BRIERE MICHAEL A (US)
| US7250641B2 | 2007-07-31 | |||
| US6265726B1 | 2001-07-24 | |||
| US7217960B2 | 2007-05-15 |
WHAT IS CLAIMED IS:
1. A Hi-Nitride semiconductor device comprising a first Hi-Nitride layer of a first composition, a second Hi-Nitride layer of a second composition different from the said first composition atop said first HI-Nitride layer, a 2DEG layer formed by the interface between said first and second IH-Nitride layers, a source contact connected to the free surface of said first HI-Nitride layer, a drain contact laterally spaced from said source contact and connected to said free surface of said first HI- Nitride layer, a gate contact coupled to said free surface of said first IH-Nitride layer and disposed laterally between said source and drain contacts, and a conductive field plate disposed between said gate and drain contacts and connected to said source contact to reduce the electric field between said gate and drain contacts when said 2DEG layer is non-conductive.
2. The device of claim 1, wherein said first layer is GaN and said second layer is AlGaN.
3. The device of claim 1, wherein said second layer is supported on a substrate.
4. The device of claim 3, wherein said substrate is silicon and includes a transition layer connected to said second layer.
5. The device of claim 1, wherein said gate contact is a Schottky contact.
6. The device of claim 1, wherein said gate contact is di electrically insulated from said surface of said first IH-Nitride layer.
7. The device of claim 1, which further includes a highly conductive El- Nitride pad disposed between said source and drain contacts and said free surface of said first Hi-Nitride layer.
8. The device of claim 2, which further includes a highly conductive El- Nitride pad disposed between said source and drain contacts and said free surface of said first El-Nitride layer.
9. The device of claim 3, which further includes a highly conductive El- Nitride pad disposed between said source and drain contacts and said free surface of said first El-Nitride layer.
10. The device of claim 5, which further includes a highly conductive El- Nitride pad disposed between said source and drain contacts and said free surface of said first El-Nitride layer.
11. The device of claim 6, which further includes a highly conductive El- Nitride pad disposed between said source and drain contacts and said free surface of said first El-Nitride layer.
12. The device of claim 1, wherein said field plate is a layer of highly conductive N + El-Nitride material.
13. The device of claim 2, wherein said field plate is a layer of highly conductive N + El-Nitride material.
14. The device of claim 3, wherein said field plate is a layer of highly conductive N + El-Nitride material.
15. The device of claim 5, wherein said field plate is a layer of highly conductive N + El-Nitride material.
16. The device of claim 6, wherein said field plate is a layer of highly conductive N + Hi-Nitride material.
17. The device of claim 7, wherein said field plate is a layer of highly conductive N + IE-Nitride material.
18. In a El-Nitride semiconductor device having a El-Nitride layer, and a 2DEG layer disposed adjacent the bottom of said El-Nitride layer; first and second laterally spaced contacts coupled to the top of said El-Nitride layer; a source contact coupled to said top of said El-Nitride layer and laterally disposed between said first and second drain contacts; first and second gate contacts coupled to the top of said El-Nitride layer and disposed between said source contact and said first drain contact and between said source contact and said second drain contact respectively; and first and second conductive field plates disposed between said first drain contact and said first gate contact and said second drain contact and said second gate contact respectively; said first and second field plate contacts connected to one another and to said source contact.
19. The device of claim 18, wherein said El-Nitride layer is GaN.
20. The device of claim 19, wherein said first and second field plates are a highly conductive El-Nitride material.
21. The device of claim 20, wherein said field plates are selected from the group including GaN and AlGaN.
22. The device of claim 1, wherein said gate contact is a Schottky contact.
23. The device of claim 1, wherein said gate contact is dielectrically insulated from said surface of said first Ill-Nitride layer.
24. The device of claim 18, which further includes a highly conductive N+ Hi-Nitride pad disposed between said surface of said DI-Nitride layer.
25. The device of claim 20, which further includes a highly conductive N+ IQ-Nitride pad disposed between said surface of said HI-Nitride layer.
