Patent Publication Number: US-9899510-B2

Title: Semiconductor device

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 14/527,831 filed on Oct. 30, 2014, which claims priority to Chinese Patent Application serial number 201320675451.6 filed on Oct. 30, 2013 and is hereby incorporated in its entirety. 
    
    
     FIELD 
     This disclosure relates to a semiconductor device, in particular, to a super-junction device. 
     BACKGROUND 
     A lot of technologies use narrow poly-silicon stripes as a controlling gate to switch the current between source and drain of a MOSFET. As the area of the gate poly silicon dominantly determines the gate charge, it may be desirable in one embodiment to have small stripes as this allows low gate driving losses, low delay times, and, therefore, a high efficiency in applications. However, especially when using very small stripes the effective resistance of these stripes and, therefore, the effective gate resistance of the device get comparably high. The effective gate resistance which is a function of the poly silicon sheet resistance depends on the doping level of the poly silicon which is limited by the solubility of the doping material. The thickness of the gate poly-silicon layer cannot be increased by any order, as a too big thickness would lead to an undesired high topology which would make the process much more complex. Therefore the sheet resistance of an n-doped poly silicon layer of 600 nm thickness cannot be considerable lower than 8-10 ohm/sq. A high effective gate resistance leads to increased switching losses and to undesired inhomogeneous switching across the chip which might end-up in oscillations or in reduced device ruggedness in worst-case. 
     Another drawback of the small width of the poly silicon stripes is an increased on-resistance because of the JFET effect. Between two opposite p-bodies, a depletion region builds-up during the on-state of the device which is narrowing the current path and, therefore, increases the on-state resistance (R dson ).This is the so-called JFET effect. It is obvious that this effect is more pronounced with a small width of the poly silicon stripes as the p-bodies are usually implanted by using the poly-silicon openings as a mask. 
       FIG. 1  shows a conventional super-junction structure for explanation purposes. The device as shown in  FIG. 1  has a semiconductor body with a compensation area comprising p-regions (p-columns)  130  and n-regions (n-columns)  134 . The compensation region is connected to a MOS transistor cell comprising a source region  118 , a body region  138  and a controlling gate  114 . An insulating structure  140 , electrically isolates the gate  114  from the body region  138 , the source region  118 , the n-regions (n-columns)  134  and a metallization layer  110 . And a part of the insulating structure  140  may act as gate insulating layer. The drain  128  of the transistor is connected to a highly doped substrate  124 . Between the substrate and the compensation area a buffer layer  126  is located. The source contacts are electrically connected by the metallization layer  110 . The drain contact is built at the device backside and is covered with metallization  128 . 
     Modern super-junction devices are featuring lower and lower pitch sizes. This trend is driven either by the reduction of E oss  which allows lower switching losses, and, even more, by the reduction of the on-resistance (R dson ) per chip area. On the one hand, a low R dson  per chip area is the major lever to reduce chip costs, and, on the other hand, it allows to provide lower R dson  values for a given package size. 
     A reduction of the R dson  per chip area automatically leads to narrower contact-holes for the source contact. Voidless filling of such narrow contact-holes with metal is nearly impossible. Therefore usually a plug process (e.g. Poly-silicon or Wolfram) is used. Today only a plug-process solely or an Anti-JFET implant solely are used. 
     SUMMARY 
     In one embodiment of the present disclosure, a semiconductor device is provided, which comprises a compensation area which comprises p-regions and n-regions, and a plurality of transistor cells on the compensation area, each of the plurality of transistor cells comprising a source region, a body region, a gate and an interlayer dielectric. The semiconductor device further comprises a source metallization layer arranged on the interlayer dielectric, and an additional n-doping region that is provided on top of the n-regions between two neighboring body regions. Further, a source plug fills a contact hole formed through the interlayer dielectric between the source and body region and the source metallization layer, so as to electrically connect the source and body region and the source metallization layer. 
     In some embodiments, the doping concentration of the additional n-doping region is 0.5×10 16  cm −3 ˜5×10 16  cm −3 . 
     In some embodiments, the gate is formed of poly-silicon stripe. 
     In some embodiments, the semiconductor device further comprises one or more gate fingers which are oriented perpendicular to the gates, each of the gate fingers electrically connecting two neighboring gates. 
     In some embodiments, each of the gate fingers is formed of a continuous stripe. 
     In some embodiments, each of the gate fingers is formed of a non-continuous stripe. 
     In some embodiments, that, the gate finger is formed of metal or poly-silicon. 
