Showing papers on "Pulsed laser deposition published in 1986"

Low‐temperature deposition of high‐quality silicon dioxide by plasma‐enhanced chemical vapor deposition

Abstract: Thin films of high‐quality silicon dioxide have been deposited at low temperatures by plasma‐enhanced chemical vapor deposition. A deposition rate much lower than that used in conventional plasma‐enhanced processes is found to be crucial in obtaining material with reproducible, good properties. Controlled, slow deposition is achieved by using very low flow rates of reactive gases, together with a much higher flow of inert carrier gas to ensure uniformity. Films deposited at usual high deposition rates (∼500 A/min) exhibit irreproducible and poor electrical properties and are porous. Those deposited slowly (∼60 A/min) have very reproducible properties, are relatively dense and exhibit very good electrical integrity. Oxides deposited using a substrate temperature of 350 °C compare favorably with those deposited at 700°C using atmospheric‐pressure chemical vapor deposition and can be deposited routinely over a wide range of oxide thickness. Deposition at 275 °C results in similar properties but with increase...

Low temperature silicon epitaxy by hot wall ultrahigh vacuum/low pressure chemical vapor deposition techniques: surface optimization

Abstract: Fundamental equilibrium considerations derived from the system have been successfully employed in the design and operation of a novel low temperature epitaxial silicon process. Films have been deposited in the range, with all resulting material epitaxial. TEM studies showed the transition to high quality, low defect density material to occur between 750° and 800°C, and such films were found to be of high chemical purity as well. In addition, UHV/CVD is shown to be a high throughput multiwafer system, achieving good film uniformities in a high wafer packing density environment, attributable to operation in the low pressure limit of chemical kinetics.

Propagation of explosive crystallization in thin Rh–Si multilayer films

Abstract: Alternating layers of Si (400–500 A thick) and Rh (200 A thick), up to 21 layers altogether, have been deposited by electron beam evaporation under high vacuum conditions on to thermally oxidized silicon substrates at room temperature. Many of the as‐deposited samples exhibit varying degrees of surface roughness. RBS and AES profiles of these samples show that layer intermixing has occurred; the number of layers consumed in the reaction correlates with the degree of surface roughness. The compounds Rh4Si5 and Rh3Si4 have been identified by x‐ray diffraction. Both compounds are known to form by nucleation‐controlled kinetics at temperatures in excess of 800 °C. However, in this case it appears that reaction occurred via an explosive crystallization process initiated in situ by the arrival of hot Si microparticles. Propagation of the crystallization wave front around secondary Si microparticles results in the formation of a variety of striking geometric surface morphologies. These morphologies can be grouped into three distinct classes or types. Though individual morphologies arise from a random process, the emission of Si microparticles during evaporation, each class of morphologies is itself phenomenologically repeatable and relates to the energy balance governing the propagation of the explosive crystallization wave front. In addition, multilayer films left unreacted after deposition have been explosively crystallized at room temperature by tapping with a stylus or by pulse laser heating, with similar results.

Laser chemical vapor deposition of gold: Part II

Abstract: The laser‐induced pyrolytic deposition (LCVD) of high purity gold metal is discussed. The effects of laser flux and cell temperature are examined for the deposition process. Rates of deposition, resistivities, and deposit quality are highlighted.

Transient nonlinear laser heating and deposition: A comparison of theory and experiment

Abstract: Time‐dependent nonlinear laser‐heating calculations have been applied to the laser chemical vapor deposition of reflective metallic coatings on absorptive low thermal conductivity substrates such as fused quartz. The surface temperature profile is modified by the changing optical properties of the substrate as the film is deposited, leading to a decrease in the surface temperature and flattening of the temperature profile with increasing irradiation time and film deposition. The results of the theoretical calculations are compared with real‐time optical measurements of the deposition rate of Ni from Ni(CO)4 on SiO2 using a CO2 laser as a function of irradiation time, yielding excellent agreement.

