METHOD AND DEVICE FOR FORMING A STRUCTURE ON A WORKPIECE

Abstract

A device and a method for forming a structure on a workpiece by processing radiation while the workpiece is moved by a transport device, in which correction data of the workpiece are acquired by optical sensors. The correction data includes movement data of the workpiece and/or position data of a structure created on the workpiece by the processing radiation, and, dependent on the correction data, the deflection of processing radiation brought about by a deflection unit is determined, in particular corrected.

Claims

1. A method for forming a structure on a workpiece (2) by processing radiation, the method comprising: a. providing the workpiece (2) on a transport device (1); b. moving the workpiece (2) along a trajectory by the transport device (1) and processing the workpiece (2) using processing radiation while the workpiece (2) is moved by the transport device (1), with, in order to form the structure, a time of processing being controlled by a control device (7) and, a location of the processing of the workpiece (2) by the processing radiation being controlled by a control device (7)-controlled optical deflection unit (4, 4) for processing radiation, and in method step B, while the workpiece (2) is processed by the processing radiation, acquiring correction data of the workpiece (2) by at least one optical sensor, the correction data comprising at least one of movement data of the workpiece (2) or position data of a structure created on the workpiece (2) the processing radiation, and, dependent on the correction data, deflection of processing radiation brought about by the deflection unit (4, 4) is determined by the control device (7).

2. The method as claimed in claim 1, further comprising in method step B, detecting a pose of the workpiece (2) in a method step B.1 before the workpiece (2) is processed by the processing radiation, and, after method step B.1, acquiring the movement data of the workpiece (2) in a method step B.2.

3. The method as claimed in claim 2, further comprising starting the acquisition of the movement data in accordance with method step B.2 no later than the implementation of method step B.1 and continuing the acquisition of the movement data at least until the structure is being created by the processing radiation.

4. The method as claimed in claim 2, further comprising, in method step B.2, acquiring the movement data of the workpiece (2) by a plurality of optical detectors.

5. The method as claimed in claim 4, further comprising, in method steps B.1 and B.2, acquiring characteristic data by different optical detectors.

6. The method as claimed in claim 5, further comprising, in method step B.1, acquiring location data of the workpiece (2) by at least one pose sensor selected from the group consisting of optical barrier, camera and optical micrometer, and, in method step B.2, acquiring the movement data of the workpiece (2) by optical tracking sensors (6a).

7. The method as claimed in claim 1, further comprising, in method step B, capturing at least one spatially resolved image of a surface of the workpiece (2), where the processing by the processing radiation takes place, and determining a pose of a structure created on the workpiece (2) by the processing radiation based on the image.

8. The method as claimed in claim 7, further comprising at least one of a) aligning structure dimensions of the structure created by the processing radiation, with the structures captured in the spatially resolved image, or b) aligning a distance of the structure formed by the processing radiation with one or more edges of the workpiece.

9. The method as claimed in claim 1, wherein, in method step B, the processing radiation is laser radiation.

10. The method as claimed in claim 1 further comprising acquiring a height profile of the workpiece (2), and carrying out at least one of the following corrections time of processing; the deflection of processing radiation brought about by means of the deflection unit (4, 4); or focusing processing radiation by means of a focusing apparatus dependent on the height profile.

11. A device for forming a structure on a workpiece (2) using processing radiation, the device comprising: a transport device (1) for moving the workpiece (2) along a trajectory, a radiation source for creating processing radiation, a control device (7) for controlling at least one of a time of processing or a deflection of processing radiation for processing the workpiece (2), and optical sensors for acquiring pose data of the workpiece (2), wherein the optical sensors comprise motion sensors for capturing a movement of the workpiece (2), and at least one optical pose sensor (5, 5) for acquiring location data of the workpiece (2).

12. The device as claimed in claim 11, wherein an acquisition region of the pose sensor is arranged in front of an acquisition region of at least a subset of the motion sensors in a transport direction of the transport device (1).

13. The device as claimed in claim 11, wherein at least a subset of the motion sensors comprise tracking sensors.

14. The device as claimed in claim 11, further comprising a height profile measuring unit (9) for determining a height profile of a workpiece (2) arranged on the transport device (1).

15. The device as claimed in claim 11, wherein, while the workpiece (2) is processed by the processing radiation, the optical sensors are configured to acquire correction data of the workpiece (2) by at least one of the optical sensors, with the correction data comprising at least one of movement data of the workpiece (2) or position data of a structure created on the workpiece (2) by the processing radiation, and the control device (7) is configured to interact with the optical sensors such that, dependent on the correction data, at least one of a time of processing or a deflection of processing radiation brought about by the deflection unit (4, 4) is corrected by the control device (7).

