Question

What is a Bragg reflector? Which technology does needs this type of reflector and why?? What is the primary advantage of this technology?

What is Immersion lithography? How can it improve the resolution? What one main issue with this technology?

Answer 1

Bragg reflector -; Bragg reflector  is a reflector used in waveguides, such as optical fibers. It is a structure formed from multiple layers of alternating materials with varying refractive index, or by periodic variation of some characteristic (such as height) of a dielectric waveguide, resulting in periodic variation in the effective refractive index in the guide.

Uses of bragg reflector -;  

A Bragg reflector structure is an essential part for vertical cavity surface emission laser (VCSEL) applications. High optical reflectance at required stopband width is one of major concern by means of application requirements. For this purpose, Bragg mirrors consisting of SiC/MgO multilayers have been developed using an RF magnetron sputtering technique at room temperature. These structures have been characterized using various measurement techniques like ellipsometry, reflectance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique.

Advantages-;

1- A higher reflectance in the reflectance band.

2- A phase-change on reflection that is close to zero and varying linearly in the band of reflection (a metal can introduce a different phase-shift);

Immersion lithography -; Immersion lithography is a photolithography resolution enhancement technique for manufacturing integrated circuits (ICs) that replaces the usual air gap between the final lens and the wafer surface with a liquid medium that has a refractive index greater than one. The resolution is increased by a factor equal to the refractive index of the liquid.

Main issue- ;   The water between the front lens and wafer forms a meniscus that moves with the exposure head across the wafer. Various physical and chemical interactions between the water and resist stack occur, leading to water immersion-related defects.