JP3391944B2 - Method of forming oxide thin film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an oxide thin film used for an optical thin film such as a multilayer antireflection film, a high reflection mirror or a dichroic filter.

[0002]

2. Description of the Related Art Optical thin films such as antireflection films, high-reflection mirrors, dichroic filters and the like, which are composed of multilayer films, require oxide thin films having a uniform refractive index in the film thickness direction and low absorption over the entire ultraviolet region, Such an oxide thin film is generally formed by sputtering.

The formation of an oxide thin film by sputtering has been conventionally performed as follows.

A target made of a metal or its oxide is manufactured, and the target is made to face an electrode. When the target is conductive, a direct current is applied. When the target is an insulating material, a high frequency voltage ( For example, 13.5MH
(RF of z) is applied, Ar gas is introduced as a sputtering gas, and O ₂ gas is introduced as a reactive gas to cause discharge. Active oxygen in plasma formed by electric discharge (oxygen atoms, oxygen radicals, ozone, oxygen ions, etc.)
And the metal component of the target material react with each other on the substrate, the surface of the target, or in plasma, and an oxide is generated and deposited on the substrate.

For example, when a stable material such as SiO ₂ which is easily oxidized is used, the ratio of Si and O is 1: 2.
You can get the oxide thin film of the same bulk composition with
When an oxide thin film such as Al ₂ O ₃ or Y ₂ O ₃ is formed, the film tends to lack oxygen. Therefore, in the step of forming such an oxide thin film, the substrate before film formation is preheated, the substrate is kept at a high temperature of 300 ° C. or higher during film formation, and further ozone or ozone for promoting oxidation is used. N ₂
Various measures have been taken such as adding an oxidation promoting gas such as O 2.

[0006]

However, according to the above-mentioned conventional technique, as described above, Al ₂ O ₃ or Y ₂ O _{3 is used.}
It is indispensable to heat the substrate to a high temperature in order to form a stable oxide thin film such as
It cannot be applied to the case of forming a film on a plastic substrate having a temperature of 00 ° C. or less, a glass substrate for an optical component that is required to maintain high surface accuracy, or the like.

When forming a film on a color filter such as an LCD, the process temperature is generally limited to 200 ° C. due to the heat resistant temperature characteristics of the material contained in the substrate.
The following film formation is required.

In such a situation where the temperature of the substrate must be controlled to 300 ° C. or lower, even if a gas such as ozone or N ₂ O is added to accelerate the oxidation, the formed oxide thin film still remains. Oxygen becomes deficient, and as a result, the absorption of the film becomes large and the required optical characteristics cannot be obtained.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to obtain a high quality oxide thin film with little absorption even if the substrate is not heated. It is an object of the present invention to provide a method for forming a film.

[0010]

In order to achieve the above object, in the method for forming an oxide thin film of the present invention, a sputtering particle of a target is deposited on a substrate in a reduced pressure atmosphere to form an oxide thin film. At least one of He gas and Ne gas, and moisture, and a sputtering gas .
The film formation is performed in a reduced pressure atmosphere introduced together with the Ar gas .

The partial pressure of water in the reduced pressure atmosphere is 1 × 10 ^-5
It is preferable to control in the range of 1 × 10 ⁻¹ Pa.

A DC voltage and a high frequency voltage of 10 to 20 MHz may be applied to the target to generate sputtered particles.

Further , the DC voltage is further 50 to 200 MH.
A high frequency voltage of z may be superimposed.

[0014]

Function: Ar is used as a sputtering gas in the decompression chamber.
As a reactive gas, O ₂ gas, ozone, N ₂ O gas, CO gas, CO ₂ gas or a mixed gas containing at least one of these gases is introduced, and at least one of He gas and Ne gas is introduced. And introduce moisture. A DC voltage or a high frequency voltage is applied to the target in the decompression chamber to generate sputtered particles, which reacts with oxygen on the target surface, plasma, or substrate surface to generate an oxide, which is deposited on the substrate. Moisture, He gas or Ne gas which is introduced into the decompression chamber together with the reactive gas or the like and is added to the decompression atmosphere is decomposed and polymerized in plasma to generate a large amount of active oxygen, which accelerates the oxidation of the sputtered particles. Therefore, even if the substrate is not heated, oxygen is not deficient, and it is possible to obtain an oxide thin film having a stoichiometric composition, low absorption and extremely high quality.

