Gas cluster ion beam apparatus

Abstract

This invention provides a gas cluster ion beam apparatus capable of planarizing a material substrate by irradiating it with a neutral beam. A neutral gas introduction device (26) is provided for a vacuum container (2). By introducing neutral gas from the neutral gas introduction device (26), the gas cluster ion beam (11) traveling along the beamline in the beam delivery system (BT) collides with the neutral gas, undergoing dissociation and neutralization to form a high-energy neutral beam (25). Furthermore, a reflective electrode (28) is provided between an electrostatic lens (9b) and the material substrate (15), and a high voltage equal to the accelerating voltage is applied to the reflective electrode.

Description

Technical Field

[0001] The present invention relates to a gas cluster ion beam apparatus, and more particularly, to a gas cluster ion beam apparatus suitable for performing advanced surface processing on substrates made of various materials using a gas cluster ion beam. Background Technology

[0002] Patent documents 1 and 2 disclose conventional gas cluster ion beam (GCIB) devices (hereinafter sometimes referred to as such) in which a gas cluster beam is ionized by electron bombardment in an ion generator (ionization chamber). The generated gas cluster ions are extracted from the ion generator using extraction electrodes with applied high voltage, and then the beam is transmitted to an irradiation chamber using an electrostatic lens or similar means, irradiating a substrate placed within the irradiation chamber to perform surface processing on the substrate. Surface processing of various material substrates using gas cluster ion beams is performed not only on the substrate itself (such as surface smoothing) but also on processes used to adjust the thickness of films formed on the substrate (such as etching, trimming, etc.). As an example of application, the use of gas cluster ion beams for frequency adjustment in surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices is known. With improvements in device performance, trimming of these devices requires extremely flat processing with no surface roughness. The irradiated ion beam is a DC beam with a constant current value.

[0003] When a gas cluster beam is ionized by electron bombardment to obtain gas cluster ions, most of the gas cluster ion beam has a small number of single-charged ions, in which an electron has already been removed from the gas cluster particles. However, in addition to the single-charged ions, multi-charged ions that are ionized into multi-charged states are also generated, but in small quantities. It is known that the energy of multi-charged ions increases proportionally to the number of charge states of the multi-charged ions, and therefore the energy of the multi-charged ion cluster beam increases, resulting in pit-like irradiation marks on the irradiated substrate (Non-Patent Document 1). Furthermore, when irradiated with a gas cluster ion beam in a high energy range with accelerating voltages exceeding tens of kV, similar pits are generated depending on the material, even when irradiated with a gas cluster ion beam including single-charged ions, making it difficult to achieve atomic-level smoothness of the substrate surface. In particular, it is known that when irradiating a gas cluster ion beam with an inert gas such as Ar, there are limitations on surface planarization, and it is difficult to obtain a surface roughness Ra of 1 nm or less.

[0004] To address this issue, Patent Document 2 proposes a new design that incorporates a high-gas-pressure region (gas chamber) within the beam delivery system of a GCIB device. A gas cluster ion beam passes through this high-pressure region, causing the gas cluster ions to dissociate through collisions with gas particles, converting them into a large number of relatively high-energy neutral particles that irradiate the substrate. To achieve sufficient dissociation and neutralization, the design must ensure that the product of the gas pressure and the length of the gas region is sufficiently large. Maintaining high gas pressure within the gas region necessitates the use of an expensive vacuum pump system with high pumping speeds. Furthermore, the gas region (so-called gas chamber) must be separated by walls with multiple holes at both ends of the beam channel. However, since gas leaks from the gas chamber into the beam delivery system through the multiple holes, the beam delivery system, and the irradiation chamber, it is necessary to further increase the pumping speed of the vacuum pumps in each region to prevent vacuum degradation, requiring the use of expensive vacuum pumps.

[0005] On the other hand, Patent Document 3 proposes a technique in which unionized neutral cluster particles in a gas cluster ionization chamber are used as residual gas, and gas cluster ions collide with this residual gas. Therefore, the ions are neutralized. When using this technique, the collision frequency between gas cluster ions and residual gas particles is lower than the collision frequency when the gas cluster ions pass through the aforementioned high-pressure gas region (gas chamber). Therefore, the neutral beam may contain unneutralized ions. To remove these unneutralized ions, it has been proposed to install two deflection electrodes in the middle of the beam delivery system and apply a high voltage to the electrodes. This results in the removal of ions by deflection. However, in this proposed scheme, although it is not necessary to increase the pumping speed of the pump in the beam delivery system, setting two long deflection electrodes introduces a new problem of making the device longer.

[0006] Related technical documents

[0007] Patent documents

[0008] Patent Document 1: WO2023 / 248856 (PCT / JP2023 / 021620)

[0009] Patent Document 2: Japanese Patent No. 4805251

[0010] Patent Document 3: Japanese Patent Application Publication No. 2014-525813

[0011] Non-patent literature

[0012] Non-Patent Literature 1: Material Processing by Cluster Ion Beam (Isao Yamada, 2015, CR C Publishing). Summary of the Invention

