GB2425539A

GB2425539A - Deposition system with three way valve

Info

Publication number: GB2425539A
Application number: GB0508867A
Authority: GB
Inventors: Mark Christopher Hope
Original assignee: BOC Group Ltd
Current assignee: BOC Group Ltd
Priority date: 2005-04-29
Filing date: 2005-04-29
Publication date: 2006-11-01
Also published as: GB0508867D0

Abstract

A vacuum system comprising a primary foreline 22 for receiving fluid from an outlet of a chamber 12 to be evacuated. First and second vacuum pumps 30,34 are provided for evacuating the chamber and first and second secondary forelines 26,28 are provided for conveying fluid from the primary foreline to the first and second vacuum pumps respectively. A three way valve 24 is provided between the primary and the secondary forelines for selectively connecting a chosen one of the first and second secondary forelines to the primary foreline. Means for controlling the three way valve are provided, to selectively divert a first reactant-rich fluid from the primary foreline into the first secondary foreline and a second reactant-rich fluid from the primary foreline to the second secondary foreline thereby to inhibit mixing of the first and second reactants within the vacuum pumps. The system may be used in atomic layer deposition (ALD) and chemical vapour deposition (CVD) systems.

Description

VACUUM SYSTEM

This invention relates to a vacuum system, in particular when incorporated into apparatus for conveying gases from a process chamber where a pulsed gas delivery system is used to supply gases to the process chamber such as may be used in atomic layer deposition (ALD) or chemical vapour deposition (CVD) techniques. In particular, the invention relates to an improvement to such systems which reduces the opportunity for cross- reaction between fluids, typically gases, in such a system.

Pulsed gas delivery systems are commonly used in the growth of multilayer thin films. Two common example applications are the manufacture of AI203 and TiN films. In such applications, reactant gases provide sources of two or more gaseous species to be deposited. A purge gas source may also be provided.

The gases are delivered to a process chamber, sequentially, by means of a valving system between the gas sources and the process chamber. Any residual reactant gas, purge gas or by-products are exhausted from the process chamber by a pump.

Typically, purge gas is passed through the reaction chamber between supplies of the species to be deposited. The purpose of the purge gas is to remove any residual (not deposited) reactant gas from the process chamber so as to prevent reaction with the next reactant gas supplied to the chamber. Were the different reactant gases allowed to cross react, this might result in impurities and imperfections in the multi-layer film.

In existing gas delivery systems, gases leaving the process chamber enter a common foreline leading to a vacuum pump. Cross reaction of any residual reactant gases can occur in the foreline and this can result in the accumulation of particulates in the foreline leading to impaired pump performance. Such impairment of pump performance may compromise the quality of the product manufactured in the process chamber. In addition, the process down time involved in repairing and maintaining affected pumps can increase the costs of manufacture.

Where it is particularly desirable to avoid mixing of these residual reactant gases, systems having a process chamber with more than one outlet are known (from WO 03/033762), each outlet being connected to a respective vacuum pump via a foreline. Such a configuration permits the different gases to be diverted to a dedicated vacuum pump such that mixing and thus reaction of the reactant gases is inhibited, if not entirely prevented.

The disadvantage of this configuration is the increased complexity and bulk of the equipment both adjacent to the tool and which must pass to the location of the vacuum pump, which is generally remote from the tool, typically in the basement of the facility.

According to the present invention there is provided a vacuum system comprising a primary foreline for receiving fluid from an outlet of a chamber to be evacuated, a first vacuum pump for evacuating the chamber, a second vacuum pump for evacuating the chamber, a first secondary foreline for conveying fluid from the primary foreline to the first vacuum pump, a second secondary foreline for conveying fluid from the primary foreline to the second vacuum pump, a three way valve for selectively connecting a chosen one of the first and second secondary forelines to the primary foreline and means for controlling the three way valve to selectively divert a first reactant-rich fluid from the primary foreline into the first secondary foreline and a second reactant-rich fluid from the primary foreline to the second secondary foreline thereby to inhibit mixing of the first and second reactants within the vacuum pumps.

The control means may be configured to receive signals indicative of the composition of the fluid in the primary foreline. The position of the three way valve may then be controlled in dependence on these signals. The signals may be generated by a controller that controls the delivery of fluids to the chamber.

The control means may be integral with the controller.

According to another aspect of the present invention there is provided a method of evacuating a chamber comprising the steps of providing a primary foreline for receiving fluid from an outlet of the chamber, a first vacuum pump for evacuating the chamber, a second vacuum pump for evacuating the chamber, a first secondary foreline for conveying fluid from the primary foreline to the first vacuum pump, a second secondary foreline for conveying fluid from the primary foreline to the second vacuum pump, and a three way valve for selectively connecting a chosen one of the first and second secondary forelines to the primary foreline and controlling the three way valve to selectively divert a first reactant-rich fluid from the primary foreline into the first secondary foreline and a second reactantrich fluid from the primary foreline to the second secondary foreline thereby to inhibit mixing of the first and second reactants within the vacuum pumps.

