Etching method and plasma processing apparatus

Abstract

The present application provides a technique for improving a selection ratio at the time of etching a laminated film in which silicon oxide films and silicon films are alternately laminated. The present application provides an etching method for a laminated film in which silicon oxide films and silicon films are alternately laminated on a substrate, which is an etching method for forming a desired etching shape by plasma, including the steps of: a step of preparing the substrate; a step of cooling the surface temperature of the substrate to -40°C or lower; a step of generating plasma of a gas containing hydrogen and fluorine by high-frequency power for plasma generation; and a step of etching the laminated film by the generated plasma.

Description

Technical Field

[0001] This disclosure relates to etching methods and plasma processing apparatus. Background Technology

[0002] For example, Patent Document 1 proposes a method for etching a multilayer film in which silicon oxide and silicon nitride films are alternately stacked. Furthermore, for example, Patent Document 2 proposes a method for etching a multilayer film in which silicon oxide and polycrystalline silicon films are alternately stacked.

[0003] In Patent Document 2, a multilayer film is etched by plasma generated from a gas containing at least one of bromine, chlorine, or iodine, and a fluorocarbon gas.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-39310

[0007] Patent Document 2: International Publication No. 2013 / 118660 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] This disclosure provides a technique for improving selectivity during etching of a laminate of alternating layers of silicon oxide and silicon films.

[0010] Methods for solving problems

[0011] According to one aspect of this disclosure, an etching method is provided, which is an etching method for forming a desired etching shape by plasma on a laminate of alternating silicon oxide film and silicon film on a substrate, comprising the following steps: preparing the substrate; cooling the surface temperature of the substrate to below -40°C; generating a plasma containing hydrogen and fluorine gases by high-frequency power for plasma generation; and etching the laminate by the generated plasma.

[0012] The effects of the invention

[0013] According to one aspect, the selectivity can be improved during the etching of a laminate of alternating layers of silicon oxide and silicon films. Attached Figure Description

[0014] Figure 1 This is a cross-sectional schematic diagram illustrating an example of the plasma processing apparatus according to the embodiment.

[0015] Figure 2This figure illustrates an example of an etching method involved in an implementation.

[0016] Figure 3 This is a diagram illustrating an example of the film structure of the etched object involved in the embodiment.

[0017] Figure 4 This is a diagram illustrating an example of the relationship between the surface temperature and etching characteristics of the substrate involved in the embodiment.

[0018] Figure 5 This is a diagram illustrating an example of the roundness and bending shape of the bottom of the recess formed by the etched laminated film according to the embodiment.

[0019] Figure 6 This is a graph illustrating an example of the relationship between the ratio of hydrogen-containing gas to fluorine-containing gas and the etching rate in an embodiment.

[0020] Figure 7 This diagram illustrates the principle of etching the recesses of a silicon oxide film using HF-based free radicals during low-temperature etching.

[0021] Figure 8 This is a graph illustrating an example of the relationship between the LF power and the surface temperature of the substrate during etching in an embodiment.

[0022] Figure 9 This figure illustrates an example of the result of adding chlorine in the etching method involved in the embodiment.

[0023] Figure 10 This is a graph illustrating an example of the relationship between the gas ratio of SF6 gas to NF3 gas and the etching rate in an embodiment.

[0024] Figure 11 This is a diagram illustrating an example of the relationship between the gas ratio of SF6 gas to NF3 gas and the bending shape in the embodiment. Detailed Implementation

[0025] Hereinafter, specific embodiments will be described with reference to the accompanying drawings. In the drawings, the same components are marked with the same reference numerals, and sometimes repeated descriptions are omitted.

[0026] [Plasma Processing Device]

[0027] For the plasma processing apparatus 1 involved in the implementation method, using Figure 1 Please provide an explanation. Figure 1 This is a cross-sectional schematic diagram showing an example of the plasma processing apparatus 1 according to the embodiment. The plasma processing apparatus 1 according to the embodiment is a parallel flat plate type plasma processing apparatus in which a platform 11 and a spray head 20 are arranged opposite each other inside a processing container 10.

[0028] The stage 11 serves to hold the substrate W, which holds the semiconductor wafer, and functions as a lower electrode. The spray head 20 serves to supply gas into the processing container 10 in a spray pattern and functions as an upper electrode.

[0029] The processing container 10 is formed of aluminum, for example, with a surface treated with an aluminum oxide film (anodized), and is cylindrical. The processing container 10 is electrically grounded. A stage 11 is disposed at the bottom of the processing container 10, on which the substrate W is placed.

