Semiconductor structure and method of manufacturing the same

Abstract

The application provides a semiconductor structure and a preparation method thereof, and relates to the technical field of semiconductors. The preparation method of the semiconductor structure comprises the following steps: providing a substrate; forming a polysilicon layer on the substrate, wherein the surface of the polysilicon layer away from the substrate has a native oxide layer; and performing a nitriding treatment on the native oxide layer so as to nitride the native oxide layer into a silicon oxynitride layer. The native oxide layer is nitrided into a silicon oxynitride layer by performing the nitriding treatment on the native oxide layer. Since the etching rate of the silicon oxynitride layer is smaller than the etching rate of the native oxide layer, the lateral etching of the silicon oxynitride layer can be avoided in the subsequent etching process, the integrity of the pattern on the silicon oxynitride layer is ensured, and then the accuracy of the pattern formed by taking the patterned silicon oxynitride layer as a mask is ensured, and the yield of the semiconductor structure is improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a semiconductor structure and its fabrication method. Background Technology

[0002] In semiconductor fabrication processes, specific patterns are typically formed in a substrate or film layer using techniques such as photolithography and etching. When a polysilicon layer is included in the mask layer or film layer, the silicon on the surface of the polysilicon layer undergoes an oxidation reaction with oxygen or moisture during its formation, resulting in a silicon dioxide layer of a certain thickness, commonly referred to as the native oxide layer. This native oxide layer can be laterally etched in subsequent processes, causing gaps in the mask pattern and affecting the performance of the semiconductor structure.

[0003] In related technologies, hydrofluoric acid (HF) solution is first used to remove the native oxide layer, and then deionized water is used to remove the hydrofluoric acid remaining on the polycrystalline layer. However, during the process of removing hydrofluoric acid, the surface of the polycrystalline silicon layer will be oxidized again to form a native oxide layer. This native oxide layer will cause the mask pattern to be missing in subsequent processes, affecting the yield of the semiconductor structure. Summary of the Invention

[0004] In view of the above problems, this application provides a semiconductor structure and its fabrication method to prevent the loss of mask patterns and improve the yield of semiconductor structures.

[0005] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0006] A first aspect of this application provides a method for fabricating a semiconductor structure, comprising the following steps:

[0007] Provide a base;

[0008] A polycrystalline silicon layer is formed on the substrate, and the surface of the polycrystalline silicon layer facing away from the substrate has a native oxide layer.

[0009] The native oxide layer is nitrided to transform it into a silicon oxynitride layer.

[0010] The method for fabricating the semiconductor structure as described above, wherein the step of nitriding the native oxide layer includes:

[0011] Nitrogen-containing gas is ionized to form nitrogen-containing plasma, which is then used to treat the surface of the original oxide layer.

[0012] In the semiconductor structure fabrication method described above, the nitrogen-containing gas includes NH3 and N2O, or the nitrogen-containing gas includes NH3 and N2, or the nitrogen-containing gas includes H2N2.

[0013] The semiconductor structure fabrication method described above, wherein after the step of forming a polycrystalline silicon layer on the substrate and before the step of nitriding the native oxide layer, the fabrication method includes:

[0014] The thickness of the original oxide layer is measured using a measuring device.

[0015] The semiconductor structure fabrication method described above, wherein after the step of nitriding the native oxide layer, the fabrication method includes:

[0016] A first mask layer and a first photoresist layer with a mask pattern are formed on the silicon oxynitride layer;

[0017] Using the first photoresist layer as a mask, a portion of the first mask layer and a portion of the silicon oxynitride layer are removed to form a plurality of mask protrusions spaced apart, with the distance between two adjacent mask protrusions being equal.

[0018] The semiconductor structure fabrication method described above, after the step of using the first photoresist layer as a mask, includes:

[0019] A mask strip is formed on the sidewall of each of the mask protrusions, and the top surface of the mask strip is flush with the top surface of the mask protrusion.

[0020] Remove the mask protrusions, retain the mask strips, and form a first opening with adjacent mask strips;

[0021] Remove the polysilicon layer exposed in the first opening to form a plurality of spaced second openings in the polysilicon layer;

[0022] Remove the portion of the substrate exposed within the second opening to form a plurality of spaced trenches within the substrate.

[0023] The semiconductor structure fabrication method described above, wherein after the step of removing the substrate exposed within the second opening to form a plurality of trenches spaced apart within the substrate, the fabrication method includes:

[0024] Insulating material is deposited in the trench to form a shallow trench isolation structure.

