WO2008145229A2

WO2008145229A2 - Method for the treatment of flat substrates, and use of said method

Info

Publication number: WO2008145229A2
Application number: PCT/EP2008/003079
Authority: WO
Inventors: Christian Schmid; Jörg LAMPPRECHT
Original assignee: Gebr. Schmid Gmbh
Priority date: 2007-05-25
Filing date: 2008-04-17
Publication date: 2008-12-04
Also published as: WO2008145229A3; TW200913031A; DE102007026082A1

Abstract

The aim of the invention is to make it easier to process flat substrates such as printed circuit boards or silicon wafers (3) with processing liquid (14) in a horizontal run through a processing device (1). Said aim is achieved by admixing ozone (O3) to the processing liquid (14) in a step of the disclosed method, thus allowing a resist to be more easily removed from printed circuit boards or silicon wafers (3) for solar cells to be more thoroughly cleaned, for example.

Description

description

Method for the treatment of flat substrates and use of the method

Field of application and state of the art

The invention relates to a method for the treatment of flat substrates in a horizontal passage through a treatment device, various uses of such a method as well as printed circuit boards or silicon wafers treated therewith.

It is known to use ozone in many ways because of its strong oxidizing effect, for example in the treatment of drinking water and wastewater, air purification or sterilization in medical technology. One of the key benefits of ozone is its good environmental performance, rapid degradation in the atmosphere, and relatively easy to produce compared to other highly oxidizing chemicals.

Task and solution

The invention has for its object to provide an aforementioned method and applications mentioned above, with which problems of the prior art can be avoided and in particular a treatment of flat substrates, such as printed circuit boards or solar cell wafers can be done in a novel way.

This object is achieved by a method with the features of claim 1 and uses with the features of claims 8, 9, 11, 13, 14, 18 or 19 and a printed circuit board with the features of claim 21 or a silicon wafer with the features of the claim 22. Advantageous and preferred embodiments of the invention are the subject matter of the further claims and will be described below. explained in more detail. Some of the features listed below are explained only once. However, they should be able to apply to both the process and the uses or the printed circuit boards or the silicon wafers independently. The wording of the claims is incorporated herein by express reference. Furthermore, the wording of the priority application DE 102007026082.4 of May 25, 2007 of the same Applicant is incorporated by express reference into the content of the present description.

According to the invention, it is provided that the substrates are guided or transported in the horizontal passage through a corresponding treatment device. In this case, at least one side of the substrates is wetted with treatment liquid or applied to this side. According to the invention, the treatment liquid is admixed with ozone or contains ozone in a certain concentration. Thus, in addition to the effect that the treatment liquid per se has on the substrate or its surface, the admixed ozone may enhance this effect or may independently act to properly treat the substrate. The individual possibilities, which effect the ozone can have on different substrates or surfaces of the substrates, will be explained in more detail later on the individual uses.

Advantageously, the ozone of the treatment liquid can be mixed in gaseous form. This has the advantage that the ozone can be generated most easily gaseous and also, especially in water-based treatment liquids, can be mixed well in gaseous form.

In a further embodiment of the invention, it is advantageously provided that the ozone is generated directly at the treatment device or in close proximity thereto. For this purpose, an appropriate generation be provided as known to those skilled in the art as an ozone generator, for example by a high voltage generator. This can be part of the treatment device in a treatment device or device according to the invention for carrying out the method. The advantage of using ozone in comparison to other strongly oxidizing chemicals is that long transport paths to a treatment chamber of the treatment device or of another mixing device in which the ozone of the treatment liquid is admixed can then be dispensed with.

The ozone can be generated either from ambient air or advantageously from an oxygen supply. The advantage of generating from the ambient air is that then a corresponding oxygen supply or the like. can be omitted. To provide an oxygen supply is advantageous because then can operate much more efficient due to the significantly higher oxygen content than in the ambient air of the ozone generator itself.

