JP2005050506A - SUBSTRATE FOR MAGNETIC RECORDING MEDIUM, MANUFACTURING METHOD THEREOF, AND MAGNETIC RECORDING MEDIUM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium substrate, preferably a small-diameter substrate having a diameter of 65 mm or less, which is advantageous in terms of physical properties and cost.
The present invention provides a magnetic recording medium substrate using a single crystal silicon wafer that has undergone one or more thermal histories and / or etching. In addition, the present invention provides a core removal step of coring a single crystal silicon wafer having a diameter of 150 mm or more and 300 mm or less that has undergone one or more thermal histories and / or etching to obtain a plurality of donut-shaped substrates having an outer diameter of 65 mm or less. The manufacturing method of the board | substrate for magnetic recording media containing this is provided. Preferably, the method further includes a chamfering step and a chamfering step for chamfering and polishing the inner peripheral end surface and the outer peripheral end surface of the obtained donut-shaped substrate.
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Description

  The present invention relates to a magnetic recording medium substrate suitable for a magnetic recording medium substrate, preferably a small-diameter substrate having a diameter of 65 mm or less, more preferably 50 mm or less.

The increase in recording density (surface density) of magnetic recording is very rapid, and during the last 10 years, the rapid increase of 50 to 200% per annum has continued. A product of 70 Gbit / inch ² is shipped at the mass production level, and a surface recording density of 160 Gbit / inch ² is doubled at the laboratory level. The surface recording density at the mass production level corresponds to 80 Gbytes per platter in a 3.5 "(""" represents inch) HDD, and corresponds to 40 Gbytes per platter in a 2.5 "HDD. The recording capacity is sufficient when a recording medium of one platter is installed in a use application of a normal desktop personal computer (3.5 "HDD installed) and a notebook personal computer (2.5" HDD installed).

Recording density is expected to continue to improve. However, the conventional longitudinal magnetic recording is imminent recording limits of thermal fluctuation, where it reaches the recording density of ^{100Gbit / inch 2 ~200Gbit / inch 2} , believed to sequentially after perpendicular magnetic recording Yes. Although it is not certain at this time what the recording limit of perpendicular magnetic recording is, 1000 Gbit / inch ² (1 Tbit / inch ² ) is considered achievable. If such a high recording density can be achieved, a recording capacity of 600 to 700 Gbytes per 2.5 "HDD platter can be obtained.

Since there is a high possibility that the large capacity up to this point will not be used up in ordinary PC applications, recording media with a smaller diameter than 2.5 "are gradually being used. "Board, 1.3" HDDs have been released in the past. Currently, HDDs of 2 "or less are very small in quantity. However, if the magnetic recording density is improved in the future, a 1.8" HDD can secure a sufficient recording capacity in a personal computer (especially a notebook personal computer). The recording capacity of a 1 "HDD is currently about 1 to 4 Gbytes, but if the capacity increases several times, not only digital cameras, but also PCs, digital video cameras, information terminals, portable music devices, mobile phones, etc. There is a possibility that it can be used in mobile applications. Small-diameter HDDs of 2 "or less and small-diameter recording media / substrates are promising applications in the future.

  As a substrate for HDD recording media, an Al alloy substrate is mainly used for the 3.5 "substrate, and a glass substrate is mainly used for the 2.5" substrate. In mobile applications such as notebook computers, HDDs are more likely to be impacted, and the 2.5 "HDDs installed in these devices may damage the recording media and heads due to head hitting, resulting in data corruption. Therefore, a glass substrate having a high hardness has been used. Therefore, a glass substrate is likely to be used even in a small-diameter substrate of 2 "or less.

  However, since small-diameter substrates of 2 "or less are mainly used for mobile applications, impact resistance is more important than 2.5" substrates mounted on notebook computers. In addition, in order to reduce the size, it is required to reduce the size and thickness of the entire component including the board. A board thickness thinner than 0.635 mm, which is the standard thickness of a 2.5 "substrate, is required for a substrate of 2" or less. From the specifications required for such a small-diameter substrate, a substrate having a high Young's modulus and sufficient strength even with a thin plate and easy to manufacture is desired. There are several problems with glass substrates in this regard.

