JPS6318546A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a high-performance magneto-optical recording medium which has a substantially large Kerr rotating angle and particularly large reproduction output at the time of recording and reproducing of information by forming a nitride film made of the compsn. in which the metals or semiconductor elements constituting nitrides are incorporated at the ratio higher than the intrinsic stoichiometrical compsn. ratio even in terms of the nitride. CONSTITUTION:The nitride to constitute the nitride film which is a transparent film to increase the Kerr rotating angle is preferably the nitride of the metal elements such as Al, Ta, Ti and Nb or the nitride of the semiconductor elements such as Si, Ge, Sn, Se, Te, and B. The ratio of the metal or semiconductor elements to be incorporated into said nitrides is preferably in the compsn. range expressed by (MnNm)1-xMx in molar fraction (where M is the metal or semiconductor element, N is nitrogen and MnNm is approximately the stoichiometrical compsn. of the nitride consisting of the metal or semiconductor element, and x denotes a 0<x<=0.5 molar fraction range). The more preferable range of x to increase the Kerr rotating angle is 0<x<=0.1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magneto-optical recording media, and in particular to Kerr's
The present invention relates to a magneto-optical recording medium that has a large rotation angle and is suitable for recording and storing information.

[Conventional technology]

BACKGROUND OF THE INVENTION Ultra-large-capacity external storage media are required for scientific and technical calculations, data processing, system design, and system control that are currently performed using computers. For this purpose, a magnetic recording medium called a magnetic disk has been used. However, in the future, there is a strong demand for new information recording media that can further increase storage capacity at an additional cost. Magneto-optical recording media are attracting attention as one of the promising candidates.

In a magneto-optical recording medium, information is recorded in a magnetic film using semiconductor laser light, and this is reproduced and information that is no longer needed is erased. Since the thermal energy of laser light is used when recording and erasing information, a high-output semiconductor laser is required. Now that semiconductor lasers with a specific output of several tens of mW have already been put into practical use, there are no fundamental problems regarding recording and erasing of magneto-optical recording media.

However, a problem arises when reproducing recorded information. In other words, in a magneto-optical recording medium, information is read using Kerr rotation caused by a magnetic film.
Since the rotation angle at this time, that is, the Kerr rotation angle, is small, there is a drawback that the reproduction output is small. In order to improve this drawback, a magneto-optical recording medium with a structure in which the Kerr rotation angle is increased by providing a transparent film with a large refractive index was proposed in Japanese Patent Laid-Open No. 58-60442 or No. 58-200447.
It is proposed in the publication No. In addition, as a nitride film,
Nitride films are advantageous in terms of stability. Therefore, for example, the eighth
On a disc-shaped plastic substrate 1 as shown in the figure,
A nitride film 2, which is a transparent film having a refractive index higher than that of the substrate 1, is formed, and a magnetic film 3. It is a conventionally known technique to sequentially stack protective films 4 to form a magneto-optical recording medium. With such a configuration, the laser light incident from the substrate 1 side causes multiple reflections within the nitride film 2.

The Kerr rotation angle of this reflected light increases as the refractive index of the nitride film 2 increases, and is theoretically 1.5 of the original Kerr rotation angle of the magnetic film 3.
It also becomes ~2 times as large.

However, in the conventional magneto-optical recording medium provided with nitride@2, gas is released from the substrate due to the rise in temperature of the substrate 1 that occurs during the formation of the nitride film 2, and the nitride film 2 is refracted due to the influence of this gas. This results in a problem that a sufficiently large Kerr rotation angle cannot be obtained.

Furthermore, due to the internal stress generated in the formed nitride film 2, minute irregularities occur on the surface of the substrate 1 and light is diffusely reflected, so that the Kerr rotation angle is also smaller than the value expected from theoretical calculations. There was a problem with this.

[Problem that the invention seeks to solve]

As mentioned above, in the prior art, the nitride film, which is a transparent film provided to increase the Kerr rotation angle of a magneto-optical recording medium, has a refractive index that decreases due to the influence of gas released from the substrate, and Due to the internal stress generated in the nitride film, WIIA1 unevenness occurs on the substrate surface, causing problems such as a decrease in the Kerr rotation angle due to diffuse reflection of light.Therefore, magneto-optical recording with a sufficiently large Kerr rotation angle and high reproduction output is required. Media not available.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a high-performance magneto-optical recording medium with a sufficiently large Kerr rotation angle and a particularly large reproduction output when recording and reproducing information.

