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mini 111 in ii ii iiiiii mi ii i ii 

(ID EP 1 040 937 A1 



(12) EUROPEAN PATENT APPLICATION 

published in accordance with Art. 158(3) EPC 





Date of publication. 


(51) 


Int. Ul. . D4IIVI O/ZO, O I ID llZ.'i 




04.10.2000 Bulletin 2000/40 








(86) 


International application number: 


{Zl) 


Application number' 98961393.0 




PCT/JP98/05717 


(22) 


Date of filing: 17.12.1998 


(87) 


International publication number 








WO 99/30908 (24 06 1999 Gazette 1999/25) 


(84) 


Designated Contracting States: 


(72) 


Inventors: 




AT BE CH CY DE DK ES Fl FR GB GR IE IT LI LU 




FURUYA, Kazuyuki 




MCNLPTSE 




Fuji-shi, Shizuoka 416-0949 (JP) 








SUZUKI, Masaru 


(30) 


Priority: 17.12.1997 JP 34811897 




Fuji-shi, Shizuoka 416-0939 (JP) 




17.12.1997 JP 34811997 








10.06.1998 JP 16256198 


(74) 


Representative: 








Weber, Thomas, Dr.Dipl.-Chem. et al 


(71) 


Applicant: 




Patentanwalte 




Asahi Kasei Kogyo Kabushiki Kaisha 




von Kreisler-Selting-Werner, 




Osaka-shi, Osaka 530-8205 (JP) 




Postfach 10 22 41 








50462 Koln (DE) 







(54) WRITE ONCE OPTICAL INFORMATION RECORDING MEDIUM 



(57) The present invention has a subject of provid- 
ing a write-once type optical information recording 
medium with low dependence on the wavelength of a 
recording laser beam and suitable to a case in which the 
recording system is mark edge recording. 

The composition of the phase change type record- 
ing layer (2) is defined within a range surrounded by four 
points of A (0.475, 0.05, 0.475), B (0.665, 0.05, 0.285), 
C (0.60, 0.40, 0) and D (0.40, 0.60, 0) in the triangular 
diagram of Fig. 1 . A compound layer (3) is disposed just 
above or just below the recording layer (2). The com- 
pound layer (3) comprises at least one compound 
selected from the group consisting of PbSe, PbTe, 
SnSe, SnTe, Bi 2 Te 3 and Sb 2 Te 3 as the main ingredient. 
The reflection layer (4) comprises a material having a 
heat conductivity of 50 W/m • K or higher. 



Europaisches P 
QjH European Patent Office 

Office europeen des brevets 



F I G. 1 




0L 
LU 



Printed by Xerox (UK) Business Services 



1 



EP 1 040 937 A1 



2 



Description 

TECHNICAL FIELD 

[0001] The present invention concerns a write-once 
type optical information recording medium having a 
phase-change type recording layer. 

BACKGROUND ART 

[0002] As an optical information recording medium 
for recording and reading data by irradiation of a laser 
beam, a write-once type optical disc capable of record- 
ing only for once and a rewritable type optical disc capa- 
ble of erasing recorded information and re-recording 
have been known. 

[0003] As the recording principle of the write-once 
type optical disc, there have been proposed, for exam- 
ple, (a) a method of forming holes in a recording layer, 

(b) a method of thermally deforming a recording layer, 

(c) a method of alloying or condensing metals, (d) a 
method of phase changing a recording layer and (e) a 
method of thermally color development of an organic 
dye. 

[0004] CD-R (Compact Disc Recordable: write- 
once type CD) recently used frequently as a write-once 
type optical disc is mainly based on the recording prin- 
ciple (e) above using an organic dye since it is required 
that the reflectivity of the disc is 65% or more. This is 
because the recording principles other than (e) can not 
satisfy the two factors in that (1) the recording layer has 
appropriate values of an optical constant and (2) record- 
ing is possible while having a high reflectivity together. 
[0005] Further, DVD-R (Digital Video Disc Recorda- 
ble: write-once type DVD) having a higher recording 
density than that of CD-R has also been put to actual 
products in recent years. DVD-R is still based on mainly 
the recording principle (e) while it is not necessary to 
make the reflectivity of the disc so high as that for the 
CD-R. The reason is as described below. In DVD-R, the 
recording method is a mark edge recording (also 
referred to as "pit edge recording", and recording is con- 
ducted at a high density. Therefore, the edge of the 
recording mark (also referred to as "recording pit") has 
to be formed at a predetermined position with an exact 
shape and clearly. It has been difficult to control such 
mark edge by the recording principle other than (e). 
[0006] However, the recording principle (e) 
described above involves a problem that the depend- 
ence on the wavelength of the recording laser beam is 
high and recording and reading are no more possible if 
the wavelength changes even only for several tens nm. 
Further, the wavelength of the laser beam capable of 
high density recording to the write-once type optical 
disc adopted the recording principle (e) is different from 
the wave length for recording to existent optical discs. 
Therefore, there is also a problem that a disc drive can 
not be used in common with existent products (that is, 



poor compatibility). 

[0007] On the other hand, various write-once type 
optical discs utilizing the recording principle (d) have 
also been put to actual products. In this case, a material 

5 occurring phase change between crystal and amor- 
phousness due to the difference of the intensity of irra- 
diated laser beams is used. In the recording principle, 
the dependence on the wavelength of the laser beam 
for the recording is lower than that in the recording prin- 

10 ciple(e). 