[0025] The semiconductor structure fabrication method described above, wherein after the step of removing the substrate exposed within the second opening to form a plurality of trenches spaced apart within the substrate, the fabrication method includes:

[0026] Character lines are formed within the groove.

[0027] In the semiconductor structure fabrication method described above, the first mask layer includes a carbon layer, a first silicon nitride layer, a first hard mask layer, and a second silicon nitride layer stacked sequentially, wherein the carbon layer is disposed on the silicon nitride layer.

[0028] The semiconductor structure fabrication method described above, wherein after the step of nitriding the native oxide layer, the fabrication method includes:

[0029] A second mask layer and a second photoresist layer with a mask pattern are formed on the silicon oxynitride layer;

[0030] Using the second photoresist layer as a mask, a portion of the second mask layer, a portion of the silicon oxynitride layer, a portion of the polysilicon layer, and a portion of the substrate are removed to form a plurality of spaced protrusions, the top surfaces of the plurality of protrusions being flush.

[0031] A conductive layer is formed between adjacent protrusions, the top surface of the conductive layer is flush with the top surface of the polysilicon layer, and the vertical distance between the top surface of the conductive layer and the bottom surface of the substrate is a constant.

[0032] The method for fabricating a semiconductor structure as described above, wherein the step of forming a conductive layer between adjacent protrusions includes:

[0033] An initial conductive layer is formed between the adjacent protrusions, and the initial conductive layer covers the top surface of each protrusion;

[0034] The initial conductive layer located on the top surface of the protrusion is removed, as well as a portion of the initial conductive layer located between adjacent protrusions, and the remaining initial conductive layer constitutes the conductive layer.

[0035] The semiconductor structure fabrication method described above, after the steps of removing the initial conductive layer located on the top surface of the protrusion and removing a portion of the initial conductive layer located between adjacent protrusions, leaving the remaining initial conductive layer as a conductive layer, the fabrication method further includes:

[0036] Remove the remaining silicon oxynitride layer.

[0037] The semiconductor structure fabrication method described above, wherein the step of removing the retained silicon oxynitride layer includes:

[0038] The remaining silicon oxynitride layer is removed using hydrofluoric acid.

[0039] In the semiconductor structure fabrication method described above, the second mask layer includes a first oxide layer, a second hard mask layer, a third silicon nitride layer, a third hard mask layer, a fourth silicon nitride layer, a second oxide layer, a fourth hard mask layer, and a fifth silicon nitride layer stacked sequentially, wherein the first oxide layer is disposed on the silicon nitride layer.

[0040] A second aspect of this application provides a semiconductor structure, which is prepared by a semiconductor structure preparation method as described above.

[0041] In the semiconductor structure and its fabrication method provided in this application embodiment, the native oxide layer is nitrided to form a silicon oxynitride layer. Since the etching rate of the silicon oxynitride layer is lower than that of the native oxide layer, the lateral etching of the silicon oxynitride layer can be avoided in the subsequent etching process, ensuring the integrity of the pattern on the silicon oxynitride layer. This, in turn, ensures the accuracy of the pattern formed by using the patterned silicon oxynitride layer as a mask, and improves the yield of the semiconductor structure.

[0042] In addition to the technical problems solved by the embodiments of this application, the technical features constituting the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions described above, other technical problems that can be solved by the semiconductor structure and its preparation method provided by the embodiments of this application, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further explained in detail in the specific implementation. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the structure for forming the primary oxide layer in the semiconductor structure fabrication method provided in the related technology. Figure 1 ;

[0045] Figure 2 This is a schematic diagram of the structure for forming the first mask layer in a semiconductor structure fabrication method provided in related technologies.

[0046] Figure 3 This is a schematic diagram of the lateral etching of the native oxide layer in the semiconductor structure fabrication method provided in related technologies;

[0047] Figure 4A schematic diagram of the formation of a silicon dioxide layer structure in a semiconductor structure fabrication method provided in related technologies;

[0048] Figure 5 This is a schematic diagram of a patterned polycrystalline silicon layer in a semiconductor structure fabrication method provided in related technologies.

[0049] Figure 6 This is a schematic diagram of the structure for forming the primary oxide layer in the semiconductor structure fabrication method provided in the related technology. Figure 2 ;

[0050] Figure 7 This is a schematic diagram of the patterned native oxide layer and polycrystalline silicon layer in the semiconductor structure fabrication method provided in the related technology;

[0051] Figure 8 This is a schematic diagram of the structure in which the initial conductive layer is formed in a semiconductor structure fabrication method provided in related technologies;

[0052] Figure 9 This is a schematic diagram of the structure in which a conductive layer is formed in a semiconductor structure fabrication method provided in related technologies.

