Method for forming semiconductor device

Abstract

A method for forming a semiconductor device. The method comprises: providing a semiconductor substrate, wherein an oxide layer and a nitride layer are sequentially formed on the semiconductor substrate; and performing at least one round of etching process to remove the nitride layer, wherein each round of etching process comprises: using a first gas to etch the nitride layer to remove at least one part of the nitride layer, wherein the first gas comprises HF and water vapor; inputting a second gas, and generating an intermediate product on the semiconductor substrate in a mixed gas atmosphere of the second gas and the first gas, wherein the second gas comprises ammonia; and heating the semiconductor substrate. In the present invention, a nitride layer can be removed by means of one or more rounds of etching processes, and the etching uniformity is effectively improved, thereby improving the device quality.

Description

Method for forming semiconductor device

[0001] This application claims priority to the Chinese patent application No. 202410425797.3, filed on April 9, 2024, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of semiconductor manufacturing, and in particular to a method for forming a semiconductor device. BACKGROUND

[0003] In a semiconductor manufacturing process, it can be necessary to form a stacked structure of an oxide layer and a nitride layer, and to remove an outer layer structure or an upper layer structure in the stacked structure after appropriate operation. For example, a nitride layer is formed on the surface of an oxide layer as a stop layer or a stress adjustment layer, and the stop layer or the stress adjustment layer needs to be removed subsequently.

[0004] However, in the existing process for removing the nitride layer, the etching uniformity is insufficient, which affects the quality of the device.

[0005] There is an urgent need for a method for forming a semiconductor device, which can effectively remove the nitride layer after sequentially forming the oxide layer and the nitride layer, and improve the etching uniformity, thereby effectively improving the quality of the device. SUMMARY

[0006] The technical problem solved by the present application is to provide a method for forming a semiconductor device, which can remove the nitride layer through one or more rounds of etching process, and effectively improve the etching uniformity and the quality of the device.

[0007] To solve the above technical problem, an embodiment of the present application provides a method for forming a semiconductor device, comprising: providing a semiconductor substrate, wherein an oxide layer and a nitride layer are sequentially formed on the semiconductor substrate; performing at least one round of etching process to remove the nitride layer; wherein each round of etching process comprises: etching the nitride layer using a first gas to remove at least a portion of the nitride layer, wherein the first gas comprises HF and water vapor; inputting a second gas, wherein an intermediate product is generated on the semiconductor substrate in a mixed gas atmosphere of the second gas and the first gas, wherein the second gas comprises ammonia; and heating the semiconductor substrate.

[0008] Optionally, removing at least a portion of the nitride layer comprises: generating a first intermediate product comprising silicic acid in the process of removing at least a portion of the nitride layer.

[0009] Optionally, the inputting the second gas, under the mixed gas atmosphere of the second gas and the first gas, generates an intermediate product on the semiconductor substrate, comprises: inputting the second gas to the etching chamber, so that the silicic acid generates SiF4 under the mixed gas atmosphere of the ammonia gas and the HF gas, and the SiF4 continues to form ammonium hexafluorosilicate under the mixed gas atmosphere of the ammonia gas and the HF gas.

[0010] Optionally, the gas concentration of the ammonia gas is greater than the gas concentration of the HF gas.

[0011] Optionally, the heating of the semiconductor substrate comprises: decomposing the intermediate product, so that at least a part of the intermediate product is heated to generate a gaseous byproduct; and inputting nitrogen gas to remove the gaseous byproduct under the nitrogen atmosphere.

[0012] Optionally, a first process temperature for generating the intermediate product is less than a second process temperature for the heating; wherein the first process temperature is 20-120℃, and / or the second process temperature is 130-250℃.

[0013] Optionally, before the performing the at least one round of etching process, the method further comprises: determining an etching time-etching rate curve of the nitride layer according to a gas concentration ratio of the HF and the water vapor contained in the first gas, wherein different gas concentration ratios have a pre-determined etching time-etching rate curve of the nitride layer, the etching rate curve comprises a uniform etching interval and a rate decreasing interval; selecting a single round etching time, the single round etching time is selected from the etching time contained in the uniform etching interval; and determining an etching round number according to the thickness of the nitride layer and the single round etching time; wherein the smaller the single round etching time, the greater the thickness of the nitride layer, and the greater the etching round number.

[0014] Optionally, the etching round number is determined by using the following formula:

[0015] wherein N is used to represent the etching round number, L is used to represent the thickness of the nitride layer, Ti is used to represent the single round etching time, Ri is used to represent the etching rate corresponding to Ti, is used to represent the upward rounding operation.

