GB2465591A

GB2465591A - Separating cut semiconductor wafers from a wafer stack

Info

Publication number: GB2465591A
Application number: GB0821357A
Authority: GB
Inventors: Hilel Richman; Oded Hamburger; Ariel Hildeshem; Eyal Shpilberg
Original assignee: CoreFlow Ltd
Current assignee: CoreFlow Ltd
Priority date: 2008-11-21
Filing date: 2008-11-21
Publication date: 2010-05-26
Anticipated expiration: 2028-11-21
Also published as: GB0821357D0; GB2465591B

Abstract

An apparatus for separating a front wafer 40 from a stack of wafers includes a chuck 10 for gripping the front wafer, coupled to a mechanical arm 21 and rotatable about at least one axis with respect to the arm, so as to allow the chuck 10 to align substantially parallel to the front wafer 40, provided with a fixing mechanism for fixing the chuck 10 in a desired orientation. Further included is a drive 23 for moving the arm in at least in two directions, one direction to bring the chuck 10 to the front wafer 40 and in another direction substantially parallel to the fixed orientation of the chuck 10 to separate the wafer from the stack of wafers 42. A stopper mechanism 46 is provided for preventing other wafers from separating from the stack while the front wafer is being separated.

Description

METHOD AND DEVICE FOR SEPARATING SLICED WAFERS

FIELD OF THE INVENTION

[0001] The present invention relates to sliced wafers. More particularly, the present invention relates to a method and device for separating sliced wafers.

BACKGROUND OF THE INVENTION

[00021 In preparing wafers for the semiconductor industry, for example for manufacturing into solar cells, an ingot of semiconductor material, such as silicon, is sliced into a stack of individual wafers. In order to maximize the number of wafers produced from a single ingot, manufacturers are motivated to reduce the thickness of the wafers. For example, a typical-wafer -may be in the form of a disk or square with diameter or side dimension of several centimeters, and thickness in the range 100 tm to 300 jtm. Such a wafer is fragile, and a bending stress applied to the wafer may cause the wafer to break.

[00031 The wafer is typically further processed to produce a usable product. For example, the wafer may be cut to a square shape and manufactured into a solar cell (typically with length of side about 160 mm). In order to process a sliced silicon wafer into a usable product, the wafer must be separated from the stack. Various forces acting between wafers in the stack prevent easy separation of a wafer from the stack. In addition, the bonding force between the wafers is increased by the slurry found between and on the edges of the wafers. The slurry, consisting of a fluid such as polyethylene glycol 300 (PEG 300) mixed with abrasive material that is used in sawing the ingot into thin wafer slices, increases the bonding force between the wafers. In order not to stress, and possibly break, the wafer, the force that is applied to separate a wafer from a stack must be applied in a lateral shear direction, perpendicular to the edge of the wafer. For this reason, the separation process has been difficult to automate. Therefore, wafers are often separated manually from the stack. In this relatively slow and low-yield process, a human worker manually separates a wafer and transfers it to the next process.

[0004] Some described devices for automatic separation of wafers, for example that described by Gibbet in US6558 109, employ a chuck fixture hold the wafer and to apply the required lateral force. In these devices, the orientation of the chuck is fixed. Since, in practice, the orientation of a wafer in a stack of wafers is likely to have a random component, and its face will not, in general, be exactly parallel to the face of the chuck. Therefore, mechanical force is applied to the wafer in order to force the orientation of the wafer to conform to the orientation of the chuck. Such applied mechanical forces increase the risk of breakage of the removed wafer.

SUMMARY OF THE INVENTION

[0005] The present invention seeks to provide a means for removing a single wafer from a stack of wafers, withoUt applying bending stress to any of the wafers.

[00061 There is thus provided, in accordance with some embodiments of the present invention, an apparatus for separating a front wafer from a stack of wafers. The apparatus comprises: a chuck for gripping the front wafer, coupled to a mechanical arm and rotatable about at least one axis with respect to the arm, so as to allow the chuck to align substantially parallel to the front wafer, provided with a fixing mechanism for fixing the chuck in a desired orientation. The apparatus may further comprise a drive for moving the arm in at least in two directions, one direction to bring the chuck to the front wafer and in another direction substantially parallel to the fixed orientation of the chuck to separate the wafer from the stack of. wafers. The apparatus may further comprise a stopper mechanism for preventing other wafers from separating from the stack while the front wafer is being separated.

