Methods of processing semiconductor wafers having silicon carbide power devices thereon

#This invention relates to microelectronic devices, and more particularly, to the fabrication of silicon carbide power devices.

#The thickness of silicon-carbide (SiC) substrates in SiC-based power semiconductor devices can affect the forward voltage needed to operate the devices at a given current level. In particular, the performance and/or operation of SiC devices such as SiC Schottky diodes, MOSFETs, BJTs, PiN diodes, n-channel IGBTs, thyristors and/or vertical JFETs may be affected by the relatively high resistance of thick SiC substrates. For example, n-type, 4H-SiC substrates may account for about 1 mohm-cm2 of the specific on-resistance of various devices. This may constitute about 50% of the on-resistance of a 600 V SiC Schottky diode, and/or about 90% of the on-resistance of a 300V SiC Schottky diode. A p-type 4H-SiC substrate may add about 50-100 mohm-cm2 to the device on-resistance. For this reason, it has not been practical to develop vertical devices, such as GTOs and n-channel IGBTs, on p-type SiC substrates.

#Present SiC device fabrication technology typically employs relatively thick (300-400 microns) substrates. Fabrication processing, including the backside ohmic contact anneal, may be performed on epilayers grown on the substrate. Since there may be subsequent processing steps after ohmic contact formation, the substrate is typically thick enough to provide adequate mechanical support for the epilayers. However, the thick substrate used for mechanical support may add to the electrical and/or thermal resistance of the device.

#The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate certain embodiment(s) of the invention. In the drawings:

#FIGS. 1A-1F are cross-sectional illustrations that illustrate methods of processing semiconductor wafers according to some embodiments of the invention;

#FIGS. 2A-2D are cross-sectional illustrations that illustrate methods of processing semiconductor wafers according to some embodiments of the invention;

#The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. However, this invention 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. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items.

#The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

#It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Like numbers refer to like elements throughout the specification.