We describe a reversible technique for locally modifying the oxygen stoichiometry and electrical transport properties of superconducting thin films. A focused argon ion laser beam is scanned across the surface of a YBa2Cu3O7-x thinfilm, contained in a vacuum, at incident power levels well below those necessary for ablation. The change in oxygen stoichiometry is monitored in-situ by the room temperature electrical resistance. We have measured the superconducting properties of these locally modified films. The resulting R vs T curve for the composite structure (film/laserstripe/film) shows the expected double transition. The first transition, corresponding to the unmodified film, occurs at 87 K while the second transition, corresponding to the modified stripe, occurs at a lower temperature and is a function of the laser induced change in the room temperature electrical resistance. The critical current for the composite structure is depressed from the original film. The laser writing can be erasedor bleached out by room temperature exposure to an oxygen plasma.

The deposition of SnO2 films has been demonstrated using an ArF (193-nm) excimer laser to drive the photochemical reactions of mixed SnCI4 and N2O vapors. Without any annealing, films 100 nm thick grown on room—temperature substrates have resistivities as low as 0.04 Ω—cm. The optical bandgap of 3.20 ev and transmission cutoff wavelength of 330 nm compare favorably with films obtained using alternate higher temperature techniques. The maximum temperature excursion during the 20—ns laser pulse is estimated to be 300 to 400 ºC.

We report here the crystallization kinetics of thin (35nm and 60nm) amorphous as-deposited Ge filins using diffraction limited laser beam irradiation and laser pulses between 30ns and IreS. The recrystallization of crystalline as-deposited films was also studied for similar laser conditions. Crystallization was observed for pulses as short as 50ns. We conclude that the use of small beam spots (-1μm) gives a very different crystallization morphology from that observed previously for larger beam diameter and same laser pulse length. In our case for short irradiation times, the nucleation process dominates over crystal growth. Laser irradiation of as-deposited crystalline films produced grains with significantly less defects than grains crystallized from as-deposited amorphous films. Temperature calculations allow us to understand these results by showing that only the small spot irradiation sustains the material at high temperature for times comparable to the pulse width.

The<111> face of an antimony single crystal was irradiated under ultra-high-vacuum conditions by the 193 rn radiation of a high-power excimer laser. The effects of the laser beam on the sample as a function of the light Energy Density (ED) and of theannealing Repetition Number are presented.

Surface studies by Auger electron spectroscopy, scanning electron microscopy and low energy electron diffraction show that an atomically clean and well ordered surface can be produced by t is method. A strong chemical reduction is induced by pulsed aser annealing above 100 to 130 mI/cm2. Surface analysis shows that, for an ED less than 500 mJ/cm2 the surface evaporates without melting deeper than 200 rim. Evidences for oxide modification and for organic molecule desorption were observed even after irradiations with an ED as low as 45 mJ/cm2.

The surface reduction is described by a thermal model involving surface heating and subsequent evaporation of the oxide layer. The desorption and diffusion processes may involve both thermal and photolytic mechanisms.

This report describes a study of the formation of TiN thin films produced by laser irradiation of titanium targets immersed in liquid nitrogen. Three fluence thresholds have been determined, corresponding to: (i) surface melting in gaseous nitrogen (0.7 J/cm2) (ii) surface melting under liquid nitrogen with TiN formation (1.2 J/cm2) and (iii) gross melting accompanied by the generation of periodic surface structures ( >2.0 J/cm2). Data obtained from transmission electron microscopy, Auger spectroscopy, and XPS studies show that the rapid solid-statecooling rates ( l010deg/sec ) result in a supersaturated, twinned hcp structure with solute contents up to 40 at% nitrogen.

Theoretical estimates suggest that the majority of the incident excimer laser radiation is absorbed by the target with subsequent thermal transfer to the liquid producing a highpressure shock wave originating at the liquid-solid interface. Pressures up to 4.3 GPa are predicted with the expanding vapor layer reaching a terminal velocity after 5 μs and a total lifetime of 28 μs. Such a lifetime is considerably longer than the thermal pulse in the substrate (from a I-dimensional heat flow analysis). The results are discussed with reference to such estimates. Because the thermal diffusivity far exceeds that of the solute, the extent of nitridation is determined predominantly by the first 200 ns of the thermal pulse experienced by the target.

A variety of data for physical etching (i.e. sputtering) and for ion-enhanced chemical etching of Si and SiO2 is analyzed in the very-low-ion-energy regime. Bombardment by inert ions alone, by reactive ions, and by inert ions in the presence of reactiveneutrals is considered. In all cases the etch yield follows a square root dependence on the ion energy all the way down to the threshold energy for etching. At the same time, the threshold energy has a non-negligible effect on the etch yield even at intermediate ion energies. The difference between physical and ion-enhanced chemical etch yields can be accounted for by a reduction in the average surface binding energy of the etch products and a corresponding reduction in the threshold energy for etching. These results suggest that, in general, the selectivity for ion-enhanced etch processes relative to physical sputtering can be increased significantly at low ion energy.

