Patterning polyimides

I would like to express thanks to Kathleen Ginn for excellent technical assistance In preparing patterned polyimide films. 

Figure 19. Process steps for patterning polyimides by wet etching and dry etching and for direct photopatterning of a photosensitive polyimide. The abbreviation PR stands for photoresist.

The second significant stage in the direct production of polyimide structures involves the thermal conversion of the patterned crosslinked film to the patterned polyimide film. It is important to understand how and under what condition the photo-crosslinked polyimide precursor is converted into polyimide as well as how completely. Mechanistically it is intriguing to determine wether the crosslinking fractures are split into small pieces or escape as pure hydroxyethylmethacrylate comparable to the zip-off depolymerization of polymethylmethacrylate. 

Thermal tempering of the photosensitive or cross-linked polymer gives the polyimide siloxane which has been previously shown to be an excellent candidate as an insulating polymer in electronics. The use of such a directly patternable polyimide for dielectric and passivation applications, particularly in microelectronics, should become increasingly important as polyimides become more widely accepted in the industry. 

Yabu, H., Tanaka, M., Ijiro, K., Shimomura, M. Preparation of honeycomb-patterned polyimide films by self-organization. Langmuir 19, 6297-6300 (2003)... 

The self-organizing nature of liquid crystal polymers is reflected in their complex flow behavior. The relaxation phenomenon of lyotropic polymer solution after shear cessation leads to band texture morphology that can be further induced to isotropic materials. Future research should focus on solvents influence on band size implicitly related to the induced pattern in polymers with different structures. Another aspect that could be explored is the imidization of patterned polyimide precursors and those conditions in which the texture is still maintained. 

Novel aspects in patterning polyimide surface morphology... 

A new approach for patterning polyimide, starting from its precursor, consists in using a lyotropic liquid crystal template,, namely hydrox) ropyl cellulose (HPC), which under... 

Figure 8. TEM and optical absorption of the sample implanted with 5 x 10 Au /cm (a) TEM cross-sectional micrograph (dashed lines represent the free surface and film-substrate interface) (b) nanoparticles size distribution (c) simulated optical spectra (1) Au cluster in a non-absorbing medium with n = 1.6 (2) Au cluster in polyimide (absorbing) (3) Au(core)-C(shell) cluster in a nonabsorbing medium with n = 1.6 (4) the experimental spectrum of Au-implanted polyimide sample, (d) X-ray diffraction patterns as a function of the implantation fiuence.

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

Schematic of the Si-nMEA fabrication process (a) sputter Au layer on double-side polished wafer (b) pattern Au layer with liftoff process (c) spincoat and cure a polyimide layer (d) perform the double-sided photolithography to pattern etch pits (e) etch Si in ICP-DRIE to form Au/Si electrode (f) dice the wafer into a single die (g) RIE etch the polyimide layer with a shadow mask to expose current collecting region (h) electroplate Pt black on Au layer (i) sandwich both electrodes with Nafion 112 in a hot-press bonder. (Reprinted from J. Yeom et al. Sensors Actuators B107 (2005) 882-891. With permission from Elsevier.)...

As insulation between the coil and the magnetic core, a hard-cured (to 200°C) photoresist insulator is patterned. It is a novolak polymer or polyimide about 5 fim thick, which is popular for its high insulator and photolithographic properties. This provides electrical insulation as well as a planar surface for subsequent deposition of copper cods. 

The present work is a report of the properties of polyimide which define functionality as an interlevel dielectric/passivant. Thus, the planarizing and patterning characteristics and electrical characteristics of current vs voltage, dissipation, breakdown field strength, dielectric constant, charge and crossover isolation are discussed in addition to the reliability-related passivation properties. 

A 3/8 inch diameter aluminum or titanium-tungsten dot pattern WLs fabricated on top of the cured polyimide film to make electrical leakage to substrate measurements for pinhole density estimation. An etch decoration technique was used to visually determine pinhole densities in polyimide films. The polyimide film was cast on substrates comprised of a layer of 200 nm thick alumimmi on blue colored field oxide with a grid pattern for area computation. Replicate holes were etched in the aluminum by a hot phosphoric acid solution. With the polyimide film removed, a good visual contrast was achieved for pinhole density counting. 

X-ray powder diffraction was recorded using a conventional x-ray powder diffractometer with Cu-Ka radiation. Polyimide film on which sample particles are deposited is glued on a glass sample holder with vacuum grease. Figure 1.6.9 shows the recorded diffraction pattern. An analysis of the pattern is made by comparing the lattice parameters and diffraction intensities of the particles and those of known iron compounds, and shows that the particles are Fe304. 

Fluorinated polyimide (PMDA/TFDB) and nonfluorinated polyimide (PMDA/DMDB) films prepared on a silicone substrate were introduced into an electron beam lithography system and subsequently exposed for square patterns (4x4 mm). The electron beam energy was 25 keV the beam current was 10 nA, and the beam dose was 300-1500 pC/cm. The 4x4 mm square was written by a 0.1-pm-wide electron beam. 

The structural anisotropy in crystalline or structurally ordered BPDA-PFMB films was studied in this laboratory with wide-angle X-ray diffraction (WAXD) methods. In brief, WAXD experiments were designed to examine both the reflection and transmission modes of thin-fihn samples. In addition, uniaxially oriented polyimide fiber WAXD patterns were obtained to aid in the identification of the film structure. The film WAXD pattern obtained from the reflection mode corresponded well to the fiber pattern scanned along the equatorial direction (Figure 16.3), " which indicates that the reflection mode pattern represents the (hkQ) diffractions. On the other hand, as shown in Figure 16.4, the (001) diffractions were predominant in the film WAXD pattern obtained via the transmission mode. This pattern corresponded to the fiber pattern scanned along the meridian direction. These experimental observations clearly indicate that the c-axes of the crystals are preferentially oriented parallel to the film surface however, within the film, they are randomly oriented. 4.2 5 j( should be pointed out that the WAXD experiments are only sensitive to crystalline or ordered structures in polyimide films. They do not provide any information on the amorphous regions. 

As a radical photoinitiator, we used 2-hydroxyisopropyl phenyl ketone (DAROCUR 1173 Ciba-Geigy), taken in an amount of 3 wt% based on polyimide (Scheme 5.13). The pattern of an exotherm obtained for the 1% solution of the polyimide (-X- = -O-), the high value of polymerisation enthalpy (352.4 J/g) and the short times of attaining the maximum peak (4.4 s) and the induction time (2.4 s) allow us to consider that this polyimide to be rather reactive from the point of view of polymerisation and formation of a crosslinked structure. 

---