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Donor generation in monocrystalline silicon by Halogen implantation
World Abstracts on Microelectronics and Reliability
1187
by the liquid encapsulated Czochralski (LEC) method from pyrolytic boron nitride crucibles is gaining favour as a direct ion implantation substrate in the fabrication of high-speed devices and integrated circuits because of superior reproducibility and uniformity. Recent work has clarified the relationship between the electrical conductivity of a gallium arsenide crystal and the composition of the melt from which it is grown. A sufficiently arsenic-rich melt makes the crystal semi-insulating by ensuring the presence of the deep donor EL2 to compensate a net excess of carbon acceptors over shallow donors. Arsenic-poor melts lead to p-type crystals containing two deep acceptors, probably stoichiometryrelated lattice defects, as well as the impurity acceptors and donors found in semi-insulating material.
It was found that by increasing the angle of incidence of deposition, the lithographic sensitivity was considerably enhanced. The increase for 60 keV protons was from 1 . 4 x l 0 - S C c m -2 to 1 . 4 x l 0 - 6 C c m -2 for vapour beam inclinations of 0 ° to 80 ° with respect to the normal. The applicability of this resist for pattern duplication using a "see-through" mask was investigated. The results are presented showing replicated mask patterns with 0.5 ~m features that were exposed in this resist by irradiating the mask with a proton beam from a conventional ion implantation system. In the ion exposed and developed patterns, the concentration of silver was found to be less along the edges than in the interior of the remaining resist. The ion beam enhanced silver dissolution mechanism is discussed.
Implantation through a window with medium to high energy ions. A. G. LUTSCHand D. N. OLIVER.Microelectron. J. 14 (1), 21 (1983). When implanting ions through a window the equidensity line of ions are influenced by higher moments of the impurity ion distribution versus depth into the substrate. This effect is particularly noticeable if the ions are light and the ion energy is high, say higher than 300keV. The shape of pn junctions of directly implanted shallow transistors is affected. Homogenization of the electrical field, being necessary for high voltage, or high frequency operation is not possible, without considering the fine structure of the ion distribution near the surface and particularly near the mask edges. The influence of higher moments is also important for the case of direct implantation of wells for CMOS. Ion equidensity distributions below a window in the mask are shown for boron and arsenic implantation into silicon at energies between 70 keV and 800 keV.
Contribution to ion implantation through a narrow slit at higher energies. A. G. K. LUTSCHand H. RUNGE.Microelectron. J. 14 (1), 15 (1983). For the implantation of boron into silicon through submicrometre-width slits (of the order of 0.5 p.m) at an energy of 1 McV, the maximum ion concentration at a distance equal to the projected range does not reach, even at the centre, the corresponding value for larger windows. Even at lower energies the mask edges have an influence on the ion concentration if the slit width is of the order of 10 I.tm.
Donor generation in monocrystalline silicon by Halogen implantation. G. GREEUWand J. F. VERWEY.Solid-St. Electron. 26 (3), 241 (1983). C1 +, F + and Ar + ions were implanted in n-type, floating zone, 2flcm, (100)-surface orientated Si wafers. The implantation doses were l0 ~4 and 1015 cm 2, the energy was 25 keV. After the implantation the wafers were annealed and/or oxidized at 1000°C. By performing capacitance-voltage measurements (e.g. HFCV and Schottky CV), the following effects were observed: an increasing n-type doping profile towards the Si-surface; increase of the oxide growth rate. The origin of the donorsites is probably a complex formed out of an implantation damage centre and a halogen atom. The increase of the oxide growth rate can be explained by catalytic reactions of the halogen ions, just as was found for oxidation in a HCI/O 2 atmosphere. In the case of the C1 implanted and oxidized samples, part of the chlorine is incorporated in the oxide, as measured with Ruterford Backscattering. However, TVS (triangular voltage sweep) measurements reveal that gettering of mobile Na + ions does not occur in these oxides.
