Papers by Author: De Ren Yang

Abstract: We report a strategy feasible for improving the internal gettering (IG) capability of iron (Fe) for n/n⁺ epitaxial silicon wafers using the heavily arsenic (As)-doped Czochralski (CZ) silicon wafers as the substrates. The n/n⁺ epitaxial silicon wafers were subjected to the two-step anneal of 650 °C/16 h + 1000 °C/16 h following the rapid thermal processing (RTP) at 1250 °C in argon (Ar) or nitrogen (N₂) atmosphere. It is found that the prior RTP in N₂ atmosphere exhibits much stronger enhancement effect on oxygen precipitation (OP) in the substrates than that in Ar atmosphere, thereby leading to a better IG capability of Fe contamination on the epitaxial wafer. In comparison with the RTP in Ar atmosphere, the one in N₂ atmosphere injects not only vacancies but also nitrogen atoms of high concentration into the heavily As-doped silicon substrate. The co-action of vacancy and nitrogen leads to the enhanced OP in the substrate and therefore the better IG capability for the n/n⁺ epitaxial silicon wafer.

Abstract: Oxygen precipitation (OP) and annihilation of voids in heavily phosphorus (P)-doped Czochralski (Cz) silicon have been investigated. It was found that the nucleation anneal at 650°C resulted in much more pronounced OP in the subsequent high temperature anneal than that at 800 or 900 °C. This was due to that SiP precipitates could be formed in heavily P-doped Cz silicon by the 650oC anneal and they acted as the heterogeneous nuclei for OP in the following anneal at high temperatures. The rapid thermal anneal (RTA) at 1200°C was proved to be an effective means to annihilate voids. Moreover, it was found that the significant OP resulting from the two-step anneal of 650°C/8 h + 1000°C/16 h could also cause the substantial annihilation of voids in heavily P-doped Cz silicon. The mechanisms for the annihilation of voids have been tentatively discussed.

Abstract: Oxygen precipitation (OP) behaviors in conventional and nitrogen co-doped heavily arsenic-doped Czocharalski silicon crystals subjected to low-high two-step anneals of 650 oC/8 h + 1000 oC/4-256 h have been comparatively investigated. Due to the nitrogen enhanced nucleation of OP during the low temperature anneal, much higher density of oxygen precipitates generated in the nitrogen co-doped specimens. With the extension of high temperature anneal, Oswald ripening of OP in the nitrogen co-doped specimens preceded that in the conventional ones. Moreover, due to the Oswald ripening effect, the oxygen precipitates in the conventional specimens became larger with a wider range of sizes. While, the sizes of oxygen precipitates in the nitrogen co-doped specimens distributed in a much narrower range with respect to the conventional ones.

Abstract: The novel concept of “impurity engineering in CZochralski (CZ) silicon ” for large scaled integrated circuits has been reviewed. By doping with a certain impurities into CZ silicon materials intentionally, such as nitrogen (N), germanium (Ge) and even carbon (C, with high concentration), internal gettering ability of CZ silicon wafers could be improved. Meanwhile, void defects in CZ silicon wafer could be easily eliminated during annealing at higher temperatures. Furthermore, it was also found that the mechanical strength could be increased, so that breakage of wafers decreased. Thus, it is believed that by impurity engineering CZ silicon wafers can satisfy the requirment of ultra large scale integrated circuits.

Abstract: Iron silicide films with two different structures were fabricated by electron beam evaporation (EBE) technique. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscope (SEM) were carried out to describe the characteristics and structures of the films. It was found that after annealing at 800oC for 5 h, the β-FeSi2 film formed in the sample with the structure of Si/Fe film on silicon substrate, while only FeSi film generated in the sample with the structure of Si/Fe/Si films on silicon substrate. It is considered that the different iron silicides may be due to the different reaction of iron with crystal silicon or amorphous silicon, which is related to diffusion of iron or silicon atoms.

Abstract: The ZnO/n+-Si heterojunction has been fabricated via depositing nominally undoped ZnO film by reactive sputtering on a heavily arsenic-doped (n+) silicon substrate. The sputtered ZnO film was n-type in conductivity with an electron concentration of 1.0×1018 cm-3. The current-voltage characteristics indicate that the ZnO/n+-Si heterojunction does not possess rectifying function. Under the forward bias with the negative voltage applied on the n+-Si substrate, the heterojunction emits ultraviolet and broad visible lights characteristics of near-band-edge and defect-related emissions of ZnO, respectively. The EL mechanism has been tentatively explained in terms of the energy-band diagram.

Abstract: The thermal donor formation at 425oC - 450oC in Ge doped Czochralski (GCZ) silicon having about 1016 cm-3 Ge content pretreated by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) has been investigated using low-temperature infrared spectroscopy (LT-IR). The measurements prove that lightly Ge doping can enhance the formation of thermal double donors in the initial stage of the low temperature annealing after RTA process. Ge induced additional grown-in oxygen precipitates during silicon ingot growth and the abundant self-interstitials during RTA may be the reason for the enhancement. However, after extending the annealing time at the low temperatures, the thermal donor concentration in the GCZ silicon is lower than that in the conventional CZ silicon. In final, the mechanism is also discussed.

Abstract: The carrier recombination activities of small angle (SA) grain boundaries (GBs) in multicrystalline Si (mc-Si) were systematically investigated by electron-beam-induced current (EBIC). At 300 K, general SA-GBs with tilt angle from 0° to 10° showed weak EBIC contrast (0- 10%) with the maximum appeared at 2°. At low temperature (100 K), all the SA-GBs showed strong EBIC contrast despite the tilt angle. Possible explanations for the variation of the EBIC contrast were discussed in terms of boundary dislocations.