JP2007087523A - Method for forming reflective film on disk substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a reflective film on a disk substrate capable of uniformly forming the film even when there are irregular parts on the surface of the disk substrate. <P>SOLUTION: This method includes the step of attaching a disk substrate to be sputtered to a substrate holder in a sputter chamber, the step of providing a reflective film forming Ag target member opposite to the disk substrate with a predetermined distance, the step of supplying a gas necessary for sputtering into the sputter chamber after air is exhausted from the sputter chamber to reach a predetermined negative pressure, the step of applying a high voltage to the target member under predetermined gas pressure, and the step of sputtering Ag molecules to the disk substrate. The film is formed under the condition that a mean free path of Ag is larger than a distance between the target member and the disk substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for forming a reflective film on a CD-R or DVD-R disc, which is a write-once type optical recording medium using a material containing an organic dye in a recording layer.

The optical recording medium targeted by the present invention is a write-once type optical recording medium using a material containing an organic dye in the recording layer, such as CD-R, DVD-R, etc., and its layer structure is, for example, There is something as shown in FIG.
In the figure, 40 is an optical recording disk, which has a transparent substrate 41 made of a transparent resin or transparent glass from the bottom, a recording layer 42 made of an organic dye thereon, and a metal reflective layer 43 on the transparent substrate 41. One or more protective layers 44 mainly composed of a resin are formed thereon.
The recording layer contains, for example, an organic dye such as a phthalocyanine dye, a cyanine dye, and an azo dye as a material, and contains a quencher and other additives as necessary. The recording layer is formed, for example, by dissolving a dye in a solvent, applying it by a spin coating method, and drying. The film thickness is 50 to 300 nm.

The metal reflective layer is formed by sputtering an alloy containing 80% or more of Ag, Al or the left (hereinafter referred to as “Ag”), and is a layer containing 80 to 100 atomic% of Ag. As the sputtering gas, a gas containing Ar as a main component is used, and the sputtering gas is formed by DC magnetron sputtering. The film thickness is 10 to 150 nm.
One or more protective layers are formed on the metal reflective layer. The lower protective layer is formed by spin-coating an ultraviolet curable resin and then curing by irradiating with ultraviolet rays. The minimum thickness of the lower protective layer in the recordable area is 2 μm or more.
Further, an upper protective layer or the like is formed on the lower protective layer by screen printing or the like.
As a conventional method for manufacturing a reflective film, the film thickness of the metal reflective layer containing Ag formed by sputtering is set to 10 to 150 nm, and a gas containing Ar as a main component is used as a sputtering gas when forming the metal reflective layer. The film was formed at a gas pressure of 1 Pa or more (see, for example, Patent Document 1).
JP 2000-285518 A

  According to Patent Document 1, as the sputtering gas pressure containing Ar gas as a main component is increased, light resistance is gradually improved, and stable characteristics regarding light resistance can be obtained. However, as the gas pressure is further increased, the film thickness distribution of the metal reflective film gradually becomes non-uniform, and when the non-uniformity becomes 65% or more, the signal characteristics such as the modulation factor and reflectivity are affected. It is described as coming out.

FIG. 6 shows a conventional sputtering apparatus for manufacturing a magneto-optical disk. Reference numeral 50 denotes a conventional sputtering apparatus. This sputtering apparatus 50 includes a sealable sputtering chamber 51. A magnetron sputtering source 52 is accommodated in the sputtering chamber 51, and the sputtering source 52 forms a target T for forming a reflective film. (For example, Ag) and electrically connected to the external power source 53.
The sputter chamber 51 includes a rotatable substrate holder 54 at the bottom, and the substrate holder 54 is connected to an electric motor 55. The substrate holder 54 holds the substrate S to be sputtered with the reflective film forming side facing the target material T during sputtering.
Further, a nitrogen gas introduction port 56, an argon gas introduction port 57, and an exhaust port 58 are provided in the wall portion of the sputtering chamber 51.

