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A new high stability resistor system
World Abstracts on Microelectronics and Reliability
nol. 4, 85 (1977). This paper discusses the preparation techniques which can be used for the examination of thick film resistor microstructures by Transmission Electron Microscopy. The application of this technique, including High Voltage Electron Microscopy and Electron Microscope Mass Analysis, to both Ruthenium Dioxide and Bismuth Ruthenate based thick film resistors, is considered.
Grain size dependence of the gauge factor of thin metallic films. C. R. TELLIER and A. J. TOSSER. Electrocomp. Sci. Technol. 4, 9 (1977). The combined effects of grain boundary, external surface and background scattering (Mayadas and Shatzkes model) are considered. Theoretical expressions of the transverse and longitudinal strain coefficient of resistance of monocrystalline and polycrystalline films are calculated. These general formulae agree with those previously proposed for infinitely thick polycrystalline films. Solder dissolution rates of evaporated and sputtered Ti, Pd, Au and NiCr-Au thin films. R. H. MINETTI and L. J. R1CKnBAUGH. Proc. Electron. Components Conf. Arlington, Va., (May 16-18 1977). p. 212. This paper describes a study to determine the dissolution rates of thin film metallizations in 60~oSn-40~oPb solder at three different temperatures (200, 240, and 280°C) using a "float" method. Several metallizations were employed in this study; namely, Pd, Ti. Pd, Ti. Pd + plated up Au, TaN + Ti. Pd + plated up Au and NiCr + plated up Au. The films were evaporated and/or sputtered on both ceramic and glass substrates. In addition to dissolution rate determination, trends in the data believed to be caused by the different deposition techniques, substrate surface roughness, and thin film thermal stabilization have been observed. The dissolution rate data determined was used to calculate the effective thickness of soluble conductor film remaining after exposure to molten solder for various time intervals and temperatures above the solder solidus temperature. Tantalum thin film applications---a new approach for capacitors. A. PERINATI. Electrocomp. Sci. Technol. 4, 69 (1977). Tantalum-based materials and process developments have increased the use of tantalum films, combined with silicon integrated circuits, to form hybrid integrated circuits which can meet the demands of telecommunication systems. This paper, after a historical review, describes the status of tantalum thin film technology used at Telettra in the implementation of circuits for telecommunication equipment. In particular, this paper focuses on the efforts devoted to the improvement of the fl-Ta capacitor process in terms of yield and reliability for RC active filter realization. The results of a new Ta2Os-fl Ta deposition process, where a Ta205 layer is first formed by d.c. reactive sputtering in oxygen in the same vacuum batch where the fl-Ta film is sequentially formed, are given. A high voltage, high performance thick film resistor system. SIDNEY J. STEIN, CORNELIUS HUANG and ALLAN S. GELB. Electrocomp. Sci. Technol. 4, 95 (1977). This paper describes a new series of thick film resistors based on a ruthenium-compound semiconducting phase, dispersed in a carefully selected and compatible glassy matrix. Analysis of the electrical properties of these resistors indicates that the conducting networks present in the structure include ohmic, non-ohmic and insulating barriers. Experimental results on the resistors are discussed in terms of resistivity and TCR vs. firing parameters. The effect of termination materials and resistor geometry, voltage coefficient of resistance, power loading and high voltage properties are also discussed. Low frequency characteristics of TiO2 (rutile)-glass thick films. B. LICZERSKIand K. N1TSCH. Electrocomp. Sci. Teeh-
265
nol. 4, 1 (1977). An analysis is made of the low-frequency characteristics of the permittivity E' and of tan 6 of a thickfilm insulator containing rutile grains bonded with an amorphous glass. The appearance of dielectric relaxation associated with a maximum of tan & as well as characteristic Debye dispersions of the electric permittivity is observed. The relaxation time does not depend on the rutile concentration in the dielectric. An equivalent circuit describing the behaviour of a capacitor with such an insulator in the low frequency range is suggested. The experimental results are shown to be consistent with an analysis based on the assumption that a titanium ion relaxation process occurs in the rutile grains. In normal ambient conditions the influence of this kind of polarization disappears at frequencies higher than 102 Hz; e' and tan 6 then change insignificantly and the value of tan 6 is conditioned by the hopping mechanism of conductivity in the glass and in rutile. New metallization process for tantalum RC hybrid integrated circuits. R. E. PETERSON and K. L. BAURLE. Proc. Electron. Component Conf. Arlington, Va., (May 16-18 1977). p. 238. A new process has been developed for depositing