Phosphorus-doped Czochralski Silicon Research Articles

Defect behavior during growth of heavily phosphorus-doped Czochralski silicon crystals. I. Experimental study

Defect behavior during growth of heavily phosphorus-doped Czochralski silicon crystals. I. Experimental study

Comprehensive understanding on phosphorus precipitation in heavily phosphorus-doped Czochralski silicon

Heavily phosphorus-doped Czochralski (HP-CZ) silicon is an important substrate material for manufacturing power electronic devices. The high concentration of phosphorus impurities may be supersaturated during the crystal growth of HP-CZ silicon or device manufacturing. Thus, understanding phosphorus precipitation in HP-CZ silicon is of technological significance. Herein, a panoramic view of phosphorus precipitation in HP-CZ silicon is presented in terms of crystallography, thermodynamics, and kinetics. It is found that the orthorhombic SiP precipitates can form during the crystal growth of HP-CZ silicon and also during the post-anneals of HP-CZ silicon at 450–1050 °C. Along with increasing annealing temperature, the formed SiP precipitates tend to adopt the platelet, polyhedron, and sphere-like shapes. Moreover, the excess point defects, i.e., silicon self-interstitials and vacancies, are found to affect phosphorus precipitation occurring in the low and high temperature regimes in different ways. In light of the kinetics of phosphorus precipitation at different temperatures, it is deduced that phosphorus precipitation follows a growth law in compliant with Ham's theory to a large extent. As an important output of this work, the temperature-dependent phosphorus solubilities in the dislocation-free silicon, which have been hardly acquired previously, are derived on the basis of investigating phosphorus precipitation in a set of HP-CZ silicon wafers with different phosphorus concentrations. Moreover, the derived solvus line for the phosphorus impurities in silicon could be a beneficial supplement to the existing phase diagram of the Si–P binary system in the extremely silicon-rich corner.

Retarded oxygen diffusion in heavily phosphorus-doped Czochralski silicon: experiments and first-principles calculations

The effect of heavy phosphorus (P) doping on oxygen diffusion in Czochralski (Cz) silicon has been experimentally and theoretically investigated. It is experimentally found that the oxygen diffusion in heavily P-doped Cz silicon is retarded, with a diffusion activation energy which is ∼0.12 eV larger than that of its lightly P-doped counterpart. First-principles calculations suggest that the P–O complexes in the –P–Si–O–Si– configuration can form in heavily P-doped Cz silicon, leading to the trapping of interstitial oxygen (Oi) atoms at the twelve equivalent second-nearest neighbors of the P atoms. Furthermore, the calculated increase of the oxygen diffusion activation energy, taking account of the trapping effect of such P–O complexes, is in accordance with the experimental result. This indicates that the retarded oxygen diffusion in the heavily P-doped Cz silicon can be ascribed to the trapping of Oi atoms associated with the formation of the aforementioned P–O complexes.

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 significant silicon phosphide (SiP) precipitation in heavily P-doped CZ Si. Summarily, enhancement of grown-in oxygen precipitates was attributed to SiP precipitation and high-concentration vacancy, tentatively. Nonetheless, further investigation on the essential of grown-in precipitates in heavily P-doped CZ Si is worthy.

Denuded Zone Formation in Germanium Codoped Heavily Phosphorus-Doped Czochralski Silicon

The formation of a denuded zone (DZ) by conventional furnace annealing (CFA) and rapid thermal annealing (RTA) based denudation processing is investigated and the gettering of copper (Cu) atoms in germanium co-doped heavily phosphorus-doped Czochralski (GHPCZ) silicon wafers is evaluated. It is suggested that both a good quality defect-free DZ with a suitable width in the sub-surface area and a high density bulk micro-defect (BMD) region could be formed in heavily phosphorus-doped Czochralski (HPCZ) silicon and GHPCZ silicon wafers. This is ascribed to the formation of phosphorus-vacancy (P-V) related complexes and germanium-vacancy (GeV) related complexes. Compared with HPCZ silicon, the DZ width is wider in the GHPCZ silicon sample with CFA-based denudation processing but narrower in the one with two-step RTA pretreatments. These phenomena are ascribed to the enhancing effect of germanium on oxygen out-diffusion movement and oxygen precipitate nucleation, respectively. Furthermore, fairly clean DZs near the surface remain in both the HPCZ and GHPCZ silicon wafers after Cu in-diffusion, except for the HPCZ silicon wafer which underwent denudation processing with a CFA pretreatment, suggesting that germanium doping could improve the gettering of Cu contamination.