[0013] Technical issues

[0014] In conventional gas cluster ion beam apparatuses disclosed in WO2023 / 248856 (Patent Document 1), the gas concentration in the beam delivery system can be increased by increasing the amount of cluster particles generated in the cluster beam generation chamber. One way to increase the number of cluster particles generated in the cluster beam generation chamber is to increase the pressure of the gas introduced into the cluster beam generation chamber. In this case, the amount of gas (including non-clustered gas molecules) flowing into the cluster beam generation chamber and beam delivery system via the interceptor also increases, causing the gas pressure in the beam delivery system to exceed a critical value required for neutralization. This not only prevents the gas cluster ion beam but also prevents the neutral beam generated by collisions and dissociation with the gas from reaching the material substrate. Therefore, there is a limitation on how much the gas pressure in the cluster beam generation chamber can be increased. In the device disclosed in Patent Document 3, a new high-pressure gas region is created between the beam delivery system and the material substrate to cause collisions and dissociation between the gas cluster ion beam and gas particles, thereby neutralizing the beam. Etching or trimming is then performed to stably obtain an extremely smooth surface (surface roughness Ra < 1 nm). Therefore, it is necessary to set the vacuum pressure (gas concentration) of the beam delivery system to a level that allows for stable operation over a long period. On the other hand, to stably operate a beam delivery system that applies a high voltage in a vacuum with gas inflow, it is necessary to maintain a gas pressure that allows for the stable application of a high voltage. This requires an expensive exhaust system capable of maintaining a high vacuum relative to the amount of gas flowing in. When neutralizing the cluster ion beam, whether the gas pressure in the cluster beam generation chamber increases or a new high-pressure gas region is created as in the device disclosed in Patent Document 3, the problem of having to use an expensive exhaust system remains. Furthermore, when a new high-pressure gas chamber is created as in the device disclosed in Patent Document 3, the device becomes longer.

[0015] The purpose of this invention is to provide a gas cluster ion beam device that, when a material substrate is irradiated with a gas cluster ion beam, achieves extremely flat processing by irradiating the material substrate with a neutral beam. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating the configuration of a gas cluster ion beam apparatus (GCIB apparatus) according to a first embodiment of the present invention.

[0017] Figure 2 This is a diagram used to explain the gas cluster ion beam apparatus according to the second embodiment, wherein a beam delivery system having a lens system excluding an insulator is used as the apparatus according to... Figure 1 Components of the GCIB device in an embodiment.

[0018] Figure 3 This demonstrates how to measure using the Faraday cup, based on... Figure 1 and Figure 2 A figure illustrating an example of the results obtained from the change in beam current flowing into the irradiation chamber caused by the introduction of gas into the GCIB apparatus of an embodiment.

[0019] Figure 4 This is a diagram used to explain the configuration of a GCIB device previously developed by the inventors and aimed at being improved by the present invention. Detailed Implementation

[0020] The gas cluster ion beam apparatus of the present invention includes: a gas generator, a cluster beam generation chamber, a cutter, a first vacuum container, an ionization chamber, an accelerating electrode and an extraction electrode, a beam delivery system, a second vacuum container, and a neutral gas introduction device. The gas generator generates a high-pressure gas for generating gas clusters. The cluster beam generation chamber has a nozzle in a vacuum. The cluster beam generation chamber generates a neutral gas cluster beam comprising clusters formed by gas atoms and / or gas molecules in the gas by injecting the high-pressure gas through the nozzle in the vacuum. The cutter is disposed at the exit port of the cluster beam generation chamber and cuts off the cluster beam from the central region of the neutral gas cluster beam. The first vacuum container communicates with the cluster beam generation chamber. The ionization chamber has a hot filament and an anode electrode and is disposed within the first vacuum container. In the ionization chamber, thermionic electrons generated by the hot filament are accelerated and collide with the cluster beam. As a result, the cluster beam introduced by the cutter is ionized and generates cluster ions. The accelerating electrode is located at the outlet of the ionization chamber, and the extraction electrode is located downstream of the accelerating electrode. Both the accelerating electrode and the extraction electrode are mounted in the first vacuum container. The beam delivery system in the first vacuum container includes one or more electrostatic lenses, to which a positive high voltage is supplied from a high-voltage power supply. Furthermore, a permanent magnet system is included in the beam delivery system. The beam delivery system is located downstream of the extraction electrode. The second vacuum container is in communication with the first vacuum container and forms an irradiation chamber within the second vacuum container. The neutralizing gas introduction device introduces neutralizing gas into at least one of the first and second vacuum containers to bring the interior of at least one of the first and second vacuum containers to the pressure required for neutralizing the cluster ion beam. The cluster ions are extracted from the ionization chamber as a cluster ion beam by the potential difference between the accelerating electrode and the extraction electrode, and the cluster ion beam delivered by the beam delivery system collides and dissociates with the neutralizing gas to generate a neutral beam, which irradiates a material substrate placed in the second vacuum chamber.

[0021] According to the present invention, the neutralizing gas introduction device is configured to adjust the pressure inside at least one of the first and second vacuum containers to the pressure required for neutralizing the cluster ion beam, thereby allowing and easily adjusting the gas pressure in the beam delivery system and achieving stable beam delivery under pressure conditions that sufficiently neutralize the gas cluster ions. Furthermore, the cluster ion beam delivered through the beam delivery system collides with the neutralizing gas to generate a neutral beam, which is then irradiated onto a material substrate placed in the second vacuum container, enabling effective neutralization of the gas cluster ions even when a specific high gas pressure region is provided.

[0022] The neutralizing gas can be: a gas of the same type as the gas used to generate gas clusters, a gas of a different type than the gas used to generate gas clusters, or a mixture of gases of the same type and different types as the gas used to generate gas clusters. For example, when generating Ar gas cluster ions, the gas flowing out of the neutralizing gas introduction device is Ar, N2, O2, Kr, etc. When generating NF3 gas cluster ions, the gas flowing out of the neutralizing gas introduction device is Ar, NF3, N2, SF6, He, H2, etc. Generally, the higher the mass number of the gas, the larger the molecular radius, which increases the probability of ion collisions and tends to improve the neutralization efficiency.

