Abstract
The invention relates to a method for marking wafers, in particular wafers for solar cell production: The method comprises the steps of manufacturing a position line (21a, 21b, 21c) on a peripheral surface of a silicon ingot or column, the ingot or column extending in an axial direction and having a longitudinal axis in the axial direction, wherein the position line extends in the axial direction along substantially the whole ingot or column and is inclined with respect to the longitudinal axis. By this position line it is possible to determine the position of a wafer cut from the ingot or column within the ingot or column, respectively. Further, an individual identification pattern (20a, 20b, 20c) of lines on the peripheral surface of the silicon ingot or column is manufactured, the individual identification pattern of lines extending in axial direction over substantially the whole ingot or column and providing an individual coding which allows to identify the silicon ingot or column.
Claims
1. Method of manufacturing silicon wafers comprising the steps of: texturing, doping and diffusion treating a wafer to produce characteristic semiconductor properties, reading an individual identification pattern comprising a number of lines on the peripheral edge of the wafer to identify the ingot or column the wafer was cut from, and reading a marking having a position line on the peripheral edge of the wafer which is inclined with respect to a longitudinal line of an ingot or column the wafer was cut from to identify the position of the wafer within the ingot or column, wherein the individual identification pattern of lines comprises a plurality of parallel lines which are distanced from each other, the lines being of different depth and wherein the individual identification pattern is provided by an individual sequence of depths of the plurality of lines, wherein the ingot or column comprises a first axial section and a second axial section extending axially along the ingot or column, wherein the first axial section comprises a first identification pattern at an upper region of the ingot or column and a first inclined position line at a lower region of the ingot or column, and wherein the second axial section comprises a second identification pattern at the lower region and a second inclined position line at the upper region.
2. Method according to the claim 1, further comprising the step of slicing the ingot or column into a number of wafers and marking the ingot or column, wherein the marking step is done before the slicing step.
3. Method according to claim 1, further comprising the steps of squaring the ingot or column by cutting it in an axial direction and marking the ingot or column on at least one of the flattened surfaces provided by the squaring process.
4. Method according to claim 1, wherein a stack of marked wafers is read out in whole.
5. Method according to claim 1, wherein the marking is used for precise adjustment of the placement or orientation of the wafer.
Description
(1) The invention will be further explained by way of exemplary preferred embodiments referring to the attached drawings.
(2) FIG. 1: shows an example for a solar cell production process incorporating the invention.
(3) FIG. 1a: shows an example for an inner process step according to FIG. 1.
(4) FIG. 2: shows an example for a one-side marking of an ingot.
(5) FIG. 3: shows a marking in three axial surface sections with variations of the marking code.
(6) FIGS. 4a-c: show different variations of the marking code.
(7) FIG. 5: shows an embodiment with three axial marking sections and an interference between the first two sections.
(8) FIG. 6: shows an example of the coding of the individual identification pattern.
(9) FIG. 6a: shows a detail of the coding of the individual identification pattern according to FIG. 6.
(10) FIG. 7: shows a schematical arrangement of the position line demonstrating the geometrical conditions to calculate the original position of a wafer.
(11) FIG. 8: shows a schematical top view of a wafer having four marking areas.
(12) FIG. 9: shows a schematic top view onto a wafer having to marking areas and moving through a reading device.
(13) FIG. 10: shows a schematic cross sectional view of a wafer wherein in the individual pattern, an individual sequence of depths of the plurality of lines is shown.
(14) Referring first to FIG. 1, the production of solar cells starts with producing of an ingot in step 1 and squaring this ingot by performing cuts in an axial direction in step two.
(15) After step 2 the squared ingots may be marked in a marking step 2a using a marking method according to the invention.
(16) Hereafter, in a further production step 3, the squared ingots are grinded and hereafter, as an alternative to step 2a, the grinded ingots may be marked in a step 3a.
(17) Hereafter, an optional block labelling may take place as step 4.
(18) After these steps the ingot is prepared and sawed to slice the ingot into a plurality of wafers in step 5.
(19) Step 5 and all subsequent steps of the manufacturing process may include an input reading step 5a to identify the wafer, a manufacturing process 5b like sawing or washing or the like and an output reading step 5c to identify the wafer after the process 5b has been conducted.
(20) Following the slicing step 5, a number of subsequent steps like washing and post-preparation, testing and sorting, texturing, doping, diffusion, surface cleaning, anti-reflex-deposition, printing, firing, edge isolation, testing and sorting, tabbing and stringing, layup, lamination, flashing, and module labelling
can be conducted to produce the solar cell in its desired configuration and as a subsequent final step a custom read-out will be done in step 6.
(21) Referring to FIG. 2, an ingot 10 is squared to have a front surface 15 and an end surface 16 and number of four side surfaces extending in longitudinal direction, wherein side surface 11 is prepared to be marked.
(22) FIG. 3 shows an example of marking in different sections on the marking side. A first marking section 11a is followed by a second marking section 11b and a third marking section 11c. In marking section 11a an individual identification pattern 20a is arranged in the upper region of the section. In the lower region of the section, an inclined position line 21a is present. The position of each wafer cut from this marking section 11a can be calculated by measuring the distance between the bottom code line of the individual identification pattern and the inclined position line at the start of the section based on a known distance 22 between these two lines and a known inclination angle of the position line.
