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Investigation of the Au-Ge-Ni system used for alloyed contacts to GaAs
World Abstractscontinued from page 41
The nature of negative photoresist scumming. Part II. NOz and ozone
induced scumming Dr D. L ~ O N
SolidState Technology, p.58 (May 1977). A detailed investigation of chemically induced negative photoresist scumming is presented. A mechanism for nitrogen dioxide and ozone induced scumming is proposed, and cures for scumming are discussed. The cause of most semiconductor industry scumming problems is thought to be nitrogen dioxide. A scum-like condition, incomplete development, and potential sources of scumming in production are also discussed. Semiconductor materials for future display devices T. L. TANSLEY and S. J. T. OWEN Electrocomponent Sci. and Technot., 3, p.67 (1976). The large majority of solid state lamps currently available take advantage of the phenomenon of electroluminineseent recombination at forward biased p-n junctions (homojunctions) in III-V compound semiconductors or related derivatives (GAP, GaAsP, etc.). The range of colours, sizes and luminous efficiencies likely to become available are subject, however, to certain fundamental limitations of the materials :used. rl'hese are related to the size and nature of the forbidden energy gap, crystal defect structure as well as other factors. Electrical conduction by percolation in thick film resistors F. FORLANI and M. PRUDENZIATYI Electrocomponent Sci. and TechnoL, 3, p.77 (1976). Thick film resistors are widely used in microelectronic devices, however the mechanism of electrical conduction in these resistors has not yet been fully understood. In particular the anomalous behaviour of the temperature coefficient of resistance (TCR) vs temperature for a purely ohmic resistor has not been explained. The anomaly is that the T C R is negative at low temperatures, is zero around room temperature and becomes positive at higher temperatures. This paper demonstrates that the electrical conduction mechanism in thick film resistors can be described by the electron percolation theory already proposed to explain charge transport in amorphous semiconductors. The thick film structure consists of conductive grains with a diameter of 0.1pm to 0.3pm separated by dielectric layers. Some of the conductive grains make contact through dielectric layers so thin that electrons are able to tunnel through the layers. The critical percolation path is through these grains. Experimental evidence is given which confirms that the resistance vs temperature characteristics satisfactorily fit the conduction equation provided by the percolation theory. The TCR anomaly can be explained in the framework of this theory, The decay. length of the electron wave-function is shown to be lower than 37.0A for a density of conductive grains in the film in the order of 10~Scm-a. Such a value is consistent with electron tunnelling through layers about 100,~ thick. Investigation of the Au-Ge-Ni system used for alloyed contacts to GaAs M. WITTMER, R. PRETORIUS, J. W. MAYER and M. A. NICOLET Solid State Electronics, 20, p.433 (1977). The Au-Ge-Ni metallisation scheme is widely used for alloyed contacts to GaAs. We have studied the interaction of these three elements upon heat treatment using an inert substrate. Our investigations showed that Ni acts as a sink for Ge in that the Ge diffuses out of the Au, with which it is usually coevaporated, into the Ni layer where it forms stable compounds. Apart from a small amount of Au diffusion into the Ni, there is no interaction between these two elements. We have also found that the ratio of the amount of evaporated Ge to that of Ni is important if uniform layers are anticipated.
5.
Production and Processing
Invited: growth and doping kinetics in molecular beam epitaxy B. A . J O Y C E andC. T. FOXON Proceedings of the 8th Conference (1976 International) on Solid State Devices, Tokyo, 1976; Japanese Journal of Applied Physics, 16, Supplement 16-1, pp.17-23 (1977). The use of modulated molecular beam techniques to obtain kinetic information relating to the growth and doping of GaAs films by molecular beam epitaxy (MBE) is discussed. The surface interaction kinetics of Ga and As4 and of Ga and As2 on ~0o oriented GaAs surfaces have been studied in some detail by measurement of surface lifetimes, sticking coefficients and reaction orders. Chemical models 42
which are consistent with the measured data have been produced. This work is summarised in the first part of the paper. In the second part the interaction behaviour of several potential dopant elements (Sn, Mg, Mn and Zn) is reported, including the direct measurement of sticking coefficients, diffusion into the bulk and surface segregation. Finally, the electrical properties of tin-doped films are described in relation to distribution and compensation effects. Properties of inlay clad wrought gold alloys R. J. RUSSELL Solid State Technology, p.39 (August 1976). Clad metal inlays for electronic connections have increased in use in recent years. As an alternative to electroplated deposits, clad metals offer advantages in less porosity, better formability, design flexibility, the economies of lower karat golds and consistency. Gold alloys were investigated for porosity, formability, hardness, wear, surface contamination, diffusion, and contact resistance. In addition, a partial investigation was conducted of the contact resistance of the several alloys - palladium, palladium-silver alloys, and a AuAgCdIn alloy. Demands of LSI are turning chip makers towards automation, production innovations
J, LYMAN
Electronics, p.81 (July 21, 1977). While there are significant improvements under way in the chip layout and wafer-production processes, the most radical adva/aces are taking place in the process that turns a raw wafer into finished IC chips. There are four major changes occurring: (1) The beginning of microprocessor-controlled conveyor be!t operation of the lithographic steps; (2) Replacement of contact pattern printing by projection printing and even more advanced methods; (3) Substitution of plasma dry.etching for acid wet etching when removing protective layers; (4) Automation by minicomputer and microprocessor of the diffusion process and related activities. Plasma reactor design for the selective etching of SiO2 on Si