Preferably, a mixing device is provided, with which the ozone of the treatment liquid is mixed. For this purpose, the treatment liquid can be brought out of the treatment device, that is led out in a separate circuit. In an advantageous static mixer, the ozone is added, for example, blown or introduced directly in the gaseous state.

In a further embodiment of the invention, the treatment device may have a tank for a larger amount of treatment liquid. The treatment liquid can be removed from the tank for ozone addition and brought into the aforementioned mixing device for ozone addition. A degassing of the treatment liquid can advantageously take place on the tank, ie, escaping gas can be sucked off. It can also be provided that after admixing of ozone, the treatment liquid is introduced back into the tank, and then such degassing or tank extraction is particularly advantageous. By means of, for example, a feed pipe for this, possibly also with nozzles or injectors, which is arranged below a liquid level in the tank, the mixing of the ozone with the treatment liquid can be additionally supported. The path of the ozone or ozone gas bubbles through the treatment liquid to the surface should be as long as possible for improved ozone uptake of the treatment liquid.

As an alternative or in addition to a previously described suction of the tank, an extraction may be provided on a treatment chamber of the treatment device. Thus, a release of ozone into the environment can be prevented, which reduces the air pollution, especially for workers.

In an embodiment of the invention can be provided that the treatment liquid is circulated in a kind of cycle, between a tank, a treatment chamber of the treatment device, in which the substrates are used with the treatment liquid, and a receptacle or the like., Which are advantageous in the lower Area of the treatment chamber is located.

There are several ways to determine the concentration of ozone in the treatment fluid. On the one hand, the concentration in the aforementioned treatment chamber or receptacle can be measured. Since usually a pump is provided for supplying treatment liquid in the receiving trough or in the treatment chamber, a measurement of the concentration before the pump or behind the pump can take place. Based on the measured ozone concentration, the ozone production or the admixture of ozone in the treatment liquid can be controlled. It can the Ozone production to be adjusted to the ozone demand. Depending on the desired use, a different ozone concentration may be provided for this purpose.

In an embodiment of the invention, it is possible that a treatment liquid is cooled. Such cooling can even be done at room temperature. By adding ozone, the effect of the treatment liquid can be enhanced. Furthermore, by cooling the treatment liquid, the half-life of the ozone is prolonged, so that it lasts longer in the treatment liquid, is less degraded and thus less ozone must be generated in total or the recoverable ozone concentration can be increased.

The ozone concentration in the treatment liquid may vary depending on the use. An ozone concentration between 2 ppm and 30 ppm is considered advantageous, more preferably between 5 ppm and 10 ppm.

One of the possible uses of a method according to the invention described above is that a resist or photoresist is removed by a stripping process from a printed circuit board as a substrate. Particularly advantageously, the method can be used according to a so-called pattern plating process. Thus, those areas of a resist can be removed, which are partially enclosed or overlapped by a subsequently applied copper structure. Since an ozone-containing corresponding treatment liquid has the effect that organic materials such as the resist are attacked very strongly and can be dissolved in gaseous components, so the removal of the resist is particularly well possible. Thus, a removal even in partially closed cavities, as can occur in a pattern plating process, very effectively and without residue. A further use according to the invention is relatively simple in that printed circuit boards are cleaned. Again, the strong effect of an ozone-containing treatment liquid on organic impurities such as residues of resist or the like can be advantageous. be used.

A further use according to the invention provides, in the case of multilayer printed circuit boards after drilling, to clean the boreholes by means of a method according to the invention with ozone-containing treatment liquid from resin smearing by drilling. In the following processes, for example, the inner layers can be connected to the borehole sleeves in an electrically conductive manner by copper coating without any defects. This so-called desmear process is carried out in the prior art with potassium permanganate at high temperature, but can be carried out considerably better according to the invention with an ozone-containing treatment liquid.

Yet another use according to an inventive aspect provides that substrates, in particular printed circuit boards, are treated before being coated with ozone-containing treatment liquid for surface activation. As a result, an improvement in the adhesion or an improvement in the wettability of the surface of the substrates can be achieved.

