Etching method and plasma processing apparatus

Abstract

The present application relates to an etching method and a plasma processing apparatus. In etching of a base film of a laminated film of a silicon oxide film and a silicon nitride film exposed in a low-temperature environment, the etching rate of the laminated film can be maintained, and the selectivity to the base film is ensured. An etching method is provided, which is an etching method of forming a recess in a laminated film of a base film, a first film and a second film alternately laminated on the base film, and a mask on the laminated film, by plasma through the mask, the etching method comprising: a step of preparing the substrate; and a step of maintaining the substrate temperature at 15°C or lower, and etching by plasma of a gas containing hydrogen, fluorine and carbon until the recess of the laminated film reaches the base film.

Description

Technical Field

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

[0002] For example, Patent Document 1 proposes the following method: using plasma generated in a low-temperature environment below -30°C to etch a laminate of silicon oxide film and silicon nitride film.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-207840 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] This disclosure provides the following technology: in etching of a stack of silicon oxide and silicon nitride films exposed at low temperatures, the etching rate of the stacked films can be maintained, and the selectivity of the substrate film can be ensured.

[0008] Solution for solving the problem

[0009] According to one aspect of this disclosure, an etching method is provided, which is an etching method for forming a recess in a substrate having a base film, a laminated film having a first film and a second film alternately stacked on the base film, and a mask on the laminated film by using plasma through the mask. The etching method includes the following steps: a step of preparing the substrate; and a step of maintaining the substrate temperature at 15°C or below and etching using plasma containing hydrogen, fluorine and carbon gases until the recess in the laminated film reaches the base film.

[0010] The effects of the invention

[0011] According to one aspect, in etching that exposes the substrate film of a stacked film of silicon oxide and silicon nitride at low temperatures, the etching rate of the stacked film can be maintained, and the selectivity of the substrate film can be ensured. Attached Figure Description

[0012] Figure 1 This is a schematic cross-sectional view illustrating an example of a plasma processing apparatus according to one embodiment.

[0013] Figure 2 The figure illustrates an example of an etching method according to one embodiment.

[0014] Figure 3 A diagram illustrating an example of the film structure of an etched object according to one embodiment.

[0015] Figure 4 This is a graph illustrating an example of the relationship between substrate temperature and selectivity in conventional over-etching.

[0016] Figure 5 The figure illustrates an example of the selectivity, etc., of CH2F2 gas in an etching method according to one embodiment.

[0017] Figure 6 A graph illustrating an example of the relationship between the ratio of H or F in the gas used in an etching method according to one embodiment and the etching rate and selectivity.

[0018] Figure 7 A graph showing the relationship between the ratio of H in the gas and the etching rate when the environment is not cryogenic.

[0019] Figure 8 This is a graph illustrating an example of the relationship between the ratio of H in the gas used in an etching method according to one embodiment and the etching rate.

[0020] Figure 9 This is a diagram illustrating an example of the relationship between substrate temperature and the amount of C and H reaching the bottom of the hole.

[0021] Figure 10 This is a diagram illustrating an example of the bottom CD when SiCl4 gas is added to the gas used in an etching method according to one embodiment.

[0022] Figure 11 This is a diagram illustrating an example of the bottom CD when various gases are added to the gas used in an etching method according to one embodiment.

[0023] Explanation of reference numerals in the attached figures

[0024] 1. Plasma processing device

[0025] 11. Platform

[0026] 20 spray heads

[0027] 12. Electrostatic Chuck

[0028] 13. Base

[0029] 14 Power Supply

[0030] 15 Cooler Unit

[0031] 19. Exhaust system

[0032] 25 Gas supply source

[0033] 30 First High-Frequency Power Supply

[0034] 31 Second High-Frequency Power Supply

[0035] 40 Control Department

[0036] 100 basement membrane

[0037] 101-layer film

[0038] 102 Mask Detailed Implementation

[0039] Hereinafter, with reference to the accompanying drawings, the manner in which this disclosure is carried out will be described. In the drawings, the same symbols are used to label the same components, and sometimes repeated descriptions are omitted.

[0040] [Plasma Processing Device]

[0041] use Figure 1 A plasma processing apparatus 1 according to one embodiment will be described. Figure 1 This is a schematic cross-sectional view illustrating an example of a plasma processing apparatus 1 according to one embodiment. The plasma processing apparatus 1 according to one embodiment is a parallel plate type plasma processing apparatus in which a platform 11 and a spray head 20 are arranged opposite each other in a processing container 10.

[0042] The stage 11 serves to hold a substrate W, such as a wafer, and also functions as a lower electrode. The spray head 20 serves to supply gas into the processing container 10 in a spray pattern and also functions as an upper electrode.

[0043] The processing container 10 is made of aluminum with an anodized surface (anodized), and is cylindrical in shape. The processing container 10 is electrically grounded. A stage 11 is disposed at the bottom of the processing container 10 for holding the substrate W.

[0044] 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 electrostatic chuck 12 is disposed on the base 13. The electrostatic chuck 12 has a structure that holds a chuck electrode 12a between insulators 12b. The chuck electrode 12a is connected to a power supply 14. The electrostatic chuck 12 utilizes the Coulomb force generated by applying a voltage from the power supply 14 to the chuck electrode 12a to attract the substrate W to the electrostatic chuck 12.

