Etching method and substrate processing device

Abstract

An etching method is provided that can improve the selectivity of an underlayer relative to an etching target film. The etching method includes: preparing a substrate having a laminated film formed thereon within a processing container, the laminated film comprising at least a silicon-containing insulating layer, an underlayer disposed below the silicon-containing insulating layer, and a mask layer disposed above the silicon-containing insulating layer; supplying a processing gas containing at least a fluorocarbon gas and a rare gas; and generating plasma within the processing container supplied with the processing gas to etch the laminated film, wherein the rare gas includes a first gas having an ionization energy higher than that of Ar gas and ionized individual particles having a momentum lower than that of individual particles of the ionized Ar gas.

Description

Technical Field

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

[0002] In the manufacture of three-dimensional stacked semiconductor memories such as 3D-NAND flash memories, there is an etching process that uses plasma to form multiple holes in a stacked film. As an example of an etching process for forming a 3D-NAND device structure, there is a process in which, when etching holes in a silicon oxide layer, the silicon layer of the substrate and the metal layer located in the middle are etched simultaneously and highly selectively. In this etching process, shallow holes are formed that expose the metal layer located in the middle of the silicon oxide layer, and deeper holes are formed that expose the silicon layer located below the metal layer. At this time, a process is required in which the selectivity of the base metal film relative to the silicon oxide layer is relatively high. In addition, in addition to the device structure of 3D-NAND, a process is also expected in which the selectivity of the base layer relative to the etching target film is relatively high and the loss of the base layer is small.

[0003] One method to ensure a high selectivity is to form a protective film on the tungsten layer using process conditions with high deposition efficiency. For example, Patent Document 1 proposes a plasma treatment method that forms a protective film on the surface of the etch stop layer while etching the oxide layer, thereby preventing clogging of the pore openings.

[0004] Patent document 2 proposes a method that supplies a processing gas containing at least fluorocarbon gas or hydrofluorocarbon gas, oxygen, nitrogen, and CO in order to achieve both metal layer selectivity and mask selectivity, and generates plasma in a processing container supplied with the processing gas to etch the stacked film.

[0005] <Prior Art Literature>

[0006] <Patent Document>

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-090022

[0008] Patent Document 2: (Japanese) Patent Publication No. 2019-036612 Summary of the Invention

[0009] <Problems to be Solved by the Invention>

[0010] The present disclosure provides an etching method capable of improving the selectivity of an underlying layer with respect to an etching target film.

[0011] <Methods used to solve the problem>

[0012] According to one embodiment of the present disclosure, an etching processing method is provided, comprising: a process of preparing a substrate on which a stacked film is formed in a processing container, the stacked film having at least a silicon-containing insulating layer, a base layer arranged below the silicon-containing insulating layer, and a mask layer arranged above the silicon-containing insulating layer; a process of supplying a processing gas containing at least a fluorocarbon gas and a rare gas; and a process of generating plasma in the processing container supplied with the processing gas to etch the stacked film, wherein the rare gas contains a first gas having an ionization energy higher than that of an Ar gas, and an ionized single particle having a momentum lower than the momentum of a single particle of the ionized Ar gas.

[0013] <Effects of the Invention>

[0014] According to one aspect, the selectivity of the base layer with respect to the film to be etched can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A diagram showing a stacked film of a 3D NAND flash memory.

[0016] Figure 2 is a diagram illustrating an example of a structure of a substrate processing apparatus according to an embodiment.

[0017] Figure 3 1 is a diagram illustrating the selection and effects of gas species in an etching method according to one embodiment.

[0018] Figure 4 This is a diagram showing the relationship between various rare gases, plasma electron density, and plasma electron temperature.

[0019] Figure 5 This is a graph showing the relationship between plasma electron temperature and gas dissociation degree.

[0020] Figure 6 is a graph showing the relationship between the degree of dissociation and the deposition rate on each surface of the pore.

[0021] Figure 7 is a graph showing the relationship between plasma electron temperature and gas dissociation.

[0022] Figure 8 is a graph showing one example of an adsorption coefficient and deposited polymer according to one embodiment.

[0023] Figure 9 : is a graph showing the relationship between the type of rare gas used in an etching method according to one embodiment and the loss of the tungsten layer.

[0024] Figure 10is a graph showing the relationship between the ratio of Ar / He and the luminous intensity of CF 2 according to one embodiment.

[0025] Figure 11 is a graph showing the relationship between the pressure of each gas and the sputtering yield.

[0026] Figure 12 This is a diagram for explaining the momentum of ions.

[0027] Figure 13 is a flowchart illustrating an etching process method according to one embodiment.

[0028] Figure 14 It is a diagram for explaining an etching method according to one embodiment. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals, and overlapping descriptions may be omitted.

[0030] For example, in MLC multi-level contact (hereinafter also referred to as "MLC") which is a process of 3D NAND, Figure 1 As shown, a tungsten layer (W) 130 serving as an electrode is formed in a stepwise manner at different depths, and a silicon oxide layer (SiO2) 140 located on the tungsten layer (W) 130 is etched. In this example, the tungsten layer 130 and the silicon oxide layer 140 have a stacked structure, forming a stacked film. The tungsten layer 130 may have a multilayer structure of, for example, 60 to 200 layers.

[0031] At this time, the oxide layer 140 is etched all at once until it reaches the respective depths of the tungsten layer 130 located at different depths above the silicon layer (Si) 110 and the silicon nitride layer (SiN) 120. As the number of stacked layers increases with device structure generations, the aspect ratio (AR) becomes significantly higher, and therefore the depth loading becomes more pronounced, leading to a predicted significant increase in etching time.

[0032] Therefore, it is necessary to increase the selectivity of the tungsten layer 130 to the silicon oxide layer 140 during a long etching time. In particular, for tungsten layers 130 located relatively shallow among the multiple tungsten layers 130, the overetching time after the tungsten is exposed becomes longer. Therefore, a high selectivity of the tungsten layer 130 to the silicon oxide layer 140 is required. Furthermore, in structures other than MLC, a process that achieves a high selectivity of the base layer to the etched film and minimizes base layer loss is also desired.

