DEVICE AND METHOD FOR ELECTROLYTIC TREATMENT OF SUBSTRATES

Abstract

The invention provides a system for electrolytic treatment of vertically oriented substrates. The system may include an elongated bath for electrolytic liquid, a conveyor for conveying substrates to be treated electrolytically, vertically oriented and suspended from the conveyor, in a transport direction according to a horizontal transport path through an electrolytic liquid in the bath, the conveyor being arranged for clamping the substrates near a top thereof during conveyance of the substrates through the electrolytic liquid in the bath. The system may further include a number of flow devices each with at least one discharge orifice in the bath, the discharge orifices being directed in a discharge direction that extends opposite to the transport direction for creating a flow of electrolytic liquid, with a flow direction that is opposite to the transport direction, in the electrolytic liquid along at least one longitudinal side of substrates suspended from the conveyor.

Claims

1. A system for electrolytic treatment of vertically oriented substrates, comprising an elongated bath for electrolytic liquid, a conveyor for conveying substrates to be treated electrolytically, vertically oriented and suspended from the conveyor, in a transport direction according to a horizontal transport path through an electrolytic liquid in the bath, the conveyor being arranged for clamping the substrates near a top thereof during conveyance of the substrates through the electrolytic liquid in the bath, and a number of flow devices each with at least one discharge orifice in the bath, said discharge orifices being directed in a discharge direction that extends opposite to the transport direction to create a flow of electrolytic liquid with a flow direction that is opposite to the transport direction in the electrolytic liquid along at least one longitudinal side of substrates suspended from the conveyor.

2. The system according to claim 1, further comprising at least one substrate suspended from the conveyor, wherein the flow devices are arranged for creating a flow of electrolytic liquid with a flow direction that is opposite to the transport direction in the electrolytic liquid along the full dimension of the at least one substrate seen in the transport direction.

3. The system according to claim 1, wherein the flow devices are arranged for creating flow of electrolytic liquid with a flow direction that is opposite to the transport direction in the electrolytic liquid over a distance which is at least equal to 90% of the length of the bath.

4. The system according to claim 1, wherein the conveyor is arranged for conveying substrates over the full length of the bath from an end of the bath to an opposite end of the bath.

5. The system according to claim 1, wherein the discharge orifices are provided seen in top view on two opposite sides of the transport path for creating the flow of electrolytic liquid along two opposite sides.

6. The system according to claim 1, wherein at least two of the number of discharge orifices form at least one row.

7. (canceled)

8. (canceled)

9. (canceled)

10. The system according to claim 1, wherein the system comprises at least one tank for electrolytic liquid, said at least one tank being installed outside the bath and the flow devices being connected to one tank of the at least one tank via supply lines that extend via a passage in a wall or the bottom of the bath.

11. (canceled)

12. (canceled)

13. (canceled)

14. The system according to claim 1, wherein each flow device is provided with not more than one discharge orifice.

15. The system according to claim 1, wherein the flow devices are eductors.

16. The system according to claim 1, wherein the system comprises at least one guide body for guiding, in the direction of the substrates, electrolytic liquid that flows in respective flow directions from discharge orifices.

17. (canceled)

18. (canceled)

19. (canceled)

20. (canceled)

21. (canceled)

22. The system according to claim 1, wherein the conveyor is arranged for clamping substrates to be treated electrolytically near a top thereof during transport of the substrates through the electrolytic liquid in the bath.

23. The system according to claim 1, wherein the bath is provided with a receiving space that is positioned directly under the transport path for receiving substrates or parts thereof that come loose from the conveyor during transport of the substrates.

24. (canceled)

25. (canceled)

26. The system according to claim 1, wherein the system comprises two or more baths which are aligned with each other, the conveyor being arranged for conveying the substrates successively through electrolytic fluid in each of the baths according to a straight transport path.