[0030] The mounting stage 11 is formed of materials such as aluminum (Al), titanium (Ti), and silicon carbide (SiC). The mounting stage 11 has an electrostatic chuck 12 and a base 13. The base 13 supports the electrostatic chuck 12. The electrostatic chuck 12 has a structure in which chuck electrodes 12a are sandwiched between insulators 12b. The chuck electrodes 12a are connected to a power supply 14. The electrostatic chuck 12 uses the Coulomb force generated by applying a voltage from the power supply 14 to the chuck electrodes 12a to attract the substrate W to the electrostatic chuck 12.

[0031] A cooling medium flow path 13a is formed inside the base 13. The cooling medium flow path 13a is connected to a cooling medium inlet pipe 13b and a cooling medium outlet pipe 13c. A cooling medium (temperature control medium) at a specified temperature is output from the cooling unit 15, and the cooling medium circulates through the cooling medium inlet pipe 13b, the cooling medium flow path 13a, and the cooling medium outlet pipe 13c. As a result, the mounting stage 11 is cooled (temperature regulated), and the substrate W is controlled to a specified temperature.

[0032] The heat transfer gas supply source 17 supplies heat transfer gases such as helium through the gas supply line 16 to the area between the surface of the electrostatic chuck 12 and the back surface of the substrate W. This improves the heat transfer efficiency between the electrostatic chuck 12 and the substrate W, and enhances the temperature controllability of the substrate W.

[0033] In the mounting stage 11, a first high-frequency power supply 30 supplying high-frequency power (HF power) for plasma generation is electrically connected via a first matching connector 30a. Furthermore, in the mounting stage 11, a second high-frequency power supply 31 supplying high-frequency power (LF power) for bias voltage at a lower frequency than the HF power is electrically connected via a second matching connector 31a. For example, the first high-frequency power supply 30 applies 40 MHz of high-frequency power to the mounting stage 11. For example, the second high-frequency power supply 31 applies 400 kHz of high-frequency power to the mounting stage 11. Additionally, the first high-frequency power supply 30 can apply high-frequency power to the spray head 20.

[0034] The first matching unit 30a matches the load impedance on the stage 11 side with the output (internal) impedance of the first high-frequency power supply 30. The second matching unit 31a matches the load impedance on the stage 11 side with the output (internal) impedance of the second high-frequency power supply 31.

[0035] The spray head 20 closes the opening of the top portion of the processing container 10 through a shielding ring 22 covered by an insulator on its periphery. The spray head 20 has a gas inlet 21 for introducing gas. A diffusion chamber 23 connected to the gas inlet 21 is provided inside the spray head 20. Gas output from the gas supply source 25 is supplied to the diffusion chamber 23 through the gas inlet 21 and introduced into the interior of the processing container 10 through a number of gas supply holes 24.

[0036] The bottom surface of the processing container 10 has an exhaust port 18, which is connected to an exhaust device 19. The exhaust device 19 exhausts air from the processing container 10, thereby controlling the vacuum level inside the processing container 10. A gate valve 27 is provided on the side wall of the processing container 10 to open and close the transport port 26. Depending on the opening and closing of the gate valve 27, the substrate W is moved into the processing container 10 through the transport port 26 and moved out of the processing container 10.

[0037] The plasma processing apparatus 1 is equipped with a control unit 40 that controls the operation of the entire apparatus. The control unit 40 includes a CPU 41, a ROM 42, and a RAM 43. The CPU 41 executes the etching process of the substrate W according to various schemes stored in the storage areas of the ROM 42 and RAM 43. The schemes are set as control information for the apparatus relative to process conditions, such as process time, pressure (gas exhaust), high-frequency power, voltage, various gas flow rates, substrate surface temperature (temperature of the electrostatic chuck 12, etc.), and the temperature of the cooling medium supplied from the cooling unit 15. Furthermore, the schemes representing these programs and processing conditions can be stored in a hard disk or semiconductor memory. Additionally, the schemes can be stored in a designated location in the storage area in a portable, computer-readable storage medium such as a CD-ROM or DVD.

[0038] During substrate processing, the opening and closing of the control gate valve 27 is used to move the substrate W, held in the transport arm, from the transport port 26 into the processing container 10, place it on the placement stage 11, and attract it to the electrostatic chuck 12. Thus, the substrate W is prepared.

