JP3478561B2 - Sputter deposition method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film sputter film forming technique used for optical members and electronic members, and more particularly to improvement of a facing target type sputter film forming method.

[0002]

2. Description of the Related Art A sputtering method is known as one of thinning methods for various materials, and various improvements have been made according to the application, and many proposals such as a magnetron sputtering method have been made.
Among them, the facing target type sputtering film forming method known in Japanese Patent Laid-Open No. 57-158380 or the like is capable of high speed and low temperature film forming, and is attracting attention as being applicable to a magnetic material. A conventional facing target type sputtering film forming method will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a facing target type sputtering apparatus.

In this apparatus, a pair of facing cathode electrodes 3A and 3B are arranged in a vacuum chamber 1 via insulating electrode supporting bases 2A and 2B, and sputtering surfaces are parallel to each other with a space on the cathode electrodes. Target 4A to face
4B is held. Ground shields 5A and 5B are arranged around the cathode electrode so as not to generate discharge between the side portion of the cathode electrode and the vacuum chamber 1, and sputter power supply sources 6A and 6B are connected to the cathode electrode. Has been done. A magnetic field coil 7 for applying a magnetic field H perpendicular to the sputtering surface of the target between the electrodes is arranged around the vacuum chamber 1. The substrate 8 on which the sputtered film is formed is held by a substrate holder 9 arranged on the side of the targets 4A and 4B and kept at a desired temperature by a substrate temperature control means (not shown). Opposing target type sputtering film formation using this apparatus is performed as follows. After the vacuum chamber 1 is evacuated to a high vacuum by the vacuum evacuation unit 10, a sputtering gas such as argon is introduced into the vacuum chamber by the gas supply unit 11 to maintain a pressure of several millitorr to several tens of millitorr. A similar amount of sputtering power is supplied from the sputtering power supply source to the cathode electrodes 3A and 3B, and the magnetic field coil 7 applies the above-mentioned magnetic field H to generate plasma between the electrodes, and the target is sputtered by the ionized sputtering gas. The sputtered particles are deposited on the substrate 8 kept at a desired temperature to form a thin film.

It is known that the facing target type sputtering film forming method has the following features.

1. Since a magnetic field is applied perpendicularly to the sputtering surface of the target, high-energy electrons are confined in the space between the opposing targets, the ionization of the sputtering gas is promoted, the sputtering speed is increased, and high-speed film formation is possible. .

2. Since the substrate is arranged on the side of the target, collisions of ions and electrons are small, heat radiation from the target is small, and the temperature rise during film formation of the substrate is small, so that a low temperature film formation can be performed.

3. Since the magnetic field is applied in the vertical direction of the target, even if a magnetic material is used for the target, the magnetic field effectively acts and high-speed film formation can be performed.

[0008]

However, in the conventional facing target type sputter deposition method, since the substrate is arranged on the side of the target, the substrate does not face the target as in the ordinary sputter deposition method. The plasma density in the vicinity of the substrate surface is smaller than that in the case where the number of ions is incident on the film surface. As a result, while so-called plasma damage is reduced, assist ion energy applied to the sputtered particles reaching the film surface is also reduced, the migration of deposited particles becomes insufficient, and the film quality such as crystallinity and denseness of the deposited film is reduced. There is a problem that it tends to get worse.

Next, when reactive gas such as oxygen or nitrogen is mixed in the sputter gas and reactive sputtering is performed by the facing target type sputtering film forming method, the plasma density in the vicinity of the substrate surface is small, so that it is excited by plasma. There is a problem in that the supplied active reactive gas is insufficiently supplied to the substrate surface, reactions such as oxidation and nitriding are likely to be insufficient, and a high-quality compound thin film cannot be stably obtained.

When a high frequency power is used as the sputtering power, the frequency is usually 13.56 MHz, so the amount of ions incident on the film surface is small, but a high frequency of 13.56 MHz is obtained by the ordinary magnetron sputtering film forming method. Similar to the case of using electric power, high-energy ions having energy of about 100 eV may be incident, and there is a problem that the film quality is likely to deteriorate.

An object of the present invention is to provide a sputtering film forming method which forms a deposited film of good film quality, forms a high quality compound thin film, and improves the response of reactive sputtering.

[0012]

The present invention has been completed by the inventors of the present invention through intensive research to solve the above-mentioned problems of the prior art. Preferred embodiments of the present invention are as follows.

That is, in the facing target type sputtering film forming method, the sputtering power supplied to the target is 3
It is characterized by supplying high-frequency power and DC power of 0 to 300 MHz.

