Etching method and etching device

Abstract

The etching method includes: a physical adsorption process, in which an object to be processed on which an etching target film is formed is cooled while an adsorbate based on the first processing gas is physically adsorbed on the etching target film under a condition in which the pressure of the first processing gas is lower than the saturated vapor pressure of the first processing gas with respect to the temperature of the object to be processed; and an etching process, in which the plasma of the second processing gas is used to make the adsorbate react with the etching target film, thereby etching the etching target film.

Description

Technical Field

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

[0002] As one method for etching a film to be etched, a method called Quasi-ALE (Atomic Layer Etching) is known. In the Quasi-ALE method, a polymer layer is deposited on the film to be etched using a process gas, and the polymer layer and the film to be etched are reacted using a rare gas plasma, thereby etching the film to be etched (see, for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-173240 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The present disclosure provides a technology capable of appropriately controlling the etching amount.

[0008] Solutions for solving problems

[0009] An etching method according to one embodiment of the present invention includes: a physical adsorption process, in which an object to be processed on which an etching target film is formed is cooled while an adsorbate based on the first processing gas is physically adsorbed on the etching target film under a condition in which the pressure of the first processing gas is lower than the saturated vapor pressure of the first processing gas for the temperature of the object to be processed; and an etching process, in which the plasma of the second processing gas is used to react the adsorbate with the etching target film, thereby etching the etching target film.

[0010] Effects of the Invention

[0011] According to the present disclosure, an effect is achieved in which the etching amount can be appropriately controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a diagram schematically showing an example of a cross section of an etching device according to an embodiment.

[0013] Figure 2 This is a diagram showing an example of a vapor pressure curve of the first process gas according to the embodiment.

[0014] Figure 3 This is a diagram showing an example of a change in film thickness of a wafer according to an embodiment over time.

[0015] Figure 4 This is a graph showing the results of measuring the change in the thickness of the adsorbate on the SiO 2 film with time when the wafer temperature is -110°C using an ellipsometer.

[0016] Figure 5 This is a graph showing the results of measuring, using QMS, the temporal change in the intensity of the gas component near the SiO 2 film when the wafer temperature is -110°C.

[0017] Figure 6 This is a graph showing the results of measuring the change in the thickness of the adsorbate on the SiO 2 film with time when the wafer temperature is -115°C using an ellipsometer.

[0018] Figure 7 This is a graph showing the results of measuring, using QMS, the temporal change in the intensity of the gas component near the SiO 2 film when the wafer temperature is -115°C.

[0019] Figure 8 This is a graph showing the results of measuring the change in the thickness of the adsorbate on the SiO 2 film with time when the wafer temperature is -120°C using an ellipsometer.

[0020] Figure 9 This is a graph showing the results of measuring, using QMS, the temporal change in the intensity of the gas component near the SiO 2 film when the wafer temperature is -120°C.

[0021] Figure 10 This is a flowchart showing an example of the flow of the etching method according to the embodiment. DETAILED DESCRIPTION

[0022] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are given to the same or corresponding parts in each of the drawings.

[0023] Furthermore, in the Quasi-ALE method, when a polymer layer formed by the process gas is deposited on the target film, the amount of the polymer layer deposited on the target film tends to increase linearly over time. This linear increase in the amount of the polymer layer deposited on the target film makes it difficult to control the thickness of the polymer layer on an atomic layer basis. Consequently, the Quasi-ALE method presents the problem of difficulty in adequately controlling the amount of the target film etched by the reaction with the polymer layer.

[0024] [Structure of etching apparatus]

[0025] First, based on Figure 1 The etching apparatus according to the embodiment will be described. Figure 1 This is a diagram schematically showing an example of a cross section of the etching apparatus 10 according to the embodiment. Figure 1 The illustrated etching apparatus 10 is a capacitive coupling type etching apparatus.

[0026] The etching apparatus 10 includes a chamber 12. The chamber 12 has a generally cylindrical shape. The interior space of the chamber 12 serves as a processing space. A plasma-resistant coating is formed on the inner wall surface of the chamber 12. The coating may be an acid-resistant aluminum film or a film formed of yttrium oxide. The chamber 12 is grounded. An opening 12g is formed on the side wall of the chamber 12. When a wafer W is loaded into the chamber 12 from outside the chamber 12 and when a wafer W is unloaded from the chamber 12 to outside the chamber 12, the wafer W passes through the opening 12g. A gate valve 14 is installed on the side wall of the chamber 12 to open and close the opening 12g.

