WO1996009420A1

WO1996009420A1 - Dynamic buffer chamber

Info

Publication number: WO1996009420A1
Application number: PCT/US1995/012385
Authority: WO
Inventors: John Bruno
Original assignee: Seagate Technology
Priority date: 1994-09-23
Filing date: 1995-09-21
Publication date: 1996-03-28

Abstract

A dynamic buffer chamber in an in-line sputtering apparatus for fabricating magnet recording disks for Winchester-type hard disk drives, the dynamic buffer chamber being positioned between first and second processes of the sputtering apparatus to isolate the respective processes from each other with respect to pressure, temperature and gaseous composition.

Description

DYNAMIC BUFFER CHAMBER

CROSS REFERENCE TO RELATED APPLICATIONS The present application is related to U.S. Application Serial No. 07/681,866, entitled APPARATUS AND METHOD FOR HIGH THROUGHPUT SPUTTERING, filed April 4, 1991, which application is assigned to the assignee of the present invention, and which application is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method and apparatus for performing in-line sputtering of thin films onto substrates to form magnetic recording media, and in particular to a method and apparatus for dynamically isolating a first process from a second process within the sputtering operation.

Description of the Related Art

Sputtering is a well-known technique for depositing uniform thin films on a particular substrate. Fundamentally, the technique involves location of a block of a target material to be deposited onto a substrate in a partial vacuum sealed chamber. The chamber is backfilled with an inert gas, typically argon, and an electric field is introduced. The electric field accelerates the ions in the gas, causing them to impinge on the target surface. As a result of momentum transfer, atoms of the target material are dislodged from the target surface in an area known as the erosion region. Dislodged target atoms then deposit on the substrate, forming the film. Sputtering is performed on one or more substrates being rotated about a target (in a "planetary" system) or being transported past a target (in an "in-line" system) .

Presently, sputtering machines are often comprised of a plurality of sputtering chambers aligned in a row, which chambers are separated by intermediate chambers such as heating chambers and dwell chambers. A pallet, carrying a plurality of substrates, is transported through the chambers such that a plurality of different thin films are deposited on the substrates. Such sputtering machines are commonly used for the fabrication of magnetic disks utilized in Winchester- type hard disk drives. An example of such a sputtering machine is disclosed in U.S. Patent Nos. 4,735,840 and 4,894,133 issued to Hedgcoth on April 5, 1988 and April 16, 1990, respectively. The disclosed apparatus includes several consecutive chambers for sputtering individual layers, through which chambers preheated disk substrates mounted on a pallet or other vertical carrier proceed at velocities up to about 10 mm/sec (1.97 ft/min) , though averaging only about 3 mm/sec (0.6 ft/min) . The first sputtering chamber deposits chromium (100 to 5,000 A) on a circumferencially textured disk substrate. The next chamber deposits a layer (200 to 1,500 A) of a magnetic alloy such as Cobalt-Nickel (CoNi) . Finally, a protective layer (100 to 800 A) of a wear- and corrosion-resistant material such as amorphous carbon is deposited. Hedgcoth does not discloses any means for varying the sputtering pressure and/or temperature from one sputtering chamber to the next. Moreover, Hedgcoth discloses argon as the only gas in each of the sputtering chambers . In addition to achieving high film deposition rates, sputtering offers the ability to tailor film properties to a considerable extent by making minor adjustments to process parameters. Of particular interest are processes yielding films with specific crystalline microstructures and magnetic properties. Consequently, much research has been conducted on the effects of varying sputtering pressures and deposition temperatures. The research has shown that it is often advantageous to sputter one film, for example the magnetic layer, at a first pressure and temperature, while sputtering another film, for example the carbon overcoat, at a second pressure and temperature.