the nichrome-palladium-gold metallization used for capacitor counterelectrodes, conducting paths and thermocompression bonding pads in Hybrid Integrated Circuits (HICs) containing precision tantalum film resistors and capacitors. The new process uses sputtering to deposit the nichrome and palladium and selective plating to deposit the gold. It replaces a previous method which used sequential vacuum evaporation to deposit all three metals. The advantages the new process offers are: more efficient gold deposition, higher circuit fabrication yields and improved capacitor properties. The new metallization process has been implemented on the RC tone generator circuit used in TOUCH-TONE ® dials. This paper presents the results of evaluation studies performed on TOUCH-TONE HICs fabricated using this process. The application of magnetically enhanced sputtering in a production cylindrical sputtering system. F. R. ARCIDIACONO. Proc. Electron. Components Conf. Arlington, Va., (May 16-18 1977). p. 232. A Penning cylindrical sputtering geometry has been used for the production of tantalum thin films. A simple magnetic field-shaping technique coupled with proper target design has produced films with a uniformity characteristic of a quality deposit. The technique has proven to be a cost effective way of producing a high throughput of product in a system designed for a cylindrical sputtering mode. A new high stability resistor system. J. R. LARRY, M. J. POPOWICH, R. C. HEADLEYand R. M. ROSENBERRY. Proc. Electron. Components Conf. Arlington, Va., (May 16-18 1977). p. 348. This paper describes new resistor compositions which provide high stability and reliability in the more demanding applications. Ranging in sheet resistivity from 100 ohms/square to 100 K ohms/square with temperature coefficients of resistance less than 50 ppm/°C, the compositions were designed for termination with silver bearing conductors and for processing in a 30 minute firing cycle. Basic resistor properties are described and the effects of firing profile, resistor geometry and repeat firings on electrical performance are considered. Laser trim performance of the new resistor series is examined and quantified using a Q switched YAG laser system. The response of stability to beam power, pulse frequency and trim speed is investigated over a wide range for two levels of resistivity. Extensive laser trim data on the new system show that resistors as small as 1 mm 2 trimmed to two times initial value exhibit resistance changes of less than 0.15% in 1000 hours based on time zero measurements of 4-50
266
World Abstracts on Microelectronics and Reliability
milliseconds after trim. Similar changes occur during storage in humid and elevated temperature (200°C) ambients. Performance of trimmed resistors under continuous power loading is also presented.
Gold- and silver-based thick-film conductors. T. T. HITCH. Proc. Electron. Components Conf. Arlington, Va., (May 16 18 1977). p. 260. Silver and gold conductor metallizations were selected for study because it was believed that their simplicity, relative to other thick-film materials, would more readily enable improvements in the fundamental understanding of thick films. In this paper state-of-theart and more typical commerical conductor inks and films are examined. Chemical analyses of the inks are presented, and on the basis of the analyses they are classified as fritbonded, mixed-bonded, or reactively-bonded. These designations were made depending on the relative proportions of copper oxide and flit in the binder constituency of each ink. After the inks were processed into fired films using matrices of firing temperatures, print thicknesses, and two alumina substrate purities, electrical resistivities and adhesion strengths were measured. Both were correlated with ink composition. Adhesion strength and its sensitivity to firing temperature were shown to be strong functions of the binder class. Reactively-bonded inks were the most sensitive to firing temperature and flit-bonded inks were least sensitive. Mixed-bonded inks offered adhesion strengths approaching those of the most adherent reactively-bonded films and had strongly reduced firing temperature sensitivity. Frit-bonded silver films demonstrated higher adhesion strengths with lower volume fractions of binder than flitbonded gold films. The best mixed-bonded silver inks firing at 950°C were about as adherent as the best reactivelybonded gold ink fired at 1030°C. Fundamental bonding mechanisms are discussed in terms of microstructures and chemical aspects. A production parylene coating process for hybrid microcircuits. V. S. KALE and T. J. RILEY. Proc. Electron. Components Co~f Arlington, Va., (May 16 18, 1977). p. 245. Application of parylene for protecting microelectronic circuits from loose particles and external environment has been visualized for many years. With a joint effort by NASA and TMD, a process has now been qualified to perform Parylene deposition on hybrid circuits on a production basis, for the Centaur inertial guidance computer. The parylene coating process developed during this program consists of (a) obtaining a hybrid cover with a hole in it, (b) sealing of the circuit with a hole in the cover, (c) Parylene coating through the hole with the external leads protected from Parylene by appropriate fixturing, and (d) sealing of the hole by soldering a pretinned Kovar tab. Development of the above process required optimization of the Parytene coater parameters to obtain a uniform 9. E L E C T R O N ,