[0008] As a structure of the optical disc of this type, 
a structure in which a metal reflection layer is disposed 
on a recording layer has been proposed (refer to Japa- 
nese Unexamined Patent Publication Nos. 

15 154341/1987 and 176185/1988). In the proposals, a 
reflection layer comprising Sb, Te or Bi as a main ingre- 
dient is disposed on a recording layer to increase the 
sensitivity and improve an optical contrast. 
[0009] However, the reflection layer materials men- 

20 tioned in the proposals are suitable where the recording 
method is a mark position recording (also referred to as 
"pit position recording"). In the mark position recording, 
different from the mark edge recording, it is not neces- 
sary to precisely control the edge of the recording mark. 

25 Then, since the edge controllability for the recording 
mark is not improved even if a reflection layer compris- 
ing Sb, Te or Bi as the main ingredient is disposed on 

the recording layer, such proposals are not suitable 

where the recording method is a mark edge recording. 

30 [0010] Japanese Unexamined Patent Publication 
No. 164937/1985 proposes to constitute a recording 
layer of an optical disc into a three layered structure 
having a light absorption layer between two phase 
change layers in order to increase the recording sensi- 

35 tivity. The phase change layer are constituted with an 
elemental Se or Se compound or Se alloy. The absorp- 
tion layer is constituted with an elemental Bi, elemental 
Te or an alloy thereof. However, this proposal is not also 
suitable where the recording method is mark edge 

40 recording. 

[0011] Japanese Unexamined Patent Publication 
No. 28045/1985 discloses an information recording 
medium having a recording layer of a two layered struc- 
ture. A first layer constituting the recording layer com- 

45 prises chalcogenide glass (for example, Sb-Se) and a 
second layer comprises a low melting point metal (for 
example, Te, Bi Sb and In) or an alloy thereof (for exam- 
ple, Bi-Te). The recording principle of the medium is 
alloying described in (C) above. 

so [0012] Japanese Unexamined Patent Publication 
No. 66668/1997 discloses an optical disc in which the 
recording layer has a three layered structure. The 
recording layer is constituted with an Sb-Se series thin 
film, a Bi-Te series thin film and an Sb-Se series thin film 

55 in this order from the side of a substrate. The recording 
principle of this medium is alloying in (C) above. 
[0013] Japanese Unexamined Patent Publication 
No. 342629/1993 discloses an information recording 



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EP 1 040 937 A1 



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medium having an auxiliary layer comprising an ele- 
mental Te, Se alloy or Te-Ge-Sb with a higher Te content 
than that of the recording layer, in contact with the 
recording layer comprising a Te-Ge-Sb series alloy. In 
the medium, recording is conducted by phase changing 
the recording layer from crystal to amorphousness. 
Therefore, for conducting stable recording from the first 
time, an initializing process of making the recording 
layer into a uniform crystal has been applied to the 
medium before supply. The auxiliary layer is disposed 
for simplifying the initialization process. Further, the 
medium is a rewritable type. 

[0014] The present invention has a subject of 
improving the edge controllability of a recording mark in 
write-once type optical information recording medium 
having a phase-change type recording layer with less 
dependence on the wavelength of a recording laser 
beam. When the edge of the recording mark is control- 
led precisely, the jitter value of a readout light is 
decreased where the recording method is mark edge 
recording. Thus, a write-once type optical information 
recording medium suitable where the recording method 
is a mark edge recording is provided. 

DISCLOSURE OF THE INVENTION 

[0015] For solving the foregoing subject, the 
present invention provides a write-once type optical 
information recording medium having a recording layer 
for recording information by phase change from amor- 
phousness to crystal at least on one surface of a trans- 
parent substrate, wherein the recording layer comprises 
a Te-Ge-Sb series alloy (other elements may be incor- 
porated in addition to Te, Ge and Sb) or a Te-Ge series 
alloy (other elements may be incorporated in addition to 
Te and Ge), in which the composition thereof is within a 
region surrounded by four points of A (0.475, 0.05, 
0.475), B (0.665, 0.05, 0.285), C (0.60, 0.40, 0), D (0.40, 
0.60, 0) in a triangular diagram, shown in Fig. 1, show- 
ing the composition of three ingredients of Te and Ge 
and Sb by a coordinate (Te, Ge, Sb), and which has a 
compound layer containing at least one compound 
selected from the group consisting of PbSe, PbTe, 
SnSe, SnTe, Bi 2 Te 3 and Sb 2 Te 3 as the main ingredient 
just above or just below the recording layer. 
[0016] The composition at the point A is 
Te47.5Ge5Sb47.5, the composition at the point B is 
Te66.5Ge5Sb28.5, the composition at the point C is 
Te60Ge40 and the composition at the point D is 
Te40Ge60. 

[0017] In the recording medium of the present 
invention, since the composition of the recording layer is 
within the range described above and has the com- 
pound layer containing the compound specified above 
as the main ingredient just above and just below the 
recording layer, stability of a recording mark to a reading 
beam is improved and the jitter characteristic upon con- 
ducting high density recording by mark edge recording 



is favorable. 

[0018] An alloy comprising at least two elements 
among the three elements of Te, Ge and Sb have high 
crystallizing rate (transfer rate from amorphousness to 
5 crystal), they have been used so far as the material for 
the recording layer of an optical information recording 
medium. 

