Patent Publication Number: US-2023132488-A1

Title: Semiconductor device and method for forming the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of Taiwan application serial no. 110140156, filed on Oct. 28, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a semiconductor device and a method for forming the same, particularly to a power semiconductor device and a method for forming the same. 
     Description of Related Art 
     The power semiconductor device requires a low gate-to-drain capacitance during operation to ensure sufficient response speed and to avoid excessive switching power loss. Such condition may be satisfied efficiently by using the trench-type metal oxide semi-transistor devices with shielded gates. 
     As the size of the power semiconductor devices has been progressively micronized, it is one of the current goals to further increase the breakdown voltage and/or reduce the on-resistance of the power semiconductor device while maintaining a low gate-to-drain capacitance. 
     SUMMARY 
     The disclosure provides a semiconductor device and a method for forming the same. The semiconductor device has an increased breakdown voltage and a reduced on-resistance while maintaining a low gate-to-drain capacitance. 
     The semiconductor device of the disclosure includes a substrate and a gate structure. The substrate has a trench. The gate structure is disposed in the trench and includes a shielded gate, a control gate, a first insulating layer, a second insulating layer, and a third insulating layer. The shielded gate includes a bottom gate and a top gate. The bottom gate includes a step structure consisting of a plurality of electrodes, and the width of one of the electrodes is smaller as the electrode is farther away from the top gate. The top gate is disposed on the bottom gate, and the width of the top gate is smaller than the width of the electrode of the electrodes that is closest to the top gate. The control gate is disposed on the shielded gate. The first insulating layer is disposed between the shielded gate and the substrate. The second insulating layer is disposed on the shielded gate to separate the shielded gate from the control gate. The third insulating layer is disposed between the control gate and the substrate. 
     In an embodiment of the disclosure, the bottom gate includes a first conductive layer and a second conductive layer, wherein the second conductive layer is disposed on the first conductive layer, and the second conductive layer includes the electrodes. 
     In an embodiment of the disclosure, the second conductive layer includes a first electrode, a second electrode, and a third electrode stacked in sequence, the width of the third electrode is greater than the width of the second electrode, and the width of the second electrode is greater than the width of the first electrode. 
     In an embodiment of the disclosure, the width of the first electrode is greater than the width of the first conductive layer. 
     In an embodiment of the disclosure, the semiconductor device further includes a substrate region and a source region. The substrate region is disposed in the substrate and between adjacent trenches, and it has a first conductivity type. The source region is disposed in the substrate region and has a second conductivity type. The first conductivity type is P-type and the second conductivity type is N-type; or the first conductivity type is N-type and the second conductivity type is P-type. 
     In an embodiment of the disclosure, the height from the top surface of the first conductive layer to the bottom surface of the first conductive layer is 1.5 μm to 2.0 μm. 
     In an embodiment of the disclosure, the height from the top surface of the first electrode to the bottom surface of the first electrode is 0.7 μm to 1.2 μm, the height from the top surface of the second electrode to the bottom surface of the second electrode is 0.7 μm to 1.2 μm, and the height from the top surface of the third electrode to the bottom surface of the third electrode is 0.3 μm to 0.6 μm. 
     In an embodiment of the disclosure, the distance between the first electrode and a sidewall of the trench is 4000 Å to 4500 Å, the distance between the second electrode and the sidewall of the trench is 3000 Å to 3500 Å, and the distance between the third electrode and the sidewall of the trench is 2000 Å to 2500 Å. 
     The method for forming the semiconductor device of the disclosure includes the following steps. First, a substrate including a trench is provided, wherein an insulating material layer is formed on the substrate, and the trench includes a first accommodating space. Next, a shielded gate is formed in the trench, a step including the following steps: step (a): fill the trench with a first conductive material layer; step (b): remove part of the first conductive material layer in the trench to expose part of the first accommodating space; step (c): remove part of the insulating material layer in the trench through isotropic etching; step (d): repeat the cycle of step (b) to step (c) several times to form a first conductive layer and a second accommodating space having a step structure in the trench; step (e): form a second conductive layer in the trench, wherein the second conductive layer is partially filled in the second accommodating space, and the second conductive layer includes the step structure consisting of a plurality of electrodes; step (f): form a sacrificial layer in the second accommodating space of the trench, wherein the sacrificial layer is disposed on a sidewall of the trench to form a third accommodating space; and step (g): form a third conductive layer in the trench, wherein the third conductive layer is partially filled in the third accommodating space. Afterwards, the sacrificial layer and part of the insulating material layer are removed in the trench. Then, a control gate is formed in the trench. The width of one of the electrodes of the second conductive layer is smaller as it is farther away from the third conductive layer, and the width of the third conductive layer is smaller than the width of the electrode closest to the third conductive layer in the second conductive layer. 
