Abstract:
A lateral insulated gate bipolar transistor (LIGBT) includes a drain-anode adjoining trenched contact penetrating through an insulating layer and extending into an epitaxial layer, directly contacting to a drain region and an anode region, and the drain region vertically contacting to the anode region along sidewall of the drain-anode adjoining trenched contact. The LIGBT further comprises a breakdown voltage enhancement doping region wrapping around the anode region. The LIGBTs in accordance with the invention offer the advantages of high breakdown voltage and low on-resistance as well as high switching speed.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to semiconductor devices, and more particularly, to an improved and novel device configuration for providing a fast switching lateral insulated gate bipolar transistor (LIGBT) with trenched contacts with higher breakdown voltage and lower on-resistance as well as higher switching speed. 
       BACKGROUND OF THE INVENTION 
       [0002]    The insulated gate bipolar transistor (hereinafter IGBT) is an integrated combination of a bipolar transistor and a metal oxide semiconductor field effect transistor and has become commercially successful due to its superior on-state characteristics and excellent safe-operating area. IGBTs in integrated circuits are commonly configured as lateral insulated gate bipolar transistors (hereinafter LIGBTs) and fabricated using a planar process sequence to minimize cost and complexity of the integrated circuit manufacturing operation. 
         [0003]      FIG. 1A  is a cross sectional view showing a conventional LIGBT  100  of prior art. The LIGBT  100  of  FIG. 1A  comprises: a P-substrate  101 ; an N epitaxial layer  103  on top surface of the P-substrate  101 ; a P buried layer  102  with higher doping concentration than the P-substrate  101  and located at a part of the top surface of the P-substrate  101  and beneath an n+ source (cathode) region  107  near top surface of the N epitaxial layer  103 ; a p++ source contact doped region  105  provided in the N epitaxial layer  103  and adjacent to a p body region  104  and the n+ source region  107 . A channel region of the illustrated LIGBT  100  is formed near top surface of the p body region  104  between the n+ source region  107  and the N epitaxial layer  103 ; a p+ anode region  108  located near the top surface of the N epitaxial layer  103  and spaced apart from the p region  104 ; a source metal  111  and a drain metal  113  contacted with the n+ source (cathode) region  107  and the p++ source contact doped region  105 , and the p+ anode region  108  by planar contact, respectively. The LIGBT  100  of  FIG. 1A  offers several important advantages over lateral diffusion metal oxide semiconductor, including high current handling capabilities, low on-resistance and high breakdown voltage. However, it has suffered from a significant drawback of switching speed because there is no n+ drain region provided for removal of electrons (minority carriers) during turn-off process. During turn-on process, the p+ anode region  108  injects holes (majority carriers) into drift region and the n+ source (anode) region  107  injects electrons into the drift region through the channel to form a low-resistance plasma modulation region. During turn-off process, the holes in the plasma modulation region are removed by flowing through the p+ anode region  108  but the electrons are removed by recombination of the electrons and the holes. Therefore, the turn-off process is determined by the recombination of electrons, and since no contact is provided for the removal of the electrons, the turn-off time is relatively long in the range of 3-10 microseconds, while turn-on time is much less than 1 microsecond. 
         [0004]    A typical prior art fast switching LIGBT  200  is shown in  FIG. 1B . Similar fast switching LIGBTs are shown in U.S. Pat. No. 4,989,058. Besides those in common with the LIGBT  100  of  FIG. 1A , the LIGBT  200  of  FIG. 1B  comprises an additional n+ drain region  209  adjacent to the p+ anode region  208  to remove the electrons (minority carriers) during the turn-off process as discussed above. Therefore, the turn-off time of the LIGBT  200  of  FIG. 1B  is shorter than that of the LIGBT of  FIG. 1A . However, the LIGBT  200  has its own constrain which is that on-resistance is significantly increased because triggered voltage Vds for holes (majority carriers) injection is larger than the typical value of 0.7 V for the LIGBT  100  as shown in  FIG. 2  due to an additional resistance R p  (as illustrated in  FIG. 1B ) existing underneath the p+ anode region  208  besides Rd (as illustrated in  FIG. 1A  and  FIG. 1B ). The Triggered voltage Vds is: I*(R d +R p )=IR d +IR p ≈IR d +0.7 V&gt;0.7 V, where I is the current flowing through the drift region to the n+ drain region  209 . From  FIG. 2  it can be seen that, the triggered voltage Vds of the LIGBT  100  is about 0.7V and the triggered voltage Vds of the LIGBT  200  is about 1.2 V as shown in  FIG. 2 . 
