Yutaka Kitagawara

Transmission Electron Microscope Observation of “IR Scattering Defects” in As-Grown Czochralski Si Crystals

Grown-in defects detected by IR laser scattering tomography (LSTDs) in Czochralski-grown Si crystals were identified for the first time by transmission electron microscopy (TEM) with a special defect positioning technique. The basic structure of each LSTD was revealed to be a composite of two or three incomplete octahedral voids with a total size of 100–300 nm. The TEM images of the defects suggest the existence of walls several nanometers thick surrounding the voids. A weak oxygen signal was detected from the defect by energy dispersive X-ray spectrometry. The thin walls surrounding the voids were considered to be made of SiOx .

High-sensitivity defect evaluation by a new preferential etching technique for highly As-doped Si crystals

A high-sensitivity preferential etching technique is presented to evaluate crystal defects in a highly As-doped silicon crystal with a resistivity lower than 0.01 Ω cm. For highly doped n-type Si, a conventional preferential etching technique, such as Secco etching, Wright etching or Dash etching becomes less useful because of a significant decrease in defect detection sensitivity. The new method is quite sensitive to dislocations, stacking faults and oxygen precipitates in highly As-doped crystals with a surface of either (111) or (100). In this method, copper is first decorated at the defect site, then the defect is preferentially etched by a dilute alkaline solution. The technique thus offers us a sensitive and Cr-free method, attractive from an environmental aspect. A correlation between the laser scattering method is also obtained for the oxygen precipitate density.

Practical Computer Simulation Technique to Predict Oxygen Precipitation Behavior in Czochralski Silicon Wafers for Various Thermal Processes

A practical computer simulation technique has been developed to predict oxygen precipitation behavior in Czochralski silicon wafers during various thermal processes. In this simulation, an empirical factor is introduced in the initial and boundary conditions of the Fokker-Planck equation of the oxygen precipitation in order to make up an incomplete assumption of a homogeneous nucleation process proposed by Schrems et al. 1 The empirical factor is constructed as a function of heat-treatment temperature and interstitial oxygen concentration so as to describe characteristic phenomena of the precipitation nucleation processes in the 450 to 800°C range. Futhermore, an experimentally measured t ermal history during a crystal growth process, which strongly influence the oxygen precipitation behavior in the subsequent thermal process, has been taken into consideration. The calculated results agree fairly well with the experimental results for a variety of thermal processes. This semi-empirical simulation technique thus provides an advantageous tool for industrial optimization of the oxygen precipitation characteristics.

Evaluation of Oxygen Precipitated Silicon Crystals by Deep‐Level Photoluminescence at Room Temperature and Its Mapping

A deep-level photoluminescence (PL), which corresponds to the DI line (0.81 eV) at 4.2 K, is investigated at room temperature for oxygen precipitated Czochralski Si crystals in their growth directions. Analyses are made of the macroscopic and microscopic distributions of the room temperature D1 line intensity (I D ) the room temperature band-to-band PL intensity (I B ), carrier lifetime (γ), and precipitated oxygen concentration (Δ[O i ])

Evaluation of Oxygen‐Related Carrier Recombination Centers in High‐Purity Czochralski‐Grown Si Crystals by the Bulk Lifetime Measurements

Present day high-purity Czochralski(CZ)-grown Si crystals are characterized by the bulk carrier recombination lifetime measurements. The bulk lifetime of the p-type as-grown Si with resistivity ∼10 Ω-cm is found to be as high as 500 μs for a CZ-Si crystal with [O i ] > 10 ppma-JEIDA and as high as ∼1 ms or even higher for a low-oxygen CZ-Si crystal with [O i ] < 10 ppma-JEIDA. The as-grown bulk lifetime is revealed to depend not only on resistivity under the framework of the Shockley-Read-Hall (SRH) relation, but also on the oxygen concentration. The dominant recombination center of the as-grown crystal is found to be an SRH-type deep-level center which is considered to be an oxygen-related defect complex. The complex is quenched easily by a heat-treatment at a temperature as low as 650°C. Effective density of a recombination center, existing after the 650°C heat-treatment in the p-type crystal, correlates well with the amount of oxygen precipitation generated by a subsequent two-step heat process [800°C for 4 h + 1000°C for 16 h]. Thus the dominant recombination center after the 650°C heat-treatment is considered to be closely related to the oxygen precipitation nuclei toward the subsequent precipitation formation heat process.