A further use according to the invention provides for structuring of printed circuit board base material, for example resin or polyimide film, before lamination processes or before electroless metallization, for example with a so-called chemical copper process. For printed circuit boards manufactured by a so-called Semi-additive (SAP) or Secondary Build-Up (SBU) process, the base material surface must be prepared for adhesion improvement prior to the application of a new conductive layer by a patterning process. This creates a microrough surface. Usual For example, in the case of glass-fiber-reinforced epoxy material or resin-coated copper (RCC), driving is currently a potassium permanganate process and polyimide is a plasma process. According to the invention, these processes can be carried out considerably better with an ozone-containing treatment liquid according to a method described above.

Yet another use according to an inventive aspect provides for structuring the free copper surface of printed circuit boards prior to lamination processes. Before laminating individual inner layers to form a multilayer printed circuit board, the copper surface is structured or prepared to improve adhesion. In the prior art, special wet-chemical processes are carried out for this purpose, for example the black-oxide process or so-called replacement processes such as multibond. According to the invention, these processes can be carried out considerably better with an ozone-containing treatment liquid according to a method described above.

Yet another use according to the invention provides that silicon wafers are treated in a production process for solar cells with ozone-containing treatment liquid. In the process, organic residues on the wafer surface can be removed. In this case, it is also possible to form an oxide layer whose thickness depends on the ozone concentration in the treatment liquid and the duration of the action. Possibly. Foreign metals present on the wafer surface are incorporated into the newly formed oxide layer and removed from the wafer in a subsequent HF etching step with which the silicon oxide layer is removed. Thus, possible recombination sites for the electrons can be reduced and thus the efficiency of a finished solar cell can be increased. Further, by an ozone treatment on the wafer surface, the interfacial tension can be reduced since the surface is hydrophobic after the treatment. Basically, such a process may include the following steps: Ozone Treatment -> Rinse -> HF Etch -> Rinse

After the ozone treatment, the wafer can be rinsed, after a previously described HF etching step, the wafer is rinsed in each case, as well as it can be dried.

The above-described treatment of a silicon wafer with a method according to the invention can be carried out after a texturing process of the silicon wafers. In particular, the wafer can be rinsed several times beforehand and HCl and / or HF etched. Again, there is the possibility to rinse the wafer after an ozone treatment. Thus, both monocrystalline and multicrystalline silicon wafers can be treated. Basically, such a process may include the following steps:

Texturing -> Rinse -> KOH Process -> Rinse -> HCI / HF Etching -> Rinse -> Ozone Treatment -> Rinse -> HF Etch -> Rinse -> Dry

In a further embodiment of the invention, the above-described method for treating silicon wafers can be carried out by a Phosphorglasätz- process, before which phosphor has been thermally baked for doping in the silicon. Here, it is necessary to perform a rinsing step after the phosphor glass etching process and before the ozone treatment. Basically, such a process may include the following steps:

HF etching (phosphorous glass etching) -> rinsing -> ozone preservation -> rinsing -> HF etching - »rinsing -> drying

In a further embodiment of the invention, prior to said phosphor glass etching process, edge isolation of the silicon wafer can be achieved. be done by etching. In this case, HF and / or HNO _ß etched and rinsed several times. Here too, an ozone treatment according to the invention can then be carried out with a possible rinsing step. Basically, such a process may include the following steps:

Edge insulation (HF / HNO3) - »Rinse -> KOH process -> Rinse -> HF etching (Phosphor glass etching) -> Rinse -> Ozone treatment -> Rinse -> HF etching -> Rinse -> Dry

