Laterally diffused metal oxide semiconductor device and preparation method thereof

Abstract

The present invention relates to a laterally diffused metal oxide semiconductor device and a method for manufacturing the same, comprising: a substrate; a body region of a first conductivity type formed in the substrate; a drift region of a second conductivity type formed in the substrate and adjacent to the body region; a field plate structure formed on the drift region, wherein the lower surface of the field plate structure at one end close to the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, the lower surface of the field plate structure at one end away from the body region is lower than the upper surface of the substrate, and the thickness of the field plate structure gradually increases from the end close to the body region to the end away from the body region to a preset value; and a drain region of the second conductivity type formed on the upper surface of the drift region and in contact with the end of the field plate structure away from the body region. While not increasing the length of the field plate structure where the lower surface is lower than the upper surface of the substrate, a field plate structure with gradually increasing thickness is formed at the position of the JEFET region, thereby improving the reliability of the device.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a laterally diffused metal oxide semiconductor device and a method for preparing the same. Background Art

[0002] NLDMOS is the core device of BCD. Breakdown voltage and on-resistance are the main indicators for measuring LDMOS device performance. To ensure that LDMOS devices have both sufficiently high breakdown voltage and sufficiently low on-resistance, the impurity distribution and field plate structure of the drift region used for voltage resistance need to be modulated. In typical process flows, LOCOS or STI structures are usually used as the longitudinal voltage-resistant field plate. By modulating the thickness and length of the field plate structure, the performance of the LDMOS device can be achieved as expected.

[0003] For LDMOS devices, in order to improve the electric field distribution and enhance the reliability of the device, it is necessary to form a field plate with a gradient thickness, that is, a field plate is required near the JEFET region of the device, and the thickness of the field plate at this position is less than the thickness of the field plate in the drift region. Although the field plate of the LOCOS structure can have a larger bird's beak, the LOCOS structure can be used as a field plate with a thickness in the JEFET region less than the thickness in the drift region, but the LOCOS structure with an overly long bird's beak will increase the pitch of the entire LDMOS device, thereby increasing the on-resistance of the device. Summary of the Invention

[0004] Based on this, a laterally diffused metal oxide semiconductor device and a method for preparing the same are provided.

[0005] A laterally diffused metal oxide semiconductor device comprising:

[0006] substrate;

[0007] a body region having a first conductivity type and formed in the substrate;

[0008] a drift region having a second conductivity type, formed in the substrate and adjacent to the body region, the second conductivity type being opposite to the first conductivity type;

[0009] a field plate structure formed on the drift region, wherein a lower surface of an end of the field plate structure close to the body region is flush with an upper surface of the substrate and has an upwardly extending inclined surface, and a lower surface of an end of the field plate structure away from the body region is lower than an upper surface of the substrate, and a thickness of the field plate structure gradually increases from the end close to the body region to the end away from the body region to a preset value;

[0010] The drain region has the second conductivity type, is formed on the upper surface layer of the drift region, and contacts an end of the field plate structure away from the body region.

[0011] In one embodiment, an angle between the inclined surface and a lower surface of the field plate structure at one end close to the body region is not less than 30 degrees and not more than 60 degrees.

[0012] In one embodiment, the field plate structure includes:

[0013] a first oxide structure, which is one end of the field plate structure close to the drain region, formed on the drift region, with an upper surface of the first oxide structure not lower than an upper surface of the substrate, the first oxide structure including a first end and a second end in a direction from the body region toward the drift region, and a thickness of the first oxide structure gradually increasing from the first end toward the second end to a preset value;

[0014] The second oxide structure is formed on the upper surface of the drift region near the body region and extends along the upper surface of the first end to the junction of the first end and the second end. The inclined surface is the upper surface of the second oxide structure near the body region.

[0015] In one embodiment, the thickness of the second oxide structure is no greater than 1500 angstroms.

[0016] In one embodiment, the first oxide structure includes a local silicon isolation oxide structure, and the local silicon isolation oxide structure is manufactured by a recess process.

[0017] In one embodiment, the laterally diffused metal oxide semiconductor device further comprises:

[0018] a source region having a second conductivity type and formed on an upper surface layer of the body region;

[0019] A polysilicon gate is formed on the field plate structure and extends along the field plate structure to cover the substrate between the source region and the field plate structure;

[0020] A shallow trench isolation structure is formed in the substrate. The shallow trench isolation structure contacts the drain region, and a portion of the lower surface of the shallow trench isolation structure contacts the drift region.

