Laser chemical vapor deposition (LCVD) is a modification of conventional CVD using a laser heat source. The film growth characteristics differ considerably from conventional CVD in several ways, however. The use of an optical heat source means that the optical properties of the film/substrate system must be considered, e.g., for metals deposited on absorbing substrates, the film thickness and diameter may “self-limit” in some cases because the deposited film reflects most of the laser energy. On the other hand, the small area heated in LCVD results in a different diffusion geometry and access to higher surface temperatures than are achievable when large areas are heated. For favorable reactant systems, these enhancement effects can yield fast deposition rates and line deposition scan speeds greater than 10 cm/sec. This paper will review results of pulsed and cw LCVD of predominantly metal films using visible and infrared lasers.

The technique of simultaneous twin-beam processing has been investigated and used to deposit thin films of silicon on a silicon substrate.

An argon ion laser was used to create a large concentration of free carriers in the Si conduction band. These carriers were spatially localized in the beam spot on the surface of the substrate. The effective absorption coefficient of 10.6 radiation (carbon dioxide laser) can thus be increased to greater than 104 cm−1 . Experimental evidence illustrates that this efficient coupling of the high-power CO2 radiation (10–30 W) to the otherwise non-absorbing silicon can be totally controlled by the low-power (1–4 W) argon ion incident beam. The difference between absorption increase due to optically created carriers and thermally created carriers is clearly illustrated.

This synergistic effect has been used to induce pyrolytic deposition of Si from SiH4 non-flowing gas onto a Si substrate. Lines and spots of various widths and thicknesses have been grown by the controlling low-power argon ion beam spot.

Preliminary investigations on the quality of the deposits using i.r. spectroscopy ellipsometry, SEM and Auger analysis have been carried out.

In this paper we report a new method of silicon deposition using the interaction between the radiation from a pulsed-ultraviolet excimer laser and the plasma species produced in a glow discharge in silane (SiH4). Examination of the deposited film by laser Raman spectroscopy and by transmission electron microscopy revealed that the morphology ranged from polycrystalline silicon at laser fluences of 0.13–0.17 J/cm2 to epitaxial silicon at fluences of 0.4–0.6 J/cm2 . Growth rates of 100 nm/min for polycrystalline silicon and 30 nm/min for monocrystalline silicon were achieved.

Various laser-based deposition methods for preparation of silicon films have been reviewed briefly with emphasis on laser chemical vapor deposition (CVD). The main body of this paper is concerned with CO2 laser CVD of silane. This is interesting because the observed dependence of deposition rates on laser wavelengths indicates that gas-phase reactions are involved in deposition processes and therefore we can apply a powerful new diagnostic means, coherent anti-Stokes Raman spectroscopy (CARS), to examine gas-phase dynamics. From N2 CARS thermometry the CO2 laser beams were found to raise the temperature of the gas containing silane, when they were tuned to absorption lines of SiH4. Silane CARS spectra were characterized by a complicated profile with double peaks. We interpreted the shape of the spectra as arising from excitation of rotational levels following gas-phase reactions. Applying this interpretation, we can judge how SiH4 molecules are disturbed differently according to CO2 laser wavelengths and a distance from a substrate.

The processes involved in the fabrication of micron-dimension transistors and small-scale integrated circuits using only the technique of direct laser-writing by localized pyrolytic surface reactions are discussed. New experimental findings in the deposition of tungsten by silicon. surface reduction of tungsten hexafluoride and doped polysilicon are presented. The techniques used to fabricate laser beam-written n-MOSFET's are being extended to make unipolar JFET's and bipolar lateral pnp transistors.

UV laser photochemical doping offers the possibility of direct fabrication of semiconductor devices by high-intensity photolithographic projection. We have recently demonstrated control of parameters such as dopant concentration and junction depth to the extent that npn structures can be readily produced.

Recent work also indicates that contact resistance can be dramatically reduced from the levels found using simple probes, by the low-temperature laser deposition of metals, and that this technique also can be used to connect elements in a circuit.

In this paper the progress made towards the fabrication of complete planar devices is described and the I-V characteristics of some simple diodes are shown.

Silane molecules have been irradiated by a pulsed CO2 laser operating at 10.59 μm. The threshold of silicon formation by homogeneous dissociation of silane has been investigated as a function of laser fluence (0.1–3.5 J/cm2) and silane pressure (1–100 Torr). Silicon films have been deposited on quartz substrates using the laser beam either perpendicular or parallel to the substrate surface. The crystallographic structure and deposition rate of these silicon films are found to be dependent on the incident angle of the laser beam, silane pressure, substrate temperature and laser fluence. The growth mechanism of these films is discussed.

Temperature distributions induced by cw laser radiation absorbed on the surface of combined structures, consisting of discs or of stripes on semi - infinite plane substrates, are calculated for different material parameters and different geometries. The relevance of the numerical results is demonstrated by comparison with earlier experimental data obtained in pyrolytic laser-induced chemical vapor deposition.

Using CMOS, poly-Si gate, single-level metal, gate-array chips, techniques have been developed to reconfigure the interconnect metallization on individual circuits without degradation of device or circuit performance. These techniques involve a laser-assisted capillary wet-etch process for highly selective removal of Al-alloy interconnects and laser CVD of doped poly-Si links. This technique may be useful for prototyping, testing and optimization of gate-array and standard-cell designs and layouts.

Films of silicon nitride have been deposited using a continuous wave CO2 laser to excite gaseous mixtures of silane and ammonia. A typical deposition rate is 150Å/min. The hydrogen film content and its dependence on the substrate deposition temperature are similar to that observed for plasma CVD silicon nitride. The CO2 laser CVD films are silicon rich with a Si/N ratio = 1.2 at a NH3/SiH4 gas flow ratio of 1000. Conformal step coverage is observed on patterned silicon oxide features.