[0045] The base 13 supports the electrostatic chuck 12. A refrigerant flow path 13a is formed inside the base 13. The refrigerant flow path 13a is connected to the refrigerant inlet pipe 13b and the refrigerant outlet pipe 13c. A cooling medium (temperature control medium) at a specified temperature is output from the cooler unit 15, and the cooling medium circulates in the refrigerant inlet pipe 13b, the refrigerant flow path 13a, and the refrigerant outlet pipe 13c. As a result, the stage 11 is cooled (temperature regulated), and the substrate W is controlled to a specified temperature.

[0046] The heat-conducting gas supply source 17 supplies heat-conducting gases such as helium through the gas supply line 16 between the surface of the electrostatic chuck 12 and the back side of the substrate W. This improves the thermal conductivity between the electrostatic chuck 12 and the substrate W, thereby enhancing the temperature controllability of the substrate W.

[0047] A first high-frequency power supply 30, providing first high-frequency (HF) power for plasma excitation at a first frequency, is electrically connected to the stage 11 via a first matching connector 30a. A second high-frequency power supply 31, providing second high-frequency (LF) power for bias at a second frequency lower than the first frequency, is electrically connected to the stage 11 via a second matching connector 31a. The first high-frequency power supply 30, for example, applies 40 MHz of first high-frequency power to the stage 11. The second high-frequency power supply 31, for example, applies 400 kHz of second high-frequency power to the stage 11. It should be noted that the first high-frequency power supply 30 can also apply the first high-frequency power to the spray head 20.

[0048] The first matching unit 30a matches the power (internal) impedance of the first high-frequency power supply 30 with the load impedance on the stage 11 side. The second matching unit 31a matches the power (internal) impedance of the second high-frequency power supply 31 with the load impedance on the stage 11 side.

[0049] The spray head 20 blocks the opening at the top of the processing container 10 by means of a shielding ring 22 covering the periphery of the insulator. A gas inlet 21 for introducing gas is formed on the spray head 20. 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 the mass gas supply holes 24.

[0050] An exhaust port 18 is formed on the bottom surface of the processing container 10, and the exhaust port 18 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 for opening and closing the feed port 26 is provided on the side wall of the processing container 10. Depending on whether the gate valve 27 is opened or closed, the substrate W is either fed into the processing container 10 through the feed port 26 or discharged out of the processing container 10.

[0051] The plasma processing apparatus 1 includes a control unit 40 for controlling the overall operation of the apparatus. The control unit 40 includes a CPU 41, a ROM 42, and a RAM 43. The CPU 41 executes an etching process on the substrate W based on various processes stored in the memory areas of the ROM 42 and RAM 43. The processes include apparatus control information for process conditions, such as process time, pressure (gas exhaust), high-frequency power, voltage, various gas flow rates, substrate temperature (temperature of the electrostatic chuck 12, etc.), and the temperature of the cooling medium supplied from the cooler unit 15. It should be noted that the processes showing these procedures and processing conditions can be stored on a hard disk or semiconductor memory. Alternatively, the processes can be stored in a storage medium that can be read by a portable computer, such as a CD-ROM or DVD, and installed at a predetermined location in the storage area.

[0052] When processing the substrate, the gate valve 27 can be controlled to move the substrate W held in the conveyor arm from the conveyor port 26 into the processing container 10 and place it on the loading stage 11, where it is adsorbed onto the electrostatic chuck 12.

[0053] Next, gas is supplied from the spray head 20 into the processing container 10, and a first high-frequency power is applied to the mounting stage 11 to generate plasma. The generated plasma is used to perform etching on the substrate W. Alternatively, both the first and second high-frequency powers can be applied to the mounting stage 11 simultaneously.

[0054] After processing, the charge on the substrate W is eliminated by a charge elimination process, and the substrate W is peeled off from the electrostatic chuck 12 and removed.

[0055] The substrate temperature (e.g., wafer temperature) is adjusted by the temperature of the electrostatic chuck 12, which is adjusted to a predetermined temperature using the cooler unit 15, being conducted to the substrate W via the surface of the electrostatic chuck 12 and the heat-conducting gas. However, the substrate W is exposed to plasma generated by a first high-frequency power for plasma excitation, and is irradiated by light from the plasma and ions introduced by a second high-frequency power for bias. Therefore, the temperature of the substrate W, especially the surface temperature of the substrate W facing the plasma, becomes higher than the adjusted temperature of the electrostatic chuck 12. In addition, the substrate temperature sometimes rises due to radiant heat from the temperature-adjusted counter electrode and the sidewall of the processing container 10, thus allowing the actual temperature of the substrate W during the etching process to be measured. When the temperature difference between the adjusted temperature of the electrostatic chuck 12 and the actual surface temperature of the substrate W can be estimated from the process conditions, the set temperature of the electrostatic chuck 12 can be reduced in order to adjust the temperature of the substrate W within a predetermined temperature range.

[0056] [Etching Method]

[0057] In the etching method of this embodiment, the substrate temperature is maintained at 15°C or below while etching the target film. Etching while maintaining the substrate temperature at 15°C or below is called "low-temperature etching". Furthermore, the substrate temperature described below is referred to as the "surface temperature of substrate W".

