Light Scattering Tomography Research Articles

Annealing Behavior of Light Scattering Tomography Defect in the Denuded Zone of Si Wafers

Light scattering tomography defects (LSTDs) have been non-destructively detected in bulk and near the surface of a Si wafer by Brewster angle illumination of infrared light scattering tomography (IR-LST). We investigated the annealing behavior of grown-in LSTDs that exist in a layer of 0 to about 20 µm depth from the wafer surface. Grown-in LSTDs were detected before annealing. Annealing behavior of such grown-in LSTDs was studied by the three-step annealing to form the denuded zone (DZ) of about 40 µm. As a result, the LSTDs mostly remained in the DZ after the three-step annealing. However, the change in the scattering intensity of the grown-in LSTDs was detected. This change suggests that the volume and/or structure was changed by the annealing treatment.

Internal oxidation of vacancy agglomerates in Czochralski silicon wafers during high-temperature anneals

Fast pulled Czochralski silicon crystals usually contain large octahedral vacancy agglomerates. These voids are known as D defects, which degrade the integrity of thin gate oxides by causing time zero dielectric breakdown. After annealing the wafers at temperatures above 1100 °C, the gate oxide integrity is clearly improved. We show by theoretical estimation, light-scattering tomography and transmission electron microscopy studies that the vacancy agglomerates can be filled with silicon oxide by internal oxidation. This is brought about by diffusion of interstitial oxygen to the voids, which can be regarded as internal surfaces. In this way they become less detrimental for thin gate oxides, because now they consist of silicon oxide itself. However, they are still present in an octahedral-like geometry and can be observed by Brewster angle infrared light-scattering tomography.

光計測の新しい潮流 光散乱トモグラフィ

光計測の新しい潮流 光散乱トモグラフィ

Misfit dislocations and stresses in GaN epilayers

GaN epilayers nitridated initially for different times have been investigated by light scattering tomography (LST) and Raman scattering. In the LST images of the plan-view epilayers, the light scattering defects mainly distribute in 〈112_0〉 directions. The density of the defects is lower in epilayer nitridated initially for a longer time. The defects are considered to be the straight threading edge dislocations on {11_00} planes. The Raman shift of E2 mode is larger in the sample initially nitridated for a longer time. Our results show that the misfit between the GaN epilayer and the Al2O3 substrate is more unfavorably accommodated by the threading edge dislocations in the epilayers initially nitridated for a longer time.

Fourier-transformed light-scattering tomography for determination of scatterer shapes

The diffraction patterns due to light scattering from precipitates in Si crystals annealed at for 6 - 18 h or at for 8 - 64 h following pre-annealing at for 4 h were observed at a de-focus position using light-scattering tomography (LST) apparatus. The patterns clearly differed from one another and every image at a focus position was a small point. The diffraction patterns obtained at a position deviating by from the focus position were transformed into an image by Fourier analysis in terms of Fresnel diffraction using tentative phase data. The process is similar to the process of X-ray structural analysis. A good similarity between the images observed here and images from transmission electron microscopy (TEM) was obtained.

Observation of the morphology and displacement of dislocations in vapour phase grown ZnSe crystals

Abstract Dislocation walls on {111} and {110) planes in vapour phase grown ZnSe crystals were studied by light scattering tomography (LST), the cathodoluminescence mode of scanning electron microscopy (CL-SEM) and molten KOH etching. Many Y shaped nodes and hexagonal nets of dislocation lines caused by reactions between the lines were clearly observed on (111) planes by LST, although many dislocations of irregular shape and some parallel arrangements of dislocations were also found. Slip lines on (111) planes were clearly observed as dark lines by CL-SEM which allowed the determination of dislocation glide planes. Undecorated dislocations and slip lines were difficult to observe by LST in these crystals of high refactive index. The dislocations constituting the main part of the dislocation walls and Y shaped nodes were immobile even when the stress was increased sufficiently to fracture the specimen, while some of the other dislocations were displaced.

Computed light scattering cross sections of oxide particles in silicon

We have used the discrete-dipole approximation (DDA) method, implemented as a modified version of the DDSCAT program of Draine and Flatau, to calculate 3D light scattering intensity diagrams for individual oxide particles present in Czochralski silicon wafers. The particles were either octahedra or plates with normalized sizes x=0.01–5. The signals that would be measured for light scattered through 90° or 180° were determined from the diagrams, these angles corresponding to the cases of light scattering tomography (LST) and reflection confocal (RC) scanning infrared microscopy (SIRM), respectively. The results show that as x increases, the signal (particle image contrast) increases ∝x6 for x<∼1, but increased more slowly and in an irregular manner for x≳∼1. The signal also depends markedly on the particle shape and orientation. These findings demonstrate the difficulty of deducing quantitative data, e.g., individual particle sizes, from SIRM image contrasts. However, they also indicate the type of measurements that need to be made and provide a basis for the quantitative interpretation of the experimental results.

