JP2001297491A - Optical information recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical information recording medium so that an extremely thin crystallization promoting layer can be uniformly formed to specified film thickness with good reproducibility and that initialization is surely made unnecessary. SOLUTION: The crystallization promoting layer is formed by the method of long throw sputtering which uses a larger distance L between a substrate 9 as the object of film forming and a target 10 than a conventional sputtering method so that the extremely thin crystallization promoting layer can be formed in a proper time because of its slow film forming rate. Thus, the extremely thin crystallization promoting layer can be uniformly formed to specified film thickness with good reproducibility and initialization is surely made unnecessary in the manufactured optical information recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical information recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, the variety and diversification of the optical disc field has been remarkable, and CD-ROMs and write-once
R, rewritable CD-RW, and DVD-RO
M, write-once DVD-R, and rewritable DVD-RW.

[0003] When such optical disks are classified according to the configuration of the recording layer, one of them is a phase-change type optical disk using a phase-change material. In the case of a phase-change type optical disk, the recording layer using AgInSbTe or GeSbTe is amorphous immediately after normal sputtering deposition.
When used as an optical information recording medium, recording and reproduction are performed so that the unrecorded portion is crystalline and the recording mark (recorded portion) is amorphous. Therefore, immediately after sputtering, the entire surface of the recording medium has the same reflectance as that in the recording state. Therefore, generally, the entire surface is crystallized by annealing with a large-diameter, large-output laser.

On the other hand, as another technique, a layer for promoting crystallization of the recording layer (crystallization promotion layer) is provided before forming the recording layer, thereby facilitating such an initialization process. There is also an optical information recording medium in which the process time is shortened or unnecessary (for example, Japanese Patent Application Laid-Open No. 5-34262).
9 and JP-A-9-161316.

[0005]

However, in the case of the former annealing method, since the initialization operation requires a time of 30 seconds or more, the throughput is reduced, and
Since a large number of devices are required, there is a problem that equipment costs are high.

On the other hand, when the latter initialization promoting layer is used, it is considered that it is desirable to make the crystallization promoting layer as thin as possible in consideration of the influence on recording characteristics and the like. However, when an attempt is made to form a very thin crystallization promoting layer, the film formation time becomes very short, so that even if there is a slight instability in the discharge state,
There is a problem that the film thickness distribution on the substrate becomes non-uniform.
As a result, depending on the film formation, the effect of the crystallization promoting layer is not obtained because the promoting layer becomes too thin, and the crystallization of the recording layer is incomplete, or the crystallization is not uniform in the substrate plane. Some problems arise.

For example, when the crystallization promoting layer is made of Bi having a film thickness of 1.5 nm, film formation by magnetron sputtering generally used in the field of optical discs takes several seconds to complete. Therefore, even if the rise time of the plasma discharge is very short, or if there is a discharge abnormality for a very short time, there is a problem that the film thickness of Bi is largely shifted (thinned) from a desired film thickness. As a specific example, when there is a discharge abnormality of 0.1 second, the film formation time is 10 seconds.
In seconds, the ratio of the abnormal discharge time to the film formation time is 1%. Therefore, in a simple calculation, when the film thickness is only 1% thinner, when the film formation time is 1 second, And the film thickness is reduced by as much as 10%.

Further, the film formation time is shortened for the same reason, so that the variation in the rise of the plasma discharge for each film formation and the variation in the discharge state appear more remarkably as the film thickness variation. . Therefore, there is a problem that the crystallization degree of the recording layer becomes remarkably different every time the film is formed, and the recording layer cannot be crystallized with good reproducibility. Such a problem becomes a serious problem such as a decrease in yield during mass production.

Incidentally, as a method of dealing with such a problem, first, a method of reducing the input power during film formation can be considered. However, when the input power is reduced, the discharge becomes unstable due to a decrease in the power density of the target, and the problem also arises that the film thickness of the accelerating layer and thus the crystallinity of the recording layer vary with each film formation. .

Secondly, a method of reducing the strength of the magnet or eliminating the magnet to reduce the plasma density and reduce the film forming rate can be considered. However, when the strength of the magnet is reduced, it is necessary to increase the gas pressure in order to generate a stable discharge, so that the film quality deteriorates. Furthermore, since the film thickness distribution deteriorates, there is a problem that the crystallization of the recording layer becomes non-uniform in the plane of the substrate.