[0039] Next, gas is supplied from the spray head 20 into the processing container 10, and high-frequency electricity for plasma generation is applied to the stage 11 to generate plasma. The generated plasma is used to etch the substrate W. High-frequency electricity for bias voltage is applied to the stage 11 along with the high-frequency electricity for plasma generation. After processing, the charge on the substrate W is removed by a de-energizing process, and the substrate W is peeled off from the electrostatic chuck 12 and removed.

[0040] Regarding the surface temperature of the substrate (e.g., the surface temperature of the wafer), the temperature of the electrostatic chuck 12, which is adjusted to the desired temperature by the cooling unit 15, is adjusted by heat transfer to the substrate W through the surface of the electrostatic chuck 12 and the heat transfer gas. However, the substrate W is exposed to plasma generated by high-frequency electricity for plasma generation, and ions introduced by high-frequency electricity for bias voltage from the plasma irradiate the substrate W. Therefore, the temperature of the substrate W, especially the surface temperature of the plasma facing the substrate W, is higher than the temperature of the adjusted electrostatic chuck 12. Furthermore, due to radiative heat from the temperature-adjusted counter electrode and the sidewall of the processing container 10, the surface temperature of the substrate W sometimes also rises, thus enabling the measurement of the actual temperature of the substrate W during the etching process. In cases where the process conditions are configured such that the temperature difference between the adjusted temperature of the electrostatic chuck 12 and the actual surface temperature of the substrate W can be inferred, the setting of the adjusted temperature of the electrostatic chuck 12 can be reduced in order to adjust the temperature of the substrate W within a predetermined temperature range.

[0041] [Etching Method]

[0042] For the etching method according to this embodiment that can be performed in the plasma processing apparatus 1 with the involved configuration, refer to... Figure 2 and Figure 3 Please provide an explanation. Figure 2 This figure illustrates an example of an etching method involved in an implementation. Figure 3 This is a diagram illustrating the film structure of the etched object involved in the embodiment.

[0043] In the etching method described in this embodiment, the surface temperature of the substrate is cooled to below -40°C, and the laminated film to be etched is then etched. Hereinafter, etching with the surface temperature of the substrate controlled to below -40°C is also referred to as "low-temperature etching".

[0044] exist Figure 2 In the etching method of this embodiment shown, the method having Figure 3(a) The substrate W of the stacked film 100, which alternately stacks silicon oxide film and polycrystalline silicon film as shown, and the mask 101 on the stacked film 100, is placed on the mounting stage 11 for preparation (step S1). In addition, the polycrystalline silicon film of the stacked film 100 is not limited to this, and can be formed of silicon film such as amorphous silicon or doped silicon.

[0045] Next, with the surface temperature of the substrate cooled to below -40°C, the laminated film is etched at low temperature by plasma generated by the plasma processing device 1 (step S2). The etching in step S2 is also referred to as the main etching.

[0046] Figure 3 (a) shows the film structure of the object to be etched, representing the initial state before etching. The substrate has a laminated film 100, a mask 101 on the laminated film 100, and a base film 102 of the laminated film 100. The mask 101 is formed of an organic material and has an opening HL. The base film 102 is formed of, for example, polycrystalline silicon. However, the base film 102 is not limited to polycrystalline silicon and can be formed of amorphous silicon or monocrystalline silicon. Furthermore, the base film 102 can be a silicide film containing a transition metal such as nickel (Ni), or a transition metal layer such as tungsten (W) or ruthenium (Ru).

[0047] In the main etching step S2, a plasma containing hydrogen and fluorine gases is generated using high-frequency electricity for plasma generation. The generated plasma is then used to etch the stacked film 100 through mask 101. The hydrogen and fluorine-containing gases are combinations of fluorocarbon gases (CF-based), hydrogen-carbon gases (CH-based), and hydrogen-containing gases. Examples of processing gases include H2 and CF4. Other examples of processing gases include H2, C4F8, CH2F2, NF3, and SF6.

[0048] Therefore, as Figure 3 As shown in (b), the laminated film 100 is etched into the pattern of the mask 101, and the laminated film 100 has recesses. Further, as... Figure 3 As shown in (c), the laminated film 100 is etched at low temperature until the base film 102 is exposed.

[0049] Thus, in the main etching, using the plasma of the processing gas supplied to the plasma processing apparatus 1, the laminated film 100 is etched at a low temperature through the opening HL of the mask 101, forming a recess in the laminated film 100. For example... Figure 3As shown in (c), in the recess of the hole shape formed by the laminated film 100, the diameter of the recess at the boundary surface between the mask 101 and the laminated film 100 is called Top CD, and the diameter of the recess at the boundary surface between the base film 102 and the laminated film 100 is called Btm CD. Furthermore, in this embodiment, an etching method for forming holes (openings HL) of the desired etching shape using plasma is described, but it is not limited to this. The etching method according to this embodiment can form grooves of the desired etching shape, i.e., recesses of the pipeline shape, using plasma.

