Rådahl, Simon (Pyrolavägen 43, 3tr, Lidingö, S-181 60, SE)
| 1. | A method for aligning a workpiece with a known shape covered at least partly with a layer of material sensitive to electromagnetic radiation, including the actions of: fetching said workpiece with a picking device attached to a robotarm, providing a laser beam, having a wavelength not affecting said material sensitive to electromagnetic radiation, and a detector, moving said workpiece in a first direction to said laser beam, detecting with said detector when a first position of an edge of said workpiece is at least partly breaking said laser beam, registering the position of the robot arm when said first position of the edge of said workpiece is at least partly breaking said laser beam, displacing said workpiece with said robot arm, moving said workpiece in said direction to said laser beam, detecting with said detector when a second position of the edge of said workpiece is at least partly breaking said laser beam, registering the position of the robot arm when said second position of the edge of said workpiece is at least partly breaking said laser beam, computing an angle error of said workpiece out of said positions of the robot arm, correcting said angle error of said workpiece by means of said robot arm, putting said workpiece onto a stage. |
| 2. | The method according to claim 1, further including the action of aligning said workpiece in at least one of an x or y direction while being arranged on said stage. |
| 3. | The method according to claim 2, wherein said alignment of said workpiece in said x and/or y direction is performed by means of detecting the position of said workpiece by means of a camera and moving said workpiece into a predetermined position by means of said stage. |
| 4. | The method according to claim 2, wherein said alignment of said workpiece is performed by detecting an edge by means of an edge detector, while the workpiece is supported by said stage and moving said workpiece into a predetermined position by means of said stage. |
| 5. | The method according to claim 4, wherein said edge detection, while the workpiece is supported by said stage, is performed by means of a detector which is capable to detect a change in property of a reflected laser beam when passing said edge. |
| 6. | The method according to claim 4, wherein said edge detection, while the workpiece is supported by said stage, is performed by the same detector as used in aligning said workpiece rotationally while fetched by said robot arm. |
| 7. | The method according to claim 1, wherein said stage is movable in an x and y direction only. |
| 8. | A method for aligning a workpiece with a known shape covered at least partly by a layer of material sensitive to electromagnetic radiation, including the actions of: fetching said workpiece with a picking device attached to a robot arm, providing a laser beam, having a wavelength not affecting said material sensitive to electromagnetic radiation, and a detector, moving said workpiece in a first direction to said laser beam, detecting with said detector when a first position of a first edge of said workpiece is at least partly breaking said laser beam, registering the position of the robot arm when said first position of the edge of said workpiece is at least partly breaking said laser beam, displacing said workpiece with said robot arm, moving said workpiece in said direction to said laser beam, detecting with said detector when a second position of the first edge of said workpiece is at least partly breaking said laser beam, registering the position of the robot arm when said second position of the edge of said workpiece is at least partly breaking said laser beam, computing an angle error out of said positions of the robot arm, computing a position of said first edge, correcting said angle error of said workpiece by means of said robot arm, rotating said workpiece so that another part of the workpiece is detectable, moving said workpiece in a direction to said laser beam, detecting with said detector when a first position of a second edge of said workpiece is at least partly breaking said laser beam, registering the position of the robot arm when said first position of the second edge of said workpiece is at least partly breaking said laser beam, computing a position of the second edge, putting said workpiece onto the stage with said first and second edges at a predetermined position. |
| 9. | The method according to claim 8, wherein said workpiece is rotated 90°. |
| 10. | A method for aligning a workpiece with a known shape, including the actions of: fetching said workpiece by means of a pick and place robot, aligning said workpiece rotationally in a plane of a surface of said workpiece while fetched by said pick and place robot, arranging said workpiece on a stage, aligning said workpiece in at least one of an x or y direction while being arranged on said stage. |
| 11. | The method according to claim 10, wherein said rotationally alignment is performed by detecting two spaced apart positions on a common edge. |
| 12. | The method according to claim 11, further including the action of determining said position of said edge out of said detected two positions before arranging the workpiece on said stage. |
| 13. | The method according to claim l l, furtller including the action of determining a position of another edge of said workpiece before arranging said workpiece on said stage. |
| 14. | The method according to claim 11, wherein said position of said edge is determined by means of an interferometer. |
| 15. | The method according to claim 10, wherein said position of said edge is determined by means of an interferometer. |
| 16. | The method according to claim 11, wherein said workpiece is at least partly covered with a layer sensitive to electromagnetic radiation and where said stage belongs to a pattern generator for patterning an arbitrary pattern onto said workpiece. |
| 17. | The method according to claim 11, wherein said position of said edge is determined by means of a detector which is capable to detect a change in property of a reflected laser beam when passing said edge. |
BACKGROUND OF THE INVENTION [0002] Before being able to pattern a workpiece in a lithographic process, using either lasers, electron beams, ions or other equivalent methods, the position of said workpiece must be known. When knowing the position of the workpiece it can be aligned with the tool for creating the pattern. Typically said workpiece must be aligned with a writing tool in six different ways. The workpiece must be horizontally aligned to said writing tool in an X-direction and in a Y-direction. The workpiece must also be rotationally aligned. Said workpiece must be placed in focus of said writing tool, i. e. be aligned in a Z-direction. Lastly, the workpiece and writing tool must be tilt aligned in two perpendicular directions, i. e. if not being tilt aligned, the pattern created by said writing tool will be out of focus for different parts of said workpiece and in focus for the remaining parts.