[0019] However, when the composition of the 
recording layer is outside of a line connecting the point 

w A and point B in the triangular diagram of Fig. 1 (that is 
, if the Ge content is less than 5 atomic%), the crystalliz- 
ing temperature is lowered and a portion not formed 
with a recording mark (the portion is "not recorded por- 
tion") tends to be crystallized by the reading beam. As a 

15 result, the boundary between the recording mark and 
the not recorded portion becomes unclear to possibly 
deteriorate the recording mark. 
[0020] Further, when the composition of the record- 
ing layer is outside of a line connecting the point B and 

20 the point C and outside of a line connecting the point D 
and the point A in the triangular diagram of Fig. 1, the jit- 
ter characteristic is worsened. 

[0021] In view of the foregoings, the composition of 
the recording layer is defined in the range described 
25 above in the recording medium according to the present 
invention. 

[0022] When the composition of the recording layer 
is a composition is within a range surrounded by the 
points A, B, C and D but near the line connecting the 

30 point A and point B in the triangular diagram of Fig. 1 
(that is a composition with a relatively low Ge content 
although being 5 atomic% or more), the difference of 
the optical constant between the amorphous state and 
the crystalline state is reduced. As a result, the ampli- 

35 tude of a readout signal is decreased and this is not 
favorable in view of the signal quality. 
[0023] A more preferred range for the composition 
of the recording layer is a range in which the coordinate 
(Te, Ge, Sb) is at E (0.47, 0.30, 0.23), F (0.58, 0.30, 

40 0.12), G (0.56, 0.44, 0) and H (0.44, 0.56, 0), respec- 
tively, in Fig. 2 which is a triangular diagram like Fig. 1. 
The composition at the point E is Te47Ge30Sb23, the 
composition at the point F is Te58Ge30Sb12 and the 
composition at the point G is Te56Ge44 and the compo- 

45 sition at the point H is Te44Ge56. 

[0024] A more preferred range for the composition 
of the recording layer is a range in which the coordinate 
(Te, Ge, Sb) is surrounded by four points at J (0.47, 
0.40, 0.13), K (0.55, 0.40, 0.05), L (0.52, 0.48, 0) and M 

so (0.44, 0.56, 0) respectively in Fig. 3 which is a triangular 
diagram like Fig. 1. The composition at the point J is 
Te47Ge40Sb13, the composition at the point K is 
Te55Ge40Sb5 and the composition at the point L is 
Te52Ge48 and the composition at the point M is 

55 Te44Ge56. 

[0025] The compound layer that the recording 
medium of the present invention has comprises at least 
one compound selected from the group consisting of 



3 



5 



EP 1 040 937 A1 



6 



PbSe, PbTe, SnSe, SnTe, Bi 2 Te 3 and Sb 2 Te 3 as the 
main ingredient. The compound layer may be formed 
with one of the compounds or may be in a mixed crystal 
state in admixture of two or more of them. With a view 
point of storage life of a disc, the main ingredient of the 5 
compound layer is preferably SnTe among the com- 
pounds described above. 

[0026] The compound layer comprises the com- 
pound specified above as the main ingredient and can 
contain other materials than described above. In this w 
case, the content of the specified compound in the 
entire material constituting the compound layer is 50 
vol% or more. If the content of the specified compound 
is less than 50 vol%, the recording layer is not favorably 
crystallized to possibly worsen the jitter characteristic of 15 
the readout light. The content of the specified com- 
pound in the compound layer is preferably 70 vol% or 
more. 

[0027] In a case where the recording medium of the 
present invention has a structure having a reflection 20 
layerfor reflecting a light transmitted through the record- 
ing layer, the reflection layer is preferably constituted 
with a material having a heat conductivity of 50 W/m • K 
or higher. This can control the length of a recording 
mark by mark edge recording accurately. 25 
[0028] The material having the heat conductivity of 
50 W/m • K or higher can include a metal selected from 
the group consisting of Al, Cr, Ni, Au, Hf, Pd, Ta, Co, Mo, 
W and Ti, or an alloy of such metals. Among the materi- 
als described above, Al-Ti alloy, Al-Cr alloy, Al-Ta alloy, 30 
Al-Pd alloy, Ti-AI alloy, Ti-V alloy and the like are pre- 
ferred as the material for the reflection layer in various 
points of view. The compositional ratio of the alloys is 
set in accordance with required characteristics. 
[0029] A synthetic resin layer comprising a UV-ray 35 
curable resin (for example, urethane, acrylic, silicon or 
polyester series) or hot-melt type adhesive is preferably 
disposed on the upper surface of the reflection layer 
(the surface opposite to the substrate) for protecting and 
reinforcing the reflection layer. 40 
[0030] An example of a layered structure for the 
recording medium of the present invention is shown in 
Fig. 4. 

