WO2013015750A1

WO2013015750A1 - A method of manufacturing glass substrates for information recording medium

Info

Publication number: WO2013015750A1
Application number: PCT/TH2011/000029
Authority: WO
Inventors: Corporation Hoya; Supagan DEEPLUB
Original assignee: Hoya Glass Disk (Thailand) Ltd
Priority date: 2011-07-25
Filing date: 2011-07-25
Publication date: 2013-01-31
Also published as: CN103875036A; WO2013015750A8; CN103875036B

Abstract

The present invention provides a method of manufacturing glass substrates for information recording medium comprising steps of polishing of several glass substrates polished at a time using sun-and-planet gear type polishing machine; selectively determining at least two different annular zones of the polishing plate and controlling the temperature variation of the determined annular zones of the polishing machine so as to suppress and control thickness variation of glass substrates. Thickness variation can be suppressed and controlled when temperature gap on different zones of polishing plate is low. It is also the object of the present invention that the temperature variation of at least two different annular zones of polishing plate of the polishing machine is determined to be not over 2 °C. By such a method according to this invention, the surface of glass substrates on different annular zones of polishing plate can be polished so as to have low thickness variations.

Description

A METHOD OF MANUFACTURING GLASS SUBSTRATES FOR INFORMATION RECORDING MEDIUM

TECHNICAL FIELD OF THE INVENTION

The invention described herein generally relates to a method of manufacturing glass substrates for information recording medium.

SUMMARY OF THE INVENTION

The present invention has been made in view of the circumstances described below, and it is an object of the invention to provide a method of manufacturing glass substrates for information recording medium comprising steps of polishing of several glass substrates polished at a time using sun-and-planet gear type polishing machine; selectively determining at least two different annular zones of the polishing plate and controlling the temperature variation of the determined annular zones of the polishing machine so as to suppress and control thickness variation of glass substrates.

To achieve the above object, the present invention disclosed the method to control an ambient temperature variation in polishing process wherein the temperature variation of at least two different annular zones of the polishing machine is determined so that the thickness variation can be controlled and suppressed when temperature variation between different zones of polishing plate is correspondingly controlled and suppressed.

It is also the object of the present invention that the temperature variation of at least two different annular zones of polishing plate of the polishing machine is determined to be not over 2 °C.

By such a method according to this invention, the surface of glass substrates on different annular zones of polishing plate can be polished so as to have suppressed thickness variations. The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed. BACKGROUND OF THE INVENTION

In recent years, with the needs in the reduction in size and the increase in capacity of information recording devices such as hard disk drives (HDDs), various information processing devices have been proposed following the advancement of information society and further. To increase the recording capacity, techniques for further reducing the flying height of magnetic head are being developed so as to decrease the unit recording area and improve the detection sensitivity for a weakened magnetic signal. In order to measure the reducing in the flying height of magnetic heads and securing the recording area, the requirements for magnetic disk substances are becoming increasingly stringent, with regards to the improvement of smoothness and flatness (the reduction of scratches, protrusions, pits and the like). To satisfy such requirements, polish process plays important role.

Theoretically, in the polishing process, the polishing rate is the relationship between the thickness and a required polishing time if a polishing rate is kept constant; that is a polishing amount is proportional to a polishing time (processing time). However, in a real industrial application, though the polishing time is determined and fixed from a relationship between an appropriate polishing rate and a desired thickness, the polishing amount of the substrates in the same operation may fluctuate because of variations of ambient temperature during a polishing process pad and/or temperature of the polishing slurry. Consistency of thickness of a glass substrate may vary due to temperature variation, high temperature leads to increase in polishing rate. This drawback affects the variations of height, flatness and smoothness of the surface of the glass substrate.

JPA2007-245265 discloses manufacture process of a glass substrate for a magnetic disk having high smoothness by providing the atmosphere temperature of the polishing liquid at 20 °C or less when supplying the polishing liquid to the surface of the glass disk, or the atmosphere temperature of 30°C or less when finishing the polishing process. In the prior art, such approaches are studied that, upon performing the polishing process of the glass substrate, temperature or the polishing process may affect surface of a polished subject The invention is therefore aimed to solve the problems of temperature variations in a polishing operation so as to suppress and control thickness variation of the glass substrates.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the principles of the present invention. It will be apparent, however, to one skilled in the art that the present principles may be practiced without these specific details. Reference in the specification to "an embodiment," "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least that one embodiment, but not necessarily in other embodiments. The various instances of the phrase "in one embodiment" or similar phrases in various places in the specification are not necessarily all referring to the same embodiment.

