Characterization and Analysis of Degradation for 1.2-kV Rated SiC Trench MOSFETs Under Repetitive Switching Impulses

The degradation behaviors and mechanism of commercial 1.2-kV rated SiC trench MOSFETs under repetitive switching impulses (RSIs) are comprehensively investigated. Two degradation regions and corresponding degradation behaviors are characterized. Region I is the gate oxide on the channel region. The electrons are trapped in region I under positive gate bias stress, which leads to a slightly positive shift of threshold voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula>) and an increment in ON-state resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {ds-ON}}$ </tex-math></inline-formula>). Region II is the gate oxide at the trench bottom corner. Hot holes are injected into the gate oxide of region II, which leads to a slight decrease in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {R}_{\text {ds-ON}}$ </tex-math></inline-formula>. The effect is intensified with the increase of thermal stress. Fortunately, the degradation of Region I is not affected by drain-source voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ds}}$ </tex-math></inline-formula>) stress, even if <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {ds}}$ </tex-math></inline-formula> is up to 80% of the breakdown voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {BR}}$ </tex-math></inline-formula>). A severe gate leakage current was observed when it experienced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.0\times 10^{{6}}$ </tex-math></inline-formula> switching impulses under 80% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 0~{V}_{\text {BR}}$ </tex-math></inline-formula>. Simulated results confirm that the leakage current path is located at the trench bottom corner, induced by a strong electric field. This simultaneously explains the degradation observed in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {ds-ON}}$ </tex-math></inline-formula>.