A KrF excimer laser exposure method has been developed for laboratory use, which employs 10 to 1 achromatic projection lens of 0.37 NA and 5x5 mm field size , and a TTL alignment system using the double diffraction method, which was realized by the use,of the achromatic lens. Novolak type mid-UV resists, such as AZ-5214 and PR-1024, were best suited for use in 248 nm exposure, considering the sensitivity and etching resistance from a practical viewpoint, and an additional post exposure baking process also improved the resist profile. The dependences of the exposure characteristics on the energy density per pulse and pulse frequency of these resists were not observed in the region of the practical exposure conditions. An alignment precision of x±30-= 0.2 μm was achieved for the alignment mark consisting of poly Si pattern. Thus, a 0.3 μm line and space pattern was realized by using tri-level resist process and a 0.2 μm gate pattern was successfully fabricated on the coplanar pattern with a 0.4 μm step.

Excimer laser projection systems are expected to become widely used photolithographic tools, capable of high throughputs at resolution well below 0.5 iffli. The design of practical devices must overcome several challenges which are specific to the short wavelength, the laser performance and the photoresist response of such systems. This paper addresses the issues of UV optical materials, the effects of laser bandwidth on optical design, and the interrelationship between resist response, resolution, and laser pulse-to-pulse stability. It is shown how the various parameters are interconnected, and directions for further technological improvements are outlined.

We report on the successful patterning of polyamic acid over wide areas using 28 kV pulsed electron beams produced in 30 mTorr air. The pattern degradation during the 350°C, 1/2 hr, imidizing thermal cure is prevented by pulsed, flood electron beam hardening of the developed polyamic acid patterns using the same soft vacuum, pulsed electron beam apparatus. It is also shown that a CW, low voltage, 1 to 3 kV electron beam sustained oxygen discharge can be used to completely strip the hardened, imidized material which is difficult to remove by wet methods. We also present, dose versus thickness remaining characteristics as a function of electron source to substrate distance and some examples of polyimide patterning.

Patterned fine-line features as small as 0.8 microns have been etched in polyimide, silicon, and copper by use of ablative and chemical techniques. KrF excimer laser pattern etching was accomplished by use of a Kohler-type projection system employing a Uv refracting microscope objective. Ablative etching of polyimide was accomplished in air, while silicon and copper were chemically etched using the vapor of chlorine or carbon tetrachloride.

193-nm excimer laser-assisted etching of polysilicon was studied in the presence of CI2. Maximum etch rates of 1.25 Å/pulse were obtained for pressures of about 400 torr and fluences exceeding 400 mJ/(cm2-pulse). The etch rate increased with both fluence (100-550 mJ/(cm2-pulse)) and pressure (50-800 torr). An adsorptive etch mechanism similar to NF3 etching has been proposed, where Cl2 molecules diffuse to the surface, adsorb, and then react after absorbing laser radiation. This is consistent with photon and molecular flux considerations and the availability of reaction sites. Thermal effects where Cl2 molecules decompose to Cl atoms on “hot” polysilicon surfaces may assist this process, and appear to dominate under conditions of lower pressure (<400 torr) and higher fluence. Etching caused by the gas phase formation of Cl atoms is minimal due to the low Cl2 absorption cross section at 193 nm.

Simple projection etching results showed that micron lines can be etched in polysilicon by use of this chemistry.

We report, for the first time, laser direct writing of high conductivity aluminum interconnects from dimethylaluminum hydride (DMALH). These lines were deposited from a metallorganic gas with a focused deep-UV laser beam and were directly connected to aluminum test structures. Electrical measurements and Auger electron spectroscopy were used to characterize the laser deposited films.

The rates of aluminum line growth, assisted by photolysis, in the normal direction to the Si (100) substrate, indicate that, in a trimethyl-aluminum + hydrogen mixture, only the change in the TMA flux and the UV laser power can play a determinant role. Possible explanation is based on the generated methyl radical “blocking” action leading to a self-limiting deposition rate, as opposed to the enhancement of methyl desorption by hydrogenation to methane. It is shown that dilution by hydrogen decreases the carbon contamination in aluminum line.

Aluminum lines have been drawn at a writing speed of 3.8 μm/s on (100) p-type Si by UV laser-assisted chemical processing, from a flow of TMA diluted in H2. These results are the experimental proof of direct writing at room temperature due to a single-step deposition process induced by a single light source. The useful (30 μQ-cm) ohmic-type resistivity obtained depends strongly on the photolytic process parameters.

