Semiconductor device and method of manufacturing same

A method of manufacturing a semiconductor device, comprising the steps of:

• (a) forming a first insulating film containing silicon and oxygen over the main surface of a semiconductor substrate;
• (b) forming a second insulating film over the first insulating film;
• (c) forming a first opening portion penetrating through the second insulating film and reaching the first insulating film;
• (d) forming a second opening portion penetrating through the first insulating film and reaching the semiconductor substrate in a region having therein the first opening portion in plan view;
• (e) forming a trench portion in a portion of the semiconductor substrate exposed from the second opening portion;
• (f) after the step (e), etching a portion of the first insulating film exposed from the second opening portion by a first etching agent;
• and
• (g) after the step (f), forming a third insulating film in the trench portion, in the second opening portion, and in the first opening portion,
• wherein an etch rate of the second insulating film by the first etching agent is smaller than an etch rate of the first insulating film by the first etching agent,
• wherein in the step (e), the trench portion is formed so as to make a trench width of the trench portion smaller than a first opening width of the first opening portion,
• wherein in the step (f), a portion of the first insulating film exposed from the second opening portion is etched by the first etching agent to make a second opening width of the second opening portion greater than the trench width of the trench portion, and
• wherein in the step (g), the trench portion is closed by the third insulating film while leaving a space in the trench portion.