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Determining the Strain Distribution Normal to Film Plane in Thin Film Deposited Onto the Substrate

IP.com Disclosure Number: IPCOM000088161D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Angilello, J: AUTHOR [+2]

Abstract

This technique is used to determine the strain distribution normal to the film plane in thin Pb films which were deposited onto Si wafers. It involves analyzing the asymmetric peak profile of the single X-ray Bragg reflection.

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Determining the Strain Distribution Normal to Film Plane in Thin Film Deposited Onto the Substrate

This technique is used to determine the strain distribution normal to the film plane in thin Pb films which were deposited onto Si wafers. It involves analyzing the asymmetric peak profile of the single X-ray Bragg reflection.

Failures of Josephson devices are caused by local strains which are introduced when devices are thermally cycled between room and liquid helium temperatures because of the thermal expansion coefficient difference between the film and the substrate. In order to eliminate these device failures, it is required to reveal the strain distributions in thin film parallel and/or normal to the film plane.

Strain distribution parallel to the film plane was evidenced by the existence of hillocks. However, the distribution or inhomogeneity normal to the film plane is not yet clarified because there exists no technique to measure in situ strains without destroying the specimen. Warren and Auerbach's X-ray diffraction technique (J. Appl. Phys. 21, 595 (1950)) determines the "average" local microscopic strains normal to the reflecting or film surface plane, but it is applicable only when the local strains are uniformly distributed throughout the sample, i.e., only when local strain variations are the same at the positions close to the film surface and close to the substrate interface. Thin Pb film deposited onto Si substrate is expected to have the nonuniform strain distribution normal to the film surface, i.e., large strains at the substrate interface and small strains at the film surface when the specimens are cooled down to desired temperatures. Such strain inhomogeneity cannot be analyzed by Warren and Auerbach's technique.

Described is a nondestructive technique for determining the nonuniform strain distribution normal to the film surface for one micron thick Pb film deposited on the Si wafer by analyzing the measured X-ray (333)-reflection peak alone. The (333)-reflections were measured for the film which was cooled down and measured at 78 degrees K. In the K(alpha 1) intensities (deconvoluted by Rachinger's technique [1], an asymmetric profile is observed, indicating the nonuniformity of strains normal to the film surface. In order to explore the strain inhomogeneity in this thin film the intensity calculation was carried out based on an assumption that the strain variation changes exponentially from one film surface to the other [2]. A compu...