WO2008133593A2

WO2008133593A2 - Cleaning process and apparatus

Info

Publication number: WO2008133593A2
Application number: PCT/SG2008/000133
Authority: WO
Inventors: Hock Huat Yeo
Original assignee: Jcs-Echigo Pte Ltd
Priority date: 2007-04-27
Filing date: 2008-04-22
Publication date: 2008-11-06
Also published as: WO2008133593A3; MY154924A

Abstract

A method for cleaning an article held by support, the method comprising the steps of applying an acoustic wave to said article and support; rotating said article and support such that an area on the article previously masked by the support is exposed to said acoustic wave.

Description

Cleaning Process and Apparatus Field of the Invention

The present invention relates to a cleaning system and method for cleaning substrates, including but not limited to disc-shaped substrates of varying materials, such as to glass, aluminium and silicon.

Background of the Invention

The computer, electronics and entertainment industries use many disc-shaped substrates for the manufacture of electronic circuits. These substrates typically comprise silicon wafers, aluminium, plastics, glass, ceramic and composite materials. For convenience, the materials referred to in this specification will discuss aluminium or glass. This is not to be construed, however, as a limitation on the application of the invention.

The substrates undergo numerous processes in manufacturing, including repeated application and removal of conductive, non-conductive and semi- conductive materials of magnetic, optical and magneto-optical materials.

During manufacturing, the substrates must be buffed, polished, etched and cleaned repeatedly. As the trend in substrate design inclines towards miniaturisation, the level of cleanliness required during the manufacturing process of substrates also increases. In particular, complicated multi-layer circuits require extremely clean substrates to be fabricated on. Otherwise, defects will arise thereby leading to a decreased yield, an increased production time and an inferior product quality.

One known design of a cleaning module for cleaning aluminium discs comprises a cleaning station having two brush cylinders arranged adjacent to each other. The two brush cylinders form two central longitudinal axes that are parallel to each other. One or more aluminium discs are then arranged between the two central longitudinal axes of the brush cylinders, so that the opposite sides of the disks can be cleaned when the brush cylinders rotate about their respective longitudinal axes.

A first disadvantage of the known cleaning module is that it may not satisfy the increased level of cleanliness as required for modern applications (for example, miniaturised integrated circuits). This is because the area of contact between each side of each disk with the respective brush cylinders is not maximised, which may inevitably lead to substrate defects as described above.

A second disadvantage of the known cleaning module is that it cleans a limited number of substrates within a given period. This is because the number of aluminfum discs being cleaned simultaneously by the two brush cylinders is restricted by the diameter of the aluminium discs. Further, the contact between the brush and disc is merely a line contact. Accordingly, the brush must move downward for the entire diameter of the disc in order to ensure full contact between the disc and brush. As a result, the residence time of the disc in the cleaning station is significant.

In addition, the known cleaning module generally has more than one cleaning station. A third disadvantage of the known cleaning module is that the aluminium discs are progressively transferred from one cleaning station to another cleaning station individually. Accordingly, this results in "idle time" during transfers between different cleaning stations sand during loading and unloading of the disks.

A further problem arises whilst the discs are in the cleaning tank. In this situation, the discs are held by supports often at two points from beneath with the discs subjected to high frequency waves. In recent times, the use of mega sonic waves has become more common, i.e. acoustic waves having a frequency typically greater than 700 kHz. These mega sonic waves are transmitted from the base of a tank in which cleaning fluid has immersed the discs with the acoustic waves causing cavitation bubbles intended to remove particles from discs. In this arrangement, the discs are subject to the mega sonic waves and then removed from the tank for the next stage in the process. However, the mega sonic waves emanate from the base of the tank, inevitably, the support upon which the discs are mounted create a shadow on the disc and so preventing the waves acting upon portions of said disc. In the past, when ultra sonic waves were more commonly used, these waves had a longer wave length and the problem of the shadow was less frequent due to the diffraction of the ultra sonic waves around the supports and so diminishing the shadow on the disc. The more common use of mega sonic waves having shorter wave lengths is less prone to diffraction and therefore, the problem of the supports "shadowing" the discs is more prominent.

A still further problem with the process particularly of the discs within the cleaning tank is the adhesion of the cleaning fluid to the discs as they are removed from the tank. Discs need to be washed after each coating process and again at the final stage prior to full assembly into a hard disk drive. As the washing process usually involves immersing the discs, together with the supports into a tank of the cleaning fluid, subsequent removal of the discs from the tank lead to adhesion of the fluid to the discs, leading to solvent stains and marks from non uniform drying of the solvent.

In a further stage of the process, discs are dried in an oven before being transferred to an unloading station. The rate of drying of the discs by the oven is dependent on a number of factors, such as, but no limited to:

i) The temperature of the air in the oven; ii) The rate and means of circulation of air in the oven; iii) Radiation effects of the oven; iv) Any additional energy sources applied, and; v) Air pressure within the oven. Making adjustments to the oven to beneficially affect the rate of drying would nevertheless involve capital cost, and so whilst speeding the drying rate is economically useful, such cost may not justify the end benefit.

In each case it would be preferable if a different arrangement of the various stages of the process so as to avoid at least one of the identified problems of the prior art.

A still further disadvantage of the prior art involves the potential for cross contamination and efficiency in cleaning through removing deposits left in suspension in the fluid medium within the immersion tank. The immersion tank is used to provide a medium through which dislodged particles are removed from the substrates following rinsing. The intention is to use the circulation of the fluid medium to bias the particles toward an outlet, such that they flow out from the tank. Accordingly, the aim is to maintain a relatively particle free medium to prevent particles re-adhering to subsequent substrates. In order for the immersion tank to provide the cleaning function, the efficient removal of the particles is critical.

Tank design involves an inlet for the medium located at one end of the tank and entering near the base. Any particles which have settled to the base can be stirred up back into suspension in a generally upward direction from the base towards a weir which permits flow of the medium proximate to the top surface layer. The design relies upon the particles to be urged into this layer such that they flow towards the weir and, on settling, are trapped within the weir. A pump will remove the medium within the weir confine and so remove the particles. It follows that with this design, dead spots within the tank which don't align with the general flow of medium from the inlet to the weir will tend to allow aggregation of particles caught in eddies formed by the flow from the inlet to the weir. A further problem involves the general biasing of the particles in the direction of the inlet flow. Whilst the placement of the inlet proximate to the base permits movement of the particles which have settled on the base, this nevertheless, creates a turbulent environment whereby particles are moved in random directions. There will be a percentage of particles which will follow the main flow to the weir and then subsequent removal. However, a substantial percentage of the particles will in fact, merely follow random paths and, therefore, stay in suspension within the immersion tank. Thus, instead of removing particles from the tank, particles which may have avoided contaminating substrates are now forced into suspension and, therefore, create a greater problem.

