Etching Method and Plasma Processing Apparatus

Abstract

To provide a technique that improves a selection ratio in etching of a laminated film in which silicon oxide films and silicon films are alternately laminated.SOLUTION: An etching method of forming a desired etching shape by plasma on a laminated film in which silicon oxide films and silicon films are alternately laminated on a substrate includes the steps of preparing the substrate, cooling a surface temperature of the substrate to -40°C or less, generating plasma of a gas containing hydrogen and fluorine by high frequency power for plasma generation, and etching the laminated film with the generated plasma.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an etching method and a plasma processing apparatus.

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present disclosure provides a technique capable of improving the selectivity in etching a laminated film in which a silicon oxide film and a silicon film are alternately laminated.

Means for Solving the Problems

[0006] According to one aspect of the present disclosure, there is provided an etching method for forming a desired etching shape by plasma on a laminated film in which a silicon oxide film and a silicon film are alternately laminated on a substrate, the method including: preparing the substrate; cooling the surface temperature of the substrate to -40°C or lower; generating a plasma of a gas containing hydrogen and fluorine by high-frequency power for plasma generation; and etching the laminated film with the generated plasma.

Advantages of the Invention

[0007] According to one aspect, the selectivity can be improved in etching a laminated film in which a silicon oxide film and a silicon film are alternately laminated.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same components, and duplicate descriptions may be omitted.

[0010] [Plasma Processing Apparatus] The plasma processing apparatus 1 according to the embodiment will be described with reference to FIG. 1. FIG. 1 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 plate type plasma processing apparatus in which a mounting table 11 and a shower head 20 are arranged opposite to each other in a processing container 10.

[0011] The mounting table 11 has a function of holding a substrate W, such as a semiconductor wafer, and also functions as a lower electrode. The shower head 20 has a function of supplying gas into the processing container 10 in a shower shape and also functions as an upper electrode.

[0012] The processing container 10 is made of, for example, aluminum whose surface is anodized (anodic oxidation treatment) and is cylindrical. The processing container 10 is electrically grounded. The mounting table 11 is installed at the bottom of the processing container 10 and mounts the substrate W.

[0013] The mounting table 11 is formed of, for example, aluminum (Al), titanium (Ti), silicon carbide (SiC), or the like. The mounting table 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. A power supply 14 is connected to the chuck electrodes 12a. The electrostatic chuck 12 adsorbs the substrate W to the electrostatic chuck 12 by the Coulomb force generated when a voltage is applied from the power supply 14 to the chuck electrodes 12a.

[0014] Inside the base 13, a refrigerant flow path 13a is formed. A refrigerant inlet pipe 13b and a refrigerant outlet pipe 13c are connected to the refrigerant flow path 13a. A cooling medium (temperature control medium) at a predetermined temperature is output from the chiller unit 15, and the cooling medium circulates through the refrigerant inlet pipe 13b, the refrigerant flow path 13a, and the refrigerant outlet pipe 13c. Thereby, the mounting table 11 is cooled (temperature controlled), and the substrate W is controlled to a predetermined temperature.

[0015] The heat transfer gas supply source 17 supplies a heat transfer gas such as helium gas through the gas supply line 16 between the surface of the electrostatic chuck 12 and the back surface of the substrate W. Thereby, the heat transfer efficiency between the electrostatic chuck 12 and the substrate W is increased, and the temperature controllability of the substrate W is increased.

[0016] A first high-frequency power supply 30 that supplies high-frequency power (HF power) for plasma generation is electrically connected to the mounting table 11 via a first matcher 30a. Further, a second high-frequency power supply 31 that supplies high-frequency power (LF power) for a bias voltage having a frequency lower than the frequency of the HF power is electrically connected to the mounting table 11 via a second matcher 31a. The first high-frequency power supply 30 applies, for example, high-frequency power of 40 MHz to the mounting table 11. The second high-frequency power supply 31 applies, for example, high-frequency power of 400 kHz to the mounting table 11. Note that the first high-frequency power supply 30 may apply high-frequency power to the shower head 20.

[0017] The first matcher 30a matches the load impedance on the mounting table 11 side with the output (internal) impedance of the first high-frequency power supply 30. The second matcher 31a matches the load impedance on the mounting table 11 side with the output (internal) impedance of the second high-frequency power supply 31.

[0018] The shower head 20 closes the opening in the ceiling of the processing chamber 10 via a shield ring 22 of an insulator that covers the peripheral portion. A gas inlet 21 for introducing gas is formed in the shower head 20. A diffusion chamber 23 connected to the gas inlet 21 is provided inside the shower head 20. The gas output from the gas supply source 25 is supplied to the diffusion chamber 23 via the gas inlet 21 and introduced into the processing chamber 10 through a number of gas supply holes 24.

