Weiyan Wang

Oxygen precipitation heterogeneously nucleating on silicon phosphide precipitates in heavily phosphorus-doped Czochralski silicon

Through comparison between the oxygen precipitation (OP) behaviors in heavily and lightly phosphorus (P)-doped Czochralski silicon (CZ-Si) crystals subjected to low-high two-step anneal of 600, 650, or 750 °C/8 h+1050 °C/16 h, we have found that in heavily P-doped CZ-Si, OP is much stronger in the case with the nucleation anneal at 600 or 650 °C while it is to some extent suppressed in the case with the nucleation anneal at 750 °C in contrast to lightly doped CZ-Si where nucleation is enhanced at 750 °C. Transmission electron microscopy investigation reveals that silicon phosphide precipitates of face-centered-cubic SiP form during the nucleation anneal at temperatures 650 °C and below. The SiP precipitates act as the heterogeneous nuclei for OP during the subsequent high temperature anneal while the oxygen precipitate nuclei containing certain amounts of P atoms generate during the nucleation anneal at 750 °C. They are further coarsened to be larger oxygen precipitates during the subsequent high temperat...

Investigation of intrinsic gettering for germanium doped Czochralski silicon wafer

The intrinsic gettering (IG) effects in a germanium-doped Czochralski (GCz) silicon wafer have been investigated through a processing simulation of dynamic random access memory making and an evaluation on IG capability for copper contamination. It has been suggested that both the good quality defect-free denuded zones (DZs) and the high-density bulk microdefect (BMD) regions could be generated in GCz silicon wafer during device fabrication. Meanwhile, it was also indicated that the tiny oxygen precipitates were hardly presented in DZs of silicon wafer with the germanium doping. Furthermore, it was found in GCz silicon wafer that the BMDs were higher in density but smaller in size in contrast to that in conventional Cz silicon wafer. Promoted IG capability for metallic contamination was therefore induced in the germanium-doped Cz silicon wafer. A mechanism of the germanium doping on oxygen precipitation in Cz silicon was discussed, which was based on the hypothesis of germanium-related complexes.

Effect of silicon interstitials on Cu precipitation in n-type Czochralski silicon

The effect of silicon interstitials induced by the prior thermal oxidation at 900°C for 2–50min on copper (Cu) precipitation in n-type silicon has been investigated by means of transmission electron microscopy and optical microscopy. For the sample without the prior thermal oxidation, the Cu precipitates exhibited to be spherelike with induced stress, and they were preferentially delineated as the etching pits. On the other hand, for the samples with the prior thermal oxidation for more than 5min, the Cu precipitate colonies, in which Cu precipitates with sizes of 10–20nm assembled on and around the dislocations, formed with different depth profiles dependent on the oxidation time. Moreover, the Cu precipitate colonies were preferentially delineated as aggregated and individual rods. Phenomenologically, the formation mechanism and depth profile of Cu precipitate colonies were explained in terms of the effect of thermal oxidation induced silicon interstitials.

Grown-in precipitates in heavily phosphorus-doped Czochralski silicon

Through comparing the oxygen precipitation in the heavily and lightly phosphorus (P)-doped Czochralski silicon (CZ Si) specimens subjected to the simulated cooling processes of silicon ingot, we researched the influences of heavily P doping on grown-in precipitates by preferential etching and transmission electron microscopy (TEM). It was found that grown-in precipitates were more significant in heavily P-doped CZ Si than in lightly one. Most grown-in precipitates in heavily P-doped CZ Si were generated at (800–600) °C. The significant grown-in oxygen precipitates in the heavily P-doped CZ Si would change the density and morphology of oxygen precipitation. TEM examination revealed that the grown-in precipitates in heavily P-doped CZ Si were amorphous oxygen precipitates composed of tiny precipitates in essential. Although more or less phosphorus may be incorporated in the grown-in precipitates, however, phosphorus cannot be detected so far. We further confirmed that extending annealing at 550 °C produced ...

Effect of point defects on copper-related deep levels in p-type Czochralski silicon

The effect of point defects on the copper (Cu)-related deep levels in p-type Czochralski (Cz) silicon has been investigated. It was found that generally five deep levels Ev+0.14eV, Ev+0.17eV, Ev+0.32eV, Ev+0.35eV, and Ev+0.46eV were related to Cu in the p-type Cz silicon. Among them, the newly found levels Ev+0.35eV and Ev+0.32eV can be influenced by the point defects introduced during rapid thermal process. The intensity of level Ev+0.35eV increased with the introduced vacancies, while that of level Ev+0.32eV was dependent on the silicon interstitials. Moreover, the electronic states of those two levels were ascribed to be localized states. Based on the experimental facts, it is believed that the origins of levels Ev+0.35eV and Ev+0.32eV are the complex of Cu and vacancy and that of Cu and silicon interstitials, respectively.

