Tatsuhiko Shigematsu

Dependence of the Grown-in Defect Distribution on Growth Rates in Czochralski Silicon

As-grown defects in 6-inch-diameter Czochralski-silicon crystals grown under different crystal growth rate conditions (0.4, 0.7, 1.1 mm/min) were studied by means of preferential etching and IR light-scattering tomography (LST). Grown-in defect images were classified into four types as follows: (a) flow patterns (wedge-shaped etch pits), (b) IR-defect images observed by LST, (c) ringlike distributed small pits, and (d) large pits. It was found by secondary ion mass spectrometry that IR defects are oxygen precipitates. Large pit defects were identified by transmission electron microscopy as large dislocation loops with a length of about 30 µm. At growth rates from 0.7 mm/min to 1.1 mm/min, flow pattern defects and IR defects coexist inside a ringlike distributed oxidation-induced stacking fault (ring-OSF) region. However, at growth rates less than 0.7 mm/min, large pit defects were observed in the region outside the ring. Characteristic ringlike distributed small pit defects were observed on the outer periphery of the ring region. Flow pattern defects were annihilated during annealing at 1100°C, while IR defects were stable at 1250°C.

Behavior of Defects Induced by Metallic Impurities on Si(100) Surfaces

The formation of defects induced by Ni, Cu and Fe and their retardation by intrinsic gettering (IG) were studied under several heat treatments. The behavior of Fe in Si was different from that of Ni and Cu. After annealing at 1150°C and subsequent cooling, shallow pits (SP) due to Ni and Cu precipitates were observed only at the surface. Fe precipitation was obtained by holding at temperatures below 850°C, where Fe was supersaturated in the matrix. We believe that metal precipitation is dominated by the diffusion rate. During additional oxidation, oxidation-induced stacking faults (OSF) were transformed from each precipitate. It seems that metal precipitates act as nuclei of OSF. Effects of IG for the three elements were compared. The retardation of defects induced by Fe was less than that of Ni and Cu. This difference is closely related to the growth rate of Fe precipitates.

Formation Behavior of Infrared Light Scattering Defects in Silicon during Czochralski Crystal Growth

The formation behavior of grown-in defects which are considered to be oxygen precipitates formed during CZ-Si crystal growth, was investigated by means of infrared light scattering tomography. The following results were obtained. (i) The density of the IR light scattering defects decreases with a reduction in the crystal pulling rate. (ii) The defects are not formed just after solidification, but they grow to a size detectable by LST during cooling to about 1100°C. (iii) The defect density decreases by slow cooling in the temperature range from to 1500 to 1000°C, while their size increases. The formation mechanism of the defects was qualitatively discussed from the point of view of the interaction between oxygen atoms and point defects by a consideration of the free energy change and the critical radii of nuclei for oxygen precipitation. It was suggested that the formation of the defects depends on the vacancy concentration. In the case of a constant vacancy concentration, their density and size are determined by the cooling rate in the temperature range from 1150 to 1000°C.

Atomic Force Microscopy Observation of Si(100) Surface after Hydrogen Annealing

Hydrogen gas play an important role in the epitaxial growth process, acting as both a high temperature precleaning ambient and the carrier gas during epitaxial growth. The effect of hydrogen on the morphology and microroughness of Si(100) and Si(111) surfaces was investigated using force microscopy under an atmospheric air ambient. The Si(100) surface after H 2 annealing showed a periodic terrace and step structure reflecting the double-domain (2×1+1×2) reconstructed structure. This structure was maintained even after subsequent HCl vapor etching and epitaxial layer deposition in the Si epitaxial process

Axial Microscopic Distribution of Grown-in Defects in Czochralski-Grown Silicon Crystals

The axial microscopic distribution of grown-in defects in Czochralski silicon was studied by means of IR light scattering tomography (LST) and preferential etching. IR scattering defects (defects observed with LST) were found to degrade the gate oxide integrity yield, and the axial density distribution of IR scattering defects and flow patterns (wedge-shaped etch patterns) fluctuated with oxygen concentration fluctuations along the growth axis. However, the defect density did not depend directly on oxygen concentration. It is considered that the formation of IR scattering defects is related to the solid-liquid intertace temperature fluctuations.

