Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of application Ser. No. 11/427,982, filed Jun. 30, 2006, which is hereby incorporated by reference herein in its entirety. 

   FIELD OF THE INVENTION 
   The invention relates generally to semiconductor device structures and fabrication methods and, in particular, to semiconductor device structures for use in constructing bipolar junction transistors and methods of fabricating such semiconductor device structures. 
   BACKGROUND OF THE INVENTION 
   Transistors are semiconductor devices in which the current flowing between two device regions is controlled or modulated by an applied voltage. Transistors may be categorized as either field effect transistors (FET&#39;s) or bipolar junction transistors (BJT&#39;s). Bipolar junction transistors are active semiconductor devices formed by a pair of P-N junctions, namely an emitter-base junction and a collector-base junction. An NPN bipolar junction transistor has a thin region of P-type material constituting the base region between two regions of N-type material constituting the emitter and collector regions. A PNP bipolar junction transistor has a thin region of N-type material constituting the base region between two regions of P-type material constituting the emitter and collector regions. The movement of electrical charge carriers that produces electrical current flow between the collector region and the emitter region is controlled by a voltage applied across the emitter-base junction. 
   Conventional bipolar junction transistors are fabricated with a vertical arrangement of the emitter, base, and collector regions in which these regions have a stacked planar construction formed on a planar surface. As a result, conventional bipolar junction transistors have a relatively large footprint that consumes a significant surface area of the active device layer. The device footprint cannot be reduced because the area of the emitter-base junction cannot be easily scaled. Consequently, the emitter-base junction in planar device designs is limited by the planar surface area. 
   What is needed, therefore, are semiconductor device structures for bipolar junction transistors and fabrication methods that overcome these and other disadvantages of conventional semiconductor device structures for bipolar junction transistors and methods of manufacturing such semiconductor device structures. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to semiconductor device structures and fabrication methods for bipolar junction transistors. The present invention overcomes the problems associated with conventional processes for manufacturing bipolar junction transistors and improves circuit packing density, circuit performance, and thermal dissipation. The fabrication method of the present invention may be readily integrated with complementary metal-oxide-semiconductor (CMOS) bulk, semiconductor-on-insulator (SOI), or fin-type field effect transistor (FinFET) technologies. 
   In accordance with an aspect of the present invention, a semiconductor device structure comprises a semiconductor body having a top surface and sidewalls extending from the top surface toward an insulating layer. The structure further includes a first region including a first semiconductor material with a first conductivity type and a second region including a second semiconductor material with a second conductivity type. The first and second regions are disposed on the top surface and the sidewalls of the semiconductor body with an at least partially overlapping relationship to define a first junction extending between the first and second regions adjacent toward the top surface and the sidewalls of the semiconductor body. In certain specific embodiments, the first region may comprise an emitter region of a bipolar junction transistor and the second region may comprise a base region of the bipolar junction transistor so that the junction is an emitter-base junction. In other specific embodiments, the first region may comprise a collector region of a bipolar junction transistor and the second region may comprise a base region of the bipolar junction transistor so that the junction is a collector-base junction. 
   In accordance with another aspect of the present invention, a method is provided for fabricating a semiconductor device structure. The method comprises forming a semiconductor body having a top surface and sidewalls extending from the top surface toward the insulating layer, and forming a first region of a first semiconductor material with a first conductivity type that is disposed on the top surface and the sidewalls of the semiconductor body. The method further comprises forming a second region of a second semiconductor material with a second conductivity type that is at least partially coextensive with the first region to define a first junction extending between the first and second regions adjacent to the top surface and the sidewalls of the semiconductor body. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
       FIGS. 1-14  are diagrammatic views of a portion of a substrate at successive fabrication stages of a processing method in accordance with an embodiment of the present invention in which A represents a cross-sectional view and B is a corresponding cross-sectional view taken generally along lines B-B in A. 
       FIG. 15  is an isometric view of the substrate portion of  FIG. 14  after contacts are formed to the emitter, base, and collector regions. 
       FIG. 16A  is a cross-sectional view taken generally along line  16 A- 16 A in  FIG. 15 . 
       FIG. 16B  is a cross-sectional view taken generally along line  16 B- 16 B in  FIG. 16A . 
