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Determination of the composition of thin film compounds using an electron-probe X-ray microanalyzer. Analyzes of nitride films
WORLD
ABSTRACTS
ON MICROELECTRONICS
electronics industries are turning to solid-state systems which utilize thick-film hybrid microcircuitry. Consumer and automotive electronic uses are exhibiting the highest rate of new thick-film circuitry adoption at the present time. Industrial usage for high power, measuring and control systems, is also increasing rapidly, and thickfilm hybrid circuits are strong candidates to replace electromechanical switching devices. T h e use of hybrid micro-circuits is forecasted to double or triple current usage on a worldwide basis by 1975. In the future, thick films are expected to play an ever increasing role in the packaging of semiconductor devices because of their low production cost and high performance advantages.
The relationship b e t w e e n the thick film conductor and substrate and its influence on conductor properties. L. HAILES and W. A. CROSSLAND. P?'oc. Tech. Prog. I N T E R N E P C O N '71, Brighton. 19-21 October (1971), p. 238. A thorough understanding of the nature and interactions of the various thick film materials is one of the keys to a successful operation in the technology. Such an understanding has generally been hampered by two factors: (1) the degree of commercial secrecy involved, giving rise to a feeling that "thick filming" is an art rather than a science; and (2) the inherent complexity of the materials. T h e situation has not been helped by the perpetuation of some quite erroneous assumptions. In this paper, we seek to dispel the generally held assumption that the substrate is an inert baseboard, to try and discuss the firing of a thick film conductor on to a substrate in terms of the model we have proposed.
Sputter etch r e m o v a l rates of insulators, s e m i conductors, and conductors. L. L. FRITZ. Solid State Technol., December (1971), p. 43. Sputter-etch has been used in the fabrication of multi-layer metal integrated circuits. The applications of this technology are not common and seldom applied by process engineers. Some of the properties of R F sputter-etching as related to insulators, semiconductors, and conductors are discussed. T h e sputter-etch removal rates of seven materials are presented with suggestions for possible useful experimental processes. T h e materials are: sputtered SiOz, thermal oxide, silicon, P-doped silicon, B-doped silicon, PSG, and aluminium. Copper is also considered but only relative to aluminum.
Ignition characteristics of v a c u u m system c o m ponents. W. WILLIAMS and R. WALKER. Vacuum 21, No. 10, p. 473. This report describes a series of tests of vacuum monitoring and vacuum producing devices in an air-hydrogen atmosphere. These tests consisted of building a suitable test vessel, obtaining desired test conditions and then introducing an explosive airhydrogen mixture, at a desired flow rate, on to the pieces of equipment being checked. Provisions were made for remote monitoring and recording of the results. T h i n - f i l m processes for microelectronic application. L. V. GREGOR. Proc. I E E E 59, No. 10 (1971),
AND
RELIABILITY
329
p. 1390. The rapid development of the microelectronics industry over the last decade has placed exceptional demands on thin-film technology since, to a large extent, it controls the technological pace of that industry. This demand has challenged the thin-film technologist to develop new and improved processes for both thin-film devices as well as for the thin-film conductors and insulation needed by semiconductor devices. T h e projected demands of the coming decade will require advances in the technology comparable to those of the past decade if the full potential of large-scale integration is to be achieved. The variety of materials and processes required to meet adequately the total needs of the industry has necessitated the development of several deposition technologies. Vacuum evaporation, sputtering, chemical vapor deposition, sedimentation, etc., are all in volume manufacturing use and the technologies of each of these techniques has been significantly improved during the past 10 yr. A similar increase in process capability and control has been necessary in the area of pattern definition in order to allow the development of fine line etching which achieves the required narrow linewidths and separations in today's microelectronic assemblies. The materials of major interest to the industry as well as the deposition techniques and photoengraving processes used in their processing are highlighted. The discussion includes the status and limitations of the technology as its exists today as well as a consideration of the advantages and disadvantages of the various processes both as of today and for the future.