A Model for the Formation of Oxidation-Induced Stacking Faults in Czochralski Silicon

The mechanism of oxidation-induced stacking fault (OSF) formation in Czochralski silicon (CZ-Si) crystals was investigated by transmission electron microscopy observations of the initial stages of OSF growth. OSFs were observed to be always generated at one of the edges of platelet oxygen precipitates. We observed previously that these platelet oxygen precititates had an expansive strain field in the direction parallel to the precipitate plate and a compressive strain field normal to the plate. Silicon self-interstitials having compressive strain are probably attracted to the expansive strain field of the precipitates, and condense to form stacking faults. A new model for OSF generation is presented taking into consideration the strain field around self-interstitials and oxygen precipitates.

Influence of melt-temperature fluctuations on striation formation in large-scale Czochralski Si growth systems

The effects of melt-temperature fluctuations on growth striations in crystals grown in a commercial-scale growth system were studied by an analysis of the fast-Fourier-transform (FFT) method applied to the melt-temperature fluctuations and to the growth striations as evaluated by X-ray topography and spreading-resistance (SR) methods. The period of the growth striations observed in crystals corresponded exactly to that of temperature fluctuations in the melt; however, the amplitude of these growth striations decreased when temperature fluctuations with a constant amplitude occurred rapidly. This phenomenon results from a delay in the response of the microscopic growth rate to rapid temperature fluctuations. The amplitude of melt-temperature fluctuations and the peak height of the FFT power spectra were observed to decrease in the radial direction toward the crystal center, and this trend was also observed for growth striations. It was concluded that temporal thermal fluctuations caused by melt convection are preserved in growth striations for crystals grown in large growth systems.

Influence of Fe Contamination in Czochralski-Grown Silicon Single Crystals on LSI-Yield Related Crystal Quality Characteristics

Influence of Fe contamination in CZ-grown silicon single crystal on oxidation-induced stacking fault (OSF) generation density, carrier recombination and generation lifetimes, and gate oxide integrity (GOI) yield characteristics was experimentally investigated. Two Fe-doped silicon ingots were grown and tested. Concentration of Fe-B ([Fe-B]) in these silicon ingots measured by deep level transient spectroscopy (DLTS) was about 5×1011 cm-3 and 5×1012 cm-3, respectively. OSF density generated by three-step annealing showed dependence on [Fe-B]. Carrier recombination lifetime (τ r) showed good correlation with [Fe-B], and a quantitative relationship was established. OSF density after one-step annealing, carrier generation lifetime (τ g) and GOI yield were not so dependent on [Fe-B].

Determination of the criteria for nucleation of ring-OSF from small as-grown oxygen precipitates in CZ-Si crystals

The behaviour of small as-grown platelet-type oxygen precipitates, known to nucleate ring-like distributed oxidation induced stacking faults (ring-OSF), was studied in CZ-Si crystals grown with modulating growth rates using IR light scattering tomography, μ-photoconductive decay lifetime analysis and preferential etching. It was found that although these oxygen precipitates were observed on the ring region, their OSF nucleation ability differed greatly depending on the crystal growth conditions. We propose that the OSF nucleation ability of an oxygen precipitate depends on its size, and in order for successful OSF nucleation, the precipitate size must lie within certain limits. Using the difference in the thermal histories of the crystals grown with modulating growth rates, we calculated that only platelet-type oxygen precipitates on the ring-OSF region having a length between 260 and 1350 A are capable of OSF nucleation.

Generation of Oxidation-Induced Stacking Faults in Czochralski-Grown Silicon Crystals Exhibiting a Ring-like Distributed Stacking Fault Region

The radial density distribution of oxidation-induced stacking faults (OSFs) and bulk micro defects (BMDs) in Czochralski-grown silicon crystals having a ring-like distributed OSF (ring-OSF) region was characterized after low-temperature pre-annealing followed by high-temperature oxidation, using optical microscopy, IR light scattering tomography and Fourier transform IR spectroscopy. Stacking faults were observed to have grown during oxidation in various radial regions of the crystal other than the ring-OSF region, depending on the radial distributions of BMDs determined by the pre-annealing conditions. The ability of these BMDs grown during pre-annealing to nucleate OSFs with subsequent oxidation is determined by the strain surrounding them. However, to realize OSF nucleation, the strain must lie within specific limits controlled by the size of the BMD.