[Means for solving problems]

The object of the present invention is to provide a magneto-optical recording medium.

The composition of the nitride film, which is a transparent film formed to increase the Kerr rotation angle, is made of a metal nitride or a nitride of a semiconductor element. By forming a nitride film with a composition higher than the original stoichiometric composition,
achieved.

The nitride constituting the nitride film, which is a transparent film for increasing the Kerr rotation angle of the present invention, is Aa.

Nitride of metal elements such as Ta, Ti, Nb or Si
, Ge, Sn, Se, Te, B, etc. are preferable, and the amount of the metal or semiconductor element contained in these nitrides is expressed by the following general formula in terms of H molecular fraction. The composition ranges shown are preferred.

(M n N +++)i −X M
represents a nearly stoichiometric composition of a nitride made of a metal or semiconductor element, or represents a range of 0<x≦0.5 in terms of atomic fraction. ) and a more preferable X for increasing the Kerr rotation angle
The range of is O<x≦0.1.

- For example, when silicon nitride is used as a nitride film, which is a transparent film for increasing the Kerr rotation angle, the Si concentration range is approximately 4 degrees, which is represented by the chemical formula of silicon nitride, Si3N4, that is, (SL3N4)i- xS
ix, a composition in which Si is excessive in a range where X is O<x≦0.5, more preferably O<x≦0.1;
For example, (S i, N,), S io. , that is, 5i4sN.

By setting (SL = 45%), the object of the present invention can be achieved.

If the film thickness of the nitride film, which is a transparent film for increasing the Kerr rotation angle of the present invention, is less than 300, the effect of increasing the Kerr rotation angle will be small, and if it exceeds 1,500, the effect as an enhancement film will deteriorate. Because I do.

The range is preferably from 300 to 1,500 people, and the more preferred range is from 500 to 1,000 people.

[Effect]

The nitride film, which is a transparent film provided to increase the Kerr rotation angle of the present invention, is made of a nitride containing a metal or semiconductor element in excess of the stoichiometric composition. The refractive index is further increased and internal stress is reduced. Therefore, even if gas is released from the substrate, it will react with the excess metal or semiconductor element, and the refractive index will be maintained above the inherent refractive index of the stoichiometric nitride. Moreover, it is possible to prevent light from being diffusely reflected due to minute irregularities on the substrate surface due to internal stress, and as a result, it is possible to increase the Kerr rotation angle.

For the sake of convenience, the effect of the silicon nitride film of the present invention containing an excessive amount of SL will be explained as an example. Stoichiometric composition of silicon nitride (Si.

SL exists in excess compared to N,). Si, N. Si has a larger refractive index and is ceramic-like.
, N4 has the effect of alleviating the brittleness, so it greatly reduces the internal stress of the nitride film. As shown in Figure 1 <, 5
When Si is added to i3N41i, the refractive index n increases. Si3'N gradually increases from the original n (approximately 2.0) and increases almost linearly toward Si's n (approximately 3.8). on the other hand.

It can be seen that the internal stress σ decreases as the addition of Si increases. Here 1 For example ( S L3 N4) a
．． In the case of 5sia-i, that is, Si*1Nss, the SL that exists in excess with respect to Si and N4 is.

When the 5i41Nss film is formed, it reacts with the gas released from the substrate, and becomes smaller than the original n of Si (approximately 3.8), eventually reducing the original size n of SL and N4.
(approximately 2.0) or higher.

Therefore, even if there is a release of gas from the substrate.

A sufficiently large Kerr rotation angle can be obtained.

In addition, the internal stress σ in the case of Si, N4 film is approximately 7×10'
dyn/a ( is large, and as SL is added to it, it gradually decreases to 1, for example (staN4)., ll5III
-1(Sl*5Nss), σ is approximately 6×10″d
Since the value of yn/aJ is greatly reduced, the occurrence of minute irregularities on the substrate surface is extremely reduced, and the Kerr rotation angle is hardly lowered due to diffused reflection of light.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in more detail with reference to the drawings. In the drawings, the same reference numerals indicate the same parts or parts having the same function or performance.

