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Electrical properties of epitaxial aluminium films
World Abstracts on Microelectronics and Reliability An empirical relationship between ,u and n, valid for carrier concentrations up to 4 x 1020 cm -3, is derived. At concentrations lower than 1019 cm-3, when the electron density coincides with the impurity concentration, this formula gives values in agreement with published data obtained on silicon samples doped during crystal growth. New method for the electronic structure of heterojunctions-Application to the (100) Ge-GaAs interfaces. J. POLLMANN and S. T. PANTELIDES. Solid St. Commun. 30, 621 (1979). A method which for the first time can treat two truly semi-infinite semiconductors in contact is introduced and used to study the electronic structure of the two polar (100) Ge-GaAs interfaces. Both the G e - G a and the Ge-As interfaces exhibit essentially three interface bands. The nature and origins of these bands are discussed in detail in terms of local densities of states. The results are used to obtain a new interpretation of the experimental data in terms of a stoichiometrically mixed interface. Impurity effects in amorphous germanium and silicon. JOSE ALZAMIR and M. M. COLLVER. Solid St. Commun. 30, 425 (1979). A systematic study of the hopping conductivity of amorphous germanium-transition metal (Cr, Co, Fe) films reveals an exponential decrease of the hopping parameter, To, as a function of the transition metal concentration. A
427
similar, but often unnoticed, behavior is found in the literature. A linear decrease in the energy gap as a function of concentration is postulated as an explanation. Effects of trichloroethane oxidation of silicon wafers on SiO2 and Si properties. A. J. LINSSEN and H. L. PEEK. Philips J. Res. 33, (5/6) 281 (1978). The effects of oxidation of (100) Si in dry 02 mixed with 1.1.1.-C2H3C13 (C33) at 1050°C up to 1200°C on SiO2 and Si properties have been investigated. The addition of C33 to the 02 flow enhanced the oxidation rate with respect to the oxidation in dry oxygen. The chlorine was found to be located within the first 300/~ of the SiO2 layer from the Si/SiO2 interface. The Na and K contents of C33 oxide layers were higher than those of dry thermal oxide layers due to the transport of Na and K from the quartz tube wall to the Si slices by the HCl. Neutralization of mobile sodium was obtained if the SiO2 surface appeared to be grainy. C33 oxide layers showed instabilities after the application of a positive and a negative field stress at 290°C. A negative oxide charge and interface states were created in the upper half of the Si bandgap. The C33 oxidations were not observed to improve the fixed oxide charge, the interface state density or the minoritycarrier bulk lifetime. Complete suppression of stacking fault generation was the predominant effect on Si bulk material.
8. THICK- AND THIN-FILM COMPONENTS, HYBRID CIRCUITS AND MATERIALS New crossovers using a combined film technique. GUNTER KIESSLING. Electrocomp. Sci. Technol. 5, 205 (1979). The increasing level of integration in film circuit technology, together with the broad-based trend toward miniaturization have led to the necessity for the development of reliable conductor crossovers. The conditions to be met by such crossovers are (a) Low capacitance with a relatively great crossover height (b) High breakdown voltage (c) Low leakage current (d) Excellent adhesion on glass and ceramic substrates (e) High mechanical stability (f) No pinhole formation (g) Economical production process. The process evolved in the basic research laboratories of the Siemens AG Components Group is an ideal combination of the advantages of thin-film and thick-film technologies within the confines of the above conditions. Adhesion mechanisms of thick film conductors. H. G. KIM, W. ROTHLINGSHOFER and G. TOMANDL. Solid St. Technol. p. 62 (March 1979). The adhesion strength of the conductive layer in thick film mechanisms is investigated. The attempt was made to develop an optimal method for quantitatively measuring the adhesion strength. In addition the mechanisms of adhesion were investigated, not only from the physical (especially surface roughness of substrates) but also from the chemical viewpoint. For this purpose experiments were conducted using the scanning electron microscope and electron probe microanalysis. A CdSe thin-film field effect transistor. M. K. RAO and S. R. JAWALEStAR. Int. J. Electronics 46, (3) 309 (1979). A thinfilm field effect transistor appears to be the most promising for an all thin-field integrated circuit. In this paper the authors have reported a coplanar device incorporating an evaporated CdSe film and an anodically grown aluminium oxide layer. The fabrication is based on optimized deposition conditions. The d.c. characteristics of the device are
