Patent Publication Number: US-2021175336-A1

Title: Lateral double-diffused transistor and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority of Chinese Patent Application No. 201911259455.4, filed on Dec. 10, 2019 and entitled by “LATERAL DOUBLE-DIFFUSED TRANSISTOR AND MANUFACTURING METHOD THEREOF”, which is incorporated herein by reference in its entirety. 
     FIELD OF TECHNOLOGY 
     The present disclosure relates to a technical field of semiconductor, in particular to a lateral double-diffused transistor and a manufacturing method of the lateral double-diffused transistor. 
     BACKGROUND 
     Power field effect transistors are an important type of transistors. The power field effect transistors mainly include vertical diffused metal oxide semiconductor (VDMOS) transistors and lateral double-diffused metal oxide semiconductor (LDMOS) transistors. Compared with the VDMOS transistors, the LDMOS transistors have many advantages, such as better compatibility with planar complementary metal oxide semiconductor (CMOS) process, better thermal stability and frequency stability, higher gain, lower feedback capacitance and thermal resistance, and constant input impedance, so that the LDMOS transistors are widely used in many applications. 
     In applications of a LDMOS transistor, it is required to reduce an on-state resistance between a source and a drain of the transistor as much as possible on a premise that a breakdown voltage BV_dss between the source and the drain of the transistor is high enough. However, optimization requirements on the breakdown voltage and the on-state resistance between the source and the drain of the transistor are contradictory. Therefore, in order to make the off-state breakdown voltage (off_BV) relatively high and the on-state resistance (Rdson) relatively low, it is necessary to make a compromise between a doping concentration of a drift region of the transistor and a thickness of an oxide layer located above the drift region, in order to make the voltage off_BV and the resistance Rdson relatively suitable. 
     In a VDMOS device in the prior art, a single field plate layer is formed on the surface of a dielectric layer. The distance between the field plate layer and the semiconductor surface is constant, and the thickness of the oxide dielectric layer is uniform, which can not meet the requirements on high off-state breakdown voltage (off_BV) and low on-state resistance (Rdson) simultaneously, resulting in a poor performance of the transistor. 
     SUMMARY 
     In view of the existing status, the present disclosure provides a lateral double-diffused transistor and a manufacturing method of the lateral double-diffused transistor. A salicidation block layer formed by a standard CMOS process is used as a second dielectric layer and at least one contact channel is used as a second field plate layer, so that a stair-shaped field dielectric layer with increasing thickness is formed and a distance between the second field plate layer and a silicon substrate is increased, effectively increasing the breakdown voltage of the transistor and reducing the on-state resistance. 
     According to one aspect of the present disclosure, provided is a lateral double-diffused transistor, wherein the transistor comprises: a substrate; a well region and a drift region both located in top of the substrate, a source region located in the well region, and a drain region located in the drift region; a first dielectric layer located on a surface of the drift region; a first field plate layer located above the surface of the drift region and covering a first portion of the first dielectric layer; a second dielectric layer partially covering a surface of the first field plate layer and stacked on a surface of a second portion of the first dielectric layer; a second field plate layer located on a surface of the second dielectric layer, wherein the second field plate layer comprising at least one contact channel. 
     In an alternative embodiment, wherein the second dielectric layer is a salicidation block layer for preventing metal silicide from forming in a region covered by the salicidation block layer. 
     In an alternative embodiment, wherein the salicidation block layer is an oxide layer. 
     In an alternative embodiment, wherein each contact channel included in the at least one contact channel is a metal plug filled in a corresponding one of at least one through hole which is formed in the second field plate layer and extends perpendicularly to the surface of the second dielectric layer. 
     In an alternative embodiment, wherein the second field plate layer comprises a plurality of contact channels, each of which is included in said at least one contact channel, arranged in a row along an extension direction from the source region to the drain region. 
     In an alternative embodiment, wherein one of the plurality of contact channels which is located above the first field plate layer has a height less than a height of another one of the plurality of contact channels which is located above the second portion of the first dielectric layer. 
     In an alternative embodiment, wherein the plurality of contact channels are respectively connected to different potentials. 
