Lithographic Pellicle Thickness Optimization for ArF Laser Transmissivity
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Solution Overview
Problem
Conventional lithographic pellicles exhibit low transmissivity and increased reflectivity for inclined incident laser beams in high-NA exposure devices, leading to exposure unevenness and reduced photolithographic quality, while thinner pellicles compromise mechanical strength.
Innovation Solution
A lithographic pellicle membrane with a thickness 1.7% to 2.8% larger than the local maximum transmissivity thickness for vertically incident ArF excimer laser beams, optimizing transmissivity for inclinedly incident beams and maintaining mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the pellicle membrane is made thinner to reduce incidence angle dependency, then transmissivity for inclined beams improves, but mechanical strength deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the pellicle membrane thickness to be within 800-850 nm, which corresponds to approximately one-quarter of the ArF laser wavelength (193 nm). This specific thickness parameter creates destructive interference for reflected light at inclined angles, thereby reducing incidence angle dependency and improving transmissivity for inclined beams while maintaining sufficient mechanical strength through the optimized thickness range
2Strength
If the pellicle membrane is made thicker to maintain mechanical strength, then strength is improved, but transmissivity for inclined beams deteriorates
Solution Approach 1:
The patent resolves this contradiction by establishing an upper thickness limit of 850 nm. Within this constrained parameter range, the pellicle maintains adequate mechanical strength while the specific thickness (800-850 nm) creates optical interference effects that improve transmissivity for inclined beams by reducing reflection losses
3Strength
If conventional pellicle thickness is used, then mechanical strength is maintained, but exposure unevenness occurs due to low transmissivity for inclined beams
Solution Approach 1:
The patent changes the thickness parameter from conventional values to the optimized range of 800-850 nm. This parameter change simultaneously achieves two objectives: maintaining adequate mechanical strength and improving exposure uniformity by reducing incidence angle dependency through optical interference effects that enhance transmissivity for the range of incident angles present in high-NA photolithography
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
Significantly increases transmissivity for inclinedly incident ArF laser beams from 15° to 19°, reducing incidence angle dependency and enhancing photolithographic quality without compromising mechanical strength.
Implementation Method 1
a lithographic pellicle for use in photolithography by using ArF excimer laser beams, which comprises a pellicle membrane having a thickness larger by 1.7% to 2.8% than a thickness with which the pellicle membrane exhibits a local maximum transmissivity to a vertically incident ArF excimer laser beam
Data Source
Figure 1~2
AI summary
The present invention provides a lithographic pellicle for optimal use in the liquid-immersion exposure-type photolithography that employs selectively only the inclinedly incident components of incident laser beams, the lithographic pellicle affording a broader range of inclined incidence transmissivity that can be used in a photolithographic procedure. A lithographic pellicle for use in photolithography by using ArF excimer laser beams, which comprises a pellicle membrane having a thickness larger by 1.7% to 2.8% than any one of thicknesses at which the pellicle membrane exhibits a local maximum transmissivity to a vertically incident ArF excimer laser beam.