presented. For the transistor the device parameters are calculated from the I - V characteristics. Improvement of adhesion, line definition, contact resistance and semiconductor properties by sputter-etching. T. KAELFASS. Electroncomp. Sci. Technol. 5, 215 (1979). In an g F sputtering unit, with suspended substrates mounted in lieu of a target, sputter-etching of the substrates and consecutive vapor deposition of Au is performed in order to achieve good adhesion of the Au-film without an adhesion layer. The method has been applied for surface-acoustic-wave filters on piezo ceramics and for noise measurements in Au-films on sapphire. The sputter-cleaning as described also reduces the disturbing contact resistance between the conductive Cr-Au-layers and the previously sputtered Ta-film. Considerable progress has also been made in the manufacture of thin-film transistors by photolithography, chemical etching, and sputter-etching instead of using evaporation masks. The limitations of reactively-bonded thick film gold conductors. M. V. COLEMAN and G. E. GURNETT. Solid St. Technol. p. 45 (March 1979). Reactively-bonded gold conductors have been found to contain copper and usually cadmium. The copper alloys to the gold and this goldcopper alloy is chemically bonded directly to the alumina. Adhesion strengths to various substrates were generally found to be considerably greater than those of the glass bonding of fritted conductors, but were reduced on substrates with a high concentration of the silicate minority constituents at the top surface. After retiring through an overglaze profile, the top surface of the conductors became blackened because of the formation of copper oxide. The effect of this copper oxide on resistor terminations and dielectric insulation for cross-overs has been examined. Electrical properties of epitaxial aluminium films. E. DOBIERZEWSKA-MOzRZYMASand F. WARKUSZ.Electrocomp. Sci. Technol. 5, 223 (1979). The resistivity of monocrystalline
428
World Abstracts on Microelectronics and Reliability
AI films was measured and compared with the resistivity calculated in terms of the function which takes into account both the external and the internal size effects. A comparison of the theoretical and experimental curves shows that the specular reflection coefficient (p) is small, while the coefficient of electron transmission through the grain boundary (r) increases with increasing film thickness. Electrical properties of RF sputtering systems. J. H. KELLER and W. B. PENNEBAKER.I B M J. Res. Dev. 23, (1) 3 (January 1979). A theory is developed that gives a relatively complete electrical characterization of rf sputtering systems. Three types of systems are analyzed: tuned substrate, driven substrate, and controlled area ratio of electrode (CARE) systems. The theory is applicable to any of these systems that do not use magnetic fields to confine the plasma. Given the input rf power and voltage at the target, and any other parameters that can be specified as independent variables (e.g., pressure, substrate drive voltage, tuning impedance, and system geometry), the theory provides explicit values for all dc and rf electrical parameters of the system. The dc bias developed at the substrate is explained and related to the resputtering energy. In addition, an approximate calculation is presented for the ion density in the plasma; this calculation allows a semiquantitative estimate of the rf voltage developed at the target for a given value of rf input power. It also shows the influence of pressure and frequency on rf sputtering system operation. Comparisons are made with real rf sputtering systems; these show that the theory is quite successful in predicting the operation of these systems. In addition, a much better understanding is achieved of some of the complex electrical phenomena encountered in these systems. The theory should prove useful both for new system design and for diagnostic work on existing equipment. Analog ICs divide accurately to conquer computation problems. Yu JEN WONG. Electronics p. 120 (12 April 1979). Housed in dual in-line packages, the hybrids can multiply, divide, or take the square root. A new analytical expression for the T.C.R. of thin monocrystalline metal films. C. R. TELLIER. Electrocomp. Sci. Technol. 