JPS6350930A - optical recording medium - Google Patents

Abstract

PURPOSE:To eliminate deterioration with age by adding at least one kind of aluminum oxide and silicon oxide to a composite film and specifying the refractive index thereof to <=215 and >=170. CONSTITUTION:The composite dielectric film 2 composed of the aluminum nitride and silicon nitride as well as the aluminum oxide and silicon oxide is formed by sputtering on the groove side of a grooved PC substrate 1. An NdDyFeCoTi film 3 which is a magneto-optical recording layer is formed thereon and furthermore, the same composite dielectric film 4 as the composite dielectric film 2 is formed thereon. The films are formed under such sputtering conditions under which the refractive index (n) of the composite dielectric films attains <=215 and >=170. The deterioration of the composite dielectric film with age is thereby eliminated for a long period of time.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to optical recording media.

[Conventional technology]

Conventional optical recording media are manufactured by irradiating a perpendicular magnetic recording layer with focused laser light to cause magnetization reversal and recording all information, or by irradiating the recording layer with laser light to change the crystal structure of the recording layer. (from crystalline to amorphous or vice versa,
Alternatively, information can be recorded through phase transformation (from hexagonal to cubic or vice versa), or holes can be made by irradiating the recording layer with laser light. Alternatively, there is a method of recording information by changing the shape of the recording part, such as by forming a bubble.

In particular, conventional magneto-optical recording media often use an entire plastic substrate (PC, PMMA, epoxy resin, etc.) with guide grooves on the substrate. This is because injection molding is possible and mass production is possible at low cost. However, plastic substrates have high hygroscopicity and gas permeability, and are suitable for magneto-optical recording layers such as GdTbFe, TbFeCo, and GdTbFe0o.
, DyFeOo, NdDyFeOo, and other rare earth transition metal alloy films are easily damaged, resulting in severe deterioration of magnetic properties. Therefore, between the plastic substrate and the magneto-optical recording layer, 5in2. By providing one more layer of oxide dielectric film such as Ello, corrosion resistance from the substrate side can be improved.

However, since these dielectrics are oxides, free oxygen completely oxidizes the magneto-optical recording layer, so the protective effect was not sufficient.

The next idea was to form a film on a non-oxide dielectric plastic substrate made of silicon nitride, aluminum nitride, zinc sulfide, or the like.

However, these non-oxide dielectric films lack adhesion to the substrate, or even if they do have adhesion, they easily crack, making them impractical.

Therefore, as a result of intensive research, the inventors of the present invention found that
As shown in No. 452, it was shown that a composite film of aluminum nitride and silicon nitride can be obtained as a complete protective film for a magneto-optical recording layer. As a result of further research, the present inventors found that in addition to the two components of aluminum nitride and silicon nitride, at least one of aluminum oxide and silicon oxide was used.
It was discovered that by adding seeds), a more stable protective film could be created.

[Problem that the invention seeks to solve]

Therefore, the present invention was developed by the inventors in Japanese Patent Application No. 60-89452.
(By adding at least one of aluminum oxide and silicon oxide to the composite film of aluminum nitride and silicon nitride shown in (1)), it is an object of the present invention to provide a perfect optical recording medium with an excellent protective effect.

[Means for solving the problems] - The optical recording medium of the present invention has an optical recording layer formed on one side of a transparent substrate, and recording, reproduction, and In optical recording media for erasing, a composite dielectric film containing two main components, aluminum nitride and silicon nitride, is provided between the optical recording layer and the transparent substrate.Aluminum oxide may be added to the composite dielectric. and silicon oxide, and has a refractive index of 2.15 or less and 1.70 or more.

[Effect]

According to the above structure of the present invention, at least one of aluminum oxide and silicon oxide is added to the composite dielectric film of aluminum nitride and silicon nitride, and the refractive index is 2.15 or more and 1.70 or more. However, it has an even more protective effect. This means that nitride alone does not provide sufficient adhesion to the plastic substrate, but adding oxide can improve adhesion. However, if too much oxide is added, there will be a large amount of free oxygen, and the rare earth transition metal alloy film will be easily oxidized.
Therefore, the amount of oxide added is 45m01% or less of the total. Also, the fact that the refractive index is higher than Z15 means that aluminum or silicon has not sufficiently reacted with nitrogen or oxygen, and unreacted aluminum and silicon exist in the film, making it difficult to weather. Since the optical constants change during the performance test (accelerated test), the magneto-optical recording medium changes over time. Furthermore, a refractive index of less than 1.70 means that the density of the dielectric film is sparse (porous), making it less effective as a protective film and causing deterioration of the magnetic recording layer. become. Therefore, the refractive index is less than 2.151
．． This means that it needs to be 70 or higher.