[0003] In the past, said alignment of the workpiece in said S-direction, Y- direction and said rotationally alignjnent has been performed by putting said workpiece in a pre aligner comprising a number of alignment pegs extending from a surface on top of which said workpiece is laid. Said alignment pegs is attached to said surface of said pre aligner for stopping said workpiece in a predetermined position.
From the pre aligner is air blown through a number of orifices beneath said workpiece. When blowing said air through said orifices a cushion is created between the surface of the pre aligner and the workpiece. Said cushion can effectively transport said workpiece in a desired direction with a minimum of friction and force applied. If the pre aligner is tilted in a direction so that said alignment pegs will be lowered, said workpiece would be moved towards said alignment pegs. If said alignment pegs have been attached to the surface correctly said workpiece would place itself in said predetermined position when coming in contact with said
alignment pegs. A gripper grips said workpiece in said known position and transports said workpiece to a stage for possible further alignment.
[0004] Said method for aligning the workpiece has the disadvantage of having a limitation in the accuracy of aligning said workpiece. Said inaccuracy may be a problem in the future when the line widths are becoming extremely small. With such small line widths there may also be a problem with contamination from said pre aligner as mentioned above, since there are at some occasions a physical contact between said workpiece and the pre aligning pegs.
[0005] Another method for aligning said workpiece is instead to use a stage, which is movable in both the X-and Y-direction and rotatable along its central axis.
The workpiece is placed, within certain tolerances, at said stage. A detector is detecting the position of the edges of said workpiece while moving said stage. The stage is in a predetermined aligned position when the actual position of the edges of said workpiece corresponds to a predetermined position.
[0006] Said method of aligning the workpiece have the disadvantages of relying on a stage, which must have the possibility of being rotatable.
[0007] What is needed is a method for aligning the workpiece, which can align the workpiece more precisely than the prior art techniques with a minimum of contamination. What is also needed is an aligning method which can use a stage movable in an x and a y direction only.
SUMMARY OF THE INVENTION [0008] Accordingly, it is an object of the present invention to provide a method of aligning a workpiece, which overcomes or at least reduces the above-mentioned problems.
[0009] This object, among others, is according to a first aspect of the invention attained by a method for aligning a workpiece covered at least partly with a layer of material sensitive to electromagnetic radiation. Said workpiece is fetched with a picking device attached to a robot arm (pick and place robot), a laser beam, having a wavelength not affecting said material sensitive to electromagnetic radiation, and a detector is provided, said workpiece is moved in a first direction to said laser beam, with said detector a first position of an edge of said workpiece is detected when said edge at least partly is breaking said laser beam. The position of the robot arm is registered when said first position of the edge of said workpiece is at least partly
breaking said laser beam. Said workpiece is displaced with said robot arm. Said workpiece is moved in said direction to said laser beam. With said detector, a second position of the edge of said workpiece is detected when said edge is at least partly breaking said laser beam. The position of the robot arm is registered when said second position of the edge of said workpiece is at least partly breaking said laser beam. An angle error of said workpiece is computing out of said positions of the robot arm. Said ang) e error of said workpiece is correcting by means of said robot arm. Said workpiece is put onto said stage.
