WO2012175331A1 - Method for processing substrates and device therefor - Google Patents

Abstract

In a method and a device for processing silicon wafers for solar cell production, an Al₂O₃ passivation layer is applied to a substrate by means of an APCVD method. Said application takes place in a gas atmosphere of an Al metal organic precursor, H₂O-containing oxidation agent and N₂. According to the method, the gases are conducted to the substrate separately from one another and only mixed with one another shortly before or as they are applied to the substrate, a first layer of oxidation agent being applied to the substrate before the precursor and then again shortly after the precursor.

Description

 description

Method for processing substrates and apparatus therefor

Field of application and state of the art

The invention relates to a method for processing substrates, in particular of silicon wafers for solar cell production, and to an apparatus for carrying out this method.

From EP 503 382 A1 it is known, by means of a multi-channel injector to bring various gases on a silicon substrate or bring it to this to treat the surface or edit. The process is a so-called APCVD process, ie a CVD process, which can be carried out without vacuum under atmospheric pressure.

Task and solution

The invention is based on the object to provide an aforementioned method and an aforementioned device with which problems of the prior art can be avoided and in particular processed reliably and with very high throughput substrates or their surfaces can be treated.

This object is achieved by a method having the features of claim 1 and a device having the features of claim 1 1. Advantageous and preferred embodiments of the invention are the subject of further claims and are explained in more detail below. Some of the features are mentioned either for the method only or for the device only. However, they should apply independently to both the process and the device. NEN. The wording of the claims is incorporated herein by express reference.

It is envisaged that an Al ₂ O 3 passivation layer is applied to a named substrate by an APCVD process. This takes place in a gas atmosphere of on the one hand aluminum-metalorganic precursor and on the other hand H ₂ O-containing oxidizing agent. In this case, the precursor and the oxidizing agent are at least partially separated spatially or temporally from one another by nitrogen or another suitable separating gas. As a substrate, a silicon wafer is advantageously used or processed and coated for solar cell production.

According to the invention, the gases, at least the precursor on the one hand and the oxidizing agent on the other hand, are introduced separately from one another to the substrate. Only shortly before hitting the substrate or on its surface or even just at this impact, the two gases are mixed together. Advantageously, this is done so that first the oxidizing agent impinges on the substrate or on its surface and immediately after the precursor is introduced or is applied, then also again the oxidizing agent and thus by the mixture on the surface of the passivation layer on the Substrate is formed. Alternatively, the precursor and the oxidizing agent may mix at least partially with each other at the last moment prior to impinging on the substrate and then impinge on the substrate in this mixed state, at which time the mixing need not necessarily be complete or even. The introduction by means of nitrogen, in particular as a kind of separation between precursor on the one hand and oxidizing agent on the other hand, has the purpose to prevent too early mixing of the two gases and thus a premature reaction, in particular special directly after the exit from the respective channels of an injector or the like, with which the gases are brought to the substrate.

In the said injector, which is known per se from the aforementioned prior art in a similar form and which has a plurality of channels, it is advantageous for each gas to have its own channel with its own channel inlet and separate channel outlet. As a result, it is very easy to adjust both the amount of the respective gas to be led to the substrate and to determine the mixing ratio via parameters such as pressure or flow rate. In the process, these parameters can be varied correspondingly both on the one hand to the precursor and on the other hand in the case of the oxidizing agent and in the case of release agents, in particular in the form of nitrogen. The separate bringing the gases by means of their own channels in the injector just serves to prevent the precursor undesirably comes prematurely together with oxygen either from the ambient air or from the oxidizing agent, resulting in precipitation of the aluminum content in powder form and thus to an obvious undesirable result including negative contamination of the substrates.

