What is a semiconductor wafer?

Semiconductor Wafer

A semiconductor wafer is a thin slice of semiconductor substance, like crystalline silicon, used in electronics for the making of integrated circuits. In the electronics jargon, a thin slice of semiconductor material is called as a wafer. It could be a silicon crystal which is used in the making of integrated circuits and other micro devices.

Wafers are made up of very pure single crystal material. In the czochralski process a cylindrical ingot of highly pure monocrystalline semiconductor like silicon or germanium is made by pulling of a seed crystal from a melt. Impurity atoms which are donors are added to the molten intrinsic material in exact amounts to ensure doping of the crystal. Thus changing the semiconductor into n type or p type semiconductor. The ingot is then sliced to form wafers.

Properties of silicon wafer

Silicon wafers are available in a variety of sizes in this case diameters. They are available from 25.4 mm to 450 mm. Semiconductor plants are known by the diameter of wafers they produce. The diameter of the wafers has increased through out to reduce costs with the current gen of fab considered to be 300 mm in diameter.

silicon wafer sizes

Different silicon wafer sizes

Wafers that are grown by making use of materials other than silicon will have different thickness from a silicon wafer. The thickness of the wafer is measured by the mechanical strength of the material used. The thickness of the wafer must be enough to support its own weight during handling.

Wafers that are under 200 mm diameter are cut into flats on one or more sides. Which indicates the crystallographic planes of the wafer. The earlier gen of wafers had a pair of flats that were placed at different angles which additionally conveyed the doping type. Wafers that are 200 mm in diameter make use of a single small notch to convey wafer orientation which gives no visual indication of the type of doping used.

Once when one or two flats are ground into the edge of the wafer, indicates crystal orientation which applies to wafers 125 mm in diameter. Flats are used to denote crystallographic and doping orientation. The red color represents material that has been removed. Wafers that are grown from crystals have a regular crystalline structure. Where silicon has a diamond cubic structure. Silicon wafers are not made of 100% silicon. But are formed with impurity doping concentration in the initial stages. Carbon and other metallic contamination is kept to a minimum. Semiconductor doping is a process whereby the intrinsic semiconductor is changed to an extrinsic semiconductor. Extrinsic semiconductors are components of many electrical devices.