     In some embodiments, the semiconductor device further comprises one or more intermitting gate fingers which interrupt the source metallization layer so as to insulate the source metallization layer and the gates of the transistor cells, the intermitting gate fingers being oriented perpendicular to the gates. 
     In some embodiments, the semiconductor device further comprise one or more continuous gate fingers which interrupt the source metallization layer so as to insulate the source metallization layer and the gates of the transistor cells, the continuous gate fingers being oriented perpendicular to the gates. 
     In some embodiments, that, the intermitting gate finger is formed of poly-silicon and metal. 
     In some embodiments, the width of the stripe of the gate formed in poly-silicon is equal to or narrower than 8 μm. 
     In some embodiments, the semiconductor device further comprises a surrounding gate ring, and the one or more gate fingers are connected to the surrounding gate ring. 
     In some embodiments, the width of the gate finger is 10-50 μm. 
     In some embodiments, the source plug is formed of polysilicon or Wolfram. 
     In some embodiments, the width of the source plug is less than 2 μm. 
     In some embodiments, the gates have a planar structure. 
     In some embodiments, the gates are located at least partially in trenches. 
     In some embodiments, the semiconductor device is a super-junction device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present disclosure will be apparent from the following detailed description with reference to the accompanying drawings, in which: 
         FIG. 1  schematically shows a cross section of a conventional super-junction structure. 
         FIG. 2  schematically shows a cross section of a super-junction structure with a gate formed of poly silicon stripes and an additional Anti-JFET-implant between two adjacent p-body regions according to the present disclosure. 
         FIG. 3  is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates with a surrounding metal gate ring and stripe-shaped contacts for the source connection according to the present disclosure. 
         FIG. 4  is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates with a surrounding metal gate ring, stripe-shaped contacts for the source connection, and one or more gate fingers according to the present disclosure. 
         FIG. 5  is a schematic top view of a network of small poly silicon stripes of the gate fingers of the super-junction structure to ensure a more homogeneous switching behavior according to the present disclosure. 
         FIG. 6  is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates with a surrounding metal gate ring and intermitted gate finger formed of poly silicon and metal according to the present disclosure. 
         FIG. 7  is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates with a surrounding metal gate ring and continuous gate fingers formed of poly silicon and metal according to the present disclosure. 
         FIG. 8  schematically shows a cross section of a super-junction structure which combines the usage of a plug process for the source contact holes and an Anti-JFET-implant according to the present disclosure. 
         FIG. 9  schematically shows a cross section of embodiment of plug process with Anti-JFET-implant for a trench gate structure according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout. Furthermore, the various layers and regions illustrated in the figures are illustrated schematically and are not necessarily drawn to scale. Accordingly, the present disclosure is not limited to the relative size, spacing and alignment illustrated in the accompanying figures. As will also be appreciated by those of skill in the art, references herein to a layer formed “on” a substrate or other layer may refer to the layer formed directly on the substrate or other layer or on an intervening layer or layers formed on the substrate or other layer. Moreover, the terms “first conductivity type” and “second conductivity type” refer to opposite conductivity types such as N or P-type, however, each embodiment described and illustrated herein includes its complementary embodiment as well. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.) 
     The figures illustrate relative doping concentrations by indicating “−” or “+” next to the doping type “n” or “p”. For example, “n−” means a doping concentration which is lower than the doping concentration of an “n”-doping region while an “n+”-doping region has a higher doping concentration than an “n”-doping region. Doping regions of the same relative doping concentration do not necessarily have the same absolute doping concentration. For example, two different “n”-doping regions may have the same or different absolute doping concentrations. 
     The present disclosure proposes a semiconductor device structure that can cope with the two major drawbacks (i.e., increased on-resistance due to the JFET effect and increased gate resistance) that arise due to the design of a controlling gate with narrow stripes of poly silicon. For the sake of simplicity, the following embodiments use a super-junction structure as example for explanation. 
       FIG. 2  is a sketch of a super-junction structure  200  according to one embodiment of the present disclosure. 
     The super-junction structure  200  shown in  FIG. 2  is substantially the same as the conventional super-junction structure shown in  FIG. 1 , except for the additional Anti-JFET-implant region  256  between two adjacent p-body regions  238 . For the sake of simplicity, descriptions of the parts of  FIG. 2  that are the same as  FIG. 1  are omitted. 