     In an alternative embodiment, wherein the transistor further comprises a side wall, which is located in a contact region between a side surface of the first field plate layer and the second dielectric layer, and used as an isolation layer. 
     In an alternative embodiment, wherein the first dielectric layer extends along a direction from the source region to the drain region and covers a part of the drain region. 
     According to another aspect of the present disclosure, provided is a method for manufacturing a lateral double-diffused transistor, the method comprises: forming a well region and a drift region in top of a substrate; forming a source region located in the well region, and a drain region located in the drift region; forming a first dielectric layer located on a surface of the drift region; forming a first field plate layer located above the surface of the drift region and covering a surface of a first portion of the first dielectric layer; forming a second dielectric layer partially covering a surface of the first field plate layer and stacked on a surface of a second portion of the first dielectric layer; forming a second field plate layer located on a surface of the second dielectric layer, wherein the second field plate layer comprising at least one contact channel. 
     In an alternative embodiment, wherein the second dielectric layer is a salicidation block layer for preventing metal silicide from forming in a region covered by the salicidation block layer. 
     In an alternative embodiment, wherein the salicidation block layer is an oxide layer. 
     In an alternative embodiment, wherein each contact channel included in the at least one contact channel is a metal plug filled in a corresponding one of at least one through hole which is formed in the second field plate layer and extends perpendicularly to the surface of the second dielectric layer. 
     In an alternative embodiment, wherein the second field plate layer comprises a plurality of contact channels, each of which is included in said at least one contact channel, arranged in a row along an extension direction from the source region to the drain region. 
     In an alternative embodiment, wherein one of the plurality of contact channels which is located above the first field plate layer has a height less than a height of another one of the plurality of contact channels which is located above the second portion of the first dielectric layer. 
     In an alternative embodiment, wherein the plurality of contact channels are respectively connected to different potentials. 
     In an alternative embodiment, wherein the method further comprises: forming a side wall located in a contact region between a side surface of the first field plate layer and the second dielectric layer. 
     In an alternative embodiment, wherein the step of forming the second dielectric layer comprises: depositing the salicidation block layer on the substrate, the first field plate layer, and the first dielectric layer; covering a surface of the salicidation block layer located above the drift region with a resist mask; and etching and removing a portion of the salicidation block layer which is uncovered by the resist mask. 
     In an alternative embodiment, wherein the step of forming the second field plate layer comprises: successively depositing an oxide layer, an etching barrier layer and an interlayer dielectric layer on the surface of the second dielectric layer; etching the interlayer dielectric layer, the etching barrier layer and the oxide layer to form the at least one through hole; depositing metal in each one of the at least one through hole to form the metal plug; and performing planarization. 
     In an alternative embodiment, wherein material of the first field plate layer comprises polysilicon, and material of the first dielectric layer comprises oxide. 
     In an alternative embodiment, wherein a thickness of the first dielectric layer is 300-800 angstroms, and a thickness of the second dielectric layer is 500-1000 angstroms. 
     In the lateral double-diffused transistor and the manufacturing method of the lateral double-diffused transistor according to embodiments of the present disclosure, the plurality of contact channels are used as the second field plate layer, which avoids an etching process on polysilicon during forming the second field plate layer, thus saving resources and area occupied by the transistor, and making the distance between the second field plate layer and the surface of the substrate large enough, improving the breakdown voltage and reducing the on-state resistance between the source and the drain. 
     In an alternative embodiment, the second field plate layer comprises the plurality of contact channels arranged in a row, which are respectively connected to different potentials to increase electrical connection between the transistor and other components. The plurality of contact channels which are arranged discontinuously can also change a distribution of electric field, thus increasing the breakdown voltage. 
