GB2601831A

GB2601831A - Conductance seal

Info

Publication number: GB2601831A
Application number: GB2019716.6A
Authority: GB
Inventors: Dicken Steven; Clements Trevor; Murray Peter; Butcher Nicholas; Astbury Robert
Original assignee: Emerson and Renwick Ltd
Current assignee: Emerson and Renwick Ltd
Priority date: 2020-12-14
Filing date: 2020-12-14
Publication date: 2022-06-15
Also published as: GB202019716D0

Abstract

An apparatus for treating a substrate comprises a chamber 25 for housing a treatment apparatus, the chamber defined in part by a wall 20, and a conduit 10 permitting transmission of a substrate between an exterior and an interior of the chamber, wherein a first side of the conduit is defined by a face of a conductance seal plate 15 attached to the wall, and wherein the surface roughness Ra of the face of the seal plate is in the range of 1 to 10 µm. A face of the seal plate may be rectangular and arranged parallel to a face of a second seal plate to form the conduit (figure 1). A face of the seal plate may be curved and a second side of the conduit may be defined by the surface of a rotatable drum 35 for conveying an elongated flexible substrate. A treatment device located within the chamber may be a device for physical vapour deposition, chemical vapour deposition, plasma treatment, sputtering, electron beam gun deposition, atomic layer deposition or reactive ion etching.

Description

Conductance Seal [0001] The present invention relates to a conductance seal plate and an apparatus for treating a substrate, specifically the invention relates to an apparatus for treating a substrate at reduced pressures.

Background

[0002] Roll-to-roll, or web, processing is well known for the manufacture of products such as wallpaper, gift-wraps, foils and plastic films. In these processes, a long and flexible substrate is unspooled from a first roll and fed through the apparatus for treatment, before being spooled onto a second roll. This approach advantageously allows for the continuous treatment of the substrate as it is simultaneously unspooled from the first roll and spooled onto the second roll.

[0003] Some treatment processes, such as metallization by sputtering, either require or are improved by low atmospheric pressures, necessitating the use of a low-pressure chamber within which the treatment process can be carried out. However, a problem arises in maintaining a high pressure differential (i.e. a low pressure in the chamber and a normal pressure outside) between the chamber interior and exterior while the substrate is passed through the chamber.

[0004] One possible solution is to process the substrate in batches. The chamber can be opened and a portion of the substrate can be loaded into the chamber. The chamber can then be sealed with the substrate inside it. The sealed chamber is then evacuated and the treatment performed. The chamber is then re-pressurised, opened and the treated substrate removed before the process is repeated. This approach is effective, but inefficient as the process repeatedly stops and starts. It can also lead to uneven application of treatments between batches. An alternative is to continuously process the substrate by squeezing the substrate between two rollers where it enters and exits the chamber to provide a seal. This allows for continuous motion of the substrate, but the roller can damage certain surface finishes where it contacts the substrate.

[0005] A further approach is to have a 'conductance seal' where the substrate enters and exits the chamber. The conductance seal provides an aperture whose cross-section (perpendicular to the direction of travel of the substrate) is marginally larger than that of the substrate, permitting free movement of the substrate into and out of the chamber while minimizing the space/gap through which atmosphere can flow into the low-pressure chamber. The conductance seal typically features plates with extensive length parallel to the substrate, effectively creating a tube, which further limits the speed at which atmosphere can flow into the low-pressure chamber. This approach allows constant movement of the substrate without risking damaging its surface, while maintaining moderate pressure differentials.

[0006] The present invention seeks to address one or more of the problems associated with existing processing techniques, whether mentioned above or otherwise, and provide an apparatus which can maintain a larger pressure differential without adversely affecting the overall process speed or finish quality. Furthermore, the present invention seeks to provide an alternative conductance seal.