[0050] [Temperature dependence of etching]

[0051] Regarding the temperature dependence of the substrate in the etching method involved in this embodiment, while referring to... Figure 4 While explaining. Figure 4 This is a diagram illustrating an example of the relationship between the surface temperature and etching characteristics of the substrate W involved in the embodiment.

[0052] For example, in the etching of 3D-NAND structures or other structures, sometimes a laminated film 100 with alternating layers of silicon oxide and polycrystalline silicon is etched. In this case, when etching a laminated film with alternating layers of silicon oxide and silicon nitride, different from that in this embodiment, is performed at a temperature condition where the substrate surface temperature is at or above room temperature (around 25°C), the optimized temperature conditions are applied to the laminated film of this embodiment, resulting in an increased arc shape CD or insufficient mask selectivity. For example, if the substrate surface temperature is controlled at 20°C and the laminated film 100 is etched, the arc shape CD increases. On the other hand, if the substrate surface temperature is controlled at 110°C or 140°C and the laminated film 100 is etched, the arc shape CD is improved, but the mask selectivity is insufficient.

[0053] Additionally, the bow CD represents the diameter of the widest portion of the recess in the laminate 100. The mask selection ratio represents the ratio of the etch rate of the laminate 100 to the etch rate of the mask 101.

[0054] Figure 4 This represents experimental results showing various etching characteristics relative to the surface temperature of the substrate. Figure 5 This example illustrates the experimental results regarding the roundness and curvature of the bottom of the recess formed in the etched laminated film 100 according to the embodiment. In this experiment, processing gases including H2, C4F8, CH2F2, NF3, and SF6 were used. Specifically, processing gases were supplied to the processing container 10 of the plasma processing apparatus 1, and plasma of the aforementioned processing gases was generated using high-frequency electricity for plasma generation, thereby conducting the experiment of etching the laminated film 100.

[0055] Figure 4 The horizontal axis represents the surface temperature of the substrate, and the vertical axis represents... Figure 4 (a) indicates the mask selection ratio (◇). Figure 4 (b) represents the etching rate (〇) of the laminated film and the etching rate (□) of the mask. Figure 4 (c) represents Bow CD(〇) and Btm CD(□). Furthermore, Figure 5 This indicates the roundness and bending shape of the bottom of the recess (bottom of the via) formed by the laminated film 100 after etching. Roundness indicates how close the cross-sectional shape of the via is to a perfect circle; the closer the bottom of the recess is to a perfect circle, the more rounded and curved it is. Figure 5 The higher the roundness, the more elliptical the bottom surface of the concave part becomes. Figure 5 The lower the roundness, the better. Bending indicates that the recess of the laminate 100 is not formed vertically, but rather bends from the mask 101 toward the bottom of the recess.

[0056] exist Figure 4 (a) and Figure 5 In the results shown, if the surface temperature of the substrate reaches -40°C or higher, the mask selectivity decreases, and the roundness of the bottom of the recess (the bottom of the via) formed by the laminated film 100 deteriorates. Specifically, if the surface temperature of the substrate reaches -37°C or higher, the roundness of the bottom of the via deteriorates.

[0057] Furthermore, if the surface temperature of the substrate becomes below -57°C, bending deteriorates. If bending deteriorates, the etching rate of the laminate 100 decreases, so it is preferable to suppress bending.

[0058] As can be seen from the above, in the etching method of this embodiment, the surface temperature of the substrate is controlled to below -40°C, and the substrate W is etched at low temperature by using a plasma containing a processing gas containing hydrogen and a fluorine gas. This improves the mask selectivity.

[0059] Next, by Figure 4 The results shown in (a) and (b) demonstrate that by controlling the surface temperature of the substrate to between -55°C and -40°C, the mask selectivity and the etching rate of the laminate 100 can be improved. Furthermore, the mask 101 can sufficiently maintain a low etching rate when the surface temperature of the substrate is controlled to between -55°C and -40°C.

[0060] Depend on Figure 4 The results of (a) and (b) show that the highest mask selectivity and etching rate of the stacked film 100 are obtained when the surface temperature of the substrate is -47°C. In the range of -55°C to -40°C, both the mask selectivity and etching rate of the stacked film 100 become good.

