FIELD

The invention relates to an apparatus including a clean mini environment.

BACKGROUND

An apparatus including a clean mini environment (M.E.), for instance in a semiconductor furnace may be useful. A schematic

representation of the apparatus is shown in figure 1.

The apparatus may include a gas recirculation circuit comprising:

• a mini environment chamber (14), provided with a chamber inlet (24) and a chamber outlet (26);

• a recirculation channel (20) connecting the chamber outlet with the chamber inlet;

• an gas pump (16) having a pump outlet and a pump inlet and being positioned in the recirculation channel; and

• a filter assembly (22) positioned in the recirculation channel

downstream of the pump (16) and upstream of the mini environment chamber inlet (24).

The apparatus additionally may include:

• a pressure release provision (28) configured and arranged to limit a pressure in the mini environment chamber;

• an air supply conduit (18) for supplying air to the gas recirculation circuit and having an air supply conduit inlet which opens into the ambient air and an air supply conduit outlet which opens in the recirculation circuit.

In use, the gas pump circulates the gas from the pump outlet through the filter assembly, the chamber inlet, the mini environment chamber, the chamber outlet and back to the pump inlet thereby maintaining the pressure (Pm.') in the mini environment chamber higher than the ambient pressure (Pam). The pressure within the mini environment chamber (P _m.' ) is typically kept around 100 Pa above the ambient pressure (Pam). In practice, the pressure drop over the inlet filter is quite large, about 150 Pa. As a consequence, the pressure between the pump outlet and the filter assembly (Phigh) must be approximately 250 Pa above the ambient pressure (Pam). Between the chamber outlet and the pump inlet, the gas pressure is typically approximately 50 Pa above the ambient pressure.

Because the pressure in the mini environment chamber and in the recirculation conduit is higher than the ambient pressure, which is typically the atmospheric pressure, gas will leak from the mini environment chamber and the gas recirculation circuit to the environment. To compensate for this leakage and optionally also for refresh the recirculating gas or air, gas or air has to be supplied to the recirculation circuit via the air supply conduit.

A source of gas or air which has a pressure which is higher than the pressure in the recirculation channel may be provided. The source may be a high pressure gas tank or an additional air pump supplying air having a higher pressure than the pressure prevailing in the gas recirculation circuit. This solution may be relatively expensive because of the presence of the additional air inlet pump or because of the high pressure gas tank which has to be replaced regularly .Alternatively, a restriction in the recirculation channel may be provided between the chamber outlet and the pump inlet so that downstream of the restriction and upstream of the pump inlet an area is formed where the pressure is sub-atmospheric, i.e. lower than the ambient pressure so that ambient air will be sucked in. However, the restriction results in energy losses which must be compensated by a pump having a larger capacity, typically twice the capacity which is needed for simply recirculating a gas through the gas recirculation circuit when such a restriction were not present. SUMMARY OF THE INVENTION

An object of the invention is to provide an apparatus including a mini environment chamber as described above in which the supply of air to the gas recirculation circuit is effected with minimal operational costs and minimal investment for auxihary devices such as air intake pumps.

To that end, the invention provides an apparatus according to claim 1.

More particular, according to the invention the apparatus described above is characterized in that the gas recirculation channel includes a recirculation restriction embodied as a throat in the gas

recirculation channel, wherein the throat defines a flow path with a diminishing cross sectional surface area relative to the cross sectional surface area of the gas recirculation channel directly upstream of the throat, wherein a downstream end of the throat defines a minimum cross sectional surface area of the throat, wherein the throat defines the pump inlet, wherein the air supply conduit outlet opens at, or slightly downstream of the downstream end of the throat which defines the minimum cross sectional surface area of the throat.