5, 209 (1979). The analysis of electrical conductivity of continuous thin monocrystalline metal film has been treated by assuming that the scattering from other sources than grain-boundaries can be described by an effective relaxation time. This relaxation time method is applied to the temperature coefficient of resistivity and leads to an analytical approximate equation in terms of the grainboundary reflection coefficient r and the reduced thickness k. Comparison of the results with those deduced from the exact equation (derived from the Mayadas and Shatzkes theory) shows that they deviate by less than 5°,, in large k-, p-, and r-ranges. RC-active filters in single-layer tantalum RC-film technology. HANS-WERNER RENZ, HOLM BAEGER, ERNST LUEDER, HANS-JUERGEN TILCH and TRAUGOTT KALLFASS. Proc. IEEE 67, (1) 37 (January 1979). A new composition of reactively sputtered Ta-oxinitride is used as a basic material for thin-film resistors as well as for thin-film capacitors; this single-layer technique enables an economic fabrication process for integrated RC circuits with lumped or distributed RC components. A bandpass circuit with lumped components for a dialing tone receiver and a voiceband low pass with distributed elements for PCM channel filtering are described; in either case a very small size allowed a complete filter to be packed in regular DIL-packages, and good performance and stability were obtained. Problems in the production and measurement of very high vacuum, especially in applications, and a new approach to
measurement based on the use of field emission. L. DE CHERNATONY and J. YARWOOD. Vacuum 29, (3) 125. Opinions are expressed about the needs in the development of vacuum systems in which a very high vacuum is to be created. Topics considered are sealing materials, new pumps, especially for an oil-free vacuum environment, a new type of gauge based on field electron emission able to indicate surface gas coverage as well as extend downwards the partial pressure range of a mass spectrometer and the further automation of industrial vacuum plant in which repetitive processes are undertaken. Miniaturized thick-film RC-active filters for PCM application. KEIJ1 SUZUKI and YUKIO KATSUTA. Proc. IEEE 67, (1) 34 (January 1979). This paper presents thick-film RC-active filters developed for use in pulse-code modulation (PCM) systems. Filters for PCM telephone transmission systems are required to be small in size and low cost in production, and they must have good performance. The filters presented have a twelve-lead single in-line package configuration. Dimensions are 5-ram thick, 10-mm high, and 30-mm wide. They meet the D3-Channel Bank requirements. The transmitting filter is a seventh-order bandpass filter (BPF). The receiving filter is a fifth-order low-pass filter (LPF) with an input RC stage which acts as a lossy sample and hold circuit. To achieve miniaturization, thick-film resistors are printed on one side of alumina substrate. On the other side, one chip of quad op-amps and monolithic ceramic-chip capacitors are assembled. Considering economical production, these filters are designed with the following features : (1) only one type of equal-valued capacitors is used; (2) to get good yields, a multiple-feedback configuration having low sensitivity to circuit elements is adopted ; (3) a fast deterministic trimming method is used with computer-controlled laser-trim equipment. Multiple insulator layers on GaAs studied by Auger analysis. J. T. GRANT, H. L. HARTNAGEL, F. L. SCHUERMEYER, B. BAYRAKTAROGLU and D. MAYS. Int. J. Electron. 46, (2) 209 (1979). Recently research was focused on the formation of multiple layer anodic insulators on GaAs to obtain superior passivation layers. In particular A1203 films in conjunction with native oxide films were evaluated. In this paper Auger analysis studies are reported on Al203-native oxide films on GaAs. The results indicate that oxygen migrates during anodization towards the interface while Ga and As migrate towards the surface. Sputtering process model of deposition rate. J. H. KELLER and R. G. SIMMONS. IBM J. Res. 23, (1) 24 (January 1979). A model of the sputtering process has been developed that predicts the deposition rate of a sputtering system with parallel-plate geometry. By using data for sputtering yield vs voltage obtained from an ion-beam sputtering system, the model applies a new theory for computing