Shigeo Sumita

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.

A Method of Quantitative Contamination with Metallic Impurities of the Surface of a Silicon Wafer

A method of quantitative and uniform contamination of the surface of a silicon wafer with a metallic impurity in low-level quantities using spin coating with a contaminated aqueous solution was developed. Fe, Ni, Cu and Al were examined and the quantities of these metallic impurities on the surface were controlled by the concentration of metal ions in the contaminated solution. Using this method, the influence on the recombination carrier lifetime was quantitatively investigated. A significant degradation of the recombination lifetime was observed for more than 1011 atoms/cm2 of impurities Cu, Ni and Fe on the surface.

Influence of Metal Impurities on Leakage Current of Si N + P Diode

Dependence of the leakage current of Si N+P diodes on the surface metal (Cu, Ni or Fe) concentration after quantitative contamination was investigated, and the causes of the leakage current were studied by SIMS, TEM and optical microscopy. Cu was gettered in the N+ area, forming many large dislocations in the N+ area and inducing some dislocations in the substrate near the junction; thus, the leakage current increased remarkably. Ni was gettered in the N+ area also, but did not form large dislocations, so the leakage current did not increase. Fe was not gettered easily, and hence the leakage current increased corresponding to the Fe concentration.

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.

Transmission Electron Microscopy Observation of Defects Induced by Fe Contamination on Si(100) Surface

The behavior of Si(100) surface defects induced by Fe contamination was studied with transmission electron microscopy. After annealing at 1150°C for 1 hour and a subsequent heat treatment at 850°C for 2 hours, Fe-containing precipitates were observed in Si substrate in close vicinity to the interface of Si and SiO2 formed during the annealing. One of these precipitates is identified as FeSi-type silicide. In addition, the inclusions which were confirmed to be Fe3O4 or γ-Fe2SiO4 were observed in the surface thermal SiO2 layer. These results demonstrate that Fe atoms diffuse into the Si substrate during annealing at 1150°C and precipitate at a Si/SiO2 interface, while Fe atoms left on the surface form inclusions in the surface SiO2 layer. Under an additional thermal oxidation at 1000°C, oxidation-induced stacking faults were formed. They were not decorated at all in contrast with those induced by Cu or Ni contamination.

TEM Observation of Defects Induced by Cu Contamination on Si(100) Surface

The behavior of a Si(100) surface defect induced by intentional Cu contamination was studied with transmission electron microscopy. After annealing at 1150°C for 1 hour in N2 atmosphere, colony precipitates lying along (110) planes were observed only on the surface of the wafer. These precipitates were estimated to be Cu6Si-type silicides by the selected area diffraction pattern. During additional annealing in an oxidation atmosphere, stacking faults were formed from each of colony precipitates. This indicated that colony precipitates were the nucleus of oxidation-induced stacking faults.

Dependence of Gettering Efficiency on Metal Impurities

The dependence of gettering efficiency on metal impurities was investigated by means of an intentional contaminating method using Ni or Fe and the MOS C-t method with an eye to using gettering techniques appropriately. The results showed that Ni is easily gettered but Fe is not. Therefore, as a second step, the condition improving gettering efficiency for Fe was investigated. It was consequently found that adding heat treatment at low temperature to the final heat cycle is effective for gettering of Fe.

Observation of Ring‐OSF Nuclei in CZ‐Si Using Short‐Time Annealing and Infrared Light Scattering Tomography

Small defects observed by IR light-scattering tomography after short-time annealing were shown to be related to the nuclei of ring-distributed oxidation-induced stacking faults (ring-OSF) in Czochralski-silicon crystals grown with growth rates of about 0.8 mm/min. The behavior of these defects was studied under different annealing conditions, and it was found that they were already present in the as-grown crystal below the detection limit of available techniques. Preannealing in nitrogen at 1150 o C introduced a stacking-fault-free region with subsequent oxidation. The reason for this was due neither to the annihilation of the ring-OSF nuclei nor to the formation of punched out dislocation loops from precipitates during nitrogen ambient annealing, but probably due to a change in the nature of the OSF nuclei occurring, making them incapable of OSF nucleation during subsequent oxidation. Various small defects were observed to exist in the as-grown crystal, and the radial position of these defects depended on their critical size. The distribution of as-grown defects within the crystal reflects the differences in the thermal stability of the defect nuclei due to point defect variations in the crystal during growth