WO2011060830A1

WO2011060830A1 - Chemical vapour deposition process and device

Info

Publication number: WO2011060830A1
Application number: PCT/EP2009/065563
Authority: WO
Inventors: Rutger Schlatmann; Jozef Lenssen; Johannes Andreas Maria Ammerlaan
Original assignee: Helianthos B.V.
Priority date: 2009-11-20
Filing date: 2009-11-20
Publication date: 2011-05-26

Abstract

A chemical vapour deposition process and device (1) for applying a deposit layer on a substrate (4) wherein a heated support surface (6) supports the substrate, while a flow of precursor gases is guided over the substrate through a gap (12) between the support, surface and an opposite guiding surface (9) from a gas precursor inlet (10) to an outlet (11). The inlet and the outlet are arranged at a different height, resulting in a non-horizontal gas flow. The width of the substrate is at least 10 times the distance between the support surface and the guiding surface (9).

Description

CHEMICAL VAPOUR DEPOSITION PROCESS AND DEVICE

The present invention relates to a chemical vapour deposition process for applying a deposit layer on a substrate, A support surface supports the substrate, while a flow of precursor gases is guided over the substrate through a gap between the support surface and an opposite guiding surface from a gas precursor inlet to an outlet. The process and device are particularly suitable for the manufacture of foil or web material provided with a deposited film, such as a photovoltaic foil. Chemical Vapour Deposition (CVD) involves the chemical

reactions of gaseous reactants on or near a substrate,

typically in a reaction chamber. Generally, gaseous precursors are supplied into a reaction chamber to undergo gas phase reactions forming intermediate species. At a high temperature above the decomposition temperatures of intermediate species inside the reactor, homogeneous gas phase reaction can occur where the intermediate species undergo subsequent decomposition and/or chemical reaction to form a dense layer and volatile byproducts in the gas phase. The volatile by-products are discharged from the reaction chamber. At temperatures below the dissociation of the intermediate phase, diffusion or convection of the intermediate species can occur across the boundary layer, which is a thin layer close to the substrate. The gaseous precursors form intermediate species which are adsorbed onto the substrate. The adsorbed intermediate species diffuse along the surface before they finally react, and the deposit constituents are built into the structure forming the deposit. Gaseous by-products and unreacted gaseous precursor are removed from the boundary layer through diffusion or convection and extracted from the reaction chamber,

A wide variety of CVD processes exist. These CVD processes can differ in the applied pressure conditions. A distinction is made between atmospheric pressure CVD (APCVD) on the one hand and low-pressure CVD (LPCVD) on the other.

In the field of semi-conductors and photovoltaic devices, CVD is typically used to apply thin films of metal oxides, silicon oxides, metals, fluorides, nitrides, silicon nitrides,

oxyni.trid.es, semiconducting materials, such as silicon and/or germanium, compound semiconductors or mixtures thereof.

WO 98/13882 discloses a process for the manufacture of

photovoltaic foils, e.g., by using a roll-to-roll process. One or more of the layers can be applied by using a CVD process, such as a transparent silica layer, a diffusion barrier layer, and/or a transparent conductive oxide layer, e.g., of indium tin oxide, cadmium sulfide or oxide, tin oxide (e.g., fluorine doped) or zinc oxide, which can for example be aluminum doped or boron doped.

The object of the present invention is to come to a deposition process and a corresponding device allowing the formation of more even layer thicknesses and stable boundaries.

The object of the invention is achieved with a chemical vapour deposition process and device for applying a deposit layer on a substrate wherein a heated support surface supports the substrate, while a flow of precursor gases is guided over the substrate through a gap between the support, surface and an opposite guiding surface from a gas precursor inlet to an outlet, wherein the inlet and the outlet are arranged at a different height and wherein the width of the substrate is at least 10 times, e.g., at least 20 or at least 30 times, the distance between the support surface and the guiding surface.

Since the inlet and outlet are at different height, the gap forms a non-horizontal reaction chamber. The mean flow

direction of the precursor gases is also non-horizontal.

It has been found, that the combination of a heated surface with a non-horizontal gap results in a buoyancy effect, which is a function of the temperature difference between the heated support surface and the cooler guiding surface. A vertically buoyancy force works on the gas flow, directed away from the heated support surface. If the gas flow runs through a

horizontal reaction chamber, the buoyancy force is

perpendicular to the flow direction of the gas flow and disturbs the laminar flow. However, the larger the angle between the reaction chamber and the horizontal, the more the buoyancy force is in line with the flow direction. This stabilizes the laminar precursor flow, so a very stable, laminar gas flow can be obtained resulting in a very constant thickness of the deposit layer and stable boundaries.

The stabilizing effect is enhanced if the angle between the precursor flow direction and the horizontal is larger. For example, the shortest line between the gas precursor inlet and the outlet can make an angle of at least 30°, e.g. at least 45°, e.g. at least 60° with the horizontal. Very good results are obtained if the shortest line between the gas precursor inlet and the outlet makes a right angle with the horizontal. The inlet can be positioned higher or lower than the outlet.