16. The device as claimed in claim 11, wherein the pose sensor comprises at least one of an optical barrier, camera or optical micrometer.

17. The device as claimed in claim 14, further comprising a focusing apparatus (8) for processing radiation, and the control unit is configured to interact with the height profile measuring unit (9) and the focusing apparatus (8) in order to control the focusing apparatus (8) dependent on height profile data from the height profile measuring unit (9).

18. The method as claimed in claim 8, wherein the aligning of the structure dimensions of the structure created by the processing radiation, includes aligning at least one distance between spaced-apart structure portions of the structure created by the processing radiation, or at least one distance between a plurality of the structures created by the processing radiation.

19. The method as claimed in claim 3, wherein the acquisition of the movement data continues until the creation of the structure by the processing radiation is completed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Further advantageous features and preferred embodiments will be explained below on the basis of exemplary embodiments and with reference to the figures. In the figures:

[0080] FIG. 1 shows a first exemplary embodiment of a device according to the invention for forming a structure on a workpiece by means of processing radiation;

[0081] FIG. 2 shows a plan view of a sensor unit of the device depicted in FIG. 1;

[0082] FIG. 3 shows a plan view of a processed workpiece, and

[0083] FIG. 4 shows a second exemplary embodiment of a device according to the invention.

DETAILED DESCRIPTION

[0084] All of the figures show schematic illustrations which are not true to scale. Identical reference signs in the figures designate identical or identically acting elements.

[0085] The exemplary embodiments of a device according to the invention for forming a structure on a workpiece by means of processing radiation, as are depicted in side views in FIGS. 1 and 4, are designed to process semiconductor substrates by means of laser radiation. The semiconductor substrates represent precursors for producing photovoltaic solar cells. The precursors comprise a substrate in the form of a silicon wafer, on which a dielectric layer, a silicon dioxide layer in the present case, is formed on a processing side located at the top in the figures. A plurality of parallel, rectilinear structures are formed through laser ablation using processing radiation in the form of laser radiation. The structures thus represent linear openings in the dielectric layer.

[0086] The first exemplary embodiment of a device according to the invention for forming a structure on a workpiece by means of processing radiation, as shown in FIG. 1, comprises a transport device 1 for moving workpieces 2, which in the present case are in the form of a precursor for photovoltaic solar cell production, as described above. The transport device 1 comprises a conveyor belt, on which the workpieces 2 are placed and moved from left to right along a rectilinear trajectory in a manner corresponding to the direction of the arrow shown in FIGS. 1 and 4.

[0087] FIGS. 1 and 4 each show a side view of the devices, and so accordingly only a respective edge of the workpieces 2 having the planar form is shown.

[0088] The device according to FIG. 1 also comprises a radiation source 3 which is embodied as a laser and serves to create processing radiation in the form of laser radiation. In the present case, the laser is designed as a solid-state laser, having a wavelength of 1064 nm and a pulse duration of 4 ns.

[0089] The device also comprises a deflection unit 4 which comprises a motor-rotatable mirror in the present case, in order to deflect a laser beam 3a from the radiation source 3 in a manner perpendicular to the transport direction and perpendicular to the processing side of the workpieces 2, located on the top, and hence in a manner perpendicular to the plane of the drawing of FIG. 1.

[0090] The device also comprises optical sensors:

[0091] In the transport direction, a pose sensor 5 is arranged in front of the region of the device where the workpieces 2 are processed by means of the laser beam 3a.

[0092] The pose sensor 5 comprises a plurality of optical barriers which are arranged in a rectilinear line perpendicular to the transport direction and hence perpendicular to the plane of the drawing in FIG. 1.

[0093] To this end, mirrors are attached in a region of the transport device 1 below the workpieces 2 that are transported by the transport device. The transport means of the transport device 1, presently the conveyor belt, is configured such that no elements of the conveyor belt are arranged in the region of the mirrors, with the result that the optical path between the housing 5 of the pose sensor 5 arranged at the top in FIG. 1 and the mirrors arranged in the transport direction 1 is only covered by the workpieces 2.

[0094] Thus, the time at which a leading edge of the workpiece 2 in the transport direction covers the optical beam path of the optical barrier is detected by means of the pose sensor 5. Moreover, by way of a coverage time offset between the individual optical barriers arranged in a straight line perpendicular to the transport direction, it is also possible to detect an oblique position of the workpiece should the leading edge of the workpiece not be perpendicular to the transport direction. Hence, the absolute pose of the workpiece 2 is detected relative to the device by means of the pose sensor.

