Browse Prior Art Database

New Alloy for Device Metal Masks/Or Silicon Masks

IP.com Disclosure Number: IPCOM000043298D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Christensen, RG: AUTHOR [+2]

Abstract

The evaporation of metal materials onto silicon wafers to add terminal connections to integrated circuit and device chips is a high temperature process presently involving the use of a molybdenum mask. The mismatch in thermal expansion characteristics between silicon (wafer material) and molybdenum (mask material) requires compensation to be designed into the mask in order to achieve acceptable aperture (pad hole or terminal via) registration during the metal evaporation process (Figs. 1 and 2). Fig. 1 shows the mask and wafer as aligned at room temperature and (after metal evaporation), when ready to separate wafer from mask. Fig. 2 shows the relative positions of mask and wafer during the metal evaporation step (high temperature). Note (Fig.

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New Alloy for Device Metal Masks/Or Silicon Masks

The evaporation of metal materials onto silicon wafers to add terminal connections to integrated circuit and device chips is a high temperature process presently involving the use of a molybdenum mask. The mismatch in thermal expansion characteristics between silicon (wafer material) and molybdenum (mask material) requires compensation to be designed into the mask in order to achieve acceptable aperture (pad hole or terminal via) registration during the metal evaporation process (Figs. 1 and 2). Fig. 1 shows the mask and wafer as aligned at room temperature and (after metal evaporation), when ready to separate wafer from mask. Fig. 2 shows the relative positions of mask and wafer during the metal evaporation step (high temperature). Note (Fig. 1) that the pad holes in the metal mask are closer to mask center at room temperature than are corresponding terminal vias. To overcome the compensation problem due to thermal mismatch, a special metal alloy formulation has been devised for use in mask fabrication which eliminates the need for temperature compensation in mask design. As disclosed, this metal alloy has a composition by weight N58% iron, N32% nickel, and N10% cobalt. It exhibits thermal expansion characteristics that closely match those of silicon over the desired temperature range, thereby eliminating the need of compensating for thermal mismatch. When coated with a thin coating of molybdenum, an alloy mask w...