Volume Change due to Intermetallic Compound Formation at the Al-Au Bond in Semiconductor Devices

Abstract

The molar volume of an Al-Au intermetallic compound was calculated and compared with those of Al and Au individually. It is well known that, though the molar volume of an AlAu₄ compound is smaller than the sum of those of Al and Au, it is larger than that of Al. It is shown that this fact can be explained by taking into consideration the differences between the densities of Al, Au and Al-Au alloys and the component ratio of the compound. Practically, it is pointed out that this volume effect can induce pores at an imperfect bond between Al films and Au wires in Si devices. This suggests that such partial openings should be distinguished from Kirkendall voids.