Patent Application
20190051500
The various aspects and embodiments described herein pertain generally to a plasma processing method and a plasma processing apparatus.
Conventionally, there is known a plasma processing method of etching a multilayered film having an oxide layer, a conductive layer such as a metal layer provided under the oxide layer and a mask layer provided on a top surface of the oxide layer (see, for example, Patent Document 1). To meet a requirement for a next-generation device, a number of layers stacked in this multilayered film is getting increased. By way of example, the number of layers stacked in a NAND type flash memory having a multilayered film of a 3D structure is getting increased. Along with this trend, an aspect ratio of a hole to be etched is also getting increased.
Patent Document 1: Japanese Patent Laid-open Publication No. 2014-090022
In plasma etching for a hole or a groove having a high aspect ratio, as the etching progresses, there occurs depth loading, that is, a phenomenon that the etching does not progress at a bottom of the hole or the groove, resulting a great increase of an etching time. For this reason, both conductive layer selectivity and mask selectivity are required to be satisfied in the plasma etching.
To improve metal selectivity, it may be desirable to supply sufficient polymer onto the bottom of the hole to form a protective film by highly dissociating a fluorocarbon-based gas as an etching gas with plasma. Since, however, dissociation of fluorine radicals serving as etchants for the mask from the fluorocarbon-based gas is accelerated at the same time, it may be regarded that the conductive layer selectivity and the mask selectivity are in a trade-off relationship.
In one exemplary embodiment, a plasma processing method includes supplying a processing gas containing at least a fluorocarbon-based gas or a hydrofluorocarbon-based gas and CO into a processing vessel in which a multilayered film having at least an oxide layer, a conductive layer provided under the oxide layer and a mask layer provided on a top surface of the oxide layer is disposed; and etching the multilayered film by generating plasma within the processing vessel into which the processing gas is supplied.
According to the exemplary embodiment, it is possible to achieve both the conductive layer selectivity and the mask selectivity.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
In the detailed description that follows, embodiments are described as illustrations only since various changes and modifications will become apparent to those skilled in the art from the following detailed description. The use of the same reference numbers in different figures indicates similar or identical items.
In the following detailed description, reference is made to the accompanying drawings, which form a part of the description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Furthermore, unless otherwise noted, the description of each successive drawing may reference features from one or more of the previous drawings to provide clearer context and a more substantive explanation of the current exemplary embodiment. Still, the exemplary embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.
Hereinafter, a plasma processing method and a plasma processing apparatus according to exemplary embodiments will be explained in detail with reference to the accompanying drawings. In the exemplary embodiments, same or corresponding parts will be assigned same reference numerals. Further, the exemplary embodiments described herein are not meant to be anyway limiting. The various exemplary embodiments can be appropriately combined as long as the contents of processings are not contradictory.
A cylindrical supporting member 14 made of an insulating material is placed on a bottom portion of the processing vessel 12. The supporting member 14 is configured to support a base 16 which is made of a metal such as, but not limited to, aluminum. This base 16 is provided within the processing vessel 12 and, in the present exemplary embodiment, the base 16 constitutes a lower electrode.
An electrostatic chuck 18 is provided on a top surface of the base 16. The electrostatic chuck 18 and the base 16 constitute a mounting table according to the exemplary embodiment. The electrostatic chuck 18 has a structure in which an electrode 20 made of a conductive film is embedded between a pair of insulating layers or insulating sheets. The electrode 20 is electrically connected with a DC power supply 22. The electrostatic chuck 18 is configured to attract and hold a processing target object (workpiece) X by an electrostatic force such as Coulomb force generated by a DC voltage applied from the DC power supply 22.
A focus ring FR is disposed on the top surface of the base 16 to surround the electrostatic chuck 18. The focus ring FR is configured to improve etching uniformity. The focus ring FR is made of a material which is appropriately selected based on a material of an etching target layer. By way of non-limiting example, the focus ring FR may be made of silicon or quartz.