Determination of the composition of thin film c o m p o u n d s using an electron-probe X-ray micro~nalyzer. Analyzes of nitrlde films. A. ITon et a[. J. Vac. Soc. ffapan 13 (12) (1970), p. 413, (In Japanese). Several refractory nitrides of transition metals, e.g. Ta2N, TaN, TiN, ZrN, etc., have been considered for use in thin film resistors because of their excellent stability but relations between composition and electrical characteristics have not been established due to difficulties in composition determination. A convenient method using an electron-probe X-ray microanalyzer is demonstrated for T i - N and Z r - N films, prepared by evaporation or reactive sputtering. The error is several per cent or less. Data obtained on film composition are adapted to show the resistivity and temperature coefficient on resistivity-composition curves for Z r - N and T i - N systems.
Production of prototype hybrid micro-electronic m o d u l e s using thin film substrates. R. H. PURCHASE. Proc. Tech. Prog. I N T E R N E P C O N '71, Brighton. 19-21 October (1971), p. 201. The usual techniques used in the manufacture of thin film microelectronic circuits are not ideally suited for research and development applications, where relatively small numbers are required. This paper describes a facility that has been established at A U W E which we consider is well suited to meet a need for hybrid microelectronic modules of high accuracy, in small numbers. It does not require the normal artwork, photographic and drawing office
330
WORLD
ABSTRACTS
ON MICROELECTRONICS
facilities; hence, the work can be done by a small selfcontained unit. In consequence, the time to produce a new circuit is very short. *RF sputtering of z i n c sulphide. R. J. WOODWARD. Signals Res. ~ Dev. Estab., Christchurch, Hants. June (1970), pp. 32. (1091-7203) T72-00679M SRDE-REP70029. Describes work done of the R F sputtering of zinc sulphide doped thin films on to silicon. Details of the sputtering process and an assessment of equipment improvements are included.
Sputtering multilayered conductor films. D. G. MUTH. J. Vac. Sci. Technol. 8, No. 1, January-February (1971), p. 99. R.f. sputtering techniques were used to deposit multilayer conductor films with Au as the top conducting layer. Appreciable interdiffusion of the layered films occurred during sputtering, with a resultant increase in the Au resistivity. The heating attributable to electron bombardment during sputtering caused the films to heat to 290°C at 0"5 kW of applied power, and as high as 550°C at 2.0 kW. After sputtering a two-layer film on NiChrome-Au at 1"0 and 2'0 kW, for example, Ni and Cr were detected throughout the 12,000-A Au layer. When sputtering at 2"0 kW., the underlying NiCr film also reacted with the Au to form an intermetallic compound, Au4Cr. Other conductor film systems included in this study were Ti-Au, T i - P d Au, Ta-Au, and Mo-Au.
The use of perfluoroalkyl polyether fluids in v a c u u m pumps. M. A. BAKER, L. HOLLAND and L. LAURENSON. Vacuum 21, No. 10 (1971), p. 479. A fluorocarbon fluid ("Fomblin")* has been investigated as a lubricant for a rotary mechanical pump. Although the backstreaming rate was only marginally (30 per cent) less than that of a mineral oil the emitted vapour and fragmented species (CF~, CF3, C3F3) were resistant to the formation of carbonaceous and polymerized films (as occurs with hydrocarbons or silicone vapours) when exposed to electron bombardment. Resistance to polymerization and carbon deposition may arise from the low adsorption time and high bond strength of CFradicals. The fluorocarbon fluid can also be evaporated by electron bombardment without leaving a decomposition residue. A rotary pump was operated at 110°C for 500 hr without signs of wear so that vapour with a saturated vp at this temperature may be pumped without gas-ballasting. The fluid shows marked resistance to reaction with exhausted gases (e.g. fluorinated species) and can afford corrosion protection to the pump. In conclusion experiments show that an all fluorocarbon system is possible with both diffusion and rotary pumps charged with the fluid, such an arrangement would be of value for electron beam systems if fluorocarbon radicals could be tolerated. However, the high cost of the fluid will currently restrict its use.
Basic requirements of equipments for manufacturing thin-film e l e m e n t s by sputtering. G. KH. SATAROV. Elektron. Tekh. Mikroelektron. 3 (1970), p. 13.
AND RELIABILITY
(In Russian.) Basic requirements of equipments for manufacturing thin-film elements by ion sputtering are discussed including permissible pressure of residual gases, working pressure of plasma-forming gas, exhausting rate, protection against oil vapour penetration, electrical voltage on the target, localization of plasma, placing of substrates, uniformity of layers, stability of supplying voltages, purification and mixing of gases, and target cooling.
