JP6647898B2 - UV reflective film and sputtering target - Google Patents

Description

  The present invention relates to an ultraviolet reflective film and a sputtering target.

  The ultraviolet reflective film is used for devices such as an ultraviolet sterilizer or a resin curing device for curing an ultraviolet curable resin, and an illumination device including an ultraviolet light emitting element or device. It is important to efficiently reflect ultraviolet rays from the viewpoint of energy efficiency, cost, and the like, and Patent Documents 1, 3, and 4 discuss ultraviolet reflecting films made of metal.

  Examples of the ultraviolet light source used in such an apparatus include a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, and the like, each having a specific peak wavelength and intensity, and depending on the purpose of use. And an appropriate light source is selected. Among them, a low-pressure mercury lamp having a strong peak at 254 nm is suitable for various uses such as sterilization and surface modification, and is widely used. Therefore, there is a need for an ultraviolet reflecting film capable of efficiently reflecting ultraviolet light of 254 nm.

JP 2015-43468 A JP-A-2002-323611 Japanese Patent No. 4981979 JP 61-148883 A JP 2011-21275 A

  However, the reflection in the ultraviolet light region has not been sufficiently studied. For example, Patent Literature 1 discloses Al, Rh, Si and alloys thereof as a reflection film used for an ultraviolet semiconductor light emitting element. However, there is no example, and the reflectance in the ultraviolet light region is sufficiently studied. Not.

  Patent Document 2 proposes an Ag alloy as a reflective film having high reflectivity and high durability. However, it is only a study in the visible light region, and does not examine a reflectivity in the ultraviolet light region. Patent Document 3 discusses obtaining a high reflectance in a region of 400 nm or less by controlling the surface roughness of the Ag alloy. However, there is no example of 375 nm or less, and there is no example of 254 nm ultraviolet light. Is not considered. Further, in general, Ag or an Ag alloy has high reflectance in the visible light region, but the reflectance sharply decreases in the ultraviolet light region of 380 nm or less, and the reflectance is approximately 25% at 254 nm.

  Patent Literature 5 describes an improvement in the reflectance in the visible light region due to alloying of Al, but does not mention the reflectance in the ultraviolet light region.

  The present invention has been made in view of the above problems, and has as its object to determine the amount of the rare earth element, Cu and the balance of Al constituting the ultraviolet reflection film, and the ratio of the rare earth element to Cu. Is to provide an ultraviolet reflecting film having a reflectance of 85% or more for ultraviolet light having a wavelength of 254 nm. Another object is to provide a sputtering target having such a composition.

The ultraviolet reflective film according to the present invention includes at least one of one or more rare earth elements: 0.2 at% or more and 3.0 at% or less, and Cu: 0.2 at% or more and 6.0 at% or less, The balance consists of Al and unavoidable impurities, and satisfies the following expression (1), and has a reflectance of 85% or more for ultraviolet rays having a wavelength of 254 nm.
X + 0.5Y <3.5 (1)
Here, X is the amount [at%] of the rare earth element, and Y is the amount [at%] of Cu.

  The rare earth element used for the ultraviolet reflecting film may be one or more elements selected from the group consisting of Sc, Nd, Gd, La, Y, Ce, Pr, and Dy.

  The thickness of the ultraviolet reflective film may be 50 nm or more and 2000 nm or less.

The sputtering target according to the present invention includes at least one of one or more rare earth elements: 0.2 at% or more and 3.0 at% or less, and Cu: 0.2 at% or more and 6.0 at% or less, with the balance being the balance. Is composed of Al and inevitable impurities, and satisfies the following expression (2).
X + 0.5Y <3.5 (2)
Here, X is the amount [at%] of the rare earth element, and Y is the amount [at%] of Cu.

  The rare earth element used for the sputtering target may be one or more elements selected from the group consisting of Sc, Nd, Gd, La, Y, Ce, Pr, and Dy.

  The ultraviolet reflective film according to the present invention, the rare-earth element constituting the ultraviolet-reflective film, the amount of Cu and the remaining Al, and the ratio of rare earth element to Cu is controlled to a predetermined range, the ultraviolet light of wavelength 254nm The reflectance is 85% or more, and has excellent reflectance. Further, the sputtering target according to the present invention can form an ultraviolet reflective film having excellent reflectance in this manner.

  Hereinafter, the details of the ultraviolet reflective film and the sputtering target of the present invention will be described.

<Ultraviolet reflective film>
[1. Composition of UV Reflecting Film]
The ultraviolet reflective film according to the present invention includes at least one of one or more rare earth elements: 0.2 at% or more and 3.0 at% or less, and Cu: 0.2 at% or more and 6.0 at% or less, The balance consists of Al and unavoidable impurities, and satisfies the following expression (1), and has a reflectance of 85% or more for ultraviolet rays having a wavelength of 254 nm.
X + 0.5Y <3.5 (1)
Here, X is the amount [at%] of the rare earth element, and Y is the amount [at%] of Cu.