[0023] In this invention, a reflective electrode can also be introduced between the beam delivery system and the material substrate. A positive voltage is applied to the reflective electrode, which reflects unneutralized ions contained in the neutral beam. The neutral beam traveling through the reflective electrode can then irradiate the material substrate. In this way, unneutralized gas cluster ion beams (i.e., ions in the neutral beam) are reflected by the reflective electrode, and only uncharged neutral beams travel through the reflective electrode and reach the material substrate. As a result, by utilizing the reflective electrode to remove (reflect) the unneutralized ion component contained in the neutral beam, and by irradiating the substrate with a neutralized beam containing fewer ions, etching or trimming processes can be performed to obtain a material substrate with low surface roughness. The length of the reflective electrode is sufficient to be approximately the same as the length of a cylindrical electrode constituting an Ainzel lens within the beam delivery system, thus preventing the beamline from becoming too long.

[0024] The reflecting electrode preferably has a cylindrical structure with a through-channel for the passage of a neutral beam. This cylindrical structure allows for a reflection action that matches the shape of the gas cluster ion beam, which tends to diffuse into a cylindrical shape, and thus allows for effective reflection.

[0025] The positive voltage applied to the reflective electrode is preferably an accelerating voltage corresponding to the energy of the cluster ion beam (corresponding to the voltage applied to the ionization chamber and the accelerating electrode). However, even if the positive voltage applied to the reflective electrode is lower than the accelerating voltage, a significant amount of ionic components will be removed. Therefore, if a reflective electrode is provided, the surface roughness of the substrate material can be reduced compared to when no reflective electrode is provided. Furthermore, it is preferable that the positive voltage applied to the reflective electrode is variable. For example, it is preferable that the positive voltage applied to the reflective electrode is first applied to the reflective electrode at a voltage lower than the accelerating voltage applied to the accelerating electrode, and then switched to the accelerating voltage or a voltage higher than the accelerating voltage. By changing and switching the positive voltage in this way, high-speed surface processing with reduced surface roughness of the substrate material can be achieved.

[0026] The gas cluster ion beam apparatus according to the invention may further include a calorimeter and a controller. The calorimeter is heated within the second vacuum chamber by irradiation with the neutral beam. The controller determines the irradiation dose of the neutral beam from the integral value of the temperature of the calorimeter and the heating duration. The controller also determines the gas flow rate from the neutral gas introduction device, and / or the current flowing to the hot filament, or the voltage applied between the hot filament and the anode rod, based on the irradiation dose. In this way, the extraction beam current and gas flow rate of the cluster ion beam extracted from the ionization chamber can be adjusted according to changes in the integral value signal from the controller. This has the advantage of allowing the neutral beam irradiation dose on the material substrate to be accurately adjusted to a desired value. The beam current of the cluster ion beam extracted from the ionization chamber is specifically adjusted by adjusting the output voltage of the ionization power supply, the current of the hot filament heating power supply, etc.

[0027] Preferably, one or more electrostatic lenses in the beam delivery system do not include insulators. High-voltage breakdown typically tends to occur in the high-voltage application section when neutralizing gas is introduced from the neutralizing gas introduction device into at least one of the first and second vacuum containers. Abnormal breakdown may occur at the electrical insulators of the electrodes of one or more electrostatic lenses in the beam delivery system. For one or more electrostatic lenses, multiple Einzer lenses can be used, each consisting of a set of three cylindrical electrodes held together by an insulator. A high voltage, equivalent to the energy of the gas cluster ions, is applied to the electrodes of the electrostatic lenses. Therefore, if the gas flow rate from the neutralizing gas introduction device increases and the gas pressure becomes higher than necessary, abnormal electrical breakdown discharge (creep discharge) may occur along the surface of the insulator holding the electrodes of the electrostatic lenses. For this reason, it is preferable to use one or more electrostatic lenses with a structure that does not include insulators. By using a structure that does not include insulators in the beam delivery system, even if the vacuum gas pressure along the beamline increases, abnormal electrical breakdown due to creep discharge along the insulator surface is significantly reduced. As a result, cluster ions are dissociated through collisions between the cluster ion beam and the neutral gas and converted into neutral particles, thus enabling the material substrate to be irradiated with a stable neutral beam.

[0028] Description of the embodiments

[0029] The invention will now be described in detail with reference to the accompanying drawings. Before describing preferred embodiments of the invention, the configuration of a gas cluster ion beam (GCIB) device previously proposed by the inventors, which is the subject of the invention, will be described, and then preferred embodiments of the invention will be described.

[0030] Figure 4 This is a diagram illustrating the configuration of a GCIB device that was previously proposed by the inventors and is an improvement upon the subject matter of this invention. Figure 4In the accompanying drawings, the reference numerals are used as follows: 1 indicates the cluster beam generation chamber; 2 indicates the first vacuum container; 3 indicates the nozzle; 4 indicates the interceptor; 5 indicates the ionization chamber of the ion generator; 6 indicates the accelerating electrode; 7 indicates the extraction electrode; 8a, 8b, and 8c indicate vacuum exhaust pumps; 9a and 9b indicate the first and second electrostatic lenses; 12 indicates the second vacuum container; 13 indicates the Faraday cup; 14 indicates the stage for the irradiated substrate; 15 indicates the material substrate; 16 indicates the tungsten hot filament; 17 indicates the anode rod; 18 indicates the pressure reducing valve; 19 indicates the high-pressure gas cylinder; 21 indicates the permanent magnet type magnet; and 22a, 22b, and 22c indicate the first high-voltage power supply, the second high-voltage power supply, and the third high-voltage power supply. The gas generator GG includes the pressure reducing valve 18 and the high-pressure gas cylinder 19. The beam delivery system BT includes the electrostatic lenses 9a and 9b and the permanent magnet type magnet 21.

[0031] exist Figure 4 In the conventional GCIB apparatus shown, when gas introduced from the high-pressure gas cylinder 19 is ejected from the nozzle 3, condensation of atoms and molecules occurs due to adiabatic expansion, forming a neutral gas cluster. Subsequently, only the high-density neutral gas clusters located at the center of the neutral gas cluster are intercepted by the interceptor 4 and then introduced into the ionization chamber 5 of the ion generator. In the ionization chamber 5, thermionic electrons generated by the hot tungsten filament 16 are accelerated to several hundred eV corresponding to the DC voltage applied to the anode rod 17 and collide with the neutral cluster, causing ionization. Therefore, the neutral cluster is effectively ionized. Figure 4 The DC voltage power supply that applies voltage to the hot wire 16 and the anode rod 17 is not shown in the diagram.