Summary of the Invention

A first aspect of the invention relates to a cleaning module for cleaning one or more substrates, comprising one or more brushes operable to move along a radial path in relation to the substrate. For example, the cleaning module may be more useful more, but not limited to, cleaning aluminium discs.

Preferably, the brush may be adjacent to a side of the substrate so that when the brush moves towards the centre of the substrate, a scrubbing portion of the brush overlaps a corresponding portion of the substrate to contact each other.

In a preferred embodiment, the cleaning module may further comprise a substrate rotation device to rotate the substrate when the substrate is in contact with the scrubbing portion of the brush. The substrate rotation device may comprise a rotatable shaft coupled to the periphery of the at least one substrate. This may permit the surface area of the substrate being cleaned by the scrubbing portion of the brush to be maximised.

Preferably, the brush may also be rotatable to maximise the area of the scrubbing portion of the brush for cleaning the substrate. In this embodiment, the brush provides an "area" contact, as compared to the line contact of the longitudinal prior art brushes. This may provide longer actual contact time per unit area, than that of the longitudinal brush for the same residence time of the disc within the cleaning station.

Preferably, both the brush and the substrate may be operable to rotate in a same direction, so that the opposing frictional force between the brush and the substrate may more efficiently clean the latter.

Designing the radius of rotation of the brush to be greater than or equal to the radius of the substrate may permit the portion of the substrate being cleaned by the scrubbing portion brush to be optimised.

In addition, the cleaning module may also comprise one or more peripheral brushes for cleaning an outer edge of the substrate, and/or one or more inner brushes for cleaning an edge of an orifice in the substrate. This may ensure a higher level of cleanliness of the substrate. This may be useful for applications involving the miniaturisation of integrated circuits.

A second aspect of the invention relates to a method of positioning one or more brushes during the cleaning of one or more substrates, comprising the step of moving the brush along a radial path in relation to the substrate. The method is more particularly, but not exclusively, for cleaning aluminium discs.

A third aspect of the invention relates to a method of cleaning one or more substrates, comprising the steps of moving one or more brushes along a radial path in relation to the substrate and overlapping a scrubbing portion of the brush with a corresponding portion of the substrate.

By rotating the substrate when the scrubbing portion of the brush overlaps with the corresponding portion of the substrate, the surface area of the substrate being cleaned by the scrubbing portion of the brush may be optimised. Preferably, the method of cleaning the substrate may further comprise the step of rotating the brush to maximise the area of the scrubbing portion of the brush for cleaning the substrate.

Preferably, the brush and the substrate rotate in a same direction, so that the opposing frictional force between the scrubbing portion of the brush and the substrate cleans the latter.

In addition, the method of cleaning the substrate may further comprise the step of moving one or more peripheral brushes adjacent to an edge of the substrate, and/or the step of moving one or more inner brushes adjacent to an edge of an orifice in the substrate, to meet a higher level of substrate cleanliness as may be required.

In a fourth aspect, the invention provides a method for cleaning an article held by support, the method comprising the steps of applying an acoustic wave to said article and support; rotating said article and support such that an area on the article previously masked by the support is exposed to said acoustic wave.

Accordingly by rotating, and so, shifting the position of the articles, the shadow caused by the supports shifts also and, therefore, permits selective exposure of the previously shadowed portions of the discs, allowing complete cleaning due to exposure to the mega sonic waves.

In a preferred embodiment, the articles may be discs, substrates, wafers or other objects having a flat smooth profile.

In a preferred embodiment, the support may comprise racks for engaging several articles at one time. In a more preferred embodiment, the means of engagement may be through gravity, and further through the articles placed on lugs projecting outwards. Alternatively, the engagement may be through vacuum or mechanical engagement, with the invention applying to those forms of engagement or supports that involve a portion of said support to form a shadow over a portion of the article.

Preferably the rotation has a center of rotation outside the disc. In this case, rotation may be achieved by a full rotation of the disc and supports. Alternatively the discs may be rotated about its own center such as through the supports acting as rollers so as to rotate the discs within the tank.

In a fifth aspect, the invention provides a cleaning system for cleaning an article comprising a support upon which the article is located an acoustic wave generator for directing an acoustic wave along a path coincident with said support and article; said support arranged to selectively rotate about a centre of rotation, and consequently rotate said article.

In a sixth aspect, the invention provides a method for removing an article from a cleaning system, comprising the steps of providing the article engaged by a support and immersed in a tank of cleaning fluid; moving the tank downwards relative to the article so as to move the article from a completely immersed position to a position where at least a portion of the article is no longer immersed; removing the article from the tank.

In a seventh aspect of the present invention provides a cleaning system for cleaning an article comprising a tank containing cleaning liquid; a support for engaging the article within the cleaning liquid; wherein said tank is selectively movable relative to said support in a direction for removing said article from said cleaning liquid.

In an eighth aspect, the invention provides a method of drying an article comprising the steps of placing said article in an oven; dehumidifying a flow of hot air then; directing said hot air flow to said oven. Factors affecting the drying of an article, such as a disc, within an oven can be addressed by undertaking modification to the oven including adding additional energy sources, increasing air circulation and increasing pressure, for instance. However, a further factor includes reducing the humidity in the oven itself. By pre-drying the flow of hot air into the oven, prior to entry into the oven, the problems associated with drying rates can be circumvented.

In a preferred embodiment, to further reduce humidity, a dehumidifier may also be added to the oven.

In a ninth aspect, the invention provides a collection chamber assembly for collecting particles suspended within an immersion tank comprising; a permeable screen through which said particles pass; a chamber within said assembly such that particles passing through the screen into the assembly enter the chamber, said chamber being in fluid communication with an outlet of said tank wherein particles entering the collection chamber assembly exit the tank through the outlet.

In a tenth aspect, the invention provides an inlet assembly for facilitating the flow of fluid into a tank, said assembly comprising; an array of apertures, said apertures in communication with a common source of fluid; said apertures arranged such that a direction of flow of the fluid from any one aperture is parallel to the direction of flow from each of the other apertures.