[0021] In the aforementioned laterally diffused metal oxide semiconductor device, a field plate structure is formed on the drift region. The lower surface of the field plate structure at one end near the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface. The lower surface of the field plate structure at one end away from the body region is lower than the upper surface of the substrate. The thickness of the field plate structure gradually increases to a preset value from the end near the body region to the end away from the body region. By setting the lower surface of the field plate structure at one end near the body region to be flush with the upper surface of the substrate and having an upwardly extending inclined surface, and the thickness of the field plate structure gradually increasing to a preset value from the end near the body region to the end away from the body region, a field plate structure with gradually increasing thickness is formed at the JEFET region without increasing the length of the field plate structure where the lower surface is lower than the upper surface of the substrate (without increasing the spacing of the LDMOS devices), thereby improving the electric field distribution on the device surface and enhancing the reliability of the device.

[0022] A method for preparing a laterally diffused metal oxide semiconductor device, comprising:

[0023] providing a substrate;

[0024] forming adjacent body regions and drift regions in a substrate, wherein the body region has a first conductivity type and the drift region has a second conductivity type opposite to the first conductivity type;

[0025] A field plate structure is formed on the drift region, wherein a lower surface of an end of the field plate structure close to the body region is flush with an upper surface of the substrate and has an upwardly extending inclined surface, and a lower surface of an end of the field plate structure away from the body region is lower than an upper surface of the substrate, and a thickness of the field plate structure gradually increases from the end close to the body region to the end away from the body region to a preset value;

[0026] A drain region of the second conductivity type is formed on the upper surface layer of the drift region, and the drain region is in contact with an end of the field plate structure away from the body region.

[0027] In one embodiment, the step of forming a field plate structure on the drift region includes:

[0028] forming a first oxide structure on the drift region, wherein the first oxide structure includes a first end and a second end in a direction from the body region to the drift region, and a thickness of the first oxide structure gradually increases from the first end to the second end to a preset value;

[0029] forming a second oxide structure on an upper surface of the drift region close to a side of the body region, wherein the second oxide structure extends along an upper surface of the first end portion to a junction between the first end portion and the second end portion;

[0030] Among them, the first oxidation structure is the end of the field plate structure away from the body region, the inclined surface is the upper surface of the second oxidation structure close to the body region, and the angle between the inclined surface and the lower surface of the end of the field plate structure close to the body region is not less than 30 degrees and not more than 60 degrees.

[0031] In one embodiment, the first oxide structure includes a local silicon isolation oxide structure, and the step of forming the first oxide structure in the drift region includes:

[0032] forming a hard mask layer on the substrate, wherein a groove is formed in the hard mask layer, and the groove exposes the substrate in a predetermined area of the first oxide structure;

[0033] forming a sidewall structure in contact with the hard mask layer on a sidewall of the groove, wherein a lower surface of the sidewall structure is flush with a bottom of the groove;

[0034] A local thermal oxidation process is performed to form a first oxide structure at the bottom of the groove.

[0035] In one embodiment, the step of forming a second oxide structure on the upper surface of the drift region close to the body region includes:

[0036] forming an oxide film on the upper surface of the substrate;

[0037] forming a photoresist mask layer on the oxide film, wherein the photoresist mask layer covers the oxide film in the preset area of the second oxide structure;

[0038] A wet etching process is performed to remove excess oxide film, thereby obtaining a second oxide structure consisting of the remaining oxide film in the preset region of the second oxide structure.

[0039] In one embodiment, the thickness of the oxide film is not less than 300 angstroms and not more than 1500 angstroms.

[0040] In one embodiment, the method for preparing a laterally diffused metal oxide semiconductor device further includes:

[0041] forming a shallow trench isolation structure in the substrate, wherein the shallow trench isolation structure contacts the drain region, and a lower surface of a portion of the shallow trench isolation structure contacts the drift region;

[0042] forming a source region having a second conductivity type on an upper surface layer of the body region;

[0043] A polysilicon gate is formed on the field plate structure. The polysilicon gate extends along the field plate structure and covers the substrate between the source region and the field plate structure.