The gap can be of constant width in flow direction and/or in the direction perpendicular to the flow direction.

Alternatively, the gap can have a width which gradually increases or decreases in flow direction.

The width of the gap, defined as the shortest distance between the support surface and the guiding surface, can for example be 1 - 25 ram, e.g. 6 - 10 iraa.

The distance between the curved surface and the congruent guiding surface can be adjusted to the desired through-flow and residence time of the precursor gases.

The substrate can for example be a foil substrate. For the production of photovoltaic foils, metal foils, in particular aluminium foil substrates can be used. Other suitable materials include polymeric foils, such as polyethylene terephthalate , poly (ethylene 2, 6naphthalene dicarboxylate) , polyvinyl

chloride, or high-performance polymer foils such as aramid or polyimide foils. These foil substrates typically have a width of 300 mm or more, e.g., 500 mm or more, but alternative widths can also be used if so desired.

Optionally, the support surface can for example be curved. It can for example be part of a drum, e.g., a rotatable drum, particularly if the process is part of a roll-to-roll process. If the curved surface is cylindrical, the slits of the outlet and the inlet may be arranged parallel to the cylinder axis of the curved surface. The substrate can be transported in a direction opposite to the flow direction of the precursor gases or it can be transported in the same direction as the direction of the precursor gas flow.

The support surface can for instance be heated to a temperature of at least 200°C, e.g., at least 350°C.

The outlet and the inlet can for example form slits of a width corresponding to the width of the reaction chamber. In this context _f the slits and the gap are considered to be of a corresponding width if any variation in width is too small to contribute to a flow disturbance that might negatively affect the uniformity of the layer thickness of the deposited layer to a noticeable extent.

The outlet slit can for example lead to an exhaust channel having the same width as the outlet slit, which exhaust channel leads away from the curved surface.

The inlet can for example be defined by an edge of the guiding surface and a rib or strip located between the guiding surface and the curved surface. This way, the gas flow coming from the supply is deflected passing the inlet slit into a flow

direction parallel to the guiding surface. This enables further- optimization of laminar gas flow. The rib can form an integral part of the wall of the supply channel. The outlet slit can be defined in a similar arrangement.

The gap can be shielded by side wails and/or end walls to reduce the risk of unintentional outflow of precursor gases or volatile by-products . This risk can be further reduced by drawing ambienent air into the reaction chamber, so that the exhaust flow will be larger than the supply flow of precursor gases . In a specific embodiment, the precursor gases can be guided to flow in tangential direction relative to the curved surface. To that end, the reaction chamber can for example comprise at two opposite ends of the guiding plate a precursor gas inlet and a gas flow outlet, respectively, the outlet and the inlet forming slits which are substantially parallel to the cylindrical axis of the curved surface.

Good deposit films are obtained if the foil is transported in a direction opposite to the flow direction of the precursor gases. Alternatively, the substrate can be transported into the same direction as the flow direction of the precursor gases in the reaction chamber.

If so desired, the device according to the invention can comprise a series of two or more reaction chambers, e.g., in serial or parallel arrangement, facing different sections of the same curved surface. The reaction chambers can for instance be used for depositing different layers or different deposition materials .

In a specific embodiment, each of the one or more reaction chambers spans less than 20 %, e.g., less than 12 %, e.g., less than 8 % of the circumference of the curved surface. The process of the present invention is particularly useful for thermally catalyzed chemical vapour deposition processes, in particular for the manufacture of photovoltaic foils. The layers applied by the CVD process of the invention can for instance be a transparent silica layer, a diffusion barrier layer, and/or a transparent conductive oxide layer, e.g., of indium tin oxide, cadmium sulfide or oxide, tin oxide (e.g., fluorine doped) or zinc oxide, which can for example be aluminum doped or boron doped.

With the process according to the invention, layers can be deposited with a thickness of, for instance, 5 nm - 5 μm or larger, e.g., 0,1 - 2 μm.

The present invention will be elucidated with reference to the drawings wherein:

Figure 1; shows schematically a cross section of a device according to the invention;

Figure 2: shows a deposition unit of the device of Figure

1;

Figure 3: shows in longitudinal cross section the

deposition unit of Figure 2;

Figure 4: shows in lateral cross section the deposition unit of Figure 2.

Figure 1 shows in cross section a device I for applying a deposition film, on a foil substrate by chemical vapour

deposition, in particular by an APCVD process. The device 1 comprises three deposition units 2 having an open end 3 directed to a foil substrate 4. The foil 4 is wound around a rotating drum or turner roller 5 formed by a cylindrical mantle 6 of a heat conductive material, such as a corrosion resistant steel. In the interior of the drum 5, five, stationary heaters 7 are arranged to heat the mantle 6, In other embodiments, the number of heaters can be less or higher, if so desired. A large number, e.g., 200 or more, of smaller heater elements can for example be used to achieve uniform heat distribution.