[0019] An exhaust port 18 is formed in the bottom surface of the processing chamber 10, and an exhaust device 19 is connected to the exhaust port 18. The exhaust device 19 evacuates the inside of the processing chamber 10, whereby the inside of the processing chamber 10 is controlled to a predetermined degree of vacuum. A gate valve 27 for opening and closing a transfer port 26 is provided on the side wall of the processing chamber 10. The substrate W is carried into the processing chamber 10 from the transfer port 26 or carried out of the processing chamber 10 according to the opening and closing of the gate valve 27.

[0020] The plasma processing apparatus 1 is provided with a control unit 40 for controlling 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 an etching process of the substrate W according to various recipes stored in the storage areas of the ROM 42 and the RAM 43. The recipes are set with process time, pressure (gas evacuation), high-frequency power and voltage, various gas flow rates, surface temperature of the substrate (temperature of the electrostatic chuck 12, etc.), temperature of the cooling medium supplied from the chiller unit 15, etc., which are control information of the apparatus for process conditions. Note that the recipes indicating these programs and processing conditions may be stored in a hard disk or a semiconductor memory. Also, the recipes may be set at a predetermined position in the storage area in a state of being accommodated in a portable computer-readable storage medium such as a CD-ROM or a DVD.

[0021] When substrate processing is performed, the opening and closing of the gate valve 27 is controlled, and the substrate W held by the transfer arm is carried into the processing container 10 from the transfer port 26, placed on the mounting table 11, and adsorbed by the electrostatic chuck 12. Thereby, the substrate W is prepared.

[0022] Next, gas is supplied into the processing container 10 from the shower head 20, high-frequency power for plasma generation is applied to the mounting table 11, and plasma is generated. The generated plasma performs an etching process on the substrate W. High-frequency power for bias voltage may be applied to the mounting table 11 together with the high-frequency power for plasma generation. After the processing, the charge of the substrate W is removed by a charge removal process, the substrate W is peeled off from the electrostatic chuck 12, and carried out.

[0023] The surface temperature of the substrate (for example, the surface temperature of the wafer) is adjusted by the temperature of the electrostatic chuck 12 adjusted to a desired temperature by the chiller unit 15 being transferred to the substrate W through the surface of the electrostatic chuck 12 and the heat transfer gas. However, the substrate W is exposed to the plasma generated by the high-frequency power for plasma generation, and the heat input from the plasma and the ions drawn in by the high-frequency power for bias voltage are irradiated onto the substrate W. For this reason, the temperature of the substrate W, particularly the surface temperature of the substrate W facing the plasma, becomes higher than the temperature of the adjusted electrostatic chuck 12. Also, the surface temperature of the substrate W may rise due to radiant heat from the temperature-adjusted counter electrode and the side wall of the processing container 10. For this reason, if it is possible to measure the actual temperature of the substrate W during the etching process or estimate the temperature difference between the adjusted temperature of the electrostatic chuck 12 and the actual surface temperature of the substrate W from the process conditions, the setting of the adjusted temperature of the electrostatic chuck 12 may be lowered to adjust the temperature of the substrate W within a predetermined temperature range.

[0024] [Etching Method] The etching method according to the present embodiment that can be executed in the plasma processing apparatus 1 having such a configuration will be described with reference to FIGS. 2 and 3. FIG. 2 is a diagram showing an example of the etching method according to the embodiment. FIG. 3 is a diagram showing the film structure to be etched according to the embodiment.

[0025] In the etching method according to the present embodiment, the surface temperature of the substrate is cooled to -40°C or lower, and the laminated film to be etched is etched. Hereinafter, controlling the surface temperature of the substrate to -40°C or lower and performing etching is also referred to as "low-temperature etching".

[0026] In the etching method according to the present embodiment shown in FIG. 2, a substrate W having a laminated film 100 in which a silicon oxide film and a polycrystalline silicon film shown in FIG. 3(a) are alternately laminated and a mask 101 on the laminated film 100 is placed on the mounting table 11 and prepared (step S1). Note that the polycrystalline silicon film of the laminated film 100 is not limited to this, and may be formed of a silicon film such as amorphous silicon or doped silicon.

[0027] Next, with the surface temperature of the substrate cooled to -40°C or lower, the laminated film is subjected to low-temperature etching by the plasma generated by the plasma processing apparatus 1 (step S2). The etching in step S2 is also referred to as main etching.

