Patent Application
20050126605
The present invention relates to a cleaning apparatus and method for removing contaminating particles off surfaces. In particular, the present invention relates to a cleaning method and apparatus employing aerodynamic principles, especially suitable for cleaning planar and smooth substrates such as silicon Wafers and similar semiconductors products, Flat Panel Displays (FPD), (masks for SC/FPD), Liquid Crystal Display (LCD) panels, Printed Circles Boards (PCB) and glass or optical surfaces, as well as media such as hard disks, CD & DVD, cardboards, and surfaces of optical lenses and devices, metallic and plastic surfaces, celluloid and film sheets, and various flat media and surfaces that are highly susceptible to contaminating particles.
Many industrial fields relate to clean flat or non-flat, essentially smooth surfaces. In particular, production lines as well as research and development sites in the semiconductors industry must be kept under extremely clean conditions. It is true also in the FPD, CD, DVD, LCD industry and in other similar production lines. In such industries, the process of manufacturing is highly sensitive to contaminating particles. Therefore, production is usually conducted in clean rooms of different classes, where the ambient air is constantly filtered to trap miniature airborne contaminating particles (including particles of sub-micron proportions). However, there are still contamination problems in clean rooms, mostly introduced by the manufacturing process itself and by the handling tools such as standard wafer grippers (for-example, end-effectors and vacuum chucks), that are commonly used in the semiconductor industry as well as in the FPD industry.
Particularly, in the semiconductors industry, it is important to remove miniature contaminating particles from both sides of the wafer. The presence of a particle in the magnitude order of only 0.1 micrometer (μm) contaminating the wafer front-side, can result in microelectronic failures. Furthermore, when the wafer undergoes a process of photolithography, the surface of the wafer has to be completely flat. The wafer is commonly held down in contact with a flat vacuum chuck, and if any particles, even of minute dimensions (in the order of 0.5 μm and more), exist on the wafer backside, it may result with local wafer deformation that can render the photolithography process unsuccessful. In addition, contaminating particles at the backside of an upper wafer may drop to the front-side of a lower wafer when both are stored one over the other in a standard wafer cassette.
Apart from the semiconductor industry, the manufacturing process of flat panel displays (FPD), liquid crystal displays (LCD), printed circuit boards (PCB), as well as the Hard-disks, DVD and CD, and many more products, is very sensitive to contaminating particles, which may cause a significant reduction of production yield.
Wafers and FPDs production lines, incorporate many cleaning stations that are mostly based on wet cleaning methods. In large scale industries cleaning stations based on dry cleaning methods are trendy.
As indicated, manufacturing processes that take place in clean rooms, mainly in the semiconductors and the FPD industries, are still susceptible to small-size contaminating particles. Therefore, in-line cleaning stations are extensively used. Such a cleaning stations must clean the substrate but must not add new contaminating particles when handling or chucking, in order to meet quality control specifications, the latter becoming increasingly demanding each year. It is relevant with respect to chucks that hold the wafers during the cleaning process and to the handling tools that unload the wafer after cleaning. Moreover, in many cases it is imperatively forbidden to touch the surfaces. For example, it is forbidden to touch the front side of a wafer when cleaning its back-side, since touching may introduce contaminating particles and contact may directly damage microelectronic patterns. Therefore a dry cleaning apparatus that supports the object by non-contact means during the cleaning process may be of great added value.
There is thus provided, in accordance with a preferred embodiment of the present invention, a method for removing contaminants from a surface of an object to be cleaned, the method comprising:
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is reduced below a predetermined distance to attain a high gradient of velocity of the gas, thereby controlling mass flow.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is regulated.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is in the order of 100 to 1000 microns.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is about 30 to 100 microns.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is about 30 microns or less.
Furthermore, in accordance with a preferred embodiment of the present invention, the narrow lip is sharp.
Furthermore, in accordance with a preferred embodiment of the present invention, the lateral scale of the high-pressure passage is about the same in size as the width of the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, the lateral scale of the high-pressure passage is significantly larger than the width of the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, the lateral scale of the high-pressure passage is significantly smaller than the width of the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is regulated.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is up to 5 bars.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is up to 20 bars.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is up to 100 bars.
Furthermore, in accordance with a preferred embodiment of the present invention, the method further comprises evacuating the gas through at least one gas evacuation passage, confining said at least one high-pressure outlet within, and having external rims, provided in the device.
Furthermore, in accordance with a preferred embodiment of the present invention, evacuating the gas through at least one gas evacuation passage is carried out by vacuum means.
Furthermore, in accordance with a preferred embodiment of the present invention, the vacuum means and the high-pressure gas supply are both regulated to induce substantially zero pressure forces on the object to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the vacuum means evacuate substantially all the gas so that in effect a dynamically closed environment is formed substantially preventing mass flow of the gas with removed contaminants from escaping to ambient atmosphere.
Furthermore, in accordance with a preferred embodiment of the present invention, comprising providing a relative motion between the active surface of the device and the surface of the object to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion is linear.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion is angular.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion is combined with linear motion.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion is substantially parallel to the surface and the direction of the gas as it accelerates in the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, the active surface of the device is occasionally relocated from point to point to clean localized portions of the surface to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is controlled using physical support.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is controlled using non-contact support.
