Growth Of Large-diameter Crystals Research Articles

Optimization of bulk microdefect performance in epitaxial silicon wafer

Bulk microdefects (BMDs) in epitaxial silicon wafers are pivotal for advanced node integrated circuits, offering enhanced mechanical strength and metal gettering capabilities. This study introduces two heat treatment procedures to optimize BMD density and radial uniformity in lightly doped wafers, addressing the challenges associated with large-diameter crystal growth and the thermal budget constraints of advanced node processes. We demonstrate that Rapid Thermal Annealing (RTA) at temperatures exceeding 1175 °C significantly improves BMD uniformity. A post-RTA stabilization step, when performed prior to epitaxial growth, enhances BMD density by retaining nuclei generated by RTA. Conversely, when the RTA with stabilization step follows epitaxial growth, a higher BMD density and larger BMD size are achieved. Light Scattering Tomography (LST) analysis confirms the optimal conditions for these treatments. The findings contribute to the semiconductor industry by optimizing wafer properties for high-performance ICs.

Theoretical Study of Impact of Internal and External Stresses on Thermal Equilibrium Concentrations of Intrinsic Point Defects in Doped Si Crystals

Intrinsic point defects (vacancy V and self-interstitial I) play an important role in a wide variety of processes in Si crystals. During large-diameter crystal growth, the thermal stress, which is the compressive internal stress, of around several tens of MPa is originated in Si crystals. In the LSI (Large Scale Integration) using Si substrate, external stress of around GPa order is applied to the channel region between source and drain in the MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) to enhance the carrier mobilities. These internal and external stresses affect V and I; thus, changing the thermal equilibrium concentrations (Ceq) of V and I in Si. To explain and engineer the intrinsic point defect behavior in Si crystals, such as in the growing Si crystals and in the channel region of Si wafers, the impact of internal or external stress on the Ceq of V (I) should be theoretically obtained in doped Si crystals. In this study, we calculated the formation energy (Ef) and relaxation volume (ΔVol) of V (I) from the 1st to 5th sites around dopant (B, C, Sn, P, and Sb) atoms in isotropically stressed Si by using density functional theory (DFT) to determine the formation enthalpy (Hf) of V and I. The impact of isotropic internal stress (σin) or isotropic external stress (σex) on the Ceq values of V (I) in doped Si was obtained using the Hf at each site around a dopant atom. The following important information was obtained from the Ceq of V (I) in doped Si crystals. (1) The Ef and ΔVol of V (I) around the dopant atoms change depending on the site position and dopant type, (2) Ef of V (I) and ΔVol of I around the dopant atoms are hardly affected by the stresses, while ΔVol of V around the dopant atoms changes due to the stresses, (3) B and C atoms make the Si crystal more I-rich, while Sn, P, and Sb atoms make the Si crystal more V-rich, and (4) the compressive σin makes the doped Si crystal more V-rich, and its impact depends on the type of dopant, while the σex has an opposite impact except for C. The data summarizing the impact of stress in doped Si are useful as the more precisely control of the point defect behavior is required in more advanced Si crystals.

Influence of reduced working frequencies on the floating‐zone growth of silicon single crystals

AbstractLowering the working frequency in the inductively heated floating zone growth of Si Single crystals will reduce the risk of arcing at the induction coil. This is of particular interest in the growth of large diameter crystals. In the current paper we present results from growth experiments at lower frequencies, 2 MHz and 1.7 MHz. It is found that the growth of dislocation‐free crystals is possible at these frequencies and cause distinct changes in the interface deflection and radial resistivity profiles. Results from numerical simulation of the melt flow at different frequencies are presented. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hot zone design for controlled growth to mitigate cracking in laser crystal growth

Cracking is a major problem during large diameter crystal growth. The objective of this work is to design an effective hot zone for a controlled growth of Yb:S–FAP [Yb3+:Sr5(PO4)3F] laser crystal by the Czochralski technology and effective cooling that can reduce stress. Theoretical and numerical analyses are performed to study the causes of cracking, mitigate the major cracking, as well as reduce cooling time. In the current system, three locations in the crystal are prone to crack, such as the top shoulder of the crystal, the middle portion above the crucible edge, and the bottom tail portion. Based on numerical simulations, we propose a new hot zone design and cooling procedure to grow and cool large diameter crystal without cracking.

