| abstract |
A thin-layer metallization structure in which the final gold layer is deposited by evaporation with the surface onto which it is evaporated maintained at an elevated temperature. The thin-film metallization pad structure is deposited onto a substrate (12), typically made of a ceramic or glass-ceramic the assembly mask through opening (23) of a metal mask (24). The assembly mask substrate is placed in an appropriate evaporation system which is pumped down to about 0,13 10 ⁻³Pa and heated to about 200° C for 15 to 30 minutes in order to outgas the assembly. In turn, the substrate is heated to 150° centigrade and an adhesion layer such as 20 nm layer (11) of chromium is deposited. Next, a cushion layer (13), such as copper, and a diffusion barrier layer (15), such as titanium, are deposited sequentially still by evaporation as the subtrate cools from the initial temperature of 150° C to about 100° C. The copper layer (13) is about 6 microns thick and the titanium layer (15) is about 1 micron thick. Now, the substrate is reheated to 200° C and a gold layer (17') of about 1 micron thick is deposited by evaporation onto the structure. The heat is then turned off and the assembly allowed to cool to 50° C or less. The gold layer (17)' encapsulates the underlying multi-layer structure to prevent oxidation and diffusion of copper and in turn, prevent corrosion. By evaporating the gold layer at an elevated substrate temperature, the gold atoms have a higher mobility, so that the gold is spread over the edges of the structure for perfect coverage thereof. |