Grown-in defects in heavily phosphorus-doped Czochralski silicon

Grown-in defects in heavily phosphorus-doped Czochralski silicon

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.

Grown-in defects in heavily phosphorus-doped Czochralski silicon

Grown-in defects in an apparently dislocation-free heavily phosphorus (P)-doped Czochralski silicon (CZ-Si) crystal ingot were investigated by preferential etching and transmission electron microscopy (TEM). It was found that large-sized grown-in oxygen precipitates and the extended defects were present in the tang-end of the ingot. It is believed that oxygen precipitation in the tang-end ingot is enhanced by carbon (C) and by vacancies. Moreover, it was considered that phosphorus atoms might preferentially segregate on oxygen precipitates and caused high strain in silicon crystal. It is suggested that the large-sized precipitate might punch out dislocation loops under exceed stress during crystal growth. Finally, a tentative explanation for generation of grown-in defects in heavily P-doped CZ-Si is presented.

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 temperature anneal. Of significance is that the oxygen precipitate nucleation mechanism operating at certain temperatures for heavily P-doped CZ-Si is found to be completely different from that of lightly P-doped CZ-Si. We believe that the present work provides a further insight into OP in CZ-Si.

Enhancement effect of nitrogen co-doping on oxygen precipitation in heavily phosphorus-doped Czochralski silicon during high-temperature annealing

Oxygen precipitation in conventional and nitrogen co-doped heavily phosphorus (P)-doped Czochralski silicon (CZ-Si) crystal subjected to various high-temperature annealing in the range of 1000–1150°C was comparatively investigated. It was revealed that oxygen precipitates hardly generated in conventional heavily P-doped CZ-Si; while they remarkably generated in the nitrogen co-doped one. Moreover, nitrogen doping could enhance oxygen precipitation during the prolonged annealing with a rapid thermal process (RTP) pre-treatment, but it has neglectable influence on oxygen precipitation for short-time annealing. It was believed that nitrogen co-doped heavily P-doped CZ-Si possesses nitrogen-related complexes that act as heterogeneous nuclei for super-saturated interstitial oxygen and then enhanced oxygen precipitation. Finally, it was found that nitrogen doping could hardly enhance oxygen precipitation in heavily P-doped CZ-Si at 1200°C.

Generation of several kinds of oxygen-related thermal donors around 520 °C in Czochralski silicon

We have found that at least four kinds of oxygen-related thermal donors are distinguishable by their deep-level transient spectroscopy peaks and generation kinetics around 520 °C for 10–106 min in phosphorus-doped Czochralski silicon. Each kind of thermal donors successively appeared with its preceding kind decaying. The first appearing kind is identified as a family of thermal donors that have been most studied by many investigators. It is suggested that several kinds of thermal donors arise from various oxygen clusters with different sizes and thermal stabilities.

Trap spectrum of the ?new oxygen donor? in silicon

Electronic properties of thenew oxygen donor generated in phosphorus-doped Czochralski-silicon at 650‡C are investigated by deep level transient spectroscopy. A continuous distribution of trap states (1014–1016 cm−3 eV−1) is detected in the upper half of the band gap with increasing values towards the conduction band. The magnitude of the state density observed increases with the oxygen content, the heat duration, and a preanneal at temperatures lower than 650‡C. The continuous trap spectrum of thenew donor is explained by interface states occuring at the surface of SiOx precipitates.