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Ion beam assisted etching for GaAs device applications
Classified abstracts 5790-5799 35 5790. Statistical measurements of irradiance fluctuations of a multipass laser beam propagated through laboratory-simulated atmospheric turbulence. (USA) Experimental results are presented for the statistics of 0.6328/~m laser irradiance fluctuations for multiple-pass propagation through a laboratory-simulated atmospheric turbulence of strength C,2=2.476× 10 1~ m 2,,3 and the smallest scale size Io=2.74 mm. The coefficients of variation 70, skewness ~'l, and excess )'2 of irradiance fluctuations are plotted as a function of path length. From the plots of72 vs 71 for various values of a 2 ( - 1.23 kV'tC2L 1~ ) in different regions within the turbulence, the following forms of the probability distribution functions for the irradiance fluctuations are considered: lognormal, RiceNakagami, m distribution, g a m m a (and exponential), and K distribution. We have also demonstrated the characteristic feature of - 8 / 3 power law behaviour of power spectrum and the shift of Tatarski's peak frequency in the case of strong turbulence. Arun K Majumdar and Hideya Gamo, Appl Optics, 21 (12), 1982, 2229 2235. 35 5791. Magnetic dipole infrared atmospheric oxygen bands. (USA) Molecular vibration and rotation constants are obtained for the metastable ~lA0 electronic state of molecular oxygen. The constants are given for the v = 0 and v = 1 vibrational levels by combining recent highresolution laboratory measurements with high-resolution observatorybased planetary and solar spectra of the magnetic dipole transitions of the system ~Ag~ X'~Zo. Laurence S Rothman, Appl Optics, 21 (13), 1982, 2428 2431. 35 5792. Probability density function of the intensity for a laser-generated speckle field after propagation through the turbulent atmosphere. (USA) It is shown that, because of the effects of the turbulent atmosphere, the probability density function of the intensity for a monochromatic, fully developed speckle pattern changes from an exponential distribution at low turbulence levels to a K distribution as the turbulence level increases. A physical model that leads to the K distribution is proposed, and the parameters of the K distribution are derived in terms of the strength of turbulence, path length, wavelength, and beam size. The work is then extended to polychromatic and partially developed speckle patterns and to speckle with a coherent background. Good agreement is obtained between the theoretical predictions and experimental measurements. V S Rao Gudimetla and J Fred Holmes, J Opt Soc Am, 72 (9), 1982, 1213 1218. 35 5793. Helium bubble and blister formation for Ni and an amorphous Fe Ni Mo B alloy during 5 keV implantation at 300 K. (GB) Results are presented for helium bubble formation in Ni and a m o r p h o u s Fe¢oNi38Mo4Bls during 5 keV He-implantation at 300 K. The formation of helium blisters on the surface is also reported. (Belgium) H Van Swijgenhoven et al, Rad E[lbcts Letts, 67 (6), 1982, 175 180. 35 5794. The effects of defects on charged particle propagation in crystalline solids. (USA) The defects present in solid materials generally have important effects on the electronic, structural, thermal, mechanical and other properties of these solids; a knowledge of these is essential from any application viewpoint. Recently ion implantation has been recognized to be an extremely versatile technique for controlling any of these properties, either by doping desired foreign atoms in the solids or by producing a known and controlled a m o u n t of damage, or both. For a complete understanding and successful application of these phenomena, a thorough knowledge of the interaction of propagating charged particles with the defects, and of the resulting damage, is required. The present state of understanding and the work done so far on this subject are reviewed in this article and the need for and direction of further work are pointed out. (India) Anand P Pathak, Rad Ell/Oct,s, 61 (1/2), 1982, 1~46. 35 5795. Effect of irradiation on CsNO~, RbNO3 and N a N O 2 crystal structure. (USA) Studies of the structure changes in heated (20 200'C) and 7-irradiated (10' 5 × 109 R,E= 1.3 MeV, Ti~,a. =40~C) crystals CsNO3, R b N O 3 and N a N O 2 have been carried out by means of X-ray diffraction methods. The investigation of temperature effect on the crystal structure has shown that the phase transformation in C s N O 3 and N a N O 2 are of continuous type while that in R b N O 3 is discontinuous. It has been found that crystal structures o f C s N O 3 and N a O 2 change under irradiation in the same way, 232
