Abstract:
This invention discloses a semiconductor power device disposed in a semiconductor substrate including an active cell areas and a termination area. The semiconductor power device further comprises a plurality of gate trenches formed at a top portion of the semiconductor substrate in the active cell area wherein each of the gate trenches is partially filled with a conductive gate material with a top portion of the trenches filled by a high density plasma (HDP) insulation layer. The semiconductor power device further comprises mesa areas of the semiconductor substrate disposed between the gate trenches wherein the mesa areas are recessed and having a top mesa surface disposed vertically below a top surface of the HDP insulation layer wherein the HDP insulation layer covering over the conductive gate material constituting a stick-out boundary-defining layer surrounding the recessed mesa areas in the active cell areas between the gate trenches.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to the manufacturing processes and structures of semiconductor power devices. More particularly, this invention relates to manufacturing processes and structural configurations of improved deep contact trench with reduced critical dimension having shrunken distance between the deep trench contacts. 
         [0003]    2. Description of the Prior Art 
         [0004]    Conventional methods of manufacturing semiconductor power device are still confronted with technical limitations to make electrical contact in trenches with high aspect ratio and small pitches between these trenches. The technical limitations often become a bottleneck that hinders further reductions of the size and dimension of the electronic device. For these reasons, many techniques have been applied in attempt to overcome these limitations. 
         [0005]    Conventional technologies by applying the photolithographic processes are employed to define patterns for opening contact trenches. Typically, photoresist layers are deposited and patterned by selectively exposing the photoresist layer by applying masks to define locations for opening the contact trenches. However, such processes are limited due to the difficulties of properly alignments. Furthermore, the depth of focus and the resolutions of the photolithographic exposures also cause deviations and inaccuracies that demand manufacturing tolerances and hinder the abilities of the manufacturing processes to fabricate device that have contact trenches with submicron pitches. 
         [0006]    In U.S. Pat. No. 8,629,019 Xu et al. disclose a method for manufacturing self-aligned contacts for a trench power MOSFET. The method includes, etching trenches in a substrate through a mask of silicon nitride deposited on an oxide layer, forming a gate oxide layer on the walls of the trenches. The gate oxide layer on the sidewalls of the trenches is then applied to self-align the gate bus by filling the gate trenches with a polysilicon layer. Similarly, contact windows to source and body regions are also defined in a silicon nitride for etching the silicon nitride on top of an oxide layer covering over the source and body region. Spacers are grown on sidewalls of these contact windows to self-align the contact metal deposited into these contact windows formed as trenches in the silicon nitride layer having spacers on the sidewalls. The methods disclosed by Xu et al. as disclosed in the patented invention are still limited by the fact that masks are applied first to define the locations on the silicon nitride layer covering over the top surface of the device. Due to the tolerance that is required for allowing small degrees of inaccuracy for the placement of the mask on a flat surface, there are still limit that would hinder the reductions of the pitches between the trench contacts. Even though different contact metals as that disclosed by Xu et al. are formed in the contact trenches in a self-aligned fashion, the contact trenches themselves are not formed by applying a self-aligned process. 
         [0007]    Therefore, a need still exists for the ordinary skill in the art to improve the methods of manufacturing of the power devices, particularly the trench contacts to be accurately formed at different locations over the entire top surface area of the power device to resolve these technical limitations. It is the purpose of this invention to provide new and improved methods of manufacturing, structural features and device configurations to precisely place the contact trenches by a self-aligned process such that the above-discussed difficulties and limitations can be overcome. 
       SUMMARY OF THE PRESENT INVENTION 
       [0008]    It is therefore an aspect of the present invention to provide a new and improved method of manufacturing a semiconductor power device by applying a selective etch process to form a self-aligned structural feature with recessed grooves in the mesa area between the trenched gates whereby the sidewalls of the recessed grooves define the outer boundaries of the locations of the trench contacts. The required tolerances to allow for inaccuracies in placing the masks relative to the trench gates as that encountered in the conventional manufacturing processes are therefore resolved. 
         [0009]    It is another aspect of the present invention to provide a new and improved method of manufacturing a semiconductor power device by further carrying out an oxide spacer on the sidewalls of the recessed groves of the epitaxial layer to further narrow and define the locations of the trench contacts substantially in the middle portion of the recess grooves. A process to etch the contact trenches with high aspect ratio can therefore carry out with precisely defined locations without requiring the conventional methods of applying masks. The locations of the contact trenches are precisely defined right in the middle of the source and body region in the mesa area in a totally self-aligned fashion. 
