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A theoretical interpretation of dislocation glide in silicon
Published in A G Cullis, S M Davidson, G R Booker, Microscopy of Semiconducting Materials, 1983, 2020
There has been much experimental work featuring dislocation motion in silicon and germanium, including its doping dependence (e.g. George, Escaravage, Champier and Schröter 1972, Patel, Testardi and Freeland 1976, Kulkarni and Williams 1976 and recently Hirsch, Ourmazd and Pirouz 1981 and Louchet 1981). Amongst the peculiarities noted in measuring dislocation velocity, the recent observation that those dislocations in swirl-free float-zone silicon subjected to the highest climb forces glide fastest, ceteris paribus, seems most strange (Alexander, Kisielowski-Kemmerich, Weber 1982). Naturally there have been parallel experiments conducted by Russian groups (e.g. Erofeev and Nikitenko 1971, Bondarenko, Erofeev, Nikitenko 1973, Nikitenko, Farber, Bondarenko 1982) which have also uncovered a host of unexplained phenomena (e.g. the asymmetry of dislocation glide and the existence of glide plane débris in the wake of moving dislocations).
Fabrication Tools
Published in Vinod Kumar Khanna, Introductory Nanoelectronics, 2020
Poly-Si is transformed into a single crystal form using a float-zone process in which the vertically held EGS rod is passed through an RF heating coil (Figure 16.2). A localized zone of molten silicon is formed from which the single-crystal silicon is grown by contacting with seed crystal from one end. The growth process is carried out in vacuum or under constant purging with an inert gas. As the float zone silicon is not in contact with any crucible, it is free of any impurities from the crucible. The oxygen and carbon content in it is below 5 × 1015 cm−3. Silicon wafers > 200 mm diameter cannot be grown using this method due to difficulties with the floating zone.
Introduction to Silicon Wafer Processing
Published in Kumar Shubham, Ankaj Gupta, Integrated Circuit Fabrication, 2021
In the FZ process, A EGS rod which is polycrystalline in nature clamped at both ends with bottom end fused with the seed of desired single crystal orientation. This is taken in an inert gas furnace and then melted along the length of the rod by a traveling radio frequency (RF) coil. RF coil provides power which generates large current in the Si and locally melts it through I2R heating. Usually the molten zone is about 2 cm long. RF field generated levitation and surface tension keep the system stable. If the seed end zone is initiated to melt and the rod is slowly moved up then solidifying region has the same orientation as of the seed. For reduction of gaseous impurities, the furnace is filled with an inert gas like argon. Also, since the process requires no crucible so it can be used to produce oxygen free Si wafers. The difficulty is to extend this technique for large wafers, since the process produces large number of dislocations. The process produces large number of dislocations so it is used for small specialty applications requiring low oxygen content wafers. Doping of the crystal can be accomplished either by starting with doped poly-silicon rod, a doped rod, or by maintaining a gaseous ambient during the FZ process that contains a dilute concentration of desired dopant. A disadvantage of float zone growth is the struggle of introducing identical concentration of dopants. There are four methods that can be used: core doping, pill doping, gas doping, and neutron transmutation. The starting material of Core doping is a doped Poly-silicon rod. On top of this rod, additional undoped poly-silicon is deposited until the average desired concentration is reached. The process can be repeated through several generations if necessary. Core doping is the preferred process for boron because its diffusivity is high and because it does not tend to evaporate from the surface of the rod. The concentration of boron in a boule is quite uniform after neglecting the first few melt lengths. Doping is accomplished through the use of gases doping material such as PH3, AsCl3, or BCl3. The gas may be injected as the poly-silicon rod is deposited, or it may be injected at the molten ring during the float zone refining. Pill doping is provided by drilling a small hole in the top of the rod and inserting the dopant in the hole. If the dopant has a small segregation coefficient then it will be carried with the melt and passes throughout the length of the boule resulting in modest non-uniformity. Gallium and indium doping work well in this manner. Finally, for light n-type doping, float zone silicon can be doped through a process known as transmutation doping. In this process, the boule is exposed to a high brightness neutron source.
Impact of germanium doping on the mechanical strength of low oxygen concentration Czochralski silicon wafers
Published in Philosophical Magazine, 2021
Junnan Wu, Robert W. Standley, Katharine M. Flores
In this work, we grow a 200 mm Ge-doped high resistivity and very low oxygen concentration silicon ingot by the CZ method, and investigate the impact of Ge on the dislocation mobility in mechanical bending experiments. The dislocation mobility in the Ge-doped sample is compared with that of N-doped CZ silicon with similar oxygen concentration, N-doped float-zone silicon with essentially zero oxygen concentration, and undoped CZ silicon samples with high oxygen concentration. Using a three-point bending technique, the resolved shear stresses required to move dislocations previously locked by impurity decoration are measured for Ge-doped and undoped control samples. By varying the temperature and duration of the impurity-locking anneal, the activation energy of oxygen diffusion and binding enthalpy of oxygen to the dislocation cores are extracted from the unlocking stress for both Ge-doped and control samples.
Laser-dilatometer calibration using a single-crystal silicon sample
Published in International Journal of Optomechatronics, 2019
Ines Hamann, Josep Sanjuan, Ruven Spannagel, Martin Gohlke, Gudrun Wanner, Sönke Schuster, Felipe Guzman, Claus Braxmaier
To verify the accuracy and systematic uncertainties of our dilatometer with respect to the CTE measurements we have chosen single-crystal silicon (SCS) as a sample material. Silicon is a standard reference material for expansion measurements. It is available in extremely high-purity form and can be used over a wide temperature range for calibration purposes based on its high melting temperature. The CTE has been well studied[21–24] for many years. Our sample was processed by Freiberger Silicium GmbH from a float-zone silicon in a tube shape size with outer diameter of 28 mm to fit in our sample support and inner diameter of 20 mm to provide grip for our mirror mounts.