Abstract:
A non-planar lateral drift MOS device eliminates the need for a field plate extension, which reduces gate width. In one example, two sources and two comparatively small gates in a raised structure allow for two channels and a dual current with mirrored flows, each traveling into and downward through a center region of a connecting well that connects the substrate with the drain areas and shallow wells containing the source areas, the current then traveling in opposite directions within the substrate region of the connecting well toward the two drains. The source and drain areas may be separate raised structures or isolated areas of a continuous raised structure.

Description:
BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention generally relates to non-planar drift-type semiconductor devices. More particularly, the present invention relates to a non-planar vertical dual source lateral drift metal-oxide non-planar semiconductor structure lacking a field plate extension. 
     Background Information 
     Conventional drift MOS (metal-oxide semiconductor) architecture uses a large gate width to accommodate a field plate extension. As semiconductor devices continue to shrink, non-planar devices come into play and space for such a large gate becomes problematic. 
     Therefore, a need exists to reduce the gate width in a non-planar drift MOS device. 
     SUMMARY OF THE INVENTION 
     The shortcomings of the prior art are overcome and additional advantages are provided through the provision, in one aspect, of a method of fabricating a non-planar lateral drift metal-oxide semiconductor. The method includes providing a non-planar semiconductor structure, the structure including a semiconductor substrate and at least one raised semiconductor structure coupled to the substrate, the at least one raised structure including alternating source and drain regions. The method further includes creating a connecting well coupling the substrate with the alternating source and drain regions, creating at least one shallow well, each shallow well encompassing a source region, creating a source in each source region, and creating a drain in each drain region. When active, a current flows around each shallow well and through the connecting well in a single channel from each source to each corresponding drain. 
     In accordance with another aspect, a non-planar semiconductor device is provided. The device includes a semiconductor substrate, at least one fin coupled to the substrate, the at least one fin including alternating source and drain regions. The device further includes a connecting well coupling the substrate with the alternating source and drain regions, at least one shallow well, each shallow well encompassing a source region, a source in each source region, and a drain in each drain region. When active, a current flows around each shallow well and through the connecting well in a single channel from each source to each corresponding drain. 
     These, and other objects, features and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one example of a starting non-planar semiconductor structure, the non-planar structure including alternating source and drain regions in three sets of raised structures, each set in this example including left, middle and right raised semiconductor structures coupled to a substrate, isolation material encompassing the raised structures, in accordance with one or more aspects of the present invention. 
         FIG. 2  depicts the semiconductor structure of  FIG. 1  after the addition of impurities (e.g., by implantation) into the isolation material, the impurities penetrating the raised structures and into the substrate, allowing for the creation of a connecting well between corresponding raised structures in a given set, the well connecting the corresponding raised structures via the substrate, in accordance with one or more aspects of the present invention. 
         FIG. 3  is a cross-sectional view of the semiconductor structure of  FIG. 2  taken across the first set of corresponding raised structures, after the creation of shallow wells at opposite sides of the middle raised structure, in accordance with one or more aspects of the present invention. 
         FIG. 4  depicts the semiconductor structure of  FIG. 3  after recessing the isolation material with impurities, and creation of dummy gates, the dummy gates surrounding portions of the relevant raised structures, in accordance with one or more aspects of the present invention. 
         FIG. 5  depicts the semiconductor structure of  FIG. 4  after creation of source implant regions in source regions of the shallow wells, the implant regions acting as sources, and drain implant regions in drain regions of the left and right raised structures, the drain implant regions acting as drains for the adjacent sources, in accordance with one or more aspects of the present invention. 
         FIG. 6  depicts the semiconductor structure of  FIG. 5  after creation of shallow well taps, and showing current paths in operation, in accordance with one or more aspects of the present invention. 
         FIG. 7  depicts an alternative form of the finished structure of  FIG. 6 , replacing each set of raised structures with a single raised structure, the various regions/wells being separated by isolation regions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting examples illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating aspects of the invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions, and/or arrangements, within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. 
     The terminology used herein is for the purpose of describing particular examples 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 “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     As used herein, the term “connected,” when used to refer to two physical elements, means a direct connection between the two physical elements. The term “coupled,” however, can mean a direct connection or a connection through one or more intermediary elements. 