Growth of silicon homoepitaxial thin films by ultrahigh vacuum ion beam sputter deposition

Abstract: Silicon homoepitaxial films have been grown by ion beam sputter deposition using an ultrahigh vacuum (UHV) apparatus with in situ diagnostic equipment. The deposition conditions are characterized and the beginning of single crystal growth occurs at 250 °C. Films of high crystalline and morphological quality are obtained at deposition temperatures above 700 °C, where good doping element transfer efficiency from the target to the film is observed. Room temperature bulk mobility is found for film thicknesses as low as 0.5 μm and deposition temperatures near 700 °C.

Plasma-Surface Interactions in Plasma-Enhanced Chemical Vapor Deposition

Abstract: The promotion of chemical reactions by glow discharges (plasmas) has been practiced for many years (I, 2). Recent interest has focussed on the use of radio frequency (rf ) glow discharges to form thin films of insulators, semiconductors, and conductors in the fabrication of electrical and optical devices. For example, numerous organic polymers (3-5) and inorganic elemental and compound materials (6-12) have been deposited by plasma­ enhanced chemical vapor deposition (PECVD). This technique takes advantage of the high energy electrons present in glow discharges to dissociate and ionize gaseous molecules, thereby forming chemically active radicals and ions. Since thermal energy is not needed to break chemical bonds, a variety of film materials can be formed on temperature-sensitive substrates (e.g. polymers or low melting point metals). The plasma environment in PECVD performs two basic functions. First, reactive chemical species are generated by electron impact collisions, thereby overcoming kinetic limitations that may exist in CVD processes. Second, the discharge supplies energetic radiation, primarily positive ions, but also neutral and metastable species, electrons, and photons, that bombard surfaces immersed in the plasma and thereby alter surface chemistry. Specifically, ion bombardment of growing film surfaces plays

Laser direct writing of single‐crystal III‐V compounds on GaAs

Abstract: Laser selective chemical vapor deposition and direct writing of GaAs and its ternary alloys with P have been achieved on GaAs substrates. An Ar+ laser is used to locally heat areas where selective deposition is desired on a substrate which is uniformly biased to a temperature in the range of 25–500 °C. Epitaxial growth was achieved by carefully controlling the deposition parameters to reach growth rates low enough, typically 20 A/s, for the reaction kinetics of the pyrolitic process to take place. Cross‐sectional transmission electron microscopy and photoluminescence results indicate that the quality of the deposited material is comparable to that grown with the conventional metalorganic chemical vapor deposition technique.

SiO 2 Film Deposition by KrF Excimer Laser Irradiation

Abstract: Deposition of SiO2 on a Si substrate by irradiating SiH4–O2–N2 mixture gas with focused KrF excimer laser (wavelength: 249 nm) was carried out. The deposition rate was 300A /min at a substrate temperature of 250°C. The deposition strongly depends on the substrate temperature, laser power and flow ratio of O2/SiH4, and these parameters have individual threshold values for the film deposition. Photo-initiation phenomena in SiO2 deposition are observed for the first time. The deposited film was evaluated by etching and infrared measurements together with electrical measurements.

Laser enhancement of thermophoretic deposition processes

Abstract: Axial CO 2 laser radiation has been shown to have a significant influence in modifying the deposition of silicon dioxide in the modified chemical vapor deposition (MCVD) fiber preform process. Experiments on soot deposition with a stationary burner have shown a doubling of both the rate of deposition and the deposition efficiency.

Apparatus and method for chemical vapor deposition using an axially symmetric gas flow

Abstract: In a chemical vapor deposition chamber, an improved technique for providing deposition materials to the growth surface is described in which the gas carrying deposition materials is constrained to have axial symmetry thereby proving a uniform deposition of materials on the substrate. As illustrated in Fig. 4 the gas can be initially directed toward the substrate (10) with a generally uniform perpendicular velocity. The gas can be introduced into the deposition chamber through a multiplicity of apertures (74) and is extracted from the vicinity of the substrate (10) in a manner to preserve the axial symmetry. The apparatus permits convenient control of the deposition process by varying the distance between apparatus introducing the gas carrying the deposition materials and the substrate. The flow of gas minimizes the problems arising from autodoping of the growth layer of material. The flow of gas and generally small size of the deposition chamber minimize particulate contamination of the growing film.