     During the on-state of the MOS transistor cell, the p-body regions  238  are connected to the source potential with the current flowing along the n-column  234 . Between the p-body region  238  and the conductive n-column  234 , a voltage drop develops. Consequently, between two opposite p-body regions  238  a depletion region builds-up which is narrowing the current path and, therefore, increases the on-state resistance (R dson ). This is the so-called JFET effect. It is obvious that this effect is more pronounced with a decreased size of the pitch between the MOS transistor cells. In order to improve the R dson , an additional n-doping is implanted on top of the Si layer (i.e., the n-column  234 ) between two neighboring body regions, and such n-doping implant is referred to as Anti-JFET-implant. After the Anti-JFET-implant, an Anti-JFET region  256  is formed between two adjacent p-body regions  238 . 
     A high concentration of the Anti-JFET region  256  can reduce the on-resistance of the super-junction structure. However, the doping level of the Anti-JFET-implant needs to be well balanced as a too high level would increase the gate charge of the super-junction structure and sacrifice the short-circuit ruggedness. In an embodiment according to the present disclosure, the concentration of the Anti-JFET region  256  is 0.5×10 16  cm −3 ˜5×10 16  cm −3 . 
     In an embodiment, the gate  214  is formed of poly silicon stripes, as shown in  FIG. 2 . 
     A super-junction transistor having a gate formed of narrow poly silicon stripes usually has no connections between two adjacent usually parallel oriented stripes, as shown in  FIG. 3 , which is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates  314  with a surrounding metal gate ring  315  and stripe-shaped contacts  310  for the source connection. Therefore during switching of the device, the gate potential is different between the edges of the gate stripe  314  located close and connected to a gate runner  317  usually formed of metal and the middle of each of the gate stripes  314 . This means that the fraction of the gate stripe  314  located close to the gate ring  315  switches first whereas the fraction towards the middle switches with a certain delay. 
     It is obvious that this inhomogeneous switching get worse with a bigger chip area of the transistor. The inhomogeneous switching can lead to massive oscillations or in worst case to device destruction as only a small fraction of the transistor can carry the current. 
     In order to provide a more homogeneous distribution of the gate signal and thus a more homogeneous switching behavior, one or more gate fingers can be introduced, as shown in  FIG. 4 , which is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates  414  with a surrounding metal gate ring  415 , stripe-shaped contacts  410  for the source connection, and one or more gate fingers  416 . 
     In this embodiment, the gate fingers  416  may be oriented perpendicular to the gate poly silicon stripes  414  and may be connected (but not necessarily) to the surrounding gate ring  415 . The implementation of the gate fingers  416  can reduce the distributed gate resistance and improve the performance and the ruggedness of the device. 
     In this case, the width of the gate fingers needs to be balanced. A small structure would not be effective enough, whereas a too wide width might lead to a significant increase of the gate charge. This balancing needs to be done depending on the diffusion length adjusted by the channel diffusion process. In an embodiment of the present disclosure, the width of the gate fingers can be 10-50 μm. 
     As shown in  FIG. 4 , the gate fingers may be composed of one or more continuous stripes, and each of the continuous stripes may be connected to a gate runner  417 . The stripes of the gate fingers may be parallel to each other. 
     In another embodiment, the gate fingers do not necessarily need to be connected to the gate runner. The concept of the gate finger generally works even without the surrounding gate ring. But it is less effective in this case. The gate fingers may also not necessarily be formed in one or more continuous stripes, but be formed in a network of several small connections, as shown in  FIG. 5 , which is a schematic top view of a network of small poly silicon stripes of the gate fingers of the super-junction structure. 
     In  FIG. 5 , the gate finger is not continuous, and is composed of a plurality of short connections  516 . Each short connection is used to electrically connect two adjacent and substantially parallel gates  514  which may be formed of poly silicon stripe. All of the short connections  516  make up a network as shown in  FIG. 5 , which is completely different from the plurality of parallel continuous stripes as shown in  FIG. 4 . By implementing the embodiment of  FIG. 5 , a more homogeneous switching behavior of the device can be achieved as compared to the embodiment of  FIG. 4 . 
     In the super-junction structures as shown in  FIGS. 2-5 , the gates are all shown to be formed of poly silicon, although all or parts of the gates may be also formed of metal. In addition, the gate fingers as shown in  FIGS. 4-5  can be formed of metal or poly silicon. 
       FIG. 6  is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates with a surrounding metal gate ring and intermitted gate finger formed of poly silicon and metal according to the present disclosure. 
     As shown in  FIG. 6 , the gate finger  616  is formed of both poly and metal. In this case, the source metallization layer  610  needs to be interrupted as shown in  FIG. 6  to prevent an electrical short circuit between the gate and the source. According to the embodiment as shown in  FIG. 6 , one or more intermitting gate fingers  616  are utilized. 
