SPECIFICATION
OPTICAL RECORDING MEDIUM AND METHOD OK MANUFACTURING SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical record.! rig medium and a method of manufacturing the same, arid more particularly, to an opt. ica: recording medium which includes a reflective film made of a 1 urn i num or a I urn i m:rr alloy, which can be used in an optical recording/reproducing «ppo rat.us using a short-wavelength laser, and a method of manufacturing the opt. i ca i recording medium.
2. Description of the Related Art
An optical recording medium such as CD and DVD, by way of example, contains a reflective film irrespective of its recording/rep rod uc i ng system • Generally, this reflective film is made of aluminum, gold, s i 1 ver, or a i '< oy thereof, or silicon. For example, an optical disk such as CD, DVI) and the like employs a thin film made of an aluminum alloy or gold, wh i '. e the DVD employs a translucent film made of a thin pure gold fi 1 in or a thin pure silicon film.
In an optical recording apparatus which uses a blue Laser at wave ! enqt M, of approximately 400 nrn for recording or reproduction, a gold en si 1 icon thin film cannot provide a sufficient reflectivity as a reflect i ve f : ''• rn of those recording media . Also, there have been prob] ems w i th a go 1 d a i i ov which involves a high cost, and with silver which is regulated by " r-'o I i utant Release and Transfer Register" regulation (PRTR).
Here, aluminum and aluminum alloys are highly advantageous over qola alloys in view of the cost and handling. On the other hand, oar I. icuiarly for a laser spot size of an optical recording apparatus based on a blue

laser, represented by Blu rayDlsc, ithasbeenquitedif f:i cu I t to su f I icientiy rediace the crystal grain diameter of such aluminum-based thin f i I ins, i . o. , specifically to a size smaller by an order of magnitude or more. For t h i s reason, a disk which employs an aluminum-based reflective 1 i Itn has suf f ored from large noise during recording and reproduction, thereby (a i I ing to accomplish sufficient recording/reproducing characteristics. SUMMARY OF THE INVENTION
It is therefore an object of the present invention to prov i dc a record i nq medium which, though having a reflective film made of a I urn i nurn or a 1 uin i nuin alloy which is desirable in view of the cost and handl i.rig, offers good recording/reproducing characteristics in an optical record i rig/roproduc i nq apparatus using a short-wavelength laser, and a method of manufacturing the recording medium.
An optical recording medium according to the present invention has i reflective film, wherein the reflective film includes an a 1uminum« 1 loy, ind an oxide of a metal other than aluminum.
Further, a met hod of manufacturing an optical record.! ng mod '. urn accord i rig ;o the present invention includes a step of forming a ref lectivo I i 1 in on i substrate by a sputter ing method. The method further i nc 1 ucies an a t mosplic i v forming step for introducing an oxide of a metal other than aluminum , nt o i sputter atmosphere together with an aluminum alloy, arid a step of 1 am i na t. ', nq :he oxide on the substrate together with the aluminum alloy. 3RIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional view of an optical disk;
Fig. 2 is a graph showing the reflectivity arid noise with respect, to the content of M (=Au) in an optical disk according to a second embodiment. of the present invention;
Fig. 3 is a graph showing the reflectivity and noise with respect to the content of M (.-Pd) in an optical disk according to a second embodiment

of the present invention;
Fig. 4 is a graph showing jitter of an optical disk according to a fourth embodiment of: the present invention, and the: re( loctivity of a reflective film which is included in the optical disk;
Fig. 5 is a graph showing the reflectivity and noise with respect to the content of M (---Pt) in an optical disk according to a fifth embodiment, of the present invention; and
Fig . 6 isacross - sectional view of a reproduction-only typed i sk ,;c:cor;i i i u to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION
An optical recording medium according to the present invent, ion will be described with reference to the accompanying drawings.
As shown in Fig , 1, the optical recording medium accord i ng to the present. invention, though not limited to the illustrated one, has a muIti layer structure which is composed, by way of example, of a reflective f i I in layer 12, a second protective layer 13, a recording film Layer 1-1, and a f i rst protective layer 15, which are laminated on a disk shaped substrate 1! in this order by a sputtering method, arid a resin cover layer- 16 which is adhered to the laminate . Light for recording or reproduc i nq i n ( orma t. i on is given to the recording film layer 14 from the resin cover layer 16 side .
The reflective film layer 12 isproducedwitha sputter i ng ta rget composed of pure aluminum or aluminum alloy added with an oxide of a metal other than aluminum, by a sputtering method. The sputtering target, on '..he other hand, may be made by a cosputter-based method which divides the target into a plurality on a material-by-material basis, such as an a 1 urni num a 1 I oy and an oxide of a metal other than aluminum,- aluminum, a metal element (or metal compound) , and an oxide of a metal other than aluminum,- and the like. Specifically, an oxide of a metal other than aluminum is i-.troducod into a sputter atmosphere together with aluminum or aluminum al I oy . '. n