Furthermore, in accordance with a preferred embodiment of the present invention, the non-contact support comprises air-cushioning.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is air.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is helium.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is Nitrogen.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is heated.
Furthermore, in accordance with a preferred embodiment of the present invention, the surface to be cleaned is heated.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is excited in high-frequency a periodic fluctuations.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is excited by piezoelectrically.
Furthermore, in accordance with a preferred embodiment of the present invention, the gas is excited by acoustically.
Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a cleaning device for removing contaminants from a surface of an object to be cleaned, the device adapted to be fluidically connected to a high-pressure gas supply, the device comprising:
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is controlled by a mechanical means.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is controlled by an aeromechanical means.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is set to be in the order of 100 to 1000 microns.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is set to be about 30 to 100 microns.
Furthermore, in accordance with a preferred embodiment of the present invention, the width of the throat section is set to be about 30 microns or less.
Furthermore, in accordance with a preferred embodiment of the present invention, the narrow lip is sharp.
Furthermore, in accordance with a preferred embodiment of the present invention, the lateral scale of the high-pressure passage is about the same in size as the width of the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, the lateral scale of the high-pressure passage is significantly larger than the width of the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, the lateral scale of the high-pressure passage is significantly smaller than the width of the throat section.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is regulated.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is up to 5 bars.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is up to 20 bars.
Furthermore, in accordance with a preferred embodiment of the present invention, pressure of the high-pressure gas supply is up to 100 bars.
Furthermore, in accordance with a preferred embodiment of the present invention, the device further comprises at least one gas evacuation passage.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one gas evacuating passage is connected to a vacuum pump.
Furthermore, in accordance with a preferred embodiment of the present invention, the device further comprises a relative motion means, for providing relative motion between the active surface of the device and the surface to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion means provides linear motion.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion means provides angular motion.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion means facilitates motion combined with linear motion.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion is provided by mechanical means.
Furthermore, in accordance with a preferred embodiment of the present invention, the relative motion is provided by aeromechanical means.
Furthermore, in accordance with a preferred embodiment of the present invention, the active surface of the device is adapted to be occasionally relocated from point to point to clean localized portions of the surface to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the cleaning head unit is supported by mechanical means.
Furthermore, in accordance with a preferred embodiment of the present invention, the cleaning head unit is supported by an air-cushion.
Furthermore, in accordance with a preferred embodiment of the present invention, the object to be cleaned is held with contact by mechanical means.
Furthermore, in accordance with a preferred embodiment of the present invention, the object to be cleaned is supported by non-contact means.
Furthermore, in accordance with a preferred embodiment of the present invention, the non-contact means comprises an air-cushion.
Furthermore, in accordance with a preferred embodiment of the present invention, the cleaning head is integrated in a non-contact supporting platform.
Furthermore, in accordance with a preferred embodiment of the present invention, the high-pressure outlet is elongated.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one lip comprises at least two elongated lips, whereby two opposing throat sections are defined having substantially equal widths.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one lip comprises at least two elongated lips, whereby two opposing throat sections are defined having different widths.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one lip comprises at least two elongated lips, whereby two opposing throat sections are defined, and wherein the passage is substantially perpendicular to the surface of the object to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one lip comprises at least two elongated lips, whereby two opposing throat sections are defined, and wherein the passage is tilted with respect to the surface of the object to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the high-pressure outlet is annular.
Furthermore, in accordance with a preferred embodiment of the present invention, the active surface is flat.
Furthermore, in accordance with a preferred embodiment of the present invention, the active surface is arcuate.
Furthermore, in accordance with a preferred embodiment of the present invention, the active surface corresponds in shape to the shape of the surface of the object to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one high-pressure passage includes a flow restrictor.
Furthermore, in accordance with a preferred embodiment of the present invention, the flow restrictor exhibits self-adaptive return spring properties.
Furthermore, in accordance with a preferred embodiment of the present invention, the flow restrictor is an electromechanical control valve.
Furthermore, in accordance with a preferred embodiment of the present invention, the device is further provided with at least one gas evacuation passage, which includes a flow restrictor.
Furthermore, in accordance with a preferred embodiment of the present invention, at least two high-pressure outlets are provided, the outlets arranged in a substantially parallel orientation.
Furthermore, in accordance with a preferred embodiment of the present invention, the device comprises at least two high-pressure outlets, the outlets arranged in a substantially orthogonal orientation.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one high-pressure outlet is provided that is divided into sectors that can be operated separately.
Furthermore, in accordance with a preferred embodiment of the present invention, the device comprises at least one high-pressure outlet that can be relocated to a new operational location between two consecutive cleaning sequences.
Furthermore, in accordance with a preferred embodiment of the present invention, the device comprises at least one high-pressure outlet that is parallel to the object where the object is oriented without any respect to gravity.
Furthermore, in accordance with a preferred embodiment of the present invention, there is provided a cleaning system for removing contaminants from a surface of an object to be cleaned, the system adapted to be fluidically connected to a high-pressure gas supply, the system comprising:
Furthermore, in accordance with a preferred embodiment of the present invention, the system is configured for round objects to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the system is configured for rectangular objects to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, the supporting means comprises a platform that supports the object, at least partly, without contact by an air-cushion from at least one side.
