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Ion implantation, a method for fabricating light guides in polymers
Classified abstracts 6959~968
31 6959. Surface cracking of vitreous fused silica induced by MeV ion beam bombardment The surface cracking behaviour of vitreous fused silica (suprasil II) induced by MeV 3~C1 and ~9F ions was observed. The crack density increases with ion fluence, reaches a maximum (for 17 MeV 35C1at 1 × 10 ~3 35C1/cm2 and for 17 MeV 19F at 5 x 1013 19F/cm 2) and then declines. The cracks close up for subsequent higher ion fluences. The surface cracking occurs in different ion fluence ranges with ion mass, for 17 MeV 3sC1 5 × 10121 × 1014 35C1/cm2; for 17 MeV 19F, 1 × 1013-3 × 1014 19F/cmZ. No surface cracks were observed for 2 MeV H ÷ for the ion fluence range of 5 × 1014--10t7 ~H/cm2. The measurements of the defects in silica samples with EPR indicate that the surface cracking occurs in the transition region where the ion damage tracks partly overlap. We tentatively suggest that the surface cracking may result from heavy ion tracks in the insulating materials, and cracks close up at higher ion fluence due to the compaction of the irradiated area. Chengru Shi and T A Tombrcflo, Radiat Effects, 105, 1988, 291 301. 31 6960. The influence of thermal relaxation on implantation induced disorder accumulation A detailed analysis is made of disorder accumulation under direct ion implantation amorphous zone generation conditions where the zone size can thermally relax both during and after implantation. It is shown that this leads to considerable complexity in the behaviour of the amorphous fraction f as a function of ion fluencc ~, ion flux density J and substrate temperature 7". Steady state and low amorphous fraction solutions show how zone expansion or contraction processes can be distinguished. G Carter et al, Radiat Effects, 105, 1988, 211 223. 31 6961. Transverse straggling of MeV oxygen ions implanted in silicon The 16C~(d,a)14N nuclear reaction was used to evaluate the lateral dispersion of oxygen ions implanted in silicon with energy ranging from 0.6 to 2 MeV. The projected range and longitudinal straggling, also measured in this experiment, are in close agreement with computer programs like TRIM or PRAL. Hovever, the lateral spread is significantly lower than predicted, saturating towards 0.3 #m for high energies. J J Grob et al, Nucl lnstrum Meth Phys Res, B30, 1988, 34-37. 31 6962. High dose uranium ion implantation into silicon Implantation of uranium ions into silicon to a dose of 6 × 10~6atoms/cm 2, with a maximum concentration of 6 × 102~ atoms/era 3, has been carried out at an ion mean energy of 157 keV. The implanted uranium content was measured by Rutherford backscattering and confirmed by a measurement of the alpha-particle activity of the buried uranium layer. The range and straggling of the uranium implant, and sputtering of the silicon target by uranium, were measured and are compared with theoretical estimates. I G Brown et al, Nucl Instrum Meth Phys Res, B31, 1988, 558-562. 31 6963. On-line measurement of the spatial dose uniformity in ion implantation processes A method is described which enables the on-line monitoring of the uniformity of an ion implantation. The position on the target-wafer where a fixed amount of dose is implanted is inferred from the two values of the scanning voltages. The procedure includes the correction for finite beam size. The method neither interrupts nor disturbs the ion beam and provides an immediately available record of the implant uniformity. An example of application is demonstrated. Thomas Stiehler, Nucl Instrum Meth Phys Res, B31, 1988, 563-566. 31 6964. Influence of boron related defects on activation of silicon implanted into undoped semi-insulating GaAs The dependence of sheet carrier concentration of a Si-implanted layer on lattice parameters of undoped liquid encapsulated Czochralski GaAs was investigated. Crystals were grown from near-stoichiometric melts with varying boron concentrations. Sheet carrier concentration increases with an increase in lattice parameters due to the reduced boron concentration. An anomalous reduction in the lattice parameter suggests that native defects such as B~a VA~are responsible for the increase in the occupancy o f implanted Si atoms on As sites. Fumio Orito et al, J appl Phys, 63, 1988, 2691-2693.