this way, the reflective film layer 12 is formed of pure a I urn i num or a I urn i riurn alloy which traps therein an oxide of the metal other than aluminum. Thin;, the crystal grains can be maintained small without reduc i rig the ref i eet i v i ty . For suppressing noise during recording and reproduction to a su( I icioitf ly practical level to improve the recording/reproducing characteristics, it. is contemplated that an average crystal grain diameter of the ref Icctivc film layer 12 is preferably smaller than a laser spot si/e (diameter) d. Forfurtherimprovingtherecording/reproducingcharacteri st i cs, the a vet age crystal grain diameter of the reflective film layer 1 2 i s p ref crab 1 y sma ! ; c : than the laser spot size d by half, more preferably one ( ifth, arid most preferably one-tenth of the laser spot size. Such a reflective f i 1m can stablyexhibi t good recording character is tics even if i t i s used , for cxamp I c ,, in a recording medium which is optically recorded arid reproduced by n short-wavelength laser such as a blue laser.
More specifically, the laser spot size (diameter) d in a laser based
optical recording apparatus is given by d=A,/NA, where A. represents the laser wavelength, arid NA the numerical aperture. Kor example, assuming
that X=400 nm arid NA-0.85, d is calculated to be 470 rim. Typical ly, the-average crystal grain diameter of the reflective film layer made of pute aluminum or aluminum alloy containing an oxide of a met a 1 other t hari a 1 urn i num, according to the present invention, is smaller than-47 nm wh i ch i s one t ent h the aforementioned value of d.
Here, when an oxide of a metal other than aluminum is introduced into a sputtering atmosphere together with aluminum or aluminum alloy for sputtering, the oxide is shattered by a discharge and trapped into the: film. The oxide impedes the growth of crystal grains of a 1 urn i num or a Lurn i num alloy, which comprises the reflective film layer 12, during a deposition process, so nhat the crystal grains can be maintained to be very sma1 1 . It is generally thought that the addition of an oxide to a reflective I : I m

is not preferable because of a resulting reduction in the reflectivity. However, as described Later, the reflective film according to the present invention exhibits a high reflectivity and good record i ng/ rep roduc i ng character! sties even i.f an oxide is added to the reflective f i 1m. Presurnab i y , this is because the miniaturization of the average crystal grain diameter of the aluminum alloy largely contributes to a reduction i n the re f lect. i v i t v due to the addition of the oxide.
The present invention is particularly character:! xed by the rc-f leot. :ve film layer 12 of the recording medium, and in examples described below. the reflective fiIm layer 12 does not depend on the type and number ol protective layers 13, 15. The protective film may be made of such: material as, for example, a metal compound such as a metal nitride sucn as /nS, S:iO2 or the like, a metal, oxide, a meta.l carbide, a metal nu I f ide or the like, or a mixture thereof.
The recording film layer 14 is also similar in that the recording f i 1m layer 14 can be made of a different material as required. Kor example . when the recording film layer 14 is made of a phase changing rruterial siu-h as SbTe, such a recording disk can serve as a rewritable recording disk. Alternatively, when the recording film layer 14 is made of a pigment i i In , the resulting disk can serve as an organic pigment record i ng d i sk . I n ot.h< r words, the recording film layer 14 can be widely used in recording rne.fi i a which utilize an optical reflective film. For example, it can be used in an optical recording or a magneto-optical recording medium in a shape other than a disk shape, such as a card type one. In addition, it can be appl i ed to a cooling layer of a heat assist magnetic recording medium. [Example 1]
A description will be given of a recording medium 1 according to a first example of the present Invention.
A spiral groove at a pitch of 0.320 jam was formed in a dink shaped

substrate 11 made of polycarbonate resin which had a thickness of 1.l mm and a diameter of 12 cm. On this substrate 11, a reflective fi 1m layer 1 2 made of Al ~SriC>2 , a second protective layer 13 made of ZnS S i O;>, a recording film layer 14 made of Bi-Ge-N, and a first protective layer i ':< ma or 0! ZnS-S.iO2 were laminated in this order by a sputter ing met hod . The sputte i i rig power was chosen to be 2000 W. Table 1 shows the layers of the recording medium disk together with their materials arid thicknesses.
Table 1

