Etching method and etching device

Abstract

An etching method according to the present disclosure includes: a step for repeating a cycle that comprises a first step for generating a reaction product between a silicon oxide film and a processing gas by supplying the processing gas into a processing chamber that houses a substrate in which the silicon oxide film is provided in a recess portion that is formed by a first layer and a second layer comprising silicon nitride is superposed in the opening direction of the recess portion on a side wall that constitutes the recess portion, and a second step for removing the reaction product by exhausting the inside of the processing chamber in a state in which the supply of the processing gas into the processing chamber is stopped; and a step for performing the first step in a first cycle among the cycles under processing conditions that are different from those of the first step in subsequent cycles in order to remove the second layer.

Description

Etching method and etching apparatus

[0001] This disclosure relates to an etching method and an etching apparatus.

[0002] In the manufacture of semiconductor devices, etching is performed on the silicon oxide film formed on the surface of a semiconductor wafer (hereinafter referred to as a wafer), which is a substrate. Patent Document 1 describes a method in which a plurality of recesses of different widths are formed by a silicon layer, and the silicon oxide film provided within these recesses is etched.

[0003] Japanese Patent Publication No. 2016-15382

[0004] This disclosure provides a technology that can suppress variations in processing across different parts of a substrate when etching a portion of a silicon oxide film formed in recesses on the surface of the substrate.

[0005] The etching method of the present disclosure includes a step of repeating a cycle comprising: a first step of supplying a processing gas into a processing container that houses a substrate in which a silicon oxide film is provided in a recess formed by a first layer, and a second layer made of silicon nitride is laminated in the direction of the opening of the recess with respect to the side wall forming the recess, thereby generating a reaction product between the silicon oxide film and the processing gas; and a second step of removing the reaction product by evacuating the processing container while stopping the supply of the processing gas into the processing container; and a step of performing the first step in the first cycle of each cycle under different processing conditions than the first step in subsequent cycles in order to remove the second layer.

[0006] This disclosure makes it possible to suppress variations in processing across different parts of a substrate when etching a portion of a silicon oxide film formed in recesses on the surface of the substrate.

[0007] This is a longitudinal cross-sectional side view of an etching module performing etching processing according to one embodiment of the present disclosure. This is a longitudinal cross-sectional side view of the surface of a wafer processed by the etching module. This is a chart showing the processing flow of a comparative example. This is a schematic diagram showing the wafer processing process in a comparative example. This is a schematic diagram showing the wafer processing process in a comparative example. This is a schematic diagram showing the wafer processing process in a comparative example. This is a longitudinal cross-sectional side view showing a recess in a wafer in a comparative example. This is a chart showing the processing flow of an embodiment. This is a chart showing the timing of each step in the processing of an embodiment. This is a process diagram showing the wafer processing process in an embodiment. This is a process diagram showing the wafer processing process in an embodiment. This is a longitudinal cross-sectional side view showing a recess in a wafer in an embodiment. This is a plan view of a substrate processing apparatus including an etching module. This is a graph showing the results of an evaluation test. This is a graph showing the results of an evaluation test. This is a graph showing the results of an evaluation test. This is a graph showing the results of an evaluation test.

[0008] One embodiment of the etching method of this disclosure is the etching of SiO formed on the surface of a wafer W. ２ Etching is performed to remove the (silicon oxide) film using a processing gas. More specifically, the wafer W is treated with a halogen-containing gas, HF (hydrogen fluoride) gas, and a basic gas, NH ３ By supplying (ammonia) gas, each of these gases and SiO ２ An etching process called COR (Chemical Oxide Removal) is performed, which generates reaction products with the film and removes these reaction products by vaporizing them.

[0009] Figure 1 is a longitudinal cross-sectional side view of an etching module 1, which is an example of an etching apparatus that performs the COR processing described above. In the figure, 11 is a processing container that constitutes the etching module 1. In the figure, 12 is a wafer W transport port opening in the side wall of the processing container 11, which is opened and closed by a gate valve 73. A stage 21 on which wafers W are placed is provided inside the processing container 11. The stage 21 is provided with a support member (not shown) that moves up and down by a lifting mechanism, and wafers W are transferred between the stage 21 and a second substrate transport mechanism 72, which will be described later, via the support member.

[0010] A temperature control unit 23 is embedded in the stage 21, and the wafer W placed on the stage 21 is heated to a predetermined temperature, for example, 50°C or higher. This temperature control unit 23 is configured as a flow path that forms part of a circulation path through which a temperature-controlling fluid, such as water, flows, and the temperature of the wafer W is adjusted by heat exchange with the fluid. However, the temperature control unit 23 is not limited to such a fluid flow path, and may be configured as, for example, a heater for resistance heating.

[0011] Furthermore, one end of an exhaust pipe 14 is open inside the processing container 11, and the other end of the exhaust pipe 14 is connected to an exhaust mechanism 16, which is composed of, for example, a vacuum pump, via a valve 15, which is a pressure changing mechanism. By adjusting the opening of the valve 15, the pressure inside the processing container 11 is set to a pressure within the range described later, and processing is carried out.

[0012] A gas shower head 17 is provided in the upper part of the processing container 11, facing the stage 21, and the gas shower head 17 discharges gas toward the surface of the wafer W on the stage 21. The downstream side of the gas supply passages 31 to 34 is connected to the gas shower head 17, and the upstream side of the gas supply passages 31 to 34 is connected to gas supply sources 36 to 39 via flow rate adjustment units 35. Each flow rate adjustment unit 35 is equipped with a valve and a mass flow controller. The gas supplied from the gas supply sources 36 to 39 is cut off to the downstream side by opening and closing the valves included in the flow rate adjustment unit 35.

[0013] From gas supply sources 36, 37, 38, and 39, HF gas, NH ３ gas, N ２ (nitrogen) gas, and Ar (argon) gas are respectively supplied. Therefore, from the gas shower head 17, these HF gas, NH ３ gas, N ２ gas, and Ar gas can be respectively supplied into the processing vessel 11. The flow rate adjustment units 35 provided in the gas supply sources 36, 37 and the gas supply paths 31, 32 correspond to the processing gas supply mechanism. Ar gas and N ２ gas are used as carrier gases and are supplied into the processing vessel 11 together with the processing gases HF gas and NH ３ gas. Also, N ２ gas and Ar gas are supplied after the supply of the processing gas into the processing vessel 11 is stopped, and also act as purge gases for purging the remaining processing gas in the processing vessel 11 from the processing vessel 11. In the following description, the value obtained by dividing the flow rate of the HF gas supplied into the processing vessel 11 by the flow rate of the NH ３ gas supplied into the processing vessel 11 (that is, the ratio of the flow rate of the HF gas supplied into the processing vessel 11 to the flow rate of the NH ３ gas supplied into the processing vessel 11) may be described as the flow rate of HF gas / NH ３ gas flow rate.