     According to an alternative embodiment, the salicidation block layer, which is commonly used in transistor manufacturing processes, is used as the second dielectric layer, so that the salicidation block layer can not only be stacked on the surface of the first dielectric layer to make the dielectric layer located above the drain region thick enough, but also protect silicon regions located below the salicidation block layer. Compared with the traditional lateral double-diffused transistor manufacturing method which requires additional processes for manufacturing the second dielectric layer and the second field plate layer, the embodiments according to the present disclosure uses the salicidation block layer as a dielectric layer, thus there is no need to etch an oxide layer to form the second dielectric layer, which reduces steps of manufacturing process. Meanwhile, the salicidation block layer is stacked on the surface of the first dielectric layer to make the dielectric layer located above the drain region thick enough, which forms a stair-shaped dielectric layer structure from the source region to the drain region, effectively increasing the breakdown voltage of the transistor and reducing the on-state resistance between the source and the drain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other purposes, features and advantages of the present invention will become more apparent from the description below with reference to the accompanying drawings. Wherein: 
         FIG. 1  shows a cross-sectional structural schematic view of a lateral double-diffused transistor according to an embodiment of the correlation techniques; 
         FIG. 2  shows a cross-sectional structural schematic view of a lateral double-diffused transistor according to an embodiment of the present disclosure; 
         FIG. 3 a -3 l    respectively show cross-sectional structural schematic views of a lateral double-diffused transistor in different stages of a manufacturing method of the transistor according to an embodiment of the present disclosure; 
         FIG. 4  shows a cross-sectional structural schematic view of a lateral double-diffused transistor according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In the various figures, the same elements are denoted by the same or similar reference numerals. For the sake of clarity, the various parts in the figures are not drawn to scale. In addition, some public information may not be disclosed. For the sake of brevity, the semiconductor structure obtained after several steps can be described in one accompanying drawing. 
     When describing the structure of a device, if a layer or a region is referred to as “on” or “above” another layer or another region, it can mean that the layer or the region is located directly on the another layer or the another region, or there are other layers or other regions between the layer or the region and the another layer or the another region. Moreover, if the device is flipped, the layer or the region will be “beneath” or “below” the another layer or the another region. 
     In order to describe the situation in which the layer or the region is directly located on the another layer or the another region, the present disclosure will adopt the expression of “A is directly located on B” or “A is on and adjacent to B”. In the present disclosure, “A is directly located in B” means that A is located in B and A is directly adjacent to B, rather than A is located in the doping region formed in B. 
     In order to better understand technical solutions of the present disclosure, many specific details, such as structure, materials, dimensions, treatment processes and techniques of semiconductor devices, are described below. However, a person skilled in the art should understand that the present disclosure can still be implemented without certain specific details. 
     Unless specifically noted below, the layers or the regions of the semiconductor devices may be composed of material well known to those skilled in the art. Semiconductor materials include III-V semiconductors, such as GaAs, InP, Gan, and SiC, and IV semiconductors, such as Si, and Ge. Gate conductor and electrode layer may be formed form various conductive materials, such as metal layer, doped polysilicon layer, stacked gate conductor including the metal layer, the doped polysilicon layer, and other conductive materials, such as TaC, TiN, TaSiN, HfSiN, TiSiN, TiCN, TaAlC, TiAlN, TaN, PtSix, Ni 3 Si, Pt, Ru, W, and a combination of the various conductive materials. Gate dielectric may consist of SiO 2  or materials with a dielectric constant greater than SiO 2 , such as oxides, nitrides, oxynitrides, silicates, aluminates, and titanates. Moreover, the gate dielectric can be formed not only from materials known to the skilled in the art, but also materials developed in the future for the gate dielectric. 
     In the present disclosure, the term “semiconductor structure” refers to the entire semiconductor structure formed during each step of the fabrication procedure of a semiconductor device, including all layers or regions that have been formed. The term “lateral extension” refers to the extension along a direction roughly perpendicular to the depth of the trench. 
     The specific embodiments of the present disclosure are further described in detail referring to the accompanying drawings and the embodiments below. 
       FIG. 1  shows a cross-sectional structural schematic view of a lateral double-diffused transistor according to an embodiment of the correlation techniques. 
     As shown in  FIG. 1 , the lateral double-diffused transistor of the correlation techniques comprises: an N-type doped semiconductor substrate  101 , such as a silicon substrate; a P-type well region  102  located in top of the semiconductor substrate  101 ; an N-type drift region  103  located laterally beside the P-type well region  102  in the semiconductor substrate  101 ; a source region  104  located in the P-type well region  102 ; and a drain region  105  located in the N-type drift region  103 . The source region  104  and the drain region  105  are both N-type doped regions. 