Research has also shown that film properties may be enhanced by a considerable degree by the addition of certain gasses in controlled amounts to the sputtering process. For example, with ever decreasing flying heights and increased contact between the head and disk during drive operation, there is a greater need to protect the magnetic film layer from wear. It is therefore desirable to provide the outer protective layer to be as hard as possible without adversely effecting the magnetic properties of the resulting recording disk. In the particular case of carbon, a maximum hardness is achieved when graphitization of the carbon is minimized during the sputtering process. One means employed to moderate graphitization of sputtered carbon films is by incorporating hydrogen into the film. Such incorporation may be accomplished by sputtering in an argon atmosphere mixed with hydrogen or a hydrogen-containing gas, such as methane or other hydrocarbons.

A problem with this approach is that magnetic films are highly susceptible to corrosion from certain gasses present even at trace concentrations within the magnetic layer sputtering chamber. Such corroding gasses include hydrogen and some hydrocarbons such as methane. Therefore, while the presence of certain gasses may improve the properties of one sputtered layer, they may have a deleterious effect on another sputtered layer.

Certain prior art sputtering machines have attempted to isolate one sputtering process from another. Fig. 1 is a representation of a portion of a prior art sputtering machine showing a first process in a chamber 20 separated from a second process in a chamber 22 by the use of a low pressure chamber 24 between the two processes. The low pressure within chamber 24 is accomplished by means of a pump 26 within the chamber 24 pulling gasses out of the chamber through pressure slits formed in the chamber wall . However, only minimal pressure and temperature differentials between chambers 20 and 22 is possible with such a system, and it is still possible that some gasses from one process will float either up-stream or down-stream and cause contamination of the other process.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a buffer chamber to physically isolate a first process from a second process to prevent gasses used in one process from being present in the other process.

It is a further object of the present invention to provide a buffer chamber to allow a substantial pressure differential between a first process and a second process within an in-line sputtering machine.

It is another object of the present invention to provide a buffer chamber to allow a substantial temperature differential between a first process and a second process within an in-line sputtering machine.

These and other objects are accomplished by the present invention which relates to a dynamic buffer chamber in an in-line sputtering apparatus for fabricating magnet recording disks for Winchester-type hard disk drives. In a preferred embodiment, the dynamic buffer chamber is positioned between the magnetic layer and carbon layer sputtering chambers and is used to isolate the respective sputtering processes from each other. However, it is understood that the buffer chamber according to the present invention may be used to isolate other contiguous processes within the sputtering machine. In operation, after a substrate-carrying pallet leaves the magnetic layer sputtering chamber, the pallet enters the dynamic buffer chamber. The buffer chamber includes an entry door and an exit door. When the pallet exits the magnetic sputtering chamber, the entry door to the buffer chamber is open and the exit door is sealed, such that the pressure and temperature conditions within the buffer chamber are substantially the same as that of the magnetic layer sputtering process. Once in the buffer chamber, both the entry and exit doors are sealed, and the chamber is evacuated by means of a high vacuum pump system associated with the buffer chamber. Thereafter, the buffer chamber is backfilled with a gas such as argon, until the pressure and temperature within the buffer chamber are substantially the same as for the carbon deposition process. With the entry door remaining sealed, the exit door is opened and the pallet is then transported to the carbon sputtering chamber.

After the pallet exits the buffer chamber to the carbon overcoat sputtering chamber, the buffer chamber is once again sealed and evacuated prior to re-opening to the magnetic process side. Thus, any gasses from the carbon process are prevented from entering the magnetic layer process. The dynamic buffer chamber, in a preferred embodiment of the present invention, therefore serves to isolate the magnetic and carbon layer sputtering processes from each other with respect to pressure and temperature. Additionally, the evacuation of the buffer chamber prevents any gasses used in one of the deposition processes from intermixing with the gasses used in the other of the deposition processes.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the drawings in which:

FIGURE 1 is a prior art representation of a portion of an in-line sputtering machine including first and second process chambers, and a buffer chamber therebetween; FIGURE 2 is a top view representation of a dynamic buffer chamber according to the present invention;

FIGURE 3 is a top view representation of a portion of an in-line sputtering machine showing the dynamic buffer chamber according to the present invention with a substrate-carrying pallet exiting the magnetic layer sputtering chamber;

FIGURE 4 is a top view representation of a portion of an in-line sputtering machine showing the dynamic buffer chamber according to the present invention with a substrate-carrying pallet inside of the dynamic buffer chamber;

FIGURE 5 is a top view representation of a portion of an in-line sputtering machine showing the dynamic buffer chamber according to the present invention with a substrate-carrying pallet exiting the dynamic buffer chamber; and

FIGURE 6 is a schematic representation of the control system for controlling the operation of the dynamic buffer chamber according to the present invention.