The channels of the injector should be relatively close to each other, at least at the channel exits, and this can also be changed by different geometry or design. In an advantageous embodiment of the invention, the gases are led to just before the substrate surface separated from each other, preferably up to a distance of less than 5mm. Particularly preferably, the gases, in particular by means of the above-mentioned injector, are guided to about 2 mm in front of the substrate surface or the injector reaches as far as the substrate surface. As a result, it can be achieved that the gases, in particular the precursor and the oxidizing agent, do not undesirably prematurely mix or only just on or very slightly in front of the substrate surface. In a further embodiment of the invention, it is possible that the nitrogen and / or the aforementioned oxidizing agent are brought in larger quantity or with more channels with the injector to the substrate as the precursor. With regard to the nitrogen, this makes it possible to increase the separation effect between the precursor and the oxidant. With regard to location or time of mixing of precursor and oxidant, it is possible by a particularly strong addition of the oxidizing agent, in case of mixing only on impact of the gases on the substrate surface while still sufficient amount of oxidizing agent to introduce the precursor so that on the Substrate surface gives the desired passivation layer.

In a further embodiment of the invention, it is possible to carry out the process at a low negative pressure. This can be, for example, up to 0.8 bar. Then, under certain circumstances, another gas stream of nitrogen may be provided outside the gas stream of the oxidizing agent as a separation from the ambient air or the atmospheric oxygen. This makes it possible, inter alia, to keep atmospheric oxygen as far as possible from the precursor or from the impact and mixing area on the substrate, which can also be regarded as a mixing zone. This enables a well-defined reaction or separation and construction of the passivation layer.

In an alternative embodiment of the invention, the method can also be carried out under atmospheric pressure. Then, under certain circumstances, another gas stream of nitrogen outside the gas stream of the oxidizing agent may be provided as a separation from the ambient air or the atmospheric oxygen.

A process temperature may advantageously be in the usual range, preferably at 100 ° C to 400 ° C. Particularly advantageous may be a process temperature at 200 ° C to 300 ° C. The substrates are preferably transported continuously during the coating. Thus, both a uniform coating is possible and ensures a high throughput of substrates to be coated. The injector is advantageous fixed. The substrates are preferably coated in an inline process or an entire system can be designed as an inline system, in particular also with regard to a transport of the substrates.

In a further embodiment of the invention, it is advantageous if the substrates are transported along a horizontal path, in particular lying, advantageously on an aforementioned inline system.

In an advantageous embodiment of the invention, the gas streams or the injector are aligned perpendicular to the transport path, which applies to the gas streams in particular with respect to their impact on the substrate. Particularly advantageously, the gases are brought from above to the substrates or the injector is arranged above the substrate. It can be provided that several injectors are provided one behind the other during the passage path of the substrates or a plurality of gas streams at least of the precursor are directed to the substrate or impinge on this. In this case, of course, that in turn surrounds each gas stream of precursor surrounded by a gas stream of nitrogen from the injector and impinging on the substrate for separation of the oxidant until just before hitting the substrate or directly to hitting the substrate, as before has been described.

There, where the precursor mixes with the oxidizing agent, a mixing zone is formed. This mixing zone is advantageously limited at least in the direction away from the injector by the substrate or the surface, but may also extend 1 mm or 2 mm over the substrate surface. The deposition of the precursor on the substrate or by the Al 2 O 3 reached passivation then takes place in this mixing zone or gas mixture region.

In a further embodiment of the invention, it is possible that a channel in the injector or the gas guide is not a single substantially round channel, but has an extension transverse to the direction of passage of the substrates. Thus, virtually over a strip, advantageously over the entire width of a substrate, the deposition on the substrate or the passivation can be carried out. The channel exits may then have the form of slot nozzles or be slit-like with the corresponding slot width.

In yet a further embodiment of the invention, the oxidizing agent may be dissolved in the form of H ₂ O in an atmosphere of nitrogen or O ₂ .

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-combination in one embodiment of the invention and in other areas 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 limit the statements made thereunder in their generality.

Brief description of the drawings

An embodiment of the invention is shown schematically in the drawings and will be explained in more detail below. In the drawings show: Fig. 1 is a side view of an inventive device for carrying out the method with an injector with multiple channels and

Fig. 2 is a plan view of a device according to FIG. 1 for

 Representation of the laterally across the substrates reaching, slit-like channels in the injector.

Detailed description of the embodiment

In Fig. 1 is shown for a device according to the invention, which has an injector 1 1, as it is known in the art per se from the basic principle. The injector 11 has a main body 12 in which a plurality of channels 13a to 13e extend in the vertical direction. In this case, the channels 13a to 13e have gas connections or fluid connections, which are not shown in more detail above, which are not shown here for the sake of simplicity, but are clear and understandable to a person skilled in the art.

