Michiyoshi Maki

Creep curve of silicon wafers

A new method of performing a creep test on silicon single crystals is described. The experiment utilizes silicon wafers. The stress applied to the wafers is provided by a Si3N4 film deposited by chemical vapor deposition on the front side of the wafer. The samples, i.e., silicon wafers with superposed Si3N4 films, are annealed in a quartz tube at 1000–1100 °C. The creep curves obtained are classified into two types according to stress. One type is related to plastic deformation of the wafer; the other is an elastic deformation. These results are available for the use of Si3N4 film in semiconductor technology.

Suppression of oxidation‐stacking‐fault generation by preannealing in N2 atmosphere

Suppression of oxidation‐stacking‐fault (OSF) generation is studied by x‐ray section topography, etching technique, and transmission electron microscopy (TEM). Microdefects (MD’s) are generated in bulk Si during N2 atmosphere annealing at about 1000–1100 °C, and their generation is confined to the inner part of the Si wafer. These MD’s grow rapidly during subsequent oxidation. The grown MD’s contribute to stacking faults (SF’s) in the inner part of bulk Si. On the contrary, surface OSF’s are not introduced by the subsequent oxidation because no MD’s are generated in the surface layer by the preannealing. The suppression effect of OSF generation by N2 atmosphere preannealing is demonstrated using several samples.

Growth of 10 cm wide silicon ribbon

Abstract The temperature distribution in the die, a most important parameter in ribbon crystal growth, is measured by a new, simplified method. The distribution determined by the new method corresponds fairly well with that measured using a thermocouple. The dependence of the temperature distribution in the die on the flow rate of Ar gas is investigated. Ribbon crystals, 10 cm in width, are grown from metallurgical and semiconductor grade silicon using a rectangular heater and controlled Ar gas flow rate. Precipitates in the ribbon are studied by infrared microscopy, and their number and form are shown to depend on the growth speed.

Growth behavior of oxidation stacking faults and microdefects in silicon during high‐temperature annealing

Growth behavior of oxidation stacking faults (OSF’s) and microdefects (MD’s) induced in bulk Si by high‐temperature annealing is studied. X‐ray section topography has been mainly utilized; however, both etching and electron microscopic observation have also supported the study. Both OSF’s and MD’s have grown at high temperature in wet O2 atmospheres and their activation energies are 2.7 and 2.6 eV, respectively. However, only MD’s have grown at high temperature in N2 atmospheres atmospheres where the activation energy is 5.1 eV. The growth rate of these defects is also investigated. Based on these investigations, the roles of O2 diffusion and Si self‐diffusion in the defect generation are discussed.

Wide silicon ribbon crystals

Abstract An improved edge-defined film-fed growth (EFG) apparatus is used for the growth of wide silicon ribbon crystals. This apparatus utilizes a specially designed heater and a thermal radiation modifier, which facilitate an appropriate temperature profile at the die top where crystals grow. A ribbon crystal as wide as 84 mm is obtained.

X-ray crystal truncation rod scattering analysis of reactive ion etched silicon

We have investigated lattice damage in reactive ion etched silicon by using x-ray crystal truncation rod (CTR) scattering. The x-ray intensity associated with the rod in the reciprocal space depends on the etching-induced lattice distortion. To estimate the magnitude of the lattice distortion, we analyzed the obtained data with a kinematic x-ray diffraction model on the assumption that the lattice distortion decays exponentially with the depth. We found that the lattice distortion extends to a depth of about 9 nm. In addition, we propose a method for quantitatively evaluating lattice damage based on our analysis. This method allows us to compare lattice damage among samples etched under different conditions. This study indicates that x-ray CTR experiments provide a useful means of characterizing lattice distortions near processed surfaces.

Self-Isolated Transistor Structures of Bipolar Integrated Circuits

Self-isolated transistor structures for bipolar integrated circuits are proposed. Some of the advantageous features of the proposed structures are; negligible minority carrier storage in collector region, low collector series resistance and large current handling capability, high packing density, and ease of processing. Cutoff frequency of about 600 MHz was observed for the graded base structure, and about 400 MHz for the uniform base structure. It is also shown that the current handling capability is improved. Epitaxial growth is one of the critical steps in producing self-isolated bipolar integrated circuits. A discussion is given for the specification of the epitaxial layer. In order to minimize the back diffusion from the buried layer to the base, a new possible way of processing is proposed which makes use of the simultaneous diffusion of Ga, As, and P.

Causes of Thickness Non-Uniformity in Silicon Ribbon Crystals

Three kinds of thickness non-uniformity in silicon ribbon crystals grown using graphite dies were observed, and the cause of each type of non-uniformity pinpointed. One of these, uneven accumulation of molten silicon around the die top, was found to result in a large non-uniform temperature distribution near the growth interface, producing a non-uniform heat release pattern in the crystals. This in turn caused the meniscus to become unstable in shape and split. Uniformly thick ribbons 90 mm wide can be grown by preventing this accumulation, and this technique is expected to help to reduce the production costs of solar energy devices.

Evaluation of Temperature Distribution of Melt in Silicon Ribbon Growth

An improved Edge-defined Film-fed Growth apparatus is used to grow wider silicon ribbon crystals. A rectangular graphite heater with a shape similar to the die top structure is used in order to increase the length of uniform temperature. A thermal radiation modifier prevents the growth of crystals with non-uniform thickness. The lateral temperature distribution at the die is quantitatively analyzed from the thickness of the grown crystal. The appropriate temperature distribution for growing wide ribbons is determined. As a result, growth of an 8.4 cm wide ribbon is achieved. The dependence of the crystal thickness and width on the growth rate and system temperature is also investigated.

X-Ray Topographic Study of Lattice Defects Related with Degradation of GaAs-Ga1-xAlxAs Double-Heterostructure Lasers

Dark-spot defects (DSD) which are primary sources of the rapid degradation of GaAs-Ga1-xAlxAs double-heterostructure (DH) lasers are studied by X-ray topography. X-ray topographs of the defective parts of a DH wafer were obtained through the use of micro-X-ray topography. This technique is effective for small specimens of 0.01~1 mm2. In addition, it is suggested that elimination of a dislocation from a DH wafer is possible, not by introducing a misfit dislocation, but by using a dislocation-free GaAs substrate.