The effects of 193 and 248 nm UV surface irradiation on the properties of Al2O3 films produced by UV laser-initiated deposition have been investigated using ellipsometry and electrical measurements. The UV irradiated region shows a higher refractive index than the unirradiated regions, indicating that densification has occurred. Energy fluences as low as 1 mJ/cm2, too low to cause significant transient heating, produce measurable effects. The results suggest that UV irradiation may be used to obtain lower deposition temperatures in a variety of deposition systems.

InP and In-oxide films have been deposited on quartz, GaAs, and InP substrates by excimer laser-induced photodecomposition of (CH3)3InP(CH3)3 and P(CH3)3 vapors at 193 nm. The oxide film refractive index and stoichiometry are close to In2O3. Phosphorus incorporation in the films was greatly enhanced by focusing the laser beam to promote multiple-photon dissociation processes. These conditions also lead to enhanced carbon inclusion in the films, due to formation of species such as CH and CH2 in the gas phase. However, this carbon inclusion could be suppressed by focusing the beam onto the surface at normal incidence. In the irradiated zone InP could be deposited with P(CH3)3-to-(CH3)3InP(CH3)3 ratios of only ∼1:1. The technique offers several potential advantages over conventional metal-organic chemical vapor deposition (MOCVD), including lower temperature, enhanced rates, safer gases, and threedimensional film composition control.

Strong atomic In emission is observed in the gas-phase above the depositing film, due to a multiple photon dissociation process. Gasphase fluorescence from P, CH, and C was also observed. These emissions give insight into the photodecomposition mechanism and also serve as a monitor of metal-organic precursor concentrations.

The properties of SiO2 and Si3 N4 films deposited by an ArF excimer laser, glow discharge electron beam and conventional plasma-enhanced CVD are compared. The deposition apparatus, technique, and conditions in addition to the physical, chemical and electrical properties of the films are discussed.

Films of Column IIIA metals (In, Tℓ and Aℓ) have been deposited on several different substrates (stainless steel, nickel and copper) by photoionizing the corresponding metal-iodide or bromide (such as TℓI, InI or AℓI3) in the vapor phase and in the presence of a uniform electric field. These experiments were prompted by the measurement of large photoionization cross-sections for ion production (i.e., MX + 2ħ ω → M+ + X + e- or MX + ħω → M+ + X-) in these molecules at 193 nm. The effective cross-sections for the photoionization of TℓI and InI at 193 nm have been measured to be 2.2·10−17 cm2 and < 7·10−18 cm2, respectively. Depletions of the metal-halide ground state greater than 60% have been observed for ArF peak laser intensities of only 5 MW − cm−2.

Excimer laser photodecomposition of Fe(CO)5 has been used to produce large-area (≳ 1 cm2) Fe films on insulating and semiconducting substrates. Films were deposited in an ultrahigh vacuum system at room temperature or 77 K. Film composition and morphology were examined with Auger-depth profiling, scanning electron microscopy, x-ray fluorescence, and resistivity measurements. At appropriate laser power densities and Fe(CO)5 pressures, adherent metallic films were obtained. These films were typically less than 500 Å thick and contained less than 13% bulk oxygen and carbon contamination.

High-rate deposition of amorphous silicon films using the mercury-photosensitized reaction of disilane gas is described. The deposition rate depends upon reactant pressure, light intensity, and concentration of mercury atoms. A maximum rate of 100 nm/min is attained at a 250°C substrate temperature and a disilane pressure of 200 Pa. This rate is about 3 times higher than that for monosilane gas.

Generally, the optical gap of the deposited films range from 1.7 to 1.8 eV, although the value decreases slightly with increasing substrate temperature. Photoconductivity under AM1 irradiation is 2×10−4 mho·cm−1 at a 250°C substrate temperature and the ratio of photoconductivity to dark is around 104. From the infrared data, amorphous silicon films are found to include only an SiH bond at substrate temperatures of 200° to 300°C. Hydrogen content is 10 to 13%. These data suggest that silicon films can be used in thin-film electronic device fabrication.

Techniques for laser-photochemically depositing localized thin films are reviewed. A comparison is made between techniques relying on gas-phase and surface-phase photochemistry. New photoreactions, confined entirely to surface phases, are described, including multimolecular reactions based on methyl methacrylate, and multicomponent reactions based on mixtures of trimethylaluminum and titanium tetrachloride. Recent developments in the use of surface photochemistry to nucleate subsequent growth by pyrolytic chemical vapor deposition are also reported.

The profiles of features etched photoelectrochemically in n-InP are studied to determine the factors which govern their distortions and to determine the factor limiting spatial resolution for etch depths in the 100–200−μm range. The optimal conditions for etching straight grooves using laser light are determined. The application to front-to-back mask registration will be discussed.

Wet and dry laser-etching experiments have been performed on polished CdS crystals, using a CW Ar laser, with the goal of writing patterns with μm linewidth. A nitric acid solution was found to exhibit no appreciable dark etching and high photoetching rate; surface roughening due to scattered light was its limitation. A dry, low-temperature (< 200°C) laser-etching process was also studied, and used to produce satisfactory line patterns with 1- to 5-μm linewidths and a 3:1 depth ratio.

By using two interfering laser beams to initiate localized chemical reactions at an interface, very high resolution, maskless microfabrication can be done over relatively large substrate areas. The resulting deposited or etched patterns can be used in a variety of electrooptical and electronic applications. In addition, this type of fabrication, which can be monitored in real time, provides insight into many new interfacial phenomena.