     As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances the modified term may sometimes not be appropriate, capable or suitable. For example, in some circumstances, an event or capacity can be expected, while in other circumstances the event or capacity cannot occur—this distinction is captured by the terms “may” and “may be.” 
     Reference is made below to the drawings, which are not drawn to scale for ease of understanding, wherein the same reference numbers are used throughout different figures to designate the same or similar components. 
       FIG. 1  is a perspective view of one example of a starting non-planar semiconductor structure  100 , including alternating source and drain regions (e.g., source regions  150 ,  152  and drain regions  154  and  156 ) in three sets of raised semiconductor structures, e.g., left  102 , middle  104  and right  106  raised semiconductor structures (raised with respect to the substrate) coupled to a substrate  108 , and including isolation material  110  encompassing the raised structures, in accordance with one or more aspects of the present invention. At this stage of fabrication, the isolation material covers to a top of the raised structures, forming a flat surface  111 . In one example, impurities may be inserted into the isolation material through the flat surface, penetrating through the semiconductor material (i.e., the raised structures and partially into the substrate), for example, by implantation. The isolation material may include, for example, shallow-trench isolation material, e.g., an oxide. 
     The starting structure may be conventionally fabricated, for example, using processes known in the art. However, it will be understood that the fabrication of the starting structure forms no part of the present invention. Further, although only a portion is shown for simplicity, it will be understood that, in practice, many such sets of raised structures would typically be included on the same bulk substrate (e.g., silicon wafer). 
     In one example, substrate  108  may include any silicon-containing substrate including, but not limited to, silicon (Si), single crystal silicon, polycrystalline Si, amorphous Si, silicon-on-nothing (SON), silicon-on-insulator (SOI) or silicon-on-replacement insulator (SRI) or silicon germanium substrates and the like. Substrate  102  may in addition or instead include various isolations, dopings and/or device features. In the present example, the substrate is of a first type (i.e., p-type or n-type). The substrate may include other suitable elementary semiconductors, such as, for example, germanium (Ge) in crystal, a compound semiconductor, such as silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), and/or indium antimonide (InSb) or combinations thereof; an alloy semiconductor including GaAsP, AlInAs, GaInAs, GaInP, or GaInAsP or combinations thereof. 
     In one example, raised structures  102 ,  104  and  106  may each take the form of a “fin.” The raised structure(s) may be etched from a bulk substrate, and may include, for example, any of the materials listed above with respect to the substrate. Further, some or all of the raised structure(s) may include added impurities (e.g., by doping), making them n-type or p-type. 
       FIG. 2  depicts the semiconductor structure of  FIG. 1  after the addition of impurities  109  of a second type throughout isolation layer  110 , penetrating the raised structures and partially into the substrate  108 . The impurity/isolation layer will subsequently be recessed, the impurities in the remaining impurity/isolation layer and the substrate creating a connecting well  112  (see  FIG. 4 ) coupling the corresponding raised structures of a set via the substrate, in accordance with one or more aspects of the present invention. In one example, where the substrate is p-type, the connecting well may be n-type. The impurities may be added to the starting structure of  FIG. 1  by, for example, implanting the same. 
       FIG. 3  is a cross-sectional view of the semiconductor structure of  FIG. 2  taken across corresponding raised structures  102 ,  104  and  106 , after delimiting shallow wells  114  and  116  at opposite sides  113  and  115  of the middle raised structure  104 , in accordance with one or more aspects of the present invention. The shallow wells encompass the source regions  150  and  152 , and extend downward about 10 nm to about 80 nm into the middle raised structure. In one example, where the substrate is p-type and the connecting well is n-type, the shallow wells may be p-type. The shallow wells may be created by, for example, implantation. 
       FIG. 4  depicts the semiconductor structure of  FIG. 3  after recessing the isolation/impurity layer about 20 nm to about 50 nm, leaving an isolation region  111  over the connecting well, and after creation of dummy gates  117  surrounding the raised structures down to a top of the isolation region, in accordance with one or more aspects of the present invention. The dummy gates act as placeholders for eventual replacement metal gates, and may include, for example, polysilicon, and may be created using, for example, conventional processes and techniques. Preferably, the dummy gates are all created in a same process. Center gates  118  and  120  will be the active gates when subsequently replaced by metal gates. The remainder of the gates delineate areas  122  and  124  for creation of two sources (see source regions of  FIG. 3 , omitted for clarity of the dummy gates), areas  126  and  128  for creation of two drains (see drain regions of  FIG. 3 ), and areas  130  and  132  for creation of two shallow well taps. 