  First, in the currently used crystallized glass substrate, the Young's modulus is not sufficient when the plate thickness is 0.635 mm or less, and the resonance frequency during rotation exists in the practical rotation range. Therefore, it is difficult to reduce the thickness further. In addition, a glass plate having a thickness of about 0.8 mm is used. However, it is difficult to make the plate further thinner in production with the glass composition required for the HDD plate. Therefore, it is necessary to adjust the thickness by lapping from a thickness of 0.8 mm to a thickness of 0.5 mm or less. Since the thickness is adjusted, the polishing time becomes considerably long, which causes an increase in processing time and processing cost.

  In addition, since the glass substrate is naturally a non-conductor, there is a problem of charge-up on the substrate in sputter deposition, and a buffer metal film is provided between the substrate and the magnetic film in order to ensure good contact with the magnetic film. It is necessary to put in. Although this technical problem has been basically overcome, it is one of the factors that make it difficult to use a glass substrate in the sputter deposition process. Therefore, if conductivity can be imparted to the substrate, it will not be over, but a glass substrate is difficult.

  As glass substrates are mainly used in 2.5 "HDDs, Al alloy substrates are completely unsuitable for mobile applications. As mentioned above, the substrate hardness is insufficient, but the substrate rigidity is insufficient. Therefore, the only way to make the resonance frequency higher than the practical rotation range is to increase the plate thickness, and it cannot be a candidate substrate for mobile applications.

  Several other alternative substrates such as sapphire glass, SiC substrate, engineering plastic substrate and carbon substrate have been proposed, but small-diameter substrates have been evaluated based on evaluation criteria such as strength, workability, cost, surface smoothness, and film formation affinity. Any of these alternative substrates is insufficient.

  It has been proposed to use a Si single crystal substrate as an HDD recording film substrate (Patent Document 1). The Si single crystal substrate is excellent as an HDD substrate because it is excellent in substrate smoothness, environmental stability, and reliability, and has higher rigidity than a glass substrate. Unlike glass substrates, conductivity is at least a semiconductor property. Further, since ordinary wafers often contain some P-type or N-type dopant, the conductivity is even higher. Therefore, there is no charge-up problem at the time of sputtering film formation as in the case of a glass substrate, and it is possible to directly deposit a metal film on a Si substrate. In addition, since the thermal conductivity is good, the substrate can be easily heated, the film can be formed even at a high temperature of 300 ° C. or higher, and the affinity with the sputter film forming process is very good. Si single crystal substrates are mass-produced for semiconductor ICs with a diameter of 100 mm to 300 mm.

JP-A-6-176339 Japanese Patent Laid-Open No. 10-334461

However, it is difficult to obtain a small diameter wafer having a diameter of 100 mm or less at present. Therefore, it is practical to cut out a desired small-diameter substrate from a 6 "to 8" wafer with a large circulation volume by core extraction. However, since the price of a semiconductor grade Si single crystal substrate is not inexpensive, it is extremely disadvantageous in terms of cost compared to a glass original plate or an Al original plate.
The present invention provides a recording medium substrate for magnetic recording, which is advantageous in terms of physical properties and cost, preferably a small-diameter substrate having a diameter of 65 mm or less, more preferably 50 mm or less.

The present invention provides a magnetic recording medium substrate using a single crystal silicon wafer that has undergone one or more thermal histories and / or etching.
In addition, the present invention cores a single crystal silicon wafer having a diameter of 150 mm or more and 300 mm or less that has undergone one or more thermal histories and / or etching, and has an outer diameter of 65 mm or less, a preferred inner diameter of 20 mm or less, and a more preferred inner diameter of 12 mm or less. There is provided a method for manufacturing a substrate for a magnetic recording medium, comprising a core removal step for obtaining a plurality of doughnut-shaped substrates. This manufacturing method preferably further includes a chamfering step for chamfering the inner peripheral end surface and the outer peripheral end surface of the obtained donut-shaped substrate, and an end surface polishing step for polishing the chamfered inner peripheral end surface and the outer peripheral end surface. Become. This manufacturing method is preferably performed before or after the coring step, for example, before the coring step, between the coring step and the chamfering step, between the chamfering step and the end surface polishing step, or after the end surface polishing step. More preferably, it includes a lapping step for grinding and removing the surface of the single crystal silicon wafer or the doughnut-shaped substrate by 10 μm to 100 μm before the core removal step, between the chamfering step and the end surface polishing step, or after the end surface polishing step. It becomes.

