Improving feature size uniformity from interference lithography systems with non-uniform intensity profiles.

The non-uniform intensity profile of Gaussian-like laser beams used in interference lithography (IL) leads to a non-uniform dose and feature size distribution across the sample. Previously described methods to improve dose uniformity are reviewed. However, here we examine the behavior of the non-uniformity from the viewpoint of photoresist response rather than the IL system configuration. Samples with a fixed intra-sample dose profile were exposed with an increasing average dose. A line/space pattern with a period of 240 nm across an area of 2 × 2 cm(2) was produced using IL on identical samples using a HeCd laser operated at 325 nm and a Lloyd's mirror IL system. A binary model of photoresist response predicts that the absolute range of line widths in nanometers should be significantly reduced as the overall sample dose is increased. We have experimentally verified a reduction in the range of line widths within a given sample from 50 to 16 nm as the overall dose is increased by only 60%. This resulted in a drop in the narrowest line width from 120 to 65 nm. An etch process is demonstrated to increase the line width by generating a wider secondary chrome hard mask from the narrowly patterned primary chrome hard mask. The subsequent fabrication of a silicon nanoimprint mold is used as a demonstration of the technique.

Sub-15 nm linewidth gratings using roll-to-roll nanoimprinting and plasma trimming to fabricate flexible wire-grid polarizers with low colour shift.

Sub-15 nm-wide gratings with a high aspect ratio of up to 16:1 were fabricated using roll-to-roll nanoimprinting and plasma trimming to achieve high optical performance (up to 12 000:1 extinction ratio with an average transmittance of 82%) and low colour shift (transmittance variation less than 3%) flexible wire-grid polarizers for display applications. We applied two imprint platforms onto glass and plastic substrates to identify the optical properties and characteristics of each fabrication process. To enhance the tolerance, reproducibility, and optical performance of the process, the grating profile symmetry and varying residual layer thicknesses were precisely simulated and controlled to achieve the design targets.

Polarized backlight with constrained angular divergence for enhancement of light extraction efficiency from wire grid polarizer.

Efficiency of liquid crystal displays highly depends on the amount of polarized light emerging from the backlight module. In this paper, a backlight architecture using a nanoimprint wire grid polarizer for polarization recycling is proposed and studied, in which the extraction efficiency of polarized light is the major concern. The backlight module is composed of the stack of a wire grid polarizer, a lenticular array and a light guide plate. The light guide plate features interleaving v-groove and trapezoidal ridge coated with aluminum on the top surface, and scattering dot array on the bottom. The angular divergence of emerging light from the light guide plate can be well constrained so as to exploit the angular range with the best transmission of polarized light for the wire grid polarizer. The prototype of a 2.5-inch module has demonstrated an angular divergence of 48°. The overall extraction efficiency of polarized light enhanced by 21% and uniformity of 76% have been achieved.