the backscatter material, and, from the results, predicts deposition rates. The model also considers the effects of charge exchange in the sheaths, and of re-emission of sputtered material at the substrate. The model is valid for magnetic, tuned substrate, driven substrate, and controlled area ratio diode systems. Comparison with observed deposition rates shows good agreement for clean systems. An experimental APL program that uses the model has been written. Trimming of thin and thick film resistors. J. P. LE PENDEVEN. Acta Electronica 21, (4) 319 (1978). (In French.) In this article devoted to the trimming of resistors in hybrid microelectronics the accent is placed on the practical aspect of the use of lasers. The article is broken down into
427
similar, but often unnoticed, behavior is found in the literature. A linear decrease in the energy gap as a function of concentration is postulated as an explanation. Effects of trichloroethane oxidation of silicon wafers on SiO2 and Si properties. A. J. LINSSEN and H. L. PEEK. Philips J. Res. 33, (5/6) 281 (1978). The effects of oxidation of (100) Si in dry 02 mixed with 1.1.1.-C2H3C13 (C33) at 1050°C up to 1200°C on SiO2 and Si properties have been investigated. The addition of C33 to the 02 flow enhanced the oxidation rate with respect to the oxidation in dry oxygen. The chlorine was found to be located within the first 300/~ of the SiO2 layer from the Si/SiO2 interface. The Na and K contents of C33 oxide layers were higher than those of dry thermal oxide layers due to the transport of Na and K from the quartz tube wall to the Si slices by the HCl. Neutralization of mobile sodium was obtained if the SiO2 surface appeared to be grainy. C33 oxide layers showed instabilities after the application of a positive and a negative field stress at 290°C. A negative oxide charge and interface states were created in the upper half of the Si bandgap. The C33 oxidations were not observed to improve the fixed oxide charge, the interface state density or the minoritycarrier bulk lifetime. Complete suppression of stacking fault generation was the predominant effect on Si bulk material.
8. THICK- AND THIN-FILM COMPONENTS, HYBRID CIRCUITS AND MATERIALS New crossovers using a combined film technique. GUNTER KIESSLING. Electrocomp. Sci. Technol. 5, 205 (1979). The increasing level of integration in film circuit technology, together with the broad-based trend toward miniaturization have led to the necessity for the development of reliable conductor crossovers. The conditions to be met by such crossovers are (a) Low capacitance with a relatively great crossover height (b) High breakdown voltage (c) Low leakage current (d) Excellent adhesion on glass and ceramic substrates (e) High mechanical stability (f) No pinhole formation (g) Economical production process. The process evolved in the basic research laboratories of the Siemens AG Components Group is an ideal combination of the advantages of thin-film and thick-film technologies within the confines of the above conditions. Adhesion mechanisms of thick film conductors. H. G. KIM, W. ROTHLINGSHOFER and G. TOMANDL. Solid St. Technol. p. 62 (March 1979). The adhesion strength of the conductive layer in thick film mechanisms is investigated. The attempt was made to develop an optimal method for quantitatively measuring the adhesion strength. In addition the mechanisms of adhesion were investigated, not only from the physical (especially surface roughness of substrates) but also from the chemical viewpoint. For this purpose experiments were conducted using the scanning electron microscope and electron probe microanalysis. A CdSe thin-film field effect transistor. M. K. RAO and S. R. JAWALEStAR. Int. J. Electronics 46, (3) 309 (1979). A thinfilm field effect transistor appears to be the most promising for an all thin-field integrated circuit. In this paper the authors have reported a coplanar device incorporating an evaporated CdSe film and an anodically grown aluminium oxide layer. The fabrication is based on optimized deposition conditions. The d.c. characteristics of the device are