       FIG. 7  is a schematic top view of a super-junction structure with stripe-shaped poly silicon gates with a surrounding metal gate ring and continuous gate fingers formed of poly silicon and metal according to the present disclosure. In fact,  FIG. 7  is a special embodiment of  FIG. 6  with continuous fingers  716  formed of poly silicon and metal. 
     Since the source metallization layer  710  needs to be interrupted to prevent an electrical short circuit between the gate and the source, in this case, the chip divides into several parts with respect to the source metallization layer  710 , as shown in  FIG. 7 , which would introduce a drawback. The drawback needs to be resolved by proper methods for the source bonding, e.g. stitch, ribbon, as this is substantially not related to the key point of the present disclosure and thus the description thereof will be omitted. 
     According to the present disclosure, in the super-junction structures as shown in  FIGS. 2-7 , the width of all of the gates in poly silicon stripe can be chosen especially to be equal to or narrower than 8 μm; and striped contacts may be utilized to electrically connect the source metallization layer and the source and body regions. In one embodiment, plug contacts instead of contact stripes may be used as the source contacts so as to electrically connect the source metallization layer and the source and body regions. 
     In order to realize low pitch sizes, the dimensions of the contact holes used for the source contacts need to be reduced. With a width of less than 2 μm, it is no longer possible to properly fill the contact holes by the metal sputtering processes used today without any voids. Voids could either lead to increased contact resistances and potential reliability problems. Consequently, for a further reduction of the pitch, new processes which have filling properties by using plugs out of poly silicon or Wolfram need to be introduced, as shown in  FIG. 8 , which schematically shows a cross section of a super-junction structure which combines the usage of a plug process for the source contact holes and an Anti-JFET-implant according to the present disclosure. 
     The super-junction structure  800  shown in  FIG. 8  is substantially the same as the super-junction structure shown in  FIG. 2 , except for the plug contacts  828  used as the source contacts. That is, in  FIG. 2 , a conventional contact stripe is used as the source contact, whereas in  FIG. 8 , the plug contact is used as the source contact. For the sake of simplicity, descriptions of the parts of  FIG. 8  that are the same as  FIG. 2  are omitted. 
     Specifically, according to the present disclosure, a plug is provided, which fills a contact hole formed through an interlayer dielectric  840  between the source and body regions  818 ,  838  and the source metallization layer  810 , to form the source plug contact  828 , so as to electrically connect the source and body regions  818 ,  838  and the source metallization layer  810 . In this embodiment, the plug contact  828  is combined with the Anti-JFET region  856  of n doping so as a further reduction of the chip size of the super-junction device can be achieved. In one embodiment, the plug contacts  828  are formed by filling the contact holes with poly silicon or wolfram. 
     According to one embodiment of the present disclosure, a planar gate structure is used for the gate as shown in  FIGS. 2 and 8  and can be also used in the super-junction structure as shown in  FIGS. 3-7 . 
     Nevertheless, a trench gate structure may be also used for the gate instead of the planar gate structure. As an example,  FIG. 9  schematically shows a cross section of embodiment of plug process with Anti-JFET-implant for a trench gate structure according to the present disclosure. 
     The super-junction structure  900  shown in  FIG. 9  is substantially the same as the super-junction structure shown in  FIG. 8 , except for the trench gate structure  914 . For the sake of simplicity, descriptions of the parts of  FIG. 9  that are the same as  FIG. 8  are omitted. 
     In  FIG. 9 , a gate is partially or completely formed in a trench which is formed in an n-region (n-column)  934 , so as to form the trench gate structure  914 . In this case, the Anti-JFET-implant region  956  is formed between the two adjacent p-body regions  938  and below them at the same time surrounding the corresponding periphery of the trench, as shown in  FIG. 9 . In this embodiment, a plug contact  928  formed of poly silicon or wolfram is used as the source contact. 
     In the above descriptions about  FIGS. 2-9 , in order to better highlight the present disclosure, only improved structures made in this disclosure are described in detail, while some semiconductor device structures known to those skilled in the art are only briefed or even omitted. In addition, the semiconductor device structure in the present disclosure can be formed by means of the semiconductor process well known to those skilled in the art, which will not be described in detail any more. 
     While the present disclosure and advantages thereof have been described in details by way of the exemplary embodiments, those skilled in the art shall understand that many substitutions and variations may be made to the present disclosure without departing from the spirit and scope of the present disclosure defined by the appended claims.