WO2012004002A1

WO2012004002A1 - Vaccum suction unit and gripper

Info

Publication number: WO2012004002A1
Application number: PCT/EP2011/003453
Authority: WO
Inventors: Ottmar Graf
Original assignee: Centrotherm Thermal Solutions GmbH and Co KG
Current assignee: Centrotherm Thermal Solutions GmbH and Co KG
Priority date: 2010-07-09
Filing date: 2011-07-11
Publication date: 2012-01-12
Anticipated expiration: 2013-01-09
Also published as: DE102010026610A1

Abstract

The application describes a vacuum suction unit for a gripper for holding a disk-shaped substrate, the vacuum suction unit comprising a base body, a nozzle body having a suction nozzle, and a substrate contact element. The nozzle body and/or the substrate contact element is/are movable with respect to the base body, and the nozzle body comprises a receptacle, which is con¬ structed in such a way that the substrate contact element, after being received in the receptacle, radially surrounds the suction nozzle and protrudes over the suction nozzle in an axial direction. Furthermore, a gripper for holding a disk- shaped substrate is described, wherein the gripper comprises a base body, a first vacuum suction unit having a first substrate contact element movable with respect to the base body, and also at least one second vacuum suction unit having a second substrate contact element. The first and second vacuum suction units are arranged in such a way that the first and second substrate contact elements are located in one plane and are able to contact a disk-shaped and preferably planar substrate to be supported at the same time and on the same substrate side. Furthermore, means for applying a vacuum to the vacuum suction units are provided, the means being adapted to independently apply vacuum to the vacuum suction units. Also, a method for loading a wafer boat is described, wherein a wafer is sucked to a wafer gripper by at least one first and one second vacuum suction unit via vacuum, wherein a substrate contact element of the first vacuum suction unit is movable with respect to the wafer gripper. After this, the wafer gripper is moved into a receiving slot between plates of the wafer boat, and thereafter, the vacuum at the second vacuum suction unit is released, such that the wafer is supported only by the first vacuum suction unit. Now, the wafer is moved into receptacles of the wafer boat, wherein the substrate contact element carries out a lateral or rotational movement when the wafer contacts one or more of the receptacles. Thereafter, the vacuum at the first vacuum suction unit is released.

Description

Vacuum Suction Unit and Gripper

The present invention relates to a vacuum suction unit for a gripper as well as to a gripper for holding a disk-shaped substrate, particularly a wafer substrate. Furthermore, the invention relates to a method for loading a wafer boat, the wafer boat comprising a plurality of plates, which are generally arranged parallel to each other in an opposed manner, and a plurality of receiving slots for receiving the wafers, said slots being formed between adjacent plates. In the art of semi-conductors and solar cells, it is known to subject disk- shaped substrates made from different materials, which are referred to as wafers hereinbelow, to different processes.

In so doing, wafers are often subjected to individual processes as well as to batch processes, i.e. processes in which several wafers are processed at the same time. For single processes as well as for batch processes, wafers need to be transferred to a desired processing position. In batch processing, this is usually done by inserting wafers into so-called boats, which comprise receptacles for a plurality of wafers. In the boats, the wafers are usually arranged parallel with respect to each other. Such boats may be constructed in different ways, and often these boats provide for holding only the lower edges of each wafer in such a way that the wafers are standing with the upper part free.

Such boats may have e.g. inserting chamfers for facilitating insertion of the respective lower edges of the wafers into the boats.

The type of wafer boat initially mentioned, which is used e.g. for plasma nitrid- ing of wafers in the art of solar cells, is formed by a plurality of electrically conductive plates, which are usually made of graphite. The plates are arranged substantially parallel to each other, and receiving slots for receiving wafers are formed between adjacent plates. The sides of the plates facing each other each comprise corresponding holding elements for wafers such that a wafer may be held at each side of the plate. In this way, two wafers may be received entirely between the plates in each receiving slot. Adjacent plates of the wafer boat are electrically isolated and may be biased with different biasing voltages during the process. By this means, it is possible to form a plasma between the substrates held at each of the plates, in order to provide for plasma processing of the substrates, such as plasma nitriding.

Usually, at least three pins are provided on each of the plates for forming holding elements. The pins comprise an enlarged head at their free end, which head comprises a guiding surface which tapers towards the pin. When inserting the wafers, the edges of the wafers are moved to the region of the pins, and thereafter, the edges are brought into contact with preferably all three pins by a rotational movement. This may be done by employing grippers, which suck the wafer to the gripper with e.g. three vacuum suction devices to thereby hold the wafer in a fixed position with respect to the robot gripper, which further transport the wafer to the wafer boat and which insert the wafer into the pins with a slight rotational movement thereof. The wafers used in this process are usually solar cell wafers made from silicon, the wafers being substantially rectangular and having a thickness of 150 pm. The outer dimensions may be between 155 mm x 155 mm and 157 mm x 157 mm, depending on the manufacturing process. On the one hand, tolerances may occur when positioning the wafers, and on the other hand, the wafers may have tolerances of the outer dimensions of +/- 1 mm; thus, there is the risk that the wafers do not sufficiently contact the pins or that the wafers get damaged during the insertion process, because the wafers are pushed too hard into the holding pins by the grippers during the rotation.