Accordingly, the present invention relates to an optical information recording medium having a crystallization promoting layer for promoting crystallization of a crystal layer, in which an extremely thin crystallization promoting layer is uniformly formed at a predetermined film thickness with good reproducibility. It is an object of the present invention to provide an optical information recording medium that can be formed and that does not require initialization, and a method of manufacturing the same.

[0012]

According to the first aspect of the present invention,
Manufacturing of an optical information recording medium having at least a first dielectric layer, a recording layer, a second dielectric layer, and a reflective heat dissipation layer laminated on a substrate and having a crystallization promoting layer in contact with at least a part of the recording layer In the method, the crystallization promoting layer is formed by a long throw sputtering method.

Therefore, since the film formation rate is slow by using the long throw sputtering method in which the distance between the substrate on which the film is to be formed and the target is made larger than that of the ordinary sputtering method, the extremely thin crystallization promoting layer can be formed. It is possible to form an optical information recording medium that can be formed in an appropriate time, can form an extremely thin crystallization-promoting layer with a predetermined film thickness uniformly and with good reproducibility, and can reliably eliminate the need for initialization.

According to a second aspect of the present invention, in the method for manufacturing an optical information recording medium according to the first aspect, a long throw sputtering method is used in which a distance between a substrate on which a film is formed and a target is 150 mm or more.

Therefore, the distance between the substrate on which the film is to be formed and the target is determined depending on the area ratio of the two, the gas pressure, etc., but by setting it to 150 mm or more, the invention of claim 1 is intended. The action can be reliably achieved.

According to a third aspect of the present invention, in the method for manufacturing an optical information recording medium according to the first aspect, a long throw sputtering method in which a distance between a substrate on which a film is formed and a target is variable.

Therefore, since the distance between the substrate and the target is variable, it is possible to easily cope with a case where there is a film forming speed due to the change of the target material by adjusting the distance between the substrate and the target.

The optical information recording medium of the invention according to claim 4 is:
It is manufactured by the manufacturing method according to any one of claims 1 to 3.

Therefore, since the optical information recording medium is manufactured by the manufacturing method according to any one of the first to third aspects, the optical information recording medium that does not require initialization can be provided at low cost.

According to a fifth aspect of the present invention, in the optical information recording medium of the fourth aspect, the thickness of the crystallization promoting layer is 10
nm or less.

Therefore, since the crystallization-promoting layer is extremely thin within a range where the effect can be exerted, the effect of mixing the crystallization-promoting layer with the recording layer has little effect on the recording characteristics. Media can be provided.

According to a sixth aspect of the present invention, in the optical information recording medium of the fourth or fifth aspect, the crystallization promoting layer is formed of Bi.
Or a compound thereof.

Therefore, an optical information recording medium that does not require initialization can be provided at low cost.

According to a seventh aspect of the present invention, in the optical information recording medium of the fourth or fifth aspect, the crystallization promoting layer is made of Sb.
Or a compound thereof.

Therefore, an optical information recording medium that does not require initialization can be provided at low cost.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. First, FIG. 1 shows an example of a layer configuration of a phase-change type optical information recording medium 1 according to the present embodiment. In the optical information recording medium 1, a first dielectric layer 3, a recording layer 4, a second dielectric layer 5, and a reflective heat dissipation layer 6 are laminated on a substrate 2, and at least The laminated structure has a crystallization promoting layer 7 in contact with a part thereof. 8 is a protective layer.

In this embodiment, in manufacturing such an optical information recording medium 1, the crystallization promoting layer 7 is formed by a long throw sputtering method. In the long throw sputtering method, for example, as shown in FIG. 2, a distance L between a substrate 9 on which a film is to be formed and a target 10 is made larger than that in a normal sputtering apparatus. The sputtered particles having a large velocity component in the direction parallel to the surface cannot be incident on the substrate 9.
Is a sputtering method in which only sputtered particles almost perpendicular to the surface reach the substrate 9. Reference numeral 12 denotes a magnet, and 13 denotes a power source for plasma discharge. For this reason, the number of target molecules reaching the substrate 9 is reduced, and the film forming speed is lower than that of the conventional sputtering apparatus. In general, the film thickness distribution is improved.