The provision of an array of inlets achieves two beneficial aspects. The first is the reduction in turbulence within the tank. Having a single large inlet according to the prior art induces flow along an axial path of the inlet. However, shear stresses between the moving and stationary fluid at the peripheral edges of that flow will form eddies and, therefore, turbulence within the tank. By providing an array of inlets, a greater and more uniform flow may be created within the tank and so limiting the influence of edge effects of the main flow. In a further aspect, the invention provides a collection chamber assembly, having a screen through which the particles may pass. Such a permeable screen may be placed at a greater depth within the tank, and may also provide an increased area into which particles may be trapped.

It should be noted that the permeability of the screen refers to the ability of particles to pass through the screen, possibly through perforations formed in the screen. The precise size of the perforation will depend on the particles being removed from the substrates, which will be a matter of common general knowledge to the skilled person.

The screen may favour the transfer of particles in one direction. For instance, the screen may allow particles to pass into the collection chamber assembly more easily than it allows them to escape. One way of achieving this is to have conically shaped perforations, such that the orifice diameter of the perforations on the "tank side" may be larger than the diameter of the orifice on the chamber side. This effect may be achieved by molding, cold press or penetrating the screen with a conical shape tool.

The weir arrangement only provides for particles located proximate to the surface. The collection chamber assembly permits particles at any depth into which the catchment chamber projects. Thus, an increase area of particle collection will inevitably catch a higher percentage of particles.

Accordingly, the dead areas associated with the prior art are reduced through the greater flow area and further, particles caught in suspension within the immersion chamber whilst previously were a problem in the prior art solution, are now beneficially placed as they can then be biased by the greater flow area towards the catchment chamber.

Brief Description of Drawings It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 illustrates a cleaning module prior to a substrate-cleaning process;

Figure 2 illustrates an example of a robotic lifter in the cleaning module of Figure 1 ;

Figure 3 illustrates a process-jig tray in the cleaning module of Figure 1 ;

Figure 4 illustrates a first cleaning station of the cleaning module of Figure 1 ;

Figure 5 illustrates a closed-up view of one of the substrates being cleaned at the first cleaning station of Figure 4; Figure 6 illustrates a second cleaning station of the cleaning module of Figure 1 ;

Figure 7 illustrates a closed-up view of one of the substrates being cleaned at the second cleaning station of Figure 6;

Figure 8 illustrates a third cleaning station of the cleaning module of Figure 1 ;

Figure 9 illustrates the cleaning module after the substrate-cleaning process; Figure 10 illustrates a side-view of the cleaning station in a different configuration;

Figure 11 illustrates the cleaning module comprising the cleaning station of

Figure 10;

Figures 12A and 12B are plan views of discs demonstrating the substrate- cleaning process according to two embodiments of the present invention.

Figures 13A to 13E show elevation views of the support and discs according to one embodiment of the present invention;

Figure 14 shows a sequential elevation view of the cleaning tank according to a further embodiment of the present invention; Figure 15 is an elevation view of an immersion tank according to the prior art;

Figures 16A and 16B are elevation views of a collection chamber assembly according to one embodiment of the present invention; Figure 17 shows a schematic view of the interaction of adjacent submerged jets within the array of inlets according to a further embodiment of the present invention, and;

Figures 18A and 18B are isometric views of an immersion tank according to a further embodiment of the present invention.

Detailed Description of the Preferred Embodiment

Figures 1 illustrates a cleaning module 101 for cleaning one or more substrates according to one embodiment. In this case, the cleaning module 101 is divided into three sections: a loading section 103; a cleaning section 105; and an unloading section 107.

The loading section 103 comprises three substrate carriers or magazines in the form of feed-jig trays 109, each for holding a stack of twenty disc-shaped substrates 110. These substrates 110 may have undergone various upstream processes (e.g. ultrasonic washings) before being transferred to the trays 109 for cleaning according to the invention.

Prior to the substrate-cleaning process, the substrates 110 at evenly-spaced positions in a particular tray 109 are transferred to a process-jig tray 113 in the cleaning station 103 by a robotic lifter. The cleaning section 103 comprises three cleaning stations 401 , 601 , 801 which will be described later. For simplicity, details of the cleaning stations are shown in the figures only in relation to the process-jig tray 113.

Figure 2 provides an example of the robotic lifter 201 arranged above the tray 109 holding 25 substrates 110. The robotic lifter 201 comprises five lifting arms 203 arranged in parallel. In addition, the respective distances between the adjacent lifting arms 203 are identical, and can be any multiples of the total number of each substrate 110. The robotic lifter 201 can lift all the (1 +kn)^th substrates simultaneously from the tray 109 to the process-jig tray 113 - the variable "k" being the multiple of the total number of substrates and the variable "n" being any integer = {0, 1 , 2, 3, ...}. For this particular embodiment, as illustrated in Figure 2, "k" has a value of 5. Thus, the lifting arms 203 will lift the 1^st, 6^th, 11 ^th, 16^th and 21^st substrates 110 simultaneously from the tray 109 to the process-jig tray 113 during the start of the cleaning process.

When the lifting arms 203 are aligned with the substrates 110 in the tray 109, they simultaneously engage the peripheral edges of the (1 +kn)^th substrates below the horizontal diametric axis of the substrates so as to transfer these selected substrates from the tray 109 to the process-jig tray 113 as shown in Figure 3.

The process-jig tray 113 comprises a substrate rotation device in the form of a motor-driven shaft 205 arranged at the periphery of the substrates 110 such that the shaft 205 contacts the circumferential of the substrates 110. The motor- driven shaft 205 is coupled to a motor 207, so that the shaft 205 rotates about a longitudinal axis that is parallel to that of the process-jig tray 113. Thus, as the shaft 205 rotates in a clockwise or anti-clockwise direction, the substrates 110 in the process-jig tray 113 will rotate accordingly in an opposing direction in relation to that of the shaft 205.

Referring again to Figure 1 , the 1^st, 3^rd, 5^th, 7^th, 9^th, 11^th, 13^th, 15^th, 17^th and 19^th substrates 110 from the left end of the tray 109 are transferred by a robotic lifter similar to the robotic lifter 201 to the process-jig tray 113 in the cleaning section 105 during the start of the cleaning cycle. In other embodiments having a different number of substrates or robotic lifters having different "k" values, the substrates to be lifted from the tray 109 to the process-jig tray 113 are identified by the expression (1+kn), n = {0, 1 , 2, 3...} and "k" being a multiple of the substrate thickness, as explained earlier.

