Field of the Invention The present invention relates to a method and apparatus for use during the processing of wafers. In particular, but not exclusively, the present invention relates to a method and apparatus for facilitating the removal of individual wafers from an array comprising a plurality of wafers. Background to the Invention

Silicon wafers for use in, for example, the manufacture of semiconductor devices such as solar cells are typically formed by sawing a block of silicon so as to produce a number of individual wafers. The sawing process is conventionally a multi-pass wire sawing method. The block of silicon is bonded to a glass plate using an adhesive and the sawing process is performed with the silicon block fixedly secured to the glass plate. The saw cuts completely through the silicon block and the resulting wafers each remain attached to the glass plate by the adhesive. In typical examples the sawing process will create several hundred thin silicon wafers (with a width between 100 and 300 urn), each separated by a distance of approximately 100 to 200 urn.

Once the silicon block has been cut to form the separate silicon wafers, the silicon wafers must be cleaned and removed from the substrate. The silicon wafers are de-glued, for example using a hot dilute organic acid such as lactic acid, to separate the wafers from the glass plate. Individual silicon wafers are subsequently isolated (referred to as "singulation") for use in subsequent manufacturing steps.

At various points during the procedure outlined above, liquid is introduced between the silicon wafers. Indeed, the silicon block is typically sawn in a wet environment and the subsequent cleaning and de-gluing processes are associated with liquids. As a result, the silicon wafers are wet, which means that they tend to be drawn together into clumps due to the effects of capillary action and surface tension. This clumping of the wafers can cause difficulties at various stages of the process. For example, it may prevent cleaning liquids passing between the wafers as required to effectively clean the wafers.

Another difficulty occurs after the silicon wafers have been de-glued from the glass plate. Once de-glued, any broken wafers are manually removed and the remaining wafers cleaned by hand to remove any remnants of the adhesive. The wafers are then manually stacked directly on top of each other to form a uniform stack. The wafers in the stack are supported in a cassette with adjacent wafers being in contact with each other over their entire large surfaces. The wafers can be removed from the stack using an automated process. However, the capillary action and surface tension between the surfaces of adjacent wafers may render it difficult to separate the wafers. This may result in an excessively large force having to be applied to separate the wafers and this can result in the breakage of some of the wafers as they are removed from the stack. The production process may have to be halted to remove broken wafers and this can cause delays and increase operational costs.

The present invention, at least in preferred embodiments, attempts to overcome or ameliorate at least some of the problems associated with the prior art techniques and apparatus.

Summary of the Invention

Viewed from a first aspect, the present invention relates to a method of handling a plurality of wafers, the method comprising the steps of:

providing a plurality of wafers, each wafer being bonded to a substrate along a first edge;

supporting the wafers at their edges in a support frame so as to maintain a space between adjacent wafers; and

separating said plurality of wafers from the substrate while they are supported in said support frame.

The wafers are held within the support frame in an array with the major surfaces of adjacent wafers facing each other. At least in preferred embodiments, the present invention enables a plurality of wafers to be supported by a support frame such that a space is maintained between adjacent wafers. Thus, the wafers are supported in a spaced array within the support frame. Advantageously, this helps individual wafers to be extracted from the array. At least in preferred embodiments, the present invention can enable extraction of the wafers with lower loads being applied to the wafers than existing methods.

A space is preferably maintained between adjacent wafers at least at the edges of the wafers. In certain instances, the wafers may deflect over their length resulting in the surfaces of adjacent wafers contacting each other. However, even if the surfaces contact each other, by maintaining a space at the edges the wafers can more readily be separated. Preferably, however, the support frame maintains adjacent wafers apart from each other such that they do not contact each other.

At least in preferred embodiments, the process according to the present invention facilitates the selection and/or removal of individual wafers from the plurality of wafers. As contact between adjacent wafers is reduced or avoided, the clumping effect encountered with prior art processes can be reduced or avoided. Moreover, removing individual wafers is less likely to result in breakage of that or any other wafer as each wafer is separated from adjacent wafers.

In preferred embodiments of the present invention, the wafers are formed of silicon (that is, the wafers are silicon wafers). The silicon wafers can be used to form solar cells, for example. The present invention may also be applicable to other types of wafers, such as wafers used in the semiconductor industry.

The wafers are preferably supported in the support frame by applying a clamping force to opposing edges of the wafers. Preferably, the clamping force is applied by at least one pair of opposing clamp members. Thus, the wafers are clamped within the support assembly. The clamp members are preferably formed of a deformable material.

The wafers are typically cut from a block bonded to a substrate and the wafers remain bonded to the substrate along one edge after the cutting process has been completed. A saw is used to cut the wafers and this forms a space between adjacent wafers. The step of supporting the wafers at their edges in a support frame is performed while the wafers are bonded to the substrate to enable the spacing between the wafers to be maintained, at least at their edges. Thus, the wafers are supported in the support frame in an array.

Passing fluid, either a liquid or a gas, between the wafers can help prevent adjacent wafers being drawn together and/or help to separate wafers which have clumped together. Preferably, the method comprises the step of establishing a fluid flow over the wafers and/or between the wafers. Preferably, the wafers are oriented such that their major surfaces are arranged substantially parallel to the direction of the fluid flow. The clamping force is preferably applied when the wafers are positioned in said fluid flow. The wafers may thereby be clamped within the support frame when they are spaced apart from each other under the action of the fluid flow. If desired, the flow of fluid can be stopped after the wafers are supported in said support frame. The flow of fluid could be provided by supplying fluid from a jet.