  According to the present invention, a Si single crystal substrate suitable for an HDD magnetic recording medium substrate, which is advantageous in terms of physical properties and cost, is provided.

The present invention provides a substrate for HDD magnetic recording medium was fabricated by coring processing from Si single crystal wafer having experienced heat treatment and / or etching one or more times, the diameter describing under 65mm diameter or less (Here nominal diameter The present invention relates to a magnetic recording medium substrate made of a single crystal of Si and a manufacturing method thereof.

FIG. 1 is a schematic process showing an example of manufacturing a magnetic recording medium substrate for HDD using a Si single crystal wafer as an original plate.
After slicing the single crystal silicon rod 1 to obtain a single crystal Si wafer 2 having a diameter of 200 mm, a doughnut-shaped substrate 3 having an outer diameter of 65 mm is obtained by a core removal process. According to the method disclosed in Patent Document 2, seven 65 mm HDD substrates can be cored from a 200 mm single crystal Si wafer. The doughnut-shaped substrate 3 is preferably chamfered on the inner peripheral end face and the outer peripheral end face, and the end face is polished. Thereafter, a small-diameter substrate is usually manufactured through an alkali etching process, a double-side polishing process, and a cleaning process.
Preferably, before or after the coring step, for example, before the coring step, between the coring step and the chamfering step, between the chamfering step and the end surface polishing step, or more preferably after the end surface polishing step, Before the core removal step, between the chamfering step and the end surface polishing step, or after the end surface polishing step, a lapping step of grinding and removing the surface of the single crystal silicon wafer or the doughnut-shaped substrate preferably by 10 μm to 100 μm may be included.

The single crystal silicon wafer used for the core removal step preferably has a plane orientation (100), a diameter of 150 mm or more and 300 mm or less, and a thickness of 0.4 to 1 mm (more preferably 0.7 mm or less).
A semiconductor grade Si single crystal wafer (prime wafer) is expensive, and even if a 65 mm diameter substrate is manufactured using the single crystal original plate, the cost is several times to nearly 10 times that of a glass substrate. No matter how excellent the characteristics of the Si single crystal substrate are, it is difficult to put it to practical use with such a cost difference.

  On the other hand, in the semiconductor IC process, a Si single crystal monitor wafer having the same diameter is used to monitor the process. The usage ratio of the monitor wafer to the prime wafer may be close to 1: 1 when a new aperture or process is started. The quality of the monitor wafer is not inferior to that of the prime wafer, but it is a little cheaper in price. The use of the monitor wafer is inevitable in the manufacturing process of the semiconductor IC, and it is difficult to use the substrate as an arbitrary number of HDD substrates, and the price of the original plate is not significantly reduced.

  In a Si single crystal substrate of a semiconductor IC process, a dummy wafer (or a reclaimed wafer) is used in addition to a prime wafer and a monitor wafer. The dummy wafer is repeatedly used at least once for process check and inspection. A monitor wafer is used once and a reclaimed wafer is obtained by scraping an oxide film or a metal film on the substrate. As a matter of course, the substrate price is in the order of prime wafer> monitor wafer> recycled wafer. The reclaimed wafer is usually used once or more and about 5 to 6 times, and various adhered films on the upper surface are polished and removed each time it is used once. At this time, since the reclaimed wafer is gradually scraped, it becomes thinner by about 10 to 100 μm each time it is used. Recycled wafers that have become thinner than a certain reference thickness are unsuitable for process checks and are discarded without further use. The standard value of the thickness varies, but it is discarded when the thickness is reduced from about 0.7 mm to 0.5 mm.

  Since the reclaimed wafer is repeatedly used, it experiences various processes of the semiconductor process. Therefore, since the thermal history of each wafer, the type of ion implantation, the dopant, the electric resistance value, and the like vary, it is difficult to use for solar cell applications and is generally discarded.

