Vladimir S. Ban

Chemical Processes in Vapor Deposition of Silicon I . Deposition from and Etching by

Chemical processes occurring in the vapor deposition of Si from SiCl/sub 2/H/sub 2/ and in the etching of Si by HCl were studied by means of a mass spectrometer coupled to the chemical-vapor-deposition reactor. This setup was successfully used for the qualitative and quantitative analysis of the composition of the vapor phase in the Si-Cl-H system. Species found in the vapor phase were H/sub 2/, HCl, SiCl/sub 2/, SiCl/sub 2/H/sub 2/, SiCl/sub 3/H, and SiCl/sub 4/, and their partial pressures were measured as a function of temperature, Cl/H ratio, and of the chemical nature of the initial gaseous mixture entering the reactor. The experimentally determined partial pressures were compared with the equilibrium partial pressures of vapor species, calculated from the newest thermochemical data for the Si-Cl-H system. Based on these results, the nature and the extent of chemical processes in systems studied are discussed. (WDM)

Mass spectrometric and thermodynamics studies of the CVD of some III–V compounds

Abstract A time-of-flight mass spectrometer has been coupled to a CVD reactor. With this set-up it has been possible to elucidate the chemistry of CVD processes occuring in the synthesis of several III-V compounds. In particular, vapor phase transport of the Group III metals, the thermal decomposition of the Group V hydrides, and the reactions leading to the deposition of III-V compounds have been studied. Results of these studies will be presented and discussed. Computer calculations based on mass spectrometric identification of vapor species and processes in the CVD reactor have been made in order to compare the actual with the calculated partial pressures of vapor species present in reactors. The applicability of thermochemical calculations in predicting proper conditions for the growth of some desired III-V material will be examined. On the basis of these results, we intend to discuss the thermodynamical and kinetical aspects of the CVD of III-V compounds.

Organic vapor phase deposition: a new method for the growth of organic thin films with large optical non-linearities

Abstract We describe a novel technique, organic vapor phase deposition, for the growth of thin films of optically non-linear organic salts. A volatile precursor of each component of the salt is carried as a vapor to a hot-wall reaction chamber by independently controlled streams of carrier gas. The components react to form a polycrystalline thin film on substrates of glass and gold. Excess reactants and reaction products are purged from the system by the carrier gas. As an example, we demonstrate the growth of polycrystalline, optically non-linear thin films of 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) with > 95% purity.

LOW PRESSURE ORGANIC VAPOR PHASE DEPOSITION OF SMALL MOLECULAR WEIGHT ORGANIC LIGHT EMITTING DEVICE STRUCTURES

A new technique for the deposition of amorphous organic thin films, low pressure organic vapor phase deposition (LP-OVPD), was used to fabricate organic light emitting devices (OLEDs) consisting of a film of aluminum tris-(8 hydroxyquinoline) (Alq3) grown on the surface of a film of N′-diphenyl-N,N′-bis(3-methylphenyl)1-1′biphenyl-4-4′diamine. The resulting heterojunction OLED was found to have a performance similar to conventional, small molecular weight OLEDs grown using thermal evaporation in vacuum. The LP-OVPD grown device has an external quantum efficiency of 0.40±0.05% and a turn-on voltage of approximately 6 V. The rapid throughput demonstrated with LP-OVPD has the potential to facilitate low cost mass production of conventional small molecule based OLEDs, and its use of low vacuum in a horizontal reactor lends itself to roll-to-roll deposition of organic films for many photonic device applications.

The chemistry and transport phenomena of chemical vapor deposition of silicon from SiCl4

The chemical vapor deposition (CVD) of silicon is among the most important synthesis methods in electronic industry. We developed and applied novel methods of characterization to studies of CVD of Si from SiCl4. In particular, we studied the chemistry of the Si-Cl-H system as well as transport phenomena, such as the momentum, heat, and mass transport in a horizontal CVD reactor. A flow visualization was used to study the flow dynamics, i.e., the momentum transport in the reactor. The heat transport was studied by measuring temperatures at various points in the reactor as a function of flow-rates and susceptor temperatures. A specially designed movable probe was used for a mass spectrometric sampling in the reactor. In these experiments, we were able to determine quantitatively partial pressures of reactants and products at some desired location in the reactor, thus studying the mass transport during the CVD of Si. The conducted studies of transport phenomena were used to establish a model which can be used to predict the efficiency and uniformity of the deposition.