Further, the rare earth element may be one or more elements selected from the group consisting of Sc, Nd, Gd, La, Y, Ce, Pr and Dy.
Hereinafter, each element and the formula (1) will be described in detail.

(1) Function of rare earth element and Cu The ultraviolet reflective film according to the present invention contains at least one of one or more rare earth elements and Cu in a predetermined amount.
When Al is formed by a sputtering method, Al becomes a film having a rough surface, and the reflectance is reduced. However, when a rare earth element or Cu is added, the rare earth element or Cu hardly diffuses on the substrate, so that it becomes an Al nucleation site on the substrate, and the nucleation density of Al increases. As a result, fine crystal grains increase and the structure becomes finer, so that the surface roughness becomes smaller.
As described above, since the surface of the ultraviolet reflective film can be made relatively flat by containing the rare earth element or Cu, even when the film is formed by the sputtering method, a decrease in the reflectance is suppressed and a high reflectance is obtained. can get.

(2) One or more rare earth elements: 0.2 at% or more and 3.0 at% or less The ultraviolet reflecting film according to the present invention comprises one or more rare earth elements at 0.2 at% or more and 3.0 at%. %, The roughness of the surface of the ultraviolet reflective film can be reduced, and the reflectance of the ultraviolet ray of 254 nm becomes 85% or more, and the film has excellent reflectance. When the amount of the rare earth element is less than 0.2 at%, the effect of making the crystal grains hard to be finely reduced and the effect of reducing the surface roughness is weakened, and a reflectance of 85% cannot be obtained. Further, when the rare earth element exceeds 3.0 at%, the reflectance of the rare earth element affects the reflectance of the ultraviolet reflection film and lowers the reflectance, so that a reflectance of 85% cannot be obtained.
From the viewpoint of obtaining even better reflectance of ultraviolet rays, the preferable upper limit of the content of the rare earth element is 1 at%, more preferably 2 at%.
Further, from the viewpoint of obtaining a better reflectance of ultraviolet light, the rare earth element is preferably at least one element selected from the group consisting of Sc, Nd, Gd, La, Y, Ce, Pr and Dy. .

(3) Cu: 0.2 at% or more and 6.0 at% or less The ultraviolet reflective film according to the present invention contains Cu at 0.2 at% or more and 6.0 at% or less, so that the surface of the ultraviolet reflective film has a rough surface. It is thought that the reflectance of ultraviolet light of 254 nm becomes 85% or more, and thus the film has an excellent reflectance. When the Cu content is less than 0.2 at%, it is considered that the crystal grains are not easily refined and the effect of reducing the surface roughness is weakened, so that a reflectance of 85% cannot be obtained. When Cu exceeds 6.0 at%, the low reflectance of Cu affects the reflectance of the ultraviolet reflective film and lowers the reflectance, so that a reflectance of 85% cannot be obtained.
From the viewpoint of obtaining even better reflectance of ultraviolet rays, the lower limit of the Cu content is preferably 0.5 at%, more preferably 1 at%, and the upper limit is preferably 5 at%, more preferably 4 at%.

( 4 ) Relationship between the amount X [at%] of the rare earth element and the amount Y [at%] of Cu (formula (1))
As described above, it is considered that both the rare earth element and Cu have an effect of reducing the surface roughness, and as a result, it is considered that excellent ultraviolet reflectance can be obtained.
On the other hand, as described above, the rare earth element and Cu have a disadvantage that the reflectance is reduced by excessive addition. Therefore, when both are used together, an ultraviolet reflective film having excellent reflectance can be obtained by containing both within a range satisfying a predetermined relational expression. That is, the amount X [at%] of the rare earth element and the amount Y [at%] of Cu satisfy the following expression (1).
X + 0.5Y <3.5 (1)
From the viewpoint of obtaining a better reflectance of ultraviolet rays, the preferable upper limit of the sum of X and 0.5Y is 3.0, more preferably 2.5.

( 5 ) Al and unavoidable impurities (remainder)
The ultraviolet reflecting film according to the present invention contains the remaining Al and unavoidable impurities in addition to the rare earth element and Cu, and can be brought in depending on the conditions of raw materials, materials, manufacturing facilities, and the like. Examples of the unavoidable impurities include Fe, In, Sn, Ni, Ti, Mg, Cr, and Zr. A preferable upper limit of the content of the unavoidable impurities is 0.03 wt%.