Another possibility for achieving the desired through-put is the use of multiple grippers, which are able to transport a plurality of wafers and to insert the wafers into the wafer receptacles at the same time. With this solution, the wafer can be inserted slowly enough into the wafer receptacles of a wafer boat;

however, positioning is very imprecise, as in e.g. variation in size of +/- 1 mm for 22 wafers which must be positioned at the same time. In order to ensure that as few as possible of these very thin wafers are damaged during loading or unloading operations, alternative grippers are provided, which have vacuum suction devices, which are supported via springs in an intricate manner to allow movement of the vacuum suction devices and thus of a wafer received thereon. By this means, tolerances during insertion of the wafers may be automatically compensated. However, with such grippers there is a risk that the wafers may move excessively with respect to the gripper during fast movement of the gripper, and thus the wafers may vibrate and get damaged. Particularly, during movement from a wafer pick-up position to the receiving slot of the wafer boat, this may result in a damage to the wafer. In order to avoid such damages, any movement of the gripper has braked slowly or attenuated when using such grippers. This again lowers the through-put of the wafers through the facility, since loading of the wafer boat becomes very time-consuming.

Thus, the problem to be solved by the present invention is to provide a gripper for holding a disk-shaped substrate, wherein the gripper allows for fast and automatic compensation of tolerances while manipulating the substrate in a simple way and wherein the gripper also avoids the risk of damage to the wa- fers during dynamic movements, as well as providing a vacuum suction unit for such a gripper. Furthermore, a problem to be solved by the invention is to provide a method for loading a wafer boat, which allows for automatic compensation of tolerances and also allows for dynamic movements during the wafer transport.

According to the invention, this problem is solved by a vacuum suction unit for a gripper according to claim 1 , as well as by a gripper for holding a disk- shaped substrate according to claim 5, and also by a method for loading a wafer boat according to claim 13. Further embodiments of the invention may be derived from the dependent claims.

A vacuum suction unit for a gripper for holding a disk-shaped substrate, particularly a wafer substrate, is provided, wherein the vacuum suction unit com- prises a base body, a nozzle body having a suction nozzle, and a substrate contact element. The nozzle body and/or the substrate contact element are movable with respect to the base body. The nozzle body comprises a receptacle which is constructed in such a way that the substrate contact element radially surrounds the suction nozzle and protrudes beyond the suction nozzle in an axial direction, in case the substrate contact element is received in the receptacle. Such a vacuum suction unit has a simple construction and is able to hold a substrate securely while allowing it to remain movable or flexible.

Preferably, the base body comprises a recess, in which the nozzle body and an elastic element radially surrounding the nozzle body are received in such a way that the nozzle body is biased toward the center of the receptacle by the elastic element. By this means, an inherent positioning of the nozzle body results, if the elastic element is not moved by external forces. This is advantageous for definitely fixing the substrate. The nozzle body may comprise a plurality of projections at its radially-outward circumference for forming receiving spaces for the elastic element.

In one embodiment of the invention, an inner diameter of the substrate contact element is at least three times as big as a diameter of the suction opening(s) of the suction nozzle, in the region of the contact area pointing in an axial direction. By this means, a high flow velocity during suction is allowed in the suction nozzle, wherein sucking may also be affected over a greater distance, such as 1 mm. Once the substrate has been sucked, the substrate contacts the substrate contact element, which has a larger diameter and thus provides good support.

The gripper for holding a disk-shaped substrate particularly comprises a base body, a first vacuum suction unit fixed to the base body, the vacuum suction unit comprising a first substrate contact element, which is movable with respect to the base body, as well as at least one second vacuum suction unit fixed to the base body. The second vacuum suction unit comprises a second substrate contact element. The first and the second vacuum suction units are arranged in such a way that the first and second substrate contact elements are arranged in one plane and may contact a planar and disk-shaped substrate at the same time on the same side of the substrate. Furthermore, means for applying vacuum to the vacuum suction units are provided, the means being adapted to independently apply vacuum to the vacuum suction units. Such a gripper allows for securely gripping or holding a substrate with different vacuum suction units, wherein at least one of the vacuum suction units is movable, in order to compensate for tolerances during loading of a wafer boat.

In one embodiment, the substrate contact element consists of an elastic material, such that a substrate contact surface thereof is movable with respect to the base body. Preferably, the first vacuum suction unit of the gripper is a suction unit of the type described above, having a movable substrate contact element, while the second substrate contact element is not movable with respect to the base body. In one embodiment of the invention, a plurality of second vacuum suction units are provided, which are arranged around the first vacuum suction unit. By this means, the substrate may be securely fixed during fast movement of the gripper.

Preferably, the first and/or the second substrate contact element is made of an elastomeric material having a temperature resistance of up to at least 120°C and particularly preferably up to 160°C in order to allow for using the gripper in these temperature ranges.

