Method for manufacturing vertical MOS transistor

1. A method for manufacturing a vertical MOS transistor comprising:

providing a mask pattern on a silicon semiconductor substrate;

patterning the silicon semiconductor substrate using the mask pattern as a mask to provide a protrusion-like region protruding upward from a predetermined plane of the silicon semiconductor substrate;

forming a silicon oxide film and a silicon nitride film in sequence on an exposed surface of the protrusion-like region and a surface of the silicon semiconductor substrate;

increasing a film thickness of at least the silicon oxide film on the silicon semiconductor substrate by thermal oxidation to form a first insulating film;

implanting an impurity into the silicon semiconductor substrate using the mask pattern as the mask and then thermally treating to form a lower impurity diffusion region;

removing the silicon oxide film except the first insulating film and the silicon nitride film to expose a silicon side of the protrusion-like region;

thermally oxidizing the exposed silicon side of the protrusion-like region to form a second insulating film having a thinner film thickness than a film thickness of the first insulating film;

forming a gate electrode over a side of the protrusion-like region;

removing the mask pattern; and

implanting an impurity into an upper portion of the protrusion-like region and then thermally treating to form an upper impurity diffusion region.

2. The method for manufacturing a vertical MOS transistor according to claim 1 , wherein

in providing a mask pattern, the mask pattern comprising a SiO 2 film having a film thickness of 5 to 10 nm and a SiN film having a film thickness of 100 to 200 nm is provided,

in forming a silicon oxide film and a silicon nitride film, the silicon oxide film having a film thickness of 5 to 10 nm and the silicon nitride film are formed, and

in increasing a film thickness of at least the silicon oxide film on the silicon semiconductor substrate, the thermal oxidation is performed in a dry oxygen atmosphere at a temperature of 800 to 1000° C. to form the first insulating film having a film thickness of 30 to 50 nm.

3. The method for manufacturing a vertical MOS transistor according to claim 1 , further comprising, between forming the gate electrode and removing the mask pattern,

removing the second insulating film on an upper portion side of the protrusion-like region so that the second insulating film remains on a side of a portion of the protrusion-like region except an upper portion; and

performing the thermal oxidation to form a third insulating film on the upper portion side of the protrusion-like region so that a film thickness of the third insulating film is thicker than a film thickness of the remaining second insulating film.

4. The method for manufacturing a vertical MOS transistor according to claim 3 , wherein

in forming a silicon oxide film and a silicon nitride film, the silicon oxide film having a film thickness of 5 to 10 nm and the silicon nitride film are formed, and

in performing the thermal oxidation to form a third insulating film, the thermal oxidation is performed in a dry oxygen atmosphere or in a water vapor atmosphere at 800 to 1000° C. to form a SiO 2 film having a film thickness of 10 to 30 nm as the third insulating film.

5. The method for manufacturing a vertical MOS transistor according to claim 1 , further comprising, between forming the gate electrode and removing the mask pattern,

removing the second insulating film on an upper portion side of the protrusion-like region so that the second insulating film remains on a side of a portion of the protrusion-like region except an upper portion;

thermally oxidizing the upper portion side of the protrusion-like region and an upper portion side of the gate electrode opposed to the upper portion side of the protrusion-like region to form a forth insulating film so that a void is created between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode;

etching the forth insulating film on the upper portion side of the protrusion-like region to expose the upper portion side of the protrusion-like region; and

forming a fifth insulating film between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode so that a void remains between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode.

6. The method for manufacturing a vertical MOS transistor according to claim 5 , wherein

in forming a fifth insulating film, thermal oxidation is performed in an oxidizing atmosphere containing water vapor in a temperature range of 650 to 850° C. to form the fifth insulating film.

7. A method for manufacturing a vertical MOS transistor comprising:

forming a protrusion-like region protruding upward from a predetermined plane of a silicon semiconductor substrate;

forming a silicon oxide film on an exposed surface of the protrusion-like region and a surface of the silicon semiconductor substrate;

increasing a film thickness of at least the silicon oxide film on the silicon semiconductor substrate by thermal oxidation to form a first insulating film;

forming a lower impurity diffusion region extending from a lower portion of the protrusion-like region to an inside of the silicon semiconductor substrate;

removing the silicon oxide film except the first insulating film to expose a silicon side of the protrusion-like region;

thermally oxidizing the exposed silicon side of the protrusion-like region to form a second insulating film having a thinner film thickness than a film thickness of the first insulating film;

forming a gate electrode over a side of the protrusion-like region; and;

forming an upper impurity diffusion region in an upper portion of the protrusion-like region.