[0033] Therefore, in the etching method according to this embodiment, a process gas containing at least a fluorocarbon gas and a rare gas is supplied. In this case, the rare gas includes a first gas having a higher ionization energy than Ar gas and a lower momentum of individual ionized particles than that of individual ionized Ar gas particles. Plasma is generated within the process container supplied with the first gas to etch the stacked film.

[0034] During the period from immediately after the tungsten layer 130 is exposed by etching the silicon oxide layer 140 to the formation of the protective film on the tungsten layer 130, the tungsten layer 130 is sputtered by ions of the rare gas. However, the first gas included in the rare gas used in this etching method is a gas having a higher ionization energy than that of the Ar gas, and the momentum of the ionized individual particles is lower than the momentum of the individual particles of the ionized Ar gas. Therefore, the sputtering yield is low, and the loss of the tungsten layer 130 can be reduced accordingly. In addition, since a high dissociation and low adsorption coefficient are generated, and a protective film is formed on the exposed tungsten layer 130, the loss of the tungsten layer 130 can be further reduced.

[0035] The following describes an etching processing method and a substrate processing apparatus according to the present embodiment, which improve the selectivity of the silicon oxide layer 140 to the underlying tungsten layer 130 while maintaining the etching rate (etching speed) of the silicon oxide layer 140 as the etching target film.

[0036] It should be noted that in the following description of one embodiment, He gas is used as an example of the first gas included in the rare gas used in the etching method, but the invention is not limited thereto. The first gas can be any gas as long as it has a higher ionization energy than Ar gas and the momentum of a single ionized particle is lower than the momentum of a single ionized Ar gas particle.

[0037] Furthermore, although the silicon oxide layer 140 is used as an example of an etching target film, the etching target film is not limited thereto, and any insulating layer containing silicon can be used. Other examples of insulating layers containing silicon include a silicon carbide layer, a stacked structure of a silicon oxide layer and a silicon nitride layer, and a low-k film layer such as silicon oxide containing an organic substance.

[0038] In addition, although the tungsten layer 130 is cited as an example as the base layer for the etching target film, the base layer is not limited to this, and any conductive layer can be used. Other examples of the conductive layer may be a metal layer or a silicon layer. As a metal layer, in addition to tungsten, titanium (Ti), aluminum (Al), and copper (Cu) may also be cited. It should be noted that as an example of a silicon layer, a conductive silicon-containing layer such as polycrystalline silicon (Poly-Si) or amorphous silicon may be cited.

[0039] Furthermore, in processes for structures other than MLC, it is sometimes desirable for the base layer to have a high selectivity with respect to the film being etched, and for the base layer to have minimal loss. In such structures, the base layer relative to the film being etched is not limited to a conductive layer such as a metal layer or a silicon layer. For example, in a self-aligned contact (SAC) structure, where the film being etched is a silicon oxide film and the base layer is a silicon nitride film, or in a via structure, where the film being etched is at least one of a silicon oxide layer and a low-k film layer, and the base layer is at least one of a silicon carbide layer and a silicon carbonitride layer, minimal loss of the base layer is also desirable.

[0040] [Structure of substrate processing apparatus]

[0041] First, refer to Figure 2 An example of the structure of a substrate processing apparatus for executing the etching processing method according to the present embodiment will be described. Figure 2 1 is a diagram showing an example of a structure of a substrate processing apparatus according to an embodiment. Here, a capacitively coupled plasma etching apparatus is cited as an example of the substrate processing apparatus 1 .

[0042] The substrate processing apparatus 1 includes a processing container 2 made of a conductive material such as aluminum, and a gas supply source 11 for supplying gas into the processing container 2. The processing container 2 is electrically grounded. Inside the processing container 2 are located a lower electrode 21 and an upper electrode 22 arranged opposite and parallel to the lower electrode 21. The lower electrode 21 also serves as a stage for placing a substrate W.

[0043] The lower electrode 21 is connected to a first high-frequency power source 32 via a first matching box 33, and to a second high-frequency power source 34 via a second matching box 35. The first high-frequency power source 32 applies a first high-frequency power (high-frequency power HF for plasma generation) having a frequency of, for example, 27 MHz to 100 MHz to the lower electrode 21. The second high-frequency power source 34 applies a second high-frequency power (high-frequency power LF for ion attraction) having a lower frequency than that of the first high-frequency power source 32, for example, 400 kHz to 13 MHz, to the lower electrode 21.

[0044] It should be noted that the first high-frequency power source 32 can be connected to the upper electrode 22 via the first matching unit 33. In addition, the first high-frequency power source 32 and the second high-frequency power source 34 can apply the first high-frequency power and the second high-frequency power while intermittently (pulsed) changing the output value of the first high-frequency power and the output value of the second high-frequency power between no output (0 W) and a maximum value in a synchronous or asynchronous manner.

[0045] The first matching device 33 matches the load impedance with the internal (or output) impedance of the first high-frequency power supply 32. The second matching device 35 matches the load impedance with the internal (or output) impedance of the second high-frequency power supply 34. This serves to clearly match the internal impedance of the first high-frequency power supply 32 and the load impedance of the second high-frequency power supply 34 when plasma is generated within the processing chamber 2.

[0046] The upper electrode 22 is mounted on the top of the processing chamber 2 via a shield ring 41 that covers the periphery of the upper electrode 22. The upper electrode 22 is provided with a gas inlet 45 for introducing gas from the gas supply source 11, and a diffusion chamber 50 for diffusing the introduced gas. Gas output from the gas supply source 11 is supplied to the diffusion chamber 50 via the gas inlet 45, and then supplied from the hole 28 to the processing space U through the gas flow path 55. In this way, the upper electrode 22 also functions as a gas showerhead.

