Manufacturing method of shallow trench isolation structure

Abstract

The invention discloses a manufacturing method of a shallow trench isolation structure, and belongs to the technical field of semiconductors, and the manufacturing method of the shallow trench isolation structure comprises the following steps: providing a substrate, and forming a front oxidation layer and a nitride layer on the substrate; etching the nitride layer, the pre-oxidation layer and a part of the substrate to form a shallow trench; depositing an isolation dielectric layer in the shallow trench and flattening the isolation dielectric layer to form a shallow trench isolation structure; removing the nitride layer, wherein the height difference between the surface of the shallow trench isolation structure and the surface of the pre-oxidation layer forms an initial step height; according to the height relation between the initial step height and the preset step height, selecting a wet oxygen oxidation process or an in-situ water vapor growth process to oxidize the substrate, and thickening the pre-oxidation layer; and performing synchronous wet etching on the shallow trench isolation structure and the pre-oxidation layer, and adjusting the initial step height to a preset step height. Through the manufacturing method of the shallow trench isolation structure disclosed by the invention, the performance of the formed semiconductor device can be improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor, and particularly relates to a manufacturing method of a shallow trench isolation structure. BACKGROUND

[0002] In an integrated circuit, a shallow trench isolation structure (STI) is arranged between adjacent semiconductor devices to prevent current leakage between the adjacent semiconductor devices and to play other electrical performance roles. The step height of the shallow trench isolation structure affects the performance of the device. When the step height is too low, stress is concentrated at the corner between the step and the front oxide layer, which forms a recess, resulting in active area leakage during use. When the step height is too high, it affects the flatness of the surface of the semiconductor device, and the step of the shallow trench isolation structure is prone to residual polysilicon during subsequent etching of polysilicon to form a gate, thereby causing short circuit of the semiconductor device and affecting the yield of the device. SUMMARY

[0003] The present application aims to provide a manufacturing method of a shallow trench isolation structure, which can solve the problem of the step height of the shallow trench isolation not meeting the expectation.

[0004] To solve the above technical problems, the present application is implemented by the following technical scheme: The present application provides a manufacturing method of a shallow trench isolation structure, comprising the following steps: providing a substrate and forming a front oxide layer and a nitride layer on the substrate; etching the nitride layer, the front oxide layer and part of the substrate to form a shallow trench; depositing an isolation medium layer in the shallow trench and planarizing to form a shallow trench isolation structure; removing the nitride layer, and the height difference between the surface of the shallow trench isolation structure and the surface of the front oxide layer forms an initial step height; selecting an in-situ water vapor growth process or a wet oxygen oxidation process to oxidize the substrate according to the height relationship between the initial step height and a preset step height to thicken the front oxide layer; and synchronously etching the shallow trench isolation structure and the front oxide layer by a wet etching method to adjust the initial step height to the preset step height.

[0005] In an embodiment of the present application, a layer of silicon oxide is deposited in the shallow trench by a high-density plasma chemical vapor deposition process to form the isolation medium layer.

[0006] In an embodiment of the present application, when the initial step height is higher than the preset step height, the in-situ water vapor growth process is used to oxidize the substrate to thicken the front oxide layer.

[0007] In one embodiment of the present application, when the initial step height is lower than the preset step height, the substrate is oxidized by using the wet oxygen oxidation process to thicken the front oxidation layer.

[0008] In one embodiment of the present application, the method for manufacturing the shallow trench isolation structure further comprises: adjusting the thickening thickness of the front oxidation layer according to the difference between the initial step height and the preset step height.

[0009] In one embodiment of the present application, the greater the difference between the initial step height and the preset step height, the greater the thickening thickness of the front oxidation layer; the smaller the difference between the initial step height and the preset step height, the smaller the thickening thickness of the front oxidation layer.

[0010] In one embodiment of the present application, the solution for synchronously etching the shallow trench isolation structure and the front oxidation layer is hydrofluoric acid solution or buffer oxide etching solution.

[0011] In one embodiment of the present application, the method for manufacturing the shallow trench isolation structure further comprises: adjusting the process condition of wet etching according to the difference between the intermediate step height of the shallow trench isolation structure after thickening the front oxidation layer and the preset step height.

[0012] In one embodiment of the present application, the adjusted process condition of wet etching comprises one or several of etching solution ratio, etching temperature and etching time.

