Patent Publication Number: US-2010108496-A1

Title: Sputtering apparatus, thin film formation apparatus, and magnetic recording medium manufacturing method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sputtering apparatus, thin film formation apparatus, and magnetic recording medium manufacturing method. 
     2. Description of the Related Art 
     Recently, magnetic recording media are being extensively researched and developed as means for recording enormous amount of information. Presently, a recording method called “perpendicular recording method” that records signals by pointing magnetization vectors in the direction perpendicular to the in-plane direction of a recording layer is being widely used. 
     In the magnetic recording media, a Co—Cr—Pt-based alloy is mainly used as a recording layer. 
     A recording layer (magnetic recording film) of the magnetic recording medium is required to have high magnetic anisotropy for thermal stability. Also, a material having high magnetic anisotropy is expected to be used in thermally assisted magnetic recording that facilitates recording nanometer-sized bits by local laser heating, or as a bit-patterned medium in which patterns are regularly arranged. Examples of promising high anisotropy material are alloys of Co and Fe such as CoPt, FePt, and CoFePt. 
     To obtain high magnetic anisotropy of a magnetic recording film, the substrate must be raised to and controlled at a predetermined temperature. For example, a thin-film stack manufacturing apparatus disclosed in Japanese Patent Laid-Open No. 2008-176847 includes a plurality of connected chambers, and a heating means for heating a film formation substrate. The film formation substrate is sequentially transferred into the chambers, and a plurality of thin films are stacked on the film formation substrate by using sputtering. A plurality of film formation substrates are simultaneously accommodated in the respective chambers. While a thin film is formed on one film formation substrate, the heating means heats another film formation substrate waiting for film formation. 
     Unfortunately, the thin-film stack manufacturing apparatus disclosed in Japanese Patent Laid-Open No. 2008-176847 has the problem that no uniform temperature control can be performed while a film is being formed or sputtered on a substrate. The thin-film stack manufacturing apparatus disclosed in Japanese Patent Laid-Open No. 2008-176847 also has the problem that the size of each chamber is large because a target as a film formation material and a first heater unit functioning as the heating means are arranged in parallel. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetic recording medium manufacturing technique capable of performing uniform temperature control on the substrate surface. 
     According to one aspect of the present invention, there is provided a sputtering apparatus comprising: 
     a first target accommodating unit to accommodate a first target for film formation on a substrate; 
     a first heater, arranged to surround the first target, for heating the substrate; and 
     a second target accommodating unit arranged to surround the first heater to accommodate a second target for film formation on the substrate. 
     According to another aspect of the present invention, there is provided a thin film forming apparatus comprising the sputtering apparatus. 
     According to still another aspect of the present invention, there is provided a magnetic recording medium manufacturing method comprising the steps of: 
     heating a substrate to a predetermined temperature using the sputtering apparatus; and 
     performing film formation on the substrate heated in the step of heating by using the sputtering apparatus. 
     According to the present invention, there can be provided a magnetic recording medium manufacturing technique capable of performing uniform temperature control on the substrate surface. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary longitudinal sectional view showing an example of a magnetic recording medium manufactured by a magnetic recording medium manufacturing method according to an embodiment of the present invention; 
         FIG. 2  is a schematic view showing an example of a thin film formation apparatus (magnetic recording medium manufacturing apparatus) according to the embodiment of the present invention; 
         FIG. 3  is a schematic view for explaining chambers  209 ,  210 , and  211  of the magnetic recording medium manufacturing apparatus according to the embodiment of the present invention; 
         FIG. 4  is a side sectional view for explaining the chamber  210  of the magnetic recording medium manufacturing apparatus according to the embodiment of the present invention; and 
         FIG. 5  is a flowchart for explaining the sequence of the magnetic recording medium manufacturing method according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will exemplarily be explained in detail below with reference to the accompanying drawings. Note that constituent elements described in the embodiments are merely examples, and the technical scope of the present invention is determined by the scope of the appended claims and is not limited by the following individual embodiments. 
