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United States Patent [191 [11] Patent Number: 4,786,538 Saito et al. [45] Date of Patent: Nov. 22, 1988

[54] OPTICAL RECORDING MEDIUM FORMED 4,500,889 2/1985 Wada et al. .. 430/945 OF CHALCOGENIDE AND METHOD 4,579,807 4/1986 Blonder et al...... 346/1351 FOR PRODUCING THE SAME 4,645,685 2/1987 Murayama . [75] Inventors: Koichi Saito; Hideki Kobayashi, both FOREIGN PATENT DOCUMENTS 1 of Kurashiki; Junji Nakagawa, 54-3725 2/1979 Japan . Ichikawa; Yoichi Murayama, Tokyo, 58-7394 l/1983 Japan . all of Japan 58-158056 9/1983 Japan . 0203094 11/1983 Japan ...... 346/1351 [73] Assignee: Kuraray Co., Ltd., Okayama, Japan 58-189850 11/1983 Japan . [21] Appl. No.: 82,909 60-179956 9/1985 Japan ...... 346/1351 [22] Filed: Aug. 10, 1987 Primary Examiner-John E. Kittle Assistant Examiner-Betsy Bozzelli Attorney, Agent, or Firm-Armstrong, Nikaido, Related U.S. Application Data Marmelstein & Kubovcik [63] Continuation of Ser. No. 808,572, Dec. 13, 1985, aban doned. [57] ABSTRACT [30] Foreign Application Priority Data Metal is vaporized under the atmosphere of gas and/or inert gas formed into a plasma by a Dec. 13, 1984 [JP] Japan 59-264128 high frequency power to thereby form a tellurium oxide Dec. 13, 1984 [JP] Japan 59-264129 (TeOx, OéXéZ) layer. The tellurium oxide layer Dec. 13, 1984 [JP] Japan 59-264130 formed in accordance with the present method is stabi Dec. 13, 1984 [JP] lized, and a suboxide having a high sensitivity which has Dec. 13, 1934 [JP] , Japan been considered to be unsuitable as an optical recording Dec. 13,1984 [JP] ‘medium due to the lack of stability can be utilized.

[51] 1111. cu ...... G11B 7/24 High frequency power, gas pressure and vaporization [52] U.S. c1...... 428/64; 428/701; speed of metal tellurium can be varied to thereby vary 430/271; 430/273; 430/945; 346/1351 the value X of TeOx from 0 to 2. When the TeOx ?lms [58] Field of Search ...... 430/945, 271, 273; whose value X thicknesswise is different are formed 428/64, 701; 346/1351 continuously within one and the same vessel and the vaporization speed is made to zero, oxidization of a film [56] References Cited surface may be carried out. Thereby, the T602 ?lm may U.S. PATENT DOCUMENTS be formed on the surface, and an optical recording medium may be obtained which is extremely stable and 3,971,874 7/1976 Ohta et a1...... 428/432 4,370,391 l/1983 Mori et al...... has excellent adhesive properties between the substrates and between the layers. 4,385,3764,403,231 9/5/1983 1983 TakaokaAndo et al.et al...... 4,433,340 2/ 1984 Mashita et a1...... 430/945 7 Claims, 1 Drawing Sheet US. Patent Nov. 22, 1988 4,786,538

FIG.

I’ IIIIIII'I'I'I‘ FIG.

