JPH10289886A - Sputtering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form films on an inner surface of a hole having a high aspect ratio at a high bottom coverage. SOLUTION: A target 2 provided in a sputtering chamber 1, which comprises a gas introducing means 4 and an exhaust system 11, is sputtered by means of a sputtering power source 3 to deposit a predetermined thin film on a substrate 50 which is held by a substrate holder 5. Predetermined laser is emitted from a laser oscillator 6 to an ionized space which is in the flight path of sputtering particles from the target 2 to the substrate 50, so that the sputtering particles are ionized. A withdrawing electric field is set on the substrate holder 5 by means of a high frequency power source 7 for applying a high frequency voltage to allow the ionized sputtering particles to efficiently withdraw from the ionized space and to efficiently arrive at the substrate 50. The ionized sputtering particles can overcome the overhung at the hole edge and efficiently arrive at the bottom of the hole owing to the withdrawing electric field, thus improving the bottom coverage of the hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering apparatus used for manufacturing various semiconductor devices, and more particularly to a sputtering apparatus suitable for forming a film in a hole having a high aspect ratio.

[0002]

2. Description of the Related Art In semiconductor devices such as various memories and logics, a sputtering process is used for forming various wiring films and a barrier film for preventing interdiffusion of different layers, and a sputtering apparatus is frequently used. I have. Although there are various characteristics required for such a sputtering apparatus, it has recently been strongly required that the inner surface of a hole formed in a substrate can be covered with good coverage.

More specifically, for example, in a CMOS-FET (field effect transistor) which is frequently used in a DRAM, a barrier film is provided on an inner surface of a contact hole provided on a diffusion layer to form a contact wiring layer and a diffusion layer. The structure which prevents cross contamination of the above is adopted. Also, in the multilayer wiring structure for wiring each momericell, in order to connect the lower layer wiring and the upper layer wiring, a through hole is provided in the interlayer insulating film, and the inside of the through hole is filled with the interlayer wiring. In this case, a barrier film is formed in the through hole to prevent cross contamination.

The aspect ratio (the ratio of the depth of the hole to the size of the opening of the hole) of such a hole is increasing year by year due to the increase in the degree of integration. For example, in a 64-Mbit DRAM, the aspect ratio is 4
At 256 megabits, the aspect ratio is about 5-6.

In the case of a barrier film, it is necessary to deposit a thin film on the bottom surface of the hole in an amount of 10 to 15% with respect to the deposition amount on the surface around the hole. However, for a hole having a high aspect ratio, bottom coverage is required. It is difficult to form a film at a high rate (the ratio of the deposition rate on the bottom surface of the hole to the deposition rate on the surface around the hole). When the bottom coverage ratio decreases, the barrier film becomes thinner at the bottom surface of the hole, which may cause a fatal defect in device characteristics such as junction leak.

As sputtering techniques for improving the bottom coverage rate, techniques such as collimated sputtering and low-pressure remote sputtering have been developed. Collimated sputtering is a technique in which a plate (collimator) with a number of holes in the direction perpendicular to the substrate is provided between the target and the substrate, and only sputtered particles that fly almost perpendicular to the substrate selectively reach the substrate. is there. Also, low-pressure remote sputtering
By increasing the distance between the target and the substrate (approximately 3 to 5 times the normal), a relatively large number of sputtered particles flying almost perpendicular to the substrate are incident on the substrate, and the pressure is set lower than usual. (Approximately 0.8 mTorr or less) This is a method of lengthening the mean free path so that these sputtered particles are not scattered.

[0007] However, collimated sputtering has a problem that sputter particles are deposited on the collimator and causes a loss, resulting in a reduction in the film forming rate. There is a problem that the film forming speed is essentially reduced because the distance is increased. Due to such problems, the collimated sputtering is only used for mass-produced products in the class of 16 Mbits having an aspect ratio of up to about 3, and devices having an aspect ratio of up to about 4 are limited even in low-pressure remote sputtering. .

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional situation, and has as an object to solve the problem of enabling a film to be formed with good bottom coverage on the inner surface of a hole having an aspect ratio of more than 4. .

