Abstract:
A thin-body bipolar device includes: a semiconductor substrate, a semiconductor fin constructed over the semiconductor substrate, a first region of the semiconductor fin having a first conductivity type, the first region serving as a base of the thin-body bipolar device, and a second and third region of the semiconductor fin having a second conductivity type opposite to the first conductivity type, the second and third region being both juxtaposed with and separated by the first region, the second and third region serving as an emitter and collector of the thin-body bipolar device, respectively.

Description:
PRIORITY INFORMATION 
     This application claims the benefits of U.S. Provisional Patent Application Ser. No. 61/219,316, which was filed on Jun. 22, 2009, and entitled “Thin-Body Bipolar Device.” 
    
    
     BACKGROUND 
     The present invention relates generally to integrated circuit (IC) designs, and more particularly to bipolar devices with a thin-body structure. This concept of this patent application can be referred to merged MOS/bipolar device in US patent publication No. 2006/0197185 and No. 2007/0105301. 
     Although complementary metal-oxide-semiconductor (CMOS) devices have advantages of low power consumption and high input impedance, they often need some specially designed I/O devices and circuits to protect them from high voltage signals. Those I/O devices and circuits usually require extra masks in the course of semiconductor processing. One way to simplify the semiconductor processing is to use bipolar devices as the I/O devices. The bipolar devices are able to sustain relatively high voltage. In addition, bipolar devices have many advantages over CMOS devices in designing analog circuitry. However, the conventional bipolar device is very complicated to manufacture. Though parasitic lateral bipolar devices can be formed through standard CMOS process, their performance is generally inferior to those formed by genuine bipolar processes. It would be desirable to design high performance bipolar devices in CMOS compatible process to achieve better performance. 
       FIG. 1  illustrates a conventional PNP bipolar transistor  10  compatible with CMOS process technologies. The LOCal Oxidation of Silicon (LOCOS) isolations  11  define three active areas  12 ,  13  and  14  on N well  15  in a semiconductor substrate. The active areas  12  and  13  doped with P-type impurities form an emitter  16  and a collector  17 , respectively. The LOCOS isolation  11  between the emitter  16  and collector  17  defines an intrinsic base  18  thereunder in the Nwell  15 . An extrinsic base  19  is electrically connected to the intrinsic base  18  via the body of the Nwell  15 . The extrinsic base  19  is doped with N-type impurities to improve its conductivity. When the emitter  16 , collector  17  and extrinsic base  19  are properly biased, carriers would flow between the emitter  16  and the collector  17  to produce amplification of currents. 
     The design of the conventional PNP bipolar transistor  10  is not suitable for ICs using three-dimensional CMOS devices. As the size of electronic devices in ICs continues to scale down, the IC design and manufacturing face new challenges. For example, failure caused by punch-though between the source and the drain of a CMOS device becomes a serious reliability issue to CMOS devices with a scale under 45 nm. As a result, many new designs have been proposed to improve the reliability of CMOS devices scaled under 45 nm. One of the proposed designs is the Fin Field Effect Transistor (FinFET) characterized by its fin-shaped source and drain, and a surrounding gate structure. The width of the fin-shaped source and drain can be controlled to eliminate the punch-through often occurred between the source and the drain of a conventional CMOS device. 
     As such, what is desired is a FinFET-like bipolar device that can be formed by regular CMOS process. 
     SUMMARY 
     The present invention discloses a thin-body bipolar device. In one embodiment of the present invention, the thin-body bipolar device includes: a semiconductor substrate, a semiconductor fin constructed over the semiconductor substrate, a first region of the semiconductor fin having a first conductivity type, the first region serving as a base of the thin-body bipolar device, and a second and third region of the semiconductor fin having a second conductivity type opposite to the first conductivity type, the second and third region being both juxtaposed with and separated by the first region, the second and third region serving as an emitter and collector of the thin-body bipolar device, respectively. The base region may be defined by a poly-silicon gate structure. Additionally, the thin-body bipolar device may be formed on an insulation layer over the substrate. Connections to the base can be made either to the top of the base region or through the substrate. 