[0016] Optionally, the etching process for removing the nitride layer has N rounds, wherein N is a positive integer and N≥2; wherein the gas concentration ratio of the HF and the water vapor contained in the first gas is a first ratio from the first round of etching process to the (N-1)th round of etching process; and the gas concentration ratio of the HF and the water vapor contained in the first gas is a second ratio in the Nth round of process; the second ratio is less than the first ratio.

[0017] Optionally, the semiconductor substrate comprises a protruding gate structure, and the oxide layer and the nitride layer comprise vertical side walls covering sidewalls of the gate structure.

[0018] Compared with the prior art, the technical scheme of the embodiment of the application has the following beneficial effects:

[0019] In the embodiment of the application, in each etching process, a first gas containing HF and water vapor can be used to etch the nitride layer to remove at least part of the nitride layer, then a second gas containing ammonia is input, and an intermediate product is generated on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas, at least part of the intermediate product can be heated to generate gaseous by-products, and then the gaseous by-products are removed from the etching chamber, so that the nitride layer can be removed by one or more etching processes. By using the above scheme, since the nitride layer is etched in a gas atmosphere all the time, the etching speed is slower than liquid etching, which effectively improves the etching flatness and improves the device quality. In addition, since the chemical reaction of forming the intermediate product and decomposing the intermediate product is a reversible reaction, by using the first gas to etch the nitride layer to remove at least part of the nitride layer, inputting the second gas, and generating the intermediate product on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas, heating the semiconductor substrate can effectively control the reaction direction of the reversible reaction. Further, by generating a first intermediate product containing silicic acid during the process of removing at least part of the nitride layer, the first intermediate product can be mixed with HF gas and water vapor in a certain proportion to react with the nitride layer to generate silicic acid, thereby etching the nitride layer. In addition, since the silicic acid is in a gaseous and / or liquid state, it will block the nitride layer after formation, resulting in a decrease in etching rate. At this time, multiple etching can be used to complete the etching of the nitride layer in a gas atmosphere.

[0020] Further, by inputting the second gas into the etching chamber, the silicic acid generates SiF4 in the mixed gas atmosphere of the ammonia and the HF gas, and the SiF4 continues to form ammonium hexafluorosilicate in the mixed gas atmosphere of the ammonia and the HF gas. Ammonium hexafluorosilicate that can be thermally decomposed can be formed in the mixed gas atmosphere of the second gas and the first gas, so that the etching of the nitride layer can be completed in a gas atmosphere.

[0021] Further, the gas concentration of the ammonia gas is greater than the gas concentration of the HF gas, and the etching ratio between the nitride and the oxide is lower than that in the prior art, which leads to excessive damage to the oxide during the removal of the nitride. The embodiments of the present application can improve the etching ratio between the nitride and the oxide, thereby protecting the oxide layer.

[0022] Further, by decomposing the intermediate product to heat at least a portion of the intermediate product to generate a gaseous byproduct, and inputting nitrogen gas to remove the gaseous byproduct in the nitrogen atmosphere, the oxide layer and the remaining nitride layer can be protected during the removal of the gaseous byproduct, thereby maintaining the etching of the nitride layer in the gas atmosphere.

[0023] Further, the first process temperature for generating the intermediate product is less than the second process temperature for heating, wherein the first process temperature is 20-120°C, and / or the second process temperature is 130-250°C. Since the chemical reaction for forming the intermediate product and decomposing the intermediate product is a reversible reaction, the above scheme can be used to etch the nitride to form the intermediate product at a lower process temperature, and to heat and decompose the intermediate product at a higher process temperature, thereby effectively controlling the reaction direction of the reversible reaction. Further, after heating, the etching chamber can be cooled to the first process temperature in the first etching process to the N-1th etching process, thereby implementing a multi-cycle etching process to improve the precision of removing the nitride layer.

[0024] Further, the etching time-etching rate curve of the nitride layer is determined according to the gas concentration ratio of HF and water vapor contained in the first gas, wherein different gas concentration ratios have a predetermined etching time-etching rate curve of the nitride layer, and the etching rate curve includes a uniform etching interval and a rate decreasing interval; a single etching time is selected from the etching time included in the uniform etching interval; and the etching cycle number is determined according to the thickness of the nitride layer and the single etching time. The smaller the single etching time, the greater the thickness of the nitride layer, and the greater the etching cycle number. The above scheme can effectively control the etching rate by including a uniform etching interval and a rate decreasing interval in the etching rate curve, and selecting the etching time from the etching time included in the uniform etching interval, thereby further improving the etching flatness. In addition, the etching cycle number can be determined according to the thickness of the nitride layer and the single etching time, thereby facilitating the preparation and implementation of subsequent processes, such as cooling the etching chamber to the first process temperature after heating in the first etching process to the N-1th etching process, further improving the smoothness between the multi-cycle etching processes, improving the production efficiency and reducing the production cost.

