WO2012028660A1

WO2012028660A1 - Gas distribution device for vacuum processing equipment

Info

Publication number: WO2012028660A1
Application number: PCT/EP2011/065052
Authority: WO
Inventors: Laurent Despont; Vitaliy Vovk; Owan Charles Watkins
Original assignee: Oerlikon Solar Ag, Trübbach
Priority date: 2010-09-03
Filing date: 2011-08-31
Publication date: 2012-03-08
Also published as: JP2013541641A; KR20130103737A; CN103097575A

Abstract

The invention relates to a vacuum chamber for accommodating a substrate to be treated in a vacuum process comprising a gas inlet (7) connected to a gas source for receiving gas (A, B) and a gas distribution system (9) for dispensing the gas (A, B) from the gas inlet (7) to a plurality of outlet openings (8) into the vacuum chamber at a plurality of locations towards the substrate, whereby the gas distribution system (9) comprises a first plate (10) and a second plate (5), each plate having a flat side, the first plate (10) exhibits a plurality of bores (4) forming the outlet openings (8), the second plate (5) exhibits a plurality of channels (6a, 6b) arranged on the flat side, the first plate (10) and the second plate (5) are mounted together with their flat sides directly contacting each other such that each bore (4) of the first plate (10) is arranged where a channel (6a, 6b) of the second plate (5) ends such that gas (A, B) is dispensable through the respective channel (6a, 6b) into the bore (4), and the individual channels (6a, 6b) merge into at least one common channel (6a, 6b) connected to the gas inlet (7) thus forming a branching arrangement. The vacuum chamber comprising the gas distribution system (9) provides for a significant improvement of the substrate coating homogeneity, thus in an improved quality of the so manufactured substrate while decreasing the manufacturing costs as well.

Description

Gas distribution device for vacuum processing equipment

Technical Field

The invention relates to a vacuum chamber for accommodating a substrate to be treated in a vacuum process comprising a gas inlet connected to a gas source for receiving gas and a gas distribution system for dispensing the gas from the gas inlet to a plurality of outlet openings into the vacuum chamber at a plurality of locations towards the substrate. In particular, the present invention relates to a system for uniformly distributing a precursor gas or gases in a low pressure chemical vapour deposition reactor. This gas distribution system can be applied in all chemical vapour deposition reactors to improve the local gas flow uniformity and thus the coating homogeneity. The system permits also to transport an e.g. reactive precursor independently without premixing close to the substrate surface to reduce the parasitic deposition on the reactor itself.

Background Art

Deposition or coating processes, especially thin film deposition processes, are well-known in the art. Especially for the manufacturing of large area coatings, deposition uniformity is an important criterion. Nowadays, layer properties realized on small scale need to be extended to large area substrates of such thin film technologies. Generally, the tighter the specification for the integration on a small area, the better the uniformities need to be on a larger area. A typical example is the IC industry, where several thin film layers are adjusted to each other. This adjustment needs to be maintained over the whole substrate area, which requires good uniformity on all involved layers in all their critical properties over the whole wafer.

A similar example is a thin film solar cell application. Here the cell properties allowing high efficiency need to be applied over the whole integrated module. Areas with properties “out of specification” will deteriorate individual cells, which will exhibit a low efficiency causing a higher resistance in a serial connection. As a consequence, areas of bad cell properties reduce the overall performance of the complete solar module.

For chemical vapour deposition (CVD) processes, temperature uniformity and gas distribution homogeneity are the most important factors. Accordingly, the most relevant parts of low pressure chemical vapour deposition (LPCVD) reactors are in a vacuum enclosure capable of being pumped to a pressure lower than atmosphere pressure (i) a heated substrate carrier, also called “hot plate”, to activate the chemical reaction of the precursor on the substrate and (ii) a gas plenum for distributing the precursors within the reaction chamber. The gas plenum may have different designs but is generally composed of a cooling part 1 to reduce parasitic coating on the gas plenum, a gas shower unit 2 and a piping net 3 to distribute the gases, as shown in prior art Fig. 1.