     First, a magnetic recording medium as an example of a thin-film stack manufactured by a magnetic recording medium manufacturing apparatus and magnetic recording medium manufacturing method according to an embodiment of the present invention will be explained. Note that in this specification, the term “magnetic recording medium” is not limited to an optical disk such as a hard disk or floppy (registered trademark) disk using only magnetism when recording and reading information. For example, a “magnetic recording medium” includes a magnetooptical recording medium such as an MO (Magneto Optical) disk using both magnetism and light, or a thermally assisted recording medium using both magnetism and heat. 
       FIG. 1  is an exemplary longitudinal sectional view showing an example of a magnetic recording medium (thin film stack) manufactured by the magnetic recording medium manufacturing apparatus and magnetic recording medium manufacturing method according to the embodiment of the present invention. In this embodiment, an ECC (Exchange-Coupled Composite) medium obtained by improving a perpendicular recording medium will be explained as an example of the magnetic recording medium. However, the spirit and scope of the present invention are not limited to this example. For example, the magnetic recording medium may also be a general perpendicular recording medium, longitudinal recording medium, bit-patterned medium, or thermally assisted recording medium. 
     As shown in  FIG. 1 , the magnetic recording medium includes a substrate  100 , and a first soft magnetic layer  101   a,  spacer layer  102 , second soft magnetic layer  101   b,  seed layer  103 , magnetic layer  104 , exchange coupling control layer  105 , third soft magnetic layer  106 , and protective layer  107  sequentially stacked on one or both of the two surfaces of the substrate  100 . 
     As the material of the substrate  100 , it is possible to use a nonmagnetic material generally used as a magnetic recording medium substrate. Examples are glass, an Al alloy having an NiP plating film, ceramics, a flexible resin, and Si. In this embodiment, the substrate  100  is a disk-like member having a central hole. However, the present invention is not limited to this, and a rectangular member or the like may also be used. 
     The first soft magnetic layer  101   a  formed on the substrate  100  is a layer preferably formed to improve the recording/reproduction characteristics by controlling a magnetic flux from a magnetic head for use in magnetic recording. However, the first soft magnetic layer  101   a  may also be omitted. As the constituent material of the first soft magnetic layer  101   a,  it is possible to use, for example, CoZrNb, CoZrTa, or FeCoBCr. 
     As the material of the spacer layer  102 , it is possible to use, for example, Ru or Cr. The second soft magnetic layer  101   b  formed on the spacer layer  102  is identical to the first soft magnetic layer  101   a.  The first soft magnetic layer  101   a,  spacer layer  102 , and second soft magnetic layer  101   b  form a soft underlayer. 
     The seed layer  103  formed on the soft underlayer is a layer preferably formed immediately below the magnetic layer  104  in order to suitably control the crystal orientation, crystal grain size, grain size distribution, and grain boundary segregation of the magnetic layer  104 . As the material of the seed layer  103 , it is possible to use, for example, MgO, Cr, Ru, Pt, or Pd. 
     A magnetic recording layer  5  includes the magnetic layer  104  having a large Ku value, the exchange coupling control layer  105 , and the third soft magnetic layer  106  having a small Ku value. 
     The magnetic layer  104  formed on the seed layer  103  and having a large Ku value affects the overall Ku value of the magnetic recording layer  5 , so a material having a maximum possible Ku value is preferably used. As the material of the magnetic layer  104  which exhibits the above characteristic, it is possible to use a material having an easy magnetization axis perpendicular to the substrate surface, and having a structure in which ferromagnetic grains are isolated by the nonmagnetic grain boundary component of an oxide. For example, it is possible to use a material obtained by adding an oxide to a ferromagnetic material containing at least CoPt. Examples are CoPtCr—SiO 2  and CoPt—SiO 2 . It is also possible to use Co 50 Pt 50 , Fe 50 Pt 50 , or Co 50-y Fe y Pt 50 . 
     The exchange coupling control layer  105  formed on the magnetic layer  104  contains a crystalline metal or alloy, or an oxide. As the material of the crystalline metal or alloy, it is possible to use, for example, Pt, Pd, or an alloy of Pt or Pd. As the crystalline alloy, it is also possible to use, for example, an alloy of an element selected from Co, Ni, and Fe and a nonmagnetic metal. A material with low magnetization such as a CoCrB alloy may also be employed. 