27. A method for electrolytic treatment of vertically oriented substrates when using a system according to one of the preceding claims, comprising the steps of conveying in a horizontal transport direction, by means of a conveyor, vertically oriented substrates suspended from the conveyor through an electrolytic liquid in an elongated bath for electrolytic liquid while the substrates are clamped near a top thereof by the conveyor during said conveyance; and creating in the bath, from at least one discharge orifice, a flow of electrolytic liquid along at least one longitudinal side of the substrates suspended from the conveyor, said flow having a flow direction that is opposite to the transport direction, electrolytic treatment of the substrates in the electrolytic liquid during transport of the substrates.

28. The method according to claim 27, wherein the created flow has a flow direction that is opposite to the transport direction over a distance which is at least equal to the full dimension of a substrate seen in the transport direction.

29. (canceled)

30. The method according to claim 27, wherein the substrates are conveyed over the full length of the bath from an end of the bath to an opposite end of the bath.

31. The method according to claim 27, wherein the magnitude of the speed difference between the substrates and the flow is between 10 metres per minute (m/min) and 40 metres per minute (m/min).

32. The method according to claim 27, wherein the speed of the substrates is between 5 metres per minute (m/min) and 10 metres per minute (m/min).

33. The method according to claim 27, wherein during the electrolytic treatment there is an average current density on the substrate of at least 30 amperes per square decimetre (A/dm.sup.2).

34. (canceled)

35. (canceled)

36. The method according to claim 27, wherein a bottom of a receiving space of the bath is located at a distance below undersides of substrates suspended from the conveyor, said distance being greater than the vertical dimension of the substrates suspended from the conveyor.

37. (canceled)

Description

[0045] The invention is explained in more detail hereunder on the basis of a possible embodiment of a system according to the invention that is suitable for carrying out the method according to the invention, referring to the following figures

[0046] FIG. 1 shows a system according to the invention in vertical cross-section;

[0047] FIG. 2 shows the system according to FIG. 1 in top view;

[0048] FIG. 3 shows schematically a part of the system in side view;

[0049] FIG. 4 shows schematically a part of the system in another side view:

[0050] FIG. 5 shows schematically a part of the system in top view.

[0051] System 1 for continuous electrolytic treatment of individual substrates 2 comprises an elongated bath 3 with electrolytic liquid 4 therein with for example copper ions, which are dissolved in the electrolytic liquid 4 from metal, for example spherical, present in anode baskets 8 and which are intended to be deposited on account of the electrolytic treatment on the substrates 2, more specifically on tracks thereon, to form a copper layer thereon. The substrates 2 are for example glass-like, such as of silicon, and are each plate-shaped, for example square, wherein the sides each have a length that is between 125 mm and 210 mm.

[0052] The longitudinal direction of the elongated bath 3 extends in horizontal direction perpendicular to the plane of the drawing according to FIG. 1. The system 1 comprises a conveyor 5 for continuously conveying the substrates 2 in a horizontal transport direction 9 following a transport path 10 in the longitudinal direction of the bath 3 from a first end of the bath 3 on the right side of FIG. 2 to a second end of the bath, opposite to the first end, on the left side of FIG. 2 through the electrolytic liquid in the bath 3. During normal operation the speed of the conveyance of the substrates 2 is constant. The conveyor 5 comprises an endless strip 6 that is wrapped around two deflection pulleys, which are provided at opposite ends of the bath 3. The conveyor 5 further comprises clamps 7, which are connected to the strip 6 at a regular distance from each other and are arranged to clamp the substrates 5, in practice at a regular distance from each other, each against the strip 6 near the upper sides of the substrates 2. The substrates 2 are thus conveyed suspended from the strip 6 leaving both longitudinal sides thereof free to be approached by metal ions in the electrolytic fluid within the bath 3 thus for the electrolytic treatment while the electrolytic fluid flows in the opposite direction with respect tot the transport directions 9, so in counterflow, as will be further explained in the following

