Reactive Ambient Research Articles

Formation of epitaxial CoSi2 on Si(100): Role of the annealing ambient

With a thin Ti layer interposed between a Si(100) substrate and a Co overlayer, the inversion of the Co and Ti films and the formation of a partly relaxed epitaxial CoSi2 layer on Si(100) can be obtained by steady-state annealing in inert as well as reactive ambients. A reactive ambient chemically binds the Ti near the surface as an oxide or nitride layer, which preserves the bilayer structure during a high temperature treatment. In a nonreactive ambient, the Ti and CoSi2 layers react further, resulting in a uniform layer of Co0.25Ti0.75Si2 and CoSi2. An eptiaxial orientation of CoSi2 is retained even in that case.

Pulsed laser deposition of electronic ceramics

Pulsed laser deposition (PLD) is a unique physical vapor deposition technique which has gained considerable attention recently in the deposition of high quality, high temperature superconductors. In this technique, a short pulsed laser (<100 ns) is focused onto a target of the material to be deposited. The rapid heating, vaporization and plasma formation at the target surface result in a highly forward directed plume of atomic and gas phase species. Unique to this technique is the stoichiometric evaporation of multicomponent materials, irrespective of the individual constituent vapor pressures. Condensation of the stoichiometric plume onto heated single-crystal substrates results in the formation of single-phase, oriented thin films. Typically, depositions are performed in high pressures of reactive gas ambients. YBa 2Cu 3O 7-δ thin films deposited by PLD have excellent d.c. and high frequency transport properties. For YBa 2Cu 3O 7-δ epitaxial multilayer structures of superconductor/dielectric/superconductor are reported. Microwave devices fabricated from superconducting thin films and multilayer films have demonstrated significant performance improvements over devices fabricated from conventional materials. High quality ferroelectric thin films are also being deposited by PLD. The deposition and electrical characterization of oriented PbZr x Ti 1- x O 3 thin films are reported. PLD is shown as a versatile physical vapor deposition technique and will soon be an important industrial coating technique.

Thermal Studies of Au-Ti Thin Films Deposited on Oxide Substrates

ABSTRACTCo-evaporated Au-Ti thin films deposited onto sapphire and silicon dioxide substrates were thermally treated over a temperature range of 300–900°C in both vacuum and reactive amb ients. Vacuum annealing produced negligible reaction between the oxide substrate and film, the Au-Ti, however, reacted to form intermetallic compounds with little net elemental redistribution in the film. Heat treating in oxygen resulted in segregation of titanium to the surface where it formed both rutile and anatase structures. In addition, the high interfacial energy between the gold and the oxide phases led to the formation of large (5 micron diameter) gold particles on the film surface or voids at the titania-gold interface. Annealing in Ammomia produced an oxynitride surface in addition to the Ti-Au separation, Au particulate formation, and/or interfacial voiding already observed. The extent of surface degradation observed during these reactive ambient anneals varied with Ti concentration and temperature. The film did not react with SiO2 under any circumstances, however, at temperatures above 650°C in reactive ambients the titanium accumulated at the Al2,O3 interface. These results were obtained by RBS, X-ray diffraction, TEM and SEM.

Controlled-ambient photolithography of polysilane resists at 193 nm

Various polysilanes have been examined as self-developed photoresists at 193 nm and the benefits of imaging these materials in controlled, reactive ambients have been determined. Plasticization of the irradiated polymer due to reaction with oxygen is avoided when dry, oxygen-free ambients are employed. In addition, the redeposition of silicon from the ablated polysilane, which is prevalent in a one-pulse imaging mode, is greatly reduced when NF3 or CF2Cl2 are used as exposure ambients. Laser desorption mass spectrometry indicates that thermally activated decomposition of the polysilanes at fluences &amp;gt;100 mJ/cm2 causes more extensive fragmentation of the desorbed molecules. This results in the formation of higher volatility products upon halogenation.

Electrical characteristics of oxynitride gate dielectrics prepared by rapid thermal processing of LPCVD SiO 2 films

High-quality oxynitride gate dielectrics have been fabricated by rapid thermal processing of LPCVD SiO2 in reactive ambients (NH3 and O2). The as-deposited CVD oxides of 200 Á in thickness show no early breakdowns. The breakdown distribution becomes tighter, the interface state density is reduced, and the interface endurance property is improved after rapid thermal nitridation and reoxidation.

Electrical properties of thin reoxidised nitrided interpolyoxides prepared by rapid thermal processing

In the letter ultrathin (150 Å) interpoly oxynitride dielectrics have been fabricated using multiple in situ rapid thermal processing in reactive ambient (NH3 and O2). It is found that rapid thermal reoxidation greatly enhances the dielectric strength and charge-to-breakdown of the rapid thermal nitridcd oxide samples with an increase in the final film thickness less than 10 Å. Breakdown fields in excess of 11 MV/cm2 have been obtained.

Performance and Reliability of Ultrathin Oxynitride Gate Dielectrics Prepared using In-Situ Multiple Rapid Thermal Processing

ABSTRACTThe electrical characteristics of ultrathin oxynitride gate dielectrics prepared by in-situ multiple rapid thermal processing in reactive ambients (O2 and NH3) have been studied. Specifically, the conduction mechanism, charge trapping properties, time-dependent breakdown, and interface hardness in oxynitride films have been characterized as a function of both RTO and RTN processing parameters. In addition, N-channel MOSFET's have been fabricated using oxynitrides as gate dielectrics and their hot carier immunity has been examined and compared with devices with pure thermal oxides. Devices with superior electrical characteristics and reliability have been produced by optimizing RTO/RTN parameters.

