Patent Document

BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to the field of semiconductor devices, and more particularly to formation of channels attached to source/drain semiconductor structures. 
         [0002]    Semiconductor device manufacturing includes various steps of device patterning processes. For example, the manufacturing of a semiconductor chip may start with, for example, a plurality of CAD (computer aided design) generated device patterns, which is then followed by effort to replicate these device patterns in a substrate. The replication process may involve the use of various exposing techniques, and a variety of subtractive (etching) and/or additive (deposition) material processing procedures. For example, in a photolithographic process, a layer of photo-resist material may first be applied on top of a substrate, and then be exposed selectively according to a pre-determined device pattern or patterns. Portions of the photo-resist that are exposed to light or other ionizing radiation (e.g., ultraviolet, electron beams, X-rays, etc.) may experience some changes in their solubility to certain solutions. The photo-resist may then be developed in a developer solution, thereby removing the non-irradiated (in a negative resist) or irradiated (in a positive resist) portions of the resist layer, to create a photo-resist pattern or photo-mask. The photo-resist pattern or photo-mask may subsequently be copied or transferred to the substrate underneath the photo-resist pattern. 
         [0003]    With continuous scale-down and shrinkage of real estate in a semiconductor wafer available for a single semiconductor device, engineers are daily faced with the challenge of how to meet the market demand for ever increasing device density. For sub-80 nm pitch patterning, one technique is to achieve twice the pattern density through a technique called sidewall imaging transfer (SIT), which is also known as sidewall spacer image transfer. In a conventional SIT process, a blanket deposition of spacer making material, such as dielectric material, is usually performed after the mandrel litho development and spacers are then made out of the blanket layer of spacer making material through a directional etching process. 
       SUMMARY 
       [0004]    According to one embodiment of the present disclosure, a structure comprising a vertical channel and a source/drain semiconductor structure connected to the vertical channel such that the source/drain semiconductor structure has a vertical side that is substantially planar with a vertical side of the vertical channel. The first source/drain semiconductor structure being located on a layer of substrate, the vertical channel being perpendicular relative to the layer of substrate. 
         [0005]    According to one embodiment of the present disclosure, a method of forming a semiconductor structure is provided. The method including forming a first vertical channel on a first layer of source/drain material that is perpendicular relative to the first vertical channel, and forming a first source/drain semiconductor structure by removing one or more portions of the first layer of source/drain material such that the first source/drain semiconductor structure has a vertical side that is substantially planar with a vertical side of the first vertical channel. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]    The following detailed description, given by way of example and not intend to limit the disclosure solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  illustrates a cross-sectional view depicting mandrels on a stack of layers from which the semiconductor devices of  FIG. 5  are fabricated, in accordance with an exemplary embodiment of the present invention. 
           [0008]      FIG. 2A  illustrates a cross-sectional view depicting the formation of fins (vertical channels) of the semiconductor devices of  FIG. 5 , in accordance with an embodiment of the present invention. 
           [0009]      FIG. 2B  illustrates a cross-sectional view depicting the deposition of a layer of filling material onto the semiconductor structures of  FIG. 2A , in accordance with an embodiment of the present invention. 
           [0010]      FIG. 3A  illustrates a cross-sectional view depicting the removal of a portion of the layer of filling material, in accordance with an embodiment of the present invention. 
           [0011]      FIG. 3B  illustrates a cross-sectional view depicting the formation of large pitch spacers, in accordance with an embodiment of the present invention. 
           [0012]      FIG. 4A  illustrates a cross-sectional view depicting the removal of filling material portions as well as portions of n-silicon, in accordance with an embodiment of the present invention. 
           [0013]      FIG. 4B  illustrates a cross-sectional view depicting the removal of large pitch spacers, in accordance with an embodiment of the present invention. 
           [0014]      FIG. 5  illustrates a cross-sectional view depicting four vertical transistor semiconductor devices that have been formed using the “L” shaped semiconductor structures of  FIG. 4B . 
           [0015]      FIG. 6  illustrates a cross-sectional view depicting the semiconductor devices of  FIG. 5 , in accordance with one embodiment of the present invention. 
           [0016]      FIG. 7  illustrates a cross-sectional view depicting the semiconductor devices of  FIG. 5 , in accordance with one embodiment of the present invention. 