Termination materials for thin-film resistors. J. S. FISHER and P. M. HALL. Proc. I E E E 59, No. 10 (1971), p. 1418. The resistance of a thin film resistor can be considered as consisting of three parts: (1) the resistance of the resistor material; (2) the resistance of the termination material; and (3) the interracial resistance. The aging of the interracial resistance can dominate the aging of low valued resistors, especially under corrosive conditions. The interfacial resistance using a distributed parameter analysis is treated and a figure of merit which can be used to describe the aging of the interface is defined. Also, a sensitive method of measuring this quantity is introduced and a sampling of data on several different termination material systems is presented. The best results were obtained with T i - P d - A u . The conclusions drawn from the figure of merit are corroborated by adhesion and thermocompression bond strength studies.
The structure of thick films and techniques for attaching flip chip microcircuits. K. I. JOHNSON, M. H. SCOTT, W. BATTARBEEand R. GRmcS. Proc. Tech. Prog. I N T E R N E P C O N '71, Brighton. 19-21 October (1971), p. 227. Components are joined to thick film circuits by soldering, by eutectic bonding (for silicon chips being back bonded) and by thermocompression and ultrasonic bonding (for fine wires). Devices for face down bonding, flip chips, are normally joined by soldering, but difficulties are sometimes encountered. Moreover, for some applications, solderless bonding is desirable. This is practicable with thin film circuitry, but not hitherto for thick films. Among the complicating factors are the relative roughness of thick films, the small contact areas involved, the fragile nature of the devices and the high joint yield and reliability required. Work was therefore undertaken to determine the structural characteristics of various thick film inks, subsequently assessing the feasibility of ultrasonically welding flip chips to such films. Concurrently with the first stage, a fluxless reflow soldering technique has been developed that has significant advantages over previously described reflow solder techniques. Section 1 of the paper deals with the examination of the structure of conducting thick films and Section 2 with flip chip attachment, primarily by reflow soldering.
S o m e problems of performance in thin film deposition by evaporation and condensation in v a c u u m . A. S. VALEEV and V. L. EVDOKIMOV. Elektron. Tekh. Mikroelektron. 4 (1970), p. 40. (In Russian.) Criteria are presented which enable comparison of different systems for the vacuum deposition of thin films and selection of
ABSTRACTS
ON MICROELECTRONICS
electronics industries are turning to solid-state systems which utilize thick-film hybrid microcircuitry. Consumer and automotive electronic uses are exhibiting the highest rate of new thick-film circuitry adoption at the present time. Industrial usage for high power, measuring and control systems, is also increasing rapidly, and thickfilm hybrid circuits are strong candidates to replace electromechanical switching devices. T h e use of hybrid micro-circuits is forecasted to double or triple current usage on a worldwide basis by 1975. In the future, thick films are expected to play an ever increasing role in the packaging of semiconductor devices because of their low production cost and high performance advantages.
The relationship b e t w e e n the thick film conductor and substrate and its influence on conductor properties. L. HAILES and W. A. CROSSLAND. P?'oc. Tech. Prog. I N T E R N E P C O N '71, Brighton. 19-21 October (1971), p. 238. A thorough understanding of the nature and interactions of the various thick film materials is one of the keys to a successful operation in the technology. Such an understanding has generally been hampered by two factors: (1) the degree of commercial secrecy involved, giving rise to a feeling that "thick filming" is an art rather than a science; and (2) the inherent complexity of the materials. T h e situation has not been helped by the perpetuation of some quite erroneous assumptions. In this paper, we seek to dispel the generally held assumption that the substrate is an inert baseboard, to try and discuss the firing of a thick film conductor on to a substrate in terms of the model we have proposed.
Sputter etch r e m o v a l rates of insulators, s e m i conductors, and conductors. L. L. FRITZ. Solid State Technol., December (1971), p. 43. Sputter-etch has been used in the fabrication of multi-layer metal integrated circuits. The applications of this technology are not common and seldom applied by process engineers. Some of the properties of R F sputter-etching as related to insulators, semiconductors, and conductors are discussed. T h e sputter-etch removal rates of seven materials are presented with suggestions for possible useful experimental processes. T h e materials are: sputtered SiOz, thermal oxide, silicon, P-doped silicon, B-doped silicon, PSG, and aluminium. Copper is also considered but only relative to aluminum.
