Solid State Phenomena Vols. 178-179

Abstract: Interaction between hydrogen (H) and irradiation induced defects in p-type silicon (Si) have been studied in H implanted pn-junctions, using deep level transient spectroscopy (DLTS), as well as minority carrier transient spectroscopy (MCTS). Two H related levels at E_v+0.27 eV and E_c-0.32 eV have been observed (E_v and E_c denote the valence and conduction band edge, respectively). Both levels form after a 10 min anneal at 125 C, concurrent with the release of H from the boron-hydrogen (B-H) complex. The correlated formation rates and absolute concentrations of the two levels support the notion that they are due to the same defect. In addition, a level at E_c-0.45 eV is observed and discussed in terms of vacancy-hydrogen related defects.

Abstract: Oxygen precipitation (OP) and annihilation of voids in heavily phosphorus (P)-doped Czochralski (Cz) silicon have been investigated. It was found that the nucleation anneal at 650°C resulted in much more pronounced OP in the subsequent high temperature anneal than that at 800 or 900 °C. This was due to that SiP precipitates could be formed in heavily P-doped Cz silicon by the 650oC anneal and they acted as the heterogeneous nuclei for OP in the following anneal at high temperatures. The rapid thermal anneal (RTA) at 1200°C was proved to be an effective means to annihilate voids. Moreover, it was found that the significant OP resulting from the two-step anneal of 650°C/8 h + 1000°C/16 h could also cause the substantial annihilation of voids in heavily P-doped Cz silicon. The mechanisms for the annihilation of voids have been tentatively discussed.

Abstract: Transient and quasi-steady-state photoconductance methods were used to measure minority carrier lifetime in p-type Czochralski silicon processed in very clean conditions to contain oxide precipitates. Precipitation treatments were varied to produce a matrix of samples, which were then characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. The lifetime component associated with the precipitates was isolated by preventing or factoring out the effects of other known recombination mechanisms. The lifetime component due to unstrained precipitates could be extremely high (up to ~4.5ms). Recombination at unstrained precipitates was found to be weak, with a capture coefficient of ~8 x 10^-8cm³s^-1 at an injection level equal to half the doping level. Strained precipitates and defects associated with them (dislocations and stacking faults) act as much stronger recombination centres with a capture coefficient of ~3 x 10^-6cm³s^-1 at the same level of injection. The lifetime associated with strained precipitates increases with temperature with a ~0.18eV activation energy over the room temperature to 140°C range. The shape of the injection level dependence of lifetime was similar for all the specimens studied, with the magnitude of the lifetime being dependent on the precipitate density, strain state and temperature, but independent of precipitate size.

Abstract: The impact of slip dislocations on the interstitial iron distribution in as-grown CZ silicon wafers is investigated by calibrated MWPCD excess charge carrier lifetime measurements, DLTS measurements and measurements of the dislocation density. In regions of high dislocation density low interstitial iron content as well as low lifetime is observed. A linear correlation between dislocation density and interstitial iron content is found. We explain this linear correlation by the thesis that slip dislocations are 60° dislocations, which have adsorbed one iron atom at each dangling bond along the dislocation axis. Interstitial iron is gettered by slip dislocations but iron silicide, which forms along the dislocation axis, is a very strong recombination center for excess charge carriers as well. Hence, gettering of interstitial iron at slip dislocations does not increase the electrical quality of silicon.

Abstract: There are investigated the structural properties of ⁶⁴Zn⁺ ion-beam induced nano-size voids in as implanted and subsequent furnace annealing SiO^{Superscript text}2/Si(100) substrates. Then ⁶⁴Zn⁺ ions with energy of E=100keV were implanted into SiO₂ layer to a fluence of D=2×10¹⁴cm^-2. After this furnace thermal annealing at temperature 400°C during 1h in neutral (nitrogen) atmosthere was made. It is revealed, that in as-implanted sample the surface is non-uniform and there is some structurization of a SiO₂ layer. In this state, metal Zn NPs an order of ten nm in diameter are formed in the depth region around the projected range. There is thus a net flux of Zn out of the nanoparticles (NPs) into an oxide layer closer to the surface. As Zn has a big diffusion constant and a high vaper pressure there are occured out-diffusion of Zn from a SiO₂ surface layer. The volume occupied by the Zn NPs becomes a void. It results to formation of cavities, which combining among themselves, form voids.

