Abstract:
An apparatus and method for cooling substrates is disclosed wherein the apparatus contains a cooling mechanism having a cooling plate, components for circulating a cooling fluid through the cooling plate, a positioning mechanism which positions the substrate relative to the cooling plate during operation of the apparatus and a housing for containing the cooling mechanism, the positioning components and the circulating components. The cooling plate has a non-planar top surface which provides an enlarged surface area used to cool the substrate. The cooling apparatus may be used in conjunction with a larger processing apparatus to fabricate an information storage disk.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to the production of information recording disks and, more particularly, to the cooling of the substrates used to fabricate information recording disks. 
     BACKGROUND OF THE INVENTION 
     Information recording disks such as magnetic recording disks used, for example, in “hard disks,” compact disks, etc. have a structure where a recording layer is formed on the surface of a substrate which is made of a metal or dielectric material. In making a magnetic disk used in a hard disk, a substrate of aluminum (Al), or other suitable metal or dielectric material is first coated with a nickel-phosphorus (NiP) layer. Next, an undercoat metal film of suitable material is deposited on a surface of the substrate and then a recording layer made from a thin magnetic film of suitable material is deposited on the metal film layer. The recording disk is completed by depositing a protective layer over the recording layer. 
     The protective layer must be composed of a durable film which has lubricating properties in order to shield the recording layer from impact and harsh environments. For example, sputtered carbon films (carbon films which have been deposited by sputtering) are commonly used as protective layers. 
     In a conventional fabrication process, the recording layer is deposited onto the substrate surface at relatively high temperatures (for example, about 200° C.-250° C.) to ensure that the recording layer has a high coercive force. It is important that the recording layer have good magnetic properties to provide reliable transfer of data to and from the magnetic recording layer. On the other hand, the protective layer is deposited at lower temperatures of, for example, about 100° C.-150° C. Thus, before the protective layer can be deposited, the recording disk must be cooled to a suitable temperature for deposition. 
     Conventionally, such cooling has been accomplished by natural heat loss, or radiation, from the recording disk. Natural heat loss, however, can be a time-consuming process as temperatures do not readily decrease in the vacuum environment commonly employed in the fabrication of information recording disks. Consequently, manufacturing “throughput” and, potentially, recording disk quality may be adversely affected. 
     SUMMARY OF THE INVENTION 
     The aforementioned and related drawbacks associated with conventional information recording disk fabrication are eliminated or substantially reduced by the apparatus and associated method for treating substrates according to the present invention. The present invention calls for the cooling of a substrate used in the fabrication of an information recording disk with a gas by means of a cooling apparatus, including a cooling block, having a non-planar surface facing the substrate to be cooled. The non-planar surface of the cooling block is established by closely packing grooves which may have a V-shaped cross-section, a conical cross section, or a pyramidal cross-section. Preferably the grooves further include protrusions formed thereon. The protrusions of the present invention may be formed on the surface of the grooves through a blasting or other suitable process. By providing a cooling block with a non-planar structure, the effective surface area of the cooling block is at least doubled which, in turn, enhances the substrate cooling process. 
     A gas, such as hydrogen or helium is delivered by a gas delivery means into the space between the non-planar surface of the cooling block and the substrate to promote substrate cooling. A cooling fluid supply system is also present within the cooling apparatus which is operative to provide a cooling fluid such as, for example, water, to flow through the cooling block to maintain the cooling block at a suitable temperature thereby promoting substrate cooling. 
     The cooling apparatus of the present invention is designed for use in a larger substrate processing apparatus having a first film deposition process chamber in which a first film deposition process is carried out at a first process temperature and a second film deposition process chamber in which a second film deposition process is carried at a second process temperature. According, to the present invention, the second process temperature is lower than the first process temperature. The cooling apparatus is established between the first and second film deposition process chambers to rapidly cool the recording disk substrate before it enters the second process chamber where it is subjected to the second process. 
     An advantage of the present invention is that it provides the ability to rapidly and efficiently cool a substrate to a suitable temperature without negatively affecting the information recording disk properties. 
     Another advantage of the present invention is that it provides the ability to maintain or enhance the coercive force properties of the magnetic film on an information recording disk. 