(Example 1) A disc-shaped PMM with a diameter of 130R1 as shown in Fig. 2
A (polymethyl methacrylate) substrate 1 was dehydrated in vacuum at a temperature of 80°C for 4 hours, and then silicon nitride (Si.N4) SL44N□((Si,N4-)) containing 10% (atomic fraction) of excess Si.
*5ia-x] Nitride film 2 was formed to a thickness of approximately 900 mm. At this time, the sputter target 8 is made of Si, N, with a purity of 99.9%, processed and formed by a hot press method, and is coated on a plate 9.
10 Si chips are arranged in a grid to occupy 10% of the area ratio.
A composite target arranged with 1 kW. Ar gas is introduced from the gas inlet 12, and the sputtering gas pressure is 10 m.
The film was formed under Torr.

Next, using the same apparatus shown in FIG. 7 as above, Tb□Fe
,. Using a sputtering target 8 made of an alloy having a composition (molecular fraction of M) of Co, 2, a magnetic film ~3 having the same composition was sputtered under the conditions of input power of 1 kW and sputtering gas pressure of 5 mT 6 rr as described above (C3LzN4). It was laminated to a thickness of 1000 on the a-s 5i11.1 nitride film 2. Finally, an SiO protective film 4 made of Si◯ was formed to a thickness of 1500 mm on the magnetic film 3 using the same apparatus as above. (S L3 N
4) As a result of measuring the refractive index n and internal stress σ (dyn/aJ) of o-s S 1a-s nitride 11i2, as shown in Fig. 1, n is about 2.2 from the original about 2 of S13N4.
showed an increase of about 10% or more, and (Si3N4)o-'
asxo, x σ of the nitride film 2 is approximately 7 x 10'dyn/
Approximately 6 x 10' dyn/aA from ci
, and an increase in Kerr rotation angle was observed.

(Example 2) Using the high frequency magnetron sputtering apparatus shown in FIG. 7 used in Example 1, a magneto-optical recording medium having the structure shown in FIG. 3 was produced. On the glass substrate 1, an ultraviolet curing resin layer 5 in which tracking guide grooves are formed at a pitch of 1.6 IIm is formed.
The thickness is about 30 mm by the photopolymerization method.
is formed. On this ultraviolet curing resin M2S, 5
A 14sNss ((SlaN4)a, 5sla, z) nitride film 2 was formed by sputtering by about 900 people. here,
The sputter target 8 is a composite target in which Si chips are arranged in a lattice pattern on a Si, N, plate processed and formed by a hot press method so that Si occupies 20% of the area, and the input power is 0. The zero-order film was formed under 5kW and sputtering gas (Ar) pressure of 20n+ Torr, Qd,
, Tb, , Fe, , Go, a composite target (10 m square Gd and Tb chips pasted on an alloy plate of Fe and Go) was used, and the input power was 0. Magnetic 11j3 having a composition of G dx 4 T bx 4 F es s COt was subjected to elrJ under a sputtering gas pressure of 5 kW and a sputtering gas pressure of 5 mTorr. Furthermore, the above Si again.

A composite target of N4 plate and Si chip is used.

Input power: 0.5 kW, sputtering gas pressure: 30 ■ Torr
To the thickness of 1000 people under (S13 N4) @, @
5ia-x protective film 6 was formed. Finally, SU 531
6 (18cr-8Ni'-2,5Mo-balance Fe)
Use the plate as a sputtering target 8, and set the sputtering gas pressure to 5■
A non-magnetic stainless steel protective film 7 having a thickness of 1000 mm was formed under Torr.

The results of investigating various properties of the magneto-optical recording medium produced by the above method are shown below.

Figures 4(a) and ('b) show silicon nitride (S13)
N4) Film A and excess Si (Si.

