Patent Publication Number: US-2023154981-A1

Title: Semiconductor power device

Description:
This application claims priority to Chinese Patent Application No. 202010763267.1 filed Jul. 31, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present application belongs to the technical field of semiconductor power devices, for example, a semiconductor power device with a slow-varying capacitance. 
     BACKGROUND 
     A semiconductor power device includes an n-shaped substrate, an n-shaped epitaxial layer located on the n-shaped substrate, a plurality of grooves recessed inside the n-shaped epitaxial layer, and a mesa structure of the semiconductor power device that is a portion of the n-shaped epitaxial layer between each two adjacent grooves. All mesa structures of semiconductor power devices in the related art have the same width. When the semiconductor power device is turned on or off, the mesa structure may be simultaneously exhausted and pinched off at the same voltage, which generates very serious voltage oscillation. 
     SUMMARY 
     The present application provides a semiconductor power device to avoid serious voltage oscillation when the semiconductor power device in the related art is turned on or off. 
     The present application provides a semiconductor power device. The semiconductor power device includes an n-shaped substrate, an n-shaped epitaxial layer positioned on the n-shaped substrate, and at least three grooves recessed inside the n-shaped epitaxial layer, where a portion of the n-shaped epitaxial layer between two adjacent grooves of the at least three grooves is a mesa structure, an upper part of the mesa structure is provided with a p-shaped body region, and an n-shaped source region is provided inside the p-shaped body region. The mesa structure includes at least one mesa structure with a lower width being a first width and at least one mesa structure with a lower width being a second width, and the second width is greater than the first width. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a section diagram in an embodiment of a semiconductor power device according to the present application. 
     
    
    
     DETAILED DESCRIPTION 
     The solution of the present application is described hereinafter through specific implementations in conjunction with the drawings in the embodiments of the present application. Apparently, the described embodiments are part, not all, of embodiments of the present disclosure. It is to be understood that the terms used in the present application such as “provided”, “comprising” and “including” do not exclude the presence or addition of one or more other components or other combinations. Meanwhile, to illustrate the embodiments of the present application more clearly, in the schematic diagrams illustrated in the drawings of the Description, the sizes of layers and regions described in the present application are enlarged, and the sizes illustrated in the drawings do not represent the actual sizes. 
       FIG.  1    is a section diagram in an embodiment of a semiconductor power device according to the present application. As shown in  FIG.  1   , the semiconductor power device includes an n-shaped substrate  20  which is disposed to form an n-shaped drain region of the semiconductor power device. An n-shaped epitaxial layer  21  is positioned on the n-shaped substrate  20  and at least three grooves  40  are recessed inside the n-shaped epitaxial layer  21 . Only three groove  40  structures are illustrated in the embodiment shown in  FIG.  1    of the present application. 
     A portion of the n-shaped epitaxial layer between each two adjacent grooves  40  is a mesa structure of the semiconductor power device. An upper part of the mesa structure is provided with a p-shaped body region  22  and an n-shaped source region  23  is provided inside the p-shaped body region  22 . The mesa structure of the semiconductor power device of the present application includes at least one mesa structure with a lower width being a first width AA and at least one mesa structure with a lower width being a second width BB. The second width BB is greater than the first width AA. Thus, the semiconductor power device of the present application is ensured to have a slow-varying capacitance. When the semiconductor power device of the present application is turned on or off, with the increase of voltage, the mesa structure with a smaller lower width is exhausted and pinched off first and then the mesa structure with a larger lower width is exhausted and pinched off, which may reduce voltage oscillation when the semiconductor power device is turned on or off. 
     It is to be noted that only three groove  40  structures, a mesa structure with a lower width being a first width AA and a mesa structure with a lower width being a second width BB are illustrated in the embodiment shown in  FIG.  1    of the present application. It is to be understood that the semiconductor power device of the present application may also include more groove structures and more mesa structures. For example, the semiconductor power device of the present application may also include a mesa structure (not shown in the figure) with a lower width is an N-th width. N&gt;2 and N is an integer and the N-th width may be different from the first width and the second width. In this manner, a slow-varying degree of the capacitance may be adjusted to reduce voltage oscillation when the semiconductor power device is turned on or off. 
     Optionally, the number of the mesa structures with the lower width being the second width BB is greater than the number of the mesa structures with the lower width being the first width AA. In this manner, the slow-varying degree of the capacitance can be adjusted to ensure a slower-varying of the capacitance of the semiconductor power device and to reduce voltage oscillation when the semiconductor power device is turned on or off. 
     For two grooves  40  located on two sides of the mesa structure with the lower width being the first width AA, a bottom of at least one groove is provided with an n-shaped injection region positioned inside the n-shaped epitaxial layer  21 . Only a structure in which the n-shaped injection region  31  is formed inside the n-shaped epitaxial layer  21  at the bottom of the groove  40  located on the left side of the mesa structure with the lower width being the first width AA is illustrated in the embodiment shown in  FIG.  1    of the present application. In this manner, the slow-varying degree of the capacitance can be adjusted to ensure a slower-varying of the capacitance of the semiconductor power device and to reduce voltage oscillation when the semiconductor power device is turned on or off. 
     A gate  25  is disposed inside a groove  40  and is isolated from the n-shaped epitaxial layer  21  through a gate oxide  24 . The gate  25  usually controls the opening and closing of a current channel positioned inside the p-shaped body region  22  through a gate voltage. Conductive polysilicon  27  is also disposed inside the groove  40  and is isolated from the n-shaped epitaxial layer  21  through an insulating dielectric layer  26 . The conductive polysilicon  27  is isolated from the gate  25  through the gate oxide  24  and is usually connected to a source voltage externally. 
     In the embodiment shown in  FIG.  1   , the gate  25  is located at an upper part of the groove  40  and the conductive polysilicon  27  is located at a lower part of each groove  40 , so the semiconductor power device of the present application is a semiconductor power device with an upper-lower gate structure. 
     Optionally, the gate may be located at an upper part of the groove and conductive polysilicon is located at a lower part of the groove and extends upward into the upper part of the groove, so the semiconductor power device of the present application is a semiconductor power device with a left-right gate structure. Meanwhile, in the semiconductor power device with a left-right gate structure, the conductive polysilicon may be isolated from the gate through a gate oxide or an insulating dielectric layer, which is not limited in the embodiment of the present application. 
     Exemplarily, in the semiconductor power device with a left-right gate structure, a width of an upper part of a groove may be greater than a width of a lower part of the groove, which is not shown in the embodiment of the present application. It is to be noted that in the semiconductor power device with an upper-lower gate structure, a width of an upper part of a groove may also be greater than a width of a lower part of the groove, which is not shown in the embodiment of the present application. 
     The semiconductor power device of the present application has at least two kinds of mesa structures with different lower width. That is, the semiconductor power device of the present application has a slow-varying capacitance. When the semiconductor power device is turned on or off, with the increase of voltage, the mesa structure with a smaller lower width is exhausted and pinched off first and then the mesa structure with a larger lower width is exhausted and pinched off, which may reduce voltage oscillation when the semiconductor power device is turned on or off. Meanwhile, a slow-varying degree of the capacitance may be adjusted through forming n-shaped injection regions inside the n-shaped epitaxial layer at the bottoms of the grooves located on two sides of the mesa structure with a smaller lower width so as to reduce voltage oscillation when the semiconductor power device is turned on or off