Methods of fabricating gallium nitride semiconductor layers by lateral growth into trenchers, and gallium nitride semiconductor structures fabricated thereby

#This invention relates to microelectronic devices and fabrication methods, and more particularly to gallium nitride semiconductor devices and fabrication methods therefor.

#Gallium nitride is being widely investigated for microelectronic devices including but not limited to transistors, field emitters and optoelectronic devices. It will be understood that, as used herein, gallium nitride also includes alloys of gallium nitride such as aluminum gallium nitride, indium gallium nitride and aluminum indium gallium nitride.

#A major problem in fabricating gallium nitride-based microelectronic devices is the fabrication of gallium nitride semiconductor layers having low defect densities. It is known that one contributor to defect density is the substrate on which the gallium nitride layer is grown. Accordingly, although gallium nitride layers have been grown on sapphire substrates, it is known to reduce defect density by growing gallium nitride layers on aluminum nitride buffer layers which are themselves formed on silicon carbide substrates. Notwithstanding these advances, continued reduction in, defect density is desirable.

#FIGS. 1-5 are cross-sectional views of first embodiments of gallium nitride semiconductor structures during intermediate fabrication steps according to the present invention.

#FIGS. 6-10 are cross-sectional views of second embodiments of gallium nitride semiconductor structures during intermediate fabrication steps according to the present invention.

#FIGS. 11-15 are cross-sectional views of third embodiments of gallium nitride semiconductor structures during intermediate fabrication steps according to the present invention.

#The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout. It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or “onto” another element, it can be directly on the other element or intervening elements may also be present. Moreover, each embodiment described and illustrated herein includes its complementary conductivity type embodiment as well.

#Referring now to FIGS. 1-5, methods of fabricating gallium nitride semiconductor structures according to a first embodiment of the present invention will now be described. As shown in FIG. 1, an underlying gallium nitride layer 104 is grown on a substrate 102. The substrate 102 may include a 6H—SiC(0001) substrate 102a and an aluminum nitride buffer layer 102b. The crystallographic designation conventions used herein are well known to those having skill in the art, and need not be described further. The gallium nitride layer 104 may be between 1.0 and 2.0 μm thick, and may be grown at 1000° C. on a high temperature (1100° C.) aluminum nitride buffer layer 102b that was deposited on the 6H—SiC substrate 102a in a cold wall vertical and inductively heated metalorganic vapor phase epitaxy system using triethylgallium at 26 μmol/min, ammonia at 1500 sccm and 3000 sccm hydrogen diluent. Additional details of this growth technique may be found in a publication by T. W. Weeks et al. entitled “GaN Thin Films Deposited Via Organometallic Vapor Phase Epitaxy on α(6H)—SiC(0001) Using High-Temperature Monocrystalline AlN Buffer Layers”, Applied Physics Letters, Vol. 67, No. 3, Jul. 17, 1995, pp. 401-403, the disclosure of which is hereby incorporated herein by reference. Other substrates, with or without buffer layers, may be used.

#Still referring to FIG. 1, the underlying gallium nitride layer 104 includes a plurality of sidewalls 105 therein. It will be understood by those having skill in the art that the sidewalls 105 may be thought of as being defined by a plurality of spaced apart posts 106, that also may be referred to as “mesas”, “pedestals” or “columns”. The sidewalls 105 may also be thought of as: being defined by a plurality of trenches 107, also referred to as “wells” in the underlying gallium nitride layer 104. The sidewalls 105 may also be thought of as being defined by a series of alternating trenches 107 and posts 106. It will be understood that the posts 106 and the trenches 107 that define the sidewalls 105 may be fabricated by selective etching and/or selective epitaxial growth and/or other conventional techniques. Moreover, it will also be understood that the sidewalls need not be orthogonal to the substrate 102, but rather may be oblique thereto. Finally, it will also be understood that although the sidewalls 105 are shown in cross-section in FIG. 1, the posts 106 and trenches 107 may define elongated regions that are straight, V-shaped or have other shapes. As shown in FIG. 1, the trenches 107 may extend into the buffer layer 102b and into the substrate 102a, so that subsequent gallium nitride growth occurs preferentially on the sidewalls 105 rather than on the trench floors. In other embodiments, the trenches may not extend into the substrate 102a, and also may not extend into buffer layer 102b, depending, for example, on the trench geometry and the lateral versus vertical growth rates of the gallium nitride.