     The construction and method of operation of the invention, however, together with additional objectives and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view of a conventional bipolar device. 
         FIG. 2  illustrates a three-dimensional view of a thin-body bipolar device in accordance with one embodiment of the present invention. 
         FIG. 3  illustrates a three-dimensional view of the thin-body bipolar device formed similarly to a FinFET in accordance with the embodiment of the present invention. 
         FIG. 4  illustrates a three-dimensional view of the thin-body bipolar device with contacts made to the top of the thin fin. 
         FIG. 5  is a cross-sectional view of the thin-body bipolar device at the base region illustrating an alternative way of making the base contact on the top of the thin fin. 
         FIG. 6  is a cross-sectional view of the thin-body bipolar device at the base region illustrating a base contact made through the substrate. 
         FIG. 7  is a cross-sectional view of the thin-body bipolar device at the base region illustrating a base contact made through the insulation layer and the substrate. 
         FIG. 8  is a two-dimensional layout view of a multi-fingered thin-body bipolar device. 
     
    
    
     DESCRIPTION 
     This invention describes a thin-body bipolar device constructed based on a FinFET structure. The following merely illustrates various embodiments of the present invention for purposes of explaining the principles thereof. It is understood that those skilled in the art will be able to devise various equivalents that, although not explicitly described herein, embody the principles of this invention. 
       FIG. 2  illustrates a three-dimensional view of a thin-body bipolar device  100  in accordance with one embodiment of the present invention. Unlike the conventional bipolar device  10  of  FIG. 1  which is formed inside the substrate  15 , the thin-body bipolar device  100  is formed in a thin fin  110  elevated above the substrate  102 . The thin fin  110 , typically made of a semiconductor material such as Silicon, is doped into three regions  112 ,  115  and  118 . When the thin-body bipolar device  100  is a PNP type, both the region  112  and  118  are doped with P-type impurities, forming an emitter and a collector of the bipolar device  100 , respectively, while the region  115  is doped with N conductivity type, or simply N-type, impurities, forming a base of the bipolar device  100 . When the thin-body bipolar device  100  is a NPN type, both the region  112  and  118  are doped with N conductivity type impurities, forming an emitter and a collector of the bipolar device  100 , respectively, while the region  115  is doped with P conductivity type, or simply P-type impurities, forming a base of the bipolar device  100 . The thin-body bipolar device  100  can be formed similarly to FinFETs by a conventional CMOS process. Since the thin-body bipolar device  100  is formed above the substrate  102  which only provides connections in certain cases described hereinafter, the substrate  102  can be made of any semiconductor materials such as silicon (Si), germanium (Ge), gallium phosphide (GaP), indium arsenide (InAs), indium phosphide (InP), silicon germanium (SiGe), galkium arsenide (GaAs), etc. That is to say the thin-body bipolar device  100  of the present invention can be incorporated into many kinds of semiconductor processes. 
       FIG. 3  illustrates a three-dimensional view of the thin-body bipolar device  100  formed similarly to a FinFET in accordance with the embodiment of the present invention. The thin fin  110 , in this case, is formed above an insulation layer  302  which is formed on top of the substrate  102 . In order to form a PNP thin-body bipolar device, an N-type impurity is first implanted in the entire thin fin  110 . Then a poly-silicon double gate  322  is deposited over a portion of the thin fin  110  that defines the base region of the thin-body bipolar device  100 . A P-type impurity is then implanted in the thin fin  110 . The region covered by the double gate  322  remains as an N-type, but the exposed regions  112  and  118  becomes P-type. In this way, a PNP thin-body bipolar device is formed in the thin fin  110  with regions  112  and  118  becomes collector and emitter, respectively. In a similar fashion, a NPN thin-body bipolar device can also be formed in the thin fin  110 . As in FinFET, there is a thin gate oxide layer  325  between the poly-silicon double gate  322  and the thin fin  110 . The thin gate oxide layer  325  also function as spacers to separate the poly-silicon double gate  322  and the collector region  112  and the emitter  118 . The poly-silicon double gate  322  can be stripped off after the formation of the thin-body bipolar device  100 , left floating or applied a controllable voltage for addition control of the base of the thin-body bipolar device  100 . In order to improve conductivity, self-aligned silicide (salicide) layers can be formed on the collector region  112  and the emitter region  118 . 