Furthermore, in accordance with a preferred embodiment of the present invention, the air-cushion is vacuum-preloaded.
Furthermore, in accordance with a preferred embodiment of the present invention, the supporting means comprises a platform that supports the object, at least partly, with contact.
Furthermore, in accordance with a preferred embodiment of the present invention, mechanical means employing friction are used to provide relative motion, by conveying the object.
Furthermore, in accordance with a preferred embodiment of the present invention, mechanical means employing gripping of the object are used to convey the object in order to provide relative motion.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one cleaning head is movable in order to provide the relative motion.
Furthermore, in accordance with a preferred embodiment of the present invention, said at least one cleaning head and the object to be cleaned are movable in order to provide the relative motion.
Furthermore, in accordance with a preferred embodiment of the present invention, the system further comprises heating means.
Furthermore, in accordance with a preferred embodiment of the present invention, the heating means comprises a heater for heating the gas.
Furthermore, in accordance with a preferred embodiment of the present invention, the heating means comprises a heater for heating the surface of the object to be cleaned.
Furthermore, in accordance with a preferred embodiment of the present invention, wetting means are provided for wetting the surface to be cleaned, in order to reduce adhesive forces acting on the contaminants.
Furthermore, in accordance with a preferred embodiment of the present invention, an ionizer is provided for ionizing the gas.
Furthermore, in accordance with a preferred embodiment of the present invention, an actuator is provided for exciting the gas to high frequencies periodic fluctuations.
Furthermore, in accordance with a preferred embodiment of the present invention, an optical scanner is provided for inspecting the surface to be cleaned and monitoring removal of contaminants.
In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals.
a illustrates, in accordance with a preferred embodiment of the present invention, a general isometric view of an elongated cleaning head unit having a flat active surface.
b illustrates, in accordance with another preferred embodiment of the present invention, a general isometric view of an annular cleaning head unit having a flat active surface.
c illustrates a cross sectional view of the cleaning head unit shown in
d depicts enlarged portion of the throat section of the cleaning head unit shown in
e depicts enlarged portion of the throat section of the cleaning head unit shown in
f-h depict enlarged partial cross-sectional views of various throat section design options of the cleaning head unit shown in
a illustrates, in accordance with another preferred embodiment of the present invention, a side view of a cleaning head unit having an arcuate active surface.
b illustrates, in accordance with another preferred embodiment of the present invention, a bottom of the cleaning head unit having a bent active surface.
a illustrates, in accordance with another preferred embodiment of the present invention, a close cross-sectional view of the sharp throat section shown in
b shows a close cross-sectional view of the sharp throat section shown in
c shows a close cross-sectional view of the sharp throat section shown in
a illustrates a close cross-sectional view of a round shaped particle subjected to removal forces.
b illustrates a close cross-sectional view of a non-regular shaped particle subjected to removal forces.
a illustrates a cross-sectional view of the interaction between a particle and the boundary layer, where the particle's typical dimensions are larger that the boundary layer thickness.
b illustrates a cross-sectional view of the interaction between a particle and the boundary layer, where the particle's typical dimensions are smaller that the boundary layer thickness.
a illustrates a cross-sectional view of an operating cleaning head unit in motion, adjacent to a surface to be cleaned.
b illustrates schematically removal force characteristics with respect to the lateral direction that is parallel to the outgoing flow direction.
a-c illustrate, in accordance with a preferred embodiment of the present invention, optional scanning modes, for covering cleaning areas.
d illustrates a bidirectional approach of applying the removal-force with respect to an elongated contaminating particle.
a illustrates, in accordance with a preferred embodiment of the present invention, a setup of a cleaning apparatus having in-contact platform and a cleaning head unit.
b illustrates, in accordance with another preferred embodiment of the present invention, a setup of a cleaning apparatus having non-contact platform and a cleaning head unit.
c illustrates, in accordance with another preferred embodiment of the present invention, a setup of a cleaning apparatus having non-contact platform, where the cleaning head unit is floating over a substrate to be cleaned.
d illustrates a bottom view of the cleaning head unit of the setup illustrates in
a illustrates, in accordance with a preferred embodiment of the present invention, a general top view of a non-contact round platform where an elongated cleaning head unit is integrated in the platform.
b illustrates, in accordance with another preferred embodiment of the present invention, a general top view of a non-contact round platform where a small movable cleaning head unit is integrated in the platform.
c illustrates, in accordance with another preferred embodiments of the present invention, several optional setups of cleaning apparatuses where two or more cleaning head units are incorporated.
a-e illustrates, in accordance with several preferred embodiments of the present invention, setups of cleaning apparatuses presenting rotational cleaning motion, where various round platforms are implemented.
f-j illustrates, in accordance with another several preferred embodiments of the present invention, setups of cleaning apparatuses presenting linear cleaning motion, where various non-contact platforms are implemented.
k-n illustrate, in accordance with preferred embodiments of the present invention, setups of cleaning apparatuses presenting linear cleaning motion, where various in-contact platforms are implemented.
a-d illustrate, in accordance with preferred embodiments of the present invention, optional non-contact platforms that are based on fluidic return spring flow restrictors.