[0031] In this example, a recording layer 2, a com- 
pound layer 3 and a reflection layer 4 are laminated sue- 45 
cessively on a transparent substrate 1 and a synthetic 
resin layer 5 are formed on the reflection layer 4. The 
thickness of each of the layers is set in accordance with 
required characteristics and, in a usual optical disc, the 
thickness of the recording layer 2 is preferably within a 50 
range of 5 nm or more and less than 50 nm. The thick- 
ness of the compound layer 3 is preferably within a 
range of 1 nm or more and less than 50 nm. The thick- 
ness of the reflection layer 4 is preferably within a range 
of 10 nm or more and less than 300 nm. 55 
[0032] If the thickness of the recording layer 2 is 
less than 5 nm, it is not preferred since the optical con- 
trast is extremely decreased. Further, if the thickness of 



the recording layer 2 is 50 nm or more, it is not preferred 
since the jitter characteristic is worsened by the diffu- 
sion of heat in a plane of the recording layer. A more 
preferred range for the thickness of the recording layer 2 
is 10 nm or more and less than 50 nm. 
[0033] The thickness of the compound layer 3 may 
be extremely small, providing that the compound layer 3 
is formed so as to be in uniform contact with the entire 
surface of the recording layer 2. However, if the thick- 
ness of the compound layer 3 is less than 1 nm, the 
layer may possibly be in an island structure not to be in 
uniform contact with the entire surface of the recording 
layer 2. 

[0034] As the thickness of the compound layer 3 
increases, more heat is accumulated in the recording 
layer 2. The recording mark tends to be degraded by the 
reading beam under the effect of the heat. If the thick- 
ness of the compound layer 3 is 50 nm or more, the 
effect of the heat becomes remarkable. 
[0035] With the view points described above, a 
more preferred range for the thickness of the compound 
layer 3 is 2 nm or more and less than 20 nm and, a fur- 
ther preferred range is 2 nm or more and less than 10 
nm. 

[0036] If the thickness of the reflection layer is less 
than 10 nm, it is not preferred since both of the function 
of reflecting light and the effect of dissipating heat (so- 
called heat sink effect) can not be obtained substan- 
tially. Further, as the thickness of the reflection layer 4 
increases, the recording sensitivity is lowered. Low 
recording sensitivity is not preferred since this requires 
a high laser power upon recording. If the thickness of 
the reflection layer is 300 nm or more, the recording 
sensitivity is lowered remarkably. 
[0037] With the view points described above, a 
more preferred range for the thickness of the reflecting 
layer 4 is 20 nm or more and less than 200 nm. 
[0038] The thickness of the synthetic resin layer 5 is 
preferably within a range of 2 u.m or more and less than 
20 |im. 

[0039] When the recording medium of the present 
invention has a structure with no reflection layer and the 
compound layer is formed just above the recording layer 
(in contact with the surface opposite to the substrate), a 
protection layer is disposed preferably on the compound 
layer. The material of the protection layer can include at 
least one member selected from oxides, carbides, 
nitrides, fluorides and sulfides of metals or semi-metals. 
They can include, specifically, oxides such as Si0 2 , SIO, 
Ta 2 0 5 and Zr0 2 , carbides such as SiC and TiC, ele- 
mental carbon, nitrides such as Si 3 N 4 and AIN, sulfides 
such as ZnS, Sms and SrS and fluorides such as MgF 2 . 
One member selected from the materials or a mixture of 
a plurality of them may be preferably used as the mate- 
rial for the protection layer. 

[0040] The structure with no reflection layer can be 
adopted, for example, where the compound layer is 
formed of a chemically stable material. 



4 



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EP 1 040 937 A1 



[0041] Referring to the method of manufacturing 
the recording medium according to the present inven- 
tion, any of a sputtering method, vacuum deposition 
method, CVD method or PVD method can be adopted 
as a method for forming the recording layer and the 5 
compound layer, and the use of the sputtering method is 
preferred in view of the productivity and the operationa- 
bility. 

[0042] The deposition method of the compound 
layer by the sputtering method includes (1) a method of 10 
using a target made of a compound constituting the 
compound layer, (2) a co-sputtering method of providing 
targets comprising each of metal elements constituting 
the compound of the compound layer and discharging 
such targets individually, and (3) a method in a case of 15 
containing a compound of a metal element and a non- 
metal element as a material for constituting the com- 
pound layer, and the method is providing a target made 
of metal elements for constituting a compound, and 
adding a gas containing a non-metal element in a sput- 20 
tering atmosphere, thereby forming the compound on a 
substrate. 

[0043] Among the methods, the method (1) is pre- 
ferred since this is excellent in productivity, controllabil- 
ity and film homogeneity. Further, in a case where the 25 
compound layer is formed as a mixed crystal film of a 
plurality of compounds, it is preferred to use a material 
comprising each of the compounds in admixture as a 
target. 

[0044] As the substrate for the recording medium 30 
according to the present invention, a transparent sub- 
strate often used so far as a substrate for an optical disc 
can be used for instance. Particularly, use of a substrate 
made of polycarbonate, polymethylmethacrylate or 
glass having favorable optical characteristic, high 35 
mechanical strength and excellent dimensional stability 
is used preferably. 

BRIEF EXPLANATION OF DRAWINGS 

40 

[0045] 

Fig. 1 is a triangular diagram showing a composi- 
tion for three ingredients of Te, Ge and Sb as a 
coordinate (Te, Ge, Sb), which shows the composi- 45 
tional range (range surrounded by four points ABC 
and D) of a recording layer of a recording medium 
according to the present invention. 
Fig. 2 is a triangular diagram showing a composi- 
tion for three ingredients of Te, Ge and Sb as a so 
coordinate (Te, Ge, Sb), which shows a preferred 
range (range surrounded by four points E F G and 
H) as a composition for the recording layer of a 
recording medium according to the present inven- 
tion. 55 
Fig. 3 is a triangular diagram showing a composi- 
tion for three ingredients of Te, Ge and Sb as a 
coordinate (Te, Ge, Sb), which shows a more pre- 



ferred range (range surrounded with four points J K 
L and M) as a composition for the recording layer of 
a recording medium according to the present inven- 
tion. 