The pipings 3 usually exhibit bores 4 easily distributed over their length in order to allow dosing of gases and/or precursors. The bores 4 may be enclosed in a chamber, separated from the actual processing space in order to allow the inflowing gases to easily distribute even at the location of the bores 4 where local pressure peaks may arise. A shower plate or shower head is a perforated plate, i.e. the gas shower unit 2, with the distribution of through holes, the bores 4, allowing the gases to transfer from the dosing chamber to the processing space.

Such distribution of gases or precursors within the plenum using the piping net 3 is known from prior art but requires a complex maintenance, which includes dismounting all pipes, checking the whole orientation of the pipes during the mounting phase, checking numerous sealings between the frame and the pipes etc.

Furthermore, the flow uniformity obtained with the piping net 3 is poor and the possibility to improve it without extremely complex design is quite limited. In this configuration, the distribution pipes of the piping net 3 are located behind the cooling/shower plate, the gas shower unit 2, in a separate volume as described above. The precursors are mixed within this volume and may even partially react. Such parasitic deposition can occur within the gas plenum and may reduce some gas distributor functionality as a function of utilization time. To avoid only chemical reactions of the precursors within the gas plenum, more than one independent piping line has to be used which increases further the complexity of the whole distribution system and reduces even more the design freedom.

Disclosure of Invention

Therefore, it is an object of the present invention to overcome before described disadvantages of prior art, i.e. to provide a vacuum chamber having a piping system that provides an improve uniformity for the gas distribution onto a substrate to be treated in the vacuum chamber and thus improves the coating homogeneity of the substrate.

This object is achieved by the independent claim. Advantageous embodiments are detailed in the dependent claims.

Particularly, the object is achieved by a vacuum chamber for accommodating a substrate to be treated in a vacuum process comprising a gas inlet connected to a gas source for receiving gas and a gas distribution system for dispensing the gas from the gas inlet to a plurality of outlet openings into the vacuum chamber at a plurality of locations towards the substrate, whereby the gas distribution system comprises a first plate and a second plate, each plate having a flat side, the first plate exhibits a plurality of bores forming the outlet openings, the second plate exhibits a plurality of channels arranged on the flat side, the first plate and the second plate are mounted together with their flat sides directly contacting each other such that each bore of the first plate is arranged where a channel of the second plate ends such that gas is dispensable through the respective channel into the bore, and the individual channels merge into at least one common channel connected to the gas inlet thus forming a branching arrangement.

Thus, the present invention is based on the central idea to provide a so-called binary tree gas distributor plate, i.e. the second plate, having channels to transport, split and/or distribute the gas, for example a “low-reactive” gas or a gas mixture, from the gas inlet to the plurality of outlet openings, resulting in a uniform flow distribution of the gas. As a consequence, the uniform gas flow is reached, which results in a uniform coating of the substrate. In sum, the vacuum chamber comprising the gas distribution system provides for a significant improvement of the substrate coating homogeneity, thus in an improved quality of the so manufactured substrate while decreasing the manufacturing costs as well.

The term “processing” in sense of the current invention comprises any chemical, physical and/or mechanical effect acting on the substrate.

The term “substrate” in sense of the current invention comprise a component, part or workpiece to be treated with the vacuum processing system according to the invention. A substrate includes but is not limited to flat-, plate-shaped part having rectangular, square or circular shape. Preferably, the substrate is suitable for manufacturing a thin film solar cell and comprises a float glass, a security glass and/or a quartz glass. More preferably, the substrate is provided as an essentially, most preferably completely flat substrate having a planar surface of a size ≥ 1 m², such as a thin glass plate.

The term “vacuum processing” or “vacuum treatment system” in sense of the current invention comprises at least an enclosure for the substrate to be treated under pressure lower than ambient atmospheric pressure.

The term “CVD”, chemical vapour deposition, and its flavours, comprises in sense of the current invention a well-known technology allowing for the deposition of layers on heated substrates. A usually liquid or gaseous precursor material, the gas, is being fed to a process system, where a thermal reaction of the precursor results in deposition of the layer. Often, DEZ, diethyl zinc, is used as precursor material for the production of TCO layers in a vacuum processing system using low pressure CVD, LPCVD. The term “TCO” stands for transparent conductive oxide, i.e. TCO layers are transparent conductive layers, whereby the terms layer, coating, deposit and film are interchangeably used within this invention for a film deposited in vacuum process, be it CVD, LPCVD, plasma enhanced CVD (PECVD) or physical vapour deposition (PVD).

