JP2003263778A - Multi-valued worm (write-once-read-many) type optical recording medium and method of multi-valued recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a WORM type optical recording medium in which highly accurate multi-valued recording is possible with the number of multi-valued levels increased and which is applicable even in a blue laser region of about 350-500 nm, and to provide its recording principle and a method of multi-valued recording. <P>SOLUTION: The optical recording medium has a layer structure through an under coating layer on a substrate. In the layer structure, an organic material layer having no absorption function with respect to the light of a recording and reproducing wavelength in non-recording is inserted between the under coating layer and an upper coating layer which have a big difference in a refractive index with respect to the organic material layer. The under coating layer or the upper coating layer has a light absorption function. In recording, a deformation direction and the position (the type) of a deformation interface are permitted to change, so that reproducing signals having different recording polarities as well as a difference in recording mark length and that in amplitude are obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a write-once type optical recording medium capable of performing multi-valued recording by changing recording polarity in addition to recording mark length and amplitude according to recording data.
The recording principle and the multilevel recording method are related.

[0002]

2. Description of the Related Art In recent years, optical recording media have been required to have larger capacities and higher densities. There is multi-valued recording as one method for realizing large capacity and high density of an optical recording medium.
Multi-valued recording means that information is recorded / reproduced by associating information with three or more values, and is distinguished from binary recording in which recording / reproduction is performed in correspondence with a binary value of “0” or “1”. Is the concept of. For details of multi-valued recording, see, for example, JP-A-6-7.
It is described in Japanese Patent No. 6399. In this conventional example, in a mark edge type recording / reproducing method, multi-valued information is recorded by shifting the position of the edge of the recording mark from the reference position in stages corresponding to the recording data. In the multi-valued recording of the mark edge method, the larger the number of shifts (the number of steps) of the edge position, the more advantageous the multi-valued recording, namely the higher recording density. However, in order to increase the number of shifts of the edge position with respect to the limited period of the reference clock, it is necessary to precisely control the formation of the edge. On the other hand, it is not easy to control the edge position of the recording mark formed by the irradiation of laser light.

As another conventional example, Japanese Patent Laid-Open No. 8-28746.
The optical recording / reproducing method described in Japanese Patent Publication No. 8 realizes multi-value recording by a pit position method instead of the mark edge method as in the above-mentioned conventional example. In this case, the central position of the recording mark is shifted stepwise with respect to the edge of the reference clock to perform multilevel recording. Still another multilevel recording technique includes the following. That is, C
In the same read-only type optical disc as the D, a multi-valued recording technology called SCIPER that shifts the edge of the pit corresponding to the recorded data in 8 steps is described in "SK
obaashi, J .; P. de Kock, T .; Ho
Rigome, H .; Yamatsu and H.M. Oo
ki, Tech. Dig. of Optical Dat
a Storage Conference, p. Thirteen
0 (1994) ". This technique has an advantage that the conventional disk structure can be used as it is, but has a problem that the signal processing circuit becomes very complicated.

Further, an 8-level multilevel recording technique in which the pit depth is changed stepwise is described in, for example, "S. Spielm".
an, B. V. Johnson, G.M. A. McDerm
Ott, M .; P. O'Neil, C.I. Pietrzy
k, T. Shafaat, D.M. K. Warland a
nd T.N. L. Wong, Proc. SPIE, 310
9, p. 98 (1997) ". With this technique, the complexity of the signal processing circuit can be suppressed to some extent, but it is difficult to manufacture the disk. Further, in a magneto-optical disk, a four-valued recording technique that introduces a plurality of magnetic recording films and selectively causes the magnetization reversal of each layer by switching the strength of a recording magnetic field is disclosed in, for example, "N. Sai.
to, R.M. Sato, N .; Kawamura and
M. Kajiura, Jpn. J. Appl. Phy
s. 28, p. 343 (1989) ".

Further, in a magneto-optical disk, a four-valued recording technique in which the magnetization reversal interval is changed stepwise by changing the period of a high-frequency magnetic field for recording is disclosed in, for example, "M.A.
rai and S. Kobayashi, Tech.
Dig. of Joint MORIS / ISOM, p.
32 (1997) ". Further, in a phase change type optical disc, a multi-valued recording technique in which the size of a recording mark is controlled by modulating the intensity of a recording laser beam is disclosed in, for example, “T. Ohta, K. Nishiuchi, K. Na.
rumi, Y. Kitaoka, H .; Ishibash
i, N. Yamada and T.M. Kozaki, J
pn. J. Appl. Phys. 39, p. 770
(2000) ”. Further, in a phase change type optical disc, a multilevel recording technique for performing 8-value recording by controlling a recording mark length by devising a recording pulse waveform using a dedicated phase change recording material is disclosed in, for example, "MP ．
O'Neil and T.M. L. Wong, Tech.
Dig. of Optical Data Storage
ge Conference, p. 170 (200
0) ”.

[0006]

To increase the density, it is necessary to increase the number of multi-valued levels, but if the number of multi-valued levels is increased, it becomes more difficult to judge the multi-valued level.
There is a problem that the reproduction reliability is significantly reduced. Also,
Conventionally, although a multi-valued recording technology applicable to a read-only optical recording medium, a magneto-optical recording medium, or a phase-change optical recording medium has been proposed, a multi-valued recording technique using an organic material is effective for a multi-valued optical recording medium. Little recording technology has been proposed. Therefore,
INDUSTRIAL APPLICABILITY The present invention solves the above-mentioned conventional problems, and is a multi-value recording technique effective for a write-once type optical recording medium using an organic material, and it is possible to perform multi-value recording with high accuracy while increasing the number of multi-value levels. It is an object of the present invention to provide a write-once type optical recording medium applicable to a blue laser region of about 350 to 500 nm, its recording principle, and a multilevel recording method.