         [0005]    Accordingly, it would be desirable to provide a new and improved LIGBT that has both low on-resistance and high switching speed. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an aspect of the present invention to provide a new and improved LIGBT to solve the problems discussed above. According to the present invention, there is provided a LIGBT, comprising: a drain-anode adjoining trenched contact penetrating through an insulating layer and extending into an epitaxial layer of a first conductivity type, directly contacting to a drain region having the first conductivity type and an anode region of a second conductivity type; and said drain region vertically contacting to said anode region along sidewall of the drain-anode adjoining trenched contact. 
         [0007]    By providing a LIGBT with the drain-anode adjoining trenched contacts described above, please refer to a preferred embodiment LIGBT  300  shown in  FIG. 3 , the triggered voltage Vds is reduced to about 0.7 V as illustrated in  FIG. 4 , which is the same value as that of the LIGBT  100  of  FIG. 1A  because no R p  exists in the LIGBT according to the present invention. Meanwhile, the on-resistance of the present invention is lower than that of the LIGBT  100  of  FIG. 1A , because there is current flowing through from drain to source before the triggered voltage. Moreover, the switching speed of the present invention is as same as that of the LIGBT  200  of  FIG. 1B  due to the drain region provided for the removal of minority carriers. 
         [0008]    In another preferred embodiment, the LIGBT according to the present invention further comprises: a trenched gate in active area; a source (cathode) trenched contact penetrating through the insulating layer and a source (cathode) region having the first conductivity type, and further extending into a body region of the second conductivity type within the epitaxial layer; and a heavily doped contact region of the second conductivity type within the body region and below the source (cathode) region, surrounding sidewall and bottom of the source (cathode) trenched contact. 
         [0009]    In yet another preferred embodiment, the LIGBT according to the present invention further comprises: a planar gate; a source (cathode) trenched contact penetrating through the insulating layer and a source (cathode) region having the first conductivity type, and further extending into a first body region having the second conductivity type within the epitaxial layer; a second body region disposed within said first body region and at least surrounding bottom of said source region, having said second conductivity type with doping concentration higher than said first body region; a heavily doped contact region having the second conductivity type within the second body region and below the source (cathode) region and surrounding sidewall and bottom of the source (cathode) trenched contact. 
         [0010]    In yet another preferred embodiment, the LIGBT of the present invention further comprises one or more detail features as below: the drain region of the first conductivity type surrounds upper portion of the sidewall of the drain-anode adjoining trenched contact while the anode region of the second conductivity type surrounds lower portion of the sidewall of the drain-anode adjoining trenched contact and wraps around bottom of the drain-anode adjoining trenched contact; the LIGBT further comprises a breakdown voltage enhancement doping region of the first conductivity type wrapping around the anode region, wherein the breakdown voltage enhancement doping region has a doping concentration lower than the drain region and higher than the epitaxial layer. Another preferred embodiment further comprises one or more detail features as below: the anode region of the second conductivity type surrounds upper portion of the sidewall of the drain-anode adjoining trenched contact while the drain region of the first conductivity type surrounds lower portion of the sidewall of the drain-anode adjoining trenched contact and wraps around bottom of the drain-anode adjoining trenched contact; the LIGBT further comprises a breakdown voltage enhancement doping region of the first conductivity type wrapping around the anode region, wherein the breakdown voltage enhancement doping region has a doping concentration lower than the drain region and higher than the epitaxial layer. The drain-anode adjoining trenched contact is filled with Ti/TiN/Al or Co/TiN/Al or Ta/TiN/Al alloys, which also acts as a drain-anode metal layer. Alternatively, the drain-anode adjoining trenched contact is filled with Ti/TiN/W or Co/TiN/W or Ta/TiN/W as metal plug connecting to an Al alloys layer as a drain-anode metal layer; the LIGBT further comprises a Ti or Ti/TiN layer underneath the drain-anode metal layer as an inter-metal contact resistance-reduction layer. 