[0047] It should be noted that a direct current (DC) power supply (not shown) may be connected to the upper electrode 22. The DC power supply may apply a DC voltage to the upper electrode 22. Furthermore, the DC power supply may apply the DC voltage while intermittently (pulsing) varying the output value of the DC voltage between no output (0 W) and a maximum value, either synchronously or asynchronously with the first high-frequency power supply 32.

[0048] An exhaust port 60 is formed on the bottom surface of the processing container 2. An exhaust device 65 connected to the exhaust port 60 exhausts the interior of the processing container 2. This maintains the interior of the processing container 2 at a predetermined vacuum level. A gate valve G is provided on the sidewall of the processing container 2. The gate valve G opens and closes the loading and unloading entrance when substrates W are loaded into and unloaded from the processing container 2.

[0049] The substrate processing device 1 is provided with a control unit 70 for controlling the operation of the entire device. The control unit 70 has a CPU 71, a ROM 72, and a RAM 73. The basic program executed by the control unit 70 is stored in the ROM 72. The process is stored in the RAM 73. The control information of the substrate processing device 1 for the process conditions (etching conditions) is set in the process. The control information includes processing time, pressure (gas exhaust), high-frequency power or voltage, various gas flow rates, chamber temperature (such as the set temperature of the substrate), etc. It should be noted that the process can be stored in a hard disk or a semiconductor memory. In addition, the process can be set at a predetermined location in the storage area in a state of being stored in a portable computer-readable storage medium such as a CD-ROM or DVD.

[0050] The CPU 71 controls the entire substrate processing apparatus 1 based on a basic program stored in the ROM 72. The CPU 71 controls the supply of predetermined gases according to the steps of the recipe stored in the RAM 73 and controls the substrate W to perform the required processing such as etching.

[0051] [Rationalization of process gas]

[0052] Next, the rationalization of the process gas that can achieve both maintaining the etching rate of the silicon oxide layer 140 and improving the selectivity of the silicon oxide layer 140 to the underlying tungsten layer 130 in the etching process method using the substrate processing apparatus 1 is described. In this embodiment, a substrate W having a stacked film formed thereon is processed. In this stacked film, a silicon layer 110, a tungsten layer 130, a silicon oxide layer 140, and a mask layer 100 are stacked in this order (see FIG. 1 ). Figure 8 ).

[0053] In the etching method according to this embodiment, the process gas contains at least a fluorocarbon gas and a rare gas, and includes a step of supplying the process gas and a step of generating plasma in the process space U supplied with the process gas to etch the stacked film.

[0054] The fluorocarbon gas used may be at least one of C4F6 gas, C4F8 gas, C3F8 gas, C6F6 gas, and C5F8 gas.

[0055] The ionization energy of He gas is "2372.3 (kJ / mol)", which is greater than the ionization energy of Ar gas "1520.6 (kJ / mol)". Therefore, among the rare gases used, He gas is used as an example of a first gas whose ionization energy is higher than that of Ar gas and whose ionized single particles have a momentum lower than that of a single particle of ionized Ar gas. However, the first gas is not limited to this, and for example, Ne gas with an ionization energy of "2080.7 (kJ / mol)" or a mixed gas of He gas and Ne gas may also be used. The first gas may also be a mixed gas of Ar gas and at least one of He gas and Ne gas. It should be noted that the characteristic point of the first gas "the momentum of a single ionized particle is lower than that of a single particle of ionized Ar gas" will be explained later.

[0056] In addition to the above-mentioned fluorocarbon gases and rare gases, the process gas may also include O2 gas, CO gas, N2 gas, and H2 gas. In addition, it may also include halogen-containing gases such as Cl2, HBr, CF4, CHF3, and NF3.

[0057] [Gas Type Selection and Effects in Etching Process]

[0058] Next, refer to Figure 3 The selection of gas species and the effects thereof in the etching method according to this embodiment will be described. Figure 3 1 is a diagram illustrating the selection and effects of gas species in an etching method according to one embodiment.

[0059] In the etching method according to this embodiment, the fluorocarbon gas used is C4F6 gas, and the rare gas used is He gas. In the comparative example, the fluorocarbon gas used is C4F6 gas, and the rare gas used is Ar gas. That is, in the etching method according to this embodiment, the rare gas is changed from the Ar gas used in the comparative example to He gas, which is lighter than Ar gas. Ar gas is an example of a heavy noble gas, and He gas is an example of a light noble gas because it is lighter than Ar gas.

[0060] Figure 4 This is a diagram showing the relationship between various rare gases, plasma electron density, and plasma electron temperature. Figure 4 The horizontal axis represents the distance from the microwave radiation window for introducing a microwave power of 2.45 GHz, the vertical axis (right) represents the plasma electron density (Ne), and the vertical axis (left) represents the plasma electron temperature (Te). Figure 4The curve shows that when the gas type changes from Ar gas to He gas, the plasma electron density decreases and the plasma electron temperature (Te) increases. The reason for this is explained below.

[0061] The ionization energy of He gas is "2372.3 kJ / mol", which is greater than the ionization energy of Ar gas "1520.6 kJ / mol". Since ionization energy is the energy required to separate electrons from atoms or molecules for ionization, the energy of He gas to attract electrons from the outermost shell of the electron orbit is higher than that of Ar gas. Therefore, He gas is more difficult to ionize than Ar gas, and the plasma electron density in the case of He gas is lower than that of Ar gas. If the plasma electron density is low, the temperature applied to each particle in the plasma is higher. Therefore, if Figure 4 As shown, when the gas type of the rare gas is changed from Ar gas, which is an example of a heavy rare gas, to He gas, which is an example of a light rare gas, the plasma electron density decreases and the plasma electron temperature increases.