Figures 4 to 9 show the process for each station. For clarity, the stations are considered individually, with the figures showing one tray 113 at a time. In a preferred embodiment, there will be trays in each station, with the cleaning process for each station conducted simultaneously. In general, the trays 113 move to each station, with the simultaneous process performed, the trays then move along a conveyor, with a new tray introduced into the first station 401 , and at the far end, the tray 113 emptied and removed from the conveyor. Empty trays 113 can then be reintroduced at the beginning of the process for receiving new discs, either by replacement by an operator, or through a separate conveyor automating the process further. The following describes the process in greater detail.

The process-jig tray 113 is arranged on a conveyor (not shown), so that it can move across opposite ends of the cleaning section 105. Figure 4 illustrates the arrangement of the process-jig tray 113 as it moves into a first cleaning station 401. In the first cleaning station 401 , each disc-shaped brush 403 is designed to clean one side of a particular substrate 110. Thus, a row of twenty brushes 403 is required to clean both sides of all the 10 substrates 110 supported by the process-jig tray 113. In this embodiment, the brushes 403 are presented as distinct pairs of brushes corresponding to each substrate, the brushes in each said pair sufficiently spaced from each other to receive the corresponding substrate 110.

As the process-jig tray 113 moves into the first cleaning station 401 , the row of brushes 403 are lowered to overlap a proportion of the disc, which is in this embodiment less than half of the surface area of each substrate 110. As the brushes 403 overlap with the substrates 110, they are brought into contact with each other.

Figure 5 illustrates a close-up view of one of the substrates 110 being cleaned by a pair of brushes 403 - one on each side of the substrate 110. As the brushes 403 move along a radial path in relation to the substrate 110, a scrubbing portion 501 of each brush overlaps with the substrate 110 to contact a corresponding portion of the substrate 110. The substrate 110 is made to rotate in a clockwise direction by operating the motor 207 to rotate the motor-driven shaft 205 in the opposing anti-clockwise direction, so that the substrate 110 is scrubbed by the scrubbing portions of the brushes 403. Likewise, the brushes 403 are also coupled to a motor (not shown) so that they rotate in the same clockwise direction as the substrate rotation. As a result, the opposing frictional forces between the scrubbing portion of the brushes 403 and the substrate 110 clean the latter.

Advantageously, the radius of rotation of the brushes 403 is the same as, or preferably, greater than the radius of the substrate 110 so that the substrate 110 is thoroughly cleaned by the brushes 403 due to the opposing frictional contact between the scrubbing portions 501 of the brushes 403 and the respective sides of the substrate 110. The radius of rotation of the brushes 403 may generally be around 5mm longer than the radius of the substrate 110.

Accordingly, the surface of the substrate 110 being cleaned by the brushes 403 within a given time may be larger than the surface of the substrate being cleaned by the prior art, since embodiments of the invention negate circular effects during the cleaning process, which will be described with reference to Figures 12A and 12B..

In this embodiment, the cleaning cycle lasts between 5 to 20 seconds, after which the row of brushes 403 is raised to the original position.

After the substrates 110 are cleaned at the first cleaning station, the process-jig tray 113 then moves along the cleaning section 105 towards a second cleaning station 601.

The second cleaning station 601 comprises a row of ten peripheral brushes 603. As the process-jig tray 113 moves into the second cleaning station 601 , the row of peripheral brushes 603 is lowered so that they contact the circumferential edge of the substrates 110. In addition, the second cleaning station 601 further comprises a row of ten inner brushes 605 for cleaning the edges of the orifices within each substrate 110.

Figure 7 illustrates a close-up view of one of the substrates 110 being cleaned by both the peripheral brush 603 and the inner brush 605. As both the peripheral brush 603 and the inner brush 605 come into contact with the circumferential edge of the substrate 110 and the edge of the orifice of the substrate 110 respectively, the substrate 110 rotates in a clockwise direction.

Thus, both the outer edge of the substrate 110 and the internal edge are cleaned by the opposing frictional contact between the substrate 110 and the brushes 603, 605.

Advantageously, the inner brush 605 is coupled to a motor (not shown) so that it rotates in the opposing anti-clockwise direction in relation to the substrate rotation. This makes the cleaning time of the substrate 110 shorter. Thus, the outer peripheral brush 603 is also advantageously made to rotate in the same clockwise direction as the substrate rotation. Thus, the opposing frictional forces between the brushes 603, 605 and substrate clean the latter.

After cleaning of the substrate 110 at the second cleaning station 601 is completed, the process-jig tray 109 then proceeds to a third cleaning station 801 shown in Figure 8. As the process-jig tray 113 moves into the third cleaning station 801 , a row of twenty brushes 803 are lowered to overlap with about half the respective surface areas of the substrates 110. It can be seen that the third cleaning station 401 is identical to the first cleaning station, and thus no further elaboration is required.

It should be appreciated that as the substrates 110 are sequentially cleaned in three cleaning stations, the level of cleanliness of the substrates 110 is improved. Further, in view of the modularity of the cleaning stations 401 , 601, 801 , the duration of each cleaning cycle at the cleaning stations 401 , 601 , 801 can be adjusted independently of one another. When the substrate-cleaning at the third cleaning station 801 is completed, the process-jig tray 109 again moves along the cleaning section 105 to the opposite end of the cleaning section 105. Another feed-jig tray 901 is arranged in the unloading section 107 adjacent to that opposite end of the cleaning section 105. The substrates 110 on the process-jig tray 109 in the cleaning section 105 are then lifted to the tray 901 in the unloading section 107 of the cleaning module 101 by means of another robotic lifter operates in an identical or similar fashion as the robotic lifter 201 of Figure 2.

After the substrates 110 are transferred to the tray 901 , they may then undergo various downstream processes (e.g. ultrasonic rinse) as required.

The robotic lifter of the cleaning module 101 then moves back to the tray 109 in the loading section 103, whilst the lifting arms are moved by the distance of one substrate thickness (or one substrate space), so that the next series of substrates 110 corresponding to the 2^nd, 4^th, 6^th, 8^th, 10^th, 12^th, 14^th, 16^th, 18^th and 20^th substrates 110 from the left end of the tray 109 can be transferred to the process-jig tray 113. The same cleaning process as described above then continues again.

Thus, a plurality of substrates 110 is transferred together from one cleaning station to the next cleaning station as the process-jig tray 113 moves across the cleaning section 105. This is in contrast with the prior art, where the substrates are generally transferred individually. Thus, it should be appreciated that the cleaning module 110 minimises the "idle time" caused by the loading and unloading of individual substrate for cleaning.

Although the three cleaning stations 401 , 601 , 801 in the cleaning module 101 are disclosed to be modular or distinct, it should however be appreciated that they can be combined to form an integral cleaning station. For simplicity, only a side-view of such an integral cleaning station (labeled as 1001) is shown in Figure 10.

The integral cleaning station 1001 comprises ten elongate members (one of which is labeled as 1002) arranged in parallel to one another and in perpendicular to the direction of motion of the process-fig tray 113.

The elongate member 1002 comprises three arms 1003, 1005, 1007 extending from an elongate portion, and the same set of brushes 403; 603, 605; 803 respectively as described earlier. Thus, it can be seen that the integral cleaning station 1001 combines the three cleaning stations 401 , 601 , 801. Accordingly, in this embodiment, the elongate member 1002 can effect simultaneous cleaning at all stations.

As the process-jig tray 113 moves into the integral cleaning station 1001 , the integral cleaning station 1001 is lowered, so that the substrates 110 on the process-jig tray 113 are cleaned by either set of the brushes 403; 603, 605; 803. A further arm (not shown) may be provided to support the disc during the cleaning process. The support arm is most advantageous for the second cleaning station to ensure the application of the peripheral brush 603 may tend to destabilize the disc during cleaning, and so push it out of alignment. By providing the support, the disc may be held in place.

Further, the support arm may provide additional drive to rotate the disc. In so doing, contact between the support arm and the disc may be with a roller, with said roller providing all or part of the required torque in order to drive the rotation of said disc.

In view of the integral cleaning station 1001 , it should be appreciated that there could be one or more process-jig trays moving in parallel in the cleaning section 105. This is because the arms 1003, 1005, 1007 can be designed to align with the substrates 110 in the one or more process-jig trays, so that the substrates 110 can be cleaned simultaneously by all sets of the brushes 401 ; 601 , 605; 803.

Figure 11 illustrates the cleaning module 110 having the integral cleaning station 1001. For simplicity, the integral cleaning station 1001 and robotic lifters are not drawn in Figure 11. In this case, the cleaning module 110 comprises three process-fig trays 113a-c. In contrast to the process jig 113 moving on the conveyor from one cleaning station to the next in the cleaning section 105, the process jigs 113a-c are fixed in position in the cleaning section 105. This is because the substrates 110 are progressively transferred between the adjacent trays along the cleaning module 101 by specialised robotic lifters.

It should be appreciated that such a design of the cleaning module 101 may be suitable if it is desirable to increase the number of substrates 110 being cleaned during the substrate-cleaning process.

It is also envisaged that the substrate rotation device may be in the form of a motor-driven shaft that is operable to secure to the walls of the central cavities of the substrates 110. However, the substrates 110 may have to be lifted from the process-jig tray 113 so that the substrates 110 can be rotated along with the motor-driven shaft to which they are secured.

In addition, it is further envisaged the brushes 403, 803 may also be made to completely overlap the sides of the substrates 110. Thus, as the brushes 403, 803 or the substrates 110 rotate, or when the brushes 403, 803 and the substrates 110 both rotate in opposing directions, so that the opposing frictional forces between the brushes 403, 803 and the substrates 110 clean the latter.

Figures 12A and 12B show the effect of differing scrubbing patterns based on the radius of rotation of the brush relative to the diameter of the disc. In Figure 12A there is shown the case where the radius of rotation 1110 is significantly less than the diameter of the disc 1105 being scrubbed. Whilst extreme this illustration indicates the deposition of dirt 1115 around the periphery of the scrubbing radius 1110. Because of the much smaller radius, the dirt remains wholly, or at least in part, on the face 1120 of the disc 1105, thus negating the benefits of the scrubbing process.

By contrast, Figure 12B shows the effect of having the radius 1210 much larger than the diameter of the disc 1205. Here, the dirt 1220, 1230 is deposited on the internal diameter, or orifice 1215 of the disc, as well as the peripheral edge 1225. By applying a scrubbing process to the orifice 1215 and the peripheral edge 1230, the dirt 1220, 1230 is removed from the disc 1205 in a two step process.

In reality, the radius of rotation of the brush will vary, providing differing benefits. Whilst the illustration shows certain benefits of a larger radius, this is not to be considered a limitation of the invention, as the efficiency of the process, irrespective of the radius of rotation, remains superior to that of the prior art.

Thus, although the invention has been described using a preferred embodiment, many variations are possible within the scope of the claims, as will be clear to the skilled reader, without departing from the scope of the invention as claimed.

Figure 13A shows a detailed view of a support 1305 which is used to engage an article, such as a disc (not shown) whilst in a cleaning tank. The cleaning tank is typically filled with a cleaning fluid such as warm de-ionized water or diluted isopropyl alcohol.

Typically the tank will have a generator of acoustic waves in the base whereby the supports lower the discs into the tank for cleaning and the acoustic wave generator generates waves and subsequently cavitation to remove particles from the discs. Traditionally ultra-sonic waves have been used at a frequency around 200 kHz with more recently mega-sonic waves, with a frequency greater than 700 kHz, have started to become more common. A characteristic of the use of mega-sonic waves is that shown in Figure 13A. Because of the high frequency, the wave lengths are shorter and so, the diffraction patterns experienced for ultra-sonic cleaning as shown in Figure 13B are less pronounced. The result being that the shadow affect 1325 being of a reduced size for ultra sonic waves as seen in Figure 13B are now replaced by much larger shadow areas 1315 for mega-sonic wave cleaning. These shadows are caused by the onset of the acoustic waves contacting the support 1305 which acts as a shield downstream from said support. Thus, whilst some level of shadow 1325 was known in the traditional ultra sonic cleaning, this problem is enhanced and accordingly is more serious with mega sonic cleaning due to the increase in the size of the shadow 1315.

Figures 13C to 13E demonstrate the solution according to an embodiment of the present invention. In traditional cleaning tanks, the discs are supported by supports having lugs or projections which contact the disc at two points in the lower sector of the disc. Figure 13C shows an arrangement similar to the traditional arrangement whereby the disc 1350 is supported by the support whereby the support may be a pair of lugs 1305 mounted to a larger rack holding several such discs. The discs are lowered into a cleaning tank 1355 and so immersed within the cleaning fluid. As the acoustic waves contact the lugs 1305, a shadow 1345 downstream from the lugs 1305 results in a portion of the disc that remains uncleaned. The solution according to this embodiment of the present invention is to rotate the disc 1350 about a center of rotation 1340 during the cleaning process. Whilst the shadow effect cannot be removed by shifting the position of the disc 1350, the shadows caused by the lugs 1305 shift to a different portion of the disc, leaving the formerly "shadowed" area of the disc exposed to the acoustic waves and thus being cleaned. As can be seen in Figure 13D, the disc 1350 has been rotated 1360 about the point of rotation 1340 such that a new shadow area 1365 is created but exposing the previous shadow to the acoustic waves and thus affecting an efficient and complete clean of the disc. To ensure a complete clean within the residence time normally associated with the cleaning process, the support can swing in the opposite direction 1370 and thus creating a further shadow zone 1375 but also exposing both of the two previous shadow areas in order to effect the clean.

