The invention is related to a gas supply for a processing furnace with a plurality of gas inlets each opening into an in- flow canal which opens into a furnace chamber of the processing furnace.

Thin film solar cells are produced by coating a substrate, like a glass substrate, with one or more surface layers. Such covered substrate, called solar cell substrate in the following, is subjected to several thermal processing steps, each treating the surface in one or another way, like changing the surface composition or structure or adding a new surface layer to the cell substrate. During those steps the solar cell sub- strate is moved through one or more processing furnaces with furnace chambers charged with one or more process gases.

It is an object of the invention, to provide a gas supply for charging a furnace chamber* equally with process gas.

This object is solved by a gas supply according to claim 1. Preferred details of the invention are described in the dependent claims. According to the invention, the plurality of gas inlets of the gas ^■ supply are furnished with different inlet cross sections and the plurality of inflow canals are furnished with different inflow cross sections opening into the furnace chamber. With different inflow cross sections at different places in the furnace chamber the gas flow cross section and volume can be adapted to the geometry of the chamber. With the different inlet cross sections the pressure in the inflow canals and with that the velocity of the gas flow into the chamber can be adjusted to the geometry of the chamber. With the combination of these two parameters, the inflow cross sections and the pressure or velocity of the inflowing gas, a very equal or. uniform gas supply into the chamber and a very equal or uniform gas flow throughout the chamber can be achieved.

The processing furnace may be a part of a segmented continuous furnace with a plurality of processing furnaces, preferably for the production of semiconductor layers with I-III-VI compounds and especially for the coating of glass or semiconduc- tor substrates for CIGS solar cells. The cross sections may be the minimum cross sections of the respective gas inlets or. inflow canals or those cross sections affecting the gas flow in the respective inlet or canal.. Further, the invention is directed to a method for treating a surface of a substrate in a processing furnace, like coating the surface with a layer, wherein process gas is lead into the furnace chamber through a gas supply, the gas supply being designed as described in claim 1.

In a preferred embodiment of the invention the cross section ratio of the inlet cross sections and those inflow cross sections coupled to the respective inlet cross sections is identical at all gas inlets. This means, that if in a first supply unit - comprising a first gas inlet and a first inflow canal - the inflow cross section is 3-times the inlet cross section, for example, then this ratio is kept constant in all the other supply units of the gas supply. With this measure it is achieved that the gas flow from all inflow canals into the chamber is uniform throughout all inflow canals. And it may be avoided that from one canal a strong or fast gas stream flows into the chamber and from another canal a weak or slow gas stream flows into the chamber. In a further embodiment of the invention the inflow cross sections are formed as straight slots. Straight slots help to generate a uniform gas flow. The straight slots open into the furnace chamber, the respective openings having the inflow cross sections. Preferably the inflow cross sections open into the furnace chamber as a series of straight slots in a

straight row.

The gas supply preferably comprises a plurality of supply units each having a gas inlet and an inflow canal. The size of the openings of the inflow canals into the furnace chamber may be equal over all inflow canals. However, equally sized openings, may lead to the problem of rhythmic alteration in gas flow through the furnace chamber. To avoid such uneven gas flow, it is proposed that the length of the slots is unequal.

To realize such non-uniformity of neighbouring canals the inflow cross sections of three neighbouring canals may be sized in such a way that the cross section of the central of the three canals is either larger than the cross section of both neighbouring canals or smaller than the cross section of both neighbouring canals.

Preferably, the cross section ratios - of the inlet cross sec- tions and those inflow cross sections coupled to the respective inlet cross sections - are sized in such a way that in each slot the same volume of gas escapes per slot length and per time from the slot. An equal gas pressure to all gas inlets is assumed to realize this embodiment of the invention. For this all gas inlets may be fed by one gas feed duct guaranteeing the same gas pressure in the feed to all gas inlets.