The wafers are typically bonded to the substrate by an adhesive. The step of removing the wafers from the substrate preferably comprises de-gluing the wafers, for example by immersing the wafers and the substrate in a de-gluing solution.

Preferably, the method further comprises the step of cleaning the wafers. It is beneficial to clean the wafers so that they may be used in processes which are sensitive to their condition. Preferably, the step of cleaning the wafers occurs after the step of supporting the wafers in the support frame. As such, the wafers can be held in position during the step of cleaning the wafers, thereby assisting in the cleaning process. The step of cleaning the wafers can be performed before and/or after the wafers have been separated from the substrate.

Preferably, the wafers are supported such that movement of the wafers in a first direction in which they are spaced apart from each other is inhibited or substantially prevented. Moreover, the step of supporting the wafers enables the wafers to be extracted in a second direction in the plane of the wafers. This arrangement allows the wafers to be individually removed from the support frame in the second direction against relatively little resistance. Preferably, the wafers can be removed from the support frame in said second direction even when the clamping force is applied. At all times, however, the separation of the wafers can be maintained by the relatively high inhibition on movement of the wafers in the first direction.

The clamping force could be applied by a mechanical actuator, such as a pneumatic cylinder, displacing at least one clamp member against the wafers. The force applied will be distributed uniformly across each of the wafers within the support frame if the actuator applies a constant clamping force. Accordingly, the clamping force applied to each wafer will vary depending on the number of wafers within the support frame. Thus, if wafers are removed from the support frame, the clamping force applied to each of the remaining wafers increases. A controller could be provided to adjust the clamping force applied by a mechanical actuator in response to the number of wafers in the support frame.

In preferred embodiments, at least one inflatable clamp member is provided. A clamping force is preferably applied by inflating said inflatable clamp member(s). This provides an effective method for ensuring the wafers are adequately secured which, at least in preferred embodiments, is relatively easy to control. Using an inflatable clamp member can help to ensure that a constant clamping force is applied to each wafer supported in the support frame irrespective of the total number of wafers therein. This is particularly desirable to avoid damaging the wafers when they are clamped.

The method according to the present invention can include the further step of arranging the wafers in a vertical array (i.e. the longitudinal axis of the array is substantially vertical) whilst they are supported in said support frame. In other words, the wafers are supported within the support frame in a stack one above the other. The method may include the step of rotating the array about its transverse axis to arrange the wafers in a vertical array one above the other. The support frame preferably maintains a space between adjacent wafers even when the array is in a vertical orientation.

The method can include the step of extracting an end wafer from the array. When the array is arranged vertically, the uppermost wafer is typically extracted from the array. Preferably, the vertical array of wafers is at least partially submerged in a liquid. At least a portion of an upper surface of the uppermost wafer is preferably raised above the level of the liquid whilst the remaining wafers in the array are partially or completely submerged. Most preferably, a leading edge of the uppermost wafer (i.e. the edge of the wafer facing in the direction of travel of the wafer as it is extracted from the array) projects above the level of the liquid when the wafer is ready for extraction. In arrangements in which the wafers are inclined at an angle relative to the horizontal, the trailing edge of the uppermost wafer (i.e. the edge facing in the opposite direction to the direction of travel as the wafer is extracted) can be submerged below the level of the liquid when the wafer is ready for extraction. Preferably, only the uppermost wafer in the array is raised above the meniscus of the liquid in the bath. In practice, however, it may be necessary to raise the top two, three or four wafers above the level of the liquid. The array of wafers is preferably raised each time a wafer is removed to maintain the uppermost wafer in substantially the same position relative to the surface of the liquid.

Preferably a flow of fluid, either a gas or a liquid, is established over at least a portion of a major surface of a wafer to be extracted from the array. The fluid can be supplied from a nozzle or by establishing a flow within a container or tank in which the array is positioned. If the fluid is supplied from a nozzle, it can be directed substantially perpendicular to, or at an acute angle to the major surface of the wafer. The fluid is preferably directed onto the exposed surface of the wafer, for example the top surface of the uppermost wafer when the array is arranged vertically. The fluid flow can help to displace debris, such as a fragment of a broken wafer, from the array. The fluid flow preferably travels over the wafer in a direction opposite to the direction of travel of the wafer as it is extracted from the array (i.e. from the leading edge of the wafer towards the trailing edge of the wafer).

A spreader plate for reducing loading on the wafers can be provided. The method can include the step of displacing the array of wafers towards the spreader plate as each wafer is extracted. Preferably, the distance between the spreader plate and the uppermost wafer is maintained substantially constant.

Although the wafers could be extracted from the support frame in batches of two or more wafers, the method preferably includes the step of extracting the wafers from the support frame one at a time. The wafers could be extracted by engaging the wafer to be extracted with a suction or vacuum pad. Preferably, however, the wafer to be extracted is engaged by a friction pad. The friction pad preferably contacts a major surface of the wafer to be extracted. The friction pad and the wafer can then be displaced together to extract the wafer from the support frame. At least in preferred embodiments, sufficient force can be applied to remove the wafer from the support frame using a friction pad without applying a suction or vacuum force to engage the wafer.

