Technical field

The present invention relates to a viewport protection system, in particular for CVD or PVT processes. The present invention further relates to a method for protecting a viewport, and the use of the viewport protection system.

Background

Viewports are essentially windows, or other openings, used to observe or monitor the interior of a process chamber, during for instance processes such as CVD and PVT or combustion. A viewport protection system is a system which may prevent or reduce contamination of a viewport window. Observations of the interior of a process chamber may be done as visual inspection, or as measurements, which often require continuous access to the interior. A very common measurement is to monitor the process temperature, which can be done with a pyrometer (a remote sensing thermometer), which requires that there the visibility through the viewport is clear, i.e. it requires stable optical properties and transmission of the relevant wavelengths to measure the temperature through the window of the viewport. In addition to visual monitoring through a window, a viewport may also include other means, such as light pipe pyrometers, which are introduced into the process chamber.

The visibility through a viewport window is however quite often impaired by deposition or condensation of particles and gases on the process side of the window, i.e. the surface facing the process chamber.

There are a number of solutions available on the market today, to ensure a clean viewport window, even in environments with reactive gases, but some of them are very large or bulky, such as the Thermionics ClearView™ system, which also requires an external power supply, and some do not allow for continuous measurement, such as systems including viewport shutters, which require an actuator to open and close the shutter. Therefore, there is a need for an improved viewport system, or entry port system, which allows for continuous monitoring of the interior of for instance a process chamber such as vacuum chamber, and which is not too bulky or requires additional and difficult installation. Preferably, a new and inventive system can also be retrofitted onto existing process chambers.

Summary

It is an object of the present disclosure, to provide an improved viewport system, and use thereof.

The invention is defined by the appended independent claims. Embodiments are set forth in the appended dependent claims and in the following description.

According to a first aspect there is provided a viewport protection system comprising a gas nozzle, wherein said gas nozzle is adapted to provide a flow of a purge gas onto a viewport window, and an outlet channel arranged in a direction facing away from said window, and being adapted to allow for a fully developed laminar pipe flow of said purge gas through said outlet channel.

By this viewport protection system there is provided a way of keeping the viewport window clean during the process, while also allowing for continuously monitoring the inside of a vacuum chamber. By releasing purge gas onto the surface of the window, and creating or allowing for a fully developed laminar pipe flow away from the viewport window. This reduces the risk of reactive gases from propagating upstream the outflow of purge gas. This design thus also ensures that no particles can reach and condensate on the viewport window surface.

The outlet channel may be adapted to be arranged between a viewport window and an inside of a process chamber.

The outflow channel may be provided with openings at both ends.

The viewport protection system according to the first aspect may further comprise a viewport window. The viewport window may further be arranged at a side of a process chamber which is facing the surrounding atmosphere, i.e. at or on the outside wall of a process chamber. According to the first aspect, a length/diameter (x/D) ratio of the outflow channel may be in the range of 0.2 to 20.

The length to diameter ratio thus ensures that a fully developed laminar pipe flow of purge gas is developed.

According to the first aspect the system may be adapted to be attached to an outside of a process chamber, such that said outlet channel is adapted to extend at least partially from an outside of a process chamber to an inside of a process chamber.

This allows for the viewport protection system to be attached to the outside wall of a process chamber, for instance by bolting the system onto the chamber, which means that it can be easily fitted onto any process chamber via through holes or flanges like KF, CF or DIN are also very commonly used, which are conventionally arranged in a wall of a process chamber.

Preferably, however, the length of the outflow channel is relatively short, and in the range of 5 to 30 mm, depending on the size of the process chamber and the thickness of the wall in the process chamber. A technical benefit of providing a short outflow channel is that the system can be configured to be more compact, and less space consuming.

According to the first aspect, a gas inlet may be provided in a wall of said outflow channel.

According to an alternative of the first aspect the gas nozzle may comprise a double wall structure, wherein an inner wall defines said outflow channel, and wherein an outer wall is provided with a gas inlet, and wherein said gas nozzle is closed at an end facing an inside of a process chamber, and open in an end facing said viewport window, and wherein a deflection rim is arranged between the inner and outer wall and extending partially from a viewport window end in a direction towards an inside of a process chamber.

