A method for manufacturing a shallow trench isolation structure

Abstract

The present invention relates to a method for manufacturing a shallow trench isolation structure, and in particular to the field of semiconductor technology. The method for manufacturing the shallow trench isolation structure comprises: providing a substrate, the substrate comprising a substrate, a pad oxide layer, a pad nitride layer and at least one trench, the pad oxide layer being formed on the surface of the substrate, the pad nitride layer being formed on the surface of the pad oxide layer, the trench being arranged in the substrate, and the upper portion penetrating the pad oxide layer and the pad nitride layer to form an opening; flattening the pad nitride layer; forming an isolation oxide layer in the trench, the isolation oxide layer covering the trench and the pad nitride layer; flattening the isolation oxide layer to obtain the shallow trench isolation structure. The method for manufacturing the shallow trench isolation structure of the present invention can reduce scratches on the surface of the trench isolation structure and improve the yield rate of the shallow trench isolation structure.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for manufacturing a shallow trench isolation structure. Background Art

[0002] In the manufacture of integrated circuits, for the isolation between various independent devices made on a substrate, such as different memory cells, a method of forming shallow trench isolation (STI) is often used. In the prior art, the method for preparing a shallow trench isolation structure is to sequentially form a pad nitride layer and a pad oxide layer on a substrate, then sequentially etch the pad nitride layer, the pad oxide layer and the substrate in a selected area to form a shallow trench, further fill the trench with an isolation oxide layer until the isolation oxide layer covers the pad nitride layer, and then chemically and mechanically polish the filled isolation oxide layer until it is flush with the pad nitride layer to form a shallow trench isolation structure in the shallow trench. The yield rate of the shallow trench isolation structure prepared by the above-mentioned traditional method is relatively low. Therefore, a method for preparing a shallow trench isolation structure is needed to improve the yield rate of the shallow trench isolation structure. Summary of the invention

[0003] In view of the above shortcomings of the prior art, the present invention provides a method for manufacturing a shallow trench isolation structure to improve the problem of low yield of the shallow trench isolation structure.

[0004] To achieve the above-mentioned object and other related objects, the present invention provides a method for manufacturing a shallow trench isolation structure, the manufacturing method comprising:

[0005] Providing a substrate, the substrate comprising a substrate, a pad oxide layer, a pad nitride layer and at least one groove, the pad oxide layer is formed on the surface of the substrate, the pad nitride layer is formed on the surface of the pad oxide layer, the groove is arranged in the substrate, and the upper part penetrates the pad oxide layer and the pad nitride layer to form an opening;

[0006] performing a planarization process on the pad nitride layer;

[0007] forming an isolation oxide layer in the trench, wherein the isolation oxide layer covers the trench and the pad nitride layer;

[0008] The isolation oxide layer is planarized to obtain the shallow trench isolation structure.

[0009] In an example of the present invention, after the pad nitride layer is planarized, the manufacturing method further includes a process of performing a first cleaning treatment on the substrate.

[0010] In an example of the present invention, planarizing the isolation oxide layer includes a first chemical mechanical polishing and a second chemical mechanical polishing, wherein the first chemical mechanical polishing uses a non-selective polishing slurry, and the second chemical mechanical polishing uses a highly selective polishing slurry.

[0011] In an example of the present invention, after the pad nitride layer is planarized, the manufacturing method further includes a process of etching back the pad oxide layer and the pad nitride layer to expose edge corners of the substrate.

[0012] In an example of the present invention, after exposing the edge corners of the substrate, the manufacturing method further includes a process of performing a second cleaning treatment on the substrate.

[0013] In an example of the present invention, after performing a second cleaning process on the substrate, the manufacturing method further includes a process of performing a rounding process on the edge corners.

[0014] In an example of the present invention, the rounded corner processing includes the following steps:

[0015] Etching the edge corners;

[0016] A line oxide layer is formed on the exposed edge corners and the bottom surface and sidewalls of the trench.

[0017] In an example of the present invention, providing the base includes: providing the substrate; depositing the pad oxide layer on the substrate; depositing the pad nitride layer on the surface of the pad oxide layer; and forming the groove on the substrate.

[0018] In an example of the present invention, chemical mechanical polishing is used to planarize the pad nitride layer, and the hardness of the polishing pad is 30-40HA.