[0010] In another embodiment said invention further comprising the action of aligning said workpiece in at least one of an x or y direction while being an-anged on said stage [0011] In another embodiment of the invention said alignment of said workpiece in said x and/or y direction is performed by means of detecting the position of said workpiece by means of a camera and moving said workpiece into a predetermined position by means of said stage.
[0012] In still another embodiment of the present invention said alignment of said workpiece is performed by detecting an edge by means of an edge detector, while tile workpiece is supported by said stage and moving said workpiece into a predetermined position by means of said stage.
[0013] In still another embodiment according to the present invention said edge detection, while the workpiece is supported by said stage, is performed by means of a detector which is capable to detect a change in property of a reflected laser beam when passing said edge.
[0014] In yet another embodiment of the present invention said edge detection, while the workpiece is supported by said stage, is performed by the same detector as used in aligning said workpiece rotationally while fetched by said robot an-n.
[0015] In yet another embodiment of the present invention said stage is movable in an x and y direction only.
[0016] The invention also relates to a method for aligning a workpiece covered at least partly by a layer of material sensitive to electromagnetic radiation. Said won-apiece is fetched with a picking device attached to a robot arm. A laser beam, having a wavelength not affecting said material sensitive to electromagnetic radiation, and a detector is providing. Said workpiece is moved in a first direction to said laser
beam. With said detector a first position of a first edge of said workpiece is detected when said edge is at least partly breaking said laser beam. The position of the robot arm is registered when said first position of the edge of said workpiece is at least partly breaking said laser beam. Said workpiece is displacing with said robot arm.
Said workpiece is moved in said direction to said laser beam. With said detector a second position of the first edge of said workpiece is detected when said edge is at least partly breaking said laser beam. The position is registered of the robot arm when said second position of the edge of said workpiece is at least partly breaking said laser beam. An angle error is computed out of said positions of the robot arm. A position of said first edge is computed. Said angle error of said workpiece is corrected by means of said robot arm. Said workpiece is rotated so that another part of the workpiece is detectable. Said workpiece is moving in a direction to said laser beam. With said detector a first position of a second edge of said workpiece is detected when said edge is at least partly breaking said laser beam. The position of the robot arm is registered when said first position of the second edge of said workpiece is at least partly breaking said laser beam. A position of the second edge is computed. Said workpiece is put onto the stage with said first and second edges at a predetermined position.
[0017] In another embodiment of the present invention said workpiece is rotated 90°.
[0018] The invention also relates to a method for aligning a workpiece where said workpiece is fetched by means of a pick and place robot. Said workpiece is aligned rotationally in a plane of a surface of said workpiece while fetched by said pick and place robot. Said workpiece is arranged on a stage. Said workpiece is aligned in at least one of an x or y direction while being arranged on said stage.
[0019] In another embodiment of the present invention said rotationally alignment is performed by detecting two spaced apart positions on a common edge.
[0020] In still another embodiment said invention further comprising the action of determining said position of said edge out of said detected two positions before arranging the workpiece on said stage.
[0021] In another embodiment the invention further comprising the action of determining a position of another edge of said workpiece before arranging said workpiece on said stage. The method according to claim 11, wherein said position of said edge is determined by means of an interferometer.
[0022] In another embodiment of the present invention said position of said edge is determined by means of an interferometer.
[0023] In another embodiment of the present invention said workpiece is at least partly covered with a layer sensitive to electromagnetic radiation and where said stage belongs to a pattern generator for patterning an arbitrary pattern onto said workpiece.
[0024] In still another embodiment of the present invention said position of said edge is determined by means of a detector which is capable to detect a change in property of a reflected laser beam when passing said edge.
[0025] Further characteristics of the invention, and advantages thereof, will be evident from the detailed description of preferred embodiments of the present invention given hereinafter and the accompanying Figs. 1-8, which are given by way of illustration only, and thus are not limitative of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS [0026] Figure 1 depicts in a perspective view an embodiment of a setup according to the present invention [0027] Figure 2a depicts in a perspective view a step of the present inventive method.
[0028] Figure 2b depicts in a perspective view another step of the present inventive method.
[0029] Figure 2c depicts in a perspective view still another step of the present inventive method.
[0030] Figure 3 depicts a top view of a workpiece fetched and about to be aligned with the robot.
DETAILED DESCRIPTION [0031] The following detailed description is made with reference to the figures.
Preferred embodiments are described to illustrate the present invention, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows.