  In the Si single crystal substrate for HDD, what kind of thermal history the single crystal wafer original plate experienced and the kind of dopant are not important. Regardless of N-type or P-type, it is only necessary to have conductivity at the semiconductor level, and it is important that the single crystal has no grain boundary on the polished surface. An important item for the HDD substrate is the surface smoothness after polishing, which is the strength required for the substrate. Since the reclaimed wafer is still a Si single crystal, there is no problem with the smoothness after polishing.

  Since the reclaimed wafer has a thermal history of one or more times, it is considered that the substrate strength is reduced when processed into an HDD substrate due to atomic level crystal defects and dislocations, and micro scratches and cracks. It has been found that if these defects are not present on the substrate surface, the substrate strength is increased. The reason for this is not clear, but it is thought that molten oxygen partially binds to Si and behaves as an aggregate. For this reason, it becomes possible to use the discarded recycled wafer having a predetermined thickness or less as a relatively inexpensive raw material substrate for HDD.

  The present invention includes a core removal step of coring a single crystal silicon wafer having a diameter of 150 mm or more and 300 mm or less that has undergone one or more thermal histories and / or etching to obtain a plurality of donut-shaped substrates having an outer diameter of 65 mm or less; Preferably, there is provided a method for manufacturing a substrate for a magnetic recording medium, comprising a chamfering step and an end surface polishing step for inner and outer peripheral end surfaces of the doughnut-shaped substrate.

A single crystal silicon wafer having a diameter of 150 mm or more and 300 mm or less that has undergone one or more thermal histories and / or etchings is a wafer other than a prime wafer, and includes a recycled wafer and a monitor wafer after use.
Single crystal silicon wafers that have undergone one or more thermal histories include wafers that have undergone one heat treatment (for example, 400 to 1350 ° C.) as monitor wafers, wafers that have undergone two or more heat treatments as reclaimed wafers, and the like. .
The single crystal silicon wafer that has undergone one or more etchings includes a wafer that has undergone various etchings during the semiconductor manufacturing process as a monitor wafer, and a wafer that has undergone two or more etchings as a recycled wafer.

In the core removal process, for example, a diameter of 150 mm or more and 300 mm or less using a cup grinding wheel, a laser processing method such as a CO ₂ gas laser, a YAG laser, a water jet processing method using high-pressure water mixed with an abrasive, a blast method, etc. A plurality of substrates having an outer diameter of 60 mm or less can be obtained from the single crystal silicon wafer.

The core removal step includes outer diameter core removal (outer peripheral core removal) and inner diameter core removal (inner peripheral core removal).
In the case of cup grindstone processing, it is more efficient to first perform the inner diameter core punching process and then use the inner diameter core portion as a presser hole to perform the outer diameter core punching process. This is because, after performing the inner diameter core cutting process, only those that pass the predetermined inspection can be efficiently manufactured if subjected to the outer diameter core core processing. However, the reverse order is also possible.

In the present invention, preferably, the recycled wafer may be either before or after the core removal step, but a lapping step for grinding and removing 10 μm to 100 μm may be provided. After the core removal step, for example, a lapping step is provided between the core removal step and the chamfering step, between the chamfering step and the end surface polishing step, or after the end surface polishing step, and preferably, the chamfering step and the end surface polishing step. A lapping step is provided during or after the end surface polishing step.
It has been found that pits and defects on the surface of the wafer original plate can be substantially removed by the lapping process, and that the substrate strength is not affected if the defects and pits can be removed. Defects and pits derived from various semiconductor processes experienced by the reclaimed wafer remain in a very shallow portion from the surface, and can generally be removed by lapping the surface from 10 μm to 100 μm. The thickness of the 200 mm monitor wafer is 0.835 mm, and the waste recycled wafer thickness is 0.6 to 0.7 mm. Since the standard thickness of the 65 mm substrate is 0.635 mm, the HDD substrate of the present invention is preferably applied to a small-diameter substrate of 65 mm or less.

  Further, in the present invention, there is a circumstance that the grinding removal layer for defect removal may be relatively thin. The HDD substrate uses both sides, but since the semiconductor wafer basically uses only one side, the back side does not need to experience various processes (other than thermal history). Therefore, the damage on the back surface is relatively small, and it is sufficient to remove the defect on the use surface of the recycled wafer. Most defects that cause a decrease in strength can be removed by lapping of 10 to 100 μm, but they appeared on the surface due to crystal defects and dislocations existing inside (the defect density is higher than that of prime wafers). Things are a problem. Defects present on the surface of the HDD substrate that cause a decrease in substrate strength can be removed by inspection in a super mirror state after double-side polishing of the etched wafer after the core removal process. is there.

