Conductivities of polyimide films

Implications of Electronic and Ionic Conductivities of Polyimide Films in Integrated Circuit Fabrication... 

Sacher, E. The DC conductivity of polyimide film, p. 33, Proc. IEEE Conf. on Elec. Ins. Dielec. Phen., 1976... 

Metal ion modified polyimide films have been prepared to obtain materials having mechanical, electrical, optical, adhesive, and surface chemical properties different from nonmodified polyimide films. For example, the tensile modulus of metal ion modified polyimide films was increased (both at room temperature and 200 0 whereas elongation was reduced compared with the nonmodif ied polyimide (i). Although certain polyimides are )cnown to be excellent adhesives 2) lap shear strength (between titanium adherends) at elevated temperature (275 0 was increased by incorporation of tris(acetylacetonato)aluminum(III) (2). Highly conductive, reflective polyimide films containing a palladium metal surface were prepared and characterized ( ). The thermal stability of these films was reduced about 200 C, but they were useful as novel metal-filled electrodes ( ). 

The increasing importance of multilevel interconnection systems and surface passivation in integrated circuit fabrication has stimulated interest in polyimide films for application in silicon device processing both as multilevel insulators and overcoat layers. The ability of polyimide films to planarize stepped device geometries, as well as their thermal and chemical inertness have been previously reported, as have various physical and electrical parameters related to circuit stability and reliability in use (1, 3). This paper focuses on three aspects of the electrical conductivity of polyimide (PI) films prepared from Hitachi and DuPont resins, indicating implications of each conductivity component for device reliability. The three forms of polyimide conductivity considered here are bulk electronic ionic, associated with intentional sodium contamination and surface or interface conductance. 

Fig. 55. Hole ( ), electron (A) mobilities and conductivity (O) versus pyrolyze temperature for 12 hours of polyimide films [318]...

Adhesion of copper films to PMDA/ODA polyimide was determined by peel tests conducted on samples that were prepared by vapor-depositing a thin layer of copper onto the polyimide and then building the thickness of the metal layer to about 18 p,m by electrodeposition of copper. Results of the adhesion measurements correlated well with substrate pretreatment. When the substrate... 

There are several difficulties in the application of this technique to the analysis of sodium barrier properties of these polyimide films. First, as we have seen above, large shifts in the surface potential characteristics of MPOS structures can be associated with electronic conduction in the polyimide and charging of the polyimide-oxide interface. These shifts are not readily separable from any that might be caused by the inward drift of sodium ions. Second, the effect of the electronic charging process is to buck out the electric field in the polyimide which is needed to drive the ion drift mechanism. As seen in Figure 6, the electric field is reduced to very small values in a matter of minutes or less, particularly at the higher temperatures where ion drift would normally be measured. 

Pyrolyzed polyimide films at 480-530 °C can change the conductivity from 10-18 to 10 2 Scm-1 and mobility from 10-11 to 10 7m 2 V-1 s 1 (Fig. 55) [318], It has been shown that carrier density increases at the initial stage of the pyrolysis and then the increase of the mobility becomes predominant as the pyrolysis progresses. Hopping charge transfer is the main conductive mechanism. 

Polyimides. In situ co-deposition of metal salts such as Co(II), or LiCl into a polyimide precursor from 3,3, 4,4 -tetracarboxybenzophenone dianhydride and 4,4 -diaminobenzophenone with subsequent thermal curing offers surface-conductive polyimide film [43]. By similar procedures, Taylor et al. prepared a series of polyimides modified with Pd, Pt, Ag, Au, Cu, Sn, Ti and magnetic-Fe [44, 45, 46]. 

Profilometer measurements of the impacted specimens revealed general distortion of the film in and around the region of impact. By profilo-metric measurements on both sides of the film, the amount of wear in the contact zone was estimated. This technique provided a comparison of wear behavior to within 15 or 20 /mi. In several cases the experiments were continued until the film was worn through. In such cases the number of impacts to failure also provided a means of comparing wear behavior. In terms of these techniques it was found that the poly (vinyl fluoride) had the best wear resistance, followed by the polyimide. For example, tests conducted with the larger hammer indicated that for the same thickness, the poly (vinyl fluoride) had approximately one-half the depth rate of wear exhibited by the polyimide. 

PPy may be similarly coated on low-density polyethylene (LDPE), whereas grafting of the LPDE surface with acrylic acid enhances film growth and adhesion.86 The in situ oxidation of pyrrole by Fe(III) can also be used to deposit PPy films on polystyrene substrates.87 In a variation of this method, polyimide films exhaustively soaked in pyrrole (with up to 14% monomer uptake) have been coated with PPy via oxidation with FeCl3 in acetonitrile solvent.88 The resultant material shows electrical conductivity of ca. 4 x 10 2 S cm-1. 

The patterned and subsequently pyrolyzed polyimide films on silicon wafers adhered well to the substrate without cracking or peeling (Figure 2). The measured conductivity of the CPI was 10 (ohm-cm). This value is about ten times lower than that reported in reference (2) and is likely due to the relatively short test wafer heating period of 30 minutes. It is suspected that if higher temperatures or extended times during heat treatment are used, conductivity should increase by a factor of 10. 

At high temperature thermolysis (1270K) of cobalt acetate with PS, PAA, and PMVK present, the metal clusters that are catalyzing an oxygen electrolytic reduction had formed [98]. As the thermal decomposition of silver trifluoro-acetyl-acetonate at 613 K occurs in polyimide film [99-101], the film becomes metallized (a structure called film on film ) and a nanocomposite is formed with high surface conductivity and light reflection coefficient (above 80%). 

SnO containing films the bulk materials and cast-side surfaces were characterized as dielectric in nature with loss and conduction. The air-side charging characteristics, on the other hand, were markedly different from the volume mode charging characteristics. No short term polarization occurred in the samples implying little or no direct contribution from the polymer matrix to the air-side electrical properties. Also, the air-side electrical resistivity of BTDA-ODA polyimide films at room temperature was reduced substantially for both cobalt chloride modified and tin chloride dihydrate modified samples (i.e. six orders of magnitude and eleven orders of magnitude, respectively). 

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