In the microelectronics packaging, the adhesion strength between Cu and polyimide is very important factor that determines the device performance and reliability. However, the adhesion strength of Cu film to polyimide is inherently poor, so the Cr layer is used as an interlayer between Cu and polyimide to enhance the adhesion properties. To enhanced the adhesion properties, it is very important to understand the characteristics of adhesion test method because there are no way to measure the true adhesion strength. Peel adhesion test is the most popular adhesion test method, because it is simpler and easier than others.
To enhance the adhesion, the polyimide surface is treated by Ar ion or others. In the case of Ar ion treatment, the electric resistance of polyimide surface is decreased and the leakage of current occurs through the layer and it induces the electrical failures in the MCM package.
In this paper, at first, it was studied that the effects of adherend and pretreatment at various Ar+ rf plasma power densities on the peel adhesion strength. At second, the method to increase the adhesion without the plasma pretreatment was studied.
In chapter 1, the microstructure, mechanical properties and the relation between strain and X-ray peak broadening of adherend Cu films are presented. It is necessary to know the effects of thickness and mechanical properties of adherend on the peel strength. As adherend thickness, the electroplated Cu thickness, increases, the grain size increases but the defects decrease. The yield strength of adherend is proportional to the $t^{-1/2}$, t means thickness, and it may be caused by the grain size and defects. X-ray peak broadening, ΔFWHM, is proportional to the plastic strain parabolically.
In chapter 2, the effects of thickness, mechanical properties of adherend and pretreatment conditions on the peel strength were presented. As the Ar+ rf plasma power density is increased, the reactions between Cr and carbon in polyimide at the interface and plastic deformation of adherend are increased. The plastic work expenditure was estimated using K. S. Kim's theory, X-ray peak broadening of peeled adherend and the results in previous chapter. The results indicate that the plastic work expenditure is increased with Ar+ rf plasma power density and it behavior is similar to the peel strength. Also the peel strength is strongly affected by the film thickness and the pretreatment condition in a synergistic way, and that the peel strength shows a maximum at an intermediate thickness level. The estimated work expenditure was close to measured peel strength for most of the cases, which indicates that the measured peel strength is more a measure of the plastic deformation during the peel test than a measure of the true interfacial fracture energy.
The peel strength is decreased as the ultimately tensile stress is increased, because it is hard to deform the adherend plastically.
In chapter 3, the effects of heat treatment on peel strength are presented. The peel strength is increased as the heat treatment time and temperature are increased without regard to the pretreatment conditions. Also the failure locus is shifted to the interior to the polyimide by heat treatment.