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present application is directed to a sputter chamber provided with an exhaust system, a target provided in the sputter chamber, and a sputter for sputtering the target. A sputtering apparatus comprising: a power supply; gas introduction means for introducing a predetermined gas into a sputter chamber; and a substrate holder for holding a substrate at a position where sputter particles are incident. A laser oscillator is provided to irradiate a predetermined laser to an ionization space set in the path to ionize sputtered particles. In order to solve the above-mentioned problem, the invention according to claim 2 is the device according to claim 1, wherein the means for setting an extraction electric field for extracting ionized sputter particles from the ionization space to reach the substrate is provided. It has a configuration of being provided. Further, in order to solve the above problem, the invention according to claim 3 is:
In the configuration of the first or second aspect, the means for setting the drawing electric field has a configuration in which a high frequency voltage is applied to the substrate holder to apply a bias voltage to the substrate. According to a fourth aspect of the present invention, in order to solve the above problem, the laser oscillator is an excimer laser oscillator in the configuration of the first, second or third aspect. According to another aspect of the present invention, there is provided a semiconductor device comprising:
According to the invention described in the first aspect, the sputter chamber includes an incident window through which a laser beam is transmitted, and the laser oscillator is provided outside the sputter chamber and the sputter chamber is sputtered from the incident window. It has a configuration in which the light enters the chamber. According to a sixth aspect of the present invention, there is provided a scanning mechanism for scanning a laser oscillated from a laser oscillator into an ionization space in the configuration of the first, second, third, fourth, or fifth aspect. It has a configuration that is. In order to solve the above-mentioned problem, the invention according to claim 7 is the configuration according to claim 1, 2, 3, 4, 5, or 6, wherein a laser oscillated from a laser oscillator passes through the ionization space a plurality of times. The reflector has a configuration in which a reflector is provided.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a schematic front view illustrating the configuration of a sputtering apparatus according to an embodiment of the present invention. The sputtering apparatus of the present embodiment includes a sputter chamber 1 having an exhaust system 11, a target 2 provided in the sputter chamber 1, a sputter power source 3 for sputtering the target 2, and a predetermined power source in the sputter chamber 1. The apparatus includes gas introducing means 4 for introducing a gas, and a substrate holder 5 for holding a substrate 50 at a position where sputtered particles emitted from the target 2 are incident.

First, the sputtering chamber 1 is an airtight container provided with a gate valve (not shown). The sputter chamber 1 is made of metal such as stainless steel, and is electrically grounded. The evacuation system 11 is constituted by a multi-stage evacuation system equipped with a turbo molecular pump, a diffusion pump, and the like, and the inside of the sputtering chamber 1 is 10 ⁻⁸ Torr.
It is possible to exhaust to the extent. In addition, the exhaust system 11
An exhaust speed adjuster (not shown) such as a variable orifice is provided to adjust the exhaust speed.

The target 2 has a disk shape with a thickness of, for example, about 6 mm and a diameter of about 300 mm, and is attached to the sputtering chamber 1 via a metal target holder 21 and an insulator 22. A magnet mechanism 30 is provided behind the target 2 so as to perform magnetron sputtering. The magnet mechanism 30 includes a center magnet 31
And a peripheral magnet 32 surrounding the central magnet 31, and a disk-shaped yoke 33 connecting the central magnet 31 and the peripheral magnet 32.
It is composed of Each of the magnets 31 and 32 is a permanent magnet, but these can be constituted by electromagnets.

The sputtering power source 3 is configured to apply a predetermined negative high voltage to the target 2. For example, in the case of titanium sputtering, a negative DC voltage of about 500 V is often applied.

The gas introducing means 4 includes a gas cylinder 41 storing a sputter discharge gas such as argon, and a gas cylinder 4.
1 is mainly composed of a pipe 42 connecting the sputtering chamber 1 and the sputtering chamber 1, and a valve 43 and a flow rate regulator 44 provided in the pipe 42 so that a predetermined process gas is introduced into a space below the target 2. Has become.

The substrate holder 5 is hermetically provided in the sputtering chamber 1 via an insulator 53, and holds the substrate 50 in parallel with the target 2. The substrate holder 5 is provided with an electrostatic suction mechanism (not shown) that sucks the substrate 50 by static electricity. The electrostatic attraction mechanism includes an attraction electrode provided in the substrate holder 5 and an attraction power supply for applying a DC voltage to the attraction electrode.
In some cases, a heating mechanism (not shown) for heating the substrate 50 during the film formation to make the film formation efficient may be provided in the substrate holder 5.