[0025] Further, the gas concentration ratio of the HF and the water vapor contained in the first gas is a first ratio from the first etching process to the N-1th etching process; the gas concentration ratio of the HF and the water vapor contained in the first gas is a second ratio in the Nth etching process; the second ratio is less than the first ratio. By using the above scheme, the etching speed and the process efficiency can be improved by using a larger gas concentration ratio from the first etching process to the N-1th etching process, and the etching rate can be reduced by using a smaller gas concentration ratio in the Nth etching process, so as to further improve the etching flatness and improve the device quality.

[0026] Further, the semiconductor substrate includes a protruding gate structure, and the oxide layer and the nitride layer include a vertical side wall covering the side wall of the gate structure. Since the gate structure and the side wall process are both key processes of the device, the requirement for etching flatness is higher, and the width of the side wall of the gate structure is often smaller, so the thickness of the stress adjustment layer formed is also smaller, for example, the thickness of the oxide layer and / or the nitride layer is in the nanometer level (such as the thickness is between 1 nanometer and 1 micrometer). At this time, the requirement for etching precision is greater, and the requirement for protection of the oxide layer is also greater. In particular, the scheme of the embodiment of the present application is required to etch the nitride layer in the gas atmosphere all the time, so as to reduce the etching speed and effectively improve the etching flatness. BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a flowchart of a method for forming a semiconductor device according to an embodiment of the present application;

[0028] FIGS. 2 to 4 are schematic diagrams of device cross-sectional structures corresponding to respective steps in a method for forming a semiconductor device according to an embodiment of the present application;

[0029] FIG. 5 is a schematic diagram of an etching time-etching rate curve of a nitride layer according to an embodiment of the present application.

[0030] Legend of reference signs:

[0031] Semiconductor substrate 200, oxide layer 210, nitride layer 220, etching chamber 20. DETAILED DESCRIPTION

[0032] As described above, in the semiconductor manufacturing process, it can be necessary to form a stack structure of an oxide layer and a nitride layer, and to remove an outer layer structure or an upper layer structure in the stack structure after appropriate operation.

[0033] In a specific application scenario, a nitride layer can be formed on the surface of the oxide layer as a stop layer, and the stop layer is removed subsequently.

[0034] In another specific application scenario, after forming the gate structure and then ion implantation is performed on the source and the drain, a nitride layer can be formed on the surface of the oxide layer as a stress adjustment layer to improve the stress effect of the whole device, and the stress adjustment layer also needs to be removed subsequently.

[0035] However, in the existing process for removing the nitride layer, the etching uniformity is insufficient, which affects the quality of the device.

[0036] It is found through research that, in the prior art, phosphoric acid is used to remove the nitride layer. Since the phosphoric acid is a liquid and the liquid etching speed is relatively fast, there are problems such as insufficient uniformity.

[0037] In the embodiment of the present application, in each etching process, a first gas containing HF and water vapor can be used to etch the nitride layer to remove at least a part of the nitride layer, then a second gas containing ammonia is input, and an intermediate product is generated on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas. The intermediate product can be decomposed by heating to make at least a part of the intermediate product generate a gaseous by-product, and then the gaseous by-product is extracted from the etching chamber, so that the nitride layer can be removed by one or more etching processes. By using the above scheme, since the nitride layer is etched in a gas atmosphere all the time, the etching speed is slower compared with liquid etching, which effectively improves the etching uniformity. In addition, since the chemical reaction of forming the intermediate product and decomposing the intermediate product is a reversible reaction, the nitride layer is etched by using the first gas to remove at least a part of the nitride layer, the second gas is input, and an intermediate product is generated on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas. Heating the semiconductor substrate can effectively control the reaction direction of the reversible reaction.