ION
Electron beam--now a practical LSI production tool. NELSON C. YEW. Solid St. Technol. 86 (August 1977). The electron beam has been experimentally explored for more than a decade as a potential means for overcoming the limitations of light optics in high resolution semiconductor device fabrication. Only recently electron resists of sufficiently high sensitivity and reliable machinery became commercially available for routine use. The throughput of less than one hour for a highly complex 4" chrome master with significant better resolution and absolute accuracy under production environment, and at a net cost substantially less than that using conventional techniques, finally proved E-beam's commercial viability.
consistent coating which could offer adequate protection to the circuits, fixture design for packages of various types, determination of the size of the deposition hole, the amount of dimer charge per run, a process to hermetically seal the deposition holes and establishment of quality control techniques or acceptance criteria for the deposited film.
A statistical approach to the analysis of dielectric breakdown strength of thin insulating films. K. KRISTIANSEN. Vacuum 27, (4) 227. Statistical models that are widely used in thc study of high voltage insulating systems are applied to thin insulating films. By use of these methods it is in many cases possible to decide whether the electrical strength of a component is bulk-limited or electrode-limited. A discussion on which type of statistical distribution function can be expected for electrical breakdown in thin films is given. By analyzing measured breakdown voltages for more than 2000 capacitors it has been shown that a description of dielectric breakdown in thin films by means of the theory of the weakest link is fruitful. It is shown that the first selfhealing breakdown has its origin at weak spots randomly distributed over the capacitor area. The variation in the results is too large to determine whether the breakdowns start at the interface electrode dielectric or within the bulk of the film. These techniques have also been successfully applied to previously published results, offering an explanation of results not previously understood. Polycrystalline semiconductor thin films. J. C. ANDERSON. Vacuum 27, (4) 263. Because of the demands of the electronic device industry, the major effect in semiconductor thin films has been in direction of epitaxial growth of good, single-crystal films. More recently, interest in the theory of amorphous materials has led to the preparation and study of amorphous thin films of semiconductors. The polycrystalline film has generally been considered only when its polycrystalline structure was unavoidable or where the electronic properties are unimportant. There are now various devices whose electrical properties depend upon polycrystalline structure, for example the thin-film transistor (TFT) and photoconductivc layers, both of which exploit the electronic properties of the grain boundary, as also does the silicon gate transistor in which the high resistance of a polycrystalline layer is used to support the gate field. It is considered that a better understanding of the electronic properties and of how to control the physical properties of polycrystalline semiconductor films will lead to their more widespread use in devices. In this paper the preparation and characterization of polycrystalline semiconductor thin films is reviewed and their electrical properties are discussed. AND
LASER
BEAMS
Boron-implanted silicon resistors. S. M. Ku. Solid-St. Electron. 20, 803 (1977). The sheet resistance of silicon resistors implanted with boron at room temperature has been experimentally determined for doses from 5 x l012 to 2 × 10 t6 cm -2. The results have been compared with the calculated values. Two methods for minimizing the temperature coefficient. TCR, are described, and their merits and disadvantages are discussed. For a 1-k~/R resistor, TCR can be reduced to 1000 pprn/°C by implanting 11B+ at low energy, 5-10 keV, and to less than 100 ppm/°C by implanting a suitable dose of Ar + damage. In a two-terminal resistor, the end effect of the total sheet resistance on TCR and on voltage coefficient VCR was also investigated.
nol. 4, 85 (1977). This paper discusses the preparation techniques which can be used for the examination of thick film resistor microstructures by Transmission Electron Microscopy. The application of this technique, including High Voltage Electron Microscopy and Electron Microscope Mass Analysis, to both Ruthenium Dioxide and Bismuth Ruthenate based thick film resistors, is considered.