     In an embodiment of the disclosure, in the step of forming the shielded gate in the trench, the cycle of the step (b) to the step (c) is repeated three times. 
     In an embodiment of the disclosure, after removing the sacrificial layer and part of the insulating material layer in the trench, it further includes forming an inter-gate insulating layer on the shielded gate, wherein the inter-gate insulating layer separates the shielded gate from the control gate. 
     In an embodiment of the disclosure, after the control gate is formed in the trench, the following steps are further included. First, a substrate region having a first conductivity type is formed in the substrate, wherein the substrate region is located between adjacent trenches. Next, a source region having a second conductivity type is formed in the substrate region. The first conductivity type is P-type and the second conductivity type is N-type; or the first conductivity type is N-type and the second conductivity type is P-type. 
     Based on the above, in the semiconductor device and the method for forming the same provided by the disclosure, the bottom gate of the shielded gate has a step structure consisting of a plurality of electrodes, such that the semiconductor device of the disclosure has an improved breakdown voltage and a reduced on-resistance. In addition, in the disclosure, the gate-to-drain capacitance may be prevented from increasing by making the width of the top gate of the shielded gate smaller than the width of the electrode of the bottom gate closest to it, thereby maintaining the electrical characteristics of the semiconductor device of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  to  FIG.  1 O  are schematic cross-sectional views of a method for forming a semiconductor device according to an embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following embodiments, the first conductivity type is P-type, and the second conductivity type is N-type; however, the disclosure is not limited thereto. In other embodiments, the first conductivity type may be P type, and the second conductivity type may be N type. The P-type dopant is, for example, boron, and the N-type dopant is, for example, phosphorus or arsenic. 
     Unless defined otherwise, all terms (including technical and scientific terms) used herein have the same meaning commonly understood by those of ordinary skill in the art to which the disclosure belongs. It is further understood that terms such as those defined in regular dictionaries should be interpreted as having meanings consistent with their meanings in the context of related technologies and the disclosure, instead of being interpreted as an idealized or overly formal meaning unless it is clearly defined as such in this article. 
     The schematic diagrams herein are only used to illustrate some embodiments of the disclosure. Therefore, the shape, number, and ratio of each element shown in the schematic diagram should not be used to limit the disclosure. 
       FIG.  1 A  to  FIG.  1 O  are schematic cross-sectional views of a method for forming a semiconductor device according to an embodiment of the disclosure. 
     First, in  FIG.  1 A , a substrate  100  is provided. In this embodiment, the substrate  100  is an epitaxial layer, but the disclosure is not limited thereto. The substrate  100  may be formed by, for example, a selective epitaxy growth (SEG) in a silicon substrate (not shown), and the disclosure is not limited thereto. In some embodiments, the doping concentration of the epitaxial layer may be less than the doping concentration of the silicon substrate. 
     After that, a plurality of trenches T are formed in the substrate  100 . In some embodiments, the ways to form the trenches T includes, for example, the following steps, but the disclosure is not limited thereto. First, a mask layer (not shown) is formed on the substrate  100 ; then, a patterning process is performed using the mask layer as a mask to remove part of the substrate  100 ; then, the mask layer is removed. 
     Next, an insulating material layer  110   a  is conformally formed on the substrate  100 . Specifically, the insulating material layer  110   a  may be formed in the trench T and extend from the surface of the trench T and cover the top surface  100 T of the substrate  100 , for example. In some embodiments, the formation of the insulating material layer  110   a  includes performing thermal oxidation or chemical vapor deposition, wherein the material of the insulating material layer  110   a  includes silicon oxide. After the insulating material layer  110   a  is conformally formed on the substrate  100 , the trench T has a first accommodating space SP 1 . The first accommodating space SP 1  here refers to an accommodating space that has not been formed or occupied by any conductive material layer in the trench T, and has, for example, a substantially fixed first width W 1 . 
