Incoming Wafers

Integrated circuits are fabricated on single-crystal silicon substrates with near-perfect crystalline properties: defect free and uniform crystal structure as well as high chemical purity. These substrates are processed in the form of wafers, so the fabrication of circuits on these wafers is known as wafer fabrication.

The steps needed to obtain wafers for circuit fabrication are very complex, but these can be simplified as follows:

1) Quartzite, a type of sand that's used as raw material for wafers, undergoes a complicated refining process to become electronic grade polysilicon (EGS).

2) The EGS material is then used to grow single crystal ultrapure silicon ingots either by the Czochralski (CZ) or Float Zone (FZ) method.

3) Each ingot then undergoes grinding, sawing, and polishing to yield many wafers.

Figure 1. Example of a Czochralski Silicon Crystal Growing Furnace

A wafer has to meet certain quality criteria or specifications for it to be ready for wafer fabrication. Electrical specifications include the conductivity type (p or n), resistivity range, radial resistivity gradient, and resistivity variations. Mechanical specifications include the diameter, thickness, total thickness variation (TTV), bow, warp, flat dimensions, chips, indents, edge contour, bulk structural defects, and surface orientation. Chemical specifications include oxygen content, carbon content, and oxidation-induced defects. Surface specifications include flatness, particle density, haze, saucer pits, and other surface attributes.


Figure 2. Example of an ingot slicer	Figure 3. Photo of a finished wafer

Wafer Fab Links: Incoming Wafers; Epitaxy; Diffusion; Ion Implant; Polysilicon;

Dielectric; Lithography/Etch; Thin Films; Metallization; Glassivation; Probe/Trim

IC Manufacturing; Wafer Fab Equipment

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