This allows for the purge gas to enter into the gas nozzle through the gas inlet, and deflect against the deflection rim, such that a more even flow of purge gas is impinged into the viewport window, this ensures a good flow conditioning of the purge gas.

According to yet an alternative of the first aspect, the gas nozzle may comprise said outflow channel, and wherein said outflow channel is enclosed by an inlet channel, wherein said inlet channel is closed at an end which during use is facing an inside of a process chamber, and open at an end which during use is facing a viewport window, and wherein a gas inlet is provided perpendicular to said inlet channel, and wherein there is a distance between the outer surface of the outflow channel and an inner surface of the inlet channel.

By this design the inlet flow of purge gas is perpendicular to the inlet channel, and to the outflow, which allows for a good distribution around the perimeter of the outflow channel, i.e. for a good flow conditioning. The space created between the outer surface of the outflow channel and the inner surface of the inlet channel may further be filled up with purge gas, as a “gaspocket” which ensures a steady flow of purge gas towards the viewport window surface. This is beneficial as it makes the system less sensitive to variations in the inflow of purge gas. Further, the gas nozzle may be adapted to be fitted onto conventional flanges, such as KF, CF, DIN flanges.

The gas flow inlet channel ensures that the flow of purge gas is distributed around the circumference and perimeter of the gas nozzle before it impinges onto the viewport window, i.e. a good flow conditioning. This further ensures that an even and fully developed laminar flow profile is created quickly in the outlet channel.

According to the first aspect the viewport may be adapted to be arranged on an outside of a process chamber, and wherein said outflow channel is adapted to be arranged in a through hole of a process chamber.

According to yet another alterative of the first aspect, said gas nozzle may comprise a circular plate, having a first side, which during use is facing an inside of a process chamber, and a second side which is provided with a solid deflection rim arranged at a distance from the circumference of said plate, a hollow outlet channel arranged at a center portion thereof and extending in a direction perpendicular to said plate, and a perforated barrier rim arranged between said deflection rim and said outlet channel.

The height of the barrier rim is this adapted such that when the nozzle is attached onto or mounted within a process chamber the barrier rim closely abuts the inside of the process chamber. Since the height of the deflection ring is less than the height of the barrier rim, the purge gas can pass over the deflection rim or ring. According to this alternative, said gas nozzle may be arranged in a process chamber, and a gas inlet is arranged to provide a first flow of gas at the deflection rim.

By this arrangement the purge gas, when in the system is in use in a process chamber, the gas flow impinges onto the deflection rim or ring, which deflects the gas flow around the circumference or perimeter of the nozzle, to create a uniform gas distribution, i.e. a flow conditioning. This creates a flow of purge gas towards the barrier rim, which in turn is perforated. Due to the perforations in the barrier rim there is an increase in the flow velocity of the purge gas. When the purge gas passes through the perforations in the barrier rim it deflects along the outside of the tubular gas flow outlet, such that it impinges the viewport window, after impinging on the viewport window the flow is deflected and enters the outlet channel, where the laminar flow forms immediately.

According to a second aspect there is provide a viewport protection system comprising a gas nozzle, a base housing, wherein said base housing comprises an outer wall and an inner wall, and wherein a purge gas inlet is provided in said outer wall, and said gas nozzle is adapted to provide a flow of a purge gas onto a viewport windo, an outlet channel formed from said inner wall arranged in a direction facing away from said window and being adapted to allow for a fully developed laminar flow of said purge gas through said outlet channel, wherein said system further comprises a window holder portion adapted to receive said viewport window, wherein said window holder portion further comprises a detachable holder rim.

This viewport protection system thus allows for a very versatile and compact system to be mounted onto a process chamber of any type. Futher to this, since the system allows for the window to be replaced, the user can chose which type of glass that is most suitable for the desired application.

According to the second aspect said gas nozzle may further be provided with a flow conditioning gas inlet adapted to distribute the incoming flow of purge gas around the inlet perimeter or circumference of the gas nozzle.

This allows for a fully developed laminar flow is established quickly in the outflow channel, which ensures that the window is kept free of contaminants and thus allows for a visual monitoring of the inside of the process chamber, manually or by continuous monitoring e.g. utilizing different optical sensors.