     In this embodiment, a step of forming a shielded gate in the trench T is performed below. In  FIG.  1 B , the trench T is filled with a conductive material layer  120   a.  In this embodiment, in addition to being formed in the trench T, the conductive material layer  120   a  may also cover the top surface  100 T of the substrate  100  as shown in  FIG.  1 B , but the disclosure is not limited thereto. In some embodiments, the formation of the conductive material layer  120   a  includes performing chemical vapor deposition, wherein the material of the conductive material layer  120   a  includes doped polysilicon. 
     In  FIG.  1 C , part of the conductive material layer  120   a  is removed in the trench T. To remove part of the conductive material layer  120   a  in the trench T, the following steps may be performed for example, but the disclosure is not limited thereto. First, a planarization process is performed on the conductive material layer  120   a  (if the conductive material layer  120   a  is formed on the top surface  100 T of the substrate  100 ; in contrast, if the conductive material layer  120   a  is not formed on the top surface  100 T of the substrate  100  in other embodiments, this step may be omitted), so that the top surface of the conductive material layer  120   a  is substantially flush with the top surface  100 T of the substrate  100 . Then, an etching process is performed to remove part of the conductive material layer  120   a  in the trench T to form the conductive material layer  120   b  and expose part of the first accommodating space SP 1 . The etching process includes wet etching and dry etching, to which the disclosure is not limited. In this embodiment, the first width W 1  of the first accommodating space SP 1  is substantially the same as the width of the conductive material layer  120   b,  but the disclosure is not limited thereto. In some embodiments, the trench T may have an arc-shaped bottom surface, and therefore the conductive material layer  120   b  may also have an arc-shaped bottom surface. 
     In  FIG.  1 D , part of the insulating material layer  110   a  is removed in the trench T using an isotropic etching process. That is, part of the insulating material layer  110   a  on the top surface  100 T of the substrate  100  and part of the insulating material layer  110   a  on the sidewalls of the trench T are removed. The isotropic etching process includes, for example, wet etching, to which the disclosure is not limited. After removing part of the insulating material layer  110   a  in the trench T, the insulating material layer  110   b  and the second accommodating space SP 21  are formed. The second accommodating space SP 21  here refers to the accommodating space in the trench T where the conductive material layer  120   b  is not formed after part of the insulating material layer  110   a  is removed, which has a second width W 21 . By removing part of the insulating material layer  110   a  using an isotropic etching process, the second width W 21  of the second accommodating space SP 21  is greater than the first width W 1  of the first accommodating space SP 1 . In addition, note that although the present embodiment adopts isotropic etching to remove part of the insulating material layer  110   a,  the disclosure is not limited thereto. In other words, any removal process may be adopted as long as it is capable of removing at least part of the insulating material layer  110   a  on the sidewall of the trench T. 
     In  FIG.  1 E , part of the conductive material layer  120   b  is removed in the trench T. To remove part of the conductive material layer  120   b  in the trench T, for example, the insulating material layer  110   b  may be adapted as a mask to perform etching to remove part of the conductive material layer  120   b  in the trench T, but the disclosure is not limited thereto. The etching process includes wet etching and dry etching, to which the disclosure is not limited. After removing part of the conductive material layer  120   b  in the trench T, the conductive material layer  120   c  is formed and part of the first accommodating space SP 1  is exposed. 