Layer
Reflective Film Layer Second Protective Layer Recording Film Layer First Protective Layer

Material
Al-SnC>2
ZnS-SiO2
Bi-Ge-N
ZnS-SiO2

Thickness 50 nm 20 nm 12 nm 25 nm

Further, a polycarbonate sheet was adhered to the laminate ( rom above using ari ultraviolet curing resin for an adhesive to fabricate a 1 ighi incident side substrate (cover layer) 1.6 of 0.1 mm thick.
Here, in the first example, two types of recording medium d'sks were fabricated by changing the amount of SnO2 in the ref I.active ( i Im l.iy<. : 12. Specifically, in a process of forming the reflective I'ilm layer 12 by a sputtering method, two types of sputter targets were prepared, I.e.. one containing 0.4 atom% of SnC>2, and the other one containing (; . 6 a;.oir.'!-; of Sn02 for deposition. Resulting reflective layers 12 had two Different compositions with 0.13 atom% and 0.25 atom% in atomic ratio of SnO;;, respectively . As wil 1 be understood from this result, a f i 1 in can be; p roaucod with an atomic ratio of SnO2 which is approximately one th i rd of the atomic ratio of SnC>2 in the sputter target. The respective record i rig men i urn <; i <;kr, are called the "disk la" and "disk 1 b," respectively.
With the two types of disks 1-a, 1-b, a 1-7 modulation randon pat.foin was recorded on a guide groove surface in a convex shape on the 1 ight i ncideni.

side at a line velocity of:" 4 . 92 rn/s using an optj cal head having a wave 1 enqt.h of 405nmandanob j eetive; Lens withanumerical apertureof 0 . 85 . Mu I t i pu i sos were used for this recording, with a window width being sot t.o l'>. 15 n:;oc . Table 2 shows total noise, recording LD power, arid post, recording jitter which were measured for the disks la, 1-b.
Table 2

(Table Remove)
Post Recordi ng
Jitter
6.5%
6.6 %

Thus, either of the disks can exhibit good post - record i rig j ill.or.
For reference, when the reflectivity was measured for each ref led ivo film which had been formed in a similar method of the disks 1 a, 1 u, the measured values were 55 % and 56 %. Stated another way, even a rof lcct. ivt film containing an oxide has a reflectivity as high as the rei iectiviiy of a reflective film made of a simple metal. More specifica1 ly, since an oxide general ly exhibits a very low deposition rate of sputter i ng as compn rrd with a simple metal arid an alloy, a small amount of oxide will be cont.ainod inadepositedfilm, withsmal 1 contributions toareductlori i ntho ref 1 cot. i v , ' y as a reflective film.
Also, SnO2 in the reflective film layer 12 may partial ly lose oxygen to produce SnOx (x<2) , but is was confirmed that such SnOx does not af feet the effect of impeding the growth of crystal grains of a 1 urn i nurn or a 1 uni i num alloy, which comprises the reflective film layer 12, during the deposition process.
The recording film layer 14 may be a recording film wh.i ch ma i n i y coi .ta i n a nitride of Bi, Sn, Fe, and one or a plurality of nitrides of Go, Ti . Si, Al. [Example 2]

A description wi]l be given of a recording medium 1 accordirig to n second embodiment of the present invention.
A spiral groove at a pitch of 0.320 |.tm was formed in a disk shnprd substrate 11 made of polycarbonate resin which had a thickness of 1. i mm and a diameter of 12 cm, as is the case iri the first example . On t h i s subst ra t c 11, a reflective film layer 12 made of Al-M SnO2 "(M is Pd or An, deta Is of which will be described later), a second protective layer 1 .-! made ol ZnS-Si02, a recording film layer 14 made of Bi-Ge-N, and a f i rst protect i ve layer 15 made of ZnS-Si02 were laminated in this order by a sputtering method. The sputtering power was chosen to be 700 W. Table 3 shows (.he-layers of the recording medium disk together with their materials and thicknesses.
Table 3

