In case of vacuum depositing metal on the polyimide, the adhesion of thin sputter-deposited Cu film to dielectric substrate is of practical importance because Cu film deposited does not chemically interact with dieletric materials as oxide, polyimide, etc. For increasing the adhesion of Cu film to dielectric material, Cr or Ti, which is reactive metals, are used as the adhesive layer. But in case of using polyimide as the dielectric material, it is not enough to increase adhesion of Cu film to polyimide. And the method of improving the surface state has been investigating and using now. There are two kinds of method for improving the surface property of the polyimide. That is wet chemical etching using solution and dry etching using gas. RF sputter cleaning method which is one of the dry etching methods was selected for improving the surface property of polyimide. The condition of rf sputter cleaning was varied for investigating the effect on the adhesion between Cr and polyimide. The $O_2$ composition was varied for investigating the effect of $O_2$ in rf sputter cleaning gas and the time for investigating the effect of rf sputter cleaning time on the adhesion. The rf sputter cleaning power density was 0.14 W/㎠ in 10 mTorr pressure. When the Cr and the Cu is sputter deposited in 50 mTorr Ar pressure, the sputter deposition rate is 4.364nm/minute and 100nm/minute. The Cr thickness was 10nm, 20nm, 40nm and the Cu thickness was 3 ㎛. The electroplated Cu of 18㎛ thickness was added in order to provide enough strength of the film for a T-peel test.
The adhesion strength of Cr to polyimide was increased by using the rf sputter cleaning. The adhesion strength of Cr to polyimide was found to decrease with the $O_2$ composition. The adhesion strength had maximam value when rf sputter cleaning time was 1 minute. But the trend of the adhesion strength with rf sputter cleaning time less than 1 minute was not obtained. The largest adhesion strength may be residued in this time region. The adhesion strength was obtained to decrease with Cr thickness. And the trend of the decrease of the adhesion strength was obtained to be smaller in case of Ar rf sputter cleaning than $O_2$ rf sputter cleaning. These trend were likely happened due to the competion of the surface cleaning effect and the damage effect of polyimide surface layer by the ion bombardment. The increase of the surface roughness by the ion bombardment was not likely affected to the adhesion strength because there was not obtained to increase the adhesion strength with rf sputter cleaning time.