[0032] Next, a voltage of tens of kV (Va in the figure) is applied to the accelerating electrode 6 from the first high-voltage power supply 22a via the high-voltage introduction flange 20a. Due to the voltage difference (e.g., electric field strength) between the accelerating electrode 6, to which the high voltage is applied, and the extraction electrode 7, which is at ground potential, cluster ions are extracted from the outlet of the ionization chamber 5 of the ion generator as a gas cluster ion beam 11. Then, using the first electrostatic lens 9a and the second electrostatic lens 9b, referred to as Einzer lenses, included in the beam delivery system BT, the ion beam is delivered to the material substrate 15 located in the second vacuum container 12, which serves as the vacuum container of the irradiation chamber. The first electrostatic lens 9a and the second electrostatic lens 9b are formed by fixing three cylindrical metal electrodes to each other via an electrical insulator 10b, and each of the first electrostatic lens 9a and the second electrostatic lens 9b has cylindrical electrodes E1 and E2 at both ends. A positive high-voltage bias voltage Vd is applied from the high-voltage power supply 22d, which serves as the bias power supply, to the cylindrical electrodes E1 and E2 via the high-voltage introduction flange 20d. Positive high voltages Vb and Vc are applied from the second high voltage power supply 22b and the third high voltage power supply 22c to the cylindrical center electrode E3 of the first electrostatic lens 9a and the cylindrical center electrode E3 of the second electrostatic lens 9b, respectively. By adjusting the voltages Vb and Vc applied to the center electrodes E3 in the first electrostatic lens 9a and the second electrostatic lens 9b, the beam shape can be controlled and the beam can be transmitted with very little current loss. Note that the high voltage introduction flanges 20a, 20b, and 20c are fixed to the first vacuum container 2 via the insulator 10a. The extraction electrodes 7 and the cylindrical electrodes E1 and E2 at both ends of the first electrostatic lens 9a and the second electrostatic lens 9b are at the same potential Vd.

[0033] A permanent magnet type magnet 21 is mounted between a first electrostatic lens 9a and a second electrostatic lens 9b in the beam delivery system BT. The magnet 21 deflects and removes single-charged ions (hereinafter referred to as monomeric ions) of single atoms or single molecules included in the gas cluster ion beam 11 to prevent them from reaching the material substrate 15. Monomeric ions penetrate deeply into the material substrate during irradiation and generate radiation defects deep within the surface; therefore, the magnet is used to remove monomeric ions.

[0034] The material substrate 15 is positioned with the stage 14 attached to the second vacuum container 12. Then, the gas cluster ion beam 11 is irradiated onto the material substrate 15. A Faraday cup 13 is attached to the stage 14 and is used to measure the current value of the gas cluster ion beam 11. The Faraday cup current measured by the Faraday cup 13 is measured by an ammeter (not shown), which is placed outside the second vacuum container 12 via a cable. When measuring the current value, the stage 14 for the material substrate 15 moves in the direction of the arrow in the figure, and the Faraday cup 13 is moved to a position where its axis coincides with the gas cluster ion beam 11, and the current value of the gas cluster ion beam 11 is measured.

[0035] exist Figure 4 In this process, the energy (eV) of the gas cluster ion beam 11 irradiating the material substrate 15 at a ground potential is the value of the voltage (Va, a few kV to tens of kV) applied to the ionization chamber 5 of the ion generator multiplied by the ion charge number (typically a single charge, i.e., 1). However, when the gas cluster ion beam 11 irradiates the material substrate 15, the atoms or molecules constituting the gas cluster ion beam 11 split apart, diffuse along the surface, and etch the material substrate 15, resulting in a phenomenon known as lateral sputtering. The average energy of each atom or molecule formed by the dissociation of the gas cluster ion beam 11 is given by dividing the aforementioned energy of the gas cluster ion beam by the cluster size (number) and is distributed in the range of a few eV to tens of eV (a few V to tens of V in voltage conversion). Compared to general ion beam processing equipment that performs surface processing by accelerating single-charge ions to a few kV, this GCIB equipment can provide surface processing that causes less damage to the surface structure of the material substrate 15. Furthermore, substrate processing (etching, etc.) using conventional ion beam processing machines primarily involves processing in a direction perpendicular to the surface. In contrast, processing using gas cluster ion beams utilizes the so-called lateral sputtering effect, in which dissociated atoms / molecules diffuse laterally along the surface to process it, as described above, and has the advantage of achieving excellent finishing processes for surface planarization.

[0036] Furthermore, by appropriately selecting the gas type, beam irradiation energy, and processing conditions (irradiation angle and irradiation amount), processing with small surface roughness (Ra values ​​indicating surface roughness of a few nm or less) can be achieved. When using the aforementioned magnets, single-charge cluster beams are deflected to a small extent and reach the material substrate. However, electron collisional ionization in the ionization chamber typically produces not only single-charged ions but also a small number of double-charged or more highly ionized ions. Because the energy of these ions increases proportionally to their charge state number, magnets designed for removing single-charged ions cannot be used to deflect and remove them. Because multi-charged cluster ion beams have high energy, they leave pitted irradiation marks on the substrate, resulting in increased surface roughness. Therefore, it is difficult to achieve irradiation processing with a surface roughness Ra of 1 nm or less. Furthermore, the magnets used to remove multi-charged ions must be very long and require high magnetic field strength, making it practically impossible to obtain universal irradiation equipment.