In another embodiment, the gripper further comprises a third vacuum suction unit fixed to the base body, the third suction unit comprising a third substrate contact element movably supported with respect to the base body, and at least one fourth vacuum suction unit fixed to the base body. The fourth vacuum suction unit comprises a fourth substrate contact element, wherein the third and fourth vacuum suction units are arranged in such a way that the third and fourth substrate contact elements are located in one plane and are directed in an opposite direction with respect to the first and second substrate contact elements and are adapted to contact a substrate to be supported at the same time on the same side. The means for applying the vacuum are adapted to independently apply vacuum to the first to fourth vacuum suction units.

Preferably, also means for applying a gas flow to the vacuum suction units are provided, wherein the means are adapted for independently applying a gas flow to the vacuum suction units, in order to allow for reliable releasing of a substrate.

In the inventive method for loading a wafer boat, wherein the wafer boat comprises a plurality of plates, which are generally arranged parallel and opposing to each other, and wherein the wafer boat comprises a plurality of receptacles for receiving the wafers between adjacently arranged plates, the following steps are provided: sucking a wafer to a wafer gripper via at least one first and one second vacuum suction unit by means of vacuum, wherein a substrate contact element of the first vacuum suction unit is supported movably with re- spect to the wafer gripper, moving the wafer gripper and the wafer into a receiving slot between plates of a wafer boat, releasing the vacuum at the second vacuum suction unit, such that the wafer is held only by the first vacuum suction unit, moving the wafer into receptacles at one of the plates forming the receiving slot, wherein the substrate contact element or at least a contact lip area of a ring body of the substrate contact element carries out a lateral movement or rotational movement, wherein the wafer contacts one or more of the receptacles, and releasing the vacuum at the first vacuum suction unit. By this means, the wafer may be securely held during movements outside the receiving slot, wherein during rotational insertion of the wafer into the recepta- cles, compensation movements relative to the wafer gripper may be admitted. While releasing the vacuum at the first and/or second vacuum suction units, preferably a gas flow is applied to the respective vacuum suction unit in order to reliably release the wafer from the gripper. In one embodiment, the method further comprises sucking another wafer to the wafer gripper by at least one third and one fourth vacuum suction unit by use of vacuum prior to moving the vacuum gripper into the receiving slot between the plates of the wafer boat. In this case, the substrate contact element of the third vacuum suction unit is supported movably with respect to the wafer gripper. Furthermore, the vacuum of the fourth vacuum suction unit is released after moving the wafer gripper into the receiving slot between the plates, such that the further wafer is held only by the third vacuum suction unit, and the other wafer is moved into the receptacles on the other plates which form the receiving slot, therein the substrate contact element of the third vacuum suction unit carries out a side or rotational movement, when the wafer contacts one or more of the receptacles. Thereafter, the vacuum of the third vacuum suction unit is released.

In the following, the invention will be explained in more detail referring to the figures; in the figures:

Fig. 1 shows a schematic side view of an apparatus for loading/unloading a wafer boat;

Fig. 2 shows a perspective view of a wafer boat used in the apparatus according to Figure 1 ;

Fig. 3 shows an enlarged schematic perspective view of a wafer gripper having vacuum suction units;

Fig. 4 shows an enlarged schematic sectional view of a first vacuum suction unit of the wafer gripper according to Figure 3;

Fig. 5 is an enlarged perspective view of a nozzle body of the vacuum suction unit, which is shown in Figure 4, the nozzle body being formed as a support; Fig. 6 is an enlarged perspective view of a suction ring of the vacuum suction unit according to Figure 4;

Fig. 7 is an enlarged schematic view of a second vacuum suction unit of the wafer gripper according to Figure 3;

Fig. 8A-C a schematic flow chart of an insertion operation for a wafer into a wafer boat according to Figure 2; and

Fig. 9 shows a schematic side view of a holding pin of a wafer boat according to Figure 8. Terms such as top, bottom, left, and right used in the specification are related to the positions in the figures, and these terms should not be regarded as limiting. However, these terms may describe preferred embodiments. The term in general, when used for parallel and perpendicular arrangements or with respect to angles, shall comprise deviations of not more than ± 3°, preferably not more than ± 2°.

Figure 1 shows a schematic side view of an apparatus 1 for loading/unloading a wafer boat 2. The apparatus 1 comprises a wafer transport robot 3, a measuring system 5, and a controller or control unit (not shown in detail) for control- ling the wafer transport robot 3 and the measuring system 5. Such an apparatus has been described in detail also in the application DE 10 2010 025 483, which also belongs to the applicant of the present application and was not published before the filing of the present application, wherein the disclosure thereof relating to the general construction of the apparatus is included into the present application by reference in order to avoid repetitions.

