability
If sub-resolution assist features are added to increase process window, then the function of SRAF is improved, but the SRAF may be imaged on the semiconductor substrate after exposure and development
Solution Approach 1:
Different regions of the mask are given different properties: the SRAF regions are designed with dimensions and optical properties that result in zero or near-zero transmission, making them non-imaging features, while the main pattern regions maintain appropriate transmission for imaging. This local differentiation ensures SRAFs provide process window benefits without being imaged on the substrate.
Solution Approach 2:
The transmission parameter of the SRAF regions is changed to be zero or near-zero through material selection and structural design, distinguishing them from the main patterns. By changing this key optical parameter, the SRAFs become non-imaging features that still influence the optical field to improve the process window for the main patterns.
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
This solution maintains the function of sub-resolution assist features, increases the process window of the photolithography process, and ensures that sub-resolution assist features are not imaged on the semiconductor substrate, while providing preferable optical properties and a larger process window compared to conventional masks.
Implementation Method 1
The phase shift layer has a transmission, and the transmission is higher than 6%. The phase shift layer has a phase shift, and the phase shift is 180 degrees.
Implementation Method 2
The shielding layer at least covers the sub-resolution assist feature of the phase shift layer, making the transmission of the sub-resolution assist feature close to zero
Data Source
AI summary
Provided is a phase shift mask including a substrate, a phase shift layer, and a shielding layer. The phase shift layer is located on the substrate. A pattern of the phase shift layer includes a main pattern and sub-resolution assist features (SRAFs). The SRAFs are disposed around the main pattern. The phase shift layer has a transmission, and the transmission is larger than 6%. The shielding layer at least covers the SRAFs of the phase shift layer.