DETAILED DESCRIPTION The present invention will now be described with reference to Figs. 1-6 which in general relate to a dynamic buffer chamber for isolating a first process from a second process within an in-line sputtering machine. In a preferred embodiment the above-mentioned first and second processes comprise deposition of magnetic and carbon overcoat layers, respectively, onto a substrate to form a recording disk for a Winchester- type hard disk drive. However, it is understood that the dynamic buffer chamber according to the present invention may be adapted for use in various sputtering machines and for deposition of thin films on substrates for various applications.

Moreover, it is understood that the dynamic buffer chamber according to the present invention may be located between any two contiguous processes within the in-line sputtering machine to isolate the processes from each other. For example, the buffer chamber according to the present invention may be located between the chromium undercoat sputtering chamber and the magnetic layer sputtering chamber, instead of or in addition to its location between the magnetic layer and overcoat sputtering chambers. Therefore, although the invention is described hereinafter as separating the magnetic layer and carbon overcoat sputtering processes, it is understood that the present invention is not limited to isolation of only these processes. As shown in Fig. 2, dynamic buffer chamber 100 is preferably constructed of one-inch thick type 304 stainless steel and has a height of approximately 39 inches, a length of approximately 44 inches, and a depth of approximately 12 inches as measured at the exterior walls of the chamber. As used above, the height is defined by a dimension perpendicular to the direction of travel of a pallet through the machine; the length is parallel to the direction of travel of a pallet; and the depth is perpendicular to the plane of the pallet. The use of electropolished stainless steel in dynamic buffer chamber 100 minimizes particulate generation from scratches and other surface imperfections. The chamber 100 further includes an access door 102 covering a substantial portion of the front of the chamber for allowing access to the chamber for maintenance or for access to a substrate-carrying pallet present in the chamber. The inclusion of buffer chamber 100 within an in-line sputtering machine increases the overall path or length of the machine. However, because the chamber 100 is able to effectively isolate processes located on either side of the chamber, as explained in greater detail below, the inclusion of the chamber improves throughput and reduces the time it takes for a substrate to travel through the sputtering machine.

The internal volume of buffer chamber 100 is reduced to approximately 8 cubic feet by the presence therein of a volume-displacing solid aluminum block 104. As shown in Fig. 2, the block 104 may be affixed to the access door 102. The block 104 may alternatively be affixed to the rear wall cf chamber 100, or a portion of block 104 may be provided on both the chamber door 102 and rear wall. The purpose of block 104 is to reduce the evacuation time necessary to pump out the gasses within the chamber. It is further understood that the volume occupied by the block 104 may vary in alternative embodiments.

The chamber 100 additionally includes pneumatically-operated process isolation doors 106_a and 106_b, mounted at the entrance and exit of chamber 100 respectively. As shown in Fig. 2, the doors 106_a and 106_b may be pivotally mounted on pneumatic cylinders 108. and 108_b so that the doors 106 pivot between an open position (shown in phantom) and sealed position. Each cylinder 108_a and 108_b includes a pair of solenoid triggers, one door-open solenoid trigger and one door- close solenoid trigger. As described in greater detail below, the doors 106 open or close in response to signals sent to the door-open or door-close solenoid triggers, respectively. It is understood that doors 106 may operate by other known mechanisms. Similarly, it is understood that doors 106 may be mounted at the entrance and exit of chamber 100 by other known methods. For example, in an alternative embodiment, the doors 106 may close by sliding across the entrance and exit to the chamber 100.