   

   DETAILED DESCRIPTION 
   With reference to  FIGS. 1A and 1B , a bipolar junction transistor  72  ( FIGS. 13A ,  13 B) is fabricated using an SOI wafer  10  comprising a handle substrate  12 , a buried insulating layer  14 , and a semiconductor or SOI layer  16  physically separated from the handle substrate  12  by the intervening buried insulating layer  14 . The handle substrate  12  may be single crystal or monocrystalline silicon, although the invention is not so limited. The SOI layer  16  is considerably thinner than the handle substrate  12  and may be advantageously composed of single crystal or monocrystalline silicon. The buried insulating layer  14  electrically isolates the SOI layer  16  from the handle substrate  12 . The buried insulating layer  14  may consist of a buried silicon dioxide (BOX) layer. SOI wafer  10  may be fabricated by any suitable conventional technique, such as a wafer bonding technique or a separation by implantation of oxygen (SIMOX) technique, familiar to a person having ordinary skill in the art. 
   The semiconductor material of SOI layer  16  is patterned by a conventional lithography and subtractive etching process to define a plurality of semiconductor mesas or fin structures, of which fin structure  18  is visible in  FIGS. 1A ,  1 B, that are mutually electrically isolated from each other by regions of the buried insulating layer  14 . The fin structure  18  represents a thin upright body of the semiconductor material originally constituting SOI layer  16  and, thus, has a “fin” type shape. The fin structure  18  has a top surface  20  and a plurality of sidewalls, of which laterally opposite sidewalls  22 ,  24  are visible in  FIG. 1A  and laterally opposite sidewalls  23 ,  25  are visible in  FIG. 1B . Each of the sidewalls  22 ,  23 ,  24 ,  25  extends from the top surface  20  toward a top surface  27  of the buried insulating layer  14 . The sidewalls  22 ,  23 ,  24 ,  25  may be tapered or flared, as opposed to the vertical construction shown in  FIGS. 1A ,  1 B. The height of each fin structure  18 , which is measured as the perpendicular distance between the top surfaces  20 ,  27 , typically ranges from about 30 nm to about 300 nm; the width of each fin structure  18  typically ranges from about 10 nm to about 100 nm. Optionally and before the formation of fin structure  18 , the SOI layer  16  may be thickened by epitaxial growth of the constituent semiconductor material (e.g., silicon). 
   The fin structure  18  is uniformly doped by ion implantation with a dose of an appropriate impurity. A subsequent thermal anneal may be required to electrically activate and/or distribute the implanted impurity in the semiconductor material of the fin structure  18 . The impurity implanted to dope the semiconductor material of the fin structure  18  may have, for example, an n-conductivity type (e.g., arsenic). Generally, the resultant dopant concentration in the fin structure  18  may range from about 1×10 18  cm −3  to about 1×10 20  cm −3 . Other alternative techniques, such as gas phase doping and solid source doping, may be employed to dope the semiconductor material of the fin structure  18 . 
   With reference to  FIGS. 2A and 2B  in which like reference numerals refer to like features in  FIGS. 1A and 1B  and at a subsequent fabrication stage, a collector region  26  of the bipolar junction transistor  72  ( FIGS. 13A ,  13 B) is defined by forming a semiconductor layer on the fin structure  18 . The semiconductor layer forming the collector region  26  may be formed by an epitaxial process, such as chemical vapor deposition (CVD) using a silicon source gas (e.g., silane). The semiconductor material constituting the collector region  26  is in situ doped during deposition with a concentration of an impurity having the same conductivity type as the fin structure  18  but doped to a lower concentration than the semiconductor material of the fin structure  18 . The doping concentration in the constituent semiconductor material of the collector region  26  is selected to provide a desired collector junction doping profile according to design parameters for the bipolar junction transistor  72  ( FIGS. 13A ,  13 B). Generally, the dopant concentration of the collector region  26  near the fin structure  18  may range from about 1×10 18  cm −3  to about 1×10 20  cm −3  to ensure relatively low series resistance with the fin structure  18  and the dopant concentration of the collector region  26  near the base region  34  ( FIGS. 5A ,  5 B) may range from about 1×10 17  cm −3  to about 1×10 18  cm −3  to provide a low-leakage collector-base junction  36  ( FIGS. 5A ,  5 B). 