According to the present invention, as the sputtering power, a power having a frequency higher than the conventional 13.56 MHz is supplied to the target, so that the probability of collision between electrons in the plasma and the sputtering gas molecules is increased, and the plasma density between the targets is increased. Is higher than that of the conventional method, and the high-speed film-forming property, which is the feature of the facing target type sputtering film-forming method described above, can be further improved. In the case of reactive sputtering, the collision probability of electrons in plasma and reactive gas is increased. , The probability of excitation of the reactive gas also increases.

Although the reason is not clear when the frequency becomes higher, the discharge region expands, and the plasma density near the surface of the substrate disposed on the side of the target increases more than before. Then, when the frequency becomes high, the ions cannot sufficiently follow the fluctuation of the sheath electric field of the plasma formed on the substrate surface, so that the energy value of the ions incident on the substrate becomes small and the energy distribution becomes sharp, so that the deposited film Damage to the plasma due to high energy ions is reduced. As a result, even if the amount of ions incident on the deposited film increases due to an increase in the plasma density near the substrate surface, soft assist energy can be applied to the deposited particles without causing plasma damage. When reactive sputtering is performed, the probability of exciting the reactive gas near the substrate surface is high.

The graph of FIG. 2 shows the power frequency dependence of the plasma density in the vicinity of the substrate surface and the incident energy value of Ar ions incident on the substrate when argon plasma is generated using the apparatus of FIG. It shows an example of power frequency dependence. Argon was used as the discharge gas, the discharge pressure was 3 mTorr, a vertical magnetic field was applied between the targets so that the magnetic flux density was 280 gauss, and high-frequency power of 1 KW was supplied to each cathode electrode, and the plasma density was It was measured by the probe method near the surface of the substrate.
The ion energy incident on the substrate is measured by providing an orifice in the center of the substrate holder and arranging an electrostatic lens type ion energy analyzer on the back surface of the substrate holder.
The incident energy value of r ion was used. As is clear from the graph of FIG. 2, as the power frequency increased, the plasma density near the substrate surface tended to increase, and the incident energy value tended to decrease. In particular, the plasma density rapidly increased and the incident energy value rapidly decreased at 30 MHz or higher.

In the present invention, the frequency of the high frequency power is preferably 30 to 300 MHz. That is, the frequency is 30
When the frequency is higher than MHz, the discharge spreads as described above, and the plasma density near the surface of the substrate arranged on the side of the target increases dramatically. However, as the frequency increases, the transmission loss of high-frequency power increases as the frequency increases, and the power utilization efficiency deteriorates, and there is also the problem that circuit design such as matching circuits becomes difficult. 300 MH
The z is the upper limit of the frequency.

When the power frequency is 30 MHz or more, the self-bias potential generated in the target sharply decreases. Therefore, in order to efficiently sputter the target, it is necessary to supply DC power as well as high frequency power as sputter power. is there.

In the facing target type sputtering apparatus used in the present invention, the sputtering power supply source may be composed of a high frequency power source 12, a matching circuit 13, a high frequency cut filter 14 and a DC power source 15, as shown in FIG. Therefore,
As long as the sputtering power supply source is provided, the conventional configuration as shown in FIG. 1 may be used.

In the present invention, a metal is mainly used as a target. For example, 1A to 7A in the periodic table of elements,
A metal element belonging to 8, 1B, 2B or a semimetal / semiconductor element belonging to 3B, 4B is used.
It should be noted that a material having a high resistivity such as Si is used by increasing the conductivity by doping an impurity.

In the present invention, any known gas can be selectively used as the reactive gas. For example, in the case of forming a nitride film, a gas containing nitrogen atoms such as nitrogen and ammonia, and in the case of forming an oxide film, oxygen, nitrogen oxide, dinitrogen oxide, carbon monoxide, carbon dioxide, etc. A gas containing an oxygen atom, a gas containing a carbon atom such as methane, ethane, ethylene, or propane when forming a carbonized film, and a hydrogen atom such as hydrogen or water vapor when forming a hydrogenated film. In the case of forming a gas containing a fluorine film, a gas containing a fluorine atom such as fluorine, hydrogen fluoride, silicon tetrafluoride, and disilicon hexafluoride can be used.

[0022]

The present invention will be described in more detail with reference to specific examples, but the present invention is not limited to these examples.

