2-23.Micropipe density

A micropipe, also referred to as “micropore”, “microtube”, “capillary defect “or “pinhole defect”, is a crystallographic defect in a single crystal substrate.It is a important parameter to manufacturers of silicon carbide (SiC) substrates which are used in a variety of industries such as power semiconductor 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 crystal surface.

Micropipe density (MPD) is a crucial parameter for silicon carbide (SiC) substrates that determines the quality, stability and yield of the semiconductor devices built on these substrates. The importance of MPD is underscored by the fact that all existing specifications for 6H- and 4H-SiC substrates set upper limits for it.

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