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Bilayer Metallic Antireflection Mirror

IP.com Disclosure Number: IPCOM000049460D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Ahn, KY: AUTHOR [+3]

Abstract

The wavelength of an all metal bilayer antireflection (AR) film mirror can be simply adjusted as a function of the thickness of Si top film with high selectivity.

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Bilayer Metallic Antireflection Mirror

The wavelength of an all metal bilayer antireflection (AR) film mirror can be simply adjusted as a function of the thickness of Si top film with high selectivity.

Conventional AR mirrors consist of multilayer dielectric films.

One of the simplest structures which uses two dielectric films MgF(2) 11 and 12 on a glass substrate 10 is shown in Fig. 1. It is based on Thin Film Optical Filters by H. A. McLeod, Adam Hilger Ltd., London, England (1969), p.55.

This so called quarter quarter coating requires materials with a precisely known index of refraction, n, to match the desired wavelength. Its reflection characteristics are shown by curve 1 in Fig. 2.

Fig. 3 shows a similar coating (see curve 3 in Fig. 2), but with the following features:
(1) The two layers 31 and 32 on a Si wafer 30 consist

of metal films, e.g., Pd (31) and Si (32) (and

possibly other noble metals).
(2) Metal film thicknesses range between 250 angstroms

and 500 angstroms to achieve the AR condition in the

visible spectrum and near the IR range.
(3) The wavelength of the minimum reflection is controlled by

adjustment of the thickness of the top film 32 (Si) alone.

As the Si thickness increases, the AR wavelength shifts

toward longer wavelengths, as shown in Fig. 4.
(4) The minimum value of the AR condition is typically 0.1

percent, as shown in Fig. 5, which is an expanded scale

of the corresponding positions of Fig. 4.
(5) The wavelength selectivity is much sh...