JP7493378B2 - Etching method and substrate processing apparatus - Google Patents

Description

This disclosure relates to an etching method and a substrate processing apparatus.

The manufacture of three-dimensional stacked semiconductor memories such as 3D-NAND flash memories involves an etching process in which multiple holes are formed in a stacked film using plasma. One example of an etching process for forming a 3D-NAND device structure 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 between are simultaneously and highly selectively etched. In this etching process, a relatively shallow hole is formed that exposes the metal layer located in the middle of the silicon oxide layer, and a deep hole is formed that exposes the silicon layer below the metal layer. At this time, it is necessary to execute a process in which the selectivity ratio of the underlying metal film to the silicon oxide layer is high. In addition to device structures other than 3D-NAND, a process that increases the selectivity of the underlying layer to the film to be etched and reduces the loss of the underlying layer is required.

One method for ensuring a high selectivity is to form a protective film on the tungsten layer using highly depository process conditions. For example, Patent Document 1 proposes a plasma processing method that can form a protective film on the surface of an etching stop layer when etching an oxide layer and can suppress blocking of the opening of a hole.

Patent Document 2 proposes a method for etching a laminated film by supplying a process gas containing at least fluorocarbon gas or hydrofluorocarbon gas, oxygen, nitrogen, and CO, in order to achieve both a metal layer selectivity and a mask selectivity, and generating a plasma in a process vessel to which the process gas is supplied.

JP 2014-090022 A JP 2019-036612 A

This disclosure provides an etching method that can improve the selectivity of the underlying layer relative to the film to be etched.

According to one aspect of the present disclosure, a method for etching a silicon-containing insulating layer includes the steps of: preparing a substrate having a laminated film formed thereon, the laminated film including at least: ( i) a silicon-containing insulating layer; (ii) underlayers disposed within the silicon-containing insulating layer and located at different depths ; and (iii) a mask layer disposed on the silicon-containing insulating layer; supplying a first process gas including at least a fluorocarbon gas and a second rare gas into the process chamber ; generating plasma of the first process gas in the process chamber to etch the laminated film to a first depth where a first underlayer of the plurality of underlayers is located ; and , after etching the laminated film to the first depth, switching the second rare gas to the first rare gas and supplying the fluorocarbon gas and the first rare gas to the first rare gas. and generating a plasma of the second process gas in the process vessel to etch the laminated film to a second depth deeper than the first depth at which a second of the plurality of base layers is located, wherein the first rare gas is a gas having a higher ionization energy than Ar gas and a momentum of one ionized particle lower than the momentum of one particle of the ionized Ar gas, and the second rare gas is Ar gas or a gas having a lower ionization energy than Ar gas.

According to one aspect, the selectivity of the underlayer to the film to be etched can be improved.

FIG. 1 is a diagram showing a stacked film of a 3D NAND flash memory. FIG. 1 is a diagram showing an example of a configuration of a substrate processing apparatus according to an embodiment. 5A to 5C are diagrams showing the selection and effect of gas species in an etching method according to an embodiment; FIG. 4 is a diagram showing the relationship between various rare gases and plasma electron density and plasma electron temperature. FIG. 4 is a graph showing the relationship between plasma electron temperature and the degree of gas dissociation. FIG. 13 is a graph showing the relationship between the degree of dissociation and the deposition rate on each side of a hole. FIG. 4 is a diagram showing the relationship between plasma electron temperature and gas dissociation. FIG. 1 shows an example of an adsorption coefficient and a polymer deposit according to an embodiment. FIG. 2 is a diagram showing a relationship between the type of rare gas used in the etching method according to the embodiment and loss in a tungsten layer. FIG. 2 is a diagram showing the relationship between the Ar/He ratio and the emission intensity of CF ₂ according to an embodiment. FIG. 4 is a graph showing the relationship between pressure and sputtering yield for each gas type. FIG. 2 is a diagram for explaining the momentum of an ion. 1 is a flowchart showing an etching method according to an embodiment. 1A to 1C are diagrams for explaining an etching method according to an embodiment;

Below, a description will be given of a mode for carrying out the present disclosure with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicate descriptions may be omitted.

For example, in MLC Multi-Level Contact (hereinafter also referred to as "MLC"), which is one step of 3D NAND, a tungsten layer (W) 130 functioning as an electrode is formed in steps at different depths, and a silicon oxide layer (SiO ₂ ) 140 on the tungsten layer (W) 130 is etched, as shown in Fig. 1. In this example, the tungsten layer 130 and the silicon oxide layer 140 are laminated to form a laminated film. The tungsten layer 130 can be a multi-layer structure, for example, 60 to 200 layers.

At this time, the silicon oxide layer 140 is etched in one go to the depth of each of the tungsten layers 130 located at different depths above the silicon layer (Si) 110 and the silicon nitride layer (SiN) 120. As the device structure advances in generation, the number of stacked layers increases, and the aspect ratio (AR) also becomes very high, which leads to more pronounced depth loading and a significant increase in etching time.

For this reason, it is necessary to increase the selectivity of the tungsten layer 130 relative to the silicon oxide layer 140 during long etching times. In particular, in the tungsten layer 130 located at a shallower portion among the multiple tungsten layers 130, the overetching time after the tungsten is exposed is long. For this reason, a high selectivity of the tungsten layer 130 relative to the silicon oxide layer 140 is required. Also, in structures other than MLC, a process in which the base layer has a high selectivity relative to the film to be etched and loss of the base layer is small is desired.