Figs. 3-5 show a portion of an in-line sputtering apparatus including the dynamic buffer chamber 100 according to the present invention. In a preferred embodiment of the present invention, the dynamic buffer chamber may be located between a magnetic layer sputtering chamber 110 and a carbon overcoat sputtering chamber 112. Dwell modules 114 and 116 may be provided as shown to allow for substrate transport system run¬ out, if necessary, during multiple substrate processing in the sputtering machine. Substrate transport system run-out occurs because some processes within the sputtering machine occur more quickly than others and the substrate-carrying pallet must be held within a dwell module upon exiting a particular chamber until the next subsequent chamber is vacated.

Deposition of the thin film magnetic layer occurs in sputtering chamber 110. Although not critical to the present invention, sputtering of the magnetic film generally occurs in an argon atmosphere at a pressure of approximately 10 mTorr. Any of various compositions may be used as the magnetic layer, although alloys of cobalt and chromium (CoCr) are highly desirable as films for magnetic recording media such as disks utilized in Winchester-type hard disk drives. The addition of other elements such as tantalum (Ta) to form a cobalt/chromium/tantalum (CoCrTa) alloy produces a film having enhanced coercivity and corrosion resistance properties.

In operation, one or more substrates may be loaded onto a substrate-carrying pallet 118, which pallet is supported for transport through the sputtering machine for deposition of the films onto the substrate (s) . Upon a substrate-carrying pallet 118 exiting the magnetic layer sputtering chamber 110, the door 106_a of the buffer chamber 100 is open while the door 106_b is closed. In this condition, shown in Fig. 3, buffer chamber 100 has the same pressure, temperature and gaseous composition as the magnetic layer sputtering chamber 110. In a preferred embodiment, this pressure and temperature are approximately 10 mTorr and 250°C, respectively. It is understood, however, that these pressure and temperature values may vary in alternative embodiments.

Once the substrate-carrying pallet 118 is positioned within the chamber 100, both doors 106_a and 106_b are closed, as shown in Fig. 4. With doors 106 and 106_b sealed, the dynamic buffer chamber 100 is isolated from the processes located both up-stream and down-stream of the chamber 100. Once isolated, the buffer chamber 100 is preferably evacuated to a pressure of approximately 10^~7 Torr in order to minimize the contaminant circulation within the chamber 100, as well as to evacuate the gasses used in the magnetic layer sputtering process. Such gasses may be harmful to a process down-stream of the chamber 100. A high vacuum pumping system 120 (Fig. 2) is used to evacuate the chamber 100. In a preferred embodiment, the pumping system 120 may be known pumping system comprised of a cryo pump, such as is available from CTI Cryogenics, a division of Helix Corporation of Santa Clara, California. The pumping system may alternatively be comprised of a turbomolecular pump of known design. Moreover, as will be appreciated by those in the art, the pumping system 120 may additionally include a standard mechanical pump to accomplish an initial pump-down of the chamber 100 prior to evacuation by the cryo pump. It is an important feature of the present invention that the dynamic buffer chamber 100 allows a significant pressure and temperature differential between processes located up-stream and down-stream of the chamber 100. It has been determined that while the magnetic layer deposition process is preferably carried out at 10 mTorr, sputtering of the carbon overcoat, is preferably carried out at approximately 5 mTorr. Therefore, after the chamber 100 has been evacuated, it is preferably backfilled with a gas composition through a gas diffuser 122 (Fig. 2) to the pressure of the carbon overcoat sputtering process. It is understood, however, that in alternative embodiments of the invention, the pressure need not be equalized to that of the carbon process. With the doors 106 sealed, the environment within chamber 100 may be controlled to a temperature and/or pressure different and independent from the temperature and pressure of both the magnetic layer and carbon overcoat deposition processes. The control of the pressure and temperature within the chamber 100 will be described in greater detail below. When the system is ready to transport the substrate-carrying pallet 118 from the buffer chamber 100 to the carbon sputtering chamber 112, the door 106_b opens while the door 106_a remains closed. In this condition, shown in Fig. 5, buffer chamber 100 has the same pressure, temperature and gaseous composition as the second process.