           [0017]      FIG. 8  illustrates a cross-sectional view depicting the semiconductor devices of  FIG. 5 , in accordance with one embodiment of the present invention. 
       
    
    
       [0018]    The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention. In the drawings, like numbering represents like elements. 
       DETAILED DESCRIPTION 
       [0019]    Exemplary embodiments now will be described more fully herein with reference to the accompanying drawings, in which exemplary embodiments are shown. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, it is to be understood that embodiments of the invention may be practiced without these specific details. As such, this disclosure may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0020]    Embodiments may include methods of forming “L” shaped vertical transistors. As described below in conjunction with  FIGS. 1-8 , a fin is formed such that the vertical side of the fin is aligned with the vertical side of a source/drain semiconductor structure to which it is connected. The method described below in conjunction with  FIGS. 1-8  may be incorporated into typical semiconductor fabrication processes, such as fin field effect transistor (FinFET) fabrication processes described below in conjunction with  FIGS. 1-8 . 
         [0021]    For purposes of the description hereinafter, terms such as “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shall relate to the disclosed structures and methods, as oriented in the drawing figures. Terms such as “above”, “overlying”, “atop”, “on top”, “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure may be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements. 
         [0022]    In the interest of not obscuring the presentation of embodiments of the present invention, in the following detailed description, some processing steps or operations that are known in the art may have been combined together for presentation and for illustration purposes and in some instances may have not been described in detail. In other instances, some processing steps or operations that are known in the art may not be described at all. It should be understood that the following description is rather focused on the distinctive features or elements of various embodiments of the present invention. 
         [0023]    As used herein, semiconductor structures refer to one or more physical structures that comprise semiconductor devices. 
         [0024]    The present invention will now be described in detail with reference to the Figures. 
         [0025]    Referring now to  FIG. 1 ,  FIG. 1  illustrates a cross-sectional view depicting mandrels on a stack of layers from which the semiconductor devices of  FIG. 5  are fabricated, in accordance with an exemplary embodiment of the present invention.  FIG. 1  illustrates at least two mandrels ( 104 ,  105 ) are on a stack of layers including hard-mask layer  110 , semiconductor layer  120 , doped semiconductor  130 , semiconductor-on-insulator layer (SOI)  140 , buried oxide layer (BOX)  150 , and substrate layer  160 . In this embodiment, mandrel  104  and mandrel  105  are composed of amorphous silicon. Mandrel  104  and mandrel  105  respectively include two sidewall spacers ( 106 ,  107  and  108 ,  109 ). In this embodiment, such sidewall spacers are composed of silicon oxide. Mandrel  104  and  105  are positioned such that distance  102 , the distance separating sidewall spacers  107  and  108 , is substantially larger than either distance  101  or  103 , which correspond to the distance separating sidewall spacers  106 ,  107  and sidewall spacers  108 , 109 . In this embodiment, distance  101  and  103  are substantially similar in length. Further, in this embodiment, mandrel pitch of mandrel  104  and  105  are configured such that after sidewall imaging transfer (SIT), there will be intentional fin pitch walking. In other words, the mandrel pitch of mandrel  104  and  105  is configured such that, post SIT, distance  202  is substantially larger than either distance  201  or  203 , as shown in  FIG. 2A . 
         [0026]    Referring to  FIG. 1 , in this embodiment, hard-mask layer  110  is comprised of silicon nitride. In other embodiments, hard-mask layer  110  comprises any material of combination of materials that will act as a protecting layer during the formation of a channel of a vertical channel of a transistor or another semiconductor structure of the like. In this embodiment, the semiconductor layer  120  is a layer of intrinsic semiconductor, also called an un-doped semiconductor or i-type semiconductor (e.g., doping concentration is less than 10 16  cm −3 ). In general, in this embodiment, the semiconductor layer  120  is a semiconductor layer with a doping concentration significantly lower than the doping concentration of the doped semiconductor layer  130 . The semiconductor layer  120  can be silicon, germanium, silicon germanium, or compound semiconductor such as III-V or II-V compound semiconductor materials. In one embodiment, the semiconductor layer  120  is an intrinsic semiconductor layer without any significant dopant species present. Doped semiconductor layer  130  is a doped with n-type dopants such as phosphorus and/or arsenic, or p-type dopants such as boron and/or indium. The doped semiconductor layer  130  can be silicon, germanium, silicon germanium, or compound semiconductor such as III-V or II-V compound semiconductor materials. In various embodiments, doped semiconductor layer  130  is any material that is suitable for use as a source or drain material of a transistor or another semiconductor structure of the like. 
