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Sputtering yield and radiation damage by neutral beam bombardment
Classified abstracts 6509-6515 field strengths and high magnetron currents. The onset o f this oscillation was associated with a region of negative differential impedance that limited the power we could supply to the magnetron. Low magnetic field strengths should, therefore, be avoided when designing magnetrons for use at high currents. A G Spencer and R P Howson, Vacuum, 38, 1988, 497498. 21 6509. Performance of a planar magnetron sputtering apparatus with complex targets A planar magnetron sputtering apparatus with complex targets has been made for depositing high quality metal films onto various substrates. The apparatus can be used in several configurations such as that for multilayer, interdigitated wedge deposition and co-sputtering. The vacuum chamber contains four pairs of two-element targets and a rotatable substrate holder, which permits eight elements to be deposited onto one substrate without removal of the substrate from the vacuum chamber. A liquid nitrogen trap is used for cooling the substrate. Taking the A1 Fe system as an example of two-element co-sputtering, amorphous and other metastable phases have been obtained. The complex target co-sputtering technique is a useful method for investigating the formation of crystalline, metastable phases in metallic systems. Qing-Ming Chen et al, Vacuum, 38, 1988, 491 495. 21 6510. Influence of the pumping speed on the hysteresis effect in the reactive sputtering of thin films Detailed analysis of the mutual dependences of the flow rates and partial pressures of inert and reactive gases inside a deposition chamber show that the hysteresis effect occurring during reactive sputtering of thin films can be overcome if the pumping speed of the pumping system is greater than the critical pumping speed. A comparison of the theory with experiment is made for the case o f dc reactive magnetron sputtering of TiNx films. S Kadlec et al, Vacuum, 37, 1987, 729-738. 21 6511. Incorporation of argon in titanium silicon multilayer structures during sputter deposition Titanium silicon multilayer structures have been produced by alternate sputtering of silicon and titanium in an argon plasma. During the sputter process, part of the titanium and silicon layers react to form a silicide at the interfaces. Because of the argon plasma, a certain amount of argon is incorporated in the growing multilayer. A model is presented in which the amount of argon incorporated in the multilayer is a function of the nominal thickness of the individual silicon layers. G C A M Janssen and P J J Wessels, Jappl Phys, 62, 1987, 3993-3995. 21 6512. In situ ellipsometry comparison of the nucleation and growth of sputtered and glow-discharge a-Si: H We report the results of ellipsometry measurements performed during the growth of hydrogenated amorphous silicon (a-Si:H) thin films on crystalline silicon substrates using ion beam sputtering. The data have been compared to our earlier results for high-quality a-Si : H prepared by glow~lischarge decomposition of Sill4, and significant differences in the initial nucleation and microstructural evolution have been deduced for the two types o f films. For the glow~lischarge a-Si : H, the in situ pseudodielectric functon data provided evidence for the convergence of initial growth microstructure in the first ~ 50/~, leaving a-Si : H of near bulk Si-Si bond-packing density at the interface to the c-Si substrate. After the nucleation process, growth was found to be nearly layer by layer. The data for the sputtered a-Si : H also reveal the formation of a low-density microstructure in the initial stages of growth. However, in contrast to the glow-discharge films, the microstructure does not converge, and an extensive layer ( ~ 200400 ~ ) of bond-packing density lower than the bulk is left at the interface to the substrate. The effect of hydrogen incorporation on this and other aspects of the microstructural evolution of the sputtered films is discussed. Finally, similarities observed between the microstructural evolution of the sputtered films is discussed. Finally, similarities observed between the microstructural evolution of the sputtered films and poorer-quality glow~tischarge films provide insights into the growth mechanisms. R W Collins and J M Cavese, J appl Phys, 62, 1987, 4146-4153. 496