Before starting sputtering, the sputtering chamber 51 is evacuated from the exhaust port 58 until a predetermined negative pressure is reached, and thereafter, nitrogen gas N2, which is a gas necessary for sputtering, is introduced into the sputtering chamber 51 from the nitrogen gas introduction port 56. And argon gas Ar is supplied from the argon gas inlet 57 to increase the gas pressure to 1 Pa or higher, and the substrate holder 54 is rotated by the electric motor 55 while a high voltage of about 360 V is applied from the power source 53 to the sputtering source 52 to T is discharged, sputtering of the target material T is performed on the disk substrate S, and the sputtering is continued until a reflective film having a predetermined thickness is formed on the surface of the disk substrate S.
In this way, a reflective film having a predetermined thickness is formed on the surface of the disk substrate S.
According to the conventional method, if the gas pressure is high, sputtering becomes active, and the film thickness quickly becomes a predetermined film thickness. Therefore, it has been considered that the gas pressure is preferably 1 Pa or more from the viewpoint of tact.

However, in the conventional optical disk, the method of forming a film at a gas pressure of 1 Pa or more was sufficient. However, for the high-density optical disk that needs to be expected to increase in the future, the above method requires the uniform density reflection required by the high-density optical disk. The Applicant has noticed that it becomes difficult to obtain a layer.
The reason for this is that when sputtering is performed at a gas (Ar) pressure of 1 Pa or more, the Ag gas molecules T0 released from the target T are likely to collide with other gas molecules Ar, and thus the distance that can go straight is shortened (ie, The mean free path becomes smaller), and the Ag gas molecules T0 land on the disk substrate S while repeatedly colliding with other gas molecules Ar. Therefore, the Ag gas molecules are perpendicular to the disk substrate S at the time of landing. It is inferred that most people land from various diagonal directions because they cannot land from the direction.

FIG. 7 shows a reflective film when Ag gas molecules are formed on the disk substrate S in an oblique direction. (A) When the surface of the disk substrate S is a mirror surface, (b) An uneven surface with a height of 5 mm is formed. In some cases, (c) is a view showing a longitudinal section in the case where there is an unevenness with a height of 10 mm.
According to the conventional method, when Ag gas molecules land on the disk substrate from an oblique direction, when the surface of the disk substrate S1 is a mirror as shown in FIG. However, when the surface of the disk substrate S2 has slight irregularities as shown in FIG. 2B, a slight hollow portion is formed when the Ag gas molecules T0 land on the disk substrate S2 from an oblique direction. H2 is formed, and the degree of embedding in the fine structure can be slightly increased. If the surface of the disk substrate S3 has an irregularity as high as 10 mm as shown in FIG. 3C, when the Ag gas molecules land on the disk substrate S3 from an oblique direction, the bridge of the Ag molecules T0 above the recesses. Is formed, and a large hollow portion H3 is formed above the concave portion, so that a fine structure cannot be obtained.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a reflective film for a disk substrate, which can form a film uniformly without forming a bridge of Ag molecules above the concave portions even if the surface of the disk substrate S is uneven. Is to provide.

  In order to solve the above-mentioned problem, the invention according to claim 1 relates to a method for forming a reflective film on a disk substrate, wherein a disk substrate to be sputtered is attached to a substrate holder in a sputtering chamber, and is opposed to the disk substrate. An Ag target material for forming a reflective film is provided at a predetermined distance, the sputtering chamber is evacuated to a predetermined negative pressure, and then a gas necessary for sputtering is supplied into the sputtering chamber. In a method for forming a reflective film on a disk substrate by applying a high voltage to the target material under a gas pressure and sputtering Ag molecules on the disk substrate, the mean free path of Ag is the target material and the disk substrate. It is characterized in that the film is formed under a condition that is larger than the distance between the two.

According to a second aspect of the present invention, in the method for forming a reflective film on the disk substrate according to the first aspect, the mean free path of the Ag is reduced between the target material and the disk substrate by lowering the pressure of the gas below 1 Pa. It is characterized by being larger than the distance between.
According to a third aspect of the present invention, in the method for forming a reflective film on the disk substrate according to the second aspect, the pressure of the gas is 0.52 Pa or less.

