ETCHING METHOD AND ETCHING APPARATUS

An etching method includes: forming straight-chain molecules containing CFx on a substrate to be etched; and irradiating the substrate on which the molecules are formed with an activation gas that activates the CFx.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-228048, filed on Nov. 28, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

Various aspects and embodiments of the present disclosure relate to an etching method and an etching apparatus.

BACKGROUND

There has been conventionally proposed an etching method that performs an etching process on a substrate placed in a processing container by alternately supplying a depositing gas for forming a protective film and an etching gas for promoting etching.

However, the conventional etching method does not control a structure of the protective film deposited on the substrate by the depositing gas. For this reason, the conventional etching method sometimes cannot etch the substrate thinly and uniformly.

SUMMARY

According to one embodiment of the present disclosure, there is provided an etching method including: forming straight-chain molecules containing CFxon a substrate to be etched; and irradiating the substrate on which the molecules are formed with an activation gas that activates the CFx.

DETAILED DESCRIPTION

Hereinafter, embodiments of an etching method and an etching apparatus of the present disclosure will be described in detail with reference to the drawings. Throughout the drawings, the same or similar parts and portions are denoted by the same reference numerals. It is to be understood that the present disclosure is not limited by the disclosed embodiments. The embodiments may be used in proper combination unless contradictory to the processing contents.

FIG. 1is a partial sectional view showing a configuration of an etching apparatus according to an embodiment.FIG. 2is a plan view of a substrate, which is held by a substrate holding part included in the etching apparatus shown inFIG. 1, when viewed from an etching target surface side of the substrate. The cross section of the substrate holding part inFIG. 1corresponds to the cross section taken along line A-A inFIG. 2.

An etching apparatus10according to the embodiment is an apparatus that performs so-called atomic layer etching (ALE) for etching a substrate S thinly and uniformly.

The substrate S has two surfaces. Among the two surfaces, one is an etching target surface S1to be etched and the other one is a non-etching target surface S2not to be etched. Material of the substrate S is not particularly limited but may include, for example, inorganic material such as SiO2(glass), Si, alumina, ceramics, or sapphire, organic material such as plastics or films, and the like. The substrate S may be a substrate having been subjected to surface treatment such as plasma treatment (plasma etching), wet cleaning treatment, film formation treatment, and the like. In the etching target surface S1of the substrate S, a pattern, which includes an etching target region to be etched and a non-etching target region not to be etched, is formed. For example, in the etching target surface S of the substrate S, a wiring pattern including a metal layer and an insulating film is formed. The insulating film is an etching target region, while the metal layer is a non-etching target region.

The etching apparatus10includes a chamber2in which the substrate S is accommodated, a substrate holding part3that holds the substrate S in the chamber2, a raw material gas supply part4that supplies a raw material gas G to be deposited on the substrate S into the chamber2, a substrate heating part51that heats the substrate S held by the substrate holding part3, and an exhaust part6that discharges an internal atmosphere of the chamber2.

As shown inFIG. 1, the chamber2includes a bottom wall portion21, a peripheral wall portion22erecting from a peripheral edge of the bottom wall portion21, and a top wall portion23sealing an upper opening of the peripheral wall portion22.

The substrate holding part3includes a frame portion31and a chuck portion32. As shown inFIGS. 1 and 2, the frame portion31has an opening30that exposes the etching target surface S1of the substrate S toward an inner wall surface210of the bottom wall portion21of the chamber2. The frame portion31supports a peripheral edge of the etching target surface S1of the substrate S and exposes the etching target surface S of the substrate S toward the inner wall surface210of the bottom wall portion21of the chamber2through the opening30. As shown inFIG. 2, an outer peripheral line and an inner peripheral line of the frame portion31have a rectangular shape in a plan view, but may have a different shape (for example, a circular shape or the like) as appropriate. A size of the opening30is, for example, 100 mm×50 mm. The chuck portion32is rotatable about an end portion of the chuck portion on the side of the frame portion31. When the substrate S is placed on the frame portion31, the chuck portion32rotates outward in a radial direction of the frame portion31and is located at a position (standby position) where the chuck portion32does not interfere with the substrate S placed on the frame portion31. After the substrate S is placed on the frame portion31, the chuck portion32rotates inward in the radial direction of the frame portion31and is located at a position (holding position) where the chuck portion32holds an outer edge portion of the substrate S supported by the frame portion31. In this manner, the chuck portion32holds the outer edge portion of the substrate S supported by the frame portion31.