[0053] Figure 10 This is a schematic diagram of the structure for removing the remaining native oxide layer in a semiconductor structure fabrication method provided in related technologies.

[0054] Figure 11 A process flow diagram of the method for fabricating the semiconductor structure provided in the embodiments of this application;

[0055] Figure 12 Schematic diagram of the structure forming the silicon oxynitride layer in the semiconductor structure fabrication method provided in this application embodiment. Figure 1 ;

[0056] Figure 13 Schematic diagram of the structure forming the silicon oxynitride layer in the semiconductor structure fabrication method provided in this application embodiment. Figure 2 ;

[0057] Figure 14 This is a schematic diagram of the structure for forming the first mask layer in the method for fabricating a semiconductor structure provided in this application embodiment;

[0058] Figure 15 This is a schematic diagram of the structure for forming mask protrusions in the method for fabricating a semiconductor structure provided in this application embodiment;

[0059] Figure 16 This is a schematic diagram of the structure forming a silicon dioxide layer in the method for fabricating a semiconductor structure provided in the embodiments of this application;

[0060] Figure 17This is a schematic diagram of the structure for forming a mask strip in the method for fabricating a semiconductor structure provided in the embodiments of this application;

[0061] Figure 18 This is a schematic diagram of the patterned polycrystalline silicon layer in the semiconductor structure fabrication method provided in the embodiments of this application;

[0062] Figure 19 This is a schematic diagram of the structure forming trenches in the semiconductor structure fabrication method provided in the embodiments of this application;

[0063] Figure 20 This is a schematic diagram of the structure for forming the second mask layer in the method for fabricating a semiconductor structure provided in this application embodiment;

[0064] Figure 21 This is a schematic diagram of the structure forming protrusions in the method for fabricating a semiconductor structure provided in the embodiments of this application;

[0065] Figure 22 This is a schematic diagram of the structure forming the initial conductive layer in the method for preparing the semiconductor structure provided in the embodiments of this application;

[0066] Figure 23 This is a schematic diagram of the structure forming the initial conductive layer in the method for preparing the semiconductor structure provided in the embodiments of this application;

[0067] Figure 24 This is a schematic diagram of the structure for removing the silicon oxynitride layer in the method for fabricating the semiconductor structure provided in the embodiments of this application.

[0068] Figure label:

[0069] 10: Substrate; 11: Trench; 12: Shallow trench isolation structure; 20: Polysilicon layer; 21: Native oxide layer; 22: Silicon oxynitride layer; 23: Second opening; 30: First mask layer; 31: Carbon layer; 32: First silicon nitride layer; 33: First hard mask layer; 34: Second silicon nitride layer; 40: First photoresist layer; 50: Mask bump; 60: Mask strip; 61: Silicon dioxide layer; 62: First opening; 70: Second mask layer; 71: First oxide layer; 72: Second hard mask layer; 73: Third silicon nitride layer; 74: Third hard mask layer; 75: Fourth silicon nitride layer; 76: Second oxide layer; 77: Fourth hard mask layer; 78: Fifth silicon nitride layer; 80: Second photoresist layer; 90: Bump; 100: Bit line; 110: Conductive layer; 111: Initial conductive layer. Detailed Implementation

[0070] As described in the background art, in related technologies, when a polysilicon layer is included in the mask layer or film layer, the surface of the polysilicon layer is easily oxidized to form a native oxide layer, and the etching rate of the native oxide layer is relatively high. When patterning the mask layer or film layer in the subsequent process, the native oxide layer is easily etched laterally, resulting in missing mask patterns and affecting the performance of the semiconductor structure.

[0071] For example, such as Figures 1 to 5 As shown, when the polysilicon layer 20 is used as a mask layer, a first mask layer 30 is usually formed on the polysilicon layer 20, the first mask layer 30 is patterned, and the pattern of the first mask layer 30 is transferred to the native oxide layer 21. Since the etching rate of the native oxide layer 21 is relatively high, under the same etching gas conditions, the native oxide layer 21 will undergo lateral over-etching, resulting in the loss of part of the native oxide layer. When the pattern on the native oxide layer is used as a mask pattern to continue etching the polysilicon layer 20, there will be missing patterns formed on the polysilicon layer 20. Consequently, when the patterned polysilicon layer 20 is used as a mask to continue etching the substrate 10, the trenches formed on the substrate 10 will be missing, reducing the yield of the semiconductor structure.