R. A. H. HEINECKE
SolidState Electronics, 19, p.1039 (1976). It has been reported in a number of publications that silicon and its compounds can be etched in a CF4 glow discharge through the formation of volatile silicon fluoride compounds. Such a process, if applied to semiconductor processing, promises a number of advantages over liquid etching methods in terms of improved yield and resolution at lower costs. However, in spite of its attraction and of there being some well-engineered equipment on the market for this purpose, the process has been little utilised for the manufacture of silicon integrated circuits. The reason has presumably been the unfavourable etch ratio between silicon and silicon oxide films. Residual lattice absorption in gallium arsenide
H. G. LIPSON, B. BENDOW and S. P. YUKON
Solid State Communications, 23, p.13 (1977). The residual lattice absorption of GaAs in the three and four phonon regime is measured over a range of temperatures. The spectra reveal persistent structural features which are interpreted theoretically in terms of phonon density of states effects. Resistance increases in gold alumininm interconnects with time and temperature D. W. BUSHMIRE IEEE Trans. Parts, Hybrids, Packaging PHP-13 (2), p.152 (June 1977). Increases in the resistance of gold aluminium interconnects with time and temperature were investigated. Aluminium wire was ultrasonicaIly bonded to Cr-Au and TiPd-Au thin-film metallisation on ceramic substrates. The interconnects were exposed to temperatures from 150 to 300°C for times up to 400h. The resistance of the interconnects was measured periodically during the exposure to elevated temperatures. There were significant increases in resistance on both types of metallisation. Some measurements indicated electrically open interconnects, but the mechanical strength remained high. If systems containing gold aluminium interconnects are anticipated to be processed or used at or above 150°C, serious consideration should be given to the effects of increased resistance on circuit performance.
The nature of negative photoresist scumming. Part II. NOz and ozone
induced scumming Dr D. L ~ O N
SolidState Technology, p.58 (May 1977). A detailed investigation of chemically induced negative photoresist scumming is presented. A mechanism for nitrogen dioxide and ozone induced scumming is proposed, and cures for scumming are discussed. The cause of most semiconductor industry scumming problems is thought to be nitrogen dioxide. A scum-like condition, incomplete development, and potential sources of scumming in production are also discussed. Semiconductor materials for future display devices T. L. TANSLEY and S. J. T. OWEN Electrocomponent Sci. and Technot., 3, p.67 (1976). The large majority of solid state lamps currently available take advantage of the phenomenon of electroluminineseent recombination at forward biased p-n junctions (homojunctions) in III-V compound semiconductors or related derivatives (GAP, GaAsP, etc.). The range of colours, sizes and luminous efficiencies likely to become available are subject, however, to certain fundamental limitations of the materials :used. rl'hese are related to the size and nature of the forbidden energy gap, crystal defect structure as well as other factors. Electrical conduction by percolation in thick film resistors F. FORLANI and M. PRUDENZIATYI Electrocomponent Sci. and TechnoL, 3, p.77 (1976). Thick film resistors are widely used in microelectronic devices, however the mechanism of electrical conduction in these resistors has not yet been fully understood. In particular the anomalous behaviour of the temperature coefficient of resistance (TCR) vs temperature for a purely ohmic resistor has not been explained. The anomaly is that the T C R is negative at low temperatures, is zero around room temperature and becomes positive at higher temperatures. This paper demonstrates that the electrical conduction mechanism in thick film resistors can be described by the electron percolation theory already proposed to explain charge transport in amorphous semiconductors. The thick film structure consists of conductive grains with a diameter of 0.1pm to 0.3pm separated by dielectric layers. Some of the conductive grains make contact through dielectric layers so thin that electrons are able to tunnel through the layers. The critical percolation path is through these grains. Experimental evidence is given which confirms that the resistance vs temperature characteristics satisfactorily fit the conduction equation provided by the percolation theory. The TCR anomaly can be explained in the framework of this theory, The decay. length of the electron wave-function is shown to be lower than 37.0A for a density of conductive grains in the film in the order of 10~Scm-a. Such a value is consistent with electron tunnelling through layers about 100,~ thick. Investigation of the Au-Ge-Ni system used for alloyed contacts to GaAs M. WITTMER, R. PRETORIUS, J. W. MAYER and M. A. NICOLET Solid State Electronics, 20, p.433 (1977). The Au-Ge-Ni metallisation scheme is widely used for alloyed contacts to GaAs. We have studied the interaction of these three elements upon heat treatment using an inert substrate. Our investigations showed that Ni acts as a sink for Ge in that the Ge diffuses out of the Au, with which it is usually coevaporated, into the Ni layer where it forms stable compounds. Apart from a small amount of Au diffusion into the Ni, there is no interaction between these two elements. We have also found that the ratio of the amount of evaporated Ge to that of Ni is important if uniform layers are anticipated.
