Temperature dependent pull speeds for drying of a wet cleaned workpiece

Drying of wet workpiece, such as a magnetic recording media, following a wet clean process where the wet workpiece is displaced from a liquid volume into a gaseous volume at a pull speed that is dependent on the temperature of the gaseous volume.

TECHNICAL FIELD

This invention relates to the field of wet cleaning of a workpiece and more specifically, to drying of wet magnetic recording media following a wet clean process.

BACKGROUND

Wet cleaning is a frequent and critical operation in the manufacture of a workpiece, such as a magnetic recording media, semiconductor wafer or LCD panel. Wet cleaning generally entails introducing a liquid, aqueous or otherwise, to the surface of the workpiece. Both throughput and cleaning efficiency of a wet clean are important considerations because throughput determines equipment cost/workpiece, which should be minimized while cleaning efficiency determines workpiece yield, which should be maximized.

Wet cleaning generally also entails drying the workpiece. Typically, a drying operation is performed by first submerging the workpiece in a volume of liquid, such as deionized ultrapure water, and then displacing the workpiece from the liquid volume to a gaseous volume to dry the liquid from the surface of the workpiece.FIG. 1illustrates a plan view of a magnetic recording media substrate130which has been wet cleaned and dried in such a manner during a media fabrication process. A residue stain131is depicted on the magnetic recording media substrate130. Such stains are frequently caused by improper drying which may occur for example when the workpiece is pulled, or withdrawn, from the liquid during the drying operation and the liquid meniscus at the liquid interface breaks poorly and leaves behind a residue.

While it is known that such residue stains are detrimental to workpiece yield, throughput of a dryer can suffer greatly if the pull speed of the workpiece is reduced significantly to reduce ripples in the liquid interface or to otherwise improve other undesirable meniscus behavior in an effort to mitigate yield loss from residue staining. For example, a mere 20 second increase in the dryer process time can translate into a 200 parts/hour throughput reduction.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth such as examples of specific, components, processes, etc. to provide a thorough understanding of various embodiment of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice various embodiments of the present invention. For example, while the exemplary embodiments pertains to drying of magnetic recording media, the methods described herein may be readily applied to processing of another workpiece, such as semiconductor substrates or LCD panels. In other instances, well known components or methods have not been described in detail to avoid unnecessarily obscuring various embodiments of the present invention.

FIGS. 2A and 2Bare orthogonal cross-sectional views illustrating an exemplary dryer module200, which may be one module of an automated wet station (AWS) or a stand-alone apparatus. A dryer module such as that depicted inFIGS. 2A and 2Bis commercially available through Invenpro, (M) Sdn. Bhd. of Malaysia. However, particular embodiments describe herein may nonetheless be practiced with any other commercially available dryer modules which have capabilities similar to those describe herein. As depicted, the dryer module200includes a tank201containing a liquid volume205. Over the liquid volume205is a gaseous volume210which further includes a dryer hood212and a dryer chamber215. The dryer hood212encloses a high temperature region to rapidly dry the disk while the gaseous volume within the dryer chamber215serves as a buffer region between the dryer hood212and liquid volume205to ensure the gas introduced into the dryer hood212does not perturb the liquid-gaseous interface206.

During operation of the dryer module200, hood doors214open and close to permit transport of a shuttle225carrying at least one workpiece, such as a magnetic recording media substrate130, to and from the dryer module200by a robot handler220. For example, when the magnetic recording media substrate130is transported to the dryer module200, the hood doors214open, the magnetic recording media substrate130is submerged in the liquid volume205so that all surfaces of the magnetic recording media substrate130are below the liquid-gaseous interface206, and the hood doors214close. For better drying efficiency, the gaseous volume within the dryer hood212is heated to a controlled setpoint by introducing a gas, such as nitrogen (N2), heated to approximately 80-125° C. Heating of the inlet gas may be controlled based on feedback from a hood temperature sensor248.

The dryer module200further includes a temperature sensor240positioned proximate to the liquid-gaseous interface206for determining the temperature of the dryer chamber215. In a specific embodiment, the temperature sensor240is positioned within approximately 50 mm of the liquid-gaseous interface206and preferably within approximately 25 mm. As discussed in further detail elsewhere herein, the temperature sensor240may be utilized for control of the speed at which the magnetic recording media substrate130is pulled from the liquid volume205into the gaseous volume210, and in particular the dryer chamber215, during the drying operation. Controlling the pull speed in this temperature dependent manner enables the drying efficiency to be improved so that workpiece staining and/or total drying time may be shortened, thereby improving dryer throughput. As further discussed herein, the pull speed may be made dependent both the geometry of the workpiece and on the temperature of the dryer to control meniscus behavior and improve drying efficiency.

