Conventional Czochralski Silicon Research Articles

Effect of nitrogen doping on denuded zone formed by rapid thermal process in Czochralski silicon wafer

Denuded zone (DZ) formed by rapid thermal process (RTP) followed with the low–high (Lo–Hi) annealing in nitrogen-doped Czochralski (NCZ) silicon wafer was studied in this paper. In comparison with the conventional CZ silicon, the DZ in NCZ silicon was a little narrower, while the bulk microdefects were much denser, as a result of nitrogen-enhanced oxygen precipitation. It was also found that DZs within CZ and NCZ silicon wafers shrunk notably when further subjected to rigorous oxygen precipitation annealing, however, a width of substantial DZ remained within either wafer. Furthermore, it is definitely proved that the nitrogen doping does not affect the formation of defect-free DZ by the RTP-based internal gettering (IG) process.

Rapid-thermal-processing-based intrinsic gettering for nitrogen-doped Czochralski silicon

In order to optimize the intrinsic gettering (IG) process based on the rapid thermal processing (RTP) for nitrogen-doped Czochralski (NCZ) silicon wafer, the effects of RTP and the following nucleation anneal on oxygen precipitation in NCZ silicon and conventional CZ silicon wafers have been comparatively investigated. It was found that, for NCZ silicon, the RTP at enough high temperature (e.g., 1250°C) was necessary for generation of high density of bulk microdefects (BMDs) in the subsequent anneals despite the nitrogen enhancement effect on oxygen precipitation. With enough high concentration of vacancies introduced by the RTP at 1250°C, for the conventional CZ silicon wafer, the vacancy enhancement effect on the nucleation of oxygen precipitates was most significant at 800°C; while for NCZ silicon wafer, the vacancies and nitrogen atoms coacted most remarkably to nucleate the oxygen precipitates during the ramping anneal from 800to1000°C. It was further found that the doped nitrogen is superior to the vacancy to enhance the nucleation of oxygen precipitates at temperatures of 900–1000°C. Moreover, in order to maximize the density of BMDs, the RTP-based IG process for NCZ silicon wafer should be different from that for the conventional CZ silicon wafer.

Extended defects in nitrogen-doped Czochralski silicon during diode process

The extended defects in nitrogen-doped Czochralski (NCZ) silicon and conventional Czochralski (CZ) silicon during the diode process were systematically investigated by means of optical microscopy and transmission electron microscopy. It was revealed that during the phosphorous diffusion (1230°C/2 h), the dislocations and stacking faults generated simultaneously in the NCZ silicon while in the CZ silicon only dislocations were observed. After the boron diffusion (1260°C/30 h), only dislocations as the extended defects were observed in both the NCZ and CZ silicon. It is preliminarily believed that the difference between the formation of extended defects in the NCZ and CZ silicon wafers is ascribed to the effect of nitrogen on oxygen precipitation.

Investigation of thermal donors in Czochralski silicon annealed at 450°C under high pressure of 1 GPa

Experiments were performed to investigate the thermal donors (TDs) generated in nitrogen-doped Czochralski (NCZ) silicon and conventional Czochralski (CZ) silicon when annealed under a high pressure (1 GPa). The specimens were first annealed at 450°C under atmospheric and high pressures, respectively, to generate thermal donors, then treated at 650°C to annihilate them. It is found that TDs’ generation rate and concentration are enhanced by the high pressure for both NCZ and CZ silicon, but can be effectively annihilated during annealing at 650°C for only 10 min. It is concluded that enhancement of the electron concentration was due to the increased diffusivity of oxygen under high pressure.

Behavior of oxidation-induced stacking faults in annealed Czochralski silicon doped by nitrogen

After oxidation at 1150 °C, oxidation-induced stacking faults (OSFs) in nitrogen-doped Czochralski crystal silicon (NCZ–Si) preannealed at 750 °C for 16 h followed by annealing at 1100 °C were investigated. It was observed that the size of OSFs in NCZ–Si samples was larger than one in the conventional Czochralski silicon (CZ–Si) samples. With the increase of the oxidation duration, the size of the OSFs in NCZ–Si decreased, while that of the OSFs in CZ–Si increased. It was also found that platelet oxygen precipitates and dislocations generated in NCZ–Si, while octahedral oxygen precipitates and stacking faults formed in CZ–Si. It is suggested that the induced dislocations in NCZ–Si could absorb self-interstitial atoms so that the OSFs shrank and dissolved with the oxidation time.

Intrinsic gettering in germanium-doped Czochralski crystal silicon crystals

The intrinsic gettering (IG) of germanium-doped Czochralski (GCZ) silicon with different concentrations of germanium has been investigated in this paper. The conventional Czochralski (CZ) and the GCZ silicon samples were annealed using a one-step high temperature process followed by a sequence of low–high temperature annealing cycles. It was found that the good defect-free denude zones in the near surface of the GCZ silicon could be achieved using simply a one-step high temperature annealing process. Furthermore, the density of bulk microdefects as IG sites was higher than that in the CZ silicon, as a result of germanium enhancing oxygen precipitation during three-step annealing. Meanwhile, the experimental results showed that germanium also enhanced the out-diffusion of oxygen. Furthermore, it is believed that germanium doping can increase the ability of IG in CZ silicon wafers.

Influence of oxygen precipitates on the warpage of annealed silicon wafers

The warpage of conventional Czochralski (CZ) and nitrogen-doped Czochralski silicon (NCZ) wafers with similar oxygen concentration were investigated. In the experiments, a two-step annealing process was taken to generate oxygen precipitates. After the elevated temperature annealing, no obvious warpage in both the CZ and NCZ silicon wafers was found, even if nitrogen was found to enhance oxygen precipitation and the stronger internal stresses were detected at the edge and center of an annealed wafer. It is considered that oxygen precipitates with relatively smaller sizes were successful in preventing the warpage of the silicon wafers, which is mainly dependent on thermal stress, because the oxygen precipitates can pin dislocations.

Mechanical strength of nitrogen-doped silicon single crystal investigated by three-point bending method

The mechanical strength of nitrogen-doped Czochralski silicon (NCZ-Si) and conventional Czochralski silicon (CZ-Si) have been investigated by three-point bending method at room temperature. It was found that the mechanical strength of silicon had been increased markedly at room temperature due to the doping of nitrogen. The effects of the surface condition and the orientation of silicon crystal on mechanical strength were determined. The mechanism of the mechanical strength increased by nitrogen in silicon is also discussed.

Minority-carrier lifetime of magnetic field applied Czochralski silicon wafers

The dependence of minority-carrier lifetimes and diffusion length on starting silicon materials grown by the magnetic field applied Czochralski (MCZ), conventional Czochralski(CZ), and float-zone (FZ) methods has been investigated with a capacitance-time relaxation technique. MCZ silicon yields longer minority-carrier lifetimes and diffusion length than those of both CZ and FZ silicon materials. The generation lifetime of MCZ silicon increases, while the recombination lifetime decreases, with the initial oxygen concentration. These characteristics are correlated with grown-in defects and gettering by oxygen-related defects.