     The lateral double-diffused transistor further comprises: a first dielectric layer  111  located on the surface of the drift region  103 ; and a first field plate layer  112  located above the drift region  103  and covering on the surface of the first dielectric layer  111 . The lateral double-diffused transistor further comprises: a gate oxide layer, which is not shown in  FIG. 1  and is arranged between the first field plate layer  112  and the semiconductor substrate  101 . The first field plate layer  112  extends to a partial surface of the N-type drift region  103  and a partial surface of the first dielectric layer  111 , which effectively reduces a peak intensity of surface electric field formed by the drift region  103  located below the first field plate layer  112  and improves the breakdown voltage. A depletion layer is formed in the drift region  103  located below the first field plate layer  112  and the first dielectric layer  111 , which improves voltage drop condition. 
     In order to further increase the breakdown voltage and reduce the on-state resistance between the source region and the drain region, the lateral double-diffused transistor further comprises: a second dielectric layer  114  and a second field plate layer  115  located on the surface of the second dielectric layer  114 , which are located on the side of the first dielectric layer  111  away from the first field plate layer  112 . The second dielectric layer  114  covers a partial surface of the drift region  103  and a partial surface of the first field plate layer  112  and contacts with a side surface of the first dielectric layer  111 . The second field plate layer  115  located on a surface of the second dielectric layer  114 . The first field plate layer  112  and the second field plate layer  115  are comprised in the gate structure of the lateral double-diffused transistor. 
     In an alternative embodiment, the lateral double-diffused transistor further comprises: a side wall  113  which is arranged between a side surface of the first field plate layer  112  and the second dielectric layer  114 , and used as an isolation layer. 
     In an alternative embodiment, materials of the source region  104  and the drain region  105  are usually metallic silicide. To avoid reaction of other silicon regions with metal to form metal silicide, a protective oxide layer formed by self-aligned silicon metallization process is used to protect transistor structure. As shown in  FIG. 1 , for example, a protective oxide layer  116  is covered on the surface of the second field plate layer  115  to form a protection layer of silicon regions located below the protective oxide layer  116 . Then, a source electrode, a drain electrode, one or more contact holes, one or more contact channels or one or more wiring terminals will be fabricated in subsequent processes. 
     The thickness of the second dielectric layer  114  located near the drain region  105  is greater than the thickness of the first dielectric layer  111  located near the drain region  105 , which in a manner reduces the on-state resistance and improves the breakdown voltage. However, the manufacturing process of the lateral double-diffused transistor device comprises two deposition steps and two photoetching steps to form two dielectric layers and two field plate layers, as well as manufacturing steps to form the salicidation block layer, the one or more contact holes, and the one or more contact channels, thus increasing process cost, production time, production complexity, and difficulties on mass production. In order to further improve transistor performance, reduce the on-state voltage drop and improve the breakdown voltage, an optimized lateral double-diffused metal oxide semiconductor device shown in  FIG. 2  is provided, by making improvement on the structure of traditional SGT (Silicon Gate Transistor) devices. 
       FIG. 2  shows a cross-sectional structural schematic view of a lateral double-diffused transistor according to an embodiment of the present disclosure. 
     As shown in  FIG. 2 , the lateral double-diffused transistor comprises: a substrate  201 ; a P-type well region  202  formed in top of the substrate  201 ; an N-type drift region  203  located laterally beside the P-type well region  202  in the substrate  201 ; a source region  204  located in the P-type well region  202 ; and a drain region  205  located in the N-type drift region  203 . The source region  204  and the drain region  205  are both N-type doped regions. 
     The lateral double-diffused transistor further comprises: a first dielectric layer  211  located on a surface of the drift region  203 ; and a first field plate layer  212  located above the drift region  203  and covering a surface of a first portion of the first dielectric layer  211 . The lateral double-diffused transistor further comprises: a gate oxide layer  241  deposited between the first field plate layer  212  and a channel layer. The first field plate layer  212  extending to a surface of part of the gate oxide layer  241  and a surface of part of the first dielectric layer  211  effectively reduces a peak intensity of surface electric field formed by the drift region  203  located below the first field plate layer  212  and is beneficial to improve the breakdown voltage. 