[0027] A support portion 15 is provided on the bottom of the chamber 12. The support portion 15 has a substantially cylindrical shape. The support portion 15 is made of, for example, an insulating material. The support portion 15 extends upward from the bottom of the chamber 12 within the chamber 12. A mounting table 16 is provided within the chamber 12. The mounting table 16 is supported by the support portion 15.

[0028] The mounting table 16 is used to mount a semiconductor wafer (hereinafter referred to as "wafer W"). Wafer W is an example of an object to be processed. The mounting table 16 includes a lower electrode 18 and an electrostatic chuck 20. The lower electrode 18 includes a first plate 18a and a second plate 18b. The first plate 18a and the second plate 18b are made of a metal such as aluminum and have a substantially disc shape. The second plate 18b is disposed on the first plate 18a and is electrically connected to the first plate 18a.

[0029] An electrostatic chuck 20 is disposed on the second plate 18b. The electrostatic chuck 20 includes an insulating layer and a film-shaped electrode disposed within the insulating layer. The electrodes of the electrostatic chuck 20 are electrically connected to a DC power supply 22 via a switch 23. A DC voltage is applied from the DC power supply 22 to the electrodes of the electrostatic chuck 20. When the DC voltage is applied to the electrodes of the electrostatic chuck 20, the electrostatic chuck 20 generates an electrostatic attraction force, attracting the wafer W to the electrostatic chuck 20 and holding the wafer W. Furthermore, a heater may be built into the electrostatic chuck 20, and the heater may be connected to a heater power supply disposed outside the chamber 12.

[0030] A focus ring 24 is provided on the periphery of the second plate 18b. Focus ring 24 is a generally annular plate. Focus ring 24 is positioned to surround the edge of wafer W and electrostatic chuck 20. Focus ring 24 is provided to improve etching uniformity. Focus ring 24 can be formed of a material such as silicon or quartz.

[0031] A flow path 18f is provided within the second plate 18b. Refrigerant is supplied to flow path 18f from a cooling unit located outside chamber 12 via pipe 26a. The refrigerant supplied to flow path 18f is returned to the cooling unit via pipe 26b. In other words, the refrigerant circulates between flow path 18f and the cooling unit. By controlling the temperature of this refrigerant, the temperature of the mounting table 16 (or electrostatic chuck 20) and the temperature of the wafer W are adjusted. Galden (registered trademark) is exemplified as a refrigerant.

[0032] The etching apparatus 10 is provided with a gas supply line 28. The gas supply line 28 is used to supply a heat transfer gas, such as He gas, from a heat transfer gas supply mechanism between the upper surface of the electrostatic chuck 20 and the back surface of the wafer W.

[0033] The etching apparatus 10 further includes an upper electrode 30. The upper electrode 30 is disposed above the mounting table 16. The upper electrode 30 is supported above the chamber 12 via a member 32. The upper electrode 30 may include an electrode plate 34 and a support 36. The lower surface of the electrode plate 34 faces the chamber 12. A plurality of gas ejection holes 34a are provided in the electrode plate 34. The electrode plate 34 may be formed of a material such as silicon or silicon oxide.

[0034] The support body 36 detachably supports the electrode plate 34 and is formed from a conductive material such as aluminum. A gas diffusion chamber 36a is provided within the support body 36. Multiple gas flow holes 36b, which communicate with the gas ejection holes 34a, extend downward from the gas diffusion chamber 36a. A gas inlet 36c for introducing gas into the gas diffusion chamber 36a is formed in the support body 36. The gas inlet 36c is connected to a gas supply pipe 38.

[0035] The gas supply pipe 38 is connected to a gas source assembly 40 via a valve assembly 42 and a flow controller assembly 44. The gas source assembly 40 includes a plurality of gas sources. The plurality of gas sources includes at least a gas source for a first process gas and a gas source for a second process gas. The first process gas is a gas that physically adsorbs onto the film to be etched on the wafer W. The second process gas is a gas used to etch the film to be etched. The plurality of gas sources may also include a gas source for a gas other than the first process gas and the second process gas.

[0036] Valve assembly 42 includes multiple valves, and flow controller assembly 44 includes multiple flow controllers such as mass flow controllers or pressure-controlled flow controllers. The multiple gas sources of gas source assembly 40 are connected to gas supply pipe 38 via corresponding valves in valve assembly 42 and corresponding flow controllers in flow controller assembly 44.

[0037] A partition member 48 is provided between the support portion 15 and the sidewall of the chamber 12. The partition member 48 is, for example, a plate-shaped member and can be formed by coating the surface of an aluminum base material with a ceramic such as Y2O3. Multiple holes are formed in the partition member 48, extending through the partition member 48. An exhaust device 50 is connected to the bottom of the chamber 12 below the partition member 48 via an exhaust pipe 52. The exhaust device 50 includes a pressure controller such as a pressure regulating valve and a vacuum pump such as a turbomolecular pump, and is capable of reducing the pressure in the chamber 12 to a desired level.