According to a third aspect there is provided the use of a viewport protection system according to any one of the alternatives of the first aspect or the second aspect, in connection with a process chamber operating at a pressure of at least 1 mbar.

This allows for the system, comprising the gas nozzle and the viewport, or the viewport protection system according to the second aspect, to be sold as off the shelf components, which can be bolted onto or into a process chamber and a gas line (gas inlet) can be installed for the flow of purge gas. The process chamber may be any type of chamber or reactor operating a pressure of at least 1 mbar, such as a PVT chamber, CVD chamber or a combustion chamber.

Brief description of drawings

Embodiments of the present solution will now be described, by way of example, with reference to the accompanying schematic drawings. Fig. 1 shows a schematic cross-sectional representation of the basic working principle of the present invention.

Fig. 2 shows a schematic cross-sectional representation of an embodiment of the present invention.

Fig. 3 shows a schematic cross-sectional representation of an alternative embodiment.

Figs. 4a and 4b shows flow simulations of the viewport protection systems as illustrated in Figs 2 and 3.

Fig. 5 shows a schematic perspective view of an embodiment of a gas nozzle.

Fig. 6 shows a schematic cross-sectional view of the gas nozzle of Fig. 5 arranged in a process chamber.

Fig. 7 shows a schematic cross-sectional view of an embodiment of a viewport protection system.

Fig. 8 shows a schematic cross-sectional view of an embodiment of an entry port protection system.

Fig. 9 shows a schematic cross-sectional view of a viewport protection system.

Description of Embodiments

As illustrated by Fig. 1 , a duct of arbitrary cross-section or outflow channel 5, is arranged in a direction facing away from a surface, such as viewport window surface 2, or an entry port, to be protected from e.g. condensation of particles from the inside 12 of a process chamber. The length of the channel in relation to the diameter thereof has to be sufficient in order for the flow of the injected purge gas to develop to a fully developed laminar L pipe flow, in a direction towards an inside 12 of a process chamber, and an opening 3. The position and design of the gas inlet for this type of device determines the required length for the outlet channel but does not influence its basic working principle. The purge gas may commonly be Argon gas, but may be any suitable gas. Preferably, the purge gas is a noble gas.

As illustrated in Fig. 2 one embodiment of a viewport protection system 1 is disclosed. The viewport protection system 1 may comprise a viewport window 2, i.e. the surface to be protected, and a gas nozzle 4. The gas nozzle comprises an outlet flow channel or duct 5. The channel or duct 5 is depicted in the drawings as having a substantially tubular cross-section, but may have any suitable cross-section such as tubular, rectangular, triangular.

A gas inlet 6 can be arranged in a wall of the gas nozzle 4, or arranged to supply gas directly into the channel 5, to impinge onto a window 2. A laminar flow L is created in the channel 5 towards an inside 12 of a process chamber and an opening 3.

As shown in Fig. 4a, this configuration creates a re-circulation area close the gas inlet and the viewport window, which requires a longer outflow channel to create a laminar flow.

Fig. 3 illustrates an embodiment and alternative configuration, where the gas nozzle 4 is provided with a flow conditioning gas inlet, to distribute the incoming flow of purge gas around the inlet perimeter or circumference of the gas nozzle 4, before the gas impinges onto a viewport window 2. The embodiment as illustrated in Fig. 3 is the working principle of the preferred embodiments having a flow conditioning inlet or gas nozzle. It is important to quickly establish the fully laminar flow profile in the outlet channel, since it allows for protection from condensation of particles onto the viewport window. Also, the inlet design ideally should create as little turbulence as possible when redirecting the purge gas into the outlet duct, even if the turbulence decreases rather quickly in the outlet duct as the velocity is lower than the injected gas due to a larger cross-sectional area of the outlet duct. In Fig. 3 a flow conditioning gas nozzle 4 is illustrated as comprising a double walled configuration, where an inner wall 7 defined the channel or duct 5, and where an outer wall 8, is provided with a gas inlet 6. The double wall configuration has a closed end 9, which during use of the system is facing an inside of a process chamber, and an open end 10, which during use is facing a surface to be protected, such as a viewport window 2. In this embodiment a deflection rim 11 is arranged between the inner 7 and outer 8 wall of the gas nozzle. The deflection rim 11 is in this embodiment arranged such that it extends partially from the open end 10 towards the closed end 9, i.e. it allows for a flow of gas, illustrated by the dotted line F, to deflect and flow over the edge of the rim and onto the viewport window 2 and towards an inside 12 of a process chamber.