The array of wafers can be oriented such that each wafer is maintained in a substantially horizontal position. Preferably, however, the array is arranged such that each wafer is inclined at an acute angle to the horizontal. The wafers are preferably inclined an angle of between 0° and 45°; or between 5° and 30° to the horizontal. Most preferably, the wafers are each inclined at an angle of approximately 15° to the horizontal.

According to a second aspect of the present invention, there is provided a support frame for use with the method of the first aspect. This support frame comprises a clamp and can be used to maintain a space between a plurality of wafers as they are removed from a substrate to which they are adhesively attached. The clamp can be used to provide a rack of separated wafers which may be individually accessed.

According to a third aspect of the present invention, there is provided a support frame for supporting a plurality of wafers and maintaining a space between adjacent wafers, the support frame comprising:

a clamping assembly having at least first and second clamps for engaging the opposing edges of a plurality of wafers to support the wafers and maintain a space between adjacent wafers;

wherein the first and second clamps are arranged to substantially prevent movement of the wafers in a first direction in which the wafers are spaced apart from each other. The first and second clamps are preferably configured to enable the wafers to be withdrawn from the support frame in a second direction in a plane of the respective wafers.

A mechanical actuator can be provided to actuate said first clamp and/or said second clamp. Preferably, however, the first clamp and/or the second clamp is/are inflatable. The clamp(s) can, for example, comprise an inflatable bladder.

A flow control device can be provided to isolate a first inflatable clamp from a second inflatable clamp. The first and second inflatable clamps can be isolated from each other when a puncture occurs in one of said clamps. The clamp members can be isolated from each other automatically. A pressure sensor may be provided to enable a control system to determine when a clamp member has been damaged and should be replaced.

In some preferred embodiments, the clamps can each comprise a removable outer element. As such, if the outer element becomes damaged or dirty it can be removed from the clamp member for repair, cleaning or replacement. Alternatively or additionally, the clamps can comprise a quantity of self-healing substance, for example a foam or liquid. The self-healing substance can act to repair or seal the clamp where holes arise, such as punctures. This is particularly useful in the case of inflatable clamp.

A spreader plate is preferably provided to control the loading applied to a wafer in the array. When a wafer is withdrawn, the loading applied on an adjacent wafer could increase, for example due to expansion of the clamp member. The spreader plate can control any such expansion and thereby maintain a substantially uniform loading on the wafers as they are handled by the support frame. The spreader plate is preferably movable relative to the first and second clamps such that, in use, the distance between the spreader plate and the uppermost wafer in the array is maintained substantially constant.

The clamps are preferably deformable so as to deform around the edges of the wafers. This deformation effectively causes a groove to form in the flexible clamps when a clamping force is applied to a wafer. The groove allows each wafer to move in its own plane (i.e. the second direction). Preferably, the clamps are formed of a resilient material, such as rubber or other elastomeric material. In other embodiments, the clamps may be rigid.

The first clamp and/or the second clamp may each comprise one or more ridges. These ridges can assist in maintaining the separation of the wafers while allowing movement of the wafers in their respective planes. Preferably the ridges extend in the direction in which the wafers are separated (the first direction).

The support frame preferably comprises means for engaging a wafer to be extracted from the support frame. The engagement means could comprise a suction or vacuum pad. Preferably, however, the engagement means comprises a friction pad for engaging a major surface of the wafer to be extracted from the support frame. In use, the friction pad is movable with the wafer to displace the wafer from the support frame, for example onto a carrier device such as an endless conveyor.

The support frame is preferably provided with at least one nozzle for directing a fluid, either a gas or a liquid, onto said wafers when they are supported in the support frame. The at least one nozzle is preferably arranged to direct a flow of fluid onto a major surface of a wafer to be extracted from the array. The nozzle is preferably arranged to direct the fluid substantially perpendicular to, or at an acute angle to the major surface of the wafer. The at least one nozzle can be mounted on the spreader plate, for example.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying figures, in which:

Figure 1A shows a side elevation of an array of silicon wafers coupled to a substrate;

Figure 1 B shows an end view of the array of silicon wafers of Figure 1A;

Figure 2A shows a side elevation of a clamping assembly according to a preferred embodiment of the present invention secured to an array of silicon wafers;

Figure 2B shows an end view of the clamping assembly according to the present invention;

Figure 3A shows an end view of the clamping assembly according to the present invention in a disengaged position;

Figure 3B shows an end view of the clamping assembly according to the present invention in an engaged position;

Figure 4 shows a plurality of silicon wafers which have adhered to each other;

Figure 5A shows the removal of the substrate from the array of silicon wafers supported in a clamping assembly according to the present invention;

Figure 5B shows an end view of the features of Figure 5A;

Figure 6A shows the removal of an individual silicon wafer from the silicon array supported in a clamping assembly according to the present invention;

Figure 6B shows a plan view of the removal of an individual silicon wafer from the supported in a clamping assembly according to the present invention;

Figures 7A and 7B show schematically a second embodiment of the present invention;

Figure 8 shows an enlarged view of the array of wafers supported in the extraction tank according to the second embodiment of the present invention; Figures 9A and 9B show schematically a modified version of the second embodiment of the present invention;

Figures 10A and 10B show schematically a third embodiment of the present invention;

Figure 1 1A and 11 B show schematically a modified version of the third embodiment of the present invention;

Figure 12 shows schematically a friction pad according to the present invention; and

Figure 13 shows schematically a pneumatic system for the clamping assembly.