         [0011]    The inventive LIGBT is either discrete device on single chip or integrated with a control IC on single chip. 
         [0012]    According to another preferred embodiment, please refer to  FIG. 11  for a IGBT  1000 , there is provided a hybrid VIGBT(Vertical IGBT)-LDMOS, comprising: a drain trenched contact penetrating through an insulating layer and an epitaxial layer of a first conductivity type, and further extending into a substrate of a second conductivity type undereneath the epitaxial layer; a vertical drain region of the first conductivity type adjacent to the drain trenched contact, extending from top surface of the epitaxial layer to top surface of the substrate or into the substrate, wherein the vertical drain region having a higher doping concentration than the epitaxial layer; and the vertical drain region contacting to a drain-anode metal layer on bottom surface of the substrate. Optionally, in some preferred embodiment, a buffer layer of the first conductivity type is offered between the substrate and the epitaxial layer, wherein the buffer layer has a higher doping concentration than the epitaxial layer, as shown in  FIG. 11 . In another preferred embodiment, a vertical drain region surrounding sidewalls and bottom of the drain trenched contact does not contact to the substrate. 
         [0013]    Another preferred embodiment has similar cross sectional view of the  FIG. 11  except that the drain trenched contact penetrates the insulation layer and extends into the epitaxial layer but does not further extend to the substrate. The drain region surrounds sidewalls and bottom of the drain trenched contact and contacts to a drain metal over the insulation layer through the metal plug filled into the drain trenched contact. The drain metal may connect to an anode metal on the bottom surface of the substrate through bonding wires, bonding ribbon or copper clips in a package. 
         [0014]    These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
           [0016]      FIG. 1A  is a cross sectional view showing a conventional LIGBT of prior art. 
           [0017]      FIG. 1B  is a cross sectional view showing a fast switching LIGBT of another prior art. 
           [0018]      FIG. 2  is a graph showing relationships between Ids and Vds of LIGBT in  FIG. 1A  and  FIG. 1B . 
           [0019]      FIG. 3  is a cross sectional view showing a preferred embodiment of the present invention. 
           [0020]      FIG. 4  is a graph showing relationships between Ids and Vds of LIGBT in  FIG. 3  and  FIG. 1B . 
           [0021]      FIG. 5  is a cross sectional view showing another preferred embodiment of the present invention. 
           [0022]      FIG. 6  is a cross sectional view showing another preferred embodiment of the present invention. 
           [0023]      FIG. 7  is a cross sectional view showing another preferred embodiment of the present invention. 
           [0024]      FIG. 8  is a cross sectional view showing another preferred embodiment of the present invention. 
           [0025]      FIG. 9  is a cross sectional view showing another preferred embodiment of the present invention. 
           [0026]      FIG. 10  is a cross sectional view showing another preferred embodiment of the present invention. 