     The strength of the exchange coupling force between the magnetic layer  104  and third soft magnetic layer  106  can most simply be controlled by changing the film thickness or composition of the exchange coupling control layer  105 . The film thickness of the exchange coupling control layer  105  is desirably, for example, 0.5 to 2.0 nm. 
     The third soft magnetic layer  106  formed on the exchange coupling control layer  105  mainly functions to reduce the magnetization reversing magnetic field, so a material having a minimum possible Ku value is preferably used. As the material of the third soft magnetic layer  106 , it is possible to use, for example, Co, NiFe, CoNiFe, or CoCrPtB. 
     The protective layer  107  formed on the third soft magnetic layer  106  is formed to prevent corrosion and damage caused by the contact between a head and the medium surface. As the protective layer  107 , it is possible to use, for example, a film containing a single component such as C, SiO 2 , or ZrO 2 , or a film obtained by adding an additive element to C, SiO 2 , or ZrO 2  as a main component. 
     A thin film formation apparatus (to be also referred to as a “magnetic recording medium manufacturing apparatus” hereinafter) used in the magnetic recording medium manufacturing method according to the embodiment of the present invention will be explained below.  FIG. 2  is an exemplary view showing an example of the magnetic recording medium manufacturing apparatus according to the embodiment of the present invention.  FIG. 3  is an exemplary view for explaining chambers  209 ,  210 , and  211  of the magnetic recording medium manufacturing apparatus.  FIG. 4  is an exemplary side sectional view for explaining the chamber  210  of the magnetic recording medium manufacturing apparatus.  FIG. 5  is a flowchart for explaining the sequence of the magnetic recording medium manufacturing method. 
     In the magnetic recording medium manufacturing apparatus as shown in  FIG. 2 , a load lock chamber  81  for loading the substrate  100  ( FIG. 1 ) on a carrier  2 , an unload lock chamber  82  for unloading the substrate  100  from the carrier  2 , and a plurality of chambers  201 ,  202 ,  203 ,  204 ,  205 ,  206 ,  207 ,  208 ,  209 ,  210 ,  211 ,  212 ,  213 ,  214 ,  215 ,  216 ,  217 , and  218  are arranged along the contours of a rectangle. Also, a transfer path is formed along the load lock chamber  81 , chambers  201  to  218 , and unload lock chamber  82 . The transfer path has a plurality of carriers  2  capable of carrying the substrate  100 . In each chamber, a processing time (tact time) required for the processing of the substrate  100  is predetermined. When this processing time (tact time) has elapsed, the carriers  2  are sequentially transferred to the next chambers. 
     For the magnetic recording medium manufacturing apparatus to process about 1,000 substrates per hour, the tact time in one chamber is about 5 sec or less, desirably, about 3.6 sec or less. 
     Each of the load lock chamber  81 , unload lock chamber  82 , and chambers  201 ,  202 ,  203 ,  204 ,  205 ,  206 ,  207 ,  208 ,  209 ,  210 ,  211 ,  212 ,  213 ,  214 ,  215 ,  216 ,  217 , and  218  is a vacuum chamber that can be evacuated by a dedicated or shared evacuating system. Gate valves (not shown) are formed in the boundary portions between the load lock chamber  81 , unload lock chamber  82 , and chambers  201 ,  202 ,  203 ,  204 ,  205 ,  206 ,  207 ,  208 ,  209 ,  210 ,  211 ,  212 ,  213 ,  214 ,  215 ,  216 ,  217 , and  218 . 
     More specifically, the chamber  201  of the magnetic recording medium manufacturing apparatus forms the first soft magnetic layer  101   a  on the substrate  100 . The direction change chamber  202  changes the transfer direction of the carrier  2 . The chamber  203  forms the spacer layer  102  on the first soft magnetic layer  101   a.  The chamber  204  forms the second soft magnetic layer  101   b  on the spacer layer  102 . The chamber  205  forms the seed layer  103  on the second soft magnetic layer  101   b.  The direction change chamber  206  changes the transfer direction of the carrier  2 . The magnetic recording medium manufacturing apparatus also includes the chamber  207  (a first heating chamber) and the chamber  208  (a second heating chamber) as preheating chambers for preheating the substrate  100 . The chamber  209  can also form the seed layer  103 . 
