Wafer Specification

Diameter and Edge Length

The wafer diameter is specified in mm or – most commonly – an integer number of inches (one inch = 25.4 mm) and the diameter tolerance (typ. < 1 mm). For bigger lots (e. g. > 100 wafers), we are often able to make arbitrary wafer diameters available.

We also offer rectangular and square wafer pieces. Der basically realisable range of the edge lengths for silicon wafers is 5 x 5 mm2 ... 100 x 120 mm2, for quartz, fused silica and glass wafers 2 x 2 mm2 ... 300 x 300 mm2. The cost / wafer piece depends on the material as well as on the number of wafer pieces required. Please contact us for an offer!

Orientation

The wafer orientation (e. g. <100>, <110> or <111>) denotes the  crystallographic plane parallel to the wafer surface. The tilt angle defines the maximum extent to which the wafer surface and crystallographic plane are inclined to each other.

Surface

Usually both sides of silicon wafers are at least lapped and etched. Surface polishing is performed either on one (SSP = Single-Side Polished) or both sides (DSP = Double-Side Polished).

Doping and Resistivity

The dopant atoms incorporated during silicon crystal growth increase the electrical conductivity via an increase in the free electron (in the case of phosphor or arsenic dopants) or hole (boron as dopant) concentration by up to many orders of magnitude beyond the value of undoped silicon.

Below a doping concentration of approx. c = 1016 cm-3 the resistivity drops reciprocally with c, towards a higher doping concentration the free carrier mobility drops which flattens the R(c) dependency (see plot right-hand).

The dependency of the electrical resistivity from the doping concentration of boron and phosphor / arsenic in crystalline silicon

Since the doping concentration is not perfectly homogeneous but axially and radially varies in the silicon crystal, the wafers are specified to a certain range (for CZ wafers typically one order of magnitude, such as 1 - 10 ohm cm, for FZ wafers often more narrow) in the electrical resistivity.

Thickness

The thickness usually measured in the centre of a wafer gives no information on
how strong the shape of the wafer deviates from an ideal (very flat) cylinder.

TTV

The Total Thickness Variation TTV specifies the difference d1 - d2 (left) between
the minimum and maximum thickness of a wafer measured at typically five or more different locations.

Bow

The bow is defined by d3 + d4 (left) corresponding to the maximum deviation of
the median surface to a reference plane.

Warp

The value d5 + d6 (left) corresponds to the deviation of the median surface of the wafer from a reference plane which is already corrected by the bow of the entire wafer.

Micro-Roughness

The Root Mean Square (“RMS“) denotes the standard height deviation of a surface scan on a wafer. The RMS values are typically < 1 nm which corresponds to a smoothness on atomic scale!

Laser-Marking

By request, laser-marking cab be performed on our wafers. Hereby, a individual identification, typically followed by consecutive numbers, is laser-marked on either the polished frontside or unpolished backside of the wafers. However, laser-marking on the polished side is not recommended: Laser-marking causes ridges around the markings, thus polishing has to follow laser-marking. However, polishing removes material, so the readability of the laser-marking becomes deteriorates.

For bigger lots (e. g. > 200 wafers), laser-marking can typically be performed for less than € 1,00 / wafer. Laser-marking of wafers we already have on stock might be more expensive.

 

Our Technical Wafer Brochure

Our technical wafer brochure with information on the production and specification of silicon, quartz, fused silica and borosilicate glass wafers can be downloaded or ordered (for free) here.