The inflow canals may open from above, below and/or the sides into the furnace chamber. Especially for surface processes of solar cells it was shown, that a design with all inflow cross sections opening from below into the furnace chamber is of special advantage. Depending on the kind of gas used it may happen, that the gas fed into the chamber settles on feed line surfaces, even a condensation of the gas may take place. An example may be selenium gas which settles downward on surfaces. A combination of settled selenium and gaseous selenium may influence the gas flow causing undesired non-uniformities in the selenium concentration in the flowing gas stream. If the inflow canals open from below into the chamber, the selenium will settle more downwards and further away from the openings, causing less undesired non-uniformities in the gas stream inside the furnace chamber. The inflow canals may open into a wide hall of the furnace ' chamber to fill the chamber uniformly. It is, however, advantageous if the gas flows more horizontally over a substrate positioned in the furnace chamber. If, therefore, the gas enters the chamber vertically it should be deflected into a more horizontal stream. To achieve this, the invention proposes ■ that at least some of the inflow cross sections, preferably all of the inflow cross sections, open into a passage between a furnace chamber of one processing furnace and a furnace chamber of a neighbouring processing furnace. Such a passage may be designed as a horizontal slot for passing solar cell substrates from the one processing furnace to the neighbouring processing furnace. With such design the inflowing gas is deflected in the slot from a vertical inflowing stream into a more horizontal stream passing the substrate. The slot or pas- sage respectively, is seen as a part of the furnace chamber, . the inflow canals open into the furnace chamber, therefore.

In solar cell production processes the surface treatments are mostly done with a certain temperature, mostly a temperature well above room temperature. For achieving high process per÷ . formance the furnace is heated, therefore, usually by heating the furnace walls. If the inflow cross sections are positioned in a face of a hot wall furnace, preferably in a heated wall, the gas is already tempered before entering the chamber. The heated wall may be a bottom or top wall, or a side, front or back wall.

Further, the invention is directed to a gate device for sealing a passage between two process furnaces, comprising a sealing element and a gas supply, preferably as described above. The gate device may serve as gas seal between the chambers of the two furnaces, however, it is not necessary, that the gas seal is perfectly gas tight.

Preferably, the inflow canals are positioned on one side of the sealing element and a gas discharge is positioned on the other side of the sealing element. With this assembly the gas supply may be positioned at one end of the furnace chamber and the gas discharge in another sealing device, preferably at an opposite side of the furnace chamber.. A gas stream travels through the whole chamber from one side to the other, passing the entire length of a substrate positioned inside the chamber.

In a preferred embodiment of the invention the gas discharge and the gas feed each open exclusively from below into the furnace chamber. Unwanted settlements of gas in the chamber or in canals or at walls near the chamber may be avoided.

If the gas discharge is symmetric to the gas feed a linear and non-turbulent gas flow through the furnace chamber and along a substrate positioned in the chamber is supported . Further, the gas discharge comprises exhaust cross sections opening into the furnace chamber. It is preferred if. the exhaust cross sections have the same size than the inlet cross sections. In a laminar gas flow situation these dimensions support a uniform gas flow from the gas feeder to the gas discharge .

In a further embodiment of the invention the gas supply comprises a feed duct with a feeding cross section, and the gas discharge comprises gas outlets opening into an outlet duct with an outlet cross section, wherein the outlet cross section is larger than the feeding cross section. In the direction of gas flow the feed duct is positioned before the gas inlet, and it feeds one or more feed ducts with gas. On the other hand, the outlet duct is positioned after the gas outlets; the gas outlets feed the outlet duct with gas. Preferably, the outlet cross section is at least twice the size, especially at least three times the size, of the feeding cross section. Even further, the . invention is related to a continuous furnace for thermal surface processing of solar cell substrates. Preferably, the continuous furnace comprises at least two processing furnaces each with a furnace chamber, the furnace chambers being open to one another. At least one of the furnace cham- bers comprises a gas supply as described above. Preferably, the gas supply is positioned in the pass between the two furnace chambers.

For sealing one furnace chamber against the other, a continu- ous furnace for thermal surface processing of solar cell substrates - with at least two processing furnaces each with a furnace chamber - may comprise a gate device as described above . The gate device may be used for a segmented continuous furnace for the manufacture of I-III-VI-compound-layers on a semiconductor substrate, and especially for the coating of glass or semiconductor substrates for ^' .CIGS solar cells. The gate device may be used for separating two neighbouring furnace chambers, wherein the gate device is preferably constructed as an intermediate module between two process furnaces. The gate device should be made for temperatures up to at least 600 °C, and is preferably furnished with an internal heating to heat at least one wall of the gate device, like the bottom wall, for example.

