Browse Prior Art Database

Electropolishing of Metal Film Structures

IP.com Disclosure Number: IPCOM000076529D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 15K

Publishing Venue

IBM

Related People

Pennebaker, WB: AUTHOR

Abstract

The methods disclosed involve the use of electropolishing to delineate metal-film structures in which the effects of local galvanic corrosion are greatly inhibited. In the methods disclosed, conditions are chosen such that the film is polished rather than etched. Under such circumstances, metal is removed selectively from the most exposed portion of a film and only slightly from areas where a protective overlay masks the structure.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 3

Electropolishing of Metal Film Structures

The methods disclosed involve the use of electropolishing to delineate metal-film structures in which the effects of local galvanic corrosion are greatly inhibited. In the methods disclosed, conditions are chosen such that the film is polished rather than etched. Under such circumstances, metal is removed selectively from the most exposed portion of a film and only slightly from areas where a protective overlay masks the structure.

Two distinct processes have been developed; one for the removal of films from a conducting substrate and the other for the removal of films from an insulating substrate.

Removal of films from a conducting substrate:

In this instance, the sample to be acted upon is immersed in an electrolyte with an electrical connection to a power supply. Once the sample is immersed, the supply is turned on establishing a potential between the sample and a cathode which is also disposed in the electrolyte. When the film is removed, the supply is turned off. As an example, consider a five-layer film structure which, starting from the top layer, consists of layers of gold, molybdenum, gold, molybdenum and nichrome disposed on a conducting substrate in which it is desired to delineate the top layer of molybdenum. The top layer of gold is first delineated by standard photoresist-chemical etching techniques and the remaining resist is removed. The sample is then clipped to an electrical lead and immersed in a room temperature electrolyte of concentrated sodium tetra ethylenediamine tetraacetate. A 5 volt potential is then established between the sample and a stainless-steel cathode and the molybdenum begins to polish. For a 1000 Angstrom molybdenum film, the etching time is about 24 seconds. The worst undercutting for these conditions is about 3500 Angstroms.

Removal of films from an insulating substrate:

In this instance, the film cannot be delineated by the preceding technique in that some portions of the film polish more slowly than others, and thus may lose electrical contact before they are cleanly removed. Once electrical contact is lost, polishing stops and islands of film remain. This problem is avoided by establishing a voltage on a sample before immersing into the electrolyte used. The sample is slowly lowered, forcing the film which first contacts the electrolyte to be removed first. Thus, a gradient in film thickness is established, and isolated conducting islands of film are avoided. Since the film removal is halted when the film becomes electrically discontinuous, a slight residue is left. In the instance of molybdenum, the residue can be removed by one or two five-minute exposures to ozone at a temperature of 250 degrees C, for example, followed by a water rinse. The rate at which the sample is lowered into the electrolyte should be sufficient to maintain the polishing action. Conditions which give excellent results for a gold and molybdenum sandwich on a sapphire subs...