Etching method and substrate processing device

Abstract

An etching method that suppresses damage to multiple base layers of varying heights while etching a silicon oxide film on each base layer to different depths. The etching method includes preparing a substrate having a first base layer and a second base layer of varying heights, a silicon oxide film formed on the first and second base layers, and a mask formed on the silicon oxide film and having a second opening above the first and second base layers; etching the silicon oxide film using a first gas to expose the first base layer; using a second gas to deposit a deposit on the first base layer while etching the silicon oxide film above the second base layer; and using a third gas to remove the deposit on the first base layer while etching the silicon oxide film above the second base layer. The etching steps using the second gas and the etching steps using the third gas are repeated multiple times.

Description

Technical Field

[0001] The present disclosure relates to an etching method and a substrate processing device. Background Art

[0002] For example, Patent Document 1 proposes a method of preparing a substrate having multiple base layers at different heights and a target film formed on the multiple base layers, and etching holes of different depths in the target film using a mask having multiple openings above each base layer.

[0003] <Prior Art Literature>

[0004] <Patent Document>

[0005] Patent Document 1: (Japanese) Patent Publication No. 2019-9259 Summary of the Invention

[0006] <Problems to be Solved by the Invention>

[0007] The present disclosure provides an etching method and a substrate processing apparatus, which suppress damage to a plurality of base layers at different heights and simultaneously etch a silicon oxide film on each base layer to different depths.

[0008] <Methods used to solve the problem>

[0009] According to one embodiment of the present disclosure, an etching method is provided, comprising: a process of preparing a substrate having a first base layer, a second base layer formed at a position deeper than the first base layer, a silicon oxide film formed on the first base layer and the second base layer, and a mask formed on the silicon oxide film, the mask having a first opening formed above the first base layer and a second opening formed above the second base layer; a process of etching the silicon oxide film from the first opening using a first gas to expose the first base layer; a process of depositing a sediment on the first base layer using a second gas and etching the silicon oxide film above the second base layer from the second opening; and a process of removing the sediment deposited on the first base layer using a third gas and etching the silicon oxide film above the second base layer from the second opening, wherein the process of etching using the second gas and the process of etching using the third gas are repeated multiple times.

[0010] <Effects of the Invention>

[0011] According to one aspect, damage to a plurality of base layers located at different heights can be suppressed while etching the silicon oxide film on each base layer to different depths. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic cross-sectional view showing a substrate processing apparatus according to one embodiment.

[0013] Figure 2 It is a diagram showing the membrane structure and conventional problems.

[0014] Figure 3 is a flowchart illustrating an etching method according to one embodiment.

[0015] Figure 4A 1 and 2 are cross-sectional views showing a film on a substrate in each step of an etching method according to one embodiment.

[0016] Figure 4B 1 and 2 are cross-sectional views showing a film on a substrate in each step of an etching method according to one embodiment.

[0017] Figure 4C 1 and 2 are cross-sectional views showing a film on a substrate in each step of an etching method according to one embodiment.

[0018] Figure 5 1 and 2 are diagrams illustrating the state inside a hole in each step of an etching method according to one embodiment.

[0019] Figure 6 : is a diagram showing the effect of the etching method according to one embodiment.

[0020] Figure 7 : is a graph showing experimental results of an etching method according to one embodiment.

[0021] Figure 8 : is a diagram showing the relationship between the types of gases and gas flow rates that can be used in an etching method according to one embodiment, and the etching mode.

[0022] Figure 9 is a graph showing the relationship between substrate temperature and etching rate in an etching method according to one embodiment. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals, and overlapping descriptions may be omitted.

[0024] [Substrate processing equipment]

[0025] use Figure 1 A substrate processing apparatus 10 according to one embodiment will be described. Figure 1 is a schematic cross-sectional view illustrating an example of a substrate processing apparatus 10 according to one embodiment.

[0026] The substrate processing apparatus 10 includes a processing container 11 and a mounting table 12 disposed therein. The processing container 11 is grounded. The mounting table 12 includes an electrostatic chuck 13 and a base 16. The base 16 supports the electrostatic chuck 13. The mounting table 12 is disposed on the bottom of the processing container 11 via a support portion 14 formed of an insulating member.

[0027] The base 16 is made of a metal such as aluminum. The electrostatic chuck 13 is made of a dielectric such as alumina (Al2O3). The electrostatic chuck 13 is generally circular in plan view. The electrostatic chuck 13 holds the substrate W using electrostatic attraction generated by applying a DC voltage to electrodes (not shown).

