Substrate processing method

Abstract

To provide a substrate processing method in which regrowth oxide is created during wet etching of a silicon nitride layer but is removed by a dry etching method in a following process.SOLUTION: A substrate processing method for etching a silicon nitride layer selectively in a substrate where a silicon oxide layer and the silicon nitride layer are stacked includes: wet-etching the silicon nitride layer with a phosphoric acid-based etching solution; and dry-etching regrowth oxide, which is formed on a surface of the silicon oxide layer in the wet etching step, with etching gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a substrate processing method, and more particularly to a substrate processing method capable of efficiently removing regrown oxide generated at corners of a silicon oxide layer during wet etching of a silicon nitride layer using a phosphoric acid-based etching solution. [Background technology]

[0002] In recent years, semiconductor devices have become more highly integrated as they become finer. Silicon nitride films are used as dielectric or insulating films having chemically stable properties, and are therefore widely used in the manufacturing processes of DRAMs and FLASH memories, not only in the basic device isolation process of memory devices, but also as a sidewall material in contact and capping processes.

[0003] Meanwhile, in the manufacture of semiconductor devices, silicon oxide layers and silicon nitride layers may be alternately formed on a substrate, and in this case, in order to selectively etch the silicon nitride layer, an etchant having a higher etch selectivity than the silicon oxide layer must be used.

[0004] Conventionally, phosphoric acid-based etching solutions have been known as etching solutions having a high etching selectivity compared to silicon oxide layers. Etching of a silicon nitride layer using a phosphoric acid-based etching solution corresponds to wet etching.

[0005] Wet etching of silicon nitride layers using phosphoric acid-based etchants is known to involve the reaction according to Reaction Scheme 1 below and is carried out at high temperatures.

[0006] [Reaction Scheme 1] 3Si3N4+27H2O+4H3PO4⇔4(NH4)3PO4+9H2OSiO2

[0007] At this time, during wet etching of the silicon nitride layer using a phosphoric acid-based etchant, generation of regrowth oxide at corners of the silicon oxide layer is problematic.

[0008] FIG. 1 is a schematic illustrating the formation and increase in thickness of regrown oxide over wet etch time.

[0009] It is known that these regrown oxides affect subsequent processes and degrade the electrical characteristics of the final semiconductor device.

[0010] It is generally known that regrown oxides are generated when phosphoric acid-based etchants contain silicon-based compounds as additives. To solve this problem, methods proposed to date include adjusting the additives contained in the phosphoric acid-based etchant to suppress the generation of regrown oxides during wet etching of the silicon nitride layer (e.g., KR10-2325905B, KR10-2019-0096785A). However, this method has the disadvantage of requiring a very long wet etching process time for the silicon nitride layer. Summary of the Invention [Problem to be solved by the invention]

[0011] The problem to be solved by the present invention is to provide a substrate processing method in which regrown oxide is generated during wet etching of a silicon nitride layer, and the regrown oxide can be removed by a dry etching method in a subsequent process, in place of the method for suppressing the generation of regrown oxide itself during wet etching of a silicon nitride layer, which has a drawback of requiring a very long process time.

[0012] Another problem to be solved by the present invention is to provide a method for processing a substrate, which increases the etching selectivity of regrown oxide relative to oxide formed by deposition or the like. [Means for solving the problem]

[0013] In order to solve the above problems, a substrate processing method according to an embodiment of the present invention is a method for selectively etching a silicon nitride layer in a substrate having a silicon oxide layer and a silicon nitride layer stacked thereon, the method comprising: (a) wet-etching the silicon nitride layer using a phosphoric acid-based etching solution, at which time a regrown oxide is generated on a surface of the silicon oxide layer; and (b) dry-etching the regrown oxide in the step (a) using an etching gas.

[0014] In the step (b), the etching gas may be composed of only hydrogen fluoride or may contain 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.

[0015] The above step (b) can be carried out at a substrate temperature of 80 to 120°C.

[0016] The above step (b) can be carried out at a process pressure of 0.3 to 1.0 Torr.

[0017] In order to solve the above problems, a substrate processing method according to an embodiment of the present invention is a substrate processing method for selectively etching regrown oxide on a surface of a silicon oxide layer, the regrown oxide having a density lower than that of the silicon oxide layer, the substrate processing method comprising the step of dry etching the regrown oxide using an etching gas.

[0018] The 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. After the dry etching, the method may further include a step of increasing the temperature of the substrate to remove reaction by-products.