Properties of thin PbF2 films deposited by cw and pulsed laser assisted evaporation.

Abstract: Thin films of lead fluoride were deposited by means of cw or pulsed laser assisted evaporation and were characterized for their structural and optical properties. Continuous wave laser evaporated films had smooth morphology, good optical transmission, and oriented columnar grain structure. The crystallinity of the pulse laser evaporated films, as measured by x-ray diffraction peak intensities, was found to be higher than the cw laser or e−-beam evaporated films and was found to depend on the laser pulse energy density (fluence). These films, however, had higher absorption in the visible range.

Wavelength dependence of laser‐induced sputtering from the (111) surface of BaF2

Abstract: Using blue tunable pulse laser radiation of low fluence, we have investigated laser‐induced sputtering from cleaved BaF2 (111) surfaces under ultrahigh vacuum conditions. Time correlated with the laser pulses the positive ions Ba+, Ba++, (BaF)+ and F+ were observed. Practically no negative ions were found. Neutral atomic fluorine (F 0) was desorbed abundantly. A pulse correlation of F 0 as well as the relative amount of F 0 and F+ could not be established at this stage. The emission yield of all positive ions as well as of F 0 was strongly wavelength dependent and showed a broad resonance around 2.9 eV.

Effect of deposition variables on the chemical vapor deposition of TiC using propane

Abstract: TiC was deposited onto cemented tungsten carbide by a chemical vapor deposition from a TiCl4–H2–C3H8 gas mixture in a horizontal resistance furnace. The deposition rate and the surface morphology of the coatings were investigated with mC/Ti, deposition temperature and total deposition pressure. Deposition rate is maximum at the mC/Ti value of about 0.9 and deposition of TiC is possible in the temperature range 850–950 °C at atmospheric pressure. By reducing the total pressure, the possible temperature range for the reaction is enlarged. The theoretical deposition efficiency and the supersaturation of reactants can also be enhanced by reducing the total pressure, which results in fine and uniform crystal size distributions. The preferred orientation of the TiC deposits is (200).

Molecular reactions at plasma-polymerized film surfaces

Abstract: The ability of a variety of molecules to stick to the surface of a growing plasma‐deposited polymer film was tested by a new technique. An inductively coupled rf plasma of an organic molecule was sampled through an orifice into a vacuum chamber. The beam of all plasma species intersected a substrate and plasma polymer was deposited. A second beam of a probe species was scattered from the surface of the film during deposition in the vacuum chamber and the IR spectra of the final film and the deposition rate were measured to determine the effect of the scattering. Molecules which are not attached to the film include 2‐vinylpyridine, deuterium, C2D2, toluene, and C2Cl4. The molecules O2 and NO readily attach to the growing film while having no effect on the deposition rate. It was also determined that ion bombardment of the film surface does not play a significant role in the deposition process.

Vacuum arc vapor deposition device

Abstract: PURPOSE:To improve the cleanliness of a substrate for vapor deposition and to form a vapor deposited film having excellent adhesiveness and density by disposing an intermediate electrode between a cathode and the substrate of a vacuum deposition device and supplying electric power for heating or high-frequency discharge thereto. CONSTITUTION:The coil-shaped intermediate electrode 18 is disposed between the cathode 8 consisting of a vapor deposition material in a vacuum vessel 2 of the vacuum deposition device and a holder 10 of the substrate 12 for vapor deposition. The inside of vacuum vessel is evacuated to a vacuum by an evacuation system 4 and an inert gas G such as Ar or N2 is introduced from a gas introducing port 6 into the vacuum vessel. A DC voltage is impressed by a DC power source 18 to the substrate 12 to generate a glow discharge near the substrate; at the same time, AC, DC or high-frequency power is applied by a power source 20 to the intermediate electrode 18 to heat the same by which thermions are released and the glow discharge is maintained in a relatively low vacuum degree. The substrate 12 is sputtered by the ionized gas such as Ar and is thereby thoroughly cleaned. The vapor deposited film consisting of the dense cathode material having the high adhesive power is in succession formed on the surface of the substrate 12 by vacuum deposition.