The wafer boat 2 used in the apparatus 1 will be explained in more detail, particularly with reference to Figures 1 and 2. The wafer boat 2 is formed by a plurality of plates 6, a plurality of clamping or chucking and isolating units 7 and support feet 8. The shown wafer boat 2 is especially adapted for plasma treatment and specifically for plasma nitriding of wafers. Each of the plates 6 is formed of an electrically conductive material and especially the plates are formed as graphite plates. Each of the plates 6 has a parallel top edge 9 and a bottom edge 10, respectively. In the top edge 9, a plu- rality of V-shaped grooves 12 are formed. In the shown embodiment, each of the plates 6 has seven of these V-shaped grooves 12. Each of the grooves 12 has a chamfer with respect to the upper surface, the chamfer generally being arranged at an angle of 45°, wherein also other angles may be provided. In the shown embodiment, a total of twenty-three plates 6 are provided, the plates 6 being arranged substantially with respect to parallel to each other via corresponding clamping and isolating units 7, in order to form receiving or receptacle slots 15 therebetween. If twenty-three plates 6 are provided, twenty- two receptacle slots 15 are formed.

Each of the plates 6 comprises groups of three receiving pins 16 each (shown in Figures 8A-C) located on the side of the plates which faces an adjacent plate 6, the holding pins 16 being arranged in such a way that they may hold a wafer therebetween. The wafers may be received in such a way that the hold- ing pins 16 contact different side edges of the wafer, respectively. As can be best seen in Figure 9, the holding pins 16 each comprise a pin portion 17, which is fixed to the corresponding plates 6 of the wafer boat, and comprise an enlarged head portion 18 at their unattached end. Each of the head portions 18 has a guiding chamfer 19 tapered to the pin portion 17.

In this arrangement, a total of seven groups of guiding elements (corresponding to the number of grooves 12) are arranged in the longitudinal direction of the plate elements, the guiding elements being provided for receiving a semiconductor wafer, as will be discussed in the following in more detail. Thus, it is possible to position seven adjacent wafer pairs in each of the receptacle slots 15. The chuck and isolating units 7 generally consist of a bolt, spacers, and a nut each. The bolt and the spacers are made from an electrically isolating material. The nut may also be formed from an electrically isolating material, which is not necessary, however. The bolts as well as the spacers may be made e.g. from ceramic. Each of the spacers has preferably the same thickness, in order to arrange the plate elements parallel with respect to each other.

The bolt is sized in such a way that it may protrude through corresponding openings of the plates 6 as well as through corresponding spacers arranged between the plates 6. The plates 6 may be chucked or clamped via the nut. In this case, also other chuck and isolating units are conceivable, which arrange the plates 6 generally parallel with respect to each other in the above- mentioned manner. A total of sixteen of the chuck and isolating units 7 are provided, wherein eight units are provided adjacent to the top edge 9 of the plates 6 and wherein eight units are arranged adjacent to the bottom edge 10 of the plates 6. The chuck and isolating units 7 are equally distanced and divide the plates 6 into seven segments in the longitudinal direction, each segment corresponding to a group of guiding elements and grooves 12. The grooves 12 in the top edge 9 are located in an edge region of a corresponding segment formed in this way. The segments formed in this way are also aligned with groups of guiding pins 16 on the corresponding plates 6. In the view according to Figure 1 , also contact elements 20 at the wafer boat 2 may be perceived, the contact elements 20 being provided for electrically contacting the ends of the plates 6. The contact elements 20 are isolated with respect to each other, even though this is not shown in detail, and it is thus possible that adjacent plate elements are biased with inverse bias voltage, as is required for producing a plasma in the receptacle slots 15. The wafer transport robot 3 has a stationary pedestal or base 22, a drive unit 24, as well as a wafer gripper 26. The pedestal 22 forms a firm base for the wafer transport robot 3 and especially for the drive unit 24. The drive unit 24 is formed by a plurality of arms 28 to 31 and a plurality of rotational joints 32 to 37, as is known in the art. One end of the drive unit 24 is connected to the pedestal, while the other end supports the wafer gripper 26.

Encoders are provided in the region of each rotational joint 32 to 37, the en- coders being able to measure the rotational position of each rotational joint and to transmit the rotational position to a controller (not shown). The controller is adapted to control the movement of the rotational joints 32 to 37, in order to position the wafer gripper 26 in a desired position and orientation, as is known in the art. To this end, the controller usually starts from a coordinate system of the wafer transport robot 3, which has a fixed reference point (especially a point of origin) e.g. in the pedestal 22. It is obvious that also another coordinate system may be the basis, the other coordinate system having a fixed reference system outside the pedestal. The wafer transport robot 3 described above is only an example, and it should be noted that also other wafer transport robots may be employed, which comprise e.g. a different drive unit for positioning a wafer gripper in a desired position and orientation. One example is a drive unit which provides for positioning in two dimensions via rails, which are perpendicularly oriented with respect to each other (usually in a horizontal direction) and which provides for positioning in a third dimension (usually in a vertical direction) via a lifting device extending perpendicular to the rails. Additionally, a rotation tilt joint may be provided between the lifting device and the wafer gripper for orienting said wafer gripper in such a drive unit. Such known wafer transport robots have, as men- tioned above, an excellent repetitive precision, however only limited absolute precision, as long as these wafer transport robots are not calibrated. Calibration may be achieved by the measuring system 5, as is described in DE 10 2010 025483, wherein the disclosure of the calibrating process is incorporated by reference into the present application. The measuring system 5 may be provided, on the one hand, for measuring the spatial position of indi- vidual plates 6 of the wafer boat 2 described above referring to Figures 1 and 2, and, on the other hand, for measuring the spatial position of a wafer gripper 26 of the wafer transport robot 3.

