WO2009098042A1

WO2009098042A1 - Device for cleaning flat substrates

Info

Publication number: WO2009098042A1
Application number: PCT/EP2009/000749
Authority: WO
Inventors: Uwe Kerat
Original assignee: Meyer Burger Ag
Priority date: 2008-02-06
Filing date: 2009-02-04
Publication date: 2009-08-13

Abstract

The present invention relates to a device and a method for cleaning flat substrates, in particular silicon wafers, in a stacked upright position by a combined rinse and ultrasonic treatment directed at the substrate sides.

Description

DEVICE FOR CLEANING FLAT SUBSTRATES

Description

State of the art

Over 80 % of the global solar cell production requires the cutting of multi- or mono- crystalline silicon blocks into wafers. For this purpose multi-wire sawing is the main slicing technique in the photovoltaic and microelectronics industry. Due to its high throughput, small kerf loss, little restriction on the size of ingots as well as its excellent wafer surface quality, this technology dominates over other techniques.

Prior to the slicing procedure multicrystalline ingots grown by directional solidification techniques reaching cross sections of more than 90 x 90 cm² and weighing over 400 kg or monocrystalline Czochralski crystals with diameters of up to 50 cm require some pre- sizing treatment.

This pre-treatment normally involves a cropping process of cutting the conical caps off the raw single crystal, e.g. on an inner diameter saw (e.g. ID saw TS207 from Meyer- Burger AG, Steffisburg, Switzerland), after which the outer diameter can be ground. The ID saw makes use of the advantage of tensioning a very thin disk with an inner hole, resulting in a disk with a much higher stability than the equivalent outer diameter saw, thus reducing kerf loss. To increase the fill factor of a solar panel the single ingots are squared. Equally, the very hard and contaminated crust must be sawed off the polysilicon ingots and bricks, with the format of the future wafers cut out of the polysilison casting. For example, this is commonly done by band saws with diamond-plated saw bands (e.g. Bandsaw BS800, 805, 830 from Meyer- Burger AG) that enable high cutting rates.

After shaping the silicon ingot having a length of up to one meter it is glued on one side to a glass support plate, which is in turn glued to a carrier mount for positioning the brick appropriately within the multi-wire saw. This multi-wire cutting device then slices the brick into wafers with a thickness of around 70 to 280 μm, e.g. on a DS 264 multi-wire saw from Meyer-Burger AG, CH. In this technique a single wire with a diameter of about 80 to 160 μm and a spool length of 600 to 1000 km is fed from a supply spool through a wire tension system to wire guide rollers that are grooved with a constant pitch. By winding the wires over these wire guide rollers a wire web is formed. At the output end a take-up spool collects the used wire. An abrasive slurry supplied from a nozzle system onto the wire web is carried with the moving wire into the sawing channel to perform the cut- lapping process. The slurry consists of hard grinding particles, generally SiC, with a diameter in the range of 5 to 15 μm that are suspended in glycol or oil. By pushing the silicon brick against the wire web it is sliced into thousands of wafers in a single run. For a review on multi-wire technology see H. B. Moller, Basic mechanisms and models of multi-wire sawing, Advanced Engineering Materials, 6, no. 7 (2004); Funke et al., Surface damage from multi wire sawing and mechanical properties of silicone wafers, 2CV.5.7, 20^th Photovoltaic Solar Energy Conference, Barcelona, Spain, 2005.

At the end of the multi-wire cut lapping process the thousands of thin wafers are still attached to the partially cut glass support plate (now having a comb-like structure) on the carrier mount. All wafer surfaces in contact with the wire now have abrasive slurry sticking to them that needs to be completely removed before further processing for photovoltaic or microelectronics purposes.