8. The method for manufacturing a vertical MOS transistor according to claim 7 , wherein

in increasing a film thickness of at least the silicon oxide film on the silicon semiconductor substrate, the thermal oxidation is performed in a dry oxygen atmosphere at a temperature of 800 to 1000° C. to form the first insulating film having a film thickness of 30 to 50 nm.

9. The method for manufacturing a vertical MOS transistor according to claim 7 , further comprising, between forming the gate electrode and forming the upper impurity diffusion region,

removing the second insulating film on an upper portion side of the protrusion-like region so that the second insulating film remains on a side of a portion of the protrusion-like region except an upper portion; and

performing the thermal oxidation to form a third insulating film on the upper portion side of the protrusion-like region so that a film thickness of the third insulating film is thicker than a film thickness of the remaining second insulating film.

10. The method for manufacturing a vertical MOS transistor according to claim 9 , wherein

in performing the thermal oxidation to form a third insulating film, the thermal oxidation is performed in a dry oxygen atmosphere or in a water vapor atmosphere at 800 to 1000° C. to form a SiO 2 film having a film thickness of 10 to 30 nm as the third insulating film.

11. The method for manufacturing a vertical MOS transistor according to claim 7 , further comprising, between forming the gate electrode and forming the upper impurity diffusion region,

removing the second insulating film on an upper portion side of the protrusion-like region so that the second insulating film remains on a side of a portion of the protrusion-like region except an upper portion;

thermally oxidizing the upper portion side of the protrusion-like region and an upper portion side of the gate electrode opposed to the upper portion side of the protrusion-like region to form a forth insulating film so that a void is formed between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode;

etching the forth insulating film on the upper portion side of the protrusion-like region to expose the upper portion side of the protrusion-like region; and

forming a fifth insulating film between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode so that a void remains between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode.

12. The method for manufacturing a vertical MOS transistor according to claim 11 , wherein

in forming a fifth insulating film, thermal oxidation is performed in an oxidizing atmosphere containing water vapor in a temperature range of 650 to 850° C. to form the fifth insulating film.

13. A method for manufacturing a vertical MOS transistor comprising:

forming a protrusion-like region protruding upward from a predetermined plane of a silicon semiconductor substrate;

forming a silicon oxide film on an exposed surface of the protrusion-like region and a surface of the silicon semiconductor substrate;

increasing a film thickness of at least the silicon oxide film on the silicon semiconductor substrate by thermal oxidation to form a first insulating film;

forming a lower impurity diffusion region extending from a lower portion of the protrusion-like region to an inside of the silicon semiconductor substrate;

removing the silicon oxide film except the first insulating film to expose a silicon side of the protrusion-like region;

thermally oxidizing the exposed silicon side of the protrusion-like region to form a second insulating film having a thinner film thickness than a film thickness of the first insulating film;

forming a gate electrode over a side of the protrusion-like region;

removing the second insulating film on an upper portion side of the protrusion-like region so that the second insulating film remains on a side of a portion of the protrusion-like region except an upper portion;

forming a third insulating film having a thicker film thickness than a film thickness of the second insulating film or an insulating region having a thicker effective film thickness than a film thickness of the second insulating film between the upper portion side of the protrusion-like region and an upper portion side of the gate electrode opposed to the upper portion side of the protrusion-like region; and

forming an upper impurity diffusion region in an upper portion of the protrusion-like region.

14. The method for manufacturing a vertical MOS transistor according to claim 13 , wherein

in forming a third insulating film or an insulating region, the upper portion side of the protrusion-like region and the upper portion side of the gate electrode are thermally oxidized to form the third insulating film so that a film thickness of the third insulating film is thicker than a film thickness of the remaining second insulating film.

15. The method for manufacturing a vertical MOS transistor according to claim 13 , wherein

in forming a third insulating film or an insulating region,

the upper portion side of the protrusion-like region and the upper portion side of the gate electrode are thermally oxidized to form a forth insulating film so that a void is formed between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode,

the forth insulating film on the upper portion side of the protrusion-like region is etched to expose the upper portion side of the protrusion-like region, and

a fifth insulating film is formed between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode so that a void remains between the upper portion side of the protrusion-like region and the upper portion side of the gate electrode.