Substrate processing method

Abstract

A substrate processing method according to one embodiment of the present invention is a substrate processing method for selectively etching a silicon nitride layer in a substrate having a silicon oxide layer and a silicon nitride layer stacked thereon, characterized by comprising the step of wet etching the silicon nitride layer using a phosphoric acid-based etching solution and the step of dry etching the regrowth oxide formed on the surface of the silicon oxide layer in the wet etching step using an etching gas.

Description

Technology Field

[0001] The present invention relates to a substrate processing method. More specifically, it relates to a substrate processing method capable of efficiently removing regrowth oxide formed at the corners of a silicon oxide layer during wet etching of a silicon nitride layer using a phosphoric acid-based etching solution. Background Technology

[0003] With the recent miniaturization of semiconductor devices, they are becoming increasingly highly integrated. Since silicon nitride films are used as dielectric or insulating films with chemically stable properties, they are widely used in the manufacturing processes of DRAM and FLASH Memory, not only for the basic device isolation process but also as sidewall materials in contact and capping processes.

[0004] Meanwhile, during the manufacturing of semiconductor devices, silicon oxide and silicon nitride layers are sometimes formed alternately in multiple layers on a substrate. In this case, to selectively etch the silicon nitride layers, an etching solution having a high etching selectivity ratio relative to the silicon oxide layer must be applied.

[0005] Conventionally, phosphoric acid-based etchants are known as etchants that have a high etching selectivity relative to silicon oxide layers. Etching of a silicon nitride layer using a phosphoric acid-based etchant corresponds to wet etching.

[0006] Wet etching of a silicon nitride layer using a phosphoric acid-based etching solution is known to involve a reaction according to the following reaction scheme 1 and is performed at a high temperature.

[0007] [Reaction Equation 1]

[0008] 3Si3N4+ 27H2O + 4H3PO4↔ 4(NH4)3PO4+9H2OSiO2

[0009] At this time, the formation of regrowth oxide in the corner portions of the silicon oxide layer during wet etching of the silicon nitride layer using a phosphoric acid-based etching solution is a problem.

[0010] Figure 1 schematically shows the formation of regrowth oxide and the increase in thickness over time during wet etching.

[0011] These regrowth oxides are known to affect subsequent processes and degrade the electrical characteristics of the final manufactured semiconductor device.

[0012] It is generally known that regrowth oxides are formed when silicon-based compounds are included as additives in phosphoric acid-based etching solutions. To address this, methods proposed so far involve suppressing the formation of regrowth oxides during wet etching of silicon nitride layers by adjusting the additives included in the phosphoric acid-based etching solution (e.g., Patent Documents 1 and 2). However, this method has the disadvantage of significantly increasing the wet etching process time for silicon nitride layers. Prior art literature

[0014] Registered Patent Publication No. 10-2325905 (Published Nov. 12, 2021) Published Patent Publication No. 10-2019-0096785 (Published Aug. 20, 2019) The problem to be solved

[0015] The problem to be solved by the present invention is that, since the method of suppressing the generation of regrowth oxide itself during wet etching of a silicon nitride layer has the disadvantage of significantly increasing the process time, the invention provides a substrate treatment method that allows the regrowth oxide to be removed by a dry etching method in a subsequent process instead of allowing the regrowth oxide to be generated during wet etching of a silicon nitride layer.

[0016] In addition, the problem to be solved by the present invention is to provide a substrate processing method capable of increasing the etching selectivity of a regrowth oxide compared to an oxide formed by deposition, etc. means of solving the problem

[0018] A substrate processing method according to an embodiment of the present invention for solving the above problem is a substrate processing method for selectively etching a silicon nitride layer in a substrate having a silicon oxide layer and a silicon nitride layer stacked thereon, characterized by comprising: (a) a step of wet etching the silicon nitride layer using a phosphoric acid-based etching solution - wherein a regrowth oxide is formed on the surface of the silicon oxide layer -; and (b) a step of dry etching the regrowth oxide formed on the surface of the silicon oxide layer in step (a) using an etching gas.