[0019] In an example of the present invention, the thickness of the pad nitride layer before planarization is 2 to 3 times the thickness after planarization.

[0020] In summary, the present invention provides a method for manufacturing a shallow trench isolation structure, which forms an isolation oxide layer in the trench after the pad nitride layer is planarized, and the isolation oxide layer covers the trench and the pad nitride layer, and finally the isolation oxide layer is planarized. The unexpected technical effect of the present application is that the pad nitride layer is planarized, which can improve the defects of the interface between the pad nitride layer and the isolation oxide layer, improve the problem that particles easily scratch the isolation oxide layer when the isolation oxide layer is planarized, improve the flatness of the surface of the shallow trench isolation structure, and improve the yield rate of the shallow trench isolation structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0022] Figure 1 A flow chart of preparing a shallow trench isolation structure in one embodiment of the present invention;

[0023] Figure 2 It is a schematic diagram of forming a pad oxide layer on a substrate in one embodiment of the present invention;

[0024] Figure 3 It is a schematic diagram of forming a pad nitride layer on a substrate in one embodiment of the present invention;

[0025] Figure 4 A schematic diagram of forming a photoresist layer in one embodiment of the present invention;

[0026] Figure 5 is a schematic diagram of forming a groove in one embodiment of the present invention;

[0027] Figure 6 A schematic diagram of a planarization process for a pad nitride layer according to an embodiment of the present invention;

[0028] Figure 7 A schematic diagram of a pad nitride layer and a back etching of the pad nitride layer in one embodiment of the present invention;

[0029] Figure 8 A schematic diagram of rounding the edge corners in one embodiment of the present invention;

[0030] Fig. 9 A schematic diagram of depositing an isolation oxide layer in one embodiment of the present invention;

[0031] Fig.10 A schematic diagram of a planarization process for an isolation oxide layer according to an embodiment of the present invention;

[0032] Fig.11 A schematic diagram of removing a pad oxide layer and a pad nitride layer in one embodiment of the present invention;

[0033] Fig.12 It is a microscopic schematic diagram after removing the pad nitride layer and the pad oxide layer according to one embodiment of the present invention;

[0034] Fig.13 A height distribution diagram after a shallow trench isolation structure is formed according to an embodiment of the present invention;

[0035] Fig.14 This is a microscopic schematic diagram of a comparative example of the present invention after the pad nitride layer and the pad oxide layer are removed;

[0036] Fig.15 This is a height distribution diagram after a shallow trench isolation structure is formed according to a comparative example of the present invention.

[0037] Component number description:

[0038] 10. Base; 100. Substrate; 110. Edge corner; 200. Pad oxide layer; 300. Pad nitride layer; 400. Groove; 410. Line oxide layer; 420. Shallow trench isolation structure; 500. Photoresist layer; 510. Groove area; 600. Isolation oxide layer. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0041] In the present invention, it should be noted that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0042] In this article, when it comes to numerical ranges, unless otherwise specified, the distribution of optional values ​​within the numerical range is considered continuous and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined.

[0043] Based on the problems existing in the background technology, the inventor has found through a large number of experiments that particles are easily formed during the formation of the pad nitride layer due to the limitations of the preparation process. If particles are generated near the interface between the pad nitride layer and the isolation oxide layer, it is easy to scrape off the particles on the pad nitride layer during the planarization process of the isolation oxide layer. The fallen particles are easy to scratch the isolation oxide layer, resulting in scratches on the surface of the prepared shallow trench isolation structure, affecting the yield rate of the shallow trench isolation structure. Therefore, the present application provides a method for manufacturing a shallow trench isolation structure to reduce scratches when the isolation oxide layer is planarized and improve the yield rate of the shallow trench isolation structure.

[0044] See also Figures 1 to 10 As shown, the method for manufacturing the shallow trench isolation structure provided by the present invention comprises the following steps:

[0045] S1. Provide Figure 5 The substrate 10 shown includes a substrate 100, a pad oxide layer 200, a pad nitride layer 300 and at least one groove 400. The pad oxide layer 200 is formed on the surface of the substrate 100, the pad nitride layer 300 is formed on the surface of the pad oxide layer 200, and the groove 400 is arranged in the substrate 100, and the upper part penetrates the pad oxide layer 200 and the pad nitride layer 300 to form an opening;

[0046] S2, planarizing the pad nitride layer 300 to form Figure 6 The structure shown;

[0047] S3, such as Fig. 9 As shown, an isolation oxide layer 600 is formed in the trench 400, and the isolation oxide layer 600 covers the trench 400 and the pad nitride layer 300;

[0048] S4, planarizing the isolation oxide layer 600 to obtain Fig.10 A shallow trench isolation structure 420 is shown.