[0058] Reference Figure 2 and Figure 3 The etching method of this embodiment will be described. Figure 2 The figure illustrates an example of an etching method according to one embodiment. Figure 3 A diagram illustrating an example of the film structure of an etched object according to one embodiment.

[0059] like Figure 2 As shown, the etching method of this embodiment is as follows: The film to be etched is etched to a predetermined depth using plasma generated by the plasma processing apparatus 1 (step S1). The etching in step S1 is also called main etching. Next, the film to be etched is etched using plasma until the substrate film of the film to be etched is exposed (step S2), and the process ends. The etching in step S2 is also called over-etching.

[0060] Figure 3 (a) shows an example of the film structure of the etched object. Figure 3 As shown in (a), the film to be etched is a laminated film 101 in which silicon oxide films and silicon nitride films are alternately stacked. The silicon oxide film is an example of a first film, and the silicon nitride film is an example of a second film.

[0061] A substrate film 100 is provided beneath the laminated film 101, and a mask 102 is provided on the laminated film 101. The substrate film 100 is formed of polycrystalline silicon. However, the substrate film 100 is not limited to polycrystalline silicon and may be formed of amorphous silicon or monocrystalline silicon. The mask 102 is an organic material and has pores h. Using plasma of gas supplied to the plasma processing apparatus 1, recesses can be formed in the laminated film 101 through the pores h of the mask 102. The recesses formed in the laminated film 101 are not limited to pores and may also be linear.

[0062] In the main etching of step S1, such as Figure 3 As shown in (b), the laminated film 101 is etched, forming recesses in the laminated film 101, and the etching ends before the base film 100 is exposed. In the over-etching of step S2, as... Figure 3 As shown in (c), the laminate 101 is further etched until the base film 100 is exposed.

[0063] The main etching is as follows: Before over-etching, etching is performed until the recesses (e.g., holes h) of the laminated film 101 reach a specified depth. The specified depth of the recesses can be 40 or more in terms of aspect ratio.

[0064] In a conventional example of main etching, the laminate 101 is etched at a low temperature, for instance, by keeping the substrate temperature below 0°C. In low-temperature etching, the etching rate of the laminate 101 increases. Furthermore, the selectivity of the mask 102 is also higher during the main etching.

[0065] However, in the case of low-temperature etching during over-etching, the selectivity of the substrate film 100 is insufficient. In low-temperature etching, the main etching is performed until the substrate film 100 is about to be exposed, and then over-etching is performed with low-temperature etching, and the time change of the amount of recess in the substrate film 100 is measured. As a result, in low-temperature etching, etching cannot be stopped even when the substrate film 100 is exposed, and the amount of recess in the substrate film 100 increases.

[0066] Therefore, as another example of previous over-etching, etching is performed by raising the substrate temperature to around 80°C. Figure 4 This graph illustrates an example of the relationship between substrate temperature and selectivity in conventional over-etching. It will be used to obtain... Figure 4 The over-etching process conditions for the experimental results shown are as follows.

[0067] <Previous over-etching process conditions>

[0068] Gas types: C4F6 / C4F8 / CH2F2 / O2

[0069] Substrate temperatures 160℃ and 130℃

[0070] Figure 4 In the diagram, the horizontal axis shows the etching time, and the vertical axis shows the recesses in the polycrystalline silicon (Si) that forms the substrate film 100. The amount of recesses in the substrate film 100 is as follows: Figure 3 As shown in (c), the depth of the recess in the base film 100 that is removed during etching is indicated. If the selection of the base film 100 for the laminated film 101 is sufficient, a smaller amount of recess in the base film 100 is preferred.

[0071] Figure 4 In the experimental results shown, when the substrate temperature is controlled at 160°C, the etching rate of silicon in the substrate film 100 is 2.7 nm / min. On the other hand, when the substrate temperature is controlled at 130°C, the recesses in the substrate film 100 at 240 seconds are worse than when the substrate temperature is controlled at 160°C, and the etching rate of silicon in the substrate film 100 becomes at least 28 nm / min. That is, when the substrate temperature is controlled at 130°C, the selectivity of the substrate film 100 decreases, and the amount of recesses in the substrate film 100 increases.

[0072] Due to the issue of selectivity for the substrate film 100 during over-etching, the main etching is performed at a low temperature to ensure selectivity for the mask 102 and a high etching rate. Over-etching involves controlling the substrate temperature above the temperature used in the main etching process to ensure selectivity for the substrate film 100. However, the above etching method suffers from the problem that the substrate temperature must be changed during both the main etching and over-etching processes, resulting in time-consuming temperature control and reduced production capacity. Alternatively, a plasma processing apparatus 1', different from the plasma processing apparatus 1 used for the main etching, can be prepared. This apparatus controls the substrate temperature above the temperature used in the main etching process (not shown) for over-etching. After the main etching, the substrate can be transported to the plasma processing apparatus 1' for over-etching, but this also suffers from reduced production capacity.