Ignition characteristics of v a c u u m system c o m ponents. W. WILLIAMS and R. WALKER. Vacuum 21, No. 10, p. 473. This report describes a series of tests of vacuum monitoring and vacuum producing devices in an air-hydrogen atmosphere. These tests consisted of building a suitable test vessel, obtaining desired test conditions and then introducing an explosive airhydrogen mixture, at a desired flow rate, on to the pieces of equipment being checked. Provisions were made for remote monitoring and recording of the results. T h i n - f i l m processes for microelectronic application. L. V. GREGOR. Proc. I E E E 59, No. 10 (1971),
AND
RELIABILITY
329
p. 1390. The rapid development of the microelectronics industry over the last decade has placed exceptional demands on thin-film technology since, to a large extent, it controls the technological pace of that industry. This demand has challenged the thin-film technologist to develop new and improved processes for both thin-film devices as well as for the thin-film conductors and insulation needed by semiconductor devices. T h e projected demands of the coming decade will require advances in the technology comparable to those of the past decade if the full potential of large-scale integration is to be achieved. The variety of materials and processes required to meet adequately the total needs of the industry has necessitated the development of several deposition technologies. Vacuum evaporation, sputtering, chemical vapor deposition, sedimentation, etc., are all in volume manufacturing use and the technologies of each of these techniques has been significantly improved during the past 10 yr. A similar increase in process capability and control has been necessary in the area of pattern definition in order to allow the development of fine line etching which achieves the required narrow linewidths and separations in today's microelectronic assemblies. The materials of major interest to the industry as well as the deposition techniques and photoengraving processes used in their processing are highlighted. The discussion includes the status and limitations of the technology as its exists today as well as a consideration of the advantages and disadvantages of the various processes both as of today and for the future.
Determination of the composition of thin film c o m p o u n d s using an electron-probe X-ray micro~nalyzer. Analyzes of nitrlde films. A. ITon et a[. J. Vac. Soc. ffapan 13 (12) (1970), p. 413, (In Japanese). Several refractory nitrides of transition metals, e.g. Ta2N, TaN, TiN, ZrN, etc., have been considered for use in thin film resistors because of their excellent stability but relations between composition and electrical characteristics have not been established due to difficulties in composition determination. A convenient method using an electron-probe X-ray microanalyzer is demonstrated for T i - N and Z r - N films, prepared by evaporation or reactive sputtering. The error is several per cent or less. Data obtained on film composition are adapted to show the resistivity and temperature coefficient on resistivity-composition curves for Z r - N and T i - N systems.
Production of prototype hybrid micro-electronic m o d u l e s using thin film substrates. R. H. PURCHASE. Proc. Tech. Prog. I N T E R N E P C O N '71, Brighton. 19-21 October (1971), p. 201. The usual techniques used in the manufacture of thin film microelectronic circuits are not ideally suited for research and development applications, where relatively small numbers are required. This paper describes a facility that has been established at A U W E which we consider is well suited to meet a need for hybrid microelectronic modules of high accuracy, in small numbers. It does not require the normal artwork, photographic and drawing office
330
WORLD
ABSTRACTS
ON MICROELECTRONICS
facilities; hence, the work can be done by a small selfcontained unit. In consequence, the time to produce a new circuit is very short. *RF sputtering of z i n c sulphide. R. J. WOODWARD. Signals Res. ~ Dev. Estab., Christchurch, Hants. June (1970), pp. 32. (1091-7203) T72-00679M SRDE-REP70029. Describes work done of the R F sputtering of zinc sulphide doped thin films on to silicon. Details of the sputtering process and an assessment of equipment improvements are included.
Sputtering multilayered conductor films. D. G. MUTH. J. Vac. Sci. Technol. 8, No. 1, January-February (1971), p. 99. R.f. sputtering techniques were used to deposit multilayer conductor films with Au as the top conducting layer. Appreciable interdiffusion of the layered films occurred during sputtering, with a resultant increase in the Au resistivity. The heating attributable to electron bombardment during sputtering caused the films to heat to 290°C at 0"5 kW of applied power, and as high as 550°C at 2.0 kW. After sputtering a two-layer film on NiChrome-Au at 1"0 and 2'0 kW, for example, Ni and Cr were detected throughout the 12,000-A Au layer. When sputtering at 2"0 kW., the underlying NiCr film also reacted with the Au to form an intermetallic compound, Au4Cr. Other conductor film systems included in this study were Ti-Au, T i - P d Au, Ta-Au, and Mo-Au.