as they change under heating. No changes of R b N O 3 crystal structure caused by irradiation have been found. Experimental results agree with an assumption that radiation-induced structure changes of high-temperature type can be observed only in the compounds, the phase transition of which is of continuous type. (USSR) E V Kolontsova et al, Rad E(['ects Letts 67 (6), 1982, 181 185. 35 5796. High resolution ion beam lithography. (USA) A new type of high resolution mask for ion beam lithography is described. The mask employs a thin membrane with regions of two different thicknesses to provide contrast for proton exposure of resist. A conventional ion implantation system is used to generate a collimated beam of protons for flood exposure of the sample. Beam energy is chosen so the protons pass through the thin areas of the mask and emerge with sufficient energy to expose the resist, but are stopped in the thick areas. Experiments using polyimide membrane masks have yielded promising results. The ability to reactive ion etch structures with nearly vertical sidewalls in polyimide allows the fabrication of masks having both high contrast and high resolution. The stopping power of polyimide was determined by measuring the transmission of protons through membranes of known thickness, as a function of incident beam energy. In the energy range from 50 200 keV, the stopping power of polyimide for protons was measured to be 4 1 0 0 keV/itm. Mask fabrication procedures and exposure experiments to determine the resolution of this technique are reported. Patterns with linewidths of <0.1 l~m have been successfully replicated. N P Economou et al, d Vac Sci Technol, 19 (4), 1981, 1172 1175. 35 5797. Ion beam assisted etching for GaAs device applications. (USA) We have developed a new anisotropic dry etching technique for GaAs that results in etched surfaces of sufficient quality for many device applications. In this technique a chemically reactive gas from a jet and an ion beam from a K a u f m a n ion source are directed on the sample surface. We have termed this technique ion beam assisted etching (IBAE) since the chemically reactive species is assisted by the independently controlled energetic ions. This method has produced anisotropically etched patterns with periods as small as 3200 A with easily attainable aspect ratios of 10:1. Schottky barrier diodes fabricated on the etched GaAs surfaces have diode ideality factors as low as 1.06 and deep level transient spectroscopy measurements indicate that near the surface trap densities are less than 1 x 1015 cm 3 This would indicate that devices that depend on a high quality Schottky barrier such as field effect transistors or permeable base transistors can be fabricated on an etched surface. G A Lincoln et al, d Vac Sci Technol, 20 (3k 1982, 786 789. 35 5798. Diffusion of gallium in quartz and bulk-fused silica. (USA) Diffusion of Ga into quartz (crystal SiO 2) and bulk-fused silica (amorphous SiO 2) was studied by neutron activation analysis. Slow and fast diffusion of Ga was observed in bulk-fused silica, while in quartz only slow diffusion was observed. The difference in the diffusion mechanisms is discussed on the basis of the difference in porosity of the two materials. In the bulk-fused silica, which has a lower density of 2.20 g c m 3 there are two regions with high and low densities. The higher density region is composed of cristobalite, which has the m a x i m u m distance between atomic strings of (at most) 6 A. The lower density region is composed of a random network of Si and O atoms, and in the network there exist many microchannels, an average diameter and the real density of which are estimated to be 17 A and 7.5x 1011 cm 2 respectively. These microchannels act as the high-speed diffusion paths, while the critobalite region is the slow diffusion path. In quartz which has a density of 2.65 g cm 3, the widest interatomic spacing perpendicular to c axis is about 5 A and only the slow (bulk) diffusion can occur. The discrepancy in the diffusion coefficients of Ga reported previously by Grove and Wagner can be explained by the present model. (Japan) Shuzo Mizutani et al, J Appl Phys, 53 (3), 1982, 1470 1473. 35 5799. General model of sodium desorption and diffusion during electron bombardment of glass. (USA) A general model for alkali Auger signal decay during electron beam analysis has been developed. All previous models were based on diffusion into the bulk, but alkali ions were shown to be first converted to a new state in the solid by electron bombardment, then either diffusion or desorption could occur. Using an analytic mathematical description of these effects, the relative contribution ofdesorption and diffusion to decay of the Auger or desorbed ion signal were calculated. The desorption crosssection of sodium was evah, ated to be about 10 ~9 cm 2 and electron
