In silicon carbide (SiC) wafers, a micropipe is a hollow, tube‑like crystallographic defect – a hollow‑core screw dislocation that runs approximately along the crystal growth direction. When the SiC boule is sliced into wafers, micropipes intersect the polished surface as small, often hexagonal pits that extend deep into the substrate.
Each micropipe can distort the local electric field, increase leakage current and dramatically lower the breakdown voltage of high‑voltage and high‑power devices. For this reason, the industry specifies micropipe density (MPD) as the number of micropipes per unit wafer area, typically in cm−2. Lower MPD means more usable die per wafer and higher chip yields.
Example SiC Micropipe Specification
A recent research request asked for Silicon Carbide (SiC) crystal substrates with the following specifications:
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Both 4H‑SiC and 6H‑SiC substrates used for power semiconductors historically suffered from relatively high micropipe densities. Continuous improvements in bulk crystal growth have reduced MPD by several orders of magnitude, and modern production wafers are often specified as “micropipe‑free” or with MPD ≤ 1 cm−2.
For many R&D projects, low but non‑zero MPD (for example < 15 cm−2) can still be acceptable when device layouts are designed so that any remaining micropipes fall outside the active area. Specifying the MPD requirement up front helps ensure that the supplied SiC substrates are appropriate for your breakdown voltage and reliability targets.
In silicon carbide (SiC), a micropipe is not a device feature that is “created” when the wafer
is cut. It is a crystallographic defect – a hollow‑core screw dislocation that forms during bulk crystal growth
and runs roughly along the growth direction (c‑axis) through the SiC boule. When the boule is sliced into wafers,
the micropipe intersects the surface as a small, usually circular or hexagonal pit with a hollow tube extending
deep into the substrate.
Commercial SiC boules are typically grown by seeded sublimation, also known as physical vapour transport (PVT). During this process:
As the boule grows, a single micropipe can extend through many millimetres of crystal and therefore intersect a large number of wafers cut from that boule.
Typical micropipes in SiC have diameters on the order of 1–10 µm at the wafer surface – large enough that even a single defect in a critical region can be a “killer” for high‑voltage or high‑power devices. A micropipe:
Because epitaxial layers grown on SiC typically inherit many defects from the underlying substrate, micropipes originating in the bulk crystal can propagate into the epi and directly limit device performance.
To quantify substrate quality, manufacturers specify micropipe density (MPD) in units of defects per square centimetre (cm−2). MPD is usually measured on the wafer surface by optical inspection or X‑ray / synchrotron topography, and can be defined across the whole wafer or in specified active areas.
Lower MPD directly translates into:
Early generations of 4H‑ and 6H‑SiC substrates often exhibited micropipe densities of hundreds of defects per cm2. Over the last two decades, improvements in seed quality, crucible design and growth process control have reduced MPD by several orders of magnitude, to the point where state‑of‑the‑art power‑device substrates are effectively micropipe‑free (MPD ≈ 0–1 cm−2).
For research and prototyping, however, material with a specified limit such as MPD < 15 cm−2 can still be very useful, especially when device layouts are designed to keep any remaining micropipes outside the active area. When you request SiC wafers or diced pieces, including an explicit MPD requirement helps match the substrate quality to your application.