Summary of the Invention

[0007] A first aspect of the present invention relates to a conductance seal plate for a chamber for housing a treatment apparatus, the chamber defined in part by a wall and having a conduit between an interior of the chamber and an exterior of the chamber, the conductance seal plate comprising: a face configured to at least in part define the conduit, and an attachment portion for attaching the plate to the wall, wherein the surface roughness (Ra) of the face is in the range of 1 to 10 pm. [0008] It has been unexpected discovered that there is an optimum range of surface roughness for conductance seal plates, with conductance seals utilising plates whose surface roughness falls within the range of about 1 to about 10 pm being capable of maintaining higher pressure differential ratios between the interior of the chamber and the exterior of the chamber than those whose surface roughness falls outside of this range. Preferably, the surface roughness of the face is in the range of about 2 to about 9 pm. More preferably, the surface roughness of the face is in the range of about 4 to about 8 pm. Furthermore, until now, there has been a long-held prejudice within the industry towards providing conductance seals which have highly polished (i.e. very low surface roughness) surfaces as conventional wisdom is that this is required to assist with cleaning the conductance seal.

[0009] The face of the conductance seal may be rectangular. This provides a conductance seal plate capable of forming a conduit of constant cross-section when two such plates are arranged substantially parallel to one another. The conductance seal plate may be curved so that, in embodiments where the conductance seal is paired with a rotatable drum, a conduit of constant cross-section may be formed.

[0010] The length of the face of the conductance seal plate may be in the range of about 50 mm to about 250 mm. It will be understood that the length of the face of the conductance seal plate refers to the length of the face in the direction parallel to the direction of travel of the substrate, in use, and that the length of the plate is equivalent to the depth of the conduit that it defines. Preferably the length of the conductance seal plate is in the range of about 75 mm to about 150 mm. More preferably, the length of the conductance seal plate is about 100 mm.

[0011] The width of the face of the conductance seal plate may be in the range of about 100 mm to about 5000 mm. It will be understood that the width of the face of the conductance seal plate refers to the width of the face in the direction perpendicular to the direction of travel of the substrate and parallel to the plane of the substrate, in use, as it passes through the conduit. Conceivably, any width may be used on the proviso that it exceeds the width of the substrate that is to be passed through the conduit.

Preferably, the width of the conductance seal plate is in the range of about 100 mm to about 4000 mm, more preferably about 100 mm to about 2000 mm, further preferably about 100 mm to about 1000 mm, yet further preferably, about 100 mm to about 500 mm. Most preferably, the width of the conductance seal plate is about 150 mm.

[0012] The face of the conductance seal plate may be formed from aluminium. It will be understood that the face of the conductance seal plate may be produced from any material that is sufficiently physically resilient and inert to maintain its form despite the application of sustained pressure differentials across its length.

[0013] The surface roughness may be achieved through bead blasting or application of a wire brush. The skilled person will understand that any suitable process applying an abrasive media may be used. In particular, the bead blasting may be performed with any suitable media, such as 20/40 garnet bead, and the wire brush may be applied to the face of the conductance seal plate as an abrasive pad on a spinning wheel.

[0014] A second aspect of the present invention relates to an apparatus for treating a substrate comprising: a chamber for housing a treatment apparatus, the chamber defined in part by a wall and a conduit permitting transmission of the substrate between an exterior of the chamber and an interior of the chamber, a first side of the conduit defined by a face of a first conductance seal plate attached to the wall; wherein the surface roughness (Ra) of the face of the conductance seal plate is in the range of 1 to 10 pm.

[0015] It has been unexpected discovered that there is an optimum range of surface roughness for conductance seal plates used in such apparatus, with conductance seals utilising plates whose surface roughness falls within the range of about 1 to about 10 pm being capable of maintaining higher pressure differential ratios between the interior of the chamber and the exterior of the chamber than those whose surface roughness falls outside of this range. Preferably, the surface roughness of the face is in the range of about 2 to about 9 pm. More preferably, the surface roughness of the face is in the range of about 4 to about 8 pm. Furthermore, as already discussed, until now, there has been a long-held prejudice within the industry towards providing conductance seals which have highly polished (i.e. very low surface roughness) surfaces as conventional wisdom is that this is required to assist with cleaning the conductance seal.

[0016] A second side of the conduit may be defined by a face of a second conductance seal plate attached to the wall. Preferably the face of the second conductance seal plate has a surface roughness of about 1 to about 10 pm. More preferably the surface roughness of the face is in the range of about 2 to about 9 pm. Most preferably, the surface roughness of the face is in the range of about 4 to about 8 pm.

