Search

This paper describes the growth mechanism of silicon whisker on a silicon substrate using hot filament CVD reactor. Only hydrogen is used as source gas. The particle layer could be obtained at high filament current condition under hydrogen ambient. XPS analysis result suggests that the particle is composed of tungsten silicide. The deposition condition of the particle layer is much depended on the substrate size, surface condition and the distance between the substrate and the filament. The experimental results suggest that the silicon hydride, which generated at the silicon surface by hydrogen radical etching, react with the tungsten filament material around the filament, depositing on the silicon substrate. The silicon surface is etched by hydrogen radical and its resultant surface morphology is much depended on the particle deposition pattern. Many silicon whiskers, which diameter is varied from 10 to 50 nm, are observed on the textured silicon surface when the residence time of the source gas in the reactor is long. Each whisker has a silicon particle on their tip. The silicon hydride generated by the hydrogen radical etching is much absorbed to the silicide particle when the source gas residence time is long, enabling the silicon whisker growth from the particle. The results suggest that nm size whisker structure is much stable compare to the bulk silicon against etching reaction.

Hydrogen plasma treatments applied on standard Czochralski silicon (Cz Si) wafers cause a structuring of the surface regions on the sub-100 nm scale, i.e. a thin ‘nano-structured’ Si layer is created up to a depth of ∼ 150 nm. The formation of the ‘nano-structures’ and their evolution in dependence on the process conditions was studied. The impact of post-hydrogenation annealing on the morphology of the structural defects was studied up to 1200 °C. The H-plasma treated and annealed samples were analyzed at surface and sub-surface regions by scanning electron microscopy (SEM), atomic force microscopy (AFM), and μ-Raman spectroscopy.

Standard p- and n-type Czochralski (Cz) silicon wafers were hydrogenated by a RF (13.56 MHz) hydrogen plasma at moderate temperatures (250 °C). After plasma hydrogenation and subsequent annealing up to 600 °C the formation and of H2 molecules in voids and platelets was investigated by Raman spectroscopy. The Raman intensities of the H2 vibration modes at ∼ 4150 cm-1 exhibited significant intensity modulations in dependence on the annealing temperature. The intensities of the H2 Raman lines indirectly monitor the evolution of the voids and platelets upon annealing. This assumption was verified by cross-sectional transmission electron microscopy (XTEM), which was applied for comparison. The intensity modulations of the H2 Raman signal can be explained by the evolution of the well known {111} and {001} platelets. At lower annealing temperatures (< 500 °C) platelets laying in {111} planes are dominant, while at elevated temperatures (> 500 °C) [001]-oriented platelets become more and more important. In addition in p-type material by XTEM also {110} platelets could be observed.

Thermal donor formation was studied in oxygen enriched high resistive float zone silicon (FZ Si:Oi). Such substrates are used e.g. for radiation hard detectors or high voltage devices. RF Plasma hydrogenation (110 MHz, 50 W) was carried out at 250°C for 1 hour. Subsequent annealing was done at 450°C/air for up to 50 h. The plasma treated and annealed FZ Si:Oi samples were analyzed by spreading resistance probe, capacitance-voltage and DLTS measurements. It is shown that a rapid formation of donors can be observed in oxidized FZ Si:Oi, but in a somewhat different way than in Czochralski (Cz) Si. While in Cz Si the hydrogen enhanced formation of ‘old’ thermal double donors occurs under the applied processes, in FZ Si:Oi most probably the formation of new hydrogen related shallow donors can be assumed.

P-type Czochralski (Cz) Si was implanted with H (180 keV, 2.7.1016 cm−2) or He (300 keV, 1.1016 cm−2) ions. The gettering of O and H atoms by the buried implantation damage layers during annealing up to 4 hours (1000°C in H2 or N2 ambient) was studied by secondary ion mass spectroscopy (SIMS) and spreading resistance probe (SRP) measurements. Buried defect layers act as good getter centers for O and H atoms at appropriate heat treatments. The enhanced gettering of O atoms in H implanted Cz Si (as compared to the gettering of O in He implanted samples) as well as the enhanced gettering of O during annealing in H2 flow (as compared to N2 ambient) can be explained by a hydrogen enhanced O diffusion towards the defect layers. According to a strong accumulation of O at the buried damage layers and near the surface some anomalies of the SRP profiles can be observed after post-implantation annealing.

The incorporation of hydrogen into standard p-type Czochralski (Cz) silicon (≥1 Ωcm) by a 110 MHz plasma treatment at 260°C leads to the formation of an n-type region due to hydrogen enhanced thermal donor (TD) formation in hydrogenated regions of the wafer, if a subsequent annealing in air is applied at 450°C. Spreading resistance probe (SRP) and light beam induced current (LBIC) measurements were used for the experimental analysis. The p-n junction depth, i. e. the counter doping by TDs, depends on the initial doping level of the p-type substrate, and therefore on the post-hydrogenation annealing time. The penetration of the n-type region into the wafer bulk is driven by a rapid hydrogen diffusion. The essential process for a TD generation is the creation of metastable hydrogen molecular species around 260°C and their decay at 450°C.

Our experiments show a hydrogen plasma assisted creation of p-n junctions in p-type Cz silicon due to a hydrogen enhanced thermal donor (TD) formation at temperatures ≤450 °C. Applying DC or HF plasma treatments a conversion of p-type into n-type Cz silicon by TD formation occurs. One can distinguish one step processes (p-n junction formation appears just after the plasma exposure) and two step processes (p-n junction formation requires subsequent post hydrogenation annealing). The samples are studied by depth resolved spreading resistance probe (SRP), capacitance-voltage (CV) and Hall measurements. For the one step processes a kinetic model for hydrogen enhanced TD formation is presented.