The measuring system 5 generally consists of a support element 42, a drive unit (not shown) therefore, as well as three sensors 45, 46, and 47, as well as an analyzing unit (not shown) for the sensor signals of the sensors. The drive unit for the support element 42 is a unit adapted for moving the support element 42 along a predetermined movement path. Alternatively, it is possible to provide a drive unit for the sensors 45, 46, and 47 in order to move these sen- sors along the support element 42.

The wafer gripper 26 is a plate-type gripper having a base body 50, a first vacuum suction unit 53, and four second vacuum suction units 55. As can be seen in Figure 4, the base body 50 consists of an upper plate element 56 and at least one back plate 58. The upper plate element 56 has a generally rectangular form, which is chamfered at one side, as may be seen in Figure 3. A plurality of openings are provided in the chamfered region, the openings being usable for fixing the base body 50 to the wafer robot 3. Fur- thermore, it is possible to provide pressure or vacuum terminals, respectively, for the vacuum suction units 53 and 54 via these openings, as will be explained in more detail in the following.

The upper plate element 56 has a plurality of recesses in the back side there- of, wherein these recesses are formed as conduits to the respective vacuum suction units 53 and 55, wherein the conduits are appropriately connectable to a vacuum suction unit/pressured air unit. As such, a recess 59 is schematically shown in Figure 7. In the region of each vacuum suction unit 53, 55, at least one respective passage opening 60 is provided, as may be seen in Figures 4 and 7. Each of the recesses 59 formed as channels in the upper plate element 56 is connectable to the opening 60 via the back plate 58. To this end, the back plate 58 comprises a corresponding recess 62, wherein the recess 62 is connected to the recess 59 on the one hand and is connected to the passage opening 60 on the other hand (see Figure 7). The back plate 58 is received in a sealed manner in a recess of the upper plate element 56 and is connected thereto. How- ever, the back plate may be simply connected thereto with a planar connection.

As may be seen in Figure 4, a recess 65 is provided in the upper surface of the plate element 56 in the region of the vacuum suction unit 53, wherein the opening 60 is arranged in the middle thereof.

The recess 65 is provided for receiving various elements of the vacuum suction unit 53, as will be explained in the following in more detail referring to Figures 4 to 6. The vacuum suction unit 53 generally consists of a nozzle body 76, a suction ring 69, a biasing unit 70, and a cover plate 72.

The nozzle body 67 has a planar back side 75, preferably formed of a material having a low coefficient of friction, such as PTFE, or coated with such a material. The planar back side 75 is formed in such a way that it slidably abuts on a planar zone of the recess 65 of the upper plate element 56.

As may be seen in the perspective view of Figure 5, the nozzle body 67 has a generally round shape, wherein outwardly facing projections 77 are provided in the region of the circumference, wherein the recesses form deflection spac- es for the biasing element 70 in between, as will be explained in more detail below. The nozzle body 67 forms an axially extending and protruding nozzle 78 in the middle region, wherein the nozzle 78 has a nozzle opening 79. The nozzle opening 79 is aligned to the opening 60 in the upper plate element 56, as can be seen in Figure 4.

The nozzle body 76 also has an elevated circumferential edge 82 spaced from the elevated or protruding nozzle 78. A ring-shaped receiving space 84 for the suction device 69 is formed between the elevated circumferential edge 82 and the elevated nozzle 78. This receiving space 84 has a radially planar bottom section adjacent to the nozzle 78 as well as a bottom section adjacently inclined with respect to the planar bottom section, the inclined bottom section ramping upward towards the elevated circumferential edge 82, as can be seen in Figure 4. The radial outer inclined bottom section is provided for centering the suction ring 69, as will be explained in more detail below.

The suction ring 69, shown in Figure 6 in perspective view, has a ring body 90 made of elastomeric material, having a central opening, wherein the central opening is sized such that the nozzle 78 fits therethrough. The outer circumference of the suction ring 69 is sized such that the outer surface is smaller than an inner circumference of the elevated circumferential edge 82 of the nozzle body 67. Thus, the suction ring 69 may be at least partially housed in the receiving space 84 of the nozzle body 67, as can be seen in Figure 4. The ring body 90 has a planar portion as well as an inclined portion inclined with respect to the planar portion at its bottom side, wherein the portions corre- spond to the planar and inclined portions of the receiving space 84 of the nozzle body 67. By this means, the suction ring 69 is automatically centered inside the receiving space 84 when the suction ring 69 is inserted into the receiving space 84. The ring body 90 has an upper contact lip region 92 having an upper surface 94 formed for contacting a wafer. The absolute height of the ring body 90 is such that the upper surface 94 protrudes over the nozzle 78 when the suction ring 69 is received in the recess 84 of the nozzle body 67. The contact lip region 92 has an inner circumference which is larger than the inner circumference of a region of the ring body 90 located at a deeper position. Furthermore, the contact lip region 92 has an outer circumference which is smaller than the outer circumference of a holding lip region 96 of the ring body 90, which is located deeper. The inner diameter of the contact lip region 92 is much larger than the diameter of the nozzle opening 79 of the nozzle 78. Preferably, the diameter of the contact lip region is at least three times as large as the diameter of the nozzle opening 79.