A coolant path 24 is provided within the base 16. A coolant of a set temperature, for example, cooling water is supplied into the coolant path 24 from an external chiller unit via pipelines 26a and 26b to be circulated therein. By controlling a temperature of the coolant circulated in this way, a temperature of the processing target object X placed on the electrostatic chuck 18 is also controlled.
Further, the plasma processing apparatus 10 is equipped with a gas supply line 28. Through the gas supply line 28, a heat transfer gas, for example, a He gas from a heat transfer gas supply mechanism is supplied into a gap between a top surface of the electrostatic chuck 18 and a rear surface of the processing target object X.
Further, an upper electrode 30 is provided within the processing vessel 12. The upper electrode 30 is disposed above the base 16, facing the base 16. The base 16 and the upper electrode 30 are arranged substantially in parallel to each other. A space between the upper electrode 30 and the base 16 functioning as the lower electrode serves as a processing space S in which a plasma etching is performed on the processing target object X.
The upper electrode 30 is supported at an upper portion of the processing vessel 12 with an insulating shield member 32 therebetween. The upper electrode 30 may include an electrode plate 34 and an electrode supporting body 36. The electrode plate 34 faces the processing space S, and is provided with a multiple number of gas discharge holes 34a. The electrode plate 34 may be made of a low-resistance conductor or semiconductor having low Joule heat.
The electrode supporting body 36 is configured to support the electrode plate 34 in a detachable manner, and is made of a conductive material such as, but not limited to, aluminum. The electrode supporting body 36 may have a water-cooling structure. A gas diffusion space 36a is formed within the electrode supporting body 36. A multiple number of gas through holes 36b are extended downwards from the gas diffusion space 36a, and these gas through holes 36b respectively communicate with the gas discharge holes 34a. Further, the electrode supporting body 36 is provided with a gas inlet opening 36c through which a processing gas is introduced into the gas diffusion space 36a, and a gas supply line 38 is connected to this gas inlet opening 36c.
The gas supply line 38 is connected to gas sources 40a to 40e via valves 42a to 42e and mass flow controllers (MFC) 44a to 44e, respectively. Further, a FCS may be provided instead of the MFC. The gas source 40a is a source of a processing gas containing a fluorocarbon-based gas or a hydrofluorocarbon-based gas. The fluorocarbon-based gas may be a CxFy gas such as, but not limited to, C4F6, C3F6, C4F8, CSF8 or C6F6. The hydrofluorocarbon-based gas may be a CHxFy-based gas such as, but not limited to, CH2F2, CHF3 or CH3F. The gas source 40b is a source of a processing gas containing a rare gas such as, but not limited to, an Ar gas. The gas source 40c is a source of a processing gas containing, for example, oxygen. The gas source 40d is a source of a processing gas containing, for example, nitrogen. The gas source 40e is a source of a processing gas containing, for example, carbon monoxide (CO). The processing gas from these gas sources 40a to 40e reaches the gas diffusion space 36a through the gas supply line 38 to be discharged into the processing space S through the gas through holes 36b and the gas discharge holes 34a. The gas sources 40a to 40e, the valves 42a to 42e, the MFCs 44a to 44e, the gas supply line 38, and the upper electrode 30 provided with the gas diffusion space 36a, the gas through holes 36b and the gas discharge holes 34a constitute a supply unit in the exemplary embodiment.
Further, the plasma processing apparatus 10 may be further equipped with a ground conductor 12a. The ground conductor 12a is of a substantially cylindrical shape, and is extended upwards from a sidewall of the processing vessel 12 to be higher than the upper electrode 30.
Further, in the plasma processing apparatus 10, a deposition shield 46 is provided along an inner wall of the processing vessel 12 in a detachable manner. The deposition shield 46 is also provided on an outer side surface of the supporting member 14. The deposition shield 46 is configured to suppress an etching byproduct (deposit) from adhering to the processing vessel 12, and is formed by coating an aluminum member with ceramic such as Y2O3.