[0044] The method for fabricating the LDMOS device described above forms a field plate structure on the drift region, wherein the lower surface of the field plate structure at one end near the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, and the lower surface of the field plate structure at one end away from the body region is lower than the upper surface of the substrate, and the thickness of the field plate structure gradually increases to a preset value from the end near the body region to the end away from the body region. By forming a field plate structure whose lower surface near the end of the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, and by gradually increasing the thickness of the field plate structure from the end near the body region to the end away from the body region to the preset value, a field plate structure with gradually increasing thickness is formed at the JEFET region without increasing the length of the field plate structure where the lower surface is lower than the upper surface of the substrate (without increasing the spacing of the LDMOS device), thereby improving the surface electric field distribution of the device and enhancing the reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0046] Figure 1 is a flow chart of a method for preparing a laterally diffused metal oxide semiconductor device in one embodiment;

[0047] Figure 2 is a schematic diagram of a process for forming a field plate structure on a drift region in one embodiment;

[0048] Figure 3 is a schematic diagram of a process for forming a first oxide structure in a drift region in one embodiment;

[0049] Figure 4 is a cross-sectional view of a device after a hard mask layer is formed on a substrate in one embodiment;

[0050] Figure 5 is a cross-sectional view of a device after forming a sidewall structure in one embodiment;

[0051] Figure 6 is a cross-sectional view of a device after forming a first oxide structure in one embodiment;

[0052] Figure 7 is a cross-sectional view of a device after a photoresist mask layer is formed in one embodiment;

[0053] Figure 8 FIG. 4 is a cross-sectional view of a device after forming a second oxide structure in one embodiment. DETAILED DESCRIPTION

[0054] To facilitate understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The accompanying drawings provide embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0056] It should be understood that when an element or layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" another element or layer, it can be directly on, adjacent to, connected to, or coupled to the other element or layer, or there can be intervening elements or layers. Conversely, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types, and / or portions, these elements, components, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, doping type, or portion from another element, component, region, layer, doping type, or portion. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer, doping type or portion discussed below may be represented as a second element, component, region, layer or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0057] Spatially relative terms such as "under," "beneath," "beneath," "under," "above," "above," etc., may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that in addition to the orientations shown in the figures, spatially relative terms also include different orientations of the device in use and operation. For example, if the device in the drawings is turned over, the element or feature described as "under" or "beneath" or "beneath" the other elements will be oriented as "above" the other elements or features. Thus, the exemplary terms "under" and "under" can include both upper and lower orientations. In addition, the device can also include alternative orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0058] As used herein, the singular forms "a," "an," and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include," "comprising," "having," and the like specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Also, in this specification, the term "and / or" includes any and all combinations of the relevant listed items.

[0059] Embodiments of the invention are described herein with reference to cross-sectional views which are schematic illustrations of idealized embodiments (and intermediate structures) of the invention, such that variations in the shapes shown due to, for example, manufacturing techniques and / or tolerances are anticipated. Accordingly, embodiments of the invention should not be limited to the specific shapes of the regions shown herein, but rather include deviations in shapes due to, for example, manufacturing techniques. For example, an implanted region shown as a rectangle typically has rounded or curved features and / or an implant concentration gradient at its edges rather than a binary change from an implanted region to a non-implanted region. Similarly, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation occurs. Accordingly, the regions shown in the figures are schematic in nature, their shapes do not represent the actual shape of the region of the device, and do not limit the scope of the invention.

[0060] Ideally, for LDMOS devices, a certain field plate thickness is desired near the JFET region to improve the electric field distribution there and enhance the reliability of the LDMOS device. Furthermore, the thickness of this field plate needs to be smaller than that of the drift region field plate and larger than the gate oxide thickness. If an STI field plate is used, a field plate with a gradually varying thickness cannot be fabricated in a single process. If a LOCOS field plate is used, a LOCOS structure with a relatively large bird's beak can be fabricated in a single process, resulting in a field plate with a gradually varying thickness. However, an excessively long bird's beak will affect the pitch of the entire LDMOS device, increasing the on-resistance of the device.

[0061] See also Figure 1 , is a flow chart of a method for preparing a laterally diffused metal oxide semiconductor device in one embodiment.

[0062] In order to solve the above problems, in one embodiment, the present application provides a method for preparing a laterally diffused metal oxide semiconductor device, such as Figure 1 , the preparation method comprises:

[0063] S102, providing a substrate.

[0064] The substrate may be made of undoped single crystal silicon, impurity-doped single crystal silicon, silicon on insulator (SOI), stacked silicon on insulator (SSOI), stacked silicon germanium on insulator (S-SiGeOI), silicon germanium on insulator (SiGeOI), and germanium on insulator (GeOI). As an example, in this embodiment, the substrate is made of single crystal silicon.

[0065] S104 , forming adjacent body regions and drift regions in the substrate.

