Elimination Of Parametric Shifts In Trench MOSFETs Using Low Alpha-Particle Solder

<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\alpha{-}$</tex> Particle have become a subject of interest in the microelectronics industry because they possess the ability to induce unwanted effects on semiconductor devices. The presence of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\alpha}{-}$</tex> particles in Pb-based solder pastes in clip-bonded MOSFETs has been shown to induce sub-threshold shifts in the device. To address this phenomenon, low <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\alpha}{-}$</tex> particle (LAP) solder pastes have been developed and have become a viable solution for clip-bonded power MOSFETs. In this study, power MOSFETs were built using LAP-solder paste and compared against control devices built using standard solder paste. The devices were subjected to high-temperature gate-bias (HTGB) reliability testing, during which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\alpha{-}$</tex> Particle-particle detection and impact measurement was done by measuring sub-threshold characteristics of the MOSFETs. Sub-threshold shifts were confirmed and the mechanism responsible for this phenomenon is explained. The probability of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\alpha}-\mathbf{strike}$</tex> event is estimated; hence a suitable range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\alpha}{-}$</tex> particle activity is suggested. Comparison of wire-bonding versus clip-bonding confirmed that the source of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\alpha}-\mathbf{particles}$</tex> comes from the clip-attach solder paste. Analysis of lifetest results showed that LAP-solder pastes practically eliminate sub-threshold shifts in product with comparable process stability during assembly. Hence, LAP solder paste is a breakthrough solution for mitigating the limitations of standard Pb-based solder paste and can be implemented in current and future power MOSFET technologies in high-volume manufacturing.