Typically, the whole cut silicon wafer block together with the glass support and carrier mount is lowered into a basin where multiple nozzles guide water jets to the side and spaces between wafers to widen the gap between individual wafers slightly and flush out the slurry. Most often this basin has a fast drain system. The jet water may be enriched with chemicals such as surfactants, etc. However, chemical components can significantly increase the costs of waste disposal and are preferably avoided. This pre-cleaned wafer block is then transferred and the wafers are separated from the glass plate, normally by chemical acid (e.g. acetic acid) treatment leading to a rather random pile of wet wafers that have a tendency of sticking to each other rather firmly. A number of devices and methods have been devised for positioning and blocking thin substrates on a cut substrate block.

For example, WO 2006/133798 A1 discloses a device for positioning and blocking thin silicon wafers after wire-sawing a silicon wafer block. Said device comprises a cassette that accommodates the wafer block and is provided with two contact strips whose sides facing the wafer block encompass elements, which engage into the narrow cutting gap between wafers so as to maintain the distance and provide support. This allows the wafers to be fixed in position even after removal of the glass plate, so that particularly the gap in the former connecting point to the removed supporting glass plate is maintained and the subsequent singulation process is simplified.

DE 199 00 671 describes a method and device for singulating disk-shaped substrates such as silicon wafers by perpendicular movement of the wafers and simultaneously introduction of a fluid flow between stacked wafers.

Regularly, the piled or cassette-positioned wafers are manually singulated for further cleaning treatment. However, complex devices for automating this cost and labor intensive step are also available and will dominate the wafer industry soon.

The pre-treated and singulated wafers need to be cleaned completely from absolutely all remaining contaminants such as silicon dust and slurry remnants before they are ready for packaging and final photovoltaic or microelectronics applications. The final treatment conventionally involves a number of ultrasonic treatment, chemical treatment, rinse and drying steps that are performed in sequence and that are arranged in a production line, where the wafers are transported in horizontal position from one treatment step to the next by a conveying system. These treatment lines take up 4 to 12 wafers in one row at the starting point and depending on the number and nature of the steps will provide clean and dry wafers after having transported them from step to step for about 6 to 20 meters in length. Treatment steps typically involve (i) submerging them into one or more fluid reservoirs for ultrasonic treatment at one or more wavelengths, (ii) submerging them into aqueous chemicals such as acid, base, surfactant, (iii) rinsing with deionized water and (iv) forced air drying. Furthermore, these final treatment lines tend to be complicated, large in their dimensions as well as costly in purchase and also maintenance due to the accumulation of large quantities of waste fluid. Figure 2 as described further below provides a schematic drawing of such a state of the art cleaning device and indicates its complexity and size.

DE 10 2005 012 244 A1 describes a method for the final cleaning of semiconductor substrates by means of sequential ultrasonic treatments in a fluid-filled basin, comprising the continuous transport of substrates in the fluid in the transport direction with at least four ultrasound source fields arranged stationary or movable, the movement being parallel, vertical or vertical and horizontal to the transport direction and the position of the ultrasound source field being either angular or parallel to the transport direction. The wafers are conveyed in the transport direction laying down in a flat horizontal position, their flat surface areas opposite of the ultrasound source fields. Preferably, the sound source fields are optimized in their position towards the wafers to maximize the oscillation maximum and different frequencies are employed. The authors allege that this method could be suited to clean wafers without having to revert to chemicals in the fluid medium even though they do not exclude chemical components perse. While this method seems to avoid chemical treatment and chemical waste disposal it still requires several expensive and sophisticated ultrasound devices, most of which need to be arranged in a movable manner and require computer control units. Furthermore, the dimensions of the treatment line and the fluid volume that needs to be periodically discarded or regenerated are quite large. A production line of this type would probably be at least 6 to 12 m in length. Fig. 3 as described further below depicts a conventional cleaning device in accordance with DE 10 2005 012 244 A1.

It is the object of the present invention to provide a device and method for cleaning flat substrates, in particular wafer substrates derived directly from the multi-wire sawing process or optionally rinse-pre-treated substrates, that are less expensive, less complicated in design and components and smaller in dimensions when compared to prior art systems.