     The lateral double-diffused transistor further comprises: a second dielectric layer  214  and a second field plate layer  215  located on a surface of the second dielectric layer  214 , which are located on a side of the first dielectric layer  211  away from the first field plate layer  212 . That is, the second dielectric layer  214  covers a surface of part of the first field plate layer  212  and is stacked on a surface of a second portion of the first dielectric layer  211 . The second field plate layer  215  locates on the surface of the second dielectric layer  214 . 
     In an embodiment of the present disclosure, the second dielectric layer  214  is a protective oxide layer formed by an existing self-aligned silicon metallization process, which is often called a salicidation block (SAB) layer or a reaction protection oxide (RPO) layer. The salicidation block layer is used as the second dielectric layer  214  which prevents a region covered by the salicidation block layer from forming metal silicide. The salicidation block layer is directly used as the second dielectric layer  214 , thus a deposition process or a photoetching process for forming a second dielectric layer is not needed. The salicidation block layer can not only be used as a protective oxide layer of a silicon region to avoid from forming metal silicide, but also can be used as a dielectric layer, which reduces manufacturing cost. The second dielectric layer  214  directly stacked on the surface of the first dielectric layer  211  increases a dielectric layer thickness near the drain region  205 , improves performances on the breakdown voltage and the on-state resistance required by the transistor, and can be formed by a simple process. 
     In an alternative embodiment, the second field plate layer  215  comprises at least one contact channel. The first field plate layer  212  and the second field plate layer  215  are comprised in the gate structure of the transistor. The at least one contact channel is used as the second field plate layer  215 , which increases a thickness of the second field plate layer  215 . That is, the distance between the second field plate layer  215  and the surface of the substrate  201  is increased, thus the breakdown voltage can be improved and the on-state resistance can be reduced. 
     In an alternative embodiment, the second field plate layer  215  comprises a plurality of contact channels. The plurality of contact channels are respectively connected to different potentials, in order to further optimize the surface electric field, improve the breakdown voltage, and reduce the on-state resistance. 
     In an alternative embodiment, the plurality of contact channels can be formed by a commonly used method in current transistor manufacturing processes. The plurality of contact channels are directly used as the second field plate layer  215 , which avoids some processes for forming a second field plate layer, such as deposition process and photoetching process, thus reducing production complexity. 
     In an alternative embodiment, the lateral double-diffused transistor further comprises: a side wall  213  located in a contact region between a side surface of the first field plate layer  212  and the second dielectric layer  214 . The side wall  213  is used as an isolation layer which has isolating function. 
     According to the embodiment of the present disclosure, deposition and etching process can be used only for forming a single dielectric layer and a single field plate layer. By using the salicidation block layer as the second dielectric layer and using the plurality of contact channels as the second field plate layer, manufacturing steps, device area and production cost can be saved. Moreover, functions implemented by two field plate layers and two dielectric layers can stilled be ensured, leading to a high breakdown voltage and a low on-state resistance. 
     By using the salicidation block layer as the second dielectric layer, not only can the thickness of the dielectric layer located above the drain region be increased by stacking the salicidation block layer on the surface of the first dielectric layer, but also the silicon located below the salicidation block layer can be protected. Compared with the traditional manufacturing method which requires additional manufacturing process during forming the second dielectric layer and the second field plate layer, the second field plate layer with the at least one contact channels according to the embodiment of the present disclosure may reduce the amount of manufacturing steps. 
     A manufacturing method of a lateral double-diffused transistor according to a specific embodiment of the present disclosure is further described in detail in combination with  FIG. 3 a   - FIG. 3   l.    
       FIG. 3 a -3 l    respectively show cross-sectional structural schematic views of a lateral double-diffused transistor in different stages of a manufacturing method of the transistor according to an embodiment of the present disclosure. 
     As shown in  FIG. 3 a   , a P-type well region  202  and an N-type drift region  203  located in the top of the substrate  201  are formed, a source region  204  located in the P-type well region  202  and a drain region  205  located in the N-type drift region  203  are formed. The step of forming the P-type well region  202 , the N-type drift region  203 , the source region  204 , and the drain region  205  can be implemented by conventional processes. N-type ions are implanted into the P-type well region  202  and the N-type drift region  203  to respectively form the source region  204  and the drain region  205 . 