[0019] In step (b) above, the etching gas may consist only of hydrogen fluoride or may include hydrogen fluoride and ammonia. The flow rate of the hydrogen fluoride may be 20 to 60 sccm, and the flow rate of the ammonia may be 40 sccm or less.

[0020] The above step (b) can be performed at a substrate temperature of 80 to 120°C.

[0021] Step (b) above can be performed at a process pressure of 0.3 to 1.0 Torr.

[0023] A substrate processing method according to an embodiment of the present invention for solving the above problem is a substrate processing method for selectively etching a regrowth oxide having a density lower than the density of the silicon oxide layer on the surface of the silicon oxide layer, characterized by including a step of dry etching the regrowth oxide formed on the surface of the silicon oxide layer using an etching gas.

[0024] The above etching gas may include hydrogen fluoride and ammonia. In this case, the flow rate of the hydrogen fluoride may be 20 to 60 sccm, and the flow rate of the ammonia may be 40 sccm or less. A step of raising the temperature of the substrate to remove reaction by-products after the dry etching may be additionally included.

[0025] The above etching gas may consist of hydrogen fluoride. In this case, the flow rate of the hydrogen fluoride may be 20 to 60 sccm. A step of raising the temperature of the substrate to reduce the fluoride content on the substrate surface after the above dry etching may be additionally included.

[0026] The above dry etching can be performed at a substrate temperature of 80 to 120°C.

[0027] The above dry etching can be performed at a process pressure of 0.3 to 1.0 Torr. Effects of the invention

[0029] According to the substrate processing method of the present invention, the regrowth oxide generated during wet etching of the silicon nitride layer can be effectively removed through dry etching.

[0030] In addition, the problem to be solved by the present invention is that the etching selectivity of the regrowth oxide compared to the oxide formed by deposition, etc. can be increased by controlling the type and flow rate of the etching gas, the substrate temperature, and the process pressure.

[0031] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the detailed description below. Brief explanation of the drawing

[0033] Figure 1 schematically shows the formation of regrowth oxide and the increase in thickness over time during wet etching. Figure 2 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to wafer temperature. Figure 3 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to process pressure. Figure 4 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to the flow rate of NH3. Figure 5 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to the flow rate of HF. Figure 6 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to the type of etching gas. Figures 7a to 7e show photographs of the patterns of the regrowth oxide before and after dry etching. Specific details for implementing the invention

[0034] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0035] When an element or layer is described as being "above" or "below" another element or layer, it includes not only being directly above or below the other element or layer, but also cases where another layer or element is interposed in the middle. Additionally, when it is stated that an element is "connected," "combined," or "joined" to another element, it should be understood that while the elements may be directly connected or joined to each other, other elements may be "interposed" between each element, or that each element may be "connected," "combined," or "joined" through other elements.

[0036] The terms used herein are for describing the embodiments and are therefore not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used in this specification, "comprising" and / or "comprising" does not exclude the presence or addition of one or more other elements, elements, steps, and / or actions to the mentioned elements, components, steps, and / or actions.

[0037] A substrate processing method according to a preferred embodiment of the present invention will be described in detail below with reference to the attached drawings.

[0039] A substrate processing method according to an embodiment of the present invention relates to a method for selectively etching a silicon nitride layer in a substrate in which a silicon oxide layer and a silicon nitride layer are stacked. The silicon oxide layer and the silicon nitride layer can be formed alternately to form a stack.

[0040] More specifically, the substrate processing method according to an embodiment of the present invention includes a silicon nitride layer wet etching step and a regrowth oxide dry etching step.

[0041] In the silicon nitride layer wet etching step, the silicon nitride layer is wet-etched using a phosphoric acid-based etchant. A known etchant containing phosphoric acid may be used as the phosphoric acid-based etchant. To increase the etching selectivity of the silicon nitride layer to the silicon oxide layer, the phosphoric acid-based etchant may include silicon-based compounds such as hexafluorosilicate, TEOS, etc.