Fig. 4 is a drawing showing an example of a layered 
structure for a recording medium according to the 
present invention. 

BEST MODE FOR PRACTICING THE INVENTION 

[0046] Embodiments of the present invention are to 
be explained. 

EXAMPLE 1 

[0047] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared. At first, on a 
clean polycarbonate substrate 1 formed with guide 
grooves (0.6 mm thickness, 0.74 um track pitch, 0.37 
urn groove width and 700 A groove depth), a recording 
layer 2 of 25 nm thickness, a compound layer 3 of 5 nm 
thickness and reflection layer 4 of 40 nm thickness were 
successively deposited by a sputtering method. Then, 
after coating a UV-ray curable resin on the upper sur- 
face of the reflection layer 4, UV-rays were irradiated on 
the coated surface to cover the upper surface of the 
reflection layer with a synthetic resin layer 5. 
[0048] The recording layer 2 was deposited by 
using a target comprising an Sb-Te-Ge alloy. The com- 
position of the target was controlled such that the com- 
position after the deposition was Sb17Te53Ge30. The 
compound layer 3 was deposited by using a target com- 
prising PbTe. The reflection layer 4 was deposited by 
using a target comprising an AITi alloy. 
[0049] The recording layer of the prepared optical 
disc is in an amorphous state, and information recording 
to the optical disc is conducted by forming a recording 
mark in a crystalline state to the recording layer by the 
irradiation of a laser beam. 

[0050] In this case, random signals of 8 - 1 6 modu- 
lation system with a shortest mark length of 0.4 u.m 
were recorded by irradiating a multi-pulse laser at a 
laser power (7 - 8 mW), with a pulse width (20 to 25 
nsec) and with optimized timing for pulse emission 
(delay time for the leading pulse of 2 to 5 nsec), while 
rotating the optical disc at a linear velocity of 6 m/sec. 
[0051] The wavelength of the laser beam is 650 nm 
and the numeral aperture of an objective lens is 0.6 in 
an optical system used for recording and reading. 
[0052] Jitter of the readout light of the optical disc 
was measured by the following method. 
[0053] When a slice signal at a predetermined volt- 
age is superposed on the readout signal waves to gen- 
erate a plurality of pulse signals having rising points at 
intersections between both of them, the rising points of 
pulse signal agrees with the rising point of a pulse signal 
showing a reference clock if the edge of the recording 
mark is formed at an exact position. However, if the 



5 



EP 1 040 937 A1 



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edge if displaced, a time difference is caused between 
the rising points. The time difference is measured for a 
number of pulse signals having the rising points at the 
intersections, and a standard deviation is calculated 
based on the distribution thereof. The value obtained by 
dividing the calculated value of the standard deviation 
with the period of the reference clock corresponds to the 
jitter. 

[0054] The jitter is measured by the method 
described above by at first setting the voltage of the 
slice signal near the center of the amplitude of the read- 
out signal. Then, measurement of the jitter by the 
method described above is repeated with varying the 
voltage for the slice signal. In this embodiment, the min- 
imum value of the jitter thus measured is defined as 
(measured value of the jitter). 
[0055] The measured value of the jitter is 8.01% 
and the jitter characteristic was favorable in this optical 
disc. 

EXAMPLE 2 

[0056] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, the compound layer 
3 was deposited by using a target comprising SnTe. 
Other procedures than those described above are iden- 
tical with those in Example 1 including the thickness of 
the compound layer 3. 

[0057] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of the readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.13% and the jitter charac- 
teristic was favorable. 

EXAMPLE 3 

[0058] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb10Te50Ge40. Other procedures than those 
described above are identical with those in Example 1 
including the thickness of the recording layer 3. 
[0059] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of the readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.28% and the jitter charac- 
teristic was favorable. 

EXAMPLE 4 

[0060] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 



manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 
the composition after the deposition was 

5 Sb27Te53Ge20. Other procedures than described 
above were identical with those in Example 1 including 
the thickness of the recording layer 2. 
[0061] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 

10 jitter of readout light was measured by the same method 
as in Example 1 . The measured value of the jitter in this 
optical disc was 8.33% and the jitter characteristic was 
favorable. 

15 EXAMPLE 5 

[0062] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a target used for the 

20 deposition of the recording layer 2 comprises an Te-Ge 
alloy and the composition was controlled for the compo- 
sition such that the composition after the deposition was 
Te50Ge50. Other procedures than described above 
were identical with those in Example 1 including the 

25 thickness of the recording layer 2. 

[0063] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of the readout light was measured by the same 
method as in Example 1 . The measured value of the jit— 

30 terwas 8.50% and the jitter characteristic was favorable 
in this optical disc. 

EXAMPLE 6 

35 [0064] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 

40 the composition after the deposition was 
Sb13Te47Ge40. The compound layer 3 was formed by 
using a target comprising SnTe. Other procedures than 
described above were identical with those in Example 1 
including the thickness of the recording layer 2 and that 

45 of the compound layer 3. 

[0065] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of readout light was measured by the same method 
as in Example 1 . The measured value of the jitter in this 

50 optical disc was 7.55% and the jitter characteristic was 
favorable. 