[0038] The etching apparatus 10 further includes a first high-frequency power supply 62 and a second high-frequency power supply 64. The first high-frequency power supply 62 is a power supply that generates a first high-frequency power (high-frequency electric energy) for generating plasma. The first high-frequency power has a frequency in the range of 27 MHz to 100 MHz, for example. The first high-frequency power supply 62 is connected to the upper electrode 30 via a matching device 63. The matching device 63 has a circuit for matching the output impedance of the first high-frequency power supply 62 with the impedance of the load side (the upper electrode 30 side). In addition, the first high-frequency power supply 62 may also be connected to the lower electrode 18 via the matching device 63.

[0039] The second high-frequency power source 64 is a power source that generates a second high-frequency power (high-frequency electric energy) for attracting ions toward the wafer W. The second high-frequency power has a frequency in the range of 400 kHz to 13.56 MHz, for example. The second high-frequency power source 64 is connected to the lower electrode 18 via a matching device 65. The matching device 65 includes a circuit for matching the output impedance of the second high-frequency power source 64 with the impedance of the load side (the lower electrode 18 side).

[0040] The operation of the etching apparatus 10 is centrally controlled by a control unit 70. The control unit 70 includes a CPU (Central Processing Unit), and is provided with a user interface 72, a storage unit 73, and a process controller 71 for controlling various components of the etching apparatus.

[0041] The user interface 72 is composed of a keyboard for a process manager to input commands for managing the etching apparatus, a display for visually displaying the operating status of the etching apparatus, and the like.

[0042] The storage unit 73 stores a recipe containing control programs (software) and processing condition data for implementing various processes performed by the etching apparatus under the control of the process controller 71. The recipes, including the control program and processing condition data, are stored in a computer-readable recording medium (e.g., a hard disk, CD, floppy disk, semiconductor memory, etc.). The recipes, including the control program and processing condition data, can also be transmitted in real time from another device, for example, via a dedicated line.

[0043] The control unit 70 operates the process controller 71 based on the control program and processing condition data stored in the storage unit 73 , thereby controlling the operation of the entire apparatus.

[0044] [Etching method]

[0045] Next, an example of a process for etching a wafer W using the etching apparatus 10 will be described. The etching apparatus 10 first performs a physical adsorption process. Specifically, while cooling the wafer W having the film to be etched formed thereon, the etching apparatus 10 physically adsorbs an adsorbate based on the first process gas onto the film to be etched, under a condition where the pressure of the first process gas is less than the saturated vapor pressure of the first process gas at the temperature of the wafer W. The etching apparatus 10 then performs an etching process. Specifically, the etching apparatus 10 uses the plasma of a second process gas to cause the adsorbate to react with the film to be etched, thereby etching the film. The film to be etched is, for example, a silicon-containing film. An example of a silicon-containing film is a SiO2 film. The first process gas is, for example, a CF-based gas. An example of a CF-based gas is C4F8. The second process gas is, for example, a noble gas. An example of a noble gas is Ar. The physical adsorption process and the etching process may be repeated multiple times. Furthermore, a replacement process may be performed between the physical adsorption process and the etching process, replacing the first process gas with a third process gas. The third process gas may be, for example, the same as the second process gas.

[0046] Furthermore, in the Quasi-ALE method, one of the methods for etching a target film, when a polymer layer formed by a process gas is deposited on the target film, the amount of the polymer layer deposited on the target film tends to increase linearly over time. This linear increase in the amount of polymer layer deposited on the target film makes it difficult to control the thickness of the polymer layer on an atomic layer basis. Consequently, the Quasi-ALE method has the problem of making it difficult to control the desired amount of etching of the target film through reaction with the polymer layer.

[0047] Therefore, the etching apparatus 10 allows the adsorbate based on the first process gas to be physically adsorbed onto the film to be etched while cooling the wafer W on which the film to be etched is formed, under the condition that the pressure of the first process gas is less than the saturated vapor pressure of the first process gas for the temperature of the wafer W. By allowing the adsorbate to be physically adsorbed onto the film to be etched while cooling the wafer W and under the condition that the pressure of the first process gas is less than the saturated vapor pressure, the adsorbate amount saturates to a constant value over time, thereby enabling the thickness of the adsorbate to be controlled with high precision on an atomic layer basis. As a result, the amount of the film to be etched, which is etched by reaction with the adsorbate, can be appropriately controlled to a desired amount.

