JP4636862B2 - Gas cluster ion beam irradiation system - Google Patents

Description

  The present invention relates to an apparatus for performing surface processing by irradiating a gas cluster ion beam.

  With the miniaturization of the wiring of a semiconductor device and the improvement of the recording density of a magnetic recording device, a gas cluster ion beam has attracted attention as a method for manufacturing a semiconductor device and a magnetic head. A gas cluster is a cluster of hundreds to thousands of gas atoms or molecules (hereinafter referred to as monomers). A large number of gas atoms or molecules constituting a gas cluster do not form chemical bonds with each other, but merely aggregate to form a single mass. The generation method is described in Patent Document 1. The ionized gas cluster ions are accelerated by the accelerating voltage and irradiated onto the workpiece. When the gas cluster ions collide with the workpiece, the incident energy is distributed to the individual atoms constituting the gas cluster ions, so that irradiation with higher density and lower energy is possible compared to the monomer ion beam.

  Non-Patent Document 1 shows that the gas cluster ion beam generated as described above has characteristics different from those of the conventional monomer ion beam. For example, when a conventional monomer ion beam is irradiated perpendicularly to the workpiece surface, surface roughness occurs, whereas when a gas cluster ion beam is irradiated perpendicularly to the workpiece surface, the uneven surface can be flattened by the lateral sputtering effect. . When a gas cluster ion beam is used, it is easy to reduce the average surface roughness to 1 nm or less. Moreover, since gas cluster ions have a large mass, irradiation at a lower speed is possible compared to monomer ions even when the same acceleration voltage is applied. Therefore, the processing damage depth can be reduced as compared with the process using monomer ions. Furthermore, a non-linear effect resulting from multiple collisions of atoms constituting the gas cluster ions can provide a sputtering rate that is about an order of magnitude higher than that of the monomer ion beam process.

  As a planarization technique, there is a conventional method of irradiating a monomer ion beam obliquely as described in Patent Document 2 as a method using an ion beam in addition to a polishing technique such as chemical mechanical polishing (CMP). Are known. According to the method of Patent Document 2, it is said that protrusions can be selectively etched by irradiating monomer ions obliquely.

JP-A-4-354865 Japanese Patent Laid-Open No. 10-200169 I. Yamada, et al, Mater. Sci. Eng. , R. 34, (2001) pp. 231-295

  The recording density of magnetic disk recording devices (HDD) is increasing at an annual rate of 60 to 100%, and this trend is said to continue in the future. Along with this, the distance between the magnetic head flying surface and the magnetic disk (head flying height) is becoming smaller, and it is essential to reduce the surface roughness and the processing damage depth of the magnetic head flying surface. In the future, it is necessary to suppress the surface roughness and the processing damage depth to about 1 nm.

  Currently, processing damage occurs in the polishing used in the flattening process of the air bearing surface of the magnetic head. Although the depth of processing damage has been reduced by improving the slurry, abrasive grain size, polishing method, etc., the value is generally estimated to be about 5 to 10 nm.

Processing damage also occurs when processing is performed using a monomer ion beam. In order to perform processing at a high sputtering rate using a monomer ion beam, it is necessary to irradiate with high energy ions. Thereby, implantation (intrusion) of primary ions occurs. Although the primary ion penetration depth can be somewhat reduced by the oblique irradiation of the monomer ion beam, it is impossible to prevent the primary ion penetration because the sputtering proceeds due to the collision cascade phenomenon. For example, according to a simulation (TRIM, copied by IBM) for determining the behavior of ions irradiated on a material surface, when ArFe is irradiated with Ni ion at 400 eV, the maximum depth is obtained when irradiated perpendicularly to the surface. Implanted to about 30 nm. Even when the same ion beam is irradiated from a direction of 85 ° with respect to the normal direction of the NiFe surface, there are those that are implanted to about 21 nm, and the effect of the irradiation angle is limited.
Further, as a problem of sputtering using a monomer ion beam, there is mixing of atoms to be sputtered. The depth of the mixing layer can be reduced by reducing the energy of ions to be irradiated or performing oblique irradiation. The mixing layer depth is estimated to be about 2 to 5 nm when primary ions are irradiated at 500 eV from a direction of 60 ° with respect to the normal of the irradiated surface.
Mixing cannot be prevented using a gas cluster ion beam. It was experimentally confirmed that when the Ar gas cluster ion beam having a cluster size of about 2,000 was irradiated at 10 keV, the thickness of the mixing layer was about 10 nm.

