JPH10273773A - Optical thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hafnium oxide film low in attenuation coefficient and dense in film structure by forming the film by at least an ion-beam sputtering method and controlling the attenuation coefficient in a specified wavelength range below a specified value. SOLUTION: A hafnium oxide film is formed by an ion-beam sputtering method in a lower vacuum than normally. Namely, a substrate is set in a device chamber, and then the device is evacuated. In this case, the vacuum is controlled to 1×10<-6> to 5×10<-7> Torr which is lower than the ultimate vacuum (1×10<-7> to 3×10<-7> Torr). Since a minute amt. of moisture is left under such a low vacuum, a film is low in absorption loss (low in attenuation coefficient) is formed by the action of the moisture. The attenuation coefficient is decreased to <=0.005 in the wavelength range from 230 to 300 nm, an optical film having such a hafnium oxide film is low in absorption loss, and the reflectance or transmittance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical thin film formed on an optical substrate.

[0002]

2. Description of the Related Art At present, almost all optical members are formed with optical thin films such as an antireflection film and a reflection enhancement film. Depending on the specifications, the optical thin film may be a multilayer film in which the number of laminations reaches several tens.

The optical thin film formed by the vacuum evaporation method has problems such as an increase in the number of layers, an increase in scattering, a crack in the film, or a permeation of moisture into the film to change the spectral characteristics. Occurs. Therefore, with the recent diversification of production forms, film formation techniques using new techniques such as a film formation method other than the vacuum deposition method and an ion process are being studied.

As a film forming technique using a new technique such as an ion process, there are an ion plating method, an ion assist method, an ion beam sputtering method, a CVD method and the like. The technical merits of the film forming technology using the ion process and the like are as follows: (1) The film characteristics can be improved (improved film hardness and film adhesion) (2) A film having a high refractive index can be obtained without increasing the substrate temperature. And the like.

In recent years, in order to increase the degree of integration of semiconductor elements, there is an increasing demand for a high-resolution reduction projection exposure apparatus (stepper) for semiconductor manufacturing. One method of increasing the resolution of photolithography using this stepper is to shorten the wavelength of the light source. As the wavelength of the optical thin film material decreases, the amount of absorption tends to increase, and the types of the optical thin film material having a short wavelength and low absorption are limited.

Above all, hafnium oxide has attracted attention as an optical thin film material that can be used up to a KrF wavelength (248.4 nm). However, when hafnium oxide is formed by a vacuum evaporation method, it has a columnar structure and has minute gaps, so that there is a problem that a temporal change such as moisture adsorption occurs and the spectral characteristics change.

Therefore, the film structure is densified and the surface roughness is improved by using the film forming technique utilizing the ion process.

[0008]

However, there is a problem that an optical thin film formed by a film forming technique utilizing an ion process or the like has a larger absorption loss than an optical thin film formed by a vacuum evaporation method. For example, the attenuation coefficient at 248.4 nm of the hafnium oxide film is 0.001 or less when the film is formed by the EB vacuum evaporation method, and is 0.005 or more when the film is formed by the ion beam sputtering method.

Therefore, the present invention has been made in view of these problems,
It is an object to provide an optical thin film having a hafnium oxide film having a small attenuation coefficient and a dense film structure.

[0010]

Means for Solving the Problems A hafnium oxide film was formed on a quartz glass substrate by using an ion beam sputtering method.
Analyzes of the cause of the absorption loss at this time revealed that the film contained only a small amount of impurities and sufficient oxygen, suggesting that the cause was a defect in the bonding state between the metal and oxygen.

Therefore, the loss was greatly reduced by baking the formed hafnium oxide film in air at 400 ° C. for 3 hours. FIG. 1 shows the effect at that time. The solid line shows the transmittance immediately after film formation, and the broken line shows the transmittance after baking. Based on the above, the present inventor has carried out the present invention as a result of intensive studies on the film forming conditions.

The present invention firstly provides an optical system having at least a hafnium oxide film formed by an ion beam sputtering method, wherein the hafnium oxide film has an attenuation coefficient of less than 0.005 in a wavelength range of 230 to 300 nm. A thin film (Claim 1) is provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hafnium oxide film according to the present invention is formed by an ion beam sputtering method. After the substrate is set in the apparatus chamber, the chamber is evacuated and evacuated to a vacuum. However, compared to the ultimate degree of vacuum (1 × 10 ^{−7 to} 3 × 10 ⁻⁷ torr) required by the normal ion beam sputtering method, the vacuum is reduced. the extent of was set to 1 × 10 ^over 6 ~5 × 10 ^-7 torr bad.

