Method of forming a MOS-controllable power semiconductor device for use in an integrated circuit
A power semiconductor device has an active region that includes a drift region. At least a portion of the drift region is provided in a membrane which has opposed top and bottom surfaces. In one embodiment, the top surface of the membrane has electrical terminals connected directly or indirectly thereto to allow a voltage to be applied laterally across the drift region. In another embodiment, at least one electrical terminal is connected directly or indirectly to the top surface and at least one electrical terminal is connected directly or indirectly to the bottom surface to allow a voltage to be applied vertically across the drift region. In each of these embodiments, the bottom surface of the membrane does not have a semiconductor substrate positioned adjacent thereto.
1. A method of forming a MOS-controllable power semiconductor device for use in an integrated circuit, the device having an active region that includes a drift region, the method comprising:
forming, in a layer provided on a semiconductor substrate, a power semiconductor device having an active region that includes a drift region;
removing at least a portion of the semiconductor substrate below at least a portion of the drift region such that said at least a portion of the drift region is provided in a membrane defined by that portion of the layer below which the semiconductor substrate has been removed, the membrane having opposed top and bottom surfaces, the bottom surface of the membrane not having a semiconductor substrate positioned adjacent thereto; and,
connecting at least one electrical terminal directly or indirectly to the top surface of the membrane and at least one other electrical terminal directly or indirectly to the bottom surface of the membrane to allow a voltage to be applied vertically across the drift region.
2. A method according to claim 1 , wherein said at least a portion of the semiconductor substrate is removed by wet etching.
3. A method according to claim 2 , wherein said at least a portion of the semiconductor substrate is removed using a buried insulating layer as an etch stop.
4. A method according to claim 1 , wherein said at least a portion of the semiconductor substrate is removed by dry etching.
5. A method according to claim 4 , wherein said at least a portion of the semiconductor substrate is removed using a buried insulating layer as an etch stop.
6. A method according to claim 1 , wherein at least one semiconductor layer is introduced by implantation, diffusion or deposition from the back-side of the device following the formation of the membrane.
7. A method according to claim 1 , wherein a bottom terminal layer is applied to the bottom of the membrane, said bottom terminal layer being in contact with at least one semiconductor layer within the membrane.