The term “solar cell” or “photovoltaic cell”, “PV cell”, comprises in sense of the current invention an electrical component, capable of transforming light, essentially sunlight, directly into electrical energy by means of the photovoltaic effect. A thin film solar cell usually includes a first or front electrode, one or more semiconductor thin film PIN junctions and a second or back electrode, which are successively stacked on a substrate. Each PIN junction or thin film photoelectric conversion unit includes an i-type layer sandwiched between a p-type layer and an n-type layer, whereby “p” stands for positively doped and “n” stands for negatively doped. The i-type layer, which is a substantially intrinsic semiconductor layer, occupies the most part of the thickness of the thin film PIN junction, whereby the photoelectric conversion primarily occurs in this i-type layer. Thus, the substrate is preferably a substrate used for manufacturing a thin film photovoltaic cell.

The term “flat” comprises in sense of the current invention a surface that is not rough, i.e. does not have grooves or alike. Preferably the term “flat” means that the surface roughness grade of the respective surface is ≤ N9.

The term “gas” in sense of the current invention means any gas suitable for providing a coating in a CVD process, especially for creating a coating required to manufacture a solar cell. Preferably, the first plate is provided as a gas shower plate, which is arranged in the vacuum chamber adjacent to the substrate. The second plate is preferably provided as a distributor plate for distributing the gas across the surface of the substrate. More preferably, each channel comprises two ends and is provided in a pipe- or tube-like manner for transporting the gas from the first end to the second end. In case where the channel is connected to a bore, it is meant that the gas transported in the channel is preferably completely dispensed into the bore, for flowing onto the substrate.

In a further preferred embodiment, the gas distribution system comprises a back plate having a flat side, the second plate exhibits two opposite flat sides and channels on the two sides, and the back plate and the second plate are mounted together with their flat sides directly contacting each other such that gas is dispensable through the channels on the two sides of the second plate. This means that each side of the second plate is designed to transport, split and/or distribute the gas, for example two different gases, independently, which may be mixed in the vacuum chamber for reacting onto the substrate. In this manner, it is further preferred that the individual channels of the two sides of the second plate per side merge into at least one common channel such that gas is dispensable to the respective channels of each side of the second plate. In other words, it is preferred that the gas distribution system comprises two different common channels each provided on one side of the second plate for providing gas to the plurality of channels. Preferably the first plate, the second plate and/or the back plate are arranged parallel to each other.

In another preferred embodiment, the second plate comprises a plurality of second bores such that gas from two channels of the two sides of the second plate is dispensable into the same bore forming a common outlet opening for the gas. This means, that two, for example different, gases are mixed, for example for becoming highly reactive, within the second plate and are afterwards and directly injected into the vacuum chamber, i.e. into the reaction chamber. For this configuration, gas pre-mixing does not occur in the gas plenum provided within the vacuum chamber, which minimizes the parasitic deposition within the gas plenum. Thus, as a consequence, the quantity of injected gas that is used for the substrate coating is increased.

In an alternative embodiment the second plate comprises a plurality of second bores each associated to a bore such that gas from channels of the two sides of the second plate is per side dispensible into a respective bore, each forming a separate outlet opening for the respective gas. This means, that according to the present embodiment the gas mixing occurs in the gas plenum, which advantageously reduces the parasitic deposition within the channel.

In an especially preferred embodiment, the end of at least one channel is located adjacent to another channel such that gas dispensed from the one channel into the another channel is equally split between the two ends of the another channel. It is further preferred, that the channels are arranged in a binary tree-manner forming the branching arrangement between the gas inlet and the outlet openings such that gas dispensed into the branching arrangement is equally split across all outlet openings. In another preferred embodiment, the channels are provided such that the gas path length is equal between the gas inlet and each outlet opening. According to those embodiments it is preferred that at least one channel branches into another channel for creating a more dendritic gas distribution system, such that the influent gas into the common channel is subdivided by the plurality of channel towards the plurality of outlet openings each having the same gas path length and preferably equally distributed along the substrate surface within the vacuum chamber. Thus, such embodiments further increase the flow uniformity for improving the coating quality of the substrate.

