CN110997973A

CN110997973A - Film forming method

Info

Publication number: CN110997973A
Application number: CN201880052555.7A
Authority: CN
Inventors: 赤松泰彦; 高桥律雄
Original assignee: Ulvac Inc
Current assignee: Ulvac Inc
Priority date: 2017-08-22
Filing date: 2018-06-25
Publication date: 2020-04-10
Also published as: JPWO2019039070A1; KR20200041932A; TW201912826A; WO2019039070A1

Abstract

The present invention provides a film forming method which can form an oxide film and a nitride film with high yield without using an RF sputtering method when an oxide or a nitride containing at least one of a metal element and a semimetal element as a constituent element is used as a target. An oxide film or a nitride film having a high resistance value is formed on the surface of a film to be formed by sputtering a target containing an oxide or a nitride containing at least one of a metal element and a semimetal element as a constituent element in a vacuum atmosphere. A plurality of targets having the same composition are arranged in parallel in the same plane, and alternating current power of a predetermined frequency is applied between a pair of targets among the targets arranged in parallel, and each target is alternately switched between an anode electrode and a cathode electrode, thereby generating plasma between the targets to sputter the target serving as the cathode electrode.

Description

Film forming method

Technical Field

The present invention relates to a film formation method for forming an oxide film or a nitride film, and more particularly, to a film formation method for forming SiO by a sputtering method₂Film, TaSiO₂Film, CrSiO₂Film and NbSiO₂A method for forming an oxide film or a nitride film having a high resistance value such as a film.

Background

For example, in a heating resistor for a thermal head used in a thermal printer, there are thin film products formed by a sputtering method and a vacuum deposition method, and it is known to use TaSiO₂Film, CrSiO₂Film and NbSiO₂Oxide films having a high resistance value such as a film are used as such thin film products. When such an oxide film is formed, the resistance value changes greatly if the composition ratio of a transition metal element such as Ta, Cr, or Nb, a semimetal element such as Si, and oxygen changes slightly. Therefore, the oxide film for the above-described application is generally formed by a sputtering method.

Specifically, an oxide containing a transition metal element such as Ta, Cr, or Nb and a semimetal element such as Si corresponding to the composition of a thin film to be formed is used as a target for sputtering, the target and a film to be formed are arranged in a vacuum chamber so as to be opposed to each other, a rare gas is introduced into the vacuum chamber in a vacuum atmosphere, a predetermined electric power is applied to the target, and plasma is formed in the vacuum chamber. Then, by causing the ions of the rare gas ionized in the plasma to collide with the target and sputtering the target, the sputtering particles made of the oxide scattered from the target are deposited and adhered on the film formation object, and an oxide film is formed on the surface of the film formation object.

In sputtering, since the target is an insulator, a high-frequency power source (frequency: 13.56MHZ) is generally used to apply a high-frequency power to the target at a level between ground potential (so-called RF sputtering method: see, for example, patent document 1). Here, when the film is formed by the RF sputtering method, the film formation rate is significantly slow as compared with, for example, film formation by the so-called DC sputtering method. Therefore, in order to form an oxide film with high yield, a faster film formation rate must be achieved. In this case, it is conceivable to increase the high-frequency power applied to the target or increase the partial pressure of the sputtering gas such as argon in the vacuum chamber during sputtering (for example, the total pressure in the vacuum chamber is 10 Pa).

However, when sputtering is performed in a state where the partial pressure of the sputtering gas is increased, the sputtering rate may be lowered and the yield may be impaired. This is considered to be caused by a fact that a typical RF sputtering apparatus capable of performing the RF sputtering method includes a baffle plate which surrounds a space between a target and an object to be processed which are arranged to face each other in a vacuum chamber and prevents sputtering particles from adhering to an inner wall surface of the vacuum chamber, but when a surface of the baffle plate is also covered with an oxide film as the film formation is repeated for the object to be processed, plasma leaks to the inner wall surface of the grounded vacuum chamber through a gap when the baffle plate is assembled in the vacuum chamber, discharge occurs also in the space between the baffle plate and the vacuum chamber, and electric power applied to the target is relatively lowered.

On the other hand, when the target is an insulator, it is conceivable to apply a Pulse-shaped direct current power to the target and sputter the target (so-called direct current Pulse (DC Pulse) discharge). In this method, a film formation rate faster than that of the RF sputtering method can be obtained, but similarly to the RF sputtering method, a vacuum chamber and a baffle plate which are grounded are used as an anode. Therefore, when the shutter or the like is covered with the insulating film, electric charges are charged, insulation breakdown is caused, and abnormal discharge occurs. As a result, there is a problem that the discharge persistence is impaired or particles are generated due to abnormal discharge.