[0007]

[Means for Solving the Problems] The above problems are solved in the following 1) to
It is solved by the invention of 11). 1) An organic material layer which does not have a function of absorbing light of a recording / reproducing wavelength when not recorded is formed on a substrate through an undercoat layer and an undercoat layer having a large refractive index difference from the organic material layer. An optical recording medium having a layer structure sandwiched between an undercoating layer and an undercoating layer, and the undercoating layer or the overcoating layer having a light absorbing function, and the deformation direction and the position (type) of the deformation interface can be changed during recording. Thus, a write-once type optical recording medium capable of multi-value recording, wherein a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude is obtained. 2) On the substrate, an organic material layer having no absorption function for light having a recording / reproducing wavelength at the time of non-recording is placed over the undercoat layer and an undercoat layer having a large refractive index difference from the organic material layer. An optical recording medium having a layer structure sandwiched between an organic material layer and an undercoating layer, wherein the undercoating layer or the overcoating layer has a light absorbing function, Recording by the recording principle of recording mark formation by pressure to the organic material layer or pressure from the organic material layer and recording principle of recording mark formation by stress relaxation of the undercoating layer or the overcoating layer or thermal expansion of the substrate. In this case, it is possible to change the deformation direction of the recording mark portion and the position (type) of the deformation interface, and this makes it possible to obtain a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude. A write-once type optical recording medium capable of recording values. 3) The main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength through the undercoat layer on the substrate, and has the absorption function for the light of the recording / reproducing wavelength at the time of unrecording. An optical recording medium having a layer structure in which an organic material layer not sandwiched is sandwiched between an undercoating layer and an overcoating layer having a large refractive index difference with the organic material layer, and the undercoating layer or the overcoating layer has a light absorbing function. So, when recording, you can change the deformation direction and the position (type) of the deformation interface,
Thus, a write-once type optical recording medium capable of multi-value recording is obtained, in which a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude is obtained. 4) The main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength through the undercoat layer on the substrate, and has the absorption function for the light of the recording / reproducing wavelength at the time of unrecording. An optical recording medium having a layer structure in which an organic material layer not sandwiched is sandwiched between an undercoating layer and an overcoating layer having a large refractive index difference with the organic material layer, and the undercoating layer or the overcoating layer has a light absorbing function. Therefore, the recording principle of the recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer due to the state change of the organic material in the organic material layer, and the undercoat layer or It is possible to change the deformation direction of the recording mark part and the position (type) of the deformation interface during recording by the recording principle of recording mark formation due to stress relaxation of the overcoat layer or thermal expansion of the substrate. In addition to the difference in amplitude and amplitude, it is possible to obtain a reproduction signal with different recording polarities. A write-once type optical recording medium capable of multi-value recording. 5) The write-once type optical recording medium capable of multilevel recording according to any one of 1) to 4), wherein the recording / reproducing wavelength is 350 to 500 nm. 6) The multi-value recordable additional recording according to any one of 1) to 5), wherein the interface shape between the organic material layer and the overcoat layer is formed to be the same as the groove shape of the substrate. Optical recording medium. 7) On the substrate, an organic material layer having no absorption function for light having a recording / reproducing wavelength at the time of non-recording is provided on the substrate through an undercoat layer and an undercoat layer having a large refractive index difference from the organic material layer. For a write-once type optical recording medium that has a layer structure sandwiched between an undercoating layer and an undercoating layer or an overcoating layer and has a light absorbing function, which is capable of multilevel recording, the direction of deformation and the position of the deformation interface (type) ) Is changed so that reproduction signals having different recording polarities in addition to differences in recording mark length and amplitude can be obtained. 8) On the substrate, an organic material layer having no absorption function for light having a recording / reproducing wavelength at the time of non-recording is formed on the substrate through an undercoat layer and an undercoat layer having a large refractive index difference from the organic material layer. A multi-level recordable write-once type optical recording medium having a layer structure sandwiched between an organic material layer and an undercoating layer or an undercoating layer having a light absorbing function, and an organic material according to a change in state of the organic material in the organic material layer. Recording principle of recording mark formation by pressure from material layer to undercoat layer or pressure from organic material layer to overcoat layer, and recording mark formation by stress relaxation of undercoat layer or overcoat layer or thermal expansion of substrate By changing the recording principle, the direction of deformation of the recording mark portion and the position (type) of the deformation interface are changed at the time of recording, so that a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude can be obtained. A multilevel recording method characterized by the above. 9) The main absorption band at the time of non-recording exists on the long wavelength side with respect to the recording / reproducing wavelength through the undercoat layer on the substrate, and has the absorption function for the light of the recording / reproducing wavelength at the time of unrecording. It has a layer structure in which an organic material layer is sandwiched between an undercoating layer and an overcoating layer having a large difference in refractive index from the organic material layer, and the undercoating layer or the overcoating layer has a light absorption function, and multilevel recording is possible. For a write-once type optical recording medium, by changing the deformation direction and the position (type) of the deformation interface at the time of recording, it is possible to obtain a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude. A multilevel recording method characterized by the above. 10) The main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength through the undercoat layer on the substrate, and has the absorption function for the light of the recording / reproducing wavelength at the time of unrecording. It has a layer structure in which an organic material layer is sandwiched between an undercoating layer and an overcoating layer having a large difference in refractive index from the organic material layer, and the undercoating layer or the overcoating layer has a light absorption function, and multilevel recording is possible. Recording principle of recording marks for a write-once type optical recording medium by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer due to the change of the state of the organic material in the organic material layer And the deformation principle of the recording mark portion and the position (type) of the deformation interface at the time of recording are changed according to the recording principle of the recording mark formation by the stress relaxation of the undercoat layer or the overcoat layer or the thermal expansion of the substrate. In order to obtain playback signals with different recording polarities in addition to differences in recording mark length and amplitude A multilevel recording method characterized by: 11) The multilevel recording method according to any one of 7) to 10), wherein the recording / reproducing wavelength is 350 to 500 nm.

The present invention will be described in detail below. (1) Outline (Characteristics of the Present Invention) In the present invention, multi-valued recording is performed by changing the deformation direction and the position (type) of the deformation interface during recording, thereby recording in addition to the difference in recording mark length and amplitude. It is possible to obtain reproduced signals having different polarities. Further, in the present invention, the pressure from the organic material layer to the undercoat layer due to the state change of the organic material in the organic material layer,
Alternatively, the recording principle of recording mark formation by pressure from the organic material layer to the upper coating layer and the recording principle of recording mark formation by stress relaxation of the lower coating layer or upper coating layer or thermal expansion of the substrate are used to control this. This allows multi-valued recording. That is, since the recording polarities were the same in the past, the so-called Hi
gh to Low (high to low) recording or L
One of ow to High recording] and an increase in the number of multi-valued levels makes it more difficult to determine the multi-valued levels, and there is a problem that the reproduction reliability is significantly reduced. In the present invention, since the reproduction signals having different recording polarities as well as the difference in the recording mark length and the amplitude can be obtained, a more reliable write-once type optical recording medium can be provided. The "state change of the organic material" referred to in the present invention refers to melting, sublimation, decomposition, explosion, structural change, etc., but usually decomposition and explosion are the main, and in this case, only the organic material is required. The characteristics of decomposition by heat (decomposition temperature,
Explosiveness, existence of a clear decomposition threshold, decomposition speed, decomposition amount, etc.) are excellent.