Such a long throw sputtering method itself is generally used in the field of semiconductors, but its main purpose is to improve the step coverage and to sacrifice the film forming speed to some extent. Increase the deposition rate as much as possible,
In the field of optical discs aiming to increase mass productivity, application for the purpose of stably forming an extremely thin crystallization promoting layer 7 is a completely new attempt.

As described above, since the long-throw sputtering method has a low film-forming speed, the extremely thin crystallization promoting layer 7 can be formed over an appropriate long time. Therefore, even if there is a slight rise time of the plasma discharge or a discharge abnormality for an extremely short time, the ratio of these to the film formation time is reduced, so that the crystallization promoting layer 7 can be formed with the desired film thickness. The optical information recording medium 1 can be formed and initialized with good reproducibility. Further, since the film thickness distribution is improved, there is also an effect that the recording layer 4 uniformly crystallized on the entire surface of the substrate can be formed.

The distance L between the substrate 9 and the target 10 is usually determined by considering the area ratio between the substrate 9 and the target 10, the gas pressure at the time of sputtering, etc., in consideration of the film thickness distribution, the efficiency of thin film formation, and the like. It is determined by a balance. In the present embodiment, the distance L between the substrate 9 and the target 10 is set to be larger than the optimal value determined as described above. For example, if the distance is about 40 mm in a typical magnetron sputtering apparatus, it is desirable to set the distance L to 100 mm or more. In general terms with a margin, the distance L is preferably set to 150 nm or more.

The distance L between the substrate 9 and the target 10
May be variable. By doing so, even if there is a film forming speed due to the change of the target material, it can be easily coped with by adjusting the distance L between the substrate 9 and the target 10. The variation of the distance L is performed by moving the substrate 9 or the target 10.

The crystallization promoting layer 7 used in the present embodiment
Are preferably those that are easily crystallized, have a similar crystal structure to the recording layer 4, and have a similar lattice constant. Specifically, Bi or its compound, Sb or its compound, or a high melting point metal represented by Hf, Ti, or the like, or Al,
In and Tl are preferred. Further, the crystallization promoting layer 7 is mixed with the recording layer 4 with the repetitive recording. However, since the composition of the crystallization promoting layer 7 is different from the composition of the recording layer 4, it affects the characteristics of the recording layer 4. Therefore, it is preferable that the crystallization promoting layer 7 is as thin as possible. Preferably it is 10 nm or less. However, if the thickness is too small, the effect as the crystallization promoting layer 7 is reduced, so that the thickness is preferably 0.5 nm to 5.0 nm.
It is. By forming such a crystallization promoting layer 7,
The optical information recording medium 1 with good reproducibility and requiring no initialization can be obtained.

The recording layer 4 is made of AgInSbTe, G
eSbTe, GeInSbTe, GeAgInSbTe
System materials. Other elements may be added to these elements for the purpose of further improving the characteristics.

[0034]

EXAMPLES Specific examples supporting the present embodiment will be described with reference to several examples. In the embodiment described below, a single-wafer sputtering apparatus having five chambers (SDS13 manufactured by Balzers) is used.
The film was formed according to 1). Although the film formation in this example was performed using an apparatus having five chambers, the number of chambers is not limited to five, and production is possible if the number is five or more.
The breakdown of film formation is shown.

Film formation chamber 1 (PC1): ZnS. SiO_Two(First dielectric layer
3) Film forming chamber 2 (PC2): crystallization promoting layer 7 Film forming chamber 3 (PC3): recording layer 4 Film forming chamber 4 (PC4): ZnS. SiO_Two(Second dielectric layer
5) Film forming chamber 5 (PC5): Al (reflective heat dissipation layer 6) [Example 1] A diameter of 120 cm and a thickness of 0.1 mm were obtained by injection molding.
6mm polycarbonate substrate (hereinafter referred to as PC substrate)
) Is formed. In PC1, ZnS.
SiO _TwoA film is formed by a sputtering method. Target material: SiO_Two(20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 190 nm

On PC2, a Bi film is formed under the following conditions. The distance L between the target 10 and the substrate 9 is changed, and
= 150 mm. Sputtering method: magnetron sputtering Target material: Bi Input power: DC 0.4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 1.5 nm At this time, the film formation time was 5 sec. .

