A method for manufacturing a shallow trench isolation structure

Abstract

This invention discloses a method for fabricating a shallow trench isolation structure, belonging to the field of semiconductor technology. The method includes the following steps: 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, with 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 oxidation process or an in-situ water vapor growth process to oxidize the substrate and thicken the pre-oxide layer; 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. The method for fabricating a shallow trench isolation structure disclosed in this invention can improve the performance of the formed semiconductor device.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, and specifically relates to a method for fabricating a shallow trench isolation structure. Background Technology

[0002] In integrated circuits, shallow trench isolation (STI) structures are placed between adjacent semiconductor devices to prevent current leakage between them and to provide other electrical performance benefits. The step height of the STI structure affects device performance. If the step height is too low, stress concentration occurs at the corner between the step and the preceding oxide layer, forming a depression that leads to leakage in the active area during operation. If the step height is too high, it affects the flatness of the semiconductor device surface, and during subsequent etching of polysilicon to form the gate, polysilicon residue can easily remain at the step of the STI, potentially causing short circuits and affecting device yield. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing a shallow trench isolation structure, which can solve the problem that the step height of shallow trench isolation does not meet expectations.

[0004] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0005] This invention provides a method for manufacturing a shallow trench isolation structure, comprising the following steps:

[0006] A substrate is provided, and a pre-oxide layer and a nitride layer are formed on the substrate;

[0007] Etch the nitride layer, the front oxide layer, and a portion of the substrate to form a shallow trench;

[0008] An isolation medium layer is deposited and planarized within the shallow trench to form a shallow trench isolation structure;

[0009] 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.

[0010] 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

[0011] 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.

[0012] In one embodiment of the present invention, 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.

[0013] In one embodiment of the present invention, 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.

[0014] In one embodiment of the present invention, 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.

[0015] In one embodiment of the present invention, 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.

[0016] In one embodiment of the present invention, 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.

[0017] In one embodiment of the present invention, 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.

[0018] In one embodiment of the present invention, 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.

[0019] In one embodiment of the present invention, the adjusted wet etching process conditions include one or more of the following: etching solution ratio, etching temperature, and etching time.

[0020] In one embodiment of the present invention, the pre-oxide layer is formed on the substrate using a wet oxygen oxidation process.

[0021] In summary, the method for fabricating a shallow trench isolation structure provided by this invention has an unexpected effect: by thickening the pre-oxide layer through different thermal oxidation processes, the density of the pre-oxide layer is changed. 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 then 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.

[0022] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the formation of a shallow trench isolation structure in one embodiment.

[0025] Figure 2 This is a schematic diagram of the structure forming a front oxide layer, a nitride layer, and a photoresist layer in one embodiment.

[0026] Figure 3 This is a schematic diagram of the structure forming a patterned photoresist layer in one embodiment.

[0027] Figure 4 This is a schematic diagram of a structure forming a shallow trench in one embodiment.

[0028] Figure 5 This is a schematic diagram of the structure forming the isolation medium layer in one embodiment.

[0029] Figure 6 This is a schematic diagram of a shallow trench isolation structure in one embodiment.

[0030] Figure 7 This is a structural schematic diagram of the initial step height in one embodiment.

[0031] Figure 8 This is a schematic diagram of the structure of the thickened pre-oxide layer in one embodiment.

[0032] Figure 9 This is a schematic diagram of the structure of the pre-oxide layer thickened by wet etching in one embodiment.

[0033] Label Explanation:

[0034] 101, Substrate; 1011, Shallow trench; 102, Pre-oxide layer; 103, Nitride layer; 104, Photoresist layer; 1041, Patterned photoresist layer; 1042, Opening; 105, Isolation dielectric layer; 1051, Shallow trench isolation structure; H1, Initial step height; H2, Intermediate step height; H3, Preset step height. Detailed Implementation

[0035] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] 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.

[0037] 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.

[0038] 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).

[0039] 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.

[0040] Step S110: Provide a substrate and form a pre-oxide layer and a nitride layer on the substrate.

[0041] Step S120: Etch the nitride layer, the pre-oxide layer and part of the substrate to form a shallow trench.

[0042] Step S130: Deposit and planarize the isolation medium layer in the shallow trench to form a shallow trench isolation structure.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Please see Figure 2As 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Please see Figures 2 to 4As 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%.

[0054] Please see Figures 2 to 4 As 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.

[0055] 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.

[0056] Please see Figures 5 to 6As 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.

[0057] Please see Figures 6 to 7 As 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.

[0058] 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, the step height of the shallow trench isolation structure 1051 needs to be readjusted.

[0059] Please see Figures 7 to 9As 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.

[0060] Please see Figures 7 to 9 As 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.

[0061] 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.

[0062] 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.

[0063] Please see Figures 7 to 9As 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.

[0064] Please see Figures 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.

[0065] 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.

[0066] Combination Figure 8 As shown in Table 1, in one embodiment of the present invention, the etching process conditions and the etching depth and etching selectivity of the etching solution on 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 are as follows.

[0067] 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.

[0068]

[0069] 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.

[0070] 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.

[0071]

[0072] 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.

[0073] 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.

[0074] 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%.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 Simultaneous wet etching of the shallow trench isolation structure and the pre-oxide layer, adjusting the initial step height to a preset step height; 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; 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.

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, 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.

4. The method for manufacturing the shallow trench isolation structure according to claim 3, 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.

5. 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.

6. 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.

7. 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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