[0014] FIG. 2 shows the surface layer portion of the wafer W before being processed in the etching module 1. A layer 41 is provided on the surface side of the wafer W. A number of recesses 42 are formed in this layer 41, and each recess 42 opens in the thickness direction of the wafer W. The side wall of the recess 42 is shown as 43. In the plane of the wafer W, the widths of the side walls 43 are different from each other. Also, the widths of the respective recesses 42 are different from each other, and the recess 42 having a relatively narrow width may be shown as 42A, and the recess 42 having a relatively wide width may be shown as 42B. And in the following description, in the surface of the wafer W, the region where the recess 42A is formed and the interval between the side walls 43 is relatively wide is described as the sparse structure portion 44A, and the region where the recess 42B is formed and the interval between the side walls 43 is relatively narrow is described as the dense structure portion 44B. Also, hereinafter, the thickness direction of the wafer W will be described as the vertical direction, the back side of the wafer W will be described as the lower side, and the surface side will be described as the upper side.

[0015] The lower part is embedded in the recess 42 so that SiO ２ A film 45 is formed, SiO ２ The upper side of the film 45 is located above the recess 42 and covers the upper surface of the side wall 43. ２ A SiN (silicon nitride) film 46 is embedded in the portion of the film 45 above the recess 42. The SiN film 46 is formed away from the upper end of the side wall 43 and overlaps the side wall 43 in a plan view. Therefore, the second layer, the SiN film 46, is positioned in the direction of the opening of the recess 42 relative to the side wall 43 of the recess 42 formed in the first layer, the layer 41. ２ The layers are stacked with film 45 in between. Layer 41 is made of a different material from the SiN film 46, specifically, for example, Si (silicon), and is less susceptible to reaction and alteration caused by the processing gas described above.

[0016] As described above, the width of the recesses 42 and the width of the side walls 43 vary in different parts of the wafer W, so the area occupied by the SiN film 46 per unit area differs in different parts of the wafer W. This SiN film 46 is, for example, a film used as a hard mask during etching when forming the surface structure of the wafer W shown in Figure 2.

[0017] In etching module 1, the etched SiO is contained within each recess 42. ２ The upper surface of the film 45 is located, that is, SiO ２ Etching is performed so that a portion of the film 45 remains in the recess 42. ２ During the etching process of film 45, the SiN film 46 is removed, exposing the upper surface of the side wall 43 of the recess 42. Etching is performed with high uniformity in each part of the wafer W, and the SiO remaining in the recess 42 after etching is removed. ２ The film 45 has high flatness, and SiO is present between each recess 42. ２ It is desirable that the film 45 be processed in a way that increases the uniformity of its height. Note that SiO remains in the recess 42 ２ Increasing the flatness of the film 45 can also be said to mean making the recessed area 42 after etching approximate a rectangular shape when viewed from the side.

[0018] Furthermore, the shape of the recess 42 is approximated to a rectangle (to increase its rectangularness), and SiO is formed between the recesses 42. ２ Increasing the uniformity of the height of the film 45 increases the uniformity of the etching amount in each part of the wafer W, and reduces the amount of SiO in and between the recesses 42 after etching. ２ It can also be said that this suppresses variations in the height of the upper surface of the film 45. The processing of this embodiment using the etching module 1 thereby increases the uniformity of the etching amount and reduces SiO in each part of the wafer W plane. ２ This can meet the requirement to suppress variations in the height of the upper surface of the film 45.

[0019] The processing of this embodiment may be referred to as the "process of the embodiment" hereafter. In order to clearly show the effect of the processing of this embodiment, the processing of the comparative example will be described first with reference to Figures 3 and 4 to 7. Figure 3 is a flowchart of the processing of the comparative example. Figures 4 to 6 are schematic diagrams showing the surface of the wafer W as changed by the processing of the comparative example. Figure 7 is a longitudinal cross-sectional side view showing an arbitrary single recess 42. In each figure, HF gas is 51, NH ３ The gas is shown as 52. Also, these processed gases (HF gas 51 and NH ３ The sublimation product of the reaction between gas 52) and the film on wafer W is shown as 50.

[0020] As shown in Figure 2, the wafer W is placed on the stage 21 and heated to a predetermined temperature, and the inside of the processing container 11 is subjected to a predetermined vacuum pressure, and HF gas 51 and NH ３ Gas 52, N ２ Gas and Ar gas are supplied into the processing container 11 at predetermined flow rates (step S11). Processing gas (HF gas 51, NH ３ Gas 52) is SiO on the surface of wafer W ２ The film 45 reacts with the SiO ２ The surface layer of film 45 is a modified layer 47 containing AFS, which is a reaction product. Similarly, the SiN film 46 reacts with the processing gas to form a modified layer 47 containing AFS.

[0021] As described above, the area occupied by the SiN film 46 per unit area differs in different parts of the wafer W. The processing gas has a relatively high adsorption capacity to the SiN film 46. In regions where the area on which the SiN film 46 is formed is relatively small, after the start of step S11 (after the start of processing gas supply), the amount of processing gas supplied per unit area of ​​the SiN film 46 is relatively large, so the SiN film 46 disappears relatively quickly by becoming the altered layer 47, thus reducing SiO2 adsorption by the processing gas. ２ The deterioration of the film 45 progresses easily. On the other hand, in regions where the area where the SiN film 46 is formed is relatively large, the SiN film 46 remains due to the size of the area, so the SiO by the processing gas ２ The deterioration of the membrane 45 is less likely to progress.

[0022] More specifically, among the side walls 43 of the recess 42, the SiN film 46 provided on the narrower side walls 43 and the wider the recess 42 formed by the side walls 43, has a smaller area of ​​SiN film 46 per unit area and therefore disappears quickly. For this reason, a relatively large amount of processing gas is supplied to the recess 42 formed by the side walls 43 during the execution of step S1, and SiO is released into the recess 42. ２ The film 45 tends to undergo significant deterioration in the depth direction. On the other hand, among the side walls 43 of the recess 42, the SiN film 46 provided on the side walls 43 that are wide and the recess 42 formed by the side walls 43 is narrow is less likely to disappear because the area of ​​the SiN film 46 per unit area is large. Therefore, the supply of processing gas to the recess 42 formed by the side walls is suppressed during the execution of step S1, and the SiO in the depth direction within the recess 42 ２ The deterioration of the membrane 45 tends to be suppressed.