26. The device of claim 1, which further includes a dielectric layer disposed between said field plate and said free surface of said first IE-Nitride layer.
27. The device of claim 26, wherein said field plate is a layer of highly conductive N + Hi-Nitride material.
28. The device of claim 18, which further includes respective dielectric layers disposed between said first and second field plates and said top surface of said HI-Nitride layer.
29. A process for forming the electrodes of a HI-Nitride semiconductor device comprising the steps of: forming a highly conductive HI-Nitride first layer over the top surface of said device; forming a second layer of a conductive material over said first layer; patterning said first and second layers to define a central gate pedestal, first and second field plates spaced from opposite edges of said central gate pedestal and first and second outer drain electrodes spaced from the opposite edges of said central gate pedestal; and forming first and second conductive gate electrodes on said top surface of said device and between and spaced from the confronting edges of the gaps formed between said first and second field plates and said first and second outer drain electrodes; and electrically connecting said first and second filed plates to said central gate electrode. |
I-NITRIDE DEVICE SEMICONDUCTOR DEVICE WITH REDUCED ELECTRIC FIELD BETWEEN GATE AND DRAIN
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/973,295, filed September 18, 2007; and U.S. Provisional Application No. 60/973,367, filed September 18, 2007, the entire disclosure of which is incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present application relates to semiconductor devices and methods of fabrication of semiconductor devices.
DEFINITION
[0003] As referred to herein IH-Nitride refers to a semiconductor alloy from the InAlGaN system, including, but not limited to, GaN, AlGaN, AlN, InGaN, InAlGaN and the like.
BACKGROUND OF THE INVENTION
[0004] It is known that the electric field between the gate electrode and the drain electrode of a El-Nitride power semiconductor device affects the breakdown voltage thereof. Thus, it is desirable to reduce the gate to drain voltage that a gate electrode "sees" during the operation of the device.
SUMMARY OF THE INVENTION
[0005] To reduce the electric field between the gate electrode and the drain electrode, a device according to the present invention includes field plates each disposed between one or more pairs a gate electrode and a drain electrode, each field plate electrically shorted to the source electrode of the device.
[0006] More specifically, according to one aspect of the present invention, a Hi-Nitride power device is provided with a field plate over its heteroj unction structure. The field plate may be comprised of a highly conductive El-Nitride body which is shorted to the source electrode of the device. As a result, the gate to drain voltage "seen" by the gate electrode is reduced, whereby the capability of the device to withstand breakdown is enhanced.
[0007] In a preferred method of fabrication of a device according to the present invention, to obtain as close a spacing between each gate electrode and a respective field plate, a wide conductive plate is fabricated using any desired method, and then the wide plate is separated into thinner respective interleaved gate electrodes and field plates, for example, through an appropriate etching step, to obtain separated gate electrodes and field plates.
[0008] Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Fig. 1 schematically illustrates a top plan view of two adjacently disposed active cells in a device according to the present invention.
[0010] Fig. 2 schematically illustrates a cross-sectional view along line 2-2 viewed in the direction of the arrows.
[0011] Fig. 3 schematically illustrates a top plan view of a device before the modification thereof using a process according to the present invention.
[0012] Fig. 4 schematically illustrates a cross-sectional view of a second embodiment of the present invention.
[0013] Fig. 5 schematically illustrates a cross-sectional view of two adjacent active cells of device according to a further embodiment of the present invention.
[0014] Figs. 6 and 7 schematically illustrate selected steps in a process for the fabrication of the device of Fig. 5 according to the present invention.
[0015] Fig. 8 schematically illustrates a cross-sectional view of two adjacent cells of a device in accordance with the invention according to a further embodiment of the invention.
[0016] Fig. 9 is like Fig. 8 and shows a still further embodiment of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0017] Referring to Fig. 1, two adjacent cells of a much larger device according to one embodiment of the present invention is shown. The device includes drain electrodes 10, a source electrode 12, gate electrodes 14 each disposed between source electrode 12 and a respective drain electrode 10, and field plates 16 each disposed between a gate electrode 14 and a respective drain electrode 10. All of electrodes 10, 12, 14 and field plate 16 may be of any desired conductive material deposited atop heteroj unction 18.