         [0010]    Therefore, by applying the manufacturing processes of this invention, the distance between the trenches can also be precisely defined and formed without the uncertainties and tolerances as that required in the conventional method such that the pitch of the cell of the power device can be reduced. 
         [0011]    In a preferred embodiment, this invention discloses a semiconductor power device disposed in a semiconductor substrate. The semiconductor power device comprises an active cell areas and a termination area. The semiconductor power device further comprises a plurality of gate trenches formed at a top portion of the semiconductor substrate in the active cell area wherein each of the gate trenches is partially filled with a conductive gate material with a top portion of the trenches filled by a high density plasma (HDP) insulation layer. The semiconductor power device further comprises mesa areas of the semiconductor substrate disposed between the gate trenches wherein the mesa areas are recessed and having a top mesa surface disposed vertically below a top surface of the HDP insulation layer wherein the HDP insulation layer covering over the conductive gate material constituting a stick-out boundary-defining layer surrounding the recessed mesa areas in the active cell areas between the gate trenches. 
         [0012]    In a preferred embodiment, this invention further discloses a method for manufacturing a semiconductor power device on a semiconductor substrate comprising an active cell areas and a termination area. The method includes steps of a) opening a plurality of gate trenches in a top portion of the semiconductor substrate in the active cell area and filling each of the gate trenches with a conductive gate material followed by etching off the conductive gate material from a top portion of the trenches; b) depositing a high density plasma (HDP) oxide layer and forming a BPSG insulation layer covering over a top surface followed by applying a self-aligned contact (SAC) photoresist mask to carry out a self-aligned contact etch to remove the BPSG insulation and the HDP oxide layers from a top surface of the semiconductor substrate in an uncovered area; and c) performing a mesa recess etch to etch the semiconductor substrate to form a mesa recess with a top mesa surface vertically below a top surface of the HDP insulation layer covering over the conductive gate material constituting a stick-out boundary-defining layer surrounding the recessed mesa areas in the active cell areas between the gate trenches. 
         [0013]    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 
         [0014]      FIGS. 1A and 1B  are side cross sectional views for depicting semiconductor power devices manufactured by applying methods and structural features of this invention. 
           [0015]      FIG. 1C  is a side cross section view for depicting special structural features of the semiconductor power device for the device shown in  FIG. 1A . 
           [0016]      FIG. 2A to 2T  are series of cross sectional views to illustrate the processing steps for manufacturing a semiconductor power device of this invention as that shown in  FIGS. 1 and 1A . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0017]      FIG. 1A  is a side cross sectional view of a power device with deep trench contact structures manufactured by applying the processing steps of this invention. The power device is supported in an N-type epitaxial layer  110  formed on top of an N-type semiconductor substrate (not shown). The semiconductor power device includes an active cell region extended over an area covered by a top source metal  190 -S and a termination area covered by a gate pad metal layer  190 -G. The power device comprises a plurality of trenched gates  130  formed in deep trenches  115  padded with a gate oxide layer  120 , where each of the trenched gates is surrounded by a P-type body region  150  with the body region  150  encompassing a N-type source region  160 . The power device further includes a plurality of source/body contacts  180  formed as a deep trench contact  180 . Each of these deep contact trenches penetrates through a HDP oxide layer  145 , vertically extends below the source regions  160  and further penetrates through a top portion of the body region  160  contacts to a contact implant region  170  formed in the body region  150  and is filled with a metal layer forming the source/body contact  180 . Each of these source/body contact  180  further directly contacts to the source metal  190 -S covering over the top of the HDP oxide layer  145  and the spacer layer  165 . The center of the source/body contact  180  is substantially aligned with the center of the mesa between two adjacent active trenches  115 . However, in the mesa between the last active trench  115  and the gate pick up trench  115 ′, the source/body contact  180 ″ is off center of the mesa closer to the last active trench. In this embodiment, the semiconductor power device further comprises a body clamping layer (BCL)  140  formed as boron implant regions for clamping the BVdss. The polysilicon gate pickup  130 ′ formed in a deep gate pickup trench  115 ′ padded with a gate oxide layer  120  contacts to the metal layer  190 -G metal layer through a pickup contact  180 ′ penetrating through the HDP oxide layer  145  and the BPSG layer  148  and vertically extending through a top portion of the polysilicon gate pickup  130 ′, where the gate pickup  130 ′has a greater width than that of the trenched gates  130  in the active cell area. A gap g separating the source metal  190 -S and gate metal  190 -G extends across the edge of the HDP oxide layer  145  and the BPSG layer  148  substantially aligned with the trench sidewall of the gate pick up trench  115 ′ closer to the active trenches  115 . 