Next, the substrate was shielded, and pre-sputtering was performed with an ion beam of argon gas without introducing oxygen to prepare an environment for the apparatus. The shielding of the substrate was removed, and the main sputtering was performed to form a film. In a state where the evacuation is insufficient and the degree of vacuum is poor, a very small amount of water is present, and this water acts during the film formation to form a film having a small absorption loss (a small attenuation coefficient).

[0015]

【Example】

Example 1 A hafnium oxide film having an optical thickness of λ / 2 was formed on a substrate by using an ion beam sputtering method. Argon gas is used for the ion source, and the target is 9 purity.
A hafnium oxide target of 9.9% or more was used.

[0016] First, after setting a substrate in the apparatus chamber is performed for about 5 hours evacuated and the vacuum degree of 1 × 10 ^{over 6} torr. Next, the substrate was shielded, and about 15 kV without introducing oxygen under the conditions of an argon gas ion beam of 1 kv and 70 mA.
Pre-sputtering was performed for one minute to prepare the environment of the apparatus. After removing the shielding of the substrate, main sputtering was performed under the same conditions as in the pre-sputtering to form a film.

As a result of measuring the spectral characteristics, λ = 248.4
The absorption loss in nm was 0.4%. If the refractive index of the hafnium oxide film is 2.28 and this is converted,
The damping coefficient is 0.0014. Furthermore, in the atmosphere,
Baking was performed at 00 ° C. for 3 hours. The absorption loss is about 0.23
%Met. When converted, the attenuation coefficient is 0.000
8

[Comparative Example 1] An ion beam sputtering method was used on the substrate under the same conditions as in Example 1 except that the evacuation was performed for about 12 hours and the degree of vacuum was reduced to less than 5 × 10 ⁻⁷ torr. A hafnium oxide film having a target film thickness of λ / 2 (λ = 248.4 nm) was formed. As a result of measuring the spectral characteristics, λ = 24
The absorption loss at 8.4 nm was 1.4% or more.
When converted, the attenuation coefficient is 0.005 or more.

[Embodiment 2] The optical film thickness on the substrate is λ / 4.
Number of layers consisting of hafnium oxide and silicon oxide
Single-layer film (hafnium oxide is H, silicon oxide is L
Then, [HL] ¹⁰ L was formed by ion beam sputtering. Using argon gas for the ion source,
Oxide targets each having a purity of 99.9% or more were used as targets.

First, after the substrate was set in the apparatus chamber, evacuation was performed for about 5 hours, and the degree of vacuum was set to 8 × 10 ^-7 torr. Next, the substrate was shielded, and a hafnium oxide target was pre-sputtered for about 15 minutes without introducing oxygen under the conditions of an argon gas ion beam of 1 kv and 70 mA,
Equipment environment was adjusted. After removing the shielding of the substrate, the main sputtering was performed under the same conditions as in the pre-sputtering to form a hafnium oxide film.

The substrate was shielded, and oxygen was introduced under the conditions of an argon gas ion beam of 1 kv and 70 mA to introduce about 15
For a minute, pre-sputter the silicon oxide target,
Equipment environment was adjusted. After removing the shield of the substrate, main sputtering was performed under the same conditions as in the pre-sputtering, and a silicon oxide film was formed. For the main sputtering, the above steps were repeated 10 times for the hafnium oxide film and 1 for the silicon oxide film.
This was repeated once to form 21 alternate layers.

As a result of measuring the spectral characteristics, λ = 248.4
The reflectivity in nm is 99.4% and the absorption loss is 0.5%
It was below. When the attenuation coefficient of silicon oxide is set to 0.0001 from the literature value and converted, the attenuation coefficient of hafnium oxide is 0.002. Furthermore, in the atmosphere,
Baking was performed at 00 ° C. for 3 hours. The reflectivity is 99.8%,
The absorption loss was less than about 0.1%. When the attenuation coefficient of silicon oxide is set to 0.0001 from the literature value and converted, the attenuation coefficient of hafnium oxide is 0.0005.

The attenuation coefficient of the hafnium oxide according to the present invention in the multilayer film is smaller than 0.005, and it has been found that the layer not in contact with the atmosphere has the effect of reducing the loss by baking.

[0024]

As described above, since the hafnium oxide film according to the present invention has an attenuation coefficient of less than 0.005, the absorption loss of the optical thin film having the hafnium oxide film according to the present invention is reduced, and the reflectance or the transmission is reduced. Rate can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the transmittance (after film formation and baking after film formation) of a hafnium oxide film formed on a substrate.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02B 5/28 G02B 1/10 Z

Claims (1)

[Claims] At least a hafnium oxide film formed by an ion beam sputtering method, wherein
An optical thin film having a hafnium oxide film having an attenuation coefficient of less than 0.005 in a wavelength range of 0 nm.