[0062] As the plasma electron temperature rises, the energy of each electron increases. Therefore, when the electrons collide with the gas, the gas dissociates more easily, generating highly dissociated free radicals or precursors of further ionized ions. These precursors contribute to polymer deposition. Radical precursors act isotropically from the plasma toward the substrate W, while ionic precursors act anisotropically. Furthermore, the precursors deposited on the film to be etched interact with the rare gas ions attracted to the substrate W by the high-frequency power LF, acting as an etchant and promoting etching of the film. Figure 5 The horizontal axis represents the plasma electron temperature and shows the relationship between the dissociation degree of C4F6 gas. If the plasma electron temperature is low, it is difficult to promote the dissociation of C4F6 gas, and the precursors with low dissociation (C3F4 radicals, C3F4 + ions, etc.), and highly dissociated precursors (CF2 radicals, CF2 + ions, etc.). If the plasma electron temperature increases, the dissociation of C4F6 gas increases, the highly dissociated CF radicals increase, and the low dissociated precursors decrease. Therefore, if the heavy noble gas is changed to a light noble gas, the low dissociated precursors in the plasma decrease, and the highly dissociated precursors increase. That is, if the heavy noble gas is changed to a light noble gas, the precursors with higher adsorption coefficients (adsorption power) such as C3F4 decrease, and the precursors with lower adsorption coefficients such as CF2 increase. However, if Figure 6 and Figure 7As shown, both highly dissociated precursors and low-dissociated precursors are present in the plasma generation region P generated in the processing space U, and the ratio of the highly dissociated precursor to the low-dissociated precursor is changed. By changing the noble gas used in etching from Ar gas to He gas, the highly dissociated precursor with a low adsorption coefficient can be relatively more abundant than the low-dissociated precursor with a high adsorption coefficient. The precursors generated in the plasma generation region P are supplied to the substrate W through the sheath region S.

[0063] It should be noted that the C2F2 radical and C2F + Ion precursors have characteristics between those of low-dissociation precursors and those of high-dissociation precursors. Figure 5 The dissociation pattern of C4F6 gas is shown in FIG. 3 , but dissociation is also promoted by the plasma electron temperature in C4F8 gas, C3F8 gas, C6F6 gas, and C5F8 gas used as fluorocarbon gas other than C4F6 gas. Depending on the type of gas used, CF3 radicals, CF3 + ion precursors.

[0064] Thus, the adsorption coefficient of the low dissociation precursor is higher, e.g. Figure 7 As shown by the arrow "←" from left to right in the sheath region S of the C3F4, it is easy to adhere to the upper surface of the mask layer 100 or the upper part (side) of the hole opening. Therefore, the low-dissociation precursor is consumed on the upper surface or side of the mask layer 100 to form a polymer 105, and it is difficult to reach the bottom surface or side of the hole H formed in the silicon oxide layer 140. It should be noted that Figure 8 As shown, the mask layer 100 is located on the silicon oxide layer 140 and can be an organic film or other materials.

[0065] In contrast, the adsorption coefficients of highly dissociated precursors are lower, e.g. Figure 7 As shown by the arrow "→" pointing from right to left in the sheath region S of the mask layer 100, the precursor is less likely to adhere to the upper surface or side surfaces of the mask layer 100. As a result, the highly dissociated precursor is not consumed on the upper surface or side surfaces of the mask layer 100, but rather, as shown by the downward arrow "→" in the hole H, easily reaches the side surfaces or bottom surface of the hole H formed in the silicon oxide layer 140. Therefore, the highly dissociated precursor is more likely to form polymers 105 on the side surfaces or bottom surface of the hole formed in the silicon oxide layer 140 than the low-dissociated precursor.

[0066] In summary, the precursor with high dissociation and low adsorption coefficient is difficult to adhere to the upper surface or side surface of the mask layer 100, and is easy to adhere to the side surface or bottom surface of the hole H. Figure 3As shown, by reducing the amount of precursors with low dissociation and high adsorption coefficients and increasing the amount of precursors with high dissociation and low adsorption coefficients, the pores are less likely to be clogged and more precursors can be supplied to the tungsten layer 130 exposed at the bottom of the pores. To this end, it is important to optimize the process conditions in such a way as to promote the dissociation of the C4F6 gas, reduce low-dissociation radicals such as C2F4 or C2F3, and increase high-dissociation radicals such as CF2 or CF.

[0067] For this reason, in the etching method according to this embodiment, He gas, which has a lower mass than Ar gas, is used as the rare gas. This can reduce the amount of precursors with a high adsorption coefficient and increase the amount of precursors with a low adsorption coefficient.

[0068] use Figure 8 The stacked film is further described. If the low dissociation precursors such as C2F4 or C3F4 increase, then Figure 8 As shown in (a), polymer 105 is deposited on the upper surface or the opening (side surface) of mask layer 100, which is prone to clogging (see A). In addition, since the precursor is consumed on the upper surface or the side surface of mask layer 100, less precursor reaches tungsten layer 130 at the bottom of hole H or the side surface deep inside hole H, making it difficult for polymer 105 to deposit on tungsten layer 130 (see B).

[0069] The higher the plasma electron temperature, the more the dissociation of C4F6 gas is enhanced, the less the precursor with higher adsorption coefficient is, and the more the precursor with lower adsorption coefficient is. Figure 8 As shown in (b), the polymer 105 is less likely to be deposited on the upper surface or opening of the mask layer 100, making it less likely to be blocked (see A'). In addition, less precursor is consumed on the upper surface or side surfaces of the mask layer 100, and more precursor reaches the tungsten layer 130 at the bottom of the hole H or the side surfaces deep inside the hole H, thereby depositing more polymer 105 on the tungsten layer 130 (see B').

[0070] Therefore, compared to the comparative example using Ar gas as the rare gas, in the etching method according to this embodiment using He gas as the rare gas, clogging of the upper portion of the opening of the etched hole H is suppressed, and CF-based radicals easily enter the bottom of the hole H. Therefore, the etching rate of the silicon oxide layer 140 can be maintained by sufficiently supplying the etchant. In addition, by forming the polymer 105 as a protective film on the tungsten layer 130, which is the base layer of the silicon oxide layer 140, the selectivity of the tungsten layer 130 with respect to the silicon oxide layer 140 can be improved.