Grain size dependence of the gauge factor of thin metallic films. C. R. TELLIER and A. J. TOSSER. Electrocomp. Sci. Technol. 4, 9 (1977). The combined effects of grain boundary, external surface and background scattering (Mayadas and Shatzkes model) are considered. Theoretical expressions of the transverse and longitudinal strain coefficient of resistance of monocrystalline and polycrystalline films are calculated. These general formulae agree with those previously proposed for infinitely thick polycrystalline films. Solder dissolution rates of evaporated and sputtered Ti, Pd, Au and NiCr-Au thin films. R. H. MINETTI and L. J. R1CKnBAUGH. Proc. Electron. Components Conf. Arlington, Va., (May 16-18 1977). p. 212. This paper describes a study to determine the dissolution rates of thin film metallizations in 60~oSn-40~oPb solder at three different temperatures (200, 240, and 280°C) using a "float" method. Several metallizations were employed in this study; namely, Pd, Ti. Pd, Ti. Pd + plated up Au, TaN + Ti. Pd + plated up Au and NiCr + plated up Au. The films were evaporated and/or sputtered on both ceramic and glass substrates. In addition to dissolution rate determination, trends in the data believed to be caused by the different deposition techniques, substrate surface roughness, and thin film thermal stabilization have been observed. The dissolution rate data determined was used to calculate the effective thickness of soluble conductor film remaining after exposure to molten solder for various time intervals and temperatures above the solder solidus temperature. Tantalum thin film applications---a new approach for capacitors. A. PERINATI. Electrocomp. Sci. Technol. 4, 69 (1977). Tantalum-based materials and process developments have increased the use of tantalum films, combined with silicon integrated circuits, to form hybrid integrated circuits which can meet the demands of telecommunication systems. This paper, after a historical review, describes the status of tantalum thin film technology used at Telettra in the implementation of circuits for telecommunication equipment. In particular, this paper focuses on the efforts devoted to the improvement of the fl-Ta capacitor process in terms of yield and reliability for RC active filter realization. The results of a new Ta2Os-fl Ta deposition process, where a Ta205 layer is first formed by d.c. reactive sputtering in oxygen in the same vacuum batch where the fl-Ta film is sequentially formed, are given. A high voltage, high performance thick film resistor system. SIDNEY J. STEIN, CORNELIUS HUANG and ALLAN S. GELB. Electrocomp. Sci. Technol. 4, 95 (1977). This paper describes a new series of thick film resistors based on a ruthenium-compound semiconducting phase, dispersed in a carefully selected and compatible glassy matrix. Analysis of the electrical properties of these resistors indicates that the conducting networks present in the structure include ohmic, non-ohmic and insulating barriers. Experimental results on the resistors are discussed in terms of resistivity and TCR vs. firing parameters. The effect of termination materials and resistor geometry, voltage coefficient of resistance, power loading and high voltage properties are also discussed. Low frequency characteristics of TiO2 (rutile)-glass thick films. B. LICZERSKIand K. N1TSCH. Electrocomp. Sci. Teeh-
265
nol. 4, 1 (1977). An analysis is made of the low-frequency characteristics of the permittivity E' and of tan 6 of a thickfilm insulator containing rutile grains bonded with an amorphous glass. The appearance of dielectric relaxation associated with a maximum of tan & as well as characteristic Debye dispersions of the electric permittivity is observed. The relaxation time does not depend on the rutile concentration in the dielectric. An equivalent circuit describing the behaviour of a capacitor with such an insulator in the low frequency range is suggested. The experimental results are shown to be consistent with an analysis based on the assumption that a titanium ion relaxation process occurs in the rutile grains. In normal ambient conditions the influence of this kind of polarization disappears at frequencies higher than 102 Hz; e' and tan 6 then change insignificantly and the value of tan 6 is conditioned by the hopping mechanism of conductivity in the glass and in rutile. New metallization process for tantalum RC hybrid integrated circuits. R. E. PETERSON and K. L. BAURLE. Proc. Electron. Component Conf. Arlington, Va., (May 16-18 1977). p. 238. A new process has been developed for depositing the nichrome-palladium-gold metallization used for capacitor counterelectrodes, conducting paths and thermocompression bonding pads in Hybrid Integrated Circuits (HICs) containing precision tantalum film resistors and