Laser writing of high quality metal interconnects has been demonstrated by several authors. However, the use of this technique for customizing integrated circuits (ICs) has been very limited. One significant problem has been the contact resistance between the laser written metal and the existing IC metallization. The existing IC metallization is usually aluminum and spontaneously forms an oxide (-50 A) upon exposure to air. The high reactivity of aluminum in air precludes the use of cleaning to remove the native oxide thus preventing high quality contacts. Switching to a noble metal such as gold would solve the contact problem but would have several undesirable effects such as poor adhesion and increased cost. In this paper, we report on the use of refractory metal overcoats on aluminum metallization to solve the contact problem. Our laser written metal is gold obtained by the pyrolytic decomposition of a spin-on gold metallo-organic ink. The resistivity of the laser written gold is approximately 30 µS2-cm. With proper cleaning, the typical contact resistance between the refractory metal coated aluminum and the laser written gold is 30 S2 for a 3 gm x 3µm contact (-3 1.1i2-cm2). This value is sufficient for a wide range of IC interconnect problems. A significant advantage of this metallization is its growing use in the IC industry. This allows customizing and/or repairing ICs without requiring any specialized processing.

Date Published: 23 February 1990
PDF: 8 pages
Proc. SPIE 1190, Laser/Optical Processing of Electronic Materials, (23 February 1990); doi: 10.1117/12.963993

Published in SPIE Proceedings Vol. 1190:
Laser/Optical Processing of Electronic Materials
Jagdish Narayan, Editor(s)