Film thickness polyimides

Baseline Process. DuPont PI2545, PI2555 and Hitachi PIQ as received from the manufacturer, were spun in a class 100 clean room environment at appropriate spin speeds to achieve 0.5 - 6 y film thickness. The silicon wafer substrates were pre-spun (5K rpm, 30") with 0.05% DuPont VM651 (y-amino propyltriethoxy silane) adhesion promoter in 95/5 (v/v) methanol/HzO. The polyimide film cast on the silane-coated silicon wafer was pre-baked... 

Figure 5. Dissipation factor D at 1 MHz vs. time at a specified temperature for a 1-ftm thick polyimide film.

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. 

Figure 2. Film thickness dependence of polyimide pin holes. Key (polyimide type) DuPont Type I—O and o, electrical and A, visual Hitachi PI— , electrical and 0, visual ---------, l-juw wool filtered and-, as received.

FDA-PFMB was used to study the effects of molecular weight and film thickness on the UNB. poj- fixed-molecular-weight samples, the refractive indexes were constant for film thicknesses below 15 pm. As the film thickness was increased above this value, the in-plane refractive index decreased, while die out-of-plane refractive index increased. On the other hand, the refractive index along the out-of-plane direction decreased while die in-plane refractive index increased when the polyimide molecular weight was increased as shown in Figure... 

Fig. 3.10. Experimental (dotted lines) and best-fit model (solid lines) IRSE spectra of a PLD-grown (0001) ZnO thin film on (001) silicon (panel (a), film thickness d 670 nm), and magnetron-sputtered ZnO thin films on metallized polyimide foil (panel (b), d 500nm) and on metallized glass (panel (c), d 30nm) [43]. ZnO phonon-mode frequencies, as obtained by best-model analysis, are marked by vertical arrows...

Y. Sano [107] described the influence of the film thickness, 8, on the drying course of water-moist polyimide films. In thick films (6 = 1 mm), the liquid-side diffusion plays an important role from the very beginning. The surface concentration quickly drops off to an equilibrium value and the temperature at the film surface increases to the drying air temperature, without reaching a constant steady-state goods temperature. A period of constant drying rate does not appear. 

Attaching thin adherent titania films to polyimide polymers demonstrates the promise of such coatings as barrier layers. Potential applications must examine the effect of the deposition process on the mechanical and thermal properties of the polymer and the requisite thickness of the ceramic layer. Nevertheless, the low-cost and convenience of LPD coatings, their mild conditions and their lack of line-of-site limitations, recommend their use. 

These principles were used to assign Cls, Ols and Nls NEXAFS spectra of polymers important to the microelectronics industry. Interpretation of polyamic acid and polyimide spectra were aided by assigning the spectra of simpler polymers and monomers. The compounds studied in the form of spun films were poly(vinyl methyl ketone) (PVMK), poly(dimethyl phenylene oxide) (PMPO), poly(pyromellitimido 4,4-methylene bis-cyclohexyl amine) (PMDA-MBCA PI), and poly(pyromellitimido oxydianiline) (PMDA-ODA PI) and in the form of MBE-deposited films were poly(amic acid) (PAA), and PMDA-ODA PI. Changes in the NEXAFS spectra as a function of evaporated Cr overlayer thickness were measured for PVMK, PMPO and PMDA-ODA PI. Evolution of the NEXAFS spectra as a function of deposited organic film thickness and thermal treatment were measured for PAA on Cu and Cr substrates. 

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. 

Methods. Polyamic acid in NMP was spin-coated onto a Si or Quartz wafer (diameter = 2.25 inches) coated with Cr, and then cured to polyimide at 400 °C. The purpose of the 500-750-A-thick layer of chromium is to enhance wettability and to give good reflectance to the Quartz wafer. Kapton H (PMDA-ODA) and Upilex S (BPDA-PDA) films were employed for gravimetric analysis. Around 5-um thick layers were used to measure the thickness change. The 100-1000-A-thick layers were employed to obtain XPS and ER IR spectra. The samples for contact angle measurement, XPS and ER IR were dried under vacuum at ambient temperature for 12-24 h and the samples for gravimetric analysis were dried at 85 °C for 12 h. The samples for film thickness measurement were fully re-cured to polyimide. 

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... 

Sample Preparation. PMDA-ODA polyimide films were prepared by spin coating polyamic acid onto silicon wafers and curing to 360°C for 1 hour. The cured film thickness was approximately 10 pm. These samples were treated downstream of an 85% CFi -15% 02 microwave plasma for 30 minutes to produce a fluorinated layer, approximately 600 thick (16). Fluorinated layers less than 600 thick were obtained by additional treatment downstream from an 02 rich (85%) microwave plasma for various times. PTFE films (25 pm thick) were used as received from E. I. duPont de Nemours Inc. 

In figure 7 we show Infrared-Reflection Absorption data for a thin polyamic acid film (a), a thin polyimide film (b) (after curing the PAA film of spectra a) and a thick (d > 10 nm) polyimide film (c) on a polycrystalline silver surface. Transmission and reflection infrared absorption spectra of thick (d > 1000 nm) spun-on polyamic acid and polyimide films have been reported previously [22-24], Salem et al. [2] presented in their pioneering paper the infrared transmission spectra for vapor deposited polyamic acid and polyimide. Except for the relative intensities between the individual absorption bands, our results for a thick polyimide film (Fig. 7c) are identical to those for spun-on and vapor deposited films, showing the unresolved symmetric and asymmetric (strong) vc Q stretches between 1700-1800 cm 1, the v (l,4-CgH4) ring... 

This universal film thickness equation immediately unifies all prior apparently conflicting film thickness data correlations. For example, one of the recurring sources of controversy and confusion in the literature is the observed variability of the exponent p in empirical and semi-empirical correlations of the form h 1/to. Some have generally assumed that p = 1/2 while others argue that p 2/3 (11,17). On the contrary, the observed values of the exponent p is in the range of 0.40-0.82 for various photoresists, electron beam resists, polyimide coatings, etc. 

Figure 4. Experimental and calculated dry film thickness of polyimide thin films deposited on silicon wafers.

Mono- and multilayer films of polyimides were successfully prepared using Langmuir-Blodgett technique. Monolayer films of polyamic acid long alkylamine salts were prepared at the air-water interface. The mono-layer films were deposited on appropriate plates to produce multilayer films of the precursor to polyimide films. Finaly, the polyimide multilayer films were obtained by treatment of the multilayer films of the polyamic acid amine salts with acetic anhydride and pyridine. The polyimide multilayer films had excellent coating ability giving a very smooth surface. They also exhibited insulating characteristics as reliable as polyimide thick films. 

Wholly aromatic polyimides are highly thermally stable engineering plastics, and have been widely used as the reliable insulating materials in microelectronics. Recent developments in this field toward higher integration of devices required ultra thin films of polyimides. Minimum thickness of polyimide films cast by spin coating was about 0.1 Urn. 

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