capacitors. The new process uses sputtering to deposit the nichrome and palladium and selective plating to deposit the gold. It replaces a previous method which used sequential vacuum evaporation to deposit all three metals. The advantages the new process offers are: more efficient gold deposition, higher circuit fabrication yields and improved capacitor properties. The new metallization process has been implemented on the RC tone generator circuit used in TOUCH-TONE ® dials. This paper presents the results of evaluation studies performed on TOUCH-TONE HICs fabricated using this process. The application of magnetically enhanced sputtering in a production cylindrical sputtering system. F. R. ARCIDIACONO. Proc. Electron. Components Conf. Arlington, Va., (May 16-18 1977). p. 232. A Penning cylindrical sputtering geometry has been used for the production of tantalum thin films. A simple magnetic field-shaping technique coupled with proper target design has produced films with a uniformity characteristic of a quality deposit. The technique has proven to be a cost effective way of producing a high throughput of product in a system designed for a cylindrical sputtering mode. A new high stability resistor system. J. R. LARRY, M. J. POPOWICH, R. C. HEADLEYand R. M. ROSENBERRY. Proc. Electron. Components Conf. Arlington, Va., (May 16-18 1977). p. 348. This paper describes new resistor compositions which provide high stability and reliability in the more demanding applications. Ranging in sheet resistivity from 100 ohms/square to 100 K ohms/square with temperature coefficients of resistance less than 50 ppm/°C, the compositions were designed for termination with silver bearing conductors and for processing in a 30 minute firing cycle. Basic resistor properties are described and the effects of firing profile, resistor geometry and repeat firings on electrical performance are considered. Laser trim performance of the new resistor series is examined and quantified using a Q switched YAG laser system. The response of stability to beam power, pulse frequency and trim speed is investigated over a wide range for two levels of resistivity. Extensive laser trim data on the new system show that resistors as small as 1 mm 2 trimmed to two times initial value exhibit resistance changes of less than 0.15% in 1000 hours based on time zero measurements of 4-50
266
World Abstracts on Microelectronics and Reliability
milliseconds after trim. Similar changes occur during storage in humid and elevated temperature (200°C) ambients. Performance of trimmed resistors under continuous power loading is also presented.
Gold- and silver-based thick-film conductors. T. T. HITCH. Proc. Electron. Components Conf. Arlington, Va., (May 16 18 1977). p. 260. Silver and gold conductor metallizations were selected for study because it was believed that their simplicity, relative to other thick-film materials, would more readily enable improvements in the fundamental understanding of thick films. In this paper state-of-theart and more typical commerical conductor inks and films are examined. Chemical analyses of the inks are presented, and on the basis of the analyses they are classified as fritbonded, mixed-bonded, or reactively-bonded. These designations were made depending on the relative proportions of copper oxide and flit in the binder constituency of each ink. After the inks were processed into fired films using matrices of firing temperatures, print thicknesses, and two alumina substrate purities, electrical resistivities and adhesion strengths were measured. Both were correlated with ink composition. Adhesion strength and its sensitivity to firing temperature were shown to be strong functions of the binder class. Reactively-bonded inks were the most sensitive to firing temperature and flit-bonded inks were least sensitive. Mixed-bonded inks offered adhesion strengths approaching those of the most adherent reactively-bonded films and had strongly reduced firing temperature sensitivity. Frit-bonded silver films demonstrated higher adhesion strengths with lower volume fractions of binder than flitbonded gold films. The best mixed-bonded silver inks firing at 950°C were about as adherent as the best reactivelybonded gold ink fired at 1030°C. Fundamental bonding mechanisms are discussed in terms of microstructures and chemical aspects. A production parylene coating process for hybrid microcircuits. V. S. KALE and T. J. RILEY. Proc. Electron. Components Co~f Arlington, Va., (May 16 18, 1977). p. 245. Application of parylene for protecting microelectronic circuits from loose particles and external environment has been visualized for many years. With a joint effort by NASA and TMD, a process has now been qualified to perform Parylene deposition on hybrid circuits on a production basis, for the Centaur inertial guidance computer. The parylene coating process developed during this program consists of (a) obtaining a hybrid cover with a hole in it, (b) sealing of the circuit with a hole in the cover, (c) Parylene coating through the hole with the external leads protected from Parylene by appropriate fixturing, and (d) sealing of the hole by soldering a pretinned Kovar tab. Development of the above process required optimization of the Parytene coater parameters to obtain a uniform 9. E L E C T R O N ,
