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A production parylene coating process for hybrid microcircuits
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.
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.