In the manufacture of the HDD substrate shown in FIG. 1, a chamfering process and an end surface polishing process for the inner and outer circumferences may be provided after the core removal process for the original plate such as a recycled wafer.
Chamfer angles and dimensions are generally defined as standard dimensions. When a prime wafer or a monitor wafer is used as an original plate, it can be made into a product by chamfering. However, when the reclaimed wafer of the present invention is used as an original plate, an internal defect exposed on the end face acts as a cause of a decrease in substrate strength. The end face refers to the inner diameter side face and the outer diameter side face portion of the donut-shaped substrate. Since it may become a starting point of substrate destruction, a defect exposed on the end face after chamfering is a problem. The present inventors have found that the substrate strength equivalent to that of a monitor wafer can be ensured even when a recycled wafer original plate is used by performing end face polishing after chamfering and then removing the strained layer by etching.

After the end surface polishing step or after the lapping step after the end surface polishing step, preferably, further, a step of alkali-etching the substrate, a step of polishing the front and back surfaces of the alkali-etched substrate, and a subsequent cleaning step, May be included.
The alkali etching step is performed, for example, by immersing in a 2 to 60% by weight NaOH aqueous solution at 40 to 60 ° C. in order to remove processing distortions in the lapping step and the end surface polishing step.
The step of polishing the front and back surfaces of the alkali-etched substrate may be performed by a known method. For example, the substrate mounted on the carrier is sandwiched between the upper surface plate and the lower surface plate and rotated, for example, using colloidal silica as abrasive grains. That's fine.
The cleaning process may be performed by well-known brush cleaning, chemical cleaning with an alkali or / and acid solution.

The magnetic recording medium substrate of the present invention can be handled in the same manner as a conventional substrate. For example, a soft magnetic layer and a recording layer can be provided to form a perpendicular magnetic recording medium. In order to improve the adhesion of the soft magnetic layer, an underlayer may be provided prior to the formation of the soft magnetic layer.
A protective layer and a lubricating layer may be provided on the recording layer.

EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to this.
The following is an overview of the examples.
A silicon single crystal wafer (plane orientation (100)) having a diameter of 200 mm that has been subjected to thermal history and / or etching, such as a semiconductor IC process, is lapped using abrasive grains to remove pits and defects. Next, a doughnut-shaped circular substrate having an outer diameter of 65 mm or less is cut out from the wafer by a laser beam from the laser beam generator to form a plurality of substrates. Next, chamfering of the inner peripheral end surface and the outer peripheral end surface of the substrate with a grindstone is performed. After alkali etching, the front and back surfaces of the substrate are polished, and a desired substrate is completed. Finally, the polishing agent and the like adhering to the substrate in the cleaning process are removed to complete the manufacture of the substrate.

Example 1
Prepare a wafer with a diameter of 200 mm and a thickness of 0.61 mm that has been subjected to a thermal history of 1000 ° C. four times. After removing 50 μm by lapping, a donut-shaped circular substrate with a diameter of 48 mm and an inner diameter of 12 mm is obtained with a YAG laser processing device. It was. Next, chamfering of the inner and outer peripheral end faces of the substrate with a grindstone (diamond) is performed, the inner and outer diameter end faces are polished, alkali etching is performed using 50 wt% sodium hydroxide at 50 ° C., and then 5 wt% colloidal. The double-sided polishing of the substrate was performed until a mirror surface appeared with silica. Next, the abrasive etc. adhering to the substrate in the cleaning process were removed to obtain a magnetic recording medium substrate. The obtained magnetic recording medium substrate is placed on a circular end of a 45 mm diameter pipe, a Zr ball having a diameter of 30 mm is arranged on the substrate at the center of the circle, and a load is applied to the substrate from the top of the ball using a load cell. In addition, the compression fracture strength was measured, and the average of 5 samples was 500N.

Example 2
Except that the lapping amount was set to 100 μm, the same processing as in Example 1 was performed and the compressive fracture strength was measured. As a result, the average of 5 samples was 550 N.