[0013] In one embodiment of the present application, the front oxidation layer is formed on the substrate by using the wet oxygen oxidation process.

[0014] In summary, the method for manufacturing the shallow trench isolation structure provided by the present application has the unexpected effect that the front oxidation layer is thickened by different thermal oxidation processes to change the compactness of the front oxidation layer, and then the etching selectivity ratio of the shallow trench isolation structure and the front oxidation layer is greater than 1 or less than 1 in the subsequent wet etching process. Therefore, under the conditions that the initial step height is greater than the preset step height and the initial step height is less than the preset step height, the initial step height can be reduced or increased by selecting the thickening process of the front oxidation layer and then synchronously etching the shallow trench isolation structure and the front oxidation layer, and then the initial step height is adjusted to the preset step height, so that the step height of the shallow trench isolation structure meets the requirements.

[0015] Of course, it is not necessary for any product implementing the present application to achieve all the advantages mentioned above. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed for the description of the embodiments. Obviously, the drawings in the following description only show some embodiments of the present application, and those skilled in the art can easily obtain other drawings from these drawings without any creative effort.

[0017] Figure 1 Flow chart for forming a shallow trench isolation structure in an embodiment.

[0018] Figure 2 Structural schematic diagram for forming a pre-oxidation layer, a nitride layer and a photoresist layer in an embodiment.

[0019] Figure 3 Structural schematic diagram for forming a patterned photoresist layer in an embodiment.

[0020] Figure 4 Structural schematic diagram for forming a shallow trench in an embodiment.

[0021] Figure 5 Structural schematic diagram for forming an isolation medium layer in an embodiment.

[0022] Figure 6 Structural schematic diagram for forming a shallow trench isolation structure in an embodiment.

[0023] Figure 7 Structural schematic diagram for an initial step height in an embodiment.

[0024] Figure 8 Structural schematic diagram for thickening a pre-oxidation layer in an embodiment.

[0025] Figure 9 Structural schematic diagram for wet etching the thickened pre-oxidation layer in an embodiment.

[0026] Label explanation: 101, substrate; 1011, shallow trench; 102, pre-oxidation layer; 103, nitride layer; 104, photoresist layer; 1041, patterned photoresist layer; 1042, opening; 105, isolation medium layer; 1051, shallow trench isolation structure; H1, initial step height; H2, intermediate step height; H3, preset step height. DETAILED DESCRIPTION

[0027] The embodiments of the present application will be described below through specific concrete examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the present specification. The present application can also be implemented or applied through other different specific embodiments, and each detail in the present specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present application.

[0028] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0029] In this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0030] The development trend of semiconductor integrated circuits is to increase density and shrink components. In integrated circuits, shallow trench isolation structures are used to isolate semiconductor devices formed on a substrate or to isolate semiconductor devices from other components. With the advancement of semiconductor manufacturing technology, shallow trench isolation technology has gradually replaced other isolation methods used in traditional semiconductor device manufacturing, such as Localized Oxidation of Silicon (LOCOS).

[0031] Please see Figures 1 to 9 As shown, in this application, the step height of the shallow trench isolation structure 1051 refers to the distance from the surface of the shallow trench isolation structure 1051 to the surface of the preceding oxide layer 102. When the step height of the shallow trench isolation structure 1051 differs from the preset step height H3, it will affect the subsequent fabrication process of the shallow trench isolation structure 1051 and the yield of the formed semiconductor device. This invention provides a method for fabricating a shallow trench isolation structure, which can make the step height of the formed shallow trench isolation structure equal to the preset height. Specifically, the method for fabricating a shallow trench isolation structure provided by this invention includes steps S110 to S160.

[0032] Step S110: Provide a substrate and form a pre-oxide layer and a nitride layer on the substrate.

[0033] Step S120: Etch the nitride layer, the pre-oxide layer and part of the substrate to form a shallow trench.

[0034] Step S130: Deposit and planarize the isolation medium layer in the shallow trench to form a shallow trench isolation structure.

[0035] Step S140: Remove the nitrided layer. The height difference between the surface of the shallow trench isolation structure and the surface of the pre-oxide layer forms the initial step height.