[0073] Therefore, in the etching method of this embodiment described below, the main etching is performed at a low temperature with the substrate temperature controlled at 15°C or below, and the over-etching is also performed at a low temperature with the substrate temperature controlled at the same temperature as the main etching. At this time, in order to ensure the selectivity of the substrate film 100 and optimize the process conditions, the over-etching also ensures a high selectivity and a high etching rate.

[0074] [Process Conditions]

[0075] The over-etching process conditions in this embodiment are as follows.

[0076] <Process conditions for over-etching in this embodiment>

[0077] Pressure inside the treatment container: 10 mT (1.333 Pa)

[0078] Gas CH2F2 / C4F8 / O2

[0079] substrate temperature 15℃

[0080] Figure 5 The figure illustrates an example of the etching rate of the laminate 101, the etching rate of the substrate 100, and the selectivity ratio relative to the ratio of CH2F2 gas to C4F8 gas in an etching method according to one embodiment. Figure 5 The horizontal axis of (a) to (c) represents the ratio of CH2F2 gas to the total amount of CH2F2 gas and C4F8 gas. Figure 5 The vertical axis of (a) represents the etching rate (E / R) of the laminate 101. Figure 5 In the above, the laminated film 101 is represented by "ON". Figure 5 The vertical axis of (b) represents the etching rate (E / R) of the substrate film 100 (Si). Figure 5The vertical axis of (c) represents the selection ratio (Sel.) of the laminated film 101 for the base film 100. It should be noted that, in the etching of the laminated film 101 based on each etching condition, a protective film is formed on the mask 102, but the ratio of O2 gas is adjusted under each etching condition to the extent that the aperture h of the mask 102 is not blocked.

[0081] Figure 5 The etching rate of the laminated film 101 shown in (a) is preferably high. Figure 5 The experimental results in (a) show that the ratio of CH2F2 gas only needs to be above 12.5%.

[0082] Figure 5 The etching rate of the substrate film 100 shown in (b) is preferably low. Figure 5 In the experimental results of (b), the proportion of CH2F2 gas only needs to be below 30.0%. Figure 5 The results of (a) and (b) show that the preferred ratio of CH2F2 gas is in the range of 12.5 to 30.0%.

[0083] like Figure 5 As shown in (c), a high selectivity was obtained for the substrate film 100 when the CH2F2 gas ratio was in the range of 12.5% ​​to 30.0%. Therefore, it can be seen that a high selectivity can be obtained during over-etching when the CH2F2 gas ratio is in the range of 12.5% ​​to 30.0%.

[0084] Next, while referring to Figure 6 The relationship between the ratio of H or F in the gas used in the etching method of one embodiment and the etching rate and selectivity will be explained. Figure 6 A graph illustrating an example of the relationship between the ratio of H or F in the gas used in an etching method according to one embodiment and the etching rate and selectivity, is provided. Figure 5 The experimental results (a) to (c) were obtained by converting the horizontal axis of the graph to the ratio of H or F in the gas.

[0085] Therefore, the relationship between the ratio of hydrogen (H) in the gas used for over-etching to the total amount of hydrogen (H), fluorine (F), and carbon (C), and the selectivity and etching rate, was obtained. Figure 6 The results for (a) and (b) are given. Additionally, the relationship between the ratio of fluorine (F) to the sum of hydrogen (H) and fluorine (F) to carbon (C) in the gas used for over-etching, and the selectivity and etching rate, is obtained. Figure 6 The results of (c) and (d).

[0086] It should be noted that the amounts of each element, namely hydrogen (H), fluorine (F), and carbon (C), are determined by summing the product of the gas volume flow rate and the valence of the elements contained in the gas, based on the structural formula of the gas used in the over-etching process.

[0087] Figure 6 The horizontal axis of (a) and (b) represents the ratio of H in the gas to the sum of H, F and C. Figure 6 The vertical axis of (a) represents the selectivity of the laminate 101 (ON) for the base film 100 (Si). Figure 6 The vertical axis of (b) represents the respective etching rates of the laminate 101 (ON) and the substrate 100 (Si).

[0088] The preferred ratio of H to the sum of H, F, and C Figure 6 In (a), the selection ratio indicated by the dashed line is 5 or more, and Figure 6 In (b), the etch rate of the stacked film (ON) indicated by the dashed line is in the range of 50 nm / min or higher. Additionally, Figure 6 In (b), the etching rate of the base film 100 is preferably less than 20 nm / min. Figure 6 The results of (a) show that when the selection ratio satisfies the condition of 5 or higher, the ratio of H to the sum of H, F, and C is in the range A of 0 to 0.06 (0 to 6%). Furthermore, from... Figure 6 As shown in result (b), when the etching rate of the laminate (ON) meets the condition of 50 nm / min or higher and the etching rate of the substrate 100 meets the condition of less than 20 nm / min, the ratio of H to the sum of H, F, and C is in the range of 0.02 to 0.06 (2 to 6%). Therefore, when both the selectivity and etching rate conditions are met, the ratio of H to the sum of H, F, and C is preferably in the range of 0.02 to 0.06 (2 to 6%).

[0089] Figure 6 The horizontal axis of (c) and (d) represents the ratio of F in the gas to H and the sum of F and C. Figure 6 The vertical axis of (c) represents the selectivity of the laminated membrane 101 for the base membrane 100. Figure 6 The vertical axis of (d) represents the etching rate of the laminate 101 and the substrate 100.