[00071 Furthermore, in accordance with some embodiments of the present invention, the chuck comprises a vacuum chuck.

[00081 Furthermore, in accordance with some embodiments of the present invention, the stopper mechanism comprises a stopper bar which is adapted to move into position adjacent to the stack of wafers, a distal end of the stopper bar stopped at a desired position relative to the chuck when fixed in the desired orientation.

[00091 Furthermore, in accordance with some embodiments of the present invention, the chuck comprises one or more spacers with which the stopper bar is to align.

[0010] Furthermore, in accordance with some embodiments of the present invention, the drive comprises a motorized drive.

10011] Furthermore, in accordance with some embodiments of the present invention, the apparatus is provided with a sensor for sensing the orientation of the chuck when substantially parallel to the front wafer.

[0012] Furthermore, in accordance with some embodiments of the present invention, the sensor comprises an encoder.

[0013] Furthermore, in accordance with some embodiments of the present invention, there is provided a method for separating a front wafer from a stack of wafers. The method comprises providing a chuck for gripping the front wafer, coupled to a mechanical arm and rotatable about at least one axis with respect to the arm, so as to allow the chuck to align substantially parallel to the front wafer, provided with a fixing mechanism for fixing the chuck in a desired orientation. The method further comprises providing a drive for moving the ann in at least in two directions, one direction to bring the chuck to the front wafer and in another direction substantially parallel to the fixed orientation of the chuck to separate the wafer from the stack of wafers. The method further comprises: moving the chuck towards the front wafer, aligning the chuck substantially parallel to the front wafer, gripping the front wafer, fixing the orientation of the chuck, and separating the front wafer from the stack of wafers by moving the chuck substantially parallel to the front wafer.

[0014] Furthermore, in accordance with some embodiments of the present invention, the step of aligning the chuck substantially parallel to the front wafer comprises contact between the chuck and the front wafer.

[00151 Furthermore, in accordance with some embodiments of the present invention, the step of aligning the chuck substantially parallel to the front wafer comprises no contact between the chuck and the front wafer.

[0016] Furthermore, in accordance with some embodiments of the present invention, the method comprises preventing other wafers from separating from the stack while the front wafer is being separated using a stopper mechanism.

[0017] Furthermore, in accordance with some embodiments of the present invention, the step of preventing other wafers from separating from the stack comprises providing a stopper bar which is adapted to move into position adjacent to the stack of wafers, a distal end of the stopper bar stopped at a desired position relative to the chuck when fixed in the desired orientation.

[0018] Furthermore, in accordance with some embodiments of the present invention, the method comprises providing the chuck with one or more spacers with which the stopper bar is to align.

10019] Furthermore, in accordance with some embodiments of the present invention, the step of providing a drive comprises providing a motorized drive.

[0020] Furthermore, in accordance with some embodiments of the present invention, the method comprises providing a sensor for sensing the orientation of the chuck when substantially parallel to the front wafer.

[0021] Furthermore, in accordance with some embodiments of the present invention, the sensor comprises an encoder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order more fully to appreciate the teachings herein and appreciate their practical applications, the following Figures are provided and referenced hereafter. It should be noted that the following description and Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals.

[0023] Fig. 1 shows a system for wafer separation in accordance with embodiments of the present invention.

100241 Fig. 2 shows a chuck for wafer separation in accordance with embodiments of the present invention.

[0025] Fig. 3 shows the exterior of a chuck in accordance with embodiments of the present invention.

[00261 Fig. 4 is a cutaway view showing the interior of the chuck in Fig. 3, viewed from the opposite side.

[00271 Fig. 5 is an enlarged view of a portion of the chuck shown in Fig. 4.

100281 Fig. 6 is a schematic illustration of a chuck for separating a wafer from a stack of wafers, in accordance with embodiments of the present invention.

[00291 Fig. 7 is a flowchart of a method for separation of a wafer from a stack of.

wafers, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0030] An apparatus and method are described for automatically removing an object, such as a wafer, from a surface to which it adheres, such as stack of similar objects.