[0028] A substrate W is placed at the center of the electrostatic chuck 13 , and an annular edge ring 15 (also referred to as a focus ring) is placed on the outer periphery to surround the substrate W.

[0029] An annular exhaust path 23 is formed between the sidewalls of the processing container 11 and the sidewalls of the mounting table 12. The exhaust path 23 is connected to an exhaust device 22 via an exhaust port 23. The exhaust device 22 comprises a vacuum pump and exhausts the gas within the processing container 11, thereby reducing the pressure in the processing space within the processing container 11 to a predetermined vacuum level. A partition 27 is provided in the exhaust path 23 to separate the processing space from the exhaust space and to control the flow of gas.

[0030] The mounting table 12 is connected to a first high-frequency power source 17 and a second high-frequency power source 18. The first high-frequency power source 17 applies, for example, 40 MHz high-frequency power HF for plasma generation to the mounting table 12. The second high-frequency power source 18 applies, for example, 400 kHz high-frequency power LF for ion attraction to the mounting table 12.

[0031] A showerhead 20 is installed at the top opening of the processing container 11, with an annular insulating member 28 interposed around the outer periphery. A gas supply source 19 supplies gas corresponding to the process conditions. The gas enters the showerhead 20 through a gas pipe 21 and is introduced into the processing container 11 in a shower-like manner. High-frequency power (HF) is capacitively applied between the mounting table 12 and the showerhead 20, generating plasma from the gas using the high-frequency power (HF).

[0032] The substrate processing apparatus 10 includes a control unit 30 . The control unit 30 controls the entire substrate processing apparatus 10 .

[0033] When processing is performed in the substrate processing apparatus 10 of this structure, a substrate W is first loaded into the processing container 11 through a gate valve (not shown) while being held by a transfer arm. The substrate W is placed on the electrostatic chuck 13. After the substrate W is loaded, the gate valve is closed.

[0034] The exhaust device 22 reduces the pressure within the processing container 11 to a set value, maintaining a vacuum state. A predetermined gas is introduced into the processing container 11 from the showerhead 20 in a shower-like manner. High-frequency power HF and high-frequency power LF are applied to the mounting table 12, generating a plasma. The plasma etches the film on the substrate W. After etching is complete, the substrate W is held on the transfer arm and removed from the processing container 11.

[0035] [Membrane structure]

[0036] Next, refer to Figure 2 The film structure on the substrate W placed on the mounting table 12 will be described. Figure 2 1 is a diagram illustrating a film structure on a substrate W and conventional problems.

[0037] During the 3D-NAND manufacturing process, lower base layers 120a1-120a3, intermediate base layers 120b1-120b3, and higher base layers 120c1-120c3 are arranged at different heights below the silicon oxide film 110 under the mask. These lower, intermediate, and higher base layers are collectively referred to as base layer 120. Base layer 120 can be made of either tungsten or silicon. An amorphous carbon film is used as a mask.

[0038] In the etching process, multiple holes H of different heights are etched into the silicon oxide film 110 at the same time until the base layers of the lower, middle and upper layers are exposed. Figure 2 In the figure, three layers are shown as the base layers of the lower layer, the middle layer, and the upper layer, and other layers are omitted. However, the number of layers of each base layer in the base layer of the lower layer, the base layer of the middle layer, and the base layer of the upper layer can be different as long as it is more than one layer.

[0039] After these base layers are exposed, fluorocarbon (CF)-based radicals or ions also enter the holes H in the lower and middle base layers until the holes H in the upper base layer are etched out, exposing the upper base layer. Therefore, there is a problem of damaging the exposed base layers at the bottoms of the holes H in the base layers and the middle base layers.

[0040] In particular, in the lower and middle layers of the base layer, the irradiation ratio of the ions in the plasma injected into the hole H is higher than that in the upper layer of the base layer. In addition, in the base layer of the middle layer, since the hole depth is deeper than that of the base layer of the lower layer, it is difficult for by-products to be deposited at the bottom of the hole. Therefore, in the lower and middle layers of the base layer, the following Figure 2 The base layers 120a1 and 120b1 shown in A are penetrated (penetrated), as shown in FIG. Figure 2The problem of erosion of the base layers 120a2 and 120a3 is shown in B.

[0041] Furthermore, the number of base layers has been increasing in recent years, leading to an increase in the thickness of silicon oxide films. Furthermore, the thinning of base layers has been progressing. Therefore, a technology is being sought that improves the selectivity between the silicon oxide film and the base layer, avoids damage to the base layer, and simultaneously forms holes of varying depths in the silicon oxide film.