           [0027]      FIG. 11  is a cross sectional view showing another preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0028]      FIG. 3  is a cross sectional view showing a LIGBT  300  according to a preferred embodiment of the present invention. The LIGBT  300  of  FIG. 3  is formed in an epitaxial layer  303  of a first conductivity type, here n-type, grown onto top surface of a semiconductor substrate  301  of a second conductivity type, here p-type. A P buried layer  302  is located at a part of the top surface of the substrate  301  and beneath an n+ source (cathode) region  307  which formed near top surface of the epitaxial layer  303 , wherein the P buried layer  302  has a higher doping concentration than the substrate  301  and the n+ source (cathode) region  307  has a higher doping concentration than the epitaxial layer  303 . A first P body region  305  is formed within the epitaxial layer  303  and encompassing the n+ source (cathode) region  307  and forming a channel region underneath a first insulating layer  315  near the top surface of the epitaxial layer  303 . A second P body region  304  is formed within the first P body region  305  and at least surrounding bottom of the n+ source (cathode) region  307 , having a doping concentration higher than the first P body region  305 . A source (cathode) metal layer  311  of Al alloys padded with a barrier layer of Ti/TiN or Co/TiN or Ta/TiN is filled directly into a source (cathode) trenched contact  317  which penetrates through a second insulating layer  314  and the n+ source (cathode) region  307  and further extends into the second P body region  304  to contact with the n+ source (cathode) region  307  and the second P body region  304 . Within the second P body region  304 , a p+ heavily doped contact region  306  is formed surrounding sidewall and bottom of the source (cathode) trenched contact  317  below the n+ source (cathode) region  307  to reduce the contact resistance between the source (cathode) metal  311  and the second P body region  304 , wherein the p+ heavily doped contact region has a higher doping concentration than the second P body region  304 . An n+ drain region  308  is formed near the top surface of the epitaxial layer  303  and spaced apart from the first P body region  305 , and a p+ anode region  309  is formed within the epitaxial layer  303 , below the n+ drain region  308 . A drain-anode metal  313  of Al alloys padded with a barrier layer of Ti/TN or Co/TiN or Ta/TiN is directly filled into a drain-anode adjoining trenched contact  316  which penetrates through the first insulating layer  315  and the n+ drain region  308  and further extends into the p+ anode region  309  to vertically contact with the n+ drain region  308  and the p+ anode region  309 , wherein the n+ drain region  308  surrounds upper portion of the sidewalls of the drain-anode adjoining trenched contact  316  and the p+ anode region  309  surrounds lower portion of the sidewalls of the drain-anode adjoining trenched contact  316  and wraps around bottom of the drain-anode adjoining trenched contact  316 . A gate metal  312  of Al alloys is filled directly into a gate trenched contact penetrating through the second insulating layer  314  to contact with a planar gate  310  of doped poly-silicon layer. 
         [0029]      FIG. 4  illustrates Ids-Vds characteristic comparison between LIGBT  300  of  FIG. 3  and LIGBT  200  of  FIG. 1B , it shows that the triggered voltage of this invention has been reduced to a typical value of 0.7V with higher switching speed. 
         [0030]      FIG. 5  is a cross sectional view showing a LIGBT  400  according to another preferred embodiment of the present invention which has a similar configuration to the LIGBT  300  in  FIG. 3  except that, the LIGBT  400  of  FIG. 5  additionally provides an n* breakdown voltage enhancement doping region  418  wrapping around the p+ anode region  409  and contacting to the n+ drain region  408 , wherein the doping concentration of the n* breakdown voltage enhancement doping region  416  is lower than that of the drain region  408  but higher than that of the epitaxial layer  403 . The n* breakdown voltage enhancement doping region is disposed underneath the n+ drain region or wrapping around both the p+ anode region and the n+ drain region. 
         [0031]      FIG. 6  is a cross sectional view showing a LIGBT  500  according to another preferred embodiment of the present invention which has a similar configuration to the LIGBT  300  in  FIG. 3  except that, the p+ anode region  509  surrounds upper portion of the sidewall of the drain-anode adjoining trenched contact  516  and the n+ drain region  508  surrounds lower portion of the sidewall of the drain-anode adjoining trenched contact  516  and wraps around bottom of the drain-anode adjoining trenched contact  516 . 
         [0032]      FIG. 7  is a cross sectional view showing a LIGBT  600  according to another preferred embodiment of the present invention which has a similar configuration to the LIGBT  500  in  FIG. 6  except that, the LIGBT  600  of  FIG. 7  additionally provides an n* breakdown voltage enhancement doping region  618  wrapping around the p+ anode region  609  and contacting to the n+ drain region  608 , wherein the doping concentration of the n* breakdown voltage enhancement doping region  618  is lower than that of the drain region  608  but higher than that of the epitaxial layer  603 . The n* breakdown voltage enhancement doping region may wraps around both the p+ anode region and the n+ drain region as another preferred embodiment. 