[0028] FIG. 3(a) shows the film structure to be etched and shows the initial state before etching. The substrate has a laminated film 100, a mask 101 on the laminated film 100, and an underlying film 102 of the laminated film 100. The mask 101 is formed of an organic material and has an opening HL formed therein. The underlying film 102 is formed of, for example, polycrystalline silicon. However, the underlying film 102 is not limited to polycrystalline silicon, and may be formed of amorphous silicon or single crystal silicon. Further, the underlying film 102 may be a silicide film containing a transition metal such as nickel (Ni), or may be a transition metal layer such as tungsten (W) or ruthenium (Ru).

[0029] In the main etching of step S2, a plasma of a gas containing hydrogen and fluorine is generated by high-frequency power for plasma generation, and the stacked film 100 is etched through the mask 101 by the generated plasma. The gas containing hydrogen and fluorine is a combination of a fluorocarbon gas (CF-based), a hydrocarbon gas (CH-based), and a hydrogen-containing gas. Examples of the processing gas include H2 gas and CF4 gas. Other examples of the processing gas include H2 gas, C4F8 gas, CH2F2 gas, NF3 gas, and SF6 gas.

[0030] As a result, as shown in FIG. 3(b), the stacked film 100 is etched into the pattern of the mask 101, and recesses are formed in the stacked film 100. Further, as shown in FIG. 3(c), low-temperature etching of the stacked film 100 is performed until the underlying film 102 is exposed.

[0031] In this way, in the main etching, the stacked film 100 is low-temperature etched through the opening HL of the mask 101 by the plasma of the processing gas supplied to the plasma processing apparatus 1, and recesses are formed in the stacked film 100. As shown in FIG. 3(c), among the hole-shaped recesses formed in the stacked film 100, the diameter of the recess at the interface between the mask 101 and the stacked film 100 is also referred to as Top CD, and the diameter of the recess at the interface between the underlying film 102 and the stacked film 100 is also referred to as Btm CD. Note that, in the present embodiment, an etching method for forming a hole (opening HL) having a desired etching shape by plasma is described, but the present invention is not limited thereto. The etching method according to the present embodiment may form a groove having a desired etching shape, that is, a line-shaped recess, by plasma.

[0032] [Temperature Dependence of Etching] The temperature dependence of the substrate in the etching method according to the present embodiment will be described with reference to FIG. 4. FIG. 4 is a diagram showing an example of the relationship between the surface temperature of the substrate W according to the embodiment and the etching characteristics.

[0033] For example, in the etching of a 3D-NAND structure or other structures, the etching of the stacked film 100 in which a silicon oxide film and a polysilicon film are alternately stacked may be performed. In this case, if temperature conditions such as the surface temperature of the substrate being normal temperature (about 25°C) or higher, or temperature conditions optimized for the etching of a stacked film different from this embodiment, in which a silicon oxide film and a silicon nitride film are alternately stacked, are applied to the stacked film of this embodiment, the bowing CD becomes large or the mask selection ratio becomes insufficient. For example, when etching the stacked film 100 with the surface temperature of the substrate controlled to 20°C, the bowing CD becomes large. On the other hand, when etching the stacked film 100 with the surface temperature of the substrate controlled to 110°C or 140°C, the bowing CD improves, but the mask selection ratio becomes insufficient.

[0034] Note that the bowing CD indicates the diameter of the most widely spread portion among the recesses of the stacked film 100. The mask selection ratio indicates the ratio of the etching rate of the stacked film 100 to the etching rate of the mask 101.

[0035] FIG. 4 shows the experimental results indicating various etching characteristics with respect to the surface temperature of the substrate. FIG. 5 shows an example of the experimental results of the roundness and bending shape of the bottom of the recess formed in the stacked film 100 after etching according to the embodiment. In this experiment, process gases such as H2 gas, C4F8 gas, CH2F2 gas, NF3 gas, and SF6 gas were used as the gas species. That is, an experiment was conducted in which a process gas was supplied into the processing chamber 10 of the plasma processing apparatus 1, the plasma of the process gas was generated by high-frequency power for plasma generation, and the stacked film 100 was etched.

[0036] The horizontal axis of FIG. 4 indicates the surface temperature of the substrate, and the vertical axis indicates that in FIG. 4(a), it is the mask selection ratio (◇), in FIG. 4(b), it is the etching rate of the laminated film (〇) and the etching rate of the mask (□), and in FIG. 4(c), it is the Bow CD (〇) and the Btm CD (□). Further, FIG. 5 shows the roundness and the bending shape of the bottom of the recess formed in the laminated film 100 (the hole bottom of the hole) after etching. The roundness indicates how close the shape of the cross-section of the hole is to a perfect circle. The higher the roundness in FIG. 5, the closer the bottom surface of the recess is to a perfect circle, and the lower the roundness in FIG. 5, the more elliptical the bottom surface of the recess becomes. Bending indicates a state where the recess in the laminated film 100 is not formed vertically and is bent from the mask 101 toward the bottom of the recess.