The contact characteristics between Al interconnections in LSI's and direct written Mo lines has been substantially improved by adopting, for the first time, short-pulse-laser induced Mo CVD. The linewidth stability upon Al interconnections has also been improved. Transient, localized heating with short laser pulses effectively overcomes the heat dissipation through Al interconnections which degraded contact characteristics and prevented fine drawing near the Al interconnection. This new scheme can appreciably widen the applicable device field of direct writing circuit restructuring.

The in situ formation of conductive carbon lines in polymeric substrates was demonstrated by “writing” with CO2 and Nd:YAG lasers. The formation of conductive carbon lines on polymer substrates proceeds through a series of steps including; absorption of light, initiation of decomposition reactions, and thermal propagation of the pyrolysis. The effect of material composition, power density, energy density, and wavelength on the electrical resistance and morphology of the carbon lines was investigated. Above a critical laser energy density (= 400 J/cm2) sufficient light is absorbed by the substrate such that initiation of the pyrolysis reactions occurs. The decomposed polymer strongly absorbs the incident radiation and the thermal propagation of the reactions forms shiny, conductive, carbon lines. The dimensions of these lines are dependent on the energy density impinging on the polymer and are independent of the wavelengths investigated. If too high a power density is employed (∼ 104 Watts/cm2), an ablated track is formed down the center of the carbon line. This results in the relative insensitivity of the linear resistance with increasing power above 104 Watts/cm2.

The repair of clear defects on X-ray masks (2 urn Si membranes) requires the localized deposition of metal films with high aspect ratios and high X-ray opacity. Laser-induced heavy metal deposition from organometal-lic gas atmospheres has been investigated with respect to these requirements. An experimental comparison of pyrolytic (W) and photolytic (esp. W, Sn) depositions on thin Si membranes was performed to find out which of these two mechanisms is more favourable for X-ray mask repair. Using a simple model, the laser-induced temperature distribution in the membrane was calculated which strongly affects pyrolytic deposition. Although photolytic deposition tends to yield X-ray opacities below corresponding bulk values, this process turned out to be more suitable due to its better spatial resolution in this case of Si membranes used as substrates.

For the past few years, there has been considerable interest in using lasers for the directed deposition of metal [1,2,3,4]. Part of this interest is driven by technological applications in microelectronics. In particular, this includes the rapid interconnection of gate arrays [5] and the repair of defects in photomasks [6]. The techniques used for the laser patterning of metal include Laser Chemical Vapor Deposition (LCVD) [7], and the decomposition of spin-coated organometallic inks [8]. In the first process, LCVD, a laser with a power of several hundred milliwatts or more is used to irradiate a substrate in the presence of an organometallic vapor. The substrate is chosen so that it absorbs the the incident laser radiation while, in general, the organometallic vapor is transparent at the laser wavelength. The absorption of the laser energy by the substrate results in a temperature rise which depends on the thermal properties of the substrate. If the temperature rise is sufficient, organometallic molecules impinging on the irradiated area decompose. Non-volatile components (such as metal fragments) remain on the surface and form a deposit. In the second process, decomposition of organometallic films, a substrate which was previously spin coated with an organometallic ink is irradiated wherever metal patterns are desired. The ink decomposes in these areas leaving a film of metal. The unirradiated areas of the ink are then washed away with a suitable solvent. Such processes have been extensively studied and developed using primarily argon, krypton, and CO2 lasers [1,2,3,4]. In general these lasers are large, expensive, require maintenance, and raise reliability concerns. These characteristics add to the challenge of introducing laser deposition processes into the manufacturing environment.

Laser direct-writing of micron-size metallic features from Pd acetate film precursors is achieved using a scanned cw Ar+ laser. Marked periodic structure is observed in these features under a wide range of exposure conditions. A model based on laser reflectivity and transmittance measurements has been developed to describe the formation of the periodic structure. The model takes into account a complex relationship between optical absorption, laser-induced heating and reaction rate. The decomposition of Pd acetate to metal is endothermic and, therefore, this system differs fundamentally from the “explosive” crystallisation of amorphous semiconductors.

The focused output from an argon ion laser (514 nm) has been used for direct writing of copper by photothermal decomposition of copper formate film on quartz and silicon substrates. The low decomposition temperature of the metallo-organic (∼200°C) allows deposition of fairlys thick copper lines at writing speeds as high as 10 mm/sec. The processing can be done in air since the rapid decomposition and cooling under scanning condition results in minimal oxidation of the deposited copper. The temperature distribution produced during laser writing on silicon substrate has been calculated to help explain some of the observed results.