The effects of the present invention will be explained in detail below based on examples.

〔Example〕

FIG. 1 is a cross section of a magneto-optical recording medium according to the present invention, and 1 is a grooved PC board with a groove pitch of 1.6 μm and a groove width of 0.5 μm.
It has one groove of 8 μm and a depth of 700 A. In No. 2, a composite dielectric film 10000ATh of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide was formed on the groove side of this PC board. This composite dielectric film was formed by reactive sputtering, and Ar+N2 gas was introduced into the target using a target rattler containing 18 mol% aluminum nitride, 72 mol% silicon nitride, 5 mol% aluminum oxide, and 5 mol% silicon oxide. power 5
The film was formed at 00W.

The film composition was the same as the target composition. On top of that, a magneto-optical bone layer N (LD7F e Oo Ti film 4
A composite dielectric film 10000A of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide, which is the same as 2, was further formed as 4.

Figure 2 shows a case in which a composite dielectric film of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide was entirely deposited using a dielectric target with the same composition as the dielectric target described above, and the sputtering conditions were changed. The figure shows the change in refractive index of .

The RF power was constant at 500 W, the film thickness was constant at 1000 A, and the N1 partial pressure was constant at 20%. It can be seen that the horizontal axis represents the total sputtering pressure and the vertical axis represents the refractive index, and the higher the total sputtering pressure, the lower the refractive index. Next, FIG. 3 shows the change in refractive index when a film is formed by changing the sJ partial pressure. In this case, R.F.
The power was 500W, the film thickness was constant at 1000A, and the total sputtering pressure was constant at 4 m Torr.The horizontal axis is the N2 partial pressure, and the vertical axis is the refractive index.The higher the N2 partial pressure, the lower the refractive index. Recognize. Furthermore, the film quality of all samples of the composite dielectric film of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide shown in Figures 2 and 3 was evaluated by an etching test using a buffered hydrofluoric acid solution at t0 solution temperature of 23°C. Fixed.

The longer the etching time, the better the film quality, which means it is denser and the reaction is more complete. The horizontal axis in FIG. 4 is the total sputtering pressure as in FIG. 2, and the horizontal axis in FIG. 5 is the Nt partial pressure as in FIG. 3. The vertical axis in both FIGS. 4 and 5 is the etching time. As you can see from Figures 4 and 5, there are places where the etching time is extremely short;
When compared with the figure, areas where the refractive index is greater than 2.15 and areas where the refractive index is less than 1.70 are regions where the etching time is short. In other words, it is considered that the composite dielectric film of the present invention having a refractive index in the range of 2.15 or less and 1.70 or more has good film quality and excellent protective effect.

Therefore, we created a magneto-optical recording medium with a composite dielectric film of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide having different refractive indexes using the medium structure diagram shown in FIG.
An accelerated test was attempted by placing the sample under a constant temperature of 60° C. and 90×RH.

FIG. 6 shows a graph of the Kerr rotation angle over time as seen from the substrate side of the medium. The horizontal axis shows the elapsed time, and the vertical axis shows the ratio of the Kerr rotation angle θkh(t) to the Kerr rotation angle θkr (0) immediately after film formation with respect to the elapsed time t. 5, the refractive index n of the composite dielectric film is 2.15.2.01.1.90°1.8
5, 1.80, 170, 6 is a medium with n of 2.24, 7 is a medium with n of 2.31, 8 is a medium with n of 1.69.1.
Among the 65 mediums, 9 is a medium with n of 1.65 and 1.60.

As can be seen from this figure, the refractive index according to the present invention is 2.1.
For media with a value of 5 or less and 1.70 or more, there is no change over time (50
Even after 00 hours have elapsed, there is no change (no change).

