The adhesion of thin sputter-deposited Cu film to dielectric substate using a Cr adhesive layer is of practical importance in the microelectronics industry in many applications such as multilayer packaging.
In the present investigation the sputter-deposited Cr/Cu thin films on alumina substrates were evaluated by the peel adhesion test as a function of Cr thickness. Cr and Cu were successively deposited onto the water-cooled substrate at the Ar pressure of $5\times10^{-2}$ torr using a three-target DC magnetron sputtering unit. The Cr thickness varied from 20 to 550 nm, but the total thickness of the sputtered Cr/Cu film was fixed at 1 ㎛. The electroplated Cu of 47㎛ thickness was added in order to provide enough strength of the film for a peel test.
The adhesion strength increased with the Cr thikness and then decreased. The maxmimum peel strength of over 500 g/mm was obtained when the Cr thickness was 150 nm. SEM and AES studies were carried out to analysis the adhesion data. The initial increase of peel strength with the Cr thickness seems to be releated to the Cr coverage on the relatively rough substrate surface and the decreasing peel strength in the thicker Cr films was due to the elasto-plastic deformation of the metal film during peeling.
