Crystal Pulling: Crystal Pulling is the next step in the Manufacturing of a Silicon wafer.
In this process the Polysilicon chunks
or granules are loaded into the Quartz crucible of the Crystal pulling furnace
along with a small amount of Boron, Phosphorus, Arsenic or Antimony dopant. The
Polysilicon is then
melted at a process temperature of 1400° C in a high purity Argon gas ambient.
Once the proper "melt” is achieved a "seed" of single crystal
Silicon is lowered into the melt. Then the temperature is adjusted and the
seed is rotated as it is slowly pulled out of the molten Silicon.
The surface tension between the seed and the molten Silicon causes a
small amount to rise with the seed, as it is pulled and cooled into a
perfect mono-crystalline ingot with the same crystal orientation as the seed.
The following view is of the lower portion of the crystal
pulling furnace, these machines can stand 12-15 feet high and are quite complex
in nature. These furnaces also must be very stable and vibration free since the
process takes hours and the slightest jarring of the furnace can break the
Ingot from the seed.
CZ Crystal Puller Furnace
An actual picture of a "Seed" and
Ingot inside of a crystal pulling furnace.
Next the finished Ingot is ground to a rough size diameter (a little larger
than a finished wafer) and it is either notched or flatted along its length to
indicate the orientation of the Ingot. This is also a point when many
inspections are made on the ingot to catch any major flaws or problems with
resistivity etc.
Silicon Crystal or Ingot
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