(2) Explanation of expression "changing deformation direction and position (type) of deformation interface" The expression "changing deformation direction and position (type) of deformation interface" in the present invention will be explained. The deformation direction means whether the deformation occurs in a convex shape or a concave shape when viewed from a certain reference side. In addition, the position (type) of the deformation interface refers to which layer interface has the uneven deformation. As the deformation interface, the interface between the substrate and the undercoat layer, the interface between the undercoat layer and the organic material layer, the interface between the organic material layer and the overcoat layer, the overcoat layer and its upper layer (protective layer, cover layer,
There is an interface with the air layer). In the present invention, a single deformation interface may be used, or a plurality of the deformation interfaces may be combined. In short, a combination of deformation interfaces,
The recording polarity and the contrast of the recording mark are changed according to the deformation direction and the deformation amount of each interface. In the present invention, the combination of deformation interfaces and the amount of deformation of each interface are controlled. These include the thickness of each layer, the magnitude of the absorption coefficient with respect to the recording wavelength,
It can be changed by thermal conductivity and hardness. The simplest method is to control the recording power to control the combination of deformation interfaces and the deformation amount of each interface.

Further, in the present invention, the deformation direction of each interface is controlled, which is realized by giving the optical recording medium a different recording principle. That is, the recording principle of recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer due to the change of the state of the organic material in the organic material layer, and the undercoat layer or the overcoat layer. The deformation direction of each interface is controlled by having the recording principle of forming the recording mark by the stress relaxation of the pulling layer or the thermal expansion of the substrate. For example, by using the recording principle of forming a recording mark by the pressure from the organic material layer to the undercoat layer due to the change of the state of the organic material in the organic material layer, the substrate or the undercoat layer can be seen from the front side of the substrate or the undercoat layer. It can be transformed into (represented as concave here).
Further, by using the recording principle of forming a recording mark by relaxing the stress of the undercoat layer or thermal expansion of the substrate, the substrate or the undercoat layer can be deformed to the inner side when viewed from the substrate side ( Expressed here as convex). An important feature of the present invention is that the direction of deformation is fixed to one side in the conventional recording principle using deformation, but in the present invention, the recording principle in which the direction of deformation is variable is used.

(3) The reason why the "organic material layer is sandwiched between the undercoating layer and the overcoating layer having a large difference in refractive index from the organic material layer" is used in the present invention. Has a structure in which it is sandwiched between an undercoating layer and an overcoating layer having a large difference in refractive index from the above. With this structure, it is possible to improve the reflectance and the signal quality, or due to the difference in the deformation direction and the position (type) of the deformation interface caused by the recording, in addition to the difference in the recording mark length and the amplitude, the recording polarity. , It is possible to efficiently generate different reproduction signals. In addition,
The refractive index difference between the organic material layer and the undercoat layer or the overcoat layer is usually 0.5 or more.

(4) Requirements of Organic Material Used for Organic Material Layer In the present invention, the deformation direction (convex deformation or concave deformation) of the recording mark is controlled in order to make the recording polarity variable.
In forming a recording mark by thermal expansion of the substrate, which is the basic deformation principle of the conventional optical recording medium (see FIG. 1), the substrate is always deformed in the direction of the organic material layer and is not deformed in the opposite direction. This is because the force due to the thermal expansion of the substrate is sufficiently large, and there is no force that inhibits it or a large force that opposes it. Therefore, the present inventor examined means for producing a force in the direction opposite to the deformation direction due to the thermal expansion of the substrate due to the thermal expansion, and as a result, the force accompanying the state change of the organic material (especially decomposition / explosive force). Is available. However, in order to effectively utilize the force associated with this state change, it is necessary to make it easy for the organic material in the vicinity of the interface between the organic material layer and the adjacent layer to cause the state change. In the configuration, since the central part of the organic material layer has the highest temperature, the organic material in the vicinity of the interface between the organic material layer and the adjacent layer does not change its state sufficiently. Therefore,
In the present invention, in order to make the state of the organic material near the interface between the organic material layer and the adjacent layer most likely to change, the light absorbing layer (the undercoat layer having a light absorbing function) is adjacent to the organic material layer. Alternatively, a structure in which an overcoat layer) is provided.

Since the absorption coefficient of this light absorption layer is set to be sufficiently larger than that of the organic material layer (while the light absorption layer has a light absorption function, the organic material layer emits light of a recording / reproducing wavelength). On the other hand, since it does not have a light absorption function, it naturally becomes so), the organic material in the vicinity of the light absorption layer becomes the highest temperature,
Due to the force associated with the change in the state of the organic material, it is possible to perform recording in a deformation direction opposite to the conventional one. By providing this light absorbing layer, it is possible to separate the light absorbing function from the organic material layer which has the conventional functions of both the recording layer and the light absorbing layer. Since this alleviates the severe optical constant conditions imposed on the organic material layer, the write-once type optical recording medium of the present invention can easily record even in the blue laser wavelength region of about 350 to 500 nm (conventional). In the layer structure of (1), since there were severe optical constant conditions in the organic material layer, there were almost no organic materials compatible with the blue laser wavelength region, and it was difficult to realize a write-once type optical recording medium using organic materials. ). Further, in the write-once type optical recording medium using the conventional organic material, it is necessary to generate heat in the organic material layer, so that the organic material layer cannot be thinned and a deep groove (for example, 150 to 180 nm) is required. However, the recording principle of the present invention makes it possible to reduce the thickness of the organic material, and since a substrate having a shallow groove excellent in moldability can be used, it is possible to provide a highly reliable write-once type optical recording medium. Become.