Example 3
Prepare a wafer with a diameter of 200 mm and a thickness of 0.55 mm after 6 times of thermal history at 1000 ° C and 4 times of etching. After removing 100 μm by lapping, donut with a diameter of 26 mm and an inner diameter of 7 mm using a YAG laser processing device. A circular substrate was obtained. Next, chamfering is performed on the inner and outer peripheral end faces of the substrate with a grindstone (diamond), and the inner and outer diameter end faces are polished, followed by alkali etching at 50 ° C. using 50 wt% sodium hydroxide for 20 minutes and then 5 wt% The substrate was polished on both sides until a mirror surface appeared with colloidal silica. Next, the abrasive etc. adhering to the substrate in the cleaning process were removed to obtain a magnetic recording medium substrate. The obtained magnetic recording medium substrate was placed on a pipe having a diameter of 20 mm, a Zr ball having a diameter of 10 mm was disposed on the inner diameter side, and the compressive fracture strength was measured.

Comparative Example 1
After preparing a wafer with a thickness of 0.74 mm that has not been subjected to thermal history and etching, lapping using abrasive grains to adjust the thickness and surface, a donut-shaped circular substrate with a diameter of 48 mm and an inner diameter of 12 mm is formed by a YAG laser processing apparatus. Obtained. Next, chamfering of the inner and outer peripheral end faces of the substrate with a grindstone (diamond) is performed, the inner and outer diameter end faces are polished, alkali etching is performed using 50 wt% sodium hydroxide at 50 ° C., and then 5 wt% colloidal. The double-sided polishing of the substrate was performed until a mirror surface appeared with silica. Next, the abrasive etc. adhering to the substrate in the cleaning process were removed to obtain a magnetic recording medium substrate. The obtained magnetic recording medium substrate was placed on a pipe having a diameter of 45 mm, a Zr ball having a diameter of 30 mm was disposed on the inner diameter side, and the compressive fracture strength was measured.

Comparative Example 2
Except that it was processed into a doughnut-shaped circular substrate with a diameter of 26 mm and an inner diameter of 7 mm, the same processing as in Comparative Example 1 was performed, placed on a pipe with a diameter of 20 mm, and a Zr ball with a diameter of 10 mm on the inner diameter side, When measured, the average of 5 samples was 50N.

  As described above, it has been found that when a magnetic recording medium substrate is manufactured using a wafer that has undergone thermal history and / or etching, it can be obtained efficiently with high strength.

6 is a schematic process showing an example of manufacturing a magnetic recording medium substrate for HDD using a Si single crystal wafer as an original plate.

Explanation of symbols

1 Single crystal silicon rod 2 Single crystal Si wafer 3 Donut substrate

Claims (6)

  A magnetic recording medium substrate using a single crystal silicon wafer that has undergone one or more thermal histories and / or etching.   Magnetic recording comprising a coring step of coring a single crystal silicon wafer having a diameter of 150 mm or more and 300 mm or less having undergone one or more thermal histories and / or etching to obtain a plurality of donut-shaped substrates having an outer diameter of 65 mm or less A method for manufacturing a medium substrate.   A chamfering step for chamfering the inner peripheral end surface and the outer peripheral end surface of the doughnut-shaped substrate; and an end surface polishing step for polishing the chamfered inner peripheral end surface and the outer peripheral end surface. A lapping step of grinding and removing the surface of the single crystal silicon wafer or the doughnut-shaped substrate between 10 μm and 100 μm between the step and the chamfering step, between the chamfering step and the end surface polishing step, or after the end surface polishing step. The method for producing a magnetic recording medium substrate according to claim 2, comprising:   The method for producing a substrate for a magnetic recording medium according to claim 2 or 3, wherein the single crystal silicon wafer used for the core removal step has a plane orientation (100) and a thickness of 0.7 mm or less.   After the end surface polishing step or after the lapping step after the end surface polishing step, a step of alkali etching the substrate, a step of polishing the front and back surfaces of the alkali etched substrate, and a subsequent cleaning step The manufacturing method of the board | substrate for magnetic recording media of Claim 3 comprising.   A perpendicular magnetic recording medium comprising the substrate according to claim 1.

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