By “flow conditioning” is thus meant a gas inlet constructed such that the flow of purge gas creates as little turbulence as possible, and a fully developed laminar pipe flow is developed as quickly as possible in the flow outlet duct or channel, and at a minimal distance from the inlet or the viewport window.

The configuration and dimensions of the conditioning inlet may vary depending on the application and on the process chamber onto which the system is to be attached.

The dimension of the outlet flow channel or duct 5 depends on the application and the chamber onto which the system is to be adapted, but generally, it has a length to diameter ratio (x/D) in the range of 0.2 to 20, or 0.6 to 20. However, one particular advantage of the flow conditioning purge gas inlet is that the system can be built to be extremely compact. As an example a total length of the outflow channel and viewport window thickness can be less than 20 mm, or even less than 15 mm, or in some embodiments less than 10 mm. In one example, the length of the outflow channel substantially corresponds to the thickness of the wall of the process chamber.

In Fig. 5 an alternative embodiment a flow conditioning gas nozzle 4 is illustrated. The nozzle 4 comprises a plate 14, having a first side which during use is facing an inside 12 of a process chamber. On an opposite and second side a deflection rim 15 is provided. The deflection rim is preferably made from a solid material. An outflow channel 5 is arranged at a center portion of the plate 14, such that it is open at both ends, i.e. both in a direction towards an inside 12 of a process chamber and an end 3 facing a viewport window (not shown). A barrier rim 16 is arranged between the deflection rim and the outflow channel. The barrier rim 16 is preferably perforated. The gas may be provided to flow towards the deflection rim, illustrated by arrow F1 , where it deflects over the rim, illustrated by arrow F2, and then penetrates the perforated barrier and flows along the outside of the channel 5, as illustrated by arrow F3.

In Fig. 6 the flow conditioning gas nozzle 4 as illustrated in Fig. 5 is shown mounted into a process chamber wall 20 and attached to a gas inlet 6. As illustrated there is a small gap between the wall 20 and the deflection rim, which allows for the flow of gas to move over the deflection rim (arrow F2 in Fig. 5). The wall 20 and an outside wall of the channel 5 forms a gas inlet channel 18, such that the purge gas can impinge onto a viewport window 2.

In Fig. 7 an alternative embodiment of viewport protection system is disclosed. In this embodiment the viewport protection system 1 , is attached to an outside 13 of a process chamber. The system 1 may for instance be bolted 19 to an outside of a process chamber (not shown), and the channel 5 has an opening 3 facing an inside of a process chamber. In this embodiment the gas nozzle 4 comprises an outer wall 8 and an inner wall 7, which defines the outflow channel 5. The gas nozzle 4 is closed at an end 9 facing an inside 12 of a process chamber, and open or at least perforated at an end 10 facing a viewport window 2. The perforation acts as a pressure barrier which helps distributing the gas evenly around the perimeter of the outflow channel. The gas nozzle is provided with a deflection rim 11 , arranged at the open end 10, and allowing for a flow of purge gas towards the window 2. A gas inlet 6 is arranged to provide a flow of purge gas into a space defined by the outer 8 and inner wall 7. Fig. 8 illustrates an embodiment where the viewport 1 instead is an entry port for introducing other means for monitoring an inside 12 of a process chamber, and a rotary feedthrough which feeds a shaft through a wall of a process chamber, such as a pyrometer or a light pipe pyrometer 21 in the outflow channel 5. The working principle of the gas flow is the same as described above. In this embodiment, the purge gas is introduced through a flow F of gas through a gas inlet 6. A fully developed laminar pipe flow is allowed to form in the outlet duct or channel 5, and along the pipe 21 or tube inserted into the process chamber. Preferably, a gas nozzle 4 comprises flow conditioning means (not shown). The laminar flow reduces the risk of particulate condensation and build up along the tube and pipe as well as the entry port wall. The flow conditioning means or gas nozzle 23 may be any one of the above-described embodiments, such as a barrier rim, or deflection rim or a combination of different flow conditioning devices. In one embodiment, the entry port comprises a ferrofluidic, or magnetic seal 22, which is also protected from particle condensation by the laminar flow of the purge gas in the outflow channel 5 of the protection system.

