Thermal Processing Techniques Research Articles

In-situ processing using rapid thermal chemical vapor deposition

Metal-Oxide-Semiconductor Capacitors (MOSCAP’s) were fabricated using Rapid Thermal Processing (RTP) techniques. MOSCAP’s that received in-situ polysilicon gate deposition after oxide growth evinced significantly tighter oxide breakdown voltage distribution as compared to devices that received ex-situ polysilicon deposition. Capacitance-Voltage (C-V) measurements of electrically unstressed and stressed devices indicate that the oxide charge, interface state density, electron trapping, and interface state generation characteristics are identical, irrespective of the mode of polysilicon gate deposition. It is concluded that, while in-situ processing may be capable of reducing particle related defects, no improvement is seen in the intrinsic properties of the oxide itself.

Rapid Thermal Alloyed Ohmic Contacts to p‐Type GaAs

A systematic study of Au/Zn/Au ohmic contacts to Be‐implanted p‐type by rapid thermal alloying is presented. The processing conditions, such as zinc composition and temperature‐time cycle, are optimized. For the peak hole concentration, about , contact resistivity as low as is obtained. The microstructure of the contact is investigated using SEM, EDXA, AES, and XRD measurements in order to explore the correlation of the structural information with electrical characteristics represented by contact resistivity. It is found that during alloying, the layer near the interface is decomposed due to Ga and As outdiffusion, enhanced by Au interdiffusion. Ga diffuses to the contact surface in a much larger extent than As does. The interaction of Au and Ga, which produces phase, plays a key role in the formation of alloyed ohmic contacts to . The rapid thermal processing technique provides better control of Au‐Ga reaction, as well as limited dissolution of the surface, which makes the optimum ohmic contact possible. The present work has demonstrated that rapid thermal alloying offers obvious advantages over the conventional furnace alloying process, including lower contact resistivity, better interface morphology by limiting interfacial liquid phase reaction, and controlled shallow penetration depth.

Si/Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors produced by limited reaction processing

Si/Si/sub 1-x/Ge/sub x/ heterojunction transistors (HBTs) fabricated by a chemical vapor deposition (CVD) technique are reported. A rapid thermal CVD limited-reaction processing (LRP) technique was used for the in situ growth of all three device layers, including a 20-mm Si/sub 1-x/Ge/sub x/ layer in the base. The highest current gains observed ( beta =400) were for a Si/Si/sub 1-x/Ge/sub x/ HBT with a base doping of 7*10/sup 18/ cm/sup -3/ near the junction and a shallow arsenic implant to form ohmic contacts and increase current gain. Ideal base currents were observed for over six decades of current and the collector current remained ideal for nearly nine current decades starting at 1 pA. The bandgap difference between a p-type Si layer doped to 5*10/sup 17/ cm/sup -3/ and the Si/sub 1-x/Ge/sub x/(x=0.31) base measured 0.27 eV. This value was deduced from the measurements of the temperature dependence of the base current and is in good agreement with published calculations for strained Si/sub 1-x/Ge/sub x/ layers on Si.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rapid thermal processing in semiconductor technology

The authors give a broad overview of some of the possible (and actual) applications of rapid thermal processing (RTP) techniques. Pioneering work done in the field of RTP is described, and a large number of references (about 90) are given. Because of the very wide range of possible applications the detail in which each is discussed may not be in direct relation to their importance for commercial or research purposes. The three main modes of RTP, the adiabatic, thermal flux and isothermal modes are described and contrasted in terms of heat flow, physical processes and suitability for various applications in the field of silicon semiconductor processing. The main types of equipment utilised for RTP research studies are briefly described, ranging from pulsed and CW laser and electron beam sources to radiant heat sources such as graphite plate and lamp systems. Three examples of the application of RTP to silicon semiconductor processing are described in some detail, with comparisons to conventional processing techniques made where relevant. The use of isothermal annealing systems for the activation of ion-implanted dopants is described and reviewed. The possible advantages of RTP are given, and the place of such technology in modern CMOS processing are briefly summarised. The formation of silicon-on-insulator structures using RTP techniques is described and compared with the competing technologies of oxygen implantation and porous silicon. Finally, the wide-ranging, new field of in situ multi-stage processing (or limited reaction processing) is briefly described, and possible applications discussed. This final section covers a subject in which much interest at the research level is presently focused.

Rapid isothermal processing

The physics and technology of a relatively new, short-time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low-cost, minimum overall thermal budget, low-power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP-dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three-dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high-mobility transistors, resonant tunneling devices, and high-efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.