An advantage of the apparatus according to the invention is that no additional gas pump or high pressure air source is required for the supply of ambient air. By virtue of the higher gas speed in the downstream end of the throat, which higher gas speed is caused by the reduced cross sectional area at the downstream end of the throat, the static pressure prevailing there is lower than the ambient pressure so that ambient air will be sucked in via the air supply conduit. Thus the power consumption for recirculation of the gas through the gas recirculation circuit and for supplying air to the recirculation circuit is less than with the know

configurations described above. The static pressure (Plow) between the chamber outlet and the upstream end of the throat will remain above the ambient pressure (P _f ,m), around 50 Pa or so. But at the downstream end of the throat, the gas flow speed is increased, causing a decrease in static pressure. This locally low static pressure is used to passively supply air via the air supply conduit to the gas circulation circuit. Because there is no significant energy loss caused by the throat with the, preferably gradually diminishing cross sectional surface area, the power needed to recirculate the gas through the gas recirculation circuit and to supply air to the gas recirculation circuit is minimal and almost comparable to the power needed to recirculate gas through the gas recirculation circuit without supplying ambient air to the gas recirculation circuit. In fact, the gas pump which is used in practice for recirculating the gas through the gas recirculation circuit includes the throat, which throat defines the pump inlet. In other words, the throat is an integral part of the gas pump. In view thereof, relative to the prior art system, the throat does not constitute an additional gas resistance because the throat is an integral part of the pump. The wording“slightly downstream of the downstream end of the throat” indicates not more than 20 mm downstream of the downstream end of the throat and, of course, upstream of the moving parts of the pump, e.g. the centrifugal vanes of the pump.

In the dependent claims various embodiments are claimed which will be further elucidated with reference to an example shown in figure 2. The embodiments may be combined or may be applied separately from each other.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is schematically shows an example of an apparatus including a mini environment chamber which is known from practice; and

Fig. 2 shows an example of an apparatus including a mini environment chamber according to the invention.

DETAILED DESCRIPTION OF THE FIGURES In this application similar or corresponding features are denoted by similar or corresponding reference signs. The description of the various embodiments is not limited to the example shown in figure 2 and the reference numbers used in the detailed description and the claims are not intended to limit the description of the embodiments, but are included to elucidate the embodiments by referring to the example shown in figure 2.

In the most general terms, the invention relates to an apparatus 10, including a gas recirculation circuit comprising:

• a mini environment chamber 14, provided with a chamber inlet 24 and a chamber outlet 26;

• a recirculation channel 20 connecting the chamber outlet 26 with the chamber inlet 24;

• a gas pump 16 having a pump outlet and a pump inlet and being

positioned in the recirculation channel 20; and

• a filter assembly 22 positioned in the recirculation channel 20

downstream of the pump (16) and upstream of the mini environment chamber inlet 24..

The apparatus additionally includes:

• a pressure release provision 28 configured and arranged to limit a pressure P _me in the mini environment chamber 14; and

• an air supply conduit 18 for supplying air to the gas recirculation circuit and having an air supply conduit inlet 18a which opens into the ambient air and an air supply conduit outlet 18b which opens in the recirculation circuit.

In use, the gas pump 16 circulates the gas from the pump outlet through the filter assembly 22, the chamber inlet 24, the mini environment chamber 14, the chamber outlet 26 and back to the pump inlet thereby maintaining the pressure P _me in the mini environment chamber 14 higher than the ambient pressure P _am , According to the invention, of which an example is shown in figure 2, the apparatus 10 is characterized in that the gas recirculation channel 20 includes a recirculation restriction embodied as a throat 30 in the gas recirculation channel 20. The throat 30 defines a flow path with a

diminishing cross sectional surface area relative to the cross sectional surface area of the gas recirculation channel 20 directly upstream of the throat 30. A downstream end 30a of the throat 30 defines a minimum cross sectional surface area of the throat 30. The throat 30 defines the pump inlet. The air supply conduit outlet opens at, or shghtly downstream of the downstream end 30a of the throat 30 which defines the minimum cross sectional surface area of the throat.