F/G. 4,786,538 1 2 sheet, a polycarbonate sheet etc. are used, these materi OPTICAL RECORDING MEDIUM FORMED OF als are relatively large in gas transmission rate, therefore CHALCOGENIDE OXIDE AND METHOD FOR posing a problem in that vapor, oxygen and the like PRODUCING THE SAME enter with the passing of time to oxidize the ide suboxide, thus reducing the sensitivity. This application is a continuation of application Ser. Many techniques intended to improve the stability of No. 808,572, ?led Dec. 13, 1985, now abandoned. the chalcogenide group recording media have already been disclosed, for example, such as scattering into BACKGROUND OF THE INVENTION metal having good corrosion-resistance (Japanese Pa 1. Field of the Invention tent Application Laid-Open No. 164,037/ 83), coating The present invention relates to an optical recording with an organic material (Japanese Patent Application medium, and particularly to an optical recording me Laid-Open Nos. 21,892/81, 125,248/83 and dium formed of a chalcogenide oxide that may be re 203,643/ 83); coating with an inorganic material Japa corded and erased by light, preferably, formed of a nese Patent Application Laid-Open No. 199,449/83); tellurium oxide, and a method for producing the same. forcible oxididation of a surface (Japanese Patent Appli More speci?cally, the invention relates to an optical cation Laid-Open Nos. 3,442/81, 94,144/83, 189,850/ 83 recording medium whose optical recording properties and 2,245/ 84), which often involve cumbersome opera are retained in a stabilized condition for a long period of tion, and insuf?cient effect). time and which has excellent adhesive properties rela tive to a substrate. 20 SUMMARY OF THE INVENTION 2. Description of the Prior Art Accordingly, it is an object of the invention to pro For the optical recording medium, there are known a vide an optical recording medium and method for pro system for forming small holes or bubbles by the heat ducing the same which improves the stability for a long energy of a laser beam and a system for varying the period of time. It is another object of the invention to optical characteristics of a ?lm. In the former system, 25 provide an optical recording medium and method for since a change of uneven shape occurs in a recording producing the same which display excellent effects also ?lm layer during the recording, the recording ?lm and in terms of adhesive properties relative to the substrate. the substrate are liable to change in quality and produce These objects of the present invention are accom corrosion with the passage of time, and therefore, usu plished by an optical recording medium in which by a ally two recording media are formed into an air sand metal tellurium vapor passing through oxygen gas and wiched construction for use. In the latter, however, /or inert gas formed into a plasma by a high frequency such construction is not necessary and two recording electric power, (a) a tellurium or tellurium suboxide media can be simply bonded together for use, and there (TeOx, 0§x<2) layer and or (b) a tellurium dioxide fore, this system has an advantage in that the manufac (T602) layer are laminated, or (a) a turing step may be simpli?ed considerably. Among (TeOg), (b) tellurium and/or a tellurium suboxide materials used for the latter system, there is known a (TeOx, 0§x<2) and (c) a tellurium dioxide (TeOZ) material having high sensitivity, that is, a material layers are laminated. Alternatively, an optical recording whose optical characteristics are greatly changed with medium can be used in which a ?lm is formed so that respect to a predetermined incident light intensity, such tellurium or tellurium oxide (TeOx) is formed and the as a chalcogenide oxide, particularly, a tellurium oxide 40 proportion x of the oxygen component in the direction TeOx, where x is 0<10-3 Torr, preferably, from 2X10"4 to 5X10-3 speed of approximately 12 A/sec. The thus formed ?lm Torr. Examples of the inert gas include argon gas, he 9 had the thickness of 0.1 pm, and the composition lium gas, gas and the like. wherein x=0.6 according to the Auger electronic spec Under this condition, a voltage of 50 to 500 Watt is 25 tral method. Next, a ?lm 10 was formed thereon at the applied to the spiral-shaped high frequency exciting coil reduced vaporization speed of approximately 4 A/sec. 4 to form a high frequency electric ?eld which excites This ?lm 10 had the thickness of 0.01 pm and composi the gas to produce a plasma. While the plasma produced tion wherein x=2.0. is controlled according to the shape and size of the coil, For the purpose of comparison, a material which the intensity of the electric ?eld and the vacuum degree, 30 the control thereof can be easily made to provide for forms no tellurium dioxide ?lm (referred to as “Com controlling with high accuracy. parative Example A”) and a ?lm obtained by simulta After the plasma has been produced, the heating boat neously vaporizing