Single crystal growth by axial vibrational control technique in Czochralski configuration

Application of the axial vibration control technique to the Czochralski crystal growth (AVC–CZ) by submerging an oscillating baffle into the melt under the crystal for the large diameter crystal growth was studied. The configuration of the submerged vibrating baffle was optimized to enlarge the growing crystal diameter while keeping control on heat–mass transfer in the melt. The equalization of melt composition in the crucible whole volume and dopant concentration distribution in AVC–CZ grown NaNO3 single crystal was demonstrated.

Thermal stress inhibition in double crucible Czochralski large diameter crystal growth

In this paper we consider the problem of thermal stress inhibition in double crucible Czochralski crystal growth by means of a thermal tube with linear temperature distribution computationally determined from solution with adiabatic boundary condition, which provides the formation of a stressless one-dimensional temperature distribution along the growing crystal. We study how this linear temperature distribution applied along the thermal tube is “transferred” into the growing crystal depending on the gap between crystal and inner tube surfaces, within which complex radiative–convective heat transfer takes place. Calculations presented in the paper suggest that linear temperature distribution along the thermal tube allows an order of magnitude stress reduction in 80–100 mm diameter crystals of LiNbO 3

Advances in superconducting magnets for commercial and industrial applications

Superconducting magnets are finding increasing applications outside research laboratories, due both to new commercial and industrial demands for high magnetic fields, and to advances in magnet design and cooling technology. Applications such as minerals separation, large-diameter crystal growth and ceramic processing may benefit from the high magnetic fields and field gradients possible with superconducting magnets. While whole-body MR imaging is a well-established application of superconducting magnets in medicine, new medical applications are emerging. The challenge in designing all such magnets is to combine stringent magnetic field parameters (field profile, gradient, etc.) with economical operating costs and industrial ruggedness. Oxford Instruments is engaged with several commercial magnet applications, and the development of Cryofree(R) and helium recondensing systems has opened new opportunities to exploit superconducting magnets in an economic and reliable way. A review of the key technologies and design constraints of such magnet systems will be given. The most recent commercial magnets constructed by Oxford Instruments will be described, giving focus to the innovative steps which have enabled their production.

Impurity Effects in the Growth of 4H-SiC Crystals by Physical Vapor Transport

ABSTRACTSiC is an important wide bandgap semiconductor material for high temperature and high power electronic device applications. Purity improvements in the growth environment has resulted in a two-fold benefit during growth: (a) minimized inconsistencies in the background doping resulting in high resistivity (>5000 ohm-cm) wafer yield increase from 10–15% to 70-85%, and (b) decrease in micropipe formation. Growth parameters play an important role in determining the perfection and properties of the SiC crystals, and are extremely critical in the growth of large diameter crystals. Several aspects of growth are vital in obtaining highly perfect, large diameter crystals, such as: (i) optimized furnace design, (ii) high purity growth environment, and (iii) carefully controlled growth conditions. Although significant reduction in micropipe density has been achieved by improvements in the growth process, more stringent device requirements mandate further reduction in the defect density. In-depth understanding of the mechanisms of micropipe formation is essential in order to devise approaches to eliminate them. Experiments have been performed to understand the role of growth conditions and ambient purity on crystal perfection by intentionally introducing arrays of impurity sites on one half of the growth surface. Results clearly suggest that presence of impurities or second phase inclusions during start or during growth can result in the nucleation of micropipes. Insights obtained from these studies were instrumental in the growth of ultra-low micropipe density (less than 2 micropipes cm−2 ) in 1.5 inch diameter boules.