In a first aspect this object is solved by a device for cleaning flat substrates (1), comprising: i) a fluid reservoir (2) containing at least one cassette (3) accommodating flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other, ii) one or more stationary and/or movable fluid jet nozzles (5) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir facing the substrate sides (4a), iii) one or more stationary and/or movable ultrasound generating devices (8) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir (2) facing the substrate sides (4a), iv) one or more inlets (11) and/or drains (12) for introducing and removing fluid, wherein a) the reservoir (2) can be filled with fluid to completely cover said upright standing substrates (4), b) the fluid jet nozzle(s) rinse and/or flush the flat substrates (4) and/or separate adhered flat substrates, c) wherein the one or more stationary and/or movable ultrasound generating device(s) (8) provide(s) ultrasound waves of one or more frequencies inside the fluid-filled reservoir (2) directed at the substrate sides (4a).

A flat substrate (4) for being cleaned in a device according to the present invention is any flat plate- or sheet-like substrate such as e.g. a slab, a tile, a panel, slice, disk or a wafer. The present invention is illustrated by reference to a device for cleaning silicon wafers, these wafers being the most preferred flat substrates for being cleaned according to the invention. However, the present invention is not restricted to devices and methods for cleaning silicon wafers.

A fluid reservoir (2) according to the invention is simply a container, e.g. tank, through, tub, capable of holding fluid. The fluid reservoir (2) is dimensioned so that it can hold at least one cassette (3) accommodating flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other and so that when the reservoir is filled, the flat substrates (4) can be completely covered with fluid.

The term "cassette" (3) according to the present invention refers to any receptacle capable of accommodating flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other. Preferably, it is a basket with rails or a grid and guides that keep the flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other. The sides of said cassette (3) are mostly barrier-free to allow free access of the flat substrates to fluid, in particular to the fluid from the jet nozzles (5), and the ultrasound from the ultrasound generating devices (8). Preferably, the cassette is equipped with two or more guides, rails and/or contact strips whose sides facing the fiat substrates sides (4a) encompass elements, which engage into the gap between substrates so as to maintain the distance and provide support. This allows the wafers to be fixed in position, e.g. even after removal of the glass plate or after manual or water jet-assisted singulation. Preferably, the guides, rails and/or contact strips comprise an elastic polymer or rubber surface or brush-like appendages for direct contact with the flat substrates so that the substrates are fixed but can still be moved or singulated, for example, manually or by fluid jet nozzles or forced air. A non-limiting example of a cassette suitable for practicing the present invention is depicted in Fig. 4 for illustrative purposes only.

In a preferred embodiment, said cassette (3) is arranged movable in vertical (up and down) and/or horizontal (2a, back and forth) position within the reservoir (2), including angular movement.

In another preferred embodiment cassette (3) is (also) movable sideways (2b) toward one (6 or 7) or both sides (6 and 7) of the reservoir (2).

This movement of the cassette (3) in one or more directions allows for positioning the cassette (3), and, thus, its flat substrates (4) relative to the one or more fluid jet nozzles (5) and/or ultrasound generating devices (8) for providing optimized action.

In a particularly preferred embodiment, the cassette (3) and/or the flat substrates (4) within the cassette (3) is/are angulated relative to the horizontal plane, so that the substrate sides (4a) are vertically angulated and fluid will follow gravity and can drop off on one side of the flat substrates (3).

In a further preferred embodiment the flat substrates (4) can be transported inside the cassette (3), e.g. by a conveying system, parallel to the sides of the reservoir (2) in direction(s) 2a (back and forth).

The term "flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other" is simply meant to refer to an arrangement such as it is common in an upright stacked musical record collection or on a book shelf.

After the degluing step for silicon wafers, i.e. separation from the support plate, some or even most silicon wafers often adhere to each other strongly. To assist singulation of adhered flat substrates a preferred device according to the invention is one, wherein the cassette (3) or a part thereof, preferably a part thereof in direct contact with one or more flat substrates, can be vibrated, bent and/or moved in one or more directions. Preferably, this vibrating bending and/or moving is done in combination with fluid from the jet nozzles pushing the adhered silicon wafers apart. More preferably, the parts of the cassette (3) in direct contact with the substrates (4) should be elastic and accommodate the movement of the substrates (4) and avoid any damage to these. The fluid in the reservoir (2) and/or ejected from the jet nozzles (5) can be any fluid suitable for rinsing and/or flushing flat substrates, the preferred fluid being aqueous, more preferably being deionized water.