[0037] In the results shown in FIGS. 4(a) and 5, when the surface temperature of the substrate was 40°C or higher, the mask selection ratio decreased and the roundness of the bottom of the recess (the hole bottom of the hole) formed in the laminated film 100 deteriorated. Specifically, when the surface temperature of the substrate was 37°C or higher, the roundness of the hole bottom of the hole deteriorated.

[0038] Also, when the surface temperature of the substrate was 57°C or lower, the bending deteriorated. Since the etching rate of the laminated film 100 decreases when the bending deteriorates, it is preferable to suppress the bending.

[0039] From the above, in the etching method according to the present embodiment, the surface temperature of the substrate is controlled to 40°C or lower, and the substrate W is etched at low temperature by the plasma of a processing gas containing a hydrogen-containing gas and a fluorine-containing gas. Thereby, the mask selection ratio can be improved.

[0040] Next, from the results shown in FIGS. 4(a) and (b), by controlling the surface temperature of the substrate to be 55°C or higher and 40°C or lower, the mask selection ratio and the etching rate of the laminated film 100 could be increased. Note that the mask 101 can maintain a sufficiently low etching rate when the surface temperature of the substrate is controlled to be 55°C or higher and 40°C or lower.

[0041] From the results of FIGS. 4(a) and (b), when the surface temperature of the substrate is -47°C, the highest mask selection ratio and the etching rate of the stacked film 100 are obtained. It was found that in the range of -55°C to -40°C, both the mask selection ratio and the etching rate of the stacked film 100 are good.

[0042] Next, from the results of FIG. 4(c), looking at the difference between the bowing CD (Bow CD) and the bottom CD (Btm CD), the difference increased as the surface temperature of the substrate decreased. The smaller the difference between Bow CD and Btm CD, the more vertically the recesses of the stacked film 100 are formed. Therefore, the smaller the difference between Bow CD and Btm CD, the better.

[0043] Next, from the results of FIG. 5, when the surface temperature of the substrate is -37°C or higher, the roundness of the hole bottom of the hole deteriorates. Also, when the surface temperature of the substrate is -57°C or lower, the shape of the side wall of the recess of the stacked film 100 deteriorates and the bending deteriorates. When the bending deteriorates, the etching rate of the stacked film 100 decreases, so it is preferable to suppress the bending.

[0044] That is, in order to improve the bending of the recess formed in the stacked film 100, it is preferable to control the surface temperature of the substrate to -55°C or higher. According to this, the recess formed in the stacked film 100 can be improved and made closer to a vertical shape.

[0045] From the above, by controlling the surface temperature of the substrate to -40°C or lower, the etching rate of the stacked film 100 can be increased. Furthermore, by controlling the surface temperature of the substrate to be -55°C or higher and -40°C or lower, the mask selection ratio and the etching rate of the stacked film 100 can be increased, and the bending can be suppressed.

[0046] Also, in the experiment shown in FIG. 4, in the H2 gas, C4F8 gas, CH2F2 gas, NF3 gas, and SF6 gas used in this experiment, the ratio of the hydrogen (H) element to the total of the hydrogen (H) element and the fluorine (F) element, that is, H / (H + F), was 58%.

[0047] Note that the amount of each of the H element and the F element is obtained from the molecular formula of the gas used as the sum of the products of the volume flow rate of the gas and the valence of the element contained in the gas.

[0048] [Gas ratio] Next, the gas species and gas ratio used in the etching method according to the present embodiment will be described with reference to FIG. 6. FIG. 6 is a diagram showing an example of the relationship between the ratio of the hydrogen-containing gas and the fluorine-containing gas and the etching rate according to the embodiment.

[0049] In this experiment, H2 gas was used as the hydrogen-containing gas and CF4 gas was used as the fluorine-containing gas. The processing gases of H2 gas and CF4 gas were supplied into the processing container 10 of the plasma processing apparatus 1, and the plasma of the processing gas was generated by high-frequency power for plasma generation. Then, experiments were conducted to etch the blanket of the mask of the organic material resist (PR) film, the blanket of the silicon oxide film (SiO2), and the blanket of the polycrystalline silicon film (Poly-Si) with the generated plasma, respectively.