[0053] Bath 3 has side walls 11a, 11b opposite each other and a bottom 12. The bottom 12 comprises a recessed portion, which in use serves as a receiving space 13 for substrates 2 or parts thereof that come loose from the conveyor 5 unexpectedly. Receiving space 13 extends over the full length of the bath 3 and has side walls 14a, 14b opposite each other and a bottom 15. The distance between the bottom 15 and the underside of a substrate 2 suspended from the conveyor 5 is greater than the height of the substrate 2, so that even if a substrate 2 were to come loose completely from the conveyor 5 and sink under the effect of gravity into the receiving space 13, this substrate 2 that has come loose would not end up in the path of upstream substrates 2 suspended from the conveyor 5. Bath 3 is provided at aforementioned first and second ends thereof with transverse walls which each join with ends of the longitudinal walls 11a, 11b, 14a, 14b and bottoms 12, 15. In each of these transverse walls vertical slits are provided through which substrates 2 enter the bath 3 at the first end thereof and exit the bath 3 at the second end thereof during conveyance of the substrates 2, thus creating a reservoir of electrolytic fluid within bath 3 for conveying the substrate 2 through this electrolytic liquid.

[0054] On the outer sides of each of the side walls 11a, 11b there are overflow spaces 21a, 21b. Electrolytic liquid 4 can flow via openings 22a, 22b in the side walls 11a, 11b into these overflow spaces 21a, 21b. Thus, the lower edges 23a, 23b of the openings 22a, 22b, said edges 23a, 23b being located at the same vertical level, largely determine, when using system 1, the level of the electrolytic liquid 4 in bath 3. At the outer sides of aforementioned transverse walls also overflow spaces have been provided for electrolytic fluid flowing from the bath 3 through the vertical slits therein.

[0055] The overflow spaces 21a, 21b are in communication via lines 31a, 31b with buffer system 32 for electrolytic liquid. The electrolytic liquid is conditioned in buffer system 32 so that it is again suitable to be returned to the bath 3. For this purpose, the electrolytic liquid is for example filtered and heated in the buffer system 32. For the purpose of supplying electrolytic liquid from the buffer system 32 to the bath 3, supply lines 34, 35a, 36a, 35b, 36b are provided, in which pump 33 is incorporated. The supply lines 35a, 35b extend through bottom 15 and open at their upper ends into respective collecting lines 37a, 37b, which also extend vertically.

[0056] The collecting lines 37a, 37b each form part of a flow device 38a, 38b, which, viewed in the transport direction 9, are provided in the bath 3 at a regular distance from each other, for example at a distance of between 40 cm and 90 cm, such as 60 cm, and on either side of the substrates 2. Uniformly distributed over the length of the collecting lines 37a, 37b, each flow device 38a, 38b is provided with three eductors 39. Each eductor 39 thus forms part of a vertical row of three eductors 39 but also of a horizontal row of eductors 39, extending parallel to the transport direction 9, the number of which is related to the length of the bath 3.

[0057] Referring to FIG. 3, in which for clarity the guide plate 51a (FIG. 4), yet to be discussed further, is not shown, the eductors 39 are substantially cylindrical in shape and they each have a discharge orifice 40, directed in a direction opposite to the transport direction 9. In addition, each of the eductors 39 has a constricted intake 41 and between said intake 41 and the associated discharge orifice 40, a number of suction openings 42, which are uniformly distributed over the perimeter of tubular shape of the eductors 39. In use, the constricted intake 41 of each eductor 39 will greatly increase the speed of the electrolytic liquid, as supplied by pump 33 to the constricted intake 41, on the exit side of the intake 41. Through the Venturi effect, this increased speed of the electrolytic liquid through the associated suction openings 42 will have a suction action on electrolytic liquid 4 in the bath 3 so that finally the volume flow of electrolytic liquid flowing from discharge orifice 40 is up to five times higher than the volume flow through the constricted intake 41.