The object is removed in such a manner as to minimize bending stress on the object. In this description, the term "wafer" refers to a stackable thin object of any shape fabricated out of any material. In applying embodiments of the present invention to the semiconductor industry, the stack may typically include wafers of semiconductor material, such as silicon, that were diced, cut, sliced, or sawed from a single ingot.

Typically, after slicing, a wafer may be disk or square shaped, with typical side dimension hundreds to thousands times greater than its thickness. Adhesive forces generally resist relative motion between wafers in the stack, thus resisting the removal of a single wafer from the end of the stack. The presence of viscous fluids, such as slurry, between, and around the edges of, the wafers in the stack may further increase the adhesive forces. . [003 1J In accordance with embodiments of the present invention, a stack of wafers may be held in a carrier. The carrier may be immersed in a fluid bath. The fluid in the bath may be of such a composition as to assure a general low viscosity as compared with the slurry. In addition, the bath may include nozzles that cause the fluid to flow within the bath in order to perform coarse cleaning of the wafers in the stack. The fluid in the bath may be pumped through a filter in order to maintain the cleanliness of the fluid.

[0032] A chuck is provided whose motion is controlled by means of a driver and control system. The chuck is inserted into the bath and moved toward the wafer stack. The chuck is capable of gripping a wafer that is at the end of the stack by mechanical or other means. For example, in the case that the chuck is a vacuum chuck, the face of the chuck that comes in contact with the wafer may be provided with a pattern of openings.

Fluid pumped out through though the openings creates suction that grips the wafer. Alternatively, the chuck may grip the wafer without contacting the wafer, for example, by means of a system of high flow resistance nozzles, such as the self adapted segmented orifice (SASO) system described by Levin et al. in US patent 6523572. The chuck may also be capable of blowing fluid outward through the openings. Blowing fluid outward may create a pressure field that may be useful in aligning the chuck.

[0033] The chuck is mounted on a mechanical arm in such a manner that when the chuck comes in contact with, or otherwise begins to apply a force to, the wafer that it is to grip, the orientation of the chuck is adjusted to match that of the wafer. For example, the chuck may be mounted on perpendicular axes about which it is free to rotate.

Contact with, or applying a force to, the wafer to be gripped causes a torque to be applied to the chuck, causing the chuck to orient itself parallel to the face of the wafer.

[0034] The chuck control determines when the chuck is oriented correctly. For example, sensors may be provided that detect when there is good contact between the chuck and the wafer. Good contact indicates that the face of the chuck is flush with that of the wafer. For example, a sensor may be provided that measures the level of a vacuum that grips the wafer by means of suction. Attainment of a predetermined level of vacuum may then indicate that the wafer is blocking suction openings on the chuck and is therefore being gripped by the suction. Alternatively, the face of the chuck may be provided with pressure-sensitive sensors that detect whether the wafer is being held with sufficient force to indicate good contact. Alternatively, a sensor may be provided that measures the torque applied to a rotation axis about which the chuck is free to rotate. Torque above a predetermined level may indicate that the chuck face is not yet parallel to the wafer face, and is still being rotated about the axis. Upon attaining its final orientation parallel to the wafer, the torque applied to the axis is reduced to a value close to zero. Alternatively, the mechanical arm on which the chuck is mounted, or a drive system adapted to moving the mechanical arm, may be provided with a sensor that senses the force required to move the arm.

[0035] Once it is determined that the chuck grips the wafer with the chuck face oriented parallel to the wafer face, the orientation of the chuck is fixed. For example, a braking, gripping, or other orientation-locking mechanism may be applied to rotation axes of the chuck to prevent further rotation. The braking mechanism is applied radially to the axis so as not to apply any torque to the axis that may possibly alter the orientation of the chuck. Alternatively, any other fixing means known in the art that are appropriate to the mounting means of chuck may be applied to fix the orientation of the chuck. For example, a braking element may be applied radially to a ball of a ball-and-socket mount. As another example, a flexible mounting element may be stiffened in such a manner as to not alter the shape of the element.

[00361 The chuck is provided with sensors that are capable of determining the orientation of the chuck. For example, an axis about which the chuck is free to rotate may be provided with an angle encoder that indicates the orientation angle of the chuck about that axis. A processor associated with the chuck control receives the sensor information regarding the orientation of the chuck. The processor then calculates the direction in which the chuck may move such that the motion of the chuck remains parallel to the face of the chuck.