A further use according to the invention of the method described above can provide for structures in an antireflection coating to be cleaned on a silicon wafer, directly after the structures have been produced. This structuring can be carried out for example with a laser. When cleaning with ozone-containing treatment liquid, residues from structuring are removed from the silicon wafer, especially on the exposed emitter. This should be done before a metallization, in which then electrical contacts are introduced into the structure, in particular metallic contacts. Again, the addition of ozone in the treatment liquid for cleaning the structures produced an improved cleaning effect. Basically, such a process may include the following steps:

Opening the antireflection layer with laser -> ozone treatment -> rinsing -> HF etching -> rinsing -> drying -> metallization (for example chemical Ni and light-induced galvanizing)

Yet another use according to the invention provides for carrying out a method described above after producing structures in a previously described antireflection layer of a silicon wafer, structuring here being achieved by masking the silicon wafer and subsequently etching the exposed antireflection layer. follows. A resist used for masking can be stripped off, preferably with NaOH. Subsequently, the treatment according to the invention of the silicon wafer in the structures produced can be carried out for cleaning with ozone-containing treatment liquid. Preferably, it is possible here that remaining impurities of the resist are removed. Basically, such a process may include the following steps:

Masking the silicon wafer with inkjet -> etching the exposed lines in the antireflection layer -> stripping the resist -> ozone treatment -> rinsing -> rf etching -> rinsing -> drying -> metallization (for example, chemical Ni and photoinduced electroplating)

These and other features will become apparent from the claims but also from the description and drawings, wherein the individual features each alone or more in the form of sub-combinations in an embodiment of the invention and in other fields be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections and subheadings does not restrict the general validity of the statements made thereunder.

Brief description of the drawings

Embodiments of the invention are shown schematically in the drawings and are explained in more detail below. In the drawings show:

Fig. 1 is a schematic side view of a treatment device according to the invention with ozone production and mixing device and Fig. 2 is a greatly enlarged sectional view through a printed circuit board after a pattern plating process.

Detailed description of the embodiments

FIG. 1 shows a treatment device 1 with a treatment chamber 12 in which planar substrates 3, for example printed circuit boards or silicon wafers for solar cells, can be treated. In the treatment device 1 is a transport system 2, which consists of below and optionally also above the path of the substrates 3 arranged transport rollers. Below the transport system 2 extends over the substantial length of the treatment chamber 12, a receptacle 4. Below, in turn, an intermediate bottom 5 is provided, which collects from the receiving trough 4 exiting treatment liquid 14 and passes through a piping system in a tank 15. The tank 15 forms the essential supply of treatment liquid 14 for the treatment device 1.

When passing through the substrates 3 with the transport system 2 through the treatment chamber 12, they are wetted with their underside by the treatment liquid 14 in the receptacle 4. In this case, for example, a cleaning or etching of the undersides of the substrates 3, as has been described above. It is possible for the substrates 3 to come into contact with the treatment liquid only with one side or its underside, and also that they are completely submerged in the treatment liquid. This is achieved by a higher overflow of the treatment liquid in the receptacle 4. Likewise, spraying with treatment liquid through the illustrated nozzles 18 from above is possible, but in principle also by other nozzles also or only from below. This is basically known in such treatment facilities. In addition, in a dipping system with overflow of the treatment liquid in the receiving tub 4, swelling devices may be provided, which are formed similarly to the illustrated nozzles 18. They are immersed in the treatment liquid and generate a flow by discharging the treatment liquid under pressure, thus providing renewal of the treatment liquid to the substrate 3 and removal of generated gas bubbles. Again, this is basically known in such treatment facilities. The swelling devices can be arranged at the top, bottom or on both sides.

The ozone concentration of the treatment liquid is measured with an ozone measuring device 8, which is acted upon by a partial flow of the treatment liquid after a pump P1. Another or alternative such ozone measuring device 8 'can be provided in the treatment chamber 12 and measure the ozone concentration in the treatment chamber 12 or directly on the substrates 3.

In a second cycle treatment liquid 14 is removed from the tank 15 by means of a pump P2 and pumped by a mixing device 6. Alternatively, only with the pump P1 and valves, the treatment liquid can be divided into two partial streams. One part is fed back to the static mixer and then into the receptacle 4 or into the tank, the other part goes directly into the receptacle.

