Koji Sumino

In situ X-ray topographic study of the dislocation mobility in high-purity and impurity-doped silicon crystals

Abstract An in situ X-ray topographic technique using a high-power X-ray generator has been used to study the dislocation mobility at elevated temperatures in the stress range 1·2-40 MN m−2 for pure and impurity-doped silicon crystals. The variation of velocity with stress for both 60° and screw dislocations in high-purity crystal is linear throughout the whole stress range investigated, the activation energies for motion being independent of stress. No previously published theoretical models are able to account for the measured velocities quantitatively. Effects of impurities, such as oxygen, carbon, nitrogen, phosphorus and boron, are investigated in detail. Generally, the impurities bring about a deviation from linearity of the variation of velocity with stress under low stresses. Dislocations originally moving in impure crystals are immobilized when the stress becomes lower than a critical value. These phenomena are interpreted in terms of the development of an impurity atmosphere around slowly moving...

Effects of nitrogen on dislocation behavior and mechanical strength in silicon crystals

The characteristics of dislocation behavior and mechanical strength in tensile tests are investigated on the silicon crystals that are doped with nitrogen at the time of crystal growth by the floating‐zone technique. These are compared with those in the usual floating‐zone‐grown silicon crystals. Nitrogen atoms dispersed in a silicon crystal are shown to have no influence on the velocities of dislocations in motion in the temperature range above 600 °C. Dislocations in the nitrogen‐doped crystal are, however, immobilized while the crystal is kept under a low or zero applied stress at elevated temperatures. Like Czochralski‐grown silicon, nitrogen‐doped silicon shows a much higher yield strength than usual floating‐zone‐grown silicon when crystals are dislocated. It is concluded that interstitial nitrogen atoms bring about the hardening of silicon crystals through locking of dislocations upon congregating on the latter.

Impurity effects on the generation, velocity, and immobilization of dislocations in GaAs

The effects of various kinds of impurities, Al, In, Si, Te, and Zn, on the dynamic behavior of dislocations in GaAs crystals are investigated. The dislocation generation from a surface scratch is suppressed by the doping of the impurities. Generally, the suppression effect of any given kind of impurities depends on the type of dislocations to be generated. However, no systematic dependence on the size misfit or the electrical activity of the impurity atom is found in the suppression efficiency. The immobilization of originally fresh dislocations due to aging at elevated temperature is investigated. The results are interpreted to be due to the gettering of impurities by the dislocations. The feature of the suppression effect in dislocation generation is well correlated to that of the dislocation immobilization due to impurity gettering. It is concluded that the suppression of dislocation generation by impurity doping originates from dislocation immobilization due to impurity gettering. Isovalent impurities...

Quantitative electron‐beam tester for defects in semiconductors (CL/EBIC/SDLTS system)

A pulsed electron beam testing system was developed for quantitative analysis of optical and/or electrical properties of defects in semiconductors. This system can control not only the electron beam but also detect and record the absolute values of light intensity: cathodoluminescence (CL), electron‐beam‐induced current (EBIC), and scanning deep level transient spectroscopy (SDLTS). Several improvements were made to enable accurate quantitative measurement. An optical system with an ellipsoidal mirror of low magnification was designed to make uniform collection efficiency of CL over a wide specimen area. A photon counting system and a lock‐in amplifying system were implemented to measure absolute value of light intensity. A quantitative EBIC or SDLTS system was also incorporated to this system. The combined system of CL/EBIC/SDLTS can both image the distribution of defects and study their characteristics.

Mechanical strength of silicon crystals as a function of the oxygen concentration

Mechanical strengths of silicon crystals involving oxygen at various concentrations up to 1018 atoms/cm3 are investigated with the use of crystals grown by the Czochralski technique in magnetic field. Oxygen atoms dispersed on interstitial sites at any concentration have almost no influence on the dislocation processes that control the mechanical behavior of a dislocation‐free crystal. Oxygen atoms in a dislocated crystal lock dislocations effectively and result in the strengthening of the crystal. Locking of dislocations becomes more effective as the concentration of oxygen in the crystal increases. Softening of crystals due to precipitation of oxygen at elevated temperature occurs rapidly in highly concentrated crystals with oxygen, but is almost absent or takes place slowly in crystals of oxygen concentrations lower than about 5×1017 atoms/cm3.

Nitrogen-Oxygen Complexes as Shallow Donors in Silicon Crystals

Optical absorption of silicon crystals involving nitrogen and oxygen is investigated at low temperature. New absorption lines are found and attributed to seven defect levels that act as shallow donors. The characteristics of the absorption lines are well described by the effective mass approximation. Five among these seven levels are related to complexes of nitrogen and oxygen atoms.

Effect of nitrogen–oxygen complex on electrical properties of Czochralski silicon

Effect of nitrogen–oxygen (N–O) complexes on electrical properties of nitrogen‐rich Czochralski (CZ) silicon grown in a nitrogen atmosphere has been investigated during annealing in the temperature range from 650 to 1000 °C. Electrical and low temperature (8 K) Fourier transmission infrared spectrometer (FTIR) measurements point out that the carrier concentration of the nitrogen‐rich silicon varies with the annealing time and temperature, which is due to the formation and elimination of the N–O complexes acting as shallow thermal donors. After the N–O complexes are eliminated by annealing above 900 °C the carrier concentration of the nitrogen‐rich silicon is stabilized. It is suggested that the N–O complexes attract more oxygen atoms to form new electrically inactive N–O clusters, and lose their electrical activity.

Influence of oxygen precipitation along dislocations on the strength of silicon crystals

The mechanical strength of dislocated crystals of Czochralski‐grown silicon as influenced by the precipitation of oxygen impurities on dislocations was investigated. The yield strength increases during the early stage of precipitation of silicon oxide, but decreases remarkably during the later stage of precipitation. The enhancement of the yield strength is brought about by the immobilization of dislocations due to locking by closely aligned precipitates along the dislocations during the early stage of precipitation. The locking effect diminishes during the late stage when precipitates on dislocations coalesce with the generation of free portions of dislocations with large separation.

Gettering of copper by bulk stacking faults and punched‐out dislocations in Czochralski‐grown silicon

The characteristics of Cu precipitation on various types of defects associated with oxygen precipitation in Czochralski‐grown silicon are investigated by transmission electron microscopy and the electron‐beam‐induced‐current technique. Specimens containing dominantly either punched‐out dislocations or bulk stacking faults were intentionally contaminated with Cu at various temperatures and cooled at three different rates. Colonies of Cu precipitates developed irrespective of cooling rate, apparently originating from punched‐out dislocations developed around oxygen precipitates. In heavily contaminated specimens cooled fast from the contamination temperature, Cu also precipitates on Frank partial dislocations bounding stacking faults. During slow cooling, precipitation of Cu takes place on Frank partials only in lightly contaminated specimens but never in heavily contaminated specimens. Cu precipitates in colonies are thermally more stable than those formed on Frank partials. It is concluded that punched‐ou...

Czochralski growth of Ge1 − xSix alloy crystals

Single crystal Ge1 − xSix alloys of composition 0 < x < 0.64 were grown by the Czochralski method. In particular, a single crystal 20 mm in diameter and 60 mm in length with variable composition 0.004 < x < 0.03 along the growth direction, and a crystal 12 mm in diameter and 20 mm in length with composition 0.21 < x < 0.25 were obtained. The crystals became Ge rich along the growth direction as determined by energy dispersive X-ray (EDX) spectroscopy. Fine striation structures in the crystals were observed by X-ray topography.