[0071] Therefore, it is possible to suppress the loss of the base layer (reduce damage to the base layer). Furthermore, by suppressing clogging of the upper portion of the opening of hole H, the etching shape of silicon oxide layer 140 can be made more vertical, without becoming curved. Furthermore, by suppressing clogging and ensuring the opening size of hole H, the amount of precursor or rare gas ions entering hole H is increased, thereby increasing the amount of precursor or rare gas ions reaching the bottom of hole H. Consequently, by promoting the etching of the etching target film, productivity is improved, and the polymer 105 serving as a protective film is formed more efficiently.

[0072] [Experimental Results]

[0073] Figure 9 The experimental results show the relationship between the type of rare gas used in etching methods according to one embodiment and a comparative example and the loss of tungsten layer 130. The experiments were conducted using the same process conditions for high-frequency power, pressure within the processing chamber, and process gases other than the rare gas in the etching methods according to one embodiment and the comparative example. Line E represents the loss of tungsten layer 130 when Ar gas was used as the rare gas in the etching method according to the comparative example, while Line F represents the loss of tungsten layer 130 when He gas was used as the rare gas in the etching method according to the present embodiment. Figure 9 The horizontal axis represents the over-etch target (Over Etch Target (%)), and the vertical axis represents the normalized loss of the tungsten layer 130. The over-etch target is expressed as a percentage of the etching time after the tungsten layer 130 is exposed, with the etching time from the start of etching the silicon oxide layer 140 to the exposure of the tungsten layer 130 being 100%. For example, 100% on the horizontal axis means that the etching time after the tungsten layer 130 is exposed is the same as the etching time required to etch the silicon oxide layer 140 until the tungsten layer 130 is exposed.

[0074] It should be noted that the tungsten layer 130 is sputtered by the rare gas ions from the moment the silicon oxide layer 140 is etched and the tungsten layer 130 is exposed to the moment the protective film is formed on the tungsten layer 130. However, since the period until the protective film is formed is short and excessively long, it is not easy to accurately measure the sputtering rate of the tungsten layer 130 during this period. Figure 9 The y-axis intercept of line E and line F in FIG. 5 is taken as the loss amount of the tungsten layer 130 due to sputtering, and is considered to be proportional to the sputtering rate.

[0075] The amount of tungsten layer 130 lost when exposed when Ar gas is used as the rare gas is set to 1. When Ar gas is used as the rare gas, the higher the percentage of the overetch target, the greater the loss. For example, when the overetch target is 100%, the loss of tungsten layer 130 increases by approximately 40%.

[0076] In contrast, when He gas was used as the rare gas, the loss of the tungsten layer 130 due to sputtering was less than that of the comparative example using Ar gas, and the loss due to sputtering was improved by 26%. In addition, when the overetching target was 100%, the loss of the tungsten layer 130 increased slightly, and the loss rate was improved by 82% compared to the comparative example using Ar gas. In this case, the loss rate represents Figure 9 The slopes of lines E and F in .

[0077] In addition, according to experimental results, when compared with an over-etching target of 100%, in the etching processing method according to this embodiment, by changing the rare gas in the processing gas from Ar gas to He gas, the thickness of the polymer on the tungsten layer 130 can be deposited 57% more than that of the comparative example.

[0078] Furthermore, after processing with an overetching target of 100%, the loss of tungsten layer 130 was reduced by 34% compared to the comparative example. Meanwhile, the etching rate of silicon oxide layer 140 decreased by only 7% compared to the comparative example. Therefore, the selectivity of tungsten layer 130 to silicon oxide layer 140 improved by 50% compared to the comparative example. Furthermore, the etching rate of organic film mask layer 100 increased by 16% compared to the comparative example.

[0079] The above experimental results indicate that the etching method according to this embodiment using He gas as a rare gas can improve the selectivity of the tungsten layer 130 to the silicon oxide layer 140 while maintaining the etching rate of the silicon oxide layer 140 .

[0080] Next, refer to Figure 10 Experimental results of the emission intensity of CF2 radicals present in plasma relative to the ratio of Ar / He gas according to one embodiment are described. Figure 10 : is a graph showing the relationship between the ratio of Ar / He gas and the luminous intensity of the wavelength representing CF2 radicals according to one embodiment.

[0081] Figure 10 The horizontal axis shows, from left to right, the case where only Ar gas was used as the noble gas in the etching process; the case where the ratio of Ar gas to He gas was approximately 2:1; the case where the ratio of Ar gas to He gas was approximately 1:2; and the case where only He gas was used. The total flow rate of the noble gas was controlled to be the same in all cases. Under these conditions, the emission intensity at a wavelength representing CF2 radicals in the plasma was measured.

[0082] The results of the measurements show that the more the ratio of He gas to Ar gas increases, the Figure 10The greater the luminous intensity of the wavelength of the CF2 radical shown on the vertical axis. From the above, it can be seen that in order to promote the high dissociation of the reaction gas, He is preferably used as the rare gas used in the etching treatment method according to this embodiment. In addition, it can be seen that even if it is not a single gas of He gas, as long as it is not a single gas of Ar gas, by controlling the ratio of He gas to Ar gas, the dissociation degree of C4F6 gas can be controlled, and the ratio of the precursor with a higher adsorption coefficient to the precursor with a lower adsorption coefficient can be controlled. In this way, the amount of the precursor deposited on the upper surface or side (opening) of the hole and the amount of the precursor deposited on the bottom or side of the hole or their ratio can be controlled.