[0049] See also Figure 5 As shown, in step S1 of the present invention, the substrate 100 can be any material suitable for forming a semiconductor structure, such as undoped single crystal silicon, single crystal silicon doped with impurities, 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). The present invention does not limit the specific material and thickness of the substrate 100, and the substrate 100 can be a P-doped semiconductor substrate or an N-doped semiconductor substrate, and the doping type of the impurity can be flexibly set according to the semiconductor structure to be formed. In this embodiment, the substrate 100 is, for example, a silicon substrate. The number of the grooves 400 can be one or more, and illustratively, the number of the grooves 400 is more than one.

[0050] It should be noted that the base 10 may be a purchased semi-finished product, or may be prepared by itself. In one embodiment, the base 10 is prepared by itself based on the substrate 100 .

[0051] See also Figures 2 to 5 As shown, the preparation method of the substrate 10 is as follows:

[0052] See also Figure 2 As shown, in one embodiment of the present invention, a pad oxide layer 200 is formed on the surface of the substrate 100. The pad oxide layer 200 can be used as a protective layer of the substrate 100, and can protect the substrate 100 covered by it in subsequent processes to prevent the substrate 100 from being damaged unnecessarily. Moreover, since the stress of the pad nitride layer 300 formed subsequently is relatively large, when the pad nitride layer 300 is formed on the substrate 100, it is easy to cause dislocation on the surface of the substrate 100. The pad oxide layer 200 can be used to provide a buffer when the pad nitride layer 300 is formed to prevent the pad nitride layer 300 from generating dislocation on the substrate 100. The material of the pad oxide layer 200 can be silicon dioxide or other materials, and the pad oxide layer 200 can be formed, for example, by any one of the methods such as dry oxygen oxidation, wet oxygen oxidation or in-situ steam growth (ISSG). In this embodiment, for example, the pad oxide layer 200 is formed by a dry oxygen oxidation method. For example, the substrate 100 is placed in a furnace tube, oxygen is introduced, and the surface of the substrate 100 reacts with the oxygen at a high temperature to generate a dense pad oxide layer 200. The preparation process of the base 10 may also include cleaning the substrate 100 before forming the pad oxide layer 200 on the substrate 100. By cleaning the substrate 100, impurities on the surface of the substrate 100 can be removed to prevent the impurities from affecting subsequent processes, thereby ensuring the performance of the device. For example, the substrate 100 can be cleaned with a cleaning liquid to clean the substrate 100, or the substrate 100 can be purged with a gas such as nitrogen to clean the substrate 100.

[0053] See also Figure 3As shown, in one embodiment of the present invention, after forming the pad oxide layer 200, a pad nitride layer 300 is formed on the pad oxide layer 200. The material of the pad nitride layer 300 can be silicon nitride, nitride oxide, and in this embodiment, the pad nitride layer 300 is, for example, silicon nitride. The pad nitride layer 300 can be prepared by any one of low-pressure chemical vapor deposition, sub-atmospheric pressure chemical vapor deposition, atmospheric pressure chemical vapor deposition, plasma enhanced chemical vapor deposition or high-density plasma chemical vapor deposition. Exemplarily, when the pad nitride layer 300 is prepared by the low-pressure chemical vapor deposition process, silicon nitride can be generated by reacting ammonia and dichlorosilane. By setting the pad nitride layer 300, it can not only be used as a mask in the subsequent trench 400 formation process, but also protect the substrate 100 from damage when etching the substrate 100, and can also protect the substrate 100 from the influence of the planarization process such as chemical mechanical polishing (CMP) involved in the process of making the shallow trench isolation structure 420.