  With the configuration described above, Ag gas molecules land on the disk substrate only from the vertical direction, so that a disk can be formed evenly even if the surface of the disk substrate is uneven.

FIG. 1 shows a reflection film forming apparatus employing a reflection film forming method according to the present invention. In the figure, reference numeral 10 denotes a sputtering apparatus according to the present invention. The sputtering apparatus 10 includes a sealable sputtering chamber 11. A magnetron sputtering source 12 is accommodated in the sputtering chamber 11. Is supported by a target T (for example, Ag), and is electrically connected to the external power source 13.
The sputter chamber 11 includes a rotatable substrate holder 14 at the bottom, and the substrate holder 14 is connected to an electric motor 15. During sputtering, the substrate holder 14 holds the disk substrate S to be sputtered with the reflective film forming side facing the target material T side.
Further, a nitrogen gas introduction port 16, an argon gas introduction port 17, and an exhaust port 18 are provided in the wall portion of the sputtering chamber 11.

Before starting the sputtering, the sputtering chamber 11 is evacuated from the exhaust port 18 until a predetermined negative pressure is reached, and thereafter, nitrogen gas, which is a gas necessary for sputtering, is introduced into the sputtering chamber 11 from the nitrogen gas inlet 16 and The argon gas Ar is supplied from the argon gas inlet 17 and the gas pressure is made less than 1 Pa according to the present invention. Then, while rotating the substrate holder 14 by the electric motor 15, a high voltage of about 360 V is applied to the sputtering source 12 from the power source 13 to discharge the target material T, and sputtering of the target material T is performed on the disk substrate S. Sputtering is continued until a reflective film having a predetermined thickness is formed on the surface of the disk substrate S.
In this way, a uniform reflective film having a predetermined thickness can be formed even on the surface of the substrate T having irregularities. The reason is that since the gas pressure is low, the Ag gas molecules T0 emitted from the target can go straight down without colliding with other gas molecules Ar, so that a uniform reflective film is formed on the surface of the uneven disk substrate S. A film is formed.

FIG. 2 shows the reflection film forming method according to the present invention. (A) When the surface of the disk substrate S is a mirror surface, (b) When there is an uneven surface with a height of 5 mm, (c) With an uneven surface with a height of 10 It is each longitudinal cross-sectional view which formed into a film about the case.
According to the method of the present invention, since the film is formed under the condition that the mean free path of the Ag gas molecules is larger than the distance between the target material and the disk substrate, the Ag gas molecules collide with other gas molecules. Therefore, the process proceeds in the vertical direction from the target material toward the disk substrate. Therefore, (a) not only when the surface of the disk substrate S is a mirror surface, but also when there is an unevenness with a height of 5 mm in (b) or an unevenness with a height of 10 mm in (c), Since it descends from above (slowly like a mist), a bridge of Ag molecules T0 is not formed above the recess, and the microstructure is uniform.

FIG. 3 is a graph of particle energy versus mean free path with Ar pressure as a parameter. In the figure, the horizontal axis is the particle energy [eV], which can be changed by the sputtering voltage. The vertical axis represents the mean free path [cm]. The parameter is Ar pressure [mTorr], P1 is 30 mTorr, P0 is 25 mTorr, and P2 is 35 mTorr.
The figure shows that increasing the particle energy increases the mean free path, and decreasing the Ar pressure increases the mean free path.
Therefore, in order to increase the mean free path (that is, to make it difficult for Ag molecules to collide with other molecules), it is better to lower the Ar pressure or increase the particle energy.