[0066] The body region has a first conductivity type, and the drift region has a second conductivity type opposite to the first conductivity type; when the first conductivity type is P-type, the second conductivity type is N-type, and when the first conductivity type is N-type, the second conductivity type is P-type. In this embodiment, the first conductivity type is P-type and the second conductivity type is N-type.

[0067] S106 , forming a field plate structure on the drift region.

[0068] The lower surface of the field plate structure at one end close to the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface. The lower surface of the field plate structure at one end away from the body region is lower than the upper surface of the substrate. The thickness of the field plate structure gradually increases from the end close to the body region to the end away from the body region to a preset value.

[0069] S108 , forming a drain region of the second conductivity type on the upper surface layer of the drift region, wherein the drain region contacts an end of the field plate structure away from the body region.

[0070] The method for fabricating the LDMOS device described above forms a field plate structure on the drift region, wherein the lower surface of the field plate structure at one end near the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, and the lower surface of the field plate structure at one end away from the body region is lower than the upper surface of the substrate, and the thickness of the field plate structure gradually increases to a preset value from the end near the body region to the end away from the body region. By forming a field plate structure whose lower surface near the end of the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, and by gradually increasing the thickness of the field plate structure from the end near the body region to the end away from the body region to the preset value, a field plate structure with gradually increasing thickness is formed at the JEFET region without increasing the length of the field plate structure where the lower surface is lower than the upper surface of the substrate (without increasing the spacing of the LDMOS device), thereby improving the surface electric field distribution of the device and enhancing the reliability of the device.

[0071] In one embodiment, the order of step S104 and step S106 is adjusted according to actual needs, for example, step S104 is performed first and then step S106, or step S106 is performed first and then step S104. For example, step S104 is performed first and then step S106.

[0072] See also Figure 2 , is a schematic diagram of a process for forming a field plate structure on a drift region in one embodiment.

[0073] like Figure 2 In one embodiment, step S106 includes:

[0074] S202 , forming a first oxide structure on the drift region.

[0075] The first oxide structure includes a first end and a second end in sequence from the body region to the drift region, and the thickness of the first oxide structure gradually increases from the first end to the second end to a preset value. The first oxide structure is an end of the field plate structure away from the body region, and the lower surface is not higher than the upper surface of the substrate.

[0076] In one embodiment, before step S104, the step further includes: forming a shallow trench isolation structure in the substrate, wherein the field plate structure is formed on the substrate between adjacent shallow trench isolation structures. In this application, a process commonly used by those skilled in the art can be used to form the shallow trench isolation structure.

[0077] See also Figure 3 , is a schematic diagram of a process for forming a first oxide structure in a drift region in one embodiment.

[0078] In one embodiment, the first oxide structure comprises a local silicon isolation oxide structure, such as Figure 3 , step S202 includes:

[0079] S302 , forming a hard mask layer on the substrate, wherein a groove is formed in the hard mask layer, and the groove exposes the substrate in a predetermined area of the first oxide structure.

[0080] See also Figure 4 , is a cross-sectional view of a device after a hard mask layer is formed on a substrate in one embodiment.

[0081] like Figure 4 First, a substrate 10 is obtained and shallow trench isolation structures 102 are formed in the substrate 10. Next, adjacent body regions 101 and drift regions 103 are formed in the substrate between adjacent shallow trench isolation structures 102. Finally, a hard mask layer 20 is formed on the substrate 10 between adjacent shallow trench isolation structures 102. The hard mask layer 20 has a recess 202 formed therein, which is located above the drift region 103. The recess 202 exposes the substrate (drift region 103) in a predetermined area of the first oxide structure.

[0082] Specifically, a hard mask film is formed on the surface of the substrate, and then the hard mask film in the preset area of the first oxide structure above the drift region 103 is removed by photolithography and etching processes to obtain a hard mask layer 20 composed of the remaining hard mask film, and a groove 202 is formed at the position of the preset area of the first oxide structure.

[0083] In one embodiment, the hard mask layer 20 includes an oxide layer, a nitride layer, or a stacked structure of the oxide layer, a nitride layer, or a silicon nitride layer.

[0084] S304 , forming a sidewall structure in contact with the hard mask layer on the sidewall of the groove, wherein the lower surface of the sidewall structure is flush with the bottom of the groove.

[0085] See also Figure 5 , is a cross-sectional view of the device after the sidewall structure is formed in one embodiment.