[0048] Figure 2 This is a diagram showing an example of a vapor pressure curve of the first process gas according to the embodiment. Figure 2 The vapor pressure curve of C4F8, used as the first process gas, is shown in FIG. The higher the temperature, the greater the saturated vapor pressure of C4F8. Therefore, as the temperature of wafer W increases, it becomes more difficult for the C4F8-based adsorbate to physically adsorb onto the film being etched. Therefore, there is an upper limit to the wafer W temperature that causes a sufficient amount of physical adsorption to aid etching, and the etching apparatus 10 cools wafer W to a temperature below this upper limit. When using C4F8 as the first process gas, the etching apparatus 10 of this embodiment cools wafer W to a temperature below, for example, -115°C.

[0049] Furthermore, when the pressure of C4F8 is lower than the saturated vapor pressure of C4F8 for the temperature of wafer W, the amount of adsorbate physically adsorbed to the film to be etched saturates to a constant value over time. This phenomenon is called adsorption equilibrium. The etching apparatus 10 of this embodiment cools wafer W while allowing C4F8-based adsorbates to physically adsorb to the film to be etched under the condition that the pressure of C4F8 is lower than the saturated vapor pressure of C4F8 for the temperature of wafer W. For example, the etching apparatus 10 cools wafer W to a temperature below -115°C while allowing C4F8-based adsorbates to physically adsorb to the film to be etched under the condition that the pressure of C4F8 is lower than the saturated vapor pressure of C4F8 for the temperature of wafer W. Figure 2 The hatched range in the figure shows the C₄F₈ pressure range set when the wafer W temperature is -115°C or below. By allowing the adsorbate to physically adsorb onto the etched film while cooling the wafer W under conditions where the C₄F₈ pressure is less than its saturated vapor pressure, the adsorbate adsorption saturates to a constant value over time. This allows the adsorbate thickness to be controlled with high precision, down to the atomic layer level. As a result, the amount of film etched by the reaction with the adsorbate can be appropriately controlled to a desired level.

[0050] Next, refer to Figure 3 A specific example of the process of etching the wafer W will be described. Figure 3 : is a diagram showing an example of a change in film thickness of a wafer W according to an embodiment over time. Figure 3 On the upper side, a graph is shown showing the change in film thickness of the wafer W over time when the physical adsorption process, the adjustment process, and the etching process are repeated for 8 cycles. Figure 3 The lower side of the Figure 3 The portion of the graph above corresponds to the seventh cycle. On the wafer W, a SiO2 film is formed as an etching target film.

[0051] The etching apparatus 10 circulates a refrigerant to cool the wafer W to -120°C. Then, while cooling the wafer W, the etching apparatus 10 supplies C4F8 from the gas source assembly 40 into the chamber 12 under a condition where the pressure of C4F8 is lower than the saturated vapor pressure of C4F8 at the temperature of the wafer W, thereby causing the adsorbate to be physically adsorbed onto the etching target film. At this time, the etching apparatus 10 does not generate plasma within the chamber 12. Figure 3 The period T1 during which the 7th cycle of the physical adsorption process is performed is shown. The amount of adsorbate physically adsorbed on the etching target film of wafer W is saturated to a fixed value over time, and the film thickness of wafer W is saturated to a fixed value. That is, the physical adsorption process is continued for a predetermined time (for example, the time of period T1) until the amount of adsorbate is saturated. In addition, when the adsorbate is physically adsorbed on the etching target film, the etching device 10 may also adjust the temperature of the wall of the chamber 12 to a value higher than the temperature of wafer W. For example, a heating unit such as a heater can be used to adjust the temperature of the wall of the chamber 12. By adjusting the temperature of the wall of the chamber 12 to a value higher than the temperature of wafer W, the amount of adsorbate physically adsorbed on the wall of the chamber 12 can be reduced.

[0052] The etching apparatus 10 allows the C 4 F 8 -based adsorbate to be physically adsorbed on the etching target film, and then supplies Ar from the gas source group 40 into the chamber 12 to replace the C 4 F 8 with Ar. Figure 3 The figure shows the period T2 during which the replacement step of the seventh cycle is performed. The C₄F₄ partial pressure is reduced by the replacement of the C₄F₄ by Ar, and a portion of the adsorbate physically adsorbed to the etched film volatilizes. As this portion of the adsorbate physically adsorbed to the etched film volatilizes, the amount of adsorbate adsorbed on wafer W decreases, reducing the film thickness of wafer W. However, the remaining portion of the adsorbate does not volatilize and remains as a residue on the etched film. This adjusts the thickness of the adsorbate to a predetermined value.