[0038] In order to make the above-mentioned purposes, features and benefits of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0039] Referring to FIG. 1, FIG. 1 is a flowchart of a forming method of a semiconductor device in an embodiment of the present application. The forming method of the semiconductor device can include steps S11 to S12:

[0040] Step S11: providing a semiconductor substrate, and an oxide layer and a nitride layer are sequentially formed on the semiconductor substrate;

[0041] Step S12: performing at least one round of etching process to remove the nitride layer, wherein each round of etching process comprises: etching the nitride layer by using a first gas to remove at least a portion of the nitride layer, wherein the first gas comprises HF and water vapor, inputting a second gas, and generating an intermediate product on the semiconductor substrate under a mixed gas atmosphere of the second gas and the first gas, wherein the second gas comprises ammonia, and heating the semiconductor substrate.

[0042] The above method is described below in combination with FIGS. 2-4.

[0043] FIGS. 2-4 are schematic diagrams of device cross-sectional structures corresponding to respective steps in a method for forming a semiconductor device according to an embodiment of the present application.

[0044] Referring to FIG. 2, a semiconductor substrate 200 is provided, and an oxide layer 210 and a nitride layer 220 are sequentially formed on the semiconductor substrate 200. The nitride layer 220 is etched by using a first gas to remove at least a portion of the nitride layer 220.

[0045] In a specific implementation, the method for forming a semiconductor device can be performed in an etching chamber 20 to etch the nitride layer 220 by using a first gas.

[0046] The semiconductor substrate 200 can be a silicon substrate, or the material of the semiconductor substrate 200 can further include germanium, silicon germanium, silicon carbide, gallium arsenide, or indium gallium. The semiconductor substrate 200 can be a silicon-on-insulator substrate or a germanium-on-insulator substrate, or a substrate with an epitaxy layer (Epi layer) grown thereon.

[0047] It is noted that the semiconductor substrate 200 can further include structures on the surface of the semiconductor substrate 200, such as a gate structure, a metal interconnection structure, and the like, and is not limited to the portion within the surface of the semiconductor substrate 200.

[0048] The oxide layer 210 can be silicon oxide, such as SiO2. The oxide layer 210 can also be germanium oxide, gallium oxide, indium oxide, or other appropriate semiconductor oxide materials.

[0049] The nitride layer 220 can be silicon nitride, such as Si3N4. The nitride layer 220 can also be germanium nitride, gallium nitride, indium nitride, or other appropriate semiconductor nitride materials.

[0050] In the following description, silicon oxide and silicon nitride are used as examples, but this does not limit the specific materials used for the oxide layer 210 and the nitride layer 220.

[0051] The first gas can include hydrogen fluoride gas (HF) and water vapor.

[0052] Further, the step of removing at least part of the nitride layer 220 can include generating a first intermediate product during the removal of at least part of the nitride layer 220, the first intermediate product including silicic acid.

[0053] In a specific implementation, the first intermediate product can be generated according to the following chemical reaction formula:

[0054] Si3N4+4H + +9H2O→3H2SiO3+4NH4 + ;

[0055] In the embodiment, by generating the first intermediate product including silicic acid during the removal of at least part of the nitride layer 220, the HF gas mixed with water vapor in a certain proportion can be introduced to react with the nitride layer 220 to generate silicic acid, so as to realize etching of the nitride layer 220. In addition, since the silicic acid is in a gaseous and / or liquid state, it will block the nitride layer 220 after formation, resulting in a decrease in etching rate. At this time, the etching of the nitride layer 220 can be completed in a gaseous atmosphere through multiple rounds of etching.

[0056] Referring to FIG. 3, a second gas is introduced, and an intermediate product is generated on the semiconductor substrate in a mixed gas atmosphere of the second gas and the first gas.

[0057] The second gas can include ammonia (NH3).

[0058] Specifically, the second gas in each round of etching process can be introduced after removing part of the nitride layer 220, so as to process a byproduct obtained after removing the part of the nitride layer 220.

[0059] It should be noted that when the thickness of the nitride layer 220 is relatively thin, only one round of etching process can be performed. The second gas can be introduced after removing all of the nitride layer 220, so as to process a byproduct obtained after removing all of the nitride layer 220.

[0060] In the embodiment of the present application, in each etching process, the nitride layer 220 can be etched by using a first gas containing HF and water vapor first to remove at least a portion of the nitride layer 220, and then a second gas containing ammonia is inputted, and an intermediate product is generated on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas, so that the nitride layer 220 can be etched in the gas atmosphere all the time, and the etching speed is slower than that of liquid etching, and the etching flatness is effectively improved.

[0061] In a specific embodiment of the embodiment of the present application, the second gas can be inputted in situ. For example, after the nitride layer is etched by using the first gas, the wafer can be kept in the original position, and the second gas is inputted into the etching chamber 20.

