Characterization of Polymer Thin Films Sputtered onto a Copper Substrate with Two Kinds of Polyimide Targets

Abstract

Polymer thin films were sputtered with two kinds of polyimide (PI) targets, pyromellitic dianhydride-oxydianiline (PMDA-ODA) and biphenyl dianhydride-p-phenylene diamine (BPDA-PDA), onto a copper substrate by a conventional RF sputtering with argon (Ar) and nitrogen (N₂). These polymer thin films were characterized, and their adhesion and tribological properties were evaluated.

Sputtering rate of the polymer thin film with PMDA-ODA target (sputtered PMDA-ODA thin film) with Ar was higher than that with BPDA-PDA target. Although the sputtering rate of the polymer thin film with the BPDA-PDA target (sputtered BPDA-PDA thin film) with Ar showed highest value at a pressure of 5 mTorr, that with N₂ showed highest value at a pressure of 60 mTorr. Nitrogen content in the sputtered BPDA-PDA thin film with N₂ increased compared to that of the sputtered BPDA-PDA thin film with Ar and target material (pristine).

Although friction coefficients of these sputtered BPDA-PDA thin films with Ar were almost the same as those of the pristine PIs, that of the sputtered BPDA-PDA thin film with N₂ was much higher than that of the pristine BPDA-PDA. The wear durability of the sputtered PMDA-ODA thin film with Ar was slightly higher than that of sputtered BPDA-PDA thin film. The wear durability of the sputtered BPDA-PDA thin film with N₂ was much higher than that of the polymer thin film sputtered with Ar.

The adhesion strength between the sputtered BPDA-PDA thin film with N₂ and copper substrate was higher than that between the thin film sputtered with Ar and copper substrate. In addition, the sputtered BPDA-PDA thin film with N₂ was introduced between the copper substrate and the sputtered BPDA-PDA thin film with Ar (Ar/N₂ laminate). The adhesion strength of this laminate was higher value than that between the sputtered BPDA-PDA thin film with Ar and copper substrate.

Keywords:

• adhesion strength
• copper substrate
• friction coefficient
• polyimide
• RF sputtering
• thin film, wear durability

Acknowledgments

The authors would like to thank Mr. Itsuo Nishiyama of DAIPLA WINTES CO. LTD for adhesion strength measurement of sputtered thin films with SAICAS.