Semiconductor substrate and its fabrication method

A semiconductor substrate fabrication method comprising the steps of:

• forming a plurality of first trenches on the surface of a semiconductor substrate and moreover forming a third trench having an opening face wider than that of the first trench;
• changing the first trenches and the third trench to one unclosed empty space having a flat spatial region and an opening face on the surface of the semiconductor substrate by applying heat treatment to the semiconductor substrate;
• and
• filling the inside of the empty space with an insulating film.

A semiconductor substrate fabrication method comprising the steps of:

• forming a plurality of first trenches respectively having an aspect ratio of 5 or more and a plurality of fourth trenches respectively having an aspect ratio of 4 or less on the surface of a semiconductor substrate;
• and
• changing the first trenches to one empty space by applying heat treatment to the semiconductor substrate;
• extinguishing the fourth trenches, and flattening the surface of the semiconductor substrate including a region in which the fourth trenches and the empty space are formed.

A semiconductor substrate fabrication method comprising the steps of:

• forming a plurality of trenches on the surface of a semiconductor substrate;
• changing the first trenches to one empty space by applying first heat treatment to the semiconductor substrate;
• and
• decreasing the difference between the pressure of an atmosphere in which the semiconductor substrate is present and the pressure in the empty space by applying second heat treatment to the semiconductor substrate and changing pressures in the empty space.

A semiconductor substrate fabrication method comprising the steps of:

• forming a plurality of first trenches on the surface of a semiconductor substrate;
• changing the first trenches to one flat empty space by applying heat treatment to the semiconductor substrate;
• forming a second trench reaching the empty space on the semiconductor substrate;
• and
• forming a thermal oxide film for generating a tensile stress in the semiconductor substrate on the empty space on inner faces of the empty space and the second trench through thermal oxidation.

A semiconductor substrate fabrication method comprising the steps of:

• forming a plurality of first trenches on the surface of a semiconductor substrate;
• forming a first semiconductor film including a second semiconducting element different from a first semiconducting element constituting the semiconductor substrate on the surface of the semiconductor substrate including the first trenches;
• changing the first trenches to one flat empty space by applying first heat treatment to the semiconductor substrate;
• forming a second trench reaching the empty space on the semiconductor substrate;
• and
• forming a second semiconductor film including the first and second semiconducting elements for generating a tensile stress in the semiconductor substrate on the empty space on inner faces of the empty space and the second trench.

A semiconductor substrate fabrication method comprising the steps of:

• forming a plurality of trenches on the surface of a semiconductor substrate;
• changing the trenches to one flat empty space by applying heat treatment to the semiconductor substrate;
• and
• etching the semiconductor substrate, selectively leaving a part of the semiconductor substrate on the empty space, and forming a semiconductor region serving as a transparent waveguide in which surroundings of the upper face, side face, and bottom face are spaces so as to be built in the semiconductor substrate.