[0086] like Figure 5, forming a sidewall structure 204 in contact with the hard mask layer 20 on the sidewall of the groove 202. Specifically, first, a sidewall film is formed on the substrate 10. The sidewall film covers the surface of the preset area of the first oxide structure (the drift region 103 exposed at the bottom of the groove 202) and extends along the sidewall of the groove 202 to the surface of the hard mask layer 20. Then, the excess sidewall film is removed through a photolithography process and a dry etching process to obtain a sidewall structure 204 composed of the sidewall film covering the sidewall of the groove 202. The lower surface of the sidewall structure 204 is flush with the bottom of the groove 202 (the upper surface of the drift region 103). By forming the sidewall structure 204, the amount of oxygen that enters the hard mask layer 20 adjacent to the sidewall of the groove 202 during the subsequent local thermal oxidation process can be reduced, thereby reducing the bird's beak length of the formed local silicon isolation oxide structure (first oxide structure) and eliminating the effect of the bird's beak length on the pitch of the entire device.

[0087] In one embodiment, the sidewall structure 204 is a silicon nitride structure. In practical applications, the sidewall structure 204 can be made of different materials as needed.

[0088] S306 , performing a local thermal oxidation process to form a first oxide structure at the bottom of the groove.

[0089] See also Figure 6 , is a cross-sectional view of the device after the first oxide structure is formed in one embodiment.

[0090] like Figure 6 After forming the sidewall structure 204, a local thermal oxidation process is performed to form a LOCOS structure (local silicon isolation structure) with a shorter bird's beak, namely the first oxidation structure 206, at the bottom of the groove 202 (the preset area of the first oxidation structure). The first oxidation structure 206 includes a first end 206A close to the body region 101 and a second end 206B away from the body region 101. The thickness of the first end 206A increases from the part close to the body region 101 to the position of the second end 206B. In the subsequent process, the source region A body region 101 is formed on the side of the first end 206A, and a drain region is formed in the drift region 103 on the side of the second end 206B. The thickness of the second end 206B close to the first end 206A is a preset value, that is, the first end 206A is close to the body region 101, and the junction (intersection position) of the first end 206A and the second end 206B is the position where the thickness of the first oxide structure 206 changes from less than the preset value to the preset value; then, the hard mask layer 20 and the sidewall structure 204 on the substrate 10 are removed.

[0091] S204 , forming a second oxide structure on the upper surface of the drift region close to the body region, wherein the second oxide structure extends along the upper surface of the first end portion to the junction of the first end portion and the second end portion.

[0092] A second oxide structure 108 is formed on the upper surface of the drift region 103 near the body region 101. The second oxide structure 108 extends along the upper surface of the first end 206A to a position where the thickness of the first oxide structure 206 changes from less than a preset value to a preset value. The inclined surface is the upper surface of the second oxide structure near the body region, and the angle between the inclined surface and the lower surface of the end of the field plate structure near the body region is not less than 30 degrees and not more than 60 degrees.

[0093] In one embodiment, step S204 includes: first, forming an oxide film 104 on the upper surface of the substrate 10; second, forming a photoresist mask layer 106 on the oxide film 104, with the photoresist mask layer 106 covering the oxide film 104 in the predetermined region of the second oxide structure; and third, performing a wet etching process to remove excess oxide film 104, thereby obtaining a second oxide structure 108 formed by the remaining oxide film 104 in the predetermined region of the second oxide structure.

[0094] See also Figure 7 , is a cross-sectional view of a device after a photoresist mask layer is formed in one embodiment. Figure 8 , is a cross-sectional view of the device after the second oxide structure is formed in one embodiment.