ION
Electron beam--now a practical LSI production tool. NELSON C. YEW. Solid St. Technol. 86 (August 1977). The electron beam has been experimentally explored for more than a decade as a potential means for overcoming the limitations of light optics in high resolution semiconductor device fabrication. Only recently electron resists of sufficiently high sensitivity and reliable machinery became commercially available for routine use. The throughput of less than one hour for a highly complex 4" chrome master with significant better resolution and absolute accuracy under production environment, and at a net cost substantially less than that using conventional techniques, finally proved E-beam's commercial viability.
consistent coating which could offer adequate protection to the circuits, fixture design for packages of various types, determination of the size of the deposition hole, the amount of dimer charge per run, a process to hermetically seal the deposition holes and establishment of quality control techniques or acceptance criteria for the deposited film.
A statistical approach to the analysis of dielectric breakdown strength of thin insulating films. K. KRISTIANSEN. Vacuum 27, (4) 227. Statistical models that are widely used in thc study of high voltage insulating systems are applied to thin insulating films. By use of these methods it is in many cases possible to decide whether the electrical strength of a component is bulk-limited or electrode-limited. A discussion on which type of statistical distribution function can be expected for electrical breakdown in thin films is given. By analyzing measured breakdown voltages for more than 2000 capacitors it has been shown that a description of dielectric breakdown in thin films by means of the theory of the weakest link is fruitful. It is shown that the first selfhealing breakdown has its origin at weak spots randomly distributed over the capacitor area. The variation in the results is too large to determine whether the breakdowns start at the interface electrode dielectric or within the bulk of the film. These techniques have also been successfully applied to previously published results, offering an explanation of results not previously understood. Polycrystalline semiconductor thin films. J. C. ANDERSON. Vacuum 27, (4) 263. Because of the demands of the electronic device industry, the major effect in semiconductor thin films has been in direction of epitaxial growth of good, single-crystal films. More recently, interest in the theory of amorphous materials has led to the preparation and study of amorphous thin films of semiconductors. The polycrystalline film has generally been considered only when its polycrystalline structure was unavoidable or where the electronic properties are unimportant. There are now various devices whose electrical properties depend upon polycrystalline structure, for example the thin-film transistor (TFT) and photoconductivc layers, both of which exploit the electronic properties of the grain boundary, as also does the silicon gate transistor in which the high resistance of a polycrystalline layer is used to support the gate field. It is considered that a better understanding of the electronic properties and of how to control the physical properties of polycrystalline semiconductor films will lead to their more widespread use in devices. In this paper the preparation and characterization of polycrystalline semiconductor thin films is reviewed and their electrical properties are discussed. AND
LASER
BEAMS
Boron-implanted silicon resistors. S. M. Ku. Solid-St. Electron. 20, 803 (1977). The sheet resistance of silicon resistors implanted with boron at room temperature has been experimentally determined for doses from 5 x l012 to 2 × 10 t6 cm -2. The results have been compared with the calculated values. Two methods for minimizing the temperature coefficient. TCR, are described, and their merits and disadvantages are discussed. For a 1-k~/R resistor, TCR can be reduced to 1000 pprn/°C by implanting 11B+ at low energy, 5-10 keV, and to less than 100 ppm/°C by implanting a suitable dose of Ar + damage. In a two-terminal resistor, the end effect of the total sheet resistance on TCR and on voltage coefficient VCR was also investigated.