[0090] The preferred ratio of F to H and the sum of F and C is... Figure 6 In (c), the selection ratio indicated by the dashed line is 5 or higher, and Figure 6 In (d), the etch rate of the stacked film (ON), indicated by the dashed line, is in the range of 50 nm / min or higher. Additionally, Figure 6 In (d), the etching rate of the base film 100 is preferably less than 20 nm / min. Figure 6 The results of (c) show that when the selection ratio satisfies the condition of 5 or higher, the ratio of F to H and the sum of F and C is in the range of 0.63 to 0.66 (63% to 66%). Furthermore, from... Figure 6 As shown in (d), when the etching rate of the laminate (ON) meets the condition of 50 nm / min or higher and the etching rate of the substrate 100 meets the condition of less than 20 nm / min, the ratio of F to the sum of H and F and C is in the range of 0.63 to 0.65 (63 to 65%). Therefore, when both the selectivity and etching rate conditions are met, the ratio of F to the sum of H and F and C is preferably in the range of 0.63 to 0.65 (63 to 65%).

[0091] As explained above, if a gas with a ratio of H to the sum of H, F, and C in the range of 0.02 to 0.06 (2 to 6%) is used, a good selectivity to the substrate film 100 and an etching rate of the laminated film 101 can be obtained, which is preferred. Furthermore, as long as the gas has a ratio of H to the sum of H, F, and C in the range of 0.02 to 0.06 (2 to 6%), the gas used in the etching method of this embodiment is not limited to CH2F2 gas, C4F8 gas, or O2 gas.

[0092] Furthermore, if a gas with a ratio of F to H and the sum of F and C in the range of 0.63 to 0.65 (63 to 65%) is used, a good selectivity to the substrate film 100 and an etching rate of the laminated film 101 can be obtained, which is therefore preferred. Moreover, as long as the gas has a ratio of F to H and the sum of F and C in the range of 0.63 to 0.65 (63 to 65%), the gas used in the etching method of this embodiment is not limited to CH2F2 gas, C4F8 gas, or O2 gas.

[0093] Furthermore, if the gas has a ratio of H to the sum of H, F and C in the range of 0.02 to 0.06 (2 to 6%) and a ratio of F to the sum of H, F and C in the range of 0.63 to 0.65 (63 to 65%), a better selectivity to the substrate film 100 and an etch rate of the laminated film 101 can be obtained.

[0094] The gas that can be used in the etching method of this embodiment, which satisfies the above conditions, 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, wherein the hydrogen-containing gas can be hydrogen gas (H2) or hydrogen halide.

[0095] Examples of hydrofluoric carbon gases (CHF series) include CH2F2, CHF3, and C3H2F4. Examples of fluorinated carbon gases (CF series) include C4F8, C4F6, and CF4. Examples of hydrocarbon gases (CH series) include CH4, C2H6, and C2H4. Examples of hydrogen halides include HBr, HCl, HF, and HI.

[0096] Next, while referring to Figure 7 The mechanism of low-temperature etching in the over-etching process of this embodiment will be explained.

[0097] Figure 7 A graph showing the relationship between the ratio of H in the gas at high temperature (room temperature) and the etching rate. Figure 7 The source of the figure is "LM Ephrath, J. Electrochem. Soc. 126, 1419 (1979)". Figure 7 The ratio of H2 in the supply gas to the etching rate of silicon (Si) and silicon oxide (SiO2) films is shown when etching is performed using plasma formed from CF4 and H2 gases.

[0098] Therefore, under high temperature (room temperature) conditions, as the ratio of H2 to CF4 gas increases, the etching rate of silicon film (Si) decreases, and when the ratio of H2 is about 40%, the etching rate of silicon film (Si) becomes basically zero (0).

[0099] When H2 gas is added to a CF4 gas plasma, the H radicals in the plasma generated by the gas (H2+CF4) react with F radicals and CF radicals to produce hydrogen fluoride (HF). As a result, F is consumed, forming a polymeric film with a low F-to-C ratio, i.e., a carbon-rich deposition film, on the silicon (Si) surface. This deposition film is considered an obstacle, reducing the etching rate of the Si (silicon film).

[0100] In contrast, under high-temperature (room-temperature) conditions, even increasing the H2 to CF4 gas ratio only slightly reduces the etching rate of SiO2 (silicon oxide film). It is believed that the deposited film on the SiO2 surface receives oxygen (O) from the SiO2 film during the etching reaction, which is then removed as CO, CO2, or COF2 gas. Therefore, this does not hinder the etching rate of the SiO2 film. Based on the above, when etching is performed at a substrate temperature above 15°C, increasing the partial pressure of hydrogen in the gas can improve the selectivity of the silicon oxide film (SiO2 / Si selectivity).

[0101] However, with Figure 5 of (a), Figure 5 (b) and Figure 6 Compared to the tendency of the etching rate of the substrate film 100 and the etching rate of the laminated film 101 containing silicon oxide film in the etching method of one embodiment shown in (b), the ratio of CH2F2 gas containing H is increased. Figure 5 of (a), Figure 5 (b) or the ratio of hydrogen (H) Figure 6 In case (b)), the etching rate of the substrate film 100 and the etching rate of the laminated film 101 both increase, therefore, with Figure 7 The tendencies are inconsistent.