     In  FIG.  1 F , part of the insulating material layer  110   b  is removed in the trench T using an isotropic etching process. That is, part of the insulating material layer  110   b  on the top surface  100 T of the substrate  100  and part of the insulating material layer  110   b  on the sidewall of the trench T are removed. The isotropic etching process includes, for example, wet etching, to which the disclosure is not limited. After removing part of the insulating material layer  110   b  in the trench T, the insulating material layer  110   c  and the second accommodating space SP 22  are formed. The second accommodating space SP 22  here refers to the accommodating space in the trench T where the conductive material layer  120   c  is not formed after a portion of the insulating material layer  110   b  is removed. The second accommodating space SP 22  has a step shape that has one step. The platform section has a second width W 22 _ 1  and the first step section has a second width W 22 _ 2 , and the second width W 22 _ 1  is greater than the second width W 22 _ 2 . In addition, due to the isotropic etching process that removes part of the insulating material layer  110   b,  the second width W 22 _ 1  and the second width W 22 _ 2  are both greater than the first width W 1 . From another point of view, the trench T has, for example, a ring-shaped step shape at this time, but the disclosure is not limited thereto. In addition, note here that although the present embodiment adopts isotropic etching to remove part of the insulating material layer  110   b,  the disclosure is not limited thereto. In other words, any removal process may be adopted as long as it is capable of removing at least part of the insulating material layer  110   b  on the sidewall of the trench T. 
     In  FIG.  1 G , part of the conductive material layer  120   c  is removed in the trench T. To remove part of the conductive material layer  120   c  in the trench T, for example, the insulating material layer  110   c  may be adapted as a mask to perform an etching process to remove part of the conductive material layer  120   c  in the trench T, but the disclosure is not limited thereto. The etching process includes wet etching and dry etching, to which the disclosure is not limited. After removing part of the conductive material layer  120   c  in the trench T, the first conductive layer  120  is formed and part of the first accommodating space SP 1  is exposed. In this embodiment, the first conductive layer  120  also has a first width W 1 . 
     In  FIG.  1 H , part of the insulating material layer  110   c  is removed in the trench T using an isotropic etching process. That is, part of the insulating material layer  110   c  on the top surface  100 T of the substrate  100  and part of the insulating material layer  110   c  on the sidewall of the trench T are removed. The isotropic etching process includes, for example, wet etching, to which the disclosure is not limited. After removing part of the insulating material layer  110   c  in the trench T, the insulating material layer  110   d  and the second accommodating space SP 23  are formed. The second accommodating space SP 23  here refers to the accommodating space in the trench T where the first conductive layer  120  is not formed after part of the insulating material layer  110   c  is removed on the sidewall of the trench T. The second accommodating space SP 23  has a step shape that has two steps. The platform section has a second width W 23 _ 1 , the first step section has a second width W 23 _ 2 , and the second step section has a third width W 23 _ 3 . The second width W 23 _ 1  is greater than the second width W 23 _ 2 , and the second width W 23 _ 2  is greater than the second width W 23 _ 3 . In addition, due to the isotropic etching process that removes part of the insulating material layer  110   c,  the second width W 23 _ 1 , the second width W 23 _ 2 , and the second width W 23 _ 3  are all greater than the first width W 1 . From another point of view, the trench T has, for example, a ring-shaped step shape at this time, but the disclosure is not limited thereto. In addition, note here that although the present embodiment adopts an isotropic etching process to remove part of the insulating material layer  110   c,  the disclosure is not limited thereto. In other words, any removal process may be adopted as long as it is capable of removing at least part of the insulating material layer  110   a  on the sidewall of the trench T. 
     Note here that in the process steps shown in  FIG.  1 C  to In  FIG.  1 H , the cycle of the following steps are repeated three times: removing part of the conductive material layer in the trench T; and removing part of the insulating material layer using an isotropic etching process. However, the disclosure does not limit the number of times the cycles are performed. In other words, in other embodiments, the above steps may be repeated twice (which is the minimum number of times to form a stepped second accommodating space) or more than four cycles. 
     In  FIG.  1 I , a second conductive layer  130  is formed in the trench T. For example, the second conductive layer  130  is partially filled in the second accommodating space SP 23 . To form the second conductive layer  130  in the trench T, the following steps may be performed for example, but the disclosure is not limited thereto. First, a second conductive material layer (not shown) filled in the trench T is formed. A planarization process is performed on the second conductive material layer (if a second conductive material layer is formed on the top surface  100 T of the substrate  100 ; in contrast, if the second conductive material layer is not formed on the top surface  100 T of the substrate  100 , this step may be omitted), so that the top surface of the second conductive material layer and the top surface  100 T of the substrate  100  are substantially flush. Then, an etching process is performed to remove part of the second conductive material layer in the trench T to form the second conductive layer  130  and expose part of the second accommodating space SP 23 . The etching process includes wet etching and dry etching, to which the disclosure is not limited. In this embodiment, the shape of the second conductive layer  130  is similar to the shape of the second accommodating space SP 23 , and it also has a step structure that has two steps. The platform section of the second conductive layer  130  has a second width W 23 _ 1 . The first step section of the second conductive layer  130  has a second width W 23 _ 2 , and the second step section of the second conductive layer  130  has a third width W 23 _ 3 . The second width W 23 _ 1  is greater than the second width W 23 _ 2 , and the second width W 23 _ 2  is greater than the second width W 23 _ 3 . The material of the second conductive layer  130  is, for example, the same as the material of the first conductive layer  120 . In other words, the material of the second conductive layer  130  includes, for example, doped polysilicon. 