[0037] exist Figure 4 In conventional equipment, when the substrate is made of an insulating material such as SiO2, alumina, or diamond, the substrate becomes charged by the irradiated ions, causing beam divergence and making it difficult for the irradiated ion beam to effectively reach the substrate. Furthermore, if the insulating substrate is thin, there is a possibility of dielectric breakdown through the thin substrate due to charging. Therefore, in Figure 4 In the conventional equipment shown, to prevent charging, the electronic source ( Figure 4 (Not shown in the image) is placed at the midway along the beamline, and electrons from this electron source are simultaneously irradiated onto the material substrate along with the gas cluster ion beam, thus preventing charging. Another method is to provide a separate high-gas-pressure region at the midway of the beam delivery. As the gas cluster ions pass through this region, the cluster ion beam is converted into a neutral beam by colliding with the neutral gas. During this collision, the collision induces the dissociation of the cluster ion beam and neutral particles with energies lower than the incident ions. The converted high-energy neutral beam then irradiates the material substrate (see Patent Document 2).

[0038] Figure 1 This is a diagram illustrating the configuration of a GCIB device according to an embodiment of the present invention, which overcomes... Figure 4 The problem with the conventional equipment shown. In this embodiment, with Figure 4Compared to conventional GCIB equipment, a neutralizing gas introduction device 26 is provided for the first vacuum container 2 to introduce neutralizing gas, thereby creating the pressure rise required to neutralize the cluster ion beam inside the first vacuum container 2. Furthermore, in this embodiment, a cylindrical reflective electrode 28 is newly provided between the Einzer lens 9b and the material substrate 15 at the final stage of the beam delivery system BT. A high voltage equal to the accelerating voltage is applied to this cylindrical reflective electrode 28, which reflects unneutralized ions contained in the neutral beam.

[0039] In this embodiment, similar to Figure 1 In a conventional gas cluster ion beam apparatus, a high-pressure gas is injected into a cluster beam generation chamber 1 through a nozzle 3 placed in a vacuum, causing the gas atoms and / or gas molecules to expand adiabatically, thereby generating a neutral gas cluster beam containing clusters formed by the gas atoms and / or gas molecules. From the neutral gas cluster beam generated in the cluster beam generation chamber 1, a cutter 4 selects and extracts clusters from the central region of the neutral gas cluster beam, and the extracted cluster beam is introduced into an ionization chamber 5. The ionization chamber 5 is at the same potential as the accelerating electrode 6, and a positive high voltage Va equal to the voltage of the high-voltage power supply 22a is applied to the ionization chamber 5. The ionization chamber 5 is provided with a hot filament 16 and an anode rod 17. The hot filament 16 generates thermionic electrons for ionization, and an electron accelerating voltage Vi is applied to the anode rod 17 to accelerate the thermionic electrons for ionization. Cluster ions are generated by colliding and ionizing the hot electrons accelerated by the electron accelerating voltage Vi with the cluster bundle introduced into the conductive shell 51 of the ionization chamber 5 via the extractor 4. Since the hot electrons are accelerated and move in the direction of the central axis of the shell 51, ionization of neutral gas clusters occurs in the region along the central axis of the shell 51. Gas cluster ions are extracted from the ionization chamber 5 by the voltage difference between the accelerating electrode 6 and the extraction electrode 7. The energy of the gas cluster ions is the accelerating voltage Va multiplied by the electron charge (1.6 × 10⁻⁶). -19 Coulomb (denoted in eV).

[0040] The beam delivery system BT (9a, 9b, 21) extracts cluster ions from the ionization chamber 5 as a gaseous cluster ion beam 11 via the potential difference between the accelerating electrode 6 and the extraction electrode 7. The accelerating electrode 6 is located at the exit port of the ionization chamber 5, and a positive high voltage is applied to the accelerating electrode 6. The extraction electrode 7 is located downstream of the accelerating electrode 6. Next, the beam diameter of the gaseous cluster ion beam 11 is adjusted by electrostatic lenses 9a and 9b, and a positive high voltage is applied to the electrostatic lenses 9a and 9b from a high-voltage power supply. Typically, the cluster ion beam with a reduced diameter is irradiated onto a material substrate 15 placed in the second vacuum container 12.

[0041] exist Figure 1In the first embodiment, a neutral gas introduction device 26 is provided for a portion of the first vacuum container 2. Similar to the gas generator GG, the neutral gas introduction device 26 includes a pressure reduction valve and a high-pressure gas cylinder. The pressure reduction valve adjusts the gas flow rate into the first vacuum container 2 under the control of a controller 30, which will be described later. In this embodiment, the neutral gas introduction device 26 is arranged such that the neutral gas flowing into the first vacuum container 2 is directed toward the beamline of the gas cluster ion beam 11 traveling between the beam delivery system BT and the reflective electrode 28. By injecting neutral gas from the neutral gas introduction device 26 into the first vacuum container 2, the gas cluster ion beam 11, moving along the beamline in the beam delivery system BT (9a, 9b, 21), collides with the introduced gas particles, undergoes dissociation and neutralization, and generates a high-energy (tens of eV or higher) neutral beam 25.

[0042] like Figure 1 As shown by the dashed line, a neutral gas introduction device 26' can also be provided for the second vacuum container 12. When providing a neutral gas introduction device 26' for the second vacuum container 12, it is also preferable to position the neutral gas introduction device 26' such that the neutral gas is guided toward the beamline of the gas cluster ion beam 11 traveling between the beam delivery system BT and the reflective electrode 28.