In many manufacturing processes such as found at the semiconductor or the FPD industries, as well as other similar manufacturing processes (for example, manufacturing processes of Liquid Crystal Display (LCD) panels and glass surfaces, as well as media such as hard disks, CD & DVD, cardboards, and surfaces of optical lenses and devices), the surfaces of the products have to be extremely clean otherwise a critical reduction in yield may result. This is the reason why such manufacturing processes are carried out in clean rooms. However, although working in clean room conditions, there are many occasions in which the surfaces are contaminated, a fact that may severely affect the production yield.
The present invention provides a new and unique cleaning apparatus that can be used for cleaning surfaces from contaminating particles by using of a dry aero-mechanic method of cleaning. For the purpose of the present invention the term “cleaning” refers to removal of any kind of contaminants, for example particles or liquid, and to drying of a surface. A surface cleaning apparatus, as will be shown herein in several preferred embodiments, comprises a housing provided with cleaning head unit having an outlet that is connected to high pressure source and through which air (or other gas) is injected and preferably through other passages air is sucked by using vacuum forces.
In essence, the cleaning head unit of the present invention is aimed at producing a substantially parallel (hereinafter referred to as “parallel”) high-speed flow, in close proximity to the surface to be cleaned, in order to generate large parallel removal forces to disconnect the contaminating particles and to carry them away from the surface. The outlet's lips of the cleaning head unit are optimized in order to provide maximum parallel removal force but yet to minimize the throughput mass flow rate. These contradictory requirements can be fulfilled when the lips of the cleaning head unit are positioned in a very close proximity to the surface of the object to be cleaned. An important feature of the present invention is the establishment of a dynamic throat section of miniature dimensions between the lips of the cleaning head unit and the surface to be cleaned. This dynamic throat section has on one side lips of special aerodynamic design (pertaining to the cleaning head) and a flat surface on the other side, being the surface to be cleaned (such as a wafer FPD, and the like). This throat section also controls the throughput mass flow rate. The flow is rapidly accelerated along the throat section thus boundary layer thickness is maintained extremely small as maximum velocity is reached, and thus the pressure forces and the shear forces acting on the particles (hereinafter referred to as “removal forces”), are maximized. Miniature scales are considered with respect to the present invention, in order to significantly scale down aerodynamic features that are associated with the flow (such as the boundary layer thickness), and limit the throughput mass flow rate thus gaining a cost effective process and avoiding an increasing risk of contaminating the surface by introducing additional particles as a large volume of mass flow is involved. The aerodynamic design of the throat section is aimed at minimizing the boundary layer growth in order to gain:
Efficiency of the cleaning apparatus is greatly increased when the lips of the cleaning head unit are brought to a very close proximity to the surface to be cleaned. Without derogating generality, the throat section width (hereinafter denoted by “ε”), is about 30 microns or less, if fine particles are to be removed. For intermediate size particles the throat section width is preferably in the order of about 30 to 100 microns, and for coarse particles the throat section is preferably in the order of about 100 to 1000 microns. With respect to the small dimensions of the throat section width, the length of the throat section (it being basically the width of the lip of the pressure outlet of the cleaning head) is preferably also of a miniature scale, preferably in the same order of its width, in order to maximize the removal force, but also to limit the pressure-forces acting on the surface.
Accordingly, an elongated miniature cleaning area of two-dimensional nature is established, and when applying aeromechanic means at the edges of the elongated cleaning head unit to separate the internal process area from the outer area, the cleaning process of the present invention can be performed in a dynamically close miniature chamber. Be the cleaning head unit elongated or not, the dynamic isolation of internal clean area can be obtained by applying circumferential vacuum suction that removes the air with the removed particles The cleaning apparatus of the present invention can be used for point-to-point cleaning of individual particles, where particles position is detected by a particles inspection system. Alternatively, it can be used to clean an entire surface when relative motion between the surface to be cleaned and the cleaning head unit is provided. When it is desired to clean entire surfaces, it is recommended to use an elongated cleaning head unit, to facilitate a faster cleaning process. Obviously, rather than using one elongated cleaning head unit, it is possible to use several cleaning head units simultaneously.
To optimize the cleaning process, It is preferable that the cleaning head is moved substantially parallel to the surface to be cleaned, it being flat or contoured, and the direction of motion must be substantially parallel to the direction of the flow at the throat section, but also large angles of up to about 45 and more degrees are effective as long as the entire surface is scanned. In order to maximize the cleaning performance it is recommended to make a cycle of cleaning where scanning motion over the substrate is performed several times. When applying such a cleaning cycle it is preferable to provide a scanning motion at different lateral directions.
The supply pressure plays a major role with respect to the cleaning performance. The task of cleaning can be classified as following with respect to the rule of the supply pressure:
Air or an alternative gas, such as N2 or He (other gases may be used too) from a high pressure reservoir may be used in order to (a) provide inertial conditions if required (b) take advantage of the thermodynamic properties of the gases.
