Toshiki Mori

Hydrogen-terminated defects in ion-implanted silicon probed by monoenergetic positron beams

Hydrogen-terminated vacancies in Si+-implanted Si were studied by means of positron annihilation. After the Si+-ion implantation, hydrogen atoms were introduced into the damaged region using a hydrogen plasma [hydrogen-atom treatment (HAT)]. Monoenergetic positron beams were used to measure Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons. It was found that the line shape parameter, S, corresponding to the annihilation of positrons trapped by vacancy-type defects, decreased after HAT. This was attributed to the trapping of positrons by H-decorated vacancy-type defects. Isochronal annealing experiments revealed a strong correlation between positron annihilation parameters and Raman intensities of Si–H, suggesting that hydrogen atoms are released from vacancy-type defects after annealing at 600 °C.

Three Different Forms of Hydrogen Molecules in Silicon.

We have studied three different H2 molecules in crystalline silicon using Raman scattering. The vibrational line at 3601 cm-1 attributable to H2 in Td site is observed both in n-type and p-type crystalline silicon. It is suggested from the hydrogenation-temperature dependence that the charge states and the sites of atomic hydrogen affects the formation of this type of H2. H2 in platelet observed at 4158 cm-1 decreased in its intensity in Si+-implanted silicon. A new vibrational line is detected at 3822 cm-1, and attributed to H2 trapped by hydrogen-related defects such as multivacancies produced by ion implantation.

Formation Mechanism of Interstitial Hydrogen Molecules in Crystalline Silicon

The formation mechanism of interstitial H2 in crystalline silicon was investigated by varying the dopant concentration and hydrogenation temperature. At low temperatures such as 125°C, the Raman peak of the interstitial H2 is observed only in heavily doped n-type silicon, suggesting that the formation of H2 includes a metastable donor-hydrogen complex as the precursor and that H2 formation out of two isolated hydrogen atoms is hindered by the Coulombic repulsion between two equally charged atoms at this temperature. At moderate temperatures such as 235°C, the interstitial H2 is formed also for intrinsic and p-type silicon. The absence of the dopant-concentration dependence in p-type silicon indicates that the H2 is created from two hydrogen atoms, at least one of which is neutralized by capturing a thermally excited electron. The formation of the interstitial H2 competes with that of extended planar defects (platelets) at high temperatures such as 305°C.

Large desorption yield of hydrogen atoms from silicon surface in homogeneous electron injection

The hydrogen desorption yield from a silicon surface in homogeneous electron injection was estimated. To enable homogeneous electron injection into a silicon surface, we used electrons produced in low-pressure argon plasma. The desorption yield we estimated was significantly large compared with that reported previously for electron injection from a sharp tip of a scanning tunneling microscope. The amount of hydrogen desorbed under normal operating conditions for the transistor is close to that for the hole current flowing across an oxide, meaning that desorption could potentially have a large influence on degradation. A positive current-density dependence of the yield was also observed.