Detailed Description

A preferred embodiment of a process and apparatus in accordance with the present invention will now be described. Figure 1A illustrates an array of silicon wafers 1 , for example to be used in the fabrication of solar cells. The wafers 1 are bonded to a substrate assembly 3 to facilitate handling during the production process described in more detail herein.

The wafers 1 are substantially rectangular in plan form and most preferably are substantially square. The corners of the wafers may be radiused or chamfered. The wafers 1 are substantially planar and each have a thickness of between 100 to 300 urn. The distance between adjacent wafers 1 at the point at which they are bonded to the substrate assembly 3 is approximately 100 to 200 urn in a longitudinal direction (i.e. perpendicular to a surface of the wafers). Typically between 500 and 2000 wafers are formed together within the array and the subsequent processing steps are performed on the entire array.

The substrate assembly 3 comprises a glass plate 3a mounted on a metal frame 3b. A silicon block is bonded to the glass plate 3a using a suitable adhesive 4. The silicon block is then cut using a conventional multi-pass sawing technique to form the individual wafers 1 making up the array. The saw cuts completely through the silicon block and typically cuts into the glass plate 3a to ensure that the resulting silicon wafers 1 are not joined together. After the cutting process has been completed, the wafers 1 each remain bonded along their top edge to the glass plate 3a by the adhesive. At each end of the array, a barrier layer 2 (or end cheek) of uncut silicon can optionally be provided to protect the array, as shown in Figure 1 B.

Figures 2A and 2B illustrate a clamping assembly according to a preferred embodiment of the present invention for supporting the array of silicon wafers. The clamping assembly is formed of a frame (not shown) carrying two pairs of opposing clamp members 5. Two of the clamp members 5 are disposed on one side of the silicon wafers 1 while the remaining two are disposed on an opposite side. By bringing an inner surface of the clamp members 5 into contact with opposing edges of the silicon wafers 1 , the silicon wafers 1 can be clamped in such a manner as to support them while maintaining the silicon wafers 1 spaced apart from each other along a longitudinal axis X of the array. Thus, the spaced array of wafers 1 is maintained when the wafers 1 are supported in the clamping assembly.

In the present embodiment, the clamp members 5 are elongate members formed from an extruded section of elastomeric material. Silicone rubber has been found to be particularly well suited for forming the clamp members 5. The clamp members 5 each have an engaging surface 6 for contacting an edge of the wafers 1 ; and an interior chamber 7. A pressurised air supply (not shown) is provided to supply pressurised air to the interior chambers 7 to inflate the respective clamp members 5 and thereby actuate the clamping assembly. As shown in Figure 3A, when the clamp members 5 are not inflated, the engaging surfaces 6 are spaced apart from the edges of the silicon wafers 1. When the clamp members 5 are inflated, the engaging surface 6 is displaced inwardly to contact the edges of the wafers 1 and thereby support each wafer in the array, as shown in Figure 3B. It is not essential that all the clamp members 5 in the clamp assembly are inflatable, for example a combination of inflatable and resilient members could be provided.

As the clamp members 5 expand and come into contact with the silicon wafers 1 , the engaging surface deforms around the edges of the silicon wafers 1. The resulting deformation limits movement of each wafer in a first direction perpendicular to the plane of the wafer. Consequently, once the clamping assembly is actuated, movement of the silicon wafers 1 in the direction in which they are separated is inhibited (i.e. in a plane extending perpendicular to the page in Figure 3B). However, movement in a second direction in the plane of the respective wafers 1 (i.e. within the plane of the page of Figure 3B) is less inhibited. The wafers 1 can thereby be withdrawn from the clamp members 5 by moving them in said second direction even when the clamping assembly is actuated.

A series of pre-formed longitudinal ridges are optionally provided on an inner surface of each of the clamp members 5, as shown in Figures 3A and 3B. The ridges serve to reduce the contact area of the clamp members 5 with the edges of the wafers 1. Moreover, the ridges may more readily be deformed and, therefore, the loading forces applied to the wafers 1 as they are clamped can be reduced. Thus, the ridges can assist in the removal of individual wafers 1 in said second direction, whilst ensuring that the wafers 1 remain adequately clamped to limit or prevent movement in said first direction.

To ensure the integrity of the clamp members 5, the inflatable tube may be formed of an external sheath and an internal bladder. If the external cover becomes damaged, dirty or in any other way defective, it is possible to remove it for cleaning, repair or replacement without removing the rest of the clamp member 5. In the present embodiment, the clamp members 5 are formed of a silicone extrusion having a hollow interior into which pressurised air is introduced to inflate the clamp members 5 and apply a clamping pressure.