     In  FIG.  1 J , a sacrificial layer SA is formed in the second accommodating space SP 23  of the trench T. The following steps may be performed to form the sacrificial layer SA in the second accommodating space SP 23  of the trench T, but the disclosure is not limited thereto. First, a sacrificial material layer (not shown) is conformally formed on the substrate  100 . Specifically, the sacrificial material layer may, for example, be formed in the trench T and extend from the surface of the trench T and cover the top surface  100 T of the substrate  100 . In some embodiments, the formation of the sacrificial material layer includes performing thermal oxidation or chemical vapor deposition. After the sacrificial material layer is conformally formed on the substrate  100 , an etching process is performed to remove the sacrificial material layer on the top surface  100 T of the substrate  100  and the bottom of the second accommodating space SP 23  of the trench T to form the sacrificial layer SA on the sidewall of the trench T. The sacrificial layer SA is disposed on the insulating material layer  110   d.  In this embodiment, the sacrificial layer SA on the sidewall of the trench T defines a third accommodating space SP 3  having a third width W 3 . Since there are more sacrificial layers SA than the second accommodating space SP 23 , the third width W 3  of the third accommodating space SP 3  is smaller than the second width W 23 _ 1  of the second accommodating space SP 23 . 
     In  FIG.  1 K , a third conductive layer  140  is formed in the trench T. The third conductive layer  140  is partially filled in the third accommodating space SP 3 , for example. The formation of the third conductive layer  140  in the trench T includes, for example, the following steps, but the disclosure is not limited thereto. First, a third conductive material layer (not shown) filled in the trench T is formed. A planarization process is performed on the third conductive material layer (if a third conductive material layer is formed on the top surface  100 T of the substrate  100 ; in contrast, if the third conductive material layer is not formed on the top surface  100 T of the substrate  100 , this step may be omitted), so that the top surface of the third conductive material layer is substantially flush with the top surface  100 T of the substrate  100 . Then, an etching process is performed to remove part of the third conductive material layer in the trench T to form the third conductive layer  140  and expose part of the third accommodating space SP 3 . The etching process includes wet etching and dry etching, to which the disclosure is not limited. In this embodiment, the third width W 3  of the third accommodating space SP 3  is substantially the same as the width of the third conductive layer  140 , but the disclosure is not limited thereto. In addition, in this embodiment, the width of the third conductive layer  140  is smaller than the width of the electrode closest to the third conductive layer  140  in the second conductive layer  130 . Specifically, the third width W 3  of the third conductive layer  140  is smaller than the second width W 23 _ 1  of the platform section of the second conductive layer  130 . The material of the third conductive layer  140  is, for example, the same as the material of the first conductive layer  120  and the material of the second conductive layer  130 . In other words, the material of the third conductive layer  140  may also include, for example, doped polysilicon. 
     So far, the fabrication of the shielded gate SG of this embodiment is completed. In other words, the shielded gate SG may be composed of, for example, the first conductive layer  120 , the second conductive layer  130 , and the third conductive layer  140 . However, although the formation of the shielded gate SG of this embodiment is described by taking the above-mentioned method as an example, it is not limited thereto. 
     In  FIG.  1 L , the sacrificial layer SA and part of the insulating material layer  110   d  are removed in the trench T. The sacrificial layer SA and part of the insulating material layer  110   d  in the trench T may be removed by, for example, performing an isotropic etching process which includes wet etching and dry etching, to which the disclosure is not limited. After removing the sacrificial layer SA and part of the insulating material layer  110   d  in the trench T, an insulating material layer  110   e  is formed. 