[0072] For example, such as Figures 6 to 10 As shown, when the polysilicon layer 20 is used as the film layer of the semiconductor structure, when the polysilicon layer 20 is patterned, since the etching rate of the native oxide layer 21 is greater than that of the polysilicon layer 20, under the same etching gas and etching rate, the etching amount of the native oxide layer 21 is larger, which causes the native oxide layer on the retained polysilicon layer to be lost, which in turn leads to the formation of grooves on the top surface of the retained polysilicon layer, affecting the performance of the semiconductor structure.

[0073] In related technologies, two common processes are used to remove the native oxide layer. One is to first clean the native oxide layer with hydrofluoric acid, and then remove the hydrofluoric acid residue on the wafer surface with deionized water. However, during the process of removing hydrofluoric acid with deionized water, the surface of the polycrystalline silicon layer will be oxidized again, forming a native oxide layer. The other is to use hydrogen fluoride gas or ammonia gas to react with the native oxide layer to form a byproduct, which is (NH4)2SIF6. Then, the byproduct is removed by sublimation through heating. However, this removal method cannot completely remove the native oxide layer, leaving a native oxide layer with a thickness of about 0.4 to 0.5 nm on the surface of the polycrystalline silicon layer.

[0074] To address the aforementioned technical issues, in this embodiment, the native oxide layer is nitrided to form a silicon oxynitride layer. Since the etching rate of the silicon oxynitride layer is lower than that of the native oxide layer, lateral etching of the silicon oxynitride layer can be avoided in subsequent etching processes, ensuring the integrity of the pattern on the silicon oxynitride layer. This, in turn, ensures the accuracy of the pattern formed using the patterned silicon oxynitride layer as a mask, thereby improving the yield of the semiconductor structure.

[0075] To make the above-mentioned objectives, features, and advantages of the embodiments of this application more apparent and understandable, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0076] This embodiment does not limit the semiconductor structure. The following description will take dynamic random access memory (DRAM) as an example, but this embodiment is not limited to this. Other semiconductor structures are also possible in this embodiment.

[0077] like Figure 11 As shown, the method for fabricating a semiconductor structure provided in this application includes the following steps:

[0078] Step S100: Provide a substrate.

[0079] For example, the substrate 10 serves as a support component for a dynamic random access memory (DRAM) to support other components disposed thereon. The substrate 10 may be made of a semiconductor material, which may be one or more of silicon, germanium, silicon-germanium compounds, and silicon-carb compounds.

[0080] Since the structure of the substrate in this embodiment is the same as that of the substrate in the prior art, its structure can be referenced. Figure 1 and Figure 6 .

[0081] Step S200: A polycrystalline silicon layer is formed on the substrate, the surface of the polycrystalline silicon layer facing away from the substrate having a native oxide layer.

[0082] For example, continue to refer to Figure 1 and Figure 6A polycrystalline silicon layer 20 of a certain thickness can be formed on the substrate 10 by a deposition process. After the polycrystalline silicon layer 20 is formed, due to the presence of oxygen or water in the storage environment or equipment, the silicon on the surface of the polycrystalline silicon layer 20 will react with oxygen or water to form a native oxide layer 21 on the surface of the polycrystalline silicon layer 20. The material of the native oxide layer 21 may include silicon oxide.

[0083] Step S300: Nitriding the native oxide layer to nitride it into a silicon oxynitride layer, the structure of which is as follows. Figure 12 and Figure 13 As shown.

[0084] For example, nitrogen-containing gas is introduced into the deposition equipment, and a plasma processor is used to form nitrogen-containing plasma. The nitrogen-containing plasma penetrates into the native oxide layer 21, causing the native oxide layer to form a nitrogen-rich silicon oxynitride layer 22. Compared with the native oxide layer, the silicon oxynitride layer 22 has a higher hardness, which reduces the etching rate of the silicon oxynitride layer 22. During subsequent etching of the silicon oxynitride layer, lateral etching of the silicon oxynitride layer will not occur, ensuring the integrity of the pattern formed on the silicon oxynitride layer.

[0085] It should be noted that the etching rate can be understood as the speed at which a certain layer of material is removed during the etching process.