[0036] Step S150: Based on the height relationship between the initial step height and the preset step height, select either wet oxygen oxidation process or in-situ water vapor growth process to oxidize the substrate and thicken the pre-oxidation layer.

[0037] Step S160: Simultaneously wet-etch the shallow trench isolation structure and the pre-oxide layer, and adjust the initial step height to the preset step height.

[0038] Please see Figure 2 As shown, in one embodiment of the present invention, a substrate 101 is first provided, which is, for example, a silicon substrate forming a semiconductor structure. The material of the substrate 101 can be undoped single-crystal silicon, doped single-crystal silicon, silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), and germanium-on-insulator (GeOI), etc. In this embodiment, the substrate 101 is doped single-crystal silicon, and is a p-type doped silicon substrate.

[0039] Please see Figure 2 As shown, in one embodiment of the present invention, a pre-oxide layer 102 is first formed on the substrate 101. The pre-oxide layer 102 serves as a buffer layer to improve the stress between the substrate 101 and the subsequently formed nitride layer 103. In this application, the substrate 101 can be oxidized by wet oxygen oxidation to form a pre-oxide layer 102 on the surface of the substrate 101. Specifically, the reaction temperature inside the furnace tube is set to, for example, 700°C to 1200°C. The substrate 101 is placed inside the furnace tube, and a predetermined ratio of oxygen and hydrogen is introduced. Inside the furnace tube, the introduced oxygen and hydrogen react to produce water. The water reacts with the silicon on the surface of the substrate 101, causing the silicon on the surface of the substrate 101 to oxidize and form silicon oxide, which is the pre-oxide layer 102. The thickness of the pre-oxide layer 102 is, for example, 100 Å to 200 Å.

[0040] Please see Figure 2 As shown, in one embodiment of the present invention, after forming a front oxide layer 102 on the substrate 101, a nitride layer 103 is formed on the front oxide layer 102. The nitride layer 103 is, for example, a silicon nitride layer, and can be formed, for example, by a method such as low-pressure chemical vapor deposition (LPCVD). The thickness of the nitride layer 103 is, for example, 1000 Å to 1800 Å. During the subsequent formation of the shallow trench 1011, the nitride layer 103 acts as a hard mask, protecting the substrate 101 from damage during the formation of the shallow trench 1011.

[0041] Please see Figures 2 to 4 As shown, in one embodiment of the present invention, after the nitride layer 103 is formed, the nitride layer 103, the pre-oxide layer 102 and a portion of the substrate 101 are etched sequentially to form a shallow trench 1011 in the substrate 101.

[0042] For details, please refer to Figures 2 to 4 As shown, in one embodiment of the present invention, after forming the nitride layer 103, a photoresist layer 104 is coated on the nitride layer 103, and the photoresist layer 104 at the location of the shallow trench 1011 to be formed is removed by an alkaline solution wet process or a dry ashing process, forming an opening 1042 on the photoresist layer 104 to form a patterned photoresist layer 1041. The opening 1042 in the patterned photoresist layer 1041 defines the location of the shallow trench 1011 on the substrate 101.

[0043] Please see Figures 2 to 4 As shown, in one embodiment of the present invention, after forming the patterned photoresist layer 1041, the nitride layer 103 and the pre-oxide layer 102 at the bottom of the opening 1042 of the patterned photoresist layer 1041 are etched sequentially. Then, the patterned photoresist layer 1041 is removed, and the substrate 101 is etched using the nitride layer 103 and the pre-oxide layer 102 as a mask layer, forming a shallow trench 1011 in the substrate 101.

[0044] Please see Figures 2 to 4 As shown, in one embodiment of the present invention, since the nitride layer 103, the pre-oxide layer 102 and the substrate 101 are made of different materials, two or more etching processes are required during etching.

[0045] Please see Figures 2 to 4 As shown, in some embodiments of the present invention, dry etching can be used when etching the nitride layer 103 and the pre-oxide layer 102. For example, a mixed gas of carbon tetrafluoride (CF4) and trifluoromethane (CHF3) can be used to remove the nitride layer 103 and the pre-oxide layer 102 below the opening 1042 in a single etching process. In other embodiments, wet etching can be used to etch the nitride layer 103 and the pre-oxide layer 102 in two steps. For example, the nitride layer 103 can be etched first with hot phosphoric acid at a temperature between 140°C and 200°C, and then the pre-oxide layer 102 can be etched with hydrofluoric acid at a concentration between 1% and 10%.

