Microfabrication of Microlens by Timed-Development-and-Thermal-Reflow (TDTR) Process for Projection Lithography.

Area of Science:

• Microfabrication
• Optical Engineering
• Materials Science

Background:

• Traditional microlens fabrication methods often lack versatility in aperture geometry and profile control.
• Achieving parabolic profiles with precise control over dimensions remains a challenge in micro-optics fabrication.

Purpose of the Study:

• To present a novel timed-development-and-thermal-reflow process for fabricating diverse microlens geometries.
• To model and control microlens characteristics like depth, radius of curvature, focal length, and surface profile.
• To demonstrate the application of fabricated microlenses in miniaturized projection lithography.

Main Methods:

• Utilizing a timed development process on uncrosslinked negative photoresist to achieve partial development.
• Employing a subsequent thermal reflow process to form smooth meniscus trenches with crosslinked sidewalls.
• Fabricating microlenses with circular, square, and hexagonal bases on a single substrate.

Main Results:

• Successfully fabricated microlenses with parabolic profiles and various aperture geometries (circular, square, hexagonal).
• Established models relating development time and aperture size to trench depth, and thickness/diameter to optical characteristics.
• Demonstrated a miniaturized projection lithography system using the microlens array for photo-reduction, achieving linewidths as small as 2.6 µm.

Conclusions:

• The timed-development-and-thermal-reflow process offers a versatile method for fabricating custom microlens arrays.
• The fabricated microlenses are suitable for micro-optical applications, including high-resolution projection lithography.
• This technique provides a scalable approach for producing micro-optical components with controlled optical properties.