[0102] Figure 8 This is a graph illustrating an example of the relationship between the ratio of H in the gas used in an etching method according to one embodiment and the etching rate of a polycrystalline silicon (Poly-Si) cover film (a flat film without a mask, etc.). Figure 8 The horizontal axis of (a) represents the ratio of hydrogen (H2) in the mixed gas (H2+CF4), and the vertical axis represents the etching rate of the polysilicon film (Poly-Si). Figure 8 In (b), the horizontal axis represents the ratio of hydrogen (H2) in the mixed gas (H2+CF4), and the vertical axis represents the etching rate of the silicon oxide film (SiO2). Squares (white) indicate low-temperature etching at a substrate temperature of -60°C, and circles (black) indicate the etching rate at a substrate temperature of 35°C. Figure 7 In contrast, observations were conducted in areas with a high H2 gas ratio, and also in two areas: high temperature (normal temperature) and low temperature.

[0103] Figure 8 In the experimental results of (a), the etching rate of the polycrystalline silicon film (Poly-Si) in the region where the H content in the mixed gas is below 30% shows a correlation with... Figure 7 The same trend is observed, but in regions where the H content in the mixed gas exceeds 40%, the etching rate of the polysilicon film (Poly-Si) increases conversely. This is presumably because the lower proportion of CF4 gas in the mixed gas reduces the supply of carbon (C), resulting in a thinner deposited film on the Poly-Si surface. Furthermore, since CF4 gas is high in sulfur (F), even with the reduced C supply due to the lower CF4 gas proportion, a large amount of F, acting as an etchant for the Poly-Si film, remains, thus promoting etching.

[0104] It should be noted that the etching rate of polycrystalline silicon (Poly-Si) films with the same H-to-H ratio in the mixed gas exhibits the same tendency under both high-temperature (room temperature) and low-temperature conditions. However, the etching rate of Poly-Si films under low-temperature conditions is faster than that under high-temperature (room temperature) conditions. This is believed to be because the adsorption coefficient of HF increases at low temperatures, leading to HF adsorption on the surface of the Poly-Si film. Furthermore, it is thought that while HF itself has low thermal reactivity with the Poly-Si film, when HF is attached to the Poly-Si film, applying energy based on ion irradiation from plasma causes the Poly-Si film to react with the F element in the HF, thus promoting the etching of the Poly-Si.

[0105] In addition, in regions where the H content in the mixed gas is above 70%, the supply of F element is also reduced, thus it is speculated that the etching rate of polysilicon film (Poly-Si) decreases.

[0106] Figure 8 In the experimental results of (b), under high temperature (room temperature) conditions, the etching rate of the silicon oxide film (SiO2) decreases with increasing H content in the mixed gas. Therefore, it shows a correlation with... Figure 7 Similarly, in regions where the H content in the mixed gas is above 40%, the etching rate of the silicon oxide film (SiO2) also shows a decreasing trend. Conversely, at low temperatures, particularly in regions where the H content in the mixed gas is below 70%, the etching rate of the silicon oxide film (SiO2) shows an increasing trend with increasing H content in the mixed gas, exhibiting a different pattern. Figure 7 Furthermore, the etching rate of silicon oxide (SiO2) films at low temperatures is faster than that at high temperatures (room temperature).

[0107] Similar to polycrystalline silicon films, the adsorption coefficient of HF increases at low temperatures, leading to HF adsorption on the silicon oxide film surface. Furthermore, during the etching reaction of silicon oxide films using CF4 gas plasma, SiF4 and water (H2O) are produced as reaction products. However, water has a low saturated vapor pressure, suggesting that at low temperatures, water saturates on the silicon oxide film surface, existing in a partially liquid state. Moreover, water reacts with HF to generate hydrofluoric acid. Therefore, it is believed that the hydrofluoric acid dissolved in water on the silicon oxide film surface promotes etching primarily based on chemical reactions, resulting in a specific increase in the etching rate.

[0108] As described above, by supplying H in a low-temperature environment with an appropriate H ratio (around 30-50%) in the mixed gas, the etching rate of the silicon oxide film can be maintained at a high speed, while the etching rate of the polycrystalline silicon film is slow, thus ensuring the selectivity of the silicon oxide film for the polycrystalline silicon film.

[0109] That is, it can be seen that in order to maintain the etching rate of the etched film (which is silicon oxide film at this time) at a high speed and the etching rate of the silicon film (which is polycrystalline silicon film at this time) at a slow speed, and to ensure the selectivity of the etched film to the silicon film, it is important to supply hydrogen (H) and fluorine (F) and carbon (C) in a proper balance at a low temperature environment (which is the ratio of H in the mixed gas at this time).