I n s i t u development of ion bombarded poly(methylmethacrylate) resist in a reactive gas ambient

Self-development of poly(methylmethacrylate) (PMMA) resist was done by irradiating various rare-gas ions at 50 keV in a mixed gas atmosphere of XeF2 and O2 to enhance the self-development rate, and the effects of various exposure parameters, including gas pressure, mixing ratio, dose, current density, pulse repetition period for pulsed beam irradiation, and ion mass, have been investigated. It was observed that the self-developing rate of PMMA for exposure without gas was very low at high doses of ≥1015/cm2, while the rate with the gas increased almost linearly with increasing dose. This is because the irradiated surface is carbonized and has a low sputtering rate after the high-dose exposure, while the ion assisted chemical process also occurs on the carbonized surface, almost independent of the surface state. It was also found that the self-developing rate depends on the current density and pulse repetition rate. This suggests that the reaction process has a decay time of a few ms.

IR transmittance studies of hydrogen-free and hydrogenated silicon nitride and silicon oxynitride films deposited by reactive sputtering

Amorphous silicon nitride and silicon oxynitride films were deposited by reactive r.f. sputtering in various reactive ambients of nitrogen, oxygen and hydrogen of different compositions. The IR transmittance of the films was studied as a function of their hydrogen content and the oxygen:nitrogen ratio. The results were discussed in terms of compensation of gap states by hydrogenation. The microscopic structure of the silicon oxynitride films is believed to depend on the oxygen:nitrogen atomic ratio.

Visible-laser etching of refractory metals by surface modification

A two‐step laser etching technique for Mo and W films is described. In the first step, the laser modifies the chemical composition of the metal surface; in the second, deep etching of the pre‐exposed areas is by broad‐area heating in a reactive ambient. The surface modification takes place in the presence of Cl2, which etches the native‐metal oxide and replaces it with a more volatile metal halide. Deep etching is performed with NF3. Since the native oxide is resistant toward etching with NF3, the second step is selective with respect to the laser‐halogenated area and is, in effect, a chemical amplification of the surface modification. Well‐delineated, high‐contrast patterns are obtained with this method.

Position and pressure effects in rf magnetron reactive sputter deposition of piezoelectric zinc oxide

c-axis oriented thin films of piezoelectric ZnO have been deposited on room-temperature substrates by rf magnetron sputtering of zinc in a reactive ambient of 100% oxygen over a pressure range from 5–70 mTorr. Below 10 mTorr the film structure, orientation, and physical properties depend on the position of the substrates with respect to the target. This is attributed primarily to resputtering of the film in the region of the target erosion area by high-energy neutral oxygen. At higher pressures where the mean free path inhibits such effects, the film structure and properties are uniform. At 700-W sputtering power, the optimum pressure lies between 20–30 mTorr leading to highly oriented ZnO over a large area of plasma with a dielectric constant of 11, conductivity at 300 °C=2×10−10 Ω−1 cm−1, and Rayleigh wave velocity=2600 m/s. The films are characterized using optical transmittance, electrical conductivity, dielectric constant and SAW, and acoustic microscope measurements.

Optimization of thin film wetting and adhesion behavior

The coatability and adhesion behavior of photoresist films on semiconductor device substrates is related to the magnitudes of the polar components of surface energy of the two materials. The best adhesion during wet etching is achieved if the polar surface energy component γ p of both the film and the substrate is small. However, in the case of a resist with a reasonably large γ p, it is necessary to make the γ p of the substrate sufficiently large to permit good wetting. It is thought that these results are applicable to other thin film-substrate combinations and to adhesion failure during exposure to many different reactive ambients.

Al 2 O 3 Films Prepared by Electron-Beam Evaporation of Hot-Pressed Al2O3 in Oxygen Ambient

This paper describes the deposition as well as the electrical and physical evaluation of Al2O3 films on silicon substrates prepared by reactively evaporating Al2O3 in an oxygen ambient. The Al2O3 was evaporated using an electron-beam gun. Several ambient parameters were varied in order to obtain their effects on film properties. Variations in the substrates preheating, in temperature of the substrates during evaporation, and rates of evaporation were made. Measurement of MOS capacitance vs voltage provided data concerning the interface properties between oxide and silicon as well as conduction of the Al2O3 with applied bias conditions. These measurements indicated that mobile charge manifested by offset voltage in the C-V plots could be reduced below 7×1011 e/cm2 either by post heat treatments or deposition on heated substrates. The dielectric constant of these films at 100 kHz ranged between 7.6 and 7.8. Ellipsometry measurements show that the index of refraction varies from 1.72 to 1.55 as the deposition parameters were altered. X-ray analysis indicates that these films are fundamentally amorphous or are finely grained polycrystalline. Etching of the films in buffered HF suggests some degree of porosity. It may be generally concluded that the films produced by electron-beam evaporation were oxygen deficient and less dense than bulk. This result suggests that the Al2O3 source dissociates during the electron-beam evaporation. Obtaining stoichiometric Al2O3 onto silicon substrates requires the confinement of the evaporant and the reactive ambient in a chamber below the substrate.