[0043] As mentioned earlier, in this embodiment, a reflective electrode 28 with a tubular (or cylindrical) structure having a through-channel 28H is disposed between the second electrostatic lens 9b and the material substrate 15, and a high voltage equal to the accelerating voltage is applied to the reflective electrode 28. The reflective electrode 28 reflects and removes unneutralized ions contained in the neutral beam 25. A positive high voltage Vr is applied to the reflective electrode 28 from the high-voltage power supply 27. Unneutralized ions have a maximum energy equal to the accelerating voltage and are acted as a potential barrier by the reflective electrode 28, which is subjected to a voltage equal to the accelerating voltage, thereby preventing unneutralized ions from passing through the reflective electrode 28. Therefore, the neutral beam 25 irradiating the material substrate 15 is only a high-speed neutral beam that does not contain any ions. Therefore, by irradiating the material substrate 15 with such a neutral beam, an extremely smooth processed surface can be obtained.

[0044] Next, as a result of dissociation caused by collisions between the introduced gas from the neutralizing gas introduction device 26 and the cluster ion beam, ions corresponding to voltages typically lower than the accelerating voltage are also generated. By adjusting the voltage applied to the reflecting electrode 28 within the range from 0V to the accelerating voltage, a portion of the incidentally generated ions (dissociated ions) can exceed the voltage barrier of the reflecting electrode 28 depending on their energy and can pass through the reflecting electrode 28. However, the energy of these ions is low (a few kV to less than the accelerating voltage), lower than the energy of the gas cluster ion beam 11 irradiated into the material substrate 15 from the beam delivery system BT without neutralizing gas, thus allowing for a much smaller surface roughness of the material substrate 15 caused by irradiation. Simultaneously, the surface roughness of the material substrate 15 can also be repaired by irradiating the material substrate 15 with a large amount of neutral beams (with energies from tens to hundreds of eV). When comparing the processing speed (amount of material etched per unit time) when etching a substrate, the processing speed using only the gas cluster ion beam 11 with relatively high energy is much greater than the processing speed using a neutral beam containing slow ions generated by collisional dissociation. Therefore, by adjusting the voltage of the reflective electrode 28 as follows, high-speed, smooth processing without surface roughness can be achieved. Specifically, during etching with gas introduced from the neutral gas introduction device 26, a voltage lower than the accelerating voltage is first applied to the reflective electrode 28 to perform etching using the high-energy gas cluster ion beam 11. Subsequently, by applying a voltage equal to or higher than the accelerating voltage to the reflective electrode 28, irradiation using the gas cluster ion beam 11 is switched to irradiation using only the neutral beam 25. In this way, high-speed, smooth surface processing without surface roughness can be achieved.

[0045] When neutralizing gas is introduced from neutralizing gas introduction device 26 into the emptied first vacuum container 2, and the gas cluster ions are dissociated and neutralized by collisions with the gas cluster ion beam 11, if the flow rate of the neutralizing gas increases and the vacuum gas pressure in the beam delivery system BT (9a, 9b, 21) becomes higher than necessary, abnormal discharges (corona discharges, creep discharges) may occur at various points in the beam delivery system BT where high voltages are applied. Of course, if the flow rate of the neutralizing gas is properly controlled, abnormal discharges will not occur.

[0046] Figure 2 The diagram illustrates the configuration of a gas cluster ion beam apparatus according to a second embodiment of the invention, employing a simple structure for actively preventing such discharges, wherein no insulator is included between the cylindrical electrode of the first electrostatic lens 9a and the cylindrical electrode of the second electrostatic lens 9b (in... Figure 1 and Figure 4(The insulator is indicated by reference numeral 10b in the accompanying drawing). In other words, the second embodiment provides a gas cluster ion beam apparatus that performs neutralization of the gas cluster ion beam with minimal abnormal discharge in the beam delivery system BT. Figure 2 In the second embodiment shown, the insulators of the first electrostatic lens 9a and the second electrostatic lens 9b included in the beam delivery system BT are removed, and their central cylindrical electrodes are directly connected to flanges 20b and 20c. This configuration was proposed by the inventors in Patent Document 3. Figure 2 In one embodiment, a neutral gas introduction device 26 is provided for the first vacuum container 2 of the bundled beam delivery system BT, and a cylindrical reflective electrode 28 is further provided between the exit port of the bundle delivery system BT (the end of the electrostatic lens 9b) and the material substrate 15, and a positive high voltage Vr is applied to the reflective electrode 28 from the high voltage power supply 27.

[0047] Figure 4 The configuration of the conventional gas cluster ion beam apparatus shown does not allow for direct electrical measurement of the irradiation dose (proportional to the substrate etching amount) of the neutral beam 25 obtained by dissociation due to collisions between the cluster ion beam and gas particles. In order to perform irradiation with good reproducibility using an energy-neutral beam, it is necessary to properly measure the amount of neutral beam flowing into the material substrate and to control the irradiation time and irradiation conditions (gas inflow rate, etc.) based on the measurement results.

[0048] Therefore, in Figure 1 and Figure 2 In the illustrated embodiment, the Faraday cup 13, attached to the measurement of the amount of ion beam, also provides a calorimeter 29 to measure the heat generated by irradiation of the neutral beam 25. Similar to the Faraday cup 13, the calorimeter 29 is attached to the stage 14 and measures the heat generated by irradiation of the neutral beam 25. When performing measurements using the calorimeter 29, the stage 14 is moved to a position where the axis of the calorimeter 29 is aligned with the axis of the neutral beam 25.

[0049] The calorimeter 29 may be a substrate of a metal or semiconductor with a small heat capacity, to which the thermocouple is attached. The calorimeter 29 is a device for measuring the heat absorbed and emitted by a material, and several types of thermocouple-type calorimeters are currently commercially available. The temperature of the calorimeter 29 increases with the onset of neutral beam irradiation and stabilizes at a constant temperature. If the amount of neutral beam is constant, the temperature of the calorimeter 29 will remain constant. The amount of neutral beam varies depending on the amount of gas cluster ion beam 11 extracted from the ionization chamber 5.