However, as a result of investigating the relationship among the Ar pressure, the sputtering power, the distance between the target T-substrate, and the film thickness uniformity in various experiments, the following (1) to (6) were found.
(1) When the Ar pressure is lowered, abnormal discharge occurs at a certain point and the film thickness becomes uniform.
The decrease in the Ar pressure is preferably less than 1 Pa and also 0.52 Pa or less.
(2) Increasing the Ar pressure increases the rate.
(3) The Ar pressure and the degree of embedding in the fine structure are as shown in FIG. 2 (low pressure) and FIG. 6 (high pressure).
(4) When the Ar pressure is increased, the mean free path is shortened and the degree of embedding in the groove is deteriorated.
(5) A similar effect can be expected by increasing the sputter power, but damage to the dye occurs, so it is not recommended to make the film thickness uniform by increasing the sputter power. After all, it is better to reduce the pressure.
(6) By shortening the distance between the target T and the substrate S, the same effect can be expected, but since the distance between the plasma and the substrate is close, damage to the dye / substrate is caused by heat. Uniform film thickness by increasing the sputtering power is not recommended. After all, it is better to reduce the pressure.

From the above, in order to obtain a disk that is uniformly formed even if the surface of the disk substrate is uneven, it is preferable that the Ag gas molecules land on the disk substrate only from the vertical direction. In order to land vertically, the mean free path should be lengthened. In order to lengthen the mean free path, it is preferable to lower the Ar pressure. The Ar pressure should not be 1 Pa (≈1.9 Tmorr) or more, but the Ar pressure should be less than 1 Pa and also 0.52 Pa or less. The reason why the gas pressure is 0.52 Pa or less can be read from the graph of FIG. FIG. 4 is a diagram of emitted particle energy versus particle quantity with pressure as a parameter. In the figure, it can be seen that the energy of the emitted particles is low at 6 mTorr to 10 mTorr, the energy of the emitted particles is high at 4 mTorr (≈0.53 Pa), and higher at 1 mTorr. Therefore, it can be said that the mean free path is long at a pressure of 4 mTorr or less.
In this way, a uniformly formed film was obtained even when the surface of the disk substrate was uneven.

1 shows a reflection film forming apparatus employing a reflection film forming method according to the present invention. The reflective film formed by the method of the present invention is as follows: (a) When the surface of the disk substrate S is a mirror surface, (b) When there is an unevenness with a height of 5 mm, (c) When there is an unevenness with a height of 10 mm FIG. It is a diagram of particle energy versus mean free path with Ar pressure as a parameter. FIG. 3 is a diagram of the energy of emitted particles versus the amount of particles with pressure as a parameter. It is a model longitudinal cross-sectional view which shows the structural example of an optical recording medium. 1 shows a reflection film forming apparatus according to a conventional method. Reflective film formed by the conventional method: (a) When the surface of the disk substrate S is a mirror surface, (b) When there is an unevenness with a height of 5 mm, (c) When there is an unevenness with a height of 10 mm It is the figure shown by the longitudinal cross-section.

Explanation of symbols

10. Sputtering apparatus 11 employing the reflective film deposition method according to the present invention 11 Sputtering chamber 12 Magnetron sputtering source 13 External power source 14 Substrate holder 15 Motor 16 Nitrogen gas inlet 17 Argon gas inlet 18 Exhaust outlet S Disk substrate T Target (for example, , Ag)

Claims (3)

A disk substrate to be sputtered is attached to a substrate holder in the sputtering chamber, and a reflective film forming Ag, Al or an alloy containing 80% or more of the left is formed at a predetermined distance facing the disk substrate (hereinafter referred to as “Ag”). )), A sputtering chamber is evacuated to a predetermined negative pressure, and then a gas necessary for sputtering is supplied into the sputtering chamber, and the target material is applied to the target material under a predetermined gas pressure. In a method for forming a reflective film on a disk substrate by applying a high voltage and sputtering Ag molecules on the disk substrate,
A method for forming a reflective film on a disk substrate, comprising forming a film under a condition that an Ag mean free path is larger than a distance between the target material and the disk substrate.   2. A reflective film on a disk substrate according to claim 1, wherein the mean free path of Ag is made larger than the distance between the target material and the disk substrate by setting the gas pressure to less than 1 Pa. Film forming method.   3. The method for forming a reflective film on a disk substrate according to claim 2, wherein the pressure of the gas is 0.52 Pa or less.

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