       FIG. 4  illustrates a three-dimensional view of the thin-body bipolar device  100  with contacts made to the top of the thin fin  110 . After forming the thin-body bipolar device  100  as shown in  FIG. 3 , the top portion of the poly-silicon double gate  322 , so that the top of the base region  114  of the thin fin  110  is exposed. Then a contact  414  is made to the base region  114 . At the same time, a contact  412  is made to the collector region  112 , and a contact  418  is made to the emitter region  118 . 
       FIG. 5  is a cross-sectional view of the thin-body bipolar device  100  at the base region  114  illustrating an alternative way of making the base contact on the top of the thin fin. Instead of removing the poly-silicon material across the board, a contact opening  502  is etched through the poly-silicon double gate  322  reaching the base region  114 . Then conventional metal materials are filled in the contact opening  502  to form the base contact. 
       FIG. 6  is a cross-sectional view of the thin-body bipolar device  100  at the base region  114  illustrating a base contact made through the substrate  102 . An Nwell  612  is formed in the substrate  102  before the N-type base region  114  of the thin fin  110  (referring to  FIG. 2 ) is formed on top of the Nwell  612 . Then an N+ implant region  616  is made in the Nwell  612  for landing a subsequent contact  626 . The connection to the base region  114  comprises, therefore, the contact  626 , the N+ region  616  and the Nwell  612  which touches the base region  114 . 
       FIG. 7  is a cross-sectional view of the thin-body bipolar device  100  at the base region  114  illustrating a base contact made through the insulation layer  302  and the substrate  102 . An Nwell  712  is formed in the substrate  102  along with an N+ region  716  for the Nwell pickup. The insulation layer  302  is grown on top of the substrate  102 . A hole  722  in the insulation layer  302  is etched before the thin-fin-device is made. The hole  722  is placed at the location of the subsequent base region  114  of the thin-body bipolar device  100  and filled up with the same material as the base region  114  when the thin fin  110  is formed. On the Nwell pickup location, a contact opening  726  is etched and filled all the way through the insulation layer  302 . Therefore, the connection to the base region  114  comprises the through-insulation-layer contact  726 , the N+ region  716 , the Nwell  712 , and the hole  722  which is merged with the base region  114 . 
     Although only connection to the N type base region  114  is illustrated in both  FIGS. 6 and 7 , one having skills in the art would apply the same principle to form a connection to a P type base region, in which case, a Pwell and a P+ pick-up, in place of the Nwell and N+ pick-up, respectively, will be disposed. Although either Nwell or Pwell are used to provide the through-substrate connection, one having skilled in the art would appreciate that other structures, such as active regions can be used in place or in junction of the Nwell or Pwell. 
       FIG. 8  is a two-dimensional layout view of a multi-fingered thin-body bipolar device  800 . Finger sections  802 ,  804  and  806  are thin-body bipolar devices formed according to the embodiment of the present invention as illustrated in  FIG. 2  through  FIG. 7 . The thin fins that form the sections  802 ,  804  and  806  are extended to a common section  812  on the top and a common section  818  at the bottom. A plurality of contacts  822  are landed on the thin fin section  812  to serve as a collector connection. A plurality of contacts  828  are landed on the thin fin section  818  to serve as an emitter connection. Apparently the multi-fingered thin-body bipolar device  800  provides a compact layout when large device size is desired. 
     The above embodiment of the present invention proposes various structures of bipolar devices based on the FinFETs. As the structure designs of the FinFETs for ICs are scaled under 45 nm, the proposed thin-body bipolar devices are suitable in IC designs and compatible with the FinFET manufacturing process. The proposed thin-body bipolar devices are particularly suitable in radio frequency (RF) applications, analog circuits, and memory chips. 
     The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims. 
     Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.