Browse Prior Art Database

Relieving Thermal Expansion Mismatch

IP.com Disclosure Number: IPCOM000073349D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Bertelsen, BI: AUTHOR [+2]

Abstract

In the vacuum deposition of contact metallurgy through an apertured mask onto a semiconductor wafer, it is necessary to maintain the apertures in the mask in dimensional alignment with the contact areas on the semiconductor wafer. Typically, a molybdenum mask is employed for this purpose. Since silicon and molybdenum have different coefficients of expansion, changes in dimensional registration do occur, which are significant in the case of very small dimensions employed.in advanced integrated circuits.

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Relieving Thermal Expansion Mismatch

In the vacuum deposition of contact metallurgy through an apertured mask onto a semiconductor wafer, it is necessary to maintain the apertures in the mask in dimensional alignment with the contact areas on the semiconductor wafer. Typically, a molybdenum mask is employed for this purpose. Since silicon and molybdenum have different coefficients of expansion, changes in dimensional registration do occur, which are significant in the case of very small dimensions employed.in advanced integrated circuits.

These changes in dimensional registration may be eliminated by placing the mask under planar, isotropic tensile stress, then allowing the stress to be relieved at elevated temperatures, rather than permitting dimensional changes in the mask relative to the wafer. This may be done by brazing a ring of the same material as the mask around the periphery of the mask while elevating the ring to a lower temperature than the mask, or by using a material having a different coefficient of expansion than that of the mask and heating the mask and ring to the same temperature during brazing. Upon cooling the mask and ring assembly, the desired stress is imparted to the mask. During use in vacuum evaporation, as the mask is heated, the stress is relieved, rather than dimensional expansion of the mask (relative to the wafer) taking place. Depending on the temperatures and/or materials employed, dimensional expansion can either be eliminated o...