Control of Boron diffusion in polysilicon for constructing overlapping polysilicon gate charge-coupled devices. A. SRIVASTAVA and J. T. BOYD. Microelectron. Reliab. 23 (1), 179 (1983). The diffusion coefficient of boron having values significantly different in silicon and silicon dioxide has been used to control the doping of boron impurity in intrinsic polysilicon deposited over the gate oxide. The method reduces the possibility of doping gate oxide while diffusing boron in polysilicon. Using the method, silicon gate p-MOSFETS and twenty bit photo-sensor, four phase, double overlapping polysilicon gate surface channel charge-coupled devices have been constructed with a transfer efficiency of 0.9990. The measured values of the threshold voltage of MOSFETS are in close agreement with their corresponding calculated values.
Germanium selenide as a negative inorganic resist for ion beam microfabrication. K. BALASUBRAMANYAM,]. ADESIDA, A. L. RUOFF and E. D. WOLF. Microelectron. J. 14 (1), 35 (1983). The ion beam exposure characteristics of an inorganic negative resist, silver sensitized a-Ge0.25S%.:5 , was studied.
Ion range statistics by a Fourier series. A. G. K. LUTSCH. Microelectron. J. 14 (1), 5 (1983). Most statistics for predicting the impurity distribution of ions implanted in solids use a Gaussian distribution multiplied by a polynomial. A range statistics is proposed using a Gaussian and elements of a Fourier series, which should be useful, in particular for range prediction at higher energies.
Plasma-enhanced deposition of tungsten, molybdenum and tungsten silicide films. C. C. TANG, J. K. CHU and D. W. HESS. Solid St. Technol., 125 (March 1983). Processes for the plasma-enhanced chemical vapour deposition of tungsten, molybdenum, and tungsten silicide are described. The effects of source gases, substrate temperatures, and post-deposition heat treatments on the properties of these films are discussed. Where appropriate, comparisons of film properties of plasmadeposited films with those of other deposition techniques are made. Mechanistic considerations in the deposition processes are suggested.
1187
by the liquid encapsulated Czochralski (LEC) method from pyrolytic boron nitride crucibles is gaining favour as a direct ion implantation substrate in the fabrication of high-speed devices and integrated circuits because of superior reproducibility and uniformity. Recent work has clarified the relationship between the electrical conductivity of a gallium arsenide crystal and the composition of the melt from which it is grown. A sufficiently arsenic-rich melt makes the crystal semi-insulating by ensuring the presence of the deep donor EL2 to compensate a net excess of carbon acceptors over shallow donors. Arsenic-poor melts lead to p-type crystals containing two deep acceptors, probably stoichiometryrelated lattice defects, as well as the impurity acceptors and donors found in semi-insulating material.
It was found that by increasing the angle of incidence of deposition, the lithographic sensitivity was considerably enhanced. The increase for 60 keV protons was from 1 . 4 x l 0 - S C c m -2 to 1 . 4 x l 0 - 6 C c m -2 for vapour beam inclinations of 0 ° to 80 ° with respect to the normal. The applicability of this resist for pattern duplication using a "see-through" mask was investigated. The results are presented showing replicated mask patterns with 0.5 ~m features that were exposed in this resist by irradiating the mask with a proton beam from a conventional ion implantation system. In the ion exposed and developed patterns, the concentration of silver was found to be less along the edges than in the interior of the remaining resist. The ion beam enhanced silver dissolution mechanism is discussed.
Implantation through a window with medium to high energy ions. A. G. LUTSCHand D. N. OLIVER.Microelectron. J. 14 (1), 21 (1983). When implanting ions through a window the equidensity line of ions are influenced by higher moments of the impurity ion distribution versus depth into the substrate. This effect is particularly noticeable if the ions are light and the ion energy is high, say higher than 300keV. The shape of pn junctions of directly implanted shallow transistors is affected. Homogenization of the electrical field, being necessary for high voltage, or high frequency operation is not possible, without considering the fine structure of the ion distribution near the surface and particularly near the mask edges. The influence of higher moments is also important for the case of direct implantation of wells for CMOS. Ion equidensity distributions below a window in the mask are shown for boron and arsenic implantation into silicon at energies between 70 keV and 800 keV.