Focused ion beam induced deposition of gold microfeatures is accomplished by 40 keV Ga+ bombardment of a substrate on which dimethyl gold hexafluoro acetylacetonate is continuously adsorbed. Under optimum conditions, deposition rates exceeding 11 Å/s have been achieved as well as high aspect ratio features, linewidths of approximately 0.1.μm, and resistivities of 500—1500 μΩcm. The microstructure, composition, and yield of the deposits have been examined as a function of various process parameters. Improved film growth and purity are observed in deposits made with lower organometallic pressures or higher current densities.

The etch rate of GaAs and AIGaAs during CC12F2:O2 reactive ion etching was measured over the temperature range 50–400ºC. For GaAs, the etch rate increases super-linearly from ∼400Å.min−1 to ∼3000Åmin−1 over this temperature range for a 0.56 W.cm−2, 4 mTorr discharge with a 19:1 CC12F2:O2 mixture. The surface morphology of GaAs undergoes a smooth-to-rough transition near 150ºC, and theresidual damage in the near-surface region appears to decrease with increasing etch temperature. The I-V characteristics of Schottky diodes fabricated on the etched surfaces show ideality factors of 1.001 for 150ºC RIE, although these worsen because of thermal degradation of higher etching temperatures. From AES and XPS data the etched GaAs shows little contamination after etching. In contrast, little temperature dependence of the etch rate of AIGaAs is observed using CC12F2:O2, although once again there is surface degradation for etching temperatures above 150ºC.

At the beginning of etching, surface asperities appeared on the top plane of the polyimide (PI) film. The formation of surface asperities is due to the ordered phase in PI film. The known dimension of the ordered phase measured by X-ray diffraction is consistant with the size of surface asperities, 100 Å, observed by TEM. Further ion doses made these asperties evolve into smooth bumps which then eroded into cones as a result of etch yield difference as a function of the angle of beam incidence Y(θ)/Y(0) which has a maximum at θ=70. Finally cones led to the development of grass-likestructure on the top plane of the PI film. The formation of platelike structure on the cross-sectional plane of PI indicates that the structural inhomogeniety of the PI film(the ordered and disordered phase) is the main cause for the surface morphological changes of PI.

Conversion electron M6ssbauer spectroscopy was used as a means of investigating radiation induced changes at thin film interfaces. 25 Å thick layers of 57Fe were evaporated onto substrates of Si,SiO2 and A12O3 andcovered with 150 Å 56Fe. Samples were then subjected to ion irradiation with 20 MeV C14+ to doses ranging from 1012 to 2x 1014 ions/cm2 and subsequently annealed in vacuum at 450 ºC. Mössbauer spectra were recorded before and after each step. The analysis revealed chemical alterations, induced by the ion bombardment, indicative of film-substrate bond formation and reconstruction of residual surface hydrocarbons. The results are interpreted in view of accompanying enhancements in thin film adhesion.

During intense electron irradiation inside the electron microscope, the electron—stimulated desorption of oxygen from the surfaces of several maximally—valent transition—metal oxides (TiO2, V2O5, Nb2 O5 and WO3) has been observed [1]. The irradiatedsurfaces become covered with a crystalline layer of the corresponding monoxide phase. These reduced phases, which are all based on cubic structures and have metallic conductivity, grow with a well— defined epitaxial relationship with the bulk oxide. Computer—drawn models of the crystal structures have been used to study the atomic arrangements implied by the epitaxial relationship, and certain structural features were found to be common to the oxides studied.

High current density electron beam irradiation with a small probe can lead to the production of holes in a variety of inorganic materials. We review some of the experimental observations of the hole formation process and compare these to the predictions of a simple model.

Structural changes occurring at the surface of NiO during electron irradiation were examined in-situ with a variable voltage high resolution electron microscope. The interaction of the specimen with the electron beam was found to be highly dependent on the state of the surface prior to irradiation. It was observed that by varying the sample preparation conditions, the Ni on the surface of NiO could either be oxidized to Ni304 spinel phase or reduced to islands of metallic Ni. The formation of the Ni3O4 spinel phase is in agreement with previous surface science studies, where chemical shift information identified the presence of Ni3+ species at the surface. This has previously been interpreted as the formation of Ni203

The use of a wide-area electron beam to aid the deposition of epitaxial silicon films has been studied. The electron beam used in this study is generated using a cold cathode, abnormal-glow discharge which allows a wide variation of electron energy and beam current. Depositions are performed on single crystal silicon substrates which are prepared using standard wet chemical silicon cleaning techniques and an in situ plasma etch using nitrogen tri-fluoride diluted in hydrogen. The beam diameter is approximately 10 cm and can readily be scaled up to accommodate larger diameters, allowing great potential for large area single wafer deposition. Using electron beams generated in this system, we have demonstrated enhanced growth rates and improved crystalline quality for films grown withelectronbeam enhancement.

The effects of plasma starting conditions on the initial stages of diamond nucleation and growth in a microwave plasma have been studied as a function of important deposition parameters. The influence of the substrate temperature on the diamond nucleation rate, quality, and final film morphology has been elucidated through various analytical measurements. The diamond films are characterized with Raman spectroscopy, X-ray diffraction, and scanning electron microscopy. Finally, methods are described for reproducibly controlling the grain size and morphology of the diamond films for tribological and abrasive applications.

We have made a-Si photoreceptors at low pressure to prevent the formation of SimHn powders and by separating the growing surface from the high density plasma. A new plasma CVD method using a hollow-cathode discharge, where the discharge electrode is the cathode, is described. There is a hollow region in the discharge electrode. Hollow-cathode discharge enables a high density plasma to form at low pressure. The gas is decomposed in the hollow cathode preventing plasma damage to the film. This method allows us to achieve a high deposition rate (10 µm/h) and good quality films for photoreceptors.

Laser direct-write processes are attractive complements to traditional methods of fabricating microelectronic circuitry. This paper is a summary of our work in applying such processes to high-density inter-chip interconnection modules, such as those using copper conductors on polyimide dielectric layers. We begin by discussing the requirements which laser processes must satisfy in order to be useful in this application. An analytical model of laser heating is then described, which aids in understanding the thermal problem of absorption of visible-wavelength laser light by polyimide. Calculations using this model are consistent with experimental observations. Finally, we focus on one laser processing technique: laser chemical vapor deposition. We describe a new process for laser chemical vapor deposition of tungsten on polyimide, which enables the formation of low resistance contacts (≈ 0.1 Ω) between the deposited tungsten films and pre-patterned nickel-coated copper conductors. Lines approximately 30 /m wide and 34 µm thick were deposited at a scan rate of 93 µm/s. From four-point resistance measurements of different lengths of deposited films, the tungsten film resistivity is estimated to be two to three times the bulk value.

A pulsed excimer laser or flashlamp-pumped dye laser is used to melt 1 to 5 µm Au layers. The size of feature which can be filled by laser planarization is limited because of the finite melt duration, but the basic goal of levelling local surface topography is accomplished.

Laser reflow of thicker films reveals fundamental differences between the excimer laser and the flashlamp-pumped dye laser, resulting from the order-of-magnitude difference in pulse duration. The excimer pulse is short compared to the thermal diffusion time of the metal layer and this can create voids and craters in the metal above discontinuities in the underlying structure. For Au thicknesses greater than about 3 µm, void formation occurs at fluences at or below that necessary to planarize the film. The dye laser has a planarization threshold similar to that of the excimer but it takes over 60% greater energy to create voids than to planarize a 5 µm film.

A second damage mode, common to both laser sources, occurs where adjacent planarization zones overlap in a patterned area: thin spots can be created by the first planarization pulse which are vaporized by the second pulse.

The fundamental differences between excimer (≈ 30 ns pulse duration) and flashlamp-pumped dye (≈ 500 ns pulse duration) laser planarization are examined for 1.5-2 µm thick gold films over SiO2 layers. Test structures containing bar patterns (square waves) of 5000 Å peak-to-trough amplitude with spatial periods ranging from 10 µm to 100 µm were prepared and laser-irradiated. A linear model is presented which describes the time-evolution of the film's surface topography when melted with a dye laser pulse. Excimer laser planarization is found to be susceptible to evaporative recoil effects which may cause undesired pattern amplification.

Selective modification of surface reactivities with lasers, using either direct writing or projection method, is intrinsically a sensitive method to prepare a surface for highresolution and high-speed area selective thin film deposition. In this paper, we demonstrated the use of laser direct-writing and projection patterning techniques for selective modification of the electrochemical property of a polyimide surface. High quality and highresolution copper patterns on polyimide surfaces are produced when the surface-modified sample is subsequently placed in an electroless plating solution. These results demonstrated that the use of laser-selective-modification of surface properties in conjunction with other batch thin film deposition processes provides an attractive approach for area-selective metallization for a variety of applications in which high writing speed and high sensitivity are required.