   The collector region  26  comprises a top segment  90  and sidewall segments  92 ,  94  that are joined by the top segment  90  to define a continuous structure. The top segment  90  of the collector region  26  is coextensive (i.e., shares a border) with the top surface  20  of fin structure  18  and the sidewall segments  92 ,  94  are respectively coextensive with the sidewalls  23 ,  25  of fin structure  18 . The sidewall segments  92 ,  94  extend from the top segment  90  along the sidewalls  23 ,  25  toward the top surface  27  of the buried insulating layer  14 . The collector region  26  also includes segments that extend from the top segment  90  along the sidewalls  22 ,  24  toward the top surface  27  of the buried insulating layer  14 . 
   With reference to  FIGS. 3A and 3B  in which like reference numerals refer to like features in  FIGS. 2A and 2B  and at a subsequent fabrication stage, a thin layer  28  of a dielectric is formed on the collector region  26  to cap the constituent semiconductor material. The dielectric layer  28  may comprise, for example, oxide grown on the semiconductor material constituting the collector region  26  using a conventional wet or dry thermal oxidation process. The dielectric layer  28  covers the top segment  90  and sidewall segments  92 ,  94  of the collector region  26 , which is disposed between the fin structure  18  and the dielectric layer  28 . 
   The dielectric layer  28  is patterned by a conventional lithography and subtractive etching process. The lithography process applies a radiation-sensitive resist  30  on dielectric layer  28 , exposes the resist  30  to a pattern of radiation (e.g., light, x-rays, or an electron beam), and develops the latent transferred pattern in the exposed resist  30  to define a representative opening  29  that extends across the top surface  20  and along the sidewalls  23 ,  25  of fin structure  18 . Thus, the opening  29  extends across the top segment  90  and along the sidewall segments  92 ,  94  of the collector region  26 . 
   With reference to  FIGS. 4A and 4B  in which like reference numerals refer to like features in  FIGS. 3A and 3B  and at a subsequent fabrication stage, the subtractive etching process, which may be an anisotropic dry etch process like reactive ion etching (RIE) or plasma etching, transfers the pattern in the resist  30  to the dielectric layer  28 . The subtractive etching process defines a base opening  32  to the collector region  26  by partially removing unmasked areas of dielectric layer  28  registered with the opening  29  in the patterned resist  30 , which serves as an etch mask. The subtractive etching process, which relies on an etchant chemistry that removes the constituent material of the dielectric layer  28  selective to the semiconductor material constituting collector region  26 , stops on the constituent semiconductor material of collector region  26 . The dielectric layer  28  includes peripheral regions that overlap with the buried insulating layer  14  peripherally of the fin structure  18 . 
   Base opening  32  extends across the top surface  20  and along the sidewalls  23 ,  25  of the fin structure  18 . Thus, the base opening  32  extends across the top segment  90  and along the sidewall segments  92 ,  94  of the collector region  26 . The top segment  90  and sidewall segments  92 ,  94  of the collector region  26  are exposed through the base opening  32  and are free of coverage by the dielectric layer  28 , which has edges that peripherally bound the base opening  32 . 
   With reference to  FIGS. 5A and 5B  in which like reference numerals refer to like features in  FIGS. 4A and 4B  and at a subsequent fabrication stage, the patterned resist  30  ( FIGS. 4A ,  4 B) is removed using a conventional solvent stripping process or by ashing. A base region  34  of the bipolar junction transistor  72  ( FIGS. 13A ,  13 B) is then formed by a selective epitaxial growth process with in situ impurity doping that fills the base opening  32  with an impurity-doped semiconductor material, such as silicon or a silicon-containing semiconductor material. Specifically, the semiconductor material forming the base region  34  is doped with an impurity having an opposite conductivity type to collector region  26 . For example, the dopant concentration of the base region  34  may be graded from about 1×10 17  cm −3  near the collector region  26  to about 5×10 18  cm −3  near the emitter region  58  (FIGS.  11 A,B). A collector-base junction  36  is defined across the interface or boundary shared by the coextensive portions of the collector region  26  and base region  34 . The impurity implanted to dope the semiconductor material of the base region  34  may have, for example, a p-conductivity type (e.g., boron). 
   The semiconductor material forming the base region  34  is doped with an impurity having an opposite conductivity type to collector region  26 . The semiconductor material of the collector region  26  may be characterized by an n-type conductivity that exhibits a higher concentration of electrons than holes so that electrons are majority carriers and dominate the electrical conductivity of the material. The semiconductor material of the base region  34  may be characterized by a p-type conductivity that exhibits a higher concentration of holes than electrons so that holes are majority carriers and dominate the electrical conductivity of the material. Alternatively, the conductivity types may be reversed. 