In one example, the outflow channel 5 may be arranged completely on an outside of the process chamber, and a through hole in the wall of the process chamber may act as an extension of the outflow channel to the inside of the process chamber. This means that the outflow channel 5 may be relatively short and the view port protection system can be made very compact, which may further ensure accurate measurements to be made on the inside of the process chamber, as well as allowing for a viewport protection system which can be made more compact.

Fig. 9 illustrates an exemplary viewport protection system 30 having a viewport window 2. The viewport system 30 comprises a base housing 31 , and can be attached to an outside of a process chamber (the process chamber is not shown in Fig. 9, however illustrated in for instance Fig. 6). The attachment to the process chamber may be facilitated through any conventional type of attachment arrangement. In the exemplary embodiment, the attachment arrangement is illustrated as a conventional KF40 flange.

The base housing comprises a gas nozzle 32. In the exemplary embodiment, the gas nozzle 32 is illustrated with a double walled configuration, having an inner wall 33 and an outer wall 34. The outer wall 34, is provided with a gas inlet 35. The inner wall 33 defines, or encloses the outflow channel or duct 36. The double wall configuration has a closed end 37, which during use of the system is facing the outside wall of a process chamber, and an open end 38, which during use is facing the viewport window 2, and thus allows for the purge gas to impinge the inside of the window 2. This means that the purge gas flows from the inlet 35 to an intermediary space 39 between the outer wall 34 and the inner wall 33. As further illustrated, a small gap G is formed between the inner wall 33 and the window 2. This gap further forms part of a flow conditioning gas nozzle 40, which distributes the flow of purge gas around the perimeter of the gas nozzle 32 before the purge gas impinges onto an inner surface 41 of the window 2, such that there is a minimum of turbulent flow created in a recirculation zone RZ in front of the window. A flow conditioning gas 40 inlet thus allows for the flow of purge gas to be distributed around the perimeter of the gas nozzle 32 before it impinges onto the window 2. In a basic design this may be accomplished by arranging the gas inlet 35 at a sufficient distance from the window 2, and allowing the purge gas to distribute in a space 37 between the inner wall 33 and the outer wall 32 before it impinges on the inner surface 41 of the window 2. In some embodiments, as described above, the flow conditioning gas inlet may include deflection rims, pressure barriers, etc. to allow for the flow of gas to be distributed evenly around the perimeter of the gas nozzle before it impinges the window. The base housing 31 further comprises a demountable or detachable lid or rim 42 which clamps the window 2 against the base housing 31 . The rim allows for the window 2 to be exchanged. The rim 42 may be attached to the base housing by any conventional fastening arrangement. The base housing may further accommodate a sealing ring 43, to provide a seal between the outer wall 34 and the window 2.

Flow Simulation

Data Flow simulations (Figs 4a and 4b) suggest that a flow-conditioning inlet is very effective in achieving the goal of reducing the needed outlet duct length to form fully developed laminar pipe flow.

Fig. 4a shows that directly injecting the purge gas into the outlet duct under an angle of 90 degree creates a major recirculation area, and turbulence T which slows down the formation of the laminar pipe flow. The recirculation area can be found at around x/D=0.7. Fully laminar flow L is not developed until around x/D«2.

In contrast, the case Fig. 4b shows flow patterns of a gas nozzle according to the present invention, provided with a simple flow conditioning inlet. The flow conditioning inlet allows for the flow of purge gas to be distributed around the perimeter of the gas nozzle before it impinges onto the window. The flow field suggests that fully laminar flow L is already developed at x/D<1 .

A design as disclosed in Fig. 3, i.e. having some type of flow constraint to ensure a flow around the circumference of the gas nozzle inlet which creates a minimum of turbulence in the recirculation area when directing the purge gas into the outlet flow channel.

Modifications and other variants of the described embodiments will come to mind to one skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure. Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Therefore, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms “comprise/comprises” or “include/includes” do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Finally, reference signs in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.