Documents of the prior art

Patent document

[ patent document 1 ] patent No. 3968128

Disclosure of Invention

Technical problem to be solved by the invention

In view of the above, an object of the present invention is to provide a film formation method that uses an oxide or nitride containing at least one of a transition metal element and a semimetal element as a constituent element as a target, in which case an oxide film and a nitride film can be stably formed until the end of the service life of the target.

Means for solving the problems

In order to solve the above-described problems, a film forming method of the present invention includes: sputtering a target containing at least one of a transition metal element and a semimetal element as a constituent element in a vacuum atmosphere, thereby depositing sputtered particles scattered from the target on a film-forming object to form an oxide film or a nitride film having a high resistance value on the surface of the film-forming object; in this sputtering method, a plurality of targets having the same composition are arranged in parallel on the same plane, alternating current power of a predetermined frequency is applied between a pair of targets among the targets arranged in parallel, and each target is alternately switched between an anode electrode and a cathode electrode to generate plasma between the targets, thereby sputtering the target serving as the cathode electrode.

It has been confirmed that, according to the present invention, as compared with the case where an oxide film having a high resistance value is formed by sputtering an equivalent target by the RF sputtering method, equivalent film quality (that is, almost no resistance value change) can be obtained, and further, stable film formation can be performed at a film formation rate 10 times or more faster until the end of the target life without increasing the partial pressure of the sputtering gas at the time of film formation, and the yield can be improved.

However, as described above, when sputtering targets by applying an alternating current power of a predetermined frequency between the paired targets, the applied power density is set to, for example, 10W/cm or less so as not to cause a problem of target cracking or melting due to insufficient cooling during sputtering²However, it was found that the frequency used in this case was sometimes frequent, and thus, it was found that sputtering occurred on the target, or a film could not be formed with a desired film thickness for a predetermined sputtering time. Therefore, in the present invention, it is preferable that the frequency of the ac power is set in the range of 20kHz to 60kHz, and the duty ratio (duty ratio) of the ac power is set in the range of 20% to 80%. Further, the composition ratio of the transition metal element and the semimetal element was set at 0.3Range of 0.8. Outside this range, there are problems that abnormal discharge occurs with the increase of the discharge voltage, and the formed thin film does not satisfy a desired resistance value or the resistance temperature change increases.

Drawings

Fig. 1 is a schematic sectional view showing a sputtering apparatus which can be used for carrying out the film forming method of the present invention.

Fig. 2 is a graph showing the experimental results showing the effect of the present invention.

Fig. 3 is a graph showing another experimental result showing the effect of the present invention.

Detailed Description

With reference to the drawings, TaSiO is formed on the surface of a glass substrate (hereinafter referred to as "substrate Sb") using the glass substrate as a film-forming material₂The embodiment of the film forming method of the present invention will be described by taking as an example an oxide film having a high resistance value.

Referring to fig. 1, SM is a magnetron sputtering apparatus capable of implementing the film deposition method of the present invention. The sputtering apparatus SM is a tandem type apparatus for performing a so-called deposition-up type (デポアップ) film formation, and has a vacuum pump Pu such as a rotary pump or a turbo-molecular pump for evacuating to a predetermined pressure (10)^-5Pa) and can maintain a vacuum atmosphere. The substrate Sb placed on the carrier 2 is disposed on the upper part of the vacuum chamber 1 with its film formation surface facing downward. At this time, although not particularly illustrated, a preparation chamber capable of forming a vacuum atmosphere is provided in connection with the vacuum chamber 1, and the substrate Sb is set on the carrier 2 in the preparation chamber and is transported to a predetermined position of the vacuum chamber 1 by the substrate transport unit in the vacuum atmosphere. Since a well-known product can be used as the substrate transport unit, a detailed description thereof will be omitted. Further, the vacuum chamber 1 has therein a baffle plate 11 which surrounds a space between the substrate Sb conveyed into the vacuum chamber 1 and a target mentioned later and prevents the sputtered particles from adhering to an inner wall surface of the vacuum chamber 1.

The vacuum chamber 1 is provided with a gas introduction unit 3. The gas introducing unit 3 is connected to a gas source 33 via a gas pipe 32, and can introduce a sputtering gas (e.g., argon) composed of a rare gas such as Ar at a predetermined flow rateCase, O used at the time of reactive sputtering₂、N₂Such a reaction gas) is introduced into the vacuum chamber 1, and a mass flow controller 31 is provided on a gas pipe 32. A cathode unit Cu is provided on the lower side of the vacuum chamber 1 so as to face the substrate Sb.

The cathode unit Cu has a pair of

targets

41a, 41b. Each of the

targets

41a and 41b has the same composition ratio, is formed in the same shape (in the present embodiment, the upper surface is formed in a rectangular outline) by a known method, and is formed of an oxide containing Ta (transition metal element) and Si (semimetal element) at a predetermined composition ratio. Further, the composition ratio of Ta and Si is set in the range of 0.3 to 0.8. Outside this range, there are problems that abnormal discharge occurs with the increase of the discharge voltage, and the formed thin film does not satisfy a desired resistance value or the resistance temperature change increases. The case where the composition ratios of the

targets

41a and 41b arranged in parallel are equal includes not only the case where the composition ratios are completely the same but also the case where, for example, the composition ratio of the metal element to the semimetal element is changed within a range of 0.3 to 0.8, the same film quality can be obtained (that is, the resistance value of the oxide film formed is hardly changed).

Each of the

targets

41a and 41b is bonded to a backing plate 42 that cools the

targets

41a and 41b by a solder material such as indium or tin, and is provided in the vacuum chamber 1 in an electrically floating state via an insulating member not shown. In this case, the

targets

41a and 41b are juxtaposed so that the upper surfaces thereof, which are sputtering surfaces when the

targets

41a and 41b are not used, are on the same plane parallel to the substrate Sb. In the present embodiment, the two

targets

41a and 41b are arranged in parallel, but the number of targets arranged in parallel is not limited to this, and is set as appropriate in consideration of the outer dimensions of the substrate Sb.

The cathode unit Cu has a magnet assembly 5 located below the

targets

41a and 41b. The magnet assembly 5 has a support plate 51 disposed parallel to each of the

targets

41a, 41b. The support plate 51 is formed of a rectangular flat plate which is smaller than the width of each of the

targets

41a and 41b and is formed to extend toward both sides along the longitudinal direction of the

targets

41a and 41b, and is made of a magnetic material which amplifies the magnetic attraction force. The support plate 51 is provided with a central magnet 52 and a peripheral magnet 53, wherein the central magnet 52 has a rod shape and is provided along the longitudinal direction of the

targets

41a, 41b, and the peripheral magnet 53 is provided along the outer periphery of the support plate 51. In this case, the volume of the central magnet 52 converted to the same magnetization is set to be equal to, for example, the sum of the volumes of the peripheral magnets 53 converted to the same magnetization (peripheral magnet: central magnet: peripheral magnet: 1: 2: 1). Thus, a balanced closed-loop tunnel-like magnetic flux is formed in front of each of the

targets

41a, 41b, and electrons ionized in front of the

targets

41a, 41b and secondary electrons generated by sputtering are captured, whereby the electron density in front of each of the

targets

41a, 41b can be increased, and the plasma density can be increased. In order to increase the utilization rate of the

targets

41a and 41b, the magnet assembly 5 may be reciprocated relative to the

targets

41a and 41b by a predetermined stroke.

Output cables Kl from a single ac power supply Ae are connected to the pair of

targets

41a, 41b, respectively. A so-called bipolar pulse power supply can be used as the ac power supply Ae, and power can be applied in a bipolar pulse manner between the pair of

targets

41a, 41b at a predetermined frequency. Since a known product having a detection circuit that detects whether or not abnormal discharge (arc discharge) occurs according to the length of the voltage drop time of the output voltage waveform to the pair of

targets

41a, 41b can be used as the bipolar pulse power source, detailed description of the bipolar pulse power source will be omitted here. A film formation method for forming an oxide film on the substrate Sb by using the sputtering apparatus SM will be described below.

First, in the preparation chamber outside the figure, the substrate Sb is set on the carrier 2, and when the preparation chamber is vacuum-exhausted to a predetermined pressure, it is transported into the vacuum chamber 1 in a vacuum atmosphere by the substrate transport unit. When the vacuum chamber 1 is evacuated to a predetermined pressure, a predetermined sputtering gas is introduced through the gas introduction unit 3. At this time, the flow rate of the sputtering gas is controlled so that the pressure in the vacuum chamber 1 during sputtering is in the range of 0.1Pa to 1.0 Pa. Then, ac power is applied to each of the

targets

41a and 41b in the pair by the ac power supply Ae. At this time, the applied power density is set to, for example, 10W/cm or less²The specified value of (1). Further, when the

targets

41a, 41b are oxides containing Ta and Si in a prescribed composition ratio, for exampleThe power density applied to the fruits exceeds 10W/cm²This causes problems such as cracking and chipping of the target, frequent occurrence of abnormal discharge, and the like.

The frequency of the ac power output from the bipolar pulse power supply as the ac power supply Ae is set in the range of 20kHz to 60 kHz. When the frequency is less than 20kHz, abnormal discharge frequently occurs, and for example, the film thickness management becomes troublesome. On the other hand, when the frequency exceeds 60kHz, there is a problem that the instantaneous discharge voltage rises and exceeds the inverter operating range as a constituent circuit of the bipolar pulse power source. The duty ratio of the ac power is set to be in the range of 20% to 80%. When the number of abnormal discharges (arc discharges) exceeds this range, the number of abnormal discharges immediately increases.

Here, if the pressure in the vacuum chamber 1 during film formation, the power applied from the ac power supply Ae, and the frequency thereof are changed, the value (V) of the root mean square Vmf of the voltage between the

targets

41a, 41b during sputtering is changed. In this case, the higher Vmf is, the higher the frequency of occurrence of abnormal discharge (arc discharge) is, and it has been confirmed that even if the Vmf value is equal, the frequency of occurrence of abnormal discharge (arc discharge) increases as the frequency decreases. From this result, it is considered that the higher Vmf is, the higher the driving force for causing insulation breakdown of the insulating film in the non-erosion region (oxide film) or the like of the

targets

41a, 41b accompanying the sputtering of the

targets

41a, 41b is, and further, when the frequency is lowered, the electric charge accumulated in the insulating film increases, and further, the time for accumulating the electric charge becomes longer, and as a result, the frequency of occurrence of abnormal discharge increases. Therefore, if the frequency of the ac power is set in the range of 20kHz to 60kHz and the duty ratio is set in the range of 20% to 80%, the driving force directly related to the occurrence of abnormal discharge is reduced, and by setting the frequency in a predetermined range, the discharge is switched before the occurrence of abnormal discharge, whereby the static electricity eliminating effect of the insulating film can be improved and the occurrence of abnormal discharge can be suppressed as much as possible.

Furthermore, if Vmf is controlled to 690V or less, the occurrence of abnormal discharge is suppressed, and if Vmf is controlled to be in the range of 630-690V, the occurrence of abnormal discharge is further suppressed. Further, the output form of the bipolar pulse power source for applying a predetermined voltage between the pair of

targets

41a and 41b is preferably a form in which a transformer is not provided between an inverter as an output switching circuit and an actual load. When the output is output by a transformer, the resonance frequency changes when the film forming factors such as the

targets

41a and 41b, the applied power, and the film forming pressure change because the resonance with the impedance of the actual load occurs. Therefore, when the frequency is set to be switched arbitrarily, it is necessary to change the capacitance and inductance in the power supply Ae. Without spacing the transformers, there is the advantage that it can be fixed at any frequency.

Thus, the two

targets

41a and 41b in the pair function as an anode electrode and a cathode electrode, respectively, and a tunnel-like leakage magnetic field is formed above each of the

targets

41a and 41b, whereby a high-density plasma in a racetrack shape is generated and passes through a position where the vertical component of the leakage magnetic field is zero. Then, the

targets

41a and 41b are alternately switched to the anode electrode and the cathode electrode according to the frequency, the

targets

41a and 41b serving as the cathode electrodes are sputtered with ions of the sputtering gas ionized in the plasma, and the sputtered particles emitted from the

targets

41a and 41b are deposited and adhered to the lower surface of the opposing substrate Sb, thereby forming a predetermined oxide film.

In this manner, as compared with the case where an oxide film having a high resistance value is formed by sputtering an equivalent target by the RF sputtering method, an equivalent film quality can be obtained, and a film formation rate 10 times or more faster can be obtained without increasing the partial pressure of the sputtering gas during film formation. Further, even if the surface of the baffle plate 11 is covered with the oxide film by repeating the film formation on the substrate Sb, the plasma is not unstable, and the film can be stably formed until the service life of the

targets

41a and 41b.

Next, in order to confirm the above effect, the following experiment was performed using the sputtering apparatus SM shown in fig. 1. In this experiment, TaSiO containing Ta in a composition ratio of 50 to 52 atomic% was used₂The resulting product is bonded to a backing plate 42 as

targets

41a and 41b after forming a rectangular outline, and the two

targets

41a and 41b are set at predetermined positions of a sputtering apparatus with a space therebetween. Between the

targets

41a, 41b and the substrate SbThe distance was set at 80 mm. Further, as sputtering conditions, the mass flow controller 31 was controlled to maintain the pressure in the vacuum chamber 1 evacuated to 0.37Pa, argon gas was introduced as a sputtering gas, the AC power supply Ae was controlled to maintain the applied power to the

targets

41a, 41b at 4kW, and TaSiO was formed on the surface of the glass substrate for a predetermined sputtering time₂A high-resistance oxide film formed of the film. The film formation rate at this time was measured to be 45nm/min, and the applied power density was 4.8W/cm for the same target as that of the applied power²Forming TaSiO by sputtering with RF sputtering method₂In the case of the film (about 4nm/min), it was confirmed that the film formation rate was 10 times or more faster.

Next, a product on which film formation was performed under the above sputtering conditions was used as sample 1, a product on which film formation was performed with an applied power of 2kW and a pressure in the vacuum chamber 1 of 0.37Pa was used as sample 2, a product on which film formation was performed with an applied power of 2kW and a pressure in the vacuum chamber 1 of 0.37Pa was used as sample 3, a product on which film formation was performed with an applied power of 4kW and a pressure in the vacuum chamber 1 of 0.85Pa was used as sample 4, frequencies of the applied powers were respectively set to 10kHz, 20kHz, 40kHz and 60kHz, and the root mean square (Vmf) of the voltage between the

targets

41a and 41b and the number of abnormal discharge occurrences were measured during sputtering, and the results are shown in fig. 2, in which- ◇ -is sample 1, - □ -is sample 2, - ● -is sample 3, - ○ -is sample 4, and in which the number of abnormal discharge occurrences was normalized by switching the frequency to 10kHz on sample 1, thereby lowering the voltage and suppressing the number of abnormal discharges.

Next, with a product on which film formation was performed with the application frequency set to 40kHz under the above sputtering conditions as sample 5 and a product on which film formation was performed with the application frequency set to 10kHz under the above sputtering conditions as sample 6, the duty ratio of the power applied to the pair of

targets

41a, 41b was set to 10% to 90%, and the number of abnormal discharges was measured, respectively, and the results are shown in fig. 3, in this case, ◇ -is sample 5 and □ -is sample 6 in fig. 3, and in addition, the number of abnormal discharges was normalized with the duty ratio set to 50% as 1 in sample 5 and sample 6, whereby the number of abnormal discharges was immediately increased when the duty ratio deviated from 50% at 10kHz, whereas the number of abnormal discharges was substantially suppressed to the same number as when the duty ratio was 50% at 40kHz, it was found that the number of abnormal discharges was substantially suppressed to the same number as when the duty ratio was 50% when the frequency was set to 20kHz, and the number of abnormal discharges was effectively suppressed to the same number as when the duty ratio was set to 50% at 60 kHz.

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Although in the above embodiment, TaSiO is formed using an oxide containing Ta and Si in a predetermined composition ratio as a target₂The case of forming an oxide film having a high resistance value as a film was described as an example, but not limited thereto, and an oxide containing Si and a transition metal element such as Ta, Cr, and Nb, and silicon oxide or aluminum oxide were used as targets, and it was confirmed that by the above-described film formation method, a film quality equivalent to that obtained by sputtering an equivalent target film formation by the RF sputtering method was obtained, a rapid film formation rate was obtained without increasing the partial pressure of the sputtering gas during film formation, and even if the film formation was repeated on the substrate Sb, the surface of the baffle plate 11 was covered with an oxide film, and the plasma did not become unstable. On the other hand, it was confirmed that the same results were obtained by the above-mentioned film formation method when a nitride film such as TaN was formed.

Description of the reference numerals

SM. is suitable for use in the sputtering apparatus, 41a, 41b target, Ae. ac power supply, Sb. substrate (film-forming material) for carrying out the present invention.

Claims

1. A film forming method, wherein an oxide or nitride containing at least one of a transition metal element and a semimetal element as a constituent element is used as a target, the target is sputtered in a vacuum atmosphere, sputtered particles scattered from the target are deposited on a film to be formed, and an oxide film or a nitride film is formed on the surface of the film to be formed; the method is characterized in that:

a plurality of targets having the same composition are arranged in parallel in the same plane, and alternating current power of a predetermined frequency is applied between a pair of targets among the targets arranged in parallel, and each target is alternately switched between an anode electrode and a cathode electrode, thereby generating plasma between the targets to sputter the target serving as the cathode electrode.

2. The film forming method according to claim 1, wherein:

the frequency of the alternating current power is set within the range of 20kHz to 60 kHz.

3. The film forming method according to claim 2, wherein:

the duty ratio of the alternating current power is set within a range of 20% to 80%.