Reference is now made to
b illustrating schematically an isometric view of a round-shaped cleaning head unit 10a of the air-scraper apparatus in accordance with another preferred embodiment of the present invention. This annular version of the cleaning head unit is suitable for point-to point cleaning, in particular when inspection system is involved in the cleaning process, detecting the presence of contaminants in specific locations. It has similar connectors for pressure 20 and vacuum 30 supply. The facing surface 11 of the round-shaped cleaning head unit 10a is seen from the bottom. Typically, the facing surface 11 has one substantially central pressure outlet 21, surrounded by an annular vacuum outlet 31, the annular lips 12 of the cleaning head unit 10 are geometrically presented on facing surface 11 and separate the central pressure outlet 21 from the surrounding annular vacuum outlet 31.
c schematically illustrates a cross sectional view of the elongated cleaning head unit 10 shown in
A dynamically close miniature chamber is created by dynamic isolation of the close cleaning area. It can be obtained by applying circumferential vacuum suction 31 that sucks away the air together with the removed particles and also sucks a limited amount of ambient air through the passage 13 with a width “e”, but without much interaction with the outer atmosphere.
When the cleaning head unit 10 is placed in close proximity to the surface 99, the high pressure air flows down from passage 22 toward the outlet 21, passes through a very small gap “ε” that is created between the lips 12 and the surface 99, and is sucked away by the vacuum outlet 31 through the passage 32 that communicates with vacuum connector 30 (linked to a vacuum reservoir). The miniature zone created between the lips 12 and the surface 99 will be referred hereafter as the “throat section” zone. As the cleaning head unit 10 has a mirror symmetry structure, two opposing miniature cleaning zones are created below the two opposing throat sections. The throat section has a very narrow width, denoted by the letter “ε”. The throat section zone is the place where the high removal forces are generated. The surface 99 of the object 100 to be clean and the lips 12 of the cleaning head unit 10 are preferably not both at rest, one of them or both are moved in a lateral motion in order to provide the relative scanning motion, necessary to cover and clean large areas or to move from one point to another (in a point-to-point mode of cleaning). Although symmetric set up is shown in
d schematically illustrates a focused cross sectional view of a contoured throat section 18a of the cleaning head unit 10 of the air-scraper 30 apparatus in accordance with another preferred embodiment of the present invention. It has contoured lips 12a. Air flow is accelerated rapidly from the high-pressure passage 22 through the throat section 15 created between the surface 99 to be cleaned and the lips 12a of the wall 16 between passages 22 and 32, and finally sucked away through vacuum passage 32. The contoured throat section 15 has a tiny width “ε” and a very short length denoted by the letter “τ”. As cleaning is performed at the throat section zone, the removed particles are evacuated through the vacuum passage 32.
e schematically illustrates a focused cross sectional view of a sharp throat section 18b of the cleaning head unit 10 of the air-scraper apparatus in accordance with another preferred embodiment of the present invention. It has sharp lips 12b. The flow is accelerated rapidly from the high-pressure passage 22 through the throat section 15 created between the surface 99 to be cleaned and the sharp lips 12b of the wall 16 between passages 22 and 32, and finally sucked away through the vacuum passage 32. The sharp throat section 15 has a tiny width “ε”. However, with respect to the contoured lips 12a, in this design it is intended to create a vanishing throat section length (there is still a minimum length due to manufacture limitations). As cleaning is performed at the throat section zone, the removed particles are evacuated through the vacuum passage 32.
f illustrates, in accordance with a preferred embodiment of the present invention, a cross sectional view close to the outlet of the high-pressure passage 22 of the cleaning head units shown in
Reference is now made to
Reference is now made to
The high removal forces are generated at the throat section area along a very short length. In order to maximize cleaning performance, the flow-field can be manipulated. Reference is now made to
In
In
High removal forces are needed to provide efficient cleaning of few micrometer & sub-micron particles. The removal forces acting on a particle are built from two contributions, acting in the same (stream-wise), direction:
Reference is made to
These two complementary stream-wise removal forces generate a resultant side force that tends to disconnect the particle from the surface by slippage. However in many cases this is not the dominant removal mechanism, as the particle can firstly disconnect by rolling with respect to the point of rotation 51, as it is subjected to aeromechanic moments (notice that the shear force span is larger as much as twice with respect to the pressure force). When the particle 50 is a perfect sphere, the adhesion force cannot provide much resistance to the aeromechanic moments as the span of the adhesion forces with respect to the point of rotation 51 is small.
Usually the larger the particle is, more irregularities in shape are found and the smaller the particle is, more regular and spherical particles are found. Generally speaking, the role of particle removal suggests that the removal forces needed for removing a particle (with respect to particle side) are increased as the typical dimension of the particle is decreased. Combining these two generalized statements, it seems that particles shaping effects mostly affect large particles where the removal forces needed are relatively smaller on one hand, and on the other hand, relatively small shaping effects affect small particles where also without the severe augmentation of removal requirements due to shaping, large removal forces are needed for providing an efficient process of cleaning.
An aerodynamic issue of significantly high importance with respect to the cleaning efficiency of the apparatus and method of the present invention is the interaction of the particles with the boundary layer.
b schematically illustrates a case where a particle 50b has a typical scale that is smaller than the thickness “δ” of the boundary layer 57. In this case the particle is mostly subjected to the weak potion of the boundary layer bounded by the practical thickness “δ1”, thus the strength of the pressure force 53b significantly deteriorates and pressure recovery does not reach its full potential. Still, the shear force 54 may not significantly be affected by the weak portion of the boundary layer. As a result, in the case of relatively smaller particles, only the shear force is directly related to the active area (reduced by square with the decrease of the particle typical scale), and the pressure force decays substantially faster when the typical scale is decreased. Accordingly, for a large particle the pressure force is the dominant part of the removal forces, but for increasingly small particle removal requirements, the shear force starts to play a major role.