[0042] In other words, in Figure 2 In etching of a film structure, it is important to strike a balance between reducing damage to the underlying layers of the lower and middle layers and promoting etching above the underlying layers of the higher layers.

[0043] Therefore, an etching method according to one embodiment is proposed below, which can suppress damage to multiple base layers located at different heights and simultaneously etch the silicon oxide film on each base layer to different depths.

[0044] [Etching method]

[0045] Reference Figure 3 and Figures 4A to 4C An etching method according to one embodiment will be described. Figure 3 is a flowchart illustrating an etching method according to one embodiment. Figures 4A to 4C 1 and 2 are cross-sectional views showing a film on a substrate W in each step of an etching method according to an embodiment. The etching method according to an embodiment is controlled by a control unit 30 .

[0046] Figure 4A (a) shows the initial state of a film on a substrate W. A lower base layer (only base layer 120a3 is shown) is formed on the substrate W. Furthermore, an intermediate base layer (only base layer 120b3 is shown) is formed deeper than the lower base layer. Furthermore, a higher base layer (only base layer 120c3 is shown) is formed deeper than the intermediate base layer.

[0047] exist Figures 4A to 4CIn the following description, although the lower base layer 120a3, the middle base layer 120b3, and the upper base layer 120c3 are shown as the lowest layers of the respective layers, this is not limiting. Base layer 120a3 can be any base layer located in the lower layers, base layer 120b3 can be any base layer located in the middle layers, and base layer 120c3 can be any base layer located in the upper layers. Each base layer extends horizontally relative to the base layer directly above it. Base layer 120a3 is an example of a first base layer, base layer 120b3 is an example of a second base layer, and base layer 120c3 is an example of a third base layer.

[0048] The mask 100 has a first opening (hole H1) formed above the base layer 120a3, a second opening (hole H2) formed above the base layer 120b3, and a third opening (hole H3) formed above the base layer 120c3. Holes H1, H2, and H3 have circular cross-sections in this embodiment, but are not limited thereto and may also be linear.

[0049] Although the etching method according to one embodiment is described with the upper base layer 120c3 located at the lowest position of the base layer 120 as an example, the present invention is not limited thereto. The total number of base layers 120, including lower, middle, and upper layers, may be, for example, 10 to 100 or more.

[0050] When to start Figure 3 After the processing, a substrate W having a silicon oxide film 110, a lower layer, an intermediate layer, and an upper layer formed thereon is provided under the mask 100 (step S1). It should be noted that "providing ... a substrate W" means carrying the substrate W into the substrate processing apparatus 10 and placing it on the mounting table 12.

[0051] Next, the first gas is converted into plasma to etch the silicon oxide film 110, exposing the underlying base layer 120a3 (step S2). Figure 4A As shown in (b), the silicon oxide film 110 is etched until the lower base layer 120a3 is exposed, forming a hole H1 as a contact hole. At this time, holes H2 and H3 are formed simultaneously with hole H1. However, since the base layer 120b3 and the base layer 120c3 are arranged at a position deeper than the base layer 120a3, the holes H2 and H3 do not reach the base layer 120b3 and the base layer 120c3. It should be noted that the process of step S2 is an example of "a first process of etching the silicon oxide film from the first opening using a first gas to expose the first base layer." In addition, the "lower base layer" in step S2 is not necessarily the base layer at the bottom of the lower layer, but can be any base layer of the lower layer.

[0052] Then, in Figure 3 In the process, the second gas is plasma-generated to deposit a deposit on the lower base layer 120a3, and at the same time, the silicon oxide film 110 above the middle and upper base layers 120b3 and 120c3 is etched (step S3). The process of step S3 is an example of "a second process of depositing a deposit on the first base layer using the second gas and etching the silicon oxide film above the second base layer from the second opening". Figure 4B As shown in (c), the byproduct R can be deposited on the base layer 120a3 at the bottom of the hole H1, and the hole H2 above the base layer 120b3 and the hole H3 above the base layer 120c3 can be etched deeper.

[0053] Then, in Figure 3 In the process, the third gas is converted into plasma to remove at least a portion of the byproduct R on the lower base layer 120a3, and the silicon oxide film 110 on the intermediate and upper base layers 120b3 and 120c3 is further etched (step S4). The process of step S4 is an example of "a third process of removing the deposits deposited on the first base layer using the third gas and etching the silicon oxide film on the second base layer from the second opening". Figure 4B As shown in (d), a portion of the byproduct R on the base layer 120a3 can be removed, and at the same time, the hole H2 above the base layer 120b3 and the hole H3 above the base layer 120c3 can be etched deeper.