[0086] The nitrogen-containing gas may include NH3 and N2O, or the nitrogen-containing gas may include NH3 and N2, or the nitrogen-containing gas may include H2N2.

[0087] During this nitriding process of the native oxide layer, the source radio frequency power is 1500-2000W, the pressure is 0.1-0.5 Torr, and the processing temperature is 450-600℃.

[0088] Because the composition of nitrogen-containing gases varies, it is necessary to control the flow rate of different nitrogen-containing gases. For example, when the nitrogen-containing gas is NH3 and N2O, or when the nitrogen-containing gas includes NH3 and N2, the flow rate of NH3 is 450-700 scm, and the flow rate of N2O / N2 is 200-300 scm. When the nitrogen-containing gas is H2N2, the flow rate of H2N2 is 1300-2000 scm.

[0089] After the step of forming a polycrystalline silicon layer on the substrate and before the step of nitriding the native oxide layer, the preparation method further includes measuring the thickness of the native oxide layer using a measuring device.

[0090] In this embodiment, before the nitriding treatment of the native oxide layer, the thickness of the native oxide layer 21 can be obtained first, and the nitriding treatment time can be adjusted according to the thickness of the native oxide layer 21 to ensure the effect of the nitriding treatment.

[0091] For example, it takes 0.4 to 0.44 seconds to nitrid 0.1 nm of the native oxide layer. Once the thickness of the native oxide layer 21 is known, the required nitriding time can be calculated based on the thickness of the native oxide layer, providing theoretical support for ensuring the nitriding effect.

[0092] To ensure complete nitriding of the original oxide layer, the nitriding time can be appropriately increased based on the above-mentioned nitriding time, for example, by 10 to 20 seconds.

[0093] Furthermore, after the nitriding treatment of the native oxide layer, the thickness of the silicon oxynitride layer can be measured using a measuring device. The thickness of the silicon oxynitride layer can be used to characterize the effect of the nitriding treatment and provide theoretical support for the subsequent process of removing the silicon oxynitride layer.

[0094] It should be noted that the polysilicon layer involved in the embodiments of the present invention can be used as a pattern transfer layer to transfer the pattern on the mask layer into the substrate; or as a film layer of a semiconductor structure, such as a bit line contact layer; when the function of the polysilicon layer is different, the preparation method after the step after the nitriding treatment of the native oxide layer is also different, please refer to the following description for details.

[0095] In one feasible implementation, such as Figures 14 to 18 As shown, a first mask layer 30 and a first photoresist layer 40 with a mask pattern are formed on the silicon oxynitride layer 22.

[0096] For example, such as Figure 14 As shown, a first mask layer 30 can be formed on the silicon oxynitride layer 22 by a deposition process. The first mask layer 30 can be a single film layer or a composite film layer. When the first mask layer 30 is a composite film layer, the first mask layer 30 may include a carbon layer 31, a first silicon nitride layer 32, a first hard mask layer 33 and a second silicon nitride layer 34. The carbon layer 31 is disposed on the silicon oxynitride layer 22.

[0097] After the second silicon nitride layer 34 is formed, the first photoresist layer 40 can be formed on the second silicon nitride layer 34 by coating.

[0098] Subsequently, the first photoresist layer 40 is patterned by exposure, development or etching to form a first photoresist layer 40 with a mask pattern.

[0099] like Figure 15 As shown, after the first photoresist layer 40 with the mask pattern is formed, the first photoresist layer 40 can be used as a mask to remove part of the first mask layer 30 and part of the silicon oxynitride layer 22 to form a plurality of mask protrusions 50 spaced apart, with the distance between two adjacent mask protrusions 50 being equal.

[0100] In this embodiment, the first mask layer 30 is a composite film layer. During the pattern transfer process, the first photoresist layer 40 with a mask pattern is first used as a mask to etch the second silicon nitride layer 34 to form a patterned second silicon nitride layer 34. Then, the patterned second silicon nitride layer 34 is used to sequentially etch the first hard mask layer 33, the first silicon nitride layer 32, and the carbon layer 31 to transfer the pattern on the second silicon nitride layer 34 to the carbon layer 31. After that, the patterned carbon layer 31 is used as a mask to etch the silicon oxynitride layer 22, and finally the pattern is transferred to the silicon oxynitride layer 22.

[0101] By employing multiple pattern transfer processes, the accuracy of the final pattern transferred onto the silicon oxynitride layer can be guaranteed.