metal tellurium and tellurium diox 2 is energized to heat, melt and vaporize the metal tellu ide from individual vaporizing sources and comprising rium 1. Vapor pressure of tellurium is determined by the 35 a tellurium low oxide having a thickness of 0.1 pm of heating temperature and the pressure within the vac X=O.6 were formed by vacuum vaporization. Next, uum vessel 3, and the amount of vaporization of tellu only the vaporizing source for the tellurium dioxide was rium is controlled by the area of the opening of the boat. heated to melt and vaporize the tellurium dioxide to Vaporized particles of tellurium having passed through form a tellurium dioxide layer on the tellurium low the plasma are partly oxidized by oxygen ions within oxide layer (hereinafter referred to as “Comparative the plasma and by impacts of radicals to be deposited on Example B”). the substrate surface together with unoxidized vapor The three kinds of recording media were subjected to ized particles, as schematically shown in FIG. 4. In recording and readout by a semiconductor laser of FIG. 4, reference numerals 5, 5' denote vaporized parti wavelength of 830 nm. The recording was carried out cles of oxidized tellurium, and 6, 6' denote unoxidized 45 with a laser power of 7 mW and the diameter of beam of vaporized particles. Examples of substrate herein used 1.0 pm, and the readout was carried out with power of include an acrylic sheet, a polycarbonate sheet and various plastics. 1 mW. As the result, no difference in characteristic was found. Next, the medium was put into a thermo-hygros The composition (value of x) of the tellurium oxide tate vessel of temperature 40° C. and relative humidity can be freely controlled by varying the magnitude of 50 the power applied to the spiral-coil like high frequency 90%, and after the passage of 30 days, laser output of 20 exciting coil 4, the partial pressure P0 of oxygen gas to 50 mW is required to effect normal recording for and/or vaporization speed of metal tellurium. For ex Comparative Examples A and B, thus showing the ample, the partial pressure P0 of the gas may be in deterioration of characteristics. However, in the Exam creased, the applied power may be increased or the 55 ple of the present invention, no change arises as com vaporization speed of metal tellurium may be reduced pared with the state immediately after the formation of to thereby increase the it. Thus, the recording medium a ?lm, which is effective in improvement in stability. shown in FIG. 1 may be obtained by ?rst forming tellu The result of the peeling test in which 100 notches rium or a tellurium suboxide layer on the substrate se each comprising a 1 mm square were formed on the ?lm lecting the high frequency power, partial pressure of 60 surface by means of a sharp edge tool and scotch tapes the gas and vaporization speed of metal tellurium, and were applied thereto to pull them by 90° shows that the then immediately varying at least more than one of the Example and Comparative Example A have no peeling conditions of high frequency power, partial pressure of between the ?lm surface and the substrate surface thus the gas and vaporization speed of metal tellurium using giving a ?lm having suf?cient strength to withstand the same vaporizing device and same vaporizing speed. 65 practical use whereas comparative Example B shows The heat treatment (annealing) applied to the TeOx complete peeling, thus showing that a strong ?lm may ?lm formed in accordance with the above-described not be formed by the mere vacuum vaporization ?lm forming method is effective to further stabilize the method. 4,786,538 5 6 EXAMPLE 2 quency coil to generate a plasma. Metal tellurium of purity 99.99% was melted and vaporized at 450° to 500° The TeOg layer 10 on the surface of the recording C. and deposited on the substrate. medium may be formed by oxidizing the recording After formation of a ?lm, vaporization of the metal medium produced in accordance with the aforemen tellurium is stopped, and the same device is used to tioned method under the atmosphere of oxygen gas introduce the oxygen gas so that the vacuum vessel is at formed into a plasma preferably by the high frequency 4.0Xl0-4 Torr). The high frequency voltage of 500 power to form part of the surface into an inactive layer Watt was applied to generate an oxygen plasma, and the which principally comprises TeOz. previously formed recording medium was exposed to Where oxidization is carried out by the same device the plasma for a predetermined period of time. (These as that which has formed a recording ?lm, vaporization are Embodiments A and B. Comparative Example A of metal tellurium is stopped upon termination of ?lm comprises a material which was merely subjected to formation, and high frequency power is applied while formation of ?lm and not exposed to the oxygen introducing oxygen gas so as to maintain partial pres plasma.) Comparative Example B comprises a material sure of the gas selected in the range of from 1X 10-4 to in which tellurium dioxide (TeOg) and tellurium (Te) 9X 10"3 Torr. By this operation, the recording ?lm is are simultaneously vaporized by the individual vaporiz gradually oxidized from the surface thereof and stabi ing sources and simultaneously deposited on the sub lized. It is to be noted that in the manufacture, a separate strate. Comparative Example C comprises a material in manufacturing device may be used after formation of which a TeOg layer (thickness 25 A) is provided the recording ?lm to form an oxidized ?lm by the simi thereon by the vacuum vaporization of TeOz alone. The lar operation. results were given in Table 1. Particularly preferably, the partial pressure of the In Table l, the values of properties were obtained as oxygen gas introduced in the present invention is in the in the following: range of from 1X lO-4 to 9X10-3 Torr) because the Adhesive Properties: 100 notches each comprising 1 stabilized plasma is generated to form an even oxidized 25 mm square were formed on the ?lm surface by a sharp ?lm on the ?lm surface in a manner similar to that when edged tool, and scotch tapes were applied thereto to the ?lm is formed. It is also possible to mix the inert gas pull them up by an angle of 90 degrees to examine the into the oxygen gas. Examples of the inert gas include number of peeled portions. argon gas, helium gas, nitrogen gas and the like. While Stability: The transmittance (indicated at T0, T3) the mixing proportion is not particularly restricted, it before and after the material is exposed to the atmo should be restricted to such extent that oxidization reac sphere of temperature 70° C. and relative humidity 90% tion is not excessively delayed. was measured. The ratio (T3/T0) was used as a standard The magnitude of high frequency power applied to of the stability. As the ratio increases from the value of the high frequency exciting coil and the time for gener 1.0, the stability deteriorates. TABLE 1 Comparative Comparative Comparative Example A Example B Example A Example B Example C Film forming method Ion plating lon plating Ion plating Vacuum vap. Vacuum vap. Composition of recording ?lm x 0.8 0.8 0.8 0.8 0.8 Thickness or recording ?lm (pm) 0.10 0.10 0.10 0.10 0.10 Oxidation Conditions: Vap0rized(TeO2 Gas partial pressure of gas (Torr) 4.0 X l0_4 4.0 X 10‘4 layer) about 25A High pressure voltage (watt) 500 500 Thickness of oxidized surface About 50 About 25 layer (A) Adhesive properties 0/100 0/100 0/100 100/100 100/100 (Peeled number/100) Stability T3/T0, 70° C., 90% R.H. 1.0 1.1 4.0 6.4 1.4 ating the plasma during the oxidization is related to the thickness of the surface layer of the recording ?lm oxi As shown in Table l, the formation of ?lm by mere dized and should be selected according to the object. If vacuum vaporization method involves a problem in the high frequency power is excessively high, the sub stability as well as adhesive properties. The oxidized strate becomes softened during the progress of oxidiz layer by vacuum vaporization method was improved in ing the surface layer, and in the excessive case, cracks stability considerably but involves a problem in adhe occur in the surface and as the result, deformation re sive properties. The formation of ?lm by ion plating is sults which makes hardly to read out dif?cult, which is excellent in adhesive properties, and when an oxidized not favorable. On the other hand, if the high frequency layer is provided thereon, the stability is apparently power is excessively low, the generation of plasma is enhanced to the extent that it can be put to practical use. not marked, and the effect of oxidization cannot be All the recording media were subjected to recording expected. Thus, the high frequency power is preferably by a semiconductor laser having a wavelength of 830 in the range of from 50 to 600 Watt (more preferably, nm. Practical recording and readout characteristics from 100 to 500 Watt). were exhibited. The device shown in FIG. 4 was used. Gas was dis charged till initial pressure P was 1X10“5 Torr, and a EXAMPLE 3 mixture of argon gas 10 vol.% and oxygen gas 90 vol. 65 In the recording medium shown in FIG. 2, a TeOz % was introduced to have a vacuum degree of layer was ?rst formed on the substrate selecting the 4.0><10~3 Torr. High frequency power of frequency high frequency power, partial pressure of gas and va 13.56 MHz and 200 Watt was applied to the high fre porization speed of metal tellurium, and immediately 4,786,538 7 8 thereafter the same vaporization device and the same ative Example B, complete peeling appeared, and a vaporization source were used to form tellurium or a strong ?lm may not be formed by vacuum vaporization. tellurium suboxide layer by varying at least more than one of the conditions of the high frequency power, EXAMPLE 4 partial pressure of gas and vaporization speed of metal According to one