[0054] See also Figure 4 and Figure 5 As shown, in one embodiment of the present invention, after forming the pad nitride layer 300, a photoresist is coated on the pad nitride layer 300 to form a photoresist layer 500. The type of photoresist material is not limited, and it can be a common positive photoresist material or a negative photoresist material. After coating the photoresist, the coated photoresist is patterned by photolithography processes such as mask exposure and development to expose the groove area 510. With the patterned photoresist layer 500 as the mask layer, the pad nitride layer 300, the pad oxide layer 200 and the substrate 100 are etched in sequence to form grooves 400. The number, position, depth, width and other parameters of the grooves 400 are set according to actual needs and are not limited here. In the present embodiment, the grooves 400 extend from the pad nitride layer 300 to the substrate 100, and the shape of the grooves 400 is rectangular. The pad nitride layer 300, the pad oxide layer 200 and a portion of the substrate 100 can be removed in sequence by dry etching to form a groove 400, and the etching gas includes, for example, one or a mixture of chlorine (Cl2), trifluoromethane (CHF3), difluoromethane (CH2F2), nitrogen trifluoride (NF3), sulfur hexafluoride (SF6) or hydrogen bromide (HBr), or a combination of them and oxygen (O2). After the etching is completed, the photoresist layer 500 is removed by wet cleaning or ashing treatment.

[0055] See also Figure 6As shown, in step S2 of the present invention, the pad nitride layer 300 is planarized to reduce particles on the surface of the pad nitride layer 300, so as to improve the problem that particles are easy to scratch the surface of the shallow trench isolation structure 420 when the subsequent shallow trench isolation structure 420 is formed. In the present invention, the thickness of the pad nitride layer 300 before planarization is 2 to 3 times the thickness after planarization, for example, any value of 2 to 3 times such as 2 times, 2.5 times or 3 times. For example, the pad nitride layer 300 is planarized by chemical mechanical polishing technology. In the semiconductor manufacturing process, the main working principle of chemical mechanical polishing technology is to make the polished surface and the polishing pad move relative to each other under a certain pressure and in the presence of polishing slurry, and to make the polished surface meet the requirements of high flatness, low surface roughness and low defects by means of the mechanical polishing action of nano-abrasives and the chemical action between various chemical reagents. In this embodiment, when grinding the pad nitride layer 300, the substrate 10 is clamped on the grinding head, and a certain pressure is applied to the substrate 10 by the grinding head, so that the substrate 10 rotates on the grinding pad driven by the grinding head for grinding. The grinding pad can be a grinding pad placed above the pad nitride layer 300, or it can be a grinding pad placed below the pad nitride layer 300. In this embodiment, the present invention is described in a manner that the grinding pad is placed below the pad nitride layer 300. Specifically, the pressure plate adsorbs the grinding pad and is placed below the surface to be ground of the pad nitride layer 300. The grinding head is used to adsorb the substrate 10 and fix it above the grinding pad for grinding, and the pad nitride layer 300 faces the grinding pad. In this embodiment, the hardness of the grinding pad is 30~40HA (Shore hardness A), for example, it can be any value between 30~40HA, such as 30HA, 33HA, 35HA, 38HA or 40HA. Selecting a grinding pad with a smaller hardness is conducive to removing particles on the surface of the pad nitride layer 300 and maintaining the integrity and flatness of the surface.

