High voltage device and manufacturing method thereof

A manufacturing method of a high voltage device, comprising:

• forming a semiconductor layer on a substrate;
• forming a well in the semiconductor layer, wherein the well has a first conductivity type;
• forming a bulk region in the semiconductor layer, wherein the bulk region has a second conductivity type, wherein the bulk region is in contact with the well;
• forming a gate on the semiconductor layer, wherein a portion of the bulk region is vertically below and in contact with the gate, to provide an inversion region of the high voltage device when the high voltage device is in an ON operation;
• and
• forming a source and a drain below a top surface of the semiconductor layer and causing the source and the drain to be in contact with the top surface of the semiconductor layer, wherein both the source and the drain have the first conductivity type, wherein the source and the drain are at two different sides of the gate, respectively, wherein the source is in the bulk region, whereas, the drain is in a part of the well which is away from the bulk region, wherein a portion of the well lies between the bulk region and the drain, to separate the bulk region from the drain;
• wherein a first concentration peak region of the bulk region is vertically below and in contact with the source, wherein the first concentration peak region completely covers a bottom of the source, so as to prevent a parasitic bipolar junction transistor to be turned on;
• wherein a concentration of a second conductivity type impurities of the first concentration peak region is higher than that of other regions in the bulk region;
• wherein a second concentration peak region of the bulk region is vertically below and in contact with the top surface of the semiconductor layer, wherein the second concentration peak region encompasses and is in contact with the source, and wherein the concentration of the second conductivity type impurities of the second concentration peak region is higher than that of other regions excluding the first concentration peak region in the bulk region.