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Browse Prior Art Database

Etchant Viscosity Control

IP.com Disclosure Number: IPCOM000044613D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Goubau, WM: AUTHOR

Abstract

Where fine line patterns are involved, etching performance can be improved with control of the viscosity of the etchant. Since the local etch rate depends on the local velocity of the etchant, the ultimate limitation on etch uniformity is set by the temporal and spatial variance from the mean of the velocity distribution. The higher the flow rate of etchant, the more difficult it becomes to control turbulence and hence etch uniformity. When an etch bath is thickened with chemically inert CAB-O-SIL S-17* (70-angstrom particles of SiO2) and the enhanced viscons drag is employed to strip the depleted etchant from the surface, high etch rates can be achieved at low flow velocities.

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Etchant Viscosity Control

Where fine line patterns are involved, etching performance can be improved with control of the viscosity of the etchant. Since the local etch rate depends on the local velocity of the etchant, the ultimate limitation on etch uniformity is set by the temporal and spatial variance from the mean of the velocity distribution. The higher the flow rate of etchant, the more difficult it becomes to control turbulence and hence etch uniformity. When an etch bath is thickened with chemically inert CAB-O-SIL S-17* (70-angstrom particles of SiO2) and the enhanced viscons drag is employed to strip the depleted etchant from the surface, high etch rates can be achieved at low flow velocities. As a particular example, CAB-O-SIL S-17, which is silicon particles, mixed 1:1 by volume with concentrated commercial FeCl copper etchant, has the consistency of honey. In the absence of agitation, the etch rate with the thickened liquid is about 10% less than that with unthickened liquid. Enhanced etch rates can be achieved by applying the thickened etch with a polishing motion, as shown in the drawing. The substrate to be etched is attached to a lapping ring moving over an etch-gel coated lint-free cloth on a flat glass plate. The substrate-cloth spacing, d, is 300-500 mm. At a given velocity, the smaller the d, the higher the shear force that strips the depleted etchant. The rough cloth prevents the gel from slipping over the glass plate. The etch rate is limit...