[0061] Next, by Figure 4 (c) shows that if a difference is observed between the bow CD and the bottom CD (Btm CD), the lower the surface temperature of the substrate, the larger the difference. The smaller the difference between the bow CD and the bottom CD, the more vertically the recesses of the laminate 100 are formed. Therefore, the smaller the difference between the bow CD and the bottom CD, the better.

[0062] Next, by Figure 5 As a result, if the surface temperature of the substrate becomes above -37°C, the roundness of the bottom of the vias deteriorates. Furthermore, if the surface temperature of the substrate is below -57°C, the shape of the sidewalls of the recesses in the laminate 100 deteriorates, and bending worsens. If bending worsens, the etching rate of the laminate 100 decreases; therefore, it is preferable to suppress bending.

[0063] That is, in order to improve the curvature of the recesses formed by the laminated film 100, it is preferable to control the surface temperature of the substrate to -55°C or higher. This improves the shape of the recesses formed by the laminated film 100, making them closer to a vertical shape.

[0064] As can be seen from the above, by controlling the surface temperature of the substrate to below -40°C, the etching rate of the laminate 100 can be increased. Furthermore, by controlling the surface temperature of the substrate to between -55°C and -40°C, the mask selectivity and etching rate of the laminate 100 can be increased, and bending can be suppressed.

[0065] In addition, Figure 4 In the experiment shown, the ratio of hydrogen (H) to the total amount of hydrogen (H) and fluorine (F) in the H2, C4F8, CH2F2, NF3 and SF6 gases used in the experiment, i.e., H / (H+F), is 58%.

[0066] In addition, the amounts of H and F elements are determined by the molecular formula of the gas used, the sum of the product of the gas volume flow rate and the valence of the elements contained in the gas.

[0067] [Gas Ratio]

[0068] Next, regarding the type and ratio of gas used in the etching method involved in this embodiment, while referring to... Figure 6 While explaining. Figure 6 This is a graph illustrating an example of the relationship between the ratio of hydrogen-containing gas to fluorine-containing gas and the etching rate in an embodiment.

[0069] In this experiment, H2 gas was used as the hydrogen-containing gas, and CF4 gas was used as the fluorine-containing gas. Processing gases of H2 and CF4 were supplied to the processing container 10 of the plasma processing apparatus 1, and plasma of the processing gases was generated using high-frequency electricity for plasma generation. Furthermore, experiments were conducted using the generated plasma to etch the rubber blankets of organic material resist (PR) films, silicon oxide (SiO2) films, and polycrystalline silicon (Poly-Si) films, respectively.

[0070] Figure 6 The horizontal axis of (a), (b) and (c) represents the ratio (%) of the volumetric flow rate of H2 gas to the sum of the volumetric flow rates of H2 gas and CF4 gas. Figure 6 (a) The vertical axis represents the etching rate of the resist (PR) film mask 101. Figure 6 (b) The vertical axis represents the etching rate of the silicon oxide film (SiO2). Figure 6 (c) The vertical axis represents the etching rate of polycrystalline silicon (Poly-Si) film. Figure 6 The symbols □ in (a), (b) and (c) represent the results of each etching rate when the surface temperature of the substrate is controlled at 45°C, the symbol 〇 represents the results when the surface temperature of the substrate is controlled at -10°C, and the symbol △ represents the results when the surface temperature of the substrate is controlled at -50°C.

[0071] exist Figure 6 In boxes A, B, and C shown in (a), (b), and (c), when the substrate surface temperature is controlled at -50°C, the etching rates of the silicon oxide film and the polycrystalline silicon film are higher compared to when the substrate surface temperature is controlled at 45°C and -10°C. In contrast, the etching rate of the resist film mask 101 remains almost unchanged between the substrate surface temperatures of -50°C and 45°C.

[0072] That is, the ratio of the volumetric flow rate of H2 gas to the sum of the volumetric flow rates of H2 gas and CF4 gas (=H2 / (H2+CF4)) is in the range of 40% to 80%, and the surface temperature of the substrate is controlled at -50°C. At this time, the mask selectivity can be improved, and the etching rate of the stacked film 100 can be increased.

[0073] If the above results are converted into the ratio of hydrogen (H) to the sum of hydrogen (H) and fluorine (F) (=H / (H+F)), it becomes 25% to 67% or less. That is, in the etching method according to this embodiment, by controlling the ratio of H contained in the processing gas to the sum of H and F to 25% to 67%, the mask selectivity of the stacked film 100 can be improved, and the etching rate of the stacked film 100 can be improved.