example of the present invention, tellurium. Subsequently, the initial conditions were tellurium or a tellurium suboxide (TeOx, x is less than 1 again restored to thereby continuously form tellurium in this example) was ?rst formed selecting the high dioxide layers. frequency powder, partial pressure of gas and/or va The device shown in FIG. 4 was used. Gas was dis porization speed of metal tellurium, and immediately charged till the initial pressure P was l X 10-5 Torr, and thereafter the same vaporization device and the same oxygen gas was introduced to 4X 10-4 Torr. High fre vaporization source were used to continuouly or step quency power of frequency 13.56 MHz and 400 Watt wisely vary at least more than one of the conditions of was applied thereto to generate a plasma. Metal tellu the high frequency power, partial pressure of gas and rium of purity 99.99% was melted and vaporized at 450° vaporization speed of metal tellurium (hereinafter re to 500° C. and deposited on a glass substrate and on a ferred to as “?lm forming conditions”), whereby the PMMA substrate at vaporization speed of approx. 4 proportion (value of x) of oxygen component in the ?lm A/sec. The thus formed ?lm had a thickness of 0.01 pm is increased to form a ?lm so that in the uppermost and the composition of ?lm was x=2.0 according to surface, x is more than 1, preferably 2 (T601), thus Auger electronic spectral method. Next, the high fre obtaining an optical recording medium in which the x is quency power and vaporinzation speed were changed to 20 varied from 0 to 2 thicknesswise from the surface of the 200 Watt and approx. 10 A/sec., respectively. The thus substrate (FIG. 3). In this recording medium, an anti~ formed ?lm had a thickness of 0.1 pm and the composi corrosive layer may be formed on the surface and a tion of ?lm was x=0.7. Subsequently, the initial ?lm layer having a high sensitivity may be formed in the forming conditions were again restored to form the vicinity of the substrate, thus providing an advantage T602 ?lm to obtain a recording medium comprising a 25 that the thickness of the optical recording medium per substrate/TeOg,0/TeOo.7/TeO2.0 (Examples). se may be decreased. According to another example of For the purpose of comparison, a material in in which the present invention, the TeOZ layer is formed by se there is no T602 ?lm is formed (which is Comparative lecting the high frequency power, partial pressure of Example A). Another comparative Example comprises gas and/or vaporization speed of metal tellurium and a material in which a metal tellurium and tellurium immediately thereafter, the same vaporization device dioxide were formed by use of the device having indi and the same vaporization source are used to continu vidual vaporization sources. First, only the vaporization ously or stepwisely vary at least more than one of the conditions out of the aforesaid ?lm forming conditions, source for the tellurium dioxide was heated to melt and vaporize the tellurium dioxide to form a tellurium diox whereby the proportion (value of x) of oxygen compo 35 nent in the ?lm is reduced to a value less than 1, prefera ide layer on the substrate. Then, the metal tellurium and bly, less than 0.1 to form a recording layer having a tellurium dioxide were simultaneously vaporized, and a sufficient thickness to record. Then, at least more than ?lm comprising a tellurium suboxide of thickness 0.1 one of the conditions of the ?lm forming conditions are pm having X=0.7 was formed by vacuum vaporiza continuously or stepwisely varied to thereby increase tion. Next, only the vaporization source of tellurium the value of x and the ?lm is formed so that the upper dioxide was heated to form a tellurium dioxide layer on most surface comprises T802 thereby decreasing the said tellurium suboxide layer to obtain a recording me value of x from the substrate surface toward the surface dium dcomprising a substrate/T eO2_0/TeO0_1/T eO2_0 layer and thus providing the increased optical recording (which is Comparative Example B). medium. These three kinds of recording media were subjected 45 The device shown in FIG. 4 was used. Gas was dis to recording and readout by a semiconductor laser hav charged till the initial pressure P was 1><10—4. High frequency with a laser power of 7 mW and a beam diameter of 1.8 power of frequency 13.56 MHz and 100 Watt was ap pm, and readout was carried out with a power of l mW. plied thereto to generate a plasma. Metal tellurium of No difference in characteristics was found in all media. purity 99.99% was melted and vaporized at 450° to 550° Next, the medium was put into a thermo-hygrostat C. and deposited on a glass substrate and on a PMMA having a temperature of 40° C. and a relative humidity substrate at vaporization speed of approximately 4 of 90%, and after the passage of 30 days, laser output of A/sec. The thus formed ?lm 12 had a thickness of 0.05 20 to 50 mW was required to effect