At a bottom side of the processing vessel 12, a gas exhaust plate 48 is provided between the supporting member 14 and the inner wall of the processing vessel 12. The gas exhaust plate 48 may be made of, by way of example, an aluminum member coated with ceramic such as Y2O3. A gas exhaust opening 12e is formed at the processing vessel 12 under the gas exhaust plate 48. The gas exhaust opening 12e is connected with a gas exhaust device 50 via a gas exhaust line 52. The gas exhaust device 50 includes a vacuum pump such as a turbo molecular pump, and is capable of decompressing the inside of the processing vessel 12 to a required vacuum level. The gas exhaust device 50 maintains the inside of the processing vessel 12 at a vacuum level equal to or less than, e.g., 0.1 mTorr (0.01 Pa). Further, a carry-in/out opening 12g for the processing target object X is provided at the sidewall of the processing vessel 12, and this carry-in/out opening 12g is opened/closed by a gate valve 54.
Further, a conductive member (GND block) 56 is provided at the inner wall of the processing vessel 12. The conductive member 56 is mounted to the inner wall of the processing vessel 12 to be substantially on a level with the processing target object X in a height direction. This conductive member 56 is DC-connected to the ground and configured to suppress an abnormal discharge. Further, the location of the conductive member 56 is not limited to the example shown in
In the exemplary embodiment, the plasma processing apparatus 10 is further equipped with a power feed rod 58 configured to supply a high frequency power to the base 16 constituting the lower electrode. The power feed rod 58 constitutes a power feed line according to the exemplary embodiment. The power feed rod 58 has a coaxial double-pipe structure, and includes a rod-shaped conductive member 58a and a cylindrical conductive member 58b. The rod-shaped conductive member 58a is extended in a substantially vertical direction from an outside of the processing vessel 12 to an inside of the processing vessel 12 through the bottom portion of the processing vessel 12. An upper end of the rod-shaped conductive member 58a is connected to the base 16. Further, the cylindrical conductive member 58b is provided coaxially with the rod-shaped conductive member 58a to surround the rod-shaped conductive member 58a, and is supported at the bottom portion of the processing vessel 12. Two sheets of insulating members 58c having substantially annular shape are provided between the rod-shaped conductive member 58a and the cylindrical conductive member 58b, so that the rod-shaped conductive member 58a and the cylindrical conductive member 58b are electrically insulated from each other.
Further, in the exemplary embodiment, the plasma processing apparatus 10 may be further equipped with matching devices 70 and 71. The matching devices 70 and 71 are connected to lower ends of the rod-shaped conductive member 58a and the cylindrical conductive member 58b. The matching device 70 and the matching device 71 are connected to a first high frequency power supply 62 and a second high frequency power supply 64, respectively. The first high frequency power supply 62 is configured to generate a first high frequency (RF (radio frequency)) power for plasma generation having a frequency ranging from 27 MHz to 100 MHz, for example, 40 MHz. Further, the first high frequency power is of 1000 W to 3000 W, for example. The second high frequency power supply 64 is configured to generate a second high frequency power for ion attraction to the processing target object X by applying a high frequency bias to the base 16. A frequency of the second high frequency power is in a range from 400 kHz to 13.56 MHz, for example, 3 MHz. Further, the second high frequency power is of 3000 W to 8000 W, for example. A DC power supply 60 is connected to the upper electrode 30 via a non-illustrated low pass filter. The DC power supply 60 outputs a negative DC voltage to the upper electrode 30. With the above-described configuration, the two different high frequency powers can be supplied to the base 16 serving as the lower electrode, and the DC voltage can be applied to the upper electrode 30. The upper electrode 30, the base 16, the first high frequency power supply 62, the second high frequency power supply 64, the DC power supply 60, and so forth constitute a plasma generation unit according to the exemplary embodiment.