It will be appreciated that a puncture in one of the clamp members 5, for example as a result of a silicon wafer 1 cutting it, could result in a reduction in the clamping force applied to support the wafers 1. To reduce the likelihood of this occurring, a self-healing fluid can optionally be provided in the clamp members 5 so as to automatically repair any punctures that form. It is anticipated that, at least in preferred embodiments, an adequate clamping force can still be applied to clamp the wafers 1 in position even if one or more of the clamp members 5 have been punctured.

One or more flow control devices can be provided to isolate each clamp member 5 from the other clamp members 5. One or more flow control devices could alternatively be provided to isolate different groups of the clamp members 5 from each other. These arrangements are advantageous since they can prevent all of the clamp members 5 deflating if one is punctured. The flow control device can, for example, comprise a self-sealing pneumatic connector, a flow restrictor or a non-return valve. In the present embodiment, the clamping assembly and the clamp members 5 are in the form of a cassette which can be transported. This cassette can be used to carry the array of silicon wafers 1 between steps of the production process. In other implementations, the clamping assembly may be retained in a fixed location with all steps that occur while the silicon wafers 1 are clamped occurring at that location.

As mentioned above, the array of silicon wafers 1 is formed from a block of silicon using a multi-pass wire sawing technique. A cutting liquid is typically employed during these processes and a slurry of liquids remains once the cutting has been completed. As such, each silicon wafer 1 is surrounded by liquid. The resulting surface tension and/or capillary action between the surfaces of adjacent wafers 1 can draw them together, resulting in a clumping effect whereby adjacent wafers 1 are in contact with each other, as illustrated in Figure 4. It can prove difficult to separate the wafers 1 when they are clumped together in this way.

In order to remove or reduce the clumping effect, a flow of liquid is introduced between the silicon wafers 1. This flow of liquid is sufficient to ensure that each wafer 1 is not in contact with any adjacent wafer 1. The wafers 1 are typically positioned in the liquid flow for between 1 and 60 seconds (though longer periods of time are envisaged) to ensure that the wafers 1 have separated from each other (in other words they have un-clumped). While this flow of liquid continues, the wafers 1 are then secured by the clamping assembly, as illustrated in Figures 2A, 2B, 3A and 3B. The clamping assembly acts to support the wafers 1 within the array whilst maintaining a space between adjacent wafers 1 , at least at their edges. The flow of liquid can optionally be stopped once the wafers 1 have been clamped into the clamping assembly as their position relative to each other (at least at their edges) is then substantially fixed by the clamping assembly.

A cleaning step should be undertaken to remove the cutting liquid and any other contaminants around the silicon wafers 1. This cleaning step may be undertaken before the silicon wafers 1 are clamped. However, it is preferable to undertake the cleaning step after the silicon wafers 1 have been clamped in the clamping assembly. This is because the clamping of the silicon wafers 1 in the clamping assembly ensures a separation between them, allowing cleaning fluids to access the entire surface area of each silicon wafer. The silicon wafers 1 are subsequently separated from the substrate assembly 3. In the preferred embodiment, this step is carried out by de-gluing the silicon wafers 1 from the substrate assembly 3. The process of de-gluing involves bathing the silicon wafers 1 in a de-gluing liquid, such as a hot dilute organic acid (preferably lactic acid at a temperature of 80°C to 90°C and having a concentration of less than 10%) or other suitable agent. The array of wafers 1 is introduced into a de-glue bath whilst it is supported in the clamping assembly. The glue coupling the silicon wafers 1 to the substrate assembly 3 is released in the de-glue bath enabling the substrate assembly 3 to be physically removed from the silicon wafers 1 , as shown in Figures 5A and 5B. The clamping assembly holds the silicon wafers 1 in the array with a space maintained between adjacent wafers 1 once the silicon wafers 1 have been released from the substrate assembly 3.

The wafers 1 can be removed individually from the clamping assembly. The step of removing individual wafers from the array is referred to herein as extraction. The wafers 1 are transferred to an extraction bath for extraction individually from the clamping assembly. The extraction bath typically comprises a dilute solution, such as water and a detergent, to help perform additional cleaning of the wafers. The wafers 1 could optionally be transferred from the de-glue bath to an intermediate cleaning bath containing a cleaning liquid.

As shown in Figure 6A, for extraction of the wafers 1 from the clamping assembly, the array is rotated about a transverse axis Y through 90° such that the longitudinal axis X of the array is arranged vertically with the wafers 1 positioned one above the other. It will be appreciated that the clamping assembly maintains a space between adjacent wafers 1 in the array even when it is arranged in this vertical orientation.

The rotation of the array of wafers 1 can be performed before/during/after the step of transferring the array to the extraction bath. If the array is transported with the wafers 1 in a vertical orientation (i.e. with the longitudinal axis X of the array arranged horizontally), the liquid between the wafers 1 tends to drain away and this can result in wafers clumping together. With this in mind, the array is preferably transported with the major surfaces of the wafers 1 held in a substantially horizontal orientation (i.e. with the longitudinal axis X of the array arranged substantially vertically) to reduce the drainage of liquid from between the wafers 1. A liquid can optionally be supplied over the wafers 1 in the array as they are transported to reduce at least some of the liquid which may drain from between the wafers 1 and thereby help prevent clumping of the wafers 1.

