Akio Takano

Quantitative Evaluation of Silicon Displacement Induced by Arsenic Implantation Using Silicon Isotope Superlattices

We established a new method for evaluating quantitatively the silicon atomic displacement as a function of the depth from the surface induced by arsenic implantation into a silicon wafer. A simulation based on a convolution integral was developed successfully to reproduce the experimental depth profiles of isotopes in the arsenic-implanted 28Si/30Si isotope superlattices, from which the average distance of the silicon displacements due to the collisions with implanted arsenic is obtained. We show that it takes the average displacement of ~0.5 nm to make the structure appear amorphous by transmission electron microscopy.

Behaviors of neutral and charged silicon self-interstitials during transient enhanced diffusion in silicon investigated by isotope superlattices

We investigated the contributions of neutral and charged silicon self-interstitials to self- and boron diffusion during transient enhanced diffusion in silicon. We simultaneously observed self- and boron diffusion in silicon using Snati/S28i isotope superlattices. A calculation based on diffusion equations involving {311} defects and boron-interstitial cluster models was employed to reproduce the diffusion profiles in silicon-implanted (intrinsic) and boron-implanted (extrinsic) silicon isotope superlattices, followed by annealing. To investigate the diffusion processes, the time evolution of the silicon self-interstitial profiles during the transient diffusion was simulated. The results directly demonstrate that excess neutral self-interstitials dominantly enhance the self-diffusion during the transient process in the intrinsic conditions, while doubly positively charged self-interstitials dominate the self-diffusion in the extrinsic conditions.

Matrix and element dependences of useful yield in Si and SiO2 matrices using laser-ionization sputtered neutral mass spectrometry

The element and/or material dependence of the useful yield in laser-ionization sputtered neutral mass spectrometry (SNMS) using a high-photon-flux laser was investigated. Useful yields obtained from Si, B, As, and O in Si and SiO2 matrices using both secondary ion mass spectrometry (SIMS) and SNMS were compared, and the possibility of the accurate analysis of impurities in multilayers was investigated in terms of tunnel ionization. The behavior of atoms released from the surface by ion bombardment was calculated, and it was considered that the flying speed of sputtered atoms depends on the mass and that this causes the elemental difference in the fractions of laser-irradiated atoms. In the case of SNMS, excluding O, whose ionization probability is considered to be much lower than for the other elements, the useful yields of Si, B, and As are within 1 order of magnitude in both the Si and SiO2 matrices, and the difference between the matrices for each element is within a factor of two. These differences are much smaller than in the result of SIMS. It was confirmed that the distribution of B in a SiO2/Si stacked layer can be analyzed more accurately by SNMS than by SIMS. SNMS with a high-photon-density laser is considered to be effective for the analysis of more than one element in multilayers.The element and/or material dependence of the useful yield in laser-ionization sputtered neutral mass spectrometry (SNMS) using a high-photon-flux laser was investigated. Useful yields obtained from Si, B, As, and O in Si and SiO2 matrices using both secondary ion mass spectrometry (SIMS) and SNMS were compared, and the possibility of the accurate analysis of impurities in multilayers was investigated in terms of tunnel ionization. The behavior of atoms released from the surface by ion bombardment was calculated, and it was considered that the flying speed of sputtered atoms depends on the mass and that this causes the elemental difference in the fractions of laser-irradiated atoms. In the case of SNMS, excluding O, whose ionization probability is considered to be much lower than for the other elements, the useful yields of Si, B, and As are within 1 order of magnitude in both the Si and SiO2 matrices, and the difference between the matrices for each element is within a factor of two. These differences ar...

Bevel depth profiling by high-spatial-resolution sputtered neutral mass spectrometry with laser postionization

Secondary-ion mass spectrometry (SIMS) sputter depth profiling is used for the quantitative depth profile analysis of impurities. However, SIMS suffers from a large quantitative uncertainty and depth-scale uncertainty at the interfaces of heteromultilayers and in the near-surface region, because the secondary ion yield and sputtering yield are significantly influenced by matrix effects and accumulation effects of the primary ion. In this paper, the authors report on the development of a new depth profiling method with good depth-scale accuracy and low matrix effects to overcome these problems. This was achieved through the combination of high-spatial-resolution bevel depth profiling and sputtered neutral mass spectrometry with laser postionization (laser-SNMS). The sample used to evaluate this new bevel depth profiling method was a silicon on insulator wafer obtained using the separation by implantation of oxygen technique and implanted with boron. Depth profiles were obtained using both SIMS and laser-SNMS and evaluated by comparison with the stopping and range of ions in matter (SRIM) simulation. Although both methods afforded quite good depth resolutions, in SIMS the secondary ion signal intensity for boron was amplified by the influence of the matrix effect and showed a discontinuous profile shape at the interfaces, whereas the profile for boron obtained using laser-SNMS was consistent with the SRIM results and exhibited high continuity. By using a combination of the bevel depth profiling method and laser-SNMS method, it was confirmed that an easy-to-analyze depth profile could be obtained for the dopant concentration in multilayer samples, which is difficult to obtain using the conventional SIMS method.Secondary-ion mass spectrometry (SIMS) sputter depth profiling is used for the quantitative depth profile analysis of impurities. However, SIMS suffers from a large quantitative uncertainty and depth-scale uncertainty at the interfaces of heteromultilayers and in the near-surface region, because the secondary ion yield and sputtering yield are significantly influenced by matrix effects and accumulation effects of the primary ion. In this paper, the authors report on the development of a new depth profiling method with good depth-scale accuracy and low matrix effects to overcome these problems. This was achieved through the combination of high-spatial-resolution bevel depth profiling and sputtered neutral mass spectrometry with laser postionization (laser-SNMS). The sample used to evaluate this new bevel depth profiling method was a silicon on insulator wafer obtained using the separation by implantation of oxygen technique and implanted with boron. Depth profiles were obtained using both SIMS and laser-SN...