[00371 The chuck moves in the calculated direction. In this manner, the chuck moves the gripped wafer in a lateral direction parallel to the plane of the wafer, minimizing the bending stress applied to the wafer. During the motion of the chuck, one or more restraining fingers or stops may apply a counteracting restraining force on one or more wafers of the stack that are adjacent to the gripped wafer. The restraining stops block motion of the adjacent wafers, ensuring that the chuck moves only the gripped wafer.

10038] At the time that the chuck is moving the gripped wafer, one or more means known in the art may be applied to reduce the force that holds the gripped wafer to the adjacent wafer in the stack. Such means may include directing a high-pressure jet of water or air, or a beam of ultrasonic waves, on the area between the gripped wafer and the adjacent wafer of the stack.

[00391 The chuck continues to move the gripped wafer until the wafer is clear of the stack. The chuck then moves the wafer, perhaps lifting it out of the bath, to the location at which the wafer is to be released. When the wafer arrives at the location at which it is to be released, the chuck releases the wafer. For example, if the chuck grips the wafer by means of suction, operation of the vacuum generation system is interrupted so that suction is not longer applied to the wafer.

[0040] We now describe embodiments of the present invention with reference to the accompanying Figures. Fig. 1 shows a system for wafer separation in accordance with embodiments of the present invention. Fig. 2 shows a chuck for wafer separation in accordance with embodiments of the present invention. Wafer stack 42 of sliced wafers is held by carrier 52. Wafer stack 42 and carrier 52 may be immersed in fluid bath 44.

Carrier 52 may be moveable, capable of transporting wafer stack 42 within a wafer processing facility. Thus, a single carrier may be used to transport wafer stack within a processing facility and to hold the wafer stack during several different processes. Using the single carrier may reduce the risk of breaking a fragile wafer when moving the wafer stack from process to process, for example, from a pre-separation cleaning station to a wafer separation station.

[004 1] Chuck 10 is mounted on arm 21 by means of brackets 13. Arm 21 is moved by chuck drive assembly 23. Controller 54 controls the chuck drive assembly 23, as well as any gripping and rotation fixing mechanisms associated with chuck 10. Chuck 10 is capable of gripping and moving a wafer from wafer stack 42, such as gripped wafer 40.

Restraining stopper 46 is provided for restraining the motion of wafer 41 and other wafers of wafer stack 42 that may be adjacent to wafer 41. Restraining stopper 46 may be in the form of a bar, beam, block, or any other shape that is suitable for restraining motion of an appropriate section of stack 42. Spacers 32 on chuck 10 ensure that restraining stopper 46 is positioned at a precise distance from chuck 10 so as not to impede the motion of gripped wafer 40 while prevention motion of wafer 41.

[0042] Fig. 3 shows a chuck in accordance with embodiments of the present invention.

Fig. 4 is a cutaway view showing the interior of the chuck in Fig. 3, viewed from the opposite side. Surface 11 of chuck 10 is adapted to have a flat object, for example a thin silicon wafer, held against it. For example, chuck 10 may be a vacuum chuck, adapted to gripping an object by applying suction to the object surface. Openings 12 on surface 11 connect to an internal manifold 16. Internal manifold 16 connects to inlet hose 14. Inlet hose 14 connects to vacuum generating device 58 (Fig. 1) via tube 56 (Fig. 1). Tube 56 may partially pass within or adjacent to arm 21. Vacuum generating device 58 may include a venture vacuum generator, or any other suitable device capable of producing a vacuum or suction. Thus, by means of inlet hose 14 and internal manifold 16, suction may be applied through openings 12. The applied suction may hold an object, such as a wafer, fast against surface 11. Vacuum generating device 58 may be reversible, enabling either an outward flow of fluid through openings 12, or an inward suction of fluid through openings 12.

[0043] The orientation of chuck 10 is free to rotate in response to an applied torque.

Such a torque may be applied, for example, when part of chuck 10 contacts an object toward which chuck 10 is being moved. An example of such an object is a wafer that is located at the front end of a stack of wafers that were sliced from a silicon ingot.