The cross sectional surface area of the throat 30 is smaller than the area of the cross-section of the gas recirculation channel 20. As a

consequence, the gas velocity of the circulated gas increases when flowing through the throat 30 up to a maximum velocity at the downstream end 30a of the throat 30 where the cross sectional surface area of the throat is smallest. When the gas velocity increases the dynamic pressure (½pv ² ) will increase and the static pressure will decrease. The difference between the static pressure at the air supply conduit outlet 18b and the ambient pressure P _a m will determine the flow of air within the air supply conduit 18. By positioning the air supply conduit outlet 18b in a region where the static pressure of the gas flow is below the ambient pressure P _am a pressure gradient will be created within the air supply conduit which will drive the ambient gas into the gas recirculation circuit. By using a substantially frictionless recirculation restriction which is embodied as a throat 30, energy losses may be minimized. Thus air may be supplied to the

recirculation circuit without the necessity to invest in an additional air supply pump or a high pressure gas source and substantially without energy losses so that the gas pump 16 capacity and/or power consumption is almost the same as in a situation wherein no air is supplied to the gas recirculation ί system and the pump is only used for pumping the gas through the gas recirculation circuit.

In order to provide the mini environment chamber 14 with clean gas, the gas supplied by the gas pump 16 may be filtered by the filter assembly 22 before it enters the mini environment chamber 14. This may be done at the chamber inlet 24 where the gas enters the mini environment chamber 14.

In an embodiment, the throat 30 may have a truncated cone shaped inner surface that is circular symmetric around a central axis, wherein a downstream part of the air supply conduit 18 extends along the central axis and opens in the central part of the downstream end 30a of the throat 30.

In the center of the throat 30 at the downstream end 30a thereof, where the cross sectional surface area is minimal, the gas velocity may be highest and thus, the static pressure is at its lowest value. Consequently, that position may be the most optimal position for positioning the air supply conduit outlet 18b because the air is sucked most effectively.

In an embodiment of the invention, the cross sectional surface area A _sc of the air supply conduit 18 may be small compared to the cross sectional surface area A _t of the downstream end 30a of the throat 30.

An air supply conduit 18 with a small cross sectional surface area A _sc compared to the cross sectional surface area A, of the downstream end 30a of the throat 30 may not, or virtually not disturb the flow of the recirculating gas in the recirculation channel 20 and the throat 30 which is beneficial from an efficiency point.

In an embodiment of the invention, the air supply conduit 18 further comprises an air inlet filter 32.

In order to keep the gas in the gas recirculation circuit as clean as possible, it is best to filter the ambient air before supplying it to the gas recirculation circuit. The apparatus could do without such filter, but an air inlet filter 32 may relieve the load of the filter assembly 22 at the mini environment chamber inlet 24.

In an embodiment, the pressure release provision may comprise a pressure release valve 34.

With the pressure release valve 34 the leakage of gas from the mini environment chamber 14 can be controlled in such a way that a constant overpressure can be maintained in the mini environment chamber 14 with respect to the surrounding environement. A pressure release valve 34 may be a simple yet effective way to realize a constant overpressure in the mini environment chamber 14.

In an alternative embodiment, the pressure release provision may comprise a small gap in the mini environment chamber which opens into the ambient environment. Such a small gap is, of course, of a very simple construction and also provides a means to limit the raise of pressure in the mini environment chamber 14.

In an embodiment, the apparatus may comprise a housing defined by external walls 38, wherein the external walls at least partly bound the mini environment chamber 14 and the recirculation channel 20. An internal wall 36 forms a boundary between the mini environment chamber 14 and the recirculation channel 20. The chamber outlet 26 is formed by a gap between an end of the internal wall 36 and an external wall 38.

Such an is relatively simple from a manufacturing

point of view.

The various embodiments which are described above may be used implemented independently from one another and may be combined with one another in various ways. The reference numbers used in the detailed description and the claims do not limit the description of the embodiments nor do they limit the claims. The reference numbers are solely used to clarify. Legend

10 - the apparatus

12 - housing

14 - mini environment chamber

16 - gas pump

18 - air supply conduit

18a - air supply conduit inlet

18b - air supply conduit outlet

20 - recirculation channel

22 - filter assembly

24 - chamber inlet

26 - chamber outlet

28 - pressure release provision

30 - throat

30a - downstream end of the throat

32 - air inlet filter

34 - pressure release valve

36 - internal wall

38 - external walls

P _{me -} mini environment chamber pressure

Pam ^— ambient pressure

A- _{e -} cross section surface area of the air supply conduit

A _{t -} cross section surface area of the throat at the downstream end

A _{r -} cross sectional surface area of the recirculation channel upstream of the throat