Study of Improvement for Substrate Current in High-Voltage NMOS with Shallow Trench Isolation

Hot carrier injection (HCI) effect is closely related to substrate current (Isub). In 25V High-Voltage NMOS, the Isub-Vg by substrate bias curve is studied and two peaks, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Isubₘₐₓ</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Iₖᵢᵣₖ</tex> are observed. Due to the inevitable Kirk effect, the process of Kirk effect in parasitic n+pn-n+ bipolar transistor is studied. A formula is proposed, which plays a guide line for the later research. When substrate bias is higher, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Isubₘₐₓ</tex> is smaller, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Iₖᵢᵣₖ</tex> is larger and Isub <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> appears later. The drain current Id-Vg (Vd=25V) curve in the saturation region is also tested, which exhibits obvious velocity saturation effect. In addition, the influence of process and device size parameters on Isub is studied, and the reasons are analyzed, which is helpful to promote the research of Isub and HCI.