Patent ID: 8143130

Claim:
A method of manufacturing a depletion metal oxide semiconductor (MOS) device, comprising: providing a substrate; forming a first conductive type well and an isolation region in the substrate to define a device area; defining a drift region, a source, a drain, and a threshold voltage adjustment region in the device area, and implanting second conductive type impurities to form the drift region, the source, the drain, and the threshold voltage adjustment region, respectively, wherein the threshold voltage adjustment region is for adjusting a threshold voltage of the depletion MOS device such that the depletion MOS device becomes normally conductive, the threshold voltage adjustment region being shallower than the drift region, and the threshold voltage adjustment region and the drain being separated by the drift region; defining a breakdown protection region between the drain and the threshold voltage adjustment region, and implanting first conductive type impurities to form the breakdown protection region, wherein the breakdown protection region is shallower than the drift region, and the implanting of first conductive type impurities to form the breakdown protection region does not fully deplete the second conductive type impurities already existing in the breakdown protection region, such that the breakdown protection region presents second conductive type property and has a second conductive type concentration lower than the concentration of the drift region, to increase the breakdown voltage of the depletion MOS device as compared with a case where the concentration of the second conductive type impurities in the breakdown protection region is not decreased; and forming a gate in the device area, wherein part of the breakdown protection region is below the gate, and the breakdown protection region surrounds an edge of the threshold voltage adjustment region.