         [0027]    In this embodiment, SOI  140 , BOX  150 , and substrate layer  160  comprise a semiconductor-on-insulator wafer upon which the doped semiconductor layer  130  and the un-doped semiconductor layer  120  are epitaxially grown. Alternatively, the doped semiconductor layer  130  can be formed by other doping techniques such as ion implantation followed by activation anneal. This is followed by deposition of hard-mask layer  110 . In general, SOI  140  is a semiconductor layer such as, for example, silicon, silicon germanium, or germanium. In general, BOX  150  is a layer of silicon dioxide or another like dielectric material that will reduce electrical current leakage from active semiconductor devices such as transistors. In this embodiment, substrate layer  160  is a support or “handle” layer at the bottom of the stack. In this embodiment, substrate layer  160  is a dielectric material. In some embodiments, substrate layer  160  may be a semiconductor material or a semiconductor on top of a dielectric material like a semiconductor-on-insulator (SOI) substrate. 
         [0028]    Here, it is to be noted that the stack of layers  110 - 160 , as being demonstratively depictured in  FIG. 1 , is one of many possible examples through which semiconductor devices may be formed. Other types of combination of dielectric and/or semiconductor layers may be used as well without deviating from the spirit of present invention. 
         [0029]      FIG. 2A  illustrates a cross-sectional view depicting the formation of fins of the semiconductor devices of  FIG. 5 , in accordance with an embodiment of the present invention. In this embodiment, the fins are formed by applying a sidewall imaging transfer (SIT) technique to the mandrels on a stack of layers of  FIG. 1 . The result of the application of the SIT technique is the formation of fins  121 ,  123 ,  125  and  127 , which include a respective protective cap  111 ,  113 ,  115  and  117 . In this embodiment, fins  121 ,  123 ,  125  and  127  are structures that form the channels of transistors (see  FIGS. 5-8 ). The formation of fins using the processes of SIT techniques is well understood by those skilled in the art and, as such, a detailed description of such processes is not presented herein. However, the position of sidewall spacers  106 ,  107  and  108 ,  109  substantially correspond to the position of the resulting fins  121 ,  123 ,  125  and  127 . As such, the resulting distance  202  separating fin  123  and fin  125  is substantially larger than either distance  201  or  203 , which respectively separate fins  121 ,  123  and fins  125 ,  127 . 
         [0030]      FIG. 2B  illustrates a cross-sectional view depicting the deposition of a layer of filling material  200  onto the semiconductor structures of  FIG. 2A . In this embodiment, filling material  200  is a conformal material, e.g., silicon oxide. In this embodiment, filling material  200  is conformally deposited using low pressure chemical vapor deposition (LPCVD) or atomic layer deposition (ALD) such that the resulting layer of filling material  200  completely fills the spaces between fins  121 ,  123  and fins  125 , 127 . Note that the space between fins  123 ,  125  is not fully filled, but instead includes a gap ( 204 ). For example, distance  201  and  203  are 60 nm and distance  202  is 100 nm. Deposition of 30 nm thick layer of filling material  200  fills distance  201  and  203  but results in gap  204  being 40 nm wide. 
         [0031]      FIG. 3A  illustrates a cross-sectional view depicting the removal of a portion of the layer of filling material  200 . The result of the removal is that the respective spaces between fins  121 ,  123  and fins  125 ,  127  are still filled with filling material  200 , shown as filling material portions  201  and  202 . In this embodiment, a chemical oxide removal (COR) etch is used to remove a portion of filling material  200 . For example, filling material  200  is 40 nm thick. A 45 nm COR etch is applied to remove a portion of filling material  200 . The etch results in the removal of a small portion of filling material  200  that is respectively between protective caps  111 ,  113  and protective caps  115 ,  117 . However, this removal does not extend down to the filling material  200  that is respectively between fins  121 ,  123  and fins  125 ,  127 . 