[0074] In addition, Figure 4 In the experiment shown, H / (H+F) = 58%, which is within the range shown above.

[0075] The gas that can be used in the etching method according to this embodiment, which satisfies the above conditions, includes at least one of fluorocarbon gas (CF-based) and hydrofluorocarbon gas (CHF-based), and at least one of hydrofluorocarbon gas (CHF-based), hydrogen carbon gas (CH-based) and hydrogen-containing gas. The hydrogen-containing gas can be hydrogen (H2) or hydrogen halide.

[0076] Examples of hydrofluorocarbon gases (CHF series) include CH2F2, CHF3, and C3H2F4. Examples of fluorocarbon gases (CF series) include C4F8, C4F6, and CF4. Examples of hydrogen-carbon gases (CH series) include CH4, C2H6, and C2H4. Examples of hydrogen halides include HF, HCl, HBr, and HI.

[0077] In a plasma containing H2 and CF4 as process gases, hydrogen radicals react with fluorine radicals to produce hydrofluoric acid (HF). The hydrofluoric acid, by reaching a low temperature, for example below -40°C, readily condenses on the bottom surface of the recess formed by the etched film. If the etched film is a silicon oxide film, etching is performed by the condensed hydrofluoric acid (HF). Therefore, the ratio (balance) of hydrogen to fluorine becomes important for the etching process.

[0078] In the etching method of this embodiment, the ratio of H contained in the processing gas to the sum of H and F is controlled to be 25% to 67% or less. This allows etching to be promoted by condensed hydrofluoric acid (HF) on the bottom surface of the recess, improving the mask selectivity of the stacked film 100 and increasing the etching rate of the stacked film 100. Hereinafter, reference will be made to... Figure 7 The importance of controlling the balance of the number of hydrogen atoms and fluorine atoms supplied to the etching region when etching the recesses of a silicon oxide film using HF-based free radicals in low-temperature etching is explained.

[0079] [Etching using HF-based free radicals]

[0080] Figure 7 This diagram illustrates the principle of etching the recesses of a silicon oxide film using HF-based free radicals during low-temperature etching.

[0081] like Figure 7As shown, HF-based free radicals (HF, hydrogen, and fluorine atoms) are supplied to the bottom surface of the recess formed in the silicon oxide film (SiO2). The Si and F in the silicon oxide film react and vaporize as SiF4. This etches the silicon oxide film. Water (H2O) is produced as a reaction product. Figure 7 (A) and (B)). According to the usual vapor pressure curve, water has a low saturated vapor pressure. On the vapor pressure curve, it is a state in which liquid and gas exist in a mixture. Therefore, it is believed that under low-temperature etching conditions where the etching pressure is controlled at about 10 to 100 m Torr and the surface temperature of the substrate is controlled at about -55°C to -40°C, the water on the bottom surface of the concave part of the silicon oxide film is saturated and exists in a certain degree of liquid state.

[0082] Furthermore, with the further supply of hydrogen fluoride relative to water, HF-based free radicals react with water to produce hydrofluoric acid. Figure 7 (C)~(D)). Therefore, it is believed that the etching rate abnormally increases primarily due to the chemical reaction, achieved by dissolving hydrofluoric acid in water on the bottom surface of the concave portion of the silicon oxide film. Thus, in the etching of silicon oxide films at low temperatures, a proper balance of hydrogen and fluorine atoms is required.

[0083] Therefore, in the etching method according to this embodiment, the ratio of H (hydrogen atoms) contained in the processing gas to the sum of H (hydrogen atoms) and F (fluorine atoms) is controlled to be more than 25% and less than 67%. As a result, in low-temperature etching, hydrogen atoms and fluorine atoms are supplied to the laminate 100 in an appropriate balance, thereby improving the mask selectivity of the laminate 100 and increasing the etching rate of the laminate 100.

[0084] Furthermore, during low-temperature etching, the adsorption coefficient of HF-based free radicals increases, and these free radicals adsorb onto the bottom surface of the concave portion of the polycrystalline silicon film. HF-based free radicals themselves have low reactivity with the thermal energy of the polycrystalline silicon film. However, when energy from ion irradiation from plasma is applied to the polycrystalline silicon film while it is in a state where HF is attached to it, the polycrystalline silicon film reacts with the F element in the HF-based free radicals, thus promoting the etching of the polycrystalline silicon film.

[0085] As explained above, according to the etching method of this embodiment, plasma containing a process gas containing hydrogen and a fluorine gas is generated during low-temperature etching where the surface temperature of the substrate is cooled to below -40°C, and the laminate 100 is etched. This improves the mask selectivity and, moreover, increases the etching rate of the laminate 100.