If an optical thin film such as a high reflection mirror is manufactured using such an oxide thin film, these optical characteristics can be greatly improved. Since the substrate can be formed without heating, it is suitable when a plastic substrate or the like is used.

The partial pressure of water in the depressurized atmosphere is set to 1 × 10 ^-5 to
By controlling in the range of 1 × 10 ⁻¹ Pa, it is possible to form an oxide thin film having a uniform refractive index in the film thickness direction and less absorption.

Further, by superposing a high frequency voltage of 50 to 200 MHz on the DC voltage, the oxidation reaction can be further promoted by expanding the discharge region. As a result, the refractive index is stable,
Moreover, it is possible to obtain a very good oxide thin film which is homogeneous and has little scattering.

[0018]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a film forming apparatus used in a method for forming an oxide thin film according to an embodiment, which includes a decompression chamber 1 evacuated by a vacuum pump (not shown) and an inside thereof facing each other. Arranged substrate holder 2 and target 3, RF power source 4 and DC power source 5 for applying high frequency voltage and DC voltage to target 3, Ar gas which is a sputtering gas and O which is a reactive gas in decompression chamber 1. Ar, O ₂ introduction line 6 for introducing ₂ gas,
Has of H ₂ O, He introduction line 7 for introducing of H ₂ O and He gas is moisture vacuum chamber 1, a high frequency voltage of the RF power source 4 is applied to the target 3 through a matching network 4a, DC power supply 5 Is applied to the target 3 through the low pass filter 5a.

Next, a process of forming an Al ₂ O ₃ film, which is an oxide thin film, on the plastic substrate W ₁ by using an Al metal target as the target 3 will be described. First, the substrate W ₁ is transferred to a load lock chamber (not shown) provided adjacent to the decompression chamber 1, the load lock chamber is evacuated, and then the substrate W ₁ is loaded into the decompression chamber 1. The substrate W ₁ is held on the substrate holder 2, the decompression chamber 1 is depressurized to a predetermined vacuum degree, and then the Ar, O ₂ introduction line 6
Introducing of H ₂ O and He gas from the Ar gas and O ₂ gas, H ₂ O, He introduction line 7, the so-called magnetron sputtering by applying a DC voltage of the high frequency voltage and the DC power supply 5 of the RF power source 4 to the target 3 A plasma P ₁ is generated by the discharge.

By this discharge, Ar ions, active oxygen (oxygen ions, oxygen atoms, oxygen radicals, ozone, etc.),
As active He (He ions, He radicals, etc.) is generated, H ₂ O molecules are decomposed and polymerized in plasma, and various kinds of oxygen atoms, hydroxide ions, H ₃ O ₂ ions, H ₅ O ₂ ions, etc. Generates active species. The Al target 3 is sputtered by positive ions of these, and is emitted toward the substrate W ₁ in a state of being partially oxidized by the oxidizing active species near the surface of the target 3. In this way, the sputtered particles that reach the substrate W ₁ are generated by the plasma P ₁
An Al ₂ O ₃ film which is completely oxidized by the oxidizing active species in the inside or near the surface of the substrate W ₁ and has no oxygen deficiency is formed on the surface of the substrate W ₁ .

That is, various oxidative active species generated from H ₂ O or He gas greatly accelerate the oxidation of the sputtered particles generated from the target 3, and a chemical that does not lack oxygen even if the substrate W ₁ is not heated. An oxide thin film having a stoichiometric composition can be formed. This is because the H ₂ O molecule has a larger molecular radius than the oxygen molecule, and the O—H bond energy is smaller than the O—O bond energy, so the probability of being activated in plasma is very high. Furthermore, He
It is presumed that the active species of gas have a large potential energy, and that metastable He atoms in particular have a function of Penning ionization of oxygen molecules and H ₂ O molecules.

Since the oxide thin film formed by such a method has the stoichiometric composition as described above, it has a low absorption and a stable refractive index in a wide frequency range. For example, Al ₂ O ₃ By combining the film and the SiO ₂ film, it is possible to manufacture an antireflection film having excellent optical characteristics, a highly reflective mirror, a highly accurate dichroic filter, or the like.