The fluid in the reservoir (2) and/or the fluid from the nozzles (5) may comprise additives, preferably acid(s), e.g. acetic acid, mineral acid, etc., base(s), e.g. NaOH, sodium acetate, KOH, etc., defoamer(s) and/or surfactant(s).

In a preferred embodiment two or more fluids having different compositions are introduced into the reservoir (2) simultaneously or sequentially. Preferably, compositions differing rather strongly in composition are introduced sequentially, optionally with a removing/draining step between additions, in order that the individual compositions are not diluted or that contaminants are removed before the next composition performs its tasks.

The purpose of the one or more stationary and/or movable fluid jet nozzles is to rinse, flush and/or separate (by applying fluid pressure) the flat substrates. The nozzles (5) and/or the cassette (3) are designed to be movable to allow for a most complete rinse, flush and/or separating action of the fluid. The skilled person can determine the mode of movement of the cassette (3) and/or nozzles (5) to optimize the fluid action without any undue burden. The skilled person can also determine the fluid jet^'s pressure, volume and shape to optimize fluid action for rinsing, flushing and separating flat substrates. While a rinse may be suitable to remove weakly adhered silicon dust and fluids of low viscosity, strongly adhered particles such as mineral oils and silicon carbide remnants from previous sawing action may require a fluid flush or even a high pressure jet. It is preferred that the fluid jet nozzles (5) are arranged in a movable manner in the fluid reservoir (2) to move up, down, left, right and angular to reach all of the substrate sides. In another preferred embodiment, stationary and/or movable fluid jet nozzles (5) are also arranged beneath and/or above cassette (3). It is generally necessary that the fluid jet has or gains (by separating adhered flat substrates) access to all surfaces of the flat substrates that need cleaning.

The ultrasound waves generated by the ultrasound generating devices (8) preferably have wavelengths in the fluid in the range of 10 mm to 80 mm and frequencies in the range of 10 to 200 kHz, preferably 20 to 132 kHz. Even more preferred, the device for cleaning flat substrates (1) of the invention comprises megasound generating devices (8a) instead of, preferably in addition to ultrasound generating devices (8), the frequencies for the megasound generating devices (8a) being in the range of 400 kHz to 3 MHz. The megasound generating devices (8a) are particularly suited to remove microparticles.

In a preferred embodiment of the device of the present invention the distance of one or more of the ultrasound generating device(s) (8) to the nearest substrate sides (4a) is at least temporarily from 1 to 20 mm, preferably 1 to 10, more preferably 1 to 5, most preferably 1 to 3 mm. "At least temporarily" means that the flat substrates (4) or the ultrasound generating device(s) (8) can moved towards or away from each other.

In a more preferred embodiment the device of the present invention may also comprise ultrasound generating device(s) (8) beneath and/or above the substrates (4).

While the temperature of the fluid is not critical for cleaning flat substrates (4) in a device according to the invention (1), it is preferred that the temperature of the fluid in the reservoir (2) and/or ejected from the nozzles (5) is in the range of 5 to 100 ⁰C, preferably 10 to 70 ⁰C, more preferably 20 to 40 ⁰C, most preferably ambient temperature of about 22 ⁰C.

In a most preferred embodiment, the present invention is directed to a device of the invention, wherein the flat substrates (4) are silicon wafers, preferably multi-wire saw-cut silicone wafers, more preferably freshly cut wafers without any prior cleaning step.

The device of the present invention described above may be a unit in functional cooperation with other devices or units for cleaning and/or preparing flat substrates, preferably silicon wafers.

