Papers by Author: Koji Sueoka

Abstract: Metallic contamination on silicon surfaces has a detrimental impact on the performance and yield of ULSI devices. Surface metal impurities degrade the gate oxide integrity while metal impurities dissolved in silicon cause recombination centers and this results in junction leakage. The diffusion behavior of these metal impurities in silicon is well-known [1]. On the other hand, these metal impurities often penetrate the silicon through the silicon oxide or silicon nitride films in ULSI processing. The surface metal impurities penetrate the silicon by colliding with the dopant during ion implantation and are also diffused in silicon by subsequent annealing [2]. While the diffusion behavior of the metal impurities penetrating silicon substrates through the silicon oxide films has been reported [3], little work has been reported on the diffusion behavior of the metal impurities penetrating silicon nitride films. We demonstrated the diffusion behavior of the metal impurities penetrating silicon substrates through a CVD SiN film due to the collision with dopant during ion implantation.

Abstract: Ge (100) thin film on Si (100) substrate is one of the new material technologies in the post scaling. In this study, we analyzed the stability of metal impurities of 4th row element around the interface of Ge (100) / Si (100) structure by using first-principles calculation. Considering the actual structure of the Ge thin film on Si (100) substrate, six calculation models were prepared. The calculated results showed that (1) Sc and Zn atoms are most stable at Ge surface, (2) Ti - Cr atoms are most stable in tensile plane-strained Si layer, (3) Mn - Cu atoms are most stable in compressive plane-strained Ge layer. These results indicate that the metal impurities concentrate on the strained region around the interface and/or Ge surface.

Abstract: We have investigated the gettering efficiency at the interface of Si (110) and Si (100) directly bonded (DSB) substrates. DSB substrates were prepared by conventional bonding and grinding back methods. DSB substrates were intentionally contaminated with 3d transition metals (Fe, Ni, Cu) and then annealed at 1000 oC. The dependence of metal concentrations on the depth was evaluated by a secondary ionization mass spectrometer (SIMS). Furthermore, we observed the interface of DSB by transmission electron microscope (TEM), and characterized the form of the gettered metals.

Abstract: Hybrid crystal orientation technology (HOT) substrates comprised of Si (100) and (110) surface orientation paralleling each <110> direction attract considerable attentions as one of the promising technology for high performance bulk CMOS technology. Although HOT substrates are fabricated by wafer bonding of Si (110) and Si (100) surfaces, it is not clear the atomic configuration of interfacial structure. Furthermore, the possibility for the interface to be an effective gettering source of impurity metals was not well studied. In this paper, we studied the interfacial structure and gettering efficiency of the atomic bonded interface by molecular simulations. The results indicate that the simulated atomic configuration and gettering efficiency of the bonded interface agreed well with the experimental results.

Abstract: Density functional theory (DFT) with local density approximation has been used to calculate the formation energy (EF) of the neutral vacancy in germanium single crystal. It was shown that careful checking of convergence with respect to the number of k-points is necessary when calculating the formation energy of the intrinsic point defects in Ge. The formation energy of the single neutral vacancy was estimated at 2.35 eV which is in excellent agreement with published experimental data.

Abstract: Theoretical consideration for technologically important phenomena in defect engineering of Czochralski silicon was performed with first principles calculation. (i) Point defect behaviour during crystal growth, (ii) enhanced oxygen precipitation in p/p+ epitaxial wafers, and (iii) Cu gettering by impurities are main topics in this work. Following results are obtained. (i) Interstitial Si I is dominant in p type Si while vacancy V is dominant in n type Si during crystal growth when dopant concentration is higher than about 1x1019atoms/cm3. (ii) In initial stage of oxygen precipitation including a few interstitial oxygen (O) atoms, BOn complex is more stable than On complex. The diffusion barrier of O atom in p+ Si is reduced to about 2.2eV compared with the barrier of about 2.5eV in intrinsic Si. (iii) In substitutional B, Sb, As, P and C atoms, only B atom can be an effective gettering center for Cu.