[0054] Then, in Figure 3 In the process, it is determined whether the base layer 120b3 of the intermediate layer is exposed (step S5). If the base layer 120b3 is not exposed, the process returns to step S3 and repeats the processes of steps S3 to S5. Thus, the second and third steps are repeated multiple times. Figure 4C (e) shows a state where the base layer 120b3 is exposed. Figure 3 In step S5, it is determined that the base layer 120b3 of the intermediate layer is exposed, and the process proceeds to step S6. It should be noted that the "base layer of the intermediate layer" in step S4 is not necessarily the lowest base layer of the intermediate layer, but may be any base layer of the intermediate layer.

[0055] Next, in step S6, the second gas is converted into plasma to deposit on the lower and middle base layers 120a3 and 120b3, while etching the silicon oxide film 110 above the upper base layer 120c3. Step S6 is an example of the "second step."

[0056] Then, in Figure 3In the process, the third gas is plasma-generated to remove at least a portion of the byproducts R on the lower and intermediate base layers 120a3 and 120b3, while further etching the silicon oxide film 110 above the upper base layer 120c3 (step S7). The process of step S7 is an example of the "third process." As a result of the processing of steps S6 and S7, as shown in Figure 4c(f), the byproducts R are deposited on the base layers 120a3 and 120b3 at the bottoms of the holes H1 and H2, and the hole H3 above the upper base layer 120c3 is etched deeper.

[0057] Then, in Figure 3 In the process, it is determined whether the base layer 120c3 of the upper layer is exposed (step S8). When it is determined that the base layer 120c3 at the bottom of the upper layer is not exposed, the process returns to step S6 and the process of steps S6 to S8 is performed again. Figure 4C When the base layer 120c3 shown in (f) is exposed, this process is terminated.

[0058] According to the etching method of the above embodiment, in the second step, etching in a deposition mode that facilitates the deposition of deposits at the bottom of the hole is performed, and in the third step, etching in a removal mode that makes it difficult for deposits to be deposited at the bottom of the hole is performed. The second and third steps are repeated in this order.

[0059] The process of repeating the second process and the third process may be as follows Figure 4B (c) and (d) are steps performed after the base layer 120a3 is exposed and before the base layer 120b3 is exposed. Figure 4B (e) and (f) show the processes performed after the base layer 120b3 is exposed and before the base layer 120c3 is exposed.

[0060] Thus, byproducts R can be used to reduce ion-induced damage to the base layers in the lower and middle layers, while actively injecting ions into the holes in the upper base layers to promote etching. Specifically, by repeating the second and third steps, damage to multiple base layers 120 at different heights can be suppressed, while the silicon oxide film 110 on each base layer 120 can be etched to different depths without causing an etch stop.

[0061] [Deposition etching / removal etching]

[0062] Next, the process conditions of the first to third steps are described below, thereby explaining why the byproduct R of the CF polymer can be actively deposited in the lower and intermediate layers while the upper base layer can be etched in the second step.

[0063] (First process)

[0064] An example of the process conditions in the first step is shown below.

[0065] <First step: process conditions>

[0066] Pressure: 15mT~30mT (2.0Pa~4.0Pa)

[0067] HF: On (4000W~5500W)

[0068] LF: On (6000W-8750W)

[0069] First gas: C4F6, O2

[0070] However, the first gas is not limited to C4F6 and O2. Any gas can be used as long as it can etch the silicon oxide film and achieve a selectivity ratio with the base layer. For example, in addition to C4F6 and O2, the first gas may also contain at least one of CO, CO2, and N2. It may further contain Ar. Some or all of the C4F6 may be replaced with C4F8. Furthermore, the first gas may be the same gas as the third gas.

[0071] (Second process)

[0072] An example of the process conditions in the second step is shown below.

[0073] <Second step: process conditions>

[0074] Pressure: 15mT~30mT

[0075] HF: On (4000W~5500W)

[0076] LF: On (6000W~8750W)

[0077] Second gas: C3F8, O2

[0078] However, the second gas is not limited to C₃F₈ and O₂. The second gas may include a second CF₂-containing gas and oxygen, and may be any gas that etches the silicon oxide film and facilitates deposition of deposits at the bottom of the hole. The second CF₂-containing gas may be different from the first CF₂-containing gas included in the third gas described later, and may have a lower C / F ratio than the first CF₂-containing gas. The second CF₂-containing gas is, for example, C₃F₈.

[0079] The second gas may contain gases other than the second CF-containing gas and oxygen. For example, in addition to C3F8 and O2, the second gas may also contain at least one of C4F6, C4F8, CO, CO2, and N2. Ar may also be contained.