Furthermore, there is a horizontal mixing characteristic when the magnetic head air bearing surface is processed by oblique irradiation of a monomer ion beam. On the air bearing surface of the magnetic head, a cross section of a multilayer laminated film composed of an extremely thin film such as metal or metal oxide is exposed. When the monomer ion beam is irradiated obliquely, knock-on atoms (recoil atoms) move to adjacent layers by the collision cascade, and horizontal mixing occurs. As a result, the desired magnetic properties are lost in the outermost surface layer, which is a problem in manufacturing the magnetic head.
It is difficult to suppress the depth of the processing damaged layer to about 1 nm using any of the methods described above. Whether it is a monomer ion beam or a gas cluster ion beam, the processing damage depth can be reduced to some extent by reducing the energy of the ion beam to be irradiated. However, in the case of a monomer ion beam, it is technically difficult to obtain a monomer ion beam having a low energy of about several tens eV and a large current due to the space charge effect. On the other hand, in a gas cluster ion beam obtained by ionizing an aggregate of several thousand atoms, it is easy to set the energy per atom to several tens eV, but processing damage of about 2 to 10 nm is formed. That is, it is difficult to obtain a magnetic head air bearing surface in which the processing damage depth is suppressed to the 1 nm level by the conventional polishing technique or ion beam technique.

In order to solve the above problems, in the present invention, an irradiation angle adjusting mechanism for adjusting an angle (irradiation angle) with respect to a normal line of a work surface of a workpiece to 50 ° or more and 90 ° or less, and a desired kinetic energy of ions Provided is a gas cluster ion beam irradiation apparatus having an ion acceleration mechanism for adjusting a value and a workpiece rotation mechanism for rotating the workpiece with the normal direction of the processed surface of the workpiece as a rotation axis.
Also, an irradiation angle adjusting mechanism for adjusting an angle (irradiation angle: θ °) with respect to the normal of the work surface of the workpiece, and an ion accelerating mechanism for adjusting ion kinetic energy (E _a ) to a desired value, A gas cluster ion beam irradiation apparatus having a cluster size (N) adjustment mechanism and a workpiece rotation mechanism for rotating a workpiece with the normal direction of the work surface of the workpiece as a rotation axis, wherein θ, E _a , N Is controlled so that 0.02 eV ≦ (E _a / N) × cos ² θ ≦ 0.5 eV.

The present invention makes it possible to reduce the energy component in the direction perpendicular to the workpiece processing surface while taking advantage of the gas cluster ion beam that provides a sputtering rate one order of magnitude higher than that of conventional monomer ion beams. Flattening with low damage that cannot be realized with an ion beam is possible. Specifically, intrusion of primary ions cannot be avoided even if irradiation is performed obliquely with a conventional monomer ion beam, but invasion of primary ions can be essentially suppressed with a gas cluster ion beam. Furthermore, gas cluster ion beam sputtering is caused by the high temperature and high pressure of the gas cluster ion collision point regardless of the collision cascade and knock-on phenomenon (recoil mixing in the irradiated material). Therefore, since the high temperature region becomes shallow by making the gas cluster ions enter obliquely, the mixing depth can be reduced. Furthermore, according to the present invention, horizontal mixing can be prevented by setting the irradiation angle of the gas cluster ion beam to an appropriate value. In addition, the projections on the workpiece machining surface have a smaller irradiation angle than the workpiece machining surface, and the sputtering rate increases, so the projection is selected with a higher sputtering rate than conventional monomer ion beams. Can be flattened. In addition, by irradiating a gas cluster ion beam obliquely with respect to the normal direction of the workpiece processing surface, the workpiece is rotated about the normal direction of the workpiece processing surface as the rotation axis, so that one projection is shaded by another projection. This prevents the phenomenon that machining does not proceed.

