Binary Phase Mask for EUV Lithography Energy Loss
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Solution Overview
Problem
Extreme ultraviolet lithography (EUVL) faces challenges with low throughput and energy loss due to the high absorption of materials used in current binary intensity masks, leading to reduced EUV energy reaching the wafer, especially in via layers, which affects the complexity and efficiency of IC processing.
Innovation Solution
A binary phase mask (BPM) with two phase states is introduced, utilizing a reflective multilayer and a second reflective layer to enhance EUV light reflection and phase shift, combined with off-axis illumination and a pupil filter to optimize EUV light distribution and intensity during the lithography process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If binary intensity masks are used in EUVL, then the mask structure is simple, but EUV energy is substantially lost due to high absorption
Solution Approach 1:
The patent changes the mask's optical parameter from absorption-based (binary intensity mask) to phase-shift-based (binary phase mask). The BPM introduces a phase shift of approximately π radians between light passing through different regions, converting the mask function from intensity modulation to phase modulation, which subsequently enhances intensity through interference effects.
Solution Approach 2:
The patent employs composite material structures in the BPM, combining materials with different optical properties to achieve the desired phase shift. The mask includes multiple layers with specific thicknesses and compositions designed to create the required phase difference while maintaining reflectivity, utilizing composite material properties to solve the energy loss problem.
2Loss of energy
If reflective optics are used in EUVL, then refraction issues are avoided, but reflectance is very low causing energy loss
Solution Approach 1:
The patent optimizes the optical parameters of the reflective mask by introducing phase shift functionality. The BPM is designed to reflect EUV light with a phase shift of approximately π radians, transforming the reflective optics from simple reflection to phase-controlled reflection, thereby enhancing energy utilization through constructive interference.
Solution Approach 2:
The patent converts the inherent limitation of low reflectance in EUV reflective optics into a benefit by using the phase shift effect. Instead of trying to increase reflectance directly, the invention uses the phase difference between reflected beams to create constructive interference in the desired regions, turning the weak reflection into effective intensity enhancement through wave interference.
3Productivity
If via layer patterns are printed, then interconnect functionality is achieved, but low transmittance through via causes low throughput
Solution Approach 1:
The patent changes the optical parameter of the via region by using phase shift masks. The BPM introduces a phase shift in the via regions, creating constructive interference that enhances the intensity of light reaching the via patterns. This phase-based approach overcomes the low transmittance issue by compensating for energy loss through interference effects.
4Productivity
If IC geometry scaling is performed, then production efficiency increases, but manufacturing complexity increases
Solution Approach 1:
The patent addresses the complexity issue by introducing phase shift functionality to the mask, which enables better control over the lithography process at scaled dimensions. The BPM provides enhanced contrast and resolution capabilities, allowing for successful patterning of smaller geometries without proportionally increasing processing complexity.
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 BPM enhances EUV light intensity by up to four times, reduces energy loss, and improves lithography throughput, particularly for IC patterns with low pattern density, while minimizing mask error enhancement factor and printability issues.
Implementation Method 1
A binary phase mask (BPM) with two phase states is introduced, utilizing a reflective multilayer and a second reflective layer to enhance EUV light reflection and phase shift
Implementation Method 2
utilizing a reflective multilayer and a second reflective layer to enhance EUV light reflection and phase shift
Implementation Method 3
A binary phase mask (BPM) with two phase states is introduced
Implementation Method 4
combined with off-axis illumination and a pupil filter to optimize EUV light distribution and intensity during the lithography process
Data Source
AI summary
The present disclosure provides a method for extreme ultraviolet lithography (EUVL) process. The method includes loading a binary phase mask (BPM) to a lithography system, wherein the BPM includes two phase states and defines an integrated circuit (IC) pattern thereon; setting an illuminator of the lithography system in an illumination mode according to the IC pattern; configuring a pupil filter in the lithography system according to the illumination mode; and performing a lithography exposure process to a target with the BPM and the pupil filter by the lithography system in the illumination mode.