[0042] As described above, when a silicon nitride layer is wet-etched using a phosphoric acid-based etchant to selectively etch the silicon nitride layer on a substrate in which a silicon oxide layer and a silicon nitride layer are stacked, a regrowth oxide may be formed on the surface of the silicon oxide layer. This regrowth oxide is distinguished from the silicon oxide layer formed by deposition or thermal oxidation in that it is not dense and has soft characteristics, having a relatively lower density compared to the silicon oxide layer formed by deposition or the like. The regrowth oxide can become silicon oxide. Since this regrowth oxide can impair the electrical characteristics of the device, it needs to be removed.

[0043] Conventionally, methods were used to suppress the generation of regrowth oxide itself during the wet etching process by controlling additives in the phosphoric acid-based etching solution, but this has the disadvantage of a very long process time. Accordingly, in the present invention, instead of suppressing the generation of regrowth oxide during the wet etching process, the regrowth oxide generated during the wet etching process is removed through dry etching.

[0044] More specifically, in the dry etching step, a etching gas is used to dry etch the regrowth oxide formed on the surface of the silicon oxide layer during the wet etching step. Specifically, the regrowth oxide on the surface of the silicon oxide layer, having a density lower than that of the silicon oxide layer, is selectively dry etched. The dry etching process can be performed in one cycle, and if necessary, it may be performed in multiple cycles (n cycles). If the dry etching process is performed in multiple cycles, additional benefits may be provided, for example, such as improved underbody damage.

[0045] At this point, it is important to increase the etch selectivity of the regrowth oxide relative to the silicon oxide layer formed in advance through deposition, thermal oxidation, etc. The etch selectivity of the regrowth oxide relative to the silicon oxide layer may be 5:1 or higher, 10:1 or higher is preferable, and 15:1 or higher is more preferable. As described below, this etch selectivity of the regrowth oxide relative to the silicon oxide layer can be controlled by adjusting the substrate temperature, process pressure, type and flow rate of the etching gas, etc.

[0046] For example, the etching gas may include hydrogen fluoride and ammonia. As another example, the etching gas may consist solely of hydrogen fluoride. Hydrogen fluoride and / or ammonia may be supplied into the reaction chamber along with an inert gas such as argon.

[0047] It is preferable that the flow rate of ammonia be 40 sccm or less, and more preferable that it be 30 sccm or less. When ammonia is not included in the etching gas, or even if it is included, the flow rate is 40 sccm or less, a high etching selectivity ratio of the regrowth oxide relative to the silicon oxide layer can be obtained. Meanwhile, although there are no major limitations on the flow rate of hydrogen fluoride, it is preferable to be 20 to 60 sccm when considering both the etching rate and the etching selectivity ratio.

[0048] Meanwhile, since an etching gas composed solely of hydrogen fluoride exhibited a significantly higher etching selectivity compared to an etching gas containing hydrogen fluoride and ammonia, it is more desirable to use an etching gas composed solely of hydrogen fluoride.

[0049] After dry etching using an etching gas containing fluorine and ammonia, a step of raising the substrate temperature to approximately 150–300°C may be added to remove reaction byproducts. Here, the heating means for raising the substrate temperature is not particularly limited, and various means such as lamp heating, susceptor heating, and high-temperature gas supply may be used. Additionally, a temperature raising step may be performed for the purpose of reducing fluorine after dry etching using an etching gas composed solely of fluorine. After the etching step and / or the temperature raising step, a purging step to purge the inside of the reaction chamber and / or a pumping step to remove gas inside the reaction chamber may be additionally included. Depending on the type of etching gas, the application of the temperature raising step and the process sequence may vary.

[0050] For example, one-cycle dry etching using an etching gas containing hydrogen fluoride and ammonia may consist of etching, heating, purging, and pumping.

[0051] As another example, one-cycle dry etching using an etching gas composed solely of hydrogen fluoride can consist of etching, purging, pumping, and heating.

[0052] As another example, n-cycle dry etching using an etching gas containing hydrogen fluoride and ammonia can consist of etching + heating n cycles, purging, and pumping.

