Francine Y. Robb

NPT-IGBT-optimizing for manufacturability

High-voltage NPT-IGBTs (non-punchthrough IGBTs) offer reasonable on-state voltages, high short-circuit ruggedness, and minimal turn-off losses without lifetime killing. In addition, NPT-IGBTs have the potential to reduce fabrication costs as compared to conventional epitaxial IGBTs because they are fabricated on low cost bulk silicon substrates, while conventional IGBTs utilize thick, expensive epitaxial layers. The key to realizing this potential cost savings, however, is the development of a manufacturable thin-wafer back end process flow. This paper will discuss NPT-IGBT process optimization, aimed at increased manufacturability. Starting material specifications, backside process optimization, and thin-wafer manufacturability issues are addressed.

Increasing the switching speed of high-voltage IGBTs

The lower on-voltages of IGBTs, as compared to power MOSFETs, make them very attractive for high-voltage applications. Their higher switching losses, however, have limited the IGBT to low (<10 kHz) frequency applications. This paper will discuss the on-voltage/off-energy (Eoff) trade-offs of 1200 V non-punchthrough (NPT) IGBTs. Adjusting the trade-offs by modifying the backside process, by incorporating an annealed aluminum drain contact, and by proton implanting are discussed. A 1200 V NPT-IGBT with a fall time equivalent to a 1200 V power MOSFET, but with one-third its on-voltage, was produced using a 3E12/cm/sup 2/, 1.6 MeV backside proton implant.

ADFET-a simple inexpensive power device

A new high-voltage power device, termed the ADFET for alloyed drain power MOSFET, provides an economical alternative to conventional power MOSFETs (epi-FETs) for many applications. Possessing qualities mid-way between a non-punchthrough (NPT) IGBT and an epitaxial power MOSFET, 1200 V ADFETs have on-voltages about half that of 1200 V epi-FETs and fall times of /spl sim/90 nsec. In addition, ADFET costs are dramatically lower than epi-FETs, not just because lower on-voltages reduce die sizes, but also because the floatzone (FZ) starting material is much less expensive than thick epitaxial layers. This paper discusses fabrication of the ADFET, provides actual 1200 V TO-220 device data with direct comparison to non-punchthrough IGBT and epitaxial power MOSFET data, and reviews MEDICI modeling performed to elucidate mechanisms.