EXAMPLE 7 

55 [0066] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 



6 



EP 1040 937 A1 12 



11 

ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb5Te55Ge40. The compound layer 3 was deposited 
by using a target comprising SnTe. Other procedures 
than described above were identical with those in 5 
Example 1 including the thickness of the recording layer 
2 and that of the compound layer 3. 
[0067] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1, the 
jitter of a readout light was measured by the same 10 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 7.61 % and the jitter charac- 
teristic was favorable. 

EXAMPLE 8 15 

[0068] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a target comprising 
an Te-Ge alloy used for the deposition of the recording 20 
layer 2 was controlled for the composition such that the 
composition after the deposition was Te52Ge48. The 
compound layer 3 was deposited by using a target com- 
prising SnTe. Other procedures than described above 
were identical with those in Example 1 including the 25 
thickness of the recording layer 2 and that of the com- 
pound layer 3. 

[0069] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1, the 
jitter of a readout light was measured by the same 30 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 7.32% and the jitter charac- 
teristic was favorable. 

EXAMPLE 9 35 

[0070] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Te-Ge alloy used for the deposition of the recording 40 
layer 2 was controlled for the composition such that the 
composition after the deposition was Te44Ge56. The 
compound layer 3 was deposited by using a target com- 
prising SnTe. Other procedures than described above 
were identical with those in Example 1 including the 45 
thickness of the recording layer 2 and that of the com- 
pound layer 3. 

[0071] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1, the 
jitter of a readout light was measured by the same so 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 7.23% and the jitter charac- 
teristic was favorable. 

EXAMPLE 10 55 

[0072] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 



manner as in Example 1 . However, a target comprising 
an Te-Ge alloy used for the deposition of the recording 
layer 2 was controlled for the composition such that the 
composition after the deposition was Te50Ge50. The 
compound layer 3 was deposited by using a target com- 
prising SnTe. Other procedures than described above 
were identical with those in Example 1 including the 
thickness of the recording layer 2 and that of the com- 
pound layer 3. 

[0073] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 7.15% and the jitter charac- 
teristic was favorable. 

EXAMPLE 11 

[0074] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, the compound layer 
3 was deposited by using a target comprising Bi2Te3. 
Other procedures than described above were identical 
with those in Example 1 including the thickness of the 
compound layer 3. 

[0075] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of a readout light was measured by the same 
method as in Example 1. The measured value of the jit- 
ter in this optical disc was 8.27 % and the jitter charac- 
teristic was favorable. 

EXAMPLE 12 

[0076] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb10Te50Ge40. The compound layer 3 was deposited 
by using a target comprising Bi2Te3. Other procedures 
than described above were identical those in Example 1 
including the thickness of the recording layer 2 and that 
of the compound layer 3. 

[0077] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.63% and the jitter charac- 
teristic was favorable, 

EXAMPLE 13 

[0078] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 



25 



45 



7 



13 



EP 1 040 937 A1 



14 



ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb27Te53Ge20. The compound layer 3 was deposited 
by using a target comprising Bi2Te3. Other procedures 
than described above were identical with those in 
Example 1 including the thickness of the recording layer 

2 and that of the compound layer 3. 

[0079] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1, the 
jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.38% and the jitter charac- 
teristic was favorable. 

EXAMPLE 14 

[0080] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a target and used for 
the deposition of the recording layer 2 comprised an Te- 
Ge alloy was controlled for the composition such that 
the composition after the deposition was Te50Ge50. 
The compound layer 3 was deposited by using a target 
comprising Bi2Te3. Other procedures than described 
above were identical with those in Example 1 including 
the thickness of the recording layer 2 and that of the 
compound layer 3. 

[0081] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1, the 
jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.66% and the jitter charac- 
teristic was favorable. 

EXAMPLE 15 

[0082] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, the compound layer 

3 was deposited by using a target comprising Sb2Te3. 
Other procedures than above were identical with those 
in Example 1 including the thickness of the compound 
layer 3. 

[0083] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1, the 
jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.41% and the jitter charac- 
teristic was favorable. 

EXAMPLE 16 

[0084] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a target used for the 
deposition of the recording layer 2 comprised an Te-Ge 
alloy and was controlled for the composition such that 
the composition after the deposition was Te50Ge50. 



The compound layer 3 was deposited by using a target 
comprising SnTe. The thickness of the compound layer 
was set to 15 nm. Other procedures than described 
above were identical with those in Example 1 including 

5 the thickness of the recording layer 2. 

[0085] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the j it— 

10 ter in this optical disc was 8.70% and the jitter charac- 
teristic was favorable. 

EXAMPLE 17 

15 [0086] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, the compound layer 
3 was deposited by using a target comprising Sb2Te3. 
The thickness of the compound layer 3 was set to 3 nm. 

20 the thickness of the reflection layer 4 was set to 1 20 nm. 
Other procedures than above were identical with those 
in Example 1 . 

[0087] After conducting recording to the optical disc 
thus prepared in the same manner as in Example 1 , the 
25 jitter of a readout light was measured by the same 
method as in Example 1 . The measured value of the jit- 
ter in this optical disc was 8.83% and the jitter charac- 
teristic was favorable. 

