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.
See
also:
Specifications for Si Wafers;
Wafers for Wafer Fab;
Single Crystal Growth
Primary Reference:
Silicon Processing for the Vlsi Era: Process Technology
