Semiconductor device and method of forming a semiconductor device
A bipolar high voltage/power semiconductor device has a low voltage terminal and a high voltage terminal. The device has a drift region of a first conductivity type and having first and second ends. In one example, a region of the second conductivity type is provided at the second end of the drift region connected directly to the high voltage terminal. In another example, a buffer region of the first conductivity type is provided at the second end of the drift region and a region of a second conductivity type is provided on the other side of the buffer region and connected to the high voltage terminal. Plural electrically floating island regions are provided within the drift region at or towards the second end of the drift region, the plural electrically floating island regions being of the first conductivity type and being more highly doped than the drift region.
1. A method of forming a bipolar high voltage/power semiconductor device having a low voltage terminal and a high voltage terminal, the method comprising:
forming a drift region of a first conductivity type and having first and second ends;
forming adjacent the first end of the drift region a region of the first conductivity type connected directly to the low voltage terminal or a region of a second conductivity type connected indirectly via a further region to the low voltage terminal;
forming a region of the second conductivity type at the second end of the drift region connected directly to the high voltage terminal; and,
forming plural electrically floating island regions within the drift region at or towards the second end of the drift region, the plural electrically floating island regions being of the first conductivity type and being more highly doped than the drift region.
2. A method according to claim 1 , comprising:
forming the plural electrically floating island regions during the same process step already existing in the fabrication process used to form one of the layers.
3. A method according to claim 2 , comprising:
forming the plural electrically floating island regions and the low voltage terminal region(s) during the same process step.
4. A method according to claim 2 , comprising:
forming the plural electrically floating island regions during the same process step used to form the source or drain of a low-power/low-voltage MOSFET formed in the same integrated chip as the power/high voltage device.
5. A method according to claim 1 , wherein at least one of the ratio (W/S) of the width of the plural electrically floating island regions to the spacing between the plural electrically floating island regions and the ratio (L/S) of the length of the plural electrically floating island regions to the spacing between the plural electrically floating island regions is set so as to optimise the injection efficiency of the junction at the high voltage terminal.
6. A method according to claim 1 , wherein at least one of the ratio (W/S) of the width of the plural electrically floating island regions to the spacing between the plural electrically floating island regions and the ratio (L/S) of the length of the plural electrically floating island regions to the spacing between the plural electrically floating island regions is set so as to optimise the trade-off between the on-state losses and the switching losses in the power device.
7. A method according to claim 1 , wherein at least one of the ratio (W/S) of the width of the plural electrically floating island regions to the spacing between the plural electrically floating island regions and the ratio (L/S) of the length of the plural electrically floating island regions to the spacing between the plural electrically floating island regions is set so as to optimise the breakdown voltage by reducing the gain of the bipolar component.
8. A method of forming a bipolar high voltage/power semiconductor device having a low voltage terminal and a high voltage terminal, the method comprising:
forming a drift region of a first conductivity type and having first and second ends;
forming adjacent the first end of the drift region a region of the first conductivity type connected directly to the low voltage terminal or a region of a second conductivity type connected indirectly via a further region to the low voltage terminal;
forming a buffer region of the first conductivity type at the second end of the drift region;
forming a region of a second conductivity type on the other side of the buffer region and connected to the high voltage terminal such that the buffer region is between the second end of the drift region and said region of the second conductivity type; and,
forming plural electrically floating island regions provided at least partly within the buffer region or at least partly within the drift region at or towards the second end of the drift region, the plural floating regions being of the first conductivity type and being more highly doped than both the drift region and the buffer layer.
9. A method according to claim 8 , comprising:
forming the plural electrically floating island regions during the same process step already existing in the fabrication process used to form one of the layers.
10. A method according to claim 9 , comprising:
forming the plural electrically floating island regions and the low voltage terminal region(s) during the same process step.
11. A method according to claim 9 , comprising:
forming the plural electrically floating island regions during the same process step used to form the source or drain of a low-power/low-voltage MOSFET formed in the same integrated chip as the power/high voltage device.
12. A method according to claim 8 , wherein at least one of the ratio (W/S) of the width of the plural electrically floating island regions to the spacing between the plural electrically floating island regions and the ratio (L/S) of the length of the plural electrically floating island regions to the spacing between the plural electrically floating island regions is set so as to optimise the injection efficiency of the junction at the high voltage terminal.
13. A method according to claim 8 , wherein at least one of the ratio (W/S) of the width of the plural electrically floating island regions to the spacing between the plural electrically floating island regions and the ratio (L/S) of the length of the plural electrically floating island regions to the spacing between the plural electrically floating island regions is set so as to optimise the trade-off between the on-state losses and the switching losses in the power device.
14. A method according to claim 8 , wherein at least one of the ratio (W/S) of the width of the plural electrically floating island regions to the spacing between the plural electrically floating island regions and the ratio (L/S) of the length of the plural electrically floating island regions to the spacing between the plural electrically floating island regions is set so as to optimise the breakdown voltage by reducing the gain of the bipolar component.