[0058] The eductors 39 extend within the height of the passing substrates 2 so that the substrates 2 are to a large extent exposed uniformly to the action of the eductors 39. Between the flow devices 38a, 38b and the substrates 2, the system further comprises substantially plate-shaped guide bodies 51a, 51b, which extend parallel to the substrates 2 and thus to the transport direction 9. In the guide bodies 51a, 51b, elongated, vertically oriented openings 52 are provided, which are separated from each other by bridge parts 53 of the guide bodies 51a, 51b. The eductors 39 extend within the length of the openings 52. In horizontal cross-section, the bridge parts 53 have a rectangular shape but alternatively shaped cross-sections are also possible, such as diamond-shaped cross-sections as shown in FIG. 5 for bridge parts 53 for alternative guide bodies 51a and 51b. In FIG. 5, the same reference numbers are used as in the preceding figures. If the components are different, a prime is added to the respective reference number. It can clearly be seen in FIG. 5 that each guide passage has a peripheral edge 58, of which, viewed in the transport direction 9, the side facing the substrate 2 is located at the front of the side turned away from the substrate 2.

[0059] Guide bodies 51a, 51b contribute to a part of the electrolytic liquid such as that from the discharge orifices 40 of the eductors 39 being led according to arrows 55 along the substrates 2, so that in the immediate vicinity of the substrates 2 there is a relatively high volume flow of electrolytic liquid, in a direction opposite to the transport direction 9. Thus, the renewal rate of electrolytic liquid near the substrates 2 is relatively high, so that an increased deposition rate of the respective metal ions from the electrolytic liquid onto the substrates 2 can take place.

[0060] At the level of the undersides of the substrates 2, the guide bodies 51a, 51b are each provided with guide edges 46a, 46b directed towards each other. Between the guide edges 46a, 46b there is a gap, the width of which is just sufficient for the substrates 2 to be conveyed through without contact. The guide edges 46a. 46b thereby contribute to the substrates 2 maintaining a vertical orientation during transport.

[0061] When using system 1 (or 1), the substrates 2 are transported through the electrolytic liquid 4 by conveyor 5 with a transport speed between 5 metres per minute and 10 metres per minute. The speed difference between the substrates 2 on the one hand and the electrolytic liquid, in so far as in the direct vicinity of the substrates 2, may however be significantly greater, for example between 10 metres per minute and 40 metres per minute, owing to the stream of electrolytic liquid 3 that is generated by eductors 39. In this way, relatively high deposition rates can be reached, such as at least 10 micrometres per minute in electrodeposition of copper and at least 20 micrometres per minute in electrodeposition of tin. The total length of the bath 3 is typically between approx. 7.2 metres and 16.8 metres, wherein the bath may be made up from a number of interconnecting bath segments each with a length of for example 2.4 metres. It can easily be calculated from the above data that the total residence time of the substrates 2 in the bath 3 is typically between approx. 0.72 minutes and 3.36 minutes. The counterflow as created by the flow devices 38a, 38b is such that the distance over which the counterflow extends within bath 3 is almost equal to, so at least 90% of, the length of the bath 3 and in any case longer the dimension of each of the pate-shaped substrates 2 seen in the transport direction 9.

[0062] Although the invention has been described above referring to an embodiment of a system having a single bath 3, in other embodiments a system may have more than one, for instance four, baths such as bath 3, which baths are aligned with each other. In such a system the conveyor conveys the substrates successively according to a straight transport path through each of those baths, the electrolytic fluids in each of those baths being in counterflow with respect to the transport direction. The system would have a single overflow space from which each bath is fed with electrolytic fluid and to which electrolytic fluid flowing over the respective overflow edges of each bath would flow.

[0063] In order to show that the process according to the invention achieves one or more of the aforementioned aims, experiments have been carried out. Examples 1a and 1b were carried out according to the prior art with continuous electrolytic deposition on substrates from an electrolytic bath with supply of electrolytic liquid by means of a supply pipe that discharges into the bath under the substrates, wherein there is no question of counterflow. Examples 2a and 2b were carried out according to the present invention with continuous electrolytic deposition on substrates from an electrolytic bath with supply of electrolytic liquid by means of counterflow. As will be seen from the following examples, one or more of the aims of the invention are obtained with the present process.