as they change under heating. No changes of R b N O 3 crystal structure caused by irradiation have been found. Experimental results agree with an assumption that radiation-induced structure changes of high-temperature type can be observed only in the compounds, the phase transition of which is of continuous type. (USSR) E V Kolontsova et al, Rad E(['ects Letts 67 (6), 1982, 181 185. 35 5796. High resolution ion beam lithography. (USA) A new type of high resolution mask for ion beam lithography is described. The mask employs a thin membrane with regions of two different thicknesses to provide contrast for proton exposure of resist. A conventional ion implantation system is used to generate a collimated beam of protons for flood exposure of the sample. Beam energy is chosen so the protons pass through the thin areas of the mask and emerge with sufficient energy to expose the resist, but are stopped in the thick areas. Experiments using polyimide membrane masks have yielded promising results. The ability to reactive ion etch structures with nearly vertical sidewalls in polyimide allows the fabrication of masks having both high contrast and high resolution. The stopping power of polyimide was determined by measuring the transmission of protons through membranes of known thickness, as a function of incident beam energy. In the energy range from 50 200 keV, the stopping power of polyimide for protons was measured to be 4 1 0 0 keV/itm. Mask fabrication procedures and exposure experiments to determine the resolution of this technique are reported. Patterns with linewidths of <0.1 l~m have been successfully replicated. N P Economou et al, d Vac Sci Technol, 19 (4), 1981, 1172 1175. 35 5797. Ion beam assisted etching for GaAs device applications. (USA) We have developed a new anisotropic dry etching technique for GaAs that results in etched surfaces of sufficient quality for many device applications. In this technique a chemically reactive gas from a jet and an ion beam from a K a u f m a n ion source are directed on the sample surface. We have termed this technique ion beam assisted etching (IBAE) since the chemically reactive species is assisted by the independently controlled energetic ions. This method has produced anisotropically etched patterns with periods as small as 3200 A with easily attainable aspect ratios of 10:1. Schottky barrier diodes fabricated on the etched GaAs surfaces have diode ideality factors as low as 1.06 and deep level transient spectroscopy measurements indicate that near the surface trap densities are less than 1 x 1015 cm 3 This would indicate that devices that depend on a high quality Schottky barrier such as field effect transistors or permeable base transistors can be fabricated on an etched surface. G A Lincoln et al, d Vac Sci Technol, 20 (3k 1982, 786 789. 35 5798. Diffusion of gallium in quartz and bulk-fused silica. (USA) Diffusion of Ga into quartz (crystal SiO 2) and bulk-fused silica (amorphous SiO 2) was studied by neutron activation analysis. Slow and fast diffusion of Ga was observed in bulk-fused silica, while in quartz only slow diffusion was observed. The difference in the diffusion mechanisms is discussed on the basis of the difference in porosity of the two materials. In the bulk-fused silica, which has a lower density of 2.20 g c m 3 there are two regions with high and low densities. The higher density region is composed of cristobalite, which has the m a x i m u m distance between atomic strings of (at most) 6 A. The lower density region is composed of a random network of Si and O atoms, and in the network there exist many microchannels, an average diameter and the real density of which are estimated to be 17 A and 7.5x 1011 cm 2 respectively. These microchannels act as the high-speed diffusion paths, while the critobalite region is the slow diffusion path. In quartz which has a density of 2.65 g cm 3, the widest interatomic spacing perpendicular to c axis is about 5 A and only the slow (bulk) diffusion can occur. The discrepancy in the diffusion coefficients of Ga reported previously by Grove and Wagner can be explained by the present model. (Japan) Shuzo Mizutani et al, J Appl Phys, 53 (3), 1982, 1470 1473. 35 5799. General model of sodium desorption and diffusion during electron bombardment of glass. (USA) A general model for alkali Auger signal decay during electron beam analysis has been developed. All previous models were based on diffusion into the bulk, but alkali ions were shown to be first converted to a new state in the solid by electron bombardment, then either diffusion or desorption could occur. Using an analytic mathematical description of these effects, the relative contribution ofdesorption and diffusion to decay of the Auger or desorbed ion signal were calculated. The desorption crosssection of sodium was evah, ated to be about 10 ~9 cm 2 and electron