[0018] According to one aspect of the present invention source electrode 12 and field plates 16 are electrically shorted to one another as schematically illustrated by Fig. 1.
[0019] Referring now to Fig. 2, a device according to the present invention is preferably a m-Nitride power field effect device, such as a high electron mobility transistor (HEMT). A device according to the present invention thus includes the m-Nitride heteroj unction 18 formed over a support body 20. El-Nitride
heteroj unction 18 includes a first Hi-Nitride body 22 serving preferably as a channel layer, and a second HI-Nitride body 24 serving as a barrier layer. The thickness and composition of first and second EH-Nitride bodies 22, 24 are selected to result in a conductive region at (or near) the heteroj unction thereof, commonly referred to as a two-dimensional electron gas (2-DEG). In the embodiment of Figs. 1, 2 and 3, first Hi-Nitride body 22 is comprised of GaN while second Hi-Nitride body 24 is comprised of AlGaN. Further, in the embodiment of Figs. 1, 2 and 3, drain electrodes 10 and source electrode 12 make ohmic contact with second ffl-Nitride body 24, while gate electrodes 14 and field plates 16 make a Schottky contact to second El-Nitride body 24. Note that support body 20 may include a substrate which is compatible with first Hi-Nitride body 22 (e.g. a GaN substrate) or may include a substrate comprised of silicon, SiC, Sapphire, or the like having a transition body or layer (e.g. an AlN body) to allow for the growth thereon of first Hi-Nitride body 22.
[0020] Referring now to Fig. 3, in a preferred method for fabricating a device according to the present invention, a HI-Nitride device is fabricated according to any suitable method to have wide gate electrodes 14 is formed between each drain electrode 10 and source electrode 12. Thereafter, each wide gate electrode 14 is split or separated into two strips (using any desired and suitable etching technique, for example) to obtain field plates 16 and gate electrodes 14 as illustrated by Fig. 1.
[0021] Referring now to Fig. 4, in which like numerals identify like features, in an alternative embodiment, gate electrodes 14 and field plates 16 are deposited over a gate insulation body 26 which is on body 24 and has a composition and thickness suitable to function as a gate dielectric. Thus, after splitting, layer 14' in Fig. 3, gate electrode 14 and field plate 16 may be capacitively coupled to body 24, rather than being Schottky coupled to body 24.
[0022] Referring next to Fig. 5, in which components similar to those of Figs. 1 to 4 are given the same identifying numeral, a device according to the another embodiment of the present invention includes the HI-Nitride heteroj unction
18 formed over a support body 20. Heteroj unction 18 includes the first Hi-Nitride body 22 formed over support body 20, and second HI-Nitride body 24 formed over first El-Nitride body 22. The thickness and composition of first and second El- Nitride bodies 22, 24 are selected to form a two-dimensional electron gas at (or near) the heteroj unction thereof, as is well known in the art.
[0023] In Fig. 5, first DI-Nitride body 22 serves as the channel layer and may be composed of GaN, and second Hi-Nitride body 24 serves as the barrier layer and may be composed of AlGaN. Support body 20 may be a substrate that is compatible with first HI-Nitride body 22, e.g. GaN, or may be a substrate (e.g. silicon, SiC or sapphire) that includes a transition layer (e.g. AlN) to allow for the growth thereon of first HI-Nitride body 22.
[0024] The embodiment of Fig. 5 further includes, in each active cell thereof, first power electrode 12 (e.g. source electrode), second power electrode 10 (e.g. drain electrode), and a gate electrode 14 disposed between first power electrode 12 and second power electrode 10. In the preferred embodiment, gate electrode 14 makes a Schottky contact with second HI-Nitride body. However, it should be understood that a gate electrode 14 may be capacitively coupled to second HI-Nitride body 24 (e.g. through a gate dielectric) without deviating from the scope and the spirit of the present invention.