31 6965. Optical investigations of ion implant damage in silicon Ion implantation damage in silicon has been studied utilizing a new optical technique (differential reflectomctry). It has been demonstrated that differential reflectometry can be used to identify whether an implanted layer is crystalline, damaged crystalline, or amorphous. The intensity of interband transitions can be used to determine the thickness of a damaged crystalline layer over a submerged amorphous layer. Interference effects were utilized to determine the thickness of an amorphous layer. Thus, differential optical reflectance has far-reaching potential for characterizing implanted substrates. R E Hummel et al, Jappl Phys, 63, 1988, 2591-2594. 31 6966. Ion implantation, a method for fabricating light guides in polymers Li ÷ and N + ions were implanted into aliphatic polymethylmethacrylate (PMMA), pelyvinylalcohol (PVA) and aromatic polyimide (PI) polycarbonate (PC) polymers in the energy range of 10(~130 keV. Planar optical waveguides guiding between one and three modes were formed. For low implantation doses (~< I 0 .4 ions/era2), total waveguide loss values at 2 = 633 nm were found to be less than 2 dB/cm. The changes in the refractive index were found to be very large (An/> 0.05) in the case of P M M A and PVA. We interpret this change in refractive index as being due to the formation of aromatic compounds in the regions of electronic scattering. J R Kulish et al, J appl Phys, 63, 1988, 2517 2521. 31 6967. Range measurements and thermal stability study of A Z I l l photoresist implanted with Bi ions The Rutherford backscattering technique has been used to determine the range parameters of Bi ions implanted into A Z i 11 photoresist film at energies from 10 to 400 keV. An overall good agreement is found between the experimental results and the theoretical predictions by Biersack, Ziegler and Littmark. It is also observed that a variation in the implantation dose does not affect the projected range and range straggling results, desire the fact that chemical modification of the implanted polymer layer is detected. In addition, we find that a shallow implantation of the polymer film with Bi ions increases the temperature at which the photoresist starts to decompose. Finally, at 300°C the implanted Bi atoms diffuse preferentially toward the bulk. For this temperature, two different diffusion coefficients are estimated, one for the damaged region De = 1.2 × 10 5 cm2/s and another for the bulk Db = 1.2 × 10 -14 cm2/5. R B Guimfiraes et al, J appl Phys, 63, 1988, 250~2506. 31 6968. Transient boron diffusion in ion-implanted crystalline and amorphous silicon Boron diffusion in ion-implanted and annealed single-crystal and amorphized Si is compared to determine the effect of amorphization on the initial transient boron motion reported for single crystal. The boron was implanted at 20 keV and at doses of 1 × 1015 and 3 × 10 ~5 cm 2. The Si was either preamorphized or postamorphized to a depth of 320 nm by implantation of Si ions at three different energies. In the amorphized samples the entire boron profile was always contained within this distar ze. The samples were annealed by furnace or rapid thermal annealing to 90(~1100°C with or without a preanneal at 600°C. The initial rapid diffusion transient in the tail region of the boron profile was observed in all the crystal samples. This transient was totally absent in the amorphized samples. This is manifest by careful comparison of boron concentration profiles determined by secondary ion mass spectrometry of single-crystal and amorphized samples after annealing. For anneals where significant motion occurs, the profiles of the amorphized samples could be fit with a computational model that did not include anomalous transient effects. It is proposed that excess intersitials cause the transient diffusion in the case of the crystalline samples. The source of interstitials is believed to be provided by the thermal dissolution of small clusters that are formed by the implantation process. They exist for only a short time, during which they enhance the boron diffusion. Since there is no enhanced diffusion in the amorphous region that regrows to single crystal, apparently interstitial clusters are neither produced by nor do they survive the regrowth process in that region. In addition, the interstitials generated by the damage beyond the amorphous~rystalline boundary are prevented from entering the regrown region by the dislocation loops formed at that boundary which act as a sink consuming the interstitials diffusing toward the surface. T O Sedgwick et al, JapplPhys, 63, 1988, 1452-1463. 987