[0050] The horizontal axes of FIGS. 6(a), 6(b), and 6(c) indicate the ratio (%) of the volume flow rate of the H2 gas to the sum of the volume flow rates of the H2 gas and the CF4 gas. The vertical axis of FIG. 6(a) indicates the etching rate of the mask 101 of the resist (PR) film, the vertical axis of FIG. 6(b) indicates the etching rate of the silicon oxide film (SiO2), and the vertical axis of FIG. 6(c) indicates the etching rate of the polycrystalline silicon film (Poly-Si). The symbol □ in FIGS. 6(a), 6(b), and 6(c) indicates the result of each etching rate when the surface temperature of the substrate is controlled at 45°C, the symbol 〇 indicates the result when the surface temperature of the substrate is controlled at -10°C, and the symbol △ indicates the result when the surface temperature of the substrate is controlled at -50°C.

[0051] In frames A, B, and C shown in FIGS. 6(a), 6(b), and 6(c), when the surface temperature of the substrate was controlled to -50°C, the etching rates of the silicon oxide film and the polycrystalline silicon film were higher than those when the surface temperature of the substrate was controlled to 45°C and -10°C. In contrast, the etching rate of the resist film mask 101 hardly changed when the surface temperature of the substrate was between -50°C and 45°C.

[0052] That is, the ratio of the volume flow rate of H2 gas to the sum of the volume flow rates of H2 gas and CF4 gas (= H2 / (H2 + CF4)) was in the range of 40% to 80%, and the surface temperature of the substrate was controlled to -50°C. At this time, the mask selectivity could be improved, and the etching rate of the stacked film 100 could be improved.

[0053] When the above results are converted to the ratio of hydrogen (H) element to the sum of hydrogen (H) element and fluorine (F) element (= H / (H + F)), it becomes 25% or more and 67% or less. That is, in the etching method according to the present embodiment, by controlling the ratio of H to the sum of H and F contained in the processing gas to 25% or more and 67% or less, the mask selectivity of the stacked film 100 can be improved, and the etching rate of the stacked film 100 can be improved.

[0054] In the experiment shown in FIG. 4, H / (H + F) = 58%, which is included in the range shown above.

[0055] As the gas that can be used in the etching method according to the present embodiment satisfying the above conditions, it includes at least one of fluorocarbon gas (CF-based) and hydrofluorocarbon gas (CHF-based), and includes at least one of hydrofluorocarbon gas (CHF-based), hydrocarbon gas (CH-based), and hydrogen-containing gas. The hydrogen-containing gas may be hydrogen gas (H2) or hydrogen halide.

[0056] Examples of hydrofluorocarbon gases (CHF-based) include CH2F2 gas, CHF3 gas, C3H2F4 gas, etc. Examples of fluorocarbon gases (CF-based) include C4F8 gas, C4F6 gas, CF4 gas, etc. Examples of hydrocarbon gases (CH-based) include CH4 gas, C2H6 gas, C2H4 gas, etc. Examples of hydrogen halides include HF gas, HCl gas, HBr gas, HI gas, etc.

[0057] In the plasma of the process gases of H2 and CF4, hydrogen radicals and fluorine radicals react to generate hydrofluoric acid (HF). Hydrofluoric acid is likely to condense on the bottom surface of the recess formed in the etching target film, for example, at a low temperature of -40°C or lower. If the etching target film is a silicon oxide film, etching proceeds due to the condensed hydrofluoric acid (HF). Therefore, the ratio (balance) of hydrogen to fluorine is important for the progress of etching.

[0058] In the etching method according to this embodiment, the ratio of H to the total of H and F contained in the process gas is controlled to be 25% or more and 67% or less. Thereby, etching can be promoted by the hydrofluoric acid (HF) condensed on the bottom surface of the recess, the mask selection ratio of the laminated film 100 can be improved, and the etching rate of the laminated film 100 can be improved. Hereinafter, with reference to FIG. 7, the importance of controlling the balance between the number of hydrogen atoms and the number of fluorine atoms supplied to the etching region when etching the recess of the silicon oxide film with HF-based radicals in low-temperature etching will be described.

[0059] [Etching with HF-based Radicals] FIG. 7 is a diagram for explaining the principle of etching the recess of the silicon oxide film with HF-based radicals in low-temperature etching.

