Polymer surfaces play essential roles in many technical arenas, but their importance in imaging science and technology has only recently been established. As optical lithography for integrated circuit applications pushes below 0.5μm feature sizes, ever shorter wavelengths and lenses with larger numerical aperatures are required. These narrow the depth-of-focus to such a degree that it eventually becomes less than the substrate topography, resist film thickness and wafer nonuniformity contributions to focus placement. Thick single-layer, surface-conforming resists will not be able to record the aerial image accurately.

Surface imaging of planarized single-layer or bilayer organic films offers a means for minimizing the depth-of-focus constraints. This paper outlines this general concept which includes radiation-induced chemical changes in the surface and near-surface regions, amplification of these events by gas-solid reactions with inorganic and organometallic agents and plasma development using an oxygen plasma. Two approaches to surface imaging are discussed. The first employs Plasmask® resist, a very absorbing diazonaphthoquinone-functionalized novolac resin which is exposed and functionalized in the topmost several hundred nm of film. According to Coopmans, Roland and coworkers [14] and Pierrat, et al., [22] two tones are possible depending upon the processing. The present study reports results obtained for both processing modes using 248.4 nm lithography.

The second approach involves imaging at the surface and utilizes one of the oldest polymer photoreactions, photo-oxidation, in the imaging step. Hydrophobic aromatic polymers are first irradiated in air to give hydrophilic groups. These sorb water selectively on the hydrophilic areas. The water is reacted in a separate step with an inorganic or organometallic compound such as TiC14 to give a metal oxide film (TiO2) on the exposed areas. Development with an oxygen plasma gives negative tone patterns because TiO2 reduces the etching rate by a factor of ∼ 500 in the exposed regions. Imaging is dependent upon the polymer structure, among other things, and is optimized at shorter wavelengths likely to be used in future exposure systems. From the present results we feel that surface imaging resists may realize 0.25 μm resolution at 193 nm and that <0.10 μm resolution may be achieved using x-ray radiation.

The surface chemistry of dimethylaluminum hydride (DMAH) and trimethylaluminum (TMA) on aluminum has been investigated with temperature programmed desorption (TPD), and Auger electron spectroscopy (AES). The TPD spectra of TMA shows a single desorption peak with a peak maximum which shifts from 190 to 200 K for surface coverages of 0.5 and 2.0 monolayers (ML) respectively. DMAH desorbs from an aluminum surface between 198 and 236 K at surface coverages ranging from 0.1 to 4.0 ML. A second DMAH desorption peak is observed at about 200 K (2.0 ML) when the aluminum surface is contaminated with carbonaceous species, resulting from the decomposition of DMAH. Both DMAH and TMA yield methane as a reaction product on the aluminum surface. The surface reactions of DMAH on aluminum also yield TMA as a reaction product.

The mechanism of metal film deposition from carbonyls as precursors is discussed in detail. It is shown that different species produced by UV laser irradiation in the gas phase contribute to film growth. Highly reactive species such as metal atoms may be important during the nucleation phase, whereas more stable carbonyls are responsible for the main growth process. This indicates that the main decarbonylation effect occurs at the surface. The higher level of impurity incorporation in chromium films in comparison with nickel films is explained by the relative position of the Fermi level in the d-band of Ni and Cr with respect to the 2π* level of CO, which favors CO bond dissociation in the case of chromium.

The fluorocarbon resin (Teflon) which is a very stable material chemically, has chemical resistance. Because of this property, it has no affinity for oil or water. Therefore, we have tried selective area modification of the resin surface b-y using an excimer laser.

Fluorocarbon resin is a polymer of C-F bonds. In our experiment, the resin surface was irradiated by an ArF excimer laser, of which the photon energy is higher than that of the C-F bond, to excite the strong C-F bonds. B radicals, the best combination for F atoms, were formed simultaneously. Consequently, F atoms of C-F bonds were pulled out by B radicals. B(CH3 )3 with absorption in agreement with the wavelength of the ArF laser were used as raw materials of the B radicals. By irradiating the gas by the ArF laser beam, the photodecomposed B radicals functioned by pulling out F atoms, and the other methyl radicals ( -CH3 ) substituted for F atoms. As the result, this resin surface turned out to be oleophilic exclusively on the areas exposed to the light.

Films of PMMA containing azobenzene were prepared by casting from polymer solutions containing the probe or by exposing pre-irradiated films to the vapor of azobenzene. These materials were irradiated at 335 nm and the amount of trans azobenzene which had been photoisomerized was monitored spectrophotometrically. The largest amount of photoisomerization was observed for the pre-irradiated samples which had been penetrated by azobenzene from the vapor, indicating that the created free volume allowed the isomerization to proceed more easily.

