Process for fabricating a semiconductor device having electrically isolated low voltage and high voltage regions

A process for fabricating a semiconductor device having electrically isolated low voltage and high voltage substrate regions includes low voltage and high voltage trench isolation structures in which a deep portion of the high voltage isolation trench provides electrical isolation in the high voltage regions. The high voltage isolation trench structures include a shallow portion that can be simultaneously formed with the low voltage trench isolation structures. The deep portion of the high voltage isolation trench has a bottom surface and shares a continuous wall surface with the shallow portion that extends from the bottom surface to the principal surface of the substrate. A process for fabricating the device includes the formation of sidewall spacers to define a minimum isolation width between adjacent high voltage nodes.