The "organic material layer used in the present invention, in which the main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength and which does not have an absorbing function for the light having the recording / reproducing wavelength", or In the expression "organic material layer that does not have a function of absorbing light having a recording / reproducing wavelength when not recorded", "does not have a function of absorbing light having a recording / reproducing wavelength" means the absorption function of the organic material layer alone. Then, it means that the temperature does not reach a temperature at which the layer adjacent to the organic material layer is deformed or the state of the organic material itself is changed (that is, it does not substantially fulfill the absorption function required as the light absorption layer. means). Therefore, specifically, it means a case where the absorption coefficient of the organic material is small or a case where the film thickness is thin. Further, "an organic material layer in which the main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength and which does not have an absorbing function for light having the recording / reproducing wavelength",
Alternatively, the reason why the “organic material layer having no absorption function for light having a recording / reproducing wavelength when not recorded” is important as a constituent of the optical recording medium of the present invention is that the conventional write-once type optical recording medium is used in the present invention. By using an undercoating layer or an overcoating layer having a relatively large absorption coefficient in place of the used organic material having a light absorption function, it is possible to reduce the absorption function in the organic material layer and improve the reflectance. This is because you can

Further, as described above, due to the improvement of the reflectance, the improvement of the signal quality, the difference in the deformation direction and the position (type) of the deformation interface caused by the recording, in addition to the difference in the recording mark length and the amplitude, the recording is performed. In order to efficiently generate signals with different polarities, a structure in which an organic material layer is sandwiched between an undercoating layer and an overcoating layer, which have a large refractive index difference with the organic material layer, is suitable. It is advantageous to set a low refractive index of the above in selecting materials for the undercoat layer and the overcoat layer. The preferred layer structure of the present invention is, for example, substrate / undercoating layer (light absorbing layer) / organic material layer / upper coating layer (reflective layer). The refractive index of the layer is usually about 0.1, which is very small, and the refractive index of the light absorbing layer is, for example, about 2.0 to 4.0, and the difference in refractive index between the organic material layer and the light absorbing layer tends to be small. . Therefore, it is important to increase the difference in refractive index. To this end, if the refractive index of the organic material layer is set to be low, the difference in refractive index between the organic material layer and the light absorption layer is increased, and This is because the range of choices can be expanded.

Therefore, "an organic material layer whose main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength and which does not have an absorbing function for light of the recording / reproducing wavelength" or "unrecorded" By lowering the refractive index of the organic material layer, it is sometimes necessary to use an "organic material layer that does not have a function of absorbing light with a recording / reproducing wavelength", that is, by greatly shifting the recording / reproducing wavelength from the maximum absorption band of the organic material. Is possible. In addition, when the recording / reproducing wavelength is 500 nm or more, for example, near the recording / reproducing wavelength of 650 nm for the DVD-based optical recording medium or near 780 nm for the recording / reproducing wavelength of the CD-based optical recording medium, the requirement of the organic material layer is “when unrecorded”. It suffices if the “organic material layer having no absorption function for the light of the recording / reproducing wavelength” is satisfied, and the size relationship between the wavelength of the main absorption band of the organic material and the recording / reproducing wavelength is hardly a problem.

However, the recording / reproducing wavelength is 350 to 500 n.
When a blue laser region of about m, for example, near 400 nm is set, the main absorption band at the time of unrecording is on the short wavelength side with respect to the recording / reproducing wavelength and has an absorption function for the light with the recording / reproducing wavelength. The state of not having means that the size of the molecule of the organic material is made extremely small. This is the pressure from the organic material layer to the undercoat layer due to the change of the state of the organic material, or the organic material. This means that the pressure from the layer to the overcoat layer is significantly reduced, and is not preferable for the write-once type optical recording medium using the recording principle of the present invention. Therefore, when the recording / reproducing wavelength is set to 350 to 500 nm, for example, near 400 nm, the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer due to the state change of the organic material is set. In order to generate enough, an organic material with a large molecular skeleton is selected, the main absorption band at the time of unrecording is on the long wavelength side with respect to the recording / reproducing wavelength, and the light absorption function for the light of the recording / reproducing wavelength. It is preferable that the organic material layer does not have.

(5) The shape of the interface between the organic material layer and the overcoat layer is
The reason why the organic material layer is formed so as to have the same groove shape as the substrate The film thickness of the organic material layer is arbitrary, and the formation form thereof is also arbitrary. This form of formation refers to what kind of shape the surface shape of the organic material layer (interface shape between the organic material layer and the overcoat layer) is. For example, the surface shape of the organic material layer is the same as the substrate shape (Fig. 8)) or the surface shape of the organic material layer may be flat (see FIG. 9). In the present invention,
It was found that the surface shape of the organic material layer is important as one of the conditions in which the recording polarity is relatively likely to change, and the surface shape of the organic material layer is the same as the substrate shape (see FIG. 8). In this case, it is found that the recording polarity is likely to change (the condition for changing the recording polarity is relaxed). However, the meaning of the description "to be formed so as to be the same" is not limited to the case where they are literally the same, and the interface shape between the organic material layer and the overcoat layer is almost the same as the groove shape of the substrate. If formed,
That is, when each layer is formed on a substrate by a normal film forming method such as sputtering, there is a case in which each layer is formed almost along the groove shape of the substrate, although there is some variation in film thickness. Let's assume. The write-once type optical recording medium of the present invention, in addition to the above layers, a conventionally known intermediate layer,
Various layers such as a back coat layer may be provided.

(6) Concomitant use of other recording principles In the present invention, in addition to the above recording principle, the organic material layer undergoes a state change due to heat generation of the undercoating layer or the overcoating layer due to the irradiation of laser light, and this state The recording principle of increasing the absorption coefficient at the recording / reproducing wavelength due to the change may be used together. However, according to this recording principle, the recording polarity becomes High to Low unless the refractive index and the film thickness of the organic material layer are significantly changed. It is limited to the case of High to Low. The recording principle due to the increase of the absorption coefficient of the organic material layer will be described with reference to FIGS. When an organic material having an absorption spectrum in an unrecorded state as shown in FIG. 18 is selected and the state of this organic material is changed (particularly decomposed or exploded), the absorption of molecules or molecular groups constituting the organic material by decomposition is absorbed. Occurs. This absorption usually has a shorter wavelength than the absorption of the organic material before decomposition and explosion, so the absorption coefficient on the shorter wavelength side than the large absorption band of the original organic material increases (see absorption spectrum in recorded state). ). If the range where the change in absorption wavelength on the short wavelength side is large and the recording / reproducing wavelength (for example, the position of the arrow in the figure) are combined,
Since the absorption coefficient at the recording / reproducing wavelength after recording can be increased, it is possible to generate the degree of modulation.