[0056] Generally, during the formation of the pad nitride layer 300, there is a problem that the thickness of the edge region is greater than the thickness of the central region. Multiple regions can be set on the grinding head, and different pressures can be set in the multiple regions respectively. Different pressures can be applied to the substrate 10 by the grinding head to achieve different grinding speeds in different regions of the pad nitride layer 300, so that the surface flatness of the ground pad nitride layer 300 is better. Specifically, since the thickness of the central region of the pad nitride layer 300 is less than the thickness of its edge, the pressure applied by the grinding head to the edge region of the pad nitride layer 300 is greater than the pressure applied to the center when the pad nitride layer 300 is subjected to chemical mechanical grinding. Taking a grinding head with a radius of 150mm as an example, there are five areas on the grinding head. With the center of the grinding head as the 0 point, along the diameter of the grinding head from the center point outward in sequence, the range of 0~40mm is the first area, the range of 40~100mm is the second area, the range of 100~130mm is the third area, the range of 130~145mm is the fourth area, and the range of 145~150mm is the fifth area. The first area is a circle with a radius of 40mm, and the second area, the third area, the fourth area and the fifth area are all annular areas coaxially arranged with the first area. There is no restriction on the zoning standard of the grinding head here. In other embodiments, the area range of the grinding head can be adaptively adjusted according to actual needs, and the pressure of each area can also be adjusted according to the thickness difference of the pad nitride layer 300. Exemplarily, the pressure of the first area is set to 1~2psi (pounds per square inch), the pressure of the second area is set to 1~2psi, the pressure of the third area is set to 1~2psi, the pressure of the fourth area is set to 2~3psi, and the pressure of the fifth area is set to 4~5psi. Applying a greater pressure to the thicker edge area of ​​the pad nitride layer 300 can speed up the grinding rate of the edge area of ​​the pad nitride layer 300, reduce the difference between the edge thickness and the center thickness of the pad nitride layer 300, and reduce the height difference of the shallow trench isolation structure 420 formed later exposed to the substrate 100, which is beneficial to the subsequent process. Setting a lower pressure on the grinding head can improve the problem of particle shedding during the grinding process, and once particles fall off during the grinding process, due to the lower pressure of the grinding head, the particles can reduce the scratches on the pad nitride layer 300, maintain the flatness of the surface of the pad nitride layer 300, and prevent the subsequent process from being affected. Within this pressure range, the particles on the surface of the pad nitride layer 300 can be removed and its surface flatness can be guaranteed, which helps to reduce stress and defects, and reduce the corrections and adjustments required in the subsequent process, thereby improving production efficiency and yield. Here, the pad nitride layer 300 is subjected to chemical mechanical grinding. Since only one material of the pad nitride layer 300 is ground, a non-selective grinding slurry can be selected, such as a grinding slurry including silicon dioxide grinding particles. In other embodiments, a selective polishing slurry may also be selected and adjusted according to actual conditions.After the planarization treatment of the pad nitride layer 300, the surface of the substrate 10 is subjected to a first cleaning treatment to remove impurities and residual grinding slurry generated during the grinding process, to prevent the impurities or grinding slurry from affecting the isolation oxide layer 600 during the subsequent planarization treatment of the isolation oxide layer 600, and to prevent the impurities or grinding slurry from falling into the groove 400 and affecting the subsequent deposition effect of the isolation oxide layer 600. In this embodiment, the cleaning liquid for the first cleaning treatment is, for example, hydrofluoric acid, and the concentration of the hydrofluoric acid can be 0.5-5%, for example, any value in the range of 0.5%, 2%, 3% or 5%, and the cleaning time can be 90-130s, for example, any value in the range of 90-130s, for example, 90s, 100s, 120s or 130s; or the cleaning liquid for the first cleaning treatment can also be, for example, an APM solution (a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water). The cleaning liquid may be a HPM solution (a mixed solution of hydrochloric acid, hydrogen peroxide and deionized water), and the cleaning time may be 20 to 40 s, for example, 20 s, 30 s, 40 s or 40 s.

[0057] See also Figure 7As shown, in one embodiment of the present invention, the method for manufacturing the shallow trench isolation structure 420 further includes performing a pull back process on the pad nitride layer 300 and the pad oxide layer 200 after planarizing the pad nitride layer 300, so as to expose the edge corner 110 of the substrate 100. For example, phosphoric acid may be used to etch back the pad nitride layer 300 first, and then hydrofluoric acid may be used to etch back the pad oxide layer 200; or hydrofluoric acid may be used to etch back the pad oxide layer 200 first, and then phosphoric acid may be used to etch back the pad nitride layer 300. Specifically, taking the example of etching the pad nitride layer 300 first and then etching the pad oxide layer 200, the substrate 10 may be first immersed in a phosphoric acid bath, and then immersed in a hydrofluoric acid bath, and the phosphoric acid and hydrofluoric acid solutions hardly corrode the substrate 100. Alternatively, the pad nitride layer 300 and the pad oxide layer 200 may be etched back in sequence by dry etching. Dry etching includes physical etching, chemical etching and physicochemical etching. Physical etching is achieved by using the sputtering effect generated by ion collision on the surface of the etched structure; chemical etching is achieved by the chemical reaction between the activated etching gas and the etched structure to produce volatile compounds; physicochemical etching is achieved by the physical and chemical interaction between the ions or active radicals in the plasma and the etched structure. The back etching process can expand the sidewalls of the pad nitride layer 300 and the pad oxide layer 200 in the direction of expanding the opening of the groove 400, so that the opening of the groove 400 is expanded, which helps to improve the filling quality of the groove 400. In some embodiments, after the pad nitride layer 300 and the pad oxide layer 200 are back-etched, a second cleaning process is also performed on the substrate 10 to prevent the by-products generated by the back etching process from falling into the groove 400 and affecting the subsequent deposition of the isolation oxide layer 600. The second cleaning treatment can use, for example, hydrofluoric acid or HPM as a cleaning solution for cleaning at room temperature, or can use, for example, APM as a cleaning solution for cleaning at 30-50°C. Exemplarily, the concentration of hydrofluoric acid is 0.5-5%, for example, 0.5%, 2%, 3% or 5%, etc., any value within the range of 0.5%-5%, and the cleaning time is, for example, 90-130s, for example, 90s, 100s, 120s or 130s, etc., any value within the range of 90-130s; the cleaning time of HPM is 20-40s, for example, 20s, 30s or 40s, etc., any value within the range of 20-40s; the cleaning time of APM is 40-70s, for example, 40s, 60s or 70s, etc., any value within the range of 40-70s.