Layer
Reflective Film Layer Second Protective Layer Recording Film Layer First Protective Layer

Material
Al-M-Sn02
ZnS-SiO2
Bi-Ge-N
Zn.S-Si02

Thickness 50 rim 20 nm 12 nm 25 nm

Further, a. polycarbonate sheet was adhered to the laminate from a Dove using an ultraviolet curing resin for an adhesive to fabricate a light incident side substrate (cover layer) 16 of 0.1 mm thick.
Here, in the second example, two types of recording medium disks were fabricated by adding different metals to the reflective f i. 1m layer 12 wnich contained the same oxide as that of the first example. Specif' ica 1 iy, in a process of forming the reflective film layer 12 by a sputtering methon, two types of sputter targets were prepared, i.e., one added with Pri and the other one added with Au, for deposition. The result ing ref lee" \v f ; i in layer 12 added with Pd had 3 . 55 atom% of Pd in atomic rat i o, wh i 1 e resu ! t ng reflective film 12 added with Au had 3.84 atom% of Au in atomic i ;u. i c. .

The respective recording medium disks are called the "disk 7. a" and "disk 2-ta," respectively. The amount of SriC>2 contained in the aloremem ioned sputter targets was 0.4 atom% in common, and either of the disk;-; 2 a, '/. h contained 0.13 atom% of SnO2 in the resulting reflective film layer i:': . In other words, each of the disks 2-a, 2-b has the ref l.ective film layer 12 in the same composition as that of the di.sk 1 in the ( i rst example. For the two types of disks 2-a, 2-b, total noise, recording 1,1) power, arid post-recording jitter were measured under similar conditions to t he-first example. Table 4 shows the total noise, recording I,I) power, and post-recording jitter which were measured for the disks 2 a, 2 b.
Table 4

(Table Remove)
Post Record i ng Jitter 5.9 % 6.1 %

Thus, either of the disks can exhibit good post - record i ng j ', tter, ,-js is the case in the f irst example . As described above, i n the second cxanu> •. e the sputtering power in the process of forming the reflective f i I m layer 12 is lower than that in the first example. A reduction in the sputter inq power promotes the growth of crystal grains during the depos i t- i on , resu I t i ng in increased noise and jitter. However, in the second example which uses lower sputtering power than the first example, the second example can have even better characteristics than the first example from the fad. that. it. can accomplish total noise and jitter close to those exhibited by •....he f i rst. example.
When the reflectivities of the reflective films, formed in a si mi . ar method to the disks 2-a, 2-b, were measured in a simi lar method to the first example , the measured values were 53 % and 50 % , respectively. Likewise--, in this result, the reflective films 12 have high reflect i v i t: i en ecu i va ! eni.

to that of a refJective film made of a simple meta.l .
The available additive metal M may include Pt, T1 , Pb, Bi, Os, '> r . Ru, Rh, In, Sn, Ni, Zn, Cu, Cd, Ti, 7,r, Hf, V, Mb, Ta, Cr, Mo, W, and Vr , in addition to the aforementioned elements. A composit ion of a p1uia i i ty of these elements may be used as well. Further, sirni lar off ecus can L>o produced as well using an alloy to which a trace of third arid f ourth c I emont s is added.
Next, in the disk having the reflective film layer made of Al M SnO;? (M is Pd or Au) , disks were created with varying contents of M to exam inn the influence of the contents of M exerted to the characteristics of the disks. A spiral groove at a pitch of 0.320 |Lim was formed in a di.sk shaped substrate 11 made of polycarbonate resin which had a thickness of u ! mm and a diameter of 12 cm. On this substrate 1.1, a reflective f i nn layer 12 made of Al-M-SnO2 (M is Pd or Au) was laminated by a sputtering met ..hod . The sputtering power was chosen tobe 300 W, and the thickness of the ref lor' : v..: film thickness 1.2 was chosen to be 50 nm. Here, for direct, ly obso i v ' rig changes in the characteristics of the reflective film . ayer 1 :••: due to a varying content of M, none of a second protective layer 13, a recording film layer 14 made of Bi-Ge-N, and a first protective film 15 made of XnS S i O;> was formed, and a polycarbonate sheet was adhered onto the ref led. i ve t i I rn layer 12 using an ultraviolet curing resin for an adhesive to fabricate a light incident side substrate (cover layer 16) of 0.1 mm thick. As s,;ch, the formation of the reflective film layer 12 will only bo described below.
The reflective film layer was formed using a sputtering target maao of an aluminum alloy added with an oxide of a metal other than aluminum by a sputtering method. Severa 1. targets were prepared wi th a va r y i riq onnt or t of Pd or Au in the a luminum alloys . When Au was added, resu 1 f i rig re f I on : ve film layers contained 0, 1.73, 3,38, 4,95, 7.82, and 11.--K) atom% o! An by the sputtering method using the targets. When Pd was added, result ing