The suction ring 69 is made of an elastomeric material having high radial dimensional stability and being slightly deformable in an axial direction. The suction ring is deformable in an axial direction by e.g. 0.06 mm when vacuum sucking a substrate. However, the suction ring 69 maintains its form in a radial direction. In order to avoid contact of a sucked wafer with the nozzle 78, the suction ring 69 protrudes over the nozzle 78 by a height which is higher than the deformability of the suction ring 69.

The biasing unit 70 is formed as an O-ring in the shown embodiment, and the biasing unit surrounds the nozzle body 67 in a radial direction. The O-ring is dimensioned in such a way that the O-ring is clamped between an outer surface of the nozzle body 67 and an inner surface of the recess 65 of the upper plate element 56, and by this means, the nozzle body 67 is centered with respect to the recess 65. As is obvious to the person skilled in the art, it is pos- sible to provide for lateral movement of the nozzle body 67 with respect to the upper plate element 56 in case a load is applied, wherein the O-ring may be at least partially moved into the deflecting spaces at the outer circumference defined by the radially outwardly facing protrusions 77. Furthermore, a certain rotational movement of the nozzle body 67 is possible.

The suction ring 69 will follow such a movement of the nozzle body 67, since the suction ring 69 is also guided by the nozzle body 67. However, a slight lateral displacement or rotational movement, respectively, of the suction ring 69 with respect to the nozzle body 67 is conceivable.

The cover plate 72 is ring-shaped and has a central opening formed for re- ceiving the contact lip region 92 of the ring body 90. Between the central opening of the cover plate 72 and an outer circumference of the contact lip region 92, sufficient clearance is provided in order to allow for a lateral movement as well as for a rotational movement of the suction ring 69 with respect to the cover plate 72. The central opening of the cover plate 72 is dimen- sioned in such a way that the central opening has a smaller inner circumference than the outer circumference of the holding lip 96 of the suction ring 90. Thus, the suction ring 69 is protected against inadvertently dropping out of the recess 84 (see Figure 5). However, the central opening is sufficiently large that it is possible to manually remove the suction ring 69 from the recess 84 in order to e.g. replace the suction ring 69. The cover plate 72 is glued to e.g. the upper surface or a corresponding recess in the upper surface of the plate element 56.

Thus, the vacuum suction unit is constructed such that the vacuum suction unit may carry out lateral and rotational movements with respect to the upper plate element 56, as will be explained in more detail in the following.

Figure 7 shows the construction of the vacuum suction unit 55. The suction unit 55 comprises a nozzle body 100, a suction ring 102, and a cover plate 104.

The nozzle body 100 has a nozzle part 108 having a nozzle opening 109. The nozzle part 108 axially extends upward from a base plate 110 and comprises the nozzle opening 109 in the middle. The nozzle opening 109 is aligned with the opening 60 in the upper plate element 56. The nozzle body 100 is tightly fitted into a stepped lower region of a corresponding recess of the upper plate element 56. An upper surface of the suction ring 102 protrudes over an upper surface of the nozzle part 108. The holding lip of the suction ring 102 extends into a stepped region of the recess in the upper plate element 56. The holding plate 104 is constructed in the same manner as the holding plate 72, and the hold- ing plate 104 maintains the suction ring 102 in its position.

In the vacuum suction unit 55 according to Figure 7, the suction ring 102 is generally kept stationary. Particularly, the suction ring is not able to move laterally with respect to the upper plate element 56. Such a lateral movement is only possible within the margins of a tolerance between the inner circumference of the suction ring 102 and the outer circumference of the nozzle part 108.

In the embodiment according to Figure 3, four vacuum suction units 55 are provided, which are arranged at four edges of an imaginary rectangle. In the middle of this imaginary rectangle, a single vacuum suction unit 53 is shown. Of course, it is also possible to provide another number of first and second vacuum suction units 53, 55, which may also be differently arranged. The vacuum suction units 53, 55 may be separately, i.e. independently, connected to vacuum or to pressurized air, respectively. The vacuum should be adjusted in such a way that a disk-like substrate to be transported can be fixedly sucked to the vacuum suction unit. The pressurized air is provided for reliably releasing each substrate from the corresponding vacuum suction unit 53, 55, in case the vacuum is released.

In the following, operation of the wafer gripper 26 will be explained in more detail referring to Figures 1 and 8. First, the wafer transport robot 3 is controlled in such a way that the wafer transport robot moves to a wafer picking position, e.g. a conveyor belt, on which the wafer is placed. The wafer gripper 26 will be positioned at a small distance of e.g. 0.5 mm above a wafer on the conveyor belt, and thereafter vacuum will be applied to the vacuum suction units 53, 55. By this means, the semiconductor wafer will be sucked towards the wafer gripper. In doing this, it is of particular advantage that the nozzle openings 79 and 109, respectively, in each of the nozzle bodies 67 and 100, respectively, are much smaller than the inner circumference of the corresponding suction ring 69 and 102, respectively. By this means, it is possible to create a high flow velocity through the corresponding nozzle opening such that semi-conductor wafers may also be sucked over a larger distance. Once the semi-conductor wafer has been sucked, the semi-conductor wafer contacts the respective suction ring 69 or 102, respectively, which has the larger inner circumference and thus provides for secure support. If a wafer is sucked to the suction ring, the height of the suction ring may be slightly reduced, e.g. by 0.06 mm. The suction ring is made of an elastomeric material, which provides for good fitting to irregularities of a semi-conductor wafer and thus for good sealing of the suction region.

