An effective diffusion barrier metallization process on copper

Ww. So et al., An effective diffusion barrier metallization process on copper, THIN SOL FI, 376(1-2), 2000, pp. 164-169
Citations number
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Material Science & Engineering
Journal title
ISSN journal
0040-6090 → ACNP
Year of publication
164 - 169
SICI code
Copper substrates have been widely used to mount semiconductor device chips due to their high electrical and thermal conductivity. To achieve high hea t conduction, solders are utilized to bond the chip on the substrate. Soft and ductile solders such as indium and lead-tin alloys are often used to he lp release the stress developed in a bonded structure through plastic defor mation and strain. In the solder joint, a major concern is the formation of intermetallics caused by the diffusion of copper atoms from the substrate to the joint. The growth of intermetallics makes the solder joint less duct ile and less capable of releasing stresses. Prevention of copper diffusion is needed in applications where the solder joint must remain soft and ducti le. On the other hand, in applications where creep movement cannot be toler ated, hard solders such as AuSn eutectic alloy should be considered. In thi s paper, we report a barrier metallization technique on copper substrates t o block copper atoms from diffusing into the solder. Indium was selected as the solder medium in this study because of its increasing applications in many photonic devices such as laser diodes and photonic switches. Other sol ders such as lead-tin alloys can be also used with the metallization proces s. The metallization consists of Ni buffer layer and Cr blocking layer. The solder joint is fabricated by the fluxless bonding technology. After accel erated aging test at 130 degreesC for 100 h, no sign of copper diffusion th rough the metallization is detected using energy dispersive X-ray (EDX). If 90 degreesC is the maximum temperature of the solder joint during device o peration, the corresponding time for no copper diffusion is 107 500 h, or 1 2.3 years. This result shows that the metallization process developed in th is research is, indeed, very effective. (C) 2000 Elsevier Science S.A. All rights reserved.