This work is aimed at studying the feasibility of laser induced, high-speed, highly selective direct deposition of metals on substrates immersed in commercial electroplating solutions without masking procedures and external electric current.

A Q-Switch Nd/YAG pulsed laser system and excimer UV pulsed laser systems operating respectively at wavelength of 532nm and at 193 and 248nm, were used in conjunction with commercial basic potassium gold cyanide and acidic gold tetrachloride solutions. The substrates were semiconductors (silicon, gallium arsenide and silicon carbide), metallic (platinum) and polymeric (polyimide).

The morphology, structure, composition and properties of the gold deposits were examined by the SEM, TEM, X-ray, AES and ESCA techniques.

Deposits were found to consist of elemental gold with thickness range from a few hundred angstroms to several micrometers, depending primarily on laser energy density and on the number of pulses. Deposition occurred wherever band gap energies (plus surface barrier) were smaller than the laser photon energy; none was observed in reverse situations, as in the cases of Si3N4 and fused SiO2.

The deposits exhibited Schottky barrier contacts on silicon, silicon carbide and gallium arsenide.

The pyrolytlc laser-assisted deposition of metals Is modeled. A finite element approach is used to solve for temperatures and gas-phase concentrations In a transient calculation. The model accommodates the use of temperature-dependent physical properties as well as the occurrence of irregularly shaped deposits. Volcano-like deposits’ are predicted under certain conditions of gas pressure and laser intensity. The effect of using substrates with different thermal conductivities is investigated. Using adsorption-desorption kinetics such that the reaction rates have sharp maxima with respect to temperature, volcanoes of varying depths are modeled.

Temperatures of laser-heated silicon microstructures on fused silica were determined by Stokes/anti-Stokes scattering using the 4880Å and 5145Å argon-ion laser lines, either separately or together to heat and probe the structure. Phonon shifts and broadening gave consistent measurements of temperature. Evaluation of temperatures from the ratio of Stokes/anti-Stokes intensities was shown to be sensitive to the details of scattering, collection, and detection.

This paper reports initial results of an experimental study of the early stages of silicon thin film growth on well prepared (100) c-Si surfaces by pyrolytic deposition from silane (SiH4) during localized laser chemical vapor deposition (LLCVD). The rate of silicon thin film growth during low pressure (< 10 Torr) deposition using tightly focussed laser beams (514.5 nm, ∼ 2.5 μm FWHM) is characterized and is shown to be much slower than expected based on the previously measured silane decomposition rate. Hybrid-heating experiments, in which laser heating induces a slight temperature increase on a uniformly heated substrate in the presence of silane gas, shows that growth is inhibited within the laser irradiation region. This result suggests that a nonpyrolytic mechanism contributes to silicon growth in laser CVD. Possible explanations for this nonpyrolytic growth mechanism are discussed.

The localized laser-induced deposition of an insulator for silicon-based microelectronics seems to be an unsolved problem. In order to understand the limiting mechanism in the deposition, the formation kinetics of silicon, silicon oxide and silicon nitride using various laser wavelengths and gas mixtures have been studied Depending upon wavelength and laser-induced temperature, various chemical reactions are involved. In the presence of ammonia, the growth rate of silicon nitride dots was found to be lower than the corresponding silicon deposition rate, indicating that deposition starts with silane decomposition followed by nitridation of silicon. By evaluating the influence of the wavelengths, the existence of a photolytic aided reaction is detected in the presence of 2.4 eV photons. In the presence of oxygen molecules and under most experimental conditions, no deposition occurs. The formation of volatile intermediate compounds can explain the difficulty of locally depositing silicon dioxide.

Laser induced temperatures in substrates irradiated with a scanning gaussian laser beam were calculated by the finite element method. A quartz substrate of a given thickness and covered with a one - micron - thick silicon coating was assumed to be either placed on a heat sink or thermally insulated. The maximum temperature in the center of the laser spot was found to be proportional to the laser power for a spot size larger than the silicon thickness. Furthermore at a given laser power, the temperature decreased with increasing laser spot diameter and the time to reach the equilibrium temperature increases with the spot radius for radii less than the substrate thickness. The laser induced temperature was found to be affected by laser - scan speeds for speed values above the heat diffusion rate.