     Yet another advantage of the present invention is that it provides increased disk fabrication throughput. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned and related advantages and features of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the following drawings where like numerals represent like elements, in which: 
     FIG. 1 presents a cross-sectional plan view of an apparatus for treating substrates according to the present invention; 
     FIG. 2 presents a cross-sectional elevation view of the apparatus for treating substrates according to the present invention; 
     FIG. 3 presents a schematic side view of the surface of the cooling block used in the apparatus for treating substrates according to the present invention; 
     FIG. 4 presents a cross-sectional plan view of a recording disk processing apparatus incorporating the apparatus for treating substrates according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention can be fully described and appreciated with reference to the Figures, in which FIGS. 1 and 2 present schematic plan and front views, respectively, of a preferred embodiment of an apparatus for treating substrates according to the present invention. The apparatus comprises a chamber  2  having an interior region  10  of sufficient size to hold at least one substrate  1  therein. The chamber  2  may be isolated from other process chambers by gate valves  3 , which are opened to transfer substrates into and out of chamber  2 . Chamber  2  is provided with a vacuum pumping system  4  comprising a vacuum pump  41  which, in a preferred embodiment, is a turbo molecular pump, and a main exhaust valve  42 . The vacuum pumping system  4  is operative to remove air from the interior region  10  of the chamber, thereby providing a vacuum within the chamber. The substrates  1  to be treated (cooled) are supported within the interior region  10  of the chamber by a carrier mechanism  6 . In this manner, the substrates are translated through the chamber  2  by a conventional transport mechanism (not shown). 
     Also provided within the interior region  10  of the chamber, is the cooling system  58  of the present invention that is operative to cool the substrates  1  being translated through the cooling system  58  by the transfer mechanism. In the preferred embodiment, the cooling system  58  includes cooling plates  51  made from a high thermal conductivity material, such as copper, and a gas delivery means  53 , operative to deliver a cooling gas such as hydrogen (H) or helium (He) into the interior region  10  of the chamber  2 . Cooling plates  51  have a non-planar top surface  50  (FIG. 3) facing the surfaces of substrates  1  to be cooled. Cooling plates  51  will be described in greater detail below. In the manufacture of magnetic disks, as described herein, both sides of the disks are employed for recording and, thus, go through the same processing steps. Accordingly, two cooling plates  51  are used. Those skilled in the art will appreciate that in other applications a single cooling plate may be all that is required. 
     The gas delivery means  53  includes a gas source (not shown) and piping  531  disposed to connect the gas delivery means  53  to the chamber  2 . In one embodiment, the gas delivery means  53  further comprises an upstream valve  532 , a downstream valve  533  and a gas reservoir  534  located between the upstream value  532  and the downstream valve  533 . The gas is provided into gas reservoir  534  at a predetermined pressure, so that a given quantity of gas is contained therein. In a preferred embodiment, hydrogen is used. 
     Coupled to the cooling plates  51  is a cooling fluid supply system  52  which is operative to cause a cooling fluid such as water to flow through the cooling plates  51  during operation of the apparatus and thereby maintain the cooling plates  51  at a desired temperature. In one embodiment, the cooling fluid supply system  52  includes an inflow pipe  521 , an outflow pipe  522  and a standard fluid pump (not shown). The inflow pipe  521  passes through the wall of the vacuum chamber  2  in a gas-tight manner and is coupled to the cooling fluid inlet port  54  of the cooling block  51 . Similarly, the outflow pipe  522  passes through the wall of the vacuum chamber  2  in a gas-tight manner and is coupled to the cooling fluid output port  56  of the cooling block  51 . During operation of the apparatus, the cooling fluid supply system  52  circulates water (or other suitable cooling fluid) through a central opening  55  in the cooling block  51  in order the maintain the cooling block  51  within a desired temperature range. The desired temperature is maintained by an external cooling system, such as a refrigeration system (not shown), for cooling the water. In one embodiment, the water temperature is held at about 20° C. 