Figure 2 shows more detail of a deposition unit 2, which is shown in Figure 3 in longitudinal cross section and in lateral cross section in Figure 4, The drum 5 rotates in the direction indicated by arrow A. The deposition unit 2 is provided with a guiding member 8 with a guiding surface 9 congruent to the opposite surface section of the drum 5. At one end of the guiding surface 9 the deposition unit 2 comprises a slit shaped inlet 10 for the supply of a precursor gas via a supply channel 17. The slit shaped inlet 10 has a width corresponding to the width of the surface to be coated of the foil substrate 4, which is more than 30 times the shortest distance between the support surface 5 and the guiding surface. 9. The supply channel 17 gradually widens form a tubular supply line 18 to the full length of the inlet slit 10, as is shown in dotted lines in Figure 4. At the opposite end the deposition unit 2 comprises an outlet 11, which is also slit shaped and which is parallel to the inlet 10, The outlet 11 leads to an exhaust 19 leading the gas flow away from the substrate 4 and the curved surface 5. The exhaust. 19 gradually narrows down from the full length of the outlet slit 11 to a discharge line 20. The inlet 10 and the outlet 11 form slits parallel to the axis of the drum 5. Between the guiding surface 9 and the foil substrate 4 is a gap 12 forming a reaction chamber for the APCVD process. The gap 12 is confined by side walls 13, a first end wall 14 close to the inlet 10, and a second end wall 15 close to the outlet 11. With all three deposition units 2 in Figure 1, the inlet 10 is at a different height than the outlet 11. In the middle deposition unit, the shortest line between the inlet 10 and the outlet 11 is under right angles with the horizontal, as is also shown in Figure 2. In the other two deposition units 2, the shortest line between the inlet 10 and the outlet 11 is under an angle of about 45° with the horizontal.

Precursor gases flow in the direction indicated by the arrows in Figure 3. The heaters 7 heat the mantle 6 of the curved surface 5. The heated mantle 6 heats the foil substrate 4. As a result, the precursor gases near the substrate react and a film is deposited on the foil substrate. The temperature difference between the heated mantle 6 and the guiding surface 9 results in buoyancy effects exerting a vertically upward force. This buoyancy force is in line with the flow direction of the gas flow. This results in a stable laminar flow.

In this embodiment, the drum. 5 rotates in the same direction as the tangential precursor gas flow. Alternatively, the

rotational direction A of the roller can be opposite to the flow direction of the precursor reactant gases.

Claims

1. A chemical vapour deposition process for applying a

deposit layer on a substrate wherein a heated support surface supports the substrate, while a flow of precursor gases is guided over the substrate through a gap between the support surface and an opposite guiding surface from a gas precursor inlet to an outlet, wherein the inlet and the outlet are arranged at. a different, height and wherein the width of the substrate is at least 10 times the distance between the support surface and the guiding surface .

2. Deposition process according to claim 1 wherein the

shortest line between the gas precursor inlet and the outlet makes an angle of at least 30°, e.g. at least 45°, e.g. at least 60° with the horizontal.

3. Deposition process according to claim 2 wherein the

shortest line between the gas precursor inlet and the outlet makes a right angle with the horizontal.

4. Deposition process according to any one of the preceding claims, wherein the inlet is positioned higher than the outler..

5. Deposition process according to any one of the preceding claims, wherein the outlet is positioned higher than the inlet . Deposition process according to any one of the preceding claims wherein in flow direction the gap is of constant 'width ,

Deposition process according to any one of the preceding claims wherein the substrate is a foil substrate and the support surface is curved.

Deposition process according to claim 7 wherein the support surface is part of a drum, e.g., a rotatable drum .

Deposition process according to claim 7 or 8, wherein the process is part of a roll-to-roll process.

Deposition process according to any one of the preceding claims wherein the substrate is transported in a

direction opposite to the flow direction of the precursor- gases .

Deposition process according to any one of the preceding claims wherein the support surface is heated to a

temperature of at least 200 °C, e.g., at least 350 °C.

Device for applying a deposition film on a substrate by chemical vapour deposition, the device comprising a support surface with one or more heating elements and one or more reaction chambers formed by a gap between the support, surface and a guiding surface, and wherein the reaction chambers comprise a precursor gas inlet at one end of the reaction chamber and an outlet at the opposite end, wherein the inlet and the outlet are arranged at a different height and wherein the width of the reaction chamber is at least 30 times the distance between the support surface and the guiding surface.

Device according to claim 12 wherein the outlet, and the inlet forming slits of a width corresponding to the width of the reaction chamber.

Device according to claim 12 or 13, wherein the curved surface is cylindrical and wherein the slits of the outlet and the inlet are parallel to the cylinder axis the curved surface.

Device according to claim 13 or 14, wherein the outlet slit leads to an exhaust channel having the same width as the outlet slit, which exhaust channel leads away from the curved surface.

Device according to any one of the preceding claims 12 - 15, wherein a series of two or more reaction chambers is positioned in a serial arrangement.