The three way valve may be moveable between first and second positions in order to divert fluid to a chosen one of the secondary forelines. The movement of the valve between the first and second positions may be carried out when a purge gas is present in the primary foreline. The length of the primary foreline may be chosen in dependence on a characteristic of a delivery sequence of purge gas to the chamber. The characteristic may be one or more of pulse pitch and pulse duration of the delivery sequence.

By using a single outlet from the process chamber, a single primary foreline and therefore a single three way valve can be used, thus reducing the complexity of the system and the quantity of pipe work in the vicinity of the chamber where space is at a premium.

By restricting the length of the primary foreline such that it represents a volume related to the volume of reactant fluid, typically gas, or purge gas issued during a single delivery step of the process, the different reactant gases used during consecutive steps of the process can be substantially separated. In this way reactions between the different reactant gases within a single vacuum pump can be further inhibited, thus enhancing the long term reliability of the vacuum pumps themselves.

The invention is described below in greater detail, by way of example only, with reference to the accompanying drawings, in which; Figure 1 illustrates a system having a single outlet feeding a primary foreline; Figure 2 illustrates a sequence of gases that may be introduced into the process chamber; and Figure 3 illustrates a typical system layout.

Figure 1 shows a process chamber 12 into which may be provided various gases via one or more delivery ports, here three such ports are represented at 15, 16, 17. The process chamber 12 is provided with an outlet 20 to which is connected a primary foreline 22. At some distance from the process chamber 12 the primary foreline 22 is provided with a three way valve 24 which selectively diverts a fluid from the process chamber 12 into one of a pair of secondary foreline ducts 26, 28 connected thereto.

These secondary foreline ducts 26, 28 are, in turn, each connected to the inlet of a respective vacuum pump 30, 34.

An atomic layer deposition (ALD) process requires rapid bursts of different gases to be sequentially introduced into the process chamber 12 in sufficient volume to ensure that a complete layer of material is deposited on the surface of the product being generated within the chamber (not shown). In other words, a quantity of reactant fluid in excess of that required to form the layer is introduced into the chamber 12. This excess quantity of reactant fluid, together with any by- products from the reactions that have taken place within the chamber is extracted from the process chamber by the vacuum pumps 30, 34 via the foreline ducts 22, 26, 28. Where a multiplicity of different fluids, typically gases, is used in the process, these gases are grouped into types that do not react with one another.

Each group is allocated a separate vacuum pump such that any mixing of gases from different groups can be minimised. In this way, further reactions between reactants within the pumps can be inhibited.

The process carried out in the process chamber comprises a number of sequential operations, each involving a different gas or combination of gases delivered to the processing chamber 12. A typical gas delivery sequence, involving two reactant gases, is illustrated in Figure 2. The first trace 40 represents the stepped delivery sequence for the first reactant gas and the second trace 42 represents the stepped delivery sequence for the second reactant gas. It can be seen that in this example the duration of each pulse of the second gas is longer than that of the first. This sequence and duration is defined for each particular process to be carried out and is governed by the volume of the particular gas required to form the respective layer on the product. The third trace 44 represents a purge gas that is introduced into the process chamber 12 between the delivery of first and second reactant gases to flush the process chamber, and therefore the product of the reactant gas and any by products generated from the previous step, before introducing the next reactant gas.

The entire process, including the control of gas delivery to the chamber, is controlled by a controller 36. The controller 36 also governs the position and timing of switching of the three way valve 24. As the first reactant gas is being introduced into the chamber in the first process step, the controller 36 switches the three way valve 24 such that a first flow path is defined through the primary foreline 22 and the first secondary foreline duct 26. This flow path is maintained during much of the following purge gas delivery step where inert purge gas is introduced to the process chamber 12 to flush any residual reactant and by- products therefrom. Just before the controller 36 initiates the introduction of the second reactant gas the three way valve 24 is switched to its second position to define a second flow path through the primary foreline 22 and the second secondary foreline duct 28. This new configuration is maintained throughout the next process step whilst the second reactant gas is introduced to the process chamber 12 and then subsequently flushed from the process chamber by the following purge gas delivery step. Towards the end of the purge gas delivery step the controller 36 instructs the three way valve 24 to return to its initial position to redefine the first flow path in anticipation of the reintroduction of the first reactant gas in the subsequent process step. Where it is necessary to separate a third reactant gas or group of gases from the first and second reactant gases or groups of gases a third vacuum pump and its associated third secondary foreline duct (not illustrated) may be incorporated into the system.

The three way valve 24 may be provided with an additional position and associated outlet to permit a third flow path to be defined between the primary foreline 22 and the third secondary foreline. Such a modified valve may typically be referred to as a four way valve.