EXAMPLES

Comparative Example 1

[0064] A continuous electrolytic deposition line for solar cells, as described in WO 2009/126021 A2, is used, comprising elongated baths for electrolytic processes, wherein first copper was deposited by vacuum deposition to a thickness of 150 nanometres on the surface of a silicon-based substrate (i.e. M6 format (166166 mm) silicon solar cells), after which an insulating mask was applied by printing to obtain copper tracks.

[0065] A number of substrates provided with tracks were suspended in an electrolytic liquid. This electrolytic liquid was prepared from copper sulphate (220 g/l CuSO.sub.4 5H.sub.2O), sulphuric acid (100 g/l H.sub.2SO.sub.4 (96%)), hydrochloric acid (70 mg/l HCl (36%)) and an additive that is known in the art and that is used to ensure good growth of the copper layer (60 m/l S-691 high speed copper additive (Sytron Pte Ltd)). The electrolytic liquid was brought to a temperature between 35 and 40 C. and the substrates were moved at a speed of 5 m/min through the electrolytic liquid.

[0066] A current density of 14 A/dm.sup.2 (deposition rate of 3.1 micrometres per minute) was used in Example 1a, and a current density of 18 A/dm.sup.2 (deposition rate of 4 micrometres per minute) in Example 1b, to obtain a substrate provided with a copper layer on the tracks with a total copper layer thickness of about 26 micrometres, to which the deposition time is adjusted. A higher current density gives a shorter deposition time to obtain the same layer thickness. The thickness, shape and roughness of the tracks provided with copper were determined visually using a 3D laser microscope, evaluating whether the tracks obtained are flat and smooth.

[0067] As can be seen in Table 1, a current density of 14 A/dm.sup.2 (example 1a) gives the desired flat, smooth contact fingers, whereas increasing the current density to 18 A/dm.sup.2 (example 1b) gives tracks wherein the edges are 25-30% thicker than in the middle because nodules have formed on the edges. It can be seen from this example that a speed difference of about 5 m/min between the substrates and the electrolytic liquid is insufficient to deposit electrolytic copper at a speed of 4 micrometres per minute or higher.

Example 2 According to the Invention

[0068] This example was carried out in the same way as in example 1, with the following adjustments. The tests were carried out in a continuous electrolytic deposition line for solar cells, as in example 1, wherein in these baths the electrolytic liquid is supplied by means of a row of three eductors placed vertically above one another on either side of the solar cell, as shown in FIGS. 1 to 3.

[0069] The substrates, solar cells of M2 format (156.75156.75 mm), were moved at a speed of 1.5 m/min through the electrolytic liquid.

[0070] A current density of 50 A/dm.sup.2 (deposition rate of 11.1 micrometres per minute) was used in Example 2a and a current density of 60 A/dm.sup.2 (deposition rate of 13.3 micrometres per minute) in Example 2b, to obtain a substrate provided with a copper layer on the tracks with a total copper layer thickness of about 20 micrometres, to which the deposition time is adjusted. The thickness, shape and roughness of the tracks provided with copper were determined visually using a 3D laser microscope, evaluating whether the tracks obtained are flat and smooth.

[0071] As can be seen in Table 1, smooth, flat substrates are obtained for current densities that are much greater than in Example 1. It can be seen from this example that a speed difference of about 20 m/min between the substrates and the electrolytic liquid (calculated speed difference based on flow rate of liquid and throughput speed of substrates) is sufficient to deposit electrolytic copper at a speed of up to 13 micrometres per minute. It can be seen from this that for Example 1 at higher current density, the surface is unevenly nodular with an excessive percentage deviation (<20%).

TABLE-US-00001 TABLE 1 Test overview Current Deposition Ex. density rate Visual Deviation Ra No. (A/dm.sup.2) (m/min) assessment (%) (m) 1a 14 3.1 Flat/smooth 17 1.1 1b 18 4 Uneven/nodular 21 1.9 2a 50 11.1 Flat/smooth 11 0.8 2b 60 13.3 Flat/smooth 5 0.5

[0072] Although the invention is explained above on the basis of an embodiment example wherein it is a question of electrodeposition, the invention may also be applied suitably with other types of electrolytic treatments of substrates, such as etching, cleaning and polishing of substrates.