[0050] The amount of neutral beam irradiation is determined by an integral value (integrated value), which is obtained by integrating over temperature and the time it is held at that temperature. Therefore, the current value of the gas cluster ion beam 11 extracted from the ionization chamber 5 is controlled to achieve the predetermined integral value. Integral control is performed by the controller 30. Figure 1 and Figure 2 In the illustrated embodiment, based on a control signal from controller 30, the current value of the extracted gas cluster ion beam and the flow rate of the gas introduced from the neutralization gas introduction device 26 are adjusted according to changes in the integral value. The current of the extracted gas cluster ion beam is adjusted by adjusting the voltage (referred to as the ionization voltage) applied to the anode rod 17 in the ionization chamber 5 and the current in the hot filament of the ionization chamber 5. In actual irradiation work, such as Figure 1 As indicated by the arrows, the substrate is mechanically scanned multiple times during the irradiation process, so the neutral beam 25 inevitably enters the calorimeter 29 during these multiple scans. Therefore, an integration process is performed based on the temperature rise measured by the calorimeter 29 when the neutral beam 25 enters the calorimeter 29 during these multiple scans, and the irradiation is adjusted based on the result of this integration process.

[0051] Figure 3 An example is shown of the relationship between the gas flow rate from the neutral gas introduction device 26 and the gas cluster ion beam current (FC beam current) measured by the Faraday cup 13 when gas is introduced using the neutral gas introduction device 26. Figure 3 In the diagram, when the accelerating voltage is 60kV, the black circle represents the FC beam current I0 when the voltage applied to the reflective electrode 28 is set to 0V, and the white circle represents the FC beam current I0 when the accelerating voltage is 60kV and a voltage of 60kV is applied to the reflective electrode 28 at a gas flow rate of 80 sccm (standard cubic centimeters per minute). 60 . Figure 3 The curves in the diagram show that when the voltage Vr of the reflective electrode 28 is set to 0V, the collisional dissociation of the gas cluster ion beam proceeds with increasing gas flow rate, the gas cluster ion beam current gradually decreases, and the gas cluster ion beam is converted into a neutral beam. The difference between the beam current at a gas flow rate of 0 sccm and the beam current at each gas flow rate corresponds to the current of the neutral beam. However, even with increased gas flow rate, the FC beam current cannot be reduced to zero completely because the proportion of beams colliding between gas cluster ion beams extracted from the ionization chamber 5 increases exponentially with distance from the extraction electrode 7. If the gas cluster ion beam is transmitted a sufficiently long distance, the FC beam current can be reduced to zero.

[0052] exist Figure 1 In the first embodiment, when the gas flow rate is from Figure 3As the conditions shown increase further, abnormal discharges (creep discharges) frequently occur in the insulator 10b of the electrodes in the electrostatic lenses 9a and 9b of the fixed beam delivery system BT, making stable irradiation difficult. Furthermore, when the gas flow rate is 80 sccm or less, the frequency of abnormal discharges decreases with decreasing gas flow rate. As described above, in Figure 3 In the diagram, when the gas flow rate is 80 sccm and the voltage applied to the reflector 28 is 60 kV, the FC beam current is close to zero, as shown by the white circle. As the voltage applied to the reflector 28 is further increased, the FC beam current becomes zero, and the unneutralized ion beam component also becomes zero. When the gas flow rate is 80 sccm and the voltage of the reflector is 60 kV or less, the FC beam current changes from a white circle to a black circle depending on the voltage of the reflector. At other flow rates, if the voltage of the reflector is set to 60 kV, the FC beam current also becomes close to zero. Therefore, at voltages less than 60 kV, a mixed irradiation beam containing both ion and neutral beams is obtained. By including the ion beam in the neutral beam, a considerably high trimming speed can be achieved. Furthermore, the presence of the neutral beam reduces the roughness of the sample surface, resulting in a flatter surface compared to irradiation with the ion beam alone. Figure 3 The results are shown when Ar ions are used as gaseous cluster ions and Ar gas is used as the neutralizing gas, but similar results were obtained with combinations of other gas species (N2, O2, Kr, CO2, SF6, NF3). Mixtures of the above gases also confirmed the results.

[0053] Next, under the condition that the voltage applied to the reflective electrode 28 is zero and the neutralizing gas is introduced at a constant flow rate ( Figure 3 (the black circle in the image), and under the condition that a voltage of 60 kV equal to the accelerating voltage is applied to the reflective electrode 28 at a gas flow rate of 80 sccm ( Figure 3 The white circle (in the diagram) was irradiated with a beam for the same fixed period of time onto a silicon wafer with a SiO2 film. As a result, etching of SiO2 was confirmed in both cases. Under the condition of the black circle, the etching amount was greater, but it was found that as the conditions approached those of the white circle, the surface roughness became a flatness of Ra < 1 nm.

[0054] exist Figure 1 and Figure 2In the illustrated embodiment, the gas used to generate gas clusters is Ar (argon), N2 (nitrogen), CO2 (carbon dioxide), O2 (oxygen), Kr (krypton), NF3 (nitrogen trifluoride), SF6 (sulfur hexafluoride), or a mixture of these gases obtained by diluting them with He, N2, etc. The neutralizing gas (suitable for causing collisional dissociation of gas cluster ions) introduced from the neutralizing gas introduction device 26 into the first vacuum container 2 or the second vacuum container 12 can be the gas used to generate clusters, or a combination of different gases. The gas to be used is appropriately selected based on the neutralization efficiency and the chemical reactivity of the neutral beam.

[0055] In the two embodiments described above, conditions for irradiating the material substrate with a neutral beam were described. However, if the voltage applied to the reflective electrode is set to be equal to or lower than the accelerating voltage, a neutral beam containing ions can be irradiated. In this case, the trimming speed can be faster than when irradiating a neutral beam that does not contain ions. However, by selecting an appropriate accelerating voltage, it has been found that a smooth surface can be obtained while maintaining an appropriate trimming speed. It has also been found that surface smoothness improves as the voltage applied to the reflective electrode approaches the accelerating voltage.