[0019] The etching gas may be hydrogen fluoride. In this case, the flow rate of the hydrogen fluoride may be 20 to 60 sccm. The method may further include a step of increasing the temperature of the substrate after the dry etching to reduce the fluorine content on the substrate surface.

[0020] The dry etching can be carried out at a substrate temperature of 80 to 120°C.

[0021] The dry etching can be performed at a process pressure of 0.3 to 1.0 Torr. Effect of the Invention

[0022] According to the substrate processing method of the present invention, the regrown oxide generated during the wet etching of the silicon nitride layer can be effectively removed by dry etching.

[0023] Another object of the present invention is to improve the etching selectivity of regrown oxide to oxide formed by deposition, etc., by controlling the type and flow rate of etching gas, substrate temperature, and process pressure.

[0024] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned above will be clearly understood by those skilled in the art from the detailed description below. [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating the formation and thickness increase of regrown oxide as wet etching time increases. [Diagram 2] 1 is a graph showing dry etch characteristics of regrown oxide and thermal oxide as a function of wafer temperature. [Diagram 3] 1 is a graph showing dry etching characteristics of regrown oxide and thermal oxide depending on process pressure. [Figure 4] 1 is a graph showing dry etch characteristics of regrown oxide and thermal oxide as a function of NH3 flow rate. [Diagram 5] 1 is a graph showing dry etch characteristics of regrown oxide and thermal oxide as a function of HF flow rate. [Figure 6] 1 is a graph showing dry etching characteristics of regrown oxide and thermal oxide depending on the type of etching gas. [Figure 7a] 1 shows pattern photographs before and after dry etching of regrown oxide. [Figure 7b] 1 shows pattern photographs before and after dry etching of regrown oxide. [Figure 7c] 1 shows pattern photographs before and after dry etching of regrown oxide. [Figure 7d] 1 shows pattern photographs before and after dry etching of regrown oxide. [Figure 7e] 1 shows pattern photographs before and after dry etching of regrown oxide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The advantages and features of the present invention, as well as the methods for achieving them, will become clear from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be embodied in various different forms. However, the embodiments are provided to complete the disclosure of the present invention and to fully inform those skilled in the art of the present invention of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0027] References to an element or layer being "on" or "under" another element or layer include not only directly on or directly under the other element or layer, but also when there are other layers or elements between. Also, when an element is described as being "coupled," "bonded," or "connected" to another element, it should be understood that the elements may be directly coupled or connected to each other, but also that there may be other elements "intervening" between each element, or each element may be "coupled," "bonded," or "connected" through other elements.

[0028] The terms used in the present specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In the present specification, the singular form includes the plural form unless otherwise stated in the text. When used in the specification, "comprises" and / or "includes" refers to a recited element, element, step and / or operation, and does not exclude the presence or addition of one or more other elements, elements, steps and / or operations.

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a substrate processing method according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0030] 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 having a silicon oxide layer and a silicon nitride layer stacked thereon, the silicon oxide layer and the silicon nitride layer being alternately formed to form a stack.

[0031] More specifically, a substrate processing method according to an embodiment of the present invention includes wet etching the silicon nitride layer and dry etching the regrown oxide.

[0032] In the wet etching step of the silicon nitride layer, the silicon nitride layer is wet etched using a phosphoric acid-based etchant. The phosphoric acid-based etchant may be a known etchant containing phosphoric acid. The phosphoric acid-based etchant may contain a silicon-based compound such as hexafluorosilicate or TEOS in order to increase the etching selectivity of the silicon nitride layer relative to the silicon oxide layer.

[0033] As described above, when the silicon nitride layer in a substrate having a silicon oxide layer and a silicon nitride layer stacked thereon is wet-etched using a phosphoric acid-based etching solution to selectively etch the silicon nitride layer, regrown oxides may be generated on the surface of the silicon oxide layer. These regrown oxides are distinguished from silicon oxide layers formed by deposition, thermal oxidation, etc. in that they have a relatively low density, are not dense, and have soft properties compared to silicon oxide layers formed by deposition, etc. The regrown oxides may become silicon oxide. These regrown oxides may impair the electrical properties of devices and therefore need to be removed.

[0034] In the past, the generation of regrown oxide during wet etching was suppressed by controlling additives in a phosphoric acid-based etchant, but this has the disadvantage of taking a long process time. Therefore, in the present invention, instead of suppressing the generation of regrown oxide during wet etching, the regrown oxide generated during wet etching is removed by dry etching.