[0110] Figure 9 This is a graph illustrating an example of the relationship between substrate temperature and the amount of C (carbon) and H (hydrogen) reaching the bottom of the hole. Figure 9 In the context of temperature, low temperature refers to a substrate temperature below 15°C, while high temperature refers to a substrate temperature above 15°C. Figure 9 The horizontal axis represents the aspect ratio (AR), which increases towards the right. Figure 9 The vertical axis represents the amount of C reaching the bottom of the hole. In the etching method of this embodiment, it is assumed that low-temperature etching is performed on recesses such as holes with an aspect ratio of 40 or greater.

[0111] When gases containing C, H, and F, such as CH2F2 or mixed gases (H2+CF4), are used for etching, C and CxFy have higher adsorption coefficients than H. Therefore, C is physically adsorbed and captured on the shallower sidewalls of the pore, thus reducing the amount of C reaching the bottom of the pore. Consequently, at the bottom of the pore h, the ratio of H and F to C is relatively increased compared to the shallower parts of the pore. Furthermore, as... Figure 9 As shown, in the case of low-temperature etching, compared with the case of high-temperature etching, the amount of C and H reaching the bottom of the hole is reduced, but the reduction rate of C is greater than that of H.

[0112] Therefore, in the case of etching holes with an aspect ratio of 40 or higher during low-temperature etching, the ratio of C, H, and F relative to the bottom of the hole becomes higher. That is, it is predicted that in the low-temperature etching of holes with an aspect ratio of 40 or higher, the ratio of H and F to C at the bottom of the hole becomes higher than that at the bottom of holes with a low aspect ratio.

[0113] In view of this, an investigation Figure 5 of (a), Figure 5 (b) and Figure 6 When considering the experimental results in (b), Figure 8 (a) and Figure 8 The experimental results in (b) suggest that the condition is achieved under low-temperature conditions with the H content in the gas mixture being close to 30-50%. Specifically, it is important that hydrogen (H), fluorine (F), and carbon (C) are supplied in a suitable balance at low temperatures, based on the aspect ratio.

[0114] Therefore, a high etching rate can be ensured in both the primary and over-etching processes at low temperatures, and a selectivity can also be maintained in the over-etching process. Furthermore, by maintaining the same substrate temperature in both the primary and over-etching processes, no substrate temperature control time is required between the primary and over-etching processes, thus improving production capacity. Additionally, primary and over-etching can be performed continuously in the same plasma processing apparatus.

[0115] [Variation Example: Improvement of the bottom CD]

[0116] In the etching method described above, if the aspect ratio becomes higher than 40, the front end shape of the recess formed in the laminated film 101 becomes thinner, and the bottom CD (hereinafter referred to as the bottom CD (Btm CD)) of the recess becomes narrower. In contrast, in a variation of the etching method of this embodiment, in order to expand the bottom CD and make the shape of the recess vertical, SiCl4 gas is added to CH2F2 gas, C4F8 gas, and O2 gas.

[0117] Figure 10 This diagram illustrates an example of the bottom CD when SiCl4 gas is added to CH2F2 gas, C4F8 gas, or O2 gas in an etching method according to one embodiment. The process conditions other than the gas in the over-etching of the modified example are as described above in <Process Conditions for Over-etching in this Embodiment>. Figure 10 In the experimental results shown, the addition of SiCl4 gas (represented by white circles) resulted in a more than 25% expansion of the bottom CD compared to the absence of SiCl4 gas (represented by black squares), and the front end shape of the concave portion became rectangular. It should be noted that the addition of SiCl4 gas involved 13% of the total amount of SiCl4 gas added, relative to the sum of CH2F2 and C4F8 gases.

[0118] Figure 11 This diagram illustrates an example of the bottom CD when SiCl4 gas or other gases are added to CH2F2 gas, C4F8 gas, O2 gas, or an etching method according to one embodiment. The process conditions other than the gas in the over-etching of the modified example are as described above in <Process Conditions for Over-etching of this Embodiment>. Figure 11 In the experimental results shown, without the addition of SiCl4 gas, Cl2 gas, or HBr gas to CH2F2 gas, C4F8 gas, or O2 gas, the Bow CD of the CD representing the most expanded part of the concave region is 90, the Btm CD is 39, and the difference is 51.

[0119] In contrast, when SiCl4 gas is added to CH2F2, C4F8, or O2 gases, Bow CD becomes 91 and Btm CD becomes 51, with a difference of 40. Furthermore, when Cl2 gas is added, Bow CD becomes 90 and Btm CD becomes 52, with a difference of 38. Additionally, when HBr gas is added, Bow CD becomes 92 and Btm CD becomes 53, with a difference of 39. With the addition of any one of SiCl4, Cl2, or HBr gas, compared to the case without addition, the difference between Bow CD and Btm CD decreases, Btm CD is improved, and the front end shape of the concave portion becomes rectangular.

[0120] It should be noted that, when adding CH2F2 gas, C4F8 gas, or O2 gas without adding SiCl4 gas, Cl2 gas, or HBr gas, when adding SiCl4 gas, or when adding Cl2 gas, the ratio of CH2F2 gas to the total amount of CH2F2 gas and C4F8 gas is 12.5%. Furthermore, when adding SiCl4 gas or Cl2 gas, 13% of SiCl4 gas or Cl2 gas is added relative to the total amount of CH2F2 gas and C4F8 gas.