         [0033]      FIG. 8  is a cross sectional view showing a LIGBT  700  according to another preferred embodiment of the present invention which has a similar configuration to the LIGBT  400  in  FIG. 5  except that, the source (cathode) trenched contact  717 , the drain-anode adjoining trenched contact  716  and the gate trenched contact are filled with a tungsten plug  721  padded by a barrier layer of Ti/TiN or Co/TiN or Ta/TiN to respectively contact with the source (cathode) metal  711 , the drain-anode metal  713  and the gate metal  712  of Al alloys which is optionally padded by a inter-metal contact resistance-reduction layer of Ti or Ti/TiN. 
         [0034]      FIG. 9  is a cross sectional view showing a LIGBT  800  according to another preferred embodiment of the present invention. The LIGBT of  FIG. 9  is formed in an epitaxial layer  803  of a first conductivity type, here n-type, grown onto top surface of a semiconductor substrate  801  of a second conductivity type, here p-type. At least a first type trenched gate  804  in active area and at least a second type trenched gate  803  in gate contact area which are implemented by filling doped poly-silicon layers in a plurality of gate trenches in the epitaxial layer  803 . An n+ source (cathode) region  807  are formed near top surface of the epitaxial layer  803  and surrounding top portion of sidewalls of the first type trenched gate  804 , wherein the n+ source (cathode) region  807  has a higher doping concentration than the epitaxial layer  803 . A P body region  805  is formed within the epitaxial layer  803  and encompassing the n+ source (cathode) region  807  and forming a channel region along the sidewalls of the first type trenched gate  804 , wherein the P body region  805  surrounds lower portion of the sidewalls of the first type trenched gate  804 . Each of a plurality of source (cathode) trenched contacts  817  filled with a tungsten plug  821  padded by a barrier layer of Ti/TiN or Co/TiN or Ta/TiN is penetrating through the insulating layer  815  and the n+ source (cathode) region  807  and further extending into the P body region  805 . Underneath each of the source (cathode) trenched contact  817 , a p+ heavily doped contact region  806  is formed within the P body region  805  and surrounding sidewall and bottom of the source (anode) trenched contact  817  below the n+ source (anode) region  807  to reduce the contact resistance between the tungsten plug  821  and the P body region  805 , wherein the p+ heavily doped contact region  806  has a higher doping concentration than the P body region  805 . An n+ drain region  808  is formed near the top surface of the epitaxial layer  803  and spaced apart from the P body region  805 , and a p+ anode region  809  is formed within the epitaxial layer  803  and below the n+ drain region  808 , meanwhile, an n* breakdown voltage enhancement doped region  816  is formed contacting to the n+ drain region  808  and wrapping around the p+ anode region  809 , wherein the n* breakdown voltage enhancement doped region  816  has a doping concentration higher than the epitaxial layer  803  but lower than the n+ drain region  808 . A drain-anode adjoining trenched contact  816  filled with a tungsten plug  820  padded by the barrier layer is penetrating through the insulating layer  815  and the n+ drain region  808  and further extending into the p+ anode region  809 . A gate trenched contact filled with a tungsten plug  822  padded by the barrier layer is penetrating through the insulating layer  815  and extending into the doped poly-silicon layer within the second type trenched gate  803 . Onto the insulating layer  815 , a gate metal  812 , a source (cathode) metal  811  and a drain-anode metal  813  of Al alloys which is optionally padded by a resistance-reduction layer of Ti or TiN is formed to be electrically connected to the tungsten metal plug  822 , the tungsten plug  821  and the tungsten plug  820 , respectively. Another preferred embodiment has a similar configuration to the LIGBT  800  except that there is no n* breakdown voltage enhancement doping region. 
         [0035]      FIG. 10  is a cross sectional view showing a LIGBT  900  according to another preferred embodiment of the present invention which has a similar configuration to the LIGBT  800  in  FIG. 9  except that, a buried oxide layer  902  is disposed between an epitaxial layer  903  and a substrate  901  for further enhancing breakdown voltage. 
