齋藤 洋司

An accelerated desorption of fluorine adsorbates from silicon surfaces is induced by atomic deuterium (or hydrogen) exposure at low substrate temperature. The reaction processes have been investigated with an situ Auger analysis and thermally stimulated desorption spectroscopy (TDS) measurements. The experimental results of both fluorine decay and TDS spectra indicate that two kinds of the reaction products including SiDF molecules desorb from the surface in the initial stage of the reaction between the atomic deuterium and the fluorinated silicon. With the decrease in fluorine coverage, SiDF molecules desorb as the main reaction products. A deuterium-passivated silicon surface is obtained by atomic deuterium treatment at 200 degrees C for 30 min from the fluorinated surface.

We have examined new etching methods using vacuum ultraviolet (VUV) light for application to fabrication of semiconductor devices. We have successfully carried out highly selective and highly anisotropic etching of silicon dioxide using anhydrous HF as an etching gas. We also obtained fine 0.1 mu m Si patterns using photo-ionized CF3 + ion etching. We carried out the low-temperature removal of native-oxide on Si(100) for very low-temperature homoepitaxy. We have explained the characteristics of VUV light-induced surface reactions on semiconductor material.

Direct oxynitridation of silicon is performed by remote-plasma excited nitrogen and oxygen gaseous mixtures at 550 degrees C. Nitrogen atoms are mainly incorporated near the SiO2-Si interfaces with Auger electron spectroscopy measurements. We have controlled the peak density of nitrogen up to at least several atomic percents, varying the partial pressure of nitrogen and oxygen, The supply of active oxygen species is required for the growth of oxynitride films, but their excess supply reduces the density of nitrogen in the films, The proposed technique is a unique process to obtain high quality ultrathin dielectrics. (C) 1996 American Institute of Physics.

Vacuum-ultraviolet (VUV) light induced etching of thermally grown silicon dioxide films was investigated near room temperature. We used synchrotron radiation as a VUV light source and anhydrous-hydrogen-fluoride as anetching gas. The silicon dioxide is etched only in the VUV light irradiated area, and etched selectively withrespect to (100) oriented singlecrystalline silicon, which is not etched even under the irradiation. Moreover, wehave found anisotropic etching with the patterned polycrystalline silicon etching mask. The ratio of the etch rateof Si02 in the vertical direction compared to the horizontal direction of the substrate surface is about 30. Fromthese results, the etching process is due to the photo-induced surface reaction. The excitation of the adsorbedAHF molecules or SiCO2surface would be a dominant process. © 1995 The Japan Society of Applied Physics.

Extraction of fluorine adsorbates on silicon surfaces is induced by exposure to atomic hydrogen. The decay process of fluorine has been investigated with Auger electron microscopy and is discussed in terms of chemical kinetics. The desorption rate depends on the hydrogen exposure time, the substrate temperature, and the supply of atomic hydrogen. In the initial stage, the reaction proceeds with second-order kinetics with an activation energy of about 0.4 eV. Moreover, two hydrogen atoms seem to take part in the reaction at the same time, according to the rate dependence on the supply of atomic hydrogen. With the decrease of the fluorine coverage, a first-order process dominates the reaction, and its activation energy is about 0.56 eV. The fluorine adsorbates on silicon are completely removed by annealing above 200-degrees-C for 30 min, using the atomic hydrogen.

Vacuum ultraviolet light from synchrotron and undulator radiation sources creates defects in hydrogenated amorphous silicon films. The dependence of the defect creation kinetics on photon energy has been investigated. The concentration of the defects induced by photons having an energy above 24 eV is proportional to the irradiation time. The rapid defect creation is due to the breaking of silicon-silicon bonds by the photo-induced plasmons.

Nonselective chemical vapor deposition of tungsten films on silicon and silicon dioxide substrates by remote-plasma excited argon and hydrogen gaseous mixtures at substrate temperatures below 350 degrees C was achieved. The growth rate shows an almost linear,relationship with the hydrogen partial pressure above 0.6 Torr, but depends slightly on the argon partial pressure. The hydrogen partial pressure also influences the resistivity of the deposited films. The sufficient supply of the excited hydrogen improves growth rate and film properties.

Hydrogenated amorphous silicon films are rapidly degraded by irradiation with vacuum-ultraviolet light from a synchrotron. The main light-induced defects are silicon dangling bonds as deduced from measurements of electron spin resonance. Defect creation is due to bond breaking of silicon-silicon bonds by excited electrons having a high energy. The value of the required activation energy (about 1 eV) has been obtained by studying the process of defect decay during thermal annealing.

Plasmaless etching using ClF3 gas has been investigated on nitride films with different composition. For the sputter deposited and thermally grown silicon nitride films containing no hydrogen, the etch rate increases and the activation energy decreases with increase of the composition ratio of silicon to nitrogen between 0.75 and 1.3. This fact indicates that the etching is likely to proceed through the reaction between Si and ClF3. The native oxide on the silicon-nitride films can also be removed with ClF3 gas. Ultra-violet light irradiation from a low pressure mercury lamp remarkably accelerates the removal of the native oxide and the etch rate of the thermally grown silicon-nitride films. For the plasma deposited films, the etch rate is strongly accelerated with increasing hydrogen content in the films, but the activation energy hardly depends on the bounded hydrogen in the films, consistent with the results for Si etching.

At room temperature, anisotropic etching of both (100) and (111) oriented single-crystalline silicon substrates is successfully achieved, using a thermally excited C1F3 molecular beam. The morphology of the etched surface is better than that using Cl2. The etching rate is more than 50 angstrom/min, and the ratio of etching rate of vertical direction to that of horizontal direction is more than eight. Process-induced damage in the metal-oxide semiconductor device was not observed from the capacitance-voltage characteristic measurements.

Silicon etching using ClF3 gas has been carried out at various substrate temperatures from -20 to 120-degrees-C. The etching properties (etch rate, pressure effect, and surface morphology) depend remarkably on the temperature. Based on the mass spectroscopic measurements, SiF4 is specified as a main product. The minor product SiF2 is also found, and the ratio of the signal intensity of SiF2 to that of SiF4 decreases with temperature. From Auger electron analyses on the etched surface, the density of fluorine atoms on the surface decreases with increasing the temperature. It is concluded that the density of the fluorosilyl species greatly influences the etching reaction process.

The thermal annealing effect on resistivity is investigated for polycrystalline silicon films passivated with plasma-enhanced chemically vapor deposited silicon-nitride (p-SiN) films. The resistivity in the heavily doped polycrystalline silicon films has a minimum value at an annealing temperature of approximately 500°C, and the resistivity in the lightly doped films monotonically increases with the increase of annealing temperature. The dependence of the resistivity on annealing temperature is explained in terms of the variations of the density and the energy level of the traps at the grain boundaries, which are caused by the adsorption or the decomposition of hydrogen atoms. These conclusions are obtained by comparing the dependence in the polycrystalline silicon films with p-SiN films with that in the plasma-hydrogenated polycrystalline silicon films without p-SiN films.