     Then, as shown in  FIG. 3 b   , a first dielectric layer  211  located on the surface of the N-type drift region  203  is formed. For example, the first dielectric layer  211  is an oxide layer, such as a silicon oxide layer. The step of forming the first dielectric layer  211  comprises: depositing an oxide layer  211  on the surface of the substrate  201 , wherein the oxide layer  211  extends from the source region  204  to the drain region  205 , and a surface of a portion of the oxide layer  211  located above the N-type drift region  203  is covered with a photoresist layer  221 . 
     Then, as shown in  FIG. 3 c   , a series of steps such as exposure, development and etching removal are performed to etch and remove a part of the oxide layer  211  which is uncovered by the photoresist layer  221 , and finally the first dielectric layer  211  is formed. The first dielectric layer  211  covers almost on the entire surface of the drift region  203  and extends to the drain region  205 . 
     Then, as shown in  FIG. 3 d   , a gate oxide layer  241  is grown. The gate oxide layer  241  is formed on the substrate  201  around the first dielectric layer  211  by a certain deposition process. A channel is covered by the gate oxide layer  241 , that is, a surface of part of the well region  202  and a surface of part of the drift region  203  are covered by the gate oxide layer  241 . The gate oxide layer  241 , such as a silicon dioxide layer, acts as a gate insulator layer of the transistor. The thickness of the gate oxide layer  241 , such as 2-10 nm, is related to the thickness of the first dielectric layer  211 . Part of the gate oxide layer  241  located on the surface of the drain region  205  is removed in a subsequent step. The manufacturing process of the gate oxide layer  241  is a standard CMOS manufacturing process, which is not described in detail here. 
     Then, as shown in  FIG. 3 e   , a first field plate layer  212  located above the N-type drift region  203  is formed and covers a surface of a first portion of the first dielectric layer  211 . The first field plate layer  212  comprised in the gate structure of the transistor is a polysilicon layer. The steps of forming the first field plate layer  212  comprises: depositing a polysilicon layer on the surface of the gate oxide layer  241  and the first dielectric layer  211  to form the first field plate layer  212  shown in  FIG. 3 e   . The first field plate layer  212  covers on the gate oxide layer  241 , the entire exposed surface of the first dielectric layer  211 , and the exposed surface of the substrate  201 . Then, the photoresist layer  221  is coated on the surface of the first field plate layer  212  located above the N-type drift region  203 , and the photoresist layer  221  is also located above part of the P-type well region  202 . 
     Then, as shown in  FIG. 3 f   , when photoetching is performed, the first field plate layer  212  uncovered by the photoresist layer  221  is completely etched, leaving only part of the first field plate layer  212  covered by the photoresist layer  221 . As a portion of the gate structure, the first field plate layer  212  covers part of the gate oxide layer  241  located on the P-type well region  202  and the N-type drift region  203 , and covers the surface of the first portion of the first dielectric layer  211 . 
     A single dielectric layer and a single field plate layer cannot simultaneously satisfy the requirements to increase the breakdown voltage and reduce the on-state resistance. Therefore, in the embodiment of the present disclosure, a second dielectric layer  214  and a second field plate layer  215  are fabricated. 
     Then, as shown in  FIG. 3 g   , a side wall  213  is formed and located at a side surface of the first field plate layer  212  in contact with the first dielectric layer  211 . For example, the side wall  213  is an oxide layer or a nitride layer functioning as an isolator. The material of the side wall  213  is one of the following materials: silicon dioxide, and silicon nitride. The height of the side wall  213  is consistent with the height of the first field plate layer  212  located on the surface of the first dielectric layer  211 . That is, the side wall  213  also covers the surface of a part of the first dielectric layer  211 . 
     The side wall  213  according to the embodiment of the present disclosure can be formed by a known manufacturing process, which will not be introduced in detail here. 