A major feature of the apparatus according to the present embodiment is that a laser oscillator 6 that irradiates a predetermined laser to an ionization space set in the flight path of the sputtered particles from the target 2 to the substrate 50 to ionize the sputtered particles. It is a point that has. In this embodiment, an excimer laser oscillator is used as the laser oscillator 6. As the excimer laser oscillator 6, for example, one having an oscillation wavelength of 193 nm excited by Ar + F gas is used. The oscillation is a pulse, and the energy of one pulse is about 10 mJ.

The laser oscillator 6 is provided outside the sputter chamber 1 as shown in FIG. 1, and the sputter chamber 1 has an incident window 12 for transmitting a laser. The entrance window 12 is formed of a material such as quartz glass or sapphire that can sufficiently transmit light of a laser wavelength.

The sputter chamber 1 has an entrance window 12
, And this opening is vacuum-sealed by a sealing member such as an O-ring. Note that the configuration in which the laser oscillator 6 is disposed outside the sputtering chamber 1 has an effect of making the entire apparatus compact without unnecessarily increasing the size of the sputtering chamber 1.
There is also an effect of preventing the atmosphere in the sputtering chamber 1 from being polluted by the members constituting the laser oscillator 6.

A scanning mechanism 61 is provided on the optical path between the laser oscillator 6 and the entrance window 12. The scanning mechanism 61 changes the direction of incidence of the laser beam on the entrance window 12 so as to irradiate a wider area of the ionization space with the laser beam. Since a laser is often oscillated in the form of a narrow beam, scanning in an ionization space is extremely effective for efficient ionization.

More specifically, the scanning mechanism 61 includes the entrance window 12
Is changed in the horizontal plane so that the laser is scanned in the ionization space. Scanning mechanism 6
As 1, a mechanism for rotating a mirror having a regular polygonal prism shape, a mechanism for rotating a plane mirror within a predetermined angle range using a galvanometer, or the like is adopted.

On the other hand, as shown in FIG. 1, the sputtering chamber 1 has an exit window 13 at a position opposite to the entrance window 12. A beam absorber 62 is arranged outside the emission window 13. Beam absorber 6
2 is a material that can efficiently absorb a laser having a wavelength oscillated by the laser oscillator 6 without reflecting the laser, for example, M
It is formed of an alloy of g0, Au, and Mo.

The laser L oscillated from the laser oscillator 6 enters the sputter chamber 1 through the entrance window 12 and is irradiated to the ionization space, and gives energy to the neutral sputter particles 200 existing in the ionization space to ionize. Ionized sputtered particles (hereinafter, ionized sputtered particles) 201 are generated. At this time, since the laser L is scanned in the ionization space by the scanning mechanism 61, the ionized sputtered particles 201 are efficiently generated.

FIG. 2 is a diagram for explaining the function of ionized sputtered particles, and is a schematic cross-sectional view of a substrate on which a film is formed. The substrate 50 has holes 5 such as contact holes.
01 is formed, and this hole 5 is formed like a barrier film.
The case where the thin film 500 is formed on the inner surface of the inner surface 01 will be described.

As shown in FIG. 2A, when a film is formed on the inner surface of the hole 501, a conventional sputtering apparatus
The thin film 50 rises at the edge of the opening of the hole 501.
0 tends to accumulate. The film deposition 502 on this portion is called an overhang. When the overhang 502 occurs, the opening of the hole 501 becomes small,
The aspect ratio of 1 is apparently higher.
As a result, a film having a low bottom coverage ratio results.

However, as shown in FIG. 2B, when the ionized sputtered particles 201 are incident on the substrate 50, the ionized sputtered particles 201 are re-sputtered at the portion of the overhang 502 and collapsed, and fall into the hole 501. can do. For this reason, a film with a high bottom coverage ratio can be formed by the neutral sputtered particles 200 and the ionized sputtered particles 201 without making the opening of the hole 501 small.

