Varying mesa dimensions in high cell density trench MOSFET
First Claim
1. A field effect transistor comprising:
- a first plurality of cells having a first cell pitch, the first plurality of cells having gates with first mesa regions extending between the gates, wherein a heavy body contact opening extends into each first mesa region, and a heavy body region extends in each first mesa regions along a bottom of corresponding heavy body contact opening; and
a second plurality of cells having a second cell pitch, the second cell pitch being narrower than the first cell pitch, the second plurality of cells having gates with second mesa regions extending between the gates, wherein no heavy body contact opening is formed in the second mesa regions, and a heavy body region extends in each second mesa region to a shallower depth than a depth to which the heavy body regions in the first mesa regions extend;
wherein each of the gates in the first and second plurality of cells is housed in a trench, each mesa region in the first and second plurality of cells including a well region, the well regions in at least the second plurality of cells including source regions having a conductivity type opposite that of the well regions;
wherein each of the heavy body regions in the first and the second mesa regions is located in a corresponding well region, the heavy body regions being of the same conductivity type as but having a higher doping concentration than the well regions.
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Abstract
Circuits, methods, and apparatus for power MOSFETs having a high cell density for a high current carrying capability while maintaining a low pinched-base resistance. One device employs a number of transistor cells having varying mesa (regions between trench gates) sizes. A heavy body etch is utilized in larger cells to reduce the pinched-base resistance. This etch removes silicon in the mesa region, which is then replaced with lower-impedance aluminum. A number of smaller cells that do not receive this etch are used to increase device current capacity. Avalanche current is directed to the larger, lower pinched base cells by ensuring these cells have a lower BVDSS breakdown voltage. The large cell BVDSS can be varied by adjusting the critical dimension or width of the trench gates on either side of the wider mesas, or by adjusting the depth of the heavy body etch.
19 Citations
20 Claims
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1. A field effect transistor comprising:
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a first plurality of cells having a first cell pitch, the first plurality of cells having gates with first mesa regions extending between the gates, wherein a heavy body contact opening extends into each first mesa region, and a heavy body region extends in each first mesa regions along a bottom of corresponding heavy body contact opening; and a second plurality of cells having a second cell pitch, the second cell pitch being narrower than the first cell pitch, the second plurality of cells having gates with second mesa regions extending between the gates, wherein no heavy body contact opening is formed in the second mesa regions, and a heavy body region extends in each second mesa region to a shallower depth than a depth to which the heavy body regions in the first mesa regions extend; wherein each of the gates in the first and second plurality of cells is housed in a trench, each mesa region in the first and second plurality of cells including a well region, the well regions in at least the second plurality of cells including source regions having a conductivity type opposite that of the well regions; wherein each of the heavy body regions in the first and the second mesa regions is located in a corresponding well region, the heavy body regions being of the same conductivity type as but having a higher doping concentration than the well regions. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A trench-gate power field effect transistor comprising:
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a first trench gate; a second trench gate displaced from the first trench gate by a first distance in a first direction, the region between the first and second trench gates being free from trench gates; a third trench gate displaced from the second trench gate by a second distance in a second direction opposite the first direction, the region between the second and third trench gates being free from trench gates; a first well region located between the first trench gate and the second trench gate, the first well region having a heavy body contact opening extending therein; a first heavy body region extending in the first well region along a bottom of the heavy body contact opening; a second well region located between the second trench gate and the third trench gate, the second well region having no heavy body contact opening extending therein; and a second heavy body region extending in the second well region to a shallower depth than a depth to which the first heavy body region extends, wherein the first distance is larger than the second distance. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A field effect transistor comprising:
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a first pair of gates with a first well region extending between the first pair of gates, and with no gates between the first pair of gates; a second pair of gates with a second well region extending between the second pair of gates, and with no gates between the second pair of gates, wherein of the first and second well regions, only the first well region has a heavy body contact opening extending therein, and the first well region has a lateral width greater than a lateral width of the second well region; a first heavy body region extending in the first well region along a bottom of the heavy body contact opening; and a second heavy body region extending in the second well region to a shallower depth than a depth to which the first heavy body region extends. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification