H. Ryssel

Oxidation inhibiting properties of Si3N4-layers produced by ion implantation

The implantation of nitrogen into silicon to produce Si3N4 layers was investigated to find an alternative to CVD-Si3N4 layers used in ISOPLANAR-and LOCOS-technology. The technological properties of the implanted Si3N4 layers in respect to oxidation inhibition and etching are comparable or superior to CVD-Si3N4 layers. The implanted layers are more resistent against oxidation for nitrogen doses of 2.4×1017 cm−2 at 30keV. The etching behavior is comparable for both types of Si3N4-layers. In the implanted layers no pinholes are found and threre is no formation of a birds beak, as is well known in the case of CVD-nitride.

CW CO2-laser annealing of arsenic implanted silicon

CW CO2-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm−2 for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm−2 and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×1015 cm−2 was obtained for 1×1016 cm−2 implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.

Electrical and backscattering measurements of arsenic implanted silicon

Measurements of doping concentration and mobility of arsenic implanted silicon at high energies and at low energies with following drive-in diffusion are presented. The electrical measurements are compared with and supported by backscattering measurements. Tails which are present after short time anneals vanish during drive-in diffusion. A temperature of at least 825°C is required to fully activate the arsenic and to obtain the same mobility as in diffused samples. Backscattering data reveal an anomaly in the annealing behavior of the damage. After prolonged annealing As shows some accumulation at the surface. For drive-in diffusions lattice location experiments were performed.

A New Method for Boron Doping of Silicon by Implantation of BF2-Molecules

The annealing behavior of variable dose implants of BF2 molecules has been studied in comparison to boron implants. In the case of a 1015 cm-2 room temperature BF2 implantation the annealing data indicate that an amorphous layer was formed; the sheet resistivity after 650°C anneal is a factor of 10 lower than for an equivalent energy boron implant and the samples are nearly completely annealed. For doses of ⩽1014 cm-2 there is no marked difference in the annealing of BF2 and boron implants. These results were compared to the annealing of predamaged samples and cold implants which show lower electrical activity. Studies of range distributions and electrical profiles were performed by He-backscattering and successive layer removal techniques and show close agreement with theoretical considerations. From the electrical point of view there is no evident influence of the fluorine component of the molecule. C-V measurements were taken to determine the BF2 behavior in SiO2. It is shown that surface states are annealed out at 400°C.

Front and back surface cw CO2-laser annealing of arsenic ion-implanted silicon

The annealing behavior of arsenic-implanted silicon under scanned cw CO2-laser irradiation from front and back surfaces is investigated. Ellipsometry, Hall effect, Rutherford backscattering measurements and neutron activation analysis indicate an enhancement of annealing efficiency by laser irradiation from the back surface, which provides complete recovery of crystal damage, high substitutionality and electrical activation of implanted arsenic atoms without redistribution of concentration profile. The enhancement of annealing efficiency under back-surface irradiation is explained by the difference in laser reflection from the front and back surface of silicon wafers. No differences in the results are found for scanned and static annealing.

Determination of the critical dose for different mass ions implanted into silicon

A simple theoretical model for the mass dependence of the critical dose of ion implanted silicon is reported in which the energy into atomic processes is considered as a basic quantity for the determination of the number of displaced target atoms. Backscattering experiments on samples implanted at an energy of 150 keV at low temperatures with B, Ne, P, Kr, Sb will be presented. The annealing behavior of damage distributions is investigated both by back-scattering of 1.3 MeV He ions and by electrical measurements for the dopant ions B, P, and Sb. A correlation between the different results for the critical dose is evaluated.

Grundlagen der Ionenimplantation

Die theoretischen Grundlagen der Ionenimplantation wurden in den letzten Jahren fusend auf den Arbeiten von Bohr [92], [93] und Rutherford [604] entwickelt. Es handelt sich um Theorien zur Reichweiteverteilung implantierter Ionen, zur Energieabgabe der Ionen wahrend der Implantation bzw. zur Verteilung der erzeugten Strahlenschadigung durch diesen Beschus und Theorien zum unterschiedlichen Verhalten im Eindringen von Ionen in amorphe und kristalline Festkorper (Channeling-Effekt).

Damage dependent electrical activation of boron implanted silicon

The important role of damage dependent electrical activation in the case of boron implanted silicon layers is whown by comparing measured acceptor concentration profiles in differently amorphized silicon layers. It is shown that the amorphous layer is completely recrystallized after a 650° C anneal for 10 min and the implanted boron is electrically active. In the heavily damaged but not amorphous region underneath the amorphous layer the implanted boron is hardly electrically active after this temperature treatment. At higher annealing temperatures the electrical activity increases, but 900° C are required for complete activation of the implanted boron. These results indicate that the process to activate the implanted boron electrically is strongly damage dependent. We thus found a new contribution to the understanding of the annealing behavior of implanted layers.

The investigation of lateral damage effects of ion-implanted layers by back-scattering techniques☆

Abstract Using a particle beam of small diameter the back-scattering technique can be applied to the microanalysis of small geometries. By moving a sample in steps of 5 μm with respect to the beam, lateral properties of the surface layers can be investigated. Particle beams of He + ions with diameters of 5–100 μm have been used. We found that the width of a damaged area which was defined by SiO 2 masking during ion implantation was smaller than the width of the window in the mask itself. A wire for masking was placed at a distance of 1 mm from the surface of the sample. In this case lateral annealing of the implanted area was observed, which might be due to an effect of the scanning ion beam.

Nd: YAG laser annealing of gallium-implanted silicon

A Q-switched Nd: YAG laser with a pulse duration of 20 ns was used to investigate effects of laser annealing in gallium implanted silicon. Rutherford backscattering and Hall-effect measurements were performed to evaluate the annealed layer. Differential Hall-effect measurements were carried out to obtain carrier concentration profiles after annealing. It was found that a maximum sheet carrier concentration of 8×1015 cm−2 can be obtained for a gallium implantation of 1016 cm−2 by laser annealing with an energy density of more than 1.0 J cm−2. Although the peak carrier concentration was found to be 8.0×1020 cm−3, the annealed layer showed polycrystalline structures even after annealing with an energy density up to 4J cm−2. The annealing took place in the solid phase in this energy density range.