On the other hand, in the apparatus of the present embodiment, there is provided means for setting an extraction electric field for extracting the ionized sputtered particles 201 from the ionization space and reaching the substrate 50. This means, as shown in FIG.
The high frequency power supply 7 applies a high frequency voltage to the substrate holder 5 to apply a bias voltage to the substrate 50. The high-frequency power supply 7 has a frequency of 13.56 MHz and an output of about 200 W, for example, and supplies high-frequency power to the substrate holder 5 via a matching unit (not shown). The high frequency power supply 7 may have a frequency of about 60 to 100 MHz.

When a sputter discharge is generated by the sputter power source 3, plasma P is generated by the discharge below the target 2. However, when a high-frequency voltage is applied to the substrate 50 by the high-frequency power source 7, a space above the substrate 50 is generated. A weak plasma P 'is also generated. Of these, the charged particles in the plasma P ′ are periodically attracted to the surface of the substrate 50. Among them, many of the electrons having high mobility are attracted to the surface of the substrate 50 as compared with the positive ions, and as a result, the surface of the substrate 50 is in the same state as when it is biased to a negative potential. Specifically, in the case of the high-frequency power supply 7 of the above-described example,
A bias voltage of about −100 V on average can be applied to the substrate 50.

The state in which the substrate bias voltage is applied is the same as that of the cathode sheath region in the case where plasma is formed by DC bipolar discharge, and the potential falling toward the substrate 50 between the plasma P ′ and the substrate 50. An electric field having a gradient (hereinafter referred to as an extraction electric field) is set. This extraction electric field causes ionized sputtered particles 201
Are efficiently extracted from the plasma P ′ and reach the substrate 50. For this reason, the effect of the ionized sputtered particles 201 can be further enhanced.

The electric field for extraction is an electric field in a direction perpendicular to the substrate 50 and acts to accelerate the ionized sputtered particles 201 perpendicular to the substrate 50.
For this reason, the ionized sputtered particles 201 can efficiently reach the bottom surface of the hole 501 formed in the substrate 50. In this regard, a film having a high bottom coverage ratio can be formed.

It should be noted that the apparatus of the present embodiment uses the sputtered particles 2
An adhesion shield 8 for preventing adhesion of 00 and 201 to unnecessary places is provided in the sputtering chamber 1.
The deposition shield 8 is a substantially cylindrical member, and is provided so as to surround the space between the target 2 and the substrate holder 5.

When sputtered particles adhere to unnecessary places such as the walls of the sputtering chamber 1, a thin film is deposited with time. When this thin film reaches a certain amount, it peels off due to internal stress or the like, and floats in the sputtering chamber 1 as particles. When the particles reach the substrate 50, a defect such as a local thickness abnormality is generated. For this reason, in the apparatus of the present embodiment, the space between the target 2 and the substrate holder 5 is surrounded by the anti-adhesion shield 8 to prevent the sputter particles 200 and 201 from adhering to unnecessary places. Note that the deposition shield 8 is configured to be separated into an upper side and a lower side of the ionization space so as not to hinder the passage of the laser L.

Next, the configuration of another embodiment of the present invention will be described. FIG. 3 is a schematic plan view illustrating the configuration of another embodiment of the present invention. In the apparatus of this embodiment, a reflector 63 is provided to allow the laser oscillated from the laser oscillator 6 to pass through the ionization space a plurality of times. More specifically, as shown in FIG. 3, the sputter chamber 1 is provided with four reflectors 63 and one exit window 13 at the same height as the entrance window 12.

The reflector 63 is made of a plate having a mirror surface film of aluminum or the like or a plate of aluminum or the like whose surface is polished, and is configured to reflect the laser efficiently. Note that each reflector 63 is configured to form a coaxial cylindrical surface with the center axis of the sputtering chamber 1. Each reflector 63 is hermetically attached to an opening provided in the sputtering chamber 1.

[0034] The four reflectors 63 are divided into a first reflector 63A and a second reflector 6 in the order in which the laser is incident.
3B, a third reflector 63C, and a fourth reflector 63D. As shown in FIG. 3, the laser L introduced into the sputtering chamber 1 via the scanning mechanism 61 passes through the ionization space, reaches the first reflector 63A, is reflected by the first reflector 63A, and is then returned to the ionization space. And reaches the second reflector 63B. Then, after being reflected by the second reflector 63B, it passes through the ionization space again, and further, the third reflector 63C, the fourth reflector 63
The light passes through the ionization space while being reflected by D, and finally reaches the emission window 13. Then, the light passes through the emission window 13, reaches the beam absorber 62, and is absorbed by the beam absorber 62.