[0102] In this embodiment, the native oxide layer is nitrided and transformed into a silicon oxynitride layer. Taking advantage of the lower etching rate of the silicon oxynitride layer compared to the native oxide layer, when transferring the mask pattern from the first photoresist layer 40 to the silicon oxynitride layer 22, lateral etching of the silicon oxynitride layer 22 is avoided. This results in the retained first mask layer 30 and silicon oxynitride layer 22 forming multiple mask bumps 50. These multiple mask bumps extend along... Figure 15 The mask bumps 50 are spaced apart in the X direction, and the distance between two adjacent mask bumps 50 is equal. That is, the horizontal distance between two adjacent mask bumps 50 in the X direction is equal. This avoids the partial loss of native oxide layer in the mask bumps 50 formed in related technologies, thus preventing the loss of part of the mask bumps 50. This also prevents the loss of patterns formed when mask bumps are used as masks, ensuring the yield of semiconductor structures.

[0103] Furthermore, after the step of using the first photoresist layer 40 as a mask, the method for fabricating the semiconductor structure further includes:

[0104] A mask strip 60 is formed on the sidewall of each mask protrusion 50, and the top surface of the mask strip 60 is flush with the top surface of the mask protrusion 50.

[0105] For example, such as Figure 16 As shown, an atomic layer deposition process can be used to form a silicon dioxide layer 61 on the top surface, side surface and top surface of the polysilicon layer 20 between adjacent mask bumps 50.

[0106] The silicon dioxide layer 61 located on the top surface of the polysilicon layer 20 and the top surface of the mask protrusion 50 is removed, while the silicon dioxide layer located on the side surface of the mask protrusion 50 is retained. The retained silicon dioxide layer forms the mask strip 60.

[0107] After the mask strip is formed, as follows Figure 17As shown, the mask protrusions 50 can be removed using an etching solution, leaving the mask strips 60, and adjacent mask strips 60 form the first opening 62.

[0108] Since the aforementioned process uses a thickness measuring device to measure the thickness of the silicon oxynitride layer 22, the concentration and amount of etching solution can be adjusted according to the thickness of the silicon oxynitride layer 22 in this step to ensure that the mask protrusions 50 can be removed without damaging the mask strip 60.

[0109] The etching solution may include hydrofluoric acid (HF).

[0110] like Figure 18 As shown, the polysilicon layer 20 exposed in the first opening 62 is removed by using an etching solution or etching gas to form a plurality of spaced second openings 23 in the polysilicon layer 20.

[0111] like Figure 19 As shown, after the second opening 23 is formed, the substrate 10 exposed in the second opening 23 can be removed by using an etching solution or etching gas to form a plurality of trenches 11 spaced apart in the substrate 10.

[0112] It should be noted that after the trench 11 is formed, subsequent process steps can be carried out according to the specific structure of the semiconductor structure. For example, if the trench 11 is used to form a shallow trench isolation structure 12, an insulating material can be deposited into the trench 11 using a deposition process to form a shallow trench isolation structure 12. The insulating material may include silicon oxide.

[0113] For example, trench 11 can be used to form a buried gate structure. A gate oxide layer can be formed on the inner wall of trench 11 first, and then a conductive layer can be formed in the area enclosed by the gate oxide layer, with the top surface of the conductive layer being lower than the top surface of the substrate.

[0114] In one feasible implementation, such as Figure 20 As shown, a second mask layer 70 and a second photoresist layer 80 with a mask pattern are formed on the silicon oxynitride layer 22.

[0115] For example, a second mask layer 70 can be formed on the silicon oxynitride layer 22 by a deposition process. The second mask layer 70 is a composite film layer. For example, the second mask layer 70 may include a first oxide layer 71, a second hard mask layer 72, a third silicon nitride layer 73, a third hard mask layer 74, a fourth silicon nitride layer 75, a second oxide layer 76, a fourth hard mask layer 77, and a fifth silicon nitride layer 78 stacked sequentially. The first oxide layer 71 is disposed on the silicon oxynitride layer 22.

[0116] After the fifth silicon nitride layer 78 is formed, the second photoresist layer 80 can be formed on the fifth silicon nitride layer 78 by coating.

[0117] Subsequently, the second photoresist layer 80 is patterned by exposure, development or etching to form a second photoresist layer 80 with a mask pattern.

[0118] like Figure 21 As shown, the second photoresist layer 80 with a mask pattern to be formed can be used as a mask to remove part of the second mask layer 70, part of the silicon oxynitride layer 22 and part of the substrate 10 to form a plurality of protrusions 90 spaced apart, with the top surfaces of the plurality of protrusions 90 being flush.

