Hydrogen-induced boron passivation in Cz Si

Acceptor deactivation in the near-surface region of as-grown, boron-doped Si wafers was detected by in-depth profiles of the free-carrier density obtained by capacitance–voltage measurements. As this deactivation was only observed in wafers subjected to the standard cleaning procedures used in Si manufacturing, we ascribed it to boron passivation by an impurity introduced during the cleaning process. From the study of the free-carrier reactivation kinetics and of the diffusion behaviour of boron–impurity complexes, we have concluded that the impurity is possibly related to hydrogen introduced during the cleaning treatments. The characteristics of the deep level associated with this impurity have been analysed by deep-level transient spectroscopy. Received: 22 August 2001 / Accepted: 27 October 2001 / Published online: 29 May 2002     

Au钝化Si(100)表面的电子特性

用TB-LMTO方法研究单层的Au原子在理想的Si(100)表面的化学吸附.计算了Au原子在不同位置的吸附能,吸附体系与清洁Si(100)表面的层投影态密度, 以及电子转移情况.结果表明, Au原子在吸附面上方的A位(顶位)吸附最稳定, Au钝化Si(100)表面可以取得明显的钝化效果, 这一结论与实验事实相符合.     

Depth profiling of melting and metallization in Si(111) and Si(001) surfaces

An original approach for measuring the depth profile of melting and metallization of the Si(111) and Si(001) surfaces is proposed and applied. The different probing depths of the Auger electron and electron energy loss (EELS) spectroscopies are exploited to study the number of molten and metallic layers within 5-30 ? from the surface up to about 1650 K. Melting is limited to 3 atomic layers in Si(001) in the range 1400-1650 K while the number of molten layers grows much faster (5 layers at about 1500 K) in Si(111) as also indicated by the L(3)-edge shift observed by EELS. The relationship between melting and metallization is briefly discussed.     

Energetics of atomic hydrogen diffusion on Si(100)

We present first principles calculations of the potential energy surface for the diffusion of a single hydrogen atom on Si(100)2 × 1. Surface relaxation is found to be very important for the energetics of diffusion. A strong anisotropy is predicted for hydrogen motion: H should diffuse mainly along dimer rows, where activation energies are ~ 1.3 eV, while the barrier for row-to-row hopping is ~ 0.5 eV higher. Our results indicate that diffusion can be considered a fast process compared to H₂ recombinative desorption.     

Characterization of Al/Si junctions on Si(100) wafers with chemical vapor deposition-based sulfur passivation

Chemical vapor deposition-based sulfur passivation using hydrogen sulfide is carried out on both n-type and p-type Si(100) wafers. Al contacts are fabricated on sulfur-passivated Si(100) wafers and the resultant Schottky barriers are characterized with current–voltage (I–V), capacitance–voltage (C–V) and activation-energy methods. Al/S-passivated n-type Si(100) junctions exhibit ohmic behavior with a barrier height of <0.078 eV by the I–V method and significantly lower than 0.08 eV by the activation-energy method. For Al/S-passivated p-type Si(100) junctions, the barrier height is ~0.77 eV by I–V and activation-energy methods and 1.14 eV by the C–V method. The discrepancy between C–V and other methods is explained by image force-induced barrier lowering and edge-leakage current. The I–V behavior of an Al/S-passivated p-type Si(100) junction remains largely unchanged after 300 °C annealing in air. It is also discovered that heating the S-passivated Si(100) wafer before Al deposition significantly improves the thermal stability of an Al/S-passivated n-type Si(100) junction to 500 °C.     

Interaction of atomic hydrogen with the Si(100)2×1 surface

The interaction of atomic hydrogen with the Si(100)2×1 surface has been investigated in detail by a field ion-scanning tunneling microscope (FI-STM). At low exposure, hydrogen atoms reside singly on top of the dimerised Si atoms, and are imaged brightly. The hydrogen chemisorption induces the buckling of dimers, indicating the strong bonding between Si and hydrogen atoms. The adsorption geometry changed from the (2×1) monohydride phase to the (1×1) dihydride phase with increasing exposure of hydrogen. The former is imaged dark compared with the unreacted Si dimers due to the reduction of the density of electronic states near the Fermi level. Surface etching was also observed during the formation of the dihydride phase. The behavior of hydrogen desorption from the H-saturated Si(100) surface was investigated as a function of annealing temperatures. Our STM results suggest that the desorbing H₂ molecules are formed by two hydrogen atoms on the same dihydride species.     

Photodesorption and photofragmentation of disilane adsorbed on a hydrogen terminated Si(100) surface

The photochemical mechanisms leading to the desorption and fragmentation of Si₂H₆ adsorbed on a hydrogen terminated Si(100) surface have been explored by recording the time-of-flight distributions of products escaping from the surface and by using electron energy loss spectroscopy to probe possible electronic excitations. Photodesorption of intact Si₂H₆ involves hot electrons that lose energy and move to the conduction band edge before initiating desorption. When the wavelength of the incident light is 193 nm, Si₂H₆ fragments give mostly Si, SiH₂, H₂ and SiH₄, but this pathway is quenched at longer wavelengths. This is consistent with direct excitation, but we also show that a negative ion resonance is accessible to substrate electrons that have been excited by 193 nm light.     

Coverage- and temperature-dependent vibrational spectra of hydrogen chemisorbed on Si(100)2 × 1

The adsorption of atomic hydrogen at Si(100)2 × 1 has been studied for coverages at and below one monolayer at temperatures between 300 and 1200 K using high-resolution Electron Energy Loss Spectroscopy (EELS) and Low Energy Electron Diffraction (LEED). Measurements of EELS frequencies, linewidths and intensities are discussed for different coverages and temperatures during exposure as well as subsequent annealing. Formation of a monohydride Si(100)2 × 1 : H adsorption phase is observed at room temperature in the sub-monolayer range, at 650 K for all coverages up to the saturation, and during thermal decomposition of the low temperature dihydride Si(100)1 × 1 : : 2H adsorption phase. The latter is formed by saturating Si(100) at 300 K with atomic hydrogen.