As shown inFIG. 1, the chamber2includes a partition wall portion24that partitions an internal space of the chamber2into a first space V1where the etching target surface S1of the substrate S held by the substrate holding part3is exposed and a second space V2where the non-etching target surface S2of the substrate S held by the substrate holding part3is exposed. The partition wall portion24extends from the frame portion31to the top wall portion23of the chamber2. A loading/unloading port (not shown) is installed in the partition wall portion24. The first space V1and the second space V2are in communication with each other through the loading/unloading port. The substrate S is loaded into and unloaded from the substrate holding part3via the loading/unloading port. When the substrate S is not held by the substrate holding part3, the first space V1and the second space V2are in communication with each other through the opening30of the frame portion31. When the substrate S is held by the substrate holding part3, the opening30of the frame portion31is closed by the substrate S held by the substrate holding part3. As a result, a self-assembled monolayer is prevented from being formed on the non-etching target surface S2of the substrate S held by the substrate holding part3.

As shown inFIG. 1, the raw material gas supply part4includes a gas generation container41, an organic compound accommodation container42installed in the gas generation container41, and a raw material gas supply pipe44for supplying the raw material gas G generated in the gas generation container41into the chamber2.

A predetermined film forming material L is accommodated in the organic compound accommodation container42. The film forming material L contains an organic compound composed of straight-chain molecules containing CFx(x being an arbitrary integer). An example of this CFxmay include fluorocarbon such as CF2, CF4or the like. When deposited on a substrate, such an organic compound a self-assembled monolayer (hereinafter sometimes referred to as “SAM”). The self-assembled monolayer refers to a monomolecular film formed by self-assembly of molecules, and has good uniformity because molecular orientation is aligned.

For example, the organic compound composed of straight-chain molecules containing CFxmay have a structure as shown in the following structural formula (1).

As described above, the film forming material L capable of forming SAM is accommodated in the organic compound accommodation container42. In the present embodiment, the film forming material L is in a liquid state. For example, the straight-chain molecule shown in the above structural formula (1) is in a liquid state when m=10 to 20.

Further, among the molecules disclosed in WO2016/190047, for example, an organic compound composed of molecules having a straight main chain of (CF2)2to (CF2)5, a functional group of alcohol or ether, and an evaporation temperature (or molecular weight) substantially the same as that of the molecules represented by the structural formula (1) may be used as the organic compound composed of straight-chain molecules containing CFx.

A heater43is installed in the organic compound accommodation container42. The heater43heats and vaporizes the film forming material L at the time of film formation. For example, when a starting temperature at which the straight-chain molecules containing CFxincluded in the film forming material L starts to be vaporized is about 200 degrees C., in the organic compound accommodation container42, the heater43heats and vaporizes the film forming material L at 200 to 400 degrees C. For example, in the organic compound accommodation container42, the heater43heats and vaporizes the film forming material L at 400 degrees C.

The raw material gas G generated by the vaporization of the film forming material L is transferred to the raw material gas supply pipe44. A shutter80is installed at an end portion of the raw material gas supply pipe44on the side of the chamber2. The shutter80is rotatable about an end portion of the shutter80, and switchable between a closed state in which the end portion of the raw material gas supply pipe44on the side of the chamber2is closed and an open state in which the end portion of the raw material gas supply pipe44on the side of the chamber2is open. In the open state in which the end portion of the raw material gas supply pipe44on the side of the chamber2is open, the raw material gas G transferred to the raw material gas supply pipe44is supplied into the chamber2. Specifically, the raw material gas G is supplied into the first space V1formed between the etching target surface S1of the substrate S held by the substrate holding part3and the inner wall surface210of the bottom wall portion21of the chamber2.

The raw material gas G is discharged toward the etching target surface S1of the substrate S from a leading end of the raw material gas supply pipe44extending into the chamber2through the bottom wall portion21of the chamber2. That is to say, the raw material gas G is supplied in a direction from the inner wall surface210of the bottom wall portion21of the chamber2toward the etching target surface S1of the substrate S held by the substrate holding part3. As a result, the film forming material L in the raw material gas G is more likely to adhere to the etching target surface S1of the substrate S held by the substrate holding part3, thereby improving efficiency of formation of SAM on the etching target surface S1of the substrate S.

The substrate heating part51includes a heater such as a resistance heater, a lamp heater (for example, an LED lamp heater), or the like. In the present embodiment, the substrate heating part51is installed on the side of the non-etching target surface S2of the substrate S held in the substrate holding part3(that is to say, in the second space V2where the non-etching target surface S2of the substrate S is exposed). Therefore, the substrate heating part51heats the substrate S from the side of the non-etching target surface S2of the substrate S.