Electron microscopy of a rigid-rod/nylon thermoplastic molecular composite physical blend

“Molecular composites” are a new class of structural polymers which are high-strength, high-modulus, thermally stable, and environmentally resistant. A rigid-rod, extended chain polymer component is used to reinforce a matrix of a ductile polymer with the intent of achieving a composite on the molecular level. The critical factor in processing a “molecular composites” is that the rigid-rod reinforcing component be well dispersed and not phase separate from the matrix component at any stage of processing. For the greatest versatility, a “molecular composites” system should be amenable to fabrication with traditional thermoplastic processing techniques. We previously reported on the morphology of “molecular composites” formed by coagulation spinning from a solution of rigid-rod/stiff-coil polymer blend and from a solution of a rigid-rod/stiff-coil triblock copolymer. Although these polymer systems formed “molecular composites”, they did not have a glass transition temperature below the degradation temperature and could not be consolidated by thermal processing techniques. In this paper we are reporting on the morphology of rigid-rod and flexible-coil thermoplastic blends which are processable by precipitation and thermal consolidation.

A Method for Rapid Thermal Annealing of Compound Semiconductors by Cw CO2 Laser Irradiation

ABSTRACTA new Rapid Thermal Processing technique based on heating by irradiation from CO2 laser is presented. It is particularly suitable for thermal treatment of low melting temperature materials such as annealing implantation induced damage in compound semiconductors.Short time heating of the sample is achieved by its contact with a quartz plate heated by photons from a CW CO2 laser. The quartz serves both as an absorbing medium for the radiation and as a proximity cap. Steady state temperature can be obtained by the simultaneous heating of the sample by the laser and its cooling by a jet of N2 gas.The present technique, when applied to ion implanted InSb (TA&lt;450°C, t=10 seconds), leads to removal of the implantation damage which is comparable to that obtained by furnace or flash lamp (Heatpulse™)annealing.

Comparative Studies of Thin-Film Ti-Si and Ti-SiO2 Rapid Thermal Reactions Using the RIP/TEM Technique

AbstractOne requirement of self-aligned microelectronics metallization processes is selectivity of reactions, e.g., a deposited, thin metal film must react with Si to form a silicide, yet avoid reaction with SiO2 Rapid thermal processing (RTP) techniques may enhance selectivity by utiliz-ing differences in competing reaction kinetics. In this paper, we apply the RTP/transmission electron microscopy (RTP/TEM) technique to determine processing temperature (T)/time (t) “win-dows” for selective sulicide formation in Ti-Si vs Ti-SiO2 reactions. Free-lying Si/Ti/Si and SiO2/Ti/SiO2 films deposited on electron microscope grids were RTP'd in pairs and immediately examined by TEM. The products of the interfacial reactions, their sequence of appearance, and the T/t conditions for silicide nucleation and growth in each system are described.

Dopant redistribution in silicides: Materials and process issues

The need to understand dopant redistribution in refractory metal silicides is important for reliable fabrication of polycide gates and other silicide-containing structures in VLSI devices. This paper will review work on dopant redistribution in silicides with emphasis on polycide structures. Of particular concern is the high-temperature sintering step required to form stable silicide and polycide structures. Results from conventional furnace sintering indicate that dopants can diffuse rapidly through certain silicides. The use of rapid thermal processing techniques to minimize dopant redistribution during the sintering step will also be reviewed. One conclusion is that our understanding of dopant redistribution in refractory metal silicides is limited and additional studies are required.

Recent advances in device processing and packaging of high-power pulsed GaAs double-drift IMPATT's at X-band

High-power multimesa GaAs hybrid double-drift IMPATT's have been developed for pulsed operation at X-band. The diodes are fabricated from GaAs material grown by a novel infinite solution liquid phase epitaxial process. The use of specialized rapid thermal processing and packaging techniques has enabled the fabrication of high-power IMPATT oscillators that have delivered peak output powers of over 40 W with 20-percent efficiency under pulsed RF operation at X-band frequencies. The diodes are constructed with an integral heat sink and bounded with a Au-Sn eutectic solder in a microwave package.

Laser Annealing of Ion Implanted Semiconductors

ABSTRACTPhoton energy from laser beams can be used to rapidly heat and melt localized regions of semiconductors with a high degree of spatial and temporal selectivity. Pulsed lasers have been successfully used to anneal displacement damage and to remove other defects. However, the number density of trapped defects increases with velocity of solidification and finally thin layers turn directly amorphous after laser-melt quenching. Annealing characteristics are found to be a strong function of ion implantation variables, which determine optical properties of materials. By both solid- and liquid-phase crystallization, supersaturated solid solutions can be formed. Residual defects in SPE grown layers primarily consist of dislocation loops. Device applications utilizing these transient thermal processing techniques are reviewed briefly.