[0058] See also Figure 7 and Figure 8As shown, since the edge corner 110 formed by the back etching process is usually sharp, in one embodiment of the present invention, after the substrate 10 is subjected to the second cleaning process, the edge corner 110 is rounded. Exemplarily, the edge corner 110 is rounded by: wet etching the edge corner 110 with a mixed solution of ammonium hydroxide, hydrogen peroxide and water, so that the edge corner 110 is roughened to obtain a rounded corner. In the mixed solution, the substrate 100 at the edge corner 110 is mainly corroded by hydrogen peroxide, so the roughening of the edge corner 110 can be accelerated by increasing the concentration of hydrogen peroxide in the mixed solution, or by increasing the temperature of the mixed solution. However, the temperature cannot be too high. Too high a temperature may cause the hydrogen peroxide to decompose, thereby causing the roughening effect and speed to deteriorate. The concentration of the mixed solution, the temperature of the mixed solution and the etching time can be adjusted to obtain rounded corners with different degrees of rounding. After the top corners are roughened to obtain rounded corners, when current is passed through the semiconductor device, the high electric field will not be concentrated at the rounded corners, thereby reducing leakage current. In addition, the mixed solution not only rounds the top corners, but also removes particles and natural oxides on the bottom surface and sidewall surface of the trench 400, which is beneficial to the subsequent formation of a liner oxide 410.

[0059] In order to further round the edge corner 110, a line oxide layer 410 is formed on the exposed edge corner 110 and the bottom surface and sidewall of the groove 400. The material of the line oxide layer 410 may be silicon dioxide. The line oxide layer 410 has good density and can repair the damage to the substrate caused during the groove etching process, such as lattice damage and unevenness. Exemplarily, the line oxide layer 410 may be an oxide layer formed by a high-temperature furnace tube. In order to reduce the stress between the line oxide layer 410 and the subsequently formed isolation oxide layer 600, before forming the line oxide layer 410, a line nitride layer may be formed on the surface of the groove 400 and the pad nitride layer 300, and the material of the line nitride layer may be silicon nitride. Exemplarily, a line nitride layer is deposited on the surface of the groove 400 and the pad nitride layer 300 by a furnace tube method. The stress of the shallow trench isolation structure 420 can be balanced by depositing the line nitride layer, so that no gap will appear after the shallow trench isolation structure 420 is formed by subsequently depositing the isolation oxide layer 600, and the carrier mobility of the device is improved.

[0060] See also Fig. 9As shown, in step S3 of the present invention, an isolation oxide layer 600 is formed in the trench 400, and the isolation oxide layer 600 covers the trench 400 and the pad nitride layer 300. The present invention does not limit the deposition method of the isolation oxide layer 600, for example, the isolation oxide layer 600 can be formed in the trench 400 by deposition methods such as chemical vapor deposition (CVD) or high aspect ratio chemical vapor deposition (HARP CVD). In this embodiment, the isolation oxide layer 600 is obtained by, for example, depositing tetraethyl orthosilicate (TEOS). Specifically, tetraethyl orthosilicate and an oxygen-containing precursor are introduced, and the oxygen-containing precursor includes, for example, one of O2 or O3, and the deposition time is controlled to obtain the isolation oxide layer 600. Among them, the chemical vapor deposition speed is fast and can be deposited at a low temperature, and the deposited isolation oxide layer 600 has a good hole filling ability and is not prone to problems such as voids. After the isolation oxide layer 600 is deposited, a high temperature annealing process may be performed to increase the density and stress of the isolation oxide layer 600 .