In the etching method according to this embodiment, a process gas containing at least a fluorocarbon gas and a rare gas is supplied. At this time, the rare gas contains a first gas having a higher ionization energy than Ar gas and a momentum of one ionized particle lower than the momentum of one particle of the ionized Ar gas. Then, a plasma is generated in the process vessel to which the first gas is supplied, and the laminated film is etched.

From immediately after the silicon oxide layer 140 is etched to expose the tungsten layer 130 until a protective film is formed on the tungsten layer 130, the tungsten layer 130 is sputtered by ions of a rare gas. However, the first gas contained in the rare gas used in this etching method has a higher ionization energy than Ar gas, and the momentum of one ionized particle is lower than that of one ionized Ar gas particle. Therefore, the sputtering yield is low, and the loss of the tungsten layer 130 can be reduced accordingly. In addition, a precursor with a high dissociation and low adsorption coefficient is generated, and a protective film is formed on the exposed tungsten layer 130, so the loss of the tungsten layer 130 can be further reduced.

The following describes an etching method and substrate processing apparatus according to this embodiment, which maintains the etching rate (etching speed) of the silicon oxide layer 140, which is the film to be etched, while improving the selectivity with the tungsten layer 130, which is the underlying layer.

In the following description of one embodiment, He gas is used as an example of the first gas contained in the rare gas used in the etching process, but the present invention is not limited to this. The first gas may be any gas that has a higher ionization energy than Ar gas and a momentum of one ionized particle that is lower than the momentum of one particle of ionized Ar gas.

Although the silicon oxide layer 140 is given as an example of the film to be etched, the film to be etched is not limited to this and may be any silicon-containing insulating layer. Other examples of silicon-containing insulating layers include a silicon nitride layer, a laminated structure of a silicon oxide layer and a silicon nitride layer, and a low-k film layer such as organic-containing silicon oxide.

Although a tungsten layer 130 is given as an example of a base layer for the film to be etched, the base layer is not limited to this and may be any conductive layer. Other examples of the conductive layer may be a metal layer or a silicon layer. In addition to tungsten, examples of metal layers include titanium (Ti), aluminum (Al), and copper (Cu). An example of a silicon layer is a silicon-containing layer having electrical conductivity, such as polycrystalline silicon (Poly-Si) or amorphous silicon.

In processes for structures other than MLC, it may be desirable for the underlayer to have a high selectivity to the film to be etched and for there to be little loss of the underlayer. In such structures, the underlayer for the film to be 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 to be etched is a silicon oxide film and the underlayer is a silicon nitride film, or in a Via structure, where the film to be etched is at least one of a silicon oxide layer and a low-K film layer and the underlayer is at least one of a silicon carbide layer and a silicon carbonitride layer, there is a desire for there to be little loss of the underlayer.

[Configuration of the Substrate Processing Apparatus]
First, an example of the configuration of a substrate processing apparatus that performs the etching method according to the present embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of the configuration of a substrate processing apparatus according to an embodiment. Here, a capacitively coupled plasma etching apparatus is given as an example of the substrate processing apparatus 1.

The substrate processing apparatus 1 has a processing vessel 2 made of a conductive material such as aluminum, and a gas supply source 11 that supplies gas into the inside of the processing vessel 2. The processing vessel 2 is electrically grounded. Inside the processing vessel 2, there is a lower electrode 21 and an upper electrode 22 arranged parallel to and facing the lower electrode 21. The lower electrode 21 also functions as a mounting table on which the substrate W is placed.

The lower electrode 21 is connected to a first high frequency power supply 32 via a first matcher 33, and to a second high frequency power supply 34 via a second matcher 35. The first high frequency power supply 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 supply 34 applies a second high frequency power (high frequency power LF for ion attraction) having a frequency lower than that of the first high frequency power supply 32, for example, 400 kHz to 13 MHz to the lower electrode 21.

The first high frequency power supply 32 may be connected to the upper electrode 22 via a first matching device 33. The first high frequency power supply 32 and the second high frequency power supply 34 may apply the first high frequency power output value and the second high frequency power output value synchronously or asynchronously while varying them intermittently (pulsed) between no output (0 W) and the maximum value.

The first matching box 33 matches the load impedance to the internal (or output) impedance of the first high frequency power supply 32. The second matching box 35 matches the load impedance to the internal (or output) impedance of the second high frequency power supply 34. As a result, when plasma is generated inside the processing vessel 2, the internal impedance and the load impedance of each of the first high frequency power supply 32 and the second high frequency power supply 34 appear to match.

The upper electrode 22 is attached to the ceiling of the processing vessel 2 via an insulating shield ring 41 that covers its periphery. The upper electrode 22 is provided with a gas inlet 45 for introducing gas introduced 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, passes through the gas flow path 55, and is supplied to the processing space U from the hole 28. In this way, the upper electrode 22 also functions as a gas shower head.

A direct current (DC) power supply (not shown) may be connected to the upper electrode 22. The direct current (DC) power supply applies a direct current (DC) voltage to the upper electrode 22. The DC power supply may also apply the DC voltage while varying the output value between no output (0 W) and a maximum value intermittently (in a pulsed manner) in synchronization or asynchronously with the first high frequency power supply 32.

An exhaust port 60 is formed on the bottom surface of the processing vessel 2, and the inside of the processing vessel 2 is evacuated by an exhaust device 65 connected to the exhaust port 60. This allows the inside of the processing vessel 2 to be maintained at a predetermined vacuum level. A gate valve G is provided on the side wall of the processing vessel 2. The gate valve G opens and closes the loading/unloading port when loading and unloading the substrate W from the processing vessel 2.