[0060] As shown in FIG. 7, HF-based radicals (HF, hydrogen atoms, and fluorine atoms) are supplied to the bottom surface of the recess formed in the silicon oxide film (SiO2), and the Si in the silicon oxide film reacts with F and vaporizes as SiF4. As a result, the silicon oxide film is etched. At this time, water (H2O) is generated as a reaction product (FIGS. 7(A) and (B)). According to a general vapor pressure curve, water has a low saturated vapor pressure. On the vapor pressure curve, a state in which liquid and gas are mixed exists. Therefore, under low-temperature etching in which the pressure during etching is controlled to about 10 to 100 mTorr and the surface temperature of the substrate is controlled to about -55°C to -40°C, it is considered that the water on the bottom surface of the recess of the silicon oxide film exists in a saturated state and to some extent in a liquid state.

[0061] And when hydrogen fluoride is further supplied to water, the HF-based radicals react with water to generate hydrofluoric acid (FIGS. 7(C) to (D)). As a result, it is considered that etching by a chemical reaction is mainly promoted by the hydrofluoric acid dissolved in water on the bottom surface of the recess of the silicon oxide film, and the etching rate specifically increases. Thus, in etching the silicon oxide film in a low-temperature environment, it is necessary to supply hydrogen atoms and fluorine atoms in an appropriate balance.

[0062] Therefore, in the etching method according to the present embodiment, the ratio of H (hydrogen atoms) to the total of H (hydrogen atoms) and F (fluorine atoms) contained in the processing gas is controlled to be 25% or more and 67% or less. Thereby, in low-temperature etching, by supplying hydrogen atoms and fluorine atoms to the stacked film 100 in an appropriate balance, the mask selection ratio of the stacked film 100 can be improved, and the etching rate of the stacked film 100 can be improved.

[0063] In addition, in low-temperature etching, the adsorption coefficient of HF-based radicals increases, and HF-based radicals are adsorbed on the bottom surface of the concave portions of the polycrystalline silicon film. The HF-based radicals themselves have low reactivity with the polycrystalline silicon film due to thermal energy. However, when energy from ion irradiation from the plasma is applied to the state where HF is attached to the polycrystalline silicon film, the polycrystalline silicon film reacts with the F element in the HF-based radicals, promoting the etching of the polycrystalline silicon film.

[0064] As described above, according to the etching method according to the present embodiment, in low-temperature etching in which the surface temperature of the substrate is cooled to -40°C or lower, plasma of a processing gas containing a hydrogen-containing gas and a fluorine-containing gas is generated to etch the laminated film 100. Thereby, the mask selectivity can be improved, and the etching rate of the laminated film 100 can be improved.

[0065] At this time, it is preferable to control the ratio of hydrogen to the total of hydrogen and fluorine to be 25% or more and 67% or less. Thereby, etching mainly by chemical reaction can be promoted by hydrofluoric acid.

[0066] Furthermore, by controlling the surface temperature of the substrate to -40°C or lower, the roundness can be improved, and by controlling the surface temperature of the substrate to -55°C or higher, bending can be suppressed.

[0067] Furthermore, by combining an increase in high-frequency power (LF power) for the bias voltage and low-temperature etching, the difference between BowCD and BtmCD can be reduced, and BowCD can be reduced. Thereby, the shape of the concave portion formed in the laminated film 100 can be improved, and the perpendicularity can be enhanced.

[0068] FIG. 8 is a diagram showing an example of the relationship between the LF power and the surface temperature of the substrate during etching according to the embodiment. The horizontal axis of FIG. 8 represents the LF power, and the vertical axis represents the surface temperature of the substrate. As shown in FIG. 8, during etching, as the LF power increases, the surface temperature of the substrate increases due to the heat input from the plasma side. When the surface temperature of the substrate increases, the etching rate decreases. To avoid this, the temperature of the mounting table 11 is controlled to decrease in response to an increase in the LF power. Thereby, the surface temperature of the substrate can be controlled to be not less than -55°C and not more than -40°C. As a result, in low-temperature etching, while increasing the mask selection ratio and the etching rate of the laminated film 100, the LF power is increased to enhance the verticality of ions, reducing the difference between BowCD and BtmCD and reducing BowCD, and the verticality of the etching shape can be enhanced.

[0069] [Addition of chlorine] Next, the improvement of the etching shape when chlorine is added to the processing gas will be described with reference to FIG. 9. FIG. 9 is a diagram showing an example of the result of adding chlorine in the etching method according to the embodiment.

[0070] In the example of FIG. 9, Cl2 gas is added to H2 gas and CF4 gas as the processing gas used in the etching method according to the embodiment. The horizontal axis of FIG. 9 represents the ratio of the volume flow rate of Cl2 gas to the total volume flow rate of H2 gas and CF4 gas. The vertical axis (left) represents the difference between BowCD and TopCD (see FIG. 3), and the vertical axis (right) represents the taper angle. The taper angle on the vertical axis (right) indicates the verticality of the recess formed in the laminated film 100. When the recess is vertical, it is 90°. The more the taper angle deviates from 90°, the more the recess becomes a tapered shape or an inverse tapered shape.