Example 1 A facing target sputtering apparatus having the structure shown in FIG. 1 was used, pure iron was used as a target, a glass substrate was used as a substrate, and a magnetic field was set so that the magnetic flux density in the central portion between the targets was 300 gauss. Is applied to each target as the sputtering power, and the high-frequency power of 13.56 to 300 MHz is 2 kW.
DC power of 0.3 kW is supplied, the pressure is maintained at 1 mTorr using argon as a sputtering gas, and a pure iron film is formed on the glass substrate kept at 50 ° C. The magnetic force was measured. However, the above description includes the case of the high-frequency power of 13.56 MHz which is the conventional method.

FIG. 4 is a graph showing the dependence of the measured saturation magnetic flux density and coercive force on the sputtering power frequency. In the figure, the ◯ mark and the ● mark correspond to the saturation magnetic flux density and the coercive force of the pure iron film formed by the sputtering film forming method of the present invention, and the Δ mark and the ▲ mark
The marks correspond to the saturation magnetic flux density and the coercive force of the pure iron film formed by the conventional sputtering film forming method. As is clear from the figure, the pure iron film formed by the sputtering film forming method of the present invention has a saturation magnetic flux density of 2 (T) or higher, which is higher than that formed by the conventional method.
The coercive force is 20 (Oe) or less, which is a value significantly lower than that formed by the conventional method.
It was possible to form a pure iron film having excellent soft magnetic properties suitable for magnetic head materials and the like.

Comparative Example 1 In order to compare with Example 1, the film forming conditions of Example 1 described above were used except the sputtering power, and only 2.3 kW of DC power was supplied to each target as the sputtering power. When a pure iron film was formed by and the saturation magnetic flux density and the coercive force were measured, the saturated magnetic flux density was 1.3 (T) and the coercive force was 170 (Oe).

Comparative Example 2 Further, in order to compare with Example 1, the film forming conditions of Example 1 described above were used except for the sputtering power, and 13.56 MHz high frequency power 2.3 was applied to each target as the sputtering power.
A pure iron film was formed by a conventional method by supplying only kW, and the saturation magnetic flux density and the coercive force were measured. The saturation magnetic flux density was 1.5 (T) and the coercive force was 140 (Oe). .

Example 2 Using a facing target type sputtering apparatus having the structure shown in FIG. 1, using pure iron as a target and a glass substrate as a substrate, a magnetic field was set so that the magnetic flux density in the central portion between the targets was 450 gauss. Is applied, and high frequency power of 100 MHz and 0.5 kW of 100 MHz is applied to each target as sputtering power.
Nitrogen was reactively sputtered on a glass substrate maintained at 60 ° C by supplying DC power of kW, using argon mixed with 20% of nitrogen as a sputtering gas, maintaining a film forming pressure of 0.8 mTorr. When an iron film was formed and the saturation magnetic flux density and coercive force of the iron nitride film were measured, the saturation magnetic flux density showed a very high value of 2.6 (T), and the coercive force was 4
(Oe), which was a very low value. In addition, except the sputtering power, the above-mentioned film forming conditions are used, and high frequency power of 250 MHz of 1.5 kW and DC power of 0.5 kW are supplied to each target as sputtering power to form an iron nitride film by reactive sputtering and saturate. When the magnetic flux density and the coercive force were measured, the saturated magnetic flux density was 2.7 (T), which was a higher value than that at 100 MHz, and the coercive force was 4 (Oe), which was a very low value. By the sputtering film formation method, it was possible to form an iron nitride film having excellent soft magnetic properties suitable for magnetic head materials and the like.

Comparative Example 3 In order to compare with Example 2, the film forming conditions of Example 2 described above were used except for the sputtering power, and the high frequency power of 13.56 MHz was 1.5 kW and 0.5 kW for each target as the sputtering power. When an iron nitride film was formed by reactive sputtering while supplying the DC power of, and the saturation magnetic flux density and coercive force were measured, the saturation magnetic flux density was 0.9 (T) and the coercive force was 1
It was 20 (Oe).

Example 3 A facing target sputtering apparatus having the structure shown in FIG. 1 was used, aluminum was used as a target, a glass substrate was used as a substrate, and the magnetic flux density in the central portion between the targets was 10
A magnetic field was applied so as to obtain 0 Gauss, 2 kW of high frequency power having a frequency of 105 MHz and 0.6 kW of direct current power were supplied to each target as sputtering power, and 50% oxygen was mixed with argon as a sputtering gas to form a film. Pressure 1
When an aluminum oxide film was formed by reactive sputtering of oxygen on a glass substrate maintained at 60 ° C. and maintained at millitorr, the deposition rate was 0.5 (nm / S). Moreover, when the optical characteristics of the film thus formed were examined,
There is no absorption for ultraviolet light and visible light with wavelengths of 230 nm or more, and the refractive indices of the films for light with wavelengths of 250 nm and 550 nm are 1.8 and 1.72, respectively, and the optical characteristics of sapphire (Al ₂ O ₃ ). As a result, a dense aluminum oxide film was obtained.

