Method for forming a back-to-back wafer batch to be positioned in a process boot, and handling system for forming the BTB wafer batch

A method for forming a package-like back-to-back wafer batch (BTB wafer batch) (14) to be positioned in a process boat (16), the back-to-back wafer batch consisting of a predetermined even number of wafers (1) disposed in rows, such as solar wafers, to be doped on one side, with each side (25) which is not to be doped abutting congruently the side (25) not to be doped of the respective adjacent wafer (1), comprising the steps of:

• providing the predetermined number of wafers (1) to be doped on one side in rows in the stacking slots of a carrier (2), which is clamped in a horizontal plane with upward facing stacking slots(4),
• moving a first half of the predetermined even number of wafers (1) for the BTB wafer batch (14) to be formed from the carrier (2)
• transferring the first half of predetermined even number of wafers in the form of a first wafer stack (9) by means of a transfer mechanism (15) to the process boat (16)
• positioning the first half of predetermined even number of wafers in an insertion position in its stacking slots,
• moving a second half of the predetermined number of wafers (1) for the BTB wafer batch (14) to be formed from the carrier (2)
• transferring the second half of predetermined even number of wafers by the transfer mechanism (15) to the process boat (16) in the form of a second wafer stack (13),
• wherein the wafers (1) of the second wafer stack (13) have previously been offset by 180° with respect to the position of the wafers (1) of the first wafer stack (9) in the insertion position of the process boat (16), positioned above wafers (1) in alignment with the insertion position of the first wafer stack (9) in the process boat (16), offset from the insertion position by a distance at least as great as the wafer thickness, and then joined together with the first wafer stack (9) in the insertion position of the process boat (16), with the sides not to be doped of the wafers (1) of the first and the second wafer stack (9 and 13, respectively) associated with each other being placed together simultaneously and congruently, and
• wherein a multi-vacuum gripper (15) of a BTB module (7) is used as the transfer mechanism, the first half of the predetermined even number of wafers (1) for the BTB wafer batch (14) to be formed is removed by the multi-vacuum gripper (15) of the BTB module (7) straight from the carrier (2) in the form of the first wafer stack (9) and then transferred by servo control to the insertion position of the process boat (16),
• in succession, the second half of the predetermined even number of wafers (1) for the BTB wafer batch (14) to be formed is removed in form of the second wafer stack (13) by the multi-vacuum gripper (15) of the BTB module (7) straight from the carrier (2) and transferred in succession by servo control to the process boat (16), and
• wherein the second wafer stack (13) taken from the carrier (2) by the multi-vacuum gripper (15) is swivelled by rotation of the multi-vacuum gripper (15) during transfer to the process boat (16) into the position which is offset by 180° with respect to the position of the first wafer stack (9) already in the insertion position of the process boat (16).

A handling system for loading a process boat (16) with several insertion positions (17) with wafer batches (14) before doping in a diffusion furnace, with an automatic transfer system by which a carrier (2) fitted with a predetermined even number of wafers (1) can be moved along a horizontal transport plane into a standby position for forming wafer stacks (9;

• 13), with a clamping module (3), from which the carrier (2) must be held aligned with upward facing stacking slots in the standby position, so that the centres of the wafers (1) in the stacking slots of the carrier (2) are precisely aligned with the comb holes of lifting combs (5a;
• 5b) that can be moved vertically of a first and a second vertical axis module, which are each rigidly disposed beneath the clamping module (3) in the standby position, wherein the first half of the predetermined number of wafers (1) in the carrier (2) held by the clamping module (3) is moved by the lifting comb (5a) of the first vertical axis module as the first wafer stack upwards into a first lifting position and is to be provided here by means of a rotating mechanism in a position offset by 180° with respect to its standby position in the lifting comb (5a) of the first vertical axis module and the lifting comb (5a) is lowered again, after which the second half of the number of wafers (1) located in the stacking slots of the carrier (2) is lifted into a second lifting position by the lifting comb (5b) of the second vertical axis module, then the second wafer stack (13) is moved without rotation into the first lifting position above the first wafer stack (9), into which the first wafer stack (9) is raised by the lifting comb (5a) of the first vertical axis module and inserted in the second wafer stack (13) and the wafers (1) of the first and the second wafer stack (9 and 13, respectively) are placed together back-to-back forming a packet-like BTB wafer batch (14) with a doubled doping surface in the lifting comb (5b), and with a transfer gripper (15), by which the formed BTB wafer batch (14) is moved from the first lifting position to the process boat (16) and deposited at one of the insertion positions, the improvement comprising:
• a back-to-back module (BTB module) (7) with a multi-vacuum gripper (6) with vacuum gripping combs (10), the back-to-back module (7) being disposed above the clamping module (3) and movable in an X-Y-Z and R direction, a vertically oriented axis of which is adapted to be rotated by a servo motor (11) via a downstream play-free gear (12) and a centring module (8), by which the number of wafers (1) of the first and second wafer stacks, respectively (9 and 13, respectively) lifted out of the carrier (2) into the first or second lifting position must be aligned at the side edges with the wafers (1) being at an exact distance from one another in the first and second wafer stack, respectively (9 and 13, respectively),
• wherein the first wafer stack (9) is adapted to be picked up from the first lifting position by the multi-vacuum gripper (6) of the back-to-back module (BTB module) (7) controlled by inductive proximity switches, swivelled through 180° and without any relative movement in relation to the lifting comb (5a) of the first vertical axis module deposited again in this in the position offset at 180° in the first lifting position and the lifting comb (5a) is lowered again, and
• wherein, the second wafer stack (13), adapted to be moved into the second lifting position, and is adapted to be picked up by the multi-vacuum gripper (6) of the back-to-back module (BTB module) (7) and moved without rotation into the first lifting position above the first wafer stack (9), after the first lifting stack is picked up from the first lifting position, and
• wherein the wafers (1) of the first wafer stack (9) raised by the lifting comb (5a) of the first vertical axis module are adapted to be moved along a servo-controlled movement path past the wafers (1) associated with the second wafer stack (13) and the wafers (1) of the second wafer stack (13) along with the wafers (1) of the first wafer stack (9) are adapted to be placed back-to-back in the raised lifting comb (5a) of the first vertical axis module.