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Contamination Resist Apertures for X-Ray Optical Systems

IP.com Disclosure Number: IPCOM000061052D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Feder, R: AUTHOR [+4]

Abstract

This article describes a method of using contamination nanolithography to form apertures of less than 10 nm in diameter for use in high resolution X-ray optical systems. This aperture is formed by the interaction of an electron beam with organic material to form a soft X-ray transparent contamination cone which is then ion milled to a diameter of less than 10 nm. Thick, wet and/or radiation sensitive specimens cannot be adequately studied using optical or electron microscopy due to resolution problems inherent in optical microscopy and sample preparation (especially vacuum compatibility) problems with electron microscopy. Soft X-ray microscopy, however, has great potential for filling this gap in analytical instrumentation [1].

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Contamination Resist Apertures for X-Ray Optical Systems

This article describes a method of using contamination nanolithography to form apertures of less than 10 nm in diameter for use in high resolution X-ray optical systems. This aperture is formed by the interaction of an electron beam with organic material to form a soft X-ray transparent contamination cone which is then ion milled to a diameter of less than 10 nm. Thick, wet and/or radiation sensitive specimens cannot be adequately studied using optical or electron microscopy due to resolution problems inherent in optical microscopy and sample preparation (especially vacuum compatibility) problems with electron microscopy. Soft X-ray microscopy, however, has great potential for filling this gap in analytical instrumentation [1]. The formation of images of living biological specimens with a resolution better than 10 nm is one particularly useful application of soft X-ray microscopy. For this application, X-rays with wavelengths around 3 nm would be used to take advantage of C, N and O absorption peaks near this wavelength. A method of forming a soft X-ray transparent aperture of less than 10 nm in diameter that is particularly useful in high resolution soft X-ray microscopy is described as follows. First, a thin layer of Si3N4 (nominally 100 nm thick) is deposited onto a Si wafer. The wafer is then etched from the back in certain places up to the Si3N4, leaving a free- standing Si3N4 membrane (Fig. 1). A 10 nm thick layer of Cr or some other metal is then deposited on the front of the wafer, followed by a one-micron-thick layer of Au (or some other high X-ray absorbing material) on the front of the wafer (Fig. 1). The thin layer of Cr promotes the adhesion of the Au to the Si3N4
. A film of resist several hundred nanometers thick with a 1 mm2 hole is then formed on top of the Au film using standard optical or electron beam lithography. Since the resist and the Si3N4 have much lower sputtering yields than the Au and Cr, subsequent ion-milling forms a 1 mm2 hole in the metal film that is not covered by resist 21 (Fig. 2). A sub-10 nm thick Cr film is then deposited on the back of the Si3N4 membrane, and an electron beam is focused onto it. The electron beam interacts with organic material at the Cr surface and forms a cone 22 of "contamination resist" [2] several 100 nanometers high. A contamination cone so formed can have a diameter of less than 10 nm. This diameter can be subsequently reduced by uniformly ion milling at a high angle relative to the longitudinal axis of the cone. After forming the contamination cone, several hundred nanometers of Au are deposited onto the backside of the wafer from an angle perpendicular to the wafer. Low angle ion milling removes the Au covering the top of the contamination cone 22, leaving the finished soft X-ray aperture (Fig. 2). The carbonaceous contamination cone appears relatively transparent to soft X-rays, while the Au appears opaque....