Contribution to ion implantation through a narrow slit at higher energies. A. G. K. LUTSCHand H. RUNGE.Microelectron. J. 14 (1), 15 (1983). For the implantation of boron into silicon through submicrometre-width slits (of the order of 0.5 p.m) at an energy of 1 McV, the maximum ion concentration at a distance equal to the projected range does not reach, even at the centre, the corresponding value for larger windows. Even at lower energies the mask edges have an influence on the ion concentration if the slit width is of the order of 10 I.tm.
Donor generation in monocrystalline silicon by Halogen implantation. G. GREEUWand J. F. VERWEY.Solid-St. Electron. 26 (3), 241 (1983). C1 +, F + and Ar + ions were implanted in n-type, floating zone, 2flcm, (100)-surface orientated Si wafers. The implantation doses were l0 ~4 and 1015 cm 2, the energy was 25 keV. After the implantation the wafers were annealed and/or oxidized at 1000°C. By performing capacitance-voltage measurements (e.g. HFCV and Schottky CV), the following effects were observed: an increasing n-type doping profile towards the Si-surface; increase of the oxide growth rate. The origin of the donorsites is probably a complex formed out of an implantation damage centre and a halogen atom. The increase of the oxide growth rate can be explained by catalytic reactions of the halogen ions, just as was found for oxidation in a HCI/O 2 atmosphere. In the case of the C1 implanted and oxidized samples, part of the chlorine is incorporated in the oxide, as measured with Ruterford Backscattering. However, TVS (triangular voltage sweep) measurements reveal that gettering of mobile Na + ions does not occur in these oxides.
Control of Boron diffusion in polysilicon for constructing overlapping polysilicon gate charge-coupled devices. A. SRIVASTAVA and J. T. BOYD. Microelectron. Reliab. 23 (1), 179 (1983). The diffusion coefficient of boron having values significantly different in silicon and silicon dioxide has been used to control the doping of boron impurity in intrinsic polysilicon deposited over the gate oxide. The method reduces the possibility of doping gate oxide while diffusing boron in polysilicon. Using the method, silicon gate p-MOSFETS and twenty bit photo-sensor, four phase, double overlapping polysilicon gate surface channel charge-coupled devices have been constructed with a transfer efficiency of 0.9990. The measured values of the threshold voltage of MOSFETS are in close agreement with their corresponding calculated values.
Germanium selenide as a negative inorganic resist for ion beam microfabrication. K. BALASUBRAMANYAM,]. ADESIDA, A. L. RUOFF and E. D. WOLF. Microelectron. J. 14 (1), 35 (1983). The ion beam exposure characteristics of an inorganic negative resist, silver sensitized a-Ge0.25S%.:5 , was studied.
Ion range statistics by a Fourier series. A. G. K. LUTSCH. Microelectron. J. 14 (1), 5 (1983). Most statistics for predicting the impurity distribution of ions implanted in solids use a Gaussian distribution multiplied by a polynomial. A range statistics is proposed using a Gaussian and elements of a Fourier series, which should be useful, in particular for range prediction at higher energies.
Plasma-enhanced deposition of tungsten, molybdenum and tungsten silicide films. C. C. TANG, J. K. CHU and D. W. HESS. Solid St. Technol., 125 (March 1983). Processes for the plasma-enhanced chemical vapour deposition of tungsten, molybdenum, and tungsten silicide are described. The effects of source gases, substrate temperatures, and post-deposition heat treatments on the properties of these films are discussed. Where appropriate, comparisons of film properties of plasmadeposited films with those of other deposition techniques are made. Mechanistic considerations in the deposition processes are suggested.