Comparative Example 4 In order to compare with Example 3, the film forming conditions of Example 3 described above were used except for the sputtering power, and as the sputtering power, a high frequency power 2 kW having a frequency of 13.56 MHz and a direct current power 0.6 kW were used. When an aluminum oxide film was formed on each target by reactive sputtering to form an aluminum oxide film, the deposition rate was 0.3 (nm / S), which was 60% of the deposition rate in the sputter deposition method of the present invention. The optical characteristics are about 350
It is a film that absorbs UV light of nm or less, and has a wavelength of 2
It was observed that the refractive indexes for light of 50 nm and 550 nm were 1.7 and 1.65, respectively, which were smaller than those of the sputter deposition method of the present invention, and the denseness of the film was lowered.

Example 4 Using the facing target type sputtering apparatus having the structure shown in FIG. 1, silicon having antimony doped to enhance conductivity as a target, a glass substrate as a substrate, and a magnetic flux in the central portion between the targets are used. A magnetic field is applied so that the density becomes 800 gauss, and the frequency is 150 M as sputter power.
High-frequency power of 1.3 Hz and direct-current power of 0.5 kW were supplied to each target, argon was used as a sputtering gas with 50% of nitrogen mixed, and the film formation pressure was maintained at 3 mTorr and glass kept at 40 ° C. A silicon nitride film was formed on the substrate by reactive sputtering of nitrogen. When the film thus formed is analyzed by RBS (Rutherford backscattering),
The ratio of Si atom: N atom is 1: 1.3, and the complete S
A good quality silicon nitride film which is very close to i ₃ N ₄ was obtained.
Also, when the etching rate against HF was measured, it was 4
0.3 nm / s for 9% hydrogen fluoride aqueous solution,
It was found that a value that was an order of magnitude lower than that of the silicon nitride film formed by the conventional forming method described later was obtained, and that a dense silicon nitride film was obtained.

Comparative Example 5 In order to compare with Example 4, the film forming conditions of Example 4 described above were used except for the sputtering power, and the sputtering power had a high frequency power of 1.3 kW with a frequency of 13.56 MHz and a DC power of 0. When 5 kW was supplied to each target to form a silicon nitride film by reactive sputtering, the ratio of Si atoms: N atoms was 1: 1.22, which was higher than that of the silicon nitride film formed by the method of the present invention. It was a scarce film. Also,
The etching rate for a 49% hydrogen fluoride aqueous solution was 3.2 nm / s.

[0033]

According to the sputter film forming method of the present invention, soft assist energy can be applied to deposited particles without plasma damage to the deposited film, and high quality deposited film can be formed. In addition, the reactivity of the reactive sputtering can be improved, and a high quality compound thin film can be formed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a configuration of a facing target type sputtering apparatus.

FIG. 2 is a graph showing the power frequency dependence of plasma density and incident ion energy.

FIG. 3 is a schematic configuration diagram of a sputtering power supply source used in the sputtering film forming method of the present invention.

FIG. 4 is a graph showing the dependence of saturation magnetic flux density and coercive force on sputtering power frequency.

[Explanation of symbols]

1 vacuum tank 2A, 2B electrode support 3A, 3B cathode electrode 4A, 4B target 5A, 5B Earth shield 6A, 6B Sputter power supply source 7 Magnetic field coil 8 substrates 9 Board holder 10 Evacuation means 11 Gas supply means 12 High frequency power supply 13 Matching circuit 14 High frequency cut filter 15 DC power supply

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-57-157511 (JP, A) JP-A-63-140077 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 14/34 C23C 14/44

Claims (2)

(57) [Claims] 1. A facing target type sputtering film forming method for forming a thin film on a substrate by arranging a substrate on a side of a facing target and applying a magnetic field between the targets in a direction opposite to each other to form a thin film on the substrate. A high-frequency power of 30 to 300 MHz and a DC power are supplied as a sputtering power to the sputtering film forming method. 2. The sputtering film forming method according to claim 1, wherein a reactive gas is mixed in the sputtering gas to form a compound thin film on the substrate by reactive sputtering.