[0119] In this embodiment, the second mask layer 70 is a composite film layer. During the pattern transfer process, the second photoresist layer 80 with a mask pattern is first used as a mask to etch the fifth silicon nitride layer 78 to form a patterned fifth silicon nitride layer 78. Then, the remaining film layers of the second mask layer 70 are sequentially etched using the patterned fifth silicon nitride layer 78 to transfer the pattern onto the first oxide layer 71. After that, the patterned first oxide layer 71 is used as a mask to etch the silicon oxynitride layer 22, and finally the pattern is transferred to the silicon oxynitride layer 22.

[0120] By employing multiple pattern transfer processes, the accuracy of the final pattern transferred onto the silicon oxynitride layer can be guaranteed.

[0121] Finally, using the silicon oxynitride layer as a mask, part of the substrate 10 was etched to form... Figure 21 The structure shown.

[0122] In this embodiment, since the native oxide layer is nitrided and transformed into a silicon oxynitride layer, and taking advantage of the fact that the etching rate of the silicon oxynitride layer is lower than that of the native oxide layer, lateral etching will not occur on the silicon oxynitride layer 22 when the mask pattern of the second photoresist layer 80 is transferred to the silicon oxynitride layer 22, unlike in related technologies. Figure 7 As shown, the remaining portion of the silicon oxynitride layer 22 is missing, ensuring that the remaining silicon oxynitride layer 22 forms multiple spaced protrusions 90, with the top surfaces of the multiple protrusions 90 being flush.

[0123] If so, in this embodiment, the polysilicon layer can be used as the initial film layer of part of the bit line contact layer, and the retained polysilicon layer can be used as part of the bit line contact layer. Then the beneficial effect of this embodiment is that by taking advantage of the low etching rate of the silicon oxynitride layer 22, the retained silicon oxynitride layer 22 is prevented from being missing, thereby preventing the shape of the retained polysilicon layer from becoming abnormal, ensuring the integrity of the bit line contact structure, and thus improving the performance of the semiconductor structure.

[0124] After the protrusions 90 are formed, a conductive layer 110 is formed between adjacent protrusions 90. The top surface of the conductive layer 110 is flush with the top surface of the polysilicon layer 20, and the vertical distance between the top surface of the conductive layer 110 and the bottom surface of the substrate 10 is a constant value. The top surface of the conductive layer 110 and the top surface of the substrate 10 are parallel to each other.

[0125] For example, such as Figure 22 As shown, an initial conductive layer 101 is first formed between adjacent protrusions 90, and the initial conductive layer 101 covers the top surface of each protrusion 90.

[0126] After that, as Figure 23 As shown, the initial conductive layer 101 located on the top surface of the protrusion 90 is removed, and a portion of the initial conductive layer 101 located between adjacent protrusions 90 is also removed. The remaining initial conductive layer 101 constitutes the conductive layer 110. The conductive layer 110 can serve as another part of the bit line contact layer. The conductive layer 110 and the remaining polysilicon layer form an integral whole to constitute the bit line contact layer.

[0127] like Figure 24 As shown, after the conductive layer 110 is formed, the remaining silicon oxynitride layer 22 can be removed using hydrofluoric acid. It should be noted that in this embodiment, other etching gases or etching solutions can also be used to remove the silicon oxynitride layer 22.

[0128] Afterwards, bit lines can be formed on the bit line contact layer using conventional processes.

[0129] This invention also provides a semiconductor structure, which is obtained by the preparation method of the semiconductor structure in the above embodiments. Therefore, the semiconductor structure has the beneficial effects of the above embodiments, and will not be described in detail here.

[0130] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0131] In the description of this specification, references to terms such as “one embodiment,” “some embodiments,” “illustrative embodiment,” “example,” “specific example,” or “some examples” refer to specific features, structures, materials, or characteristics described in connection with an embodiment or example that are included in at least one embodiment or example of this application.

[0132] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more implementations or examples.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method of fabricating a semiconductor structure, characterized by, The method comprises the following steps: providing a substrate; forming a polysilicon layer on the substrate, the polysilicon layer having a native oxide layer on a surface thereof facing away from the substrate; nitriding the native oxide layer to form a silicon oxynitride layer; forming a first mask layer and a first photoresist layer having a mask pattern on the silicon oxynitride layer; using the first photoresist layer as a mask, removing part of the first mask layer and part of the silicon oxynitride layer to form a plurality of mask protrusions arranged at intervals, the distance between two adjacent mask protrusions being equal.