[0071] In the example of Fig. 9, it was found that by adding Cl2 gas to H2 gas and CF4 gas, the verticality (taper angle) of etching can be controlled, and the difference between BowCD and BtmCD can be controlled. That is, by controlling the addition amount of Cl2 gas added to H2 gas and fluorocarbon gas, the taper shape of etching can be controlled. As a result, BowCD - TopCD can be reduced, BowCD can be reduced, and the etching shape can be controlled.

[0072] The reason why the taper shape of etching can be controlled will be explained. By adding Cl2 gas to H2 gas and fluorocarbon gas, SiCl4 will be included in the by - products generated during etching. SiCl4 in the by - products is less likely to become a gas than the by - product SiF4 generated during etching by H2 and fluorocarbon gas. Therefore, SiCl4 adheres to the side walls of the recesses of the stacked film 100 and becomes a protective film on the side walls. It is considered that this has achieved the reduction of BowCD - TopCD and the reduction of Bow CD, and the improvement of the etching shape.

[0073] In the example of Fig. 9, Cl2 gas was added, but it is not limited to this. The same effect can be obtained with chlorine - containing gases such as HCl gas and CCl4 gas. Also, for gases containing bromine or iodine such as HBr gas and HI gas, SiBr4 and SiI4 are generated as by - products, and these by - products are also less likely to become a gas than the by - product SiF4. That is, by adding halogen - containing gases other than fluorine, the reduction of BowCD - TopCD and the reduction of Bow CD can be achieved, and the etching shape can be improved.

[0074] [Gas ratio of SF6 gas and NF3 gas] Next, the gas ratio of SF6 gas and NF3 gas contained in the processing gas will be described with reference to FIGS. 10 and 11. FIG. 10 is a diagram showing an example of the relationship between the gas ratio of SF6 gas and NF3 gas and the etching rate according to an embodiment. FIG. 11 is a diagram showing an example of the relationship between the gas ratio of SF6 gas and NF3 gas and the bending shape according to an embodiment.

[0075] The horizontal axis of FIG. 10 shows the ratio of the volume flow rate of SF6 gas to the sum of the volume flow rates of SF6 gas and NF3 gas as "SF6ratio". The vertical axis of FIG. 10 is the etching rate (E / R) of the stacked film 100. From the results of FIG. 10, there is a trade-off that the etching rate decreases when the SF6 gas ratio (SF6ratio) is high, and the etching shape deteriorates when the NF3 gas ratio is high (the SF6 gas ratio (SF6ratio) is low). From the etching rate results in FIG. 10, it is desirable that the SF6 gas ratio be 67% or less. Also, from the results regarding bending in FIG. 11, it is desirable that the SF6 gas ratio be 33% or more and 67% or less. By setting the ratio of the volume flow rate of SF6 gas to the sum of the volume flow rates of SF6 gas and NF3 gas to 33% or more and 67% or less, it is possible to suppress bending while maintaining the etching rate and improve the etching shape.

[0076] In addition, when the above results are converted to the ratio of hydrogen (H) element to the sum of hydrogen (H) element and fluorine (F) element (=H / (H+F)), it becomes 49% or more and 52% or less, which is included in the range defined from the results of FIG. 6.

[0077] As described above, according to the etching method and the plasma processing apparatus according to the present embodiment, the stacked film 100 in which a silicon oxide film and a silicon film are alternately stacked on a substrate is etched by the plasma of a processing gas containing a gas containing hydrogen and fluorine. By means of low-temperature etching in which the surface temperature of the substrate is controlled to -40°C or lower, the selectivity can be improved and the etching rate of the stacked film 100 can be increased.

[0078] Moreover, bending can be suppressed by controlling the surface temperature of the substrate to -55°C or higher. Furthermore, by adding Cl2 gas to the processing gas, the taper shape of the etching can be controlled. As a result, the reduction of BowCD-TopCD and the reduction of Bow CD can be achieved, and the etching shape can be improved.

[0079] The etching method and plasma processing apparatus according to the embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The embodiments can be modified and improved in various forms without departing from the scope and gist of the appended claims. The matters described in the above plurality of embodiments can also adopt other configurations within a non-conflicting range and can be combined within a non-conflicting range.

