Modeling and Analysis of 3-D Core-Shell Superjunction Structures

Abstract

Conventional superjunction (SJ) structures are composed of p- and n-type doped pillars extending longitudinally as linear stripes (LSs). The reduced surface field (RESURF) effect in these structures is essentially due to a 2-D depletion. A 3-D RESURF is expected to be better than a 2-D RESURF and may further improve the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {BV}-\text {R}_{\text {DS}{(} \text {on} {)},\text {sp}}$ </tex-math></inline-formula> tradeoff for SJ devices. A natural 3-D RESURF structure is a core-shell (CS) SJ structure with a cylindrical unit cell. To identify and leverage the advantages that a 3-D RESURF can offer, the CS SJ is theoretically and numerically analyzed in this article. We develop an analytical model that results in closed-form expressions for the electric field profiles in both CS and LS structures. A very close agreement is observed between the analytical results and numerical simulations. The efficacy of 2-D and 3-D RESURF is compared using the model, and it is found that neither of these designs is universally better. The superior design is determined by the fabrication technology limitations. For trench refill type technologies, the CS design can offer substantial improvement, but, for lithography limited technologies, the CS design shows a significant deterioration in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {BV}-\text {R}_{\text {DS}{(} \text {on} {)},\text {sp}} $ </tex-math></inline-formula> tradeoff compared with the LS design.