[2. Reflectivity of UV reflective film]
In this specification, the reflectance of the ultraviolet reflective film is a value obtained by measuring the spectral reflectance using an ultraviolet spectrophotometer, and is a ratio of the reflected light intensity of the ultraviolet reflective film to the reflected light intensity of the reference mirror. Examples of the ultraviolet spectrophotometer include a visible / ultraviolet spectrophotometer “V-570” (manufactured by JASCO Corporation).
The ultraviolet reflective film according to the present invention has a reflectance of 254 nm ultraviolet light of 85% or more. A preferred lower limit of the reflectance is 87%, more preferably 89%.

[3. Transmittance of UV reflective film]
When the ultraviolet transmittance of the ultraviolet reflective film is high, a material (resin or the like) in the vicinity of the ultraviolet reflective film is irradiated with ultraviolet light, which may cause deterioration of the material. preferable. The ultraviolet reflective film of the present invention is an Al-based alloy having a thickness of 50 nm or more, and thus has a low transmittance.
In the present specification, the transmittance of the ultraviolet reflective film is a value obtained by measuring the spectral reflectance using an ultraviolet spectrophotometer, and is a ratio of the transmitted light intensity of the ultraviolet reflective film to the transmitted light intensity of the reference mirror. Examples of the ultraviolet spectrophotometer include a visible / ultraviolet spectrophotometer “V-570” (manufactured by JASCO Corporation).
The preferable upper limit of the transmittance of ultraviolet light of the ultraviolet reflective film according to the present invention is 0.1%.

[4. UV reflective film thickness]
In the present specification, the thickness of the ultraviolet reflective film is a value measured using a step meter. As the step gauge, for example, “Alpha-Step” manufactured by KLA Tencor is mentioned.
The preferable lower limit of the thickness of the ultraviolet reflective film according to the present invention is 50 nm, more preferably 100 nm, and the reflectance of ultraviolet light is further improved. The preferable upper limit is 2,000 nm, more preferably 1,000 nm, and the reflectance of ultraviolet rays becomes better.

[5. Manufacturing method of ultraviolet reflective film]
The ultraviolet reflective film according to the present invention can be manufactured by a known sputtering method, for example, a magnetron sputtering method.
If there is sufficient energy for the added rare earth element or Cu to diffuse on the substrate, the number of Al nucleation sites may decrease and reflectivity may decrease. Specifically, by increasing the power at the time of film formation, or by reducing the distance between the substrate and the target, the energy of the sputtered particles increases, and as a result, the surface roughness increases and the reflectance decreases. Sometimes. Therefore, the film forming conditions may be changed according to the equipment used.

<Sputtering target>
[1. Composition of sputtering target]
The sputtering target according to the present invention includes one or more rare earth elements: 0.2 at% or more and 3.0 at% or less, and Cu: any one of 0.2 at% or more and 6.0 at% or less, The balance consists of Al and unavoidable impurities, and the amount X [at%] of the rare earth element and the amount Y [at%] of Cu satisfy the following expression (2).
X + 0.5Y <3.5 (2)

  By using the sputtering target according to the present invention, the above-described ultraviolet reflective film can be formed.

[2. Manufacturing method of sputtering target]
The method for manufacturing the sputtering target is not particularly limited, and various methods can be applied. However, it is preferable to apply a spray forming method. This is because the sputtering target manufactured by the spray forming method is excellent in the uniformity of the component structure, and thus, can form an ultraviolet reflective film having a uniform component structure.

<Deposition of UV reflective film>
After attaching a 4-inch diameter disk-shaped sputtering target having the composition described in Example 1 of Table 1 to an electrode in a chamber of a DC magnetron sputtering apparatus “CS-200” manufactured by ULVAC, the pressure in the chamber was reduced to 3 ×. It was adjusted to 10 ⁻⁶ Torr. Next, Ar gas (gas flow rate: 19 sccm) was introduced into the chamber, and the pressure in the chamber was adjusted to 2 mTorr. Thereafter, a sputtering power of 500 W was applied to the sputtering target at room temperature, and a 100 nm-thick film having the composition described in Example 1 of Table 1 was placed on an alkali-free glass plate (plate thickness 0.7 mm, diameter 4 inches). An ultraviolet reflective film was formed.
In Examples 1 to 19 and Comparative Examples 1 to 9 in Table 1, ultraviolet reflective films having a thickness of 100 nm were formed in the same manner as described above.
In Examples 20 to 23 in Table 2, an ultraviolet reflecting film having a film thickness shown in Table 2 was formed by changing the film forming time.

  The obtained ultraviolet reflective film was subjected to composition analysis, reflectance measurement and transmittance measurement by the following methods. The evaluation results are shown in Tables 1 and 2. In addition, among the elements and numerical values described in Tables 1 and 2, underlined ones denote that they are out of the range of the present invention.