[0095] The optical sensors also comprise a motion sensor array 6. The motion sensor array 6 comprises a plurality of optical tracking sensors 6a, which are arranged on the intersection points of a grid which is a square grid in this case. FIG. 2 shows a plan view of the motion sensor array 6 from above, with the optical tracking sensors being depicted as a circle in each case. The optical tracking sensor 6a at the top left corner has been provided with a reference sign by way of example.

[0096] In the present case, the optical tracking sensors are designed as described in the patent U.S. Pat. No. 7,057,148 B2. In the present case, a single tracking sensor consists of an optical detector, with 3030 pixels in the present case, an integrated illumination and a microcontroller which contains a digital signal processor unit for calculating the movement data.

[0097] Hence, the movement of the workpiece 2 is detected by means of the optical tracking sensors of the motion sensor array 6, from the moment at which the pose of the workpiece is detected by means of the pose sensor 5 and at least until the time at which the workpiece is processed by means of the laser beam 3a. A movement of the workpiece over time and likewise also a rotation of the workpiece can be detected on account of the multiplicity of optical tracking sensors 6a and on the basis of differences in the movement velocity and, in particular, components of the movement velocity perpendicular to the transport direction.

[0098] The acquisition region of the optical tracking sensors 6a is consequently arranged behind the acquisition region of the pose sensor in the transport direction.

[0099] FIG. 3 depicts a plan view from above of a workpiece 2 that has already been fully processed. The black parallel lines label the cutouts created by laser ablation by means of the laser beam 3a. The rectilinear cutouts are created parallel to the transport direction during the processing. However, in the device depicted in FIG. 1, the laser beam can only be moved perpendicular to the transport direction by means of the deflection unit 4, as described above. However, movement of the laser beam and ablation of the dielectric layer to form the cutouts is implemented at a significantly higher speed than the movement speed of the workpiece 2 on the transport device 1. Thus, adjacent portions of the structures can always be created in sequential order. On account of an extent of the ablations created by means of the laser parallel to the movement direction as well, respective cutouts that overlap in the transport direction are thus successively created in each structure, and so a continuous rectilinear cutout is formed for each structure.

[0100] The device according to the exemplary embodiments depicted in FIGS. 1 and 4 comprises a control device 7 in each case. The latter is connected to the optical sensors in order to acquire the measurement data from the optical sensors and connected to the radiation source 3 in order to switch beam creation on and off, and also connected to the deflection unit in order to control the deflection of the laser beam 3a by means of the deflection unit.

[0101] The connection to the motion sensor array 6 has not been depicted pictorially in order to provide a better overview.

[0102] The device according to FIG. 1 is designed to carry out an exemplary embodiment of a method according to the invention:

[0103] A workpiece 2 is provided on the transport device 1 in a method step A. In method step B, the workpiece 2 is moved by the transport device 1 along the rectilinear trajectory labeled by an arrow, and the workpiece 2 is processed by means of processing radiation in the form of a laser beam 3a while the workpiece 2 is moved by means of the transport device 1. The control device 7 is used to control the time of processing and the optical deflection unit 4, which is controlled by the control device 7, is used to control the location where the workpiece is processed by means of processing radiation, in order to form the rectilinear, parallel structures shown in FIG. 3.

[0104] It is essential that, in method step B, while the workpiece is processed by means of processing radiation, correction data of the workpiece are acquired by means of the sensors 5 and 6.

[0105] In the present case, the correction data comprise the position data acquired by means of the pose sensor 5 and the movement data of the workpiece 2 acquired by means of the optical tracking sensors 6a of the motion sensor 6.

[0106] Dependent on the correction data, the time of processing and/or the deflection of processing radiation brought about by means of the deflection unit 7 is corrected by means of the control device.

[0107] For example, should the plurality of optical barriers of the pose sensor 5 detect that the leading edge of the workpiece 2 is not perpendicular but at an angle to the transport direction, the time for creating the structures is modified accordingly since, in the case of a workpiece 2 entering the processing region at an angle, only one structure is formed first, followed by an increasing number of structures in order to ensure a uniform distance of the start of the structures from the edge of the workpiece.

[0108] Moreover, the deflection of the laser beam 3a by means of the deflection unit 7 is corrected since the structures must be formed as structures running at an angle in the reference system of the processing device in accordance with the angle, as detected by means of the pose sensor 5, included between the leading edge of the workpiece 2 and the transport direction in order to form structures on the workpiece 2 that run parallel to the side edges or perpendicular to the leading edge of the workpiece 2.

[0109] FIG. 4 shows a second exemplary embodiment of a device according to the invention. Essential elements and functionalities correspond to those of the first exemplary embodiment. Thus, in order to avoid repetition, only the essential differences are discussed below:

[0110] In the device shown in FIG. 4, the pose sensor 5 is in the form of a spatially resolving camera, with a CMOS chip in the present case.

