Polyimide surface

It is necessary to prebake the PI film to 200°C to improve its resistance towards negative photoresist with a commercial stripper. After baking, remove the photoresist with a commercial stripper which is usually composed of phenol, strong mineral acids and solvents. 11) Neutralization and rinse. 12) final cure. Typical schedules are 30 min. at 350°C or 15 min. at 400°C. 10)PIasma,chemically etching) or physically (roughening) treat the polyimide surface to improve adhesion for next level metal. 

Compared with conventional photolithography, laser drilling is a dry process and keeps the surface of polyimide gate dielectric layer away from water, etching solution, or other solvent, which often degrade the polyimide surface. We have confirmed that the electronic performance of transistors with laser via holes is identical with that without laser via holes. 

Figure 2. Vibrational fingerprints from a polyimide surface (a) and (b) electron induced spectra of a sample as introduced, and after heating in vacuo, respectively (c) infrared optical absorption spectrum adapted from Ref. 8.

Summarizing, the very first A1 atoms deposited onto the polyimide surface do interact electronically with the carbonyl PMDA electrons and induce a conformation change in the ODA entities. 

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

Polyimide surface modification with KOH or NaOH aqueous solution is well defined. The reaction initially gives potassium or sodium polyamate which is then protonated with acid to yield polyamic acid. The outermost layer (5 A) of PMDA-ODA can be completely modified within a minute of reaction in KOH solution. The depth of modification can be measured by a method using an absorbance-thickness relationship established with ellipsometry and external reflectance IR. The modification depth of PMDA-ODA treated with 1 M KOH aqueous solution at 22 °C for 10 min is approximately 230 A. Surface topography and film thickness can be maintained while a strong... 

Further reactions of the functional groups in the modified polyimide surface as well as adhesion experiments on BPDA-PDA are under investigation. 

The polyamic acid surface has greater wettability than the polyimide surface. 

Laery, H.J. Campbell, D.S. "ESCA Studies of Polyimide and Modified Polyimide Surfaces" Photon. Electron, and Ion Probes ACS Washington, DC, 1981. 

There are additional reasons why the (arene)Cr(CO)3 compounds can be misleading as models for PMDA-ODA polyimide/Cr interactions. Formation of (arene)Cr(CO)3 compounds of model PMDA or ODA systems suggests that it-complexes can be formed at the polyimide surface in the early stages of metal deposition. But the (arene)chromium(tricarbonyl) complexes can give little additional chemical or physical insight into surface phenomena because the properties of... 

Previous studies have shown that a trend exists in the behavior of some evaporated metals on polyimide surfaces x-ray and ultraviolet photoelectron (XPS, UPS) as well as high resolution electron energy loss (HREELS) measurements have indicated that while for some metals such as aluminum, titanium and chromium there is bond formation with the PMDA carbonyl oxygen of the polyimide (2, 10-13). other metals such as copper, palladium and gold undergo little reaction or interaction (10,12,14,15). It has, however, since been postulated that metals, in order to adhere well at all to a polymer under a wide variety of conditions, must form metal- polymer bonds (10). 

Fig. 4 Suggested mechanism for the adsorption of Al on polyimide surface. The dot on the carbon is not a radical but indicates an increase of electronic density.

This paper describes a process for activating polyimide surfaces for electroless metal plating. A thin surface region of a polyimide film can be electro-chemically reduced when contacted with certain reducing agent solutions. The electroactivity of polyimides is used to mediate electron transfer for depositing catalytic metal (e.g., Pd, Pt, Ni, Cu) seeds onto the polymer surface. The proposed metal deposition mechanism presented is based on results obtained from cyclic voltammetric, UV-visible, and Rutherford backscattering analysis of reduced and metallized polyimide films. This process allows blanket and full-additive metallization of polymeric materials for electronic device fabrication. 

This paper describes a new seeding process for electroless metallization of polyimides and other electroactive polymers. Polyimide films can be reduced electrochemically at an electrode surface or by contact with an appropriate reducing agent in an electrolyte solution. In the latter case, only the outer surface of the film undergoes reduction. Once the polyimide surface is reduced it then can mediate electron transfer to metal ions or metal complexes in solution causing metal to be deposited at the surface with concurrent reoxidation of the polyimide. 

Redox-Mediated Metal Deposition. A reduced polyimide surface can function as a reducing substrate for subsequent deposition of metal ions from solution. For metal reduction to occur at a polymer surface, the electron transfer reaction must be kinetically uninhibited and thermodynamically favored, i.e., the reduction potential of the dissolved metal complex must be more positive than the oxidation potential of the reduced film. Redox-mediated metal deposition results in oxidation of the polymer film back to the original neutral state. The reduction and oxidation peak potential values for different metal complexes and metal deposits in nonaqueous solvents as measured by cyclic voltammetry are listed in Table III. 

Figure 5. RBS profile for a Kapton film prepared by reducing for 15 sec in a 5 percent reduced benzil/ACN solution followed by a 30 sec immersion in a 0.05 M PdCl2/DMF solution shows the presence of a Pd metal deposit at the polyimide surface.

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