That is, it passes through the ionization space five times before reaching the beam absorber 62.
For this reason, the efficiency with which the energy is supplied from the laser to the neutral sputter particles existing in the ionization space increases,
It can be ionized with higher efficiency. As a result, the effect of the ionized sputtered particles can be more enhanced. In this embodiment, the scanning mechanism 61 also scans the laser so that the ionization space is evenly irradiated with the laser.

Next, the overall operation of the sputtering apparatus of each of the above embodiments will be described. The substrate 50 is carried into the sputtering chamber 1 through a gate valve (not shown), and is placed on the substrate holder 5. The inside of the sputtering chamber 1 is evacuated to about 10 ⁻⁸ Torr in advance, and after the substrate 50 is placed, the gas introducing means 4 operates to introduce a process gas such as argon at a predetermined flow rate.

The evacuation speed controller of the evacuation system 11 is controlled to evacuate the inside of the sputtering chamber 1 by, for example, 0.2 to 10 mTorr.
The sputter discharge is started in this state.
That is, a predetermined voltage is applied to the target 2 by the sputtering power source 3 and the ionized process gas 40 hits the target 2 to generate a magnetron sputter discharge. Thereby, plasma P is formed below the target 2. At the same time, the laser oscillator 6 is operated to irradiate the ionization space with the laser L. In addition, the high-frequency power supply 7 is also operated to set an extraction electric field in the ionization space.

The neutral sputtered particles 200 emitted from the target 2 by the sputter discharge fly toward the substrate 50. During the flight, when passing through the ionization space, the laser L is irradiated and ionized, and the ionized sputtered particles 201 are formed. The ionized sputtered particles 201
It is efficiently extracted from the plasma P by the extraction electric field and is incident on the substrate 50. The sputtered particles 200 and 201 incident on the substrate 50 reach the bottom and side surfaces of the hole 501 formed on the substrate 50 to deposit a film, thereby covering the inside of the hole 501 efficiently. When a thin film having a predetermined thickness is formed, the operations of the laser oscillator 6, the sputter power supply 3, and the gas introducing unit 4 are stopped, and the substrate 50 is unloaded from the sputter chamber 1.

When a barrier film is formed, a titanium thin film is formed by first using a titanium target and introducing argon as a process gas. Then, a nitrogen gas is introduced as a process gas, and a titanium nitride thin film is formed while using the reaction between titanium and nitrogen in an auxiliary manner. Thus, a barrier film in which the titanium nitride thin film is laminated on the titanium thin film is obtained.

As a configuration for ionizing sputter particles, there is a configuration in which a separate plasma is formed in a flight path of the sputter particles from the target 2 to the substrate 50, and the sputter particles are ionized in the plasma. However, in the case of this configuration, in order to perform ionization efficiently, it is necessary to form a strong plasma near the substrate 50. Therefore, charged particles (mainly electrons) in the plasma cause
0 may be damaged. However, when the sputtered particles 200 are ionized by the laser L as in the present embodiment, the problem of damage to the substrate 50 due to such charged particles in the plasma does not occur.

[0041]

EXAMPLES Examples belonging to the above embodiments include the following examples. Type of process gas: Argon Process gas flow rate: 10 cc / min Pressure during film formation: 0.25 mTorr Size of target 2: diameter 300 mm, thickness 6 mm Material of target 2: titanium Applied voltage to target 2: -500 V Input power to target 2: 9 kW Type of laser oscillator 6: excimer laser oscillator Output of laser oscillator 6: 100 W Oscillation frequency of laser oscillator: 193 nm Laser pulse width: 10 ns Laser repetition frequency: 25 Hz Maximum pulse of laser Energy: 10mJ High frequency power supply 7: frequency 400kHz output 150W

FIG. 4 shows the result of forming a film on the inner surface of the hole of each aspect ratio by operating the apparatus under the above conditions. FIG. 4 is a diagram showing the result of confirming the effect of the apparatus of the embodiment of the present invention, and also shows the result of film formation by the conventional apparatus for reference. The conventional example is an apparatus of a low-pressure remote sputtering method, in which the distance between the target and the substrate is 340 mm, and the pressure at the time of film formation is 0.3 mTorr.
This is an example in which the operation is performed under the following conditions.