The substrate heating part51heats the substrate S held by the substrate holding part3to a predetermined temperature range from the start temperature at which the straight-chain molecules including CFxstart to be vaporized. For example, the substrate heating part51heats the substrate S to a temperature, which is set to be equal to or higher than the start temperature at which the straight-chain molecules including CFxstart to be vaporized and is equal to or lower than a set temperature of the organic compound accommodation container42. For example, when the start temperature at which the straight-chain molecules including CFxstart to be vaporized is about 200 degrees C., the substrate heating part51heats the substrate S to 200 to 300 degrees C., specifically, 200 to 250 degrees C., and more specifically, 200 to 230 degrees C. As a result, the straight-chain molecules are formed on the substrate S with good uniformity.

The etching apparatus10further includes an irradiation part90for irradiating the substrate S with an activation gas that activates CFxin the straight-chain molecules formed on the substrate S. For example, the etching apparatus10includes, as the irradiation part90, a gas source91for supplying the activation gas, a mass flow controller92for controlling a flow rate of the activation gas, and a gas supply pipe93for supplying the activation gas into the chamber2.

The activation gas supplied from the gas source91is supplied to one end of the gas supply pipe93via the mass flow controller92. The mass flow controller92controls the flow rate of the activation gas supplied to the one end of the gas supply pipe93. The other end of the gas supply pipe93is arranged below the substrate holding part3in the chamber2. In addition, an ion gun is installed in the gas supply pipe93. The activation gas supplied to the one end of the gas supply pipe93is ionized with predetermined energy by the ion gun, and is discharged from the other end of the gas supply pipe93.

The activation gas may be any gas as long as the activation gas has a weight enough to allow etching and can activate CFxin the straight-chain molecules. An example of the activation gas may include a rare gas such as an argon (Ar) gas or the like.

The irradiation part90ejects the activation gas from the other end of the gas supply pipe93to irradiate the substrate S with the activation gas. The activation gas is ionized with energy at least enough to impart straightness to the etching.

The activation gas with which the substrate S is irradiated activates CFxin the straight-chain molecules formed on the substrate S. In addition, the activation gas collides with and etches a film of CFxin the straight-chain molecules formed on the substrate S.

Now, an etching method according to the present embodiment will be described. The etching apparatus10according to the present embodiment performs an atomic layer etching process for thinly and uniformly etching the substrate using the etching method according to the present embodiment.FIGS. 3A to 3Care views for explaining the etching method according to the present embodimentFIGS. 3A to 3Cshow a flow of etching in the etching method according to the present embodiment.

The substrate S has a pattern of a metal layer P1and an insulating film P2formed on the etching target surface S1. In the example ofFIGS. 3A to 3C, the metal layer P1is made of Cu and the insulating film P2is made of SiO2.

In the etching method according to the present embodiment, the substrate S is heated to a predetermined range of temperature from the start temperature at which the straight-chain molecules containing CFxstart to be vaporized, and the straight-chain molecules containing CFxare deposited on the substrate S by supplying the raw material gas G from the raw material gas supply part4. As a result, as shown inFIG. 3B, a molecular layer L1in which the straight-chain molecules containing CFxare arranged side by side is formed on the substrate S. Since the straight-chain molecules according to the present embodiment mainly contains carbon (C), fluorine (F), and oxygen (O), the element constitution of the molecular layer L1is represented by “CxFyOz” in the example ofFIGS. 3A to 3C.

When the substrate S on which the molecular layer L1is formed is irradiated with Ar ions, the molecular layer L1is activated by the Ar ions and CF is generated. Further, when the substrate S is irradiated with the Ar ions, physical etching by collision of the Ar ions is performed.

The surface of the insulating film P2is chemically etched by reaction with CF generated in the molecular layer L1. For example, the insulating film P2is etched by a reaction as represented by the following chemical expression (2).

On the other hand, the metal layer P1is not chemically etched since the metal layer P1does not react with CF.

That is to say, the insulating film P2is chemically and physically etched. On the other hand, the metal layer P1is physically etched. As a result, a difference in etching rate occurs between the insulating film P2and the metal layer P1. For example, when the substrate S is irradiated with the Ar ions at 1 keV, the metal layer P1is physically etched only at an etching rate of 22 Å/min. On the other hand, the insulating film P2is both physically and chemically etched at an etching rate of 30 Å/min. Due to the difference in etching rate between the insulating film P2and the metal layer P1, the insulating film P2is etched more than the metal layer P1per unit time. As a result, as shown inFIG. 3C, the insulating film P2is etched more than the metal layer P1.