The substrate processing apparatus 1 is provided with a control unit 70 that controls the operation of the entire apparatus. The control unit 70 has a CPU 71, a ROM 72, and a RAM 73. The ROM 72 stores basic programs executed by the control unit 70. The RAM 73 stores a recipe. The recipe sets control information for the substrate processing apparatus 1 with respect to process conditions (etching conditions). The control information includes process time, pressure (gas exhaust), high-frequency power and voltage, various gas flow rates, and temperature inside the chamber (for example, the set temperature of the substrate). The recipe may be stored in a hard disk or semiconductor memory. The recipe may also be set in a predetermined position in the storage area while being stored in a portable computer-readable storage medium such as a CD-ROM or DVD.

The CPU 71 controls the entire substrate processing apparatus 1 based on the basic program stored in the ROM 72. The CPU 71 controls the supply of a predetermined type of gas according to the recipe procedure stored in the RAM 73, and controls the desired processing, such as an etching processing method, for the substrate W.

[Optimization of processing gas]
Next, an explanation will be given of optimization of the processing gas that can maintain the etching rate of the silicon oxide layer 140 and improve the selectivity with respect to the underlying tungsten layer 130 in the etching method performed using the substrate processing apparatus 1. In this embodiment, a substrate W on which a laminated film is formed in which a silicon layer 110, a tungsten layer 130, a silicon oxide layer 140, and a mask layer 100 are laminated in this order is processed (see FIG. 8).

In the etching method according to this embodiment, the processing gas contains at least a fluorocarbon gas and a rare gas. The method includes a step of supplying the processing gas and a step of generating a plasma in the processing space U to which the processing gas is supplied, to etch the laminated film.

_{The fluorocarbon} gas used may be at least one of _C4F6 gas _{, C4F8} gas _{, C3F8} gas, _C6F6 gas, _{and C5F8} gas.

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, the rare gas used has a higher ionization energy than Ar gas, and the momentum of one ionized particle is lower than that of one particle of ionized Ar gas. He gas is used as an example of the first gas. However, the first gas is not limited to this, and a mixture of Ne (neon) gas, He gas, and Ne gas, which has an ionization energy of 2080.7 (kJ/mol), may be used. The first gas may be a mixture of Ar gas and at least one of He gas and Ne gas. The characteristic of the first gas that the momentum of one ionized particle is lower than that of one particle of ionized Ar gas will be described later.

The process gas may include _O2 gas, CO gas, _N2 gas, and _H2 gas in addition to the above-mentioned fluorocarbon gas and rare gas. It may also include halogen-containing gases such as _Cl2 , HBr, _CF4 , _CHF3 , and _NF3 .

[Selection and effect of gas species in etching processing method]
Next, the selection of gas species and the effects in the etching method according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a diagram showing the selection of gas species and the effects in the etching method according to one embodiment.

In the etching method according to the present 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 the present 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 rare gas (Heavy Noble Gas), and He gas is an example of a light rare gas (Light Noble Gas) because it is lighter than Ar gas.

Figure 4 shows the relationship between various rare gases and plasma electron density and plasma electron temperature. The horizontal axis of Figure 4 indicates the distance from the microwave radiation window into which 2.45 GHz microwave power is introduced, the vertical axis (right) indicates plasma electron density (Ne), and the vertical axis (left) indicates plasma electron temperature (Te). The graph in Figure 4 shows that when the gas type is changed from Ar gas to He gas, the plasma electron density decreases and the plasma electron temperature (Te) increases. The reason for this will be explained.

The ionization energy of He gas is 2372.3 kJ/mol, which is greater than that of Ar gas, which is 1520.6 kJ/mol. Ionization energy is the energy required to ionize an atom or molecule by removing an electron from it. Therefore, He gas has a higher energy to remove electrons from the outermost shell of the electron orbit than Ar gas. Therefore, He gas is less likely to ionize than Ar gas, and therefore the plasma electron density is lower in He gas than in Ar gas. When the plasma electron density is lower, the temperature given to each particle in the plasma is higher. As a result, as shown in FIG. 4, when the type of 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 is lowered and the plasma electron temperature is raised.

When the plasma electron temperature rises, the energy of one electron becomes higher, so that when the electron collides with the gas, the gas is easily dissociated, and precursors such as highly dissociated radicals and further ionized ions are easily generated. The generated precursors contribute to the deposition of polymers. Radical precursors act isotropically from the plasma to the substrate W, and ionic precursors act anisotropically. In addition, the precursors deposited on the film to be etched contribute as etchants that promote the etching of the film to be etched by interacting with the ions of the rare gas drawn into the substrate W by the high frequency power LF. The horizontal axis of FIG. 5 shows the plasma electron temperature, and the relationship with the degree of dissociation of C ₄ F ₆ gas is shown. When the plasma electron temperature is low, the dissociation of C ₄ F ₆ gas is not easily promoted, and there are many low dissociated precursors (C ₃ F ₄ radicals, C ₃ F ₄ ⁺ ions, etc.) and few highly dissociated precursors (CF ₂ radicals, CF ₂ ⁺ ions, etc.). When the plasma electron temperature increases, the _dissociation of _C4F6 gas advances, the number of highly dissociated CF radicals increases, and the number of poorly dissociated precursors decreases. Therefore, when a heavy rare gas is changed to a light rare gas, the _number of poorly dissociated precursors decreases and the number of highly dissociated precursors increases in the plasma. In other words, when a heavy rare gas is changed to a light rare gas, the number of precursors with high adsorption coefficients (adsorption power) such as _C3F4 decreases, and the number of precursors with low adsorption coefficients such as _CF2 increases. However, as shown in Figures 6 and 7, both highly dissociated precursors and poorly dissociated precursors exist in the plasma generation region P generated in the processing space U, and the ratio of the highly dissociated precursors to the poorly dissociated precursors changes. By changing the rare gas used for etching from Ar gas to He gas, the number of precursors with high dissociation and low adsorption coefficients can be relatively increased compared to the precursors with low dissociation and high adsorption coefficients. The precursors generated in the plasma generation region P are supplied to the substrate W through the sheath region S.

