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Mask for X-Ray Lithography with Optically Transparent Registration Window

IP.com Disclosure Number: IPCOM000050471D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Behringer, U: AUTHOR [+4]

Abstract

The mask consists of a thin silicon membrane with a registration area that is completely oxidized to form an optical window of high transparency in the visible part of the spectrum.

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Mask for X-Ray Lithography with Optically Transparent Registration Window

The mask consists of a thin silicon membrane with a registration area that is completely oxidized to form an optical window of high transparency in the visible part of the spectrum.

Mask membrane 1 is formed by etching a silicon wafer 2, whose surface layer is doped with boron which acts as an etch stop when the desired membrane thickness (some Mu) has been reached. Metal mask pattern 3 as well as registration pattern 4 for the mutual alignment of mask and wafer are deposited on the membrane surface. Registration pattern 4 is applied to an area 5 of the membrane which has been entirely transformed into silicon dioxide, whose transparency in the visible part of the spectrum facilitates the registration problem in X-ray lithography systems.

For oxidation, the silicon membrane is thinned in area 5 to approximately half its original thickness (broken lines 6a, 6b) by dry or wet etching, using a nitride mask layer. Then the remaining silicon is fully oxidized into SiO(2), doubling its volume, so that the original thickness of the silicon mask is again reached. As area 5 is relatively large (up to several mm ); small height steps (typically 0.1 Mum) in the Si membrane are not critical. To counterbalance the compressive stress in the SiO(2) window, the whole membrane mask is covered with a nitride layer 7 which exerts a high tensile stress.

The optical transparency of the resulting SiO(2)/SiN wind...