Thermal modeling of a double-neck large diameter crystal growth process

This paper describes a unique method to reduce temperature at the end of the Dash thin neck during the process of crystal growth. The thin neck from the conventional Czochralski process is subjected to larger tensile and torsional stresses in growing large diameter crystals (>200 mm) than with small diameter crystals. The challenge is how to reduce these combination stresses so that they won't exceed the yield strength of the crystal at the end of the thin neck. In this paper, we propose that after growing the thin neck, to grow a second neck with a diameter between 10 and 50 mm and about 25-76 mm long. In this way, the temperature at the thin neck will be much lower than that without the second neck and the corresponding yield strength of the silicon will be increased. A two-dimensional (2-D), axisymmetric heat conduction model was developed to predict temperature field within a crystal and demonstrated the advantage of using the double-neck method. This simplified model includes both convective and radiative boundary conditions on the crystal surfaces and applies the concept of "effective ambient temperature" to calculate radiation heat transfer. This model was validated from the conventional Dash thin neck technique. By applying this model to the double-neck method, it concludes that the height of the second neck has a major impact in reducing the crystal temperature at the end of the first thin neck. By comparing with the Dash thin-neck technique, the double-neck method can reduce the temperature at the end of the thin neck by as much as 123/spl deg/C or 12%. This dramatic temperature reduction accounts for /spl sim/2.5 times increase in the yield strength of the silicon.

Solar furnace satellite for large diameter crystal growth in space

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Oxygen in Czochralski silicon crystals grown under an axial magnetic field

Results are reported of an experimental study of axial magnetic field effects (including the effect of a weak magnetic field) on oxygen in 105–155 mm diameter silicon crystals grown in a conventional Czochralski crystal puller and in a puller with a double-crucible arrangement. The oxygen concentration and distribution in the crystals depend upon the conditions of oxygen-rich melt transport from the crucible wall to the melt-crystal interface. A regime of low oxygen (down to 2×10 17 cm -3), large diameter crystal growth has been found. The features of oxygen distribution in the crystals are qualitatively explained.

Optical properties of color centers in calcium-stabilized gadolinium gallium garnets.

The addition of small amounts of calcium during the crystal growth of large-diameter, gadolinium gallium garnet (GGG) crystals creates color centers that absorb in the near-uv region of the spectrum. Ultraviolet and \ensuremath{\gamma}-ray irradiation of the crystals produced changes in the intensities of the uv color-center bands along with a broad absorption throughout the visible spectrum. The color center that gives rise to an absorption band at 350 nm serves as a photoionizable donor center so that uv excitation results in a visible coloration of the crystals. The effects of oxidation and reduction treatments on the strength of the color-center bands and on the radiation response of the material were examined. Photoluminescence bands were observed in both reduced GGG crystals as well as crystals that were irradiated with neutrons. Visible coloration is likely to occur during flashlamp pumping of laser rods that utilize large-diameter GGG crystals as the laser host. The changes in the optical properties of the material under uv excitation indicate that the addition of small amounts of calcium to assist in the growth of large-diameter crystals is likely to result in the degradation of laser performance.

Growth of 40 mm diameter silicon crystals by a pedestal technique using electron beam heating

Silicon crystals 40 mm in diameter were grown in vacuum from a 100 mm diameter polycrystalline pedestal rod using electron beam heating. The pedestal is consumed as crystal growth progresses, thus providing a continuous, crucibleless process. An eccentric placement of the annular electron beam impact ring on the pedestal melt is essential for process continuity and large diameter crystal growth. Crystals up to 0.9 m in length are grown by this process at growth rates in excess of 4.0 mm/min. The properties of these silicon crystals are similar to those of one-pass vacuum zoned crystals: dislocation density = 3 × 10 4/cm 2, lifetime > 50 μsec, oxygen and carbon content - none detected at 0.1 and 0.3 ppma detection limits respectively, radial resistivity variation < 10% for 30 ohm-cm, n-type doping. No tungsten contamination from the electron gun filament was seen at the 1.0 ppbw detection limit. Outstanding practical features of the pedestal method are the high crystal purity coupled with a relatively low material cost and fast crystal growth rate.