[0023] From the above, as shown on the left side of Figure 4, the SiN film 46 tends to disappear on the side walls 43 of the recesses 42 that form the sparse structure portion 44A, and the thickness of the altered layer 47 formed in the recesses 42 of the sparse structure portion 44A tends to be larger. On the other hand, the SiN film 46 does not disappear easily on the side walls 43 of the recesses 42 that form the dense structure portion 44B, and the thickness of the altered layer 47 formed in the recesses 42 formed by the side walls 43 tends to be smaller.

[0024] After a predetermined time has elapsed since the start of supplying the processing gas into the processing container 11, the supply of the processing gas is stopped, and N continues to enter the processing container 11. ２ Gas and Ar gas are supplied as purge gases, and the processing gas remaining in the processing container 11 is purged (step S12, right side of Figure 4). At the start of step S12, the SiN film 46 has been removed from some of the side walls 43, while the SiN film 46 has not been removed from other parts of the side walls 43.

[0025] After a predetermined time has elapsed since the supply of the processing gas was stopped, the supply of the processing gas into the processing container 11 is resumed. In other words, step S11 is performed again (left side of Figure 5). As shown in the figure, in the recess 42 formed by the side wall 43 where the SiN film 46 remains, the supply of processing gas into the recess 42 is suppressed by the adsorption of the processing gas onto the SiN film 46. Therefore, the SiO in the recess 42 ２ The alteration of the film 42 is slow to progress, and the thickness of the altered layer 47 does not increase easily. On the other hand, in the recess 42 formed by the side wall 43 from which the SiN film 46 has been removed, no adsorption of the processing gas onto the SiN film 46 occurs, so a relatively large amount of processing gas is supplied into the recess 42. Therefore, the SiO in the recess 42 ２ The alteration of the film 42 progresses easily, and the thickness of the altered layer 47 tends to increase.

[0026] The explanation continues with reference to Figure 7. In the case of the recess 42 formed by the side wall 43 where the SiN film 46 has not been removed, the processing gas is adsorbed onto the SiN film 46 on the side wall 43, resulting in a relatively large difference in the amount of processing gas supplied between the recess 42 near the side wall 43 and the recess 42 relatively far from the side wall 43, as shown on the left and in the center of Figure 7. Consequently, the thickness of the altered layer 47 becomes relatively small near the side wall 43, while the thickness of the altered layer 47 becomes relatively large at positions relatively far from the side wall 43. In this way, there is a risk that the thickness of the altered layer 47 within the recess 42 will vary considerably.

[0027] After a predetermined time has elapsed since the start of the re-supply of the processing gas into the processing container 11, the supply of the processing gas into the processing container 11 is stopped, and the processing gas remaining in the processing container 11 is purged. In other words, step S12 is performed again (right side of Figure 5). In this second step S12, the altered layer 47 is removed, but as described above, there is a difference in the thickness of the formed altered layer 47 between the recesses 42 depending on whether or not the SiN film 46 remains. Therefore, in these second steps S11 and S12, the SiO between the recesses 42 ２ A difference in height occurs on the upper surface of the film 45. In the first step S12, SiO is already formed between these recesses 42. ２ If there is a difference in height on the upper surface of the film 45, that difference will be amplified by the second steps S11 and S12.

[0028] Furthermore, in the recess 42 shown on the left and in the center of Figure 7, the height of the altered layer 47 was unevenly formed, so as shown on the right side of Figure 7, the removal of this altered layer 47 exposed SiO ２ The height also varies on the upper surface of the film 45. ２ Regarding the shape of the upper surface of the film 45, the position near the side wall 43 is higher than the position relatively farther from the side wall 43. Therefore, SiO ２ The flatness of the upper surface of the film 45 is low.

[0029] After a predetermined time has elapsed since the supply of the processing gas into the processing container 11 was stopped, the supply of the processing gas into the processing container 11 is resumed. That is, the third step S11 is performed, and then the third step S12 is performed. The cycle consisting of steps S11 and S12 is repeated thereafter. When the control unit 100, which controls the operation of the etching module 1 described later, determines that the cycle consisting of steps S11 and S12 has been performed a predetermined number of times (step S13), the repetition of steps S11 and S12 is stopped, and the wafer W is removed from the processing container 11. The wafer W is then transported to the heat treatment module 70 described later and subjected to heat treatment at a relatively high temperature, where the altered layer 47 remaining on the wafer W is removed as sublimated material 50, and the processing of the wafer W is completed (Figure 6, step S14).

[0030] As the reaction proceeds as described above, until the SiN film 46 is removed from the entire surface of the wafer W during the above process, each time the cycle of steps S11 and S12 is repeated, SiO is released between the recesses 42. ２ The height difference of the upper surface of the film 45 continues to increase. And in some of the recesses 42, the SiO in the recess 42 ２ The height difference of the upper surface of the film 45 also continues to increase. As a result, in the processed wafer W, as shown in Figure 6, the dense structure 44B has more SiO than the sparse structure 44A. ２ The upper surface of the film 45 tends to be higher (i.e., the amount of etching is smaller). Therefore, when the area of ​​the etching target differs between structures on which the etching target is provided, a phenomenon called the loading effect occurs, in which the amount of etching of the etching target differs. Also, as shown at the tip of the arrow in Figure 6, some of the recesses 42 after etching are SiO ２ This results in a decrease in the flatness of the upper surface of the film 45 (and thus a decrease in the rectangularity of the recess 42).

[0031] Therefore, in the embodiment, the process involves repeating a cycle consisting of supplying a processing gas into the processing container 11 and exhausting the processing container 11 without supplying a processing gas. The processing conditions for the first cycle's processing gas supply are different from those for the second and subsequent cycles' processing gas supply. During the first cycle's processing gas supply, the entire SiN film 46 is transformed into the altered layer 47. That is, the processing gas supply in the first cycle is a gas treatment performed to provide processing conditions suitable for etching the SiN film 46, and this gas treatment under these processing conditions may hereafter be referred to as surface etching. The processing gas supply in the second and subsequent cycles is SiO ２ This gas treatment is performed to create conditions suitable for etching the film 45, and this gas treatment under these conditions may hereafter be referred to as the main etching.

[0032] The operation of the etching module 1 during the second and subsequent cycles (steps S3 and S4 described later) in the process of the example is the same as the operation of the etching module 1 during the cycle consisting of steps S11 and S12 in the comparative example. Therefore, the process of the example performs surface etching as a pretreatment for the process described in the comparative example. For this reason, step S11 in the process of the comparative example may also be referred to as the main etching from now on. The surface etching in the process of the example is step S1 in the flow described later, and the preceding stage (step S1A) and the succeeding stage (step S1B) use HF gas and NH ３ This is a two-stage process that involves changing the gas flow rate in each stage.