A wafer sucked in this way will be fixedly maintained with respect to the wafer gripper 26, particularly by the outwardly arranged vacuum suction units 55, such that the wafer may be handled at high speeds. Particularly, the wafer gripper and a wafer W sucked to the wafer gripper, as is schematically indicated in Figures 8A-8C, will be moved into a reception slot between adjacent plates 6 of the wafer boat 2. This movement may be carried out at a high speed, since the wafer is firmly held to the wafer gripper 26.

Once the wafer gripper 26 is located in one of the receiving slots of the wafer boat 2, the vacuum suction units 55 are deactivated, i.e. the vacuum is released. Furthermore, a slight positive pressure may be generated by an air blow or gas blow, respectively, and this positive pressure may be supplied to the vacuum suction units and to the wafer in order to provide for reliable releasing of the wafer from the vacuum suction units 55. The vacuum suction unit 53 remains activated, i.e. connected to vacuum, such that the wafer W will be supported by the vacuum suction unit. Since the suction ring 69 of the vacuum suction unit 53 is movable in lateral and in rotational directions, the wafer W may now also slightly move with respect to the wa- fer gripper 26.

Figures 8A to 8C show an insertion sequence of a wafer W between the holding pins 16 by rotation. This is done in such a way that the wafer W is first moved freely between the pins 16 in a position shown in Figure 8A. Thereaf- ter, the wafer W is rotated by a corresponding movement of the wafer gripper 26, wherein the rotational movement is preferably around its central point. In doing so, the edges of the wafer now contact the guiding chamfers 19 of the head portion 18 of the holding pins 16. During a further rotation, the wafer W is guided by the guiding chamfers 19 in the direction of the corresponding plate 6 and is securely supported by the pins 16. Since the wafer W is held by the movably supported suction ring 69 at this point in time, it is possible that the wafer W carries out a lateral movement with respect to the wafer gripper 26 as well as a rotational movement with respect to the wafer gripper 26. This is advantageous since, due to imprecise positioning of the wafer gripper 26 and due to tolerances in the wafer dimensions, damages may otherwise occur during rotational insertion, according to Figures 8A-8C.

The corresponding movability of the suction ring 69 prevents an excessive load on the wafer during the rotational insertion process. Once the wafer W is completely inserted, the first vacuum suction unit is supplied with a pressurized air blow, in order to release the wafer. Thereafter, a new wafer may be picked up and may be moved into a receiving slot.

The wafer gripper 26 was described in such a way that first and second vacu- urn suction units 53, 55 are provided on one side of the wafer gripper. Corresponding vacuum suction units may also be provided on the back side, wherein each of the vacuum suction units located on the opposed sides is isolated from the other vacuum suction units. By this means, it would be possible for the wafer gripper 26 to pick up and transport a wafer both on its front side and on its back side. Thus, the wafer gripper could insert two wafers W into a corresponding receiving slot 15 of a wafer boat 2 directly in sequence, wherein during each rotational insertion process of a wafer only the central vacuum suction unit with a movably supported suction ring would be activated.

After the rotational insertion process of the wafers W, a positive air blow may again be applied to the wafer in order to reliably release the wafer from the wafer gripper 26.

For loading of wafer boats 2, the spatial position of the plates 6 and thus the spatial position of the receptacles for wafers located thereon, may be determined in advance by the measuring system 5. From this spatial position, a corresponding loading position may be determined, which needs to be ap- proached by the wafer gripper 26 of the wafer transport robot 3.

The apparatus has been explained in more detail with reference to preferred embodiments of the invention wherein the inventive concept was referred to, however the invention is not limited to the directly shown embodiments.

Particularly, the wafer boat or the wafer transport robot could be constructed in another way. Also, the number of first and second vacuum suction units may deviate from the shown number. According to one aspect, the vacuum suction units may also be constructed in another way. Particularly, it is also possible to provide a generally stationary suction ring and to provide for sufficient resilience by means of material selection in order to allow for compensating tolerances.

Claims

A gripper for holding a disk-shaped substrate, wherein the gripper comprises:

a base body;

a first vacuum suction unit at the base body comprising a first substrate contact element movable with respect to the base body;

at least a second vacuum suction unit at the base body comprising a second substrate contact element, wherein the first and second vacuum suction units are arranged in such a way that the first and second substrate contact elements are located in one plane and are able to contact a substrate to be supported at the same time and on the same side; and

means for applying a vacuum to the vacuum suction units, wherein the means are adapted for independently applying vacuum to the vacuum suction units.