Submersing the array of wafers 1 in a liquid, for example contained in the extraction bath, allows any wafers 1 which may have clumped together during the transportation step to separate from each other. When the wafers 1 are supported in the clamping assembly, it is not necessary to establish a fluid flow between them to separate them.

The clamping assembly is positioned within the extraction bath with the longitudinal axis Y of the array arranged substantially vertically. As can be seen in Figure 6A, the majority of the wafers 1 are submerged in the cleaning liquid, while at least the top surface of the uppermost wafer 1 is presented above the surface 8 of the liquid. Preferably the top wafer 1 is displaced above the meniscus of the liquid while the other wafers 1 in the array remain submerged in the liquid in the extraction bath. This arrangement is desirable since it facilitates removal of the uppermost wafer 1 from the array while the remainder of the wafers remain supported within the clamping assembly.

As shown in the enlarged view in Figure 6A, the uppermost wafer 1 ' can be withdrawn laterally from the array by sliding it within its own plane in said second direction, illustrated by the arrow A in Figure 6A. It will be appreciated that the top wafer 1 ' can be withdrawn from the clamping assembly in this way when the clamping members are inflated. The uppermost wafer 1 ' is illustrated as being partially removed from the array in Figure 6A.

Figure 6B shows a plan view of the array of silicon wafers 1 and illustrates the second direction in which a silicon wafer 1 may be removed from the array. A stop or guide member could be provided to prevent the withdrawal of the wafer in the opposite direction.

A friction pad 9 is provided to engage the top surface of the uppermost wafer V and slide it out from between the clamp members 5. The friction pad 9 is smooth and flexible to accommodate variations in the vertical position of the uppermost wafer 1 ' within the clamping assembly. The friction pad 9 can be formed of leather, a polyurethane elastomer (such as Sylomer®) or other material having adequate friction toward the surface of the uppermost wafer 1'. Instead of or in addition to the friction pad 9, a suction or vacuum pad could be used to engage the uppermost wafer 1 '. A central portion of the friction pad 9 could, for example, form a vacuum pad. However, a relatively low force should be applied to reduce the risk of damaging the uppermost wafer 1 '. The suction pad can be formed from a foraminous material (such as Sylomer®). A wafer handling device 17 for engaging the uppermost wafer 1 ' is described below with reference to Figure 12.

The uppermost wafer 1 ' is typically displaced from the clamping assembly onto an endless conveyor or other transportation means for further processing.

To help reduce the loads applied to the wafers 1 , a spreader plate 10 is provided at the top of the clamping assembly. The spreader plate 10 moves relative to the clamping members 5 such that its position in relation to the uppermost wafer 1 ' in the array remains substantially constant as wafers 1 are extracted from the clamping assembly. The spreader plate 10 is typically displaced between 1 and 10 mm from the uppermost wafer 1 ', and is preferably approximately 5mm from the wafer 1'. The spreader plate 10 helps to reduce expansion of the clamping members 5 (due to inflation) in the region immediately above the remaining wafers 1. Without the spreader plate 10, the clamping members 5 would expand as a wafer 1 is removed resulting in the application of an increased load on the next wafer 1 in the array (typically the wafer V located at the top of the array).

The spreader plate 10 is preferably generally U-shaped and comprises two arms (not shown) spaced apart from each other. An actuator (not shown), such as a pneumatic cylinder, is provided to move the arms relative to each other. The actuator can displace the arms towards each other to reduce the effective width of the spreader plate 10 and allow it to be positioned between the clamping members 5 above the array of wafers 1. Once in position, the actuator extends the arms outwardly in a transverse direction so that the spreader plate 10 engages the clamping members 5. The spreader plate 10 has substantially the same width as the wafers 1 when the arms are in their extended position. The arms of the spreader plate 10 remain extended throughout the process of extracting the wafers 1 from the clamping assembly.

As each wafer 1 ' is extracted, the clamping assembly is displaced upwardly to raise the array of wafers 1 progressively out of the liquid in the extraction bath such that at least the top surface of the next wafer 1 " in the array is displaced out of the liquid. As the clamping assembly is displaced upwardly, the spreader plate 10 slides along the clamping members 5 such that its position relative to the uppermost wafer 1 ' remains substantially fixed. A low friction coating, such as Teflon®, could optionally be provided on the arms of spreader plate 10 in those regions in contact with the clamping members 5 to facilitate sliding of the spreader plate 10. Preferably, however, at least the arms of the spreader plate 10 are made of a low friction material, such as Teflon® or glass.

At least one nozzle (not shown) is provided to direct a fluid flow onto the upper surface of the uppermost wafer V in the array. A plurality of nozzles is provided in the present embodiment to direct liquid onto the uppermost wafer V to create a fluid flow over its upper major surface. The nozzles are provided on the arms of the spreader plate 10 and are arranged to direct liquid substantially perpendicular to the top surface of the uppermost wafer 1'. The resulting flow of liquid can assist in cleaning of the wafers 1 , for example by displacing any strips of glue which have separated from the substrate assembly 3 and become trapped between the wafers 1. Moreover, the flow of liquid can displace fragments of any broken wafers 1 which may otherwise be transported by the friction pad 9.

Instead of or in addition to directing liquid onto the uppermost wafer 1' from one or more nozzles, a flow of liquid can be established within the extraction bath to assist with cleaning of the wafers 1 and removal of any fragments of broken wafers 1. The flow is preferably established in a direction opposite to the direction in which the wafers 1 are removed from the array. The flow can be established by providing a sump into which liquid flows from the extraction bath along with any debris. In this arrangement the liquid in the extraction bath is replenished constantly, either by introducing a fresh supply of liquid or by recycling liquid from the sump. Suction can be used to improve the flow of liquid within the extraction bath and/or regulate the force applied.

With the longitudinal axis X of the array arranged substantially vertically, the clamping assembly allows the wafers 1 to be removed laterally but inhibits vertical movement of the wafers 1. As such, each individual wafer 1 can be selected automatically in turn from the clamping assembly but a space is maintained between the wafers 1 at all times. Even though the wafers 1 are each supported at opposing edges, they can flex and bend sufficiently that the faces of adjacent wafers 1 come into contact with each other. However, the arrangement of the present invention whereby at least the edges of the wafers 1 are spaced apart from each other allows the wafers 1 to be extracted from the array more readily. If required, a liquid can be introduced between the wafers 1 to promote separation of the facing surfaces of adjacent wafers 1. The liquid can be introduced as a flow of liquid between the wafers 1 or merely by maintaining the wafers 1 at least partially submerged.

A second embodiment will now be described with reference to Figures 7A and 7B. This embodiment utilises the same apparatus as the first embodiment described herein and like reference numerals have been used for like components.

The wafers 1 are introduced into a de-glue bath 11 while they are bonded to the glass substrate 3a. The de-glue bath 11 contains a de-gluing solution, such as a hot organic acid, and a flow of the de-gluing solution is established within the de- glue bath 1. As illustrated by the arrows B in Figure 7A, the de-gluing solution flows in a transverse direction relative to the wafers 1 to promote the flow of liquid between the wafers 1 and thereby to help prevent the wafers 1 clumping together. The clamping assembly is then positioned around the array of wafers 1 and a clamping force applied to support the wafers 1 within the clamping assembly. Thus, the wafers 1 are supported in the clamping assembly within the de-glue bath 11 with the longitudinal axis X of the array extending horizontally.

The adhesive bonding the wafers 1 to the substrate 3a is released in the de-glue bath 11 and the substrate assembly 3 is removed leaving the wafers 1 supported in an array within the clamping assembly. The clamping assembly is supported by an automated handling apparatus referenced generally in Figure 7A by the reference numeral 12.

The clamping assembly is rotated through 90° about a longitudinal axis X of the array (illustrated by arrow C) and through 90° about a transverse axis Y of the array (illustrated by arrow D) such that the wafers 1 are arranged directly above each other in the array. The wafers 1 can optionally then be transported to an extraction bath 13 whilst supported within the clamping assembly with the longitudinal axis X of the array being substantially horizontal. It will be appreciated that the rotation of the array about the longitudinal axis X and the transverse axis Y can be performed simultaneously or as two distinct phases in either order. Furthermore, the rotation of the clamping assembly can be performed within the de-glue bath 1 1 or externally of the de-glue bath 11. The wafers 1 are introduced into the extraction bath and the clamping assembly oriented such that the longitudinal axis X of the array is inclined at an angle to the vertical, as shown in Figure 8. In the present embodiment, the longitudinal axis X of the array is inclined at an angle of approximately 15°. Thus, the wafers 1 are each inclined at an angle of approximately 15° to the horizontal. The wafers 1 are then extracted from the clamping assembly in the same way as described above for the first embodiment.

By inclining the wafers 1 , debris and/or fragments of broken wafers are more readily transported off of the top surface of the uppermost wafer V. The supply of liquid onto an upper surface of the uppermost wafer 1 ' is particularly effective in displacing any debris when the array is inclined such that the surface of the wafer 1 ' is inclined at an acute angle to the horizontal.

As in the first embodiment, the clamping assembly is raised upwardly as each wafer 1 is extracted from the array. A spreader plate (not shown) is again provided to reduce the loading on each wafer 1 prior to extraction.

The wafers 1 are extracted by a friction pad 9 mounted on an automated carrier referenced generally in Figure 7B by the reference numeral 14. The wafers 1 are delivered by the friction pad 9 onto a belt conveyor 15 for transporting the wafers 1. The wafers 1 may, for example, undergo a further washing cycle and/or a drying cycle before final inspection. The wafers 1 can then be classified and packaged.

A modified version of the second embodiment of the present invention is illustrated in Figures 9A and 9B. Like reference numerals have been used for like components in this modified version. The main difference in this arrangement is that the wafers 1 are introduced into a clamping bath 17 while they are bonded to the glass substrate 3a. The clamping assembly is positioned around the wafers 1 within the clamping bath 17 and a clamping force applied while fluid flows between the wafers 1 (as illustrated by the arrows B) to help prevent them clumping together. The wafers 1 are supported within the clamping assembly and then transferred to the de-glue bath 1 1. The remainder of the process is unchanged from that described above for the second embodiment. A third embodiment of the present invention is illustrated in Figures 10A and 10B. This embodiment utilises the same apparatus as the first and second embodiments described herein and like reference numerals have again been used for like components. The primary difference between this embodiment and the second embodiment is the stage at which the clamping assembly is re-oriented to position the wafers 1 for extraction. In the present embodiment the array of wafers 1 is removed from the clamping assembly with the longitudinal axis X of the array arranged substantially horizontally. Thus, the wafers 1 are arranged substantially vertically when they are removed from the de-glue bath. The wafers 1 are transported to the extraction bath 13 in this orientation before being rotated through 90° about said longitudinal axis X of the array (illustrated by arrow E) and through 90° about said transverse axis Y of the array (illustrated by arrow F). The re-orientation of the wafers 1 can be performed externally of the extraction bath 13 or within the extraction bath 13.