Explaining this recording principle in a little more detail, the organic material used in the present invention is an organic material in which small molecules or molecular groups are bound to each other, or a complex or association is formed to form a large conjugated system. Therefore, it has a larger absorption band on the long wavelength side than the intrinsic absorption wavelength of the molecule or molecular group (corresponding to absorption spectra A and B in FIG. 19),
The unique absorption band of each molecule or group disappears,
Alternatively, it has an attenuated absorption spectrum (corresponding to absorption spectrum C in FIG. 20). For such an organic material, FIG.
If λ1 as shown in is selected as the recording / reproducing wavelength, the absorption that is small at λ1 when unrecorded causes the absorption unique to the molecule or molecular group that formed a large molecule due to decomposition or explosion. 19 (see FIG. 19), the absorption at λ1 also increases, and the recording portion can be formed by the change of the absorption coefficient. Therefore, a molecule in which only a small molecule or a molecular group is bound and a conjugate system does not form a spread is in the state as shown in FIG. 20, that is, the intrinsic absorption of the molecule or the molecular group. Since the band disappears or decays and a state in which a new large sharp absorption band is formed is not realized, the change in the absorption coefficient before and after recording does not become large, and the recording pit cannot be formed.

(7) Material of each layer The material of the substrate has excellent thermal and mechanical properties, and has excellent light transmission properties when recording / reproducing is performed from the substrate side (through the substrate). There is no special limitation as long as it is good. Specific examples include polycarbonate, polymethylmethacrylate, amorphous polyolefin, cellulose acetate, polyethylene terephthalate, and the like, and polycarbonate and amorphous polyolefin are preferable. The thickness of the substrate depends on the application and is not particularly limited.

A material having a relatively low thermal conductivity is suitable for the undercoating layer or the overcoating layer that functions as a light absorbing layer that absorbs light and generates heat. The reason for selecting a material having a relatively low thermal conductivity is to efficiently deform the interface of each layer (at low recording power), and further to efficiently change the state of the organic material (at low recording power). Is. The term "relatively low thermal conductivity" as used herein means that the thermal conductivity reaches a temperature at which the state of the organic material is locally changed by recording. From the above points, it is preferable to use ceramics such as SiC, semimetals such as Si, metals such as Ge, or a mixture thereof for the undercoating layer and the overcoating layer that function as the light absorption layer. Further, the thickness of the undercoat layer and the overcoat layer is usually 20 to 500 Å.

A ceramic which is a material for the undercoat layer and the overcoat layer.
As a cous, Al_TwoO_Three, MgO, BeO, Zr
O_Two, UO_Two, ThO_TwoSimple oxide-based oxides such as;
SiO_Two2MgO / SiO_Two, MgO / SiO_Two, C
aO ・ SiO_Three, ZrO_Two・ SiO_Two3 Al_TwoO_Three・
2 SiO_Two2MgO / 2Al_TwoO_Three・ 5 SiO_Two, L
i _TwoO ・ Al_TwoO_Three・ 4SiO_TwoSilicate-based acids such as
Compound; Al_TwoTiO₅, MgAl_TwoO_Four, Ca₁₀(P
O_Four)₆(OH)_Two, BaTiO_Three, LiNbO_Three, P
ZT [Pb (Zr, Ti) O_Three], PLZT [(Pb,
La) (Zr, Ti) O_Three], Double oxidation such as ferrite
Physical oxides; Si_ThreeN_Four, Si_6-ZAl _ZO_ZN
_8-ZNon-oxidizing nitrides such as Al, AlN, BN and TiN
Thing; SiC, B _FourCarbide-based non-carbon materials such as C, TiC, and WC
Oxide; LaB₆, TiB_Two, ZrB_TwoBoride such as
System non-oxides: CdS, MoS_TwoSulfide-based non-acid such as
Compound; MoSi_TwoNon-oxides of silicides such as; Amole
Carbon-based non-oxides such as faux carbon, graphite and diamond
Etc. can be used. As the metal, A
u, Al, Ag, Cu, Pd, Pt, Ti, Ta, C
r, Ni, Fe, and alloys of these can be used
It

As the organic material used for the organic material layer, a so-called dye is preferable. Further, in order to sufficiently deform the undercoat layer or the overcoat layer, a dye having a high sublimation property or decomposition / explosion property, or a dye having a substituent group having a high sublimation property or decomposition / explosion property introduced therein is preferable. Further, in order to secure high decomposition and explosiveness, an organic material having a large molecular skeleton is preferable.
Further, a dye that causes a volume change due to a structure change can also be used. Dyes satisfying the above requirements include polymethine dyes, naphthalocyanine dyes, phthalocyanine dyes, squarylium dyes, croconium dyes, pyrylium dyes, naphthoquinone dyes, anthraquinone (indanthrene) dyes, xanthene dyes, triphenylmethane dyes, azulene dyes. , Tetrahydrocholine-based dyes, phenanthrene-based dyes, triphenothiazine-based dyes, and metal complex compounds. The film thickness of the dye layer is 100 Å to 10 μm, preferably 100 to 2000 Å.

The dye layer is formed by vapor deposition, sputtering,
It can be carried out by a usual means such as CVD or solvent coating. When the coating method is used, the dye or the like is dissolved in an organic solvent, spraying, roller coating,
It can be performed by a conventional coating method such as dipping or spin coating. As the organic solvent used, alcohols such as methanol, ethanol and isopropanol are generally used; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylacetamide and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide. Ethers such as tetrahydrofuran, dioxane, diethyl ether and ethylene glycol monomethyl ether; Esters such as methyl acetate and ethyl acetate; Aliphatic halogenated carbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane;
Aromatic compounds such as benzene, xylene, monochlorobenzene, and dichlorobenzene; cellosolves such as methoxyethanol and ethoxyethanol; hexane, pentane,
Hydrocarbons such as cyclohexane and methylcyclohexane are included.

The undercoating layer or the overcoating layer that does not function as the light absorbing layer is preferably metal or ceramics. As the metal or ceramic, it is preferable to use a material having a refractive index difference from that of the organic material layer in order to improve the reflectance or the recording / reproducing characteristics. Of the undercoating layer and the overcoating layer, if the layer on the front side with respect to the incident laser light has a light absorbing ability, in order to improve the reflectance or the recording / reproducing characteristics, the depth of the incident laser light is increased. The side layer is preferably metallic. On the contrary, in the case of the undercoating layer and the overcoating layer, if the layer on the back side with respect to the incident laser light has a light absorbing ability, the incident laser light is used to improve the reflectance or the recording / reproducing characteristics. On the other hand, the front layer is preferably made of ceramics having a small absorption coefficient (about 0.02 or less) with respect to the recording / reproducing wavelength. As the metal, Au, Al, Cu, Cr, A
A metal selected from the group consisting of g, Ti and alloys thereof is preferable, and as the ceramics having a small absorption coefficient for the recording / reproducing wavelength (here, near the blue region), the above-mentioned ceramics, ZnS.SiO _{2 and the} like are preferable. .
These materials are generally 50 to 5000 Å, preferably 50 to 3000 Å by vacuum deposition or sputtering.
Formed with a thickness of.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 (To clarify that the write-once type optical recording medium of the present invention can provide a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude, and to confirm the recording principle. Example) On a polycarbonate substrate having a guide groove with a groove depth of 50 nm, a film thickness of 1 which functions as a light absorption layer by a sputtering method.
An undercoating layer (SiC) having a thickness of 0 nm is provided, and an organic material represented by the following [Chemical formula 1] is formed thereon by a spin coating method (film thickness of about 60 nm). An optical recording medium was produced by providing a coating layer (Ag).