  Examples will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a first embodiment of the present invention. When high-pressure Ar gas is ejected from the nozzle 2 connected to the pipe 1 to the cluster generation chamber 3, a neutral gas cluster beam having no electric charge is generated. The cluster generation chamber 3 is evacuated below the pressure generated by the cluster by a vacuum pump (not shown). Further, the central portion of the gas cluster beam is extracted by the skimmer 4 and introduced into the ionization chamber 5. The ionization chamber is also evacuated to a pressure that does not hinder ionization and ion beam transport by a vacuum pump (not shown). This pressure depends on the size and energy of the gas cluster ions, but when irradiating gas cluster ions of size 2000 at 20 keV, the pressure is 2.5 × 10 ⁻⁵ Torr (≈3.3 × 10 ⁻³ Pa) or less. is there. Clusters that have entered the ion source 6 (known as the EI ion source) installed in the ionization chamber 5 are ionized by collision with the thermal electrons generated from the filament 7 to form monovalent gas cluster ions, and further the electrode 8 , 9 and 10 are extracted from the ion source 6 as a gas cluster ion beam 17. The gas cluster ions are accelerated so as to have a predetermined kinetic energy by an ion acceleration mechanism including the electrodes 8, 9, and 10. The accelerated gas cluster ions are transported to the irradiation chamber 13 and irradiated onto the work 15 fixed to the work holder 14. Although not shown, the work holder 14 includes an irradiation angle adjusting mechanism for adjusting an angle (irradiation angle: θ) with respect to the normal 16 of the processing surface to a desired angle of 50 ° or more and 90 ° or less, and the normal. Is provided with a rotation mechanism for rotating around the center axis.

  In the ion source 6, a current that causes the filament 7 to red heat is supplied by a power source (not shown), and the generated thermoelectrons are accelerated to Ar ionization voltage (15.7 eV) or more and collide with a neutral gas cluster. Gas cluster ions are generated.

  The ion acceleration mechanism is composed of electrodes 8, 9, and 10. The electrode 8 is equipotential with the ion source 6, a positive high voltage, for example, 20 kV is applied thereto, a negative high voltage, for example, −20 kV is applied to the electrode 9, and the electrode 10 is a ground electrode. In this case, the voltage applied to the electrode 8 becomes the acceleration voltage of the gas cluster ions. With such a configuration, a gas cluster ion beam having an irradiation energy of 20 keV can be obtained.

  A magnet 11 for generating a magnetic field perpendicular to the beam is installed on the trajectory of the gas cluster ion beam. When passing through this magnetic field, monomer ions contained in the beam are strongly influenced by the Lorentz force and deviate from the initial trajectory. This monomer ion is generated when the gas cluster is ionized. The gas cluster ions are also affected by the Lorentz force, but the influence is negligible because the mass-to-charge ratio (m / z, m is the mass number and z is the charge number) is large. That is, the magnet 11 functions as an energy filter known as an alpha filter or the like, and prevents irradiation with monomer ions having a low mass-to-charge ratio (easily accelerated) of the workpiece 15 (workpiece). The work 15 is irradiated with monovalent gas cluster ions by lowering its energy resolution in the vicinity of the mass-to-charge ratio of the valent gas cluster ions (for example, m / z ≧ 1,000). Therefore, when an aperture having an appropriate hole diameter is provided between the ionization chamber 5 and the irradiation chamber 13, only gas cluster ions pass through the aperture and monomer ions are prevented from being irradiated onto the workpiece.