         [0018]      FIG. 1B  is a side cross sectional view of an alternative power device of this invention, which is similar to the power device of  FIG. 1A , excepting that the termination area does not include the BCL layer  140 . 
         [0019]      FIG. 1C  shows the special structural features of the semiconductor power device for the device shown in  FIG. 1A . 
         [0020]    Specifically, the width of the source/body trench contacts  180  is now reduced to about 0.1 to 0.2 micron, for example 0.13 micron, and the pitch between the deep contact trenches is reduced to about 0.2 to 0.3 micron, for example 0.25 micron. 
         [0021]      FIGS. 2A to 2T  are a series of side cross sectional views illustrating the processing steps of forming the deep trench contact structures to reduce the cell pitches of a semiconductor power device of  FIG. 1A  according to the configuration and methods of the present invention. In  FIG. 2A , a thermal oxide layer  112 , which is a hard mask, is grown on top of an N-type epitaxial layer. The epitaxial layer  110  is formed on top of an N-type semiconductor substrate (not shown). The thickness of the thermal oxide layer  112  is approximately 2700 Angstroms. In  FIG. 2B , a trench photoresist mask  113 , with a critical dimension (CD) substantially around 0.25 micrometers for active trenches and 0.9 micrometers for the gate pickup trench is applied to pattern the hard mask  112  forming a trench hard mask layer  112 ′ followed by removal of the mask  113  as that shown in  FIG. 2C . 
         [0022]    In  FIG. 2D , an etch process is carried out to open trenches  115 ,  115 ′ with a trench depth for active trenches  115  of approximately 1.45 micrometer. The trench sidewalls are opened not exactly perpendicular relative to the top surface of the substrate and having an angle of about 86.5 degrees. After the trench etch process, a CARO cleaning process is carried out and a portion of the hard mask  112 ′ having a layer thickness of about 1200 Angstroms still remains. In FIG.  2 E, a sacrificial oxide pre-cleaning process is carried out using Standard Clean 1 (SC1) process with HF to remove the oxide layer having a thickness of about 50 Angstroms followed by growing another sacrificial oxide layer of about 100 Angstroms and removing 130 Angstroms of a target oxide layer. Then a gate oxide layer  120  having a thickness of about 310 Angstroms covering over the trench sidewalls is grown. The remaining hard mask oxide layer  112 ′ has a thickness of about 1000 Angstroms. In  FIG. 2F , an in-situ phosphoric doped polysilicon layer  130 ″ is deposited into the trenches  115 ,  115 ′ and atop the surface of the hard mask  112 ′ followed by a chemical-mechanical planarization (CMP) process to planarize the top surface of the polysilicon layer  130 ″ and the hard mask layer  112 ′ as that shown in  FIG. 2G . The remaining hard mask layer  112 ′ has a thickness of about 800 Angstroms. Then a pre-anneal cleaning process is carried out using CARO, Standard Clean 1 (SC1) and Standard Clean 2 (SC2) cleaning processes followed by performing a poly-anneal process on the polysilicon layer  130 ″ at a temperature of about 1150 degree Celsius. 
         [0023]    In  FIG. 2H , the processes proceed with the application of a BCL photoresist mask  132  to carry out multiple steps of BCL implantations. In an exemplary embodiment, the implantations includes a) BF2 dopant with a doping concentration of 2E15 cm −3  implanted at 2100 Key; b) Boron dopant with a doping concentration of 1E15 cm −3  implanted at 100 Kev; c) Boron dopant with a doping concentration of 2E12 cm −3  implanted at 460 Kev; and d) Boron dopant with a doping concentration of 2E12 cm −3  implanted at 700 Kev to form the BCL regions  140 . In  FIG. 2I , the BCL implant mask  132  is removed followed by first carrying out an oxide break through etch to remove a top portion of the hard mask oxide layer  122 ′ of about 300 Angstroms on top of the polysilicon layer  130 ″. Then a polysilicon etch back process is carried out to etch the polysilicon layer  130 ″ to a depth of about 0.4 micrometers below the top surface of the silicon substrate  110  forming the trenched gates  130  and polysilicon pickup gate  130 ′ in the trenches  115  and  115 ′. The remaining hard mask oxide layer has a layer thickness of about 200 Angstroms. 
