Polyimide metal films

This observation is further dramatized by some rather limited isothermal measurements on selected films (TABLE III). This data is typical of the metal ion filled BTDA + p,p -DABP poly-imides which we have examined. No changes in chemical functionality in the polyimide-metal film were apparent as judged by infrared spectral comparisons of polyimide alone and polyimide plus metal regardless of the metal employed. 

Integration of Cu with a dielectric introduces new problems and challenges [1(b), 34-36] (Fig. 19.8). For example, if polyimides are used as intermetal dielectrics, reliability concerns are corrosion of underlying metal and adhesion of metal films to polyimide underlayers [1(b)]. 

Materials. Biaxially oriented polypropylene (PP) films of 50 um thickness were obtained from 3M and have been described (2). PMDA-ODA (PI) was Kapton H polyimide from Dupont. Copper-plated PTFE films were obtained from Spire Corporation (Bedford, MA). They were prepared using the Ion Beam Enhanced Deposition (IBED) process in which a 100 nm thick Cu film was vapor-deposited onto a PTFE substrate in the presence of a beam of 400 eV Ar+ ions of 25 uA/cm2 (IQ). Shortly before SIMS analysis, the Cu film was removed slowly by peeling at 90° in ambient conditions. Metal-coated PI films were prepared by sputtering 50 nm Cr and 1 um Cu onto a 50 um thick Kapton film on both sides. Thermal annealing was performed in a vacuum chamber at 2xl0 6 torr using a quartz lamp as the heating source. The samples were held for 15 min at the desired temperature and then cooled down to ambient temperature inside the chamber for about 2 hours. Just prior to SIMS analysis, the metal films were peeled slowly at 90° and then immediately introduced into the vacuum chamber of the instrument. 

Polvimide-Metal Interfaces. Several technological applications including semiconductor packaging and metallization demand a reliable and durable adhesion properties of the metal films. In the development of multilayer devices consist of alternating layers of metal and polyimides several reliable techniques are needed to study both thin films and their interfaces. The usefulness of the nuclear scattering techniques to study the metallization and the associated interfacial elemental diffusion processes under the effects of various temperature and humidity treatments on the metal-polyimide systems, such as Al, Cu, N, and Au on Du Pont Kapton type H have already been reported (21., 22.). Only a couple of examples are presented here to illustrate the ERD application. 

A more dramatic failure results in peel strengths of 0-10 g/mm and is characterized as an adhesive failure at the polyimide/metal oxide interface.This was the only failure mode observed in Ti and Zr films. Isotopically tagged water used with SIMS analysis shows that on annealing water reacts with the Ti with oxygen segregating to the metal/polyimide interface and hydrogen penetrating into the bulk of the Ti, in these samples. 

In order make an effort to bring the polyimide-metal adhesion problem to an even more fundamental level, we have previously proposed that model molecules, chosen as representative of selected parts of the polyimide repeat unit, may be used to predict the chemical and electronic structure of interfaces between polyimides and metals (12). Relatively small model molecules can be vapor deposited in situ under UHV conditions to form monolayer films upon atomically clean metal substrates, and detailed information about chemical bonding, charge transfer and molecular orientation can be determined, and even site-specific interactions may be recognized. The result of such studies can also be expected to be relevant in comparison with the results of studies of metal-polymer interfaces. Another very important advantage with this model molecule approach is the possibility to apply a more reliable theoretical analysis to the data, which is very difficult when studying complex polymers such as polyimide. 

The deposition of metals such as Pd, Pt, Ni, and Cu renders the surface active towards further metal deposition from conventional electroless metal plating baths. Well-adhering metal films can be formed on polyimides by this method. The main process steps for blanket metallization of a polyimide film, illustrated in Scheme I, involve polymer reduction, metal seeding, and electroless metal plating. Specific details of each process step are provided in the discussion below. 

