Jiahe Chen

Enhancement effect of germanium on oxygen precipitation in Czochralski silicon

Oxygen precipitation in germanium (Ge)-doped Czochralski (CZ) silicon has been investigated through a series of isothermal anneals at temperatures ranging from 550to950°C. It is found that the nucleation of oxygen precipitates can be enhanced in a wide temperature range and the onset temperature for precipitate nucleation can be increased by the germanium doping. Furthermore, it is also revealed that the oxygen precipitates with a higher density and smaller sizes can be formed in germanium-doped CZ silicon in comparison with those in conventional CZ silicon. These two phenomena are ascribed to the reduction in the critical radius for oxygen precipitation and the increase in the concentration of heterogeneous nuclei due to the germanium doping.

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.

On the assumed impact of germanium doping on void formation in Czochralski-grown silicon

The assumed impact of Ge doping on void formation during Czochralski-growth of silicon single crystals, is studied using scanning infrared microscopy. It has been reported that Ge doping leads to a reduction in the flow pattern defect density and of the crystal originated particle size, both suggesting an effect of Ge on vacancy concentration and void formation during crystal growth. The present study however reveals only a marginal-if any-effect of Ge doping on grown-in single void size and density. Double and multiple void formation might however be suppressed partially by Ge doping leading to the observed decrease in flow pattern defect density. The limited effect of Ge doping on single void formation is in agreement with earlier findings that Ge atoms are only a weak trap for vacancies at higher temperatures and therefor should have a smaller impact on the vacancy thermal equilibrium concentration and on single void nucleation than, e.g., interstitial oxygen and nitrogen.

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.

Intrinsic gettering Based on rapid thermal annealing in germanium-doped Czochralski silicon

The intrinsic gettering (IG) effects under different thermal processes involved with rapid thermal annealing (RTA) in Czochralski (CZ) silicon wafers with germanium doping have been investigated. It has been shown that both good quality denuded zones and high-density bulk microdefect regions could be generated in germanium-doped CZ (GCZ) silicon wafers through thermal cycles of RTA treatments plus either low-high temperature two-step annealing or high temperature single-step annealing. Moreover, more oxygen precipitation was formed in GCZ silicon wafers in comparison with conventional CZ silicon wafers, indicating the enhancement of IG capability for CZ silicon wafers by the germanium doping. The phenomena have been considered to be ascribed to the increase of vacancy concentration associated with the presence of germanium, which results in the generation of Ge-V-related complexes in GCZ silicon wafers during RTA treatments.

Ge-vacancy pair in Ge-doped Czochralski silicon

The potential configurations of Ge-vacancy pairs in a Ge-doped Czochralski Si (GCz-Si) crystal have been identified through first-principles theory using a total-energy pseudopotential method. The Ge atoms in the GCz-Si lattice are suggested to aggregate with the vacancy/vacancies to generate the Ge-related complexes. The total energy of the GCz-Si lattice configuration containing multivacancies decreases with the reduction of bond lengths among the vacancies and decreases with the reduction of bond lengths between the Ge atom and the vacancies. It is suggested that the Ge atom introduced in the GCz-Si crystal tends to accumulate with the vacancy and then seeds for the Ge-vacancy pairs.

Enhanced oxygen out-diffusion in silicon crystal doped with germanium

Out-diffusion of oxygen during high temperature annealing has been investigated in Czochralski silicon with germanium doping through the spreading resistance profile and secondary ion mass spectrometry techniques. It has been suggested that oxygen out-diffusion in silicon could be enhanced by germanium doping when annealed at 1050 °C−1200 °C. Such enhancement effect increases with the annealing temperature applied to materials as well as increases with the germanium concentration introduced in silicon. It is proposed that the enhanced oxygen out-diffusion may be due to the fast diffusion channel for the interstitial oxygen atoms, which is induced by the substituted germanium atoms in silicon.

Impact of firing on surface passivation of p-Si by SiO2/Al and SiO2/SiNx/Al stacks

Firing impacts on surface passivation provided by a SiO2 and SiO2/SiNx stack with evaporated Al films are studied by capacitance-based techniques on MIS capacitors. For devices with insulator layers consisting solely of as-deposited SiO2, the densities of either interface states (Dit) or fixed charges (Qfc) are hardly influenced by firing. Capping the SiO2 layer with a SiNx layer results in a shift of the peak activation energy of Dit toward the valence band (Ev) of Si. Firing this SiO2/SiNx stack leads to an increase of Qfc, a reduction of Dit, and a moderate shift of peak activation energy of Dit toward Ev. Co-firing with the Al film on top significantly reduces the Qfc, Dit, and Dit peak activation energy, which is resulting from the atomic hydrogen passivation. These results are of particular interest for the development of solar cells with rear surface passivation and local contacts.

Effects of heavy phosphorus-doping on mechanical properties of Czochralski silicon

The mechanical properties including hardness, Young’s modulus, and fracture toughness of heavily phosphorus (P)-doped Czochralski (Cz) silicon have been investigated by means of nanoindentation and microindentation. In view of the results of nanoindentation characterization, it is derived that the hardness of heavily P-doped Cz silicon is essentially the same as that of lightly P-doped Cz silicon. While, the Young’s modulus of Cz silicon is to a certain extent decreased by the heavy P-doping. With the same microindentation load, the lengths of the radial and lateral cracks in the heavily P-doped silicon are shorter than those in the lightly P-doped silicon, indicating that the heavily P-doped Cz silicon possesses a higher indentation fracture toughness.

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 ...