Experiments have shown that the same effect as described above can be obtained by using Ne gas instead of He gas.

In some cases, both He gas and Ne gas may be used.

The film forming apparatus shown in FIG. 2 is the RF of the apparatus shown in FIG.
In addition to the RF voltage in the RF region by the power source 4 and the DC voltage by the DC power source 5, the frequency variable type VHF power source 16
Is configured to apply a high frequency in the VHF region having a particularly high frequency to the target 3, and the absorption of the oxide thin film formed on the substrate W ₂ is further reduced by overlapping the high frequency voltage in the VHF region. can do. In addition,
A matching network 16a and a bypass filter 16b are provided between the VHF power supply 16 and the target 3.

Further, the film forming apparatus shown in FIG. 3 uses H ₂ O and H _2
2 gas by individual gas inlet line 27, 28 which was constructed to introduce into the vacuum chamber 1, H ₂ O
A partial pressure monitor 27a for monitoring the partial pressure of H ₂ O in the decompression chamber 1 is provided in the gas introduction line 27 for introducing
As a result, the H ₂ O partial pressure of the decompression chamber 1 during film formation can be controlled to a predetermined value, and the deterioration of the optical characteristics of the oxide thin film and the variation in the optical characteristics of each product can be prevented.

Next, a specific example will be described.

An Al ₂ O ₃ film having a film thickness of 2000 Å was formed on a quartz substrate by using the film forming apparatus shown in FIG. 0.4Pa the total pressure of the vacuum chamber during film formation, and controlling the oxygen partial pressure 0.08 Pa, Sample A ₁ the one formed without introducing of H ₂ O and He gas, H ₂ O only The sample A ₂ was introduced and the partial pressure thereof was controlled to 0.2 Pa, and the He gas was introduced only and the sample partial pressure was controlled to 0.1 Pa, and the sample A ₃ , H ₂ O and He gas were introduced. Table 1 shows the results of examining the extinction coefficient of each of A _{1 to} A _{4 at} a wavelength of 248 nm, using the sample A ₄ whose partial pressure was controlled to 0.2 Pa and 0.1 Pa, respectively.

[0030]

[Table 1] As is clear from this table, the absorption cannot be sufficiently reduced only by Ar gas and O ₂ gas. Although the total pressure is constant in this table, the absorption could not be reduced even if the sputtering gas was only O ₂ gas or the total pressure was several Pa. This is because a sufficient amount of active oxygen could not be generated by magnetron sputter discharge by RF and DC. When He gas is introduced here, the active excited species of He formed during the discharge form oxygen atoms by the reaction with oxygen molecules and promote the oxidation reaction. The Al ₂ O ₃ film samples A ₃ This result formed the sample A ₁
The extinction coefficient is reduced by more than one digit compared to. Also, Ar
Sample A _{2 in} which H ₂ O is introduced in addition to gas and O ₂ gas
In the case of H ₂ O molecules, oxidation is promoted by active species formed by decomposition and polymerization of H ₂ O molecules, and the extinction coefficient is also reduced by one digit. This is because the molecular radius of H ₂ O molecules is larger than that of oxygen atoms, and the binding energy of O—H is smaller than the binding energy of O—O, so that the probability of activation in plasma increases. is there.

Further, the extinction coefficient of the Al ₂ O ₃ film of the sample A ₄ into which H ₂ O and He gas were introduced at the same time decreased to below the measurement limit. This is due to the above-mentioned effect of the He excited species and the synergistic effect of the active species generated from H ₂ O.

The absorption of the Al ₂ O ₃ film is apt to change depending on the distance between the target and the substrate, the applied power, etc., but the simultaneous introduction of He gas and H ₂ O into the atmosphere reduces the absorption over a wide range. It was peeled off. It is considered that this is because the density of active species could be increased.

As will be described later, almost the same effect can be obtained by introducing Ne gas instead of He gas. Further, it has been empirically proved that similar effects can be obtained by introducing He gas and Ne gas at the same time.