The scaling between the particle typical scale and the boundary layer is of great importance with respect to efficiency of removing small-scale particles, in particular sub-micron particles. It is mostly important in connection with the present invention to reduce the physical scales of the throat section zone, and to obtain a miniature active cleaning area at the throat section zone. When the width of the throat section is extremely small, a feature preferably achieved by implementing one of the above mentioned aerodynamic mechanisms to create a narrower throat section effective-width, the boundary layer thickness also becomes smaller. As the length of the throat section become shorter (preferably a sharp throat section) the flow rapidly accelerates along a very short downstream distance to a sonic flow. According to the role of boundary layers thickness growth, the shorter the distance from the origin of the flow, the smaller the boundary layer thickness. Miniature scales and rapid acceleration (less than 10 micro-meters is needed to accede sonic speed), provide almost vanishing boundary layer thickness at the throat section zone, where the flow reaches a sonic speed. The throat section zone is the most effective zone with respect to removal forces and further downstream the removal forces become smaller. It is of course related to particle—boundary-layer interaction as was already mentioned hereinabove. As the boundary layer thickness is smaller, smaller particles may be subjected to the full potential lateral pressure force without significantly deteriorating effects resulting from the weak flow portion of the boundary-layer.
In order to perform an effective cleaning process aimed at cleaning large surfaces, it is suggested to perform a scanning motion with the cleaning head unit of the present invention. Relative motion between the cleaning head unit and the surface to be cleaned is employed.
a-d illustrates some proposed relative motion effects.
Other important issue with respect to the present invention is the thermal conditions that exist during the cleaning process. Air or other gas that is used in the cleaning process can be pre-heated. In that case, removal forces that depend on the thermodynamic properties of the gas (such as viscosity or density) are augmented or at least do not severely deteriorate. Nevertheless, the main reason for heating the gas is for reducing the adhesion forces. If the heated air heats the particles and the surface to be clean underneath it to a temperature of more than 100° C., water trapped between the particles and the surface evaporates. As the water disappears, the capillary portion of the adhesion force not longer exists. Capillary force is the significant part of the adhesion force and accordingly it makes the task of particle removal easier when it disappears. Another alternative is to pre-heat the object to be clean and/or to heat it during the cleaning process in order to evaporate the water and to diminish significantly the adhesion force. Heating can be performed using an in-contact platform where heating elements are used (heat conduction mechanism), or by pre-heating air that is used to produce an air-cushion, when a non-contact platform is used (heat convection mechanism). On the other hand, it is also an option to spray the surface with water to reduce the capillary forces, or to apply other solutions, in order to weaken the adhesion forces. There are many known commercial solutions that are used for that end. However such an approach that involves wet conditions around the particles is not preferable as it leads to a semi-dry cleaning process and it is difficult to exercise. In addition, it is also an option, with respect to reducing adhesion force, to add ionizer to the flow in order to reduce the electrostatic adhesion force.
In order to maximize removal forces, it is an option to provide periodic fluctuations to the flow, to be effective at the throat section area. It can be done by acoustic means or by using electromechanical means (including piezoelectric elements). From an aerodynamic point of view, periodic (time dependent) fluctuations affect temporarily the boundary layer thickness and the velocity gradients close to the surface. Moreover, periodic fluctuation frequencies can be correlated with the miniature scales of the smaller particles where the removal task becomes harder. It means that high frequencies can be effective for removing miniature (submicron) particles, but the operational frequencies must be lower than a critical frequency, since fluid acts like a low-pass filter and does not response to extremely high frequencies.
A cleaning system in accordance with the present invention comprises a cleaning apparatus that has at least one cleaning head unit, an optional platform for supporting the object to be clean, with or without contact, where the surface of the that object is safely held in close proximity to the cleaning head unit, and moving means for providing a substantially parallel relative motion, linear or rotational, between the cleaning head unit and the surface of the object to be cleaned. There are many set-ups being consistent with this definition. With respect to the cleaning apparatus of the present invention and without derogating generality, several preferred embodiments of the present invention are presented in
a illustrates a preferred embodiment of the present invention, a setup where the object to be cleaned 100 is held in position from its backside in physical contact to platform 83. This setup is equipped with a cleaning head unit 10 having pressure inlet 20 and vacuum outlet 30. The cleaning head unit 10 is held in close proximity to the surface 99 to be cleaned of object 100. An arm 81, optionally being a robotic arm, holds the cleaning head unit 10. Arm 81 is connected to a vertical element 82, being a mechanism for controlling the gap between the cleaning head unit 10 and the surface 99 to be cleaned of the object 100.