[0053] After replacing C₄F₈ with Ar, the etching apparatus 10 supplies Ar into the chamber 12 from the gas source assembly 40 and applies a first high-frequency power from the first high-frequency power supply 62 to the upper electrode 30, thereby generating Ar plasma in the chamber 12 for etching. At this time, the etching apparatus 10 may also apply a second high-frequency power from the second high-frequency power supply 64 to the lower electrode 18. Figure 3FIG. 3 shows a period T3 during which the seventh etching cycle is performed. The generation of Ar plasma promotes the collision of Ar ions with adsorbates on the target film, causing a reaction between the adsorbates and the target film. This reaction between the adsorbates and the target film causes the target film on wafer W to be etched in proportion to the thickness of the adsorbate. The thickness of the target film decreases over time, and the thickness of wafer W decreases. When the reaction between the adsorbate and the target film is complete, the reduction in the thickness of the target film ceases. In other words, the etching process continues until the reaction between the adsorbate and the target film is complete.

[0054] In this manner, the etching apparatus 10 allows the adsorbate to be physically adsorbed onto the etching target film while cooling the wafer W under the condition where the pressure of C4F8 is lower than the saturated vapor pressure of C4F8 at the temperature of the wafer W, thereby saturating the adsorbate adsorption amount to a fixed value. Consequently, the etching apparatus 10 can control the thickness of the adsorbate with high precision on an atomic layer basis, and as a result, can appropriately control the amount of etching of the etching target film, which is achieved through reaction with the adsorbate, to a desired amount.

[0055] Furthermore, even when an adsorbate is physically adsorbed onto the target film in the etching apparatus 10, the adsorbate may completely volatilize before etching the target film. For example, in the etching apparatus 10, when the temperature of the wafer W is relatively high (e.g., above -115°C), a C4F8-based adsorbate physically adsorbed onto the SiO2 film may completely volatilize before etching. If the adsorbate completely volatilizes before etching, the reaction between the adsorbate and the target film cannot occur, and therefore, etching of the target film cannot be achieved.

[0056] Figure 4 This is a graph showing the results of measuring the change in the thickness of the adsorbate on the SiO 2 film with time when the temperature of the wafer W is -110°C using an ellipsometer. Figure 5 This is a graph showing the results of measuring the temporal change in the intensity of the gas component near the SiO 2 film when the temperature of the wafer W is -110° C. using a QMS (Quadrupole Mass Spectrometer). Figure 4 and Figure 5 The results are obtained by changing the pressure of C4F8 supplied to the chamber 12 and measuring the thickness of the adsorbate on the SiO2 film and the intensity of the gas component near the SiO2 film. Figure 4 and Figure 5 In FIG. 1 , for each pressure of C 4 F 8 , a graph is used to show the temporal change in the thickness of the adsorbate on the SiO 2 film and the temporal change in the intensity of the gas component near the SiO 2 film.

[0057] Figure 4 The graph shows the following situation: when the temperature of the wafer W is -110°C, C4F8 is supplied into the chamber 12 so that the adsorbate based on C4F8 is deposited on the SiO2 film. Figure 5 The graph shows that when the temperature of the wafer W is -110°C, after the exhaust of C4F8 is started, all the adsorbates temporarily physically adsorbed on the SiO2 film are rapidly volatilized as gas components.

[0058] Figure 6 This is a graph showing the results of measuring the change in the thickness of the adsorbate on the SiO 2 film with time when the temperature of the wafer W is -115°C using an ellipsometer. Figure 7 This is a graph showing the results of measuring, using QMS, the temporal change in the intensity of the gas component near the SiO 2 film when the temperature of the wafer W is -115°C. Figure 6 and Figure 7 The results are obtained by changing the pressure of C4F8 supplied to the chamber 12 and measuring the thickness of the adsorbate on the SiO2 film and the intensity of the gas component near the SiO2 film. Figure 6 and Figure 7 In FIG. 1 , for each pressure of C 4 F 8 , a graph is used to show the temporal change in the thickness of the adsorbate on the SiO 2 film and the temporal change in the intensity of the gas component near the SiO 2 film.

[0059] Figure 6 The graph shows a case where, when the temperature of the wafer W is -115°C, C4F8 is supplied into the chamber 12 so that the adsorbate based on C4F8 is physically adsorbed on the SiO2 film. Figure 7 The graph shows that when the temperature of the wafer W is -115°C, after the exhaust of C4F8 is started, all the adsorbates temporarily physically adsorbed on the SiO2 film are rapidly volatilized as gas components. Figure 4 、 Figure 5 、 Figure 6 as well as Figure 7 It is shown that the time during which the adsorbate temporarily physically adsorbed on the SiO 2 film remains on the SiO 2 film can be extended when the temperature of the wafer W is -115° C., compared with the case where the temperature of the wafer W is -110° C.