31 6959. Surface cracking of vitreous fused silica induced by MeV ion beam bombardment The surface cracking behaviour of vitreous fused silica (suprasil II) induced by MeV 3~C1 and ~9F ions was observed. The crack density increases with ion fluence, reaches a maximum (for 17 MeV 35C1at 1 × 10 ~3 35C1/cm2 and for 17 MeV 19F at 5 x 1013 19F/cm 2) and then declines. The cracks close up for subsequent higher ion fluences. The surface cracking occurs in different ion fluence ranges with ion mass, for 17 MeV 3sC1 5 × 10121 × 1014 35C1/cm2; for 17 MeV 19F, 1 × 1013-3 × 1014 19F/cmZ. No surface cracks were observed for 2 MeV H ÷ for the ion fluence range of 5 × 1014--10t7 ~H/cm2. The measurements of the defects in silica samples with EPR indicate that the surface cracking occurs in the transition region where the ion damage tracks partly overlap. We tentatively suggest that the surface cracking may result from heavy ion tracks in the insulating materials, and cracks close up at higher ion fluence due to the compaction of the irradiated area. Chengru Shi and T A Tombrcflo, Radiat Effects, 105, 1988, 291 301. 31 6960. The influence of thermal relaxation on implantation induced disorder accumulation A detailed analysis is made of disorder accumulation under direct ion implantation amorphous zone generation conditions where the zone size can thermally relax both during and after implantation. It is shown that this leads to considerable complexity in the behaviour of the amorphous fraction f as a function of ion fluencc ~, ion flux density J and substrate temperature 7". Steady state and low amorphous fraction solutions show how zone expansion or contraction processes can be distinguished. G Carter et al, Radiat Effects, 105, 1988, 211 223. 31 6961. Transverse straggling of MeV oxygen ions implanted in silicon The 16C~(d,a)14N nuclear reaction was used to evaluate the lateral dispersion of oxygen ions implanted in silicon with energy ranging from 0.6 to 2 MeV. The projected range and longitudinal straggling, also measured in this experiment, are in close agreement with computer programs like TRIM or PRAL. Hovever, the lateral spread is significantly lower than predicted, saturating towards 0.3 #m for high energies. J J Grob et al, Nucl lnstrum Meth Phys Res, B30, 1988, 34-37. 31 6962. High dose uranium ion implantation into silicon Implantation of uranium ions into silicon to a dose of 6 × 10~6atoms/cm 2, with a maximum concentration of 6 × 102~ atoms/era 3, has been carried out at an ion mean energy of 157 keV. The implanted uranium content was measured by Rutherford backscattering and confirmed by a measurement of the alpha-particle activity of the buried uranium layer. The range and straggling of the uranium implant, and sputtering of the silicon target by uranium, were measured and are compared with theoretical estimates. I G Brown et al, Nucl Instrum Meth Phys Res, B31, 1988, 558-562. 31 6963. On-line measurement of the spatial dose uniformity in ion implantation processes A method is described which enables the on-line monitoring of the uniformity of an ion implantation. The position on the target-wafer where a fixed amount of dose is implanted is inferred from the two values of the scanning voltages. The procedure includes the correction for finite beam size. The method neither interrupts nor disturbs the ion beam and provides an immediately available record of the implant uniformity. An example of application is demonstrated. Thomas Stiehler, Nucl Instrum Meth Phys Res, B31, 1988, 563-566. 31 6964. Influence of boron related defects on activation of silicon implanted into undoped semi-insulating GaAs The dependence of sheet carrier concentration of a Si-implanted layer on lattice parameters of undoped liquid encapsulated Czochralski GaAs was investigated. Crystals were grown from near-stoichiometric melts with varying boron concentrations. Sheet carrier concentration increases with an increase in lattice parameters due to the reduced boron concentration. An anomalous reduction in the lattice parameter suggests that native defects such as B~a VA~are responsible for the increase in the occupancy o f implanted Si atoms on As sites. Fumio Orito et al, J appl Phys, 63, 1988, 2691-2693.