       FIG. 5  depicts the semiconductor structure of  FIG. 4  after creation of impurity regions  134  and  136  in the shallow wells of the middle raised structure  104  to act as sources (i.e., impurities in the source regions), and creation of impurity regions  138  and  140  in the left  102  and right  106  raised structures, respectively, adjacent the sources to act as drains (i.e., impurities in the drain regions), in accordance with one or more aspects of the present invention. In one example, the sources and drains may take the form of epitaxy. The epitaxy may be created by, for example, first etching the relevant portions of the raised structures to create cavities of about 20 nm to about 60 nm in depth for the epitaxy. The etching may be accomplished using, for example, conventional processes and techniques. Where the raised structures are, for example, silicon based, the n-type epitaxy may include epitaxial silicon doped with phosphorus (eSiP), and the p-type epitaxy may include epitaxial silicon germanium (eSiGe). The epitaxy may be grown, for example, using conventional processes and techniques. 
     In another example, the sources and drains take the form of impurities (e.g., by implanting), and are preferably relatively dense with impurities compared to the shallow wells. 
     For either process of forming the sources and drains, in one example, where the substrate is p-type, the connecting well is n-type and the shallow wells are p-type, the sources and drains may be n-type. In another example, where the substrate is n-type, the connecting well is p-type and the shallow wells are n-type, the sources and drains may be p-type. The sources and drains are preferably created in a same process. 
       FIG. 6  depicts the semiconductor structure of  FIG. 5  after creation of shallow well taps  142  and  144 , and showing current paths  146  and  148  in operation (after downstream creation of replacement metal gates), in accordance with one or more aspects of the present invention. As one skilled in the art will know, the well taps serve the purpose of body contact to ensure a good control of the channel. In one example, similar to the example for the sources and drains described above, the well taps may take the form of epitaxy of the first type. The epitaxy may be created by, for example, first etching the relevant portions of the raised structures to create cavities of about 20 nm to about 60 nm in depth for the epitaxy. The etching may be accomplished using, for example, conventional processes and techniques. Where the raised structures are, for example, silicon based, the n-type epitaxy may include epitaxial silicon doped with germanium (eSiGe), and the p-type epitaxy may include epitaxial silicon germanium (eSiGe). The epitaxy may be grown, for example, using conventional processes and techniques. 
     In another example, the well taps may take the form of impurities created, for example, by implantation. Preferably, the well taps are relatively dense with impurities compared to the shallow wells. In one example, where the substrate is p-type, the connecting well is n-type and the shallow wells are p-type, the well taps may be p-type. The well taps are a same type as the shallow wells. 
     Also shown in  FIG. 6 , are current paths  146  and  148  in operation, which assumes the presence of replacement metal gates, which may be, for example, conventional replacement gates including, e.g., tungsten. The current paths travel from each source  134  and  136  toward the center of middle raised structure  104 , vertically downward into the substrate region of connecting well  112 , and then in opposite directions toward their respective drains  138  and  140 . In one example, the finished structure may take the form of a non-planar dual source lateral drift metal-oxide semiconductor device. 
       FIG. 7  depicts one example of an alternate version of the semiconductor structure of  FIG. 6 , including a semiconductor substrate, and replacing each set of raised structures with a single, continuous semiconductor raised structure, the continuous raised structure including the shallow wells, sources, drains and gates as in  FIG. 6 , except that the various regions are all situated within the continuous raised structure and separated by isolation regions, rather than separation via multiple raised structures. 
     In a first aspect, disclosed above is a method of fabricating a non-planar lateral drift metal-oxide semiconductor. The method includes providing a non-planar semiconductor structure, the structure including a semiconductor substrate and raised semiconductor structure(s) coupled to the substrate, the raised structure(s) including alternating source and drain regions. The method further includes creating a connecting well coupling the substrate with the alternating source and drain regions, creating shallow well(s) encompassing the source region(s), creating a source in each of the source region(s), and creating a drain in each drain region. When active, a current flows around each shallow well and through the connecting well in a single channel from each source to each corresponding drain. 