[0046] Please see Figures 2 to 4As shown, in one embodiment of the present invention, one or more of chlorine (Cl2), difluoromethane (CF2), nitrogen trifluoride (NF3), sulfur hexafluoride (SF6), and hydrogen bromide (HBr), or one or more of them mixed with nitrogen (N2) and oxygen (O2), can be used to dry etch the substrate 101. Specifically, for example, a mixed gas of chlorine (Cl2), nitrogen (N2), and oxygen (O2) is used to etch the substrate 101 to form shallow trenches 1011.

[0047] Please see Figures 4 to 6 As shown, in one embodiment of the present invention, after forming a shallow trench 1011 on a substrate 101, an isolation dielectric layer 105 is deposited in the shallow trench 1011 and planarized to form a shallow trench isolation structure 1051. In this application, a layer of silicon oxide is first deposited in the shallow trench 1011 using a high-density plasma-chemical vapor deposition (HDP-CVD) process to form the isolation dielectric layer 105. The isolation dielectric layer 105 fills the shallow trench 1011, and the height of the isolation dielectric layer 105 is higher than that of the nitride layer 103, covering the nitride layers 103 on both sides of the shallow trench 1011. The thickness of the isolation dielectric layer 105 is, for example, 4000 Å to 5500 Å. Specifically, when depositing the isolation dielectric layer 105 using the high-density plasma-chemical vapor deposition process, the deposition and etching processes are performed cyclically within the same reaction chamber. The isolation dielectric layer 105 is deposited by introducing silane (SiH4) and oxygen (O2) into the reaction chamber, and etched by sputtering argon (Ar) and oxygen (O2). During the cyclic deposition and etching process, pinch-offs and voids can be avoided during the deposition of the isolation dielectric. Furthermore, the isolation dielectric layer 105 formed by the high-density plasma chemical vapor deposition process exhibits high density, good step coverage, and excellent dielectric properties.

[0048] Please see Figures 5 to 6 As shown, in one embodiment of the present invention, after the isolation medium layer 105 is formed, it is ground by a chemical mechanical polishing (CMP) process. During this process, the nitride layer 103 can be used as a stop layer in the CMP process of the isolation medium layer 105. The ground isolation medium layer 105 forms a shallow trench isolation structure 1051, and the height of the formed shallow trench isolation structure 1051 is consistent with that of the nitride layers 103 on both sides.

[0049] Please see Figures 6 to 7As shown, in one embodiment of the present invention, after forming the shallow trench isolation structure 1051, the nitride layer 103 is removed. Specifically, the nitride layer 103 can be removed by wet etching. The etchant used in wet etching is, for example, hot phosphoric acid, which can be heated to, for example, 85% concentrated phosphoric acid at, for example, 150°C to 180°C to etch the nitride layer 103. At this time, the etching rate of the etchant on silicon oxide is extremely low, which can avoid damage to the shallow trench isolation structure 1051 and the pre-oxide layer 102.

[0050] Please see Figures 6 to 7 As shown, in one embodiment of the present invention, after removing the nitride layer 103, the shallow trench isolation structure 1051 is higher than the preceding oxide layer 102, forming a step between the shallow trench isolation structure 1051 and the preceding oxide layer 102. The height difference between the surface of the shallow trench isolation structure 1051 and the surface of the preceding oxide layer 102 forms the initial step height H1. At this time, due to the preceding chemical mechanical polishing and wet etching processes, the initial step height H1 may be higher than or lower than the preset step height H3. When the step height is higher than the preset step height H3, it will not only affect the flatness of the subsequently formed semiconductor device surface, but also, in the subsequent gate formation and gate etching processes, polysilicon is likely to remain at the step of the shallow trench isolation structure 1051, leading to short circuits in the semiconductor device and affecting device yield. When the step height is lower than the preset step height H3, stress concentration occurs at the corner between the step and the preceding oxide layer 102, forming a depression, which leads to leakage in the active area of ​​the semiconductor device. Therefore, after removing the nitrided layer 103, it is necessary to readjust the step height of the shallow trench isolation structure 1051.