[00441 In embodiments of the present invention, the variation in orientation of chuck 10 in response to an applied torque is achieved by providing two perpendicular rotation axes about which chuck 10 is free to rotate. Alternatively, chuck 10 may be mounted by means of a ball-and-socket mechanism, on a flexible rod, or by any other mounting means that allow at least limited free variation in orientation.

[00451 In embodiments of the present invention, chuck 10 is free to rotate about a vertical or rotation axis 20, and about a horizontal or elevation axis 22. When chuck 10 is brought near to a flat object such as the front silicon wafer on a stack, the flat object applies a torque to surface 11. The origin of the torque may be a mechanical contact with the front wafer. Alternatively, the origin of the torque may be a pressure gradient that is formed across surface 11. The gradient is due to the dependence on the width of the gap between the front wafer and surface 11 of the pressure caused by an outward flow of fluid through openings 12. Thus, if surface 11 is not parallel to the surface of the front wafer, the fluid pressure at some points on the surface will be greater than at others, resulting in an applied torque. The applied torque causes chuck 10 to rotate about vertical axis 20 and horizontal axis 22. The rotation tends to align surface 11 parallel to the surface of the flat object. When surface 11 is parallel to the surface of the flat object, the net torque applied by the surface of the flat object is reduced to close to zero, and chuck 10 no longer rotates. At this point, surface 11 is parallel to, the surface of the flat object. Chuck 10 may be provided with one or more sensors (not shown) that measure the torque applied to vertical axis 20 or to horizontal axis 22.

[00461 In some embodiments of the present invention, fluid may be caused to flow outward through openings 12 as surface 11 approaches the front wafer. When surface 11 is close to the front wafer, perhaps to within a few millimeters, the pressure in the gap between surface and the front wafer begins to increase. The gradient in pressure described above causes surface 11 to align parallel to the surface of the front wafer. As surface 11 continues to approach the surface of the front wafer, a sharp increase in fluid pressure may occur that resists continued motion of surface 11 toward the front wafer.

Mechanical arm 21 (Fig. 1), chuck drive assembly 23 (Fig. 1), vacuum generating device 58 (Fig. 1), or any other suitable part of the system may be provided with a sensor that senses the increase in pressure or the increased resistance to motion. At this point, the flow of fluid through openings 12 may be reversed, and suction applied to openings 12.

100471 Alternatively, chuck 10 may be provided with a sensor to detect the level of fluid pressure, or vacuum, within internal manifold 16. As long as surface 11 is not in maximum contact with the surface of the front wafer, suction is not applied maximally to the object by means of openings 12. Rather, the suction sucks fluid at least partially into at least part of openings 12. After the torque applied by contact with the front wafer brings surface 11 into maximum contact with the object surface, openings 12 are maximally blocked by the object surface. At this point, a vacuum is formed within internal manifold 16 and suction causes chuck 10 to grip the flat object. A pressure sensor may detect the formation of the vacuum.

[0048] In order to minimize any torque applied to chuck 10 other than the flat object to be gripped, inlet hose 14 may connect to internal manifold 16 via a hollow passageway 18 that is open to manifold 16 and is incorporated into a rotation axis such as horizontal axis 22.

[0049] Movement of chuck 10 toward a flat object to be gripped applies torque to chuck and causes it to rotate until surface 11 completely contacts the surface of the flat object. At this point, suction applied via openings 12 causes chuck 10 to grip the flat object, such as a wafer. Once a state is attained where chuck 10 grips the flat object, further motion of chuck 10 toward the flat object is no longer desirable. Furthermore, in this state, rotation of chuck 10 about vertical axis 20 and horizontal axis 22 is no longer desirable. The attainment of this state may be determined, for example, by means of a sensor that detects the reduction in torque applied to chuck 10, by means of a sensor that detects the increase in vacuum level that results the object blocking openings 12, by means of a mechanical, acoustic, electromagnetic, optical, or other sensor that detects full contact between surface 11 and the flat object, by means of a sensor that measures the force holding the object to surface 11, by means of a sensor that measures flow through openings 12, internal manifold 16, inlet hose 14, or through another portion of the suction-creating means, or by any other means capable of determining that chuck 10 grips an object.

