Interfacial behavior of Cr–Au films in the 423–573-K temperature range

Abstract

Thin film layers of Cr–Au were subjected to temperatures in the range 423–573 K for various periods of time and the morphology of the Cr layer was examined with optical and scanning electron microscopy. A preferential depletion of Cr was found beneath the Au grain boundaries and intergranular spaces which was not fully compensated by diffusion of Au into the Cr. Since the Au grain boundaries intersect, this results in islands of remaining Cr surrounded by a labyrinth of voids or channels. This phenomenon renders the entire Cr–Au interface vulnerable to the entry of corrosives. By using transmission optical microscopy in conjunction with a photometer, the optical transmission of the Cr layer was measured and related to the Cr depletion as a function of time and temperature. From these measurements two mathematical models were devised to calculate the activation energy for the Cr diffusion resulting in values of 1.30 and 1.36 eV, respectively.

Gold/chromium metallizations for electronic devices

“…This bulk contamination of gold by chromium results in resistivity increases of 25 per cent in only 2 hours at 300°C. Another effect of grain boundary diffusion was first noticed by Kendrick (33) and then studied in detail by Hampy et al (37). As a result of diffusion, chromium is preferentially removed from the adhesion layer where gold grain boundaries emerge.…”

“…The facts that only samples stored for appreciable times exhibited failure and that failure rates peaked in spring and summer when humidity was high point to a significant part played by environmental conditions. Not unexpectedly, the chromium-depleted labyrinth observed by Hampy et al (37) increases the danger of corrosion. The small interconnecting network of voids allows liquid formation at lower relative humidities and reduces the areas over which corrosion must occur in order to cause loss of adhesion.…”

“…Thus, the pattern of chromium islands separated by a labyrinth of voids, which is arrowed here, resulted. After (37) voids is connected to the environment at the edge of conductors, corrosion of the remaining chromium islands' may be greatly enhanced as discussed below.…”

Adhesion of Ni-structures on Al 2 O 3 ceramic substrates used for the sacrificial layer technique

“…Similarly sputtering of the chromium layer at low temperature (<100°C) leads to a porous surface (zone I) and consecutively to a decrease of adhesion of the gold layer, since the surface of the substrate is not covered completely with the bonding agent. Loss of adhesion also occurs, if the sputter temperature is higher than 200°C, because chromium diffuses into the gold layer [3] and the effect of the adhesive agent is lost. Because of the long sputtering process, the temperature of the substrate increases up to 400°C (Fig.…”

“…For starting electroforming it is necessary that the surface of the substrate is electrically conducting. This can be performed by sputtering a combination of a thin chromium/gold layer (5 nm/1.6 lm), which is used as the conductive layer on ceramic substrates for hybrid microcircuits as well as for semiconductor applications [3]. The gold acts as a conducting seed layer and the chromium as a bonding agent between the substrate and gold.…”