Micropipe

A micropipe is a defect in a single crystal substrate. Today this is of great interest to makers of silicon carbide (SiC) substrates which are used in a variety of industries such as power devices for vehicles and high frequency communication devices.

However, during the production of these materials, the crystal undergoes internal and external stresses causing growth of defects, or dislocations, within the atomic lattice.

A screw dislocation is a common dislocation that transforms successive atomic planes within a crystal lattice into the shape of a helix. Once a screw dislocation propagates through the bulk of a sample during the wafer growth process, a micropipe is formed. The presence of a high density of micropipes within a wafer will result in a loss of yield in the device manufacturing process.

Micropipes and screw dislocations in epitaxial layers are normally derived from the substrates on which the epitaxy is performed. Micropipes are considered to be empty-core screw dislocations with large strain energy (i.e. they have large Burgers vector); they follow the growth direction (c-axis) in silicon carbide boules and substrates propagating into the deposited epitaxial layers.

Factors which influence formation of micropipes (and other defects) are such growth parameters as temperature, supersaturation, vapor phase stoichiometry, impurities and the polarity of the seed surface.

Many laboratories in universities and companies are striving to perfect the micropipe-free substrate. One of the pioneers of the commercialization of SiC materials and devices is Cree Inc. which in May 2007, announced that it had achieved 100-mm (4-inch), Zero-Micropipe, n-type SiC substrates. It is therefore possible to eliminate these defects in large-area wafers as well as smaller fragments and should open up the commercialization of this area of microelectronic devices.