     Then, as shown in  FIG. 3 h    and  FIG. 3 i   , a second dielectric layer  214  is formed, covers a surface of part of the first field plate layer  212  and is stacked on a surface of a second portion of the first dielectric layer  211 . The step of forming the second dielectric layer  214  comprises: depositing a salicidation block layer  214  on the surface of the substrate  210 , the first field plate layer  212 , and the first dielectric layer  211 ; covering the surface of the salicidation block layer  214  located above the N-type drift region  203  with a resist mask  222 ; and etching and removing a portion of the salicidation block layer  214  which is uncovered by the resist mask  222 . After etching, the second dielectric layer  214  is formed, as shown in  FIG. 3   i.    
     Self-aligned silicon metallization process refers to a process of depositing a layer of metal on the surface of polysilicon and reacting at a certain temperature to form compounds of metals and silicon, i.e. metal silicide. The salicidation block layer formed by the self-aligned silicon metallization process is a reaction protection oxide layer to prevent the silicon regions from reacting with metal to form metal silicide. The second dielectric layer  214  is the salicidation block (SAB) layer, so a region covered by the second dielectric layer  214  can not form metal silicide, while a region uncovered by the second dielectric layer  214 , such as the drain region  205 , will form metal silicide later. 
     The salicidation block layer is used as the second dielectric layer  214  and directly stacked on the surface of the second portion of the first dielectric layer  211  uncovered by the first field plate layer  212 , and the second dielectric layer  214  covers part of the surface of the first field plate layer  212  and also covers the surface of the side wall  213 , so that the dielectric layer located near the drain region  205  can be thick enough, ensuring a high breakdown voltage and a low on-state resistance. 
     For example, the salicidation block layer  214  used to cover a device that does not need to form self-aligned metal silicide, is manufactured by plasma enhanced chemical vapor deposition (PECVD) or sub-atmospheric pressure chemical vapor deposition (Sub-Atmosphere CVD). 
     Since the salicidation block layer is used as the second dielectric layer  214 , there is no need to perform additional steps to deposit and etch an oxide layer to form the second dielectric layer  214 . That is, only a single dielectric layer is needed to be formed by corresponding manufacturing steps according to the embodiment of the present disclosure, greatly simplifying the process flow and reducing the production cost. Moreover, since the first dielectric layer  211  is covered by the second dielectric layer  214 , the thickness of the dielectric layer located near the drain region  205  is effectively increased. 
     In the traditional manufacturing process of the transistor with double field plate layers and double dielectric layers, it is necessary to form two dielectric layers, two field plate layers, and a salicidation block layer to protect the silicon regions from reacting. However, in the manufacturing process of the transistor with double field plate layers and double dielectric layers according to the embodiments of the present disclosure, the salicidation block layer is used as the second dielectric layer, which simplifies the manufacturing process of the transistor, reduces the volume and thickness of the transistor, and improves the performance of the transistor. 
     Then, as shown in  FIG. 3 j    and  FIG. 3   l,  a second field plate layer  215  is formed and located on the surface of the second dielectric layer  214 , wherein the second field plate layer  215  comprises at least one contact channel. The second field plate layer  215  is formed by deposition and etching process. 
     Specifically, the step of forming the second field plate layer  215  comprises: successively depositing an oxide layer  231 , an etching barrier layer  232  and an interlayer dielectric layer  233  on the surface of the second dielectric layer  214 , as shown in  FIG. 3 j   ; etching the interlayer dielectric layer  233 , the etching barrier layer  232  and the oxide layer  231  to form at least one through hole  234 , the at least one through hole  234  each serves as a corresponding one of at least one contact hole, as shown in  FIG. 3 k   ; depositing metal in the at least one through hole  234  to form at least one metal plug and performing planarization, as shown in  FIG. 3   l,  thus the second field plate layer  215  can be formed. The material of the at least one metal plug comprises one of the following materials: tungsten, and titanium. 
     Each contact channel included in the at least one contact channel can be a cylinder extending along the direction perpendicular to the surface of the second dielectric layer  214 , and is located in a corresponding one of the at least one contact hole  234 . Due to the technical reasons, a width of a first end of each contact channel can be larger than a second end of that contact channel, wherein the first end is away from the second dielectric layer  214  and the second end is close to the second dielectric layer  214 . That is, each contact channel may has a taper-type shape with a decreasing width from top to bottom. 
