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CRYSTAL GROWTH, PROCESS, EXPLANATION, PROCESS, INTRO, ALL ABOUT WAFER,…
CRYSTAL GROWTH
WAFER PROCESSING
- a procedure composed of many repeated sequential processes to produce complete electrical or photonic circuits
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WAFER ORIENTATION
- The orientation of the crystallographic plane in which the crystal grew.
Types
PRIMARY FLAT
- indicates crystallographic planes of high symmetry
SECONDARY FLAT
- it's position relative to primary flat or its absence is indicating the doping type and the orientation of wafer.
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PROCESS
Discovered:Polish scientist Jan Czochralski, in 1916
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This material cools gradually, taking on the same crystalline structure as the seed crystal.
pulled from the melt, it draws with it a layer of molten material
Dopant impurity atoms can added to the molten intrinsic material to dope changing it into n-type or p-type extrinsic
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controlling the temperature gradients, rate of pulling and speed of rotation, it , single-crystal from the melt.
During growth, the walls of the crucible also dissolve into the melt
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EXPLANATION
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principle of the Bridgman technique is the directional solidification by translating a melt from the hot zone to the cold zone of the furnace.
the polycrystalline material in the crucible needs to be melted completely in the hot zone and be brought into contact with a seed at the bottom of the crucible
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seed will be re-melted after the contact with the melt. This provides a fresh interface for the crystal growth
After the whole crucible is translated through the cold zone the entire melt converts to a solid single-crystalline ingot.
temperature at the bottom of the crucible falls below the solidification temperature and the crystal growth is initiated by the seed at the melt-seed interface.
Merely 60% of the polycrystal silicon can be processed to wafers for photovoltaics. The rest gets lost in the sawing and cutting process.
Due to a directed and controlled cooling process of the cast, zones of aligned crystal lattices are created.
PROCESS
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A needle-eye coil that can run through the rod is activated to provide RF power to the rod, inducing strong edy current and melting a 2-cm long zone in the rod
Starting from the seed end, the coil is then moved through the rod, and the molten zone moves along with it.
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polycrstalline rod is mounted vertically inside a chamber, which may be under vacuum or filled with an inert gas
FZ growing equipment can also use a stationary coil, coupled with a mechanism that can move the rod through it.
movement of the molten zone through the entire length of the rod purifies the rod and forms the near-perfect single crystal.
In the float zone process, dopants and other impurities are rejected by the re-growing of silicon crystal.
Impurities tend to stay in the liquid and refining can be accomplished, especially with multiple passes
INTRO
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CZ technique has to face problems arising from the very high pressures of As and P at the melting temperature of the compounds.
Different vapour pressures of the compound constituents causing the more volatile one to evaporate away from the melt.
At the temperature required to melt the higher temperature material, the lower melting-point material has evaporated.
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It seals the melt by covering it with a molten layer of a second materialencapsulate must of course be made of a material that is less dense than the material in the crucible and must not be absorbed in the melt
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INTRO
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method of crystal growth used to obtain single crystals of semiconductors (silicon, germanium) ,metals(platinum, silver, gold) and synthetic gemstones
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Discovered:Polish scientist Jan Czochralski, in 1916
INTRO
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Harvard physicist Percy Williams Bridgman(1882-1961) and MIT physicist Donald C. Stockbarger (1895–1952).
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The process can reliably produce single crystal ingots, but does not necessarily result in uniform properties through the crystal.
EXPLANATION
The purity of an ingot produced by the FZ process is higher than that of an ingot produced by the CZ process
The float zone (FZ) process is a method for growing and purfying single-crystal silicon, GaAs, InP or other materials.
It involves the passing of a molten zone
through a polycrstalline rod that approximately has the same dimensions as the final ingot
As such, devices that require ultra pure starting substrate materials should use wafers produced using the FZ method
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Type of Crystal Growth
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Raw Silicon Preparation
REDUCTION > Raw material (sand) is mixed with carbon and heated to form metallurgical grade Silicon (MGS)
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ADVANTAGE
allows big crystal diameters and lower production cost per wafer– compared to the float-zone technique described in the following section.
allows big crystal diameters and lower production cost per wafer– compared to the float-zone technique described in the following section.
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DIFFERENT
vertical Bridgman technique enables the growth of crystals in circular shape, unlike the D-shaped ingots grown by horizontal Bridgman technique.
horizontally exhibit high crystalline quality (e.g. low dislocation density) since the crystal experiences lower stress due to the free surface on the top of the melt and is free to expand during the entire growth process
Instead of moving the crucible, the furnace can be translated from the seed end while the crucible is kept stationary
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EXPLANATION
Principle & Process
Heating Polycrystalline materials above melting point and slowly cooling it from one end and its container where seed crysral is located
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