As previously explained, sputtering of carbon onto the magnetic film preferably occurs in an argon atmosphere which may also include other gasses such as hydrogen and/or a hydrogen gas such as methane or other hydrocarbons. These gasses would have a detrimental effect on the magnetic properties of the magnetic layer if allowed to flow up-stream from the carbon sputtering chamber 112 into the magnetic layer sputtering chamber 110. Therefore, after the substrate-carrying pallet 118 exits the buffer chamber 100 to the carbon chamber 112, the doors 106_a and 106_b are sealed, and the chamber 100 is once again evacuated by pumping system 120. In this way, any gasses or other contaminants present in chamber 100 from the carbon sputtering chamber 112 are substantially flushed away prior to once again opening the chamber 100 to the magnetic layer process side. After the chamber 100 has been evacuated, the chamber may be backfilled to a pressure substantially equal to the sputtering pressure within the magnetic layer buffer chamber 110.

In one embodiment of the invention, after evacuation, the chamber 100 may be backfilled with argon both prior to opening the chamber to the magnetic process side and prior to opening the chamber to the carbon overcoat process side. However, in an alternative embodiment, the chamber 100 may be backfilled with different gaseous compositions depending on which process it is about to open to. For example, the chamber 100 may be backfilled with argon just prior to opening to the magnetic layer process side, but may be backfilled with an argon atmosphere including hydrogen or other gasses just prior to opening to the carbon overcoat process side. As explained, such additional gasses are often included as part of the carbon sputtering process. As is known in the art, the diffuser 122 may include at least two different diffusion tubes (not shown) to allow the chamber 100 to be backfilled with more than one type of gaseous composition.

As discussed above, the isolation provided by dynamic buffer chamber according to the present invention allows a significant pressure and temperature differential between processes located up-stream and down-stream of the chamber 100. For example, it is contemplated that the pressure differential between contiguous processes on either side of buffer chamber 100 may be as high 760 Torr (i.e. , the approximate difference between sputtering and atmospheric pressures) . Similarly, the temperature differential between the first and second processes may be as high as approximately 200°C. It is understood that in alternative embodiments of the invention, the maximum pressure and temperature differentials between processes on either side of chamber 100 may be greater or lesser than that described above.

The pressure and temperature within the chamber 100 are dictated by the pumping system 120 and gas diffuser 122, which evacuate and backfill the chamber 100, respectively, as described above. The diffuser, which may be a known mass flow controller, controls gas flow within the chamber 100 so that, as gas is let in, the temperature of the substrates and substrate- carrying pallet within the chamber may decrease as much as 50°C in a preferred embodiment. This occurs as result of conductive heat transfer using the backfilled gas atoms to transfer heat away from the substrate- carrying pallet and substrates. It is understood that in alternative embodiments of the invention, buffer chamber 100 may additionally include heating panels of a conventional design to control the temperature of the substrates within the chamber.

The chamber doors 106_a and 106_b, the pumping system 120 and the gas diffuser 122 are controlled by an electronic control system as described in U.S. Serial No. 07/681,866, entitled APPARATUS AND METHOD FOR HIGH THROUGHPUT SPUTTERING, previously incorporated by reference herein. A portion of such a control system is shown generally at reference numeral 200 in Fig. 6, specifically in connection with the dynamic buffer chamber 100.

Control system 200 generally performs two functions with respect to buffer chamber 100: (1) monitoring the chamber environment by sensing pressure and temperature data from within the chamber 100, and providing such data to the system operator (s) ; and (2) controlling the chamber 100 environment by providing user-controlled and automatically generated control signals to the functional elements of the chamber 100.

The control system includes at least one central processing unit (CPU) 216 which sends signals to and receives feedback signals from the dynamic buffer chamber 100 via the network interface 214. Feedback data from the chamber 100 is relayed through the CPU 216 to one or more operators through a user interface 218, which includes a view screen and input/output means such as a keyboard or touch screen.