Next, in this example, the H ₂ O partial pressure was 1 × 10 ⁻⁵ Pa, 1 × 10 ⁻⁴ Pa, and 1 × 10 ⁻⁴ Pa, respectively, under the film forming conditions in which the Al ₂ O ₃ film could be formed with the lowest absorption. 1 x 10
Table 2 shows the results of examining the loss at these wavelengths of 248 nm as samples B _{1 to} B ₆ which were formed by controlling film formation under the conditions of ⁻³ Pa, 1 × 10 ⁻² Pa, 1 × 10 ⁻¹ Pa, and 1 Pa. .

[0035]

[Table 2] It is understood that the loss increases when the H ₂ O partial pressure becomes 1 × 10 ⁻¹ Pa or more. This is because the scattered light is increasing. When the H ₂ O partial pressure is 1 × 10 ⁻¹ Pa or more, as can be seen by naked eyes, a lump of voids is formed in the film, and light is scattered. Since this scattering increases as the wavelength of light decreases, it becomes a serious problem when considering the use of an optical thin film for ultraviolet rays. Also, H ₂ O
Even if the partial pressure is 1 × 10 ⁻⁵ Pa or less, the low absorption becomes insufficient. Therefore, in order to obtain an oxide thin film that can be used as an optical thin film, the H ₂ O partial pressure is 1 × 10 ⁻⁵ Pa to ¹ × 10 ⁻¹ P.
must be within the range of a.

Table 3 shows the results of examining the relationship between the Al ₂ O ₃ film and the absorption at a wavelength of 248 nm by changing the distance between the target and the substrate. The sputtering conditions were fixed to the conditions where a low-absorption film was obtained as in the above.

[0037]

[Table 3] As is clear from this table, the absorption gradually increases as the distance from the target increases. This is because the active species formed in the vicinity of the target are not sufficiently transported to the vicinity of the substrate.

Then, using the film forming apparatus of FIG. 2, the target is 105 M from the VHF power source under the same film forming conditions as above.
Table 4 shows the results of examining the loss when a high frequency voltage of He was applied.

[0039]

[Table 4] It can be seen that the extinction coefficient is smaller than that in Table 2. This is because the high-frequency discharge of 105 MHe circulates to the vicinity of the substrate, increasing the concentration of active species.

As described above, by superimposing a high frequency, particularly a high frequency in the VHF region, and introducing an appropriate partial pressure of H ₂ O gas into the atmosphere of the sputtering gas, low absorption is achieved at almost all positions in the decompression chamber. A thin oxide thin film can be formed.

The VHF electric power for expanding the discharge region may be applied to the target, but even if it is applied through the third electrode in order to simplify the device structure, the effect of low absorption does not change.

When the target is metallic and conductive, the effect is the same even if the RF power is not applied and only the VHF power and the DC power are used for sputtering.

Further, while monitoring the partial pressure of H ₂ O in the decompression atmosphere of the decompression chamber using the apparatus of FIG. 3, Al ₂ O ₃
A film was formed. H ₂ O partial pressure during film formation is 1 × 10 each
^-5 Pa, ^{1x10 -4} Pa, ^{1x10 -3} Pa, ^{1x10 -2}
Table 5 shows the results of examining the refractive index of the Al ₂ O ₃ film at a wavelength of 248 nm as samples C _{1 to} C ₅ which were formed by controlling the film thickness to 1 × 10 ⁻¹ Pa.

[0044]

[Table 5] As is clear from Table 5, the refractive index of the Al ₂ O ₃ film is very sensitive to the H ₂ O partial pressure in the reduced pressure atmosphere of the reduced pressure chamber. Therefore, if the H ₂ O partial pressure fluctuates during film formation, the refractive index changes in the film thickness direction and becomes non-uniform, making it impossible to obtain the target optical characteristics.

Therefore, the H ₂ O partial pressure during film formation is set to 1 × 10 ^−3.
Samples D _{1 to} D ₄ are manufactured by keeping the pressure at Pa and repeating the film formation cycle of the Al ₂ O ₃ film four times.
Table 6 shows the results of examining the refractive index at 8 nm.

[0046]

[Table 6] As can be seen from Table 6, if the H ₂ O partial pressure during film formation is the same, the variation in the refractive index is very small, so that a high-quality optical thin film in which the optical characteristics may not vary from product to product can be manufactured. .