[0060] Figure 8 This is a graph showing the results of measuring the change in the thickness of the adsorbate on the SiO 2 film with time when the temperature of the wafer W is -120°C using an ellipsometer. Figure 9This is a graph showing the results of measuring, using QMS, the temporal change in the intensity of the gas component near the SiO 2 film when the temperature of the wafer W is -120°C. Figure 8 and Figure 9 The results are obtained by changing the pressure of C4F8 supplied to the chamber 12 and measuring the thickness of the adsorbate on the SiO2 film and the intensity of the gas component near the SiO2 film. Figure 8 and Figure 9 In FIG. 1 , for each pressure of C 4 F 8 , a graph is used to show the temporal change in the thickness of the adsorbate on the SiO 2 film and the temporal change in the intensity of the gas component near the SiO 2 film.

[0061] Figure 8 The graph shows a case where, when the temperature of the wafer W is -120°C, C4F8 is supplied into the chamber 12 so that the adsorbate based on C4F8 is physically adsorbed on the SiO2 film. Figure 9 The graph shows that when the temperature of the wafer W is -120°C, after the exhaust of C4F8 is started, all the adsorbates temporarily physically adsorbed on the SiO2 film are rapidly volatilized as gas components. Figure 6 、 Figure 7 、 Figure 8 as well as Figure 9 It is shown that the time during which the adsorbate temporarily physically adsorbed on the SiO 2 film remains on the SiO 2 film can be extended when the temperature of the wafer W is -120° C., compared with the case where the temperature of the wafer W is -115° C.

[0062] Therefore, the etching apparatus 10 of this embodiment allows the adsorbate to be physically adsorbed onto the etching target film while cooling the wafer W to a temperature of -115° C. or lower. This prevents the adsorbate from completely volatilizing before etching, thereby enabling stable etching of the etching target film.

[0063] However, even when the wafer W is cooled to a temperature below -115°C, if the pressure of C4F8, the first process gas, is sufficiently lower than the saturated vapor pressure of C4F8 for the temperature of the wafer W, the C4F8-based adsorbate will readily volatilize. For example, if the C4F8 pressure is less than 0.5 Pa, the C4F8-based adsorbate will readily volatilize. Therefore, the etching apparatus 10 of this embodiment allows the adsorbate to be physically adsorbed onto the etching target film under the condition that the pressure of the first process gas is at least a lower limit value predetermined according to the type of the first process gas and is less than the saturated vapor pressure of the first process gas. For example, if the first process gas is C4F8, the lower limit value predetermined according to the type of the first process gas is, for example, 0.5 Pa. By setting the pressure of the first process gas to be at least the lower limit value predetermined according to the type of the first process gas, the volatilization of the adsorbate can be suppressed.

[0064] Next, the flow of the etching method according to this embodiment will be briefly described. Figure 10 This is a flowchart showing an example of the flow of the etching method according to the embodiment.

[0065] The etching apparatus 10 circulates the refrigerant between the flow path 18 f and the cooling unit to cool the mounting table 16 and the wafer W to −115° C. or lower (step S11 ).

[0066] While cooling the wafer W, the etching apparatus 10 supplies C4F8 from the gas source assembly 40 into the chamber 12 under the condition that the pressure of C4F8 is lower than the saturated vapor pressure of C4F8 at the temperature of the wafer W, thereby causing the adsorbate to be physically adsorbed onto the etching target film (step S12). Step S12 is an example of a physical adsorption process. The C4F8 in step S12 is an example of a first process gas.

[0067] Etching apparatus 10 supplies Ar from gas source assembly 40 into chamber 12, replacing C₄F₂ with Ar (step S13). The Ar replacement of C₄F₂ reduces the partial pressure of C₄F₂, causing a portion of the adsorbate physically adsorbed to the etched film to volatilize. The remaining portion of the adsorbate remains non-volatile, remaining as a residue on the etched film. This adjusts the thickness of the adsorbate to a predetermined thickness. Step S13 is an example of a replacement process. The Ar in step S13 is an example of a third process gas.

[0068] The etching apparatus 10 supplies Ar gas from the gas source assembly 40 into the chamber 12 and applies first high-frequency power from the first high-frequency power supply 62 to the upper electrode 30, thereby generating Ar plasma in the chamber 12 to etch the target film (step S14). Step S14 is an example of an etching process. The Ar gas in step S14 is an example of a second process gas.