[0051] Please see Figures 7 to 9 As shown, in one embodiment of the present invention, when adjusting the step height of the shallow trench isolation structure 1051, the substrate 101 is first oxidized using a wet oxygen oxidation process or an in-situ steam generation (ISSG) process based on the height relationship between the initial step height H1 and the preset step height H3, thereby thickening the pre-oxide layer 102. Specifically, when the initial step height H1 is higher than the preset step height H3, the substrate 101 is oxidized using an in-situ steam generation process to thicken the pre-oxide layer 102. When the initial step height H1 is lower than the preset step height H3, the substrate 101 is oxidized using a wet oxygen oxidation process to thicken the pre-oxide layer 102.

[0052] Please see Figures 7 to 9As shown, in this application, both wet oxidation and in-situ water vapor growth processes are types of thermal oxidation processes, which are completed through diffusion and chemical reactions. During thermal oxidation, silicon in substrate 101 reacts with oxygen to form a silicon oxide layer on the silicon surface. When growing, for example, 1 Å of silicon oxide, 0.44 Å of silicon is consumed. Therefore, after forming the thickened pre-oxide layer 102, the step height of the shallow trench isolation structure 1051 has an intermediate step height H2.

[0053] Please see Figures 7 to 9 As shown, this application does not limit the thickness of the thickened pre-oxide layer 102 or the intermediate step height H2 of the shallow trench isolation structure 1051 after thickening the pre-oxide layer 102. Specifically, the thickness of the pre-oxide layer 102 can be adjusted based on the difference between the initial step height H1 and the preset step height H3. The larger the difference between the initial step height H1 and the preset step height H3, the larger the thickness of the pre-oxide layer 102 and the smaller the intermediate step height H2 of the shallow trench isolation structure 1051. The smaller the difference between the initial step height H1 and the preset step height H3, the smaller the thickness of the pre-oxide layer 102 and the larger the intermediate step height H2 of the shallow trench isolation structure 1051.

[0054] Please see Figures 7 to 9 As shown, it should be noted that the intermediate step height H2 formed in this application will be less than the initial step height H1. When it is necessary to increase the initial step height H1, the step of thickening the pre-oxide layer 102 will reduce the initial step height H1. In this case, the reduction in the intermediate step height H2 and the reduction in the initial step height H1 can be achieved using a wet etching process. When simultaneously wet etching the shallow trench isolation structure 1051 and the pre-oxide layer 102, the etching selectivity ratio of the shallow trench isolation structure 1051 and the pre-oxide layer 102 can be increased.

[0055] Please see Figures 7 to 9 As shown, in this application, the wet oxidation process involves reacting a mixture of oxygen (O2) and water vapor (H2O) with silicon at a high temperature of, for example, 800°C to 1200°C to generate silicon oxide (SiO2). During the formation of the silicon oxide layer using the wet oxidation process, water molecules decompose into hydroxyl radicals at high temperatures, which diffuse faster than oxygen, resulting in a higher oxidation rate. Furthermore, the silicon oxide layer formed using the wet oxidation process has a relatively loose structure and low density. In contrast, the in-situ water vapor growth process directly introduces hydrogen (H2) and oxygen (O2) into the oxidation furnace, generating water vapor (H2O) in situ at a high temperature of, for example, 900°C to 1100°C, thereby oxidizing the silicon on the substrate 101. Moreover, the silicon oxide layer formed using the in-situ water vapor growth process has a denser structure and higher density.

[0056] Please seeFigures 7 to 9 As shown in this application, during the process of thickening the pre-oxide layer 102 using a wet oxidation process or an in-situ water vapor growth process, the performance of the dense shallow trench isolation structure 1051 remains unchanged, while the performance of the porous pre-oxide layer 102 changes. This results in an etch selectivity ratio greater than 1 between the shallow trench isolation structure 1051 formed using a high-density plasma chemical vapor deposition process and the pre-oxide layer 102 thickened using an in-situ water vapor growth process during subsequent simultaneous wet etching. Conversely, when simultaneously wet etching the shallow trench isolation structure 1051 formed using a high-density plasma chemical vapor deposition process and the pre-oxide layer 102 thickened using a wet oxidation process, the etch selectivity ratio between the shallow trench isolation structure 1051 and the pre-oxide layer 102 is less than 1. Therefore, when the initial step height H1 is higher than the preset step height H3, the pre-oxide layer 102 is thickened using an in-situ water vapor growth process. During simultaneous wet etching of the shallow trench isolation structure 1051 and the pre-oxide layer 102, the etching rate of the shallow trench isolation structure 1051 is greater than that of the pre-oxide layer 102, thus reducing the step height. When the initial step height H1 is lower than the preset step height H3, the pre-oxide layer 102 is thickened using a wet oxygen oxidation process. During simultaneous wet etching of the shallow trench isolation structure 1051 and the pre-oxide layer 102, the etching rate of the shallow trench isolation structure 1051 is less than that of the pre-oxide layer 102, thus increasing the step height. This allows for the redefinition of the step height by changing the thickening process of the pre-oxide layer 102.

