Oxidation-induced Stacking Fault Ring Research Articles

The influence of point defect on the behavior of oxygen precipitation in CZ-Si wafers

The effect of heat treatment conditions and point defects on oxygen precipitation was investigated with various grown-in defect region wafers. The behavior of oxygen precipitation depends on the nucleation temperature and the type and the concentration of point defects. The peak temperature of nucleation for oxygen precipitation is 687–734°C in vacancy-rich, oxidation-induced stacking fault ring, interstitial Si-rich and interstitial pure regions. In vacancy-pure region, the peak temperature of nucleation is about 870°C. The vacancy plays an important role in increasing the peak temperature of nucleation for oxygen precipitation.

Parallel computation of radiative heat transfer in an axisymmetric closed chamber: an application to crystal growth

Parallel computation of view factors for gray diffuse surfaces is studied using a combination of methods developed by the authors and other researchers, exploiting the strengths and advantages of the respective methods. Kobayashi and Miyahara (Numer. Heat Transfer Part B 28 (1995) 437) introduced the use of a path integral to calculate the view factor and this method is accurate and robust, especially near the corners which are typically problematic. Dupret et al. (Int. J. Heat Mass Transfer 33 (1990) 1849) have a less preferred means of calculating the view factor integral but their visibility or blocking algorithm allows analysis of completely arbitrary axisymmetric closed geometries. In this paper, we introduce optimizations to the Dupret blocking algorithm. The computation of view factors and blocking requires more computer time than solving for the flux, and the parallel code developed exhibits excellent scalability. The code was applied to the design of a heat shield with a controlled temerature. The growth velocity and temperature gradients are measured and studied in terms of the constraint imposed by the equation for the formation of an oxidation induced stacking fault ring, V g/ G s> C crit.

Engineering analysis of microdefect formation during silicon crystal growth

The quality of single crystalline silicon wafers used as substrates for microelectronic devices is measured in terms of the type, size and number density of microdefects formed during crystal growth and subsequent processing. Native point defects—vacancies and self-interstitials—and impurities, such as oxygen and carbon, in the silicon crystal convect, diffuse, react and aggregate, driven by species super-saturation, to form defect structures at densities that are microscopically visible. We model defect dynamics using diffusion–reaction theory in which defect types are represented as chemical species and have concentrations that are governed by conservation laws, chemical thermodynamics and kinetics, using self-consistent values of equilibrium, transport and kinetic parameters for point defects and impurities. We refer to this approach as crystal defect dynamics analysis. The purpose of this paper is to demonstrate that this approach leads to a wide range of predictions that are consistent with experiments. The results presented here focus on the two-dimensional predictions of microdefect structures under growth conditions where both voids (cluster of vacancies) and self-interstitial aggregates are seen in regions of the crystal separated by the oxidation-induced stacking fault ring (OSF-ring). The location and structure of the OSF-ring is predicted in terms of point defect dynamics near the melt/crystal interface, which results in an annular region with almost balanced point defect concentrations (centered at r≡RΔ=0), and in terms of a peak (centered at r≡RCV,max) in the residual vacancy concentration after cluster formation. This residual vacancy concentration facilitates oxide precipitation during crystal growth, which seeds stacking fault formation during subsequent oxidation. Calculations show that RCV,max⩽RΔ=0 with both values scaling with V/G(R), where V is the crystal pull rate and G(R) is the axial temperature gradient at r=R along the melt/crystal interface. An annulus just outside the OSF-ring (centered at r≡Rfree,RCV,max⩽Rfree⩽RΔ=0) is identified where almost no microdefects are present, thereby identifying the temperature field that leads to almost perfect silicon.

Nitrogen-doping effect in a fast-pulled Cz-Si single crystal

In the nitrogen-doped and fast-pulled crystals, the nitrogen plays a role to disturb the growth of vacancy clusters by reducing the vacancy-rich region and the vacancy concentration. Thus, the oxidation-induced stacking fault ring (OSF-ring) is formed near the edge region and its width depends on the nitrogen-doping concentration. The vacancy clustering is severely suppressed and the increased residual vacancy causes the anomalous oxygen precipitation. A conceptual model based on the reduction of point defect concentration could explain the nitrogen-doping effects.

Numerical analysis for the dynamics of the oxidation-induced stacking fault in czochralski-grown silicon crystals

The continuum model of point defect dynamics to predict the concentration of interstitial and vacancy is established by estimating expressions for the thermophysical properties of point defects and the point defect distribution in a silicon crystal and the position of oxidation-induced stacking fault ring (R-OiSF) created during the cooling of crystals in Czochralski silicon growth process are calculated by using the finite element analysis. Temperature distributions in the silicon crystal in an industrial Czochralski growth configuration are measured and compared with finite volume simulation results. These temperature fields obtained from finite volume analysis are used as input data for the calculation of point defect distribution and R-OiSF position. Calculations of continuum point defect distributions predict the transition between vacancy and interstitial dominated precipitations of microdefects as a function of crystal pull rate (V). The dependence of the radius of R-OiSF (ROiSF) on the crystal length with fixed growth rate for a given hot zone configuration is examined. The ROiSF is increased with the increase of crystal length. These predictions from point defect dynamics are well agreed with experiments and empirical V/G correlation qualitatively, where G. is the axial temperature gradient at the melt/crystal interface.