The number of oscillations of the discs and the time taken during this oscillation will vary according to the type of cleaning being undertaken and it will be clear to the skilled person how long a residence time in the bath is required in order to completely clean any areas which have been subject to the shadow.

Thus rotation of the disc can avoid the problems associated with the shadow areas. It will be appreciated that the location of the point of rotation may vary according to the nature of the cleaning process and will be a matter of routine experimentation to determine the ideal point of rotation for any particular situation. For instance, the invention also includes having the point of rotation within the area of the disc and, for instance, at the center of the disc such that the disc itself is rotated with the support staying stationary. This could be achieved by having the lugs acting as rollers and so rotating the disc through rotation of the lug/rollers in order to expose the shadowed areas to the acoustic cleaning wave.

Figure 14 shows a cleaning tank 1405 in which an article to be cleaned, in this case a disc 1410, is being immersed within the cleaning fluid and supported by lugs 1415. Traditional means of removal of the article following the cleaning process would involve lifting the article clear of the cleaning fluid. This would, however, result in a significant volume of the cleaning fluid adhering to the article causing stains as the article dries and, further, marks forming from the non uniform drying of the fluid remaining on the article. The solution according to the present invention involves a number of steps aimed at minimizing the adhesion of the fluid to the article. In the first step, similar to the convention method, the article, in this case a disc 1410, is lifted through raising the lugs 1420 of the support until the disc 1410 is proximate to the surface 1406 of the cleaning fluid 1407. Then the tank 1405 is lowered 1425 rather than the disc being lifted. The electrostatic attraction of the greater volume of fluid within the tank therefore, tends to draw the fluid from the surface of the disc which would not be possible in the reverse situation of lifting the disc from the tank. This principle is known as "dynamic de-wetting". The tank is then lowered until the central orifice 1421 of the disc is clear of the surface of the cleaning tank whereupon the lowering process 1425 is stopped. Finally a projection 1430 is inserted within the orifice 1421 and the disc lifted clear off the supports 1415 so as to clear the disc from the cleaning fluid.

The problem associated with existing methods is enhanced by the central orifice in the disc. The orifice created a disturbance in the surface of the cleaning fluid as the disc is lifted from the cleaning tank in one continuous step. It is observed that a break line across the disc where the cleaning fluid surface contacts the orifice. Thus the solution seeks to reduce this break line by lifting the disc to the level of the orifice and then lowering the entire cleaning tank instead of lifting the disc from the solvent.

A further problem of lifting the disc out of the cleaning surface in one continuous movement is the relative speed with which the solvent flows off the surface of the disc. The surface area remaining on the cleaning fluid still adhering to the disc surface gets smaller and therefore, increases the rate of formation of micro droplets of the cleaning fluid on the disc surface due to different rates of flow of the cleaning fluid of the disc surface. By lowering the entire tank, a significant volume if not all the adhering cleaning fluid, flows off the disc surface and so the risk of micro droplets of the cleaning fluid forming is greatly reduced.

Further still, in order to speed the drying process the solvent is heated so as to increase the rate of vaporization of any remaining solvent on the disc. Typically the temperature of the solvent is raised to between 50⁰C and 60⁰C.

A further problem with the prior art is the ability to remove particles from an immersion tank following the removal of the particles from the substrates. Typically, after the cleaning process, the substrates are rinsed and so leaving particles in suspension or as sedimentary deposits at the base of the tank. To avoid cross contamination of substrates following the removal of the rinsed substrates, the particles are removed from the tank using an arrangement shown in Figure 15. As will be demonstrated, the process is not particularly efficient in that a significant proportion of the particles remain within the tank, affecting the cleanliness of the subsequent batches of substrates to be rinsed.

Such a tank 1500 of the prior art will have an inlet 1505 facilitating the flow of fluid such as de-ionized water into the tank 1500. As the inlet 1505 acts as a submerged jet, flowing fluid of the same viscosity as the submerging fluid, a typical dispersion gradient 1511 of 1 to 4 will be experienced, though this will be limited by the jet's proximity to the walls and base of the tank. Thus for a large diameter inlet 1505, the diffusion of the jet will increase with the length of the jet into the tank. The diffused jet 1530 is directed horizontally towards an opposed end of the tank. Particles 1535 held in suspension within the tank 1500 are then directed 1540 outward from the jet, and upwards through the rising flow of fluid as it fills the tank, and subsequently over the weir to be collected in the base 1555. Typically, the base 1555 will be in communication with a pump, with the circulation of the fluid from the inlet 1505 to the weir 1515 leading to a process of removing of the particles 1550.

However, the use of such an inlet 1505 leads to areas of turbulence outside the diffusion area. This causes eddies 1560A, B which are effectively formed by the shear between the moving fluid and the static fluid outside the diffusion area. The eddies 1560A, B will trap particles 1565A, B within the eddies and so make removal more difficult. Further for those areas outside the diffusion flow 1530 which are located near the base of the tank, a dead zone is formed whereby no amount of circulation of the fluid will remove sediments 1565A from such a dead zone. Accordingly, a significant proportion of the particles and particularly those which have settled as a sediment deposit will remain in the tank and may only be removed through manual cleaning of the tank. One solution to this problem is the embodiment according to the present invention shown in Figures 16A and 16B. Because the weir arrangement of the prior art requires particles to firstly be in suspension and secondly, removed from the base of the tank, it is difficult to ensure that the weir can effectively collect all the particles. Thus according to the present invention, a collection chamber assembly 1605 can be mounted in a tank 1600. In this case, the collection chamber assembly comprises a screen 1620 which is essentially a sheet having perforations, but may equally be a mesh or other such planar member having openings through which the particles may pass.