[0017] In certain embodiments, the apparatus is configured such that the substrate is unsupported within the conduit and is kept substantially planar at the point where it passes through the conduit due to tension within the substrate. In such embodiments the spacing between the substrate and the first and/or second side of the conduit (and hence the surface of the first conductance plate and/or the surface of the second conductance plate, respectively) may be substantially constant.

[0018] A second side of the conduit may be defined by the surface of a rotatable drum. In certain embodiments, the apparatus is configured such that the substrate is supported on a surface of the drum whilst it passes through the conduit. The drum may be passively rotating (i.e. rotated due to contact between the drum and the moving substrate), or it may be driven (e.g. by a motor) to rotate, preferably such that its surface moves at the same speed as the substrate. In such embodiments, the conductance seal plate may be curved so that a conduit formed between the conductance seal plate and the rotatable drum is of constant cross-section.

[0019] The separation between the first side of the conduit and the second side of the conduit may be about 1 mm to about 5 mm. Preferably the separation is about 1 mm to about 3 mm. More preferably, the separation is about 2 mm. In principle, any separation between the first and second sides of the conduit may be used so long as it permits sufficient separation between the static surfaces of the conduit and the substrate to prevent damage while the substrate passes through the conduit, and to maintain a sufficient differential pressure (or pressure ratio) between the interior and exterior of the chamber for the treatment process to be effective.

[0020] The apparatus may be configured to maintain a differential pressure ratio between the chamber interior and the chamber exterior of at least about 80. Preferably, the apparatus is configured to maintain a differential pressure ratio between the chamber interior and the chamber exterior of at least about 85. More preferably, the apparatus is configured to maintain a differential pressure ratio between the chamber interior and the chamber exterior of at least about 90. Most preferably, the apparatus is configured to maintain a differential pressure ratio between the chamber interior and the chamber exterior of at least about 95. The apparatus is configured through the selection of appropriate conductance seal plates (e.g. one or more conductance seal plates having a surface with an appropriate surface roughness) and conduit dimensions (and hence the dimensions of the one or more conductance seal plates which at least in part form the conduit).

[0021] The wall may further define an outlet in communication with the chamber interior configured to connect to a vacuum pump.

[0022] The apparatus may further comprise a treatment device within the chamber, such as apparatus for pre or post treatment, physical vapour deposition, chemical vapour deposition, Plasma Treatment, thermal evaporative deposition, sputtering, plasma assisted chemical vapour deposition (PACVD), electron beam gun deposition (E-Beam), Atomic layer deposition (ALD), or Reactive Ion etching (RIE).

[0023] The first and/or second conductance seal plate may be as defined in the first aspect of the present invention.

[0024] A third aspect of the present invention relates to the use of a conductance seal plate for forming one or both sides of a conduit permitting transmission of a substrate between an exterior of a chamber and an interior of the chamber, wherein the conductance seal plate has a surface roughness (Ra) of about 1 to about 10 pm. Preferably, the surface roughness of the face is in the range of about 2 to about 9 pm. More preferably, the surface roughness of the face is in the range of about 4 to about 8 pm. The conductance seal plate may be as defined in the first aspect of the present invention.

[0025] A fourth aspect of the present invention relates to a method of maintaining a differential pressure between an exterior of a chamber and an interior of a chamber, the chamber defined in part by a wall, comprising the steps of attaching a first conductance seal plate to the wall such that the face of the first conductance seal plate defines a first side of a conduit permitting transmission of the substrate between an exterior of the chamber and an interior of the chamber; and reducing the pressure in the chamber, wherein the surface roughness (Ra) of the face of the conductance seal plate is in the range of 1 to 10 pm. Preferably, the surface roughness of the face is in the range of about 2 to about 9 pm. More preferably, the surface roughness of the face is in the range of about 4 to about 8 pm.

[0026] The method may further comprise the step of attaching a second conductance seal plate to the wall such that the face of the second conductance seal plate defines a second side of the conduit. Preferably the face of the second conductance seal plate has a surface roughness of about 1 to about 10 pm. More preferably the surface roughness of the face is in the range of about 2 to about 9 pm. Most preferably, the surface roughness of the face is in the range of about 4 to about 8 pm.