100501 When it has been determined that chuck 10 grips an object such as a wafer, the orientation of chuck 10 is locked or fixed. Fig. 5 is an enlarged view of a portion of the chuck shown in Fig. 4. According to embodiments of the present invention, an actuating force, such as compressed air forced into chamber 30, exerts pressure on pistons 26, pushing them outward. The outward force on pistons 26 pushes braking elements 24 radially against vertical axis 20 and horizontal axis 22, preventing the rotation of the axes. Alternatively, braking elements 24 may be actuated by mechanical, electromagnetic, or hydraulic means, or by any other means suitable for causing a brake to press against an axis. Alternatively, braking elements 24 may be replaced with clamps or any other mechanical, electromagnetic, or other means known in the art for immobilizing chuck 10 without applying a torque that may change its orientation.

[00511 The orientation of chuck 10 at the time that it is immobilized is measured by one or more sensors. For example, the sensors may include an encoder 17 (Fig. 2) that senses rotation of horizontal axis 22. Alternatively, a rotation transmission mechanism may be connected to the axis, the transmission mechanism transmitting the rotation motion to an encoder at a different location. Alternatively, orientation may be determined by a level sensor, by any other type of sensor known in the art that employs mechanical, optical, electromagnetic, or other means to determine orientation.

100521 The orientation data is input to a processor associated with chuck drive 23 (Fig. 1). The processor calculates the direction in which the chuck drive must move chuck 10 such that the direction of chuck motion remains parallel to surface 11 (Fig. 3). Motion parallel to surface 11 moves a gripped flat object gripped by chuck 10 in a direction tangential to the flat surface of the gripped object, minimizing bending stress on the object. Until the gripped object is free from any forces that may impede the motion of the object (such as a stack of wafers that exerts friction, adhesive, or viscous forces on the gripped object), motion may limited to a direction along, or parallel to, the vertical axis of the chuck mount (axis 20 in Fig. 4). Limiting motion to a direction parallel to the vertical axis may obviate the need for an orientation sensor about the vertical axis.

[0053] Fig. 6 is a schematic illustration of a chuck removing a wafer from a stack of wafers, in accordance with embodiments of the present invention. Fig. 7 is a flowchart of a method for separation of a wafer from a stack of wafers, in accordance with embodiments of the present invention It should be understood that the organization into discrete steps, as well as the order of the steps, indicated in the flowchart is for illustrative purposes only. The organization into discrete steps, as well as the order of execution of some of the steps, may be altered without affecting the results of the method. All such variations should be considered to be within the scope of the present invention: Chuck 10 is moved toward the front end of wafer stack 42 (step 60). During this motion, chuck 10 is free to rotate in response to a torque exerted on chuck 10 by wafer stack 42. Motion continues until it is determined that chuck 10 is parallel to the front surface of wafer stack 42, or that chuck 10 is at a desired distance from the front surface (step 62). At this point, motion of chuck 10 is stopped (step 64). Chuck 10 grips front wafer 40 of wafer stack 42 (step 66). In some embodiments of the present invention, chuck 10 may be gripping front wafer 40 prior to stopping motion of chuck 10. The orientation of chuck 10 is fixed so that,rotation of chuck 10 is no longer enabled (step 68). The orientation of chuck 10 is sensed (step 70).

[0054] Stopper 46 is positioned above wafer stack 42 (step 72). The stopper 46 is maintained at the desired distance from chuck 10 with the aid of spacers 32. Chuck 10 moves gripped wafer 40 in the direction indicated by the arrow, parallel to the sensed orientation of chuck 110 and the surface of gripped wafer 40 (step 74). Motion of gripped wafer 40 in the direction of the arrow slides gripped wafer 40 across the surface of adjacent wafer 41 of wafer stack 42. Friction, viscous, or other forces may resist relative motion between gripped wafer 40 and adjacent wafer 41. The resisting force may tend to drag adjacent wafer 41, and perhaps other wafers of wafer stack 42, in the direction of motion of gripped wafer 40. Restraining stopper 46 prevents this dragging.

Spacers 32 ensure that restraining stopper 46 does not impede the motion of gripped wafer 40.