For the medium 6.7 with a −1 refractive index greater than 2.15, a change occurs at the beginning of the accelerated test (10 to 50 hr) and remains constant thereafter. This indicates that the dielectric film with a refractive index higher than 2.15 contains unreacted At and S1, so the unreacted components change into stable oxides etc. during the accelerated test. . As a result, θkr (t) changes, causing a significant change in the recording/reproducing characteristics (0/N) of the medium. Moreover, in the media 8 and 9 whose refractive index is smaller than 1.70,
A change occurs approximately 100 hours after the accelerated test, and the change gradually occurs until θkr(1) approaches 0. This indicates that the dielectric film having a refractive index of less than 1.70 is not dense, that is, is sparse, and therefore moisture and reactive gases enter during the accelerated test. As a result, the deterioration of the magneto-optical recording layer progresses and θkr(t) changes.

This also causes a significant change in the recording/reproducing characteristics (0/N) of the medium.

Next, FIG. 7 shows a diagram of the change in coercive force of the medium over time. The horizontal axis shows the elapsed time, and the vertical axis shows the ratio of the coercive force He(t) to the coercive force Ha(o) immediately after film formation with respect to the elapsed time t. 10 has a refractive index n of 2.15, 2.01°1.90
．． 1.85.1.80.1.70. and 2.24.2.
31 medium, 11 has n of 1.69. With t65 medium,
12 is a medium in which n is 1.65 and 1.60. From this figure, it can be seen that the coercive force of a medium with a refractive index n smaller than 1.70 changes with time. This is due to deterioration of the magneto-optical recording layer due to the sparse quality of the dielectric film mentioned above. (The magneto-optical recording layer has a transition metal rich composition)
The coercive force of a medium with an n of 1.70 or more does not change over a long period of time, but a medium with an n of more than 2.15 is not suitable as a protective film, as shown in FIG.

Next, magneto-optical recording media with composite dielectric films of various compositions were formed under sputtering conditions such that the refractive index n was 2.0.
The changes over time (60°C, 90% RH) were observed.

Table 1 shows the composition used. For convenience, aluminum nitride is referred to as AtN, silicon nitride as SiN, aluminum oxide as Ato, and silicon oxide as EIiO.

Table 1 a...5iNsa(Atoe, l5iOo, *)+
* mot%b ... (AtNe, ot SiN o
,ss )so (AtOo5810o,s )+o
mot%c ”・(AtNo, z 81Na, g) s
o (AtOO,s 5iOo,s)temOt%d,
-(AtN…81Na, os,) so (Azo
o, 5 SiOo, s) u mOt%e...
(AtNt*s Sin o,.,),. (ALOas
810 o, s) 1゜mot%f...AtN
165iNse mot%g”・(AtN0.2Si
N IIJ ) ss, * (At0o, s SiOo
, s ) o, t mat%h ”・(AtNo, t
5iNo,s )ss (AtOas 5iOe,g
)45 mo1%i −(AtNo, zsiNo,
s ) 144 (At0eIISiOo, g ) 48.
1 moL%j −(AtNo,z 81No,s
)9o AtOso mob%k”・(AtNo,
*5iNo,s) to SiO1o mot% 4th%
is a diagram of BBR over time, and 15 is an uninvented medium, as shown in Table 1, c, l.

gm h* 1e j-” medium, 14 is f medium,
15 is the medium of a and e, and 16 is the medium of 1.

The medium of f shows an increase in BER after about 5000 hr, but is sufficiently durable for practical use. However, the medium of the present invention is completely stable even after 10,000 hours and can be said to be a perfect medium. In addition, the BER of media a and e increases from around 400 hr, and after 10,000 hr it has become five times the initial value, making it impractical. This is because a is a medium that does not contain aluminum nitride and lacks density, and eld
This is because too much aluminum nitride causes cracks to occur.

Furthermore, medium 1 is not suitable for practical use because the amount of oxide added is too large and the free acid buildup deteriorates the magneto-optical recording layer.