In an embodiment, the speed at which a workpiece is displaced out of a liquid is dependent on the geometry of the workpiece. The geometry of the workpiece determines the surface topologies which pass through the liquid-gaseous interface206forming a meniscus. Generally, the interface meniscus is stronger at higher pull speeds and therefore the pull speed may be relatively lower in zones where the workpiece surface breaks the meniscus.

FIG. 3is an expanded side view ofFIG. 2B, depicting the magnetic recording media substrate130standing upright within a liquid volume205. The magnetic recording media substrate130has an annular disk-shape. In particular embodiments, the outer diameter (OD) varies between approximately 48 mm to 95 mm while the inner diameter (ID) ranges from approximately 20 mm to 25 mm. However, other dimensions are also possible, depending on the application of the magnetic recording media.

In an embodiment where the drying operation is performed as part of a post-sputter wet cleaning (PSC) module, the magnetic recording media substrate130includes a magnetic recording layer on the surface of the disk. The magnetic layer may be of any known composition, such as a cobalt (Co) alloy. The magnetic layer may be formed on both sides of magnetic recording media substrate130to form a double-sided magnetic recording disk. Alternatively, a single sided perpendicular magnetic recording disk may be formed. In an alternate embodiment where the drying operation is performed as part of a pre-sputter wet cleaning, the magnetic recording media substrate130may be, for example, a glass material, a metal, and/or a metal alloy material. Glass substrates that may be used include, for example, silica containing glass such as borosilicate glass and aluminosilicate glass. Metal and metal alloy substrates that may be used include, for example, aluminum (Al) and aluminum magnesium (AlMg) substrates, respectively. The magnetic recording media substrate130may also be plated with a nickel phosphorous (NiP) layer.

During a drying operation, workpiece zones332,333,334,335and336pass through the liquid-gaseous interface206as a robot handler traverses the displacement distances D1, D2, D3, D4and D5, respectively. In particular embodiments, the pull speed of the robot handler depends on positional teach points to define the displacement distances D1-D5and thereby account for the geometry of magnetic recording media substrate130. Thus, workpiece zones332-336form a pull speed profile across the major surfaces of the magnetic recording media substrate130. As shown, the initial zone332includes a top OD surface of the magnetic recording media substrate130. It has been found that a relatively lower pull speed for the initial zone332is advantageous. Too high of a pull speed in the initial zone332has been correlated with severe staining near the top of the magnetic recording media substrate130. The meniscus is broken along the displacement distance D1as the initial zone332passes through the liquid-gaseous interface206. The displacement distance D1may be between 1 and 10 mm, depending on the substrate OD and ID and is preferably between 4 and 6 mm for a substrate having a 95 mm OD and a 25 mm ID.

The pull speed may then be increased to a first intermediate pull speed for the displacement distance D2, which may be between 10 mm and 40 mm, depending on the substrate OD and ID and is preferably between 20 mm and 30 mm for a substrate having a 95 mm OD and a 25 mm ID. The high speed pull zone333passes through the liquid-gaseous interface206at this first intermediate pull speed. Increasing the pull speed above that used for the initial zone332shortens drying time, advantageously increasing dryer throughput. In one embodiment, the first intermediate pull speed may be approximately 1.7 mm/s.

The first intermediate pull speed may then be reduced to a second intermediate pull speed upon reaching the ID slow pull zone334where the meniscus is again broken by the ID surface of the magnetic recording media substrate130. The transition between the first intermediate pull speed and the second intermediate pull speed occurs upon the ID surface being submerged approximately 1-5 mm below the liquid-gaseous interface206, with the displacement distance D2to be maximized and displacement distance D1minimized for highest throughput. Generally, the ID slow pull zone334extends to approximately one half of the ID. For an exemplary 25 mm ID, the displacement distance D3is between 15 mm and 20 mm. In one exemplary embodiment, the second intermediate pull speed is approximately 0.7 mm/s.