Effect of annealing atmosphere on the recombination activity of copper precipitates formed by rapid thermal process in conventional and nitrogen-doped Czochralski silicon wafers

The effect of annealing atmosphere of Ar, N2, or O2 on the recombination activity of copper (Cu) precipitates, formed by the rapid thermal process (RTP), in conventional Czochralski (CZ) silicon and nitrogen-doped CZ (NCZ) silicon wafers have been investigated. It was revealed that the recombination activity of Cu precipitates formed under N2, Ar, and O2 atmospheres decreased in turn. Moreover, the RTP under O2 atmosphere led to a higher critical temperature for Cu precipitation in comparison with the RTP under Ar or N2 atmosphere. Furthermore, it was found that the Cu precipitates formed under the same conditions possessed stronger recombination activity in CZ silicon than in NCZ silicon. The above results have been tentatively explained.

Copper precipitation in nitrogen-doped Czochralski silicon

Copper (Cu) precipitation behaviors in p-type conventional Czochralski (CZ) and nitrogen-doped Czochralski (NCZ) silicon have been comparatively investigated by means of transmission electron microscopy and optical microscopy. Within the CZ silicon, the Cu precipitates exhibited as spheres with size of about 100 nm and generated stress in the matrix. In this case, they were preferentially delineated as etching pits. On the other hand, within the NCZ silicon, the Cu precipitates were revealed as colonies in which spherelike Cu precipitates with sizes of 10–30 nm assembled on and around the climbing dislocations. As a result, they were preferentially etched as aggregated rods. The formation of Cu precipitate colonies in NCZ silicon was explained in terms of the effect of large grown-in oxygen precipitates on Cu precipitation.

Effect of rapid thermal annealing condition on the structure and conductivity properties of polycrystalline silicon films on glass

The effect of rapid thermal annealing (RTA) temperature (700~1200 °C) and time (1~8 min) on the structure and conductivity properties of polycrystalline silicon (Si) films on glass, grown by RTA crystallization of magnetron sputtering (MS) deposited amorphous Si (a-Si) films, was investigated by means of X-ray diffraction (XRD) and UV reflectance. It was observed the critical temperature for crystallizing a-Si films was ~750 °C and ~700 °C based on XRD and reflectance measurements, respectively. As soon as RTA temperature reached and exceeded the critical value, the structural property of polycrystalline Si films increased with RTA temperature or time. The above results were related to the thermal and photon effects induced by RTA. Moreover, it was revealed that the resistivity of polycrystalline Si films decreased with RTA temperature, however, even the resistivity of the polycrystalline Si films annealed at 1200 °C was 2 orders of magnitude higher than that of Si target, attributed to the carrier scattering by grain boundaries or defects. The polycrystalline Si films on glass fabricated by MS deposition combined with RTA crystallization may endow them with great application potentials in Si thin-film solar cells.

Aluminum-Doped Zinc Oxide as Transparent Electrode Materials

Pristine and Al-doped zinc oxide nanopowders were synthesized via a surfactant-assisted complex sol-gel method, possessing a pure ZnO phase structure and controllable grain size which was characterized by X-ray diffraction and scanning electron microscopy. Using these nanopowders, the pristine and Al-doped ZnO magnetron sputtering targets were prepared following a mold-press, cold isostatical-press and schedule sintering temperature procedure. The relative density of these as-prepared targets was tested by Archimedes’ method on densitometer. All of the results were above 95 theory density percents, and the resistivity was tested on four-probe system at a magnitude of 10-2 Ω cm. Related pristine ZnO thin films and Al-doped ZnO thin films were fabricated by magnetron sputtering method, respectively. The pristine and Al-doped ZnO films deposited on the quartz glass by dc sputtering owned a (002) orientation with a thickness of 350 nm at a deposition power of 100 W for two hours under an argon plasma. A good optical transparency above 80% and low resistivity of 1.60×10-3 Ω cm were obtained with a deposition temperature of 573 K. The optical energy bandgap could be tailored by Al doping at 4 at.% Al.

Copper Precipitation in Germanium-Doped Czochralski Silicon

Copper (Cu) contamination, especially Cu precipitates in Czochralski (CZ) silicon is of great concern due to its detrimental effects on device reliability and yields. It has been reported that Cu precipitation behavior depends on multiple factors, including annealing conditions and existing defects in silicon. Recently, germanium-doped Czochralski (GCZ) silicon wafer has sparked intensive interests due to its desirable properties. It is well known that GCZ silicon possesses more grown-in oxygen precipitates, especially the ones with larger sizes, with respect to conventional CZ silicon. However, whether the Cu precipitation behaviors in CZ and GCZ silicon are different have hardly been concerned up to now.