[0033] Furthermore, in describing the processing in the examples, the period during which no processing gas is supplied in the above cycle may be described as a purging period for removing the processing gas from inside the processing container 11. In the processing of the examples, the processing conditions for the purging period of the first cycle (the period during which step S2 of the flow described later is performed) are different from the processing conditions for the purging period of the second cycle (the period during which step S4 of the flow described later is performed). This ensures that the altered layer 47, which is formed relatively thickly by surface etching, is completely removed, and that the altered layer 47 does not affect the main etching.

[0034] The processing of the embodiment will be described in detail below with reference to Figures 8 to 13. Figure 8 is a flowchart showing the flow of the processing of the embodiment, and Figure 9 is a time chart showing the progress of each step in the processing. Figures 10 to 12 are schematic diagrams showing the wafer W that changes due to the processing of the embodiment. Figure 13 shows the SiO in the recess 42 ２ This is a longitudinal cross-sectional side view showing the membrane 45.

[0035] First, the wafer W shown in Figure 2 is placed on the stage 21 and heated to a predetermined temperature, and the inside of the processing container 11 is set to a predetermined pressure A1 Torr. Specifically, this pressure A1 Torr is, for example, 3 Torr (400 Pa). Then, HF gas 51, NH ３ Gas 52, N ２Gas and Ar gas are supplied into the processing container 11 at predetermined flow rates of D1 sccm, D2 sccm, D3 sccm, and D4 sccm, respectively (time t1, step S1A). Furthermore, from the evaluation test described later, the flow rate of HF gas / NH is used to efficiently remove the SiN film 46. ３ The gas flow rate = D1 / D2 is preferably set to a value greater than, for example, 3.33, and in this example, it is set to 5. SiO ２ The surface layer of the film 45 is treated with the gas (HF gas 51 and NH ３ It reacts with gas 52) to transform into an altered layer 47. This altered layer 47 expands downward, and its lower end reaches the recess 42. In addition, a portion of the SiN film 46 also transforms into the altered layer 47 (left side of Figure 10).

[0036] At time t2, a predetermined time has elapsed from time t1, NH ３ While the supply of gas 52 into the processing container 11 is stopped, the flow rate of HF gas 51 increases to a predetermined D5 sccm, which is greater than D1 sccm (step S1B). Therefore, in step S1B, the flow rate of HF gas / NH is greater than in step S1A. ３ This is considered a large value for gas flow rate. Thus, HF gas flow rate / NH ３ The gas flow rate is changed by the HF gas flow rate / NH, as will be shown in the evaluation test described later. ３ The higher the gas flow rate, the more SiO ２ This is to ensure the removal of the SiN film 46, as the etching amount of the SiN film 46 is greater than the etching amount of film 45. Note that at time t2, N ２ The gas flow rates and Ar gas flow rates are also changed to decrease from the flow rates D3 and D4 in step S1A, respectively.

[0037] In this step S1B, the flow rate of HF gas / NH ３ As the gas flow rate increases, the transformation of the SiN film 46 into the altered layer 47 is accelerated, and the entire SiN film 46 becomes the altered layer 47. ３ Although the gas supply has been stopped, NH remains in the processing container 11. ３ With the use of gas, the reaction in which the SiN film 46 becomes the altered layer 47 continues to proceed. Similarly, SiO ２The reaction in which the film 45 becomes the altered layer 47 also continues to proceed.

[0038] By the way, as the thickness of the altered layer 47 increases, the processing gas permeates through the altered layer 47 and SiO ２ Since reaching the surface of the film 45 is suppressed, the amount of increase in thickness is reduced. Therefore, as shown on the left side of Figure 10, even if the thickness of the altered layer 47 varies within each recess 42 during step S1, as shown on the right side of Figure 10, the thickness of the altered layer 47 formed within each recess 42 becomes uniform during the execution of step S1.

[0039] Then, at time t3, a predetermined time has elapsed from time t2, the supply of HF gas 51 into the processing container 11 is stopped, and N ２ Gas and Ar gas are supplied as purge gases at predetermined flow rates. At this time t3, the pressure inside the processing container 11 decreases to A2 Torr, which is lower than A1. The removal of the altered layer 47 proceeds due to the action of the exhaust flow inside the processing container 11 caused by the purge gas and the heating by the stage 21. Because the pressure inside the processing container 11 is relatively low, the removal of the altered layer 47 proceeds efficiently (left side of Figure 11). This step S2 is performed for a sufficiently long time so that all of the altered layer 47 is removed.

[0040] At time t4, after a predetermined time has elapsed from time t3, the processing gas (HF gas 51 and NH) is introduced into the processing container 11. ３ As the supply of gas 52) is resumed and the pressure inside the processing container 11 rises to A1 Torr, step S2 ends and step S3 begins. In step S3, HF gas 51, NH ３ Gas 52, N ２ Gas and Ar gas are supplied into the processing container 11 at D1 sccm, D2 sccm, D3 sccm, and D4 sccm respectively, just as when step S1A is executed, and the flow rate of HF gas / NH ３ The gas flow rate is also the same as in step S1A.

[0041] As described above, the process in step S3 is the same as the process in step S11 described in the comparative example, and the SiO remaining in each recess 42 ２The surface layer of film 45 changes into the altered layer 47 (right side of Figure 11). However, unlike the comparative example, since the SiN film 46 has been removed, adsorption of the processing gas onto this SiN film 46 does not occur, and the processing gas is supplied to each recess 42 with high uniformity. As a result, the SiO inside is supplied with high uniformity between the recesses 42. ２ The film 45 changes into an altered layer 47 towards the bottom. In other words, the thickness of the altered layer 47 is uniform between the recesses 42. Also, looking at any one recess 42, as shown on the left and in the center of Figure 13, SiO ２ Regarding the film 45, the processing gas is supplied to each part with high uniformity. That is, as explained in the comparative example, the SiO due to the residual SiN film 46 ２ The uneven distribution of the processing gas supplied to each part of the film 45 is suppressed. As a result, a modified layer 47 with a highly uniform thickness is formed in each part of the recess 42.

[0042] At time t5, a predetermined time has elapsed from time t4, the supply of processing gas into the processing container 11 is stopped, and the purge gas (N ２ The altered layer 47 on the wafer W surface is removed by the action of the exhaust flow in the processing container 11 (using gas and Ar gas) and heating by the stage 21 (step S4). The pressure in the processing container 11 in step S4 is set to A1 Torr, for example, the same as in step S3. As described above, the process in step S4 is the same as the process in step S12 described in the comparative example. Since the thickness of the altered layer 47 is uniform between each recess 42, the SiO exposed by the removal of the altered layer 47 in step S4 ２ The upper surface of the film 45 has the same height between each recess 42 (Figure 12, left side). Furthermore, looking at the inside of the recess 42, the altered layer 47, which is formed with a highly uniform thickness in each part, is removed, and as shown in Figure 13, the exposed SiO ２ The upper surface of the film 45 has high flatness.