[0086] At this point, it is preferable to control the ratio of hydrogen to the total of hydrogen and fluorine to be more than 25% and less than 67%, thereby enabling the etching caused by the chemical reaction to be mainly promoted by hydrofluoric acid.

[0087] Furthermore, by controlling the surface temperature of the substrate to below -40°C, the roundness can be improved, and by controlling the surface temperature of the substrate to above -55°C, bending can be suppressed.

[0088] Furthermore, by increasing the high-frequency power (LF power) used for the bias voltage and combining it with low-temperature etching, the difference between BowCD and BtmCD can be reduced, and BowCD can be reduced in size. This improves the shape of the recess formed by the laminated film 100 and enhances its verticality.

[0089] Figure 8 This is a graph illustrating an example of the relationship between the LF power and the surface temperature of the substrate during etching in an embodiment. Figure 8 The horizontal axis represents LF power, and the vertical axis represents the substrate surface temperature. For example... Figure 8 As shown, during etching, increasing the LF power leads to a higher substrate surface temperature due to heat input from the plasma side. If the substrate surface temperature increases, the etching rate decreases. To avoid this, the temperature of the stage 11 is controlled by decreasing it in accordance with the increase in LF power. This allows the substrate surface temperature to be controlled between -55°C and -40°C. As a result, in low-temperature etching, the mask selectivity and etching rate of the stacked film 100 can be improved, and the ion perpendicularity can be improved by increasing the LF power, thereby reducing the difference between BowCD and BtmCD, reducing BowCD, and improving the perpendicularity of the etched shape.

[0090] [Addition of chlorine]

[0091] Next, regarding the improvement of the etched shape when chlorine is added to the processing gas, while referring to... Figure 9 While explaining. Figure 9 This figure illustrates an example of the result of adding chlorine in the etching method involved in the embodiment.

[0092] exist Figure 9 In the example, Cl2 gas is added to H2 gas and CF4 gas as the processing gas used in the etching method involved in the implementation. Figure 9 The horizontal axis represents the ratio of the volumetric flow rate of Cl2 gas to the sum of the volumetric flow rates of H2 gas and CF4 gas; the vertical axis (left) represents the Bow CD and Top CD (see reference). Figure 3 The difference is represented by the vertical axis (right), which indicates the cone angle. The cone angle on the vertical axis (right) indicates the verticality of the recess formed by the laminated film 100. When the recess is vertical, it is 90°. The further the cone angle is from 90°, the more the recess becomes a cone shape or an inverted cone shape.

[0093] exist Figure 9 In the example, it can be seen that by adding Cl2 gas to H2 and CF4 gases, the verticality (taper angle) of the etching can be controlled, and the difference between BowCD and TopCD can be controlled. That is, by controlling the amount of Cl2 gas added to H2 and fluorocarbon gases, the cone shape of the etching can be controlled. Thus, the BowCD-TopCD can be reduced, the BowCD can be reduced, and the etching shape can be controlled.

[0094] The rationale for controlling the cone shape of the etching is explained. By adding Cl2 gas to H2 and fluorocarbon gases, SiCl4 is included in the byproducts generated during etching. Compared to SiF4, a byproduct generated during etching using H2 and fluorocarbon gases, SiCl4 is less likely to become gaseous. Therefore, SiCl4 adheres to the sidewalls of the recesses in the laminated film 100, forming a protective film on the sidewalls. Thus, it is believed that reducing the Bow CD-Top CD and the Bow CD can improve the etching shape.

[0095] In addition, Figure 9 In the example, Cl2 gas was added, but it is not limited to this. The same effect is achieved with chlorine-containing gases such as HCl and CCl4. Furthermore, if bromine- or iodine-containing gases such as HBr and HI are used, SiBr4 and SiI4 are generated as byproducts. These byproducts, like SiCl4, are less likely to become gases compared to the byproduct SiF4. In other words, by adding halogen-containing gases other than fluorine, the reduction of Bow CD-Top CD and Bow CD can be achieved, thus improving the etched shape.

[0096] [SF6 gas to NF3 gas ratio]

[0097] Next, regarding the gas ratio of SF6 to NF3 contained in the treated gas, while referring to... Figure 10 and Figure 11 While explaining. Figure 10 This is a graph illustrating an example of the relationship between the gas ratio of SF6 gas to NF3 gas and the etching rate in an embodiment. Figure 11 This is a diagram illustrating an example of the relationship between the gas ratio of SF6 gas to NF3 gas and the bending shape in the embodiment.

