Double diffused metal oxide semiconductor device and manufacturing method thereof

A manufacturing method of a double diffused metal oxide semiconductor (DMOS) device, comprising:

• providing a substrate having a first conductive type, the substrate having a top surface and a bottom surface opposing to each other along a vertical direction;
• forming an epitaxial layer on the substrate, wherein the epitaxial layer has an epitaxial surface opposite to the top surface along the vertical direction, and wherein the epitaxial layer is stacked on and in contact with at least a portion of the top surface of the substrate;
• forming a high voltage well having a second conductive type in the epitaxial layer, wherein the high voltage well is stacked on and in contact with the top surface along the vertical direction, wherein the high voltage well and the top surface of the substrate form a first PN junction;
• forming a body region having the first conductive type in the epitaxial layer, wherein the body region is beneath the epitaxial surface and connects the epitaxial surface in the vertical direction, wherein, as seen from a cross-section view, the body region and the high voltage well form a channel junction in a channel direction;
• forming a gate on the epitaxial layer, wherein the gate is stacked on and in contact with the epitaxial surface in the vertical direction, wherein, as seen from the cross-section view, the gate covers at least a part of the channel junction;
• forming a source having the second conductive type in the epitaxial layer, wherein the source is stacked beneath and connects the epitaxial surface in the vertical direction, wherein, as seen from the cross-section view, the source is located in the body region;
• forming a drain having the second conductive type in the epitaxial layer, wherein the drain is beneath and connects the epitaxial surface in the vertical direction, wherein the source and the drain are located at different sides of the channel junction, and wherein, as seen from the cross-section view, the drain and the gate are separated by the high voltage well;
• forming a drift buried region having the second conductive type in the epitaxial layer, wherein, as seen from the cross-section view, a part of the drift buried region is located vertically under the drain, and wherein a length of the drift buried region is greater than or equal to a length of the drain;
• and
• forming a buried region having the first conductive type between the substrate and the epitaxial layer, wherein a part of the buried region is located in the substrate and another part of the buried region is located in the epitaxial layer in the vertical direction, wherein, as seen from the cross-section view, at least a part of the buried region is located vertically under the drift buried region, and wherein a length of the buried region is greater than or equal to a length of the drain, and wherein the length of the buried region is greater than or equal to a length of the drift buried region;
• wherein, as seen from the cross-section view, the drift buried region and the buried region or the high voltage well and the buried region form a second PN junction along a channel direction;
• wherein, as seen from the cross-section view, the first PN junction and the second PN junction have respective depths, wherein the depth is defined as a distance extending from the epitaxial surface downward along the vertical direction, and the depth of the second PN junction is shallower than the depth of the first PN junction;
• wherein, the drift buried region, along the channel direction, has a first boundary close to the gate and a second boundary away from the gate, and wherein, the buried region, along the channel direction, has a third boundary close to the gate and a fourth boundary away from the gate;
• wherein, the first boundary and the third boundary, along the channel direction, are between the drain and the channel junction, and wherein the second boundary and the fourth boundary, along the channel direction, at least extend beyond a fifth boundary, in which the fifth boundary is between the drain and an isolation structure close to the drain;
• wherein, the isolation structure defines an operation region of the DMOS device.