[0061] See also Fig.10As shown, in step S4 of the present invention, after forming the isolation oxide layer 600, the isolation oxide layer 600 is planarized, for example, the isolation oxide layer 600 is planarized by chemical mechanical polishing, and a portion of the isolation oxide layer 600 is removed by chemical mechanical polishing to obtain a shallow trench isolation structure 420. The present invention does not limit the isolation oxide layer 600 to be planarized to a specific position, and it can be set at any position according to the design requirements of the semiconductor device, for example, the isolation oxide layer 600 in a portion of the trench 400 is planarized to be flush with the pad nitride layer 300 on both sides. In this embodiment, the planarization of the isolation oxide layer 600 includes a first chemical mechanical polishing and a second chemical polishing, and the hardness of the polishing pad is 50~60HD (Shore hardness D), for example, any value of 50HD, 53HD, 55HD, 58HD or 60HD, etc., from 50 to 60HD. When the isolation oxide layer 600 is subjected to the first chemical mechanical polishing, a non-selective polishing slurry may be selected for polishing, for example, a polishing slurry including silicon dioxide polishing particles may be selected to polish the isolation oxide layer 600. In this embodiment, the thickness of the remaining isolation oxide layer 600 after the first chemical mechanical polishing may be adaptively adjusted according to actual needs. Exemplarily, the thickness of the isolation oxide layer 600 on the surface of the pad nitride layer 300 is polished to 1200Å~1500Å by controlling the polishing time, for example, any value of 1200Å~1500Å such as 1200Å, 1300Å, 1400Å or 1500Å. In this embodiment, during the first chemical mechanical polishing, the pressure of the first region is set to 3~4psi, the pressure of the second region is set to 3~4psi, the pressure of the third region is set to 3~4psi, the pressure of the fourth region is set to 2~3psi, and the pressure of the fifth region is set to 6~7psi. When the isolation oxide layer 600 is subjected to the second chemical mechanical polishing, a polishing slurry with higher selectivity is selected for polishing, for example, a polishing slurry including cerium oxide polishing particles is selected for polishing. The polishing rate of the isolation oxide layer 600 is faster when a relatively high polishing slurry is selected, and the polishing rate of the pad nitride layer 300 is slower, so the pad nitride layer 300 can be used as a stop layer for the second chemical mechanical polishing. In this embodiment, during the second chemical mechanical polishing, the pressure of the first area is set to 3~4psi, the pressure of the second area is set to 3~4psi, the pressure of the third area is set to 3~4psi, the pressure of the fourth area is set to 3~4psi, and the pressure of the fifth area is set to 7~8psi. During the two chemical mechanical polishings, the edge pressure of the polishing head is set to be greater than the center pressure, which can further reduce the height difference of the shallow trench isolation structure 420 exposed to the substrate 100, that is, reduce the difference in the height difference between the active area and the shallow trench isolation structure 420 in the edge area and the center area. After each chemical mechanical polishing, the surface of the substrate 10 is cleaned to remove impurities and residual polishing slurry generated during the polishing process to prevent affecting subsequent production.

[0062] See also Fig.11 As shown, in one embodiment of the present invention, after the isolation oxide layer 600 is planarized, the pad oxide layer 200 and the pad nitride layer 300 on the surface of the substrate 100 are removed. The present invention does not limit the removal method of the pad oxide layer 200 and the pad nitride layer 300, for example, dry etching, wet etching, or a combination of dry etching and wet etching are used to remove them. In this embodiment, for example, phosphoric acid is used to etch the pad nitride layer 300, and hydrofluoric acid is used to remove the pad oxide layer 200.