[0055] Means may be utilized to reduce any friction, viscous, or other forces that resist relative motion between gripped wafer 40 and adjacent wafer 41. For example, high pressure jet 48 of low viscosity fluid, such as water, may be directed at wafer stack 42 in order to assist in reducing the viscosity of the fluid in the gaps between adjacent wafers. Beam 50 of ultrasonic waves may be directed at wafer stack 42 in order to reduce the adhesion force between gripped wafer 40 and adjacent wafer 41.

100561 Chuck 10 continues to move gripped wafer 40 in the direction of the arrow until gripped wafer 40 is free of stack 42. At this point, the chuck drive may move chuck 10 to the location, either inside or outside of bath 44, to where further processing is to be performed on wafer 40. When gripped wafer 40 is brought to the desired location, chuck 10 releases wafer 40. For example, the vacuum generating device that applies the suction that holds wafer 40 to chuck 10 may be turned off.

[00571 The orientation of chuck 10 may remain fixed until it is again moved near to the next wafer of wafer stack 42 to be gripped and moved. This ensures that the initial orientation of chuck 10 is approximately parallel to the surface of the next wafer of the stack. Alternatively, means may be provided to actively orient chuck 10 in the last sensed orientation prior to moving chuck 10 near the next wafer to be gripped.

100581 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.

[0059] It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the present invention.

Claims

CLAIMS1. An apparatus for separating a front wafer from a stack of wafers, the apparatus comprising: a chuck for gripping the front wafer, coupled to a mechanical arm and rotatable about at least one axis with respect to the arm, so as to allow the chuck to align substantially parallel to the front wafer, provided with a fixing mechanism for fixing the chuck in a desired orientation; a drive for moving the arm in at least in two directions, one direction to bring the chuck to the front wafer and in another direction substantially parallel to the fixed orientation of the chuck to separate the wafer from the stack of wafers; a stopper mechanism for preventing other wafers from separating from the stack while the front wafer is being separated.
2. The apparatus of claim 1, wherein the chuck comprises a vacuum chuck.
3. The apparatus of claim 1, wherein the stopper mechanism comprises a stopper bar which is adapted to move into position adjacent to the stack of wafers, a distal end of the stopper bar stopped at a desired position relative to the chuck when fixed in the desired orientation.
4. The apparatus of claim 3, wherein the chuck comprises one or more spacers with which the stopper bar is to align.
5. The apparatus of claim I, wherein the drive comprises a motorized drive.
6. The apparatus of claim 1, provided with a sensor for sensing the orientation of the chuck when substantially parallel to the front wafer.
7. The apparatus of claim 6, wherein the sensor comprises an encoder.
8. A method for separating a front wafer from a stack of wafers, the method comprising: providing a chuck for gripping the front wafer, coupled to a mechanical arm and rotatable about at least one axis with respect to the arm, so as to allow the chuck to align substantially parallel to the front wafer, provided with a fixing mechanism for fixing the chuck in a desired orientation, a drive for moving the aim in at least in two directions, one direction to bring the chuck to the front wafer and in another direction substantially parallel to the fixed orientation of the chuck to separate the wafer from the stack of wafers; moving the chuck towards the front wafer, aligning the chuck substantially parallel to the front wafer, gripping the front wafer and fixing the orientation of the chuck; separating the front wafer from the stack of wafers by moving the chuck substantially parallel to the front wafer.
9. The method of claim 8, wherein the step of aligning the chuck substantially parallel to the front wafer comprises contact between the chuck and the front wafer.
10. The method of claim 8, wherein the step of aligning the chuck substantially parallel to the front wafer comprises no contact between the chuck and the front wafer.
11. The method of claim 8, comprising preventing other wafers from separating from the stack while the front wafer is being separated using a stopper mechanism.
12. The method of claim 11, wherein the step of preventing other wafers from separating from the stack comprises providing a stopper bar which is adapted to move into position adjacent to the stack of wafers, a distal end of the stopper bar stopped at a desired position relative to the chuck when fixed in the desired orientation;
13. The method of claim 12, comprising providing the chuck with one or more spacers with which the stopper bar is to align.
14. The method of claim 8, wherein the step of providing a drive comprises providing a motorized drive.
15. The method of claim 8, comprising providing a sensor for sensing the orientation of the chuck when substantially parallel to the front wafer.
16. The method of claim 15, wherein the sensor comprises an encoder.