As previously explained, the doors 106_a and 106_b are preferably operated by pneumatic cylinders 108_a and 108_b, each cylinder having a pair of solenoid triggers, one door-open solenoid trigger and one door-close solenoid trigger. The CPU 216 sends a pulsed signal via the door control 202 to either the door-open solenoid or the door-close solenoid to thereby effect opening and closing, respectively, of the doors 106_a, 106_b as described above. The open or closed position of each door 106 is sensed via a door position sensor 208 and relayed to the CPU 216. Initiation/termination of the chamber 100 evacuation process by pumping system 120 as described above is accomplished in response to an on/off control signal from the CPU 216. The signal is received in the pumping system 120 via the pumping system control 204. Similarly, diffusion of gas through diffuser 122 is accomplished in response to an on/off signal from the CPU 216 to initiate/terminate the backfill of chamber 100 with a volume of gas. The signal is received in the gas diffuser 120 via gas diffuser control 206. The electronic controls 200 further include a pressure sensor 210 and a temperature sensor 212 to indicate the instantaneous pressure and temperature within chamber 100.

Operation of the door control 202, pumping system control 204, and gas diffuser control 206 may be accomplished automatically by the CPU 216 in response to timing signals and feedback signals such as a signal indicating a position of the substrate-carrying pallet 118 within the sputtering machine. Alternatively, the dynamic buffer chamber controls 202, 204 and 206 may be manually controlled via the user interface 218. Additionally, the user interface 218 may be used to manually enter set point values for the pressure conditions within the chamber 100. Moreover, as will be appreciated by those in the art, the control system 200 may alternatively control the composition of gas within the chamber 100 so as to provide different gasses and/or vary the ratio of gasses within the composition. Although the invention has been described in detail herein, it should be understood that the invention is not limited to the embodiments herein disclosed. Various changes, substitutions and modifications may be made thereto by those skilled in the art without departing from the spirit or scope of the invention as described and defined by the appended claims.

Claims

I Claim:

1. A method of providing a buffer zone for isolating a first process from a second process in an in-line sputtering machine where a transport travels from the first process to the second process, comprising the steps of : opening the buffer zone to the first process while the buffer zone is sealed against the second process to allow entry of the transport into the buffer zone; opening the buffer zone to the second process while the buffer zone sealed against the first process to allow exit of the transport from the buffer zone; and after the transport enters or exits the buffer zone, and prior to opening the buffer zone to the first or second processes: sealing the buffer zone against the first and second processes, and removing a volume of gas from the buffer zone.

2. A method of providing a buffer zone for isolating a first process from a second process as recited in claim 1, wherein said first process comprises deposition of a magnetic layer onto a substrate during the formation of magnetic recording disk for use in a hard disk drive.

3. A method of providing a buffer zone for isolating a first process from a second process as recited in claim 1, wherein said second process comprises deposition of a carbon layer onto a substrate during the formation of magnetic recording disk for use in a hard disk drive.

4. An apparatus for isolating first and second processes from each other in a sputtering machine where a transport travels from the first process to the second process, comprising: a chamber including a first door at an entrance to said chamber and a second door at an exit of said chamber; means for having said first door open and said second door closed upon said transport entering said chamber from the first process; means for having said first door closed and said second door open upon said transport exiting said chamber to the second process; and means for removing a volume of gas from said chamber after said transport has entered or exited said chamber and before said chamber opens to the first or second processes, said evacuating means comprising means for closing said first and second doors and means for pumping said volume of gas out of said chamber.

5. An apparatus for isolating a first process from a second process in a sputtering machine as recited in claim 4, wherein said first process comprises deposition of a magnetic layer onto a substrate during the formation of magnetic recording disk for use in a hard disk drive.

6. An apparatus for isolating a first process from a second process in a sputtering machine as re-rited in claim 4, wherein said second process comprises deposition of a carbon layer onto a substrate during the formation of magnetic recording disk for use in a hard disk drive.

7. An apparatus for isolating a first process from a second process in a sputtering machine as recited in claim 4, wherein the first process is carried out at a first pressure and the second process is carried out at a second pressure different from said first pressure.

8. An apparatus for isolating a first process from a second process in a sputtering machine as recited in claim 4, wherein the first process is carried out at a first temperature and the second process is carried out at a second temperature different from said first temperature .