[0027] A second side of the conduit may be defined by the surface of a rotatable drum. In such embodiments, the conductance seal plate used may be curved so that a conduit formed between the conductance seal plate and the rotatable drum is of constant cross-section [0028] The separation between the first side of the conduit and the second side of the conduit may be about 1 mm to about 5 mm. Preferably the separation is about 1 mm to about 3 mm. More preferably, the separation is about 2 mm. In principle, any separation between the first and second sides of the conduit may be used so long as it permits sufficient separation between the static surfaces of the conduit and the substrate to prevent damage while the substrate passes through the conduit, and to maintain a sufficient differential pressure (or pressure ratio) between the interior and exterior of the chamber for the treatment process to be effective.

[0029] The method may maintain a pressure differential between the chamber interior and the chamber exterior is at least 80. Preferably, the differential pressure ratio between the chamber interior and the chamber exterior of at least about 85. More preferably, the differential pressure ratio between the chamber interior and the chamber exterior of at least about 90. Most preferably, the differential pressure ratio between the chamber interior and the chamber exterior of at least about 95.

[0030] The pressure in the chamber may be reduced with a vacuum pump. The first and/or second conductance seal plate may be as defined in the first aspect of the present invention.

[0031] Where appropriate, any of the optional features discussed above in relation to one aspect of the invention may be applied to another aspect of the invention.

Brief Description of the Drawings

[0032] Figure 1 is a schematic of a conduit formed of two opposed conductance seal plates.

[0033] Figure 2 is a schematic of a conduit formed of a conductance seal plate in combination with a rotating drum.

[0034] Figure 3 is a schematic of a chamber defined by of a wall and a rotating drum, with each conductance seal being formed by the drum and a conductance seal.

[0035] Figure 4A is a schematic of air flow over a smooth conductance seal plate.

[0036] Figure 4B is a schematic of air flow over a rough conductance seal plate [0037] Figures 5A and 5B display the results of the trials performed with a conduit formed with two treated conductance seal plates.

[0038] Figures 6A and 6B display the results of the trials performed with a conduit formed with a treated conductance seal plate and an untreated conductance seal plate.

Detailed Description

[0039] Substrates are typically made of flexible materials and are extremely long, have an intermediate, constant width and are thin. For practicality, they are stored and transported on rolls when not being processed or used. In order to surface treat a substrate, the substrate is unspooled from a first roll and passed into a chamber through a first conduit. Within the chamber the substrate is treated, it is then removed from the chamber through a second conduit, and is spooled onto a final roll. At all times, the substrate is held under tension between the first and final rolls. This keeps the substrate taut and holds it so that it is essentially planar as it travels between the rolls.

[0040] Where the substrate is required to turn, the substrate is guided by the surface of a roller, or a rotatable drum. Again, the substrate is kept taught and essentially planar between each adjacent roller. Depending on the length of the unrolled substrate, the roller may be passive, rotating with the substrate, or it may be driven such that its surface moves at the same speed as the substrate.

[0041] Fig. 1 shows a schematic of a first embodiment in which the conduit 10 is formed of two opposing conductance seal plates 15. Each of the plates 15 has a face with a length of 150 mm and a width of 100 mm and has perpendicular portion serving as an attachment portion. The perpendicular portions include through-holes which align with through-holes located on the wall 20 of the chamber, permitting the plates 15 to be attached to the wall 20 with bolts. Of course, any other suitable attachment/fixing means may be used. Once fitted to the wall 20, the faces of the plates 15 form, at least in part, a conduit 10 permitting transmission of the substrate, while limiting the flow of gas to maintain a differential pressure between the interior 25 and the exterior 30 of the chamber defined by the walls 20.

[0042] The separation of the faces of the conductance seal plates 15 is approximately 2 mm. This gives sufficient clearance to prevent contact between the faces and the substrate, which could damage the substrate, while minimizing the opening through which gas can be drawn due to the differential pressure.

[0043] Fig. 2 shows a schematic of a second embodiment in which the conduit 10 is formed at least in part by a conductance seal plate 15 and an outer surface of a rotatable drum 35. The plate 15 is as described in the first embodiment, and is attached to the wall 20 such that the face of the plate 15 is substantially parallel to the tangent plane of the rotating drum 35 closest to the wall 20 where the plate 15 is attached. The plate 15 is shaped to follow the curve of the rotatable drum 35, such that the face of the plate 15 maintains a substantially constant separation from the surface of the rotatable drum 25. In chambers including the conduit 10 of Fig. 2, a portion of the chamber is defined by the drum 35.

[0044] Fig. 3 shows a schematic of a chamber formed by a wall 20 in combination with a rotating drum 35. The chamber includes two conduits 10 as described above in reference to Fig. 2, one on each side of the drum 35.

[0045] It will be understood that, other than the conduits 10, the walls 20 of the chamber are impermeable to gas. Further outlets and inlets may be included in the wall of the chamber.

[0046] It is usual for a chamber to have two conduits, one for the entrance of the substrate and one for its exit, although more may be used. There is no restriction on which types of conduits may be used in combination. For example, a chamber comprising two conduits may have each conduit formed from a pair of conductance seal plates, one conduit formed a pair of conductance seal plates and one conduit formed from the combination of a conductance seal plate and a roller, or two conduits formed from the combination of a conductance seal plate and a roller.

[0047] A single chamber may be used. Alternatively, further chambers may be included in series (i.e. the substrate moving sequentially from one chamber to the next). In embodiments with multiple chambers, the multiple chambers may be adjacent to one another such that the conduit is between the interior of one chamber and the interior of the next. It will be appreciated that in this case the interior of one chamber may be considered to be the exterior of another chamber. Such arrangements are particularly beneficial for sensitive treatment processes as the outer chambers may act as a buffer to atmosphere, for example introducing an inert gas (e.g. N2) to further limit the flow (or potential flow) of air (or atmosphere) into the subsequent chamber. Alternatively, such chambers may be nested such that a first chamber is fully contained within a second chamber.

[0048] The differential pressure that can be maintained by a conduit depends on the dimensions of the conduit, which may be determined by the dimensions of the faces of the conductance seal plates and their separation from each other, or the drum if used. Increasing the length of the plates, decreasing the width of the plates, and decreasing the separation between the plates all increase the differential pressure that can be maintained. However, there are practical limits to all of these due to the need to avoid contact between the conduit walls (and hence plate(s)) and the substrate.

[0049] Conductance seal plates commonly have a smooth surface finish. Unexpectedly, it has been found that a moderate increase in surface roughness improves the differential pressure that can be maintained. Without wishing to be bound by theory, it is thought that a smooth surface permits the gas to flow unimpeded (see Fig. 4A), while a moderately rough surface increases the rate of backscatter, effectively reducing the average velocity of gas molecules moving along the conduit (see Fig. 4B). This is shown in Figs. 4A and 4B, which schematically depict the pathways of gas molecules. However, at higher levels of surface roughness the differential pressure that can be maintained decreases. It is thought that, as plate separation is measured from the closest points of the or each plate (i.e. the point that extends furthest into the conduit through which the webbing will be passed), excessive surface roughness effectively increases the plate separation, reducing the differential pressure that can be maintained. Alternatively, or in addition, it is possible that above a particular level of surface roughness, the surface not only leads to an increase in the rate of backscatter, but also an increase in subsequent re-backscattering of gas molecules moving along the conduit, and consequently more gas passing through the conduit, thereby reducing the differential pressure that can be maintained.

[0050] Advantageously, the surface roughness of the face of the conductance seal plate can be in the range of 1 to 10 pm. More beneficially, the surface roughness can be in the range of 2 to 9 pm, even more beneficially the surface roughness can be in the range of 4 to 8 pm.

[0051] The desired surface roughness can be achieved through any suitable mechanical method, such as application of an abrasive (e.g an abrasive pad on a spinning wheel) or bead blasting with suitably sized media. Any other appropriate method may be used, such as chemical or laser etching.