[0062] In the embodiment of the present application, by inputting the second gas containing ammonia in situ, and generating an intermediate product on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas, the etching of the nitride layer 220 in the gas atmosphere all the time can be further effectively ensured.

[0063] Further, the step of inputting the second gas and generating an intermediate product on the semiconductor substrate in the mixed gas atmosphere of the second gas and the first gas can include: inputting the second gas into the etching chamber 20, so that the silicic acid is generated in the mixed gas atmosphere of the ammonia and the HF gas, and the SiF4 continues to form (NH4)2SiF6 in the mixed gas atmosphere of the ammonia and the HF gas.

[0064] It should be particularly pointed out that in the process of generating SiF4 and (NH4)2SiF6, the first gas still exists, so the step of generating silicic acid is still in progress. It can be understood that the silicic acid covers the silicon nitride layer 220, and as described above, because the silicic acid is in a gas mist state and / or a liquid state, it will block the nitride layer 220 after being formed, resulting in a decrease in etching rate, so the reaction speed of generating silicic acid will theoretically slow down.

[0065] In a specific implementation, the following chemical reaction formula can be used to generate the intermediate product: H2SiO3+4HF+4NH3→SiF4+3H2O+4NH3; SiF4+2HF+2NH3→(NH4)2SiF6;

[0066] In the embodiment of the present application, the second gas is input into the etching chamber 20 to make the silicic acid generate SiF4 in the mixed gas atmosphere of the ammonia and the HF gas, and the SiF4 continues to form ammonium hexafluorosilicate in the mixed gas atmosphere of the ammonia and the HF gas, so that the ammonium hexafluorosilicate capable of being thermally decomposed can be formed in the mixed gas atmosphere of the second gas and the first gas, thereby keeping the etching of the nitride layer 220 completed in the gas atmosphere.

[0067] As can be seen from the above, the intermediate product can contain SiF4 and ammonium hexafluorosilicate. In other words, in the process of generating the intermediate product, the step of generating SiF4 and the step of generating ammonium hexafluorosilicate are both continuously performed.

[0068] Further, the gas concentration of the ammonia can be greater than the gas concentration of the HF gas.

[0069] In the embodiment of the present application, the gas concentration of the ammonia is greater than the gas concentration of the HF gas, which is lower than the etching ratio of phosphoric acid to nitride and oxide in the prior art, resulting in excessive damage to the oxide in the process of removing the nitride. The scheme of the embodiment of the present application can improve the etching ratio of the nitride and the oxide, thereby protecting the oxide layer 210.

[0070] Still further, the ratio of the gas concentration of the ammonia to the gas concentration of the HF is greater than or equal to 3.

[0071] It should be particularly pointed out that in the mixed gas atmosphere of the first gas containing HF and the second gas containing ammonia, the oxide can also react with HF and ammonia. By setting the ratio of the gas concentration of the ammonia to the gas concentration of the HF to be greater than or equal to 3, the concentration ratio can be more disparate than the ratio of 2:1 (i.e., the gas concentration of the ammonia is 2 times the gas concentration of the HF), so that the etching of the nitride layer 220 can be performed while effectively protecting the oxide layer 210.

[0072] Referring to FIG. 4, the semiconductor substrate is heated.

[0073] In a specific implementation, the intermediate product can be decomposed by heating to make at least a part of the intermediate product generate a gaseous byproduct, and then the gaseous byproduct is extracted from the etching chamber 20.

[0074] In a specific implementation of the embodiment of the present application, the heating step can be performed in situ. For example, after the intermediate product is generated, the wafer can be kept in place for in-situ heating.

[0075] In the embodiment of the present application, by in-situ heating, the intermediate product can be further decomposed in-situ to make at least part of the intermediate product generate gaseous by-products by heating, so that the nitride layer 220 can be etched in a gaseous atmosphere all the time.

[0076] In an embodiment of the present application, the annealing operation can be realized by heating and then cooling down in each round of etching process.

[0077] Specifically, since the chemical reaction of forming the intermediate product and decomposing the intermediate product is a reversible reaction, by heating and then cooling down, the intermediate product can be decomposed by using a higher process temperature, and then the nitride can be etched to form the intermediate product by using a lower process temperature, so as to effectively control the reaction direction of the reversible reaction.

[0078] In another specific embodiment of the present application, after the semiconductor substrate is heated in the first round of etching process, the temperature after heating can be maintained until the temperature is lowered again in the last round of etching process.