[0121] Furthermore, when HBr gas is used as the added gas, the ratio of CH2F2 gas to the total of CH2F2 gas and C4F8 gas is 0%, and the ratio of HBr gas to the total of CH2F2 gas and C4F8 gas is 14.3. When HBr gas is used, due to the presence of hydrogen, etching of the stacked film 101 can be achieved even without CH2F2 gas during over-etching.

[0122] As can be seen from the above, the gas used in the etching method is preferably a gas containing halogens other than fluorine, such as CH2F2, C4F8, O2, SiCl4, Cl2, or HBr. Therefore, by extending the Btm CD instead of the Bow CD, the front end shape of the recess can be made rectangular.

[0123] It should be noted that the gases containing halogens other than fluorine include SiCl4, Cl2, HBr, as well as HCl, HI, Br2, CF2Br2, etc.

[0124] As explained above, the etching method and plasma processing apparatus according to this embodiment can maintain the etching rate and ensure the selectivity during over-etching in which the substrate film of the stacked film of silicon oxide film and silicon nitride film is exposed in a low-temperature environment.

[0125] The etching method and plasma processing apparatus of the disclosed embodiments are exemplary in all respects and should be considered without limitation. The embodiments can be modified and altered in various ways without departing from the appended claims and their spirit. The features described in the foregoing embodiments can also be other configurations and combinations thereof without contradiction.

[0126] The plasma processing apparatus disclosed herein can be used in any type of apparatus, including atomic layer deposition (ALD) apparatus, capacitively coupled plasma (CCP) apparatus, inductively coupled plasma (ICP) apparatus, radial line slot antenna (RLSA) apparatus, electron cyclotron resonance plasma (ECR) apparatus, and helicon wave plasma (HWP) apparatus.

Claims

1. An etching method comprising etching a substrate having a base film, a laminated film having alternating layers of a first film and a second film on the base film, and a mask on the laminated film, wherein a recess is formed in the laminated film by passing plasma through the mask. The etching method comprises the following steps: The process of preparing the substrate; and, The process involves maintaining the substrate temperature below 15°C and etching using a plasma containing hydrogen, fluorine, and carbon gases until the recesses of the laminated film reach the base film. The ratio of hydrogen in the gas to the total amount of hydrogen, fluorine, and carbon is 0.02 to 0.

06.

2. The etching method according to claim 1, wherein, The ratio of fluorine to the total amount of hydrogen and carbon in the gas is 0.63 to 0.

65.

3. The etching method according to claim 1 or 2, wherein, The gas contains: At least one of fluorocarbon gas (CF series) and hydrofluorocarbon gas (CHF series), And includes: At least one of hydrofluoric acid gas (CHF series), hydrocarbon gas (CH series), and hydrogen-containing gas. The hydrogen-containing gas is hydrogen gas or hydrogen halide.

4. The etching method according to claim 1 or 2, wherein, Before the etching process up to the base film, the following process is performed: etching the recesses of the laminated film up to a predetermined depth.

5. The etching method according to claim 1 or 2, wherein, The specified depth of the recess is 40 or more in terms of aspect ratio.

6. The etching method according to claim 1 or 2, wherein, The substrate temperature in the process of etching the recess to a specified depth is below 15°C, and is the same as the substrate temperature in the process of etching until the base film is reached.

7. The etching method according to claim 1 or 2, wherein, The gas also contains gases containing halogens other than fluorine.

8. The etching method according to claim 1 or 2, wherein, The first film is a silicon oxide film, and the second film is a silicon nitride film.

9. The etching method according to claim 1 or 2, wherein, The substrate film is any one of polycrystalline silicon, amorphous silicon, or monocrystalline silicon.

10. An etching method comprising etching a substrate having a base film, a laminated film having alternating layers of a first film and a second film on the base film, and a mask on the laminated film, by using plasma through the mask to form recesses in the laminated film. The etching method comprises the following steps: The process of preparing the substrate; and, The process involves maintaining the substrate temperature below 15°C and etching using a plasma containing hydrogen, fluorine, and carbon gases until the recesses of the laminated film reach the base film. in, The ratio of fluorine to the total amount of hydrogen and carbon in the gas is 0.63 to 0.

65.

11. A plasma processing apparatus having a control unit for controlling an etching process in which a recess is formed in a substrate having a base film, a laminated film having alternating layers of a first film and a second film on the base film, and a mask on the laminated film by using plasma through the mask. The control unit controls the following processes: The process of preparing the substrate, and The process involves maintaining the substrate temperature below 15°C and using plasma containing hydrogen, fluorine, and carbon gases to etch until the recesses of the laminated film reach the base film. The ratio of hydrogen in the gas to the total amount of hydrogen, fluorine, and carbon is 0.02 to 0.

06.

12. A plasma processing apparatus having a control unit for controlling an etching process in which a recess is formed in a substrate having a base film, a laminated film having alternating layers of a first film and a second film on the base film, and a mask on the laminated film by using plasma through the mask. The control unit controls the following processes: The process of preparing the substrate, and The process involves maintaining the substrate temperature below 15°C and using plasma containing hydrogen, fluorine, and carbon gases to etch until the recesses of the laminated film reach the base film. The ratio of fluorine to the total amount of hydrogen and carbon in the gas is 0.63 to 0.65.

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