[0080] (Third Process)

[0081] An example of the process conditions in the third step is shown below.

[0082] <Third step: process conditions>

[0083] Pressure: 15mT~30mT

[0084] HF: On (4000W~5500W)

[0085] LF: On (6000W~8750W)

[0086] Third gas: C4F6, O2

[0087] However, the third gas is not limited to C4F6 gas and O2 gas. The third gas may include the first CF-containing gas and oxygen gas, and may be any gas as long as it is used to etch the silicon oxide film and prevents deposits from being deposited at the bottom of the hole. The first CF-containing gas may have a C / F ratio greater than that of the second CF-containing gas. The first CF-containing gas is, for example, C4F6, and may be C4F8 gas. In addition, the third gas may include gases other than the first CF-containing gas and oxygen. For example, in addition to C4F6 and O2, the third gas may include at least one of C3F8, C4F8, CO, CO2, and N2. Ar may further be included.

[0088] The role of the gases in each step will be described. Of the first gases used in the first step, C₄F₆ gas primarily contributes to etching, while O₂ gas primarily contributes to controlling the amount of polymer byproduct R generated during etching of the silicon oxide film 110. In other words, controlling the amount of O₂ gas suppresses necking.

[0089] Figure 5 FIG. 1 is a diagram showing the state of the hole H1 in each step of the etching method according to one embodiment. In the first step, the first gas is used, so that Figure 5 As shown in (a), the etching of the hole H1 can be promoted by the radicals of C 4 F 6 and the ions in the plasma, and the necking caused by the byproducts R attached to the opening of the mask 100 can be suppressed.

[0090] When the first gas contains CO gas, CO gas, and N gas in addition to C4F6 gas and O2 gas, CO gas and CO2 gas are used as dilution gases to increase the selectivity of the tungsten base layer to the silicon oxide film 110. N2 gas helps control the amount of polymer by-products and is used to suppress necking. When Ar gas is further contained, Ar is used as a dilution gas to increase the selectivity of the base layer.

[0091] On the other hand, in the first gas, the by-product R easily adheres to the opening of the hole H1 or the upper part of the mask 100. Therefore, in the etching method according to this embodiment, after a certain degree of etching is performed using the first gas in the first process, etching is performed using the second gas in the second process. Among the second gases used in the second process, C3F8 gas mainly contributes to etching. In addition, O2 gas mainly contributes to controlling the amount of the by-product R of the polymer. In the case where the second gas contains CO gas, CO2 gas, N2 gas, and C4F6 gas in addition to C3F8 gas and O2 gas, since the functions of each gas are the same as those of the gases contained in the first gas, their description is omitted here.

[0092] C3F8 gas has a higher degree of dissociation than C4F6 gas, and its adsorption coefficient is lower than that of C4F6 gas at the same temperature. For example, the adhesion of CF-based gas radicals to the target film generally depends on the ratio of the number of carbon atoms to the number of fluorine atoms in a single radical molecule (i.e., the C / F ratio). A higher C / F ratio indicates higher adhesion to the target film. Therefore, in the second step, based on etching conditions (such as temperature and dwell time), C3F8 gas is selected, which has a higher degree of dissociation than C4F6 gas and a lower adsorption coefficient than C4F6 gas at the same temperature.

[0093] In other words, when C4F6 and C3F8 are used as CF-based gases, although some of the C4F6 radicals dissociate into CF at normal etching temperatures, x , but mainly exists as C4F6 free radicals. On the other hand, most of the C3F8 free radicals dissociate at normal etching temperatures and exist mainly as C2F4 free radicals.

[0094] Therefore, C4F6 with higher adhesion is used as the first gas in the first process at the beginning of plasma etching to obtain a selectivity with respect to the base layer 120, and C3F8 with lower adhesion is used as the second gas in the second process after the first process.

[0095] Thus, in the second step, Figure 5As shown in (b), the byproduct R is less likely to adhere to the opening or upper portion of the mask 100 and is more likely to reach the bottom of the hole or the side near the bottom. In addition, since the C3F8 gas is a gas with a lower ratio of C to F than the C4F6 gas, the amount of byproduct R is less than when the C4F6 gas is used. As a result, the byproduct R is more likely to be deposited from the bottom of the hole in a bottom-up manner. Therefore, as Figure 4B As shown in (c), byproduct R can be deposited on the base layer 120a3 at the bottom of hole H1. Furthermore, in the second step, hole H2 above base layer 120b3 and hole H3 above base layer 120c3 can be etched deeper. The reason for this will be explained below.