(23) In marking section 11b the individual identification pattern 20b is arranged in the lower region of the section and an inclined position line 21b is arranged in the upper region of the section and is inclined in a different angle when compared to position line 21a. By this, any interference between the markings in marking section 11a and those in marking section 11b can be avoided.
(24) Consequently, in marking section 11c the individual identification pattern 20c is positioned in the upper region and the inclined position line 21c in the lower region of the marking section.
(25) FIGS. 4a-c show examples of further variations of the position line and the individual identification patterns. In FIG. 4a an individual identification pattern serving as a coding to identify the ingot or column is arranged in the upper region of the marking section and two position lines inclined in contrary angles to each other 121, 122 are present in the lower region of the section.
(26) In FIG. 4b a first part 220 of the individual identification pattern is arranged in the upper region of the section and a second part 223 of the individual identification pattern is arranged in the lower region of the section. Between these two parts of the individual identification pattern 220, 223 two position lines 221, 222 which are inclined in a contrary angle to each other are present.
(27) FIG. 4c demonstrates on the left side a similar arrangement having two parts of individual identification pattern 320, 323 in the upper and lower region of the marking section and inclined position lines 321, 322 extending over the whole section. The individual identification pattern parts 320 323 in the upper and lower region are not further present in the right hand side of the section and instead there is provided one single individual identification pattern 324 in the middle region. The patterns 320, 323 on the left hand side and the pattern 324 on the right hand side overlap in the central axial region of the section and by its arrangement do not interfere with the inclined position lines 321, 322.
(28) FIG. 5 shows another example of markings in axial surface sections. In a first axial section 411a an individual identification pattern 420a is arranged in the upper region and an inclined position line 421a in the lower region. Adjacent to this first axial section a second axial section 411b is arranged having an individual identification pattern 420b in the lower region and an inclined position line 421b in the upper region. The individual identification pattern 420a extends a small amount in the second axial section 411b and the individual identification pattern 420b extends a small amount in the first axial section 411a. In the same way, the inclined position line 421a extends a small amount in the second axial section 411b and the inclined position line 421b extends a small amount in the first axial section 411a. By this, it is assured that a reading of the markings can be performed independently of the position of the slicing cut and each wafer can be determined with regard to its origin ingot and its position in the origin ingot.
(29) FIG. 6 shows schematically an example of an individual identification pattern based on a matrix pattern which is a grid line pattern with lines shown to basis 16. Only those lines shown in continuous lines are marked whereas the lines shown in dotted lines are not marked. As shown in this example, place no. 1 corresponding to 4 and place no. 2 corresponding to 7 are marked in this example. The coding comprises a number of six matrix pattern fields 20a-f (N=6). Each matrix pattern field comprises a total of sixteen lines (M=16). The position of each line is predetermined and the position of each line is depicted in dotted lines in FIGS. 6 and 6a. Only one line is manufactured in each matrix pattern field and this line is depicted as continuous line in FIGS. 6, 6a. Thus, it can be seen that in the matrix pattern fields 20b and 20c the second line and the seventh line, respectively, are manufactured in the coding scheme shown in FIGS. 6, 6a, thus only six lines have to be manufactured to provide an individual coding and thus 16.777.215,00 different individual codings can be manufactured with this coding scheme.
(30) FIG. 7 schematically shows the calculation of the position of a wafer in an ingot using the position line. A position line 21 is provided at a predetermined inclined angle. A first wafer (not shown) has a known distance 61 between the position line 21 and a base line 60. Wafer no. N40 is positioned in such a positioned in such a position where the distance between the position line 21 and the base line 60 is X1. A second wafer 41 is positioned such that the distance between position line 21 and base line 60 is X2. Between the wafers 40 and 41a curve loss 50 is present which is a result of the slicing process. As will be apparent to the skilled person, the position of each wafer in the ingot can be calculated when knowing the distance 61 of the first wafer, the angle of inclination of the position line 21, the thickness of the wafers and the curved loss by measuring the distance between the position line 21 and the base line 60 for the wafer which position is sought for.
(31) FIG. 8 shows a top view onto a wafer which has been marked on each of the four flattened sides. As it is schematically shown, the arrangement of the markings in the different marking areas 511, 512, 513, 514 is different, thus producing an asymmetrical coding which allows to define and determine a crystal orientation 570 of the wafer.
(32) It should be noted, that the number of marked surfaces can be more or less than four, too. In particular applications, markings may be applied to other surfaces, e.g. to all eight surfaces of an octagonal shape.
(33) Further, in FIG. 9 a top view of a wafer 740 if shown having two marking areas 612, 614 being arranged on opposed peripheral sides of the wafer. The wafer 740 is moving in a direction 740a and thus passes reading devices 700, 701 which are adapted to read the codings in marking areas 612, 614, respectively. By this, simultaneous reading of the codings in the marking area 612 and 614 and be conducted and thus read errors and read failures can be minimized.