[0083] For example, in Figure 1 When etching the stacked film shown in FIG. 1 , the ratio of Ar gas to He gas can be controlled as follows. However, this etching method is an example of controlling Ar gas and He gas, and is not limited thereto. Figure 1As shown, when the tungsten layer 130 is located at different depths with significant differences, during the etching process to expose the tungsten layer 130 located in the shallower region, only Ar gas or a mixed gas in which He gas is mixed at a first ratio to Ar gas can be used as a rare gas, and etching can be performed at a higher etching rate. Then, during the etching process to expose the tungsten layer 130 located in the deeper region, a mixed gas in which He gas is mixed at a second ratio higher than the first ratio to Ar gas or only He gas can be used as a rare gas. Thus, by etching the shallower region using only Ar gas or a mixed gas in which Ar gas has a higher ratio to He gas, etching of the silicon oxide layer 140 can be accelerated compared to the case of using a mixed gas in which He gas has a higher ratio to Ar gas or using only He gas. Furthermore, by using only Ar gas or a mixed gas with a high ratio of Ar gas to He gas, a precursor with low dissociation and a high adsorption coefficient can be generated compared to the case of using a mixed gas with a high ratio of He gas to Ar gas or using only He gas. This allows the polymer 105 deposited thickly on the surface of the mask layer 100 to function as a protective film, and improves the selectivity of the mask layer 100 with respect to the silicon oxide layer 140. Furthermore, if the tungsten layer 130 is located in a relatively shallow area, even a precursor with low dissociation and a high adsorption coefficient can be sufficiently deposited on the surface of the tungsten layer 130, forming the polymer 105 as a protective film. On the other hand, by etching a relatively deep area using a mixed gas with a high ratio of He gas to Ar gas or using only He gas, the loss of the tungsten layer 130 can be reduced compared to the case of using only Ar gas or a mixed gas with a high ratio of Ar gas to He gas, without clogging the hole openings. That is, by controlling the ratio of Ar gas and He gas as rare gases according to the etching depth, it is possible to achieve a balance between the etching rate of the silicon oxide layer 140 , the selectivity of the tungsten layer 130 , and the selectivity of the mask layer 100 .

[0084] Alternatively, etching can be performed while repeating at least once a step of using only Ar gas or a mixed gas containing He gas at a first ratio to Ar gas as a rare gas, and a step of using a mixed gas containing He gas at a second ratio higher than the first ratio to Ar gas, or a step of using only He gas as a rare gas. In the step of using only Ar gas or a mixed gas containing a high ratio of Ar gas to He gas, a precursor with low dissociation and a high adsorption coefficient is generated, and polymer 105 is deposited thickly on the surface of mask layer 100. Then, in the step of using a mixed gas containing a high ratio of He gas to Ar gas or using only He gas, the deposited polymer 105 can function as a protective film, and etching can be performed while increasing the selectivity of mask layer 100 to silicon oxide layer 140. In other words, by repeatedly controlling the steps of using different ratios of Ar gas to He gas as rare gases, it is possible to balance the etching rate of silicon oxide layer 140, the selectivity of tungsten layer 130, and the selectivity of mask layer 100. At this time, in the step of using only Ar gas or a mixed gas in which the ratio of Ar gas to He gas is high, since the polymer 105 is deposited not only on the upper surface of the mask layer 100 but also on its side surfaces, it is preferable to adjust the processing time, etc. to a degree that does not clog the opening of the hole.

[0085] Furthermore, by combining a process of adjusting the ratio of Ar gas to He gas, which are noble gases, according to the etching depth, with a process of repeatedly controlling steps with different ratios of Ar gas to He gas, it is possible to further balance the etching rate of the silicon oxide layer 140, the selectivity of the tungsten layer 130, and the selectivity of the mask layer 100.

[0086] It should be noted that the ionization energy of Kr gas is "1350.8 (kJ / mol)", and the ionization energy of Xe gas is "1170.4 (kJ / mol)", which are smaller than the ionization energy of Ar gas, "1520.6 (kJ / mol)". In addition, the metastable energy level of Kr gas is "9.92 (eV)", and the metastable energy level of Xe gas is "8.32 (eV)", which are smaller than the metastable energy level of Ar gas, "11.55 (eV)". When Kr gas or Xe gas is used instead of Ar gas as the rare gas, it can be expected that a precursor with low dissociation and high adsorption coefficient will be generated, similar to when Ar gas is used, so that the polymer 105 deposited thickly on the surface of the mask layer 100 can act as a protective film and the selectivity of the mask layer 100 with respect to the silicon oxide layer 140 can be improved.

[0087] [The momentum of the ionized particle]

[0088] The above describes the operation, effects, and experimental results of the etching method according to this embodiment when He, which has a higher ionization energy than Ar gas, is used as the first gas included in the rare gas included in the processing gas.

[0089] Next, the reason why the first gas needs to satisfy not only the condition of "having an ionization energy higher than that of Ar gas" but also the condition of "being a gas whose ionized single particle has a momentum lower than that of a single particle of ionized Ar gas" will be explained.

[0090] If the tungsten layer 130 is exposed on the bottom surface of the hole, it will be sputtered by the incident ions. When Ar gas is used as the rare gas, the surface of the tungsten layer 130 is sputtered by Ar ions. When He gas is used as the rare gas, the surface of the tungsten layer 130 is sputtered by He ions.

[0091] Sputtering is a physical reaction in which atoms forming a solid are released into space due to the exchange of momentum when accelerated particles collide with a solid surface. The sputtering yield is the number of atoms released into space when ions collide with a solid surface. In other words, the sputtering yield of a solid surface when accelerated ions collide with the solid surface is proportional to the momentum of the accelerated ions.

[0092] Figure 11 is a graph showing the relationship between the pressure of each gas and the sputtering yield. Figure 11 The horizontal axis represents the pressure in the processing container, and the vertical axis represents the sputtering yield. Figure 11 The source of the sputtering phenomenon is a study of high-frequency rare gas plasma / Nagoya Institute of Technology Hiroji Masui [Nagoya Institute of Technology Bulletin 50 (1998)].

[0093] exist Figure 11 In the sputtering process, the sputtering yield is represented by the weight loss of the target when various gases collide with the target having a diameter of 60 mm. -3 At a pressure of 100 mmHg (mmHg), the sputtering yield of He is lower than that of Ar. Therefore, when using He gas, desorption due to ion collisions is less. Therefore, when using He gas as a rare gas, the sputtering rate tends to decrease compared to using Ar gas.