[0043] At time t6, after a predetermined time has elapsed from time t5, the processing gas is supplied to the processing container 11 again, and step S3 is restarted. Then, at time t7, after a predetermined time has elapsed from time t6, step S3 ends and step S4 is restarted. In these subsequent steps S3 and S4, as the SiN film 46 is removed, a modified layer 47 is formed with a highly uniform thickness at various locations within the recesses 42, similar to the first steps S3 and S4, and this modified layer 47 is removed. That is, at various locations between and within the recesses 42, SiO ２ To increase the uniformity of the height of the upper surface of the film 45, the SiO ２ The film 45 is etched.

[0044] Steps S3 and S4 are repeated thereafter. When the control unit 100 determines that steps S3 and S4 have been performed a predetermined number of times (step S5), the repetition of the cycle of steps S3 and S4 stops, the wafer W is removed from the processing container 11 and transported to the heat treatment module 70 where it undergoes heat treatment at a relatively high temperature. As a result, the altered layer 47 remaining on the wafer W is removed as sublimated material 50, and the processing of the wafer W is completed (right side of Figure 12, step S6).

[0045] In the above embodiment, the surface etching step S1 consists of steps S1A and S1B. For example, the processing conditions in step S1A are the same as the processing conditions in step S3. Therefore, between steps S1A and S3, the pressure inside the processing container 11, the flow rate of each supplied gas, and the flow rate of HF gas / NH are as described in the processing instructions. ３ In addition to the gas flow rate, the execution time is also the same. Since the execution time is the same for step S1A and step S3, when comparing step S1 and step S3, step S1 has a longer execution time.

[0046] As described above, the difference in execution time between steps S1 and S3 is preferable in that, looking at step S1, it allows for more reliable removal of the SiN film 46 as the altered layer 47. And, looking at step S3, as described above, as the thickness of the altered layer 47 increases, SiO ２The change from the film 45 to the altered layer 47 is less likely to occur, which is preferable from the viewpoint of preventing the implementation time from becoming longer than necessary. Note that steps S1 and S3 correspond to the first step, and in some cases, the period during which step S1 or S3 is performed is described as the processing gas supply period.

[0047] Also, in the above example, the implementation time of step S1B (time t2 to t3) is set longer than the implementation time of step S1A (time t1 to t2). For example, the implementation time of step S1A is 15 seconds, and the implementation time of step S1B is 30 seconds. In this way, by setting the period during which the flow rate of HF gas / NH ３ gas is high (the implementation period of step S1B) to be longer than the period during which the flow rate of HF gas / NH ３ gas is low (the implementation period of step 1A), the SiN film 46 can be more reliably removed, which is preferable. By the way, in the above example, for step S1B, the supply of NH ３ gas into the processing vessel 11 is stopped (the flow rate of NH ３ gas is set to 0 sccm), so that the flow rate of HF gas / NH ３ [[ID=X]] gas becomes higher than that in step S1A.As such, when increasing the flow rate of HF gas / NH ３ [[ID=1X]] gas in step S1B, NH ３ gas may be supplied at a relatively low flow rate. That is, in step S1B, the flow rate of NH ３ gas is not limited to 0 sccm.

[0048] Note that the change in the flow rate of HF gas / NH ３ gas during the implementation of step S1 is not limited to an increase. By performing step S1A for a relatively long time, the SiN film 46 may be made into the altered layer 47. That is, step S1 is not limited to a process consisting of steps S1A and S1B with different flow rates of HF gas / NH ３ gas, and may be a process consisting only of step S1A, and the processing conditions between steps S1 and S3 may differ only in the length of the implementation time.

[0049] Therefore, in the process of the above embodiment, a cycle consisting of a processing gas supply period and a purge period is repeated. When repeating this, in the first cycle, the flow rate of HF gas / NH ３ is made to include a period during which the flow rate of gas is higher than that in the second and subsequent cycles (in other words, step S1 includes step S1B in which the flow rate of HF gas / NH ３ is higher than that in step S3), but it is not limited to this. However, in order to surely remove the SiN film 46 as described above, it is preferable that step S1B in which the flow rate of HF gas / NH ３ is higher is performed.

[0050] Also, when repeating the above cycle, the processing conditions in the purge period (step S2) in the first cycle are set to be different from the processing conditions in the purge period (step S4) in each of the second and subsequent cycles. Specifically, as the processing conditions, the length of the purge period and the pressure in the processing vessel 11 are set to be different. By setting different processing conditions in this way, the altered layer 47 is surely removed in step S2, and the implementation time is prevented from becoming longer than necessary in step S4. In the above processing example, both the pressure in the processing vessel 11 and the implementation time are made different for steps S2 and S4 so that the altered layer 47 is more surely removed, but only one of them may be changed. Note that these steps S2 and S4 correspond to the second step.

[0051] Also, although the processing conditions are changed between the first cycle and the second and subsequent cycles for each of the processing gas supply period and the purge period, it is not limited to this. The processing conditions in the processing gas supply period or the processing conditions in the purge period may be made different between the first cycle to the Nth cycle and the (N + 1)th cycle to the last cycle. N is an integer of 2 or more. That is, the removal of the SiN film 46 described above may not end in the first cycle and may be performed so as to span a plurality of cycles. Therefore, for example, after repeating steps S1 and S2, steps S3 and subsequent steps may be executed.

[0052] As described above, in this technology, the processing conditions are different for the first cycle and subsequent cycles, but the subsequent cycle is not limited to the second cycle. However, as shown in the description of the comparative example, if the SiN film 46 is not removed, SiO will be released in and between the recesses 42 each time the cycle is repeated. ２ Since the height difference of the film 45 widens, it is preferable to complete the removal of the SiN film 46 in the first cycle. That is, it is preferable to change the processing conditions between the first cycle and the second and subsequent cycles.

[0053] Note that the last cycle of the N+1 cycle to the last cycle mentioned above may also refer to the N+1 cycle. That is, the SiO to be etched. ２ With respect to the film 45, depending on the target etching amount, steps S3 and S4 may be performed only once after changing the processing conditions, without being repeated.

[0054] Next, a substrate processing apparatus 6, which is one embodiment of the apparatus in which steps S1 to S6 are performed and which includes the etching module 1 described above, will be described with reference to the plan view of Figure 14. The substrate processing apparatus 6 includes an loading / unloading section 61 for loading and unloading wafers W, two load lock chambers 71 provided adjacent to the loading / unloading section 61, two heat treatment modules 70 provided adjacent to each of the two load lock chambers 71, and two etching modules 1 provided adjacent to each of the two heat treatment modules 70.