     In  FIG.  1 M , an insulating layer IL is formed on the shielded gate SG. In some embodiments, the formation of the insulating layer IL includes performing thermal oxidation or chemical vapor deposition, where the material of the insulating layer IL includes silicon oxide. In addition to being formed on the shielded gate SG in the trench T, the insulating layer IL of this embodiment may also, for example, conformally extend from the top surface of the shielded gate SG to the top surface  100 T of the substrate  100  and cover the top surface  100 T of the substrate  100 . 
     In  FIG.  1 N , a control gate CG is formed in the trench T. To form the control gate CG in the trench T, the following steps may be performed for example, but the disclosure is not limited thereto. First, a control gate material layer (not shown) filled in the trench T is formed. A planarization process is perform on the control gate material layer (if the control gate material layer is formed on the top surface  100 T of the substrate  100 ; in contrast, if the control gate material layer is not formed on the top surface  100 T of the substrate  100 , this step may be omitted), so that the top surface of the control gate material layer and the top surface  100 T of the substrate  100  are substantially flush. Then, an etching process is performed to remove part of the control gate material layer in the trench T to form the control gate CG. The etching process includes wet etching and dry etching, to which the disclosure is not limited. The material of the control gate CG is, for example, the same as the material of the shielded gate SG. In other words, the material of the control gate CG also includes, for example, doped polysilicon. In this embodiment, the control gate CG and the shielded gate SG form the gate part of the gate structure G. In addition, the insulating layer IL and the insulating material layer  110   e  form the insulating layer  110  together. The insulating layer  110  includes: a first insulating layer  112  between the shielded gate SG and the substrate  100 ; a second insulating layer  114  between the control gate CG and the shielded gate SG; a third insulating layer  116  between the control gate CG and the substrate  100 ; and a fourth insulating layer  118  on the top surface  100 T of the substrate  100 . The first insulating layer  112 , the second insulating layer  114 , and the third insulating layer  116 , for example, constitute the insulating layer of the gate structure G. 
     In  FIG.  1 O , a substrate region  200  having a first conductivity type and a source region  300  having a second conductivity type are sequentially formed in the substrate  100 . The substrate region  200  may be formed, for example, by performing an ion implantation and then a heat treatment, where the dopant implanted in the ion implantation process is, for example, boron, and the disclosure is not limited thereto. In addition, the source region  300  may also be formed by, for example, performing an ion implantation and then a heat treatment. The dopant implanted in the ion implantation process is, for example, phosphorus or arsenic, which is not limited in the disclosure. In some embodiments, the substrate region  200  is disposed between adjacent trenches T, and the source region  300  is disposed in the substrate region  200 . 
     Please proceed to see  FIG.  1 O . After the substrate region  200  having the first conductivity type and the source region  300  having the second conductivity type are sequentially formed in the substrate  100 , an insulating layer  400  is formed on the substrate  100 . The insulating layer  400  covers the top surface of the insulating layer  110  and fills the trench T, for example. In some embodiments, the formation of the insulating layer  400  includes performing thermal oxidation or chemical vapor deposition, wherein the material of the insulating layer  400  includes silicon oxide. In this embodiment, the insulating layer  400  is adopted as an interlayer dielectric layer, but the disclosure is not limited thereto. 
     In  FIG.  1 O , after the insulating layer  400  is formed on the substrate  100 , a contact window  500 A and a contact window  500 B penetrating through the insulating layer  400  and the insulating layer  110  are formed. The contact window  500 A and the contact window  500 B are respectively electrically connected to the source region  300  and the control gate CG. In some embodiments, the formation of the contact window  500 A and the contact window  500 B includes performing the following steps. First, a mask layer (not shown) is formed on the top surface of the insulating layer  400 ; afterwards, a patterning process is performed using the mask layer as a mask to remove part of the insulating layer  400  and the insulating layer  110  to form a plurality of openings, wherein the openings expose part of the source region  300  and part of the control gate CG; next, the mask layer is removed; then, a conductor layer is filled in the openings to respectively form a contact window  500 A electrically connected to the source region  300  and a contact window  500 B electrically connected to the control gate CG. In some embodiments, the formation of the conductor layer includes performing chemical vapor deposition, wherein the material includes a metal, which may be tungsten. 
