Granted Patent B2

US 6,893,947 · App. 10/179,769 · Granted May 17, 2005

Abstract

Claims (48)

1. A method for making an enhancement mode RF device, comprising the steps of:

providing a substrate having a stack of semiconductor layers formed thereon, the stack including a doped cap layer and a central layer defining a device channel;

disposing a mask over the cap layer, thereby defining a masked region and an unmasked region; and

in any order, (a) creating an implant region in the unmasked region, and (b) removing the cap layer from the unmasked region.

2. The method of claim 1 , wherein the mask is a dielectric mask.

3. The method of claim 1 , wherein the mask is a photoresist mask.

4. The method of claim 1 , wherein, after steps (a) and (b) are performed, the implant region and the cap layer region do not substantially overlap.

5. The method of claim 1 , wherein the implant region is created before the cap layer is removed from the unmasked region.

6. The method of claim 1 , wherein the implant region is created after the cap layer is removed from the unmasked region.

7. The method of claim 1 , wherein the stack of semiconductor layers further comprises a source and a drain, wherein the implant region is formed in the stack of semiconductor layers so as to define an implant-free area in the device channel between the source and drain, and wherein the implant-free area is essentially self-aligned with the cap layer.

8. The method of claim 7 , further comprising the steps of:

etching the stack of compound semiconductor layers at the source and drain to form source contact and drain contact areas; and

in any sequence, forming a device insulation structure over the implant-free area and etching a gate opening through the device insulation structure and the cap layer of the stack compound semiconductor layers over the implant-free area.

9. The method of claim 8 , further comprising the step of depositing gate metal in the gate opening to form a gate contact.

10. The method of claim 8 , wherein the stack of compound semiconductor layers includes an electrically insulating layer disposed between the cap layer and the central layer, wherein the stack is etched through the cap layer and partially through the electrically insulating layer, and wherein the method further comprises the step of depositing electrical contacts on the exposed portion of the insulating layer in the source contact area and the drain contact area.

11. The method of claim 1 , wherein the implant region is an N + implant region.

12. The method of claim 1 , wherein the cap layer comprises GaAs.

13. The method of claim 12 , wherein the photoresist mask is removed before steps (a) and (b) are performed.

14. A method for making an enhancement mode RF device, comprising the steps of:

providing a substrate having a stack of semiconductor layers formed thereon, the stack including a doped cap layer and a central layer defining a device channel;

depositing a dielectric layer over the cap layer;

depositing a photoresist over the dielectric layer; and

in any order, (a) forming a dielectric mask out of the dielectric layer, (b) creating an implant region, (c) selectively removing a portion of the cap layer, thereby defining a capped region and an uncapped region, and (d) removing the photoresist;

wherein, after steps (b) and (c) are performed, the implant region and the capped region do not substantially overlap.

15. A method for making an enhancement mode RF device, comprising the steps of:

providing a semiconductor construct having a first layer comprising GaAs disposed over a second layer comprising AlGaAs;

disposing a dielectric layer on the first layer;

forming a photoresist mask over the dielectric layer, thereby defining a first masked region and a first unmasked region, the first unmasked region including a first portion of the first layer;

patterning a hardmask in the dielectric layer, thereby defining a second masked region and a second unmasked region, the second unmasked region including a second portion of the first layer;

removing the photoresist;

creating an N + implant in the second unmasked region; and

removing the first and second portions of the first layer.

16. A method for making an enhancement mode RF device, comprising the steps of:

providing a substrate having a stack of compound semiconductor layers formed thereon, the stack including (a) a doped cap layer, and (b) a central layer defining a device channel; and

implanting a source and drain in the stack of semiconductor layers so as to define an implant-free area in the device channel between the source and drain which substantially coincides with the cap layer.

17. The method of claim 16 , wherein the stack further comprises a buffer, and wherein the source and drain extend at least into the buffer.

18. The method of claim 17 , further comprising the steps of, in any sequence, forming a device insulation structure over the implant-free area, and etching a gate opening through the device insulation structure and the cap layer of the stack compound semiconductor layers in the implant-free area, the gate opening being spaced from the source and the drain.

19. A method for making an enhancement mode RF device, comprising the steps of:

providing a substrate having a stack of semiconductor layers formed thereon, the stack including doped a cap layer and a central layer defining a device channel;

disposing a first mask over the cap layer, thereby defining a first masked region and a first unmasked region;

in any order, (a) creating an implant region in the first unmasked region, and (b) removing the cap layer from the first unmasked region;

removing the first mask;

disposing a second mask, distinct from said first mask, over the cap layer, thereby defining a second masked region and a second unmasked region; and

forming a gate opening through the cap layer in the second unmasked region.

20. The method of claim 9 , wherein the implant region comprises a source and a drain, and wherein the gate is disposed between the source and drain.

21. The method of claim 1 , wherein the cap layer and the implant region are not in physical contact.

22. The method of claim 14 , wherein the cap layer and the implant region are not in physical contact.

23. The method of claim 16 , wherein the cap layer is not in physical contact with either the source or the drain.

Assignments (17)