In a preferred embodiment, the present invention relates to a multifunctional device, comprising a device according to the invention for cleaning silicon wafers and further at least one precleaning, degluing and/or separating device and optionally a conveying system for transporting the flat substrates from one device to the next. Even though the device of the present invention can be designed to completely clean and/or separate silicon wafers it may be advantageous to include at least one precleaning, degluing and/or separating step and/or other useful steps for processing silicon wafers in one multifunctional device. For example, for silicon wafers freshly cut by multi wire saw it may be advantageous to perform a precleaning step separately to get rid of most of the adhesive, abrasive and viscous slurry that would otherwise contaminate and clog the cleaning device of the present invention and its gadgets, e.g. ultrasound generating devices, drains, etc., that can only be cleaned with difficulty, i.e. by intense labour. Also, a degluing unit could be integrated into a multifunctional device. Moreover, it might be of use to employ a separating device after precleaning and/or degluing the sliced brick before entering the device of the present invention or to add subsequent separating and/or processing steps after the flat substrates have exited the device of the present invention.

A combined device functionally integrating a device of the present invention with other devices and preferably some kind of a conveying system for transporting the flat substrates (4) from one device to the next is designated a multifunctional device of the invention.

In a preferred embodiment, the present invention is directed to a multifunctional device, comprising a device of the invention as detailed above and further at least one precleaning, degluing and/or separating device and optionally a conveying system for transporting the flat substrates from one device to the next.

More preferably, said multifunctional device comprises more than one device selected from and arranged in the order of (i) optional precleaning device, (ii) degluing device and (iii) device according to the invention, wherein devices (i) and (ii) may be switched in order and said devices are in functional interaction with a conveying system for transporting flat substrates from one to the next device.

In a most preferred embodiment the present invention is directed to a device or a multifunctional device as described above, wherein the flat substrates (4) are silicon wafers, preferably multi-wire saw-cut silicone wafers.

The advantage of the cleaning device of the present invention is its compact design that allows for thoroughly cleaning flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other. It is much more efficient with regard to the amount of fluid, the space and time used in comparison to the long multiunit production lines with the substrates lying down flat that were previously employed in the art.

In a second aspect, the present invention relates to a method for cleaning flat substrates (4), comprising the following steps: a) loading flat substrates (4) in a cassette (3) in an upright position stacked in a row with the flat surfaces facing each other, b) positioning the cassette (3) with the flat substrates (4) in a reservoir (2), if the cassette (3) was not already located in the reservoir (2) during the loading step a), c) rinsing and/or flushing the flat substrates (4) and/or separating adhered flat substrates (4) with fluid from one or more stationary and/or movable fluid jet nozzles (5) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir (2) facing the substrate sides (4a), d) filling reservoir (2) with fluid to completely cover the upright standing substrates

(4) and providing ultrasound waves of one or more frequencies inside the fluid reservoir (2) directed at the substrate sides (4a) from one or more stationary and/or movable ultrasound generating device(s) (8) arranged in parallel and/or angular to one (6) or both sides (7) of the reservoir (2) facing the substrate sides (4a), wherein the order of steps c) and d) can be reversed and/or steps c) and d) can be performed simultaneously, and the fluid in the reservoir can be removed or substituted with fluids of the same or different compositions during, between or after steps c) and d).

In the following a method of the invention employing a device of the invention as detailed above is discussed for illustrative purposes only.