In general, a glass substrate for magnetic disk as an information recording medium (hereinafter, simply referred to as glass substrate) is made of a glass workpiece. A glass substrate can be formed of a glass comprising Si0₂ as a main component for forming a glass network structure. Other components such as A1₂0₃, Zr0₃, CaO, BaO, Li0₂ and Na₂0 may be also used as the essential components to contribute an increasing glass transition temperature, an improved durability, stabilization of a glass structure and an improved rigidity of the glass substrate. A substrate is manufactured by carrying out a plurality of processes including the following step:

(1) Shaping Lapping and Chamfering Process

A glass substrate is manufactured by shaping a molten glass to obtain a plate-shaped glass. The plate-shaped glass is cut out into a disk-shaped glass. A glass substrate may then be formed by subjecting the disk-shaped glass to several other specific processes using various processing machines. For example, a lapping process is performed on both main surfaces of the disk-shaped glass using a lapping machine, such as a double-sided lapping machine employing a planetary gear-type mechanism, so as to obtain a glass base member having substantially flat principal surfaces. Thereafter, the glass base member obtained from the first lapping process is removed from the first lapping machine and subjected to a cutting process using a diamond cutter to form a disk-shaped glass substrate, followed by a coring process wherein a concentric inner hole is formed using a cylindrical drill so as to obtain an annular glass substrate. Thereafter, a forming and chamfering process is applied to the inner edge surface and outer edge surface using diamond grindstones. A second lapping process may then be performable on both principal surfaces of the glass substrate to remove fine irregularities on the principal surfaces. After said second lapping process, the glass substrate is then removed from the second lapping machine and placed into one or more edge surface polishing machines to achieve a mirror surface state on the inner edge surface and the outer edge surface of the glass substrate.

(2) Polishing process

Typically, one or more surface polishing processes are then carried out on the principal surfaces using, for example, double-sided polishing machines, such as those having a planetary gear-type mechanism, and using varying hardness resin polishing pads and varying polishing liquids having varying sized cerium oxide abrasive grains. The polishing step is performed in a state in which the polishing pads are attached to the lower polishing plate and the upper polishing plate by sliding the polishing pads along the surface of the raw material glass plate. Loading and unloading of the substrates is typically accomplished by separating the upper and lower polish plates by a distance sufficient to allow a machine operator or an automated load/unload device to grasp and remove the substrates, thereafter replacing the polished substrates with fresh substrates in preparation for a subsequent cycle of operation. In the polishing step, the sliding of the polishing pads polishes and smoothes the surface of the raw material glass plate. For example, in applying a two-step polishing process, after a glass substrate is subjected to polishing in a first polishing machine using a first hard resin polishing pad and a first polishing liquid, the glass substrate is carefully removed from the first polishing machine and placed into a carrying tray or container. Thereafter, the glass substrate is carefully placed into a second polishing machine to undergo a second polishing process using a similar polishing machine and using a softer resin polishing pad and polishing liquids having smaller grains.

The polishing slurry of the invention is a slurry dispersion of colloidal particles in water. The colloidal particles comprise metal oxide as the abrasive component. The metal oxide that may be used includes, but is not limited to, alumina, silica, copper oxide, iron oxide, nickel oxide, manganese oxide, silicon carbide, silicon nitride, tin oxide, titania, titanium carbide, tungsten oxide, yttria, zirconia, and combinations thereof. The metal oxide may be individual single particles or aggregates of individual particles. Therefore, the term "particle" as it is used herein refers to both aggregates of at least one primary particle as well as to single particles.

(3) Chemical Strengthening Process

The glass substrate is preferably chemically strengthened. A chemical strengthening process may be performed on the glass substrate by a known method. The glass substrate is immersed in a molten salt containing Na ion or K ion, to carry-out ion- exchange with Li ion or Na ion having a smaller atomic size in the glass substrate surface so as to form a compressive stress layer at the surfaces of the glass substrate, thereby completing the manufacturing of a glass substrate for use in an information recording medium.