     The chambers  210  can function as sputtering apparatus for forming the magnetic layer  104  on the seed layer  103 . The cooling chamber  211  cools the substrate  100  on which the magnetic layer  104  is formed. The direction change chamber  212  changes the direction of the carrier  2 . The cooling chamber  213  further cools the substrate  100 . The chamber  214  forms the exchange coupling control layer  105  on the magnetic layer  104 . The chamber  215  forms the third soft magnetic layer  106  on the exchange coupling control layer  105 . The direction change chamber  216  changes the direction of the carrier  2 . The chambers  217  and  218  form the protective layer  107 . 
       FIG. 3  is a view for explaining details of the chamber  209  for forming the seed layer  103 , the chambers  210  (sputtering apparatuses) for forming the magnetic layer  104 , and the cooling chamber  211  for cooling the substrate in the magnetic recording medium manufacturing apparatus shown in  FIG. 2 . Arrows indicate the substrate transfer direction. 
     Referring to  FIG. 3 , the front surface (first surface) of the substrate  100  is surface A, and the rear surface (second surface) of the substrate  100 , which is opposite to (faces) surface A, is surface B. In the arrangement shown in  FIG. 3 , the substrate  100  is clamped at the outer edges of surfaces A and B. Referring to  FIG. 3 , “a” attached to each reference numeral indicates the arrangement on the side of surface A, and “b” indicates that on the side of surface B. 
     In the chamber  209  for forming the seed layer  103 , targets  41   a  and  41   b  are installed facing each other. This makes it possible to form the seed layers  103  on the two surfaces of the substrate  100 . As the target material for forming the seed layers  103 , it is possible to use, e.g., Cr, MgO, Pt or Pd. Note that a turbo molecular pump (to be referred to as a “TMP” hereinafter)  31  for evacuating a chamber is connected to each of the chambers  209 ,  210 , and  211 . 
     Next, the chamber  210  for forming the magnetic layer  104  will be explained in detail below as the feature of the present invention. 
     The chamber  210  functions as a sputtering apparatus and forms the magnetic layers  104  on the substrate by sputtering target materials set in the chamber  210 . The chamber  210  has a first target accommodating unit for accommodating a first target  42   a  for film formation on the substrate, a heating means  52   a  (first heating means) that is formed to surround the periphery of the first target and heats the substrate, and a second target accommodating unit that is formed to surround the periphery of the heating means  52   a  (first heating means) and accommodates a second target  43   a  for film formation on the substrate. 
     The chamber  210  further includes a third target accommodating unit, second heating means  52   b,  and fourth target accommodating unit. The third target accommodating unit is arranged to face the first target accommodating unit and accommodates a third target  42   b  for film formation on the substrate. The second heating means  52   b  is arranged to face the heating means  52   a  (first heating means) and surround the third target  42   b,  and heats the substrate. The fourth target accommodating unit is arranged to face the second target accommodating unit and surround the heating means  52   b  (second heating means), and accommodates a fourth target  43   b  for film formation on the substrate. 
     The substrate  100  is disposed between the round and annular target and heater assemblies such that the surfaces are parallel. 
     The first target  42   a,  the heating means  52   a  (first heating means), and the second target  43   a  are concentrically arranged on the side of the first surface (surface A) of the substrate. The first target  42   a  is formed in a disk-like shape. The heating means  52   a  is concentric with the first target  42   a  and has an annular shape. The second target  43   a  is concentric with the first target. The heating means  52   a  concentrically surrounds the target  42   a.    
     The third target  42   b,  the heating means  52   b  (second heating means), and the fourth target  43   b  are concentrically arranged on the side of the second surface (surface B) located on the side (opposing side) opposite to the first surface (surface A). The third target  42   b  is formed in a disk-like shape. The heating means  52   b  is concentric with the third target  42   b  and has an annular shape. The fourth target  43   b  is concentric with the third target and is annular in shape so as to surround the heating means  52   b.  The heating means  52   a  (first heating means) and the heating means  52   b  (second heating means) are arranged at positions interposed by the substrate to allow simultaneous heating the substrate from the two surfaces (first and second surfaces). This makes it possible to perform uniform temperature control and or maintain a high temperature on the substrate surfaces within the limited processing time in order to increase the throughput. 
