Semiconductor Wafer – Orientation Flat on Semiconductor Wafer

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On semiconductor wafers there is a straight line, which is called Orientation Flat.

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What exactly are these and how they are formed?

Best Answer

As stevenh says one of the purposes is to ensure correct orientation during handling. The other reason is to indicate the crystal orientation of the lattice and the wafer doping. From BYU's cleanroom website:

Wafer Flats

Purpose and Function

  1. Orientation for automatic equipment

  2. Indicate type and orientation of crystal.

Primary flat – The flat of longest length located in the circumference of the wafer. The primary flat has a specific crystal orientation relative to the wafer surface; major flat.

Secondary flat – Indicates the crystal orientation and doping of the wafer. The location of this flat varies.

For large crystals no flats are ground. Instead a notch is machined for positioning and orientation purposes.

The crystal lattice is defined by how the wafer grew from the initial seeding.
It is important to cut the wafers along the crystal lattice if you want a clean break.

crystal lattice structure

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