reflective film layers contained 0, 0.04, 0.65, 1.52, 2.4V, 4.81, '/. 5:,, 9.20, and 11.20 aLom% of Pd. These reflective film layers were prepared on disks in a similar method through the aforementioned processes. For measuring the reflectivity of the reflective film layer alone, composed of the aluminum alloy containing Pd or Au and the oxide, for purpose's ol comparison, a sample was also created by forming a reflective f i 1m layer alone on a flat plate, other than the preparation on the disks.
First, a measurement of the reflectivity of the aforementioned sample having the reflective film layer alone on the flat plate? was made. Further, the reflectivity and noise were measured for the di.sks (not .shown) formed onlywith the reflective film layer 12 . The noise wasmeasure.dat two local, ions on the groove and Ln the groove on the convex guide groove surface on the light incident side. The results of the foregoing measurements arc shown in Figs. 2 and 3.
As can be, seen from Fig. 2, in the disk which includes the A i An SnOy
reflective film layer added with Au, noise is largely reduced as compare/a withadisk includinganAl -SnC>2 reflective filmlayer. Howeve r, the rednet i on in noise reaches a minimum when about 1.5 atom% of Au is added, and us the amount of Au is subsequently increased, the noise levels at a constant. value approximately between 46.5 dB arid -47.0 dB, though it exhibits a slight increase. Stated another way, with the addition of a certa i n amount. or more of Au, improvements on noise of approximately 2 dB on the groove., and approximately 1 to 2 dB in the groove aree measurecj as compared w:i h a reflective film which is riot added with Au. On the other hand, t he mi \ re>' reflectivity and disk reflectivity monotonously decrease us the amour.t. of added Au is increased. The disk reflectivity has~a si i grit i y 1 a rqer s 1 ope' than the mirror reflectivity.
From the foregoing results, the amount of added Au is preferably ' atom% when a reduction in the disk reflectivity is permittee! up to in % ,

more preferably 5 atom% when a reduction in the d.i sk ref 1 ect, i v i t.y i s oe rm i t. Led up to 8 %, and further more preferably, 3 atom% when a reduction in the disk reflectivity Is permitted up to 6 % . Most preferably, the amount, o: added Au is 2 atom%, in which case a reduction in nose is maximixed.
Next, as can be seen from Fig. 3, in the disk including the Al Pd 5;nO;,> reflective film layer added with Pd, noise is largely reduced as we? i I , as compared with the disk including the Al-SnO2 reflective f i Im layer. However, while a reduction in noise reaches a minimum when approximately 0.6 atom% of Pd is added, the noise slightly increases subsequently, but. levels at a constant value approximately between -47.0 dH and A 8.0 dh. Stated another way, with the addition of a certain amount or more of Pd .. improvements on noise of approximately 1.5 dB can be measured boi h on thu groove and in the groove, as compared with a reflective (Mm whieh i ;.:• not addedwithPd. Ontheotherhand, themirrorref lectivityaridd i sk ref loot ivity monotonously decrease as the amount of added Pd is increased.
From the foregoing results, the amount of added Pd is preferably 8 atom% when a reduction in the disk reflectivity is permitted up to 10 -;,, more pref erab ly 6 atom% when a reduction in the disk ref 1 ect i v i ty i s pe rm i t ted up to 8 %, and further more preferably 3 atom% when a reduction in the disk reflectivity is permitted up to 6 %. Most preferably, the amount ol added Pd is 0.6 atom%, in which case a reduction in nose is maximixod. [Example 3]
A description will be given of a recording medium 1 according to i third example of the present invention. In this example, the dc<,cr i pt. i on will focus on total noise, recording LD power, and post recording i h.tcr when the amount of SnO2 is varied iri the deposited ref lective f ; ! m layer 11 .
A spiral groove at a pitch of 0.320 (.im was formed in a disk shaped substrate 11 made of polycarbonate resin which had a thickness of 1.1 mm