Finally, instead of introducing only O ₂ gas as a reactive gas using the apparatus of FIG. 1, ozone gas is added to O ₂ gas, or N ₂ O gas, CO gas,
A CO ₂ gas was introduced to form an Al ₂ O ₃ film having a film thickness of 1000 Å, and these were used as samples E _{1 to} E _{4 and had} a wavelength of 248.
Table 7 shows the results of examining the absorption in nm.

During the film formation of each sample E _{1 to} E ₄ , H ₂
The O partial pressure was controlled to 1 × 10 ⁻³ Pa.

[0049]

[Table 7] Further, Table 8 shows the results of examining the absorption at these wavelengths of 248 nm for samples F _{1 to} F _{4 formed} by the same method as above except that Ne gas was used instead of He gas.

[0050]

[Table 8] From Table 7 and Table 8, ozone, N ₂ O, and C were added as reactive gases.
It can be seen that even if O, CO ₂ gas or the like is used, an oxide thin film with less absorption can be formed as in the case of using only O ₂ gas.

In particular, in forming the Al ₂ O ₃ film, A
Impurity gas such as CO gas or CO ₂ gas is Al ₂ O ₃ because 1 atom has a property of being more easily oxidized than N or C.
On the contrary, these oxidative powers do not affect the absorption of the membrane and
_Since it is stronger than the _two gases, it has the advantage of increasing the process range in which a stable oxidation reaction can be obtained.

[0052]

Since the present invention is configured as described above, it has the following effects.

Even if the substrate is not heated, a high-quality oxide thin film with little absorption can be formed. By using such an oxide thin film, it is possible to obtain an optical thin film such as a multilayer reflection film or a high reflection mirror having excellent optical characteristics.

In particular, it is suitable for forming a film on a plastic substrate or precision optical component which is not preferable to be heated to a high temperature, and can greatly contribute to the cost reduction and high performance of such an optical component.

When an antireflection film, a high reflection mirror, a dichroic filter or the like is manufactured by using two kinds of oxide thin films of an Al ₂ O ₃ film and a SiO ₂ film, both oxide thin films are formed in a stoichiometric composition. It is possible to obtain an extremely high-quality product that is film-formed and has little scattering and absorption in the excimer laser wavelength range (193 nm, 248 nm).

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a film forming apparatus used in a method for manufacturing an optical thin film according to an embodiment.

FIG. 2 is an explanatory diagram illustrating a modified example of the film forming apparatus in FIG.

FIG. 3 is an explanatory diagram illustrating another modified example of the film forming apparatus in FIG.

[Explanation of symbols]

1 Decompression chamber 2 Substrate holder 3 Target 4 RF power supply 5 DC power supply 6 Ar, O ₂ introduction line 7 H ₂ O, He introduction line 16 VHF power supply 27, 28 Gas introduction line 27a Partial pressure monitor

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP 62-154676 (JP, A) JP 4-242017 (JP, A) JP 2-255507 (JP, A) JP 63- 140077 (JP, A) JP-A-6-330305 (JP, A) JP-A-2-112112 (JP, A) JP-A-8-17267 (JP, A) JP-A-7-70749 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 14/34 C23C 14/44 G02B 1/10 G02B 5/08 C23C 14/08

Claims (5)

(57) [Claims] 1. A step of depositing a sputtering particle of a target on a substrate in a reduced-pressure atmosphere to form an oxide thin film, wherein at least one of He gas and Ne gas and moisture are used as a sputtering gas of Ar. A method of forming an oxide thin film, which comprises forming the film in a reduced pressure atmosphere introduced together with a gas . 2. The partial pressure of water in a reduced pressure atmosphere is set to 1 × 10 ^−5.
The method for forming an oxide thin film according to claim 1, wherein the film thickness is controlled to be in the range of 1 × 10 ^-1 Pa. 3. The method for forming an oxide thin film according to claim 1, wherein a DC voltage and a high frequency voltage of 10 to 20 MHz are applied to the target to generate sputtered particles. 4. The method for forming an oxide thin film according to claim 3, wherein a high frequency voltage of 50 to 200 MHz is further superimposed on the DC voltage. 5. An O ₂ gas, an ozone gas, an N ₂ O gas, a CO gas, a CO ₂ gas or a mixed gas containing at least one of these gases is introduced into the reduced pressure atmosphere as a reactive gas. Item 5. A method for forming an oxide thin film according to any one of items 1 to 4.