[0056] Industrial applications

[0057] According to the present invention, a neutralizing gas introduction device is provided to adjust the pressure inside at least one of a first vacuum container and a second vacuum container to the pressure required for neutralizing the cluster ion beam, making it possible and easy to adjust the gas pressure in the beam delivery system and achieve stable beam delivery at a pressure that can sufficiently neutralize the gas cluster ions. Furthermore, the cluster ion beam delivered through the beam delivery system collides with neutralizing gas particles to generate a neutral beam, which is then irradiated onto a material substrate placed in the second vacuum container, such that the gas cluster ions can be effectively neutralized without providing a special high gas pressure region.

[0058] [Figure Labels]

[0059] 1... Cluster bundle generation chamber

[0060] 2...First vacuum container

[0061] 3…… Nozzle

[0062] 4... interceptor

[0063] 5...Ionization Chamber

[0064] 6...Accelerating Electrode

[0065] 7……Electrode Extraction

[0066] 8a, 8b... Vacuum exhaust pumps

[0067] 9a, 9b... First electrostatic lens and second electrostatic lens

[0068] 10a, 10b, 10c... Insulators

[0069] 11... Gas Cluster Ion Beam

[0070] 12...Second Vacuum Container

[0071] 13... Faraday Cup

[0072] 14... Platform

[0073] 15……Material Substrate

[0074] 16... Hot wire

[0075] 17……Anode rod

[0076] 18... Pressure Reduction Cocktail

[0077] 19... gas cylinder

[0078] 20……High Voltage Inlet Flange

[0079] 21...Permanent magnet type magnet

[0080] 22a, 22b, 22c... First to third high-voltage power supplies

[0081] 22d...Separate high-voltage power supply

[0082] 23……Common Electrode

[0083] 24……Insulators

[0084] 25……neutral bundle

[0085] 26…… Neutralization gas introduction device

[0086] 27……High-voltage power supplies for reflective electrode applications

[0087] 28……Reflecting Electrode

[0088] 29……calorimeter

[0089] 30……Controller

Claims

1. A gas cluster ion beam device, comprising: A gas generator for generating high-pressure gas for generating gas clusters; A cluster beam generation chamber having a nozzle in a vacuum, the cluster beam generation chamber generating a neutral gas cluster beam comprising clusters of gas atoms and / or gas molecules in the gas by injecting the high-pressure gas through the nozzle in the vacuum. A cutter is disposed at the exit of the cluster bundle generation chamber, and the cutter cuts off the cluster bundle from the central region of the neutral gas cluster bundle; A first vacuum container, which is connected to the cluster bundle generation chamber; An ionization chamber having a hot filament and an anode electrode and disposed within the first vacuum container, wherein hot electrons generated by the hot filament are accelerated and collide with the cluster beam to ionize the cluster beam introduced through the interceptor and generate cluster ions; An accelerating electrode and an extraction electrode are provided, wherein the accelerating electrode is disposed at the outlet of the ionization chamber and the extraction electrode is disposed downstream of the accelerating electrode, and both the accelerating electrode and the extraction electrode are disposed in the first vacuum container; A beam delivery system is disposed in the first vacuum container, the beam delivery system comprising one or more electrostatic lenses and permanent magnet type magnets, and a positive high voltage is applied to the one or more electrostatic lenses from a high voltage power supply; A second vacuum container, which is connected to the first vacuum container, and forms an irradiation chamber within the second vacuum container; and A neutralizing gas introduction device is provided for introducing neutralizing gas into at least one of the first vacuum container and the second vacuum container, so that the interior of at least one of the first vacuum container and the second vacuum container reaches the pressure required for neutralizing the cluster ion beam; The cluster ions are extracted from the ionization chamber as a cluster ion beam by means of the potential difference between the accelerating electrode and the extraction electrode, and the cluster ion beam transmitted by the beam delivery system collides with the neutralizing gas to generate a neutral beam, which is then irradiated onto a material substrate placed in the second vacuum chamber.

2. The gas cluster ion beam device according to claim 1, wherein, A reflective electrode is disposed between the beam delivery system and the material substrate. A positive voltage is applied to the reflective electrode, which reflects unneutralized ions contained in the neutral beam. The neutral beam traveling through the reflective electrode is guided onto the material substrate.

3. The gas cluster ion beam device according to claim 2, wherein, The reflective electrode has a cylindrical structure, and the cylindrical structure is provided with a through channel for the neutral beam to pass through.

4. The gas cluster ion beam apparatus according to claim 2, wherein, The positive voltage applied to the reflective electrode is variable.

5. The gas cluster ion beam apparatus according to claim 4, wherein, After applying a voltage lower than the acceleration voltage applied to the acceleration electrode to the reflective electrode, the positive voltage applied to the reflective electrode is switched to the acceleration voltage or a voltage equal to or higher than the acceleration voltage.

6. The gas cluster ion beam apparatus according to claim 1, wherein, The neutralizing gas is a gas of the same type as the gas used to generate the gas clusters, a gas of a different type than the gas used to generate the gas clusters, or a mixture of gases of the same type and different types used to generate the gas clusters.

7. The gas cluster ion beam apparatus of claim 1 further includes a calorimeter and a controller, the calorimeter being heated by irradiation of the neutral beam within the second vacuum container, the controller determining the irradiation amount of the neutral beam from the integral value of the temperature of the calorimeter and the heating duration, and the controller determining, based on the irradiation amount, the gas flow rate from the neutral gas introduction device, and / or the current flowing to the hot filament, or the voltage value applied between the hot filament and the anode rod.

8. The gas cluster ion beam apparatus according to claim 1, wherein, One of the electrostatic lenses in the beam delivery system does not include an insulator.

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