b illustrates, with accordance with another preferred embodiment of the present invention, a setup resembling the setup described with respect to
c illustrates, in accordance with another preferred embodiment of the present invention, another setup resembling to the setup described with respect to
In accordance with another preferred embodiment of the present invention, it is convenient to design a setup where the cleaning head unit is integrated with the non-contact platform of dry cleaning apparatus. Without derogating generality, several integral platforms having an integral cleaning had unit, are shown in
b illustrates, in accordance with another preferred embodiment of the present invention, a circular non-contact platform where a small traveling cleaning head unit 10a having a round outlet 21 of the high pressure passage (of the cleaning head unit 10), is integrated in a round non-contact platform 90 having an active surface 91. The cleaning head unit 10a is of much smaller size with respect to the radius of the non-contact platform 90. The facing surface 11 of the cleaning head unit 10a is included in the active surface 91 of the non-contact platform 90. In order to provide radial scanning motion, the cleaning head unit is moved during the cleaning process along a radial slider 92. In this case, coverage of the entire surface to be cleaned is completed by simultaneously turning the object to be clean (not seen in the figure).
c illustrates, in accordance with another preferred embodiment of the present invention, several options where more than one cleaning head units are integrated within the non-contact platform 90, where the facing surface of each cleaning head unit is incorporated in the active surface 91 of the non-contact platform 90. One option is to use several cleaning head unit segments 10f arranged in a radial orientation but at different angles, where each segment cleans an annular slice and all the segments together provide full coverage of the surface to be cleaned. Still, coverage of the entire surface to be cleaned may also be completed by turning the object to be clean (not seen in the figure). Another option is to apply removal forces acting in two substantially perpendicular directions, by replacing each of the integral segments 10f with two segments 10g, having substantially perpendicular orientation (only the central slice is shown). In this case cleaning process efficiency may be improved as explained with respect to
a-h illustrate, in accordance with another preferred embodiment of the present invention, optional setups that can be applied for the dry cleaning system where it is intended to clean flat surfaces. Without derogating generality,
a illustrates, in accordance with a preferred embodiment of the present invention, a setup having circular geometry for front-side cleaning where a cleaning head unit 10a is facing the surface 99 of the object to be cleaned that is held down in contact, to the platform 90c of the dry cleaning system. The cleaning head unit can be equipped with side non-contact active plates that generate air-cushion to support the cleaning head unit as described in
b illustrates, in accordance with another preferred embodiments of the present invention, a setup having circular geometry for front-side cleaning where a stand-alone cleaning head unit 10a is facing the surface 99 of the object to be cleaned that is supported by a non-contact platform 90 of the dry cleaning system. In this setup (and also with respect to
c illustrates, in accordance with another preferred embodiment of the present invention, a setup having circular geometry for backside cleaning where the cleaning head unit 10 is integrated within the non-contact platform 90 of the dry cleaning system. The integral cleaning head unit 10 is facing the backside surface 99 of the object to be cleaned 100 that is supported by a non-contact platform 90 of the dry cleaning system. In this setup, only the object to be cleaned 100 is rotating in order to provide the relative scanning motion 94r. Again, rotational motion to the round object 100 can be provided by a rotating mechanism such as a drive-wheel 95 that is attached to the edge of the round object 100 (such as silicon wafer). Other rotational drive mechanisms were discussed with reference to
d illustrates, in accordance with another preferred embodiment of the present invention, a setup having circular geometry for cleaning both the front-side and the backside of a round object. This setup includes both a cleaning head unit 10a for cleaning the front-side 99f of object 100, and an opposing integral cleaning head unit 10, integrated within the platform 90 of the dry cleaning system, for cleaning the backside 99b of object 100. The object to be cleaned 100 that is supported by a non-contact platform 90 of the dry cleaning system. In this setup, only the object to be cleaned 100 is rotating in order to provide the relative scanning motion 94r. Yet again, rotational motion to the round object 100 can be provided by a rotating mechanism such as a drive-wheel 95 that is attached to the edge of the round object 100 (such as silicon wafer). Other rotational drive mechanisms were disclosed with respect to
e illustrates, with respect to another preferred embodiment of the present invention, a setup having circular geometry for cleaning both the front-side 99f and the backside 99b of a round object 100. This setup includes two opposing integral cleaning head units 10, integrated in two opposing plates 90 of a dual-side non-contact platform (it is a mirror-symmetry platform), of the dry cleaning system. The object to be cleaned 100 is supported by a dual-side non-contact platform of the dry cleaning system. In this case it is preferable to implement the dual side PP-type (pressure preloading) air-cushion, or a dual-side vacuum-preloaded PV-PV type air-cushion (see PCT/IL02/01045, incorporated herein by reference). These dual-side supporting air-cushions provide inherently stable non-contact platform for high performance cleaning. In this setup, only the object to be cleaned 100 is rotating in order to provide the relative scanning motion 94r. Again, rotational motion to the round object 100 can be provided by a rotating mechanism such as a drive-wheel 95 that is attached to the edge of the round object 100 (such as silicon wafer). Other rotational drive mechanisms were disclosed with respect to
Without derogating the generality,
g illustrates, in accordance with another preferred embodiment of the present invention, a setup having rectangular geometry for backside cleaning of rectangular substrates such as FPD, where an elongated integral cleaning head unit 10 is integrated within the non-contact platform 90 of the dry cleaning system. The integral cleaning head unit 10 is facing the backside 99 of the object 100 to be cleaned as it supported by a non-contact rectangular platform 90 of the dry cleaning system. This case is similar in most details to the setup described in