  Further, a neutralizer 12 is installed in the vicinity of the trajectory of the gas cluster ion beam 17 from the ion source 6 to the workpiece 15. In the neutralizer 12, the work 15 and the work holder 14 are irradiated with the positively charged gas cluster ion beam 17 and are positively charged, so that the gas cluster ion beam 17 does not easily reach the charged work 15 thereafter. To solve the problem. The neutralizer 12 passes through a filament connected to a power source (not shown) by a current that is red-hot, and irradiates the work 15 and the work holder 14 with thermoelectrons (negative charges) generated from the filament. Is prevented from being positively charged. The thermoelectrons generated from the neutralizer 12 reach the workpiece 15 along a trajectory generally similar to that of the gas cluster ion beam 17.

  FIG. 2 shows an irradiation angle θ of 50 ° or more while rotating a workpiece 15 fixed to a workpiece holder 14 having an irradiation angle adjustment mechanism and a rotation mechanism in an irradiation chamber 13 around the normal 16 of the workpiece surface. An enlarged view of the state in which the gas cluster ion beam 17 is irradiated with the temperature adjusted below is shown. In FIG. 2, the rotation mechanism of the work holder 14 and the irradiation angle adjustment mechanism are not shown. Further, FIG. 3 shows an enlarged view of the vicinity of the irradiation surface 18 of the work 15. As shown in FIG. 3, by irradiating with the gas cluster ion beam irradiation apparatus according to the present invention, the irradiation angle (θ ′) to the surface of the projection 19 scattered on the workpiece surface 18 is set to the irradiation to the workpiece surface 18. It becomes smaller than the angle (θ). The irradiation angles θ and θ ′ are defined as deviations in the incident direction of the gas cluster ion beam 17 with respect to the normals 16 and 20 with respect to the respective surfaces of the workpiece 15 and the protrusion 19, and the smaller the value, the more the gas cluster ion beam. 17 is incident in a state of being nearly perpendicular to the surface. Therefore, the degree to which the surface of the protrusion 19 is etched by the gas cluster ion beam 17 (etch rate) is larger than the etch rate of the workpiece surface 18. Therefore, the protrusion 19 is selectively etched and removed, and as a result, the work surface 18 is flattened. Further, since the work holder 14 is rotated with the normal 16 of the work surface 18 as the rotation axis, the incident direction of the gas cluster ion beam 17 is fixed with respect to the work surface 18 (the work surface 18 is not rotated). In some cases, the projections 19 are behind the projections 19 when viewed from the incident direction of the gas cluster ion beam 17, and other projections (not shown) where etching does not proceed can also be etched, thereby speeding up the flattening of the entire work surface 18. be able to.

FIG. 4 shows the content of elements in a sample having a 50 nm thick NiFe film formed in the depth direction from the surface of the NiFe film using a secondary ion mass spectrometer (hereinafter referred to as SIMS). The results measured along are shown. SIMS ionizes elements existing at the excavated depth while digging the NiFe film with primary ions (gallium (Ga), cesium (Cs), etc. are used) irradiated on its surface, and this is secondary Identify as an ion. 4A shows the NiFe film with an Ar (argon) gas cluster ion beam, and FIG. 4B shows the NiFe film with an Ar monomer ion beam. The irradiation energy is 20 keV and the dose (the direction of travel of the ion beam). The content (arbitrary unit) of each element of Ni, Fe, and Ar in the sample irradiated under the condition of 5 × 10 ¹⁵ ions / cm ² , which is orthogonal to the unit cross-sectional area orthogonal to the surface of the NiFe film It is shown as a so-called “depth profile” measured along the depth direction. On the other hand, FIG. 4C shows the depth profile of each of Ni, Fe, and Ar in the NiFe film that is not irradiated with any of such ion beams. Ar detected in the depth profile (thickness: 0 to 50 nm) in the depth profile (FIG. 4C) of the NiFe film that is not irradiated with Ar gas cluster ions or monomer ions, A sputtering target containing nickel (Ni) and iron (Fe) was sputtered with Ar ions while depositing Ni atoms and Fe atoms on the sample surface (NiFe film forming process), and was incorporated into this NiFe film. Is.