The wafers 1 are again positioned in the extraction bath 13 with the longitudinal axis X of the array arranged at approximately 15° to the vertical. Thus, the wafers 1 are inclined at approximately 15° to the horizontal. The wafers 1 are then extracted from the clamping assembly in the same manner as described above for the second embodiment.

A modified version of the third embodiment of the present invention is illustrated in Figures 1 A and 1 1 B. Like reference numerals have been used for like components in this modified version. As in the modified version of the second embodiment, the main difference is that the wafers 1 are introduced into a clamping bath 17 and clamped into the clamping assembly before being introduced into the de-glue bath 11. A flow of liquid is established between the wafers 1 to help prevent them clumping together. With the wafers 1 separated from each other, the clamping force is applied to support them within the clamping assembly spaced apart from each other. The wafers 1 are transferred to the de- glue bath 11. The remainder of the process is unchanged from that described above for the third embodiment.

The wafer handling device 17 illustrated in Figure 12 comprises a pad 9 mounted on a housing 19 which is fixedly mounted on a back plate 21. A series of chambers 23 are formed in the housing 19 in fluid communication with the pad 9. A vacuum hose 25 connected to a pump (not shown) is mounted on the back plate 21 for operatively reducing the pressure within the chambers 23. The pad 9 is porous and can serve as a friction pad and/or a suction pad to engage the uppermost wafer 1' to enable it to be withdrawn from the top of the stack of wafers. It will be appreciated that a relatively small reduction in pressure within the chambers 23 can be sufficient to engage the wafer 1'.

The pad 9 can be a feraminous material, for example formed from a porous material or an open cell foam material. Alternatively, or in addition, a plurality of holes or can be formed in the pad 9 for establishing fluid communication with the chambers 23. In the latter arrangement, the pad 9 could be formed from leather. In a preferred arrangement, however, the pad 9 is a PUR based elastomer, such as Sylomer®.

A schematic diagram of the pneumatic system for actuating the clamp members 5 is shown in Figure 13. The system comprises four inflatable clamp members 5 each having a flow control device 25 to isolate the clamp member 5 in the event of a puncture (for example caused by the wafers cutting through the inflatable clamps). The fluid for inflating the clamp members 5 is pressurised by a pump 27 (for example a compressor) supplied from an air supply 29. The clamp members 5 are arranged on separate branches of the pneumatic system and each branch has a flow regulator 31 and, optionally, a pressure sensor 33.

A control system (not shown) is provided to control the pneumatic system. The pressure sensor 33 can be used by the control system to detect damaged inflatable clamp members 5 and flag them for replacement.

The flow control devices 25 in the present arrangement are self-sealing pneumatic connectors 25 connected in the pressurised supply line to each clamp member 5. In the event of a puncture, the pneumatic connectors seal the supply line to the punctured clamp member 5 and prevent or reduce the escape of pressurised fluid. In the absence of a flow control device to seal the supply line, a puncture could result in all of the clamp members 5 deflating (partially or fully) and the clamping force applied to support the wafers 1 being reduced.

It will be appreciated that other types of flow control device 25 can be employed. Alternatively, or in addition, more than one fluid pump 27 could be provided for supplying pressurised fluid to the clamping members 5. For example, each clamping member 5 could be associated with a dedicated fluid pump 27.

Various changes and modifications are envisaged for the methods and apparatus described herein. For example, to ensure the correct pick out position of wafers 1 within the clamping assembly, the apparatus can include a sensor system to provide positioning data of the location of the uppermost wafer 1 in the array. The sensor could be mechanical or electronic (laser/I R/visible light). The position of the friction pad 9 can be controlled responsive to said positioning data.

Moreover, it will be appreciated that several of the clamping assemblies can be supported in a carousel arrangement to enable continuous wafer production and handling. Alternatively, the clamping assemblies can by supported in a linear queuing system. The clamping assemblies can be sequenced within the linear system one after the other to enable the various processes to be performed in parallel.

The references herein to the orientation of the wafers 1 is in respect of their major surfaces unless specified otherwise. In particular, references to the wafer 1 being arranged horizontally refer to the major surfaces of the wafer 1 being horizontal; and references to the wafer 1 being arranged vertically refer to the major surfaces of the wafer 1 being vertical. Likewise, references to the array being arranged vertically refer to the longitudinal axis X of the array being vertical; and references to the array being arranged horizontally refer to the longitudinal axis X being horizontal.

The described embodiments of the invention serve only as an example of how the invention may be implemented. Modifications, variations and changes to the described embodiment will occur to those having appropriate skills and knowledge. These modifications, variations and changes may be made without departure from the scope of the invention defined in the claims and its equivalents.