As shown in FIG. 4, according to the apparatus of the above embodiment, the bottom coverage ratio is about 60% for holes having an aspect ratio of 3, and the bottom coverage rate is about 30% for holes having an aspect ratio of 5. The bottom coverage ratio is about three times that of the conventional example. For this reason, it can be a very effective device for manufacturing an integrated circuit of 256 megabit or 1 gigabit class exceeding aspect ratio 4.

In each of the above embodiments, an excimer laser oscillator is used as the laser oscillator 6. However, other lasers capable of oscillating a high energy laser (often in the ultraviolet region) such as a YAG laser oscillator or a carbon dioxide laser oscillator are used. It is also possible to use a laser oscillator. Further, the ionization sputtering apparatus of the present invention,
In addition to various semiconductor devices, it can be used for manufacturing liquid crystal displays and other various electronic products.

[0045]

As described above, according to the invention of each claim of the present application, since the sputtered particles from the target are ionized by the laser, the film is formed with a sufficient bottom coverage ratio for a hole having a high aspect ratio. It can be performed. According to the second and third aspects of the present invention, the electric field for extraction is set between the ionization space and the substrate, so that the above-mentioned effect can be further enhanced. According to the fifth aspect of the present invention, the laser oscillator is provided outside the sputter chamber. In particular, according to the invention of claim 6,
Since the laser is scanned by the scanning mechanism, ionization efficiency is increased, and a film having a high bottom coverage ratio can be formed. According to the seventh aspect of the present invention, since the laser is irradiated to the ionization space a plurality of times, the ionization efficiency is further increased and the bottom coverage ratio is further increased.

[Brief description of the drawings]

FIG. 1 is a schematic front view illustrating a configuration of a sputtering apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the function of ionized sputtered particles, and is a schematic sectional view of a substrate on which a film is formed.

FIG. 3 is a schematic plan view illustrating a configuration of another embodiment of the present invention.

FIG. 4 is a diagram showing the result of confirming the effect of the apparatus of the embodiment of the present invention, and also shows the result of film formation by the conventional apparatus for reference.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sputter chamber 11 Exhaust system 2 Target 200 Neutral sputter particle 201 Ionized sputter particle 3 Sputter power source 30 Magnet mechanism 4 Gas introduction means 5 Substrate holder 50 Substrate 6 Laser oscillator 61 Scanning mechanism 62 Beam absorber 63 Reflector 7 High frequency power supply 8 Anti-shielding shield

Claims (7)

[Claims] A sputter chamber having an exhaust system;
A target provided in the sputtering chamber, a sputtering power source for sputtering the target, gas introducing means for introducing a predetermined gas into the sputtering chamber, and a substrate holder for holding the substrate at a position where sputtered particles are incident on the target were provided. A sputtering apparatus, comprising: a laser oscillator that irradiates a predetermined laser to an ionization space set in a flight path of sputter particles from a target to a substrate to ionize sputter particles. 2. The sputtering apparatus according to claim 1, further comprising means for setting an extraction electric field for extracting ionized sputter particles from the ionization space and reaching the substrate. 3. The means for setting the electric field for extraction includes:
3. The sputtering apparatus according to claim 2, wherein a high-frequency voltage is applied to the substrate holder to apply a bias voltage to the substrate. 4. The sputtering apparatus according to claim 1, wherein said laser oscillator is an excimer laser oscillator. 5. The sputter chamber has an incident window through which a laser beam is transmitted, and the laser oscillator is provided outside the sputter chamber and allows the laser beam to enter the sputter chamber from the incident window. The sputtering apparatus according to claim 1, 2, 3, or 4. 6. The sputtering apparatus according to claim 1, further comprising a scanning mechanism for scanning a laser oscillated from the laser oscillator into the ionization space. 7. A reflector provided to allow a laser oscillated from the laser oscillator to pass through the ionization space a plurality of times.
The sputtering apparatus according to 2, 3, 4, 5, or 6.