At first, the flat substrates (4) are loaded into a cassette (3) in an upright position stacked in a row with the flat surfaces facing each other. Then cassette (3) with the flat substrates (4) is positioned into a reservoir (2). Alternatively, the cassette (3) may already be positioned in the fluid reservoir during the loading of the flat substrates. The (optionally) adhered flat substrates (4) are rinsed and/or flushed and/or separated with fluid from one or more stationary and/or movable fluid jet nozzles (5) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir (2) facing the substrate sides (4a). The fluid either rinses weakly adhered contaminants from the flat substrates (4), e.g. acidic or basic or other previously employed fluids of low viscosity and little adhesive strength, e.g. fluid for degluing silicon wafers, flushes particle contaminants, adhesive or highly viscous fluids, e.g. the remaining abrasive slurry from multi-wire cutting silicon wafers, off the flat substrates (4) and/or separates the flat substrates (4) from each other by applying fluid pressure onto the sides of the substrates. When rinsing, flushing and/or separating the substrates (4), the nozzles (5) and/or the cassette (3) may be moved to position the substrates (4) relative to the fluid jet (5). Preferably, there are further fluid jet nozzles (5) located beneath and/or above the cassette (3) rinsing, flushing and/or separating the substrates (4). The fluid reservoir (2) is filled with fluid to completely cover the upright standing substrates (4) and ultrasound waves of one or more frequencies inside the fluid reservoir (2) are directed at the substrate sides (4a) from one or more stationary and/or movable ultrasound generating device(s) (8) arranged in parallel and/or angular to one (6) or both sides (7) of the reservoir (2) facing the substrate sides (4a). While the flushing and separating steps detailed above may also be performed with a partially or completely filled fluid reservoir (2), ultrasound action will require that the flat substrates are immersed in fluid. Therefore, the rinsing, flushing and/or separating can be performed before or after filling the reservoir and simultaneously to the ultrasound treatment. Alternatively, the reservoir can be filled and drained arbitrarily, e.g. for removing contaminants in the fluid, as long as the ultrasound action is done with immersed substrates (4). All rinsing, flushing separating and/or ultrasound steps may be repeated to adapt the procedure to a particular mode and substrate.

In order to assist singulation of adhered substrates (4) it is preferred to vibrate, bend and/or move the cassette (3) in one or more directions. The resulting strain will aid singulation, in particular in combination with fluid jet action. For example, the guides of the cassette holding the flat substrates vertically in place may be made from flexible or even soft materials, e.g. rubbers, polymers, that will not damage the substrates sides (4a). However, said material can be moved, e.g. twisted, bent, stretched, etc., to move the substrates relative to their neighbouring substrates, in order to assist singulation.

The fluid in the reservoir (2) and/or from the nozzles (5) is preferably aqueous, more preferably it is deionized water, optionally comprising additives, preferably acid(s), base(s), defoamer(s) and/or surfactant(s).

For practicing the method of the present invention, it may be advantageous to introduce two or more fluids having different compositions into the reservoir (2), e.g. a fluid for neutralizing acidic or basic fluid remaining from previous steps, e.g. the degluing step of wire-saw cut silicon wafers, distilled water for rinsing, flushing and/or separating substrates.

The method of the present invention is particularly suited for cleaning silicon wafers, preferably multi-wire saw-cut silicone wafers.

The ultrasound waves employed in the method preferably have wavelengths in the fluid in the range of 10 mm to 80 mm and frequencies in the range of 10 to 200 kHz, preferably 20 to 132 kHz. The one or more ultrasound generating device(s) (8) employed are at least temporarily moved to the nearest substrate sides at a distance of at least from 1 to 20 mm, preferably 1 to 10, more preferably 1 to 5, most preferably 1 to 3 mm.

In addition, megasound may be employed, preferably with frequencies of 400 kHz to 3 MHz, to remove microparticles on the flat substrates.

The temperature of the fluid in the reservoir (2) and/or from the nozzles (5) is in the range of 5 to 100 ⁰C, preferably 10 to 70 ⁰C, more preferably 20 to 40 ⁰C, most preferably ambient temperature of about 22 ⁰C.

In a further aspect, the present invention is directed to the use a device according to the invention in a method as described above.

The following figures are meant to illustrate the present invention and are not to be construed as limiting the scope of the present invention as indicated in the appended claims.

Figures

Fig. 1 schematically illustrates a top view of a device for cleaning flat substrates according to the invention.