Below the injector 1 1, a gas mixing zone 15 is formed for the gases emerging from the channels 13a to 13e at channel exits 14a to 14e. This will be explained in more detail below.

Under the injector 1 1 substrates 17 pass, which are to be processed, this being silicon wafer for solar cell production, which should be provided with an Al ₂ 0 ₃ passivation layer on a substrate top 18. In this case, the substrates 17 run on a Roller conveyor 20 under the injector 1 1 and its channel outputs 14a to 14e and past the gas mixing zone 15. The distance of the injector 1 1 or its underside or the channel exits 14a to 14e to the substrate upper side 18, which is indicated by d, may advantageously be less than 5 mm. It is particularly advantageous about 2mm, so it is relatively low. In the plan view of Fig. 2 it is clear that the injector 1 1 projects laterally beyond the substrates 17. Furthermore, the channels 13a to 13e are formed as slots or as longitudinal slots at least with respect to the lower channel exits 14a to 14e shown in FIG. These longitudinal slots likewise project laterally beyond the substrates 17, so that it becomes clear that fumigation on the one hand and coating as a result on the other hand take place simultaneously and substantially uniformly over the entire width of the substrates 17. This also means that the gas mixing zone 15 extends over the full width of the substrates 17, which is also important for a uniformity of the passivation or coating with a passivation layer seen across the width of the substrates 17.

As can be seen from the figures, an Al-metalorganic precursor is introduced at the channel entrance for the channel 13c, preferably as so-called TMA or trimethyl aluminum. This precursor is well known and need not be explained in detail. Further suitable precursors are trialkylaluminum, triethylaluminum and aluminum 2,4-pentaerytionates.

In the two directly adjacent channels 13b and 13d nitrogen is introduced as a kind of separating agent or as a separator and discharged at the corresponding channel exits 14b and 14d in the gas mixing zone 15th

In the laterally outermost channels 13a and 13e, an oxidizing agent in the form of H ₂ 0 is introduced at their channel entrances, which enters the gas mixing zone 15 at the respective channel exits 14a and 14e. This H ₂ O can be dissolved in an atmosphere of N ₂ , alternatively in an atmosphere of 0 ₂ .

The preferred process temperature is about 200 ° C to 300 ° C. In the gas mixing zone 15, the precursor thus hits the upper side of the substrate 18, so to speak in the middle region below the injector 11. In this case, the precursor encounters oxidizing agent, which has already been applied by the movement of the substrate 17 shortly before and is still located on the substrate upper side 18. Thus, a first contact or a first mixing of the precursor with the oxidizing agent takes place and thus a first incipient build-up of the passivation layer.

The precursor is protected to the left and to the right by the separator nitrogen during the bridging of the distance d from the direct contact with the oxidant flowing laterally therefrom, so that no oxidation of the precursor takes place quasi in the middle of the air. This would have the consequence that only white powder is precipitated from the precursor and no more desired reaction takes place on the substrate top 18. The above-described mixing of the precursor with the oxidant present on the substrate 17 takes place on the substrate surface 18 and is therefore desirable.

On the substrate top side 18 itself, on the other hand, the now secondarily applied gases swirl, as it were, and through the gas layer of the separator, the oxidizing agent can further oxidize the precursor on the substrate top side 18. This then results in the reaction on the substrate top side 18 and continues to build up the Al ₂ O ₃ passivation layer on the substrate top side 18.

Due to the configuration of the channels 13a to 13e or the channel exits 14a to 14e as longitudinal channels or slot nozzles, which extend over more than the width of the substrates 17, this reaction can also take place continuously with continuously passing substrates 17. Thus, a uniform passivation layer on the substrate top 18 can be produced. Due to the very small distance d between the underside of the injector 1 1 and channel exits 14a to 14e and substrate top 18 can be generally achieved that possibly a certain or low mixing of the precursor with the laterally and simultaneously applied oxidant shortly before the impact of the corresponding Gas mixture can be made on the substrate top 18. However, this impingement then takes place so rapidly or immediately after the first mixing that, as it were, the oxidation or deposition takes place on the substrate top side 18 and not already in the air atmosphere.