presented. For the transistor the device parameters are calculated from the I - V characteristics. Improvement of adhesion, line definition, contact resistance and semiconductor properties by sputter-etching. T. KAELFASS. Electroncomp. Sci. Technol. 5, 215 (1979). In an g F sputtering unit, with suspended substrates mounted in lieu of a target, sputter-etching of the substrates and consecutive vapor deposition of Au is performed in order to achieve good adhesion of the Au-film without an adhesion layer. The method has been applied for surface-acoustic-wave filters on piezo ceramics and for noise measurements in Au-films on sapphire. The sputter-cleaning as described also reduces the disturbing contact resistance between the conductive Cr-Au-layers and the previously sputtered Ta-film. Considerable progress has also been made in the manufacture of thin-film transistors by photolithography, chemical etching, and sputter-etching instead of using evaporation masks. The limitations of reactively-bonded thick film gold conductors. M. V. COLEMAN and G. E. GURNETT. Solid St. Technol. p. 45 (March 1979). Reactively-bonded gold conductors have been found to contain copper and usually cadmium. The copper alloys to the gold and this goldcopper alloy is chemically bonded directly to the alumina. Adhesion strengths to various substrates were generally found to be considerably greater than those of the glass bonding of fritted conductors, but were reduced on substrates with a high concentration of the silicate minority constituents at the top surface. After retiring through an overglaze profile, the top surface of the conductors became blackened because of the formation of copper oxide. The effect of this copper oxide on resistor terminations and dielectric insulation for cross-overs has been examined. Electrical properties of epitaxial aluminium films. E. DOBIERZEWSKA-MOzRZYMASand F. WARKUSZ.Electrocomp. Sci. Technol. 5, 223 (1979). The resistivity of monocrystalline
428
World Abstracts on Microelectronics and Reliability
AI films was measured and compared with the resistivity calculated in terms of the function which takes into account both the external and the internal size effects. A comparison of the theoretical and experimental curves shows that the specular reflection coefficient (p) is small, while the coefficient of electron transmission through the grain boundary (r) increases with increasing film thickness. Electrical properties of RF sputtering systems. J. H. KELLER and W. B. PENNEBAKER.I B M J. Res. Dev. 23, (1) 3 (January 1979). A theory is developed that gives a relatively complete electrical characterization of rf sputtering systems. Three types of systems are analyzed: tuned substrate, driven substrate, and controlled area ratio of electrode (CARE) systems. The theory is applicable to any of these systems that do not use magnetic fields to confine the plasma. Given the input rf power and voltage at the target, and any other parameters that can be specified as independent variables (e.g., pressure, substrate drive voltage, tuning impedance, and system geometry), the theory provides explicit values for all dc and rf electrical parameters of the system. The dc bias developed at the substrate is explained and related to the resputtering energy. In addition, an approximate calculation is presented for the ion density in the plasma; this calculation allows a semiquantitative estimate of the rf voltage developed at the target for a given value of rf input power. It also shows the influence of pressure and frequency on rf sputtering system operation. Comparisons are made with real rf sputtering systems; these show that the theory is quite successful in predicting the operation of these systems. In addition, a much better understanding is achieved of some of the complex electrical phenomena encountered in these systems. The theory should prove useful both for new system design and for diagnostic work on existing equipment. Analog ICs divide accurately to conquer computation problems. Yu JEN WONG. Electronics p. 120 (12 April 1979). Housed in dual in-line packages, the hybrids can multiply, divide, or take the square root. A new analytical expression for the T.C.R. of thin monocrystalline metal films. C. R. TELLIER. Electrocomp. Sci. Technol. 