and a diameter of 12 cm. On this substrate 11, a" reflective f i i in 1-rye i 12 made of Al-SnC>2 (or pure aluminum), a second protective I aye 1 i made of ZnS- Si02 , a record ing film layer 14 made of Bi -Ge - N, and a f i rst protect i ve layer 15 made of ZnS-SiO2 were laminated in this order by a sputtering method. The sputteringpower was chosen to be 700 W. Further, a po 1 yea rbonaLe sheet was adhered to the laminate from above using an ultraviolet curing resin for an adhesive to fabricate a light incident side substrate (cover layer) 16 of 0.1 mm thick.
In this example, in a process of forming the reflective Him layer 12 by a sputtering method, several sputter targets were prepared by adding SnC)2 chips to pure a luminum targets as appropriate, and di sks we: re; f a br i ca t.c d with the amount of SnO2 being varied from zero to 5.0b atom'% within t-!;e deposited reflective film layer 12. Table 5 shows measured total noi.st. , recording LDpower, and post-recording j itter of the disks . The measurement ;; were made by the same method as in the aforementioned embodiments.
(Table Remove)
As described in the second example, as the sputtering power is reduced.
the noise and jitter increase. Here, the result of the experiment, reveals that the jitter increases by approximately 2 % when the sputter-ing power-is reduced from 2000 W to 700 W. Thus, in the third example, satisfactory j itter equivalent to that in the first and second examples can be accomp I i shed by increasing the sputtering power to 2000 W under the conditions of the disks 3-3 to 3-10.
Also, any of the disks exhibits a high reflectivity measured (or the-reflective films alone, equivalent to the reflectivity of a reflective film made of a simple metal.
Referring now to Fig. 4, the amount of SnO2 is preferably equal to or more than 0.02 atom% and less than 1.0 atom% arid equal to or more t han 1 . 8 atom% . More preferably, the amount of SnO2 is less than 2 . !> a tonVk booa ur-^ the reflectivity is lower in the disks 3 -6 to 3 -10 . Note: that such corid i t i or.:; need not be taken into consideration if the reflectivity can be suf t i c i ent i y compensated for by other layers such as the recording film Jayer 14. [Example 4]
A description will be given of a recording medium 1 according !o a fourth embodiment of the present invention. In this example, though not limited, the recording medium 1 is an optical disk which has a rcf loctivo film layer 12 added with TiO or Nb2O3 which is a different oxide; from that used in the first to third embodiments. In other words, any ox-de may bo used as long as it impedes the growth of crystal grains of a!-..mi nun, or aluminum alloy which comprises the reflective film layer 1 .< during U,< deposition process.
A spiral groove at a pitch of 0.320 jam was formed in a disk shaped substrate 11 made of polycarbonate resin which had a thickness ol 1.1 mm and a diameter of 12 cm, as was the case in the first and second examples. On this substrate 11, a reflective film layer 12 made of TiO or Ntvy')^, which is a different oxide from that used in the first and second embod i iri^ni ,
a second protective layer 13 made of ZnS~S:i02, a recording f i 1 in layer II made of Bi-Ge-N, and a first protective layer 15 made of XnS SiO;> were laminated in this order by a sputtering method. The sputtering power wan chosen to be 700 W. Table 6 shows the layers of the recording mod i urn disk together with their materials and thicknesses.
Table 6

Layer
Reflective Film Layer Second Protective Layer Recording Film Layer First Protective Layer

