Growth Of Single-crystal Silicon Research Articles

Potential of using inert gas flows for controlling the quality of as-grown silicon single crystal

We have improved the well-known Czochralski single crystal silicon growth method by using two argon gas flows. One flow is the main one (15–20 nl/min) and is directed from top to bottom along the growing single crystal. This flow entrains reaction products of melt and quartz crucible (mainly SiO), removes them from the growth chamber through a port in the bottom of the chamber and provides for the growth of dislocation-free single crystals from large weight charge. Similar processes are well known and have been generally used since the 1970s world over. The second additional gas flow (1.5–2 nl/min) is directed at a 45 arc deg angle to the melt surface in the form of jets emitted from circularly arranged nozzles. This second gas flow initiates the formation of a turbulent melt flow region which separates the crystallization front from oxygen-rich convective flows and accelerates carbon evaporation from the melt. It has been confirmed that oxygen evaporated from the melt (in the form of SiO) acts as transport agent for nonvolatile carbon. Commercial process implementation has shown that carbon content in as-grown single crystals can be reduced to below the carbon content in the charge. Single crystals grown with two argon gas flows have also proven to have highly macro- and micro-homogeneous oxygen distributions, with much greater lengths of single crystal portions in which the oxygen concentration is constant and below the preset limit. Carbon contents of 5–10 times lower than carbon content in the charge can be achieved with low argon gas consumption per one growth process (15–20 nl/min vs 50–80 nl/min for conventional processes). The use of an additional argon gas flow with a 10 times lower flowrate than that of the main flow does not distort the pattern of main (axial) flow circumvention around single crystal surface, does not hamper the “dislocation-free growth” of crystals and does not increase the density of microdefects. This suggests that the new method does not change temperature gradients and does not produce thermal shocks that may generate thermal stresses in single crystals.

On the role of thermal gradient related stress in intrinsic defect formation during single crystal silicon growth from the melt

The incorporation of intrinsic point defects during silicon crystal growth from the melt is discussed using recent data for intrinsic point defect thermal equilibrium and diffusivity. It is shown that the impact of compressive stress on the thermal equilibrium concentration and diffusivity of vacancies and self-interstitials should be taken into account. An analytical expression is derived to quantify the relation between crystal diameter and the critical pull rate window to grow defect free crystals. The results are compared with published experimental data on grown-in defect formation for crystal diameters ranging from 1 to 40cm. It is shown that both the thermal stress due to the axial thermal gradient at the melt/solid interface and the silicon yield stress at high temperature play a crucial role. An empirical expression is proposed to describe the dependence of the thermal gradient on pulling rate.

On the impact of stress on intrinsic defect formation during single crystal silicon growth

The incorporation of intrinsic point defects during silicon crystal growth from the melt is discussed using most recent data for intrinsic point defect thermal equilibrium concentration and diffusivity. It is shown that by taking into account the impact of stress on the thermal equilibrium concentration of vacancies and self-interstitials, the intrinsic point defect properties derived from self- and metal-diffusion experiments can be used to model point defect incorporation and clustering during silicon crystal growth from the melt. The solution is however not unique and a large uncertainty still remains on the real thermodynamic parameters of both intrinsic point defects. Only comparison with a wide range of experimental data from crystal pulling experiments—taking into account also the stress effects—will allow to further narrow down the uncertainty ranges on the intrinsic point defect properties in silicon.

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. © 2002 The Electrochemical Society. All rights reserved.

Rapid Thermal Chemical Vapor Deposition: Selective Epitaxial Silicon Growth (SEG)

ABSTRACTRapid Thermal Chemical Vapor Deposition (RTCVD) offers great promise for deposition of high-quality, thin, abrupt interface epitaxial films. In addition, RTCVD systems operate under cold wall environment to minimize particles and cross contamination. SEG of silicon provides both isolation and active device wells with fine dimensional control. A combination of RTCVD and SEG holds great promise for future VLSI circuit technologies. In this paper, we present our results on selective growth of single crystal silicon using RTCVD.

Silicon whisker growth and epitaxy by the vapour-liquid-solid mechanism

A study has been made of the growth of single crystal silicon by the recently proposed vapour-liquid-solid mechanism. The reduction of silicon tetrachloride with hydrogen has been used to deposit silicon via thin liquid alloy zones of gold/silicon and nickel/silicon on to single crystal substrates. Epitaxial layers and orientated whiskers are obtained using gold, while the growth from nickel appears random. Various growth forms are explained in terms of the temperature variation of the surface tension of the liquid alloy. The work emphasizes the value of the vapour-liquid-solid mechanism and has shown the importance of temperature and temperature gradients in its control.