Furthermore, separation of the precursor from ambient air or atmospheric oxygen is achieved by the mutual application of the separator nitrogen. In many cases, this could already cause unwanted oxidation in the precursor. Furthermore, it can be provided on the outer sides of the channel output 14c for the precursor that, for improved shielding, the channel outputs 14b and 14d of the separator are pulled even further to the side for better shielding of the precursor. Under certain circumstances, they may even be arcuately closed and thus in the plan view of FIG. 2, the middle channel output 14c actually fully enclose.

The substrates 17 are advantageously carried out continuously under the injector 11. In this case, their distance from each other can also be considerably less than shown, for example just so much that it is ensured that the opposite edges of the substrates 17 do not abut one another due to the risk of breakage.

The outflow of gases from the injector 1 1 can take place continuously, whereby it can also be achieved that, as it were, stable and balanced or leveled conditions prevail in the gas mixing zone 15 and optimum deposition of passivation layers on the substrate top side 18 can be achieved. The method according to the invention is particularly preferably used for p-type and n-type crystalline solar cells.

Claims

claims 1. A method for processing substrates, in particular silicon wafers for solar cell production, wherein an Al ₂ O ₃ passivation layer is applied to a substrate by an APCVD method, wherein this deposition in a gas atmosphere of organometallic precursor, H ₂ 0-containing oxidant and N ₂ is carried out, characterized in that the gases are introduced separately from one another to the substrate, wherein the gases are mixed only shortly before or when hitting the substrate. 2. The method according to claim 1, characterized in that the gases are introduced by means of an injector having a plurality of channels to the substrate, wherein preferably for each gas a separate channel input is provided in the injector, in particular a separate channel output. 3. The method according to claim 1 or 2, characterized in that the gases are separated until they exit from the injector or until mixed by means of the channels in the injector. 4. The method according to any one of the preceding claims, characterized in that the gases are led to shortly before the substrate surface separated from each other, preferably with a distance of less than 5mm, in particular about 2mm. 5. The method according to any one of the preceding claims, characterized in that first the oxidizing agent impinges on the substrate or on the substrate surface and directly thereafter the precursor is introduced, in particular with incipient formation of a passivation layer, in which case the oxidizing agent is subsequently introduced again, wherein the passivation layer is formed or reinforced on the substrate by the mixture on the surface. 6. The method according to any one of the preceding claims, characterized in that N ₂ and / or the H ₂ O-containing oxidizing agent is brought in larger quantities or with more channels through the injector to the substrate as the precursor. 7. The method according to any one of the preceding claims, characterized in that the method is carried out under a slight negative pressure, preferably up to 0.8 bar. 8. The method according to any one of claims 1 to 6, characterized in that the method is carried out under atmospheric pressure. 9. The method according to any one of the preceding claims, characterized in that the process temperature is at 100 ° C to 400 ° C, preferably at 200 ° C to 300 ° C. 10. The method according to any one of the preceding claims, characterized in that the substrates are transported continuously during the coating, preferably as an in-line method, in particular with a fixed injector, wherein preferably the substrates are transported along a horizontal path. 1 1. A method according to claim 10, characterized in that the gas flows or the injector perpendicular to the transport path of the Substrates are aligned, wherein preferably the gases are brought from above to the substrates or the injector is arranged above the substrate. 12. An apparatus for carrying out the method according to any one of the preceding claims, characterized in that at least one injector is provided with a plurality of channels for separately bringing the gases to the substrates, wherein the injector is guided to just before the substrates and the gases separated from each other in are passed through the injector and separate from each other for mixing in a mixing zone directly on the substrate. 13. The apparatus according to claim 12, characterized in that the injector extends to just before the substrate surface, preferably with a distance of less than 5mm, in particular about 2mm. 14. The apparatus of claim 12 or 13, characterized in that at least one channel in the injector or the gas guide has an extension transverse to the direction of passage of the substrates, preferably as a slot nozzle at the channel exit.