In the PC3, AgInSb was obtained under the following conditions.
A Te-based film is formed. Target material: Ag ₃ In ₄ Sb ₆₂ Te ₃₁ Input power: DC 0.4 kW / 8 inch Target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

On PC4, ZnS. Si
An O ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

An Al film is formed on the PC 5 under the following conditions. Target material: Al Input power: DC 5 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 140 nm After applying a UV curable resin, UV light is irradiated.

Comparative Example 1 Diameter 120c by injection molding
m, a PC board having a thickness of 0.6 mm is formed. On PC1,
Under the following conditions, ZnS. An SiO ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 190 nm

On PC2, a Bi film is formed under the following conditions. The distance L between the target 10 and the substrate 9 is L = 60
mm. Sputtering method: magnetron sputtering Target material: Bi Input power: DC 0.4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 1.5 nm At this time, the deposition time is 0.4 sec. there were.

In the PC3, AgInSb was obtained under the following conditions.
A Te-based film is formed. Target material: Ag ₃ In ₄ Sb ₆₂ Te ₃₁ Input power: DC 0.4 kW / 8 inch Target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

On PC4, ZnS. Si
An O ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

An Al film is formed on the PC 5 under the following conditions. Target material: Al Input power: DC 5 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 140 nm After applying a UV curable resin, UV light is irradiated.

Example 2 Diameter 120c by injection molding
m, a PC board having a thickness of 0.6 mm is formed. On PC1,
Under the following conditions, ZnS. An SiO ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 190 nm

An Sb film is formed on PC2 under the following conditions. The target 10 was moved, the distance L from the substrate 9 was changed, and L was set to 200 mm. Sputtering method: magnetron sputtering Target material: Sb Input power: DC 0.4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 2.0 nm At this time, the film formation time was 5 sec. .

On PC3, GeSbTe is used under the following conditions.
A system film is formed. Target material: Ge ₂₆ Sb ₂₂ Te ₅₂ Input power: DC 0.4 kW / 8 inch Target gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

On PC4, ZnS. Si
An O ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

An Al film is formed on the PC 5 under the following conditions. Target material: Al Input power: DC 5 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 140 nm After applying a UV curable resin, UV light is irradiated.

[Comparative Example 2] A diameter of 120c was obtained by injection molding.
m, a PC board having a thickness of 0.6 mm is formed. On PC1,
Under the following conditions, ZnS. An SiO ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 190 nm

An Sb film is formed on the PC 2 under the following conditions. The distance L between the target 10 and the substrate 9 is L = 60
mm. Sputtering method: magnetron sputtering Target material: Sb Input power: DC 0.4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 2.0 nm At this time, the film formation time is 0.3 sec. there were.

On PC3, GeSbTe was obtained under the following conditions.
A system film is formed. Target material: Ge ₂₆ Sb ₂₂ Te ₅₂ Input power: DC 0.4 kW / 8 inch Target gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

In PC4, ZnS. Si
An O ₂ film is formed by a sputtering method. Target materials: SiO ₂ (20.5 mol%), ZnS (7
(9.5 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 20 nm

An Al film is formed on the PC 5 under the following conditions. Target material: Al Input power: DC 5 kW / 8 inch target Gas pressure: 26.6644 Pa (= 2 mTorr) Gas type: Ar Film thickness: 140 nm After applying a UV curable resin, UV light is irradiated.

These Examples 1, Comparative Examples 1, Examples 2,
For Comparative Example 2, ten media were produced and evaluated. Table 1 shows the results.

[0056]

[Table 1]

According to the results shown in Table 1, the media of Examples 1 and 2 were 650 nm for all 10 media.
The laser light had a reflectance of 20% or more and was crystallized. Since the crystallization promoting layer 7 is extremely thin, the influence on the recording characteristics is negligible, and information can be recorded without any problem. On the other hand, in the case of the medium of Comparative Example 1, seven sheets were crystallized, but the remaining three sheets were insufficiently crystallized on the entire surface or a part of the substrate. In the case of the medium of Comparative Example 2, six sheets were crystallized, but the remaining four sheets were insufficiently crystallized on the entire surface or a part of the substrate. As a result, in order to record information, a laser initialization operation was required.