Advantages of the invention are described in connection with the figures. The figures show advantageous embodiments of the invention. However, the invention is not restricted to these or other embodiments described above or with the figures. The description given above and the description given in connection with the figures contain numerous details which may be combined in various ways and different then given in the spe- cific descriptions. It is explicitly stated that every detail may be combined with the independent or any dependent claim, either alone or in combination with any other detail.

The figures show:

FIG 1 a facility for processing solar cells with a continuous furnace comprising a plurality of processing furnaces ,

FIG 2 the processing furnaces of the facility arranged in a straight line,

FIG 3 a processing furnace in a perspective view with gate .

devices positioned on both sides, the gate devices being gas seals, FIG 4 a sectional drawing through one of the gas seals showing two side plates of the two adjacent processing furnaces along the line IV-IV in FIG 3,

FIG 5 one of the side plates of FIG 4,

FIG 6 the side plate seen from the other side, and

FIG 7 a sectional drawing through the gas seal of FIG 4 along the line VII-VII in FIG 4.

FIG 1 shows a facility 2 for processing solar cells, compris- ing a base frame 4, in which a plurality of processing furnaces 6 are positioned. The embodiment shown comprises seven processing furnaces 6 which are part of a continuous furnace 8. Above the processing furnaces 6 control boxes 10 are arranged containing control electronics for controlling a proc- essing of solar cell substrates moved through the continuous furnace 8 of the facility 2.

The segmented processing furnace is used for the production of coated substrates, like applying one or more layers, like I- III-VI-compound semiconductor layers, on a glass substrate or semiconductor substrate, which may be used solar cells, like CIGS solar cells, for example. Accordingly, the control electronics, called control unit in the following, is prepared to control a method for treating a surface of a substrate in a processing furnace, like coating the surface with a layer, especially as described above.

The solar cell substrates may be substrates for thin film solar cells, but may be, on the other hand, any other plate like substrate for other products, especially semiconductor products.

During this process or method solar cell substrates are moved from an area outside the facility 2 into the facility 2, and are move through a plurality of furnace chambers of the processing furnaces 6. For this, each processing furnaces 6 comprises a furnace chamber 12 (see FIG 2), the substrates are being moved from one furnace chamber 12 to the following chairi- ber 12 and are subjected several processing steps.

The seven processing furnaces 6 of the facility 2 are shown in FIG 2 in more detail. Only for the reason of easier description the five latter furnaces 6 are. shown without upper part, so that the furnace chambers 12 are visible from above. The chambers 12 are all connected together to one continuous processing chamber. This continuous processing chamber is segmented by gate devices 14 made as gas seals, such gate device being arranged before the first and after the last processing furnace 6 as well. All together, the facility comprises one gate device 14 more than processing furnaces 6. Generally, the gate devices form a transfer from one furnace chamber to the neighbouring furnace chamber 12. The gas seals are prepared to prevent a gas flow from one furnace chamber to the next fur- nace chamber 12, whereupon a gas tight sealing between the furnace chambers 12 is not necessary.

As described, FIG 2 shows some of the furnaces 6 with the upper part removed for showing the furnace chambers 12. Inside the chambers 12 a platelike solar cell substrate 16 is positioned, which is shown only schematically and almost transpar ^¬ ent for enabling a view on the lower part of the process chamber 12. The process chambers 12 are surrounded by the upper and a lower part, each part comprising a graphite muffle in- side a steal shell. The shell - and preferably the muffle as well, comprises a tempering unit for heating or cooling the shell or muffle, respectively, to enabling each furnace cham ^¬ ber 12 to reach processing temperatures between 0°C and at least 600°C. The gate devices 14 comprise such a tempering unit as well or are connected to a tempering unit of a

neighbouring furnace 6, so that ^' the inside walls of the gatedevices 14 may be brought to the same temperature than the. muffle of an adjacent furnace 6.

