FR2963985A1 - Gallium nitride vertical Schottky diode, has heavily doped p-type and n-type gallium nitride guard rings respectively provided at peripheries of electrode and lightly doped layer, where electrode is arranged on lightly doped layer - Google Patents

Abstract

The invention relates to a vertical Schottky diode comprising successively, on a conductive substrate (20), a layer (14) of strongly doped GaN type N; a layer (13) of lightly doped GaN type N; a Schottky contact (22) on the lightly doped N-type GaN layer.

Description

FIELD OF THE INVENTION The present invention relates to a Schottky diode comprising a Schottky contact between a layer of gallium nitride (GaN) and a metal layer.

BACKGROUND OF THE PRIOR ART Schottky diodes with gallium nitride have interesting qualities, in particular because their reverse breakdown voltage is very high (of the order of 600 volts for less than 10 g / cm thick) and their direct voltage drop is particularly low, less than 2 V for an active surface area less than 4 mm 2 and for currents of 4 to 8 A. Figure 1 is a sectional view intended to illustrate a conventional method of manufacturing a Schottky diode with gallium nitride. For this, we start from a crystalline substrate 1, for example sapphire (Al203), silicon or silicon carbide. On this substrate, to obtain a mesh with GaN, it is necessary to provide an intermediate buffer layer 2, for example silicon nitride, aluminum nitride or gallium nitride. On the intermediate buffer layer 2, epitaxially grown a layer of GaN 3 strongly doped N (N +) then a layer of gallium nitride 4 weakly B9707 - 09-T0-222

2 doped N-type to obtain a Schottky contact with an upper layer 5, for example tungsten, titanium-tungsten, tungsten nitride, titanium nitride, nickel, gold, nickel-gold, platinum, platinum-gold, platinum-nickel ...

A problem arises because it results from this manufacturing process the existence of an insulating buffer layer 2 between the substrate 1 and the Schottky diode structure. This buffer layer is insulating and prohibits the production of a vertical diode between the substrate 1 and the Schottky contact 5.

FIGS. 2A and 2B illustrate two embodiments of Schottky diodes obtained from the structure described in FIG. 1. In FIGS. 2A and 2B, the same elements are designated with the same references as in FIG. 1. FIG. a Schottky diode structure of mesa type. The surface of the lightly doped N-type layer 4 above the heavily doped N-type layer 3 is limited so that a peripheral portion of the layer 3 is apparent and a second layer can be placed therein. electrode 6. To obtain a layer of GaN 4 of limited extent, it is necessary either to carry out a selective epitaxy over an unmasked part of the layer 3, or to etch the layer 4 after its formation. A disadvantage of this structure lies in its difficulty of manufacture.

Another disadvantage is that such a diode is not a vertical diode and therefore its live voltage drop is not minimal for a given chip area. FIG. 2B shows another possible structure in which, after manufacture of a diode by the method illustrated in FIG. 1, apertures are pierced from the rear face, these openings passing through all the substrate 1 and the buffer layer 2 to unblock in the layer 3 of heavily doped GaN type N. These openings are then filled with a conductive material 7. A rear face metallization 8 is in contact with this conductive material 7.

B9707 - 09-T0-222

This type of structure has the disadvantage of having a particularly complex manufacturing process and does not actually constitute a vertical diode. There is therefore a need for a gallium nitride Schottky diode with truly vertical operation. SUMMARY It is an object of one embodiment of the present invention to provide such a gallium nitride Schottky diode that is vertical and does not exhibit at least some of the disadvantages of the prior art devices. Thus, an embodiment of the present invention provides a vertical Schottky diode comprising successively, on a conductive substrate, a N-type heavily doped GaN layer; a lightly doped N type GaN layer; A Schottky contact on the N-type lightly doped GaN layer. According to one embodiment of the present invention, the conductive substrate comprises a highly doped silicon substrate coated with a metal layer at the interface with the layer. strongly doped type N GaN. According to one embodiment of the present invention, the Schottky contact on the N-type lightly doped GaN layer is located. According to one embodiment of the present invention, the periphery of the Schottky contact region is surrounded by a heavily doped P-type guard ring in the GaN layer. According to one embodiment of the present invention, the outer periphery of the N-type lightly doped GaN layer comprises a heavily doped N-type channel stop ring. The present invention also provides a method of manufacturing a vertical Schottky diode, comprising the steps of: forming on a first substrate a buffer layer; B9707 - 09-T0-222