After the ID slow pull zone334has passed through the liquid-gaseous interface206, the pull speed is then increased to a third intermediate pull speed along the displacement distance D4where the high speed pull zone335passes through the liquid-gaseous interface206. The higher third intermediate pull speed further improves the dryer throughput and in an advantageous embodiment, the third intermediate pull speed is greater than first intermediate pull speed. The displacement distance D4again depends on the substrate OD and ID and is preferably between 20 mm and 30 mm for a substrate having a 95 mm OD and a 25 mm ID. In one exemplary embodiment, the third intermediate pull speed is approximately 1.7 mm/s.

The pull speed is then reduced from the third intermediate pull speed to a final pull speed as the final zone336, including the bottom OD surface of the magnetic recording media substrate130, passes through the liquid-gaseous interface206over the displacement distance D5. The displacement distance D5depends on the substrate OD and ID and is preferably between 5 mm and 10 mm for a substrate having a 95 mm OD and a 25 mm ID. In one exemplary embodiment, the final pull speed is approximately 0.7 mm/s. Thus, in the exemplary pull speed profile depicted inFIG. 3, pull speed depends on the workpiece geometry such that the pull speed is a non-linear function of the displacement of the workpiece.

The temperature of the gaseous volume within the dryer chamber215increases by convective heat transfer such that a considerable temperature delta may exist between the dryer hood212and dryer chamber215. For example, the highest temperature T1is in the dryer hood proximate to the gas inlet213with a lowest temperature T3, in the chamber proximate to the liquid-gaseous interface206at the distal end of tank, furthest from the gas inlet213. An intermediate temperature T2may be found in a region of the gaseous volume there between. Through experimentation, it has been found that the temperature of the gaseous volume in the dryer chamber215, particularly the temperature proximate to the liquid-gaseous interface, has a large impact on at least some of the mechanisms responsible for the staining of a workpiece during a drying operation. Generally, with lower chamber temperatures, the pull speed must be lowered to reduce staining.

FIG. 4is a graph illustrating dryer chamber temperature dependence upon time and hood door position during a drying cycle. As depicted, the temperature in the dryer chamber215(e.g., as measured by the temperature sensor240) declines by approximately 40° C. from the time the hood door214opens at the 0 second time mark until the hood door214is closed, at approximately the 45 second time mark, as dryer heat dissipates to the relatively colder air entering the opened door. During the 45 second time interval that the hood door214is open, the robot handler220transports the magnetic recording media substrate130through the dryer hood212and dryer chamber215and submerges the media in the liquid volume205.

After the hood door214is closed and the media is submerged, the heated N2is then introduced into the dryer hood212. Although the temperature in the dryer hood212jumps immediately upon closing the hood doors214, the chamber temperature does not. Instead, the temperature within the dryer chamber215increases by approximately 30° C. from the 45 second time mark to the 85 second time mark. Notably, in addition to the long transition time there is significant variation (e.g., 15 to 20° C.) across multiple runs processing substantially the same workpiece batch size.

Generally, to increase dryer throughput the pull speed may be increased and the hood drying time reduced. However in so doing, the drying which occurs as the workpiece zones pass through the dryer chamber215becomes more important to the overall drying efficiency. However, as shown inFIG. 4the temperature within the dryer chamber215may still be at a very low temperature (i.e., significantly below the hood temperature) so that drying efficiency within the dryer chamber215is poor.

In an embodiment, to mitigate the effects of the lagging dryer chamber temperature while maximizing dryer throughput, the speed at which a workpiece is displaced out of a liquid and into a gaseous volume is determined based on the temperature of a gaseous volume within the dryer.FIG. 5is a flow diagram illustrating a workpiece pulling method500in which a workpiece is displaced from a liquid volume to gaseous volume at a pull speed that is dependent on the temperature of the dryer chamber215. In one such embodiment, the pull speed is set by an automated control system executing the workpiece pulling method500.

For clarity, the workpiece pulling method500is described with reference to the dryer module200depicted inFIG. 2AandFIG. 2B. The workpiece pulling method500begins at operation501with submerging the workpiece in a liquid volume. At operation505, with the dryer hood doors214closed, the dryer hood212is heated toward setpoint, convectively heating the dryer chamber215. At operation510, the actual temperature of the dryer chamber215is measured, for example with the temperature sensor240. In one such embodiment, the heating of the dryer hood212and sensing of the temperature in the dryer chamber215is initiated once the magnetic recording media substrate130is submerged in the liquid volume205. During operation510, the chamber temperature may be sensed at any nominal sampling rate, for example one measurement/second.