The ratio of perforations to the total area of the screen may vary according to the type of material used. For instance, in one embodiment, a metal sheet, such as stainless steel, of dimensions of 300 mm by 200 mm will have a total area of 0.06m². In this sheet, apertures or perforations may be formed, such as through punching, in the range of 1 to 2 mm diameter. At a spacing of 10 mm, ratio of aperture or perforation area to the area of the entire sheet is in the range 0.7% to 2.9%.

It will be appreciated that in place of a metal sheet, a plastic sheet, such as polyethylene or polypropylene may be used, whereby the apertures may be punched or molded.

In a further embodiment, the screen may be a wire mesh, using stainless steel wire of a diameter of, say 1 mm. For an aperture of 1 mm, the spacing is reduced to 2mm, increasing the ratio to approximately 20%.

It will be appreciated that the selection of the actual perforation size and spacing will vary based on user preferences, as will the selection of the type and construction of the screen. Many alternative arrangements can be used but in this embodiment, the screen spans the full length of the collection chamber assembly having an even distribution of perforations within said screen. Because in this embodiment, the collection chamber assembly spans the substantial distance from the base of the tank to the surface, any particles in motion within the tank may be collected by the collection chamber rather than only those near the surface. Thus, in the case of an eddy 1640 being formed, particles 1645 within the eddy 1640 which remain in motion may nevertheless be passed through the screen 1620 as the eddy 1640 moves the particles in a direction towards the screen during its spiral motion. Once the particles 1635 are within the chamber, the screen will act as a barrier preventing a portion of those particles from flowing out of the chamber 1637. Further, the screen itself will act as a baffle, dissipating the flow caused by the eddy. Thus once the particles enter the chamber 1637, much of the energy imparted by the eddy 1640 will have been reduced and so the particles 1635 being relatively de-energized compared to those outside the chamber. Subsequently the particles will sink 1636 and settle on the base 1639 of the chamber whereupon they can be removed 1638 by pump or other means to facilitate the outflow of fluid from the tank 1600.

Thus the present invention incorporating the collection chamber assembly 1605 is capable of removing particles from the tank irrespective of eddies being formed within dead zones of the tank. Thus, means to keep the particles in motion whether or not this be directly biased towards the collection chamber 1605 or merely moving proximate to the assembly, will lead to particle removal.

A further solution to the problem shown in Figure 15 is the replacement of a single inlet with an array of inlets 1705A, B, C. Such an array of inlets may cumulatively have the same area as the single inlet of the prior art. However, the broader distribution of the array of inlets 1705A, B, C leads to a broader band of diffusion 1710 and so, the flow distribution 1725 is much greater at an earlier location within the tank 1700. Because of the greater uniformity 1725 of the flow distribution, the creation of dead zones is dramatically reduced if not completely eliminated and thus particles collecting in such positions are markedly reduced. It will be appreciated that the geometry of the tank, the flow rate through the inlets and the distribution and concentration of particles within the tank may dictate the direction of flow from the inlets in order to achieve the optimum result.

In a further embodiment of the present invention, the solutions of Figures 16A, B and Figure 17 can be combined into a solution shown in Figures 18A and 18B. Here a tank 1800 is shown in two separate views in order to clearly see both features combined into the single embodiment. Accordingly, an array of inlets 1805 is arranged to one end of a generally elongate tank 1800. The array of inlets 1805 are achieved by three pipes projecting horizontally across the tank along one end of said tank. Each pipe has a row of inlets so as to have a high level of concentration of inlets across the tank. The three pipes themselves also provide a two dimensional array of inlets so as to create a very broad distribution of flow through the inlets. The pipes are connected to a manifold having a source 1810 of fluid through which the fluid is dissipated to the inlets. The inlets are directed longitudinally down the tank 1825 in a direction parallel to the surface of the tank and generally directed towards a collection chamber assembly 1815. In this embodiment the collection chamber assembly includes a screen which substantially covers the far end wall of the tank 1800 so as to receive the broad diffused flow from the inlets 1805. Acting in the manner shown in Figures 16A and 16B, particles within the tank will be moved by the diffused flow 1825 and directed through the screen 1830 of the collection chamber assembly 1815. Thus the embodiment shown Figures 18A and 18B show the benefit of all the beneficial embodiments described herein in that a broad diffused flow avoids the creation of eddies and subsequently the collection of particles in a dead zone. With the flow from the inlets 1805 directed towards the collection chamber assembly 1815, all particles caught within the flow will for a very high probability pass through the screen if not immediately, will eventually pass through the screen under the constant flow 1825. Accordingly, particles will be trapped in the collection chamber assembly. With the screen acting as both a receiving face and also a means to dissipate the flow, the de-energized particles within the assembly 1815 will fall to the base of the assembly where upon they can be removed through the outlet 1820 located adjacent the base of the collection chamber.

Thus it will seen that the various aspects of the present invention can individually provide a benefit over the prior art and collectively, provide a very efficient means for the removal of particles from the tank 1800.

Claims

1. A cleaning module for cleaning at least one substrate, the module comprising at least one brush operable to move along a radial path in relation to the at least one substrate.

2. The cleaning module according to claim 1 , wherein a scrubbing portion of the at least one brush overlaps a corresponding portion of the at least one substrate as the at least one brush moves along the radial path.

3. The cleaning module according to any one of the preceding claims, further comprising a substrate rotation device to rotate the at least one substrate.

4. The cleaning module according to claim 3, wherein the substrate rotation device comprises a rotatable shaft engaged with the periphery of the at least one substrate.

5. The cleaning module according to any one of the preceding claims, wherein the at least one brush is rotatable.

6. The cleaning module according to claims 3 to 5, wherein the at least one substrate and the at least one brush are operable to rotate in a same direction.

7. The cleaning module according to claim 5 or claim 6, wherein the radius of rotation of the at least one brush is greater than or equal to the radius of the at least one substrate.

8. The cleaning module according to any one of the preceding claims, further comprising at least one peripheral brush for cleaning an outer edge of the at least one substrate.

9. The cleaning module according to any one of the preceding claims, further comprising an inner brush for cleaning an edge of an orifice in the at least one substrate.

10. A cleaning module for cleaning a plurality of substrates, the module comprising: a tray for supporting said substrates in a pre-determined spaced relation; a plurality of brushes located at a first station, each brush corresponding to one of said plurality of substrates; wherein each brush is operable to move along a radial path in relation to the respective substrate brush corresponding to one of said plurality of substrates.

11. The module according to claim 10, wherein the first tray supports the substrates such that planes defined by the substrates are parallel.

12. The module according claims 10 or 11 , further comprising a second plurality of said brushes located at a second station, and; a conveyor for moving the tray from the first station to the second station.