[Chemical 1]

Using the optical recording medium DPU-1000 (wavelength: 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. on the above optical recording medium, the recording power at the time of recording under the following recording conditions. At a time interval of 6.0
Recording was performed by switching between (mW) and 10.0 (mW). <Recording conditions> Recording linear density: 1T = 0.0917 (μm) Recording linear velocity: 6.0 (m / s) Recording strategy: Basic strategy T _top −T _mp = 1.40−0.75 (T) Recording power: 6.0 (mW), 10.0 (mW) Recording pattern: 8-16 modulated signal As a result, as shown in FIG. 2, the recording power is 6.0 (mW).
It was confirmed that when the recording power is W), the Low to High recording can be performed, and when the recording power is 10.0 (mW), the High to Low recording can be performed.

Next, in order to confirm whether this recording is performed based on the recording principle as described above, S
The deformation state of the interface between the iC and the organic material layer is measured by AFM (atomic force microscope, atomic force).
It was measured by microscope). FIG. 3 shows the Low to which occurred when the recording power was 6.0 (mW).
This is the result of three-dimensionally expressing the deformation state of the interface between the SiC and the organic material layer in the High recording portion (the lower side is the substrate). Note that in FIG. 3, the height is represented by shading, in which a light color portion is high and a dark color portion is low. FIG. 4 is a two-dimensional view of FIG. 3A and a cross-sectional view (concave and convex shape) of a recording track (b). From the results shown in these figures, it is found that the interface between the SiC and the organic material layer is deformed (concave deformed) toward the substrate side in the Low to High recording portion generated when the recording power is 6.0 (mW). It could be confirmed.

On the other hand, in FIG. 5, the recording power is 10.0 (m
W) of High to Low recording part
It is the result of three-dimensionally expressing the deformation state of the interface between SiC and the organic material layer (the lower side is the substrate). Note that, in FIG. 5, the height is represented by shading, in which a light color portion is high and a dark color portion is low. FIG. 6 is a two-dimensional view of FIG. 5 (a).
3B is a diagram (b) showing a cross-sectional view (uneven shape) of the recording track. From the results shown in these figures, High to which occurred when the recording power was 10.0 (mW)
It was confirmed that the interface between the SiC and the organic material layer was deformed (convexly deformed) in the direction opposite to the substrate side in the Low recording portion.

From the above results, it becomes clear that the write-once type optical recording medium of the present invention can record by changing the recording polarity in addition to the recording mark length and the amplitude, and this recording polarity is at least that of SiC and the organic material layer. It was confirmed that it was caused by the difference in the deformation direction of the interface shape. In this embodiment, recording is performed on the land portion to make the AFM image easy to see, but the present invention is not limited to land recording. Further, the interface shape between the SiC and the organic material layer was measured for the ease of measuring the deformed shape, but other interfaces may be deformed at the same time. Furthermore, in the conventional optical recording medium using an organic material, it was necessary to generate heat in the organic material layer,
The organic material layer cannot be thinned and deep grooves (for example, 150 to 1) are formed.
However, the recording principle of the present invention made it possible to make the organic material into a thin film, and it was confirmed that a substrate having a very shallow groove of 50 nm can be applied. This is a great merit in producing a highly reliable optical recording medium.

Comparative Example 1 The same experiment as in Example 1 was conducted except that polymethyl methacrylate was used instead of the organic material in Example 1. As a result, the portion recorded at 6.0 (mW) is also 1
The recording polarity was the same in the portion recorded at 0.0 (mW), and the interface between the SiC and the polymer layer was deformed in the direction opposite to the substrate (convex deformation) as in FIGS. As a result, the phenomenon that the interface between the SiC and the organic material layer is deformed (depressed) toward the substrate side in Example 1 is due to the action of the organic material, and the state change (decomposition / explosion) of the organic material.
It has been proved that has contributed to this concave deformation.

Example 2 It is extremely difficult to accurately measure the deformation direction of the recording portion and the position (type) of the deformation interface in practice (in Example 1, the interface between the undercoat layer and the organic material layer). Only the condition was evaluated), and here it was proved that by changing the deformation direction and the position (type) of the deformation interface by optical simulation, it is possible to obtain a reproduction signal with different recording polarities in addition to the difference in recording mark length and amplitude. To do. Under the following calculation conditions, the recording conditions were changed as shown in (i) to (iv) below, and how the reproduced signal changed was calculated. (I) Recording portion (land portion or groove portion) (ii) Forming state of organic material layer [The surface shape of the organic material layer is the same as the substrate shape (see FIG. 8), or the surface shape of the organic material layer is flat ( (See FIG. 9)] (iii) Recording mark forming interface (only the interface between the undercoat layer and the organic material layer is deformed (see FIGS. 10, 11, 14 and 15), or the interface between the undercoat layer / organic material layer and the organic layer) The interface between the material layer and the overcoat layer is deformed (see FIGS. 12, 13, 16 and 17). (Iv) Recording mark deformation direction [Concave deformation toward the substrate (FIG. 14-
17), or convex deformation toward the upper coating layer side (see FIGS. 10 to 13)]

<Details of Calculation Conditions> In the following, the length and size are expressed in terms of the recording / reproducing wavelength λ.・ Beam shape: Gaussian distribution ・ Radius with amplitude of 1 / e (x direction, y direction): 600
0λ, 6000λ · Objective lens aperture radius: 3000λ · Objective lens NA (numerical aperture): 0.60 · Objective lens focal length: 5000λ · Groove shape [A, B, C, D, ζ (see FIG. 7)]: ( 0.
2λ, 0.8λ, 1.0λ, 1.8525λ, 0.13
75λ) -Substrate refractive index: 1.60 (incident on substrate side) -Undercoat layer complex refractive index: 2.810-i0.561, film thickness = 0.025λ-Organic material layer complex refractive index: 1.500-i0 .050,
Film thickness = 0.150λ ・ Upper layer complex refractive index: 0.1078-i2.0495,
Film thickness = 0.250λ ・ Detector: 4-division PD ・ Radius of detector (x direction, y direction): 3000λ, 30
00λ ・ Record mark length, width, height: 1.0λ, 0.60λ,
± 0.10λ