[0025] According to one aspect of the invention as shown in Fig. 5, field plate 16 that is comprised of highly conductive (e.g. N+) HI-Nitride material (e.g. GaN or AlGaN) is disposed over second IH-Nitride body 24 and between a gate electrode 14 and drain electrode 10. Field plates 16 are preferably electrically shorted to source electrode 12, whereby the voltage between gate electrode 14 and drain electrode 10 is reduced to improve the breakdown voltage of the device. The short can be formed in any desired manner.
[0026] In the embodiment of Fig. 5, each drain electrode 10 and source electrode 12 resides atop and is ohmically coupled to a respective highly
conductive (e.g. N+) EH-Nitride (e.g. GaN or AlGaN) pedestal 36 which is formed over second EH-Nitride body 24, whereby ohmic connection between the power electrodes 10, 12 and second Hi-Nitride body 24 is improved.
[0027] Referring now to Figs. 6 and 7, to fabricate a device according to the embodiment of Fig. 5, the IE-Nitride heteroj unction 18 is formed over a support body 20 according to any suitable method. Thereafter, a highly conductive Hi-Nitride layer 38 (e.g. a layer of N+ GaN or N+ AlGaN) is grown over second Hi- Nitride body 24. Next, a layer of conductive material for forming power electrodes 10, 12 is formed on second IH-Nitride body 24 and patterned to obtain electrodes 10 and 12.
[0028] Layer 38 is then patterned to include a plurality of gaps 40, 41
(Fig. 7) in order to obtain or define field plates 16 and pedestals 36. Note that gaps 40 and 41 serve to physically isolated field plates 16 and pedestals 36. Thereafter, gate electrodes 14 are formed in gaps 41 of Fig. 7 on second IH-Nitride body 24, and field plates 16 and source electrode 12 are electrically shorted to obtain a device according to the present invention.
[0029] Referring next to Fig. 8 in which numerals identify like features of the preceding Figures, the device is an enhancement mode device and field plates 16 may be any conductive material including metallic materials as well as a highly conductive IH-Nitride laser or body as described above. An enhancement mode device according to this embodiment, includes a 2-DEG layer having an interrupted region or a region of reduced carrier density 50 under gate electrode 14. To obtain the interrupted region or the region of reduced carrier density many different methods may be used. For example, a recess may be formed in the body 24, an implanted region may be formed in either body 24 or 22, the surface of body 24 may be treated using CF4 under the gate, or local decomposition as set forth in US Application No. 11/906,842 filed October 4, 2007, entitled HI-Nitride Heterjunction Semiconductor Device and Method of Fabrication (IR-3282) (incorporated by
reference) may be employed to obtain an interrupted 2-DEG or a 2-DEG of reduced density under gate electrode 14. US Application No. 11/040,657 filed January 21, 2005, entitled Enhancement Mode m-Nitride FET (IR-2663) (incorporated herein in its entirety by reference) sets forth various way to obtain a 2-DEG layer having an interrupted region or a region of reduced carrier density under the gate electrode thereof. Note that in the embodiment of Fig. 8 gate electrode 14 is Schottky coupled to body 16.
[0030] It has been found that the combination of a field plate 16 that is shorted to the source electrode in an enhancement mode device (i.e. a device with an interrupted 2-DEG or a 2-DEG with a reduced carrier density under the gate) results in a IQ-Nitride enhancement mode device that is stable during operation which up to now has eluded those skilled in the art.
[0031] Referring next to Fig. 9, in which like numerals identify like features of the prior Figures, in a device according to the third embodiment of the present invention, and, as in Fig. 4, a gate dielectric 26 may be disposed between the gate electrodes 14 and body 24. Furthermore, dielectric body 26 may be disposed between field plates 16 and body 24. Note that in the embodiments of Figs. 8 and 9, pedestals 26 may be omitted without deviating from the scope and the spirit of the present invention. Thus, electrodes 14 and 16 may be coupled ohmically to body 16.
[0032] Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein.
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