[0035] More specifically, in the dry etching step, the regrown oxide formed on the surface of the silicon oxide layer in the wet etching step is dry-etched using an etching gas. Specifically, the regrown oxide on the surface of the silicon oxide layer, which has a density lower than that of the silicon oxide layer, is selectively dry-etched. The dry etching can be performed in one cycle, or multiple cycles (n cycles) as necessary. When the dry etching is performed in multiple cycles, it can bring about additional advantages, such as improvement of bottom damage.

[0036] At this time, it is important to increase the etching selectivity of the regrown oxide to the silicon oxide layer previously formed by deposition, thermal oxidation, etc. The etching selectivity of the regrown oxide to the silicon oxide layer may be 5:1 or more, preferably 10:1 or more, and more preferably 15:1 or more. The etching selectivity of the regrown oxide to the silicon oxide layer can be controlled by adjusting the substrate temperature, process pressure, type and flow rate of the etching gas, etc., as described below.

[0037] In one example, the etching gas may include hydrogen fluoride and ammonia. In another example, the etching gas may consist of only hydrogen fluoride. The hydrogen fluoride and / or ammonia may be supplied to the interior of the reaction chamber along with an inert gas, such as argon gas.

[0038] The flow rate of ammonia is preferably 40 sccm or less, more preferably 30 sccm or less. When the etching gas does not contain ammonia, or when the flow rate is 40 sccm or less, a high etching selectivity of the regrown oxide to the silicon oxide layer can be obtained. On the other hand, the flow rate of hydrogen fluoride is not significantly limited, but is preferably 20 to 60 sccm in consideration of both the etching rate and the etching selectivity.

[0039] On the other hand, since an etching gas consisting of only hydrogen fluoride exhibits a significantly higher etching selectivity than an etching gas containing hydrogen fluoride and ammonia, it is more preferable to use an etching gas consisting of only hydrogen fluoride.

[0040] After the dry etching using an etching gas containing fluorine and ammonia, a step of heating the substrate to about 150 to 300° C. can be added to remove reaction by-products. Here, the heating means for heating the substrate is not particularly limited, and various means such as lamp heating, susceptor heating, and high-temperature gas supply can be used. In addition, even after the dry etching using an etching gas consisting of only fluorine, a heating step can be performed for the purpose of reducing fluorine. After the etching step and / or the heating step, a purging step for purging the inside of the reaction chamber and / or a pumping step for removing the internal gas of the reaction chamber can be further included. Depending on the type of etching gas, whether or not a heating step is applied and the process order can be different.

[0041] For example, a one cycle dry etch using an etching gas containing hydrogen fluoride and ammonia may consist of etching, heating, purging, and pumping.

[0042] In another example, a one cycle dry etch using an etching gas consisting of only hydrogen fluoride can consist of etching, purging, pumping, and ramping up.

[0043] In yet another example, an n-cycle dry etch using an etching gas containing hydrogen fluoride and ammonia can consist of n cycles of etch & heat up, purging, and pumping.

[0044] In yet another example, an n-cycle dry etch using an etching gas consisting of only hydrogen fluoride can consist of n cycles of etch & purge, pumping, and ramping up.

[0045] The dry etching step for removing the regrown oxide is preferably performed at a substrate temperature of 80 to 120° C. If the substrate temperature is less than 80° C., it is difficult to obtain an etching selectivity ratio of the regrown oxide to the silicon oxide layer of 5:1 or more. On the other hand, if the substrate temperature is more than 120° C., it may be difficult to obtain a high etching selectivity ratio of the regrown oxide to the silicon oxide layer, and the etching rate of not only the silicon oxide layer but also the regrown oxide may decrease rapidly, resulting in an etch stop.

[0046] In addition, the dry etching step for removing the regrown oxide is preferably 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 of the regrown oxide 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 of the regrown oxide to the silicon oxide layer, and an etch stop may occur.

[0047] The present invention will be described in more detail below with reference to preferred embodiments thereof, which are presented as preferred examples of the present invention and are not to be construed as limiting the present invention in any way.

[0048] Contents not described here can be fully inferred from a technical standpoint by a person skilled in the art, and therefore explanations thereof will be omitted.

[0049] In FIG. 2 and the following drawings, the etching selectivity means the etching amount of the regrown oxide when the etching amount (unit: angstrom unit; au) of the silicon oxide layer is set to 1, that is, the etching amount of the regrown oxide divided by the etching amount of the silicon oxide layer.

[0050] [Evaluation of etching characteristics of regrown oxide by substrate temperature] The process conditions are as follows:

[0051] Process temperature: 60℃, 80℃, 100℃, 110℃, 120℃, 140℃ Process pressure: 1 Torr Etching gas: HF 28sccm + NH3 19sccm + Ar 126sccm Number of cycles: 1 cycle

[0052] FIG. 2 is a graph showing the dry etch characteristics of regrown oxide and thermal oxide as a function of substrate temperature.