[0098] Figure 10 The horizontal axis represents the ratio of the volumetric flow rate of SF6 gas to the sum of the volumetric flow rates of SF6 gas and NF3 gas, expressed as the "SF6 ratio". Figure 10 The vertical axis represents the etching rate (E / R) of the laminate 100. Figure 10The results show a trade-off: a high SF6 gas ratio leads to a lower etching rate, while a high NF3 gas ratio (low SF6 gas ratio) results in a deterioration in the etched shape. Figure 10 Based on the etching rate results, the expected SF6 gas ratio is below 67%.

[0099] In addition, by Figure 11 The desired SF6 gas ratio is between 33% and 67% for bending-related results. By maintaining the ratio of SF6 gas volumetric flow rate to the sum of SF6 and NF3 gas volumetric flow rates at 33% to 67%, it is possible to maintain the etching rate while suppressing bending and improving the etched shape.

[0100] Furthermore, if the above results are converted into the ratio of hydrogen (H) to the sum of hydrogen (H) and fluorine (F) (=H / (H+F)), it becomes 49% to 52%, which is included in... Figure 6 Within the scope of the results specified.

[0101] As explained above, according to the etching method and plasma processing apparatus of this embodiment, a laminated film 100 on a substrate, on which silicon oxide films and silicon films are alternately stacked, is etched by plasma containing a processing gas containing hydrogen and fluorine. By controlling the surface temperature of the substrate to a low-temperature etching state below -40°C, the selectivity can be improved, thereby increasing the etching rate of the laminated film 100.

[0102] Furthermore, by controlling the surface temperature of the substrate to above -55°C, bending can be suppressed. Moreover, by adding Cl2 gas to the processing gas, the cone shape of the etching can be controlled. This enables the reduction of BowCD-TopCD and Bow CD, improving the etching shape.

[0103] The etching method and plasma processing apparatus disclosed herein are illustrative in all respects and should not be considered limiting. The embodiments can be modified and improved in various forms without departing from the appended claims and their spirit. Other configurations can be selected for the matters described in the foregoing embodiments without contradiction, and furthermore, combinations can be made without contradiction.

[0104] The plasma processing apparatus disclosed herein is also applicable to any type of apparatus, including atomic layer deposition (ALD) apparatus, capacitive coupled plasma (CCP), inductively coupled plasma (ICP), radial line slot antenna (RLSA), electron cyclotron resonance plasma (ECR), and helical wave plasma (HWP).

Claims

1. An etching method for forming a desired etching shape by plasma on a laminate of alternating silicon oxide and silicon films on a substrate, comprising the following steps: The steps for preparing the substrate; The step of cooling the surface temperature of the substrate to below -40°C; The steps of generating plasma containing hydrogen and fluorine gases using high-frequency electricity for plasma generation; and The step of etching the stacked film using generated plasma. The gas containing hydrogen and fluorine includes SF6 gas and NF3 gas. The proportion of NF3 gas relative to the sum of SF6 gas and NF3 gas is more than 33% and less than 67%.

2. The etching method according to claim 1, wherein the cooling step is to cool the substrate to -55°C or higher.

3. The etching method according to claim 1 or 2, In the gas, the proportion of hydrogen to the total amount of hydrogen and fluorine is more than 25% and less than 67%.

4. The etching method according to claim 1 or 2, The gas contains at least one of fluorocarbon gas and hydrofluorocarbon gas. It includes at least one of hydrofluorocarbon gas, hydrogen-carbon gas, and hydrogen-containing gas. The hydrogen-containing gas is hydrogen gas or hydrogen halide gas.

5. The etching method according to claim 1 or 2, wherein a halogen-containing gas other than fluorine is added to the gas.

6. A plasma processing apparatus, comprising: The processing container; and a control unit that controls an etching process, wherein the etching process uses plasma to form a desired etch shape for a laminate of alternating silicon oxide and silicon films stacked on a substrate placed on a stage within the processing container. The control unit is configured to perform the following steps: The steps for preparing the substrate; The step of cooling the surface temperature of the substrate to below -40°C; The steps of generating plasma containing hydrogen and fluorine gases using high-frequency electricity for plasma generation; and The step of etching the stacked film using generated plasma. The gas containing hydrogen and fluorine includes SF6 gas and NF3 gas. The proportion of NF3 gas relative to the sum of SF6 gas and NF3 gas is more than 33% and less than 67%.

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