5.
Production and Processing
Invited: growth and doping kinetics in molecular beam epitaxy B. A . J O Y C E andC. T. FOXON Proceedings of the 8th Conference (1976 International) on Solid State Devices, Tokyo, 1976; Japanese Journal of Applied Physics, 16, Supplement 16-1, pp.17-23 (1977). The use of modulated molecular beam techniques to obtain kinetic information relating to the growth and doping of GaAs films by molecular beam epitaxy (MBE) is discussed. The surface interaction kinetics of Ga and As4 and of Ga and As2 on ~0o oriented GaAs surfaces have been studied in some detail by measurement of surface lifetimes, sticking coefficients and reaction orders. Chemical models 42
which are consistent with the measured data have been produced. This work is summarised in the first part of the paper. In the second part the interaction behaviour of several potential dopant elements (Sn, Mg, Mn and Zn) is reported, including the direct measurement of sticking coefficients, diffusion into the bulk and surface segregation. Finally, the electrical properties of tin-doped films are described in relation to distribution and compensation effects. Properties of inlay clad wrought gold alloys R. J. RUSSELL Solid State Technology, p.39 (August 1976). Clad metal inlays for electronic connections have increased in use in recent years. As an alternative to electroplated deposits, clad metals offer advantages in less porosity, better formability, design flexibility, the economies of lower karat golds and consistency. Gold alloys were investigated for porosity, formability, hardness, wear, surface contamination, diffusion, and contact resistance. In addition, a partial investigation was conducted of the contact resistance of the several alloys - palladium, palladium-silver alloys, and a AuAgCdIn alloy. Demands of LSI are turning chip makers towards automation, production innovations
J, LYMAN
Electronics, p.81 (July 21, 1977). While there are significant improvements under way in the chip layout and wafer-production processes, the most radical adva/aces are taking place in the process that turns a raw wafer into finished IC chips. There are four major changes occurring: (1) The beginning of microprocessor-controlled conveyor be!t operation of the lithographic steps; (2) Replacement of contact pattern printing by projection printing and even more advanced methods; (3) Substitution of plasma dry.etching for acid wet etching when removing protective layers; (4) Automation by minicomputer and microprocessor of the diffusion process and related activities. Plasma reactor design for the selective etching of SiO2 on Si
R. A. H. HEINECKE
SolidState Electronics, 19, p.1039 (1976). It has been reported in a number of publications that silicon and its compounds can be etched in a CF4 glow discharge through the formation of volatile silicon fluoride compounds. Such a process, if applied to semiconductor processing, promises a number of advantages over liquid etching methods in terms of improved yield and resolution at lower costs. However, in spite of its attraction and of there being some well-engineered equipment on the market for this purpose, the process has been little utilised for the manufacture of silicon integrated circuits. The reason has presumably been the unfavourable etch ratio between silicon and silicon oxide films. Residual lattice absorption in gallium arsenide
H. G. LIPSON, B. BENDOW and S. P. YUKON
Solid State Communications, 23, p.13 (1977). The residual lattice absorption of GaAs in the three and four phonon regime is measured over a range of temperatures. The spectra reveal persistent structural features which are interpreted theoretically in terms of phonon density of states effects. Resistance increases in gold alumininm interconnects with time and temperature D. W. BUSHMIRE IEEE Trans. Parts, Hybrids, Packaging PHP-13 (2), p.152 (June 1977). Increases in the resistance of gold aluminium interconnects with time and temperature were investigated. Aluminium wire was ultrasonicaIly bonded to Cr-Au and TiPd-Au thin-film metallisation on ceramic substrates. The interconnects were exposed to temperatures from 150 to 300°C for times up to 400h. The resistance of the interconnects was measured periodically during the exposure to elevated temperatures. There were significant increases in resistance on both types of metallisation. Some measurements indicated electrically open interconnects, but the mechanical strength remained high. If systems containing gold aluminium interconnects are anticipated to be processed or used at or above 150°C, serious consideration should be given to the effects of increased resistance on circuit performance.