  In the NiFe film irradiated with the Ar monomer ion beam, Ar ions of 5,000 to 50,000 as arbitrary units are detected over the entire thickness (50 nm) as shown in FIG. 4B. However, in the NiFe film irradiated with the Ar gas cluster ion beam, as shown in FIG. 4A, only about 100 Ar ions were detected in an arbitrary unit, and the values thereof were It is approximately the same as the Ar ion shown in 4 (c). Therefore, in the NiFe film irradiated with the Ar monomer ion beam, Ar is implanted over the entire thickness (50 nm) as shown in FIG. In the NiFe film irradiated with the beam, as shown in FIG. 4A, the penetration of Ar is substantially suppressed.

5A and 5B, Ni, Fe, and Ni in a 50 nm-thick NiFe film irradiated with a gas cluster ion beam of argon atoms at an irradiation energy of 20 keV and a dose of 1 × 10 ¹⁵ ions / cm ² are shown. The depth profile of O is shown. The NiFe film showing the depth profile in FIG. 5A is irradiated with a gas cluster ion beam at an irradiation angle of 0 °, and the NiFe film showing the depth profile in FIG. 5B at an irradiation angle of 60 °. ing. FIG. 5C shows the Ni, Fe, and O depth profiles of the NiFe film before irradiation with the gas cluster ion beam. As shown in FIG. 5C, a natural oxide film 24 is formed on the film before irradiation. As shown in FIG. 5A, when irradiation is performed at an irradiation angle of 0 °, a mixing layer 22 of a natural oxide film on the surface and a NiFe film is formed, and compositional deviation is also observed. In this mixing layer, oxygen atoms contained in the natural oxide film on the surface and oxygen atoms such as water molecules adsorbed on the surface enter the NiFe film due to collision of gas cluster ions. On the other hand, when irradiation is performed at an irradiation angle of 60 ° as shown in FIG. 5 (b), compared to FIG. 5 (c), there is no increase in the oxide film thickness due to mixing, and the compositional deviation is suppressed, Processing was possible with processing damage of 1 nm or less. The oxide film 23 (film thickness is about 1 nm) in FIG. 5B is a natural oxide film. Further, the surface roughness Ra of the sample of FIG. 5B was 0.5 nm before irradiation, but could be reduced to 0.3 nm after processing.
When the irradiation angle is smaller than 50 °, the surface roughness of the processed surface increases as the irradiation angle is increased from 0 °, and the processing damage depth similar to that shown in FIG. 5A increases. .
In the same processing, the relationship between the size (N) of the gas cluster ion to be irradiated, the irradiation energy (E _a ), and the irradiation angle (θ) is 0.02 eV ≦ (E _a / N) × cos ² θ ≦ 0.5 eV. This can also be realized. Here, the irradiation energy E _a of the gas cluster ion, multiplied by the elementary charge acceleration voltage. In the case of the apparatus shown in FIG. 1, the cluster size is determined by the pressure on the primary side of the nozzle 2, the current flowing through the filament 7, and the energy of thermoelectrons emitted from the filament 7. If the value of (E _a / N) × cos ² θ is smaller than this, the irradiation energy of gas cluster ions is too small and the processing does not proceed. On the other hand, if it is larger than this, a high etching rate can be obtained, but processing damage of about 2 to 10 nm remains on the film surface as in the case shown in FIG.
By the way, the size of gas cluster ions contained in an actual beam is not monodispersed but has a distribution. In this case, the size N is a characteristic numerical value of the distribution such as an average value or a mode value.
As described above, when the gas cluster ion beam irradiation apparatus of the present invention is used, it is possible to prevent intrusion of primary ions and to obtain a processed surface having a depth of 1 nm or less that causes processing damage such as mixing and composition shift.
In the gas cluster ion beam irradiation apparatus of the above embodiment, the cluster size, acceleration voltage (irradiation energy), irradiation angle, rotation speed of the work holder 14 and the like can be controlled from the outside without breaking the vacuum. A process can consist of multiple steps. That is, when the surface roughness before processing is large or the processing amount is large, for example, cluster ions of size 2000 are irradiated with an irradiation energy of 20 keV and an irradiation angle of 45 °, without regard to the irradiation energy and irradiation angle. After the surface roughness Ra reaches 1 nm or less or the remaining processing amount reaches 10 nm or less, the finishing process is performed by adjusting the irradiation energy, the irradiation angle, etc. within the above range. This is a gas cluster ion beam irradiation apparatus having a function. It may have a function of finely adjusting the acceleration voltage, irradiation angle, and the like to increase the number of steps to three or more from roughing to finishing.
By the way, in the said Example, although the system which consists of three chambers, the cluster generation chamber 7, the ionization chamber 5, and the irradiation chamber 13, was shown, if the cluster generation mechanism, the ionization mechanism, and the ion acceleration mechanism are provided, a chamber structure May be in other forms. The cluster generation mechanism is such that high-pressure Ar gas is ejected into the vacuum through the nozzle 2, but may be generated by other methods. The gas used is not limited to Ar. In particular, when a gas cluster ion composed of Cl ₂ , SF ₆ or the like is irradiated onto a material having reactivity with these gases, an increase in processing speed due to a chemical reaction can be expected. In addition, although ionization of the gas cluster is caused by the impact of thermoelectrons emitted from the filament, it may be photoionization by vacuum ultraviolet light, X-ray or the like. Negative ions may be generated by electron attachment or the like. The ion acceleration mechanism may have a configuration other than the above (number of electrodes, polarity of applied high voltage, etc.). In addition, when the number of monomer ions contained in the gas cluster ion beam is sufficiently small, the magnet 11 need not be installed. Further, although the neutralizer 12 is of a type that supplies electrons from a filament, any method may be used, such as a device using plasma as an electron source. In addition, the neutralizer 12 itself may not be provided if charging due to irradiation with the gas cluster ion beam does not matter, such as when the workpiece is grounded or the amount of charge is sufficiently smaller than the beam energy. Absent.