[0053] As another example, n-cycle dry etching using an etching gas composed solely of hydrogen fluoride can consist of etching + purge n cycles, pumping, and heating.

[0055] It is preferable that the dry etching step for removing the regrowth oxide be performed at a substrate temperature of 80 to 120°C. If the substrate temperature is below 80°C, it is difficult to obtain an etch selectivity ratio of the regrowth oxide to the silicon oxide layer of 5:1 or higher. On the other hand, if the substrate temperature exceeds 120°C, it may become difficult to obtain a high etch selectivity ratio of the regrowth oxide to the silicon oxide layer, and the etching rate of the regrowth oxide as well as the silicon oxide layer decreases rapidly, which may result in an etch stop.

[0056] In addition, it is preferable that the dry etching step for removing the regrowth oxide be performed at a process pressure of 0.3 to 1.0 Torr. If the process pressure exceeds 1.0 Torr, it may be difficult to obtain a high etching selectivity ratio of the regrowth oxide relative to the silicon oxide layer. On the other hand, if the process pressure is less than 0.3 Torr, it may be difficult to obtain a high etching selectivity ratio of the regrowth oxide relative to the silicon oxide layer, and etching stoppage may occur.

[0058] Hereinafter, the structure and operation of the present invention will be explained in more detail through preferred embodiments of the present invention. However, these are presented as preferred examples of the present invention and should not be interpreted in any way as limiting the present invention.

[0059] Details not listed here can be sufficiently technically inferred by a person skilled in this field, so their explanation will be omitted.

[0060] In FIG. 2 and the drawings described below, the etching selectivity refers to the amount of etching of the regrowth oxide when the amount of etching of the silicon oxide layer (unit: angstrom unit; au) is set to 1, i.e., the amount of etching of the regrowth oxide ÷ the amount of etching of the silicon oxide layer.

[0062] Evaluation of Regrowth Oxide Etching Characteristics According to Substrate Temperature

[0063] The process conditions are as follows.

[0064] Process Temperature: 60℃, 80℃, 100℃, 110℃, 120℃, 140℃

[0065] Process pressure: 1 Torr

[0066] Etching gas: HF 28 sccm + NH3 19 sccm + Ar 126 sccm

[0067] Number of cycles: 1 cycle

[0068] Figure 2 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to substrate temperature.

[0069] Referring to Figure 2, when the substrate temperature is 80 to 120°C, it can be seen that not only is the etching amount, or etching rate, fast, but the etching selectivity of the regrowth oxide relative to the silicon oxide layer is also high. On the other hand, when the substrate temperature is too low at 60°C, it can be seen that the etching amount of the silicon oxide layer increases significantly, and the etching selectivity of the regrowth oxide relative to the silicon oxide layer decreases significantly. Furthermore, when the substrate temperature is too high at 140°C, it can be seen that not only is the etching selectivity of the regrowth oxide relative to the silicon oxide layer low, but the etching amount of the silicon oxide layer and the regrowth oxide itself is very low.

[0071] Evaluation of Regrowth Oxide Etching Characteristics According to Process Pressure

[0072] The process conditions are as follows.

[0073] Process temperature: 110℃

[0074] Process pressure: 0.1 Torr, 0.3 Torr, 0.5 Torr, 0.8 Torr, 1 Torr, 1.5 Torr

[0075] Etching gas: HF 28 sccm + NH3 19 sccm + Ar 126 sccm

[0076] Number of cycles: 1 cycle

[0077] Figure 3 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to process pressure.

[0078] Referring to Figure 3, when the process pressure is 0.3 to 1.0 Torr, it can be seen that not only is the etching amount high, but the etching selectivity of the regrowth oxide relative to the silicon oxide layer is also high. On the other hand, when the process pressure is too high at 1.5 Torr, it can be seen that the etching amount of the silicon oxide layer increases significantly, and the etching selectivity of the regrowth oxide relative to the silicon oxide layer decreases significantly. In addition, when the process pressure is too low at 0.1 Torr, it can be seen that the etching amount of the silicon oxide layer and the regrowth oxide is very low.