At operation515the workpiece zone is determined, for example based on the position of the robot handler220. At operation520, a lookup table (LUT) is accessed to determine a pull speed based on the sensed chamber temperature. Exemplary LUT are depicted inFIG. 6. In one embodiment illustrated inFIG. 6, a temperature dependent pull speed LUT601includes an array of chamber temperatures, each associated with a maximum pull speed. As depicted, the maximum pull speed decreases with lower chamber temperature. It should be noted however, that the actual values populating the LUT601are merely exemplary and the pull speed dependency on chamber temperature may be either a linear or non-linear.

Referring back toFIG. 5, the maximum pull speed determined at operation520may then be scaled based on the workpiece zone being displaced through the liquid-gaseous interface. In this manner, the pull speed is made both a function of the chamber temperature and a function of the geometry of the workpiece. In an alternate embodiment, the temperature dependent pull speed LUT605may be accessed at operation520. As depicted inFIG. 6, the temperature dependent pull speed LUT605includes an array of chamber temperatures and an associated pull speed for each of a number of workpiece zones. The actual values of populating the LUT605are merely exemplary. In such an embodiment, a specific pull speed based on both the chamber temperature and the workpiece zone may be determined directly at operation520and a secondary scaling of a maximum pull speed is unnecessary.

The workpiece pulling method500diverges at operation525to allow for a chamber temperature ramp delay if the pull from the liquid has not yet begun. As depicted inFIG. 4, waiting 20 seconds before displacing the initial workpiece zone (e.g., zone332inFIG. 3) permits the chamber temperature to increase approximately 15 to 20° C. The higher chamber drying efficiency at the elevated temperature then enables a faster pull speed and potentially a shorter hood drying time. Such a chamber temperature ramp delay entails a later drying start time for the benefit of the greater drying efficiency possible with a higher temperature drying chamber.

Returning toFIG. 5, if the chamber temperature is determined to be below a minimum temperature threshold at operation530, then the workpiece pulling method500returns to operation510to again read the actual temperature, thereby delaying a pull of the workpiece from the liquid volume205for each iteration of operations510-530by at least the temperature sample rate until the chamber temperature increases. For example, where operation510is performed at a sample rate of approximately one sample/sec, the delay period will be a multiple of the one sample/sec rate. If the chamber temperature is determined to be at or above a minimum temperature threshold at operation530, the pull is immediately initiated at operation540to displace the initial zone from the liquid volume205at the initial pull speed as determined operation515. In alternate embodiments, where a temperature ramp delay is avoided, the operation530is eliminated and, at operation540, the initial pull commences immediately at a speed based on chamber temperature.

Following operation540, the workpiece pulling method500returns to operation510to again read the chamber temperature, determine the workpiece zone at operation515and determine a new pull speed based on the temperature at operation520. Because the dryer chamber215becomes warmer with time and the workpiece zone has incremented into an intermediate zone, the pull speed determined this time at operation520may be considerably higher than it was for the initial workpiece zone.

The workpiece pulling method500then continues to operation525, and because the pull has been initiated, the workpiece pulling method500proceeds this time to operation545to begin displacing the next zone (N) from the liquid volume205to the gaseous volume (e.g., within dryer chamber215). The workpiece pulling method500then continues to operation550, at which point the method diverges. If all workpiece zones have been pulled through the liquid-gaseous interface206, the workpiece pulling method500completes at operation560and the workpiece may then be completely dried within the dryer hood212. If not all workpiece zones have been pulled through the liquid-gaseous interface206, the workpiece pulling method500repeats the cycle by returning to operation510for another chamber temperature sample and another iteration of the operations515,520,525,545and550.

Depending on the time required to pull a particular zone through the liquid-gaseous interface206, the rate at which the chamber temperature increases and the granularity of the temperature dependent pull speed LUT, the pull speed for any particular zone may be updated multiple times as the workpiece is displaced through the zone. For example, referring back toFIG. 3, the first pull speed of approximately 0.7 mm/s for the high speed pull zone333may be modified to be approximately 0.8 mm/s upon a second temperature determination.