[0095] like Figure 7 、 Figure 8First, an oxide film 104 is formed on the upper surface of the substrate 10. Next, a photoresist mask layer 106 is formed on the oxide film 104. The photoresist mask layer 106 covers the oxide film 104 in the predetermined region of the second oxide structure near the body region 101. The projection of the photoresist mask layer 106 on the substrate 10 surrounds the first end 206A, and the projection of the side of the photoresist mask layer 106 near the first oxide structure 206 on the substrate 10 is aligned with the junction of the first end 206A and the second end 206B. The projection of the side of the photoresist mask layer 106 away from the first oxide structure 206 on the substrate 10 is located on the drift region 103 between the body region 101 and the first oxide structure 206, i.e., it is a certain distance away from the first end 206A. Next, a wet etching process is performed to remove excess oxide film 104, obtaining a second oxide structure 108 consisting of the remaining oxide film 104 in the predetermined region of the second oxide structure. The second oxide structure 108 covers the upper surface of the substrate 10 and extends along the upper surface of the first end portion 206A to the junction of the first end portion 206A and the second end portion 206B. That is, the second oxide structure 108 covers a portion of the drift region 103 on the side close to the body region 101 and the upper surface of the first end portion 206A. The sum of the thicknesses of the second oxide structure 108 and the first end portion 206A covering the first end portion 206A is no greater than the thickness of the flat region (the region where the thickness remains constant) of the second end portion 206B. That is, the sum of the thicknesses of the second oxide structure 108 and the first end portion 206A covering the first end portion 206A is no greater than a predetermined value. As a result, the thickness of the field plate structure gradually increases, and a gradient electric field distribution is obtained on the polysilicon gate structure 116 formed on the field plate structure. The upper surface 110 of the second oxide structure 108, which is adjacent to the body region, forms an inclined surface of the field plate structure. The angle φ formed between the upper surface 110 and the upper surface of the substrate 10 (the interface between the field plate structure and the upper surface of the substrate 10) is greater than or equal to 30 degrees and less than or equal to 60 degrees. The second oxide structure 108 and the first oxide structure 206 together form the field plate structure. By adjusting the adhesion between the photoresist mask layer 106 and the oxide film 104, the etch rate of the wet etching process, and the etching liquid, the angle φ can be adjusted to adjust the rate at which the thickness of the field plate structure gradually changes from the body region to the drift region, thereby adjusting device performance.

[0096] In other embodiments, the overlapping portion of the second oxide structure 108 and the first oxide structure 206 is adjusted according to the morphology of the first oxide structure 206 .

[0097] Compared with using only the first oxide structure 206 , by covering the first end 206A of the first oxide structure 206 with the second oxide structure 108 , the thickness gradient rate of the field plate structure formed by the first oxide structure 206 and the second oxide structure 108 can be adjusted to form a field plate structure with gradually varying thickness.

[0098] In one embodiment, the first oxide structure 206 and the second oxide structure 108 are both silicon dioxide structures.

[0099] In one embodiment, the oxide film 104 is formed on the upper surface of the substrate 10 by a chemical vapor deposition process.

[0100] In one embodiment, the thickness of the oxide film 104 is not less than 300 angstroms and not more than 1500 angstroms.

[0101] In one embodiment, the method for preparing a laterally diffused metal oxide semiconductor device further includes:

[0102] In the first step, a source region with a second conductivity type is formed on the upper surface of the body region 101 ; in the second step, a polysilicon gate is formed on the field plate structure, and the polysilicon gate extends along the field plate structure and covers the substrate between the source region and the field plate structure.

[0103] like Figure 8 , a doping process is performed to form a source region 112 of the second conductivity type on the upper surface of the body region 101, and a drain region 114 of the second conductivity type is formed in the drift region 103 between the first oxide structure 206 and the shallow trench isolation structure 102. One end of the drain region 114 contacts the first oxide structure 206, and the other end contacts the shallow trench isolation structure 102. Then, a polysilicon gate structure 116 is formed on the field plate structure. The polysilicon gate structure 116 extends along the field plate structure and covers the substrate 10 between the source region 112 and the field plate structure. That is, the polysilicon gate structure 116 extends along the field plate structure and covers the substrate 10 between the source region 112 and the second oxide structure 108.

[0104] In one embodiment, the method for fabricating a LDMOS device further includes forming a heavily doped region 118 of the first conductivity type in the body region 101 between the source region 112 and the shallow trench isolation structure 102 .

[0105] In one embodiment, the method for preparing a laterally diffused metal oxide semiconductor device further includes the steps of forming a gate oxide layer and a metal interconnection layer.

[0106] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 1At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily performed at the same time, but can be performed at different times. The order of execution of these steps or stages is not necessarily one by one, but can be performed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0107] like Figure 8 In one embodiment, the present application further provides a laterally diffused metal oxide semiconductor device, comprising:

[0108] The substrate 10 may be made of undoped single crystal silicon, impurity-doped single crystal silicon, silicon-on-insulator (SOI), stacked silicon-on-insulator (SSOI), stacked silicon-germanium-on-insulator (S-SiGeOI), silicon-germanium-on-insulator (SiGeOI), or germanium-on-insulator (GeOI). As an example, in this embodiment, the substrate 10 is made of single crystal silicon.

[0109] The body region 101 , having a first conductivity type, is formed in the substrate 10 .

[0110] The drift region 103 has a second conductivity type and is formed in the substrate 10 adjacent to the body region 101. The second conductivity type is opposite to the first conductivity type. When the first conductivity type is P-type, the second conductivity type is N-type. When the first conductivity type is N-type, the second conductivity type is P-type. In this embodiment, the first conductivity type is P-type and the second conductivity type is N-type.