Precursors such as _C2F2 radicals and _C2F ⁺ ions, which are intermediate stages from low dissociation to high dissociation _{, have characteristics between low dissociation precursors and high dissociation precursors. Although the dissociation pattern of C4F6 gas} is shown in _Figure 5, dissociation is _also promoted by _{the plasma electron temperature in C4F8 gas} , _C3F8 gas _{, C6F6} gas, and _C5F8 gas used as fluorocarbon gases other than _C4F6 gas. _Depending on the gas species used, precursors such as _CF3 radicals and _CF3 ⁺ _ions are generated.

Thus, the low dissociation precursor has a high adsorption coefficient, and as shown by the arrow "←" pointing from left to right, which is the behavior of C ₃ F ₄ in the sheath region S in Fig. 7, it is likely to adhere to the upper surface of the mask layer 100 and the upper part (side surface) of the hole opening. Therefore, the low dissociation precursor is consumed on the upper surface and side surface of the mask layer 100, forms a polymer 105, and is difficult to reach the bottom surface and side surface of the hole H formed in the silicon oxide layer 140. The mask layer 100 is on the silicon oxide layer 140 as shown in Fig. 8, and may be an organic film or other material.

In contrast, the highly dissociated precursor has a low adsorption coefficient and is _less likely to adhere to the upper surface or side surface of the mask layer 100, as shown by the arrow "→" pointing from right to left, which is the behavior of CF2 in the sheath region S in Fig. 7. As a result, the highly dissociated precursor is not consumed on the upper surface or side surface of the mask layer 100, and is more likely to reach the side surface or bottom surface of the hole H formed in the silicon oxide layer 140, as shown by the arrow "→" pointing downward in the hole H. Therefore, the highly dissociated precursor is more likely to form a polymer 105 on the side surface or bottom surface of the hole formed in the silicon oxide layer 140, compared to the low dissociated precursor.

From the above, a precursor with a high dissociation and a low adsorption coefficient is unlikely to adhere to the upper surface or side surface of the mask layer 100, but is likely to adhere to the side surface or bottom surface of the hole H. Therefore, as shown in Fig. 3, by reducing the precursor with a low dissociation and a high adsorption coefficient and increasing the precursor with a high dissociation and a low adsorption _coefficient , the hole is unlikely to be clogged, and a large amount of precursor can be supplied to the _tungsten layer 130 exposed at the bottom of the hole. For this purpose, it is important to optimize the process conditions so as to promote the dissociation of _{C4F6 gas} , reduce the low dissociation radicals such as _C2F4 and _C2F3 , and increase the high dissociation radicals such as _CF2 and CF.

For this reason, in the etching method according to this embodiment, He gas, which has a smaller mass than Ar gas, is used as the rare gas. This makes it possible to reduce precursors with high adsorption coefficients and increase precursors with low adsorption coefficients.

8, when the _amount of low dissociation precursors such as _C2F4 , _{C3F4 ,} etc. increases, polymer 105 is deposited on the upper surface and opening (side surface) of mask layer 100 as shown in Fig. 8(a) and tends to cause blockage (see A). In addition, because the precursors are consumed on the upper surface and side surface of mask layer 100, there are few precursors that reach tungsten layer 130 at the bottom of hole H or the side surface at the back of hole H, and polymer 105 is difficult to deposit on tungsten layer 130 (see B).

The higher the plasma electron temperature, the more the C ₄ F ₆ gas dissociates, the fewer the precursors with a high adsorption coefficient, and the more the precursors with a low adsorption coefficient. As a result, as shown in FIG. 8B, the polymer 105 is less likely to be deposited on the upper surface and openings of the mask layer 100, and the openings are less likely to be blocked (see A'). Also, fewer precursors are consumed on the upper surface and side surfaces of the mask layer 100, and more precursors reach the tungsten layer 130 at the bottom of the hole H and the side surfaces at the back of the hole H, and the polymer 105 is more likely to be deposited on the tungsten layer 130 (see B').

As a result, compared to the comparative example in which Ar gas is used as the rare gas, the etching method according to the present embodiment in which He gas is used as the rare gas prevents the upper opening of the etched hole H from being blocked, and makes it easier for CF radicals to penetrate to the bottom of the hole H. As a result, the etching rate of the silicon oxide layer 140 can be maintained by supplying a sufficient amount of etchant. In addition, by forming the polymer 105 as a protective film on the tungsten layer 130, which is the underlayer of the silicon oxide layer 140, the selectivity of the tungsten layer 130 to the silicon oxide layer 140 can be improved.

As a result, loss of the underlayer can be suppressed (damage to the underlayer can be reduced). Furthermore, by suppressing blockage of the upper opening of hole H, the etching shape of the silicon oxide layer 140 can be made more vertical without becoming a bowing shape. Also, by suppressing blockage and ensuring the opening dimensions of the opening of hole H, the amount of precursor and rare gas ions that enter the opening of hole H increases, and as a result, the amount of precursor and rare gas ions that reach the bottom of hole H increases, which promotes etching of the film to be etched, leading to improved throughput and more effectively forming polymer 105 as a protective film.