Defect engineering of Czochralski single-crystal silicon

Modern microelectronic device manufacture requires single-crystal silicon substrates of unprecedented uniformity and purity. As the device feature lengths shrink into the realm of the nanoscale, it is becoming unlikely that the traditional technique of empirical process design and optimization in both crystal growth and wafer processing will suffice for meeting the dynamically evolving specifications. These circumstances are creating more demand for a detailed understanding of the physical mechanisms that dictate the evolution of crystalline silicon microstructure and associated electronic properties. This article describes modeling efforts based on the dynamics of native point defects in silicon during crystal growth, which are aimed at developing comprehensive and robust tools for predicting microdefect distribution as a function of operating conditions. These tools are not developed independently of experimental characterization but rather are designed to take advantage of the very detailed information database available for silicon generated by decades of industrial attention. The bulk of the article is focused on two specific microdefect structures observed in Czochralski crystalline silicon, the oxidation-induced stacking fault ring (OSF-ring) and octahedral voids; the latter is a current limitation on the quality of commercial CZ silicon crystals and the subject of intense research.

Defects in the Oxidation-Induced Stacking Fault Ring Region in Czochralski Silicon Crystal

We have examined the defects in the oxidation-induced stacking fault (OSF) ring region in the as-grown Czochralski silicon crystals subjected to in situ annealing by the halt of pulling during crystal growth using secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) in order to investigate the nature of OSF nuclei. Oxygen aggregates were observed in the ring region in the crystals held for 4 h and 16 h using SIMS. The aggregate density in the crystal held for 16 h corresponded to the density of the grown-in defects without a flow pattern revealed by non-agitated Secco etching. TEM observation indicated that one of the grown-in defects in the ring region in the crystal held for 4 h was oxygen precipitate with a dislocation loop. OSF density decreased with holding time and density of another defect which was not an OSF increased with holding time in the ring region held at temperatures below about 1060°C. We believe that the OSF nuclei were oxygen precipitates and the dislocation loop was appeared around the precipitate during the halt of pulling process, so that OSF nuclear density was decreased.

Crystal Defects in Highly Boron Doped Silicon

Si wafers with boron concentrations up to 2 ⋅ 1019 cm−3 were characterized by delineating defects with SC1 solution and analyzing them with respect to crystal originated particles (COP). No oxidation induced stacking fault (OSF) ring appears, and the whole wafer displays a homogeneous COP density after SC1 treatment for low boron doped ingots in a resistivity range of several ohms centimeter and appropriate pulling conditions. Without modification of the crystal pulling process but increasing boron concentration the radial COP distribution changes. The area with a high COP density shrinks and vanishes in the center of the wafer when the boron concentration approaches a level of about 1019 cm−3. Adjacent to the area of high COP density an OSF ring is found, similar to the case of low boron doped material at reduced pulling rate. It is assumed that boron doping at a sufficiently high level modifies the balance of vacancies and interstitials generated in the crystal pulling process and changes the radial defect distribution in the silicon crystals.

Influence of boron concentration on the oxidation-induced stacking fault ring in Czochralski silicon crystals

The influence of the boron doping level in the range of 1 × 1015-2 × 1019 cm−3 on the position of the oxidation-induced stacking fault ring (R-OSF) in silicon crystals has been investigated by experiments and numerical simulation. For low boron-doped crystals, the position of the R-OSF is described by a critical value Ccrit defined by the ratio of the pull rate and the temperature gradient in the crystal at the solid/liquid interface. Boron concentrations higher than 1017 cm−3 shift the position of the R-OSF towards the wafer center without change of growth parameters. The critical value Ccrit converts into a function Ccrit(CB, depending linearly on the boron concentration CB. Crystal-originated particles (COP) and gate oxide integrity (GOI) yield distributions which are consistent with the R-OSF pattern. A low COP density and a high GOI yield are observed outside the ring; a high COP density and a medium GOI yield in the inner region bordered by the ring. It is assumed that boron atoms modify the thermodynamical properties of vacancies and self-interstitials.

Transient computer simulation of a CZ crystal growth process

The use of numerical simulation for improving the bulk growth process is illustrated by means of two sets of investigations. On the one hand, the time dependent heat transfer during CZ silicon growth has been numerically simulated and compared to experiments for an industrial furnace. An excellent agreement between simulation and experiment is observed for both heater power and crucible temperature. On the other hand, 4″, 6″ and 8″ CZ crystals were grown with different heat shields. It has been found that the critical pull rate Vcrit, under which the oxidation induced stacking fault (OSF) ring vanishes in the wafer center, varies with the crystal diameter and the type of heat shield. A calculation of the axial temperature gradient at the solid/liquid interface for each combination reveals that the critical pull rate is proportional to this axial temperature gradient, which, in turn, is a function of the crystal diameter and heat shield. A precise law governing OSF ring formation has been established. In addition, improved processing conditions can be determined by an extensive use of simulation results.

Some unsolved problems on Czochralski growth of silicon from the viewpoint of materials modeling

In this report the oxidation-induced stacking fault ring in Czochralski-grown Si, which is not fully understood in spite of the practical importance, is discussed, as well as the necessity of materials modeling to understand it.

The dependence of bulk defects on the axial temperature gradient of silicon crystals during Czochralski growth

4″, 6″ and 8″ Cz crystals were grown with different heat shields which protect the growing crystals against radiation emitted from the melt surface and hot graphite parts, thereby determining their thermal environment. It was found that the critical pull rate, at which the oxidation induced stacking fault (OSF) ring vanishes in the wafer centre, varies with the crystal diameter and the type of heat shield. A calculation of the axial temperature gradient at the solid/liquid interface for each crystal diameter/heat shield combination revealed that the critical pull rate is proportional to this axial temperature gradient G, which, in turn, is a function of the crystal diameter and heat shield. Thus, the critical pull rate is entirely determined by the axial gradient G. The OSF ring appears in the wafer centre when the equation V G = C crit = 1.3 × 10 7t-3 cm 2 min −1 K −1 holds ( V is the pull rate). For V G > C crit flow pattern/D-defects are observed, whereas V G < C crit describes the condition for the growth of large pit defects.