Fig. 2 depicts a conventional multifunctional solar wafer separation and cleaning device E-300070 from Rena, DE. It is more than 16 m long and consists of storage (1)/input(2)-, preclean (3)-, ingot handling- (4) , unglue (5)-, separating (6)-, chemical rinse (7)-, rinse 1 (9)-, ultrasound (US) 1 (10)-, rinse 2 (11)-, US 2 (12)-, rinse 3 (13)-, US 3 (14)-, final rinse 1 to 3 (15)-, drying (16)- and output-units (17). The cleaning device (7-18) itself is more than 11 m in length.

Fig. 3 depicts a conventional cleaning device in accordance with DE 10 2005 012 244 A1. In a fluid filled reservoir six ultrasound generating devices (8) are arranged in 3 pairs of two (5a to c) separated by two partitions beneath a conveying system (II) for transporting silicon wavers in a lying down position from inlet 9 in direction 4.

Fig. 4 is a picture of a top view of a cassette accommodating a number of silicon wafers held in upright position made from stainless steel with elastic guides in contact with the wafers at the bottom and both sides that can be immersed into a fluid reservoir of a device according to the invention.

Claims

1. A device for cleaning flat substrates (1 ), comprising:

5 i) a fluid reservoir (2) containing at least one cassette (3) accommodating flat substrates (4) held in upright position stacked in a row with the flat surfaces facing each other, ii) one or more stationary and/or movable fluid jet nozzles (5) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir facing 10 the substrate sides (4a), iii) one or more stationary and/or movable ultrasound generating devices (8) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir (2) facing the substrate sides (4a), iv) one or more inlets (11) and/or drains (12) for introducing and removing 15 fluid, wherein a) the reservoir (2) can be filled with fluid to completely cover said upright standing substrates (4), b) the fluid jet nozzle(s) rinse and/or flush the flat substrates (4) and/or 20 separate adhered flat substrates, c) wherein the one or more stationary and/or movable ultrasound generating device(s) (8) provide(s) ultrasound waves of one or more frequencies inside the fluid-filled reservoir (2) directed at the substrate sides (4a).

U _

25 2. Device according to claim 1 , wherein the cassette (3) is movable in vertical and/or horizontal (2a) position within the reservoir (2).

3. Device according to claim 1 or 2, wherein the cassette (3) is movable sideways (2b) toward one (6 or 7) or both sides (6 and 7) of the reservoir (2).

30

4. Device according to any one of claims 1 to 3, wherein the flat substrates (4) can be transported inside the cassette (3) parallel to the sides of the reservoir (2) in direction(s) 2a.

5. Device according to any one of claims 1 to 4, wherein the cassette (3) can be vibrated, bent and/or moved in one or more directions to assist singulation of adhered substrates.

6. Device according to any one of claims 1 to 5, wherein the fluid in the reservoir (2) and/or from the nozzles (5) is aqueous, preferably deionized water.

7. Device according to any one of claims 1 to 6, wherein the fluid in the reservoir (2) and/or the fluid the nozzles (5) comprises additives, preferably acid(s), base(s), defoamer(s) and/or surfactant(s).

8. Device according to any one of claims 1 to 7, wherein two or more fluids having different compositions are introduced into the reservoir (2).

9. Device according to any one of claims 1 to 8, wherein the flat substrates (4) are silicon wafers, preferably multi-wire saw-cut silicone wafers.

10. Device according to any one of claims 1 to 9, wherein said ultrasound waves have wavelengths in the fluid in the range of 10 mm to 80 mm and frequencies in the range of 10 to 200 kHz, preferably 20 to 132 kHz.

11. Device according to any one of claims 1 to 10, wherein the distance of one or more of the ultrasound generating device(s) (8) to the nearest substrate sides is at least temporarily from 1 to 20 mm, preferably 1 to 10, more preferably 1 to 5, most preferably 1 to 3 mm.

12. Device according to any one of claims 1 to 11 , wherein the temperature of the fluid in the reservoir (2) and/or from the nozzles (5) is in the range of 5 to 100 ⁰C, preferably 10 to 70 ⁰C, more preferably 20 to 40 ⁰C, most preferably ambient temperature of about 22 ⁰C.