The molecular layer L1is also physically etched by collision with the Ar ions. When the molecular layer L1disappears, the metal layer P1and the insulating film P2are physically etched only and have little difference in etching rate. For this reason, the substrate S is irradiated with the Ar ions for a predetermined period of time enough to consume the molecular layer L1completely. This predetermined period of time is obtained in advance by experiments or the like. For example, the irradiation part90ionizes an Ar gas with energy of 500 to 1,000 eV and irradiates the substrate S with Ar ions at an ion current of about 100 to 500 [μA] for one minute. In addition, in order to increase controllability of etching, the irradiation part90may reduce the ion current and prolong the irradiation time.

In the etching method according to the present embodiment, by depositing the straight-chain molecules containing CFxon the substrate S, it is possible to form the molecular layer L1on the substrate S thinly and uniformly. In the etching method according to the present embodiment, by activating the thin and uniform molecular layer L1formed as described above, it is possible to etch the substrate S thinly and uniformly. For example, in the etching method according to the present embodiment, the insulating film P2can be etched in units of, for example, 1 to 2 nm with respect to the metal layer P1.

Further, in the etching method according to the present embodiment, a required amount of etching can be obtained by repeating formation of the molecular layer L1on the substrate S as shown inFIG. 3Band irradiation of the substrate S with the Ar ions as shown inFIG. 3C.

Further, in the etching method according to the present embodiment, in a state in which the temperature of the substrate S is adjusted to a predetermined range of temperature from the start temperature at which the straight-chain molecules containing CFxstart to be vaporized, the straight-chain molecules are deposited on the substrate S. Among the molecules deposited on the substrate S, molecules not in contact with the substrate S become unstable and are vaporized. As a result, a film (molecular layer L1) in which molecules constituting SAM are arranged side by side is formed on the substrate S.FIG. 4is a schematic view showing a state of molecules formed on a substrate. As shown inFIG. 4, a film in which molecules constituting SAM are arranged side by side is formed on the substrate S. Since the SAM is a monomolecular film having aligned orientation of molecules, the SAM is formed thinly and uniformly. Thus, in the etching method according to the present embodiment, the substrate S can be etched thin and uniformly.

Here, when deposition using a deposition gas is performed on a substrate as in a conventional etching method, for example, a part of a film deposited on the substrate may be thick and the film may be accordingly formed with poor uniformity.FIG. 5is a schematic view showing a state in which a film is deposited on the substrate using a conventional depositing gas. The example ofFIG. 5shows a state in which a film of CFxmolecules is deposited on the substrate S using the depositing gas. As shown inFIG. 5, the CFxmolecules are stacked and deposited on the substrate S. In this way, according to the conventional etching method, it is not possible to form a thin film of CFxmolecules with good uniformity. As a result, the conventional etching method cannot etch the substrate thinly and uniformly.

Return toFIG. 1, the exhaust part6includes one or more exhaust ports61installed in a wall portion (the peripheral wall portion22in the present embodiment) of the chamber2, a pressure regulating valve63connected to the exhaust port61via an exhaust pipe62, and a vacuum pump64connected to the pressure regulating valve63via the exhaust pipe62. As the vacuum pump64sucks the internal atmosphere of the chamber2through the exhaust port61and the exhaust pipe62, the internal atmosphere of the chamber2is discharged and the internal pressure of the chamber2is reduced.

As shown inFIG. 1, a loading/unloading port71for loading and unloading the substrate S is installed in a wall portion (the peripheral wall portion22in the present embodiment) of the chamber2. The loading/unloading port71can be opened and closed by an airtight shutter72such as a gate valve or the like.

The loading/unloading port71is connected to a load lock chamber (not shown) via the airtight shutter72. The substrate S is mounted on the frame portion31of the substrate holding part3by a transfer arm installed in the load lock chamber.

The overall operation of the etching apparatus10configured as above is controlled by a controller100. The controller100is, for example, a computer and controls various parts of the etching apparatus10. The operation of the etching apparatus10is generally controlled by the controller100.

The controller100is constituted by, for example, a computer having a CPU, an MPU, a RAM, a ROM, and the like. Programs for controlling various processes to be executed by the etching apparatus10are stored in a storage part such as the RAM or the ROM. For example, an etching program for performing an etching process of an etching method to be described later is recorded on the storage part. A main control part such as the CPU or the MPU controls the operation of the etching apparatus10by reading out and executing the programs stored in the storage part such as the RAM or the ROM. The program may be recorded on a computer-readable storage medium or may be installed from the storage medium into the storage part of the controller100. Examples of the computer-readable storage medium may include a hard disk (HD), a flexible disk (FD), a compact disk (CD), a magneto optical disk (MO), a memory card, and the like.