[0080] The plasma processing apparatus of the present disclosure is applicable to any type of apparatus such as an Atomic Layer Deposition (ALD) apparatus, a Capacitively Coupled Plasma (CCP), an Inductively Coupled Plasma (ICP), a Radial Line Slot Antenna (RLSA), an Electron Cyclotron Resonance Plasma (ECR), and a Helicon Wave Plasma (HWP).

Description of Reference Numerals

[0081] 1 Plasma processing apparatus 11 Mounting table 20 Shower head 12 Electrostatic chuck 13 Base 14 Power supply 15 Chiller unit 19 Exhaust device 25 Gas supply source 30 First high-frequency power supply 31 Second high-frequency power supply 40 Control unit 100 Stacked film 101 Mask 102 Underlayer film

Claims

1. An etching method for forming a desired etching shape in a laminated film in which a silicon oxide film and a silicon film are alternately laminated on a substrate by plasma, comprising: 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 from a processing gas containing hydrogen and fluorine by high-frequency power for plasma generation; a step of etching the laminated film with the generated plasma, wherein the processing gas includes SF6 gas and NF3 gas, and the ratio of the NF3 gas to the sum of the SF6 gas and the NF3 gas is 33% or more and 67% or less. Etching method.

2. An etching method for forming a desired etching shape in a laminated film in which a silicon oxide film and a silicon film are alternately laminated on a substrate by plasma, comprising: 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 from a processing gas (excluding a processing gas containing sulfur) containing hydrogen and fluorine by high-frequency power for plasma generation; a step of generating plasma from the processing gas; a step of etching the laminated film with the generated plasma, wherein the etching step etches the laminated film with HF-based radicals in the plasma. Etching method.

3. The cooling step cools the substrate to -55°C or higher. The etching method according to claim 1 or claim 2.

4. In the processing gas, the ratio of the hydrogen element to the sum of the hydrogen element and the fluorine element is 25% or more and 67% or less. The etching method according to any one of claims 1 to 3.

5. The processing gas includes at least one of fluorocarbon gas (CF-based) and hydrofluorocarbon gas (CHF-based), includes at least one of hydrofluorocarbon gas (CHF-based), hydrocarbon gas (CH-based), and hydrogen-containing gas, wherein the hydrogen-containing gas is hydrogen gas or hydrogen halide gas. The etching method according to any one of claims 1 to 4.

6. Adding a halogen-containing gas other than fluorine to the processing gas. The etching method according to any one of claims 1 to 5.

7. The processing gas is selected from fluorocarbon gas (CF-based), hydrocarbon gas (CH-based), and hydrogen-containing gas. The etching method according to claim 1 or claim 2.

8. The hydrogen-containing gas is hydrogen halide gas. The etching method according to claim 7.

9. A processing container having a gas introduction hole connected to a gas supply source, A mounting table in the processing container, including a base including a flow path through which a temperature control medium output from a chiller unit circulates, and an electrostatic chuck disposed on the base and adsorbing a substrate. A high-frequency power supply for supplying high-frequency power for plasma generation, A control unit, a plasma processing apparatus having, The control unit controls each part of the plasma processing apparatus, Placing the substrate including a laminated film in which a silicon oxide film and a silicon film are alternately laminated on the mounting table; Cooling the temperature of the substrate to -40°C or lower with the temperature control medium; Supplying a processing gas containing hydrogen and fluorine into the processing container through the gas introduction hole, the processing gas including SF6 gas and NF3 gas, and the ratio of the NF3 gas to the sum of the SF6 gas and the NF3 gas being 33% or more and 67% or less. Supplying high-frequency power for plasma generation from the high-frequency power supply to generate plasma from the processing gas; Etching the laminated film with the plasma; A plasma processing apparatus configured to execute.

10. A processing container having a gas introduction hole connected to a gas supply source, A mounting table in the processing container, including a base including a flow path through which a temperature control medium output from a chiller unit circulates, and an electrostatic chuck disposed on the base and adsorbing a substrate. A high-frequency power supply for supplying high-frequency power for plasma generation, A control unit, a plasma processing apparatus having, The control unit controls each part of the plasma processing apparatus, Placing the substrate including a laminated film in which a silicon oxide film and a silicon film are alternately laminated on the mounting table; Cooling the temperature of the substrate to -40°C or lower with the temperature control medium; Supplying a processing gas (excluding a processing gas containing sulfur) containing hydrogen and fluorine into the processing container through the gas introduction hole. ). Supplying high-frequency power for plasma generation from the high-frequency power source to generate plasma from the processing gas; Etching the laminated film with the plasma; configured to execute; In the etching step, the laminated film is etched by HF-based radicals in the plasma. Plasma processing apparatus.

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