N4), , Sx, , (Sx4sNts) The thickness of the nitride film h(
FIG. In addition, FIG. 4(a) shows that after the ultraviolet curing resin layer 5 is provided using the 2P method, the temperature is 30°C and the relative humidity is 80%.
Figure 4(b) shows the case where the nitride film and the upper film were laminated after being held for one hour in an environment of 140°C in a vacuum. So, 1
This is a case where a nitride film and an upper layer thereof are formed after performing a heating dehydration treatment for a period of time. Comparing these two.

It can be seen that in the magneto-optical recording medium using si, N, s (A curve), the Kerr rotation angle is greatly affected by the moisture contained in the ultraviolet curable resin layer 5. However, (SisN*')o-asi. , 2 membranes (8
Curve 2) shows that the Kerr rotation angle increases significantly with almost no influence from the above-mentioned moisture. Further, FIG. 5 shows a magneto-optical recording medium A using Si, N, and a film as the nitride film shown in FIG. 4(b) and a nitride film (S x -3N 4 ). ,,Si0. As is clear from Figure 0, which shows the results of measuring the surface of magneto-optical recording medium B using a film using a Talysurf (surface roughness meter), S
The i□N4 film is 1010d as shown in Figure 1 above.
Because it has a large internal stress of about yn/cJ, ultraviolet curing resin P! Minute irregularities occur on the surface of J5. Therefore, in the magneto-optical recording medium A, this becomes the core, and the unevenness is further expanded by the stress of the film formed in the upper layer, so that the film surface has a roughness of about 30 degrees.

On the other hand, (S, 13N4). The magneto-optical recording medium B having the .

(Example 3) In the magneto-optical recording medium described in Example 2, Si, N4
Example 2 was carried out in the same manner as in Example 2, except that a nitride film of a mixture of TiN and Ti was used instead of a nitride film of a mixture of TiN and Ti. To form this nitride film, a composite target was used as a target in which Ti chips (5 m x 5 mm x 1 nm) were attached to a TiN plate manufactured by a one-reaction sintering method so that the area ratio was 5%, and N2 was heated at 20 v.
The sputtering was carried out using Ar containing 1% o as a sputtering gas at a total gas pressure of 20 m Torr. Been formed(
When TiN)-Tili was analyzed, 5% of Ti existed in the state of metallic Ti, and (TiN)o, 5sTio
,. It was a nitride film with a composition of . The obtained magneto-optical recording medium exhibited a large Kerr rotation angle as in Example 2.

(Example 4) In the magneto-optical recording medium described in Example 2, Si, N,
Example 2 was carried out in the same manner as in Example 2, except that a nitride film of a mixture of TaN and Ta was used instead of a nitride film of a mixture of TaN and Ta. To form this nitride film, a T a N plate manufactured by a reaction sintering method is used as a target.
The area ratio of the chip a (5nn x 5wn x 1mm) is 10%
Analysis of the (TaN)-Ta film fabricated using a composite target attached so that There is 5% Ta existing in the state of metallic Ta, (TaN)(1,ss Ta
It was a nitride film exhibiting a composition of n-as. The obtained magneto-optical recording medium exhibited a large Kerr rotation angle as in Example 2.

(Example 5) In the magneto-optical recording medium described in Example 2.

Example 2 was carried out in the same manner as in Example 2, except that a nitride film made of a mixture of MN and All was used instead of a nitride film made of a mixture of Si, N, and Si. To form this nitride film, a gunwale tip (5 m x 5 m XL + am) was placed on an AIIN plate manufactured by sintering AjlN fine powder as a target.
The sputtering was carried out under a total gas pressure of 30 m Torr, using a composite target having an area ratio of 30%, using Ar containing 10 vol % of N2 as a sputtering gas. The formed (A-N)-An nitride film is
QN) o, s^aa-2, and the magneto-optical recording medium using this exhibited a large Kerr rotation angle as in Example 2.

In Examples 1 to 5 above, silicon nitride, titanium nitride, tantalum nitride, and aluminum nitride were used as transparent films for optical interference. It has been confirmed that nitride films such as tin nitride, ron nitride, and niobium nitride have the same effect as in this example. In other words, the metals or semiconductor elements constituting these nitride films all have a larger refractive index than those of the nitride films, and the effect on internal stress is - considering the malleability of the metal or semiconductor element. (S is N4)l −xSiX
It is obvious that it has the same effect as the membrane.

