Semiconductor device fabrication method for improving capability for burying a conductive film in the trenches of trench gates

A method of fabricating a semiconductor device, said semiconductor device having trench gates as gate electrodes of transistors;

• said method comprising the steps of:
• forming on a substrate element isolation parts that enclose a plurality of active regions in which said transistors are formed, wherein profiles of said element isolation parts in a perpendicular direction with respect to a substrate surface are reverse-tapered shapes;
• after forming said element isolation parts, forming an oxidation-resistant insulation mask that covers the regions of sources and drains of said transistors in said plurality of active regions;
• subjecting said substrate to anisotropic etching from above said oxidation-resistant insulation mask to form trenches for said trench gates in said active regions;
• removing a natural oxidation film that has formed on a substrate surface of said trenches;
• after removing said natural oxidation film, carrying out an annealing process by performing a heat treatment in a hydrogen atmosphere;
• after said annealing process, removing said oxidation-resistant insulation mask;
• after removing said oxidation-resistant insulation mask, carrying out a cleaning process by cleaning with a mixture containing ammonium-hydrogen peroxide;
• and
• after said cleaning process, forming a gate oxide film on a substrate surface of said trenches by a thermal oxidation method.