30 COMPARATIVE EXAMPLE 1 

[0088] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 

35 an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb40Te40Ge20. This composition is out of the range of 
the present invention. Other procedures than described 

40 above were identical with those in Example 1 including 
the thickness of the recording layer 2. 
[0089] After conducting recording to the thus pre- 
pared optical disc by the same method as in Example 1 , 
the jitter of a readout light was tried to measure by the 

45 same method as in Example 1 . However, since crystal- 
lization upon recording was insufficient in this optical 
disc, the jitter could not be measured. 

COMPARATIVE EXAMPLE 2 

50 

[0090] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
55 ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb20Te40Ge40. This composition is out of the range of 
the present invention. Other procedures than described 



8 



15 



EP 1 040 937 A1 



16 



above were identical with those in Example 1 including 
the thickness of the recording layer 2. 
[0091] After conducting recording to the thus pre- 
pared optical disc by the same method as in Example 1 , 
the jitter of a readout light was tried to measure by the 
same method as in Example 1 . However, since crystal- 
lization upon recording was insufficient in this optical 
disc, the jitter could not be measured. 

COMPARATIVE EXAMPLE 3 

[0092] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1 . However, a layer comprising 
Sb of 40 nm thickness was deposited instead of the 
compound layer 3 on the recording layer 2 and a protec- 
tion layer comprising ZnS-Si02 of 20 nm thickness was 
deposited thereon. A synthetic resin layer 5 was depos- 
ited on the protection layer without deposition of the 
reflection layer 4. Other procedures than above were 
identical with those in Example 1. 
[0093] After conducting recording to the thus pre- 
pared optical disc by the same method as in Example 1 , 
the jitter of a readout light was measured in the same 
manner as in Example 1. In the optical disc, the meas- 
ured value of the jitter was 12.53%, which was as high 
as by about 4% compared with each of the examples 
described above and the jitter characteristic was poor. 

COMPARATIVE EXAMPLE 4 

[0094] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 
the composition after the deposition was 
Sb40Te40Ge20. This composition is out of the range of 
the present invention. The compound layer 3 was 
deposited by using a target comprising Bi2Te3. Other 
procedures than described above were identical with 
those in Example 1 including the thickness of the 
recording layer 2 and that of the compound layer 3. 
[0095] After conducting recording to the thus pre- 
pared optical disc by the same method as in Example 1, 
the jitter of a readout light was tried to measure by the 
same method as in Example 1. However, since crystal- 
lization upon recording was insufficient in this optical 
disc, the jitter could not be measured. 

COMPARATIVE EXAMPLE 5 

[0096] A write-once type optical disc of a layered 
structure shown in Fig. 4 was prepared in the same 
manner as in Example 1. However, a target comprising 
an Sb-Te-Ge alloy used for the deposition of the record- 
ing layer 2 was controlled for the composition such that 
the composition after the deposition was 



Sb20Te40Ge40. This composition is out of the range of 
the present invention. The compound layer 3 was 
deposited by using a target comprising Bi2Te3. Other 
procedures than described above were identical with 

5 those in Example 1 including the thickness of the 
recording layer 2 and that of the compound layer 3. 
[0097] After conducting recording to the thus pre- 
pared optical disc by the same method as in Example 1 , 
the jitter of a readout light was tried to measure by the 

10 same method as in Example 1. However, since crystal- 
lization upon recording was insufficient in this optical 
disc, the jitter could not be measured. 

INDUSTRIAL APPLICABILITY 

15 

[0098] As has been explained above, according to 
the present invention, in a write-once type optical infor- 
mation recording medium having a phase change type 
recording layer, stability of the recording mark to the 

20 reading beam is improved and the jitter characteristic is 
favorable in a case of conducting high density recording 
by mark edge recording. Thus, a write-once type optical 
information recording medium with less dependence on 
the wavelength of a recording laser beam and suitable 

25 to a case where the recording system is mark edge 
recording is provided. 

[0099] Particularly, in a write-once type optical infor- 
mation recording medium having a reflection layer, con- 
trol for the length of the recording mark by mark edge 
30 recording can be conducted accurately by constituting 
the reflection layer with a material having a heat con- 
ductivity of 50 W/m • K or higher. 

Claims 

35 

1. A write-once type optical information recording 
medium having, at least on one surface of a trans- 
parent substrate, a recording layer in which infor- 
mation is recorded by phase change from 

40 amorphousness to crystal, wherein 

the recording layer comprises a Te-Ge-Sb 
series alloy or a Te-Ge series alloy, in which the 
composition thereof is within a range sur- 

45 rounded by four points of A (0.475, 0.05, 

0.475), B (0.665, 0.05, 0.285), C (0.60, 0.40, 0) 
and D (0.40, 0.60, 0) in a triangular diagram 
showing the composition of three ingredients of 
Te, Ge and Sb by an coordinate (Te, Ge, Sb), 

50 and wherein 

a compound layer containing at least one com- 
pound selected from the group consisting of 
PbSe, PbTe, SnSe, SnTe, Bi 2 Te 3 and Sb 2 Te 3 
as the main ingredient is disposed just above or 

55 just below the recording layer. 

2. A write-once type optical information recording 
medium as defined in claim 1, wherein the record- 



9 



17 EP 1 040 937 A1 18 

ing layer comprises a Te-Ge-Sb series alloy or a Te- 
Ge series alloy in which the composition thereof is 
within a range surrounded by four points of J (0.47, 
0.40, 0.13), K (0.55, 0.40, 0.05), L (0.52, 0.48, 0) 
and M (0.44, 0.56, 0) in a triangular diagram show- 5 
ing the composition of three ingredients of Te, Ge 
and Sb by an coordinate (Te, Ge, Sb). 