[0052] It will be understood that the foregoing explanation and description relate to limited embodiments of the apparatus and that, in practice, the apparatus may vary depending on the demands of the substrate and the treatment process it is subjected to. Such variations, additions, and modifications of the presently described apparatus are within the scope of the present invention.

Examples

[0053] Aluminium conductance seal plates were used for the trials, with a face length of 100 mm and a face width of 150 mm. The conductance seal plates were treated to achieve different levels of average surface roughness (Ra). Treatment methods employed included wire brushing with an abrasive wheel, and bead blasting (with varying grit sizes).

[0054] The surface roughness of each treated conductance seal plate was measured in terms of Ra using a Surtronic Duo Surface Roughness Tester (produced by Taylor Hobson Limited, UK). Several readings were taken across the surface of each seal plate and an average value determined.

[0055] Each of the conductance seal plates was, in turn, affixed to the wall between two chambers, the first of which was connected to a nitrogen source providing N2 gas and the second of which was connected to a vacuum pump. The vacuum pump was switched on and the system left to reach a steady state, at which point the pressure in the first chamber, Pi, and the pressure in the second chamber, P2, were noted and used to calculate a differential pressure ratio (dP) between the chambers using the following equation: dP = -P1 P2 [0056] A first group of experiments were performed with conduits formed from two treated conductance seal plates in the absence of a substrate. The interfacial separation of the conductance seal plates was set to 2 mm, N2 was introduced to the first chamber at a rate of 50 cm3/s, and the vacuum pump was operated at a speed of 225 Us. Each sample was analysed in triplicate and the average pressure differential ratio recorded. The results are shown in Table 1 and displayed graphically in Figures 5A and 5B.

Sample Treatment Surface roughness dP (Ra) (pm) Untreated N/A 0.496 79.77 A Wire Brush 4.088 89.74 B1 20/40 Garnet 7.89 92.30 Blasted

Table 1

[0057] It can be seen that the untreated conductance seal plates, with their low surface roughness of approximately 0.5 pm, provide a differential pressure ratio of below 80.

Conversely, the conductance seal plates that had been treated with a wire brush or blasted with the fine 20/40 garnet media, with surface roughness of approximately 4 to 8 pm, achieved differential pressures of approximately 90.

[0058] This unexpected result demonstrated that altering the surface roughness of the conductance seal plates could have a significant influence on the differential pressure that could be obtained within the treatment chamber.

[0059] Further conductance seal plates were treated to confirm the previous result and test the effect of further increasing the surface roughness. In order to reduce the fabrication burden, the conduits were formed from a single treated conductance seal plate in combination with an untreated conductance seal plate in the absence of a substrate. The interfacial separation of the conductance seal plates was set to 2 mm, N2 was introduced to the first chamber at a rate of 20 cm3/s, and the vacuum pump was operated at a speed of 225 Us. Each sample was analysed in triplicate and the average pressure differential ratio recorded. The results are shown in Table 2 and displayed graphically in Figures 6A and 6B.

Sample Treatment Surface roughness dP (Ra) (pm) Untreated N/A 0.496 79.77 A Wire Brush 4.088 89.74 B1 20/40 Garnet 7.89 92.30 Blasted B2 20/40 Garnet 6.718 85.57 Blasted B3 20/40 Garnet 7.338 85.49 Blasted Cl Engineering Grade 10.458 76.92 Grit Blasted 02 Engineering Grade 11.432 79.48 Grit Blasted 03 Engineering Grade 11.67 73.58 Grit Blasted

Table 2

[0060] It can be seen that the untreated conductance seal plate, with its low surface roughness of approximately 0.5 pm, and the conductance seal plates that were blasted with the larger engineering grade media, with their high surface roughness of approximately 10 to 12 pm, all produced less effective seals, with differential pressure ratios between the chambers all being below 80.

[0061] Conversely, the conductance seal plates that were either treated with a wire brush or blasted with the finer 20/40 garnet media, with intermediate surface roughness of approximately 4 to 8 pm, all produced more effective seals with differential pressure ratios all be over 80.

[0062] These results demonstrate the surprising result that there is an optimal range of surface roughness for achieving higher differential pressure ratios between the chambers.