Further, in the exemplary embodiment, the plasma processing apparatus 10 may further include a control unit Cnt. The control unit Cnt is implemented by a computer including a processor, a storage unit, an input device, a display device, and so forth. The control unit Cnt is configured to control individual components of the plasma processing apparatus 10 such as a power supply system, a gas supply system, a driving system, and so forth. In the control unit Cnt, an operator can input commands through the input device to manage the plasma processing apparatus 10. Further, an operational status of the plasma processing apparatus 10 can be visually displayed on the display device. Further, the storage unit of the control unit Cnt stores therein a control program for controlling various processings performed in the plasma processing apparatus 10 by the processor, or a program for allowing each component of the plasma processing apparatus 10 to perform a processing according to processing conditions, i.e., a processing recipe.
To perform the etching in the plasma processing apparatus 10, the processing target object X is placed on the electrostatic chuck 18. The processing target object X may have an etching target layer and a resist mask provided on the etching target layer. While evacuating the processing vessel 12 by the gas exhaust device 50, the processing gas is supplied from the gas sources 40a to 40e into the processing vessel 12 at a preset flow rate, and an internal pressure of the processing vessel 12 is set to be in a range from, by way of example, but not limitation, 5 mTorr to 500 mTorr (0.67 Pa to 66.5 Pa).
Thereafter, the first high frequency power supply 62 supplies the first high frequency power to the base 16 serving as the lower electrode. Further, the second high frequency power supply 64 supplies the second high frequency power to the base 16. Furthermore, the DC power supply 60 supplies a first DC voltage to the upper electrode 30. As a result, a high frequency electric field is formed between the upper electrode 30 and the base 16 serving as the lower electrode, and the processing gas supplied into the processing space S is excited into plasma. The etching target layer of the processing target object X is etched by positive ions or radicals generated by this plasma.
Now, an example of the processing target object X etched by the above-described plasma processing apparatus 10 will be explained. The processing target object X is used to form, for example, a NAND type flash memory having a multilayered film of a three dimensional structure.
In the NAND type flash memory having the multilayered film of the three dimensional structure, a number of layers stacked is getting increased. Along with such an increase, an aspect ratio of a hole to be etched is also getting increased. In the plasma etching for a hole or a groove having such a high aspect ratio, the depth loading may occur as the etching progresses, so that an etching time will be greatly increased. For this reason, in the plasma etching, both a conductive layer selectivity and a mask selectivity are required to be satisfied.
The present inventors have found out that both the conductive layer selectivity and the mask selectivity can be achieved by appropriately adding a carbon monoxide (CO) gas to the processing gas used in the etching. It may be deemed to be because CO forms COF by being bonded with a F radical to scavenge the F radical. That is, the present inventors have found out that the scavenging of the fluorine radical generated by the plasma is effective to obtain both the conductive layer selectivity and the mask selectivity. Particularly, the carbon monoxide (CO) gas allows the fluorine radical to be scavenged as it is exhausted by being selectively bonded with the fluorine radical.
In the plasma processing apparatus 10 according to the exemplary embodiment, a processing gas containing at least a fluorocarbon-based gas or a hydrofluorocarbon-based gas and CO is used as a processing gas for etching. A rare gas may be further added to the processing gas. By way of example, the plasma processing apparatus 10 according to the exemplary embodiment performs an etching processing of forming a hole in the processing target object X by supplying, from the gas sources 40a to 40e, the fluorocarbon-based gas or the hydrofluorocarbon-based gas, the rare gas, the oxygen, the nitrogen and the CO at preset flow rates as the processing gas for the etching into the processing vessel 12. Accordingly, in the plasma processing apparatus 10, the conductive layer selectivity and the mask selectivity can be both achieved. It may be desirable to use the fluorocarbon-based gas as the processing gas and to use a C4F6 gas as the fluorocarbon-based gas. Further, since the CO scavenges the F radical, the same effect of improving the conductive layer selectivity and the mask selectivity may be obtained even when another fluorocarbon-based gas or hydrofluorocarbon-based gas other than the C4F6 gas is used as the processing gas.