2. The method of claim 1, wherein the semiconductor structure is prepared by a method comprising: In the step of nitriding the native oxide layer, the method comprises: ionizing a nitrogen-containing gas to form a nitrogen-containing plasma, and then using the nitrogen-containing plasma to treat the surface of the native oxide layer.

3. The method of claim 2, wherein the semiconductor structure is prepared by a method comprising: The nitrogen-containing gas comprises NH3 and N2O, or the nitrogen-containing gas comprises NH3 and N2, or the nitrogen-containing gas comprises H2N2.

4. The method of producing a semiconductor structure according to any one of claims 1 to 3, characterized in that, After the step of forming the polysilicon layer on the substrate and before the step of nitriding the native oxide layer, the method comprises: measuring the thickness of the native oxide layer by a measuring device.

5. The method of claim 4, wherein the semiconductor structure is prepared by a method comprising: After the step of using the first photoresist layer as a mask, the method comprises: forming a mask strip on the sidewall of each mask protrusion, the top surface of the mask strip being flush with the top surface of the mask protrusion; removing the mask protrusions and retaining the mask strips, the adjacent mask strips forming a first opening; removing the polysilicon layer exposed in the first opening to form a plurality of second openings arranged at intervals in the polysilicon layer; removing part of the substrate exposed in the second openings to form a plurality of trenches arranged at intervals in the substrate.

6. The method of claim 5, wherein the semiconductor structure is prepared by a method comprising: After the step of removing the substrate exposed in the second openings to form a plurality of trenches arranged at intervals in the substrate, the method comprises: depositing an insulating material in the trenches to form a shallow trench isolation structure.

7. The method of claim 5, wherein the step of forming the semiconductor structure is performed by a method comprising: After the step of removing the substrate exposed in the second openings to form a plurality of trenches arranged at intervals in the substrate, the method comprises: forming a word line in the trenches.

8. The method of producing a semiconductor structure according to any one of claims 5 to 7, wherein The first mask layer comprises a carbon layer, a first silicon nitride layer, a first hard mask layer and a second silicon nitride layer arranged in sequence, and the carbon layer is arranged on the silicon oxynitride layer.

9. The method of claim 1-3, wherein After the step of nitriding the native oxide layer, the method comprises: forming a second mask layer and a second photoresist layer having a mask pattern on the silicon oxynitride layer; using the second photoresist layer as a mask, removing part of the second mask layer, part of the silicon oxynitride layer, part of the polysilicon layer and part of the substrate to form a plurality of protrusions arranged at intervals, the top surfaces of the plurality of protrusions being flush; forming a conductive layer between the adjacent protrusions, the top surface of the conductive layer being flush with the top surface of the polysilicon layer, and the vertical distance between the top surface of the conductive layer and the bottom surface of the substrate being a constant value.

10. The method of claim 9, wherein the semiconductor structure is prepared by a method comprising: In the step of forming a conductive layer between the adjacent protrusions, the method comprises: forming an initial conductive layer between the adjacent protrusions, the initial conductive layer covering the top surface of each protrusion; removing an initial conductive layer on top surfaces of the protrusions and removing part of the initial conductive layer between adjacent protrusions, the remaining initial conductive layer constituting the conductive layer.

11. The method of claim 10, wherein the semiconductor structure is prepared by a method comprising: After the step of removing an initial conductive layer on top surfaces of the protrusions and removing part of the initial conductive layer between adjacent protrusions, the remaining initial conductive layer constituting the conductive layer, the preparation method further comprises: removing the remaining silicon oxynitride layer.

12. The method of claim 11, wherein the semiconductor structure is prepared by a method comprising: In the step of removing the remaining silicon oxynitride layer, comprising: removing the remaining silicon oxynitride layer with hydrofluoric acid.

13. The method of fabricating a semiconductor structure according to any one of claims 10-12, wherein, The second mask layer comprises a first oxide layer, a second hard mask layer, a third silicon nitride layer, a third hard mask layer, a fourth silicon nitride layer, a second oxide layer, a fourth hard mask layer and a fifth silicon nitride layer which are sequentially stacked, and the first oxide layer is arranged on the silicon oxynitride layer.

14. A semiconductor structure, characterized by The semiconductor structure is prepared by the preparation method of the semiconductor structure according to any one of claims 1-13.

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