[0063] As previously mentioned, the foregoing examples are for the illustration of the invention and should not be construed as limiting to the scope of the invention in any way.

Claims

CLAIMS: 1. A conductance seal plate for a chamber for housing a treatment apparatus, the chamber defined in part by a wall and having a conduit between an interior of the chamber and an exterior of the chamber, the conductance seal plate comprising: a face configured to at least in part define the conduit, and an attachment portion for attaching the plate to the wall, wherein the surface roughness (Ra) of the face is in the range of 1 to 10 pm.
The conductance seal plate of claim 1, wherein the face is rectangular.
3. The conductance seal plate of claim 1 or claim 2, wherein a length of the face is in the range of 50 mm to 250 mm.
4. The conductance seal plate of any preceding claim, wherein a width of the face is in the range of 100 mm to 5000 mm.
The conductance seal plate of any preceding claim, wherein the face comprises aluminium.
6. The conductance seal plate of any preceding claim, wherein the surface roughness of the face is achieved through bead blasting or application of a wire brush.
7. An apparatus for treating a substrate comprising: a chamber for housing a treatment apparatus, the chamber defined in part by a wall; and a conduit permitting transmission of the substrate between an exterior of the chamber and an interior of the chamber, a first side of the conduit defined by a face of a first conductance seal plate attached to the wall; wherein the surface roughness (Ra) of the face of the conductance seal plate is in the range of 1 to 10 pm.
8. The apparatus of claim 7, wherein a second side of the conduit is defined by a face of a second conductance seal plate mounted to the wall.
9. The apparatus of claim 7, wherein a second side of the conduit is defined by the surface of a rotatable drum.
10. The apparatus of claim 8 or claim 9, wherein the separation between the first side of the conduit and the second side of the conduit is 1 mm to 5 mm.
11. The apparatus of any of claims 7 to 10, wherein the apparatus is configured to maintain a differential pressure ratio between the chamber interior and the chamber exterior of at least 80.
12. The apparatus of any of claims 7 to 11, wherein the wall further defines an outlet in communication with the chamber interior configured to connect to a vacuum pump
13. The apparatus of any of claims 7 to 12, wherein the apparatus further comprises a treatment device within the chamber, such as apparatus for pre or post treatment, physical vapour deposition, chemical vapour deposition, Plasma Treatment, thermal evaporative deposition, sputtering, plasma assisted chemical vapour deposition (PACVD), electron beam gun deposition (E-Beam), Atomic layer deposition (ALD), or Reactive Ion etching (RIE).
14. The apparatus of any of claims 7 to 13, wherein the first and/or second conductance seal plate is as defined in any one of claims 1 to 6.
15. Use of a conductance seal plate for forming one or both sides of a conduit permitting transmission of a substrate between an exterior of a chamber and an interior of the chamber, wherein the conductance seal plate has a surface roughness (Ra) of about 1 to about 10 pm.
16. The use of claim 15, wherein the conductance seal plate is as defined in any of claims 1 to 6.
17. A method of maintaining a differential pressure ratio between an exterior of a chamber and an interior of a chamber, the chamber defined in part by a wall, comprising the steps of: attaching a first conductance seal plate to the wall such that the face of the first conductance seal plate defines a first side of a conduit permitting transmission of the substrate between an exterior of the chamber and an interior of the chamber; and reducing the pressure in the chamber, wherein the surface roughness (Ra) of the face of the conductance seal plate is in the range of 1 to 10 pm.
18. The method of claim 17, further comprising the step of attaching a second conductance seal plate to the wall such that the face of the second conductance seal plate defines a second side of the conduit.
19. The method of claim 17, wherein a second side of the conduit is defined by the surface of a rotatable drum.
20. The method of claim 18 or claim 19, wherein the separation between the first side of the conduit and the second side of the conduit is 1 to 5 mm.
21. The method of any of claims 17 to 20, wherein the differential pressure ratio between the chamber interior and the chamber exterior is at least 80.
22. The method of any of claims 17 to 21, wherein the pressure in the chamber is reduced with a vacuum pump.
23. The method of any of claims 17 to 22, wherein the first and/or second conductance seal plate is as defined in any one of claims 1 to 6.