Abstract: Effects of a kHz-frequency ultrasonic cleaning of silicon wafers on free carrier lifetimes and the photovoltage magnitude are addressed. It is found that the initial photovoltage decay, taken before ultrasonic treatments, can be fitted to a double-exponent form, exhibiting the involvement of shorter- and longer time recombination and trapping centers. The decay speeds up remarkably due to the treatment, and the rapid component of the decay grows at the expense of the slow component. It is also found that, before the treatment, the decay time is markedly non-uniform over the wafer surface, implying the existence of distributed sites affecting carrier lifetimes. The cleaning causes an overall smoothening of the lifetime distribution, which is accompanied by the above shortening. A likely explanation of the effects is based on two facts: (i) the cavitating bubbles are capable of locally removing the surface oxide layer affecting the dangling bonds on the bare Si surface, and (ii) the oxygen and hydrogen, decomposed in water at elevated pressures and temperatures occurring inside a cavitating bubble, can micro-precipitate the Si wafer thus affecting the recombination rate.

Abstract: It is shown that the X-ray beam induced current method (XBIC) can be realized at the laboratory X-ray source using the polycapillary x-ray optics. The images of iron contaminated grain boundaries in multicrystalline Si are obtained. It is shown that the grain boundary XBIC contrast is 2-3 times smaller than the EBIC one. A simulation of XBIC and EBIC contrast values for two-dimensional defects is carried out and a good correlation between the experimental and calculated values is obtained. The dependence of grain boundary XBIC contrast on the X-ray beam width is calculated.

Abstract: The dislocation-related luminescence (DRL) in the vicinity of D1 band (0.8 eV) in hydrophilically bonded n- and p-type silicon wafers is investigated by means of recently developed pulsed trap refilling enhanced luminescence technique (Pulsed-TREL). The shallow and deep dislocation related electronic states in both upper and lower part of the band gap are determined and characterized by means of DLTS. Among those traps we have established ones which directly participate in D1 DRL. We have shown that D1 luminescence goes via shallow dislocation related states (SDRS) located close to the conduction and valence bands with thermal activation energy of about 0.1 eV whereas deep levels do not participate in D1 DRL. The model explaining the fact how the 0.8 eV luminescence may go through levels which interlevel energy is at least 0.97 eV in terms of Coulomb interaction between ionized SDRS is suggested.

Abstract: Methods for the analysis of the oxide-silicon interface were compared for their ability to reveal metal segregation at the interface and organic contamination. The impact of these contaminations on surface recombination velocity measurements, on capacitance vs. voltage, conductance vs. voltage and capacitance vs. time measurements and on MOS-DLTS spectra was studied. Niobium-contaminated wafers were used as an example of metal surface segregation, because it was previously shown that niobium is prone to surface segregation. Interface state density measurements obtained by the conductance method showed a limited impact of niobium implantation. Vice versa significant effects were found in MOS-DLTS spectra. For what concerns organic contamination, MOS-DLTS showed the most significant effects from the point-of-view of the intrinsic properties of the silicon oxide - silicon interface, and GOI tests demonstrate a clear impact of the organic contamination on MOS capacitors oxide breakdown events.

Abstract: Oxygen precipitation (OP) behaviors were investigated for Czochralski (Cz) silicon wafers, which were coated with silicon nitride (SiNx) films or not, subjected to two-step anneal of 800C/4 h+1000°C/16 h following rapid thermal processing (RTP) at different temperatures ranging from 1150 to 1250C for 50 s. It was found that OP in the Cz silicon wafers coated with SiNx films was stronger in each case. This was because that nitrogen atoms diffused into bulk of Cz silicon wafer from the surface coated SiNx film during the high temperature RTP. Furthermore, it was proved that the RTP lamp irradiation facilitated the in-diffusion of nitrogen atoms, which was most likely due to that the ultraviolet light enhanced the breakage of silicon-nitrogen bonds.