[0055] The loading / unloading section 61 includes an atmospheric pressure transport chamber 63, which is equipped with a first substrate transport mechanism 62 and is maintained at atmospheric pressure, and a carrier mounting table 65 provided on the side of the atmospheric pressure transport chamber 63 on which a carrier 64 for storing wafers W is placed. In the figure, 66 is an aligner adjacent to the atmospheric pressure transport chamber 63, and is provided to rotate the wafer W to optically determine the eccentricity and align the wafer W with respect to the first substrate transport mechanism 62. The first substrate transport mechanism 62 transports the wafer W between the carrier 64 on the carrier mounting table 65, the aligner 66, and the load lock chamber 71.

[0056] Each load lock chamber 71 is provided with a second substrate transport mechanism 72, for example, having a multi-joint arm structure, which transports the wafer W between the load lock chamber 71, the heat treatment module 70, and the etching module 1. The processing container that makes up the heat treatment module 70 is under a vacuum atmosphere, similar to the processing container 11 that makes up the etching module 1, and the load lock chamber 71 can switch between an atmospheric pressure atmosphere and a vacuum atmosphere so that the wafer W can be transferred between these vacuum-atmosphere processing containers and the atmospheric pressure transport chamber 63.

[0057] In the figure, 73 is a gate valve that can be opened and closed, and is provided between the atmospheric pressure transport chamber 63 and the load lock chamber 71, between the load lock chamber 71 and the heat treatment module 70, and between the heat treatment module 70 and the etching module 1. The heat treatment module 70 includes the above-mentioned processing container, an exhaust mechanism for evacuating the inside of the processing container to form a vacuum atmosphere, and a stage provided inside the processing container that can heat the wafer W placed on it, and is configured to perform the heat treatment of step S6 described above under vacuum pressure.

[0058] The transport path of the wafer W in the substrate processing apparatus 6 will now be explained. As explained in Figure 2, a carrier 64 containing wafers W on which each film has been formed is placed on a carrier mounting table 65. Then, the wafer W is transported in the following order: atmospheric pressure transport chamber 63 → aligner 66 → atmospheric pressure transport chamber 63 → load lock chamber 71, and then transported to the etching module 1 via the heat treatment module 70. Then, steps S1 to S4 are performed as explained in the flow chart of Figure 8. Subsequently, after the determination in step S5, the wafer W is transported to the heat treatment module 70, and sublimation in step S6 is performed.

[0059] Furthermore, the substrate processing apparatus 6 is equipped with a control unit 100, which is a computer, and this control unit 100 is equipped with a program, memory, and CPU. The program incorporates instructions (each step) to perform the processing and transport of the wafer W as described above, and this program is stored in a storage medium, such as a compact disk, hard disk, magneto-optical disk, DVD, etc., and installed in the control unit 100. The control unit 100 outputs control signals to each part of the substrate processing apparatus 6 using this program and controls the operation of each part. Specifically, the operation of the substrate processing apparatus 6 controlled in this manner includes, for example, adjusting the temperature of the fluid supplied to the stage 21 (i.e., the processing temperature of the wafer W), supplying each gas from the gas supply sources 36 to 39 to the processing container 11, switching between supplying and stopping the supply of each gas to the processing container 11 by each flow rate adjustment unit 35 and adjusting the flow rate, adjusting the exhaust flow rate by the valve 15 (i.e., adjusting the pressure inside the processing container 11), and the operation of the first substrate transport mechanism 62 and the second substrate transport mechanism 72.

[0060] By the way, in the embodiment described in the flowchart of Figure 8, the wafer W remains continuously in the same processing container 11 from the start of step S1 until the end of the final step S4, and the wafer W is not removed from the processing container 11. However, it is not limited to keeping the wafer W in the same processing container 11 in this way. For example, after the end of step S2, the wafer W may be removed from the processing container 11 and heated in the heat treatment module 70 to remove the altered layer 47 on the back surface of the wafer W. After that, the wafer W may be transported to the etching module 1 again and steps S3 and S4 may be performed. However, from the viewpoint of preventing a decrease in the throughput of the apparatus, it is preferable to keep the wafer W in the same processing container 11 continuously from step S1 to the final step S4 and perform the processing, as in the process of Figure 8. To enable processing in the same processing container 11 in this way, different processing conditions are set for step S2 than for step S4, and the altered layer 47 generated in step S1 can be reliably removed in step S2.

[0061] In the above embodiment, in step S1 (surface etching) and step S3 (main etching), HF gas and NH are introduced into the processing container 11. ３ The timing of the gas supply commencement is synchronized, but it is not limited to supplying each gas in this manner. In other words, the timing of the commencement of HF gas supply and NH ３ There may be a delay in the timing of the start of gas supply. In addition, in step S1B of step S1, in addition to HF gas as described above, NH ３ Gas may also be supplied, but HF gas and NH ３ The timing of the gas supply shutdown may or may not be synchronized. In step S3, HF gas and NH ３ The timing of the gas supply shutdown can be slightly different.

[0062] In the above embodiment, we described an example where the pressure inside the processing container 11 is the same for steps S1 and S3, but the length of the execution time (processing time) is different. However, it is preferable to make the pressure inside the processing container 11 different as well. To add to step S3, as the thickness of the altered layer 47 increases, SiO ２ Since the change from film 45 to altered layer 47 becomes less likely, there is no need to extend the execution time of step S3. More specifically, in order to prevent the etching from stopping as reaction products accumulate in the recesses 42 of the dense structure portion 44B and the altered layer 47 thickens, while etching continues in the recesses 42 of the sparse structure portion 44A, it is preferable to set the execution time of step S3 to be relatively short.

[0063] By setting the pressure inside the processing vessel 11 in step S3 to a relatively high level, even if the thickness of the altered layer 47 increases, the SiO of the processing gas will not increase. ２ The amount adsorbed onto the film 45 can be increased. That is, in step S3, if the execution time is kept constant, the thickness of the altered layer 47 in each recess 42 can be more reliably made uniform by increasing the pressure inside the processing container 11 to prevent etching from stopping in the sparse structure portion 44A. And by increasing the pressure in this way, the SiO in each recess 42 can be increased. ２Since the adsorption of the processing gas onto the film 45 becomes more active, sufficient etching can be performed even if the execution time of step S3 is relatively short, as described above. As a result, the throughput of the etching process can be increased.

[0064] Therefore, it is preferable to set the pressure inside the processing container 11 in step S3 higher than the pressure inside the processing container 11 in step S1, for example, 3 Torr to 50 Torr (6.67 × 10⁻¹⁰). ３ Let Pa be used. More specifically, for the pressure in question, for example, 11 Torr (1.47 × 10⁻¹⁰). ３ It is effective to set it to Pa. Even when the pressure in step S3 is higher than that in step S1, the pressure inside the processing container 11 during the purging period in step S4 may be the same as the pressure inside the processing container 11 in step S3, for example, as in the above embodiment.