     The annular heating means  52   a  is interposed between the first target  42   a  and the second target  43   a  to obtain a uniform film on the substrate. Their positions roughly correspond to the erosion patterns of a round target for achieving good uniformity. For example, as disclosed in the sputtering apparatus in FIGS. 7 and 8 of Japanese Patent Laid-Open No. 11-80948, as is known well, the erosion at the central portion and near the end portion of the target becomes shallow, while the erosion between the central portion and the end portion becomes deep. This undesirably results in the nonuniform film thickness of a film formed on the substrate. According to the structure of the present invention shown in  FIG. 3 , this problem can also be solved. 
     Note that as the “heating means” herein mentioned, it is possible to use, for example, a heater, block heater, or lamp heater. 
     The above-mentioned magnetic layer material can be used as the material of the first target  42   a,  third target  42   b,  second target  43   a,  and fourth target  43   b.  For example, it is possible to use a material obtained by adding an oxide to a ferromagnetic material containing at least CoPt. Examples are CoPtCr—SiO 2  and CoPt—SiO 2 . It is also possible to use Co 50 Pt 50 , Fe 50 Pt 50 , or Co 50-y Fe y Pt 50  as another target material. 
       FIG. 4  is a schematic side sectional view showing the chamber  210  in the substrate transfer direction (the substrate transfer direction is perpendicular to the drawing surface). That surface of the first target  42   a  which faces the substrate and that surface of the third target  42   b  which faces the substrate are arranged in positions almost symmetrical with respect to the substrate. Similarly, that surface of the heating means  52   a  which faces the substrate and that surface of the heating means  52   b  which faces the substrate are arranged in positions almost symmetrical with respect to the substrate. Further, that surface of the second target  43   a  which faces the substrate and that surface of the fourth target  43   b  which faces the substrate are arranged in positions almost symmetrical with respect to the substrate. 
     Note that magnet units  420   a  and  420   b  are installed at the back of the first target  42   a,  and the third target  42   b,  and magnet units  430   a  and  430   b  are installed at the back of the second target  43   a,  and the fourth target  43   b.    
     The magnet units  420   a  and  420   b  also provide a first means to generate an electric field at a predetermined voltage on the targets  42   a  and  42   b,  respectively. The magnet units  430   a  and  430   b  provide a second means to generate an electric field at a predetermined voltage on the targets  43   a  and  43   b.  The electric fields promote plasma formation in the presence of a working gas in the chamber that effects sputtering. 
     Though  FIG. 4  shows the surfaces of the first target  42   a,  heating means  52   a,  and second target  43   a  which face the substrate are aligned and form a single plane, the surfaces need not be co-planar. Likewise, the surfaces of the third target  42   b,  heating means  52   b,  and fourth target  43   b  are parallel but need not be co-planar. 
     For the magnetic recording medium manufacturing apparatus to process about 1,000 substrates per hour, the tact time in one chamber must be shortened to about 5 sec or less, desirably, about 3.6 sec or less as described previously. To achieve a heating process (temperature control) for heating the substrate to a desired temperature (about 400° C. to 600° C.) while the tact time is thus limited, the surfaces of the heating means  52   a  and  52   b  are preferably arranged at a distance of, for example, 50 mm or less, desirably, 30 mm or less from the substrate surface. 
     Referring back to  FIG. 3 , the cooling chamber  211  shown in  FIG. 3  has cooling mechanisms  61   a  and  61   b  facing each other, in order to cool the two surfaces of the substrate on which the magnetic layers  104  are formed. The two surfaces of the substrate having the magnetic layers  104  formed by heating to the desired temperature in the chambers  210  are cooled by the cooling mechanism  61   a  (first cooling mechanism) and cooling mechanism  61   b  (second cooling mechanism) in the cooling chamber  211 . The cooling process in the cooling chamber  211  can cool the substrate to a temperature optimum for later formation of the protective layers  107 , for example, to about 200° C. or less. 