21 6513. An optimized in situ argon sputter cleaning process for device quality low-temperature (T ~< 800°C) epitaxial silicon: bipolar transistor and pn junction characterization A novel in situ argon sputter cleaning process has been developed for the deposition of high-quality low-temperature (Td~p ~< 800°C) epitaxial silicon films. A conventional in situ argon sputter cleaning process requires a room-temperature sputter followed by a high-temperature anneal in an ultrahigh vacuum system to prevent the deposition of a heavily dislocated epitaxia[ layer. We have found that by reducing the ion energy and flux by an order of magnitude to ~ 100 eV and ~ 4 x 10 ~3 ions/cm2s, respectively, and reducing the total ion dose by two orders of magnitude to ~ 3 x 10 ~6 ions/cm 2, the sputter temperature may be increased to the deposition temperature without degrading the quality of the epitaxial film. Having a common sputter and deposition temperature is extremely important since it allows the in situ argon sputter cleaning process to be incorporated into a standard high-vacuum chemical vapor deposition process for the low-temperature deposition of epitaxial silicon layers. This paper will report the results of experiments designed to correlate the effects of the sputter temperature, and the ion energy, flux, and dose with the electrical and structural properties of subsequently deposited epitaxial films. We have found that an ion energy of either 200 or 300 eV inevitably leads to the severe degradation of device electrical characteristics and the generation of > 108 dislocations/era 2. However, a 100-eV ion energy permits the deposition of high-quality epitaxial layers at temperatures at least as low as 750°C. The optimum ion flux and close for the subsequent deposition of dislocation-free epitaxial layers are strong functions of temperature. A mere doubling of either the optimum ion flux or dose at 750°C leads to the generation of dislocations; increasing the temperature to 800°C for these same sputter conditions permits the deposition of essentially dislocation-free epitaxial silicon layers (no dislocations were detected from measurements of the emitter-collector shunt density in bipolar transistors, which statistically requires the dislocation density to be < 100/cm2). The electrical quality of devices fabricated in the subsequently deposited epitaxial layers (extracted from dislocationfree devices) is only a weak function, if at all, of the ion flux and dose; the electrical quality is primarily determined by the deposition conditions. It is believed that the key to obtaining dislocation-free films when sputtering at elevated temperatures is to contain the damage created by the argon implantation to the top several monolayers where low-temperature surface annealing is effective. The sputter temperature then determines the amount of damage that can be continuously self-annealed, which in turn determines the temperature dependence of the optimum ion flux and dose. The low-temperature in situ argon sputter cleaning process has facilitated the deposition of essentially dislocation-free epitaxial silicon at 800°C with electrical characteristics comparable or superior to bulk silicon. This was accomplished in a system utilizing only standard highvacuum chemical vapor deposition technology. W R Burger and R Reif, Jappl Phys, 62, 1987, 42554268. 21 6514. Sputtering yield and radiation damage by neutral beam bombardment To clarify the difference between ion beam etching and neutral beam etching, a low-energy ( 1 0 ~ 1000 eV) Ne ° neutral beam obtained by charge exchange reaction has been used to bombard Cu, Si, and SiO2 surfaces. The sputtering yields of Cu and Si by Ne ° have been found to be the same as those by Ne +. The sputtering yield of SiO2 by Ne ° is slightly smaller than that by Ne +. It is believed that electronic sputtering mechanisms play only a small role in the sputtering of these materials at these low ion energies. C - V measurements show that the amount o f radiation damage caused by Ne ° neutral beam bombardment of the SiO2/Si structure is significantly less than that by a Ne + ion beam. When the Ne + dosage increases, the fiat-band voltage shift increases and the thin SiO2 films on Si eventually break down. In Ne ° neutral bombardment, the flat-band voltage shift saturates with increasing dosage and no breakdown of SiO2 occurs. It is assumed that, in neutral beam bombardment, the surface potential of SiO2 is limited by secondary emission of charged particles whose energies arc at most 10 20 eV and the resulting surface potential is not large enough to cause dielectric breakdown. Tatsumi Mizutani and Shigeru Nishimatsu, J Vac Sci Technol, A6, 1988, 1417 1420. 2l 6515. The bombarding-angle dependence of sputtering yields under various surface conditions Using the ACAT code, the bombarding angle-dependence of sputtering