In another preferred embodiment, the channels are provided in a narrowing manner between the common channel and the end of the respective channel located at the bore, the common channel having a depth of ≤ 3 mm and a width of ≤ 16 mm, the end of the channels arranged at the bore having each a depth of ≤ 1,5 mm and a width of ≤ 3 mm and the bores having each a diameter of ≤ 2,2 mm. Designing the channel with before-mentioned dimensions allows for a significantly improved coating quality of the substrate, compared to prior art systems, e.g. for a thin film solar cell, especially when providing the channels in a narrowing manner having the same gas path length for all outlet openings to result in a very uniform gas distribution over the complete substrate surface to be treated. It is further preferred, that the thickness of the second plate is ≤ 15 mm, thus reducing manufacturing costs compared to prior art systems.

Generally, the gas flow within the channels may have any flow rate. However, it has been found that it is especially advantageous if the channels and the bores are provided such that the gas flow from the gas inlet to the outlet openings is ≤ 1 slm (standard liter per minute), per side of the second plate. Designing the channels and bores this way further optimize the coating quality due to an increased uniform distribution of the precursors, i.e. the gas. It has been found that a variation of 1% of DEZ flow as gas and 1°C of the substrate temperature induces a variation of about 6 nm and 25 nm of the thickness coating respectively.

In another preferred embodiment, the gas distribution system comprises a means for cooling the second plate, whereby the means preferably comprises water cooling, preferably with13 l water per min at 24°C. The cooling means avoids deposition of the surface of the second plate exposed to the hot reactor part of the vacuum chamber but also to reduce the parasitic deposition within the gas distribution system, especially if the gases are pre-mixed according to the before described embodiment.

Generally, the channels can be provided in any way known from prior art for dispensing the gas from the gas inlet to the outlet openings, whereby it is especially preferred that the channels are provided as grooves. In similar manner, the bores are preferably provided as holes through the first plate, thus allowing an easy manufacturing.

Brief Description of Drawings

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 shows a gas distribution system according to prior art,

Fig. 2 shows a top view of a binary tree gas distribution system according to a preferred embodiment of the invention,

Fig. 3 shows a side view of the binary tree gas distribution system according to the preferred embodiment of the invention,

Fig. 4a shows gas mixing in a binary tree gas distribution system according to a further preferred embodiment of the invention,

Fig. 4b shows gas mixing in a binary tree gas distribution system according to a further embodiment of the invention,

Fig. 5a shows a side view of the binary tree gas distribution system according to a further embodiment of the invention, and

Fig. 5b shows a top view of the binary tree gas distribution system according to a further embodiment of the invention.

Detailed Description of Drawings

In order to uniformly and independently distribute different precursors with a reaction chamber, i.e. a vacuum reaction chamber for treating a substrate in a vacuum process, the current invention composes a new design without using a piping distribution net 3 as shown in prior art Fig. 1.

In this new design, the gas distribution is controlled using a so-called binary tree gas distributor plate, i.e. with a second plate 5 as shown in Fig. 2 in a top view. The second plate 5 has grooved

channels

6a, 6b on both sides, as can be seen in Fig. 3. Each side is designed to transport, split and distribute one “low-reactive” gas A, B or gas mixture from one gas inlet 7 to all outlet openings 8. The groove size of the

channels

6a, 6b has been selected such that a smooth pressure change within the binary-tree gas distribution system 9 is obtained from the gas inlet 7, e.g. a separate gas inlet 7 for a different gas on each side of the second plate 5, to the 1024 outlet openings 8.

For reducing the manufacturing costs using a faster drilling, larger but cellular grooves can be made. As a consequence, the second plate 5 having 15mm can be used as gas distributor plate. In one embodiment the groove depth are between 3 mm at the entrance close to the

gas inlet

7 and 1,5mm where the

channels

6a, 6b ends at the outlet openings 8. At the same time, the width of the

channel

6a, 6b is reduced from 16mm down to 3mm, resulting in an outlet opening 8 diameter of 2,2mm. The gas A, B flows used with such configuration of the second plate 5 are about 1 slm per distributor side, i.e. per side of the second plate 5.