     Please proceed to see  FIG.  1 O . After forming the contact window  500 A and the contact window  500 B on the substrate  100 , an interconnection layer  600 A and an interconnection layer  600 B are formed. The interconnection layer  600 A and the interconnection layer  600 B are electrically connected to the contact window  500 A and the contact window  500 B, respectively. In some embodiments, the formation of the interconnection layer  600 A and the interconnection layer  600 B includes the following steps. First, an interconnect material layer (not shown) is formed on the insulating layer  400 ; afterwards, a mask layer (not shown) is formed on the top surface of the insulating layer  400 ; then, a patterning process is performed using the mask layer as a mask to remove part of the interconnect material layer to form the interconnect layer  600 A and the interconnect layer  600 B. In some embodiments, the formation of the interconnection layer  600 A and the interconnection layer  600 B includes chemical vapor deposition or physical vapor deposition, and the material includes metal, which may be copper, aluminum, aluminum copper, or other suitable metals. 
     The fabrication of the semiconductor device  10  of the disclosure is completed to this point. 
     Although the method for forming the semiconductor device  10  of this embodiment is described by taking the above method as an example, the method for forming the semiconductor device  10  of the disclosure is not limited thereto. 
     Please proceed to see  FIG.  1 O .  FIG.  1 O  illustrates a schematic cross-sectional view of a semiconductor device  10  according to an embodiment of the disclosure. It must be noted here that please refer to the description and effects of the foregoing embodiments for the following description of the omitted parts, as the same description is not repeated in the following embodiments. 
     In some embodiments, the semiconductor device  10  includes a substrate  100 , a gate structure G, a substrate region  200 , and a source region  300 . 
     The substrate  100  is, for example, an epitaxial layer having a second conductivity type. For example, the substrate  100  may be an N-type epitaxial layer, but the disclosure is not limited thereto. The substrate  100  has, for example, a plurality of trenches T, and the gate structure G described later is disposed in the trenches T. 
     The gate structure G is disposed, for example, in the trench T, and includes a shielded gate SG, a control gate CG, a first insulating layer  112 , a second insulating layer  114 , and a third insulating layer  116 . The shielded gate SG includes, for example, a bottom gate SG 1  and a top gate SG 2  provided on the bottom gate SG 1 . The bottom gate SG 1  is composed of, for example, a first conductive layer  120  and a second conductive layer  130 . The top gate SG 2  is composed of, for example, a third conductive layer  140 . In this embodiment, the bottom gate SG 1  includes a step structure consisting of a plurality of electrodes, and the width of one of the electrodes is smaller as it is farther away from the upper electrode SG 2 . Specifically, the bottom gate SG 1  includes a step structure composed of the first conductive layer  120  and the second conductive layer  130 . 
     The first conductive layer  120  has, for example, an approximately rectangular shape and a first width W 1 . In some embodiments, the height from the top surface of the first conductive layer  120  to the bottom surface of the first conductive layer  120  is 1.5 μm to 2.0 μm. The first conductive layer  120  may, for example, have an arc-shaped bottom surface, and the disclosure is not limited thereto. 
     The second conductive layer  130  has, for example, a step structure. The second conductive layer  130  in this embodiment has a step that has two steps, and includes a first electrode  132 , a second electrode  134 , and a third electrode  136  stacked in sequence, but the disclosure is not limited thereto. In some embodiments, the height from the top surface of the first electrode  132  to the bottom surface of the first electrode  132  is 0.7 μm to 1.2 μm, the height from the top surface of the second electrode  134  to the bottom surface of the second electrode  134  is 0.7 μm to 1.2 μm, and the height from the top surface of the third electrode  136  to the bottom surface of the third electrode  136  is 0.3 μm to 0.6 μm. In addition, in some embodiments, the distance between the first electrode  132  and the sidewall of the trench T is 4000 Å to 4500 Å, the distance between the second electrode  134  and the sidewall of the trench T is 3000 Å to 3500 Å, and the distance between the third electrode  136  and the sidewall of the trench T is 2000 Å to 2500 Å. 