[0079] Specifically, by maintaining the temperature after heating, the reaction temperature can no longer be frequently adjusted, and since the adjustment of the chamber temperature often takes a long time, the production efficiency can be effectively improved by using this scheme.

[0080] Further, the step of heating the semiconductor substrate can include: decomposing the intermediate product to make at least part of the intermediate product generate gaseous by-products by heating; and inputting nitrogen (N2) to evacuate the gaseous by-products in the nitrogen atmosphere.

[0081] In a specific embodiment of the embodiment of the present application, the step of inputting nitrogen can be performed in-situ. For example, after the gaseous by-products are generated, the wafer can be maintained at the original position, and nitrogen can be inputted in-situ.

[0082] In the embodiment of the present application, by inputting nitrogen in-situ, the gaseous by-products can be further evacuated in-situ, so that the nitride layer 220 can be etched in a gaseous atmosphere all the time.

[0083] In a specific implementation, the intermediate product can be decomposed by using the following chemical reaction formula to make at least part of the intermediate product generate gaseous by-products by heating:

[0084] Specifically, the intermediate product contains ammonia hexafluorosilicate, which has the property of decomposing by heating, and can generate gaseous by-products by heating.

[0085] It is to be noted that, in the case that SiF4 is not completely reacted to form ammonium hexafluorosilicate, part of the intermediate product (i.e. ammonium hexafluorosilicate) is heated to generate gaseous by-products; in the case that SiF4 is completely reacted to form ammonium hexafluorosilicate, all of the intermediate product (i.e. ammonium hexafluorosilicate) is heated to generate gaseous by-products.

[0086] In the embodiment of the present application, by decomposing the intermediate product, at least part of the intermediate product is heated to generate gaseous by-products; by inputting nitrogen gas, the gaseous by-products are extracted in the nitrogen atmosphere, the protection of the oxide layer 210 and the remaining nitride layer 220 can be realized by inputting nitrogen gas in the process of extracting gaseous by-products, so that the etching of the nitride layer 220 is completed in the gaseous atmosphere.

[0087] Further, the first process temperature for generating the intermediate product can be less than the second process temperature for heating; wherein the first process temperature is 20-120°C; and / or the second process temperature is 130-250°C.

[0088] In the embodiment of the present application, by generating the intermediate product at the first process temperature which is less than the second process temperature for heating; wherein the first process temperature is 20-120°C; and / or the second process temperature is 130-250°C, since the chemical reaction of forming the intermediate product and decomposing the intermediate product is a reversible reaction, the above scheme can be used to etch the nitride to form the intermediate product at a lower process temperature, and to decompose the intermediate product at a higher process temperature, so as to effectively control the reaction direction of the reversible reaction.

[0089] Further, the number of etching processes for removing the nitride layer 220 is N, wherein N is a positive integer and N≥2; after the heating, the etching chamber 20 can be cooled to the first process temperature.

[0090] In the embodiment of the present application, by cooling the etching chamber 20 to the first process temperature, the multiple etching processes can be implemented in a cycle, so that the multiple etching processes are used to improve the fineness of removing the nitride layer 220.

[0091] In one specific embodiment of the embodiment of the present application, before the at least one etching process is performed, the step of pre-determining the number of etching rounds can be further included.

[0092] Specifically, before the performing the at least one round of etching process, the method can further include: determining an etching time-etching rate curve of the nitride layer 220 according to a gas concentration ratio of the HF and the water vapor contained in the first gas, wherein different gas concentration ratios have a pre-determined etching time-etching rate curve of the nitride layer 220, the etching rate curve includes a uniform etching interval and a rate decreasing interval; selecting a single round etching time, the single round etching time is selected from the etching time contained in the uniform etching interval; determining the number of etching rounds according to the thickness of the nitride layer 220 and the single round etching time; wherein the smaller the single round etching time, the greater the thickness of the nitride layer 220, the greater the number of etching rounds.

[0093] In a specific implementation, the etching time-etching rate curve of the nitride layer 220 can be determined in a pre-determined manner for different gas concentration ratios. For example, it can be obtained by performing etching experiments and measuring or calculating using the same or similar process products, or it can be obtained by measuring or calculating based on historical experience data.

[0094] In combination with reference to FIG. 5, FIG. 5 is a schematic diagram of an etching time-etching rate curve of a nitride layer 220 in an embodiment of the present application.

[0095] As shown in FIG. 5, the etching time-etching rate curve of the nitride layer 220 can include a uniform etching interval and a rate decreasing interval. The uniform etching interval can include etching time between T1 and T2, and the rate decreasing interval can include etching time greater than T2.