[0057] Please see Figures 7 to 9As shown, in one embodiment of the present invention, after thickening the pre-oxide layer 102, the shallow trench isolation structure 1051 and the pre-oxide layer 102 are simultaneously wet-etched to adjust the intermediate step height H2 to a preset step height H3, thereby adjusting the initial step height H1 to the preset step height H3. In this application, the etching solution for simultaneously wet-etching the shallow trench isolation structure 1051 and the pre-oxide layer 102 is a hydrofluoric acid (HF) solution or a buffered oxide etch (BOE). When simultaneously wet etching the shallow trench isolation structure 1051 and the pre-oxide layer 102 using an etchant, the etching selectivity range of the etchant for the shallow trench isolation structure 1051 formed by high-density plasma chemical vapor deposition (HDPV) and the pre-oxide layer 102 thickened by in-situ water vapor growth is, for example, 1.4:1 to 1.6:1. The etching selectivity range of the etchant for the shallow trench isolation structure 1051 formed by HDPV and the pre-oxide layer 102 thickened by wet oxygen oxidation is, for example, 1:4 to 1:2.5. Therefore, before simultaneously wet etching the shallow trench isolation structure 1051 and the pre-oxide layer 102, the etching process conditions can be adjusted based on the difference between the intermediate step height H2 and the preset step height H3, thereby adjusting the intermediate step height H2 to the preset step height H3.

[0058] Combination Figure 8 As shown in Table 1, in one embodiment of the present invention, the relationship between etching process conditions and etching solution on the etching depth and etching selectivity of the shallow trench isolation structure 1051 formed by high-density plasma chemical vapor deposition and the pre-oxide layer 102 thickened by in-situ water vapor growth process is as follows.

[0059] Table 1. Relationship between etching process conditions and etching solution on the etching depth and etch selectivity of shallow trench isolation structures formed by HDP process and pre-oxide layer thickened by ISSG process.

[0060] Combination Figure 8 As shown in Table 2, in one embodiment of the present invention, the relationship between etching process conditions and etching solution on the etching depth and etching selectivity of the shallow trench isolation structure 1051 formed by high-density plasma chemical vapor deposition and the pre-oxide layer 102 thickened by wet oxygen oxidation process is as follows.

[0061] Table 2. Relationship between etching process conditions and etching solution on the etching depth and etch selectivity of shallow trench isolation structures formed by HDP deposition and pre-oxide layers thickened by wet oxidation.

[0062] As shown in Table 1, when the etch solution ratio of wet etching is different, the etching depth and etch selectivity of the wet etching solution for the shallow trench isolation structure 1051 formed by high-density plasma chemical vapor deposition process and the pre-oxide layer 102 thickened by in-situ water vapor growth process are different.

[0063] As shown in Table 2, when the etch solution ratio, etching temperature and etching time of wet etching are different, the etching depth and etching selectivity of the wet etching solution for the shallow trench isolation structure 1051 formed by high-density plasma chemical vapor deposition process and the pre-oxide layer 102 thickened by wet oxygen oxidation process are different.

[0064] In Tables 1 and 2, the etching solution ratios refer to the volume ratios of the solutions. H₂O:HF = 10:1 means the volume ratio of H₂O to HF is 10:1; H₂O:HF = 100:1 means the volume ratio of H₂O to HF is 100:1; and the mass percentage of HF concentration ranges from 40% to 49%, specifically 49%. HF:NH₄F = 6:1 means the volume ratio of HF to NH₄F is 6:1; and the mass percentage of NH₄F concentration ranges from 15% to 40%, specifically 40%.