[0094] Figure 12 This diagram illustrates the momentum of ions. First, when the charge is q and the potential applied to the sheath region S between the plasma generation region P and the substrate W is E, the kinetic energy K of the ions in the plasma is expressed by equation (1). M is the mass of the ion, and v is the velocity of the ion.

[0095] [Number 1]

[0096]

[0097] Formula (2) is obtained by transforming formula (1).

[0098] [Number 2]

[0099]

[0100] Formula (3) is derived from the momentum P=mv of the ion and formula (2).

[0101] [Number 3]

[0102]

[0103] The mass of each particle of He ions is "4", which is less than the mass of each particle of Ar ions, "18". Therefore, according to formula (3), the momentum of each particle of He ions is less than the momentum of each particle of Ar ions. As described above, when He gas is used, the surface of the tungsten layer 130 is difficult to be sputtered compared to when Ar gas is used, which will act in the direction of reducing the sputtering rate of the tungsten layer 130. In addition, even if the surface of the tungsten layer 130 is sputtered when the tungsten layer 130 is exposed at the bottom of the hole and the sputtering rate of the tungsten layer 130 is increased, the precursor of the CF-based gas will then be deposited on the surface of the tungsten layer 130 and act as a protective film. Therefore, it was found that the loss amount of the tungsten layer 130 can be suppressed.

[0104] In contrast, the etching rate is determined by the interaction between surface adsorption of free radicals and desorption due to ion collisions. While desorption due to thermal energy also interacts with desorption due to ion collisions and surface adsorption of free radicals, in an environment where ions are attracted to the substrate W by high-frequency power LF, this contribution is low compared to desorption due to ion collisions and is therefore not considered here.

[0105] The etching rate is shown in formula (4).

[0106] [Number 4]

[0107]

[0108] In formula (4), k is the reaction probability of ionic desorption, E i is the ionization energy, Γ ion is the ion incident dose, “kE i Γ ion " is the item representing "desorption due to ion collision". In formula (4), s is the adsorption probability relative to the surface, Γ radical is the supply of free radicals, "s·Γradical " is an item indicating "surface adsorption of free radicals". It should be noted that n c Indicates the material of the film to be etched.

[0109] In formula (4), k (reaction probability of ion desorption) is proportional to the sputtering yield. When the sputtering yield is high, the etching rate tends to increase, and when the sputtering yield is low, the etching rate tends to decrease. Therefore, when He gas is used as the rare gas, the etching rate tends to decrease because the sputtering yield decreases compared to when Ar gas is used.

[0110] However, since He gas is used as a rare gas, the fluorocarbon gas is highly dissociated and a precursor with a low adsorption coefficient is generated. As a result, the radicals that will become the etchant are supplied to the bottom of the hole H, so that Γ ion Therefore, it is considered that the etching rate can be maintained even when He gas is used as the rare gas.

[0111] As described above, it can be seen that in order to suppress the loss of tungsten layer 130 and improve the selectivity of tungsten layer 130 to silicon oxide layer 140, it is important to ensure that the precursor reaches the tungsten layer 130 at the bottom of the hole and reduce the momentum of the ions. Therefore, in the etching method according to this embodiment, the rare gas contained in the process gas is changed from Ar gas to He gas. This can achieve an improvement in the selectivity of tungsten layer 130 to silicon oxide layer 140 while maintaining the etching rate of silicon oxide layer 140.

[0112] [Etching treatment method]

[0113] Next, refer to Figure 13 and Figure 14 An etching method according to one embodiment will be described. Figure 13 is a flowchart illustrating an etching process method according to one embodiment. Figure 14 This is a diagram for explaining an etching method according to one embodiment. Figure 2 The substrate processing device 1 is executed by Figure 2 The control unit 70 controls.

[0114] When the process starts, first, a substrate W formed with a stacked film is moved into a processing container 2 and placed on a lower electrode (carrier) 21 (step S1), in which a silicon layer 110, a tungsten layer 130, a silicon oxide layer 140, and a mask layer 100 are stacked in sequence.

[0115] Next, a fluorocarbon gas (C x F yA process gas consisting of He gas and Hg gas is supplied into the process container 2 (step S2). High-frequency power HF and LF are then applied from the first and second high-frequency power sources 32 and 34 to generate plasma (step S3). The stacked film is then etched (step S4), and the process is completed.

[0116] According to the etching method of this embodiment, during the etching of the stacked film, Figure 14 As shown in (a), the fluorocarbon gas such as C4F6 gas in the processing gas is highly dissociated. In addition, the silicon oxide layer 140 is formed by CF2, CF3 radicals or CF2 + CF3 + Ion precursor (shown as CF in the figure) x CF x + ) and He ion etching.

[0117] At this time, although the precursor is deposited at the bottom of the recess of the silicon oxide layer 140, it is simultaneously consumed as an etchant in the etching of the silicon oxide layer 140 due to the interaction with He ions and changes into volatile gases such as SiF4 and CO, so no polymer is formed as a deposit.

[0118] like Figure 14 As shown in FIG. 1( b ), when the etching of the silicon oxide layer 140 is completed and the tungsten layer 130 is exposed, the precursor is not consumed as an etchant and thus begins to be deposited as a polymer. However, immediately after the etching of the silicon oxide layer 140 is completed, the polymer has not yet been deposited on the surface of the exposed tungsten layer 130, and the surface of the tungsten layer 130 is mainly sputtered by He ions, resulting in the loss of the tungsten layer 130 (see symbol G).

[0119] Then, if Figure 14 As shown in (c), when the process is continued, the etching rate of the tungsten layer 130 decreases because the precursor is deposited as a polymer on the surface of the tungsten layer 130 and acts as a protective film (see symbol I).

[0120] As described above, according to the etching method of this embodiment, the selectivity of the base layer with respect to the film to be etched can be improved.