(4) Glass Substrate Inspection

A thickness of a glass substrate of each arbitrarily sampled glass substrate in any batch is carried out by a known manner to determine whether the thickness variation of the sampled glass substrates was very good (thickness variation < 1 μιη), good (Ιμηι < thickness variation < 2 μπι), bad (2μπι < thickness variation < 4 μπι) or very bad (thickness variation greater than 4 μιη) based on the calculated standard deviation.

Additionally, a roughness of a glass substrate of each arbitrarily sampled glass substrate in any batch is also carried out by a known manner to determine whether the roughness of the sampled glass substrates was very good (variation highly suppressed), good (variation suppressed), bad (variation not highly suppressed) or very bad (variation not suppressed) based on the calculated standard deviation. Various substrate manufacturing developments have enabled the continuous production of larger quantities of substrates. For example, typical planetary gear-type polishing machines in use today include those having capabilities to polish one hundred substrates in a single step. Operable reliability of high capacity information recording devices obtained from such producing of large quantities of substrates can be affected in many ways, such as altering substrate polishing conditions to achieve improved flatness, waviness and micro-waviness of the useable recording area and, more recently, improving the maximum variation in height of the surface of a peripheral portion of the substrate.

The polishing machine polishes the upper and lower surfaces of the glass substrates at the same time. The polishing machine comprises an upper polishing plate for pressing the substrate and a lower polishing plate for supporting the substrates. These polishing plates are arranged coaxially with each other. Additionally, a plurality of carries, which performs sun- and-planet rotation while holding the substrates, is arranged between the upper polishing plate and the lower polishing plate in the circumferential direction thereof. A substrate is fitted in a through-hole of each carrier and moved together with the carrier. By rotating the polishing plates, both surfaces of each substrate can be polished. However, as a result of the motion between the carriers and the polishing pad, the temperature variation of different annular zones of the polishing machine is raised.

It was discovered that variations in roughness average (Ra) occurred in the same batch of glass substrates produced in large quantities; that is the glass substrates presented high Ra and low Ra. This was not a problem in the past since high Ra values were acceptable, and of course low Ra values were acceptable as well. However, nowadays, glass substrates are required to have lower Ra values, and therefore the conventional methods that produced glass substrates having variations in Ra are no longer acceptable, or in another word, high Ra is no longer acceptable. Being unable to achieve low Ra causes problems with different temperature of polishing process.

It has been discovered that the Ra variations among glass substrates in the same batch produced in large quantities are in fact attributed to the inherent variations in thickness (i.e. Variations in stock removal) of substrates under conventional methods. In this regard, it is recognized in this invention that variations in thickness among substrates produced in large quantities can in fact be suppressed and controlled by suppressing the variations in temperature between the zones of polishing machine.

The method for reducing variations in thickness of a glass substrate of the invention is applicable to various glass substrates to be processed with any sun-and-plant gear type machine.

The present invention relates to a method of reducing variations in thickness of a glass substrate. As described above, consistency of surface height of a glass substrate may vary due to temperature variation, high temperature leads to increase in polishing rate. It is the object of this invention to control an ambient temperature variation in polishing process to suppress and control surface height variations. The temperature variation is determined from the ambient temperature of at least two different annular zones in the polishing machine.

Other objects and effects of the invention will become apparent from the following description. A potential advantage of the present invention described herein is that it can significantly suppress and control thickness variation of a glass substrate at any polishing operation by controlling the temperature variation of different annular zones of the polishing machine.

Embodiments of the invention are explained below. However, the invention should not be construed as being limited to the following embodiments. Embodiments which are in agreement with the spirit of the invention and produce the same effect are encompassed by the invention.

As described above, an object of the invention is to provide a method of manufacturing glass substrates for information recording medium comprising steps of polishing of several glass substrates polished at a time using sun-and-planet gear type polishing machine; selectively determining at least two different annular zones of the polishing plate; detecting an ambient temperature of each annular zone; and controlling the temperature variation of the annular zones so as to suppress and control thickness variation of glass substrates. It has been found that the lower temperature gap of the different annular zones of the polishing plates, the lower thickness variation of glass substrates. Accordingly, the temperature variation is controlled to be not over 2 °C. It is preferable to have the temperature variation is controlled to be not over 1 °C. Specifically, the invention provides the method that suppresses and controls the thickness of glass substrate wherein inner and outer annular zones of the polishing plate are determined and the temperature variation of these zones is controlled. Preferably, three different annular zones of polishing plate are determined.