[0096] It is found through research that, since silicic acid is in an aerosol state and / or a liquid state, the formation of silicic acid will block the silicon nitride layer 220, resulting in a decrease in etching rate.

[0097] In an embodiment of the present application, by including a uniform etching interval and a rate decreasing interval in the etching rate curve, and selecting etching time from the etching time contained in the uniform etching interval, the etching speed can be effectively controlled, and the etching flatness can be further improved.

[0098] Further, the number of etching rounds can be determined according to the thickness of the nitride layer 220 and the single round etching time; wherein the smaller the single round etching time, the greater the thickness of the nitride layer 220, the greater the number of etching rounds.

[0099] In a specific implementation, by pre-determining the number of etching rounds, it can be beneficial for the preparation and implementation of subsequent processes. For example, as mentioned in the foregoing, from the first round of etching process to the N-1th round of etching process, the etching chamber 20 needs to be cooled to the first process temperature after heating, and this step can only be performed after the number of etching rounds is pre-determined.

[0100] Further, the following formula can be used to determine the number of etching rounds:

[0101] wherein N is used to represent the number of etching rounds, L is used to represent the thickness of the nitride layer 220, Ti is used to represent the single-round etching duration, Ri is used to represent the etching rate corresponding to Ti, is used to represent the upward rounding operation.

[0102] In the embodiment of the present application, the number of etching rounds is determined according to the thickness of the nitride layer 220 and the single-round etching duration, so that the number of etching rounds can be determined in advance, thereby facilitating the preparation and implementation of subsequent processes, further improving the smoothness between multiple etching rounds, and improving the production efficiency and reducing the production cost.

[0103] Further, the number of rounds of the etching process for removing the nitride layer 220 is N, wherein N is a positive integer and N≥2; wherein the gas concentration ratio of HF to water vapor contained in the first gas is a first ratio from the first round of etching process to the N-1th round of etching process; in the Nth round of process, the gas concentration ratio of HF to water vapor contained in the first gas is a second ratio; and the second ratio is less than the first ratio.

[0104] In the embodiment of the present application, the gas concentration ratio of HF to water vapor contained in the first gas is relatively large from the first round of etching process to the N-1th round of etching process, and the gas concentration ratio of HF to water vapor contained in the first gas is relatively small in the Nth round of process. By using the above scheme, the etching speed and process efficiency can be improved by using a larger gas concentration ratio from the first round of etching process to the N-1th round of etching process, and the etching rate can be reduced by using a smaller gas concentration ratio in the Nth round of process, thereby further improving the etching flatness and improving the device quality.

[0105] Further, the first ratio can be 2 to 10 times the second ratio.

[0106] In the embodiment of the present application, by setting the first ratio to be one order of magnitude (i.e., 10 times) of the second ratio, the second ratio can be controlled within a reasonable range, and a better balance between the smaller etching rate and the higher etching flatness improvement effect can be achieved.

[0107] Further, the semiconductor substrate 200 can include a protruding gate structure, and the oxide layer 210 and the nitride layer 220 can include vertical side walls covering the sidewalls of the gate structure.

[0108] Specifically, the semiconductor substrate 200 can include a gate structure as shown in FIG. 2. The gate structure can be formed on the surface of an N-type substrate, and can also be formed on the surface of a P-type substrate. The top and sidewall of the gate structure can also have a SiGe layer or other appropriate sub-structure layer. The oxide layer 210 and the nitride layer 220 can cover the SiGe layer or other appropriate sub-structure layer.

[0109] It should be noted that in the structure shown in FIG. 2, the nitride layer 220 can correspondingly cover different areas according to the different performance of the devices formed on the N-type substrate and the P-type substrate, but the coverage range of the oxide layer 210 and the nitride layer 220 in the embodiments of the present application is not limited by FIG. 2.

[0110] The nitride layer 220 formed on the surface of the oxide layer 210 can also serve as a stress adjustment layer, and can also serve as other appropriate functional layers.

[0111] In the embodiments of the present application, the semiconductor substrate 200 includes a protruding gate structure, and the oxide layer 210 and the nitride layer 220 are vertical side walls covering the sidewall of the gate structure. Since the gate structure and the side wall process are both key processes of the device, the requirement for etching flatness is higher, and the width of the sidewall of the gate structure is often smaller, so the thickness of the stress adjustment layer formed is also smaller. For example, the thickness of the oxide layer 210 and / or the nitride layer 220 is in the nanometer level (such as the thickness is between 1 nanometer and 1 micrometer) or even in the angstrom level (such as the thickness is between 1 angstrom and 1 nanometer). At this time, the requirement for etching precision is greater, and the requirement for protection of the oxide layer 210 is also greater. Therefore, it is necessary to use the scheme of the embodiments of the present application to etch the nitride layer 220 in a gas atmosphere, so as to reduce the etching speed and effectively improve the etching flatness.