         [0032]      FIG. 3B  illustrates a cross-sectional view depicting the formation of large pitch spacers ( 301 ,  302 ,  303  and  304 ), in accordance with an embodiment of the present invention. In this embodiment, large pitch spacers  301 ,  302 ,  303  and  304  are amorphous carbon spacers formed from an amorphous carbon layer (ACL) that was deposited onto the semiconductor structures of  FIG. 3A  and then etched to form spacers ( 301 ,  302 ,  303  and  304 ), which abut fins  121 ,  123 ,  125  and  127  respectively. The formation of such amorphous carbon spacers is well understood by those skilled in the art and, as such, a more detailed description of such processes is not presented herein. 
         [0033]      FIG. 4A  illustrates a cross-sectional view depicting the removal of filling material portions  201  and  202  as well as portions of doped semiconductor layer  130 . This removal results in the formation of source/drain (S/D) semiconductor structures  131 ,  133 ,  135  and  137 . In this embodiment, the removal of filling material portions  201  and  202  as well as portions of doped semiconductor layer  130  is achieved using two different etching techniques. The first etch (e.g., a selective silicon oxide wet etching process) selectively removes filling material portions  201  and  202  and the second etch (e.g., reactive ion etching) removes portions of doped semiconductor layer  130  that are not protected by large pitch spacers  301 ,  302 ,  303  and  304 . The techniques and application of selective etching is well understood by those skilled in the art and, as such, a more detailed description of such processes is not presented herein. 
         [0034]    The removal of portions of doped semiconductor layer  130  that are not protected by large pitch spacers  301 ,  302 ,  303  and  304  results in the formation of S/D semiconductor structures  131 ,  133 ,  135  and  137 , which respectively have S/D vertical sides  132 ,  134 ,  136  and  138  that are in substantial vertical planar alignment with fin vertical sides  122 ,  124 ,  126  and  128  of respective fins  121 ,  123 ,  125  and  127 . The alignment of a vertical side of a fin with the vertical side of a source/drain semiconductor structure yields a distinctive “L” shape. Such a formation reduces the size of the source/drain semiconductor structure, which in turn increases the limit of packing density of vertical transistors (and like structures) that are created using such “L” shaped semiconductor structures. 
         [0035]      FIG. 4B  illustrates a cross-sectional view depicting the removal of large pitch spacers  301 ,  302 ,  303  and  304 , in accordance with an embodiment of the present invention. The removal of large pitch spacers  301 ,  302 ,  303  and  304  further illustrates the “L” shape of the semiconductor structures shown in  FIG. 4A  (which respectively include a fin and a S/D semiconductor structure). In this embodiment, the selective removal of large pitch spacers  301 ,  302 ,  303  and  304  is accomplished using a reactive ion etching (REI) technique. The techniques and application of selective etching is well understood by those skilled in the art and, as such, a more detailed description of such processes is not presented herein. 
         [0036]      FIG. 5  illustrates a cross-sectional view depicting four vertical transistor semiconductor devices that have been formed using the “L” shaped semiconductor structures of  FIG. 4B .  FIG. 5  depicts gate structures  521 ,  523 ,  525  and  527  respectively surrounding fins  121 ,  123 ,  125  and  127 , further respectively. Gate structures  521 ,  523 ,  525  and  527  respectively include a layer of gate dielectric material (e.g., silicon dioxide, silicon nitride, silicon oxynitride, other dielectric material such as high-k, or any suitable combination of those materials) interposed between a layer of gate conducting material (e.g., doped silicon, metals, conducting metal compound materials, or any suitable combination of those materials) and respective fins  121 ,  123 ,  125  and  127 .  FIG. 5  further includes a layer of silicon nitride ( 500 ) and source/drain (S/D) semiconductor structures  511 ,  513 ,  515  and  517 , which are respectively connected to fins  121 ,  123 ,  125  and  127 . In this embodiment, S/D semiconductor structures  511 ,  513 ,  515  and  517  are composed of the same type of material as S/D semiconductor structures  131 ,  133 ,  135  and  137 . Note that the present embodiment depicts the formation of four “L” shaped vertical transistor semiconductor devices. However, such techniques as described above in the discussions of  FIGS. 1-4  can be modified to produce a range of “L” shaped semiconductor device with as few as one “L” shaped semiconductor device to many “L” shaped semiconductor devices. 