13. The module according to claim 12, further comprising a plurality of peripheral brushes, for cleaning an outer edge, and a plurality of inner brushes, for cleaning an edge of an orifice, of each substrate; the plurality of peripheral and inner brushes located at a third station intermediate the first and second station; wherein said conveyor is further adapted to move the tray from the first station to the third station and then to the second station.

14. A method of positioning at least one brush during the cleaning of at least one substrate, the method comprising the step of moving the at least one brush along a radial path in relation to the at least one substrate.

15. A method of cleaning at least one substrate, the method comprising the steps of moving at least one brush along a radial path in relation to the at least one substrate and overlapping a scrubbing portion of the at least one brush with a corresponding portion of the at least one substrate.

16. The method according to claim 15, the method further comprising the step of rotating the at least one substrate.

17. The method according to claim 15 or claim 16, further comprising the step of rotating the at least one brush.

18. The method according to claim 16 or claim 17, wherein the at least one substrate and the at least one brush rotate in a same direction.

19. The method according to any one of claims 15 to 18, further comprising the step of moving at least one peripheral brush adjacent to an edge of the at least one substrate.

20. The method according to any one of claims 15 to 19, further comprising the step of moving at least one inner brush adjacent to an edge of an orifice in the at least one substrate.

21. A method for cleaning an article held by support, the method comprising the steps of: applying an acoustic wave to said article and support; rotating said article and support such that an area on the article previously masked by the support is exposed to said acoustic wave.

22. The method according to claim 21 wherein said acoustic wave is a unidirectional mega-sonic or ultrasonic wave.

23. The method according to claims 21 or 22 wherein said support and article are immersed in a liquid.

24. The method according to any one of claims 21 to 23 wherein said support maintains the article in a vertical orientation with said acoustic wave directed upwards towards said article.

25. The method according to any one of claims 21 to 24 wherein said support includes lugs contact a peripheral edge of said article.

26. A cleaning system for cleaning an article comprising a support upon which the article is located an acoustic wave generator for directing an acoustic wave along a path coincident with said support and article; said support arranged to selectively rotate about a centre of rotation, and consequently rotate said article.

27. The cleaning system according to claim 26 wherein the support is arranged to position the article so as to be immersed within a liquid, said acoustic wave generator arranged to generate a wave through said liquid.

28. The cleaning system according to claim 26 or 27 wherein the degree of rotation of said article and support is sufficient to allow the entire article to be exposed to said acoustic wave.

29. The cleaning system according to any one of claims 26 to 28 wherein said acoustic wave generator generates mega-sonic waves.

30. A method for removing an article from a cleaning system, comprising the steps of: providing the article engaged by a support and immersed in a tank of cleaning fluid; moving the tank downwards relative to the article so as to move the article from a completely immersed position to a position where at least a portion of the article is no longer immersed; removing the article from the tank.

31. The method according to claim 30 wherein the portion is greater than 50% of the article.

32. The method according to claim 30, wherein the article includes an orifice and the portion that part of the article such that the orifice is no longer immersed.

33. The method according to any one of claims 37, further including a second support for engaging the article when at least a portion of said article projects from the cleaning liquid.

34. The cleaning system according to claim 38 wherein the second support includes a projection arranged to insert within an orifice of said article.

35. The cleaning system according to claim 26 or 29, wherein the article is any one or a combination of: discs, wafers and substrates.

36. The cleaning system according to claim 26 or 29 wherein said support is arranged to engage a plurality of said articles.

37. The method according to claim 30 or 36, wherein the article is any one or a combination of: discs, wafers and substrates.

38. The cleaning system according to claim 1 or 29, wherein said support is arranged to engage a plurality of said articles.

39. A method of drying an article comprising the steps of: placing said article in an oven; dehumidifying a flow of hot air then; directing said hot air flow to said oven.

40. The method according to claim 39 further including the step of dehumidifying air in the oven prior to the step of directing the flow of hot air to the oven.

41. A collection chamber assembly for collecting particles suspended within an immersion tank comprising; a permeable screen through which said particles pass; a chamber within said assembly such that particles passing through the screen into the assembly enter the chamber, said chamber being in fluid communication with an outlet of said tank wherein particles entering the collection chamber assembly exit the tank through the outlet.

42. The assembly according to claim 41 wherein said assembly is located within the tank at a point coinciding with a direction defined by flow entering the tank through an inlet in said tank.

43. The assembly according to claim 41 or 42 wherein said screen comprises a sheet having a plurality of perforations penetrating said sheet.

44. The assembly according to claim 43 wherein in use, the assembly is arranged such that a lower portion of the sheet is free from perforations such that particles residing on a base of said chamber are prevented from exiting the chamber through said screen.

45. The assembly according to any one of claims 41 to 44 wherein said assembly is placed adjacent to said outlet such that fluid within said tank is prevented from exiting the outlet without passing through said assembly.

46. The assembly according to any one of claims 41 to 45 wherein the ratio of perforations to total area of the screen is less than 10%.

47. The assembly according to any one of claims 41 to 46 wherein said assembly is arranged such that the outlet is contiguous with the base of the chamber.

48. The assembly according to any one of claims 41 to 47 wherein the assembly is located within the tank such that the base of the chamber is proximate to the base of the tank.

49. The assembly according to claim 48 wherein the assembly is located within the tank such that the screen projects from the surface of fluid within said tank whilst in use.

50. The assembly according to claim 48 or 49 wherein a submerged portion of the screen includes uniformly distributed perforations.

51. An inlet assembly for facilitating the flow of fluid into a tank, said assembly comprising; an array of apertures, said apertures in communication with a common source of fluid; said apertures arranged such that a direction of flow of the fluid from any one aperture is parallel to the direction of flow from each of the other apertures.

52. The inlet assembly according to claim 51 wherein said direction of the flow is parallel to the surface of fluid within said tank.

53. The inlet assembly according to claim 51 or 52 wherein said inlets are located proximate to each other on one face of said tank

54. A tank containing an immersion fluid comprising an array of inlets for facilitating the flow of fluid into said tank; a collection chamber assembly having a permeable screen immersed in said fluid, through which particles may pass such that the collection chamber assembly being in fluid communication with an outlet of said tank and arranged such that fluid within the tank passes through said collection chamber assembly before exiting through said outlet.

55. A tank containing an immersion fluid comprising an inlet assembly according to any one of claims 51 to 53 and a collection chamber assembly according to any one of claims 41 to 50.