Stepwise Monolayer Growth of GaAs by Pulsed Laser Metal Organic Vapor Phase Epitaxy

Abstract: Atomic layer epitaxy (ALE) of GaAs by pulsed laser metal organic vapor phase epitaxy is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for ideal ALE. This is achieved by a photo-catalytic decomposition of adsorbed trimethylgallium (TMG). Selective enhancement of the decomposition rate for adsorbed TMG on As, with no enhancement for that on Ga is the main reason for suspension of Ga deposition at 100% coverage. A decomposition rate for TMG on As which is about 100 times faster than that on Ga is estimated from a comparison between theory and experiment.

Metal Deposition By Electron Beam Exposure Of An Organometallic Film

Abstract: Metal Deposition by Electron Beam Exposure of an Organometallic FilmL. M. Schiavone and H. G. CraighheadBell Communications Research, Holmdel, New Jersey 07733AbstractWe describe a method of metal deposition by electron beam exposure and pyrolysis of agold containing organometallic polymer. We have demonstrated the formation of metalpatterns on Si, GaAs, and multilayer resist systems with line widths as small as 0.25 um.There has been considerable work on direct deposition of materials by laser drivenprocesses. These methods usually involve depositions of films by pyrolysis or photolysisof gas phase precursors. The handling of these reactive gases, which can be a problem,was eliminated in a recently described technique of laser pyrolysis of solid organometallicfilms.2'3 In this technique, heat from a focused laser beam decomposes an organometallicpolymer removing the organic component and leaving a metal film. Organometallic polymersare commercially available with a wide range of metals and have been used for optical,electrical and decorative coatings.4 The advantage of the organometallic films is thatno vacuum film deposition is required and the handling is similar to standard photoresistprocessing. The laser thermal process provides a way of forming patterns in this material,but the spatial resolution is limited by both the diffraction of light and thermaldiffusion making submicrometer dimensions difficult to obtain.In this letter we describe metal deposition by electron beam exposure and pyrolysisof an organometallic film. This combines the ease of polymer film use with the highresolution possible with electron beam processes. Electron beam lithography is wellestablished for defining submicrometer patterns and is widely used to make photomasks forintegrated circuit fabrication. Organometallic electron beam resists, mostly Sicontaining, are being investigated because of their resistance to etching processes.5However, these have not been used directly for depositing usable patterned metal films.In addition to the higher resolution of electron beam deposition the ease of alignmentand pattern generation lends itself well to the generation of custom circuit connectionsor mask repair. Since electron beam instruments are used to inspect and verify thefidelity of photomasks it is possible that defects of missing absorber film could becorrected in the same instrument used for inspection. There is also a substantialadvantage to eliminating the vacuum deposition process as one less step to introducedefects.The patterning process is outlined in Fig. 1, showing typical dimensions. A scannedelectron beam renders the exposed area insoluble in a developer. The entire sample ofpatterned nonconducting polymer is heated in air to remove the organic material and leavea thinn r metal film. The pyrolysis step, is presumably the same as that of the laserheating 03 and is well developed for these materials.Englehard materials 6854 and NW gold containing 5.5 and 20 wt % Au respectively, wereused in this study. These are proprietary compositions consisting of a gold mercaptidewith organic binders and a small amount of other ingredients to promote adhesion. Theseare true solutions and each was filtered prior to spinning to improve pattern quality.Films were formed by spin coating on Si, GaAs, Glass and polymide substrates and bakedat 120 °C to remove the solvents. Films for electron beam exposure were 0.75 µm thickon Si substrates.We performed test electron beam exposures in a scanning electron microscope with a30Kev beam. Line scans were done at various scan rates with constant beam currents.Currents were on the order of 100 pA and scan rates of several um /Sec. The exposedfilms were developed in methylene chloride which dissolved only unexposed material.The results of one series of exposures for each formulation is shown in the electronmicrographs in Figure 2. Here a series of lines was exposed on each film startingon top with a line dose 'of 0.5 µC /cm. The dosage was decreased by 0.05 ,tC /cm for eachconsecutive line. Figure 2a is of 6854 gold and 2b is of NW gold. From these micrographs,it is seen that eight of the ten lines written in the NW film and only six out of in the6854 film received a high enough line dosage to expose the film. From this we canconclude that NW is more sensitive to the electron beam. This may be due to the higherAu content being more absorbing. The area does sensitivity for these materials appears

Deposition of laser mirrors by laser beam evaporation

Abstract: A 200W c.w. CO2 laser has been used to evaporate thin multilayer films of HfO2-SiO2 and ZrO2-SiO2. Higher values of laser damage resistance were found compared to similar layers produced by electron-beam evaporation.

Influence of water vapor on the output energy of a pulsed oxygen-iodine laser

Abstract: Experimental studies showed that the output energy of a pulsed chemical oxygen-iodine laser depended weakly on the partial water vapor pressure in the resonator right up to values which were three times higher than the oxygen pressure, which corresponded to thermally insulated operation of a generator supplying singlet oxygen to the laser.

Low-Temperature Silicon Epitaxial Growth by CO2 Laser CVD Using SiH4 Gas

Abstract: Silicon epitaxial growth at a low substrate temperature by CO2 laser chemical vapor deposition using SiH4 has been investigated. Single-crystalline Si was grown at a deposition rate of 15 A/s at 650°C under an SiH4 pressure of 0.05 Torr and a CO2 laser power of 6 W/cm2 on an Si substrate. The crystalline quality of deposited Si films was examined by reflection high-energy electron diffraction, and it was found that the deposition rate depends on the incident angle and the polarization of the CO2 laser beam. This is the first report on low-temperature Si epitaxial growth by CO2 laser CVD.

Mechanisms for the deposition of thin metallic films by laser driven gas phase reactions

Abstract: Gas phase processing makes laser deposition over large areas possible but homogeneous nucleation of large atomic clusters must be avoided if films are to be produced. Clusters can be highly variable in size from a few atoms to significant fractions of a micrometer. If conditions do not allow for complete quenching of the clusters produced in the gas phase, these clusters can arrive at the substrate with sufficient energy to self sinter into homogeneous films which are substantially different from metallic films grown by thermal techniques. Using transmission electron microscopy (TEM), we have characterized the microstructure of thin metallic films deposited by laser breakdown chemical vapor deposition and identified a range of deposition conditions which can lead from powders to homogeneous polycrystalline films and mixed phase materials. Gas phase nucleation is dependent on reactant partial pressures and the gas phase quench rate which can be varied in part by adjusting the H/sub 2/ content of the source gas. Manipulation of these parameters can vary powder size from about one micrometer to less than 2 nanometers. Variation of the quench rate during the deposition of polycrystalline films varies the grain size in the films. Heating the substrate drastically changes the conditionsmore » under which the film is formed and as a consequence, can radically alter the microstructure of the film itself. 6 refs., 2 figs.« less

Chemical Vapor Deposition of Gold

Abstract: Chemical vapor deposition of gold from dimethyl-2,4-pentandionato gold (III) and two fluorinated derivatives is reported. At substrate temperatures of 200–300°C, high purity gold films were obtained on SiO2 and Si substrates. Films with resistivities down to 1.3 times that of bulk gold were obtained at deposition temperatures of ~200°C, where films with very small grain size could be deposited.

Ion-Assisted Processes In Optical Thin Film Deposition

Abstract: The microstructure, crystallinity, and stoichiometry of vacuum deposited thin films are modified substantially if the layer is bombarded by ions during growth. The properties of optical films prepared by ion-assistance are often superior to those produced in vapor deposition. These ion-induced modifications will be explained in terms of recently developed theories and computer simulations.