         [0037]    As an example, and not by limitation, the semiconductor device of  FIG. 5  is produced using the following process. A dielectric material ( 500 ) such as silicon nitride, silicon oxide, SiBCN, SiOCN, is deposited in two layers. The first layer of the dielectric material  500  is deposited such that it covers S/D semiconductor structures  131 ,  133 ,  135  and  137  and a lower portion of fins  121 ,  123 ,  125  and  127 . A layer of gate dielectric material is deposited as well as a layer of gate material. Etching techniques are used to remove portions of the deposited layers gate dielectric material and gate material creating gate structures  521 ,  523 ,  525  and  527 . The second layer of the dielectric material  500  is deposited to a depth that includes protective caps  111 ,  113 ,  115  and  117 . The first and the second layers of the dielectric material  500  may comprise the same or different materials. A chemical mechanical polishing (CMP) technique is used to remove a portion of dielectric material  500  that includes protective caps  111 ,  113 ,  115  and  117  but does not substantially remove upper portions of fins  121 ,  123 ,  125  and  127 . In an alternate example, selective etching is used to remove protective caps  111 ,  113 ,  115  and  117  in the case where the second layer of dielectric material  500  does not fully cover protective caps  111 ,  113 ,  115  and  117 . A layer of source/drain material is deposited and then etched to form S/D semiconductor structures  511 ,  513 ,  515  and  517 . 
         [0038]      FIG. 6  illustrates a cross-sectional view depicting the semiconductor devices of  FIG. 5 , in accordance with one embodiment of the present invention.  FIG. 6  depicts a layer of interlayer dielectric material ( 600 ) covering the semiconductor devices of  FIG. 5 . A number of openings were etched through portions of one or both of interlayer dielectric material  600  and dielectric material  500 . These openings were then filled with a contact material (such as tungsten, titanium, titanium nitride, copper, or any suitable combination of those materials), thereby forming contacts  621 ,  623 ,  625  and  627  that respectively form electrical connection with S/D semiconductor structures  131 ,  133 ,  135   137 ,  511 ,  513 ,  515  and  517 , further respectively. 
         [0039]      FIG. 7  illustrates a cross-sectional view depicting the semiconductor devices of  FIG. 5 , in accordance with one embodiment of the present invention.  FIG. 7  depicts a layer of interlayer dielectric material ( 600 ) covering the semiconductor devices of  FIG. 5 . A number of openings were etched through portions of one or both of interlayer dielectric material  600  and dielectric material  500 . These openings were then filled with a contact material (such as tungsten, titanium, titanium nitride, copper, or any suitable combination of those materials), thereby forming contacts  621 ,  624 ,  626  and  627 , and strap contact  629  that respectively form electrical connection with S/D semiconductor structures  131 ,  133 ,  135   137 ,  511 ,  513 ,  515  and  517 , further respectively. Note that strap contact  629  is connected to both of S/D semiconductor structures and  133  and  135 . 
         [0040]      FIG. 8  illustrates a cross-sectional view depicting the semiconductor devices of  FIG. 5 , in accordance with one embodiment of the present invention.  FIG. 8  depicts a layer of interlayer dielectric material ( 600 ) covering the semiconductor devices of  FIG. 5 . A number of openings were etched through portions of one or both of interlayer dielectric material  600  and dielectric material  500 . These openings were then filled with a contact material (such as tungsten, titanium, titanium nitride, copper, or any suitable combination of those materials), thereby forming contacts  621 ,  624 ,  626  and  627  that respectively form electrical connection with S/D semiconductor structures  131 ,  137 ,  139 ,  511 ,  513 ,  515  and  517 , further respectively. Notice that S/D semiconductor structures  133  and  135  do not exist. Instead, a common S/D semiconductor structure exists that is connected to both fins  123  and  125 . Such a structure could be used certain circuits, such as for a NAND gate structure. 
         [0041]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable other of ordinary skill in the art to understand the embodiments disclosed herein.

Technology Category: h