   In one embodiment, the silicon-containing semiconductor material constituting the base region  34  may be an impurity doped silicon-germanium alloy (Si x Ge 1-x ) in which the silicon atomic concentration ranges from about 65% to about 90% and the germanium atomic concentration ranges from about 10% to about 35%. The Si x Ge 1-x  may be deposited using any conventional epitaxial growth method capable of growing a SiGe alloy with in situ doping that is substantially free from defects, i.e., misfit and threading dislocations. An illustrative example of such an epitaxial growth process capable of growing substantially defect free films is a low-pressure chemical vapor deposition (LPCVD) process using silane (SiH 4 ) and germane (GeH 4 ) as reactant gasses and conducted at a relatively low process temperature. 
   Base region  34  is physically separated from the fin structure  18  by the collector region  26 . Base region  34  has a top segment  96  that is coextensive with the top segment  90  of collector region  26  and sidewall segments  98 ,  100  that are respectively coextensive with the sidewall segments  92 ,  94  of collector region  26 . The sidewall segments  98 ,  100  are joined by the top segment  96 . The base region  34  extends across the top surface  20  and along the sidewalls  23 ,  25  of the fin structure  18 . Thus, the base region  34  contacts the top segment  90  and sidewall segments  92 ,  94  of the collector region  26 . The collector-base junction  36  is defined across the coextensive, contacting surface areas of the doped semiconductor material of the collector region  26  having one conductivity type and the doped semiconductor material of the base region  34  having the opposite conductivity type. The collector and base regions  36 ,  34  at least partially overlap to define the collector-base junction  36 . 
   The periphery of the base region  34 , which is designated by the lateral extent of the base opening  32  and the process forming the base region  34 , is selected such that a contact pad  75  of the collector region  26  extends laterally of the periphery of the base region  34 . The contact pad  75  is not overlapped by the base region  34  and, thus, does not participate in forming the collector-base junction  36 . The contact pad  75  is employed to electrically contact the collector region  26 , as described below. 
   With reference to  FIGS. 6A and 6B  in which like reference numerals refer to like features in  FIGS. 5A and 5B  and at a subsequent fabrication stage, a layer  38  of a dielectric is conformally deposited across the fin structure  18 . The dielectric in layer  38  may be silicon nitride (Si 3 N 4 ) formed by a thermal CVD process like low pressure chemical vapor deposition (LPCVD) or by a plasma-assisted CVD process. The dielectric layer  38  extends across the top surface  20  and along the sidewalls  22 ,  23 ,  24 ,  25  of the fin structure  18 . 
   With reference to  FIGS. 7A and 7B  in which like reference numerals refer to like features in  FIGS. 6A and 6B  and at a subsequent fabrication stage, the dielectric layer  38  is patterned by a conventional lithography and subtractive etching process. The lithography process applies a radiation-sensitive resist  40  on dielectric layer  38 , exposes the resist  40  to a pattern of radiation, and develops the latent transferred pattern in the exposed resist  40  to define an opening  42 . The opening  42  extends across the top surface  20  and along the sidewalls  23 ,  25  of the fin structure  18 . 
   With reference to  FIGS. 8A and 8B  in which like reference numerals refer to like features in  FIGS. 7A and 7B  and at a subsequent fabrication stage, an emitter area  44  is defined across the top segment  96  and sidewall segments  98 ,  100  of the base region  34  by transferring the pattern in the resist  40  ( FIGS. 7A ,  7 B) to the dielectric layer  38  using an anisotropic dry etch process like RIE or plasma etching. The dry etching process defines the emitter area  44  by removing an unmasked portion of dielectric layer  38  registered with the opening  42  in patterned resist  30 , which operates as an etch mask. The dry etching process, which has an etchant chemistry that removes the constituent material of the dielectric layer  38  selective to the semiconductor material of the base region  34 , stops on the constituent semiconductor material of base region  34 . The top segment  96  and sidewall segments  98 ,  100  of base region  34  are exposed across the emitter area  44 . The resist  40  ( FIGS. 7A ,  7 B) is subsequently removed using a conventional solvent stripping process or by ashing. 
