National Semiconductor Corporation

Peter P Meng

Sheldon Aronowitz

George P Walker

Farrokh Mohammadi

Bhaskar V Gadepally

An improved method for simulating the surface contours of a layer of material to be formed over a base structure using a string algorithm is described. The method of the string algorithm includes the steps of defining old surface points along the base structure, defining a set of possible new surface points, and defining a set of orderly array of points, from the set of new surface points, which define the surface contours of the simulated layer of material formed over the base structure.

Method for simulating the surface contours of a layer material to be

Body to drain junction breakdown, due to avalanching in DMOST devices, can be controlled. The invention lowers the electric field gradients in the vicinity of the PN junction. The structure employed to enhance breakdown behavior is specifically applied to a vertical DMOST. The N type doping profile in the vicinity of the body to drain junction is tailored by constructing a P-nu-N-N.sup.+ type diode structure where nu is a low N type impurity concentration region. The N type region is of higher impurity concentration and is more extensive. With the nu region having one-half of the impurity concentration of the N region and an extent of about two microns, the avalanche breakdown voltage is about 27% higher than the conventional PN junction diode. By making the nu region impurity concentration one-fourth that of the N region, the breakdown voltage is 40% higher.

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Sunnyvale, CA, United States of America

Peter P Meng