[0032] Further, the preferred embodiments are described with reference to a laser as an edge-detecting source. It will be obvious to one ordinary skill in the art that sources other than lasers will be equally applicable; for example a sound emitting device or a heat-emitting device with appropriate detectors used.
[0033] The invention relates to alignment of a workpiece, such as a semiconductor wafer or a mask substrate. A pattern is to be created on said workpiece using any kind of radiation, i. e. , light from IR to EUV, x-ray or particle beams such as electron, ion or atom beams.
[0034] Figure 1 shows an exemplary setup for aligning a workpiece according to the present invention. Said setup comprises a laser source 110, a robot 150, a workpiece storage magazine 170, a stage 140 and a detector 180. The robot 150 comprises an arm 160 rotatable at a connection point 162 and at points 164 and 166.
The robot itself is rotatable at 152 around its own longitudinal axis. The rotatable points 162,164, 166 and 152 give the possibility to place a workpiece at any position within reach of the arm 160. The exemplified type of robot is just an example, any kind of robot, which is capable to pick and place, can be used, however different types of robots may have different limitations in their flexibility which in some cases must be compensated for. Said compensation may comprise a movement of the stage 140 in an appropriate direction.
[0035] The laser source emits radiation, which will not affect a coating on top of said workpiece. Said coating may be sensitive to electromagnetic radiation, such as any type of photo resist.
[0036] The laser source 110 may be arranged in the pattern generator so that a detector 180 will receive an emitted radiation beam 130 from said) aser source 110.
Said laser may be arranged above the stage 140 and the detector 180 may in such case integrated with the stage 140. Instead of the detector 180 and the laser 110 another type of arrangement may be used with simi ! ar properties. Such an arrangement is a retro r eflective milTor at the place of the detector and a detector arranged within the laser source. However, since a position of the robot 150 in relation to the stage 140 is known and stationary the laser 110 and the detector 180 may be arranged outside the stage 140. Although the laser 110 and detector 180 are arranged outside the stage 140, said workpiece 120 may nevertheless be put on the stage 140 at a predetermined position, since a distance between the detector 180 and the stage 140 is known.
[0037] The workpiece storage magazine 170 stores workpieces 120 and is arranged within reach of the arm 160 of the robot 150. The robot 150 picks one of the stored workpieces 120 and moves it towards the beam 130 of the laser 110. A gripper device 168 attached to the arm 160 of the robot 150 may be operated by vacuum, such
as a suction device. The gripper device may also be of a purely mechanical type, for instance the jaws of the tongues.
[0038] Figure 2a depicts the workpiece 220 in vicinity of the beam of the laser 230. The beam of the laser 230 will, at a certain point, be cut by a first edge of the workpiece 220 at a point 222 when moving the workpiece 220 by said arm of the robot towards said beam of the laser. The position of the arm of the robot is registered when the beam is cut, i. e., when no illumination impinges onto the detector 280, if such an arrangement is used. There is also a possibility to detect a certain drop in an intensity received by the detector, i. e. , detecting only partial cutoff of the illumination.
[0039] After having registered the position of the robot arm when cutting the beam of the laser wholly or partly at point 222 of said first edge of said workpiece 220, said workpiece 220 is displaced so that another part of the same edge will cut the same beam 230 of the same laser. Figure 2b illustrates that the workpiece will cut the beam of the laser at point 224 after said displacing of the workpiece 220. The position of the robot arm is registered when said beam of the laser is wholly or partly cut at said point 224. Since the shape, i. e., rectangular, rhombic, triangular, circular, elliptical etc, of the workpiece 220 is known and the displacement is known, a rotation of said workpiece 220 can be computed using said positions of the arm 160 of the robot 150 when said workpiece 220 is cutting said beam at point 222 and at point 224.
[0040] From said registered positions of said arm 160 of the robot 150 when cutting said beam of the laser can a position of the edge comprising said points 222 and 224 be determined.
[0041] Figure 3 illustrates a top view of a workpiece 340, which is to be aligned.
Points 322 and 324 will be detected as described above. The distance between said points are known, which will tell us a possible error of rotation of said workpiece.
[0042] Line a, b, c are drawn in figure 3 for simplification of understanding only.
Line a goes through point 322 and is parallel with a desired position of an edge comprising said points 322 and 324. Line c is parallel with line a, and goes through point 324. Line b is parallel with line a and line c, and goes through the middle of the edge comprising said points 322 and 324.