MEDIUM FIELD BREAKDOWN ORIGIN ON METAL OXIDE SEMICONDUCTOR CAPACITOR CONTAINING GROWN-IN CZOCHRALSKI SILICON CRYSTAL DEFECTS

The medium field breakdown of metal oxide semiconductor capacitor due to the Czochralski silicon crystal originated defect was studied in view of both electrical and structural analyses. By analyzing the local tunneling current which initiates the medium field breakdown, phenomenological defect sizes were calculated from the local tunneling current by assuming the local oxide thinning model. They were the defect diameter as 5 to 50 nm and the local oxide thinning as ~25 nm. These data were confirmed by direct defect observation using high precision defect isolation procedure followed by transmission electron microscopy. Direct observation revealed that the real defect size was ~200 nm which correlated well with other recently reported works. The real local oxide thinning,however,was not as large as phenomenological calculation. To explain the differences between phenomenological and real local oxide thinning, the poly-Si grain protrusion induced stress model was proposed.

Tem Observation Of Grown-In Defects In CZ-Si Crystals And Their Secco Etching Properties

Grown-in defects detected by IR laser scattering tomography (LSTDs) in Czochralski-grown Si crystals were identified by transmission electron microscopy (TEM) with a special defect positioning technique. The basic structure of the LSTD was revealed to be a composite of two or three incomplete octahedral voids with the 100–300nm total size. The TEM images of the defect showed existence of 2∼4nm-thick walls surrounding the voids. These thin-walls are considered to be made of oxide, SiO x . These LSTDs are indeed dominant grown-in defect species in most of the commercial CZ-Si walers. The LSTD after 1200°C oxidation was also observed by TEM. The resulting image shows that the defect changed from void to filled oxide precipitate by the high temperature heat treatment. On the other hand, in very slowly pulled crystals with ∼0.4mm/min rate, interstitial type dislocation loops were observed as major defect species. Non-agitated Secco etching of these grown-in defects delineates “flow patterns” (FPs) or pits without the flow patterns. The FP forming property is shown to disappear by oxidation at temperature above 1150°C, while the defect itself remains stable. This implies that the grown-in defects lose their chemical properties to form FPs by the high-temperature oxidation. It is further revealed that the grown-in defects, which once lost the FP forming property by the high-temperature oxidation, can form FPs again by an intentional Cu contamination. Thus a possible FP formation factor is Cu decoration at the grown-in defect site. Defect formation model of the as-grown twin-type LSTD is also proposed.

Novel evaluation method of silicon epitaxial layer lifetimes by photoluminescence technique

A novel method, the short wavelength laser excited photoluminescence (PL) technique at room temperature, is applied to evaluate carrier lifetime characteristics of silicon epitaxial (epi) layers, which are grown on heavily doped p+ substrates with approximately 1019 cm-3 of boron. The band-edge PL intensity of the epi-layer is closely related to the carrier recombination lfietime at room temperature. The carrier excitation at 488 nm wavelength and the existence of the p/p+ structure, which acts as a stopper for the excess carrier diffusion, enable one to evaluate the epi-layer lifetime characteristics of the epi-layer thicker than 3 micrometers . Applying the method to epi-quality evaluation of the p/p+ epi-wafers, trace metallic contamination in epi-layers introduced by the epi- growth processes has been evaluated successfully. It has been found that a dilute HF cleaning is enough for the sample preparation instead of surface passivation heat treatment, which is usually required for other lifetime measurements. This is a great advantage of the method which enables one to do an in-line epi-quality monitoring. We also found that molybdenum contamination degraded the epi-lifetime and the time dependent dielectric breakdown of thin oxide films grown on p/p+ epi-wafers in this study.

EQUILIBRIUM CONSTANT OF SEGREGATION-INDUCED FE GETTERED BY HEAVY BORON DOPING IN SI

The equilibrium constant of segregation-induced Fe gettering by heavy boron (B) doping in Si is obtained by experimental determination of the activation energy and the site density parameter of the gettering reaction. The activation energy is determined to be 0.68±0.03 eV by analyzing the temperature dependence of the equilibrium constant of the reaction. This result indicates that the Fe gettering is strongly related to formation of the Fe–B complex whose binding energy is very close to the value determined for the activation energy. Furthermore, the gettering site density is found to be proportional to the doped B concentration in the substrate crystal. It is understood from the activation energy value that the Fe gettering ability of each reaction site for heavy B doping is less than that for thin polycrystalline Si film on the back surface of a substrate. The well known high overall gettering capability of the heavily B-doped substrate is not simply due to the activation energy effect it is predominan...

Accurate Evaluation Techniques of Interstitial Oxygen Concentrations in Medium‐Resistivity Si Crystals

Accurate evaluation methods for interstitial oxygen concentrations ([O i ]) by infrared absorptiometry at 1107 cm -1 are investigated for medium resistivity Si crystals with carrier concentrations betwee 3×10 15 and 5×10 16 cm -3 , which correspond to resistivities between 5 and 0.5 Ω-cm for p-type crystals. Difficulty of accurate [O i ] measurements for these crystals originates from the strong dependence of the internal multiple reflection effect inside the sample crystal on the free-carrier absorption intensity. Neglect of this effect introduces an error as large as 1 ppma for a p-type ∼1 Ω-cm crystal