     In one example, the raised structure(s) may further include, for example, multiple raised structures, each raised structure including one or more of the alternating source and drain regions, and the non-planar semiconductor structure may further include, for example, insulation material separating the multiple raised structures. 
     In one example, the multiple raised structures may include, for example, source raised structure(s) and drain raised structure(s), each source raised structure including shallow well(s) and each drain raised structure including one drain. Further, the drain raised structure(s) may include, for example, multiple drain raised structures, each drain raised structure including a drain region, the source raised structure(s) being situated between drain raised structures, the shallow well(s) including multiple shallow wells situated at opposite sides of the source raised structure(s), and the connecting well separating the shallow well(s) and coupling the substrate with the source regions in the shallow well(s) and the drain regions in the drain raised structures. 
     In one example, each of the raised structure(s) of the method of the first aspect may include, for example, the source region(s) and the drain region(s) isolated from each other. 
     In one example, the method of the first aspect may further include, for example, creating a separate gate lacking a field gate extension adjacent each shallow well. Further, each gate may include, for example, a dummy gate, or a conductive gate. Where a conductive gate is present, when active, each gate controls a single channel. 
     In one example, the method of the first aspect may further include, for example, creating a well tap in each shallow well at an edge of the raised structure in which the shallow well is located. 
     In a second aspect, disclosed above is a non-planar semiconductor device. The device includes a semiconductor substrate, raised structure(s) coupled to the substrate, the raised structure(s) including alternating source and drain regions. The device further includes a connecting well coupling the substrate with the alternating source and drain regions, shallow well(s) encompassing the source region(s), a source in each of the source region(s), and a drain in each drain region. When active, a current flows around each shallow well and through the connecting well in a single channel from each source to each corresponding drain. 
     In one example, the semiconductor device of the second aspect may further include, for example, a separate gate lacking a field gate extension adjacent each shallow well. Further, each gate may include, for example, a dummy gate, or a conductive gate. Where a conductive gate is present, when active, each gate controls a single channel. 
     In one example, the semiconductor device of the second aspect may further include, for example, a well tap in each shallow well at an edge of the raised structure in which the shallow well is located. 
     In one example, the semiconductor substrate of the device of the second aspect may further include, for example, a bulk semiconductor substrate, the non-planar semiconductor device including multiple of the non-planar semiconductor devices on the bulk substrate. 
     In one example, the semiconductor device of the second aspect, when active, may have, for example, a current flowing from each source through the connecting well and to the drain. 
     In one example, the raised structure(s) may include, for example, multiple raised structures, each raised structure including one or more of the alternating source and drain regions, and the non-planar semiconductor structure may further include, for example, insulation material separating the multiple raised structures. 
     In one example, the multiple raised structures may include, for example, source raised structure(s) and drain raised structure(s), each source raised structure including shallow well(s) and each drain raised structure including one drain. Further, the drain raised structures may include, for example, multiple drain raised structures, each drain raised structure including a drain region, the source raised structure(s) being situated between drain raised structures, the shallow well(s) including multiple shallow wells situated at opposite sides of the source raised structure(s), and the connecting well separating the shallow well(s) and coupling the substrate with the source regions in the shallow well(s) and the drain regions in the drain raised structures. 
     In one example, each of the raised structure(s) of the semiconductor device of the second aspect may include, for example, the source region(s) and the drain region(s) isolated from each other. 
     While several aspects of the present invention have been described and depicted herein, alternative aspects may be effected by those skilled in the art to accomplish the same objectives. For example, the finished structure may take the form of a n-type VDSMOS. The connecting well for the n-type VDSMOS would be p-type and would be isolated from a p-type substrate by a conventional triple n-type well. Conventional processes and techniques could be used to fabricate an isolated p-well on a p-type substrate. As another example, the finished structure may simply be one half of the dual-source version of  FIG. 6 , either half, delimited by line  158 . Accordingly, it is intended by the appended claims to cover all such alternative aspects as fall within the true spirit and scope of the invention.