In further detail of the embodiment, temperatures at any zones of polishing plate are in a range of 24-26 °C.

The temperature of this present invention is detectably measurable when upper and lower polishing plates are uncovered.

In various aspects of the invention, if desired, the temperature variation is controllably adjustable by regulating polishing slurry temperature or coolant flow rate. The invention will be illustrated and explained below in detail by reference to the following Examples of the invention. The invention should not be construed as being limited to the constitutions of the following Examples.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein.

Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

EXAMPLES

An example process of manufacturing large quantities of 2.5 inch (65 mm) glass substrates for use in high capacity information recording mediums will now be described hereinafter with references to some examples and comparative examples. In representing the production of large quantities of glass substrates, one hundred glass substrates were produced in each substrate production process, and each process was repeated for one hundred times so as to produce a total of 10,000 glass substrates for each of the examples and comparative examples. It is to be understood herein that example embodiments of said method are applicable to other types of substrates and those of other predetermined sizes and shapes, such as those that are 3.5 inches (89 mm), 2.5 inches (65 mm), 1.8 inches (48 mm), 1 inch (27.4 mm), 0.8 inches (21.6 mm), or smaller.

Description is made on an example using a glass substrate with a disk shape having dimensions of an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm.

In accordance with this invention, the polishing pad can be any types of pads, for example a standard pad or a fixed abrasive pad. The carriers provide a controllable load on the glass substrate to push it against the polishing pad. Polishing slurry is typically supplied to the surface of the polishing pad. The polishing slurry includes common compositions containing at least one chemically reactive agent.

One of an example embodiment is a method of the present invention to suppress and control the thickness of glass substrate by controlling the temperature variation of different annular zones of the polishing machine comprising the following steps: at least two different positions on different annular zones of the polishing machine are set; (the two different annular zone is different radius position on the polishing plate that is round shape)

- temperature of said positions is detected and the temperature gap is measured;

- each of thickness of glass substrates is measured and the thickness variation is analyzed;

- the temperature variation of the polishing machine is controllably adjusted and determined to achieve an appropriate thickness variation. Subsequently, the ten sample substrates were subjected to be polished using the following polishing apparatus under the following polishing conditions.

Polishing Conditions

Polishing machine: sun-and-planet gear type Polishing pad: polyurethane form type pad having pore (nap pad)

Rotation number of polishing surface plate: 30-40 rpm

Polishing time: 10-100 minutes

Polishing load:30-120 g/cm²

Temperature recorders are mounted on different zones of the polishing machine. The temperatures on each annular zones are recorded when upper and lower polishing plates are uncovered. In this case, the two annular zones are defined inner position and outer position of the circular polishing plate.

The roughness (Ra) was evaluated using a surface roughness measurement device, such as an atomic force microscope (AFM).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows sun-and-planet gear type polishing machine BEST MODE FOR CARRYING OUT THE INVENTION

As disclosed in the detailed description of the invention.

Claims

CLAIMS (rewritten)

1. A method of manufacturing glass substrates for information recording medium comprising steps of: polishing of several glass substrates polished at a time using sun-and-planet gear type polishing machine; determining at least two different annular zones of the polishing plate and each annular zones are different radius position on the polishing plate that is round shape; selectively detecting an ambient temperature of each annular zone; and controlling the temperature variation of the annular zones so as to suppress and control thickness variation of glass substrates.

2. The method according to anyone of preceding claims wherein the temperature variation is controlled to be not over 2 °C.

3. The method according to anyone of preceding claims wherein the temperature variation is controlled to be not over 1 °C.

4. The method according to claim 1 wherein the temperature variation of inner and outer annular zones is controlled.

5. The method according to claim 1 or claim 2 wherein the temperature variation of inner, medium and outer annular zones is controlled.

6. The method according to any one of preceding claims wherein temperatures at any zones of polishing plate are in a range of 24 to 26 °C.

7. The method according to any one of preceding claims wherein the temperature variation is controllably adjustable by regulating polishing slurry temperature.

8. The method according to any one of claims 1 to 6 the temperature variation is controllably adjustable by regulating coolant flow rate.

9. The method according to any one of preceding claims wherein the temperature variation is detectably measurable when upper and lower polishing plates are uncovered.