EUV Mask Three-State Reflection Coefficients for High Resolution
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Solution Overview
Problem
Current extreme ultraviolet lithography (EUVL) techniques face limitations in achieving high resolution due to the smoothing of step heights in multilayer structures, which restricts the achievable resolution and contrast in phase-shifting mask technologies like alternating phase-shifting masks (AltPSM).
Innovation Solution
The implementation of an EUV lithography system using a reflective EUV mask with three states having specific reflection coefficients and a nearly on-axis illumination with partial coherence less than 0.3, where the first and second states are assigned to adjacent polygons and the third state to the field, enhancing aerial image contrast and throughput by utilizing balanced diffracted light orders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multilayer structures are formed over steps to generate phase-shifting regions in AltPSM, then phase-shifting capability is achieved, but the multilayer smooths out the step height, leading to a large transition area and limiting resolution
Solution Approach 1:
The patent changes the physical parameters of the mask structure by introducing three distinct states with specific reflection coefficients (r1, r2, r3 where r3≈(r1+r2)/2) instead of using traditional two-state phase-shifting masks. This parameter optimization allows for controlled phase shifts while maintaining sharp transitions and avoiding the smoothing problem inherent in multilayer structures.
Solution Approach 2:
The mask is segmented into three distinct reflective states rather than using a continuous multilayer structure. This segmentation into discrete states (first state with reflection coefficient r1, second state with r2, third state with r3) enables precise control over the phase-shifting regions while maintaining sharp boundaries, thus resolving the contradiction between achieving phase-shifting capability and maintaining high resolution.
2Device complexity
If conventional binary intensity masks with on-axis illumination are used in EUVL, then the lithography process is simple, but adequate aerial image contrast for future nodes cannot be achieved
Solution Approach 1:
The patent optimizes the illumination parameters by using nearly on-axis illumination with partial coherence (σ < 0.3) combined with the three-state mask structure. This parameter optimization enhances aerial image contrast for future technology nodes while keeping the lithography process relatively simple, avoiding the need for complex off-axis illumination systems.
3Manufacturing precision
If the third state is assigned to the field region with reflection coefficient close to the average of first and second states, then balanced diffracted light orders are achieved, but mask fabrication complexity increases
Solution Approach 1:
The patent specifies that the third state's reflection coefficient r3 should be close to (r1+r2)/2, creating a balanced diffraction pattern. This parameter relationship simplifies the optimization process during mask fabrication, as it provides a clear target value for the third state's reflectivity, thereby reducing fabrication complexity while maintaining high aerial image contrast.
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 pattern contrast and resolution, enabling better imaging quality and process window for future nodes in semiconductor manufacturing by optimizing the reflection coefficients and illumination method.
Implementation Method 1
the EUV mask with three states having reflection coefficients r1, r2, and r3, respectively... collecting and directing the diffracted light and the not removed non-diffracted light
Implementation Method 2
exposing the EUV mask by a nearly on-axis illumination with partial coherence σ less than 0.3 to produce diffracted light and non-diffracted light
Data Source
AI summary
An extreme ultraviolet lithography (EUVL) system is disclosed. The system includes an extreme ultraviolet (EUV) mask with three states having respective reflection coefficient is r1, r2 and r3, wherein r3 is a pre-specified value that is a function of r1 and r2. The system also includes a nearly on-axis illumination (ONI) with partial coherence σ less than 0.3 to expose the EUV mask to produce diffracted light and non-diffracted light. The system further includes a projection optics box (PUB) to remove a portion of the non-diffracted light and to collect and direct the diffracted light and the remaining non-diffracted light to expose a target.