Split-gate power mos device and manufacturing method thereof

A manufacturing method of a split-gate power metal oxide semiconductor device, comprises:

• forming an epitaxial layer of a first doping type on a substrate, and forming a trench in the epitaxial layer;
• forming a first insulation layer on a surface of the epitaxial layer and in the trench, wherein the first insulation layer covers an surface of the trench to form a cavity;
• filling the cavity with polycrystalline silicon;
• performing back-etching process on the polycrystalline silicon, removing a portion of the polycrystalline silicon to form a first gate conductor layer and expose an upper portion of the cavity;
• performing spin-coating process on a surface of the first gate conductor layer positioned in the cavity to form a second insulation layer;
• forming a mask on the second insulation layer;
• removing a portion, which is positioned on the surface of the epitaxial layer and on a sidewall of the mask in the trench, of the first insulation layer, to expose an upper portion of the trench;
• forming a gate oxide layer on a sidewall of the upper portion of the trench and the surface of the epitaxial layer;
• and
• forming a second gate conductor layer in the upper portion of the trench.