FIG 3 shows a processing furnace 6 in a perspective view with gate devices 14 positioned on both sides. The processing furnace 6 comprises an upper part 18 and a lower part 20, which - when put together - form the furnace chamber 12 in between.. In processing direction 22, which is the direction in which the solar cell substrates 16 move through the processing furnaces 6, each furnace chamber 12 is terminated by a gas seal on each side. One of the gate devices 14 are shown in FIG 4 in a sectional drawing along the line IV-IV in FIG 3. The gate device 14 comprises a travel chamber 24 - which is a part of the furnace chamber 12 - through which a solar cell substrate 16 travels on its way from one furnace chamber 12 into the furnace cham- ber 12 of the following processing furnace 6. The travel chamber 24 has the form of a slit and is a passage from a furnace chamber 12 of one processing furnace 6 to a furnace chamber 12 of a neighbouring processing furnace 6. A sealing element 26 may be levelled into this travel chamber 24 for locking one furnace chamber 12 against the other furnace chamber 12 with respect to an unwanted gas transfer. Bordering the gate device 14 side elements 28 of the adjacent processing furnaces 6 are positioned, which border to the up- per part 18 and the lower part 20, either directly or intermediately via an intermediate wall 29. The upper part 18 and the lower part 20 may be fastened to the respective side element 28, like a screwing connection or the like. The side elements 28 can be seen as part of the respective processing furnace 6 of the gate device 14.

One of the side elements 28 is shown in FIG 5 in a perspective view from the direction of a furnace 6 to the gate device 14. FIG 6 shows the gate device 14 from the opposite side. So, FIG 5 shows the side facing the furnace chamber, however, this side is covered by the intermediate wall 29 leaving open only the slit of the travel chamber 24.

The side elements .28 each comprise a gas supply 30, through which process gas may be fed into the processing chamber 12. The gas supply 32 comprises a plurality of gas inlets 32a, 32b, 32c, 32d, which are formed as cylindrical canals with circular inlet cross section. The size of these circular inlet cross sections determines the strength or volume of the gas flow through the respective gas inlets 32a-d.

Each of the gas inlets 32a-d open into an inflow canal 34a, 34b, 34c, 34d, which are formed as planar slits, and which open as a slit into the furnace chamber 12. The slits result from recesses 36 (see FIG 4) in the side element 28 together with the adjacent intermediate wall 29. The length of the slits depends on the width of the inflow canals.34a-d.

All of the inflow canals 34a-d with their inflow cross sec- tions open from below into the furnace chamber 12. Heavy elements of the gas condensing inside the inflow canals 34a-d due to unwanted temperature differences in different canal sections or elsewhere tend to sink down in the inflow canals 34a- d keeping clear of the furnace chamber 12 and of the substrate. To prevent unwanted temperature differences the inflow cross sections are positioned in a face of a hot wall of the furnace chamber 12 which is heated by a tempering element. The inlet cross sections of the gas inlets 32a-d are different for different gas inlets 32a-d. Accordingly the inflow cross sections of the inflow canals 34a-d are different for differ- ent inflow canals 34a-d. The inflow cross sections are the cross sections of the openings of the slits or inflow canals 34a-d into the furnace chamber 12. However, the ratio of the inlet cross sections to the inflow cross sections is equal for all gas inlets 32a-d and inflow canals 34a-d respectively. The larger an inlet cross section is the larger is the inflow cross section opening into the travel chamber 24 and furnace chamber 12 respectively.

The size of an inlet cross section is determined by the cylin- der diameter _. of the respective gas inlet 32a-d. The size of the inflow cross section is determined by the length L of the respective slit of the inflow canals opening into the furnace chamber 12. ■ The gas supply 30 comprises two groups of gas inlets 32a-d, each group containing a plurality of gas inlets 32a-d of which each and every gas inlet 32a-d is unique in its diameter and inlet cross section. However, every gas inlet 32a-d of the first group has a correspondent gas inlet 32a-d of the second group being identical in diameter and inlet cross section. The identical pairs of gas inlets 32a-d are mirror-like arranged opposite each other, preferably the mirror plane being arranged in the centre line of a substrate 16 positioned in the furnace chamber 12, or in a centre line of the chamber 12 as such, or in a centre line of the side element 28. The pairs are arranged in such a way that the distance of each element of one pair to the centre line is the same. This is true for every pair. Further, the gas inlets 32a-d which are different in size and inlet cross section are arranged relative to one another, that larger gas inlets 32b, 32d alternate with smaller gas inlets 32a, 32c. So, the larger gas inlet 32d is positioned next to the smaller gas inlet 32c, next to which a larger gas inlet 32b is arranged, next ^, to which a smaller gas inlet 32a is located. Or in other words: Next to a larger gas inlet 32b two, smaller gas inlets 32a, c are located, and next to a smaller gas inlet 32c two larger gas inlets 32b, d are located.