Piled-up dislocations in a vapour-phase-grown ZnSe crystal

Abstract A new structure of piled-up dislocations, called a dislocation wall, was observed by light-scattering tomography (LST) for the first time on some {111} planes in a ZnSe crystal grown by a vapour phase method. The walls are flat platelets, about 10–15 μm in thickness, where many dislocations are randomly and abnormally piled up. Other characteristics of the dislocation walls observed by LST were studied by molten KOH etching and the cathode-ray luminescence (CL) mode of scanning electron microscopy (SEM). Many other dislocation lines were also clearly observed outside of the walls by LST and CL SEM.

Morphology and size distribution of oxide precipitates in as-grown Czochralski silicon crystals

The morphology and size distribution of oxide precipitates in as-grown Czochralski (CZ) silicon crystals, with growth rates of about 1.1 mm/min, have been studied using infrared light scattering tomography (LST). The following results were obtained. (1) The morphology of oxide precipitates in as-grown CZ silicon is polyhedral. (2) The length of the side of the polyhedral precipitates is about 80 nm. According to their morphology and size distribution, it was concluded that they were formed in the high temperature range (≥1000 °C) during crystal growth.

Detection of Bulk Microdefects underneath the Surface of Si Wafer Using Infrared Light Scattering Tomography

A new method has been developed to detect bulk microdefects (BMD) underneath the surface of a Si wafer using infrared light scattering tomography. In this method, infrared light enters from the cleaved surface obliquely and is totally reflected at the surface of the wafer, in order to eliminate the effect of scattering at the surface. BMD not only underneath the surface of the polished silicon wafer, but also underneath the wafer surface on which devices are fabricated, are easily detected by this method.

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.

Characterization of dielectric crystals by light scattering tomography

Abstract Optical characterization of dielectric crystals is very useful if they include heavy elements as constituent components of the crystals. The principle of light scattering tomography (LST), which has been developed as laser scanning ultramicroscopy, and some results obtained by LST are reviewed here.

Characteristics of dislocations in beta-barium metaborate bulk crystals investigated via light scattering tomography

General characteristics of dislocations in beta-barium metaborate (BBO) bulk crystals have been investigated via light-scattering tomography (LST). The dislocations induced by inclusions and the residual products which can reflect the interaction process between the dislocation loops were observed in the experiment. Moreover, the decoration of the dislocation lines in BBO crystals with impurity atoms was also demonstrated by LST images.

Observation of microdefects and microprecipitates in Si crystals by IR scattering tomography

A new instrument of IR light scattering tomography (LST) with an excellent image processing software (MILSA) has been developed for non-destructive detection of microdefects and microprecipitates in semiconductor crystals. Using LST with MILSA the growth striations, denuded zone layers and microprecipitates as well as oxidation induced stacking faults in silicon crystals were detected clearly and correctly by a beam from a YAG laser.

A quantitative light scattering tomography technique for measuring microprecipitate concentrations in GaAs and InP

We have built an infrared light scattering tomography (LST) apparatus where the sensor is a linear array of silicon charge coupled device detectors. We demonstrate the use of this system to produce LST images from which quantitative information can be extracted. Samples of semi-insulating (SI) LEC GaAs quenched from different temperatures have been analyzed using this equipment. The apparatus is also useful in performing Infrared transmission measurements to map EL2 concentrations in similar material. We compare data obtained using the new apparatus with that obtained by conventional EL2 imaging.

Studies of Plane Type Defects in Ferroelectric Ca2Sr(C2H5CO2)6 Single Crystal by Light Scattering Tomography

Crystal defects in ferroelectric Ca2Sr(C2H5CO2)6 have been studied in detail by light-scattering tomography. Most of the crystal defects observed have been found to be the plane type parallel to the {101} or the {110} planes. The shape of the {101} plane type defects is fundamentally a hexagon which satisfies “the law of constancy of facial angles.” The formation mechanism of the plane type defects is studied and discussed.

Infrared light scattering tomography with an electrical streak camera for characterization of semiconductor crystals

An electrical streak camera has been developed for IR imaging. Integration for noise reduction and subtraction of dark current were successfully performed using a 16-bit personal computer, improving the signal-to-noise ratio of a PbO–PbS visicon for IR detection. In this paper, the camera was applied to infrared light-scattering tomography for characterization of semiconductor crystals such as GaAs, InP, and CdTe crystals. In this streak camera, the IR detector can be replaced by a photodiode array such as HgCdTe, to detect even much longer wavelength radiation, which will be useful to study some electronic centers in semiconductors.