2022-09-18 15:13 Status: # Wafers Start with a top of molten silicon - starting seed crystal you dip into the silicon and slowly pull out as you rotate it. This creates an [ingot](ingot.md)  Then- take a thin slice of ingot to create wafers.  ## Zone Purification Need to purify the ingot first. Place in an RF field (coil - high current creates [eddy currents](eddy%20currents.md) in the ingot). This melts a small section of the silicon.  Moving the molten zone up tends to concentrate impurities, so you can 'filter'them out by moving this zone along the ingot.  ## Common Sizing ~10-30cm  ## Types of Wafer ### P-type Normal disc (not often: use [n-type](n-type.md)) ### Epi-wafer Low doped on top then high doped below.  Heavy doping prevents latch up - not good for transistors though. Downside - can't have separate analogue and digital ground.[^1] ### Insulator on top(typically SO2), then p-type.  Lower parasitics means a faster device - need to add silicon on top to manufacture transistors. --- # References [^1]: [vr-4602-wk01-sc02-wafers](../../Spaces/University/ELEC4602%20–%20Microelectronics%20Design%20and%20Technology/Lectures/W1/vr-4602-wk01-sc02-wafers.mp4)