[0053] 2, when the substrate temperature is 80 to 120° C., not only is the etching amount, i.e., the etching rate, high, but also the etching selectivity of the regrown oxide to the silicon oxide layer is high. On the other hand, when the substrate temperature is too low, i.e., 60° C., the etching amount of the silicon oxide layer increases significantly, and the etching selectivity of the regrown oxide to the silicon oxide layer decreases significantly. Also, when the substrate temperature is too high, i.e., 140° C., not only is the etching selectivity of the regrown oxide to the silicon oxide layer low, but the etching amounts of the silicon oxide layer and the regrown oxide themselves are very low.

[0054] [Evaluation of etching characteristics of regrown oxide depending on process pressure] The process conditions are as follows:

[0055] Process temperature: 110℃ Process pressure: 0.1 Torr, 0.3 Torr, 0.5 Torr, 0.8 Torr, 1 Torr, 1.5 Torr Etching gas: HF 28sccm + NH3 19sccm + Ar 126sccm Number of cycles: 1 cycle

[0056] FIG. 3 is a graph showing the dry etching characteristics of regrown oxide and thermal oxide as a function of process pressure.

[0057] 3, when the process pressure is 0.3 to 1.0 Torr, not only is the etching amount high, but also the etching selectivity of the regrown oxide to the silicon oxide layer is high. On the other hand, when the process pressure is too high, such as 1.5 Torr, the etching amount of the silicon oxide layer increases significantly, and the etching selectivity of the regrown oxide to the silicon oxide layer decreases significantly. Also, when the process pressure is too low, such as 0.1 Torr, the etching amounts of the silicon oxide layer and the regrown oxide themselves are very low.

[0058] [Evaluation of regrowth oxide etching characteristics by NH3 flow rate] The process conditions are as follows:

[0059] Process temperature: 110℃ Process pressure: 0.8 Torr Etching gas: HF 28 sccm + Ar 126 sccm + NH 30 sccm, 19 sccm, 30 sccm, 40 sccm, 50 sccm, 60 sccm Number of cycles: 1 cycle

[0060] FIG. 4 is a graph showing the dry etch characteristics of regrown oxide and thermal oxide as a function of NH3 flow rate.

[0061] 4, it can be seen that the NH3 flow rate affects the etching selectivity and the amount of etched regrown oxide, and taking both of these into consideration, it can be said that the NH3 flow rate is preferably 40 sccm or less. On the other hand, when the NH3 flow rates are 0 sccm, 19 sccm, and 30 sccm, a particularly high etching selectivity of the regrown oxide to the silicon oxide layer is shown, and unusually, when the NH3 flow rate is 0 sccm, that is, when the etching gas is composed only of HF, a higher etching selectivity is shown.

[0062] [Evaluation of regrowth oxide etching characteristics by HF flow rate] The process conditions are as follows:

[0063] Process temperature: 110℃ Process pressure: 0.8 Torr Etching gas: HF 28sccm, 45sccm, 60sccm + NH 30sccm + Ar 126sccm Number of cycles: 1 cycle

[0064] FIG. 5 is a graph showing the dry etch characteristics of regrown oxide and thermal oxide as a function of HF flow rate.

[0065] 5, when only HF is used as the etching gas, the etching selectivity and the amount of regrowth oxide etched are affected to some extent by the HF flow rate, but good etching amounts and etching selectivity are shown at 28 sccm, 45 sccm, and 60 sccm. In this respect, it is preferable that the HF flow rate is 60 sccm or less. However, when the HF flow rate is less than 20 sccm, the amount of regrowth oxide etched may be significantly reduced, so when only HF is used as the etching gas, the HF flow rate is more preferably 20 to 60 sccm, and most preferably 45 to 60 sccm.

[0066] FIG. 6 is a graph showing the dry etching characteristics of regrown oxide and thermal oxide depending on the type of etching gas.

[0067] The left side of Fig. 6 shows the results of evaluating the etching characteristics of the regrown oxide when hydrogen fluoride and ammonia were used as the etching gas, with one cycle of HF 28 sccm, NH 319 sccm, and Ar 126 sccm at 110°C and 0.8 Torr. On the other hand, the right side of Fig. 5 shows the results of evaluating the etching characteristics of the regrown oxide when only hydrogen fluoride was used as the etching gas, with one cycle of HF 56 sccm, NH 30 sccm, and Ar 126 sccm at 110°C and 1.2 Torr.