It is desirable to set the flow rate of the CO to be equal to or higher than 55% of a total flow rate of the rare gas and the CO. Further, it may be more desirable to set the flow rate of the CO to be equal to or higher than 71% of the total flow rate of the rare gas and the CO. Further, it is desirable to set the flow rate of the CO to be equal to or higher than about 55% of a total flow rate of the processing gas. Furthermore, it is desirable to set the flow rate of the CO to be in a range from 9.3 times to 13 times the flow rate of the C4F6 gas. By setting the flow rate of the CO in this range, the plasma processing apparatus 10 is capable of implementing etching requiring both the high conductive layer selectivity and the high mask selectivity, for example, the etching for forming the holes for the metal contacts MC1 to MC4 of the NAND type flash memory having the multilayered film of the three dimensional structure.
So far, the various exemplary embodiments have been described. However, the exemplary embodiments are not limiting, and various modifications may be made. By way of example, in the above-described exemplary embodiments, although the two high frequency power supplies are connected to the base 16 serving as the lower electrode, the first high frequency power supply configured to generate the first high frequency power for plasma generation may be connected to either one of the base 16 and the upper electrode 30.
Hereinafter, specific examples where the present inventors have investigated the conductive layer selectivity and the mask selectivity by performing the hole etching on the multilayered film will be explained to describe the aforementioned effects. In the following experimental examples, the hole etching is performed on a multilayered film having a metal layer as the conductive layer, and the mask selectivity and the metal layer selectivity as the conductive layer selectivity are investigated.
The multilayered film 300 has a substrate 301, a metal layer 302, an insulating layer (oxide layer) 303, and an ACL 304. The substrate 301 is made of, by way of non-limiting example, Si. The metal layer 302 is formed on the substrate 301 and made of, by way of example, but not limitation, tungsten (W). In the NAND type flash memory, for example, the metal layer 302 is a portion serving as the conductive layer 100 (100a to 100d) and the etching stop layer in the multilayered wiring layers 200. A thickness of the metal layer 302 ranges from about 40 nm to 50 nm. The insulating layer 303 is formed on the metal layer 302 and made of, by way of example, SiO2 or the like. In the NAND type flash memory, for example, the insulating layer 303 is a portion serving as the insulating layer 101 (101a to 101d), the insulating layer 102 and the interlayer insulating layer 104 in the multilayered wiring layers 200. The insulating layer 303 has a thickness of, e.g., 4.7 μm. On top of a top surface 303a of the insulating layer 303 in a stacking direction, the ACL 304 is disposed as the mask layer. The ACL 304 has an opening 304a. The ACL 304 has a thickness of, e.g., 1.6 μm.
Further, in the present exemplary embodiment, conditions for obtaining the high metal layer selectivity and the high mask selectivity are as follows.
Metal layer selectivity>300 Condition (1)
Mask selectivity>7.8 Condition (2)
The condition (1) for the metal layer conductivity is set based on a case where the thickness of the metal layer 302 is in the range from 40 nm to 50 nm and an etching amount thereof is equal to or less than 30% (15 nm) of the thickness of the metal layer. Further, the condition (2) for the mask selectivity is set based on a case where the mask layer remains in a thickness of 300 nm or more. Since the metal layer 302 is made of the tungsten, a tungsten selectivity (W sel) is calculated as the metal layer selectivity. Further, since the mask layer is implemented by the ACL 304, an ACL selectivity (ACL sel) is calculated as the mask selectivity.
A variation in the etching as a result of adding the CO gas to the processing gas will be explained by using experimental examples.
