Abstract: A semiconductor substrate used for fabricating vertical devices, such as vertical MOSFET, capable of maintaining low ON-stage resistance and of ensuring a necessary level of OFF-stage breakdown voltage is provided. A heavily-doped arsenic layer of 0.5 to 3.0 ?m thick is inserted between a heavily-doped phosphorus layer 11 composing the drain of a vertical MOSFET and an n?-type drift layer. The heavily-doped arsenic layer functions as a barrier layer which prevents phosphorus from diffusing from the heavily-doped phosphorus layer into the n?-type drift layer. This is successful in maintaining spreading of the depletion layer during OFF time of the vertical MOSFET to thereby improve the OFF-stage breakdown voltage, and in maintaining the low ON-stage resistance.

Abstract: A method for fabricating dissimilar devices in an integrated circuit. In one embodiment, the method can be used to fabricate flash memory, including MOS transistors and flash cells. The method can be used to substantially cofabricate the MOS transistors and flash cells, particularly their gates. The method includes forming layers of adjacent materials for the MOS transistor gates and the flash cell gates, and simultaneously forming the MOS transistor gates and the flash cell gates from the layers of adjacent materials. The method further includes defining drains of the flash cells separate from defining sources of the flash cells.