Title

Back-etch method for plan view transmission electron microscopy sample preparation of optically opaque films

Authors

Authors

B. Yao;K. R. Coffey

Comments

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Abbreviated Journal Title

J. Electron Microsc.

Keywords

back-etch method; TEM; sample preparation; Si; opaque films; Microscopy

Abstract

Back-etch methods have been widely used to prepare plan view transmission electron microscopy (TEM) samples of thin films on membranes by removal of the Si substrate below the membrane by backside etching. The conventional means to determine when to stop the etch process is to observe the color of the light transmitted through the sample, which is sensitive to the remaining Si thickness. However, most metallic films thicker than 75 nm are opaque, and there is no detectable color change prior to film perforation. In this paper, a back-etch method based on the observation of an abrupt change of optical reflection contrast is introduced as a means to determine the etch endpoint to prepare TEM samples for these films. As the acid etchant removes the Si substrate material a rough interface is generated. This interface becomes a relatively smooth and featureless region when the etchant reaches the membrane (film/SiO2). This featureless region is caused by the mirror reflection of the film plane (film/SiO2 interface) through the optically transparent SiO2 layer. The lower etch rate of SiO2 (compared with Si) gives the operator enough time to stop the etching without perforating the film. A clear view of the morphology and control of Si roughness during etching are critical to this method, which are discussed in detail. The procedures of mounting wax removal and sample rinsing are also described in detail, as during these steps damage to the membrane may easily occur without appropriate consideration. As examples, the preparation of 100-nm-thick Fe-based amorphous alloy thin film and 160-nm-thick Cu-thin film samples for TEM imaging is described.

Journal Title

Journal of Electron Microscopy

Volume

57

Issue/Number

2

Publication Date

1-1-2008

Document Type

Article

Language

English

First Page

47

Last Page

52

WOS Identifier

WOS:000253856100002

ISSN

0022-0744

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