4 growing on the buffer layer a lightly doped N-type GaN layer; growing on the lightly doped layer a strongly doped N-type GaN layer; assembling the resulting structure with a second, highly conductive substrate on the side of the heavily doped N-type layer; removing the first substrate and the buffer layer; A brief description of the drawings. These and other objects, features, and advantages will be discussed in detail in the following description of particular non-limiting embodiments. in relation to the attached figures among which: Figure 1 is a sectional view for illustrating a method of manufacturing a Schottky gallium nitride structure according to the prior art; FIGS. 2A and 2B are cross-sectional views showing two exemplary embodiments of Schottky diodes according to the prior art; FIGS. 3A and 3B illustrate two steps of manufacturing a gallium nitride Schottky diode according to one embodiment of the present invention; and Figures 4 and 5 are sectional views illustrating two exemplary embodiments of Schottky diodes according to embodiments of the present invention. For the sake of clarity, the same parts or elements have been designated with the same references in the various figures and, moreover, as is customary in the representation of the microelectronic circuits, the various figures are not drawn to scale. DETAILED DESCRIPTION FIG. 3A represents a first step of fabricating a gallium nitride Schottky diode in a B9707-09-T0-222 mode.

embodiment of the present invention. Firstly, a first wafer W1 comprising a substrate 11, for example sapphire (Al2O3), silicon or silicon carbide coated with a buffer layer 12, for example SiN, AlN, GaN, AlGaN, is produced. On this buffer layer, a N-type lightly doped gallium nitride layer 13 is grown followed by a heavily doped N-type gallium nitride layer 14. It will be noted that the formation order of the layers 13 and 14 is reversed. relative to the order of the layers 3 and 4 of FIG. 1. A second wafer W2 is then produced intended to be contiguous to the upper surface of the wafer W1. This wafer W2 is made of a conductive material, for example a heavily doped silicon wafer. Optionally, on the upper surface of the GaN (N +) layer 14, a conductive bonding layer is formed, for example a metal layer 15. Next, the W1 and W2 wafers are bonded together and the substrate 11 and the buffer layer are removed. 13 to obtain the structure illustrated in FIG. 3B. It then remains to form a Schottky contact on the apparent surface of the lightly doped GaN layer 13 and possibly also a contact on the apparent face of the highly conductive wafer 20. Thus, after turning, the structure shown in FIG. wherein the Schottky electrode 22 is located by an anterior deposition of an insulating layer 23, for example oxide (USG, PSG, BSG, BPSG, TEOS, or other). Thus, a completely vertical Schottky diode has been obtained between the metallization 22 and a rear-face contact 24. By way of example, and without being limiting: the silicon wafer 20 may have a final thickness of 100 to 300 the optional metal layer 15 may be tungsten and have a thickness of 50 to 500 nm, for example of the order of 0.2 μm, B9707-09-T0-222

6 - the N-type strongly doped GaN 14 layer (N +) may have a thickness of 0.2 to 3 μm, and the N-type lightly doped GaN layer 13 may have a thickness of 1 to 10 μm; depending on the desired reverse voltage behavior of the Schottky diode. FIG. 5 represents a variant of the structure of FIG. 4 in which there is provided a P-type guard ring 31 at the periphery of the Schottky diode, and possibly a strongly doped N-type ring 32 at the periphery of the 10 jump to serve as a channel stop. Thus, according to a main advantage of the described embodiments of the present invention, a perfectly vertical Schottky diode is obtained without there being an insulating interface (the buffer layer of the diodes of the prior art).

It will be appreciated that the present invention is capable of many variations with respect in particular to the nature of the substrate 20 and the possible presence of a metal layer 15. At various locations of the present disclosure, "weakly" doped regions are mentioned. "strongly" doped. Those skilled in the art will be able to interpret these mentions without ambiguity by taking into account the function of the corresponding regions, for example to ensure a resistance in tension or to have a role of ohmic contact.

Among the dopants that can be used for doping GaN, it will be possible to choose for the type N Si, S and Ge and for the type P Mg, Be, Zn and C.

Claims (6)

REVENDICATIONS1. A vertical Schottky diode comprising successively, on a conductive substrate (20): a layer (14) of strongly doped GaN type N; a layer (13) of lightly doped GaN type N; a Schottky contact (22) on the N-type weakly doped GaN layer. The Schottky diode according to claim 1, wherein the conductive substrate (20) comprises a highly doped silicon substrate coated with a metal layer at the interface with the GaN N-type strongly doped layer (14). 3. Schottky diode according to claim 1 or 2, wherein the Schottky contact on the N-type low-doped GaN layer (13) is located. The Schottky diode according to claim 3, wherein the periphery of the Schottky contact region is surrounded by a P-type heavily doped guard ring (31) in the GaN layer. The Schottky diode according to claim 3 or 4, wherein the outer periphery of the N-type lightly doped GaN layer (13) comprises a strongly doped N-type channel stop ring (32). 6. A method of manufacturing a vertical Schottky diode according to claim 1, comprising the steps of: forming on a first substrate (11) a buffer layer (12); growing on the buffer layer (12) a layer (13) of lightly doped GaN type N; growing on the lightly doped layer a layer (14) of heavily doped N-type GaN; assembling the resulting structure with a second, highly conductive substrate (20) on the side of the heavily doped N-type layer; removing the first substrate and the buffer layer; forming a Schottky contact (22) on the weakly doped N-type layer.