Metal thin films deposited on polymers are widely used in various industrial domains such as microelectronics (capacitors), magnetic recording, packaging, etc. Despite much attention that has been paid in the recent literature on the adhesive properties of metals films on polyimide (PI)( 1 - 5 ) and polyethyleneterephtalate (PET)((L) it appears that a better knowledge of the metal/polymer interface is needed. In this paper we focus ourself on the relationship between the adhesion and the structural properties of the aluminum films evaporated (or sputtered) on commercial bi-axially stretched PET (Du Pont de Nemours (Luxembourg) S.A.). A variety of treatment (corona, fluorine,etc.) have been applied in order to improve the adhesion of the metallic layer to the polymer. The crystallographic... 

A number of cell designs have been employed in EXAFS studies of electrochemical systems. Of these, two general types can be identified depending on whether a transmission or a fluorescence mode of detection is employed. In a transmission mode, cells should be designed so as to minimize absorption losses due to the window material, elecrolyte, and the electrode itself. As a result, the windows are typically made of thin films (25/an) of low absorbing materials such as polyethylene and polyimide (Kapton). The electrolyte layer thickness is typically small, and electrodes are generally metal films evaporated on a thin polymer film or small particles dispersed in a low Z matrix. Carbon can be employed in a variety of forms and shapes because of its low absorption. 

Electrochemical cells for x-ray absorption spectroscopy (XAS) must be designed to minimize absorption losses in the cell windows and electrolyte. Thus, cell windows are typically thin films of polyethylene or polyimide, and only thin layers of solution (—10 pirn) are used. The sample itself must be sufficiently thin (e.g., a metal film no thicker than a few microns on a transparent substrate) that appreciable transmission is observed (165). 

Fig. 1. Structural Model of Polyimide/Metal Composite Films.

Thin-film flexible electrodes such as shown in Figure 4.4g have been used for monitoring neonates. They are basically the same as the metal plate electrodes only the thickness of the metal in this case is less than a micrometer. These metal films need to be supported on a flexible plastic substrate, such as polyester or polyimide. The advantage of using only a thin metal layer for the electrode lies in the fact that these electrodes are x-ray transparent. This is especially important in infants, in whom repeated placement and removal of electrodes, so that x-rays may be taken, can cause substantial skin irritation. 

Fig.5. Measured fracture energy for thin metal films debonded from (un)treated polyimide...

The substrates or support coated on include paper and paper board, cellophane, polyCethylene terephthalate), poly(ethylene naphthalate), polyethylene, polypropylene, polystyrene, polyCvinyl chloride), polyCvinyl fluoride), poly(vinylidene fluoride), polyimide, metal foils, woven and nonwoven fabrics, fibers, and metal coils. The surfaces of these supports can be impervious as in plastic films, or there may be a pore structure such as in paper. Primer coatings... 

Laser-based etching has been used to define feamres by ablation process. It is particularly useful for polymers, dielectrics, metals, and semiconductors. Examples of laser-assisted chemical etching and laser ablation include patterning of polyimide and thin metal films [42]. 

Polyimides are known as good insulators with high thermal stability for microelectronics. Ultrathin films of polyimides were obtained by the LB technique [306,307]. The film was almost pin-hole free with a smooth surface [308] and the conduction mechanism in MIM (metal-insulator-metal) configuration was examined [309]. An electrical memory switching phenomenon was also observed in polyimide LB film incorporated in MIM devices [310]. 

Kreuz and Zytkus reported corona treatment of FEP under an atmosphere of acetone (<5%—40% by volume in nitrogen), which had the advantage over the previous atmospheric compounds of producing a film that did not block in roll form. Treated FEP could be printed and marked with inks, was heat sealahle, and adhered well to metals. Adhesion of FEP film (25 p.m thick) to metal was accomplished by first laminating it to a thin polyimide (PI) film (13 p.m thick) using a nip roll at 250—270 °C and at a pressure of 270 kPa. The treated FEP surface was then laminated to a 13-p.m-thick (Fig. 5.12) aluminum foil in a nip roll at a speed of 6—9 m/min. In some cases, the laminate was postheated to test the effect of heat on the bond strength and the locus of bond failure (Table 5.5). 

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