[0111] The deflection unit 4 of the device according to FIG. 4 comprises two galvanometric mirrors which allow a deflection in all the desired spatial directions along the processing plane, with the result that the laser beam 3a can be deflected not only with components perpendicular to the transport direction but likewise with components parallel to the transport direction of the transport device 1.

[0112] In a modification of the exemplary embodiment, use is made of a combination of a polygon mirror wheel and a galvanometer as a deflection unit 4, in order to be able to move the beam particularly quickly parallel to the workpiece and perpendicular to the movement direction. The correction of the movement along the transport direction then resides with the galvanometer while the beam is moved uniformly perpendicular to the transport direction. An advantage of this embodiment lies in the option of being able to realize a particularly large processing field for a large numerical aperture with a very high processing speed.

[0113] Additionally, a focusing apparatus 8 for focusing the laser beam 3a on the processing side of the workpiece 2 located at the top in FIG. 4 is arranged on the deflection unit 4.

[0114] Furthermore, the device according to FIG. 4 comprises a height profile measuring unit 9 for measuring a height profile of the processing side of the workpiece 2.

[0115] Pose sensor 5, focusing apparatus 8 and height profile measuring unit 9 are also connected to the control unit 7.

[0116] In the device depicted in FIG. 4, an image of the processing region can thus be recorded in a continuous sequence by means of the pose sensor 5 in the form of a camera. A leading edge of the workpiece 2 is detected by image analysis. These data thus allow detection of the pose of the workpiece 2 upon entry into the processing region of the device and, in particular, also a detection of an oblique position of the entering leading edge of the workpiece 2 should the latter not be perpendicular to the transport direction of the transport device 1. This enables a correction as already described in relation to exemplary embodiment 1.

[0117] Moreover, the device shown in FIG. 4 allows the pose of the structures created by means of processing radiation to be detected by means of the pose sensor 5. In the present exemplary embodiment, the distance between the structures and the distance from the edges of the workpiece 2 are specified. The distance between the structures and the distance from the edges can be determined by means of image analysis during the structure creation. Should these not correspond to the specified distance values, the deflection of the laser beam by means of the deflection unit 4 is corrected in order to form the correct distances, at least during subsequent processing.

[0118] The device according to FIG. 4 additionally comprises a height profile measuring unit 9. In the present case, the latter is designed to capture a two-dimensional height profile of the workpiece 2. To this end, the height profile measuring unit is designed as a laser triangulation measuring head in the present case.

[0119] The height profile of a workpiece 2 as determined by means of the height profile measuring unit 9 is transmitted to the control device 7 which controls the focusing apparatus 8 accordingly such that the focus is always located at the height at the current location of processing as specified by the height profile and hence always located on the surface of the processing side of the workpiece 2.

[0120] The device according to FIG. 4 additionally comprises the motion sensor array 6 for acquiring movement data, which was already described in relation to FIG. 1. Thus, redundant information is available with regards to the location and the movement of the workpiece 2. Hence, the accuracy when acquiring the characteristic data of the workpiece can be increased by way of correction functions, for example by forming an arithmetic mean.

[0121] In a modification of an exemplary embodiment of a method according to the method, characteristic data are only acquired by means of the pose sensor 5, which acquires position data of the structure created on the workpiece by means of processing radiation, in the present case the position data of the rectilinear cutouts on the workpiece 2 created by means of the laser beam 3a.

[0122] In the exemplary embodiment shown in FIG. 4, the laser beam 3a is deflected on a cylindrical lens 10 by the deflection unit 4. The cylindrical lens 10 is aligned with its cylinder axis transverse to the transport direction. The use of a cylindrical lens allows the formation of particularly narrow structures, in particular narrow lines parallel to the cylinder axis of the cylindrical lens. The cylindrical lens 10 has a particularly short focal length, approximately 150 mm in the present case, and can thus be particularly advantageously combined with the transport system since, as a result of the movement of the workpiece, only a small movement of the beam in the transport direction needs to be ensured. Since the area to be processed is not restricted along the transport direction, very small structures can be realized on a large area. The distance between cylindrical lens 10 and workpiece 2 is in the range of between 1 cm and 5 cm.

LIST OF REFERENCE SIGNS

[0123] 1 Transport device

[0124] 2 Workpiece

[0125] 3 Radiation source

[0126] 3a Laser beam

[0127] 4, 4 Deflection unit

[0128] 5, 5 Pose sensor

[0129] 6 Motion sensor array

[0130] 6a Optical tracking sensors

[0131] 7 Control device

[0132] 8 Focusing apparatus

[0133] 9 Height profile measuring unit

[0134] 10 Cylindrical lens