It should be noted that in practical terms the different gases are unlikely to be completely separated down stream of the process chamber 12. The fluids conveyed to the first vacuum pump 30 via the first secondary foreline duct 26 are, therefore, likely to be rich in the first reactant rather than entirely composed of this gas. Similarly the fluid being conveyed to the second vacuum pump 34 via the second secondary foreline duct 28 is likely to contain traces of by-products and possibly even of the first reactant, it can therefore be regarded as being a second reactant-rich fluid rather than entirely composed of the second reactant gas.

Figure 3 illustrates a schematic of a typical ALD process tool 52 having a process chamber 12 and a vacuum pumping system associated with the tool. Space in the vicinity of the process chamber 12 around the tool itself is at a premium and it is therefore beneficial to locate as much equipment as possible remote from the tool. To this end, the vacuum pumps (e.g. 30, 34) associated with the tool 52 are often located in a basement area 54 or otherwise remote from the tool area. In a preferred embodiment of the present invention the duration and frequency of the gas delivery pulses 40, 42 and in particular 44 are sufficient to allow the primary foreline 22 to be of adequate length that the valve 24 can be located at the remote site 54 as shown in Figure 3.

It follows that the longer the duration of the delivery of a particular gas the greater the volume of gas that is being delivered. Consequently, where the delivery pulses are short there must be a correspondingly rapid switching of the three way valve 24 to divert each fluid stream to its dedicated vacuum pump 30, 34. Ideally, the chamber and the entire primary foreline 22 will be engulfed in purge gas before the status of the valve 24 is changed to effect diversion of the fluid stream to the vacuum pump 30, 34, dedicated to the reactant type to be delivered in the subsequent step. Where the purge gas delivery is short, it follows that the primary foreline 22 should be correspondingly short. Conversely, where the pulses are increased in length, especially the purge gas delivery pulse, the length of the primary foreline 22 can be increased in length whilst ideal conditions are maintained. In this way the valve 24 can be positioned at a greater distance from the tool, thus reducing congestion in the vicinity of the chamber 12.

Where the duration of the purge gas pulses is shorter, such that a reduced volume of purge gas is delivered to the primary foreline 22 after each process step, a correspondingly shorter length of primary foreline is provided. In other words, the valve 24 is located closer to the tool 52 and the secondary foreline ducts 26, 28 become longer and thus take up more space. However, so long as the valve 24 is located at some distance from the tool 52 the benefits of creating space in the location of the chamber 12 can be achieved.

Where the pitch and duration of the gas delivery pulses 40, 42, 44 are particularly short, it may be necessary to change the status of the valve 24 in dependence on a predicted estimate of the composition of fluid in the primary foreline upstream of the valve 24. The predicted estimate may be based on information relating to the gas delivery sequence coupled with information relating to the geometry of the vacuum system, in particular the volume of the chamber 12 and the volume of the primary foreline 22.

Claims

1. A vacuum system comprising: a primary foreline for receiving fluid from an outlet of a chamber to be evacuated; a first vacuum pump for evacuating the chamber; a second vacuum pump for evacuating the chamber; a first secondary foreline for conveying fluid from the primary foreline to the first vacuum pump; a second secondary foreline for conveying fluid from the primary foreline to the second vacuum pump; a three way valve for selectively connecting a chosen one of the first and second secondary forelines to the primary foreline; and means for controlling the three way valve to selectively divert a first reactant-rich fluid from the primary foreline into the first secondary foreline and a second reactant- rich fluid from the primary foreline to the second secondary foreline thereby to inhibit mixing of the first and second reactants within the vacuum pumps.

2. A vacuum system according to Claim I, wherein the control means is configured to receive signals indicative of the chemistry of fluid in the primary foreline, and to control the position of the valve in dependence thereon.

3. A vacuum system according to Claim 2, wherein the signals are generated by a controller for controlling delivery of fluids to the chamber.

4. A vacuum system according to Claim 3, wherein the control means is integral with the controller.

5. A method of evacuating a chamber comprising the steps of providing a primary foreline for receiving fluid from an outlet of the chamber, a first vacuum pump for evacuating the chamber, a second vacuum pump for evacuating the chamber, a first secondary foreline for conveying fluid from the primary foreline to the first vacuum pump, a second secondary foreline for conveying fluid from the primary foreline to the second vacuum pump, and a three way valve for selectively connecting a chosen one of the first and second secondary forelines to the primary foreline; and controlling the three way valve to selectively divert a first reactant-rich fluid from the primary foreline into the first secondary foreline and a second reactant-rich fluid from the primary foreline to the second secondary foreline thereby to inhibit mixing of the first and second reactants within the vacuum pumps.

6. A method according to Claim 5, wherein the three way valve is moveable between a first position and a second position to divert fluid to a chosen one of the secondary forelines.

7. A method according to Claim 6, wherein the position of the valve is changed when a purge gas is present in the primary foreline.

8. A method according to any of Claims 5 to 7, wherein the length of the primary foreline is chosen in dependence on at least the pulse pitch and pulse duration of a delivery sequence of purge gas to the chamber.