[0121] [Metastable energy levels of rare gases]

[0122] The potential of the metastable state of the first gas used in the etching treatment method according to the present embodiment is preferably higher than the potential of the metastable state of the Ar gas. For example, the metastable energy level of He gas is "19.82 (eV)", which is higher than the metastable energy level of Ar gas "11.55 (eV)". The metastable energy level of Ne gas or a mixed gas of He gas and Ne gas with a metastable energy level of "16.62 (eV)" is also greater than the metastable energy level of Ar gas. During the etching process, the rare gas is excited to the metastable state due to the interaction with the plasma. In the case of normal atoms or molecules being excited, the average time (spontaneous emission lifetime) to radiate energy such as light and spontaneously transition to the ground state again is microseconds or shorter. Since the spontaneous emission lifetime of the metastable state is on the order of 1 second, there may be a large amount of metastable rare gases with higher energy in the plasma generation space. The rare gases in the metastable state release energy due to collision and transition to the ground state.

[0123] Therefore, a large amount of metastable noble gases with relatively high energy are present in He and Ne gases, whose metastable energy levels are greater than that of Ar gas. As a result, these gases collide with fluorocarbon gases such as C4F6 gas in the sheath region S, which serves as a transport space to the plasma generation space or substrate W. This allows the degree of dissociation of the fluorocarbon gases to be controlled to be high.

[0124] Thus, in an etching method according to one embodiment, the use of He gas reduces the amount of polymers with a high adsorption coefficient and increases the amount of polymers with a low adsorption coefficient compared to when using Ar gas. This allows more polymer to be supplied to the base layer while suppressing clogging of the openings of the etched holes, thereby improving the selectivity of the base layer to the film being etched.

[0125] The etching method and substrate processing apparatus disclosed herein are intended to be illustrative in all respects and not restrictive. The above-described embodiment may be modified and improved in various ways without departing from the scope and spirit of the appended claims. The various embodiments described above may employ other configurations and be combined without conflict.

[0126] The substrate processing device disclosed herein can be applied to any type of device including capacitively coupled plasma (CCP: Capacitively Coupled Plasma), inductively coupled plasma (ICP: Inductively Coupled Plasma), radial line slot antenna (RLSA: Radial Line Slot Antenna), electron cyclotron resonance plasma (ECR: Electron Cyclotron Resonance Plasma), and helicon wave plasma (HWP: Helicon Wave Plasma).

Claims

1. An etching method, comprising: A step of preparing a substrate having a stacked film formed thereon in a processing container, the stacked film comprising at least a silicon-containing insulating layer, base layers disposed within the silicon-containing insulating layer and each located at a different depth, and a mask layer disposed on the silicon-containing insulating layer; supplying a first process gas containing at least a fluorocarbon gas and a second rare gas into the process container; generating plasma of the first process gas in the process container to etch the stacked film to a first depth where a first base layer among the plurality of base layers is located; After etching the stacked film to the first depth, switching the second rare gas to a first rare gas and supplying a second process gas containing at least the fluorocarbon gas and the first rare gas into the process container; and generating plasma of the second processing gas in the processing container to etch the stacked film to a second depth where a second base layer among the plurality of base layers is located, wherein the second depth is deeper than the first depth; wherein the first noble gas is a gas having a higher ionization energy than that of Ar gas and a momentum of a single ionized particle thereof being lower than the momentum of a single ionized particle of Ar gas, The second rare gas is Ar gas or a gas having lower ionization energy than Ar gas.

2. The etching method according to claim 1, wherein: The potential of the metastable state of the first rare gas is higher than the potential of the metastable state of the Ar gas.

3. The etching method according to claim 1, wherein: The first rare gas includes at least one of He gas or Ne gas.

4. The etching method according to claim 1, wherein: The gas having lower ionization energy than Ar gas is Kr gas or Xe gas.

5. The etching method according to claim 1, wherein: The step of etching the stacked film to the second depth includes: generating the first precursor in a plasma formed from the second process gas in such a manner that the amount of the first precursor is relatively greater than the amount of the second precursor; The first precursor is a precursor that has a high dissociation rate and a lower adsorption coefficient than the second precursor.

6. The etching method according to any one of claims 1 to 5, wherein: The fluorocarbon gas is at least one of C4F6 gas, C4F8 gas, C3F8 gas, C6F6 gas, and C5F8 gas.

7. The etching method according to any one of claims 1 to 5, wherein: The silicon-containing insulating layer is formed of a silicon oxide layer.

8. The etching method according to any one of claims 1 to 5, wherein: The base layer is a conductive layer.

9. The etching method according to claim 8, wherein: The conductive layer is formed of a metal layer or a silicon layer.

10. The etching method according to claim 9, wherein: The metal layer is formed of tungsten.

11. The etching method according to any one of claims 1 to 5, wherein: The silicon-containing insulating layer is formed of a silicon oxide layer, The base layer is formed of a silicon nitride layer.

12. The etching method according to any one of claims 1 to 5, wherein: The silicon-containing insulating layer is formed of at least one of a silicon oxide layer and a low dielectric constant film layer. The base layer is formed of at least one of a silicon carbide layer and a silicon carbonitride layer.

13. A substrate processing apparatus, comprising: Processing containers; a mounting table for placing a substrate on which a stacked film is formed, the stacked film having at least a silicon-containing insulating layer, base layers arranged inside the silicon-containing insulating layer and each located at a different depth, and a mask layer arranged on an upper layer of the silicon-containing insulating layer; as well as Control Department, The control unit controls the following processes: a step of preparing the substrate in the processing container; supplying a first process gas containing at least a fluorocarbon gas and a second rare gas into the process container; generating plasma of the first process gas in the process container to etch the stacked film to a first depth where a first base layer among the plurality of base layers is located; After etching the stacked film to the first depth, switching the second rare gas to a first rare gas and supplying a second process gas containing at least the fluorocarbon gas and the first rare gas into the process container; and generating plasma of the second processing gas in the processing container to etch the stacked film to a second depth where a second base layer among the plurality of base layers is located, wherein the second depth is deeper than the first depth; the first noble gas is a gas having higher ionization energy than that of Ar gas and having a momentum of a single ionized particle lower than that of a single ionized Ar gas particle, The second rare gas is Ar gas or a gas having lower ionization energy than Ar gas.

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