1. A semiconductor device comprising:
a semiconductor substrate, which forms a source region of a first conduction type, wherein the semiconductor substrate has a top surface and a back surface, wherein the back surface is opposite to the top surface;
a base region of a second conduction type, wherein the base region extends perpendicularly from the top surface in the substrate;
a drift region of the first conduction type, wherein the drift region has an impurity concentration lower than that of the source region and extends perpendicularly from the top surface within the base region;
a drain region extending perpendicularly from the top surface within the drift region;
a gate insulating film formed on a surface that defines a trench, wherein the gate insulating film extends perpendicularly from the top surface and extends in a lateral direction from the source region to the drift region through the base region; and
a gate electrode formed on a surface of the gate insulating film such that, when a voltage is applied to the gate electrode, a channel region is generated in the vicinity of a surface of the base region adjacent to the trench, wherein the flow of the channel occurs in the lateral direction.
2. The semiconductor device of claim 1, wherein the drain region is an epitaxially grown layer of the first conduction type in which two opposed parts of the grown layer have met one another.
3. The semiconductor device of claim 1, wherein the drain region, the drift region, and the base region have substantially homogeneous impurity concentrations in the perpendicular and the lateral directions.
4. The semiconductor device of claim 1 further comprising a metal layer, which is embedded at a boundary between the source region and the base region to electrically connect the source region and the base region.
5. The semiconductor device of claim 1 further comprising:
a first metal layer extending perpendicularly from the top surface to approximately the depth of the drain region at a boundary between the source region and the base region to electrically connect the source region and the base region; and
a second metal layer extending perpendicularly in the drain region from the top surface to approximately the depth of the drain region.
6. The semiconductor device of claim 1 further comprising a metal film formed on the back surface to electrically connect the source region and the base region.
7. The semiconductor device of claim 1, wherein the base region, the drift region, the drain region, the gate insulating film, and the gate electrode are parts of a cell, and the cell is one of a plurality of similar cells, and a drain electrode is connected to the drain region of each cell to form a plurality of transistors in a chip.
8. A semiconductor device comprising:
a semiconductor substrate, which forms a source region of a first conduction type, wherein the semiconductor substrate has a top surface and a back surface, wherein the back surface is opposite to the top surface;
a base region of a second conduction type, wherein the base region extends perpendicularly from the top surface in the substrate;
a drift region of the first conduction type, wherein the drift region has an impurity concentration lower than that of the source region and extends perpendicularly from the top surface within the base region;
a drain region extending perpendicularly from the top surface within the drift region;
a gate insulating film formed on a surface that defines a trench, wherein the gate insulating film extends perpendicularly from the top surface and extends in a lateral direction from the source region to the drift region through the base region;
a gate electrode formed on a surface of the gate insulating film; and
at least one RESURF layer of the second conduction type, wherein the RESURF layer extends perpendicularly from the top surface in the drift region such that, when a voltage is applied to the gate electrode, a channel region is generated in the vicinity of a surface of the base region adjacent to the trench, wherein the flow of the channel occurs in the lateral direction.
9. The semiconductor device of claim 8, wherein the drain region, the drift region, the base region, and the RESURF layer have homogeneous impurity concentrations in the perpendicular and the lateral directions.
10. The semiconductor device of claim 8, wherein the RESURF layer is one of a plurality of RESURF layers, which are formed to completely deplete the drift region with depletion layers formed respectively about the RESURF layers when the voltage is not applied to the gate electrode.
11. The semiconductor device of claim 8, wherein the RESURF layer contacts the base region.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method comprising the steps of:
heating an elongated metal bar to a forming temperature within a temperature range suitable for creep deformation of the metal bar;
applying a stretching force to the heated metal bar at a strain rate no greater than 0.05 inchinchsecond; and
wrapping the heated metal bar around a die to form a wrapped metal bar.
2. The method of claim 1 wherein the step of applying includes the step of applying a stretching force to the heated metal bar at a strain rate no greater than 0.05 inchinchsecond to a strain ranging from 0.5% to 15.0%.
3. The method of claim 2 wherein the step of heating includes the step of heating a metal bar formed of a titanium alloy to a forming temperature ranging from 0.45 to 0.60 Tm wherein Tm is the melting point of the titanium alloy.
4. The method of claim 2 wherein the step of applying includes, prior to the step of wrapping, the step of applying a stretching force to the heated metal bar at a strain rate no greater than 0.05 inchinchsecond to a strain ranging from 0.5% to 3.0%; and wherein the step of applying includes, during the step of wrapping, the step of applying a stretching force to the heated metal bar at a strain rate no greater than 0.05 inchinchsecond to a strain ranging from 0.5% to 15.0%.
5. The method of claim 1 wherein the step of heating includes the step of heating a metal bar formed of a titanium alloy to a forming temperature ranging from 0.45 to 0.60 Tm wherein Tm is the melting point of the titanium alloy.
6. The method of claim 1 wherein the step of heating includes the step of heating the metal bar to a temperature ranging from 650\xb0 C.-925\xb0 C. (1202\xb0 F.-1690\xb0 F.).
7. The method of claim 1 wherein the step of heating includes the step of heating a metal bar formed of a titanium alloy to a temperature ranging from 1250\xb0 F.-1450\xb0 F.
8. The method of claim 1 wherein the step of applying includes the step of applying a stretching force to the heated metal bar at a strain rate ranging from 0.00005 inchinchsecond to 0.005 inchinchsecond.
9. The method of claim 1 wherein the step of heating includes the step of passing an electrical current through the metal bar to heat the metal bar resistively.
10. The method of claim 9 further including the step of maintaining the metal bar at temperature which is substantially uniform throughout the metal bar and which is substantially constant throughout the steps of applying and wrapping.
11. The method of claim 9 wherein the step of wrapping includes the step of wrapping the heated metal bar around a die face of a metal die with a layer of electrically insulative material separating the die face from the heated metal bar to prevent electrical communication between the metal bar and the metal die.
12. The method of claim 1 further including the steps of holding the wrapped metal bar against the die after the step of wrapping and simultaneously maintaining the temperature of the wrapped metal bar within the temperature range for at least 5 minutes.
13. The method of claim 12 further including the step of maintaining the temperature of the wrapped metal bar within the temperature range for at least 10 minutes.
14. The method of claim 13 further including the step of maintaining the temperature of the wrapped metal bar within the temperature range for at least 20 minutes.
15. The method of claim 11 further including the step of maintaining the metal bar at a temperature which is within 30.0\xb0 C. of the forming temperature throughout the steps of applying, wrapping, holding and maintaining.
16. The method of claim 1 further including the step of positioning thermal insulation around the die and metal bar to reduce heat loss from the metal bar.
17. The method of claim 1 wherein the step of heating includes the step of heating the metal bar to a temperature which is substantially uniform throughout the metal bar.
18. The method of claim 17 further including the step of maintaining the substantially uniform temperature throughout the steps of applying and wrapping.
19. The method of claim 18 wherein the step of wrapping includes the step of wrapping the heated metal bar around a die face of the die and a layer of thermally insulative material disposed between the die face and the heated metal bar without independently heating the die face.
20. The method of claim 1 wherein the step of wrapping includes the step of wrapping the heated metal bar around a working surface which is formed of at least one of a thermally insulative material and an electrically insulative material.