The 248 nm excimer laser-induced etching of Ti, Cr, Fe, Co, Ni, and Cu by Br2 has been studied. The experiment consists of focusing the pulsed UV laser beam at normal incidence onto the surface of a quartz crystal microbalance (QCM) coated with 1μm of polycrystalline metal. Absolute etch rates are determined as a function of the Br2 pressure and the laser fluence. On the basis of the kinetic information, four mechanisms are proposed to explain the etching of these transition metals.

Photochemical etching of Si and SiO2 using synchrotron radiation (SR) is carried out. The etching rate of SiO2 is much higher than those of poly-Si and single crystal Si. The etching rate of poly-Si increases as dopant concentration decreases. These material selectivities are quite different from those for plasma- or laser-excited etching. These new phenomena in SR-stimulated etching can be explained by a reaction model that contains reaction centers that are produced by both core and binding electronic excitation of Si and fluorinated Si in the surface layers. These centers are quenched by majority carriers.

This paper reviews several laser-based area-selective processing techniques developed for high-density multichip interconnection applications. Key material and process requirements for the development of a viable laser-direct-write interconnect technique on polyimide are addressed.

Thermal laser-induced chemical vapor deposition of gold deposits has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when laser source is modulated. Time-resolved reflectance measurements have been used to study the surface reflectance during growth with modulated and unmodulated laser source. The reflectance measurements indicated that surface melting does not occur under unmodulated cw irradiation at equivalent laser intensities. Variation in the modulation duty cycle indicates that there is a minimum laser-off cycle time length required for surface melting to be observed. Evidence is presented which suggests that surface melting is due to the heat released by the exothermic decomposition of reactant adsorbed during the time that the laser intensity is off.

Cobalt interconnects were deposited with a cw visiblewavelength laser from gaseous Co2 (CO)8. The deposited material was high-purity Co, and its electrical resistivity was as low as 13 μΩ-cm (twice that of bulk resistivity). The deposition is initiated by photochemical decomposition of Co2 (CO)8, and therefore process parameters (pressure, power, writing speed) are insensitive to the optical and thermal properties of the substrate.

Direct write of W on bare Si and native SiO2/Si substrates has been investigated in an laser chemical vapor deposition (LCVD) system. W deposits on bare Si surface via the Si and/or H2 reduction of WF6 were self-limited in thickness to 200 - 600 Å in both cases. Auger electron spectroscopic analysis showed that Si-H bonds could be poisoning the further growth of W. W deposits on native SiO2/Si were only obtainable via the H2 reduction of WF6 in our laser direct-write system. Our experimental kinetic study indicated that HF desorption from the surface is the rate-controlling step for W deposition via the H2 reduction of WF6. The as-deposited W line deposits were 2 - 10 μm wide, 0.2 - 6 μm thick with resistiiities in the range of 11 - 56 μΩ-cm. Growth rates as high as 2.2 mm/s have been achieved.

Thin films of GaN were grown on the Al2O3 (0001) substrate by the laserinduced chemical vapor deposition technique. Morphology were different for the films grown with and without laser irradiation. Moreover, the density of nucleus and the growth rate in the case of the growth with the parallel irradiation were greater than those without irradiation. Differences were attributed to presence of photo-dissociated species in the case of the laser irradiation. Additional irradiation normal to the substrate decreased the rate, probably because of the accelerated desorption of the reactive adsorbed species.

Commercially available polyimides and SiO2:TiO2 coatings are experimentally studied for their potential application in optical guided-wave interconnect networks. Optical properties are measured, including transmission spectra, refractive index and loss, with the aim of determining the materials most suited for this application. On the most promising candidates, direct writing of strip waveguides with Ar-ion laser at 514.5 and 457.9 nm was performed. Localized thermal curing by writing with speeds up to 250 microns per second allows the achievement of multimode guiding structures. Light propagation loss measurements reveal that attenuation in strip waveguides is of the same order as in slab structures of the same material, typically 5-10 dB/cm at 633 nm.

We have demonstrated that the selective area deposition of palladium on polyimide substrates is possible through the U.V. photolysis of (π-allyl)(π-cyclopentadienyl) palladium. This photolytic deposition process did not result in any apparent damage to either the Ultem 1000 (polyetherimide) or Kapton substrates (polyimide substrates). The resistivity of the palladium films (< 0.lum) suggests that the films are porous.

