EUV Lithography Mask Phase Shift for Dimensional Accuracy
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Solution Overview
Problem
In EUV lithography techniques, the use of oblique incidence of EUV light on masks with absorber patterns leads to directional differences in shadow formation, resulting in reduced resolution and dimensional accuracy of transferred patterns due to interference between incident and reflected light, causing variations in pattern transfer depending on the direction of incidence.
Innovation Solution
A mask structure is developed with a difference in level between its regions, where the absorber pattern is formed on a multilayer film that reflects EUV light, and the incident light is directed such that its projective component intersects with the difference in level, minimizing shadow formation and enhancing dimensional accuracy by using the phase shift effect to achieve a 180-degree phase difference between reflected light from different regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If oblique incidence of EUV light is used on masks with absorber patterns, then the energy reaching the object to be exposed is improved, but shadow formation occurs leading to reduced resolution and dimensional accuracy
Solution Approach 1:
The mask structure introduces a difference in level between the first and second regions, creating local structural variation. This local quality change causes the reflected light from each region to have different optical paths, generating a phase difference that produces interference patterns to enhance pattern transfer accuracy while maintaining oblique incidence configuration
Solution Approach 2:
The mask deliberately introduces asymmetry through the difference in level between regions, breaking the symmetric reflection pattern. This asymmetric structure ensures that the phase difference between reflected lights from different regions creates constructive interference at desired locations, improving resolution despite oblique incidence shadow formation
2Ease of operation
If oblique incidence of EUV light is used on masks, then the exposure process can be performed, but interference between incident and reflected light causes directional differences in shadow formation
Solution Approach 1:
The invention changes the physical parameter of the mask surface by introducing a difference in level between regions. This parameter change modifies the optical path length of reflected light, creating a phase difference that generates interference patterns. The phase difference compensates for the directional shadow effects caused by oblique incidence, maintaining resolution across different exposure directions
3Ease of manufacture
If a flat mask structure is used, then the manufacturing process is simpler, but phase difference control between reflected light regions is difficult
Solution Approach 1:
The mask structure pre-establishes a difference in level between the first and second regions before the exposure process. This preliminary structural configuration ensures that when EUV light reflects from different regions, the optical path difference automatically generates the required phase difference. This preliminary action eliminates the need for complex real-time phase control during exposure, maintaining manufacturing simplicity while achieving precise phase control
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 approach improves the dimensional accuracy and resolution of patterns transferred onto semiconductor substrates by reducing shadow formation and maintaining consistent contrast, thereby enhancing the overall performance of EUV lithography techniques.
Implementation Method 1
a multilayer film which is formed in the first region and the second region of the mask substrate and reflects the extreme ultra violet light
Implementation Method 2
an absorber which is formed on the multilayer film and absorbs the extreme ultra violet light
Implementation Method 3
the incident light is directed such that its projective component intersects with the difference in level, minimizing shadow formation and enhancing dimensional accuracy by using the phase shift effect to achieve a 180-degree phase difference between reflected light from different regions
Data Source
AI summary
Provided is a technique capable of improving the dimensional accuracy of a transfer pattern in a lithography technique in which EUV light is used and the EUV light is incident obliquely on a mask and an image of the EUV light reflected from the mask is formed on a semiconductor substrate (resist film), thereby transferring the pattern formed on the mask onto the semiconductor substrate. The present invention is based on a lithography technique in which EUV light is used and an exposure optical system in which the EUV light is obliquely incident on a mask is used. In this lithography technique, an absorber and a difference in level are formed on the mask, and a projective component projected on a mask surface out of a direction cosine component of the incident light is set to be almost orthogonal to an extending direction of the difference in level.