     In a possible implementation embodiment, as shown in  FIG. 3   l,  the second field plate layer  215  comprises a plurality of contact channels arranged in a row along an extension direction from the source region  204  to the drain region  205 . And the height of one of the plurality of contact channels on the surface of the second dielectric layer  214  located above the first field plate layer  212  is less than the height of one of the plurality of contact channels located above the second portion of the first dielectric layer  211 . In other words, a row of contact channels are arranged in the direction extending from the source region  204  to the drain region  205 , and since part of the first field plate layer  212  is covered by the second dielectric layer  214 , the height of each contact channel located above the first field plate layer  212  is less than that located above the second portion of the first dielectric layer  211 . In a possible implementation embodiment, the plurality of contact channels are arranged at equal intervals. 
     The plurality of contact channels in the second field plate layer  215  can be connected to a same potential which may be a potential of the drain electrode or the source electrode of the transistor. The plurality of contact channels can also be respectively connected to different potentials, each selected from potentials such as the potentials on the source electrode, the drain electrode, the gate electrode of the transistor, and any other intermediate potentials generated by a corresponding circuit comprising the transistor. Different potentials can be connected according to actual needs. Each of the plurality of contact channels can be connected to different potential to further optimize the surface electric field, so that the breakdown voltage can be further increased and the on-state resistance can be further reduced. 
       FIG. 4  shows a cross-sectional structural schematic view of a lateral double-diffused transistor according to an embodiment of the present disclosure. 
     In the embodiment of the present disclosure, as shown in  FIG. 4 , the second field plate layer  215  comprises a contact channel with a wide width. For example, the contact channel is on the surface of the second dielectric layer  214  located above the first dielectric layer  211 . Compared with the embodiment shown in  FIG. 3   l,  wherein the width of the plurality of contact channels are relatively uniform, the embodiment shown in  FIG. 4  only has a single contact channel, thus the width of the contact channel is preferred to be larger than that of any one of the plurality of contact channels shown in  FIG. 3   k.    
     In the embodiment of the present disclosure, the contact channel is directly used as the second field plate layer, so there is no need to perform additional steps to deposit and etch an oxide layer to form the second dielectric layer, which greatly simplifies the process flow. In addition, because the height of the contact channel is large enough, a long distance between the second field plate layer and the substrate can be achieved, which improves the breakdown voltage and reduces the on-state resistance. The thickness of the first field plate layer  212  can be around 2000 angstroms (Å), the thickness of the second field plate layer  205  can be around 8000 angstroms, the thickness of the first dielectric layer  211  can be around 300-800 angstroms, and the thickness of the second dielectric layer  214  can be around 500-1000 angstroms. 
     To sum up, according to the embodiments of the present disclosure, the manufacturing process of the second dielectric layer and the second field plate layer of the lateral double-diffused transistor is optimized, compared with the traditional lateral double-diffused transistor structure. The salicidation block layer commonly used in the transistor manufacturing process is used as the second dielectric layer of the transistor, thus not only can the silicon located below the second dielectric layer be protected by the salicidation block layer, but also the salicidation block layer can serve as a dielectric layer, so that there is no need to etch the oxide layer again to form a second dielectric layer, simplifying the manufacturing process. Meanwhile, the salicidation block layer is stacked on the surface of the first dielectric layer, which increases the thickness of the dielectric layer located above the drain region, thus effectively increasing the breakdown voltage of the transistor and reducing the on-state resistance. Moreover, the at least one contact channel is used as the second field plate layer, so that there&#39;s no need to etch metal or polysilicon to form a second field plate layer, saving resources and the volume occupied by the transistor. Meanwhile, the distance between the second field plate layer and the substrate can be large enough, achieving the improvement on the breakdown voltage and the reduction of the on-state resistance. 
     According to the embodiments of the present disclosure described above, these embodiments neither describe all the details in detail, nor limit the present disclosure to only the specific embodiments described. Obviously, according to the above description, many modifications and changes can be made. In order to better explain the principle and practical application of the present invention, the present specification selects and specifically describes these embodiments, so that the person skilled in the technical field can make good use of the present invention and the modification based on the present invention. The present invention is only limited by the claims, full scope and equivalents of the claims.