h illustrates, in accordance with another preferred embodiments of the present invention, a setup having a rectangular geometry for cleaning both the front-side 99f and the backside (not shown in the figure) of a thin rectangular object 100 such as FPD. This setup includes both a cleaning head unit 10a for cleaning the front-side 99 of object 100, and an opposing cleaning head unit 10, integrated within the non-contact platform 90 of the dry cleaning system, for cleaning the backside of object 100. The object to be cleaned 100 is supported by a non-contact rectangular platform 90 of the dry cleaning system. This case is similar in most details to the setup described in
i illustrates, in accordance with another preferred embodiments of the present invention, a setup having rectangular geometry for front-side cleaning of rectangular substrates such as FPD, where much shorter cleaning head unit 10a with respect to FPD width is provided. In this setup the process of cleaning is performed consecutively on longitudinal slices; The object to be cleaned 100 is moved forward and backward (94d) and the cleaning head unit is moved laterally (95a) to new lateral position in a predetermined time frame between the two opposing movements. Such a setup can reduce significantly the mass flow rate of the cleaning system. Other relevant details are similar to the setups described in
j illustrates, in accordance with another preferred embodiments of the present invention, illustrates a setup having rectangular geometry for front-side cleaning of rectangular substrates such as FPD, where two elongated cleaning head units 10a and 10b are provided. In this setup the process of cleaning is performed in a parallel manner, where the cleaning process is completed by moving longitudinally (94c) to only half of the substrate length. Such a setup provides a significantly smaller footprint of the cleaning system (by 25% or so). Another alternative to obtain similar reduction of the cleaning system footprint is by using only one moving cleaning head unit 10b where at the same time that the substrate moves forwards 94c half way of the substrate length, the cleaning head unit 10b is moved backwards 95b half way. Other relevant details are similar to the setups described in
Without derogating the generality,
The orientation of the cleaning head with respect to the surface to be cleaned may vary. The device of the present invention can operate horizontally, vertically and in fact in any desired orientation.
Reference is now made to
Cleaning head unit 110 of the dry cleaning system 400 in accordance with a preferred embodiment of the present invention is placed in close proximity above the surface 99 to be clean of object 100, stiffly connected to a supporting mechanism 115. The supporting mechanism 115 is capable of regulating the distance between the facing surface of the cleaning head unit 110 and the surface 99 of the object to be clean 100. Proximity sensor 111 is attached to the cleaning head unit 110 in order to provide control of this distance. In addition, the supporting mechanism 115 can rotate the cleaning head unit 100 sideward, to allow free loading and unloading of object 100 by bringing it laterally to central position, moving it vertically down and put it on landing elements 212 and vise versa.
Pressurized gas (such as air) is supplied to the cleaning head unit 110 by pressure pipe-line 120, having pressure control valve 121 and sub-microns filter 122. It is preferable that the filter 122 will be mounted after the valve 121 to reduce risk of contamination. Similarly, vacuum is supplied to the cleaning head unit 110 by vacuum pipe-line 130, having a vacuum control valve 131. Both the pressurized air and the vacuum are supplied to the cleaning head unit 110 through the base 200 and the supporting mechanism 115. Pressure sensor 112 and vacuum sensor 113 are integrated in the cleaning head unit 110. The pressurized air can be manipulated by unit 116 for providing high frequency periodic fluctuations. It can be done by acoustic device (electromechanical device) or piezoelectric device. In addition, a utility unit 125 can be fluidically connected at the entrance to pipeline 130. The utility unit 125 may include heating elements 123 and ionizer 124.
Pressurized gas (such as air) is supplied to the PV-type non-contact platform 210 by the pressure pipe-line 220, having a pressure control valve 221 and a sub-microns filter 222. It is preferable that the filter 222 will be mounted after the valve 221 to reduce risk of contamination. Similarly, vacuum is supplied to the PV-type (vacuum preloaded) platform 210 by vacuum pipe-line 230, having a vacuum control valve 231. Both the pressurized air and the vacuum are supplied to the PV-type non-contact platform 210 through the base 200. Pressure sensor 214 and vacuum sensor 215 are integrated in the PV-type non-contact platform 210.
Central control unit 300 of the dry cleaning system is designed to control the cleaning process of the dry cleaning system 400 by connections 310 and the external supply pipes by connections 320, 330, to provide all information needed to control the cleaning process. It also includes connection to external equipment and computer 350 for monitoring and communication.
Central control unit can be an external unit or it may be internally installed inside base 200. Accordingly valves 121 and 131 as well as valves 221 and 231 can be assembled inside base 200. In addition, an optical scanning device 450 may be incorporated with the cleaning system 400 to provide either lateral the location of the contaminating particles (in particular when point-to-point cleaning process is applied) and/or to provide pre- and post-process analysis of the cleaning process.
According to a preferred embodiment of the present invention, a PA-type non-contact platform is applied for supporting the object to be cleaned.
According to another preferred embodiment of the present invention, a PV-type (vacuum preloaded) non-contact platform is applied for clamping without contact the object to be cleaned, in cases where the non-contact platform is fully covered.
According to another preferred embodiment of the present invention, a PV-type non-contact platform is applied for clamping without contact the object to be cleaned, in cases where the non-contact platform is not fully covered.
It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope.
It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the embodiments described in the accompanying Figures and the present specification and yet remain within the scope of the present invention.