As can be seen further in Fig. 2, at least one

channel

6a, 6b is located adjacent to another

channel

6a, 6b such that gas A, B dispensed from the one

channel

6a, 6b into the another

channel

6a, 6b is equally split between the two ends of the another

channel

6a, 6b. This way, the gas distribution system 9 forms a binary tree branching arrangement between the gas inlet 7 and all outlet openings 8.

For mixing two different gases A, B, two different configurations are possible, as shown in Fig. 4a and Fig. 4b. In the first configuration, shown in Fig. 4a, the gases A, B are mixed within a first plate 10 in the outlet opening 8, which is provided as a bore 4, and thereafter injected into a reaction chamber 11 of the vacuum chamber. In this configuration, no gas A, B pre-mixing occurs in the gas line or in a gas plenum, e.g. in the reaction chamber 11, which minimizes the parasitic deposition within the plenum. The real quantity of injected gas A, B, that is used for the substrate coating, the gas utilization ratio, is thus increased. Furthermore, the gas shower plate, i.e. the first plate 10, is water cooled by a cooling means 12. With a cooling rate of 13 l/min at 24°C, not only to avoid deposition on its surface exposed to the hot reactor part but also to reduce the parasitic deposition within the gas shower piping 5 where the gases A, B are premixed, i.e. within the outlet opening 8.

As can be seen from Fig. 4a and 4b, the first plate 10 and a second plate 5 are mounted together with their flat sides directly contacting each other such that each bore, the outlet opening 8, of the first plate 10 is arranged where a

channel

6a, 6b of the second plate 5 ends such that the gas A, B is dispensible through the

respective channel

6a, 6b into the outlet opening 8.

In the second configuration shown in Fig. 4b no pre-mixing of the gases A, B occurs within the gas shower plate, the first plate 10, but directly within the reaction chamber 11. This configuration reduces the parasitic deposition within the grooves of the

channels

6a, 6b to a minimum.

According to the design of the gas distribution system 9 of the invention, the gas path length between the gas inlet 7 and each outlet opening 8 is the same for all different gas routes within the second plate 5, thus resulting in a uniform gas A, B flow distribution. Having such uniform gas A, B flow, the uniform coating of the substrate can be obtained, when having a uniform substrate temperature as well. For such process, a variation of 1% of DEZ, dietyhlzinc, flow and 1°C of the substrate temperature may induce a variation of about 6 nm and 25 nm of the thickness coating respectively.

The configuration shown in Fig. 4a and 4b further exhibit a separation plate 13 provided between the first plate 10 and the second plate 5 as well as a back plate 14 such that the

channels

6a, 6b on both sides of the second plate 5 are provided between the second plate 5 and the back plate 14 respectively between the second plate 5 and the separation plate 13. The second plate 5 comprises a plurality of second bores 15 such that gas A, B from two

channels

6a, 6b of the two sides of the second plate 5 is dispensable into the same bore 4, Fig. 4a, respectively that gas A, B is per side dispensable into a respective bore 4, Fig. 4b.

In the before-described binary tree gas distribution system 9 according to the invention it is possible to directly integrate the gas A, B from the reactor side and not from the top anymore as known from prior art and shown in Fig. 5a with reference sign 16. Thus, only one additional groove 17 forming the

common channel

6a, 6b is required, see also Fig. 5b. Such modification permits to drastically reduce the whole plenum thickness suitable for the integration in a stacked arrangement of reactors, compared to prior art. The replacement of traditional piping with an additional groove 16 to transport the gas A, B into the middle of the plate 5 reduces also the manufacturing costs.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

Reference Signs List

1 Cooling unit
2 Gas shower unit
3 Piping net
4 Bore
5 Second plate
6a, 6b Channel
7 Gas inlet
8 Outlet opening
9 Gas distribution system
10 First plate
11 Reaction chamber
12 Means for cooling
13 Separation plate
14 Back plate
15 Second bores
16 Reference sign
17 Additional groove