     The third conductive layer  140  also has, for example, an approximately rectangular shape and a third width W 3 . In some embodiments, the height from the top surface of the third conductive layer  140  to the bottom surface of the third conductive layer  140  is 0.1 μm to 0.3 μm. In addition, in some embodiments, the distance between the third conductive layer  140  and the sidewall of the trench T is 3000 Å to 3500 Å. 
     From another perspective, in this embodiment, the third electrode  136  (the platform section of the second conductive layer  130 ) has a second width W 23 _ 1 , the second electrode  134  (the first step section of the second conductive layer  130 ) has a second width W 23 _ 2 , and the first electrode  132  (the second step section of the second conductive layer  130 ) has a second width W 23 _ 3 . The second width W 23 _ 1  is greater than the second width W 23 _ 2 , the second width W 23 _ 2  is greater than the second width W 23 _ 3 , and the second width W 23 _ 3  is greater than the first width W 1 . In this embodiment, the width of the top gate SG 2  is smaller than the width of the electrode of the bottom gate SG 1  closest to the top gate SG 2 . Specifically, the electrode closest to the top gate SG 2  is the third electrode  136  in the second conductive layer  130  as shown in  FIG.  1 O , and the third width W 3  of the top gate SG 2  is smaller than the second width W 23 _ 1  of the third electrode  136 . The control gate CG is, for example, disposed on the shielded gate SG and separated by the second insulating layer  114 . In some embodiments, the control gate CG and the shielded gate SG includes similar materials, which may be doped polysilicon. 
     The first insulating layer  112  is, for example, disposed between the shielded gate SG and the substrate  100 . The second insulating layer  114  is, for example, disposed on the shielded gate SG and serves as an inter-gate insulating layer to separate the shielded gate SG from the control gate CG. The third insulating layer  116  is, for example, disposed between the control gate CG and the substrate  100 . In some embodiments, the first insulating layer  112 , the second insulating layer  114 , and the third insulating layer  116  include similar materials, which may be silicon oxide. 
     The substrate region  200  is, for example, disposed in the substrate  100  and located between adjacent trenches T. In some embodiments, the substrate region  200  has the first conductivity type. For example, the substrate region  200  may be a P-type well region and include boron. The source region  300  is disposed, for example, in the substrate region  200 . In some embodiments, the source region  300  has the second conductivity type. For example, the source region  300  may be an N-type well region and include phosphorus or arsenic. 
     In some embodiments, the semiconductor device  10  may further include a contact window  500 A, a contact window  500 B, an interconnect layer  600 A, and an interconnect layer  600 B. Please refer to the foregoing embodiments for the materials, functions, and formation of the contact window  500 A , the contact window  500 B, the interconnection layer  600 A , and the interconnection layer  600 B, as the same is not repeated here. 
     In this embodiment, the electric field distribution of the semiconductor device  10  of this embodiment may be improved by providing the second conductive layer  130  of the shielded gate SG a step structure and the above parameter design, thereby improving the breakdown voltage of the semiconductor device  10 . In addition, since the second conductive layer  130  has a step structure, the first insulating layer  112  between the sidewall of the trench T and the shielded gate SG is thinner than the corresponding insulating layer in the semiconductor device of the prior art. Therefore, the pitch between the semiconductor devices  10  of this embodiment may be shortened to reduce the on-resistance of the semiconductor device  10 . Furthermore, by making the third width W 3  of the third conductive layer  140  smaller than the width of the electrode of the bottom gate SG 1  closest to the top gate SG 2  (the second width W 23 _ 1  of the third electrode  136 ), the semiconductor device  10  of the present embodiment may avoid generating excessive gate-to-drain capacitance due to the step structure design of the second conductive layer  130 , and avoid increasing the switching power loss of the semiconductor device  10 . 
     In summary, the disclosure provides a semiconductor device including a shielded gate design in which the shielded gate includes a bottom gate and a top gate. The bottom gate includes a step structure consisting of a plurality of electrodes. The width of the top gate is smaller than the width of the electrode of the bottom gate closest to it. Based on this, the semiconductor device of the disclosure has an improved breakdown voltage and a reduced on-resistance, and may prevent the gate-to-drain capacitance from increasing, thereby maintaining the electrical characteristics of the semiconductor device of the disclosure and improving the clamping capability.