[0096] exist Figure 4B In holes H2 and H3 shown in (c), silicon oxide film 110 is etched. Therefore, byproduct R generated during etching includes the oxygen component in the etched silicon oxide film 110. Therefore, even if the C3F8 gas dissociates and the carbon component enters holes H2 and H3, carbon and oxygen react to form carbon monoxide (CO), which then volatilizes.

[0097] On the other hand, Figure 4B In hole H1 shown in (c), etching has already completed down to the tungsten in base layer 120a3, so etching of silicon oxide film 110 does not proceed in the second step. Consequently, the byproduct R at the bottom of hole H1 does not contain the oxygen component. Therefore, even if the C3F8 gas dissociates and the carbon component enters hole H1, the reaction between carbon and oxygen is not promoted at the bottom of hole H1, and the carbon at the bottom of hole H1 is not consumed. Therefore, while carbon is consumed and the amount of carbon decreases at the bottoms of holes H2 and H3, it is not consumed at the bottom of hole H1, and the amount of carbon increases. Therefore, as shown in FIG4(c), although the polymer byproduct R is deposited at the bottom of hole H1, it is not deposited at the bottoms of holes H2 and H3, and etching is promoted.

[0098] As described above, in the etching method according to this embodiment, in the initial stage of etching, C 4 F 6 gas contained in the first gas is used in the first step to promote etching of the bottom of the hole by radicals and ions of C 4 F 6 .

[0099] Then, in the second step, etching is performed using C3F8 gas contained in the second gas. This allows byproducts R to be deposited at the bottom of holes where the base layer 120 is exposed, thereby reducing the risk of the base layer 120 being damaged by thinning the bottom of the holes. Furthermore, etching can continue for holes where the base layer 120 is not exposed.

[0100] In the etching method according to this embodiment, the third step is performed after the second step. The second and third steps are performed a predetermined number of times. The predetermined number of times is preferably two or more.

[0101] In the third step, etching is performed using C4F6 gas and O2 gas contained in the third gas. Figure 5 As shown in (c), the byproduct R at the bottom of the hole H1 can be removed by the radicals of C4F6 and the ions in the plasma, and the necking caused by the byproduct R attached to the opening of the mask 100 can be suppressed. Figure 4B As shown in (d), etching of the holes H2 and H3 can be accelerated.

[0102] Here, the second step is performed again before all the byproducts R at the bottom of the hole H1 are removed in the third step. Figure 4B As shown in (c) and (d), the second and third steps are repeated a predetermined number of times, thereby completely removing the byproducts R at the bottom of the hole H1 and effectively preventing the base layer 120 from being damaged.

[0103] In summary, according to the etching method in this embodiment, Figure 6 As shown, it is possible to inhibit damage in the lower or middle basal layers ( Figure 6 C), while etching the high-level or middle-level silicon oxide film 110 to different depths.

[0104] It should be noted that the processing time of the second step is preferably shorter than that of the third step. In the second step, since a more sedimentary etching is performed than in the third step, byproducts R are more likely to adhere not only to the bottom of the hole but also to the sides of the hole or the opening of the mask 100. Therefore, by making the processing time of the second step shorter than that of the third step, excessive adhesion of byproducts R can be prevented, and etching stop can be avoided. For example, the processing time of the third step can be approximately 10 times that of the second step.

[0105] [Experimental Results]

[0106] Reference Figure 7 An example of experimental results of etching performed under various process conditions in the first to third steps using the etching method according to this embodiment will be described. Figure 7 is a diagram showing one example of experimental results of an etching method according to one embodiment.

[0107] In this experiment, the etching method according to this embodiment was used to carry out Figure 7 (a) shows the deep hole and Figure 7 (b) Two types of etching for shallow holes. The depth of the deep hole is 10 to 20 times the depth of the shallow hole.

[0108] As a result of the experiment, the bottom of the shallow hole was magnified. Figure 7 The lower left figure shows that a polymer by-product R with a thickness of more than 50 nm is deposited at the bottom of the shallow hole, and the protective effect of the base layer 120 is confirmed.

[0109] Figure 7 The lower right figure shows the state after the byproduct R deposited at the bottom of the shallow hole is removed by ashing. As a result, the tungsten consumption of the base layer 120 is 13nm. The tungsten consumption generated by the etching method using the process conditions of the first step is 26nm. It can be seen that the etching method according to this embodiment can reduce the consumption of tungsten, suppress damage to multiple base layers 120 of different heights, and at the same time, can etch the silicon oxide film 112 on each base layer 120 to different depths.