         [0024]    In  FIG. 2J , the manufacturing processes continue with a step of depositing a HDP oxide layer  145  having a layer thickness of about 3000 Angstroms followed by forming a BPSG layer  148  having a layer thickness of about 4300 Angstroms on top of the HDP oxide layer  145 . In  FIG. 2K , a self-aligned contact (SAC) photoresist mask  149  is applied to carry out a self-aligned contact oxide etch to remove the HDP oxide layer  145  and the BSPG layer  148  from the uncovered portion and stop at the top surface of the silicon substrate  110 , where the edge of HDP oxide layer  145  and the BPSG layer  148  after masked etching is substantially aligned to the trench sidewall of the gate pickup trench  115 ′ closer to the active trenches  115 . In  FIG. 2L , a mesa recess etch is performed to etch the silicon substrate to form a mesa recess  155  having a recess depth of about 0.3 micrometers. In  FIG. 2M , the photoresist mask  149  is removed followed by a blanket body implantation with boron ions firstly at an energy level between 100 Kev and then at 600 Kev to form the body regions  150 . In  FIG. 2N , the processes proceeds by carrying out a blanket implantation to form the source regions  160  with Arsenide dopant at a doping concentration of about 4E15 cm −3  and at 80 Kev followed by an anneal process at 950 degree Celsius for 30 second. In  FIG. 2O , a low temperature oxide deposition is carried out to form a thin oxide layer of about 800 Angstroms atop the structure followed by a blanket oxide etching process, for example plasma dry etch, to form an oxide spacer on each side surface of the oxide layer  145 . Then, in  FIG. 2P , a contact etch is performed, for example plasma dry etch, to open contact openings  168  with a contact trench depth 0.25 micrometers below the mesa surface. As shown in  FIG. 2O , the pair of spacers  165  on top of the mesa between two active trenches  115  are symmetric through the center of the mesa such that the center of the contact opening  168  is substantially aligned with the center of the mesa. However in the mesa between the last active trench  115  and the gate pickup trench  115 ′, the spacer  165 ″ attached to the edge of the oxide layer  145  and the BPSG layer  148  is thicker and higher than the spacers  165  and spacer  165 ′ attached on the side surface of the oxide layer  145  atop of the last active trench  115  such that the center of the contact opening formed by the spacers  165 ′ and  165 ″ is off center of the mesa between the last active trench  115  and the gate pickup trench  115 ′ and closer to the last active trench  115 . The spacer  165 ′ has substantially the same size as the spacer  165 . In  FIG. 2Q , a contact implant  170  is formed at the bottom of the contact trenches  168 , for example BF2 dopant with a doping concentration of 1E14 cm −3  at 20 Kev. In  FIG. 2R , a poly pickup contact mask  172  is applied to open a polysilicon pickup contact trench  174 . 
         [0025]    In  FIG. 2S , the mask  172  is removed followed by a rapid thermal anneal (RTA) followed by the deposition of the barrier layer on the side surface of the openings  168  and  174  (not shown), for example Ti/TiN barrier layer, then the contact trenches  168  and  174  are filled with tungsten then etched back to form tungsten plugs (W-plugs)  180 ,  180 ′ and  180 ″, where the center of the source/body contact  180  is substantially aligned with the center of the mesa between two adjacent active trenches  115  and the source/body contact  180 ″ is off center of the mesa closer to the last active trench  115 . In  FIG. 2T , the processes are completed with the formation and patterning of source contact  190 -S and gate pad  190 -G followed by standard passivation formation and patterning processes (not specifically shown). As mentioned above, the gap g separating the source metal  190 -S and gate metal  190 -G extends across the edge of the HDP oxide layer  145  and the BPSG layer  148  substantially aligned with the trench sidewall of the gate pickup trench  115 ′ closer to the active trenches  115 . 
         [0026]    Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations 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 alterations and modifications as fall within the true spirit and scope of the invention.