[Experimental result]
9 shows the results of an experiment showing the relationship between the type of rare gas used in the etching method according to the embodiment and the comparative example and the loss of the tungsten layer 130. In the etching method according to the embodiment and the comparative example, the experiment was performed under the same process conditions for the high frequency power, the pressure in the processing vessel, and the processing gas other than the rare gas. Line E shows the loss of the tungsten layer 130 when Ar gas is used as the rare gas in the etching method according to the comparative example, and line F shows the loss of the tungsten layer 130 when He gas is used as the rare gas in the etching method according to the present embodiment. The horizontal axis of FIG. 9 indicates the over etch target (%), and the vertical axis indicates the normalized loss amount 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, assuming that the etching time from the start of etching of the silicon oxide layer 140 until the tungsten layer 130 is exposed is 100%. For example, 100% on the horizontal axis indicates that the etching time performed after the tungsten layer 130 is exposed is the same as the etching time when the silicon oxide layer 140 is etched until the tungsten layer 130 is exposed.

The tungsten layer 130 is sputtered by rare gas ions from immediately after the silicon oxide layer 140 is etched to expose the tungsten layer 130 until a protective film is formed on the tungsten layer 130. However, since the time until the protective film is formed is instantaneous and increases transiently, it is not easy to accurately measure the sputtering rate of the tungsten layer 130 during that time. Therefore, the y-intercepts of lines E and F in Figure 9 are considered to be the amount of loss of the tungsten layer 130 due to sputtering, and are proportional to the sputtering rate.

The amount of loss when the tungsten layer 130 is exposed when Ar gas is used as the rare gas is set to 1. When Ar gas is used as the rare gas, the amount of loss increases as the percentage of the over-etch target increases. For example, when the over-etch target is 100%, the amount of loss of the tungsten layer 130 increases by about 40%.

In contrast, when He gas was used as the rare gas, the amount of loss due to sputtering of the tungsten layer 130 was less than when Ar gas was used in the comparative example, and the amount of loss due to sputtering was improved by 26%. Furthermore, when the overetch target was 100%, the amount of loss of the tungsten layer 130 only increased slightly, and the loss rate was improved by 82% compared to when Ar gas was used in the comparative example. In this case, the loss rate refers to the slope of lines E and F in Figure 9.

In addition, according to the experimental results, when compared with the case where the overetch target is 100%, the etching method according to this embodiment was able to deposit 57% more polymer on the tungsten layer 130 than the comparative example by changing the rare gas in the processing gas from Ar gas to He gas.

After processing with a 100% overetch target, the loss of the tungsten layer 130 was reduced by 34% compared to the comparative example. On the other hand, the etching rate of the silicon oxide layer 140 was only reduced by 7% compared to the comparative example. Therefore, the selectivity of the tungsten layer 130 to the silicon oxide layer 140 was improved by 50% compared to the comparative example. The etching rate of the organic film mask layer 100 was increased by 16% compared to the comparative example.

The above experimental results show that the etching method according to this embodiment, which uses He gas as the rare gas, can improve the selectivity of the tungsten layer 130 relative to the silicon oxide layer 140 while maintaining the etching rate of the silicon oxide layer 140.

Next, the experimental results of the emission intensity of _CF2 radicals present in plasma versus the ratio of Ar/He gas according to one embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram showing the relationship between the ratio of Ar/He gas according to one embodiment and the emission intensity of the wavelength showing the _CF2 radical.

The horizontal axis of Fig. 10 shows, from the left, the case where only Ar gas is used as the rare gas in the etching process, the case where the ratio of Ar gas to He gas is about 2:1, the case where the ratio of Ar gas to He gas is about 1:2, and the case where only He gas is used. In each case, the total flow rate of the rare gas was controlled to be the same. Under these conditions, the emission intensity of the wavelength indicating the _CF2 radical in the plasma was measured.

As a result of the measurement, the emission intensity of the wavelength showing the _CF2 radical shown on the vertical axis of FIG. 10 increased as the ratio of He gas to Ar gas increased. From the above, it was found that the rare gas used in the etching method according to this embodiment is preferably He gas in order to promote high dissociation of the reactive gas. In addition, it is not necessary to use only He gas, and it is sufficient to use only Ar gas. It was found that the dissociation degree of _C4F6 gas can be controlled by controlling the ratio of _He gas to Ar gas, and the ratio of precursors with high adsorption coefficients to precursors with low adsorption coefficients can be controlled. This makes it possible to control the amount of precursors deposited on the top surface and side surface (opening) of the hole and the amount or ratio of precursors deposited on the bottom and side surface of the hole.

For example, when etching the laminated film shown in FIG. 1, the ratio of Ar gas to He gas may be controlled as follows. However, this etching method is an example of controlling Ar gas and He gas, and is not limited thereto. As shown in FIG. 1, when the tungsten layer 130 is located at different depths, etching may be performed at a higher etching rate by using only Ar gas or a mixed gas in which the ratio of He gas to Ar gas is mixed at a first ratio as a rare gas during etching to expose the tungsten layer 130 located in the shallow region. Then, during etching to expose the tungsten layer 130 located in the deep region, a mixed gas in which the ratio of He gas to Ar gas is mixed at a second ratio higher than the first ratio or only He gas may be used as a rare gas. According to this, by using only Ar gas or a mixed gas in which the ratio of Ar gas to He gas is high for etching the shallow region, etching of the silicon oxide layer 140 can be promoted more than when a mixed gas in which the ratio of He gas to Ar gas is high or only He gas is used. In addition, 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 high adsorption coefficient is generated, and the polymer 105 deposited thickly on the surface of the mask layer 100 acts as a protective film, and the selectivity of the mask layer 100 to the silicon oxide layer 140 can be increased by using only Ar gas or a mixed gas with a high ratio of He gas to Ar gas. In addition, if the tungsten layer 130 is located in a shallow region, even a precursor with low dissociation and high adsorption coefficient can be sufficiently deposited on the surface of the tungsten layer 130 to form the polymer 105 as a protective film. On the other hand, by using only a mixed gas with a high ratio of He gas to Ar gas or only He gas for etching of a deep region, the loss of the tungsten layer 130 can be reduced without blocking the opening of the hole, compared to the case of using only Ar gas or a mixed gas with a high ratio of Ar gas to He gas. 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 both the etching rate of the silicon oxide layer 140, the selectivity of the tungsten layer 130, and the selectivity of the mask layer 100.

Etching may be performed by repeating at least once or more steps of using only Ar gas or a mixed gas in which the ratio of He gas to Ar gas is mixed at a first ratio as the rare gas, and using a mixed gas in which the ratio of He gas to Ar gas is mixed at a second ratio higher than the first ratio as the rare gas, or using only He gas. In the step in which only Ar gas or a mixed gas in which the ratio of Ar gas to He gas is high is used, a precursor with low dissociation and high adsorption coefficient is generated, and polymer 105 is deposited thickly on the surface of the mask layer 100. Then, in the step in which a mixed gas in which the ratio of He gas to Ar gas is high or only He gas is used, the deposited polymer 105 acts as a protective film, and etching can be performed by increasing the selectivity of the mask layer 100 to the silicon oxide layer 140. That is, by repeatedly controlling steps in which the ratios of Ar gas and He gas are different as the rare gas, it is possible to achieve both the etching rate of the silicon oxide layer 140, the selectivity of the tungsten layer 130, and the selectivity of the mask layer 100. At this time, in the step using only Ar gas or a mixed gas with a high ratio of Ar gas to He gas, polymer 105 accumulates not only on the top surface of mask layer 100 but also on the side surfaces, so it is desirable to adjust the processing time so that the opening of the hole is not blocked.

In addition, the ratio of Ar gas and He gas as rare gases is controlled according to the etching depth, and steps in which the ratio of Ar gas and He gas as rare gases is different are repeatedly controlled. This makes it 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.

The ionization energy of Kr gas is 1350.8 (kJ/mol), and the ionization energy of Xe gas is 1170.4 (kJ/mol), which is smaller than the ionization energy of Ar gas, 1520.6 (kJ/mol). The metastable level energy of Kr gas is 9.92 (eV), and the metastable level energy of Xe gas is 8.32 (eV), which is smaller than the metastable level energy of Ar gas, 11.55 (eV). Therefore, when Kr gas or Xe gas is used instead of Ar gas as the rare gas species, a precursor with low dissociation and high adsorption coefficient is generated, as when Ar gas is used, and the polymer 105 deposited thickly on the surface of the mask layer 100 acts as a protective film, which is expected to increase the selectivity of the mask layer 100 to the silicon oxide layer 140.

[Momentum of ionized particles]
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 contained in the rare gas contained in the processing gas.

Next, we will explain why the first gas must satisfy the condition that "the momentum of one ionized particle is lower than that of one ionized particle of Ar gas" in addition to the condition that "the ionization energy of the first gas is higher than that of Ar gas."

When the tungsten layer 130 is exposed at the bottom of the hole, it is 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.

Sputtering is a physical reaction that occurs when accelerated particles collide with a solid surface, causing the atoms that make up the solid to be released into space due to momentum exchange. The sputtering yield is the number of atoms released into space when ions collide with a solid surface. In other words, the sputtering rate of a solid surface when accelerated ions collide with it is proportional to the momentum of the accelerated ions.

Figure 11 shows the relationship between pressure and sputtering yield for each gas type. The horizontal axis of Figure 11 shows the pressure inside the processing vessel, and the vertical axis shows the sputtering yield. The source of Figure 11 is "Research on the sputtering phenomenon of high-frequency rare gas plasma" by Masui Kanji, Nagoya Institute of Technology [Nagoya Institute of Technology Bulletin Vol. 50 (1998)].

In Fig. 11, the sputtering yield is shown as the weight loss of a target having a diameter of 60 mm when various gases are collided with the target. According to this, at a pressure of about 13 x ^10-3 (mmHg), the sputtering yield of He is lower than that of Ar. Therefore, desorption due to ion collision occurs less when He gas is used. Therefore, when He gas is used as the rare gas, the sputtering rate tends to be lower than when Ar gas is used.

Figure 12 shows a diagram to explain the momentum of ions. First, the kinetic energy K of an ion in plasma is expressed by equation (1), where q is the amount of charge and E is the potential applied to the sheath region S between the plasma generation region P and the substrate W. m is the mass of the ion, and v is the velocity of the ion.

Transforming equation (1) gives equation (2).

Equation (3) is derived from the ion's momentum P = mv and equation (2).

The mass per particle of a He ion is "4", which is smaller than the mass per particle of an Ar ion, "18". Therefore, from formula (3), the momentum per particle of a He ion is smaller than the momentum per particle of an Ar ion. From the above, when He gas is used, the surface of the tungsten layer 130 is less likely to be sputtered than when Ar gas is used, and the sputtering rate of the tungsten layer 130 decreases. 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 increases, the precursor of the CF-based gas is deposited on the surface of the tungsten layer 130 and acts as a protective film. Therefore, it was found that the amount of loss of the tungsten layer 130 could be suppressed.

In contrast, the etching rate is a value determined by the interaction between the surface adsorption of radicals and desorption due to ion collision. In addition, desorption due to thermal energy also occurs due to the interaction between desorption due to ion collision and the surface adsorption of radicals, but in an environment where there are ions present in an amount that can be attracted to the substrate W by the high frequency power HF, the contribution rate of this is lower than that of desorption due to ion collision, and therefore is not considered here.
The etching rate is shown in formula (4).

In formula (4), k is the reaction probability of ionic desorption, _Ei is the ionization energy, _Γion is the amount of incident ions, and " _kEi · _Γion " is a term indicating "desorption due to ion collision." In formula (4), s is the probability of adsorption to the surface, _Γradical is the amount of radicals supplied, and "s· _Γradical " is a term indicating "surface adsorption of radicals." Note that _nc indicates the material of the film to be etched.

In equation (4), k (the reaction probability of ionic desorption) is proportional to the sputtering yield; if the sputtering yield is high, the etching rate tends to increase, and if the sputtering yield is low, the etching rate tends to decrease. For this reason, when He gas is used as the rare gas, the sputtering yield is lower than when Ar gas is used, and the etching rate tends to decrease.

However, by using He gas as the rare gas, the fluorocarbon gas is highly dissociated and a precursor with a low adsorption coefficient is generated. This causes radicals that become etchants to be supplied to the bottom of the hole H, increasing Γ _ion (amount of ion incidence). It is believed that this is why the etching rate could be maintained even when He gas was used as the rare gas.

As explained above, in order to suppress the loss of the tungsten layer 130 and increase the selectivity with the silicon oxide layer 140, it has been found that it is important to make the precursor arrive on the tungsten layer 130 at the bottom of the hole and to reduce the momentum of the ions. Therefore, in the etching method according to this embodiment, the rare gas contained in the processing gas is changed from Ar gas to He gas. This makes it possible to 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.

[Etching Method]
Next, an etching method according to an embodiment will be described with reference to Fig. 13 and Fig. 14. Fig. 13 is a flow chart showing the etching method according to an embodiment. Fig. 14 is a diagram for explaining the etching method according to an embodiment. This etching method is performed in the substrate processing apparatus 1 of Fig. 2 and is controlled by the control unit 70 of Fig. 2.

When this process is started, first, a substrate W on which a laminate film is formed by stacking a silicon layer 110, a tungsten layer 130, a silicon oxide layer 140, and a mask layer 100 in that order is carried into the process vessel 2 and placed on the lower electrode (mounting table) 21 (step S1).

Next _, a process gas containing a _fluorocarbon gas ( _CxFy gas) such as _C4F6 gas and He gas is supplied into the process vessel 2 (step S2). Next, high frequency powers HF and LF are applied from the first high frequency power source 32 and the second high frequency power source 34 to generate plasma (step S3). Next, the laminated film is etched (step S4), and the process is completed.

According to the etching method of the embodiment, while etching the stacked film, _fluorocarbon gas such as _C4F6 gas in the processing gas is highly dissociated as shown in Fig. 14A. Then, the silicon oxide layer 140 is etched by precursors such as _CF2 and _CF3 radicals, _CF2 ⁺ and _CF3 ⁺ ions (indicated as _CFx and _CFx ⁺ in the figure) and He ions.

At that time, the precursor is deposited at the bottom of the recess in the silicon oxide layer 140, but at the same time, it is consumed as an etchant for etching the silicon oxide layer 140 through interaction with He ions and is converted into volatile gases such as _SiF4 and CO, so that no polymer is formed as a deposit.

As shown in FIG. 14(b), when etching of the silicon oxide layer 140 is completed and the tungsten layer 130 is exposed, the precursor is no longer consumed as an etchant and begins to deposit as a polymer. However, immediately after etching of the silicon oxide layer 140 is completed, no polymer has been deposited on the exposed surface of the tungsten layer 130, and the surface of the tungsten layer 130 is sputtered mainly by He ions, resulting in loss of the tungsten layer 130 (see symbol G).

As the process continues, the precursor is deposited as a polymer on the surface of the tungsten layer 130, acting as a protective film (see symbol I), as shown in FIG. 14(c), and the etching rate of the tungsten layer 130 decreases.

As a result, the etching method according to this embodiment can improve the selectivity of the underlying layer relative to the film to be etched.

[Metastable energy of rare gases]
The potential of the metastable state of the first gas used in the etching method according to this embodiment is preferably higher than the potential of the metastable state of Ar gas. For example, the metastable level energy of He gas is 19.82 (eV), which is higher than the metastable level energy of Ar gas, 11.55 (eV). The metastable level energy of Ne gas, which has a metastable level energy of 16.62 (eV), and the mixed gas of He gas and Ne gas are also higher than the metastable level energy of Ar gas. During the etching process, the rare gas is excited to a metastable state by interaction with the plasma. When a normal atom or molecule is excited, the average time (spontaneous emission lifetime) for emitting energy such as light and naturally transitioning back to the ground state is on the order of microseconds or less. Since the spontaneous emission lifetime of the metastable state is on the order of one second, a large amount of rare gas in a metastable state with high energy can exist in the plasma generation space. The rare gas in a metastable state transitions to the ground state by emitting energy through collision.

Therefore, in the case of He gas and Ne gas, which have metastable level energies larger than that of Ar gas, a large amount of rare gas in a metastable state with high energy is present. As a result, these gases collide with _fluorocarbon gas such as _C4F6 gas in the plasma generation space or the sheath region S, which is the transport space to the substrate W, and the degree of dissociation of the fluorocarbon gas can be controlled to a high level.

As a result, in the 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 the use of Ar gas. This makes it possible to supply a large amount of polymer to the underlayer while suppressing blockage of the opening of the hole to be etched, thereby improving the selectivity of the underlayer to the film to be etched.

The etching method and substrate processing apparatus according to the presently disclosed embodiment should be considered in all respects as illustrative and not restrictive. The above-described embodiment may be modified and improved in various ways without departing from the spirit and scope of the appended claims. The matters described in the above-described embodiments may be configured in other ways without any inconsistency, and may be combined without any inconsistency.

The substrate processing apparatus disclosed herein can be applied to any type of apparatus, including Capacitively Coupled Plasma (CCP), Inductively Coupled Plasma (ICP), Radial Line Slot Antenna (RLSA), Electron Cyclotron Resonance Plasma (ECR), and Helicon Wave Plasma (HWP).

1 Substrate processing apparatus 2 Processing vessel 11 Gas supply source 21 Lower electrode (mounting table)
22 Upper electrode 32 First high frequency power supply 34 Second high frequency power supply 70 Control unit 100 Mask layer 110 Silicon layer 130 Tungsten layer 140 Silicon oxide layer H Hole W Substrate

Claims (13)

A process of preparing a substrate having a laminated film formed thereon, the laminated film including at least : (i) a silicon-containing insulating layer; (ii) underlayers disposed in the silicon-containing insulating layer and positioned at different depths ; and (iii) a mask layer disposed on the silicon-containing insulating layer, in a processing chamber;
supplying a first process gas containing at least a fluorocarbon gas and a second rare gas into the process vessel ;
generating a plasma of the first process gas in the processing chamber , and etching the stacked film to a first depth at which a first base layer of the plurality of base layers is located ;
After etching the stacked film to the first depth, the second rare gas is switched to a first rare gas, and a second process gas containing at least the fluorocarbon gas and the first rare gas is supplied into the process chamber;
generating a plasma of the second process gas in the processing chamber, and etching the stacked film to a second depth deeper than the first depth at which a second base layer of the plurality of base layers is located;
the first rare gas has a higher ionization energy than Ar gas and a momentum of one ionized particle is lower than a momentum of one particle of the ionized Ar gas;
The second rare gas is Ar gas or a gas having an ionization energy lower than that of Ar gas.
1. An etching method comprising: The metastable state potential of the first rare gas is higher than the metastable state potential of Ar gas.
The etching method according to claim 1 . The first rare gas includes at least one of He gas and Ne gas.
The etching method according to claim 1 or 2 . The gas having an ionization energy lower than that of Ar gas is Kr gas or Xe gas.
The etching method according to any one of claims 1 to 3 . _{The fluorocarbon} gas is at least one of _C4F6 gas _{, C4F8} gas _{, C3F8} gas, _C6F6 gas, _{and C5F8} gas;
The etching method according to any one of claims 1 to 4 . The silicon-containing insulating layer is formed of a silicon oxide layer.
The etching method according to any one of claims 1 to 5 . The underlayer is a conductive layer.
The etching method according to any one of claims 1 to 6 . The conductive layer is formed of a metal layer or a silicon layer.
The etching method according to claim 7 . The metal layer is formed of tungsten.
The etching method according to claim 8 . The silicon-containing insulating layer is formed of a silicon oxide layer,
The underlayer is formed of a silicon nitride layer.
The etching method according to any one of claims 1 to 5 . The silicon-containing insulating layer is formed of at least one of a silicon oxide layer and a low-k film layer,
The underlayer is formed of at least one of a silicon carbide layer and a silicon carbonitride layer.
The etching method according to any one of claims 1 to 5 . The step of etching the film stack to the second depth includes:
generating a first precursor in a plasma formed from the second process gas such that an amount of the first precursor is relatively greater than an amount of the second precursor;
The first precursor has a high dissociation and a low adsorption coefficient compared to the second precursor.
The etching method according to any one of claims 1 to 11. A processing vessel;
a mounting table for mounting a substrate having a laminated film formed thereon, the laminated film including at least: (i) a silicon-containing insulating layer; (ii) underlayers disposed in the silicon-containing insulating layer and positioned at different depths ; and (iii) a mask layer disposed on the silicon-containing insulating layer;
A substrate processing apparatus having a control unit,
The control unit is
providing the substrate in the process chamber;
supplying a first process gas containing at least a fluorocarbon gas and a second rare gas into the process vessel ;
generating a plasma of the first process gas in the processing chamber , and etching the stacked film to a first depth at which a first base layer of the plurality of base layers is located ;
After etching the stacked film to the first depth, the second rare gas is switched to a first rare gas, and a second process gas containing at least the fluorocarbon gas and the first rare gas is supplied into the process chamber;
generating a plasma of the second process gas in the processing chamber, and etching the stacked film to a second depth deeper than the first depth at which a second of the plurality of base layers is located;
the first rare gas has a higher ionization energy than Ar gas and a momentum of one ionized particle is lower than a momentum of one particle of the ionized Ar gas;
The second rare gas is Ar gas or a gas having an ionization energy lower than that of Ar gas.
Substrate processing equipment.

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