[0063] In one embodiment of the present invention, the shallow trench isolation structure 420 is prepared by the manufacturing method of the present application. After removing the pad oxide layer 200 and the pad nitride layer 300, the surface microstructure is as follows: Fig.12 As shown, the height distribution diagram before removing the pad oxide layer 200 and the pad nitride layer 300 is as shown in FIG. Fig.13 As a control, the pad nitride layer 300 is not planarized, and other preparation conditions are kept the same. The surface microstructure after removing the pad oxide layer 200 and the pad nitride layer 300 is as shown in FIG. Fig.14 As shown, the height distribution diagram before removing the pad oxide layer 200 and the pad nitride layer 300 is as shown in FIG. Fig.15 shown. Fig.12 and Fig.14 By comparison, it can be seen that the surface of the shallow trench isolation structure 420 manufactured according to the manufacturing method of the present invention has no obvious scratches, while the surface of the shallow trench isolation structure 420 manufactured in the comparative example has obvious scratches. Fig.13 and Fig.15 By comparison, it can be seen that the shallow trench isolation structure 420 manufactured by the manufacturing method of the present invention has a relatively flat surface and a small height difference, while the height difference of the shallow trench isolation structure 420 manufactured in the comparative example is large. Furthermore, the height difference of the semiconductor surface can also be evaluated by specific numerical values, and the formula is U%=(maximum height-minimum height) / (average height*2).

[0064] In summary, the present invention provides a method for manufacturing a shallow trench isolation structure, which forms an isolation oxide layer in the trench after the pad nitride layer is planarized, and the isolation oxide layer covers the trench and the pad nitride layer, and finally the isolation oxide layer is planarized. The unexpected technical effect of the present application is that the pad nitride layer is planarized, which can improve the defects of the interface between the pad nitride layer and the isolation oxide layer, improve the problem that particles easily scratch the isolation oxide layer when the isolation oxide layer is planarized, improve the flatness of the surface of the shallow trench isolation structure, and improve the yield rate of the shallow trench isolation structure.

[0065] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for manufacturing a shallow trench isolation structure, characterized in that: include: Providing a substrate, the substrate comprising a substrate, a pad oxide layer, a pad nitride layer and at least one groove, the pad oxide layer is formed on the surface of the substrate, the pad nitride layer is formed on the surface of the pad oxide layer, the groove is arranged in the substrate, and the upper part penetrates the pad oxide layer and the pad nitride layer to form an opening; Performing a planarization treatment on the pad nitride layer, wherein the thickness of the pad nitride layer before the planarization treatment is 2 to 3 times the thickness after the planarization treatment; forming an isolation oxide layer in the trench, wherein the isolation oxide layer covers the trench and the pad nitride layer; Performing a planarization process on the isolation oxide layer until the isolation oxide layer in the trench is flush with the pad nitride layers on both sides, thereby obtaining the shallow trench isolation structure; In the process of planarizing the pad nitride layer, the pressure applied by the grinding head used to adsorb the substrate to the edge area of ​​the pad nitride layer is greater than the pressure applied to the center of the pad nitride layer, and the hardness of the grinding pad used to grind the pad nitride layer is 30~40HA.

2. The method for manufacturing a shallow trench isolation structure according to claim 1, characterized in that: After the pad nitride layer is planarized, the manufacturing method further includes a process of performing a first cleaning treatment on the substrate.

3. The method for manufacturing a shallow trench isolation structure according to claim 1, characterized in that: The planarization treatment of the isolation oxide layer includes a first chemical mechanical polishing and a second chemical mechanical polishing. The first chemical mechanical polishing uses a non-selective polishing slurry, and the second chemical mechanical polishing uses a highly selective polishing slurry.

4. The method for manufacturing a shallow trench isolation structure according to claim 1, characterized in that: After the pad nitride layer is planarized, the manufacturing method further includes a process of etching back the pad oxide layer and the pad nitride layer to expose the edge corners of the substrate.

5. The method for manufacturing a shallow trench isolation structure according to claim 4, characterized in that: After exposing the edge corners of the substrate, the manufacturing method further includes a process of performing a second cleaning treatment on the substrate.

6. The method for manufacturing a shallow trench isolation structure according to claim 5, characterized in that: After the substrate is subjected to a second cleaning process, the manufacturing method further comprises a process of rounding the edge corners.

7. The method for manufacturing a shallow trench isolation structure according to claim 6, characterized in that: The rounding process comprises the following steps: Etching the edge corners; A line oxide layer is formed on the exposed edge corners and the bottom surface and sidewalls of the trench.

8. The method for manufacturing a shallow trench isolation structure according to claim 1, characterized in that: The providing of a substrate comprises: providing the substrate; depositing the pad oxide layer on the substrate; Depositing the pad nitride layer on the surface of the pad oxide layer; The trench is formed on the substrate.

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