[0112] It should be understood that the term "and / or" herein only describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " herein represents an "or" relationship between the front and rear associated objects.

[0113] "Multiple" appearing in the embodiments of the present application means two or more.

[0114] The first, second, and the like appearing in the embodiments of the present application are only for illustrative and distinguishing description objects, and there is no order, nor does it represent a special limitation on the number of devices in the embodiments of the present application, which cannot constitute any limitation on the embodiments of the present application.

[0115] Although the present application has been disclosed with reference to the above embodiments, the application is not limited to the above embodiments. It will be apparent to those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the application. The scope of the application should be limited only by the appended claims.

Claims

1. A method for forming a semiconductor device, characterized in that: include: Providing a semiconductor substrate, on which an oxide layer and a nitride layer are sequentially formed; performing at least one etching process to remove the nitride layer; Each round of etching process includes: Etching the nitride layer using a first gas to remove at least a portion of the nitride layer, wherein the first gas comprises HF and water vapor; Inputting a second gas, wherein an intermediate product is generated on the semiconductor substrate in a mixed gas atmosphere of the second gas and the first gas, wherein the second gas comprises ammonia; The semiconductor substrate is heated.

2. The method according to claim 1, characterized in that Removing at least a portion of the nitride layer comprises: A first intermediate product is generated during the removal of at least a portion of the nitride layer, the first intermediate product comprising silicic acid.

3. The method according to claim 2, characterized in that The inputting of the second gas, wherein an intermediate product is generated on the semiconductor substrate in a mixed gas atmosphere of the second gas and the first gas, comprises: The second gas is input into the etching chamber to make the silicic acid generate SiF 4 in the mixed gas atmosphere of the ammonia gas and the HF gas, and the SiF 4 further forms ammonium hexafluorosilicate in the mixed gas atmosphere of the ammonia gas and the HF gas.

4. The method according to any one of claims 1 to 3, characterized in that The gas concentration of the ammonia gas is greater than the gas concentration of the HF gas.

5. The method according to claim 1, characterized in that ； The step of heating the semiconductor substrate comprises: decomposing the intermediate product so that at least a portion of the intermediate product is heated to generate a gaseous by-product; Nitrogen gas was introduced to extract the gaseous by-products under the nitrogen atmosphere.

6. The method according to claim 1 or 5, characterized in that The first process temperature for generating the intermediate product is lower than the second process temperature for heating; Wherein, the first process temperature is 20°C to 120°C; and / or The second process temperature is 130°C to 250°C.

7. The method according to claim 1, characterized in that Before performing at least one etching process, the method further includes: Determining an etching time-etching rate curve for the nitride layer according to a gas concentration ratio of HF and water vapor contained in the first gas, wherein different gas concentration ratios have pre-determined etching time-etching rate curves for the nitride layer, and the etching rate curve includes a uniform etching rate interval and a rate decreasing rate interval; Selecting a single-round etching duration, wherein the single-round etching duration is selected from the etching duration included in the uniform etching interval; Determining the number of etching rounds according to the thickness of the nitride layer and the duration of the single-round etching; The shorter the single-round etching time is, the thicker the nitride layer is, and the greater the number of etching rounds is.

8. The method according to claim 7, characterized in that The number of etching rounds is determined using the following formula: Wherein, N is used to represent the number of etching rounds, L is used to represent the thickness of the nitride layer, Ti is used to represent the duration of a single etching round, and Ri is used to represent the etching rate corresponding to Ti. Indicates a round-up operation.

9. The method according to claim 1 or 8, characterized in that The number of rounds of the etching process for removing the nitride layer is N, where N is a positive integer and N≥2; wherein, from the first etching process to the N-1th etching process, the gas concentration ratio of HF and water vapor contained in the first gas is a first ratio; In the Nth round of process, the gas concentration ratio of HF and water vapor contained in the first gas is a second ratio; The second ratio is smaller than the first ratio.

10. The method according to claim 1, characterized in that The semiconductor substrate includes a protruding gate structure, and the oxide layer and the nitride layer include vertical sidewalls covering sidewalls of the gate structure.

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