<Composition analysis>
The composition (at%) of the ultraviolet reflective film was calculated by ICP emission analysis.

<Reflectance measurement>
Using a visible / ultraviolet spectrophotometer “V-570” manufactured by JASCO Corporation, the spectral reflectance in the range of 850 to 250 nm was measured for the ultraviolet reflective film formed on the alkali-free glass plate. The reflectance of 254 nm ultraviolet light was determined according to the following evaluation criteria. ○ and △ indicate that the ultraviolet reflective film is at a practical level. In addition, the reflectance of 375 nm ultraviolet light is shown as a reference value.
[Evaluation criteria]
：: 87% or more △: 85 or more, less than 87% ×: less than 85%

<Transmission measurement>
Using a visible / ultraviolet spectrophotometer “V-570” manufactured by JASCO Corporation, a spectral transmittance in a range of 850 to 250 nm was measured for an ultraviolet reflective film formed on an alkali-free glass plate. Table 2 shows the transmittance of 254 nm ultraviolet light.

All of the ultraviolet reflective films of Examples 1 to 23 are at least one of one or more rare earth elements: 0.2 at% or more and 3.0 at% or less, and Cu: 0.2 at% or more and 6.0 at% or less. And the balance consists of Al and unavoidable impurities, and satisfies the above equation (1). Therefore, it is considered that the surface roughness is reduced, and the reflectance of ultraviolet rays having a wavelength of 254 nm of 85% or more is excellent. Had.
In addition, all of the ultraviolet reflective films of Examples 20 to 23 had a low transmittance of ultraviolet light of 254 nm of less than 0.01%, and were excellent in blocking ultraviolet light.

  On the other hand, since the ultraviolet reflecting film of Comparative Example 1 is formed only of Al, it is considered that the effect of reducing the surface roughness cannot be obtained, and the reflectance of the ultraviolet light having a wavelength of 254 nm is 83.6%. It was low and did not meet the evaluation criteria.

  Since the ultraviolet reflecting films of Comparative Examples 1 to 5 are formed from Al and an element (In, Zn, Sn or Bi) other than the rare earth element, it is not possible to obtain the effect of reducing the surface roughness. It is considered that the reflectance of ultraviolet rays having a wavelength of 254 nm was as low as 72.4 to 84.2%, and did not satisfy the evaluation criteria. It is considered that In, Zn, or Sn contained in each of the ultraviolet reflective films of Comparative Examples 1 to 4 cannot reduce the surface roughness, and as a result, it is considered that the reflectance of these ultraviolet reflective films was low. . Further, it is considered that Bi contained in the ultraviolet reflective film of Comparative Example 5 was deposited on the surface of the ultraviolet reflective film, thereby lowering the reflectance of the reflective film.

  The ultraviolet reflective film of Comparative Example 7 was formed from Al and the rare-earth element Nd. However, since the content of Nd was 4.0 at%, which was larger than the specified amount, the low reflectance of the contained Nd caused the ultraviolet reflection. The reflectance of the film was affected, and the reflectance of ultraviolet light having a wavelength of 254 nm was as low as 84.8%, which did not satisfy the evaluation criteria.

  The ultraviolet reflective film of Comparative Example 8 was formed from Al and Cu. However, since the Cu content was 7.0 at%, which is larger than the specified amount, the low reflectance of the contained Cu caused the ultraviolet reflective film to have a low reflectance. The reflectivity was affected, and the reflectivity of ultraviolet rays having a wavelength of 254 nm was as low as 84.4%, which did not satisfy the evaluation criteria.

  Although the ultraviolet reflective film of Comparative Example 9 is formed from Al, the rare-earth elements Nd and Cu, the above-mentioned formula (1) is not satisfied. This affected the reflectance of the reflective film, and the reflectance of ultraviolet light having a wavelength of 254 nm was as low as 84.9%, which did not satisfy the evaluation criteria.

Claims (3)

One or more rare earth elements: 0.2 at% or more and 3.0 at% or less, and Cu: at least one of 0.2 at% or more and 6.0 at% or less, with the balance being Al and unavoidable impurities,
Satisfies the following equation (1),
An ultraviolet reflective film having a reflectance of 85% or more of ultraviolet light having a wavelength of 254 nm.
X + 0.5Y <3.5 (1)
Here, X is the amount [at%] of the rare earth element, and Y is the amount [at%] of Cu.   The ultraviolet reflective film according to claim 1, wherein the rare earth element is one or more elements selected from the group consisting of Sc, Nd, Gd, La, Y, Ce, Pr, and Dy.   The ultraviolet reflective film according to claim 1 or 2, wherein the film thickness is 50 nm or more and 2000 nm or less.