Further, the largest gas inlet 32d lies next to the centre line of the furnace chamber 12 or side element 28, and, preferably, the smallest gas inlet 32c lies adjacent to this largest gas inlet 32d. Due to the mirror symmetry the pair of the . largest gas inlets 32d are located closest to the centre line. The smallest gas inlets 32c each are located adjacent. The two outmost gas inlets 32a are larger then the smallest gas inlets 32 c and smaller than the second gas inlet 32b next to them. The arrangement and relative size of the inflow canals 34a-d are the same than described with respect to the gas inlets 32a-d. That means, that everything said above about the gas inlets 32a-d is true for the inflow canals 34a-d. Due to this arrangement of the gas inlets 32a-d and the inflow canals 34a-d respectively, a very homogenous gas flow through the furnace chamber 12 is achieved. The gas inlets 34a-d open into the chamber 12 in an area outside the area in which the substrate 16 is located inside 'the chamber 12 during the treatment process, or - in the processing direction 20 - before or after the substrate 16. This arrangement results in a very homogenous gas flow along the substrate 16, in the embodiment shown along the upper and lower side of the substrate 16. FIG 6 shows the gas inlets 32a-d viewed from the back of the side plate 28. All gas inlets of one group are connected with a feed duct 40 which is shaped as a groove inside the side element 28. The feed duct 40 is supplied with process gas by another feed duct 42 located more inside the ^' gate device 14 than the side plate 28 ^' . Whereas each of the feed ducts 40 supply only one group of gas inlets 32a-d and inflow canals 34a- d, the feed duct 42 supplies both feed ducts 40 and all gas inlets 32a-d and inflow canals 34a-d with process gas.

FIG 7 shows a sectional drawing through the gate device ,14 of FIG 4 along the line VII-VII of FIG 4. The gas supply 30 comprises as gas discharge 44 which is part of the gate device 14 as well. The gas discharge 44 is positioned, shaped and sized analogous to the gas supply 30 with one difference: the exhaust cross section of an outlet duct 46 of the gas discharge 44 is more than 3-times larger than the feeding cross section of a feed duct 50 of the gas supply 30. The gas discharge 44 comprises gas outlets 48a-d, which open into the furnace chamber 12 and travel chamber 24 respectively. The outlet duct 46 and the feed duct 50 are located inside the gate device 14.

The inflow canals 32a-d are positioned on one side of the sealing element 26 and the gas discharge 44 is positioned on the other side of the sealing element 26. With respect to two gate devices 14 opposite each other at one furnace chamber 12 the inflow canals 32a-d are positioned on one side of the furnace chamber 12 and the gas discharge 44 is positioned on the other side of the furnace chamber. Both, the inflow canals

32a-d and the gas outlets 48a-d of the gas discharge 44 open exclusively from below into the furnabe chamber 12 and into the travel chamber 24 of the gate device 14. For the reason of homogenous gas flow, the gas discharge 44 is symmetric to the gas supply 30, or in other words, the inflow canals 32a-d are and the gas outlets 48a-d are symmetric to one another. This- symmetry is realized in sizes as well: The exhaust cross sections of the gas outlets 48a-d opening into the furnace chamber 12 have the same form and size than the inflow cross sections of the inflow canals 34a-d.

List of reference numerals

2 facility for processing solar cells

4 base frame

6 processing furnace

8 continuous furnace

10 control box

12 furnace chamber

14 gate device

16 solar cell · substrate

18 upper. part

20 lower part

22 processing direction

24 travel chamber

26 sealing element

28 side element

29 intermediate wall

30 gas supply

32a gas inlet

32b gas inlet

32c gas inlet

32d gas inlet

34a inflow canal ,

34b inflow canal

34c inflow canal

34d inflow canal

36 recess

40 feed duct

42 feed duct

44 gas discharge

46 outlet duct

48a gas outlets

48b gas outlets

48c gas outlets gas outlets feed duct