[0111] A field plate structure is formed on the drift region 103. The lower surface of the field plate structure at one end close to the body region 101 is flush with the upper surface of the substrate 10 and has an upwardly extending inclined surface 110. The lower surface of the field plate structure at one end away from the body region 101 is lower than the upper surface of the substrate 10. The thickness of the field plate structure gradually increases from the end close to the body region 101 to the end away from the body region 101 to a preset value.

[0112] The drain region 114 , having the second conductivity type, is formed on the upper surface of the drift region 103 and contacts an end of the field plate structure away from the body region 101 .

[0113] In one embodiment, the angle φ between the inclined surface 110 and the lower surface of the field plate structure near the body region 101 is no less than 30 degrees and no greater than 60 degrees. By adjusting the angle φ, the rate at which the thickness of the field plate structure gradually changes from the body region 101 to the drift region 103 can be adjusted, thereby adjusting device performance.

[0114] In one embodiment, the field plate structure includes:

[0115] The first oxide structure 206 is one end of the field plate structure close to the drain region 114 and is formed on the drift region 103. The upper surface of the first oxide structure 206 is not lower than the upper surface of the substrate 10. The first oxide structure 206 includes a first end and a second end in the direction from the body region 101 to the drift region 103. The thickness of the first oxide structure 206 gradually increases from the first end to the second end to a preset value. The junction between the first end and the second end is the position where the thickness of the first oxide structure 206 changes from less than the preset value to the preset value.

[0116] The second oxide structure 108 is formed on the upper surface of the drift region 103 near the body region 101 and extends along the upper surface of the first end to the junction of the first end and the second end. The inclined surface 110 is the upper surface of the second oxide structure near the body region.

[0117] In one embodiment, the thickness of the second oxide structure 108 is no greater than 1500 angstroms.

[0118] In one embodiment, the first oxide structure 206 includes a local silicon isolation oxide structure, and the local silicon isolation oxide structure is formed by a recess process.

[0119] In one embodiment, the laterally diffused metal oxide semiconductor device further comprises:

[0120] The source region 112 has the second conductivity type and is formed on the upper surface layer of the body region 101;

[0121] A polysilicon gate 116 is formed on the field plate structure and extends along the field plate structure to cover the substrate 10 between the source region 112 and the field plate structure;

[0122] The shallow trench isolation structure 102 is formed in the substrate 10 . The shallow trench isolation structure 102 contacts the drain region 114 , and a portion of the lower surface of the shallow trench isolation structure 102 contacts the drift region 103 .

[0123] In the aforementioned laterally diffused metal oxide semiconductor device, a field plate structure is formed on the drift region. The lower surface of the field plate structure at one end near the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface. The lower surface of the field plate structure at one end away from the body region is lower than the upper surface of the substrate. The thickness of the field plate structure gradually increases to a preset value from the end near the body region to the end away from the body region. By setting the lower surface of the field plate structure at one end near the body region to be flush with the upper surface of the substrate and having an upwardly extending inclined surface, and the thickness of the field plate structure gradually increasing to a preset value from the end near the body region to the end away from the body region, a field plate structure with gradually increasing thickness is formed at the JEFET region without increasing the length of the field plate structure where the lower surface is lower than the upper surface of the substrate (without increasing the spacing of the LDMOS devices), thereby improving the electric field distribution on the device surface and enhancing the reliability of the device.

[0124] Throughout this specification, references to terms such as "some embodiments," "other embodiments," and "desired embodiments" indicate that a particular feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Although these terms are used interchangeably throughout this specification, they do not necessarily refer to the same embodiment or example.

[0125] The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features of the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0126] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A laterally diffused metal oxide semiconductor device, characterized in that: include: substrate; a body region having a first conductivity type and formed in the substrate; a drift region having a second conductivity type, formed in the substrate and adjacent to the body region, the second conductivity type being opposite to the first conductivity type; a field plate structure formed on the drift region, wherein a lower surface of an end of the field plate structure close to the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, a lower surface of an end of the field plate structure away from the body region is lower than the upper surface of the substrate, and a thickness of the field plate structure gradually increases from the end close to the body region to the end away from the body region to a preset value; an angle between the inclined surface and the lower surface of the end of the field plate structure close to the body region is not less than 30 degrees and not more than 60 degrees; a drain region having a second conductivity type, formed on an upper surface layer of the drift region and contacting an end of the field plate structure away from the body region; The field plate structure comprises: a first oxide structure, which is an end of the field plate structure away from the body region, formed on the drift region, and wherein an upper surface of the first oxide structure is not lower than an upper surface of the substrate, the first oxide structure sequentially including a first end and a second end in a direction from the body region toward the drift region, and a thickness of the first oxide structure gradually increases from the first end toward the second end to the preset value; A second oxide structure is formed on the upper surface of the drift region close to the body region, and extends along the upper surface of the first end to the junction of the first end and the second end, and the inclined surface is the upper surface of the second oxide structure close to the body region; the preset value is the thickness of the second end close to the first end.

2. The laterally diffused metal oxide semiconductor device according to claim 1, wherein: The thickness of the second oxide structure is no more than 1500 angstroms.

3. The laterally diffused metal oxide semiconductor device according to claim 1, wherein: The first oxidation structure includes a local silicon isolation oxidation structure, and the local silicon isolation oxidation structure is manufactured by a recess process.

4. The laterally diffused metal oxide semiconductor device according to claim 1, wherein: Also includes: a source region having a second conductivity type and formed on an upper surface layer of the body region; a polysilicon gate formed on the field plate structure and extending along the field plate structure to cover the substrate between the source region and the field plate structure; A shallow trench isolation structure is formed in the substrate, wherein the shallow trench isolation structure contacts the drain region, and a portion of a lower surface of the shallow trench isolation structure contacts the drift region.

5. A method for preparing a laterally diffused metal oxide semiconductor device, characterized in that: include: providing a substrate; forming adjacent body regions and drift regions in the substrate, wherein the body region has a first conductivity type and the drift region has a second conductivity type opposite to the first conductivity type; A field plate structure is formed on the drift region, wherein a lower surface of an end of the field plate structure close to the body region is flush with the upper surface of the substrate and has an upwardly extending inclined surface, and a lower surface of an end of the field plate structure away from the body region is lower than the upper surface of the substrate, and a thickness of the field plate structure gradually increases from the end close to the body region to the end away from the body region to a preset value; an angle between the inclined surface and the lower surface of the end of the field plate structure close to the body region is not less than 30 degrees and not more than 60 degrees; forming a drain region of the second conductivity type on the upper surface layer of the drift region, wherein the drain region is in contact with an end of the field plate structure away from the body region; The step of forming a field plate structure on the drift region includes: forming a first oxide structure on the drift region, wherein the first oxide structure includes a first end and a second end in a direction from the body region to the drift region, and a thickness of the first oxide structure gradually increases from the first end to the second end to the preset value; forming a second oxide structure on an upper surface of the drift region near a side of the body region, wherein the second oxide structure extends along an upper surface of the first end portion to a junction between the first end portion and the second end portion; The first oxide structure is an end of the field plate structure away from the body region, the inclined surface is an upper surface of the second oxide structure close to the body region; and the preset value is the thickness of the second end close to the first end.

6. The preparation method according to claim 5, characterized in that The first oxide structure includes a local silicon isolation oxide structure, and the step of forming the first oxide structure in the drift region includes: forming a hard mask layer on the substrate, wherein a groove is formed in the hard mask layer, and the groove exposes the substrate in a predetermined area of the first oxide structure; forming a sidewall structure contacting the hard mask layer on a sidewall of the groove, wherein a lower surface of the sidewall structure is flush with a bottom of the groove; A local thermal oxidation process is performed to form a first oxidation structure at the bottom of the groove.

7. The preparation method according to claim 5, characterized in that The step of forming a second oxide structure on the upper surface of the drift region close to the body region comprises: forming an oxide film on the upper surface of the substrate; forming a photoresist mask layer on the oxide film, wherein the photoresist mask layer covers the oxide film in the preset area of the second oxide structure; A wet etching process is performed to remove excess oxide film, thereby obtaining a second oxide structure consisting of the remaining oxide film in the preset region of the second oxide structure.

8. The preparation method according to claim 7, characterized in that The thickness of the oxide film is not less than 300 angstroms and not more than 1500 angstroms.

9. The preparation method according to claim 5, characterized in that Also includes: forming a shallow trench isolation structure in the substrate, wherein the shallow trench isolation structure contacts the drain region, and a lower surface of a portion of the shallow trench isolation structure contacts the drift region; forming a source region having a second conductivity type on an upper surface layer of the body region; A polysilicon gate is formed on the field plate structure. The polysilicon gate extends along the field plate structure and covers the substrate between the source region and the field plate structure.

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