Shunsuke Niisaka

Preparation of MgF2-SiO2 thin films with a low refractive index by a solgel process.

Porous MgF(2)-SiO(2) thin films consisting of MgF(2) particles connected by an amorphous SiO(2) binder are prepared by a solgel process. The films have a low refractive index of 1.26, sufficient strength to withstand wiping by a cloth, and a high environmental resistance. The refractive index of the film can be controlled by changing the processing conditions. Films can be uniformly formed on curved substrates and at relatively low temperatures, such as 100 degrees C. The low refractive index of the film, which cannot be achieved by conventional dry processes, is effective in improving the performance of antireflective coatings.

Development of optical coatings for 157-nm lithography. II. Reflectance, absorption, and scatter measurement

The total loss that can be suffered by an antireflection (AR) coating consists of reflectance loss, absorption loss, and scatter loss. To separate these losses we developed a calorimetric absorption measurement apparatus and an ellipsoidal Coblentz hemisphere based scatterometer for 157-nm optics. Reflectance, absorption, and scatter of AR coatings were measured with these apparatuses. The AR coating samples were supplied by Japanese vendors. Each AR coating as supplied was coated with the vendors coating design by that vendors coating process. Our measurement apparatuses, methods, and results for these AR coatings are presented here.

Development of low-loss optical coatings for 157-nm lithography

In the F2 laser lithography, it is essential to reduce the loss of the optical coatings deposited on calcium fluoride lenses. In order to make low loss optical coatings, we have developed measurement apparatus, evaluated the coatings with various analyses, and found a correlation with the optical constants. In this paper we describe the optical loss measurement apparatus and the evaluation results analyzed for either single layer coatings or multi-layer anti-reflection coatings.

Thin Film Retardation Plates of Silica Glass Fabricated by Oblique Depositions

We developed thin film retardation plates of silica glass which work with normally incident lights at a wavelength as short as 300 nm. By depositing silica from an oblique direction (70°° from the substrate surface-normal) onto substrates, unique microscopic columnar structures were obtained. The columns of approximately 20 nm in diameter were inclined to the deposition direction which cause birefringence. Although obliquely deposited thin films often become opaque because of coalescence of the columns enhanced by absorbing moisture after the deposition processes, the opacity was suppressed using stacked structures of obliquely deposited and normally deposited layers.

Laser durability improvement of deep UV fluoride coatings

Fluoride materials are typically used as optical coatings for Deep UV applications such as semiconductor lithography steppers/scanners equipped ArF excimer laser (193nm). To extend its lifetime, laser durability of fluoride optical coatings deposited by conventional thermal evaporation method were investigated. From relation between coating defects amount and LIDT, it was apparent the laser durability of fluoride multilayer coatings are strongly spoiled by their coating defects. These defects are observed by naked eyes, Nomarski microscopy, AFM and SEM for more details. Finally it was found that defects broke the coating structures.