     As explained above, this embodiment can provide a sputtering apparatus and magnetic recording medium manufacturing apparatus capable of performing uniform temperature control on the substrate surfaces especially during sputtering. 
     Next, a magnetic recording medium manufacturing method using the magnetic recording medium manufacturing apparatus according to the embodiment of the present invention will be explained below with reference to  FIGS. 1 and 5 . 
     In step S 501 , a substrate is carried into the load lock chamber  81  and placed on the carrier  2  by a substrate transfer robot (not shown). 
     In step S 502 , the substrate is heated to a predetermined temperature T 1  (about 100° C.) in the load lock chamber  81 , thereby removing contaminants and water sticking to the substrate. 
     In step S 503 , soft underlayers are formed. More specifically, first soft magnetic layers  101   a  are formed in the chamber  201 , spacer layers  102  (the thickness is 0.7 to 2 nm) are formed in the chamber  203 , and second soft magnetic layers  101   b  are formed in the chamber  204 . 
     In step S 504 , the substrate is sequentially transferred to the chamber  207  (first heating chamber) and chamber  208  (second heating chamber), and heated to a temperature T 2  (about 400° C. to 700° C.) higher than the temperature T 1  (about 100° C.) in step S 502 . This step is a preparation step of increasing the magnetic anisotropy of magnetic recording layers when forming magnetic layers  104  later. In the magnetic recording medium manufacturing apparatus, the processing time (tact time) in one chamber is limited in order to increase the throughput. In the chambers  210  for forming magnetic layers  104 , it is difficult to heat the substrate to a temperature required to increase the magnetic anisotropy of magnetic layers  104  within the limited time. Therefore, the magnetic recording medium manufacturing apparatus includes the chamber  207  (first heating chamber) and chamber  208  (second heating chamber) for preheating (preliminary heating). In the magnetic recording medium manufacturing apparatus, the chamber  207  (first heating chamber) and chamber  208  (second heating chamber) function as preliminary heating means. 
     Since the substrate temperature decreases before the substrate is completely transferred to the chamber  210  for forming magnetic layers  104 , the substrate must be heated (preliminarily heated) in the chamber  207  (first heating chamber) and chamber  208  (second heating chamber) to a temperature equal to or higher than the temperature required to increase the magnetic anisotropy in the chamber  210 . If the substrate made of glass is overheated, however, it may plastically deform and fall from the carrier  2 . In the chamber  207  (first heating chamber) and chamber  208  (second heating chamber), therefore, the glass substrate is preferably heated to a temperature below where plastic deformation occurs. For some glass substrates this may be up to, for example, 600° C. 
     In step S 505 , seed layers  103  are formed to suitably control the crystal characteristics of magnetic layers  104 . Note that the seed layers  103  may also be formed in the chamber  205  before the heating step in step S 504 . 
     In step S 506 , the substrate is transferred to the chambers  210  for forming magnetic layers  104 , and magnetic layers  104  are formed while the substrate is heated to a predetermined temperature T 3  (about 400° C. to 600° C.). In this step, the magnetic layers  104  are formed while the substrate is uniformly heated in the chamber  210  as described previously. 
     In step S 507 , the substrates are sequentially transferred to the cooling chambers  211  and  213  and cooled to a temperature optimum for the formation of protective layers  107 . When using carbon as the material of the protective layers  107 , the substrate must be cooled to, for example, about 200° C. or less. 
     In step S 508 , the substrate is transferred to the chambers  217  and  218  for protective layers  107  deposition which may be formed by CVD. 
     Note that ultra-thin exchange coupling control layers  105  may also be formed between the magnetic layers  104  and protective layers  107  in the chamber  214 . Note also that third soft magnetic layers  106  may also be formed in the chamber  215  after the substrate is cooled and before the protective layers  107  are formed. 
     Finally, in step S 509 , the substrate is unloaded as it is removed from the carrier  2  in the unload lock chamber  82 . 
     As explained above, this embodiment can provide a magnetic recording medium manufacturing method capable of performing uniform temperature control on substrate surfaces. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2008-282383 filed on Oct. 31, 2008, which is hereby incorporated by reference herein in its entirety.