By means of an ozone generator 7 is generated from oxygen or O ₂ ozone, ie O ₃ . The oxygen supply can be done either from the ambient air or a separate oxygen tank, where it is not shown here. The generated ozone is mixed by the ozone generator 7 either as shown in a solid line in the mixing device 6 of the treatment liquid, and then in turn fed back into the tank 15. Within the tank 15 may be a kind of nozzle assembly 17 or a feed tube below the Liquid level be provided for a particularly good mixing of the ozone-containing treatment liquid 14 with the tank 15 located. Alternatively, the ozone can be mixed in the first described circuit behind the pump P1 and before the ozone meter 8 of the treatment liquid 14 by the dashed lines, so shortly before the introduction into the receptacle 4. Then the separate ozone addition to the treatment liquid 14 in Tank 15 accounts.

By means of a controller 9, which is connected to both the ozone generator 7 and the ozone measuring devices 8 and 8 ', the ozone concentration in the treatment liquid 14 can be adjusted or regulated to a desired value, for example the values mentioned above. Furthermore, the controller 9 can perform additional tasks of the treatment device 1, for example controlling the pumps P1 or P2 and various valves or the like.

At the top of the treatment chamber 12 is a suction 11. This sucks ozone-enriched air from the treatment chamber 12, which would otherwise reach the ambient air. Again, the controller 9 could monitor the strength of the suction 11 and regulate if necessary.

The exact composition of the treatment liquid 14 and the desired ozone concentration therein can significantly depend on the purpose and also on the nature of the substrates 3 and are set differently and favorably.

Furthermore, a cooling device 10 is provided, which cools the treatment liquid 14, advantageously in the tank 15 or by a heat exchanger in the circuit. As a result, a decomposition of the ozone can be slowed down, so that less ozone must be produced or with the existing generator power a higher ozone concentration is reached. Of course, it is important to ensure a sufficiently good effect and process reliability of the treatment of the substrates 3 with the treatment liquid 14.

In Fig. 2, a circuit board 3 'is shown in high magnification. On it are structures 19 formed by a resist. Between the individual structures 19, copper 21 for printed conductors or the like is used in a pattern plating process. applied. In this case, the copper 21 can form overhangs 22 over the structures 19 of the resist. As a result, treatment liquid reaching from above onto the printed circuit board 3 'only reaches a part of the surface of the structure 19 for its removal, so that the removal of the resist there lasts longer or has to be carried out with more aggressive treatment liquids. If this treatment liquid is now mixed with ozone as a possible use, then the structure 19 made of resist is particularly strongly attacked and dissolved, above all largely dissolved in gaseous constituents. This is particularly advantageous especially when the overhangs 22 extend further beyond the structures 19.

Claims

claims

1. A method for the treatment of flat substrates (3, 3 '), in particular circuit boards (3 ^' ), in the horizontal passage through a treatment device (1), wherein on at least one side of the substrates (3, 3 ^' ) treatment liquid (14) is brought , characterized in that the treatment liquid (14) ozone (O ₃ ) is admixed.

2. The method according to claim 1, characterized in that the treatment device (1) has a tank (15) and the tank with treatment liquid (14) is filled, wherein the treatment liquid from the tank (15) is removed and for ozone addition to the mixing device (6), wherein preferably gas bubbles escape from the treatment liquid in the tank (15) and this gas is sucked out of the tank.

3. The method according to claim 1 or 2, characterized in that the treatment liquid (14) between a treatment chamber (12) of the treatment device (1) with a receiving trough (4) for the treatment liquid (14) and a tank (15) is continuously circulated , preferably by means of a pump (P1).