Epitaxial growth and properties of semiconducting ScN

Epitaxial growth of ScN has been investigated in the temperature range 750–1150 °C, using the reaction of ammonia with the volatile scandium halides produced by the reaction of HCl, HBr or HI with Sc metal. The optimum temperature range for epitaxial growth of ScN on α-Al2O3 was found to be 850–930 °C. The linear thermal expansion coefficient of ScN was measured to be 8.1 × 10−6/°C, a relatively good match to α-Al2O3. Mass spectrometric studies suggest that the vapor species formed by the reaction of HCl with Sc metal is ScCl2, and that this reacts further with NH3, which is only 5–10% decomposed at 950 °C, to form ScN. As-grown ScN is n-type with electron concentrations in the range 1020–1021 cm−3, and halogen or hydrogen appears to be the principal donor. Doping with C and Si during growth did not give p-type material, nor did post-growth annealing in Mg and Zn vapor. The Hall mobility of ScN is 150 cm2 V −1sec−1 at 300 °K for an electron concentration of 1 × 1020 cm−3, and exhibits a T−1.85 dependence between 300 °K and 77 °K. The optical energy gap of ScN is 2.1 eV at 300 °K.

Langmuir evaporation from the (100), (111A), and (111B) faces of GaAs

Abstract We have measured the Langmuir evaporation of Ga and As from the (100), (111A), and (111B) faces of GaAs above and below the congruent evaporation temperature T c . We have found that T c is lowest for the (111B) face and highest for the (111A) face. These differences can be understood in terms of the different lifetimes of surface Ga on these faces. Furthermore, we have deduced that the evaporation processes are the rate limiting steps in the decomposition of GaAs. Below T c , decomposition is controlled by the evaporation of Ga; above T c it is controlled by the evaporation of As.

Dark current analysis and characterization of In/sub x/Ga/sub 1-x/As/InAs/sub y/P/sub 1-y/ graded photodiodes with x>0.53 for response to longer wavelengths (>1.7 mu m)

The dark current properties of In/sub x/Ga/sub 1-x/As photodiodes, where x is varied from 0.53 to 0.82 for extending the long wavelength cutoff from 1.7 to 2.6 mu m, are described. Detailed analyses of optoelectrical parameters of In/sub 0.82/Ga/sub 0.1/As photodiodes are presented. Dark current, which is a critical parameter and limits the operation of the photodiode, is analyzed and compared with the experimental values. Typical characteristics of photodiodes with cutoff wavelengths of 1.7 mu m (x=0.53), 2.2 mu m (x=0.72), and 2.6 mu m (x=0.82) are presented. The typical and best values of the dark currents obtained are presented. >

Intense second harmonic generation and long‐range structural ordering in thin films of an organic salt grown by organic vapor phase deposition

We discuss the growth of thin films of the organic salt, 4′‐dimethylamino‐N‐methyl‐4‐stilbazolium tosylate (DAST) by the novel process of organic vapor phase deposition (OVPD). These films show long‐range structural ordering and very intense second harmonic generation efficiencies (SHG) significantly greater (when normalized for thickness) than that of randomly oriented pure DAST powders. This is the first demonstration of such intense SHG radiation and long‐range ordering for a thin film sample of a nonlinear organic salt. Furthermore, this work suggests that OVPD represents a general technique for growing thin films of highly polar, nonlinear optical materials such as DAST.

Novel reactor for high volume low-cost silicon epitaxy

Abstract The chemical vapor deposition of epitaxial layers of silicon is a widely used process in the electronic industry. It is a batch process and the relatively small capacity (i.e., 20–30 wafers) of epitaxial reactors significantly contributes to the expense of the process. We thus embarked on a research project aimed at a significant expansion of the reactor capacity. The first step was to conduct a complete characterization of the presently used reactors by means of flow visualization, temperature measurements and mass spectrometric studies; results of these studies will be briefly presented and discussed. The main conclusion from these studies was that up-scaling of present reactors is not economical. We thus designed and constructed a novel epitaxial reactor, radically different from current types. In this reactor the susceptor structure consists of parallel graphite discs. Wafers are fastened to one or both sides of these discs. The nutrient gaseous mixture is injected into spaces between discs by a specially designed gas distributor, which delivers the same amount of the mixture to all interdisc spacings, thus insuring the wafer-to-wafer thickness uniformity. A combination of the rotation of the susceptor discs with the gas distributor motion insures the on-the-wafer thickness uniformity. The above described parallel packing allows much higher reactor capacities (e.g., 50–100 wafers). It also results in a more economical reactor in terms of consumption of energy and chemicals. We shall illustrate the application of the novel reactor (known as the “RCA Rotary Disc Reactor”) to epitaxial deposition of silicon from SiCl 2 H 2 .