5, 209 (1979). The analysis of electrical conductivity of continuous thin monocrystalline metal film has been treated by assuming that the scattering from other sources than grain-boundaries can be described by an effective relaxation time. This relaxation time method is applied to the temperature coefficient of resistivity and leads to an analytical approximate equation in terms of the grainboundary reflection coefficient r and the reduced thickness k. Comparison of the results with those deduced from the exact equation (derived from the Mayadas and Shatzkes theory) shows that they deviate by less than 5°,, in large k-, p-, and r-ranges. RC-active filters in single-layer tantalum RC-film technology. HANS-WERNER RENZ, HOLM BAEGER, ERNST LUEDER, HANS-JUERGEN TILCH and TRAUGOTT KALLFASS. Proc. IEEE 67, (1) 37 (January 1979). A new composition of reactively sputtered Ta-oxinitride is used as a basic material for thin-film resistors as well as for thin-film capacitors; this single-layer technique enables an economic fabrication process for integrated RC circuits with lumped or distributed RC components. A bandpass circuit with lumped components for a dialing tone receiver and a voiceband low pass with distributed elements for PCM channel filtering are described; in either case a very small size allowed a complete filter to be packed in regular DIL-packages, and good performance and stability were obtained. Problems in the production and measurement of very high vacuum, especially in applications, and a new approach to
measurement based on the use of field emission. L. DE CHERNATONY and J. YARWOOD. Vacuum 29, (3) 125. Opinions are expressed about the needs in the development of vacuum systems in which a very high vacuum is to be created. Topics considered are sealing materials, new pumps, especially for an oil-free vacuum environment, a new type of gauge based on field electron emission able to indicate surface gas coverage as well as extend downwards the partial pressure range of a mass spectrometer and the further automation of industrial vacuum plant in which repetitive processes are undertaken. Miniaturized thick-film RC-active filters for PCM application. KEIJ1 SUZUKI and YUKIO KATSUTA. Proc. IEEE 67, (1) 34 (January 1979). This paper presents thick-film RC-active filters developed for use in pulse-code modulation (PCM) systems. Filters for PCM telephone transmission systems are required to be small in size and low cost in production, and they must have good performance. The filters presented have a twelve-lead single in-line package configuration. Dimensions are 5-ram thick, 10-mm high, and 30-mm wide. They meet the D3-Channel Bank requirements. The transmitting filter is a seventh-order bandpass filter (BPF). The receiving filter is a fifth-order low-pass filter (LPF) with an input RC stage which acts as a lossy sample and hold circuit. To achieve miniaturization, thick-film resistors are printed on one side of alumina substrate. On the other side, one chip of quad op-amps and monolithic ceramic-chip capacitors are assembled. Considering economical production, these filters are designed with the following features : (1) only one type of equal-valued capacitors is used; (2) to get good yields, a multiple-feedback configuration having low sensitivity to circuit elements is adopted ; (3) a fast deterministic trimming method is used with computer-controlled laser-trim equipment. Multiple insulator layers on GaAs studied by Auger analysis. J. T. GRANT, H. L. HARTNAGEL, F. L. SCHUERMEYER, B. BAYRAKTAROGLU and D. MAYS. Int. J. Electron. 46, (2) 209 (1979). Recently research was focused on the formation of multiple layer anodic insulators on GaAs to obtain superior passivation layers. In particular A1203 films in conjunction with native oxide films were evaluated. In this paper Auger analysis studies are reported on Al203-native oxide films on GaAs. The results indicate that oxygen migrates during anodization towards the interface while Ga and As migrate towards the surface. Sputtering process model of deposition rate. J. H. KELLER and R. G. SIMMONS. IBM J. Res. 23, (1) 24 (January 1979). A model of the sputtering process has been developed that predicts the deposition rate of a sputtering system with parallel-plate geometry. By using data for sputtering yield vs voltage obtained from an ion-beam sputtering system, the model applies a new theory for computing the backscatter material, and, from the results, predicts deposition rates. The model also considers the effects of charge exchange in the sheaths, and of re-emission of sputtered material at the substrate. The model is valid for magnetic, tuned substrate, driven substrate, and controlled area ratio diode systems. Comparison with observed deposition rates shows good agreement for clean systems. An experimental APL program that uses the model has been written. Trimming of thin and thick film resistors. J. P. LE PENDEVEN. Acta Electronica 21, (4) 319 (1978). (In French.) In this article devoted to the trimming of resistors in hybrid microelectronics the accent is placed on the practical aspect of the use of lasers. The article is broken down into