   With reference to  FIGS. 9A and 9B  in which like reference numerals refer to like features in  FIGS. 8A and 8B  and at a subsequent fabrication stage, a layer  46  of a semiconductor material is formed on top surface  20  and sidewalls  22 ,  23 ,  24 ,  25  of the fin structure  18 . The semiconductor layer  46  may be composed of polycrystalline silicon (i.e., polysilicon) deposited by a CVD process. Semiconductor layer  46  is doped during deposition with a concentration of an impurity having the same conductivity type as the semiconductor material of collector region  26  but the opposite conductivity type in comparison with the semiconductor material of base region  34 . The semiconductor layer  46  is coextensive with the base region  34  across the emitter area  44 , which is bounded peripherally by the encircling edges of the dielectric layer  38 . A protective cap layer  50 , which may comprise a layer of oxide deposited by a CVD process, is formed on the semiconductor layer  46 . 
   With reference to  FIGS. 10A and 10B  in which like reference numerals refer to like features in  FIGS. 9A and 9B  and at a subsequent fabrication stage, the semiconductor layer  46  and cap layer  50  are patterned by a conventional lithography and subtractive etching process. The lithography process applies a radiation-sensitive resist  52  on cap layer  50 , exposes the resist  52  to a pattern of radiation, and develops the latent transferred pattern in the exposed resist  52  to define a residual strip or island of resist  52  covering a portion of the semiconductor layer  46  and cap layer  50 . The residual island of resist  52  extends across the top surface  20  and along the sidewalls  23 ,  25  of the fin structure  18 . 
   With reference to  FIGS. 11A and 11B  in which like reference numerals refer to like features in  FIGS. 10A and 10B  and at a subsequent fabrication stage, the subtractive etching process removes portions of the semiconductor layer  46  and cap layer  50  not masked by the residual island of resist  52 . The portion of the semiconductor layer  46  masked during the subtractive etching process comprises an emitter region  58  of the bipolar junction transistor  72  ( FIGS. 13A ,  13 B). The subtractive etching process includes one or more anisotropic dry etch processes, like RIE or plasma etching, that patterns the cap layer  50  using the resist  52  as an etch mask and then patterns the semiconductor layer  46  using the patterned cap layer  50  and resist  52  as an etch mask. The subtractive etching process, which may be conducted in a single etching step or multiple steps, stops on the dielectric layer  38 . After the emitter region  58  is defined, the resist  52  ( FIGS. 10A ,  10 B) is removed using solvent stripping or ashing. 
   The emitter region  58 , which has a top segment  102  and sidewall segments  104 ,  106  joined by the top segment  102 , is physically separated from the collector region  26  by the base region  34 . The top segment  102  is coextensive with the top segment  96  of base region  34  and the sidewall segments  104 ,  106  are respectively coextensive with the sidewall segments  98 ,  100  of base region  34 . The top segment  102  and sidewall segments  104 ,  106  of emitter region  58  extend adjacent to the top surface  20  and the sidewalls  23 ,  25  of the fin structure  18 . Thus, the emitter region  58  extends across the top segment  96  and along the sidewall segments  98 ,  100  of the base region  34 . The lateral extent of the emitter region  58 , which is designated by the lateral extent of the resist  52 , is selected such that the contact pad  68  of the base region  34  is outside of the perimeter or periphery of the emitter region  58 . 
   With reference to  FIGS. 12A and 12B  in which like reference numerals refer to like features in  FIGS. 11A and 11B  and at a subsequent fabrication stage, the SOI wafer  10  is annealed at a temperature and for a time that promotes impurity diffusion from the doped semiconductor material of the emitter region  58  into the base region  34  across the emitter region  58 . The anneal may be performed in either a vacuum or inert environment, where an inert environment may comprise, for example, a non-reactive atmosphere of helium (He), argon (Ar), or nitrogen (N 2 ), and at a substrate temperature in the range of 950CE to 1100EC. The volume of semiconductor material of the base region  34  receiving the diffused impurity is doped with a net impurity concentration that is graded across a zone  53  from one conductivity type (i.e., n-type) near the emitter region  58  to the opposite conductivity type (i.e., p-type) of the base region  34 . An emitter-base junction  54  is defined by the locus of points or transition between conductivity types in the graded zone  53  for which the net doping concentration is null or zero. The bulk of the emitter region  58  may have a dopant concentration of about 5×10 19  cm −3  to about 5×10 20  cm −3 . The emitter-base junction  43  is generally defined by the at least partial overlap between coextensive portions of the emitter region  78  and the base region  48 . 