[0110] [Etching Mode]

[0111] Reference Figure 8 An example of process conditions for determining whether the etching mode in the first to third steps of the etching method according to this embodiment is set to deposition or removal will be described. Whether the etching mode is deposition or removal depends on the amount of C used to generate the deposit and the amount of O used to remove the deposit. Figure 8 : is a diagram showing the relationship between the gas types and gas flow rates that can be used in the etching method according to this embodiment, and the etching mode.

[0112] exist Figure 8 The table calculates the ratio of the amount of C to the amount of O (i.e., the C / O ratio) under seven conditions. For example, under the "C4" condition, 30 sccm, 30 sccm, 425 sccm, and 21 sccm of C4F6 gas, C3F8 gas, CO gas, and O2 gas are supplied, respectively. In this case, the total amount of C (C amount) is 30 × 4 (C4F6 gas) + 30 × 3 (C3F8 gas) + 425 (CO gas) = ​​635. The total amount of O is 425 (CO gas) + 21 × 2 (O2 gas) = ​​467. Therefore, under the "C4" condition, the C / O ratio is 1.36 (= 635 / 467).

[0113] As a result of the above calculation under 7 conditions, C / O is Figure 8As shown in the table. Regarding etching performed under seven conditions, as indicated by the modes, "Etch" is a subtractive etch and "Depo" is a deposition etch. As described above, the gas types and gas flow rates when the C / O ratio is less than 1.3 can be used as a reference for the process conditions for the "Etch" etching mode, i.e., the gas types and gas flow rates for subtractive etching. Furthermore, the gas types and gas flow rates when the C / O ratio is greater than 1.3 can be used as a reference for the process conditions for the "Depo" etching mode, i.e., the gas types and gas flow rates for deposition etching.

[0114] Therefore, in the third step, the C / O ratio in the third gas is preferably less than 1.3, and in the second step, the C / O ratio in the second gas is preferably greater than 1.3. This allows deposition etching to be performed in the second step and removal etching to be performed in the third step. Furthermore, in the first step, the C / O ratio in the first gas is preferably less than 1.3.

[0115] Furthermore, the relative flow rate of the O2 gas contained in the second gas used in the second step is preferably lower than the flow rate of the O2 gas contained in the third gas used in the third step. This allows for a more depositive etching in the second step and a more removable etching in the third step. However, the flow rate of the O2 gas contained in the second gas must be controlled to prevent necking.

[0116] [Temperature dependence]

[0117] Finally, refer to Figure 9 The temperature dependence of etching will be described. Figure 9 is a graph showing the relationship between substrate temperature and etching rate in an etching method according to one embodiment.

[0118] Figure 9 The horizontal axis represents the substrate temperature. Figure 9 "W ER" represents the etching rate when tungsten (W) is used as the base layer. "Ox ER" represents the etching rate of the silicon oxide film 110. "Ox / W sel." represents the selectivity of the silicon oxide film 110 to the tungsten (W) base layer. The substrate temperature is approximately equal to the temperature of the electrostatic chuck 13.

[0119] Figure 9The "W ER" line in FIG. 3 shows that the etching rate of the base layer decreases as the substrate temperature increases. However, the rate of decrease in the etching rate decreases as the substrate temperature increases. Meanwhile, the "Ox ER" line shows that the etching rate is constant when the substrate temperature is approximately 110°C to approximately 160°C, and decreases when the substrate temperature exceeds approximately 160°C. The "Ox / Wsel." line shows that the selectivity increases when the substrate temperature is approximately 110°C to approximately 160°C, and decreases when the substrate temperature exceeds approximately 160°C.

[0120] The higher the temperature, the harder it is for ions or radicals in the plasma to be adsorbed. That is, the higher the substrate temperature, the harder it is for ions or radicals in the plasma to adhere to the upper portion of the pores, while the lower the substrate temperature, the easier it is for ions or radicals to adhere to the upper portion of the pores.

[0121] Therefore, the adsorption coefficient of the second CF-containing gas, exemplified by C3F8 gas, is preferably smaller than the adsorption coefficient of the first CF-containing gas, exemplified by C4F6 gas. Furthermore, the substrate temperature in the second and third steps is preferably within a range of approximately 110°C to 160°C. This reduces the adhesion coefficients of C3F8 and C4F6 gases. This facilitates the deposition of polymer byproducts R from the bottom of the pores, improving the Ox / W selectivity.

[0122] As described above, according to the etching method and substrate processing apparatus 10 of this embodiment, damage to a plurality of base layers at different heights can be suppressed while etching the silicon oxide film on each base layer to different depths.