Material Al-TiO (or
ZnS-Si02
Bi-Ge-N
ZnS-SiO2

Thickness 50 nm 20 nm 12 nm 2 5 rim

Further, a polycarbonate sheet was adhered to the laminate from above using an ultraviolet curing resin for an adhesive to fabricate1 a 1 ight. incident side substrate (cover layer) 16 of 0.1 mm thick.
Here, in the fourth example, two types of recording medium disks worn fabricated with different oxides added to the reflective f i I in layers \ ".••.. Specifically, in a process of forming the reflective film layer \'.>. by a sputtering method, two types of sputter targets were; prepared, i . e. , one added with TiO chips and the other one added with Nb^O3 chi ps , for depos i t i or The respective recording medium disks are called "disk 4 a" and "disk 1 b, " respectively.
For the two types of disks 4-a, 4-b, total noise, recording l,l) powei ,. and post-recording jitter were measured under similar conditions ro tin-first and second examples. Table 1 shows the total noise, recording 1,1) power, and post-recording jitter which were measured for the disks '.-. u, 2-b.
Table 7

Total Noise

Recording LD Power

Post Record i nc Jitter

Disk 4-a Disk 4-b

-38.6 dB -38". 6 dB

6 mW 6 mW

10.0 9.7 £

The disks 4-a, 4-b present a good result of reduced post, record ing jitter, as compared with the disk 3-1 of the third example which has no oxide added to the reflective film layer 12.
When the reflectivities of the sole reflective films, formed i n a s i m i I a r method to the disks 4-a, 4-b, were measured, and the measured va ues were 56 % and 55 %, respectively. Likewise, the reflective f i Ims have: high, reflectivities equivalent to that of a reflective fUm made of a simple metal. [Comparative Example]
A comparative example will be described for a recording ined imi which includes a reflective film layer that does not contain any oxide.
The recording medium of the comparative example is the same as the recording media according to the aforementioned first and second examples of the present invention except for the reflective film layer . Tot. a 1 no i so , recording LDpower, andpost - recording j itter were measured for the recording medium according to the comparative example in a si.mi lar method.
Specifically, a spiral groove at a pitch of 0.320 f.im was formed i r. a disk-shaped substrate 11 made of polycarbonate resin which had a fh i oknesn of 1.1 mm and a diameter of 12 cm. On this substrate 11 , a ref loctivc i 1m layer made of Al or Al-SnO2 / without containing an oxide, a second protect :>,,e layer made of ZnS-SiC>2, a recording film layer made"of Hi Ge N, ami a f i r.st. protective layer made of ZnS~SiO2 were laminated in this order by a sputte r i rig method. The sputtering power was chosen to be 2000 W DC for the recording medium having the reflective film made of Al, and 700 W DC for the record! ng medium having the reflective film made of Al-Pd (4 .1 atom%) . The respect i vo layers had the; same thicknesses as their counterparts in the f i rst and second examples. Also, the comparative example is simi lar in that a

polycarbonate sheet was adhered to the laminate from above us i ng an u I L rav i a 1 ot curing resin for an adhesive to fabricate a light incident side sub:;t.rate: (cover layer) 1.6 of 0.1 mm thick.
With the disk: as described above, total noise, recording 1,1) powei , and post-recording jitter were measured under similar conditions to the aforementioned examples . Table 8 shows the total noise, record i ng i,l) power, and post-recording jitter which were measured for the disks ha vino the Al reflective f i Lm Layer and the A] -Pd reflective film 1 ayer , respect i ve i y .
Table 8

Al Reflective Film Disk Al •Pd Reflective Film Disk

I'l'otal Noise
42.0 dB
--45.1 dB

Recording LD Power
5 mW
6 mW

Post Record i ng
Jitter
7 . h %
6.9 %

In comparison with the first and second examples described above, the comparative example failed to exhibit satisfactory jitter, though there is not a large difference in the disk, noise. Specif i ca I ly, it. .should he understood that the recording media 1 according to the examples ol tie present invention can improve jitter in particular with the addition o an oxide of a metal, other than aluminum, to the reflective f i I in made' of aluminum or aluminum alloy. However, a satisfactory di.sk no 1st: value i :• notalwaysassociatedwithasatisfactoryrecordingj itterva I tie . Genera i iy, a thermal distribution is produced within the reflective f i 1m oepend.i ng on the size and shape of crystal grains. Therefore, even record rig media producing the same disk noise exhibi.t different jitter due to GiMereiit thermal distributions if they differ in the size and shape of crysta I gi a i ns of their respective reflective films.