[0058]

According to the first aspect of the present invention, at least a first dielectric layer, a recording layer, a second dielectric layer,
A method for manufacturing an optical information recording medium having a crystallization promoting layer in which a reflective heat dissipation layer is laminated and brought into contact with at least a part of the recording layer, wherein the crystallization promoting layer is formed by a long throw sputtering method. Since the film formation rate is slow by using the long throw sputtering method, an extremely thin crystallization promoting layer can be formed over an appropriate time, and the extremely thin crystallization promoting layer can be formed at a predetermined thickness. It is possible to manufacture an optical information recording medium that can be formed uniformly and with good reproducibility and that can reliably eliminate the need for initialization.

According to a second aspect of the present invention, in the method for manufacturing an optical information recording medium according to the first aspect, a long throw sputtering method in which a distance between a substrate on which a film is formed and a target is 150 mm or more is used. By doing so, the intended effect of the invention described in claim 1 can be reliably obtained.

According to the third aspect of the present invention, in the method for manufacturing an optical information recording medium according to the first aspect, a long throw sputtering method in which a distance between a substrate on which a film is formed and a target is variable is used. Thus, even if there is a film forming speed due to a change in the target material, it can be easily coped with by adjusting the distance between the substrate and the target.

According to the optical information recording medium of the fourth aspect of the present invention, since the optical information recording medium is manufactured by the manufacturing method of any one of the first to third aspects, the optical information recording medium which does not need to be initialized can be reduced. Can be provided at cost.

According to the fifth aspect of the present invention, in the optical information recording medium of the fourth aspect, the thickness of the crystallization promoting layer is 1
The thickness is set to 0 nm or less, and the thickness is extremely thin within a range where the crystallization-promoting layer can exert its effect, so that the mixing of the crystallization-promoting layer with the recording layer has little effect on the recording characteristics. Can be provided.

According to the sixth aspect of the present invention, in the optical information recording medium of the fourth or fifth aspect, the crystallization promoting layer is formed of B
Since it is made of i or a compound thereof, an optical information recording medium that does not require initialization can be provided at low cost.

According to the seventh aspect of the present invention, in the optical information recording medium of the fourth or fifth aspect, the crystallization promoting layer is formed of S
Since it is made of b or its compound, an optical information recording medium that does not require initialization can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a principle sectional view showing a laminated structure of an optical information recording medium according to an embodiment of the present invention.

FIG. 2 is a principle diagram showing a long throw sputtering method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical information recording medium 2 substrate 3 first dielectric layer 4 recording layer 5 second dielectric layer 6 reflective heat dissipation layer 7 crystallization promoting layer 9 substrate on which film is to be formed 10 target L distance

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Deguchi, 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Wataru Otani 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Ryuichi Furukawa 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Inside Ricoh Company (72) Inventor Kiyoto Shibata 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Yasumichi Aman 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Nobuaki Onagi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. Reference) 4K029 AA11 BA01 BA03 BA46 BA51 BB02 BD12 CA05 DC03 DC04 DC05 5D029 NA07 5D121 AA03 EE03 EE09

Claims (7)

[Claims] 1. A light having a crystallization promoting layer in which at least a first dielectric layer, a recording layer, a second dielectric layer, and a reflective heat dissipation layer are laminated on a substrate, and is in contact with at least a part of the recording layer. A method for manufacturing an information recording medium, wherein the crystallization promoting layer is formed by a long throw sputtering method. 2. The method for manufacturing an optical information recording medium according to claim 1, wherein a long throw sputtering method is used in which a distance between a substrate on which a film is formed and a target is 150 mm or more. 3. The method for manufacturing an optical information recording medium according to claim 1, wherein a long throw sputtering method is used in which a distance between a substrate on which a film is formed and a target is variable. 4. An optical information recording medium manufactured by the manufacturing method according to claim 1. 5. The optical information recording medium according to claim 4, wherein said crystallization promoting layer has a thickness of 10 nm or less. 6. The optical information recording medium according to claim 4, wherein the crystallization promoting layer is made of Bi or a compound thereof. 7. The optical information recording medium according to claim 4, wherein the crystallization promoting layer is made of Sb or a compound thereof.