UV excimer laser-induced deposition of palladium from spin coated palladium acetate films in air is described. We have investigated mainly the deposition of palladium on aluminum oxide and quartz substrates and its dependence on the fluence and the number of excimer laser pulses. The decomposition mechanism was studied by measuring in situ the transmitted pulse energy during the exposure process. We have found that the excimer laser-induced decomposition of palladium acetate films is mainly pyrolytic and a simple model can be used to describe the decomposition process.

In situ measurement of resistance has been used for the realtime monitoring of metallorganic chemical vapor deposition (CVD) growth characteristics. In particular, a novel technique for measuring metallorganic CVD activation energies is presented. The micron scale geometry of the experiment makes it relevant to work in localized laser CVD. The technique has been used to measure the CVD activation energy of dimethylaluminum hydride (DMAlH). In addition, a variant of the technique has been used to study the growth stage of a resistless two-step metallization process (nucleation / selective CVD) employing DMAIH as the source gas in both steps.

Gold tracks have been deposited on thermally oxidised and single crystal silicon, gold and nichrome coated silicon wafers by pyrolytic decomposition of gaseous alkyl (triethyl phosphine) gold(I) complexes using focussed 514 nm radiation from an argon ion laser. The precursors, RAu(I)Et3P, R = CH3, C2H5 are low melting point crystalline solids with relatively high vapour pressures (∼5 mtorr). They are representative of a class of compounds being evaluated for laser deposition of gold. Differential scanning calorimetry, DSC, shows that the thermal decomposition of MeAu(I)Et3P in the solid state is a two-stage process. The decomposition temperature is 63 ± 1°C. Tracks were deposited at laser scan speeds up to 35 μm s−1 with a beam diameter (1/e2) at the focus of ∼12 μm. SIMS, EDX and laser ionisation microprobe analysis, LIMA, were used to determine the chemical composition of the tracks. The purity of >98% is consistent with the measured resistivities (4.2 μΩ cm) at room temperature compared to bulk gold (∼2 μΩ cm). These resistivities were achieved without post deposition annealing. Stylus profilimetry and SEM data showed the lines produced from MeAu(I)Et3P have a virtually rectangular cross-section. Together with the absence of the ubiquitous λ-ripples, this feature suggests that deposition is more rapid on the gold surface than on the SiO2 substrate. Laser power thresholds are lower for silicon substrates coated with thin (5 - 10°A) films of gold or nichrome.

Thickness profile of aluminum thin films deposited from dimethylaluminum hydride on silicon substrate changed with wavelengths of light chosen from the wide emission spectra of a deuterium lamp. Under illumination of the VUV around 160 nm deposits were formed preferentially in illuminated regions, while such area selectivity was lost and uniformly thick films were deposited all over the substrate when the UV around 240 nm was used. The observed area selectivity can be interpreted as arising from a wavelength-dependent nucleation mechanism; namely, surface photochemical reactions leading to nucleation are induced only by the VUV, while the UV photons are capable of producing photofragments in gas phase responsible for nucleation.

We have investigated the deposition of titanium lines from TiCl4 induced by KrF excimer laser (248 nm). Substrates are primarily LiNbO3, for the possible formation of Ti:LiNbO3 optical waveguides, as well as silicon and glass. Titanium lines contain [Cl] < 2 at% and are typically 200 to 1000 Angstroms thick with a width ranging from 3 to 20 μm. Results suggest that the process is controlled by photochemistry of TiCl4 but it is difficult at this point to assert which of the gas or adsorbed layer is the primary source of thin film growth.

Selective depositions of germanium thin films have been investigated in a cold-wall, lamp heated rapid thermal processor. Films were deposited at low pressures (1 Torr-8 Torr) using the thermal decomposition of germane. Selectivity was maintained throughout the temperature range investigated, 350°C-600°C. Growth rates as high as 800 Å/min were obtained at 425°C where deposition is controlled by the surface reactions, making germanium compatible with the throughput requirements of single wafer manufacturing. Three dimensional growth was seen at temperatures above 450°C resulting in a rough surface morphology. Smooth films were deposited below 450°C with the films characterized by two dimensional growth. In this work, germanium is considered as a potential material to fabricate MOS transistors with raised source and drain junctions (UPMOS). Kelvin structures were fabricated to study the effect of the intermediate germanium layer between aluminum and silicon on contact resistance. It is shown that contact resistivity is improved by approximately 17% using an Al/p-Ge/p+-Si structure. In this work, it is also shown that titanium germanide formation can be used as a means of reducing the resistivity of the Ge buffer layer.