[0065] The processing gas is not limited to HF gas; HCl, HBr, HI, SF6 can be used instead. ４ Gases containing halogens such as the following can be used. Note that this refers to the presence of halogens as constituent components, not as impurities. In addition, among the processing gases, NH is used as the basic gas. ３ Not limited to the use of gas, the NH ３ Instead of gas, various amine compound gases such as trimethylamine, dimethylamine, dimethylethylamine, diethylamine, triethylamine, monotertiarybutylamine, pyrrolidine, and pyridine can be used. Furthermore, as other specific examples of amine compounds, various amine gases such as compounds in which some or all of the C-H bonds of the above compounds are replaced by C-F bonds (e.g., 1,1,1-trifluorodimethylamine) can be used. While the wafer W shown has a configuration where the recess 42 opens upwards, the application of this technology is not limited to such a wafer W. For example, the recess 42 can open laterally, and the technology can also be applied to a wafer W in which a SiN film 46 is laminated from the side against the side wall 43 of the recess 42.

[0066] Up to this point, wafers have been used as an example of substrates to be processed, but the substrates processed in the processing container 11 include, in addition to wafers, substrates for manufacturing flat panel displays, substrates for manufacturing exposure masks used in photolithography, and dummy substrates processed for the purpose of testing and setting processing parameters in the substrate processing apparatus. Furthermore, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The above embodiments may be omitted, replaced, modified, and combined in various ways without departing from the scope and spirit of the attached claims.

[0067] [Evaluation Tests] The evaluation tests conducted in connection with this embodiment will be described below.

[0068] • Evaluation Test 1 As Evaluation Test 1, a test was conducted to verify the processing conditions suitable for surface etching in step S1. In this Evaluation Test 2, SiO was applied to the surface. ２ The wafer W on which the film and SiN film are formed is transported to the etching module 1, and HF gas and NH are used as processing gases. ３ The gas was supplied. The supply of this processing gas was carried out under different processing conditions for each wafer W. After the supply of the processing gas, the inside of the processing container 11 was purged to remove the reaction products, and SiO ２ The etching amount of the film and the SiN film was measured. The etching selectivity ratio = SiO ２ The etching amount of the film / etching amount of the SiN film was calculated. As described in the embodiment, surface etching is SiO ２ Since this is a process of etching both the film 45 and the SiN film 46, it is preferable that the etching selectivity ratio is as close to 1 as possible.

[0069] For evaluation tests 1-1 to 1-6, the above processing conditions were HF gas flow rate / NH ３ The gas flow rate was changed between wafers W for processing. More specifically, the flow rate of HF gas supplied into the processing container 11 for each wafer W and NH were changed. ３ By changing the combination with the gas flow rate between wafers W, the HF gas flow rate / NH ３The gas flow rate was changed between wafers W. For evaluation tests 1-1 to 1-6, HF gas and NH were used. ３ The gas supply time is constant (X seconds) between wafers W. Furthermore, for evaluation tests 1-7 to 1-9, the above processing conditions were used, with HF gas and NH ３ The gas supply time was changed for each wafer W during the processing. In this evaluation test 1-7 to 1-9, the flow rate of HF gas and NH supplied into the processing container 11 were changed. ３ The gas flow rate has not been changed.

[0070] To be more specific about the processing conditions, the flow rate of HF gas / NH ３ Regarding the gas flow rate, it was set to 5, 3.33, 10, 2, 1, and 8 in evaluation tests 1-1, 1-2, 1-3, 1-4, 1-5, and 1-6, respectively. In evaluation tests 1-7 to 1-9, the HF gas flow rate / NH was used. ３ The gas flow rate was set to 5, and in evaluation tests 1-7, 1-8, and 1-9, the supply time of the processed gas was set to 15 seconds, 5 seconds, and 3 seconds, respectively. In these evaluation tests 1-1 to 1-9, HF gas and NH gas were used. ３ The timing of starting the supply of gas into the processing container 11 is synchronized, and the timing of stopping the supply is also synchronized for each.

[0071] Figure 15 is a graph showing the results of Evaluation Test 1. The etching amount in the graph is a normalized value obtained by dividing the measured value by a positive value. In the explanation of the evaluation test, the etching amounts shown from this point onward are normalized values ​​in the same way as those shown in this graph, and each value calculated from the etching amount is also a normalized value. In the graph of Figure 15, the flow rate of HF gas / NH ３ Looking at the results of evaluation tests 1-7 to 1-9, where the gas flow rate is 5, the etching selectivity ratio is relatively high in evaluation tests 1-8 and 1-9, where the processing gas supply time is 5 seconds or less. However, in evaluation test 1-7, where the processing gas supply time is 15 seconds, the etching selectivity ratio is lower than in evaluation tests 1-8 and 1-9. Therefore, it can be seen that a longer processing gas supply time results in a lower etching selectivity ratio, which is preferable.

[0072] Furthermore, looking at the results of evaluation tests 1-1 to 1-6, the flow rate of HF gas / NH ３In evaluation tests 1-3 and 1-7, where the gas flow rate was set to relatively high values ​​of 10 and 8, the etching selectivity ratio was relatively low. On the other hand, in HF gas flow rate / NH ３ In evaluation tests 1-2 and 1-5, where the gas flow rate was set to relatively small values ​​of 3.33 and 1, the etching selectivity ratio was relatively high. Therefore, the HF gas flow rate / NH ３ It can be seen that a higher gas flow rate tends to result in a lower etching selectivity ratio, which is desirable.

[0073] • Evaluation Test 2 As Evaluation Test 2, similar to Evaluation Test 1, a test was conducted to verify the processing conditions suitable for surface etching in step S1. In this Evaluation Test 2, the HF gas flow rate / NH was applied to the wafer W as explained in Figure 2. ３ The gas flow rate was set to 5 and the processing gas was supplied to the wafer W. After the supply of the processing gas, the processing container 11 was purged to remove the reaction products, and SiO was processed in the same manner as in evaluation test 1. ２ The etching amount of film 45 and SiN film 46 was measured, and the etching selectivity ratio was calculated. The supply time of the processing gas was changed for each wafer W and set to 3 seconds, 8 seconds, or 15 seconds. Figure 16 is a graph showing the results of evaluation test 2. As shown in this graph, the etching selectivity ratio was approximately 2 when the etching time was 3 seconds, which was a relatively high value, but when the etching time was 8 seconds and 15 seconds, it was approximately 1, which was a favorable result.