[0080] NH 3 Evaluation of Regrowth Oxide Etching Characteristics According to Flow Rate

[0081] The process conditions are as follows.

[0082] Process temperature: 110℃

[0083] Process pressure: 0.8 Torr

[0084] Etching gas: HF 28 sccm + Ar 126 sccm + NH 30 sccm, 19 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm

[0085] Number of cycles: 1 cycle

[0086] Figure 4 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to the flow rate of NH3.

[0087] Referring to Figure 4, it can be seen that the etching selectivity and the amount of etched regrowth oxide are affected by the flow rate of NH3. Considering all of these factors, it can be seen that the flow rate of NH3 should be 40 sccm or less. Meanwhile, particularly high etching selectivity of the regrowth oxide relative to the silicon oxide layer was observed at NH3 flow rates of 0 sccm, 19 sccm, and 30 sccm. Notably, a higher etching selectivity was observed when the NH3 flow rate was 0 sccm, i.e., when the etching gas consisted only of HF.

[0089] Evaluation of Regrowth Oxide Etching Characteristics According to HF Flow Rate

[0090] The process conditions are as follows.

[0091] Process temperature: 110℃

[0092] Process pressure: 0.8 Torr

[0093] Etching gas: HF 28 sccm, 45 sccm, 60 sccm + NH 30 sccm + Ar 126 sccm

[0094] Number of cycles: 1 cycle

[0095] Figure 5 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to the flow rate of HF.

[0096] Referring to FIG. 5, when only HF is used as the etching gas, the etching selectivity and the amount of etched regrowth oxide are affected to some extent depending on the flow rate of HF, but good etching amounts and etching selectivity were observed at 28 sccm, 45 sccm, and 60 sccm. In this regard, it is preferable that the flow rate of HF be 60 sccm or less. However, when the flow rate of HF is less than 20 sccm, the amount of etched regrowth oxide may be significantly reduced; therefore, when only HF is used as the etching gas, it is more preferable that the flow rate of HF be 20 to 60 sccm, and most preferable that it be 45 to 60 sccm.

[0098] Figure 6 is a graph showing the dry etching characteristics of regrowth oxide and thermal oxide according to the type of etching gas.

[0099] The left side of Fig. 6 shows the case where hydrogen fluoride and ammonia were used as etching gases, and the etching characteristics of the regrowth oxide were evaluated under 1 cycle conditions of HF 28 sccm, NH3 19 sccm, Ar 126 sccm at 110°C and 0.8 Torr. On the other hand, the right side of Fig. 5 shows the case where only hydrogen fluoride was used as etching gas, and the etching characteristics of the regrowth oxide were evaluated under 1 cycle conditions of HF 56 sccm, NH3 0 sccm, Ar 126 sccm at 110°C and 1.2 Torr.

[0100] Referring to Figure 6, it can be seen that using only hydrogen fluoride as an etching gas is more advantageous for the etching selectivity characteristics of the regrowth oxide than using hydrogen fluoride and ammonia.

[0102] Figures 7a to 7e show pattern photographs of the regrowth oxide before and after dry etching.

[0103] More specifically, FIG. 7a shows a pattern photograph of the regrowth oxide before dry etching, that is, a pattern photograph after etching with a phosphoric acid-based etchant.

[0104] Figure 7b shows a pattern photograph of a regrowth oxide etched under 1 cycle conditions of HF 56 sccm, NH 30 sccm, Ar 126 sccm at 110°C and 1.2 Torr.

[0105] Figure 7c shows a pattern photograph of a regrowth oxide etched under 3 cycle conditions of HF 28 sccm, NH 30 sccm, Ar 126 sccm at 80°C and 0.8 Torr.

[0106] Figure 7d shows a pattern photograph of a regrowth oxide etched under 80°C, 0.8 Torr conditions, HF 28 sccm, NH 30 sccm, Ar 126 sccm, and 1 cycle.

[0107] Figure 7e shows a pattern photograph of a regrowth oxide etched under 1 cycle conditions of HF 28 sccm, NH3 19 sccm, Ar 126 sccm at 110℃ and 0.8 Torr.