         [0036]      FIG. 11  is a cross sectional view showing a hybrid IGBT comprising VIGBT (Vertical IGBT)-LDMOS  1000  according to another preferred embodiment of the present invention. The hybrid VIGBT-LDMOS  1000  is formed in an epitaxial layer  1003  of a first conductivity type, here n-type, grown onto top surface of a semiconductor substrate  1001  of a second conductivity type, here p-type. Between the epitaxial layer  1003  and the substrate  1001 , there is an N* buffer epitaxial layer  1002  having higher doping concentration than the epitaxial layer  1003 . At least a first type trenched gate  1004  in active area and at least a second type trenched gate  1003  in gate contact area which are implemented by filling doped poly-silicon layers in a plurality of gate trenches in the epitaxial layer  1003 . An n+ source (cathode) region  1007  are formed near top surface of the epitaxial layer  1003  and surrounding top portion of sidewalls of the first type trenched gate  1004 , wherein the n+ source (cathode) region  1007  has a higher doping concentration than the epitaxial layer  1003 . A P body region  1005  is formed within the epitaxial layer  1003  and encompassing the n+ source (cathode) region  1007  and forming a channel region along the sidewalls of the first type trenched gate  1004 , wherein the P body region  1005  surrounds lower portion of the sidewalls of the first type trenched gate  1004 . Each of a plurality of source (cathode) trenched contacts  1017  filled with a tungsten plug  1021  padded by a barrier layer of Ti/TiN or Co/TiN or Ta/TiN is penetrating through the insulating layer  1015  and the n+ source (cathode) region  1007  and further extending into the P body region  1005 . Underneath each of the source (cathode) trenched contact  1017 , a p+ heavily doped contact region  1006  is formed within the P body region  1005  and surrounding sidewall and bottom of the source (anode) trenched contact  1017  below the n+ source (anode) region  1007  to reduce the contact resistance between the tungsten plug  1021  and the P body region  1005 , wherein the p+ heavily doped contact region  1006  has a higher doping concentration than the P body region  1005 . A gate trenched contact filled with a tungsten plug  1022  padded by the barrier layer is penetrating through the insulating layer  1015  and extending into the doped poly-silicon layer within the second type trenched gate  1003 . An N+ vertical drain region  1008  is formed adjacent to sidewalls of a drain trenched contact  1016 , wherein the N+ vertical drain region  1008  is extending from top surface of the epitaxial layer  1003 , penetrating through the epitaxial layer  1003  and the N* buffer epitaxial layer  1002  and to top surface of the substrate  1001  while the drain trenched contact  1016  filled with a conductive plug  1020  of doped poly-silicon or tungsten plug is penetrating through the insulating layer  1005 , the epitaxial layer  1003  as well as the N* buffer epitaxial layer  1002  and extending into the substrate  1001 . Onto the insulating layer  1015 , a gate metal  1012 , a source (cathode) metal  1011  which is optionally padded by a resistance-reduction layer of Ti or TiN is formed to be electrically connected to the tungsten metal plug  1022 , the tungsten plug  1021 , respectively. Onto bottom surface of the substrate  1001 , a drain-anode metal  1013  such as Ti/Ni/Ag is formed connecting with the n+ vertical drain region  1008  by the drain trenched contact  1016 . In another preferred embodiment, the N+ vertical drain region  1008  surrounding not only sidewalls but also bottom of the drain trenched contact  1016 . 
         [0037]    Another preferred embodiment has similar cross sectional view of the  FIG. 11  except that the drain trenched contact penetrates the insulation layer and extends into the epitaxial layer but does not further extend to the substrate. The N+ drain region surrounds sidewalls and bottom of the drain trenched contact and contacts to a drain metal over the insulation layer through the metal plug filled into the drain trenched contact. The drain metal connects to an anode metal on the bottom surface of the substrate through bonding wires, bonding ribbon or copper clips in a package. 
         [0038]    Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.