     FIG. 3 presents a schematic cross sectional side view of the surface of a cooling block  51  of the present invention. As shown, the surface  50  of the cooling block has a saw-tooth like cross section. The saw-tooth cross sectional surface of the cooling block may be formed, for example, by cutting or moving a triangle shaped cutting tool in parallel, fixed spaced, lines across the top surface of the cooling block  51 . Pyramidal grooves may be formed by forming parallel grooves in one direction and then cutting an additional grooves at a right angle to the first set of grooves. In a preferred embodiment the inclined portions of the saw-tooth grooves are formed with an angle of approximately 60°, with the depth of the grooves, measured from the top of the surface  50  of the cooling plate being in the range of about one millimeter (1 mm) to about two millimeters (2 mm). As further shown in FIG. 3, the saw-toothed grooves  50  of the cooling block  51  may further be provided with fine protrusions  57  having a substantially V-shaped cross section. These fine protrusions  57  may be created on the surface of the saw-toothed grooves by a blast treatment. For example, in one embodiment, sand or alumina particles, having a diameter of about 100 microns, are blasted onto the saw toothed grooves  50  at a pressure of about 2 kg/cm 2 . By providing a cooling block  51  having a non-planar operating surface, as described above, the effective surface area of the cooling block becomes at least twice as large as the surface area of a conventional planar cooling surface. The benefits of having the increased cooling surface area will be discussed in greater detail below. 
     Although described in a preferred embodiment as having a substantially V-shaped cross-section, the fine protrusions  57  formed on the cooling grooves  50  of the cooling block  51  may also have any suitable shape. Many processes which may be used to form the protrusions will result in protrusions having somewhat random shapes. The key is to provide protrusions that will increase the effective surface area of the cooling surface  50  of the cooling block that faces, or is adjacent to, the substrate to be treated. 
     The method described above for providing the fine protrusions on the grooves of the cooling surface  50  is not limited to a blast process. Any other suitable physical or chemical method may be employed. For example, the fine protrusions may be provided by flame coating the cooling surface with a suitable fine granular material. Also, the fine protrusions may be provided by etching the cooling surface with a suitable etchant, for example, nitric acid. 
     The substrate cooling method of the present invention will now be described with reference to FIGS. 1-3. The substrate  1  to be cooled is provided within the chamber  2  through a gate valve  3  and is positioned at a distance of approximately 6 mm from the cooling surface  50  of the cooling block  51 . The gate valve  3  is closed after the substrate  1  has been placed within the chamber  2 . After the gate valve  3  is closed, the atmospheric pressure within the chamber  2  is reduced to at about 10 −4  Pascal (Pa) by vacuum pumping system  4 . The cooling fluid, in a preferred embodiment, water maintained at a temperature of approximately 20° C., is circulated through the central opening  55  of the cooling block  51  at a rate of approximately 5 liters/min by the cooling fluid supply system  52  as described above. Next, the gas delivery means  53  provides that the upstream valve  532  is placed in an open position and that the down stream valve  533  is placed in a closed position thereby causing a predetermined amount of gas, such as hydrogen, to be transferred to the gas reservoir  534 . 
     In one embodiment, once the substrate  1  has been positioned within the chamber  2  adjacent the cooling block  51 , the main exhaust valve  42  of the pumping system  4  is closed. Next, the downstream valve  533  of the gas delivery means  53  is opened causing the hydrogen gas stored in the gas reservoir  54  to be delivered to the interior region  10  of chamber  2  at a pressure in the range of between about 50 Pa and about 500 Pa, preferably approximately 200 Pa. After being delivered by the gas delivery means  53 , the hydrogen gas diffuses and quickly fills the interior region  10  raising the pressure of the chamber to approximately 200 Pa. As a result of this increased pressure, the transmission of heat between the substrate  1  and the cooling block  51  is greatly enhanced through the transfer of thermal energy by the gas molecules traveling between the substrate to be cooled and the cooling plate. In addition, some of the energy is dissipated by radiation from the surface of the substrate. 
     The hydrogen molecules present within the interior region  10  of the chamber promote heat exchange by first contacting the substrate  1 . This increases the thermal energy of the hydrogen molecules which then transport the heat energy to cooling block  51 , by colliding with the cooling block (shown as g in FIG.  3 ). The heat received by the cooling block  51  is absorbed and removed from the chamber by the flow of the water through the cooling block. The collisions of hydrogen gas molecules between the substrate  1  and the cooling block  51  rapidly reduces the substrate temperature. After a predetermined time interval, the main exhaust valve  42  is opened and the downstream valve  533  is closed causing the chamber  2  to be placed at a predetermined post cooling pressure. Gate valve  3  is then opened and the cooled substrate  1  is transported from the chamber  2  to a subsequent processing chamber for further processing. 
