Silicon-on-insulator (SOI) device having variable thickness device layer and corresponding method of production
A method of producing power semiconductor devices from a silicon-on-insulator (SOI) wafer is described. The SOI wafer includes a silicon device layer, a bulk silicon wafer, and a buried oxide layer separating the silicon device layer from the bulk silicon wafer. The method includes: forming a hard mask on the silicon device layer, wherein the hard mask covers one or more first regions of the silicon device layer and exposes one or more second regions of the silicon device layer; and before forming any field oxide structures and before implanting any device regions, selectively growing epitaxial silicon on the one or more second regions of the silicon device layer exposed by the hard mask such that the thickness of the one or more second regions is increased relative to the one or more first regions. Various devices produced according to the method are also described.
1. A method of producing power semiconductor devices from a silicon-on-insulator (SOI) wafer that includes a silicon device layer, a bulk silicon wafer, and a buried oxide layer separating the silicon device layer from the bulk silicon wafer, the method comprising:
forming a hard mask on the silicon device layer, wherein the hard mask covers one or more first regions of the silicon device layer and exposes one or more second regions of the silicon device layer; and
before forming any field oxide structures and before implanting any device regions, selectively growing epitaxial silicon on the one or more second regions of the silicon device layer exposed by the hard mask such that the thickness of the one or more second regions is increased relative to the one or more first regions.
2. The method of claim 1 , wherein the power semiconductor devices are lateral power MOSFETs (metal-oxide-semiconductor field-effect transistors), and wherein the one or more second regions of the silicon device layer exposed by the hard mask during the selectively growing of the epitaxial silicon correspond to drift zones of the lateral power MOSFETs.
3. The method of claim 2 , wherein the one or more first regions of the silicon device layer covered by the hard mask during the selectively growing of the epitaxial silicon correspond to contact regions of the lateral power MOSFETs.
4. The method of claim 3 , wherein a plurality of rows of the contact regions are laterally spaced apart from one another along a length of the drift zones, and wherein during the selectively growing of the epitaxial silicon, the drift zones are made thicker between the rows of the contact regions but not below the rows of the contact regions.
5. The method of claim 3 , wherein a first row of the contact regions are source contact regions having a thickness that remains unchanged by the selectively growing of the epitaxial silicon, and wherein a second row of the contact regions are drain contact regions having a thickness that remains unchanged by the selectively growing of the epitaxial silicon.
6. The method of claim 1 , wherein the power semiconductor devices are lateral JFETs (junction field-effect transistors), and wherein the one or more second regions of the silicon device layer exposed by the hard mask during the selectively growing of the epitaxial silicon correspond to drift zones of the lateral JFETs.
7. The method of claim 6 , wherein the one or more first regions of the silicon device layer covered by the hard mask during the selectively growing of the epitaxial silicon correspond to source contact regions and drain contact regions of the lateral JFETs, and wherein both the source contact regions and the drain contact regions have a thickness that remains unchanged by the selectively growing of the epitaxial silicon.
8. The method of claim 7 , wherein the drift zones are devoid of contact regions, and wherein the one or more second regions of the silicon device layer expose an entirety of the drift zone area between the source contact regions and the drain contact regions during the selectively growing of the epitaxial silicon.
9. The method of claim 1 , wherein the one or more second regions of the silicon device layer exposed by the hard mask during the selectively growing of the epitaxial silicon correspond to drift zones of the power semiconductor devices, and wherein the one or more first regions of the silicon device layer covered by the hard mask during the selectively growing of the epitaxial silicon correspond to additional semiconductor devices having a lower breakdown voltage than the power semiconductor devices.
10. The method of claim 1 , wherein the one or more first regions of the silicon device layer covered by the hard mask during the selectively growing of the epitaxial silicon correspond to field oxide regions of the power semiconductor devices.
11. The method of claim 1 , wherein the one or more first regions of the silicon device layer covered by the hard mask during the selectively growing of the epitaxial silicon correspond to contact regions of the power semiconductor devices.
12. The method of claim 1 , wherein the power semiconductor devices are PMOS devices having a breakdown voltage greater than 600V, and wherein the one or more first regions of the silicon device layer covered by the hard mask during the selectively growing of the epitaxial silicon correspond to additional semiconductor devices having a breakdown voltage less than 600V.
13. The method of claim 1 , wherein before the selectively growing of the epitaxial silicon, the silicon device layer has a single thickness in a range of 100 to 200 nm.
14. The method of claim 1 , wherein the hard mask comprises tetraethoxysilane formed by low-pressure chemical vapor deposition.