The calculation results are as shown in FIGS. FIG. 21 shows the result when the recording is made in the groove and the organic material layer is formed so that the surface shape of the organic material layer is the same as the substrate shape as shown in FIG. . The height of the recording portion was ± 0.10λ (± 40n when the recording / reproducing wavelength was 400 nm).
m). The legend "+40 nm-0,4" indicates that the recording portion is shown in FIG. 16, and the legend "-40 nm-0,4" indicates
The fact that the recording part is shown in FIG. 12 means that the legend “+40 nm-0,
2 "indicates that the recording unit is shown in FIG.
"m-0,2" indicates that the recording unit is shown in FIG. In the above figures, the state of recording in the groove portion is shown, but also in the case of the land portion, the deformation direction of the recording portion and the position (type) of the deformation interface are the same.

FIG. 22 shows a case of recording on a land, and the organic material layer is formed so that the surface shape of the organic material layer is the same as the substrate shape as shown in FIG. The result. The height of the recording area is ± 0.10λ
(± 40 when the recording / reproducing wavelength is 400 nm)
nm). The legend "+40 nm-0,4" indicates that the recording part is shown in FIG. 16, and the legend "-40 nm-0,4".
Indicates that the recording part is as shown in FIG.
0, 2 ”indicates that the recording unit is shown in FIG.
0 nm-0,2 "indicates that the recording unit is shown in FIG.

FIG. 23 shows the case where recording is made in the groove, and the state of formation of the organic material layer is the result when the surface shape of the organic material layer is flat as shown in FIG. . The height of the recording portion was ± 0.10λ (± 40 nm when the recording / reproducing wavelength was 400 nm).
Will be). The legend "+40 nm-0,4" indicates that the recording portion is shown in FIG. 17, and the legend "-40 nm-0,4" indicates that the recording portion is shown in FIG.
2 "indicates that the recording unit is shown in FIG.
"m-0, 2" indicates that the recording unit is shown in FIG. In the above figures, the state of recording in the groove portion is shown, but also in the case of the land portion, the deformation direction of the recording portion and the position (type) of the deformation interface are the same.

FIG. 24 shows a case where recording is performed on a land and the organic material layer is formed so that the surface shape of the organic material layer is flat as shown in FIG. . The height of the recording section was ± 0.10λ (± 40 nm when the recording / reproducing wavelength was 400 nm). In the legend "+40 nm-0,4", the recording part is shown in FIG.
7, the legend “−40 nm−0,4” indicates that the recording portion is FIG. 13, and the legend “+40 nm−0,2”.
Indicates that the recording part is as shown in FIG.
"0, 2" indicates that the recording unit is shown in FIG.

From the results of FIGS. 21 to 24, it was proved in principle that the idea that the recording polarity can be controlled by changing the deformation direction of the recording mark and the position (type) of the deformation interface is correct. From the results shown in FIG. 24,
As shown in FIG. 9, when the organic material layer is formed such that the surface shape of the organic material layer is flat, it is understood that the recording polarity hardly appears in the land recording. That is, in claim 6, "an optical recording medium capable of multilevel recording, wherein the interface shape between the organic material layer and the overcoat layer is formed to be the same as the groove shape of the substrate".
However, it was confirmed that it is preferable as an optical recording medium using an organic material that enables multilevel recording. However, since the condition that the recording polarity changes depending on the complex refractive index of each layer, the change of the complex refractive index of each layer due to recording, or the height and shape of the recording mark changes, the surface shape of the organic material layer should be flat. It does not deny the case of being formed.

[0041]

According to the present invention, it is possible to perform highly accurate multi-value recording while increasing the number of multi-value levels.
A write-once type optical recording medium applicable to a blue laser region of about 0 nm and a multilevel recording method can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a layer structure of a conventional optical recording medium.

FIG. 2 is a diagram showing that recording marks having different recording polarities are formed on the recording medium of the present invention.

FIG. 3 is a view showing a result of observing a portion where low-to-high recording is performed on the recording medium of the present invention with an AFM.

FIG. 4 is another diagram showing a result of observing a portion where Low to High recording is performed on the recording medium of the present invention by AFM. (A) Two-dimensional representation of FIG. 3 (b) Cross-sectional view of recording track (uneven shape)

FIG. 5 is a view showing a result of observing with AFM a portion where High to Low recording is performed on the recording medium of the present invention.

FIG. 6 is another diagram showing a result of observing a portion where High to Low recording is performed on the recording medium of the present invention by AFM. (A) Two-dimensional view of FIG. 5 (b) Cross-sectional view of recording track (uneven shape)

FIG. 7 is a view for explaining parameters of groove shapes used in Example 2;

FIG. 8 is a diagram showing a layer structure of the invention, and is a diagram for explaining one formation mode of an organic material layer.

FIG. 9 is a diagram showing a layer structure of the invention, and is a diagram for explaining another one formation mode of the organic material layer.

FIG. 10 is a diagram showing an example of a formation form of an organic material layer and a formation form of a recording mark.

FIG. 11 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 12 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 13 is a view showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 14 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 15 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 16 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 17 is a diagram showing another example of the formation form of the organic material layer and the formation form of the recording mark.

FIG. 18 is a diagram for explaining a recording principle due to an increase in absorption coefficient of an organic material.

FIG. 19 is a diagram for explaining the characteristics of the organic material layer that can realize the recording principle by increasing the absorption coefficient of the organic material.

FIG. 20 is a diagram for explaining characteristics of an organic material layer that can realize the recording principle by increasing the absorption coefficient of the organic material.

FIG. 21 is a diagram showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 8 and recording is performed in a groove portion.

FIG. 22 is a diagram showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 8 and recording is performed on a land portion.

FIG. 23 is a diagram showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 9 and recording is performed in a groove portion.

FIG. 24 is a diagram showing a result of calculating a reproduction signal when an organic material layer is formed as shown in FIG. 9 and recording is performed on a land portion.