[Example 5]
A description will be given of a recording medium "I according to a fifth example of the present invention.
An investigation was made on the influence of the content, of Pt on the characteristic of a disk having a reflective film layer made of A I Pt Sn(>> by creating such disks with different contents of Pt. A spi ra 1 groove: at. apitchof 0 . 320f.imwasf ormedina disk-shapedsubst rate 11 made of po i yea rbonat o resin which had a thickness of 1.1 mm and a diameter of 12 cm. On this substrate 11, a reflective film layer 12 made of Al-Pt SnO;; was i dm i na t ,od by a sputtering method. The sputtering power was chosen to be JOO w, a no the thickness of the reflective film layer 12 was chosen to be bO rim. Here, for directly observing changes in the characteristics of the ref Irctive film layer 12 due to a change in the content of Pt, none of a second protect i ve layer 13, a recording film layer 14 made of Bi-Ge-N, and a f i rst protect ive film 15 made of ZnS-Si02 was formed, and a polycarbonate sheet was adhered onto the reflective film layer 12 using an ultraviolet curing resin tor an adhesive to fabricate a light incident side substrate (cover layer 1 f~} of 0 .1 mm thick . Subsequently, the reflective film layer 1 7, a I ore war, f orrned ,
Further, similar to the fist and second examples, a mi nor ref 1 oct i " t.y was measured for the aforementioned sample which had an A1 Ft-SriO? ref led : vo film layer alone formed on a flat plate. Further, -a disk ref led. i vi ty and noise were measured for the disk (not shown) formed only wi th the ref I oet. '. ve film layer 1.2 . The results of the foregoing measurements arc shown i n Tab! e 9 and Fig. 5.

(Table Remove)
As is apparent, from Table 9 and Fig . 5, 0.4 atom% or more of Pt, c.:oru,a i nod in the reflective film layer, ensures a noise level improving effect of , for example, 0.5 dB or more, as compared with a reflective f i 1m layer which is not added with Pt. On the other hand, since a larger amount, of added Pt results ina lower reflectivity, alargeamountofadditi on :i s not prof crab I o because the reflectivity becomes extremely low, when such a rcf leotivo film layer is appl led to a recordable disk, causing dif f icu 1 t i es i n record i ng and reproduction. Assuming that up to 10 % of reduction in reflect ivity is permitted with respect to a reflective film layer not addec with Pt., an upper limit of the amount of added Pt is 5 atom% . Consequently, an opt i nia 1 range for the amount of added Pt is 0.4 atom% or more and b atorn% or less, and more preferably, 0.4 atom% or more and 1 atom% or less. Ku i -tnt-i , as is apparent from Table 9 and Fig. 5, the noise level improving effect is expected even in a range for the amount of added Pt equal to or more than 0.1 atom% and equal to or less than 0.4 atom%. [Example 6]
Refferring to Fig. 6, explanation will be made on a further embodiment, of the present invention in which the reflective film layer 12 made; ol Al-Pd-SnO2 is provided in a reproduction-only type disk . 1 n order to con! i nn the effect of the present invention, a reproduction jitter of tnr
reproduction-only disk of this embodiment was compared w:i th the reproduc;. i on jitter of a reproduction-only type disk having a conventional ref lectivr film layer made of AT Ti.
As shown in Fig. 6, a disk-shaped substrate 11 made of polycarbonate resin having a thickness of 1.1 mm and a diameter of 12 cm was used for this embodiment. A pit train in spiral form with a pitch of 0.320 uir was formed in the substrate 11. The recording information i.s hold in the- pi; train. In this embodiment, 1-7 modulated signal of random data was recorded as a pattern having a minimum pit length of 0.149 \m. The recording capaco t.y of the disk was 2b GigaBytes,
On the substrate 11, a reflective film layer 12 made of Al Pd SnO;.; was formed by sputtering.
Since the disk of this embodiment is solely for reproduct i on, the record i ng film layer 14 made of Bi-Ge-N, and the first protective layer } l, madr of ZnS-SiC>2 were not formed. Instead, a polycarbonate sheet was adhered to the reflective fiim 12 from above using an ultraviolet cur-ing resin UM an adhesive to fabricate a light incident side substrate (cover layer) 16 of 0.1 mm thick.
As an example of the conventional disk, a reflective layer made: of A. Ti was f ormedbysputte ringonasubstratewhichwasthesameas theabove dose i" • be