The gripper of claim 1 , wherein the substrate contact element is made of an elastic material, such that a substrate contact area thereof is movable with respect to the base body.

The gripper of claim 1 or 2, wherein the first vacuum suction unit comprises:

a base body;

a nozzle body having a suction nozzle comprising at least one suction opening; and

a substrate contact element having an axially facing contact area;

wherein the nozzle body and/or the substrate contact element are supported movably with respect to the base body, and wherein the nozzle body comprises a receptacle constructed in such a way that the substrate contact element radially surrounds the suction nozzle and protrudes over the suction nozzle in an axial direction. The vacuum suction unit of claim 3, wherein the base body comprises a recess, in which the nozzle body and an elastic element radially surrounding the nozzle body are received in such a way that the nozzle body is biased by the elastic element towards the middle of the recess.

5. The vacuum suction unit of claim 4 wherein the nozzle body comprises a plurality of protrusions on the radially outwardly facing circumference thereof.

6. The vacuum suction unit of any one of claims 3 to 5, wherein an inner diameter of the substrate contact element in the region of the axially facing contact area is at least three times as large as a diameter of the suction opening(s) of the suction nozzle.

7. The gripper of any one of the preceding claims, wherein the second substrate contact element is not movable respect to the base body. 8. The gripper of any one of the preceding claims, wherein a plurality of second vacuum suction units is provided, wherein the vacuum suction units are arranged around the first vacuum suction unit.

The gripper of any one of the preceding claims, wherein the first or the

second substrate contact element is made of an elastomeric material having a temperature resistance of at least 120°C and preferably up to at least 160°C.

10 The gripper according to any one of the preceding claims, wherein the gripper further comprises:

a third vacuum suction unit at the base body comprising a third substrate contact element movable with respect to the base body; and at least a fourth vacuum suction unit at the base body comprising a fourth substrate contact element, wherein the third and fourth vacuum suction units are arranged in such a way that the third and fourth substrate contact elements are located in one plane, are facing opposing directions with respect to the first and second substrate contact ele- ments, and are able to contact a substrate to be supported at the same time and on the same side,

wherein the means for applying a vacuum are adapted for independently applying a vacuum to the first to fourth vacuum suction units.

The gripper of any one of the preceding claims, wherein means for applying a gas flow to the vacuum suction units are provided, and wherein the means are adapted for independently applying a gas flow to the vacuum suction units.

A method for loading a wafer boat having a plurality of plates, which are arranged generally parallel to each other in an opposed manner, and wherein the wafer boat comprises a plurality of receptacles for receiving the wafers between adjacently located plates,

the method comprising the following steps:

sucking a wafer to a wafer gripper by at least one first and one second vacuum suction unit by means of vacuum, wherein a substrate contact element of the first vacuum suction unit is supported movably with respect to the wafer gripper;

moving the wafer gripper and the wafer into a receiving slot between the plates of the wafer boat;

releasing the vacuum at the second vacuum suction unit such that the wafer is supported by the first vacuum suction unit only;

moving the wafer into receptacles at one of the plates forming the receiving slot, the substrate contact element thereby moving laterally or rotationally when the wafer contacts one or several of the receptacles; and

releasing the vacuum at the first vacuum suction unit.

13. The method of claim 13, wherein a gas flow is applied to the first and/or second vacuum suction unit while releasing the vacuum at the respective vacuum suction unit.

14. The method of claim 13 or 14, wherein the method comprises the following step prior to moving the wafer gripper into the receiving slot between the plates of the wafer boat:

sucking another wafer to the wafer gripper by at least one third and one fourth vacuum suction unit via a vacuum, wherein a substrate contact element of the third vacuum suction unit is supported movably with respect to the wafer gripper, and wherein the method comprises the following steps after moving the wafer gripper into the receiving slot between the plates:

releasing the vacuum at the fourth vacuum suction unit, such that the other wafer is supported by the third vacuum suction unit only;

moving the wafer into the receptacles at one of the plates forming the receiving slot, wherein the substrate contact element of the third vacuum suction moves laterally or rotationally when the wafer contacts one or more of the receptacles; and

releasing the vacuum from the third vacuum suction unit.

15. A vacuum suction unit for a gripper for holding a disk-shaped substrate, particularly for holding a wafer, the vacuum suction unit comprising the following:

a base body;

a substrate contact element having an axially facing contact area;

wherein the nozzle body and/or the substrate contact element are sup- ported movably with respect to the base body, and wherein the nozzle body comprises a receptacle constructed in such a way that the substrate contact element radially surrounds the suction nozzle and protrudes over the suction nozzle in an axial direction. The vacuum suction unit of claim 15, wherein the base body comprises a recess, in which the nozzle body and an elastic element radially surrounding the nozzle body are received in such a way that the nozzle body is biased by the elastic element towards the middle of the recess.

The vacuum suction unit of claim 16, wherein the nozzle body comprises a plurality of protrusions on the radially outwardly facing circumference thereof.

The vacuum suction unit claims 15 to 17, wherein an inner diameter of the substrate contact element in the region of the axially facing contact area is at least three times as large as a diameter of the suction opening^) of the suction nozzle.