   The emitter-base junction  54 , which is defined at the location of coextensive portions of the base region  34  and emitter region  58  for which the net doping concentration is null or zero, is collectively defined by a top segment  108  and sidewall segments  110 ,  112  joined by the top segment  108 . Hence, the emitter-base junction  54  comprises a three-dimensional, non-planar feature of the bipolar junction transistor  72 . The emitter-base junction  54  (as well as the collector, base, and emitter regions  26 ,  34 ,  58  and collector-base junction  36 ) has a length slightly greater than the height of fin structure  18  at sidewall  23 , plus the width of fin structure  18  across the top surface  20 , plus the height of fin structure  18  at sidewall  25 . The base region  34 , emitter region  58 , and emitter-base junction  54  are a continuous region of semiconductor material. The top segment  108  and sidewall segments  110 ,  112  of the emitter-base junction  54  extend adjacent to the top surface  20  and the sidewalls  23 ,  25  of the fin structure  18 . 
   With reference to  FIGS. 13A and 13B  in which like reference numerals refer to like features in  FIGS. 12A and 12B  and at a subsequent fabrication stage, insulating spacers  60  are formed on the peripheral edges of the emitter region  58  and insulating spacers  62  are formed on the peripheral edges of the base region  34  by a conventional film deposition and anisotropic etching process. Dielectric layer  38 , which may be composed of the same material as the film (e.g., nitride) deposited to form the spacers, is also anisotropically etched during spacer formation. Insulating spacers  64  are also formed on the vertical surfaces flanking the fin structure  18  as an artifact of the process forming spacers  60 ,  62 . Forming the spacers  60 ,  62 ,  64  concludes the fabrication of the bipolar junction transistor  72 . 
   The anisotropic etching process removes portions of the dielectric layer  38  to expose the peripheral contact pad  68  of the base region  34 . The contact pad  68  is not overlapped by the emitter region  58  and, thus, does not participate in forming the emitter-base junction  54 . The contact pad  68  is used to electrically contact the base region  34 , as described below. 
   Although illustrated as having an NPN doping configuration for the collector region  26 , base region  34 , and emitter region  58 , the fabrication of the bipolar junction transistor  72  may be modified to provide a PNP doping configuration for the collector region  26 , base region  34 , and emitter region  58  as understood by a person having ordinary skill in the art. 
   With reference to  FIGS. 14A and 14B  in which like reference numerals refer to like features in  FIGS. 13A and 13B  and at a subsequent fabrication stage, a contact region  70  is formed on a top surface of the contact pad  68  of the base region  34 . The contact region  70  may be, for example, self-aligned silicide or salicide contacts formed using a conventional silicidation or salicidation process well known to a person having ordinary skill in the art, which includes forming a layer of refractory metal, such as titanium (Ti), cobalt (Co), tungsten (W), or nickel (Ni), on the silicon-containing semiconductor material comprising the base region  34  and heating the metal/silicon-containing material stack by, for example, a rapid thermal annealing process to transform the stack to form a silicide. Thereafter, any non-reacted refractory metal is removed utilizing a conventional wet chemical etchant. The silicidation may be conducted in an inert gas atmosphere or in a nitrogen-rich gas atmosphere. Contact region  70  provides a low resistance contact to the semiconductor material constituting the base region  34 . Cap layer  50  protects emitter region  58  during formation of the contact region  70 . 
   With reference to  FIGS. 15 ,  16 A, and  16 B in which like reference numerals refer to like features in  FIGS. 14A and 14B  and at a subsequent fabrication stage, a blanket layer  74  of an insulating material is applied across the bipolar junction transistor  72  and planarized by a conventional planarization process like chemical mechanical planarization (CMP). The insulating material of the blanket layer  74 , which provides an interlayer dielectric for contact formation, may be composed of a spin-on glass (SOG) material applied by coating the SOI wafer  10  with the SOG material in liquid form, spinning the SOI wafer  10  at high speeds to uniformly distribute the liquid on the surface by centrifugal forces, and baking at a low temperature to solidify the SOG material. Alternatively, the insulating material of the blanket layer  74  may include multiple coatings of different dielectric materials as understood by a person having ordinary skill in the art. 