[0069] The etching apparatus 10 determines whether steps S12 to S14 have been repeated multiple times (step S15). If steps S12 to S14 have not been repeated multiple times ("No" in step S15), the etching apparatus 10 proceeds to step S12. Thus, the physical adsorption step, the replacement step, and the etching step are repeated multiple times.

[0070] On the other hand, when steps S12 to S14 are executed for a plurality of cycles (YES in step S15 ), etching apparatus 10 ends the etching method.

[0071] As described above, the etching method involved in this embodiment includes a physical adsorption step and an etching step. In the physical adsorption step, while cooling the object to be processed on which the etching target film is formed, the adsorbate based on the first process gas is physically adsorbed on the etching target film under the condition that the pressure ratio of the first process gas is the saturated vapor pressure of the first process gas relative to the temperature of the object to be processed. In the etching step, the adsorbate reacts with the etching target film using the plasma of the second process gas, thereby etching the etching target film. In this way, the thickness of the adsorbate can be controlled with high precision in units of atomic layers. As a result, the etching amount of the etching target film etched by the reaction with the adsorbate can be appropriately controlled to a desired amount. In this way, the uniformity of the etching amount within the surface of the object to be processed can be improved, and the difference in the etching amount between each object to be processed can be suppressed.

[0072] Furthermore, in the etching method according to this embodiment, during the physical adsorption step, when the adsorbate is physically adsorbed onto the etching target film, the temperature of the chamber walls in which the object to be processed is disposed is adjusted to a value higher than the temperature of the object to be processed. This can reduce the amount of adsorbate physically adsorbed onto the chamber walls.

[0073] Furthermore, in the etching method according to this embodiment, the physical adsorption step is continued until the adsorption amount of the adsorbate reaches saturation, thereby enabling the thickness of the adsorbate to be controlled to a desired thickness.

[0074] In the etching method according to this embodiment, the physical adsorption step and the etching step are repeated in a plurality of cycles, thereby enabling the etching amount in each repeated cycle to be controlled to a desired amount.

[0075] Furthermore, the etching method according to this embodiment further includes a replacement step of replacing the first process gas with a third process gas, thereby suppressing the occurrence of etching defects caused by the influence of residual gas.

[0076] In the etching method according to this embodiment, the third process gas is the same as the second process gas, thereby suppressing etching defects caused by switching the process gases.

[0077] Furthermore, in the etching method according to this embodiment, the etching step is continued until the reaction between the adsorbate and the film to be etched is completed, thereby achieving self-controlled etching.

[0078] In the etching method according to this embodiment, the first processing gas includes a CF-based gas. This allows the etching amount of the etching target film to be appropriately controlled to a desired amount by the reaction with the adsorbate based on the CF-based gas.

[0079] Furthermore, in the etching method according to this embodiment, during the physical adsorption step, the adsorbate is physically adsorbed onto the etching target film while the target object is cooled to a temperature of -115°C or lower. This prevents the adsorbate from completely volatilizing before etching, thereby enabling stable etching of the target film.

[0080] Furthermore, in the etching method according to this embodiment, in the physical adsorption step, the adsorbate is physically adsorbed onto the etching target film under the condition that the pressure of the first process gas is at least a lower limit value predetermined according to the type of the first process gas and is less than the saturated vapor pressure of the first process gas. This can suppress volatilization of the adsorbate.

[0081] In the etching method according to the present embodiment, the first process gas is C 4 F 8 , and the pressure of the first process gas is greater than or equal to 0.5 Pa. This can suppress the volatilization of adsorbates based on C 4 F 8 .

[0082] In the etching method according to this embodiment, the second processing gas includes a rare gas, thereby allowing the adsorbate to react with the etching target film using the plasma of the rare gas.

[0083] [other]

[0084] In addition, the technology disclosed in the present application is not limited to the above-described embodiment, and various modifications can be made within the scope of the gist of the technology.

[0085] For example, in the above embodiment, the physical adsorption process is performed in a single step, but it can also be performed in two steps. For example, the physical adsorption process can also include a first step and a second step. In the first step, the adsorbate is physically adsorbed under the condition that the pressure of the first process gas is higher than the pressure at which the adsorbate is saturated. In the second step, the adsorbate is physically adsorbed under the condition that the pressure of the first process gas is at the pressure at which the adsorbate is saturated. This can shorten the time required for the adsorbate to be saturated to a fixed adsorption amount.

[0086] Furthermore, in the above-described embodiment, the pressure of the first process gas and the temperature of the object to be processed (wafer W) are not changed during the repetition of the physical adsorption step and the etching step. However, this is not limited to the disclosed technology. For example, at least one of the pressure of the first process gas and the temperature of the object to be processed may be changed each time the physical adsorption step and the etching step are repeated. This allows the etching amount to be varied as the etching proceeds.