[0108] Referring to Fig. 7a, it can be seen that the thickness of the silicon oxide layer at the pattern end increased after wet etching with a phosphoric acid-based etchant, which means that regrowth oxide was formed on the surface of the silicon oxide layer during wet etching.

[0109] Referring to FIGS. 7b to 7e, it can be seen that the thickness of the silicon oxide layer at the pattern end is reduced again by dry etching the regrowth oxide with hydrogen fluoride or by dry etching the regrowth oxide using hydrogen fluoride and ammonia, which means that the regrowth oxide was successfully removed through this dry etching.

[0110] In addition, when comparing Fig. 7c, in which n cycles (1 minute x 3 times) are applied, with Fig. 7d, in which 1 cycle (3 minutes) is applied, it was found that the case of Fig. 7c, in which n cycles are applied, is relatively more advantageous for improving lower body damage.

[0112] As explained above, according to the substrate processing method of the present invention, the regrowth oxide generated during wet etching of the silicon nitride layer can be effectively removed through dry etching, and the etching selectivity of the regrowth oxide compared to the oxide formed by deposition, etc. can be increased by controlling the type and flow rate of the etching gas, the substrate temperature, and the process pressure.

[0114] Although the present invention has been described above with reference to embodiments, various changes and modifications may be made by those skilled in the art. Such changes and modifications are considered to be within the scope of the present invention as long as they do not depart from the scope of the present invention. Accordingly, the scope of rights of the present invention should be determined by the claims set forth below.

Claims

Claim 1 A substrate processing method for selectively etching a silicon nitride layer in a substrate having a silicon oxide layer and a silicon nitride layer stacked thereon, comprising: (a) a step of wet-etching the silicon nitride layer using a phosphoric acid-based etching solution, wherein a regrowth oxide is formed on the surface of the silicon oxide layer; and (b) a step of dry-etching the regrowth oxide formed on the surface of the silicon oxide layer in step (a) using an etching gas, wherein step (b) is performed at a substrate temperature of 80 to 120°C and a process pressure of 0.3 to 1.0 Torr. Claim 2 A substrate processing method according to claim 1, wherein in step (b), the etching gas comprises hydrogen fluoride and ammonia. Claim 3 A substrate treatment method according to claim 2, characterized in that the flow rate of the hydrogen fluoride is 20 to 60 sccm and the flow rate of the ammonia is 40 sccm or less. Claim 4 A substrate processing method according to claim 1, wherein in step (b), the etching gas is composed of hydrogen fluoride. Claim 5 A substrate treatment method according to claim 4, characterized in that the flow rate of the hydrogen fluoride is 20 to 60 sccm. Claim 6 A substrate processing method for selectively etching a regrowth oxide having a density lower than that of the silicon oxide layer on the surface of the silicon oxide layer, comprising the step of dry etching the regrowth oxide formed on the surface of the silicon oxide layer using an etching gas, wherein the dry etching step is performed at a substrate temperature of 80 to 120°C and a process pressure of 0.3 to 1.0 Torr. Claim 7 A substrate processing method according to claim 6, characterized in that the etching gas comprises hydrogen fluoride and ammonia. Claim 8 A substrate treatment method according to claim 7, characterized in that the flow rate of the hydrogen fluoride is 20 to 60 sccm and the flow rate of the ammonia is 40 sccm or less. Claim 9 A substrate processing method according to claim 7, further comprising a step of raising the temperature of the substrate to remove reaction by-products after the dry etching. Claim 10 A substrate processing method according to claim 7, characterized in that the etching gas is composed of hydrogen fluoride. Claim 11 A substrate treatment method according to claim 10, characterized in that the flow rate of the hydrogen fluoride is 20 to 60 sccm. Claim 12 A substrate processing method according to claim 10, further comprising a step of raising the temperature of the substrate to reduce the fluorine content on the substrate surface after the above dry etching. Claim 13 delete Claim 14 delete Claim 15 delete Claim 16 delete

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