[0123] The etching method and substrate processing apparatus according to one embodiment disclosed herein should be considered in all respects to be illustrative and non-restrictive. The above embodiment may be modified and improved in various ways without departing from the scope and spirit of the appended claims. The contents described in the above embodiments may be adopted in other configurations and combined without conflict.

[0124] The substrate processing device disclosed in the present invention can be applied to any type of device including atomic layer deposition (ALD: Atomic Layer Deposition) device, capacitively coupled plasma (CCP: Capacitively Coupled Plasma), inductively coupled plasma (ICP: Inductively Coupled Plasma), radial line slot antenna (RLSA: Radial Line Slot Antenna), electron cyclotron resonance plasma (ECR: Electron Cyclotron Resonance Plasma), and helicon wave plasma (HWP: Helicon Wave Plasma).

Claims

1. An etching method comprising: A step of preparing a substrate having a first base layer, a second base layer formed at a position deeper than the first base layer, a silicon oxide film formed on the first base layer and the second base layer, and a mask formed on the silicon oxide film, the mask having a first opening formed above the first base layer and a second opening formed above the second base layer; a step of etching the silicon oxide film through the first opening using a first gas to expose the first base layer; a step of depositing a precipitate on the first base layer using a second gas, and simultaneously etching the silicon oxide film above the second base layer through the second opening; as well as a step of removing deposits deposited on the first base layer using a third gas and etching the silicon oxide film above the second base layer through the second opening; wherein the etching process using the second gas and the etching process using the third gas are repeated multiple times, The third gas includes the first CF-containing gas and oxygen. The second gas includes a second CF 2 -containing gas different from the first CF 2 -containing gas, and oxygen.

2. The etching method according to claim 1, wherein The C / F ratio of the second CF2-containing gas is smaller than the C / F ratio of the first CF2-containing gas.

3. The etching method according to claim 1 or 2, wherein: The adsorption coefficient of the second CF 2 -containing gas within a predetermined temperature range is smaller than the adsorption coefficient of the first CF 2 -containing gas within the predetermined temperature range.

4. The etching method according to claim 1 or 2, wherein: The first CF-containing gas is C4F6, and the second CF-containing gas is C3F8.

5. The etching method according to claim 1 or 2, wherein: The C / O ratio contained in the third gas is less than 1.3, and the C / O ratio contained in the second gas is greater than or equal to 1.

3.

6. The etching method according to claim 1 or 2, wherein: The flow rate of oxygen contained in the second gas is smaller than the flow rate of oxygen contained in the third gas.

7. The etching method according to claim 3, wherein: The predetermined temperature range is 110°C to 160°C.

8. The etching method according to claim 1 or 2, wherein: The first base layer and the second base layer are tungsten.

9. The etching method according to claim 1 or 2, wherein: The first base layer and the second base layer are silicon.

10. The etching method according to claim 1 or 2, wherein: A processing time of a process of etching using the second gas is shorter than a processing time of a process of etching using the third gas.

11. The etching method according to claim 1 or 2, wherein: The step of repeating the etching process using the second gas and the etching process using the third gas is performed before the second base layer is exposed.

12. The etching method according to claim 11, wherein a third base layer formed at a position deeper than the second base layer, wherein the silicon oxide film is formed on the third base layer; The step of repeating the etching process using the second gas and the etching process using the third gas is performed before the second base layer is exposed, and then performed after the second base layer is exposed and before the third base layer is exposed.

13. A substrate processing apparatus, comprising: a gas supply source for supplying gas; a high-frequency power supply for applying high-frequency power; a plasma generating section for generating plasma from supplied gas using high-frequency power; as well as Control Department, The control unit controls the following processes: A step of preparing a substrate having a first base layer, a second base layer formed at a position deeper than the first base layer, a silicon oxide film formed on the first base layer and the second base layer, and a mask formed on the silicon oxide film, the mask having a first opening formed above the first base layer and a second opening formed above the second base layer; a step of etching the silicon oxide film through the first opening using a first gas to expose the first base layer; a step of depositing a precipitate on the first base layer using a second gas, and simultaneously etching the silicon oxide film above the second base layer through the second opening; and a step of removing deposits deposited on the first base layer using a third gas and etching the silicon oxide film above the second base layer through the second opening; The control unit controls so that the etching process using the second gas and the etching process using the third gas are repeated multiple times. The third gas includes the first CF-containing gas and oxygen. The second gas includes a second CF 2 -containing gas different from the first CF 2 -containing gas, and oxygen.

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