   Another particularly advantageous dielectric material that may be employed to form the insulating material of the blanket layer  74  is diamond-like carbon or diamond deposited by a thermal or plasma CVD process, which may improve heat dissipation because of diamond&#39;s relatively high thermal conductivity. This ability to dissipate heat may be important for effectively cooling the bipolar junction transistor  72  when the integrated circuit is powered and operating. Other dielectric materials having a high thermal conductivity and a low electrical conductivity may be employed to form the insulating material of the blanket layer  74  as understood by a person having ordinary skill in the art. 
   The blanket layer  74  of insulating material is then lithographically patterned in a conventional manner to form via holes to the collector region  26 , base region  34 , and emitter region  58 . A conductive material is deposited into the via holes using conventional processing, such as CVD or plating to form electrical contacts  76 ,  78 ,  80  that extend to the collector region  26 , base region  34 , and emitter region  58 , respectively. Conductive materials suitable for the contacts  76 ,  78 ,  80  may include, but are not limited to, metals such as tungsten, copper, aluminum, silver, gold, and alloys thereof. 
   Electrical contact  76  extends through the blanket insulating layer  74  and the dielectric layer  28  to the depth of the collector region  26  and is electrically coupled with the peripheral contact pad  75  of the collector region  26 . The contact pad  75  of collector region  26  is not overlapped by the base region  34  and, thus, does not participate in forming the emitter-base junction  54 . Contact pad  75  of collector region  26  also extends laterally of the emitter region  58  so that the emitter region  58  does not occlude the path for establishing the contact  76 . Electrical contact  78  extends through the blanket insulating layer  74  to the depth of the peripheral contact pad  68  of the base region  34  and is electrically coupled with the contact region  70  of, for example, salicide. Electrical contact  80  extends through the blanket insulating layer  74  and the cap layer  50  to the depth of the emitter region  58  and is electrically coupled with the emitter region  58 . 
   As best shown in  FIG. 16B , the collector region  26 , base region  34 , and emitter region  58 , as well as junctions  36 ,  54 , of the bipolar junction transistor  72  each wrap about the top surface  20  and sidewalls  23 ,  25  of the fin structure  18  so that each extends about three sides of the fin structure  18  in a non-planar construction. The emitter-base junction  54  also wraps about the top surface  20  and sidewalls  23 ,  25  of the fin structure  18 , which significantly increases the bipolar junction area and current per unit area of silicon real estate on the SOI wafer  10 . Instead of forming the collector region  26 , base region  34 , emitter region  58  and emitter-base junction  54  on planar surfaces, as done during the fabrication of conventional bipolar junction transistors, bipolar junction transistor  72  utilizes the relatively large surface area on fin structure  18  of semiconductor material to provide a three-dimensional, non-planar device structure. As a result, the emitter-base junction  54  is not limited by the planar surface area of a conventional handle substrate. The collector region  26 , base region  34 , and emitter region  58  of the bipolar junction transistor  72  have a tiered configuration for the respective structural peripheral edges that facilitates forming contacts  76 ,  78 ,  80  by exposing contact pad  68  of the base region  34  peripherally of the emitter region  58  and by exposing contact pad  75  of the collector region  26  peripherally of the base region  34 . 
   References herein to terms such as “vertical”, “horizontal”, etc. are made by way of example, and not by way of limitation, to establish a frame of reference. The term “horizontal” as used herein is defined as a plane parallel to the top surface  20  of fin structure  18 , regardless of its actual three-dimensional spatial orientation. The term “vertical” refers to a direction perpendicular to the horizontal, as just defined. Terms, such as “on”, “above”, “below”, “side” (as in “sidewall”), “higher”, “lower”, “over”, “beneath” and “under”, are defined with respect to the horizontal plane. It is understood that various other frames of reference may be employed for describing the present invention without departing from the spirit and scope of the present invention. 
   The fabrication of the semiconductor structure herein has been described by a specific order of fabrication stages and steps. However, it is understood that the order may differ from that described. For example, the order of two or more fabrication steps may be switched relative to the order shown. Moreover, two or more fabrication steps may be conducted either concurrently or with partial concurrence. In addition, various fabrication steps may be omitted and other fabrication steps may be added. It is understood that all such variations are within the scope of the present invention. It is also understood that features of the present invention are not necessarily shown to scale in the drawings. 
   While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.

Technology Category: h