From the above results, the composition of the composite dielectric film of the present invention is (aluminum nitride) x (silicon nitride), -XO〈 x 〈
B, 95, and (At5iN) too-z ((aluminum oxide)y
(Silicon oxide) s-y)z O〈z≦45 mob% 0≦y≦1 In this example, PO was used for the substrate, but PMMA
The present invention is also effective on plastic substrates made of epoxy resin, and the film forming method is not limited to sputtering, but may also be vapor deposition, OVD, etc. Furthermore, the targets used were sintered targets of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide, which were prepared using reactive sputtering with Ar1N and -1-02 gas using metal targets of gold, aluminum, and silicon. However, the effects of the present invention are not hindered in any way. Moreover, the magneto-optical recording layer is also TbFe0o, GdTbFe
I have no problem with that.

Furthermore, the present invention is not only suitable for use as a protective film for magneto-optical recording media, but is also effective for sealing off gas and moisture from plastic substrates, and is also effective for phase-change optical recording media.

〔Effect of the invention〕

As described above, the optical recording medium according to the present invention has a composite dielectric material of aluminum nitride and silicon nitride, which is the main composition of the dielectric film disposed between the optical recording layer and the transparent substrate, and one of aluminum oxide and silicon oxide. At least one kind is fully added, and the refractive value of the composite dielectric film is 2.15 or less 1.7
By making it more than e, there is no change over a long period of time (50 years or more), and there is an effect that can guarantee reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a magneto-optical recording medium according to the present invention. FIG. 2 is a diagram showing the dependence of refractive index on sputtering total pressure. FIG. 6 is a diagram showing the dependence of refractive index on sputtering N1 partial pressure. FIG. 4 is a diagram showing the dependence of etching time on sputtering total pressure. FIG. 5 is a diagram showing the dependence of etching time on sputtering N2 partial pressure. FIG. 6 is a diagram of the change in Kerr rotation angle over time in an accelerated test at 60° C. and 90% RH. FIG. 7 is a diagram of the change in coercive force over time in an accelerated test at 60° C. and 90% RH. FIG. 8 is a graph of BKR changes over time in an accelerated test at 60° C. and 90% RH. 1... Grooved po substrate 2... Composite dielectric film of aluminum nitride, silicon nitride, aluminum oxide, and silicon oxide 3... Magneto-optical recording layer NaDyFe0oTi film 4... Aluminum nitride, silicon nitride, and aluminum oxide Composite dielectric film 5 of silicon oxide and silicon oxide...The refractive index n of the composite dielectric film is 2.15.
,2.01゜1.90.1.85. t80.1.70
medium. 6...Medium where n is 2.24 7...Medium where n is 2.31...Medium 9 where n is 1.69, 1.65-N is 1.
63, 1.60 medium 10...n is 2.15.2.01. i, 90.1.
85, 1.80°1.70. and 2.24, 2.31 medium 110.・Medium 12 where n is 1.69, 1.65...
・Medium 13 with n of 1.63, 1.60...Medium 14 with be Cy dt g, 11t 1e j shown in Table 1...Medium 15 with f shown in Table 1...No. Medium 16 of a and e shown in Table 1... Medium 1 shown in Table 1. that's all

Claims (3)

[Claims] (1) In an optical recording medium in which an optical recording layer is formed on one side of a transparent substrate, and recording, reproduction, and erasing are performed by irradiating the optical recording layer with a focused laser beam, the optical recording layer and the transparent At least one of aluminum oxide and silicon oxide is added to a composite dielectric of aluminum nitride and silicon nitride, which is the main component of the dielectric film disposed between the substrates, and the refractive index of the composite dielectric film is 2.15 or less and 1.70 or more. (2) The optical recording medium according to claim 1, wherein the ratio of the aluminum nitride and silicon nitride components, which are the main components of the composite dielectric film, is within the range expressed by the following formula. (Aluminum nitride)_x (Silicon nitride)_1_-_
x0<x≦0.95 (3) When the aluminum nitride and the silicon nitride, which are the main components of the composite dielectric film, are expressed as AlSiN, the component ratio of the aluminum oxide and the silicon oxide to be added is within the range shown by the following formula. An optical recording medium according to claim 1, characterized in that: (AlSi
N)_1_0_0_-_z((aluminum oxide)_y
(Silicon oxide)_1_-_y)_z 0<z≦45mol% 0≦y≦1