     In testing performed by the inventors, after treating the substrate in the cooling apparatus of the present invention, a substrate was cooled from a temperature of about 165° C. to about 120° C. in about 4.6 seconds. In contrast, cooling a substrate using a cooling surface having a conventional planar surface, under the same operating conditions, took approximately 6 seconds. The rapid cooling time provided by the apparatus of the present invention was principally accomplished because the cooling block has a non-planar cooling surface adjacent to the substrate. By providing grooves on the cooling surface of the cooling block  51 , the effective surface area of the cooling surface is substantially increased, thus causing an increased number of cooling gas collisions between the substrate and the cooling surface, thereby causing the substrate to cool more rapidly. 
     If the surface  50  of a cooling block  51  is flat, there will be, on average, only one gas molecule collision with the surface  50  of the cooling block for each collision with the substrate. On the other hand, by using a non-planar surface on cooling block  51 , the probability that a hydrogen gas molecule will collide with the cooling surface  50  multiple times is increased as shown in FIG.  3 . This result is further enhanced by the use of protrusions on the surfaces of the non-planar grooves. With an increased number of hydrogen gas molecule collisions between the substrate  1  and the cooling surface  51 , more of the thermal energy carried by the gas molecule is imparted to the cooling block; thereby providing that more heat from the substrate  1  is absorbed by the cooling block. Consequently, by having a non-planar surface act as a cooling surface, more gas molecule collisions occur which promotes the rapid cooling of the substrate. 
     Now, having described the operation of the substrate cooling apparatus, the use of such a cooling apparatus will now be described in the context of a larger processing apparatus. 
     FIG. 4 presents a cross sectional plan view of a magnetic recording disk fabrication apparatus incorporating the substrate cooling system of the present invention. As shown in FIG. 4, the recording disk processing apparatus includes a series of substrates  1  contained within a cassette  11 . The substrates  1  are mounted inside a loading chamber  21  by a mounting robot  211 . The mounting robot  211  sequentially places the substrates  1  onto a carrier  6  which translates the substrates throughout the recording disk processing apparatus. A directional control mechanism  28  is employed to control the direction of travel of the carrier  6 . After the substrates  1  have been loaded onto the carrier  6  by the mounting robot  211 , the substrates  1  are transferred into process chambers  231  and  232  where they are heated to a temperature of about 230° C. After being heated, the substrates  1  are transferred into a film deposition process chamber  233 , where a chromium (Cr) film is deposited as an undercoat film on the substrate. Sputter sources  73 , disposed within the process chamber  233 , deposit the chromium film onto the surfaces of the substrate by a conventional sputtering process. 
     After the chromium sputtering process has been completed, the sputtered substrate is then transferred to process chambers  234  and  235  where a layer of magnetic material such as CoCrTa is deposited onto the previously sputtered substrate to provide the recording layer of the information recording disk. Processing system  74 ,  75  within the process chambers  234  and  235 , respectively, deposits the magnetic film of a prescribed thickness onto the surface of the substrate by any suitable conventional methods. The depositing of the recording layer is performed at a deposition temperature of about 200° C. to ensure that the coercive force property of the magnetic recording layer is high. 
     After the recording layer has been deposited onto the substrate, the substrate is transferred to process chamber  236 , which includes the substrate cooling apparatus of the present invention, where the substrate is cooled to a temperature of approximately 120° C. before the protective layer is deposited onto the substrate. According to one embodiment of the present invention, the processing time required to reduce the temperature of the treated substrate from approximately 240° C. to about 120° C. is about 5 seconds. 
     After the temperature of the treated substrate has been reduced to about 120° C., the cooled substrate is then transferred to final process chambers  237  and  238  where a carbon film layer is deposited onto the recording layer to act as a protective layer. Processing system  77 ,  78  within the final processing chambers  237  and  238 , respectively, deposits a carbon film of a prescribed thickness onto the treated substrate by a standard sputtering process. After the protective layer has been deposited on the substrate, the resulting information recording disk is then transferred to an unloading chamber  22  where a recovery robot  221  removes the finished substrates (information recording disks) from the carriage  6  and places them into a cassette  12  for removal from the recording disk processing apparatus. 
     The foregoing detailed description of the invention is provided for the purposes of illustration and is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. For example, although the preferred embodiment of the invention has been discussed with respect to a cooling apparatus being established separately from the individual processing chambers, the cooling chamber may be established as part of each of the individual film deposition process chambers. Accordingly, the scope of the present invention is to be defined by the claims appended hereto.