[0068] Referring to FIG. 6, it can be seen that using only hydrogen fluoride as an etching gas is more advantageous in terms of etching selectivity characteristics of regrown oxide than using hydrogen fluoride and ammonia as an etching gas.

[0069] 7a-7e show the pattern photographs before and after dry etching of the regrown oxide.

[0070] More specifically, FIG. 7a shows a pattern photograph before dry etching of the regrown oxide, and after etching with a phosphoric acid-based etchant.

[0071] FIG. 7b shows a pattern photograph of the etched regrown oxide at 110° C., 1.2 Torr, HF 56 sccm, NH 30 sccm, Ar 126 sccm, 1 cycle.

[0072] FIG. 7c shows a pattern photograph of the etched regrown oxide at 80° C., 0.8 Torr, HF 28 sccm, NH 30 sccm, Ar 126 sccm, 3 cycles.

[0073] FIG. 7d shows a pattern photograph of the etched regrown oxide at 80° C., 0.8 Torr, and one cycle of HF 28 sccm, NH 30 sccm, and Ar 126 sccm.

[0074] FIG. 7e shows a pattern photograph of the etched regrown oxide at 110° C., 0.8 Torr, with 1 cycle of HF 28 sccm, NH 3 19 sccm, and Ar 126 sccm.

[0075] Referring to FIG. 7a, it can be seen that the thickness of the silicon oxide layer on the pattern end side increases after wet etching with a phosphoric acid-based etchant, which means that regrown oxide is generated on the surface of the silicon oxide layer during wet etching.

[0076] Referring to Figures 7b to 7e, it can be seen that the thickness of the silicon oxide layer on the pattern end side is further reduced by dry etching the regrown oxide with hydrogen fluoride or by dry etching the regrown oxide using hydrogen fluoride and ammonia, which means that the regrown oxide is successfully removed by these dry etches.

[0077] In addition, comparing Figure 7c, in which n cycles (1 min x 3 times) were applied, with Figure 7d, in which 1 cycle (3 min) was applied, it was shown that the case of Figure 7c, in which n cycles were applied, was more advantageous in terms of relatively improving the lower damage.

[0078] As described above, according to the substrate processing method of the present invention, regrown oxide generated during wet etching of a silicon nitride layer can be effectively removed by dry etching, and the etching selectivity of the regrown oxide 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.

[0079] Although the present invention has been described above with a focus on the embodiments, various modifications and variations may be made by those skilled in the art. These modifications and variations are within the scope of the present invention. Therefore, the scope of the present invention should be determined by the scope of the claims set forth below.

Claims

1. 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) wet-etching the silicon nitride layer using a phosphoric acid-based etchant, whereby a regrown oxide is generated on a surface of the silicon oxide layer; (b) dry etching the regrown oxide produced in (a) using an etching gas; The step (b) is performed at a substrate temperature of 80 to 120° C. and a process pressure of 0.3 to 1.0 Torr. A method for processing a substrate.

2. In the step (b), the etching gas contains hydrogen fluoride and ammonia. The method for processing a substrate according to claim 1 .

3. The flow rate of the hydrogen fluoride is 20 to 60 sccm; The flow rate of the ammonia is 40 sccm or less. The substrate processing method according to claim 2 .

4. In the step (b), the etching gas is made of hydrogen fluoride. The method for processing a substrate according to claim 1 .

5. The flow rate of the hydrogen fluoride is 20 to 60 sccm. The substrate processing method according to claim 4 .

6. 1. A method for processing a substrate, comprising selectively etching a regrown oxide on a surface of a silicon oxide layer, the regrown oxide having a density lower than that of the silicon oxide layer, the method comprising: dry etching the regrown oxide with an etching gas; The dry etching is performed at a substrate temperature of 80 to 120° C. and a process pressure of 0.3 to 1.0 Torr. A method for processing a substrate.

7. The etching gas contains hydrogen fluoride and ammonia. The substrate processing method according to claim 6 .

8. The flow rate of the hydrogen fluoride is 20 to 60 sccm; The flow rate of the ammonia is 40 sccm or less. The substrate processing method according to claim 7 .

9. The method further comprises the step of increasing the temperature of the substrate after the dry etching to remove reaction by-products. The substrate processing method according to claim 7 .

10. The etching gas is made of hydrogen fluoride. The substrate processing method according to claim 6 .

11. The flow rate of the hydrogen fluoride is 20 to 60 sccm. The method of claim 10.

12. The method further comprises the step of increasing the temperature of the substrate after the dry etching to reduce the fluorine content on the substrate surface. The method of claim 10.

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