Mechanical properties of thermally cycled CuIn alloys

A thermal processing technique of refining the grain size of CuIn alloys has been developed. The process consists of annealing transformed alloys in the α phase field. The grain size dependence of the yield strength of thermally processed alloys can be conveniently represented by the Hall-Petch relationship. Values of the Hall-Petch constants, σ 0 and k y, are found to fall in the range of values reported for f.c.c. Cu-base alloys. During multi-cycle thermal processing, the mechanical properties are found to be improved due to the contribution to strengthening from transformation-induced dislocations. Reverse transformation during precipitate dissolution follows three distinct stages, namely, precipitate coarsening, the formation of microduplex structure and, finally, the formation of fine grained structure.

Samarium-cobalt magnets resistant to 750°C

H ci losses in high coercivity plasma-sprayed samarium-cobalt magnets (at temperatures of 700 to 800°C) are much less severe than those observed for sintered magnets. Magnets with initial coercivities of about 60 kOe show values of 35 to 50 kOe, after exposures of several hundred hours to temperatures of 700 and 750°C. The data collected on sprayed magnets indicates that H ci losses at these temperatures can be related to a narrowing SmCo 5 homogeneity range and to processes involving oxygen dissolution and precipitation. These losses do not result from eutectoid decomposition of the SmCo 5 phase as is widely accepted. The findings of this study will find extensive use in the development of thermal processing techniques that will employ slow cooling of magnets from elevated temperatures.

Polymer–ceramic composite for tooth‐root implant

A new polymer-ceramic composite suitable for tooth-root implants has been developed in this study. This material exhibited the desirable combination of good mechanical properties, controlled porosity, and ease of processing. A thermal processing technique was utilized to polymerize acrylic acid (AA) in the presence of either 0.3 or 0.05 mu alumina particles. Porosity and pore size distribution were influenced by the alumina particle size and the processing technique. For a 50 vol % AA solution, the composite had an average compressive strength of 18,000 psi and 38% porosity when 0.3 mu filler particles were used. In comparison, the 0.05 mu alumina-filled composite had an average compressive strength of 28,000 psi with a 15% porosity. Data on the physical and structural characteristics of the composite are presented in this study. Based on these results, the composite material shows good potential for use in tooth-root implants as well as other orthopedic implant applications.

Structure and properties of a microduplex maraging steel

A simple two-step thermal processing technique was devised to impart a microduplex structure in a high strength 250 grade commercial maraging steel. A martensite grain size of approximately 1 μm was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below theMd temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The micro-duplex structure exhibited a slight improvement in fracture toughness at high strain rate in contrast to the martensitic structure in which the rate effect significantly reduced the toughness.

Structure and properties of a microduplex maraging steel

A simple two-step thermal processing technique was devised to impart a microduplex structure in a high-strength 250-grade commercial maraging steel. A martensite grain size of approximately 1 ..mu..m was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below the M/sub d/ temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The microduplex structure exhibited a slight improvement in fracture toughness at high strain rate, in contrast to the martensitic structure in which the rate effect significantly reduced the toughness.more » 10 figures, 3 tables.« less

Thermal Processing of Tantalum Nitride Resistors

A study of the thermal oxidation of tantalum nitride (Ta-N) thin films has led to the development of a thermal processing technique by which these metal films can be made to exhibit superior resistor characteristics. The thermal process simply involves heating the Ta-N film resistors in air at some temperature between 450° and 700°C. Radiant heating has been found to be most convenient for this purpose. While the resistor is maintained at the elevated temperature, its resistance is monitored. When the resistor reaches the desired value, the heat source is quickly removed. Resistors can be easily trimmed to O.B%, and by exercising some care, 0.1% and less may be attained. In comparison with the usual "anodic" processing of Ta-N resistors, the thermal technique holds promise of greater economy in manufacture by reducing the number of process steps and by increasing the resistor yield. The latter benefit derives from the fact that the electrical behavior of thermally oxidized Ta-N resistors shows a marked insensitivity to certain deposition parameters which are normally controlled with some care. Accelerated tests of resistors made by this method are being carried out at various load levels and under high humidity conditions. Resistance changes as low as 0.1% per thousand hours have been recorded for nominal 1/2 watt resistors operating at 1 watt. Processing parameters such as substrate material, nitrogen doping level, trim rate, and amount of trim have been investigated. Although continued evaluation will be required before thermal processing is fully qualified, it is already clear that it will be of considerable importance to the Ta-N discrete and integrated resistor technology.