[0043] If said workpiece is not r otationally aligned, said robot will detect a difference in distance indicated by 380 in figure 3. Said error of rotation can be
corrected by rotating said workpiece corresponding to half said detected distance 380 indicated in figure 3 by 370.
[0044] Having computed the error of rotation, the position of said edge may easily be determined, i. e. , an alignment in a first direction of the workpiece.
[0045] The arm of the robot can compensate an error of rotation. Having compensated the error of rotation, a new positioning of the workpiece may be checked by registering the position of the arm of the robot when said points 222 and 224, or two other points at said edge, is cutting said beam of the laser. A deviation in relation to an expected positioning of the robot arm for said points 222 and 224 is further compensated and possibly checked again. Alternatively more than two points are detected for increasing the accuracy of the computed error of rotation. If only two points are used they are preferably separated from each other as much as possible along the edge of the workpiece.
[0046] By rotating the workpiece 90 degrees, an alignment of the workpiece in a direction orthogonal to the first direction may be performed, see figure 2c. If said workpiece having a rectangular shape, an edge of said workpiece orthogonal to the one comprising said points 222 and 224 is moved towards said beam of the laser.
When said edge is cutting said beam of the laser wholly or partly a position of said edge can be determined by registering the position of the arm of the robot. Having done that, a complete knowledge of an orientation of said workpiece in two orthogonal directions and its rotation is completed. By using the registered positions of the arm of the robot, said workpiece may be put anywhere on the stage as desired with its edges and rotation known. A tilt alignment as well as an alignment of the workpiece orthogonal, i. e., a z direction, to said two orthogonal directions, i. e. , a x and y direction respectively, is supposed to be taken care of by the stage according to well known techniques in the art.
[0047] If said workpiece has the shape of a semi conducting wafer, i. e. , essentially circular with one of its crystal directions marked with a flat edge, the rotation of said workpiece and the determination of the position of said edge, i. e. , alignment in a first direction, may be performed as described above. By making three measurements at different positions along the circular section one may determine the shape of said circular section and thereby making it possible to determine the position of the
circular section. When the shape is known the position can be deducted from one of said measurements.
[0048] The alignment in said second direction may also be performed after said workpiece has been put on the stage. If said workpiece has a rectangular shape an edge of said workpiece, orthogonal to the one already aligned, may be located by a CCD camera while moving said stage. Said edge may also be located by illuminating said edge by said beam of the laser and simultaneously detecting differences in reflectance of said beam. When said beam is passing the edge a characteristic behavior of the reflected beam can be detected. Said characteristic behavior depends on the differences of reflectance of the stage and the workpiece and the slope of said edge of the workpiece. Using said laser, said retro reflective mirror and said detector within the laser could also perform the alignment in the second direction.
[0049] If said workpiece only has one flat edge, as commonly is the case with the semi conducting wafer, the CCD camera may align said workpiece in one or two direction given that the workpiece is rotationally aligned. Errors in alignment in said x and/or y direction may be compensated by moving the stage on top of which the workpiece is attached.
[0050] By aligning the workpiece at least rotationally by the pick and place robot before placing said workpiece on said stage will reduce the alignment which must be made when said workpiece is placed on said stage. This procedure will be more time efficient instead of aligning said workpiece on said stage. This will also make it possible to use a stage which is only movable in an x and y direction.
[0051] If the workpiece is further aligned in one or two directions, x and y respectively, before being attached to the stage the alignment on stage can be reduced to a minimum if needed at all.
[0052] The present aligning method is particularly useful in the lithography industry, where a workpiece must be aligned more or less exactly before patterning the desired pattern. The alignment becomes more and more important the smaller line widths said industry is trying to manufacture in large scales. However, the present method is equally applicable in other technical areas where an object must be correctly arranged before being further processed, such areas may be different cutting techniques such as with lasers, drilling, punching, where each technique may require different accuracy.
[0053] Any practitioner in the field will be able to devise alternative designs of the robot 150 in figure 1. For example may the robot be in a fixed position in relation to the stage 140 of the pattern generator or movable back and forth from said stage 140. The distance between the robot 150 and the stage may be constantly monitored using techniques well known in the art, such as us an interferometer, a sound wave or equivalent methods.
[0054] While the preceding examples are cast in terms of a method, devices and systems employing this method are easily understood. A magnetic memory containing a program capable of practicing the claimed method is one such device. A computer system having memory loaded with a program practicing the claimed method is another such device.
[0055] While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.
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