A flow of etching the substrate S by the etching apparatus10will be described below.

The substrate S is mounted on the frame portion31of the substrate holding part3by the transfer arm installed in the load lock chamber. When the substrate S is mounted on the frame portion31of the substrate holding part3, the etching apparatus10closes the airtight shutter72and decompresses the interior of the chamber2by means of the exhaust part6. The internal atmosphere of the chamber2is maintained at a reduced pressure of, for example, 10 to 10−9Pa, specifically 10−3to 10−6Pa, by the exhaust part6.

The etching apparatus10performs the etching process of the etching method according to the present embodiment on the substrate S.FIG. 6is a flow chart showing a process flow of an etching program that performs an etching process of the etching method according to the present embodiment.

The etching apparatus10deposits straight-chain molecules containing CFxon the substrate S (step S10). For example, the controller100controls the substrate heating part51to heat the substrate S held by the substrate holding part3to a predetermined range of temperature from the start temperature at which the straight-chain molecules containing CFxstart to be vaporized. For example, when the start temperature at which the straight-chain molecules containing CFxstarts to be vaporized is about 200 degrees C., the substrate heating part51heats the substrate S to 200 to 300 degrees C. In addition, the controller100turns on the heater43of the gas generation container41to heat and vaporize the film forming material L by means of the heater43. The controller100rotates the shutter80to open the end portion of the raw material gas supply pipe44on the side of the chamber2and supply the raw material gas G of the film forming material L from the raw material gas supply pipe44. Thus, a film of straight-chain molecules containing CFxis formed on the substrate S. After performing film formation for a predetermined period of time required for the film formation, the controller100rotates the shutter80to close the end portion of the raw material gas supply pipe44on the side of the chamber2and stop the supply of the raw material gas G.

Thus, as shown inFIG. 3B, the molecular layer L1in which the straight-chain molecules containing CFxare arranged side by side is formed on the substrate S.

The etching apparatus10performs an etching process by irradiating the substrate S with an activation gas for activating CFx(step S11). For example, the controller100controls the irradiation part90to irradiate the substrate S with the activation gas for a predetermined period of time enough to consume the molecular layer L1completely. The activation gas is ejected and the substrate S is irradiated with the activation gas.

Thus, the substrate S is thinly and uniformly etched as shown inFIG. 3C. As a result, as shown inFIG. 3C, the insulating film P2is etched more than the metal layer P1.

The etching apparatus10determines whether or not a required amount of etching has been completed (step S12). For example, the controller100determines whether or not the etching process has been performed a predetermined number of times enough to obtain the required amount of etching. When the etching process has not been performed the predetermined number of times (“No” in step S12), the controller100returns the procedure to step S10and the etching process is performed again. When the etching process has been performed the predetermined number of times (“Yes” in step S12), the controller100ends the etching process.

In this manner, the etching apparatus10according to the present embodiment forms a film of straight-chain molecules containing CFxon the substrate S to be etched. The etching apparatus10irradiates the substrate S on which the film of molecules are formed with the activation gas for activating the CFx. As a result, the etching apparatus10can etch the substrate S thinly and uniformly.

In the etching apparatus10according to the present embodiment, the straight-chain molecules containing CFxhave a chemical structure of CF3—(CF2—CF2—CF2—O—)m—CH2—CH2—Si—(OCH3)3(m=10 to 20). By depositing the straight-chain molecules on the substrate S, it is possible to form a film on the substrate S thinly and uniformly.

In addition, in the etching apparatus10according to the present embodiment, the activation gas is an Ar gas. The Ar gas can efficiently activate the CFxcontained in the straight-chain molecules.

Further, in the etching apparatus10according to the present embodiment, the straight-chain molecules containing CFxare deposited on the substrate S in a state where the temperature of the substrate S is adjusted to a predetermined range of temperature from the start temperature at which the molecules start to be vaporized. As a result, the etching apparatus10can form a film of straight-chain molecules on the substrate S thinly and uniformly.

It has been described in the above embodiment with a case where the straight-chain molecules containing CFxare deposited on the etching target surface S1of the substrate S facing downward and the substrate S is irradiated with the activation gas from below the substrate S. However, the present disclosure is not limited thereto. For example, the straight-chain molecules containing CFxmay be deposited on the etching target surface S1of the substrate S facing upward and the substrate S may be irradiated with the activation gas from above the substrate S.

According to the present disclosure in some embodiments, it is possible to etch a substrate thinly and uniformly.