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# Apparatus for Evaporating Thin Coatings With In Situ Control of Thickness

IP.com Disclosure Number: IPCOM000089825D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 40K

IBM

## Related People

Fowler, AB: AUTHOR [+2]

## Abstract

Thin metallic coatings are required for devices that need both an electrical contact and the transmission of light. The electrical conductance and the optical transmission are strong functions of the thickness, and accurate control is required. If the usual evaporation rate monitors are used with their lowest useful evaporation rate, the evaporation times become very short and difficult to control for thin films (less than or equal to 100 Angstroms thick).

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Apparatus for Evaporating Thin Coatings With In Situ Control of Thickness

Thin metallic coatings are required for devices that need both an electrical contact and the transmission of light. The electrical conductance and the optical transmission are strong functions of the thickness, and accurate control is required. If the usual evaporation rate monitors are used with their lowest useful evaporation rate, the evaporation times become very short and difficult to control for thin films (less than or equal to 100 Angstroms thick).

Figs. 1 and 2 show the use of a rotating disk to effectively decrease the evaporation rate. If the angle of the slit is omega and the evaporation rate measured by the rate monitor is R(A), then the effective rate will be given by R(E) = R(A) Omega over 2PI with omega being as small as desired

An equivalent method would consist of rotating the sample instead of the disk with slit, as shown in Fig. 3.

Another approach is to provide an in situ thickness monitor for an additional means of control, as shown in Fig. 4. In this case the sample can be used for thickness monitoring, or a separate substrate can be provided. The thickness is measured by measuring the effect of eddy currents in the film on the impedance of the coil. As the thickness of the film increases, the resistance decreases, and this can be detected and used to control the film thickness.

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