Method for manufacturing trench in semiconductor substrate, and semiconductor device

A method for manufacturing a trench in a semiconductor substrate, comprising:

• providing the semiconductor substrate;
• forming a hard mask layer on the semiconductor substrate, a material of the hard mask layer having a melting point higher than that of a semiconductor material of the semiconductor substrate;
• performing exposure and development after forming a photoresist pattern on the hard mask layer to etch the hard mask layer and the semiconductor substrate to form a trench in the semiconductor substrate, the trench having a side surface and a bottom surface with an angle therebetween being greater than 90 degrees, and removing the photoresist pattern;
• performing a pull-back process on the hard mask layer to expose top corners of the semiconductor substrate on both sides of the trench;
• irradiating the top corners of the semiconductor substrate on the both sides of the trench and at least one of the side surface or the bottom surface of the trench with a laser beam, such that the semiconductor material of a part of the semiconductor substrate that is at a distance from the side surface or the bottom surface of the trench not exceeding a first distance is melted, and such that the top corners of the semiconductor substrate on the both sides of the trench are rounded, wherein the hard mask layer protects the semiconductor material of a part of the semiconductor substrate that is below the hard mask layer from being melted due to the irradiation with the laser beam;
• and
• cooling the semiconductor substrate, such that the at least one of the side surface or the bottom surface of the trench is re-shaped to have a surface roughness lower than that before the irradiation with the laser beam,
• wherein irradiating the trench with the laser beam comprises causing a plurality of laser beams to scan the trench at a preset scanning speed in a scanning direction parallel to a length direction of the trench, the scanning being started when a preset delay period of time has elapsed from start of the irradiation, and
• wherein when causing the plurality of laser beams to scan the trench at the preset scanning speed in the scanning direction, irradiation areas of every two adjacent laser beams of the plurality of laser beams partially overlap each other in the scanning direction.