normal recording in pm and composition of ?lm was x=0 by Auger elec Comparative Examples A and B, thus showing the 55 tronic spectral method, that is, a Te ?lm was formed. deterioration of the characteristics. However, accord Next, the gas to be introduced was changed to oxygen ing to the Examples of the present invention, no change gas having a high purity, and the vacuum degree was occurs as compared with that immediately after forma made to be 4X10‘4 Torr and metal tellurium was tion of ?lm, which is effective in terms of increase in melted and vaporized, while gradually increasing the stability. high frequency power, to form a ?lm 10 till the high 100 notches each comprising 1 mm square are formed frequency power reaches 400 Watt. The composition of in the ?lm surface by a sharp edged tool and scotch the ?lm 11 on the uppermost surface was x=2.0, that is, tapes are applied thereto to pull them up by an angle of the TeOz ?lm was formed. It has been con?rmed in the 90 degrees for the peeling test. The result showed that composition of the interior of the ?lm that the composi in the Examples and Comparative Example A, no peel 65 tion from x=0 near the substrate surface to x: 2.0 in the ing was found between the ?lm surface and the sub uppermost surface layer was continuously varied. For strate surface, thus was obtained a ?lm having suf?cient the purpose of comparison, metal tellurium and tellu strength to put it to practical use. However, in Compar rium dioxide were formed by use of the device having 4,786,538 9 10 individual vaporization sources. First, only the vapori test. The result shows that no peeling occured and a zation source for the metal tellurium was heated to melt ?lm having a sufficient strength for practical use was and vaporize the tellurium to form a tellurium layer on obtained. the substrate. Next, only the vaporization source for the tellurium dioxide was heated to form a tellurium dioxide EXAMPLE 6 layer on the tellurium layer to obtain a recording me The device shown in FIG. 4 was used. Gas was dis dium comprising a substrate/T e/T e010 (which is Com charged till the initial pressure P was 1X 10-5 Torr, and parative Example A). a mixture of argon gas 10 vol.% and oxygen gas 90 These two kinds of recording media were subjected vol.% was introduced and the vacuum degree within to recording and readout by a semiconductor laser hav the device was made to l.0><10-3 Torr. Then, high ing a wavelength of 830 nm, and excellent recording frequency power of frequency 13.56 MHz and 100 Watt and readout characteristics were exhibited. Then, the was applied to the high frequency coil to generate a medium was put into a thermo-hygrostat of temperature plasma. The vacuum degree within the device was 40° C. and relative humidity 90%, and after the passage made to 4X 10-4 Torr while melting and vaporizing of 30 days, the increased laser output was required to metal tellurium of purity 99.9% at 450° to 500° C., after effect normal recording in Comparative Example A, which a shutter provided between a glass or plastics thus showing the deterioration of the characteristics. substrate (for example, PMMA sheet) and a vaporiza However, in the Example of the present invention, no tion source was opened to form a ?lm on the substrate. change is found as compared to that immediately after ‘Next, the amount of the mixture was gradually in formation of ?lm, showing that it is effective in im 20 creased and the ?nal vacuum degree was made to provement in stability. 1.0><10-3 Torr to form a ?lm, after which the shutter 100 notches each comprising 1 mm square were was closed to terminate formation of the ?lm. The ?lm formed in the ?lm surface by a sharp edged tool and forming speed was 4 A/sec. in all cases. scotch tapes were applied thereto to pull them up by an It has been found from the measurement of a compo angle of 90 degrees for peeling examination. The result 25 sition in the direction of thickness of the formed ?lm by shows that in the Example, no peeling is found between the Auger electronic spectral method that the layer the ?lm surface and the substrate surface, thus was near the substrate surface comprises x=0, or Te alone, obtained a ?lm having a suf?cient strength to withstand and the uppermost surface comprises x-2.0, or TeOZ practical use whereas in Comparative Example A, com alone. It was further con?rmed that an intermediate plete peeling appeared, indicating that a strong ?lm may 30 layer has gradually increased in x from the layer near not be formed by the vacuum vaporization method. the substrate surface. Also, the wall thickness of the EXAMPLE 5 formed ?lm was 0.12 nm. This recording medium was subjected to recording The device shown in FIG. 4 was used. Gas was dis by a semiconductor laser having a wavelength of 830 charged till the initial pressure P was 1X 10—5, and high nm. The result showed that the excellent recording and purity oxygen gas was introduced to 4>