[0065] Therefore, after thickening the pre-oxide layer 102, one or more of the following can be adjusted during wet etching: the etchant ratio, etching temperature, and etching time. Then, the shallow trench isolation structure 1051 and the pre-oxide layer 102 are simultaneously wet-etched, adjusting the intermediate step height H2 to the preset step height H3.

[0066] In summary, this invention provides a method for fabricating a shallow trench isolation structure. The semiconductor structure fabrication method includes: providing a substrate and forming a pre-oxide layer and a nitride layer on the substrate; etching the nitride layer, the pre-oxide layer, and a portion of the substrate to form a shallow trench; depositing and planarizing an isolation dielectric layer within the shallow trench to form a shallow trench isolation structure; removing the nitride layer, and the height difference between the surface of the shallow trench isolation structure and the surface of the pre-oxide layer forming an initial step height; based on the height relationship between the initial step height and a preset step height, selecting a wet oxygen oxidation process or an in-situ water vapor growth process to oxidize the substrate and thicken the pre-oxide layer; adjusting the etchant ratio and simultaneously wet etching the shallow trench isolation structure and the pre-oxide layer to adjust the initial step height to the preset step height.

[0067] The present invention provides a method for fabricating a shallow trench isolation structure, with the unexpected effect of thickening the pre-oxide layer through different thermal oxidation processes, thereby altering the density of the pre-oxide layer. This results in an etching selectivity ratio between the shallow trench isolation structure and the pre-oxide layer that is greater than or less than 1 during subsequent wet etching. Therefore, under both conditions where the initial step height is greater than or less than the preset step height, by selecting the pre-oxide layer thickening process and simultaneously wet etching the shallow trench isolation structure and the pre-oxide layer, the initial step height can be reduced or increased, thereby adjusting the initial step height to the preset step height, ensuring that the step height of the shallow trench isolation structure meets the requirements.

[0068] The embodiments of the present invention disclosed above are merely illustrative of the invention. The embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for manufacturing a shallow trench isolation structure, characterized in that, Includes the following steps: A substrate is provided, and a pre-oxide layer and a nitride layer are formed on the substrate; Etch the nitride layer, the front oxide layer, and a portion of the substrate to form a shallow trench; An isolation medium layer is deposited and planarized within the shallow trench to form a shallow trench isolation structure; After removing the nitride layer, the height difference between the surface of the shallow trench isolation structure and the surface of the pre-oxide layer forms an initial step height. Based on the height relationship between the initial step height and the preset step height, either in-situ water vapor growth process or wet oxygen oxidation process is selected to oxidize the substrate, thereby thickening the pre-oxide layer; and The shallow trench isolation structure and the pre-oxide layer are simultaneously wet-etched to adjust the initial step height to a preset step height.

2. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, A layer of silicon oxide is deposited in the shallow trench using a high-density plasma chemical vapor deposition process to form the isolation medium layer.

3. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, When the initial step height is higher than the preset step height, the substrate is oxidized using the in-situ water vapor growth process to thicken the pre-oxide layer.

4. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, When the initial step height is lower than the preset step height, the substrate is oxidized using the wet oxidation process to thicken the pre-oxide layer.

5. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, The method for manufacturing the shallow trench isolation structure further includes: adjusting the thickness of the pre-oxide layer based on the difference between the initial step height and the preset step height.

6. The method for manufacturing the shallow trench isolation structure according to claim 5, characterized in that, The greater the difference between the initial step height and the preset step height, the greater the thickness of the pre-oxide layer; the smaller the difference between the initial step height and the preset step height, the smaller the thickness of the pre-oxide layer.

7. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, The solution used for simultaneous wet etching of the shallow trench isolation structure and the pre-oxide layer is a hydrofluoric acid solution or a buffered oxide etching solution.

8. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, The method for fabricating the shallow trench isolation structure further includes: adjusting the wet etching process conditions based on the difference between the intermediate step height of the shallow trench isolation structure and the preset step height after thickening the pre-oxide layer.

9. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, Adjusted wet etching process conditions include one or more of the following: etching solution ratio, etching temperature, and etching time.

10. The method for manufacturing the shallow trench isolation structure according to claim 1, characterized in that, The pre-oxide layer is formed on the substrate using a wet oxygen oxidation process.

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