Abstract
Vapor deposition polymerization (VDP) polyimide (PI) thin and ultrathin films were prepared and characterized in this dissertation. The main subjects were discussed as followed process and characterization of VDP - PI thin films, process and characterization of VDP - PI ultrathin films, the effect of various process parameters on VDP - PI films, the study of metal / polyimide interfaces. For the first part, markedly different characteristics were observed for the VDP - PI films when compared with the conventional ones. Thermogravimetrical analysis (TGA), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) results consistently showed that the VDP - PI filmswere somewhat less stable at the elevated temperatures.The VDP-PI films showed higher thermal and hygroscopic stresses and much lower water diffusion rate. They had imidized more markedly at lower curing femperatures. They remained intact in the etching solution employed when cured at 250℃ or above. Lithographic patterns of the films had been obtained by using a photolithography and wet - etching process. The dielectric constant and dissipation factor of the films were 3.5 and 0.012 at lk Hz testing frequency. The dielectric strength was from 2.0 to 3.2 MV / cm. For the second part, pinhole free properties, surface topologies, thermomechanical properties, hygroscopic stress, diffusion properties, and dielectric strength of the resultant ultrathin films were investigated. A testing device having a conductor / insulator (VDP - PI) / conductor multi - layered structure was developed to charactenze the corresponding pinhole free yield. Greater pinhole free yield had been obtained when using a gold electrode (top conductor layer). After annealing the top aluminum layer of the testing devices at 160℃ for 3 hrs, the yield greatly improved However, when top conductor layer was chromium or gold, the yield unchanged or even slightly decreased. Greater yield had been obtained when using an ITO - glass with a smoother substrate surface. The yield increased as the film curing temperature increased. The resultant films were made almost completely pinhole free for thickness of 250 A and 90% or more pinhole free for 180A. As estimated, the film can be reduced to 50A and still maintain a 75% pinhole free area. The surface became roughened when curing above 300℃. By using a bending beam technique and a ultrathin silicon substrate with a thickness of 5 □m, thermomechanical and hygroscopic diffusion properties were successfully characterized. The molecular struture of the films varied with the different film thicknesses and curing temperatures. A greater thermomechanical characteristic and thermal stress variation were observed in the thinner ultrathin VDP - PI films or when those films were treated at a lower curing temperature. The dielectric strength dropped which ranged from 0.25 to 1.9 MV / cm. For the third part, markedly different film structures were observed when different stoichiometric ratios, substrate temperatures, depossiton rates, and degrees of vacuum were used. Unreacted monomers were found in all the resultant films with the different stoichiometric ratios. The unreacted amount was the least when the ratio was close to 1. However, a higher yield of polyamic acid was obtained when either monomer was excess. Phase separation or crystallization was observed when excess amount of the unreacted monomers existed in the films. The deposition rate and unreacted monomers decreased as the substrate temperature increased. When the distance from boat to substrate increased, the deposition rate decreased but the unreacted monomers increased, the deposition rate decreased but the unreacted monomers increased. Greater deposition rate and less amount of unreacted monomers were observed at higher process vacuum. For the forth part, the interfaces of metal / PI were investigated, using AFM and secondary ion mass spectrometer (SIMS). The interfacial topographies were also markedly different for the different metals deposited. However, after annealing the metal / PI at 160℃ for 3hrs, interesting changes at the interfaces were observed. The roughness of the AI / PI interface was markedly reduced, while that of the Au / PI interface slightly increased. That of the Cr / PI interface almost unchanged.