3. A write-once type optical information recording 
medium having, at least on one surface of a trans- 10 
parent substrate, a recording layer in which infor- 
mation is recorded by phase change from 
amorphousness to crystal and a reflection layer for 
reflecting light transmitted through the recording 
layer, wherein 15 

the recording layer comprises a Te-Ge-Sb 
series alloy or a Te-Ge series alloy, in which the 
composition thereof is within a range sur- 
rounded by four points of A (0.475, 0.05, 20 
0.475), B (0.665, 0.05, 0.285), C (0.60, 0.40, 0) 
and D (0.40, 0.60, 0) in a triangular diagram 
showing the composition of three ingredients of 
Te, Ge and Sb by an coordinate (Te, Ge, Sb), 
and wherein 25 
a compound layer containing at least one com- 
pound selected from the group consisting of 
PbSe, PbTe, SnSe, SnTe, Bi 2 Te 3 and Sb 2 Te 3 
as the main ingredient is disposed just above or 
just below the recording layer, and 30 
the reflection layer comprises a material having 
a heat conductivity of 50 W/m • K or higher. 

4. A write-once type optical information recording 

medium as defined in claim 3, wherein the record- 35 
ing layer comprises a Te-Ge-Sb series alloy or a Te- 
Ge series alloy in which the composition thereof is 
within a range surrounded by four points of J (0.47, 
0.40, 0.13), K (0.55, 0.40, 0.05), L (0.52, 0.48, 0) 
and M (0.44, 0.56, 0) in a triangular diagram show- 40 
ing the composition of three ingredients of Te, Ge 
and Sb by an coordinate (Te, Ge, Sb). 

5. A write-once type optical information recording 
medium as defined in claim 3, wherein the reflec- 45 
tion layer comprises a metal selected from the 
group consisting of Al, Cr, Ni, Au, Hf, Pd, Ta, Co, 
Mo, W and Ti, or an alloy of such metals. 

6. A write-once type optical information recording so 
medium as defined in any one of claims 1 to 5, 
wherein the thickness of the compound layer is 2 

nm or more and less than 20 nm. 

7. A write-once type optical information recording 55 
medium as defined in any one of claims 1 to 5, 
wherein the thickness of the compound layer is 2 

nm or more and less than 10 nm. 



10 



EP 1 040 937 A1 



F IG. 1 




Te 




11 



EP 1 040 937 A1 




FIG. 4 




~—5 






4 

--—2 









12 



EP 1 040 937 A1 



INTERNATIONAL SEARCH REPORT 



PCT/JP98/05717 



According to International Patent Classification (IPC) of to both national classification and IPC 
B. FIELDS SEARCHED 
Minimum documentation seai 

Int. CI' B41M5/26' 



sd (classification system followed by class 



Documentation searched other th 

Jitsuyo Shinan Koho 1926-1999 Toroku Jitsuyo S 

Kokai Jitsuyo Shinan Koho 1971-1999 

Electronic data base consulted during the international search (ns 



C. DOCUME NTS CONSIDERED TO BE RELEVANT 
Citation of document, with indication, wh 



e appropriate, of the relevant passages 



Relevant to daim No. 



, 2-219688, A (Toshiba Corp.), 
3 September, 1990 (03. 09. 90), 
Claims ; page 3, lower left column to page 4, lo^ 
right column & DK, 4005315, A 

JP, 6-119657, A (Toshiba Corp.), 
28 April, 1994 (28. 04. 94), 
Claims ; Par. Nos. [0009] to [0022] (Family: none) 

JP, 7-93805, A (Toshiba Corp.), 
7 April, 1995 (07. 04. 95), 
Claims ; Par. Nos. [0010] to [0030] (Family: none) 



27 September, 1996 (27. 09. 96), 

Claims ; Par. Nos. [0021], [0026] to [0043] 

(Family: none) 



[x] Further documents are listed in the continuation of Box C. Q See patent family 




Form PCT/ISA/210 (second sheet) (July 1992) 



13 



EP 1 040 937 A1 



INTERNATIONAL SEARCH REPORT 


International application No. 
PCT/JP98/05717 






C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT 




Category* 


Citation of document, with indication, when appropriate, of the relevant passages 


Relevant to daim No. 




Y 
Y 
Y 


JP, 8-258418, A ( Hitachi, Ltd. ) , 
8 October, 1996 (08. 10. 96), 

Claims ; Par. Noa. [0008], [0032], [0043] to [0074] 
& US, 5753413, A 

JP, 59-171045, A (Hitachi,Ltd.), 

27 September, 1984 (27. 09. 84), 

Claims ; page 2, upper right column to page 3, lower 
right column (Family: none) 

JP, 60-164937, A ( Hitachi, Ltd. ) , 

28 August, 1985 (28. 08. 85), 

Claims ; page 2, upper right column to page 3, lower 
right column { Family s none) 

jp, 2-217289, A (Mitsui Petrochemical 

Industries, Ltd. ) , 

30 August, 1990 (30. 08. 90), 

Claims ; page 3, upper right column to page 5, lower 
right column (Family; none) 


3-5 
6, 7 
6, 7 

5-7 













Form PCT/ISA/210 (continuation of second sheet* tfulv 1992* 



14