Electrical Specifications for Silicon Wafers

Silicon wafers, especially those used in VLSI manufacturing, must adhere to stringent mechanical, electrical, chemical, and other special specifications. Below are the most common electrical specifications for silicon wafers:

1) Conductivity Type

- specifies whether the wafers are p- or n-type.

- specifies which element was used as dopant for the wafer

2) Resistivity or Resistivity Ranges

- usually measured in ohm-cm

- specifies the average resistivities or range of resistivities of the wafers

- the resistivity of the wafer is related to the doping density or concentration of dopants in the wafer

- wafer resistivity is often measured using the 4-point probe method defined by ASTM Std F-43

3) Radial Resistivity Gradient

- usually measured in % variation

- specifies the variation of the radial resistivity exhibited by the wafers as measured from the center to selected points in the outer regions of the wafers

- minimum radial resistivity gradient is desired to keep device characteristics in control

- radial resistivity is a function of the process used in growing the crystal as well as the dopants used

- radial resistivity gradient is often measured using the 4-point probe method used by ASTM Std-F-81

4) Local Resistivity Variations

- provides a measure of localized variations in resistivity exhibited by the wafers

- local resistivity variations are often due to remelt phenomena, and are usually more pronounced in FZ than CZ wafers

- local resistivity variation is often measured using the 4-point probe method defined by ASTM Stds F-81 and F-525.

Primary Reference: Silicon Processing for the Vlsi Era: Process Technology

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