Susumu Sakai

ANALYSIS OF OXYGEN EVAPORATION RATE AND DISSOLUTION RATE CONCERNING CZOCHRALSKI SI CRYSTAL GROWTH : EFFECT OF AR PRESSURE

A small sessile drop sample and a small crucible sample were used for measuring oxygen evaporation rate and dissolution rate. Dependence of the oxygen evaporation rate (from surface of silicon melt) and dissolution rate (from silica glass to silicon melt) on Ar pressure from 20 to 3800 Torr was investigated at different temperatures. The oxygen evaporation rate and dissolution rate increased monotonically with decreasing Ar pressure, and increased remarkably with increasing temperature. The relationship between the oxygen dissolution rate and the interfacial phase of the brownish rings has also been investigated. The interfacial phase disappeared when the oxygen dissolution rate was sufficiently high.

Analysis of an Oxygen Dissolution Process Concerning Czochralski (CZ) Si Crystal Growth using the Sessile Drop Method.

A new sessile drop method has been developed for measuring the oxygen dissolution rate from silica glass to silicon melt. Compared to the oxygen dissolution rate obtained using a conventional measurement method, a much larger value has been obtained with the sessile drop method. The experimental accuracy of the sessile drop method was analyzed, and it was found that the main error resulted from the weight change of a blank silica plate following heat treatment. A rectification method was suggested.

Surface of Silica Glass Reacting with Silicon Melt: Effect of Raw Materials for Silica Crucibles.

The density of brownish spots formed on the surface of silica glass through the reaction with silicon melt is studied using three types of silica glass, that are made from natural quartz powder, synthetic silica powder, and Al-doped synthetic silica powder. The density of the brownish spots was higher in natural quartz glass (NQG) than in synthetic silica glass (SSG) and in Al-doped synthetic silica glass (ASG). The result is consistent with that of the devitrification of silica glass observed in the interior of the bulk glass after a heat treatment. Aluminum and calcium are detected as aggregates in the devitrification spots of NQG. It is noted that ASG, containing a comparable concentration of well-dispersed aluminum, shows a significantly lower density of brownish spots and internal devitrification spots than NQG. Thus, it is considered that the formation of the brownish spots originates from the devitrification of silica glass caused by aggregates of impurities.

Effect of TiO2 Photocatalyst on Odorous Gases Using Glass Fiber Filter for Repeatable Use

A glass fiber filter coated with TiO2 was adopted as a photocatalyst to remove methyl mercaptan and ammonia gases under black light irradiation. A single filter alone had a high capacity to remove about 30% of both gases within 3–4 h. Sulfate ion (SO42-) from the methyl mercaptan, nitrogen oxide (NOx) and nitrate ion (NO3-) from ammonia were generated due to the photocatalyst reaction. However, the majority of ammonia gas trapped on the filter was stuck to the surface without any reactions. Rinsing with distilled water was a very effective procedure for cleaning the filter.

Expansion Behavior of Bubbles in Silica Glass Concerning Czochralski (CZ) Si Growth

The expansion behavior of bubbles in silica glass concerning Czochralski silicon crystal growth has been investigated. It is found that most of the bubbles expand considerably under an Ar atmosphere of 20 Torr and 1500°C. The bubble expansion can be classified into three groups. The first group shows huge expansion which is related to the existence of carbon in the silica glass. In the second group the expansion seems to obey some rule, and most of the bubbles in the silica glass undergo this kind of expansion. The expansion shown by the second group is called normal expansion in this work. The normal expansion depends on the silica material. In the third group some bubbles expand only slightly, and this kind of expansion occurs only near the surface of the glass.

Transient analysis of LE‐VGF growth of compound semiconductors

A finite difference simulation for the bulk single crystal growth of indium phosphide by the liquid encapsulated vertical gradient freezing (LE‐VGF) method with a flat bottom crucible is presented. In order to treat a curvature interface, the boundary fixing method is applied. The transient behavior of the flow and temperature fields, the melt/crystal interface shape and the growth rate during growth are studied numerically. The crystal growth rate is not constant although the temperature lowering rate is constant. The effect of crucible thickness, thermal conductivity of the crucible and temperature of the growth furnace wall on the crystal growth behavior are discussed.

AXISYMMETRIC TWO-DIMENSIONAL STEADY MARANGONI CONVECTION IN A FLOATING HALF-ZONE UNDER MICROGRAVITY CONDITIONS

Laminar, steady, and two-dimensional Marangoni convection in a liquid bridge of the floating half-zone configuration under a microgravity field was numerically analyzed. In order to obtain accurate solutions, a nonuniform mesh was used. The effect of mesh refinement on the numerical results is discussed. After confirmation of the validity of the numerical code by comparing the experimental results obtained using a drop shaft and the present results, the effects of the Prandtl number, the rotation of the upper and /or lower rod, the aspect ratio, and the liquid volume on flow and temperature fields are discussed.

Determination of oxygen dissolution rate from silica to silicon melt at solid (silica glass)/melt/gas triple junction

In growth of single crystal silicon by the Czochralski technique, it is important to know the actual value of the oxygen dissolution rate from silica glass to silicon melt at the triple-junction point of solid (silica glass)/liquid (silicon melt)/gas (argon). For the purpose of determining this value, a numerical simulation model was developed for the sessile drop experiment. In order to satisfy the presence of oxygen concentration along the melt/gas interface, a new interface condition was introduced in the model. Numerical simulation results are in good agreement with experiments. The values of oxygen dissolution rate at the condition corresponding to the triple-junction point (a very small drop that is not possible to form experimentally) were computed. The computed value at this point is about two times larger than the experimentally measurable value by the sessile drop method.

Development of a Sessile Drop Method Concerning Czochralski Si Crystal Growth

A sessile drop method for the measurement of the oxygen dissolution rate from silica glass to silicon melt proposed previously has been further developed. The main error in the measurement was the weight loss of the silica plate itself because of the reaction between the silica plate and the carbon crucible. A pyrolytic boron nitride (PBN) plate was placed between the silica plate and carbon crucible, and results showed that the error was reduced effectively using the protective PBN plate. As an application of the sessile drop method, the effect of OH content in different silica materials on the oxygen dissolution rate was also investigated. There was no evident difference in the dissolution rate from the different kinds of silica materials with different OH concentrations.