Longfei Gong

Influence of germanium doping on the mechanical strength of Czochralski silicon wafers

The mechanical strength in germanium-doped Czochralski silicon (GCz-Si) wafers has been investigated through the on-line warpage statistics analysis, indentation tests, and fracture structure measurements. It was found that the wafer warpage during manufacturing processes could be statistically suppressed by the germanium doping slightly. The enhancement effect of germanium doping on the mechanical strength in GCz-Si wafers could be shown obviously when the germanium concentration was higher than 1018cm−3. Meanwhile, the fracture strength for both the as-grown and the postannealed GCz-Si wafers might be greater compared to that of the conventional Czochralski (Cz-Si) wafers. Moreover, the generation and mobilization of the dislocations induced by indentation in Cz-Si wafers could be suppressed by the germanium doping. These phenomena are interpreted through a dislocation pinning-up effect associated with the smaller-sized higher-density oxygen precipitates formed in GCz-Si wafers.

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...

Microstructure and crystal defects in ZnMgO pleated nanosheets

Dislocations in the ZnMgO pleated nanosheets were observed from high-resolution transmission electron microscopy (TEM). The Burgers vector was identified as 1/3⟨112¯3⟩ from the Fourier filtered TEM images. Raman spectra revealed that there were microstructure defects in the ZnMgO nanosheets with the increasing Mg content. The incorporation of the Mg impurities in the ZnMgO nanosheets may promote the congregation of oxygen vacancies and thus facilitate the generation of dislocations. The oxygen deficiency as well as surface dislocations played an important role in determining the optical properties of ZnMgO pleated nanosheets.

Formation of a denuded zone in nitrogen-doped Czochralski silicon wafer treated by ramping anneals

The formation of a denuded zone (DZ) and the bulk-microdefects (BMDs) region within conventional and nitrogen-doped Czochralski (NCZ) silicon subjected to ramping anneals has been investigated. It was found that the terminal temperature of the ramping anneal should be high enough to create a DZ while the starting temperature should be low enough to generate desirable high density of BMDs. Comparatively speaking, with the same heat treatment, the NCZ silicon possesses higher density of BMDs and a narrower DZ than CZ silicon. Moreover, for NCZ silicon, the ramping anneal can initiate at relatively higher temperature to generate an appropriately high density of BMDs. Of importance is that the ramping anneal with a final isothermal anneal at an elevated temperature such as 1150 °C can effectively create a substantial DZ, where there were no defects generated in the subsequent heat treatment significantly enabling oxygen precipitation.

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 ...

Transparent conductive and near-infrared reflective Ga-doped ZnO/Cu bilayer films grown at room temperature

Bilayer films consisting of Ga-doped ZnO (GZO) and Cu layers were grown at room temperature by magnetron sputtering. The structural, electrical, and optical properties of GZO/Cu bilayer films were investigated in detail. The crystallinity and transparent-conductive properties of the films were correlated with the Cu layer thickness. The GZO/Cu bilayer film with the Cu layer thickness of 7.8 nm exhibited a low resistivity of 7.6×10−5 Ω cm and an average visible transmittance of 74%. The reflectance was up to 65% in the near-infrared region for this film. The transparent conductive and near-infrared reflective GZO/Cu bilayer films could be readily deposited at room temperature. The GZO/Cu bilayer films were thermally stable when annealed at temperatures as high as 500 °C.

Oxygen precipitation in heavily phosphorus-doped Czochralski silicon: effect of nitrogen codoping

Oxygen precipitation (OP) in the conventional and nitrogen-codoped heavily phosphorous (P)-doped Czochralski silicon (CZ-Si) wafers subjected to various low- (650–850 °C) and high-temperature (1050 °C) two-step annealing conditions have been comparatively investigated. It was found that the nucleation annealing at 650 °C led to remarkable OP and the resulting bulk micro defect densities were nearly the same in both kinds of silicon wafers. While in the case with the nucleation annealing at 750 or 850 °C, the conventional heavily P-doped CZ-Si featured slight OP, in contrast to the nitrogen-codoped counterpart that put up considerably intense OP. The heavily P doping is believed to exert a significant enhancement effect on oxygen precipitate nucleation at 650 °C but not at 750 and 850 °C, while the nitrogen codoping offers heterogeneous centers for oxygen precipitate nucleation at 750 or 850 °C. It is reasonably believed that nitrogen codoping is also an effective pathway to enhance oxygen precipitation in heavily P-doped CZ-Si.

On the Impact of Heavy Doping on Grown-In Defects in Czochralski-Grown Silicon

The effects of heavy doping of Si on grown-in void size-density distributions and on Flow Pattern Defect (FPD) and Secco Etch Pit Defect (SEPD) density are discussed. Grown-in defects are studied using Scanning Infra Red Microscopy (SIRM) and Secco etching. Doping with 10(20) Ge atoms cm(-3) has a limited effect on the grown-in void size-density distribution but has a clear effect on the FPD density. The observed lower FPD density is most probably related to a decrease of the multiple void density. Co-doping with 10(20) B atoms cm(-3) leads to strong a suppression of the void density by nearly two orders of magnitude in agreement with the reported strong reduction of Crystal Originated Particle (COP) density in low resistivity p-type Si.