[0087] Furthermore, in the above embodiment, an example of performing a replacement step between the physical adsorption step and the etching step to replace the first process gas with a third process gas is described. However, this is not limited to the disclosed technology. For example, an exhaust step to exhaust the first process gas may also be included between the physical adsorption step and the etching step.

[0088] In the above embodiment, an exhaust step of exhausting the second process gas may be included after the etching step. In the above embodiment, a replacement step of replacing the second process gas with a fourth process gas may be included after the etching step.

[0089] Furthermore, the embodiments disclosed herein are intended to be illustrative in all respects and are not restrictive. In practice, the embodiments described above can be implemented in a variety of ways. Furthermore, the embodiments described above can be omitted, replaced, or modified in various ways without departing from the scope of the appended claims and their gist.

Claims

1. An etching method comprising the following steps: a physical adsorption step of cooling the object on which the etching target film is formed and causing an adsorbate based on the first process gas to be physically adsorbed onto the etching target film under a condition where the pressure of the first process gas is lower than the saturated vapor pressure of the first process gas at the temperature of the object; a replacement step of replacing the first process gas with a third process gas that volatilizes a portion of the adsorbent to adjust the thickness of the adsorbent; as well as In the etching step, the plasma of the second process gas is used to cause the adsorbate to react with the etching target film, thereby etching the etching target film.

2. The etching method according to claim 1, wherein In the physical adsorption step, when the adsorbate is physically adsorbed on the etching target film, the temperature of the wall of the chamber in which the object to be processed is arranged is adjusted to a value higher than the temperature of the object to be processed.

3. The etching method according to claim 1 or 2, wherein: The physical adsorption process is continued until the adsorption amount of the adsorbate is saturated.

4. The etching method according to claim 1, wherein The physical adsorption process includes the following steps: a first step of physically adsorbing the adsorbate under a condition in which the pressure of the first process gas is higher than a pressure at which the adsorption amount of the adsorbate is saturated; as well as In the second step, the adsorbate is physically adsorbed under the condition that the pressure of the first process gas is a pressure at which the adsorption amount of the adsorbate is saturated.

5. The etching method according to claim 1, wherein The physical adsorption step and the etching step are repeated for a plurality of cycles.

6. The etching method according to claim 5, wherein: Whenever the physical adsorption step and the etching step are repeated, at least one of the pressure of the first processing gas and the temperature of the object to be processed is changed in the physical adsorption step.

7. The etching method according to claim 1, wherein: An exhaust step of exhausting the first processing gas is included between the physical adsorption step and the etching step.

8. The etching method according to claim 1, wherein The third process gas is the same as the second process gas.

9. The etching method according to claim 1, wherein: The etching process is continued until the reaction between the adsorbate and the etching target film is completed.

10. The etching method according to claim 1, wherein After the etching step, an exhaust step of exhausting the second processing gas is further included.

11. The etching method according to claim 1, wherein: After the etching process, a replacement process of replacing the second process gas with a fourth process gas is further included.

12. The etching method according to claim 1, wherein: The first processing gas includes a CF-based gas.

13. The etching method according to claim 1, wherein: In the physical adsorption step, the adsorbate is physically adsorbed onto the etching target film while the target object is cooled to a temperature of -115°C or lower.

14. The etching method according to claim 1, wherein: In the physical adsorption step, the adsorbate is physically adsorbed onto the etching target film under the condition that the pressure of the first process gas is greater than or equal to a lower limit value determined in advance according to the type of the first process gas and less than the saturated vapor pressure of the first process gas.

15. The etching method according to claim 14, wherein: The first processing gas is C4F8, The pressure of the first processing gas is greater than 0.5 Pa.

16. The etching method according to claim 1, wherein: The second process gas includes a rare gas.

17. An etching device comprising: a chamber in which the object to be processed is disposed; an exhaust portion for reducing the pressure in the chamber; a gas supply portion for supplying a processing gas into the chamber; and A control unit that performs a physical adsorption process, a replacement process, and an etching process. In the physical adsorption process, while cooling a target object formed with an etching target film, an adsorbate based on the first processing gas is physically adsorbed on the etching target film under a condition that the pressure of the first processing gas is lower than the saturated vapor pressure of the first processing gas for the temperature of the target object. In the replacement process, the first processing gas is replaced by a third processing gas that volatilizes a portion of the adsorbate to adjust the thickness of the adsorbate. In the etching process, the adsorbate is reacted with the etching target film using the plasma of the second processing gas, thereby etching the etching target film.

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