[0074] Based on the results of the above evaluation tests 1 and 2, in order to reliably remove the SiN film 46 when performing the treatment in the example, HF gas and NH are used in step S1. ３ It is preferable to have both gases flowing simultaneously for 8 seconds or more, and more preferably for 15 seconds or more. More specifically, in the processing example shown in Figure 8, in step S1A, HF gas and NH ３ Both gases are supplied, and in step S1B, only HF gas is supplied. If only HF gas is supplied in step S1B, it is preferable to make step S1A last 8 seconds or more, and more preferably 15 seconds or more. Also, from the results of evaluation tests 1 and 2, the flow rate of HF gas in step S1 / NH ３Regarding the gas flow rate, it is preferable to set it to be greater than 3.33, and more preferably to be 5 or greater.

[0075] - Evaluation Test 3 As Evaluation Test 3-1, the wafer W described in Figure 2 was transported to the etching module 1 and the process of the embodiment described in the flow chart of Figure 8 was performed. Then, the SiO in the recesses 42 forming the sparse structure portion 44A and the recesses 42 forming the dense structure portion 44B were evaluated. ２ The height difference on the upper surface of the film 45 was measured. Furthermore, evaluation test 3-2 was conducted in the same manner as evaluation test 3-1, except that steps S1 and S2 were omitted. Therefore, in evaluation test 3-2, the wafer W was subjected to the comparative example treatment described in the flow chart of Figure 3.

[0076] The graph in Figure 17 shows the results of evaluation test 3. The vertical axis of the graph represents the measured SiO ２ The normalized value is shown by dividing the height difference on the upper surface of the film 45 by a predetermined positive value. Therefore, the smaller the normalized value, the smaller the actual height difference. As shown in the graph, both the recesses 42 of the sparse structure 44A and the recesses 42 of the dense structure 44B show that evaluation test 3-1 yields a higher SiO2 than evaluation test 3-2. ２ The height difference on the upper surface of the film 45 is small. Therefore, from this evaluation test 3, according to the treatment of the example, SiO in the recess 42 ２ The effectiveness of this technology was confirmed, specifically that it can improve the flatness of the upper surface of the film 45.

[0077] ・Evaluation Test 4 As Evaluation Test 4-1, the wafer W described in Figure 2 was subjected to the same treatment as in Evaluation Test 3-1, and the etching amount in each part of the recess 42 forming the sparse structure 44A was measured to calculate the average value A1, and the etching amount in each part of the recess 42 forming the sparse structure 44A was measured to calculate the average value A2. Then, the loading value was calculated as average value A1 - average value A2. Therefore, the closer this loading value is to 0, the greater the difference in etching amount between the recesses 42 (i.e., SiO ２This means that the difference in height of the upper surface of the film 45 is suppressed. Furthermore, evaluation test 4-2 was conducted in the same manner as evaluation test 4-1, except that steps S1 and S2 were omitted, and the comparative example was treated instead of the example.

[0078] The graph in Figure 18 shows the results of evaluation test 4. As shown in the graph, the loading value in evaluation test 4-1 was closer to 0 than in evaluation test 4-2. Therefore, from this evaluation test 4, it can be concluded that, according to the processing of the embodiment, SiO between the recesses 42 ２ The effectiveness of this technology was confirmed, as it can suppress variations in the height of the upper surface of the film 45.

[0079] W wafer 41 layer 42 recess 43 side wall 45 silicon oxide film (SiO ２ (Membrane) 46 Silicon nitride film (SiN film) 47 Modified layer 51 HF (hydrogen fluoride) gas 52 NH ３ (Ammonia) gas

Claims

1. An etching method comprising: a step of repeating a cycle comprising:

1. A silicon oxide film provided in a recess formed by a first layer, and a second layer made of silicon nitride laminated in the direction of the opening of the recess against the side wall forming the recess, by supplying a processing gas into a processing container that houses the substrate, thereby generating a reaction product between the silicon oxide film and the processing gas; and 2. A step of removing the reaction product by evacuating the processing container while stopping the supply of the processing gas into the processing container; and 3. A step of performing the first step in the first cycle of each cycle under different processing conditions than the first step in subsequent cycles in order to remove the second layer.

2. The etching method according to claim 1, wherein the step of repeating the cycle is performed without removing the substrate from the processing container.

3. The etching method according to claim 2, wherein the second step of the first cycle is performed under different processing conditions than the second step of the subsequent cycle.

4. The etching method according to claim 3, wherein the processing conditions that differ between the second step of the first cycle and the second step of the subsequent cycle include at least one of the execution time of the second step and the pressure inside the processing vessel, wherein the pressure inside the processing vessel in the second step of the first cycle is lower than the pressure inside the processing vessel in the second step of the subsequent cycle, or the execution time of the second step of the first cycle is longer than the execution time of the second step of the subsequent cycle.

5. The etching method according to claim 4, wherein the subsequent cycles are each cycle from the second cycle onward.

6. The etching method according to claim 2, wherein the different processing conditions between the first step of the first cycle and the first step of the subsequent cycle include the execution time of the first step, and the first step of the first cycle is longer than the first step of the subsequent cycle.

7. The etching method according to claim 6, wherein the processing conditions that differ between the first step of the first cycle and the first step of the subsequent cycle include the pressure inside the processing vessel, and the pressure inside the processing vessel in the first step of the subsequent cycle is higher than the pressure inside the processing vessel in the first step of the first cycle.

8. The etching method according to claim 6, wherein the processing gas comprises a halogen-containing gas and a basic gas, and the processing conditions which differ between the first step of the first cycle and the first step of the subsequent cycle include the ratio of the flow rate of the halogen-containing gas supplied to the processing container to the flow rate of the basic gas supplied to the processing container, and the ratio for the first cycle is longer than that for the subsequent cycle.

9. The etching method according to claim 8, further comprising a step of increasing the ratio during the execution of the first step in the first cycle.

10. An etching apparatus comprising: a processing container for storing a substrate in which a silicon oxide film is provided in a recess formed by a first layer, and a second layer made of silicon nitride is laminated in the direction of the opening of the recess with respect to the side wall forming the recess; a processing gas supply mechanism for supplying a processing gas into the processing container that reacts with the silicon oxide film to generate reaction products; an exhaust mechanism for exhausting the inside of the processing container; a step of repeating a cycle consisting of a first step of supplying a processing gas into the storage processing container to generate reaction products between the silicon oxide film and the processing gas, and a second step of exhausting the inside of the processing container with the supply of the processing gas into the processing container stopped to remove the reaction products; and a control unit that outputs a control signal to perform the first step in the first cycle of each cycle under different processing conditions than the first step in subsequent cycles in order to remove the second layer.

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