Daxi Tian

The effect of germanium doping on oxygen donors in Czochralski-grown silicon

In this paper the effect of germanium doping on oxygen donors in Czochralski (CZ) silicon has been investigated. It is found that germanium suppresses the formation of thermal donors during annealing at 450??C, as a result of the reaction of Ge with point defects in CZ silicon. Meanwhile, it is clarified that germanium enhances the formation of new donors in CZ silicon, which is proposed to be a process associated with the nucleation enhancement of oxygen precipitation by germanium doping.

Intrinsic gettering in germanium-doped Czochralski crystal silicon crystals

Abstract 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 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...

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 ...

Effect of rapid thermal processing on high temperature oxygen precipitation behaviour in Czochralski silicon wafer

The effect of rapid thermal processing (RTP) on the oxygen precipitation occurring at 1050 °C in a Czochralski (CZ) silicon wafer has been investigated. It has been proved that the RTP-induced vacancies only enhance the early stage oxygen precipitation at 1050 °C in terms of the precipitation rate. Furthermore, it is somewhat unexpected that after a lengthy 1050 °C anneal the oxygen precipitates generated in the CZ silicon wafer with prior RTP treatment had considerably lower density and larger sizes in comparison with those generated in the CZ silicon wafer without prior RTP treatment. The reason for this is that the prior RTP treatment will dissolve some of the grown-in oxygen precipitates, thus making the RTP-treated wafer possess fewer nuclei contributing to oxygen precipitation in the subsequent 1050 °C anneal. Moreover, the numbers of resulting precipitated oxygen atoms due to a lengthy 1050 °C anneal were nearly the same in the CZ silicon wafers with and without prior RTP treatment. Additionally, it has been illustrated that the high temperature RTP has superior capability to dissolve the existing oxygen precipitates. It is worthwhile to point out that, when addressing the effect of RTP on the oxygen precipitation behaviour during the subsequent anneal, two functions arising from the RTP treatment, that is, the injection of vacancies into the silicon wafer and the dissolution of grown-in oxygen precipitates existing in the silicon wafer, should be taken into account.

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.

Oxygen precipitation in 1020 cm−3 germanium-doped Czochralski silicon

We have investigated the effects of germanium (Ge)-doping at the level of 1020 cm−3 on oxygen precipitation (OP) behaviors in Czochralski (CZ) silicon subjected to different low-high two-step anneals without or with prior high temperature rapid thermal processing (RTP). It is found that Ge-doping remarkably suppresses OP in CZ silicon without prior RTP. However, Ge-doping significantly enhances OP in CZ silicon with prior RTP. The suppressed OP in the case of the absence of prior RTP is primarily due to the fact that the 1020 cm−3 Ge-doping introduces compressive strain into silicon crystal lattice, which increases the critical size of oxygen precipitate nuclei for a given nucleation temperature. Moreover, it is revealed that the 1020 cm−3 Ge-doping facilitates the formation of vacancy-oxygen (V-O) complexes and may introduce Ge-V-O complexes in CZ silicon during high temperature RTP. More vacancy-related complexes in CZ silicon not only reduce the critical size of oxygen precipitate nuclei but also provi...

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 ...

Oxidation-induced stacking faults and related grown-in oxygen precipitates in nitrogen-doped Czochralski silicon

In this paper, we investigate oxidation-induced stacking faults (OSFs) and related grown-in oxygen precipitates of nitrogen-doped Czochralski (NCZ) silicon. The samples were oxidized at 1150 °C or were annealed under different conditions. It was found that OSFs with different densities in the NCZ silicon distributed not only in the OSF-ring region, but also in the inner region of the ring. Furthermore, the OSF ring was extended by nitrogen doping. In addition, the investigation of oxygen precipitates indicates that nitrogen changes the size and density distribution of grown-in oxygen precipitates in the OSF-ring and void regions of the NCZ silicon during crystal growth, and therefore the OSF behaviour is changed. Based on the experimental facts, in particular we discuss the mechanism of nitrogen affecting the distribution of OSFs in different regions.