31 6965. Optical investigations of ion implant damage in silicon Ion implantation damage in silicon has been studied utilizing a new optical technique (differential reflectomctry). It has been demonstrated that differential reflectometry can be used to identify whether an implanted layer is crystalline, damaged crystalline, or amorphous. The intensity of interband transitions can be used to determine the thickness of a damaged crystalline layer over a submerged amorphous layer. Interference effects were utilized to determine the thickness of an amorphous layer. Thus, differential optical reflectance has far-reaching potential for characterizing implanted substrates. R E Hummel et al, Jappl Phys, 63, 1988, 2591-2594. 31 6966. Ion implantation, a method for fabricating light guides in polymers Li ÷ and N + ions were implanted into aliphatic polymethylmethacrylate (PMMA), pelyvinylalcohol (PVA) and aromatic polyimide (PI) polycarbonate (PC) polymers in the energy range of 10(~130 keV. Planar optical waveguides guiding between one and three modes were formed. For low implantation doses (~< I 0 .4 ions/era2), total waveguide loss values at 2 = 633 nm were found to be less than 2 dB/cm. The changes in the refractive index were found to be very large (An/> 0.05) in the case of P M M A and PVA. We interpret this change in refractive index as being due to the formation of aromatic compounds in the regions of electronic scattering. J R Kulish et al, J appl Phys, 63, 1988, 2517 2521. 31 6967. Range measurements and thermal stability study of A Z I l l photoresist implanted with Bi ions The Rutherford backscattering technique has been used to determine the range parameters of Bi ions implanted into A Z i 11 photoresist film at energies from 10 to 400 keV. An overall good agreement is found between the experimental results and the theoretical predictions by Biersack, Ziegler and Littmark. It is also observed that a variation in the implantation dose does not affect the projected range and range straggling results, desire the fact that chemical modification of the implanted polymer layer is detected. In addition, we find that a shallow implantation of the polymer film with Bi ions increases the temperature at which the photoresist starts to decompose. Finally, at 300°C the implanted Bi atoms diffuse preferentially toward the bulk. For this temperature, two different diffusion coefficients are estimated, one for the damaged region De = 1.2 × 10 5 cm2/s and another for the bulk Db = 1.2 × 10 -14 cm2/5. R B Guimfiraes et al, J appl Phys, 63, 1988, 250~2506. 31 6968. Transient boron diffusion in ion-implanted crystalline and amorphous silicon Boron diffusion in ion-implanted and annealed single-crystal and amorphized Si is compared to determine the effect of amorphization on the initial transient boron motion reported for single crystal. The boron was implanted at 20 keV and at doses of 1 × 1015 and 3 × 10 ~5 cm 2. The Si was either preamorphized or postamorphized to a depth of 320 nm by implantation of Si ions at three different energies. In the amorphized samples the entire boron profile was always contained within this distar ze. The samples were annealed by furnace or rapid thermal annealing to 90(~1100°C with or without a preanneal at 600°C. The initial rapid diffusion transient in the tail region of the boron profile was observed in all the crystal samples. This transient was totally absent in the amorphized samples. This is manifest by careful comparison of boron concentration profiles determined by secondary ion mass spectrometry of single-crystal and amorphized samples after annealing. For anneals where significant motion occurs, the profiles of the amorphized samples could be fit with a computational model that did not include anomalous transient effects. It is proposed that excess intersitials cause the transient diffusion in the case of the crystalline samples. The source of interstitials is believed to be provided by the thermal dissolution of small clusters that are formed by the implantation process. They exist for only a short time, during which they enhance the boron diffusion. Since there is no enhanced diffusion in the amorphous region that regrows to single crystal, apparently interstitial clusters are neither produced by nor do they survive the regrowth process in that region. In addition, the interstitials generated by the damage beyond the amorphous~rystalline boundary are prevented from entering the regrown region by the dislocation loops formed at that boundary which act as a sink consuming the interstitials diffusing toward the surface. T O Sedgwick et al, JapplPhys, 63, 1988, 1452-1463. 987