13. Multifunctional device, comprising a device according to any one of claims 1 to 12 for cleaning silicon wafers and further at least one precleaning, degluing and/or separating device and a conveying system for transporting the flat substrates from one device to the next.

14. Multifunctional device according to claim 13, comprising more than one device selected from and arranged in the order of (i) optional precleaning device, (ii) degluing device and (iii) device according to any one of claims 1 to 12, wherein devices (i) and (ii) may be switched in order and said devices are in functional interaction with a conveying system for transporting flat substrates from one to the next device.

15. Method for cleaning flat substrates (4), comprising the following steps: a) loading flat substrates (4) in a cassette (3) in an upright position stacked in a row with the flat surfaces facing each other, b) positioning the cassette (3) with the flat substrates (4) in a reservoir (2), if the cassette (3) was not already located in the reservoir (2) during the loading step a), c) rinsing and/or flushing the flat substrates (4) and/or separating adhered flat substrates (4) with fluid from one or more stationary and/or movable fluid jet nozzles (5) arranged parallel and/or angular to one (6 or 7) or both sides (6 and 7) of the reservoir (2) facing the substrate sides (4a), d) filling reservoir (2) with fluid to completely cover the upright standing substrates (4) and providing ultrasound waves of one or more frequencies inside the fluid reservoir (2) directed at the substrate sides (4a) from one or more stationary and/or movable ultrasound generating device(s) (8) arranged in parallel and/or angular to one (6) or both sides (7) of the reservoir (2) facing the substrate sides (4a), wherein the order of steps c) and d) can be reversed and/or steps c) and d) can be performed simultaneously, and the fluid in the reservoir can be removed or substituted with fluids of the same or different compositions during, between or after steps c) and d).

16. Method according to claim 15, wherein the cassette (3) is moved in vertical and/or horizontal (2a) position within the reservoir (2) during steps c) and/or d).

17. Method according to claim 15 or 16, wherein the cassette (3) is moved sideways (2b) toward one (6 or 7) or both sides (6 and 7) of the reservoir (2a) during steps c) and/or d).

18. Method according to any one of claims 15 to 17, wherein the flat substrates (4) are transported inside the cassette (3) parallel to the sides of the reservoir (2) in direction(s) 2a.

5 19. Method according to any one of claims 15 to 18, wherein the cassette (3) is vibrated, bent and/or moved in one or more directions to assist singulation of adhered substrates.

20. Method according to any one of claims 15 to 19, wherein the fluid in the reservoir 10 (2) and/or from the nozzles (5) is aqueous, preferably deionized water.

21. Method according to any one of claims 15 to 20, wherein the fluid in the reservoir (2) and/or the fluid the nozzles (5) comprises additives, preferably acid(s), base(s), defoamer(s) and/or surfactant(s).

15

22. Method according to any one of claims 15 to 21 , wherein two or more fluids having different compositions are introduced into the reservoir (2).

23. Method according to any one of claims 15 to 22, wherein the flat substrates (4) are 20 silicon wafers, preferably multi-wire saw-cut silicone wafers.

24. Method according to any one of claims 15 to 23, wherein said ultrasound waves have wavelengths in the fluid in the range of 10 mm to 80 mm and frequencies in

•^"" the range of 10 to 200 kHz, preferably 20 to 132 kHz.

25

25. Method according to any one of claims 15 to 24, wherein the one or more ultrasound generating device(s) (8) are at least temporarily moved to the nearest substrate sides at a distance of at least from 1 to 20 mm, preferably 1 to 10, more preferably 1 to 5, most preferably 1 to 3 mm.

30

26. Method according to any one of claims 15 to 25, wherein the temperature of the fluid in the reservoir (2) and/or from the nozzles (5) is in the range of 5 to 100 ⁰C, preferably 10 to 70 ⁰C, more preferably 20 to 40 ⁰C, most preferably ambient temperature of about 22 ⁰C.

35

27. Use of a device according to any one of claims 1 to 14 in a method according to any one of claims 15 to 26.