The workpiece pulling method500may be looped in this manner continuously such that the pull speed for each workpiece zone may be maximized as a function of both zone and chamber temperature. The pull speeds in the specific geometrically-based workpiece zones depicted inFIG. 3may be adapted to additionally depend on chamber temperature for increased throughput and reduced staining. For example, in one particular embodiment where the exemplary workpiece pulling method500is applied to the magnetic recording media substrate130, the initial pull speed and first intermediate pull speed are each set based on the temperature of a gaseous volume. For example, over the initial zone332, the pull speed may be reduced to approximately 0.75+/−0.25 mm/s, depending on the dryer chamber temperature. Such a low, temperature dependent, pull speed will achieve mush less residual liquid staining on the side of the magnetic recording media substrate130, near the top surface. The slower initial pull speed would improve the drying efficiency of the relatively cooler dryer chamber because the poor meniscus behavior is reduced or eliminated by the slower pull speed. Additionally, the total pull duration is not increased greatly because the displacement distance D1is small and the pull speed temperature dependence accounts for the significant run-to-run variation in the chamber temperature.

In a further embodiment, to minimize total pull duration, the pull speed for certain workpiece zones is modified to compensate for a relatively slower pull speed in other workpiece zones dictated by the lower dryer temperature. In this manner, the pull speed in a second workpiece zone is made dependent on the pull speed of a first workpiece zone. For example, where the pull speed in a first workpiece zone is temperature dependent and performed at a rate relatively lower than a nominal value, the pull speed in a second workpiece zone, which may not be temperature dependent (e.g., one of the intermediate zones, such as high speed pull zones333or335), is increased to compensate (based on displacement distance and pull rate) toward a nominal total pull duration.

In another embodiment however, the pull speed at each of the five depicted workpiece zones332-336is determined based on the dryer chamber temperature. Such an embodiment incurs little additional implementation overhead and additional throughput gains may be achieved by increasing the pull speed in other workpiece zones. For example, the third intermediate pull speed, at which the high speed pull zone335passes through the liquid-gaseous interface206, may be increased to approximately 1.75-2.0 mm/s based on the measured chamber temperature.

In certain embodiments, the final pull speed (e.g., displacing final zone336through the liquid-gaseous interface206) is set to be higher than the initial pull speed. For example, where the final pull speed for a 95 mm OD magnetic recording media substrate130is approximately 0.75 mm/s, the initial pull speed may vary as approximately 0.75+/−0.25 mm/s because the initial pull speed may be limited by both the lower chamber temperature and the meniscus issues pertaining to the top OD surface while the final pull speed is only limited by the meniscus issues pertaining to the bottom OD surface.

In a further embodiment, the final zone336including the bottom surface of the magnetic recording media substrate130passes through the liquid-gaseous interface206at a final pull speed that is faster than the second intermediate pull speed, at which the ID slow pull zone334passes through liquid-gaseous interface206. For example, where the final pull speed for a 95 mm OD magnetic recording media substrate130is approximately 0.75 mm/s, the second intermediate pull speed is approximately 0.5 mm/s.

FIG. 7is a block diagram illustrating a dryer control system700for displacing a workpiece from a liquid volume to gaseous volume at a pull speed dependent on the temperature of the gaseous volume, in accordance with an exemplary embodiment. As depicted, a dryer controller701, such as a programmable logic controller (PLC), includes a processor702, a memory705and I/O715. The dryer controller701is an automated control system responsible for controlling pulling of a workpiece from a liquid volume into a gaseous volume to dry the workpiece, such as that described in reference toFIG. 5. The memory705may be of any conventional type, such as non-volatile memory (flash, etc.). The memory705stores a temperature based pull speed LUT601, as described elsewhere herein. In the exemplary embodiment, the memory705stores an additional displacement based pull speed LUT710including at least one robot positioning teach point associated with a particular nominal pull speed which may be used as a scaling factor for determining a temperature-based, zone-based pull speed.

As further depicted, the dryer control system includes a chamber temperature sensor240which is coupled to the dryer controller701through I/O715and is to provide chamber temperatures717to the dryer controller701. Through the I/O715, the dryer controller sends a pull speed setpoint718to a robot controller720. I/O715may further interface with other dryer subsystems, such as a heater controller, liquid level controller, hood door controller (not depicted). Based on the pull speed setpoint718, the robot controller720sends a motor command722to a robot motor730. The robot controller720controls the robot motor730to the pull speed setpoint718based on motor position and/or motor speed feedback received from the robot position sensor735.

In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary features thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense.