High refractive index nanocomposite fluids for immersion lithography.

Area of Science:

• Materials Science
• Optical Engineering
• Nanotechnology

Background:

• Immersion lithography requires high refractive index fluids to improve resolution.
• Existing fluids face limitations in achieving desired refractive indices and stability.
• Nanoparticle dispersions present a novel approach to overcome these limitations.

Purpose of the Study:

• To theoretically and experimentally investigate nanoparticle dispersions as high refractive index fluids for immersion lithography.
• To understand the factors controlling stability and refractive index in these dispersions.
• To demonstrate the feasibility of using these dispersions in lithography.

Main Methods:

• Theoretical modeling using statistical thermodynamics and percolation theory to predict demixing and gelation.
• Estimation of stabilizer layer thickness based on hard sphere models and van der Waals attractions.
• Experimental preparation and characterization of nanoparticle suspensions.
• Optical measurements at 193 nm wavelength.
• Imaging experiments using nanoparticle dispersions.

Main Results:

• Short stabilizing brushes can control gelation and demixing in high solid dispersions.
• Refractive indices above 1.8 are achievable with transparent materials at 193 nm.
• Experimental suspensions with 4 nm particles increased refractive index by 0.2.
• Refractive index and density are proportional to volume fraction.
• Successful imaging was demonstrated with silica nanoparticle dispersions.

Conclusions:

• Nanoparticle dispersions are a viable option for creating high refractive index fluids in immersion lithography.
• Controlling particle interactions is key to achieving stable and effective immersion fluids.
• This approach enables higher resolution in advanced lithography processes.