Note that as the content of metal or semiconductor elements in the nitride film as an optical interference layer increases, the absorption of light gradually increases approximately in proportion to this, which causes practical problems1. 1000 people thick (S 1s N 4)
Wavelength 830 of nitride film with composition consisting of i - w S ix
When the light transmittance in nm is examined, it is as shown in FIG.

In other words, if a film with a light transmittance (%) of 80% or less is used, the reflectance as a magneto-optical recording medium will be low;
The functions of the automatic focusing servo mechanism and automatic tracking servo mechanism will deteriorate, making it unsuitable.
The limit for Q is approximately 50% in terms of atomic fraction, and this trend is similar for other metals or semiconductor elements, and their content is limited to approximately 50%.

〔Effect of the invention〕

As explained in detail above, the magneto-optical recording medium using the nitride film of the present invention as a transparent film for optical interference can prevent the refractive index from decreasing due to the influence of moisture from the substrate, and the nitride film Since the internal stress is reduced, it is possible to extremely reduce the occurrence of minute irregularities on the substrate surface caused by the internal stress, thereby preventing a reduction in the Kerr rotation angle due to diffuse reflection of light, and as a result, reducing the Kerr rotation angle. This makes it possible to obtain an excellent magneto-optical recording medium particularly suitable for recording and storing information.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the refractive index and internal stress of the nitride film, which is an optical interference film used in the magneto-optical recording medium in Examples 1 and 2 of the present invention, and FIG. A schematic diagram showing the configuration of a magneto-optical recording medium, FIG. 3 is a schematic diagram showing the configuration of a magneto-optical recording medium in Example 2 of the present invention, and FIGS. 4(a) and (b) are Example 2 of the present invention. SL, N, films (A) and (Si3N4) in. -11sI
11.1 A graph showing a comparison of the relationship between the Kerr rotation angle and the thickness of the nitride film for the film (B), FIG. 5 shows the Si, N4 film (A) and (Sl:1N4) in Example 2 of the present invention. ,. Si0
．． FIG. 6 is a graph showing a comparison of the roughness of the substrate surface when forming the 2i sample (B), which is an example of the present invention (S13N
4) A graph showing the change in light transmittance in a nitride film with a composition of l-XSiX. Fig. 7 is a schematic diagram showing the structure of the high frequency magnetron sputtering apparatus used in the embodiment of the present invention. Fig. 8 is a graph showing the structure of the high frequency magnetron sputtering apparatus used in the example of the present invention. FIG. 1 is a schematic diagram showing the configuration of a magneto-optical recording medium. 1... Substrate 2... (S 13 N4). , 5sxa- as a nitride film (
Transparent film) 3... Magnetic film 4... SiO protective film 5... Ultraviolet curing resin layer 6... (S L3 N 4 ). -1sII+-2 protective film 7...Nonmagnetic stainless steel protective film 8...Sputter target 9...Si□N4 plate 10...Si chip 1
1...High frequency power supply 12...Gas inlet 13
...Exhaust system 14...Vacuum chamber 15...
board holder

Claims (1)

[Claims] 1. A magneto-optical recording medium in which a transparent film for optical interference is provided on a substrate directly or via an underlayer, and a magnetic film and a protective film are successively laminated on the transparent film. , the transparent film has the following general formula, (M_nN_m)_1_−_xM_x (where M is a metal or semiconductor element, N is nitrogen,
M_nN_m represents a nearly stoichiometric composition of a nitride made of a metal or semiconductor element, and x is an atomic fraction of 0≦x≦
The range of 0.5 is shown. ) A magneto-optical recording medium comprising a nitride having a composition represented by: 2. The nitrides that make up the transparent film are Al, Ta, Ti, and N.
The magneto-optical recording medium according to claim 1, characterized in that the magneto-optical recording medium is made of a nitride of at least one metal or semiconductor element selected from among B, Si, Ge, Sn, Se, Te, and B. . . 3. The nitride constituting the transparent film has the following general formula, (Si_
From a nitride with a composition shown as The magneto-optical recording medium according to claim 1, characterized in that: 4. The thickness of the transparent film made of nitride is 300 to 1500
3. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is in the range of .ANG.