Claims

A vacuum chamber for accommodating a substrate to be treated in a vacuum process comprising a gas inlet (7) connected to a gas source for receiving gas (A, B) and a gas distribution system (9) for dispensing the gas (A, B) from the gas inlet (7) to a plurality of outlet openings (8) into the vacuum chamber at a plurality of locations towards the substrate, whereby

the gas distribution system (9) comprises a first plate (10) and a second plate (5), each plate having a flat side,

the first plate (10) exhibits a plurality of bores (4) forming the outlet openings (8),

the second plate (5) exhibits a plurality of channels (6a, 6b) arranged on the flat side,

the first plate (10) and the second plate (5) are mounted together with their flat sides directly contacting each other such that each bore (4) of the first plate (10) is arranged where a channel (6a, 6b) of the second plate (5) ends such that gas (A, B) is dispensable through the respective channel (6a, 6b) into the bore (4), and

the individual channels (6a, 6b) merge into at least one common channel (6a, 6b) connected to the gas inlet (7) thus forming a branching arrangement.
Vacuum chamber according to the preceding claim, whereby the gas distribution system (9) comprises a back plate (14) having a flat side, the second plate (5) exhibits two opposite flat sides and channels (6a, 6b) on the two sides, and the back plate (14) and the second plate (5) are mounted together with their flat sides directly contacting each other such that gas (A, B) is dispensable through the channels (6a, 6b) on the two sides of the second plate (5).
Vacuum chamber according to the preceding claim, whereby the individual channels (6a, 6b) of the two sides of the second plate (5) per side merge into at least one common channel (6a, 6b) such that gas (A, B) is dispensable to the respective channels (6a, 6b) of each side of the second plate (5).
Vacuum chamber according to any of the preceding claims 2 or 3, whereby the second plate (5) comprises a plurality of second bores (15) such that gas (A, B) from two channels (6a, 6b) of the two sides of the second plate (5) is dispensable into the same bore (4) forming a common outlet opening (8) for the gas (A, B).
Vacuum chamber according to any of the preceding claims 2 or 3, whereby the second plate (5) comprises a plurality of second bores (15) each associated to a bore (4) such that gas (A, B) from channels (6a, 6b) of the two sides of the second plate (5) is per side dispensable into a respective bore (4), each forming a separate outlet opening (8) for the respective gas (A, B).
Vacuum chamber according to any of the preceding claims, whereby the end of at least one channel (6a, 6b) is located adjacent to another channel (6a, 6b) such that gas (A. B) dispensed from the one channel (6a, 6b) into the another channel (6a, 6b) is equally split between the two ends of the another channel (6a, 6b).
Vacuum chamber according to any of the preceding claims, whereby the channels (6a, 6b) are arranged in a binary tree-manner forming the branching arrangement between the gas inlet (7) and the outlet openings (8) such that gas (A, B) dispensed into the branching arrangement is equally split across all outlet openings (8).
Vacuum chamber according to any of the preceding claims, whereby the channels (6a, 6b) are provided such that the gas path length is equal between the gas inlet (7) and each outlet opening (8).
Vacuum chamber according to any of the preceding claims, whereby the channels (6a, 6b) are provided in a narrowing manner between the common channel (6a, 6b) and the end of the respective channel (6a, 6b) located at the bore (4), the common channel (6a, 6b) having a depth of ≤ 3 mm and a width of ≤ 16 mm, the end of the channels (6a, 6b) located at the bore (4) having each a depth of ≤ 1,5 mm and a width of ≤ 3 mm and the bores (4) having each a diameter of ≤ 2,2 mm.
Vacuum chamber according to any of the preceding claims, whereby the thickness of the second plate (5) is ≤ 15 mm.
Vacuum chamber according to any of the preceding claims, whereby the channels (6a, 6b) and the bores (4) are provided such that the gas flow from the gas inlet to (7) the outlet openings (8) is ≤ 1 slm per side of the second plate (5).
Vacuum chamber according to any of the preceding claims, whereby the gas distribution system (9) comprises a means for cooling (12) the second plate (5).
Vacuum chamber according to any of the preceding claims, whereby the channels (6a, 6b) are provided as grooves.
Vacuum chamber according to any of the preceding claims, whereby the bores (4) are provided as holes through the first plate (10).