4. The method according to claim 3, characterized in that a concentration of ozone (O ₃ ) in the treatment liquid (14) in the receptacle (4) in the treatment device (1) is measured, in particular after the pump (P1) for the supply of Treatment liquid (14) in the receptacle or in the drip pan, wherein the ozone production is controlled depending on the measured ozone concentration, in particular to an adjustable constant value is controlled.

5. The method according to claim 3, characterized in that an admixture of ozone (O3) takes place in the treatment liquid (14) behind the pump (P1) and in front of the receptacle (4) of the treatment device (1), wherein the pump (P1) Treatment liquid (14) from a tank (15) in the receiving trough (4) pumps.

6. The method according to any one of the preceding claims, characterized in that the treatment liquid (14) is cooled (10), preferably below room temperature.

7. The method according to any one of the preceding claims, characterized in that the ozone concentration is between 2 ppm and 30 ppm, preferably between 5 ppm and 10 ppm.

8. Use of a method according to one of the preceding claims for removing a resist (19) from a printed circuit board (3 ^' ) as a substrate, preferably after a pattern plating process of the printed circuit board, in particular for removing areas of a resist, from Copper structures (21, 22) are partially enclosed.

9. Use of a method according to one of claims 1 to 7 for cleaning printed circuit boards (3 ').

Use according to claim 9 for cleaning printed circuit boards (3 ') in multi-layer circuit boards after drilling the bores, wherein the bores or the surrounding areas of the circuit boards are cleaned by the ozone-containing treatment liquid from resin fouling by drilling.

11. Use of a method according to any one of claims 1 to 7 for the surface activation of the substrates (3, 3 ^' ) before a coating to improve the adhesion or for better wettability.

12. Use according to claim 11 for structuring printed circuit board base material as substrate, preferably of resin or polyimide film as printed circuit board base material, before lamination processes or before an electroless metallization, in particular with a chemical copper process.

13. Use of a method according to any one of claims 1 to 7 for structuring the free copper surface of printed circuit boards prior to lamination processes, wherein preferably the copper surface is patterned before lamination of individual inner layers to form a multi-layer circuit board for adhesion improvement by the ozone-containing treatment liquid.

14. Use of a method according to one of claims 1 to 7 for treating silicon wafers (3) for solar cells, wherein preferably the silicon wafers are HF-etched after a treatment with ozone-containing treatment liquid (14) and in particular then rinsed.

15. Use according to claim 14, characterized in that the method is carried out after a texturing process of the silicon wafer (3), in particular after a multiple rinsing and HCI / HF etching.

16. Use of a method according to claim 14 after a Phosphorglasätzprozess, before which phosphor has been baked for doping in the silicon wafer (3), wherein in particular the silicon wafer (3) after the Phosphorglasätzprozess and before the treatment with ozone-containing treatment liquid (14) is rinsed.

17. Use according to claim 16, characterized in that before the phosphor glass etching edge insulation of the silicon wafers (3) by etching, preferably by HF / HNO ₃ - etching and repeated rinsing.

18. Use of a method according to one of claims 1 to 7 for cleaning structures in an antireflection layer on Si wafern silicon (3) directly after the production of the structures, in particular the structures are generated with a laser, wherein thereby residues of generating the structures are removed and the exposed emitter of the silicon wafer (3) is cleaned before a metallization in which electrical contacts are introduced into the structure.

19. Use of a method according to one of claims 1 to 7 after the formation of structures in an antireflection layer on a silicon wafer (3) by masking the silicon wafer and subsequent etching of the exposed antireflection layer, wherein subsequently a resist for masking is removed, in particular by stripping NaOH, and then the silicon wafers are treated with ozone-containing treatment liquid (14).

20. Use according to claim 19, characterized in that the emitter exposed by the structuring of the silicon wafer (3) is cleaned, in particular of remaining impurities of the resist for masking the silicon wafer.

21. Printed circuit board (3), characterized in that it has been treated by a method according to one of claims 1 to 7.

22 silicon wafer (3), in particular for the production of solar cells, characterized in that it has been treated by a method according to one of claims 1 to 7.