Trenched semiconductor devices and their manufacture
In semiconductor devices which include an insulated trench electrode ( 11 ) in a trench ( 20 ), for example, trench-gate field effect power transistors and trenched Schottky diodes, a cavity ( 23 ) is provided between the bottom ( 25 ) of the trench electrode ( 11 ) and the bottom ( 27 ) of the trench ( 20 ) to reduce the dielectric coupling between the trench electrode ( 11 ) and the body portion at the bottom ( 27 ) of the trench in a compact manner. In power transistors, the reduction in dielectric coupling reduces switching power losses, and in Schottky diodes, it enables the trench width to be reduced.
1. A method of forming a semiconductor device including an insulated trench electrode in a trench, the trench extending through a semiconductor body portion of the device, and the trench electrode being dielectrically coupled to the body portion by an insulating layer at a side-wall of the trench, the method including the steps of:
(a) etching a trench into the body portion;
(b) providing a layer of filler material over the bottom of the trench;
(c) providing trench electrode material in the trench with a path defined through the trench electrode material to the underlying filler material;
(d) etching to remove filler material between the trench electrode material and the bottom of the trench; and
(e) closing the path through the trench electrode material to leave a cavity between the trench electrode material and the bottom of the trench, which cavity reduces the dielectric coupling between the trench electrode and the body portion at the bottom of the trench.
2. A method of claim 1 wherein step (c) comprises forming spacers of trench electrode material over opposing side-walls of the trench.
3. A method of claim 1 wherein step (e) comprises oxidising the trench electrode material to grow oxide spanning the path.
4. A method of claim 1 , wherein the filler material is the same as that of the trench electrode insulating layer.
5. A method of claim 1 , wherein the filler material is selectively etchable with respect to that of the trench electrode insulating layer.
6. A method of forming a semiconductor device of claim 1 , wherein the cavity is defined by the deposition of the trench electrode material.