C4F6 gas: 54 sccm
N2 gas: 100 sccm
CO gas: 200 sccm
Ar gas: 500 sccm
O2 gas: 42 sccm
CO gas: 500 sccm
Ar gas: 200 sccm
O2 gas: 42 sccm
CO gas: 500 sccm
Ar gas: 200 sccm
O2 gas: 39 sccm
In each of the experimental examples 1 to 3 shown in
In the experimental example 2, the flow rates of the CO gas and the Ar gas contained in the processing gas are switched from those of the experimental example 1. In case of switching the flow rates of the CO gas and the Ar gas, the maximum width (Bow CD) of the hole is increased by being affected by O of the CO gas. In the experimental example 3, a flow rate of the O2 gas is adjusted such that the maximum width (Bow CD) of the hole becomes equal to that of the experimental example 1. In the experimental example 3, the maximum width (Bow CD) of the hole is 252 nm, which is close to 251 nm of the experimental example 1.
In the table of
By way of example, a region 400a in the table of
A state in which the ratio of the flow rate of the CO gas to the total flow rate of the CO gas and the Ar gas is 0% is a case where the processing gas does not contain the CO gas, and states in which the ratios of the flow rate of the CO gas to the total flow rate of the CO gas and the Ar gas are 29%, 50%, 71% and 100%, respectively, are cases where the processing gas contains the CO gas. As shown in
Further, as depicted in
Now, an example of a variation of the etching depending on the variation of the ratio of the flow rate of the CO gas to the total flow rate of the CO gas and the Ar gas while the total flow rate of the CO gas and the Ar gas is maintained constant is explained. Here, the description will be provided for a case where the total flow rate of the CO gas and the Ar gas is set to be 700 sccm.
CO gas: 0 sccm
Ar gas: 700 sccm
O2 gas: 42 sccm
CO gas: 700 sccm
Ar gas: 0 sccm
O2 gas: 39 sccm
Each of the experimental examples 1, 4 and 5 depicted in
The experimental example 4 indicates a case where the processing gas does not contain the CO gas. The experimental examples 1 and 5 indicate cases where the processing gas contains the CO gas. In the experimental examples 1 and 5, the tungsten selectivity and the mask selectivity are found to be improved as compared to the experimental example 4. That is, in
Now, ranges which satisfy the conditions (1) and (2) exhibiting the high metal selectivity and the mask selectivity in the present exemplary embodiment will be discussed.
In
From the graphs shown in
Furthermore, in
Regarding the range of the flow rate of the CO gas with respect to the total flow rate of the processing gas, by setting the flow rate of the CO gas to be equal to or higher than 55% of the total flow rate of the processing gas, both the tungsten selectivity of the condition (1) and the mask selectivity of the condition (2) can be achieved. That is, by setting the flow rate of the CO gas to be equal to or higher than 55% of the total flow rate of the processing gas, the plasma processing apparatus 10 is capable of implementing the plasma etching in which both the tungsten selectivity of the condition (1) and the mask selectivity of the condition (2) are achieved.
In addition, if CO is considered in terms of a scavenger of F, the flow rate of the CO gas can be expressed as a ratio with respect to the flow rate of the C4F6 gas. By way of example, if the flow rate of the C4F6 is set to 1, the following Expression (3) is obtained.
9.3≤CO/C4F6≤13.0 (3)
That is, by setting the flow rate of the CO gas to be in the range from 9.3 times to 13 times the flow rate of the C4F6 gas, the plasma processing apparatus 10 is capable of implementing plasma etching in which both the tungsten selectivity of the condition (1) and the mask selectivity of the condition (2) are achieved.
From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting. The scope of the inventive concept is defined by the following claims and their equivalents rather than by the detailed description of the exemplary embodiments. It shall be understood that all modifications and embodiments conceived from the meaning and scope of the claims and their equivalents are included in the scope of the inventive concept.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-156313 | Aug 2017 | JP | national |
This application claims the benefit of Japanese Patent Application No. 2017-156313 filed on Aug. 14, 2017, the entire disclosures of which are incorporated herein by reference.