21 6513. An optimized in situ argon sputter cleaning process for device quality low-temperature (T ~< 800°C) epitaxial silicon: bipolar transistor and pn junction characterization A novel in situ argon sputter cleaning process has been developed for the deposition of high-quality low-temperature (Td~p ~< 800°C) epitaxial silicon films. A conventional in situ argon sputter cleaning process requires a room-temperature sputter followed by a high-temperature anneal in an ultrahigh vacuum system to prevent the deposition of a heavily dislocated epitaxia[ layer. We have found that by reducing the ion energy and flux by an order of magnitude to ~ 100 eV and ~ 4 x 10 ~3 ions/cm2s, respectively, and reducing the total ion dose by two orders of magnitude to ~ 3 x 10 ~6 ions/cm 2, the sputter temperature may be increased to the deposition temperature without degrading the quality of the epitaxial film. Having a common sputter and deposition temperature is extremely important since it allows the in situ argon sputter cleaning process to be incorporated into a standard high-vacuum chemical vapor deposition process for the low-temperature deposition of epitaxial silicon layers. This paper will report the results of experiments designed to correlate the effects of the sputter temperature, and the ion energy, flux, and dose with the electrical and structural properties of subsequently deposited epitaxial films. We have found that an ion energy of either 200 or 300 eV inevitably leads to the severe degradation of device electrical characteristics and the generation of > 108 dislocations/era 2. However, a 100-eV ion energy permits the deposition of high-quality epitaxial layers at temperatures at least as low as 750°C. The optimum ion flux and close for the subsequent deposition of dislocation-free epitaxial layers are strong functions of temperature. A mere doubling of either the optimum ion flux or dose at 750°C leads to the generation of dislocations; increasing the temperature to 800°C for these same sputter conditions permits the deposition of essentially dislocation-free epitaxial silicon layers (no dislocations were detected from measurements of the emitter-collector shunt density in bipolar transistors, which statistically requires the dislocation density to be < 100/cm2). The electrical quality of devices fabricated in the subsequently deposited epitaxial layers (extracted from dislocationfree devices) is only a weak function, if at all, of the ion flux and dose; the electrical quality is primarily determined by the deposition conditions. It is believed that the key to obtaining dislocation-free films when sputtering at elevated temperatures is to contain the damage created by the argon implantation to the top several monolayers where low-temperature surface annealing is effective. The sputter temperature then determines the amount of damage that can be continuously self-annealed, which in turn determines the temperature dependence of the optimum ion flux and dose. The low-temperature in situ argon sputter cleaning process has facilitated the deposition of essentially dislocation-free epitaxial silicon at 800°C with electrical characteristics comparable or superior to bulk silicon. This was accomplished in a system utilizing only standard highvacuum chemical vapor deposition technology. W R Burger and R Reif, Jappl Phys, 62, 1987, 42554268. 21 6514. Sputtering yield and radiation damage by neutral beam bombardment To clarify the difference between ion beam etching and neutral beam etching, a low-energy ( 1 0 ~ 1000 eV) Ne ° neutral beam obtained by charge exchange reaction has been used to bombard Cu, Si, and SiO2 surfaces. The sputtering yields of Cu and Si by Ne ° have been found to be the same as those by Ne +. The sputtering yield of SiO2 by Ne ° is slightly smaller than that by Ne +. It is believed that electronic sputtering mechanisms play only a small role in the sputtering of these materials at these low ion energies. C - V measurements show that the amount o f radiation damage caused by Ne ° neutral beam bombardment of the SiO2/Si structure is significantly less than that by a Ne + ion beam. When the Ne + dosage increases, the fiat-band voltage shift increases and the thin SiO2 films on Si eventually break down. In Ne ° neutral bombardment, the flat-band voltage shift saturates with increasing dosage and no breakdown of SiO2 occurs. It is assumed that, in neutral beam bombardment, the surface potential of SiO2 is limited by secondary emission of charged particles whose energies arc at most 10 20 eV and the resulting surface potential is not large enough to cause dielectric breakdown. Tatsumi Mizutani and Shigeru Nishimatsu, J Vac Sci Technol, A6, 1988, 1417 1420. 2l 6515. The bombarding-angle dependence of sputtering yields under various surface conditions Using the ACAT code, the bombarding angle-dependence of sputtering