[Explanation of symbols]

A Width between the top edge of the land and the bottom edge of the adjacent groove that is closer to the land B Width between the top edge of the land and the bottom edge of the adjacent groove that is farther from the land C land Width between the upper surface end of the land and the upper surface end of the adjacent land closer to the land D The upper surface end of the land and the upper end of the adjacent land farther from the land ζ land Height (depth of groove)

Claims (11)

[Claims] 1. An organic material layer which does not have a function of absorbing light of a recording / reproducing wavelength when unrecorded is formed on a substrate through an undercoating layer, and the undercoating layer has a large difference in refractive index from the organic material layer. An optical recording medium having a layer structure sandwiched between a layer and an overcoat layer, wherein the undercoat layer or the overcoat layer has a light absorbing function, and changes the deformation direction and the position (type) of the deformation interface during recording. A write-once type optical recording medium capable of multi-value recording, which is capable of producing a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude. 2. An organic material layer which does not have a function of absorbing light of a recording / reproducing wavelength when unrecorded is formed on a substrate through an undercoat layer, and the undercoat layer has a large difference in refractive index from the organic material layer. An optical recording medium having a layer structure sandwiched between a layer and an overcoating layer, wherein the undercoating layer or the overcoating layer has a light absorbing function, and the organic material layer from the organic material layer accompanying a change in state of the organic material in the organic material layer Recording principle of recording mark formation by pressure on the undercoat layer or pressure from the organic material layer to the overcoat layer, and recording principle of recording mark formation by stress relaxation of the undercoat layer or the overcoat layer or thermal expansion of the substrate It is possible to change the deformation direction of the recording mark part and the position (type) of the deformation interface at the time of recording, and this makes it possible to obtain a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude. A write-once type optical recording medium capable of multi-value recording. 3. A main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength on the substrate through an undercoat layer, and absorbs light of the recording / reproducing wavelength at the time of unrecording. A light having a layer structure in which an organic material layer having no function is sandwiched between an undercoating layer and an overcoating layer having a large refractive index difference with the organic material layer, and the undercoating layer or the overcoating layer has a light absorbing function. It is a recording medium, and it is possible to change the deformation direction and the position (type) of the deformation interface at the time of recording, so that a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude is obtained. A write-once type optical recording medium capable of multi-value recording. 4. A main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength on the substrate through an undercoat layer, and absorbs light of the recording / reproducing wavelength at the time of unrecording. A light having a layer structure in which an organic material layer having no function is sandwiched between an undercoating layer and an overcoating layer having a large refractive index difference with the organic material layer, and the undercoating layer or the overcoating layer has a light absorbing function. A recording medium, the recording principle of forming a recording mark by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer due to the state change of the organic material in the organic material layer, and The deformation direction of the recording mark portion and the position (type) of the deformation interface can be changed during recording by the recording principle of the recording mark formation by the stress relaxation of the pulling layer or the overcoat layer or the thermal expansion of the substrate. A reproduction signal with different recording polarities in addition to differences in recording mark length and amplitude can be obtained. A write-once type optical recording medium capable of multi-value recording. 5. The write-once type optical recording medium capable of multilevel recording according to claim 1, wherein the recording / reproducing wavelength is 350 to 500 nm. 6. The multilevel recording according to claim 1, wherein the interface shape between the organic material layer and the overcoat layer is formed to be the same as the groove shape of the substrate. Possible write-once type optical recording medium. 7. An organic material layer, which has no absorption function for light having a recording / reproducing wavelength when not recorded, is formed on a substrate through an undercoating layer, and the undercoating layer has a large difference in refractive index from the organic material layer. A write-once type optical recording medium having a layer structure sandwiched between a layer and an overcoat layer, and the undercoat layer or the overcoat layer having a light absorption function and capable of multi-valued recording is used to record the deformation direction and the deformation interface at the time of recording. A multilevel recording method characterized in that a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude can be obtained by changing the position (type). 8. An organic material layer, which does not have a function of absorbing light having a recording / reproducing wavelength when unrecorded, is formed on a substrate through an undercoating layer by undercoating with a large difference in refractive index from the organic material layer. A layer structure sandwiched between a layer and an overcoat layer, the state change of the organic material in the organic material layer for a multi-value recordable write-once optical recording medium in which the undercoat layer or the overcoat layer has a light absorbing function. The recording principle of the recording mark formation by the pressure from the organic material layer to the undercoat layer or the pressure from the organic material layer to the overcoat layer and the stress relaxation of the undercoat layer or the overcoat layer, or the thermal expansion of the substrate Depending on the recording principle of recording mark formation, the deformation direction of the recording mark portion and the position (type) of the deformation interface are changed at the time of recording, whereby a reproduction signal having different recording polarities in addition to the difference in recording mark length and amplitude can be obtained. A multi-valued recording method characterized by: 9. A main absorption band at the time of non-recording exists on the long wavelength side with respect to the recording / reproducing wavelength through an undercoat layer on a substrate, and absorbs light of the recording / reproducing wavelength at the time of unrecording. It has a layered structure in which an organic material layer having no function is sandwiched between an undercoating layer and an overcoating layer having a large difference in refractive index from the organic material layer, and the undercoating layer or the overcoating layer has a light absorbing function. By changing the deformation direction and the position (type) of the deformation interface at the time of recording with respect to the write-once type optical recording medium capable of value recording, a reproduction signal having a different recording polarity in addition to a difference in recording mark length and amplitude can be obtained. A multi-valued recording method characterized by: 10. A main absorption band at the time of unrecording exists on the long wavelength side with respect to the recording / reproducing wavelength on the substrate through the undercoat layer,
Further, it has a layer structure in which an organic material layer having no absorption function for light having a recording / reproducing wavelength when not recorded is sandwiched between an undercoating layer and an overcoating layer having a large difference in refractive index from the organic material layer. For a write-once type optical recording medium capable of multi-valued recording, in which the undercoating layer or the overcoating layer has a light absorbing function, the pressure from the organic material layer to the undercoating layer due to the state change of the organic material in the organic material layer, or the organic The recording principle of recording mark formation by pressure from the material layer to the overcoat layer,
Depending on the recording principle of recording mark formation due to the stress relaxation of the undercoat layer or the overcoat layer or the thermal expansion of the substrate, the position (type) of the deformation direction and the deformation interface of the recording mark part is changed during recording. A multilevel recording method characterized in that a reproduction signal having a different recording polarity in addition to a difference in length and amplitude is obtained. 11. The multilevel recording method according to claim 7, wherein a recording / reproducing wavelength is 350 to 500 nm.