The present invention aims to reduce processing damage to the nanometer level. As the performance of semiconductor devices, magnetic heads, magnetic disks, and other magnetic devices, liquid crystal displays and other display devices, and optical devices increases, the need for processing with low processing damage increases. In these devices, the present invention can be applied to a flattening process while suppressing processing damage.

Schematic diagram of gas cluster ion beam irradiation device with beam irradiation angle adjustment mechanism and work holder rotation mechanism Schematic of work holder with irradiation angle adjustment mechanism and rotation mechanism Illustration of workpiece surface during gas cluster ion beam irradiation Depth profiles of Ni, Fe and Ar measured by SIMS Depth profiles of Ni, Fe, and O measured by SIMS

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas piping, 2 ... Nozzle, 3 ... Cluster generation chamber, 4 ... Skimmer, 5 ... Ionization chamber, 6 ... Ion source, 7 ... Filament, 8, 9, 10 ... Electrode, 11 ... Magnet, 12 ... Neutralizer, DESCRIPTION OF SYMBOLS 13 ... Irradiation chamber, 14 ... Work holder, 15 ... Work, 16 ... Normal of work surface, 17 ... Gas cluster ion beam, 18 ... Work surface, 19 ... Projection of work surface, 20 ... Protrusion produced on work surface Surface normal, 22 ... mixing layer, 23, 24 ... natural oxide film.

Claims (2)

A gas cluster ion beam irradiation apparatus including a cluster generation mechanism, an ionization mechanism of a cluster generated by the cluster generation mechanism, and an acceleration mechanism of cluster ions ionized by the ionization mechanism, and the size of gas cluster ions to be irradiated ( N), the irradiation energy (E _a ), and the relationship of the angle (irradiation angle: θ °) with respect to the normal line of the work surface to be controlled so that 0.02 eV ≦ (Ea / N) × cos 2θ ≦ 0.5 eV. A gas cluster ion beam irradiation apparatus characterized by that . The gas cluster ion beam irradiation apparatus according to claim 1 , further comprising a control device for controlling at least the cluster size, irradiation energy, and irradiation angle from the outside without breaking a vacuum.

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