The use of perfluoroalkyl polyether fluids in v a c u u m pumps. M. A. BAKER, L. HOLLAND and L. LAURENSON. Vacuum 21, No. 10 (1971), p. 479. A fluorocarbon fluid ("Fomblin")* has been investigated as a lubricant for a rotary mechanical pump. Although the backstreaming rate was only marginally (30 per cent) less than that of a mineral oil the emitted vapour and fragmented species (CF~, CF3, C3F3) were resistant to the formation of carbonaceous and polymerized films (as occurs with hydrocarbons or silicone vapours) when exposed to electron bombardment. Resistance to polymerization and carbon deposition may arise from the low adsorption time and high bond strength of CFradicals. The fluorocarbon fluid can also be evaporated by electron bombardment without leaving a decomposition residue. A rotary pump was operated at 110°C for 500 hr without signs of wear so that vapour with a saturated vp at this temperature may be pumped without gas-ballasting. The fluid shows marked resistance to reaction with exhausted gases (e.g. fluorinated species) and can afford corrosion protection to the pump. In conclusion experiments show that an all fluorocarbon system is possible with both diffusion and rotary pumps charged with the fluid, such an arrangement would be of value for electron beam systems if fluorocarbon radicals could be tolerated. However, the high cost of the fluid will currently restrict its use.
Basic requirements of equipments for manufacturing thin-film e l e m e n t s by sputtering. G. KH. SATAROV. Elektron. Tekh. Mikroelektron. 3 (1970), p. 13.
AND RELIABILITY
(In Russian.) Basic requirements of equipments for manufacturing thin-film elements by ion sputtering are discussed including permissible pressure of residual gases, working pressure of plasma-forming gas, exhausting rate, protection against oil vapour penetration, electrical voltage on the target, localization of plasma, placing of substrates, uniformity of layers, stability of supplying voltages, purification and mixing of gases, and target cooling.
Termination materials for thin-film resistors. J. S. FISHER and P. M. HALL. Proc. I E E E 59, No. 10 (1971), p. 1418. The resistance of a thin film resistor can be considered as consisting of three parts: (1) the resistance of the resistor material; (2) the resistance of the termination material; and (3) the interracial resistance. The aging of the interracial resistance can dominate the aging of low valued resistors, especially under corrosive conditions. The interfacial resistance using a distributed parameter analysis is treated and a figure of merit which can be used to describe the aging of the interface is defined. Also, a sensitive method of measuring this quantity is introduced and a sampling of data on several different termination material systems is presented. The best results were obtained with T i - P d - A u . The conclusions drawn from the figure of merit are corroborated by adhesion and thermocompression bond strength studies.
The structure of thick films and techniques for attaching flip chip microcircuits. K. I. JOHNSON, M. H. SCOTT, W. BATTARBEEand R. GRmcS. Proc. Tech. Prog. I N T E R N E P C O N '71, Brighton. 19-21 October (1971), p. 227. Components are joined to thick film circuits by soldering, by eutectic bonding (for silicon chips being back bonded) and by thermocompression and ultrasonic bonding (for fine wires). Devices for face down bonding, flip chips, are normally joined by soldering, but difficulties are sometimes encountered. Moreover, for some applications, solderless bonding is desirable. This is practicable with thin film circuitry, but not hitherto for thick films. Among the complicating factors are the relative roughness of thick films, the small contact areas involved, the fragile nature of the devices and the high joint yield and reliability required. Work was therefore undertaken to determine the structural characteristics of various thick film inks, subsequently assessing the feasibility of ultrasonically welding flip chips to such films. Concurrently with the first stage, a fluxless reflow soldering technique has been developed that has significant advantages over previously described reflow solder techniques. Section 1 of the paper deals with the examination of the structure of conducting thick films and Section 2 with flip chip attachment, primarily by reflow soldering.
S o m e problems of performance in thin film deposition by evaporation and condensation in v a c u u m . A. S. VALEEV and V. L. EVDOKIMOV. Elektron. Tekh. Mikroelektron. 4 (1970), p. 40. (In Russian.) Criteria are presented which enable comparison of different systems for the vacuum deposition of thin films and selection of