WO2014170697A1

WO2014170697A1 - Cracker valve control

Info

Publication number: WO2014170697A1
Application number: PCT/GB2014/051241
Authority: WO
Inventors: Victor Bellido-Gonzalez; Dermot Partick MONAGHAN; Joseph BRINDLEY; Benoit DANIEL; Iván FERNÁNDEZ; Ambiörn WENNBERG; Fernando Briones
Original assignee: Gencoa Ltd; Nano4Energy Slne
Priority date: 2013-04-19
Filing date: 2014-04-22
Publication date: 2014-10-23
Also published as: GB201307097D0

Abstract

This invention relates to the control of cracker valves for the injection of reactants into a reaction system and the control method of such valves, reactants, processes and systems. The present invention also relates to sensors, actuators and algorithms involved in such systems. According to the present invention a control feedbackmethod of cracker valve is disclosed. Cracker valves could be operated in continuous or pulsed mode or a combination of those modes. Pulsed frequencies of vapour in the process of the present invention could be, although not exclusively, from 1 Hz to 100 kHz. Different pulsed packages are also part of the present invention. The frequency (or period), time on/off, amplitude, maximum and minimum input values and phase of each pulse could also be varied according to the present invention. A feedback controller able to control in open loop or closed loop mode the totality or any one of the pulses is also part of the present invention.

Description

Title: Cracker valve control

Description:

This invention relates to the control of cracker valves for the injection of reactants into a reaction system and the control method of such valves, reactants, processes and systems. The present invention also relates to sensors, actuators and algorithms involved in such systems.

Cracker valves are used in extensively in vacuum deposition systems to introduce gasses, in particular, reactive gasses, into the process chamber. The gasses so introduced typically condense on substrates to form deposited layers, or act as reagents or catalysts that interact with the substrate or with other layers thereon.

A cracker valve typically comprises an evaporation chamber containing a quantity of material, e.g. metals, chalcogens (group 16 elements) or organic materials, to be evaporated, and a control valve to control the egress of the vapour into a delivery system, which is typically a perforated tube extending into the process chamber. A cracking heater element is interposed between the evaporation chamber and the delivery system to crack the vapour into a desired reagent for the process.

Existing cracker vales, such as those disclosed in patent application numbers ES2067381, US5431735 and GB1307073.5, employ needle valves to control the flow of vapour or cracked vapour into the delivery system and hence into the process chamber of the overall system.

Needle valves have proven to be a good choice in most circumstances because a finely-tapered needle valve affords relatively accurate control of the flux of gas, as well as being reliable. For these reasons, existing cracker valves use needle valves to control the flow of gas into the process chamber.

The disadvantages of using needle valves, however, are manifold. Firstly, in order to obtain highly accurate control of the needle valve setting, a finely-pitched screw thread needs to be used to obtain the necessary granularity in its setting. This necessarily requires many turns of the needle valve to move it from a fully-open to a fully-closed position. Even using motorised actuators for rotating the needle valve, the time it takes to actuate a needle valve can be unacceptably slow, especially where the gas flux is a rapidly-changing process parameter.

Further, because the needle valve is controlled by a screw thread to convert rotation into axial displacement of the needle relative to the aperture, the screw thread provides sufficient mechanical advantage that even gentle manipulation of the needle valve upon collision of the needle with the aperture (i.e. when in the fully-closed position), can lead to plastic deformation of the needle. Thus, a needle valve needs to be re-calibrated every time it is first used, to counteract the plastic deformation of the needle that occurred the previous time it was fully-closed. Having to re-calibrate the needle valve is time-consuming and inconvenient.

A need therefore exists for an improved and/or alternative type of cracker valve that overcomes or addresses one or more of the above problems and/or which functions differently to existing cracker valves.

A first aspect of the invention provides a cracker valve comprising an evaporation chamber, a delivery system and a conduit in fluid communication with the evaporation chamber and the delivery system, a high temperature heating element located in the conduit and a flow controller for controlling the flux of a gas into the delivery system, characterised in that the flow controller comprises an on/off valve and a controller for controlling the on/off state of the valve.

A second aspect of the invention provides a method of controlling a cracker valve comprising an evaporation chamber, a delivery system and a conduit in fluid communication with the evaporation chamber and the delivery system, a high temperature heating element located in the conduit and an on/off valve for controlling the flux of a gas into the delivery system, the method being characterised by using PWM to control the on/off valve to control the flux of gas into the delivery system.

By providing an on/off valve, as opposed to a variable-setting valve, such as the needle valve of known systems, some or all of the problems identified above may be overcome or ameliorated. Specifically, an on/off valve typically has a faster switching speed (from the fully-on to the fully-off position), thereby enabling the flow controller to react more quickly to changes in controller inputs. Further, because an on/off valve generally comprises a planar closing surface, as opposed to the tapered needle arrangement of a needle valve, plastic deformation of the contacting parts of the on/off valve is avoided upon closing thereof. This may reduce, or avoid, the need for re-calibration each time the flow controller is first used.

Further, in systems having variable control valves, such as needle valves, the flux of gas into the system is variable. At relatively low fluxes, especially of organic monomers, a plasma process may produce mainly cracking, but also a black carbonaceous coating, which is a result of the dynamics of the reaction, whereby relatively low concentrations are able to react fully and thus produce the carbonaceous coating. However, by pulsing the flux such that short bursts of relatively high concentrations of evaporate are delivered, the overall amount of evaporate is moderated (i.e. the total amount of evaporate per unit time), but because it is delivered in short, relatively high-concentration bursts, the dynamics of the reaction are not able to keep up, thus reducing the amount of black carbonaceous coating in the process. This is, of course, just an example, and it will be appreciated that the dynamics of a range of chemical reactions in the process can be better controlled by pulsing. For example, water could be introduced into the system, and under needle-valve control, the water might be cracked into H and O, whereas, by pulsing the on/off valve, it may be possible to avoid cracking the water to deliver H₂0 into the process, which reacts differently to H and O.

The cracker valve can be used to evaporate, and deliver into a process, any substance that is able to produce a vapour and which needs injection control into a process system. For example, the substance can be a metal, or an organic.

This invention relates to the control of cracker valves for the injection of reactants into a reaction system and the control method of such valves, reactants, processes and systems. The present invention also relates to sensors, actuators and algorithms involved in such systems. According to the present invention a control feedback method of cracker valves is provided. Cracker valves could be operated in continuous or pulsed mode or a combination of those modes. Pulsed frequencies of vapour in the process of the present invention could be, although not exclusively, from 1 Hz to 100 kHz. Different pulsed packages are also part of the present invention. The frequency (or period), time on/off, amplitude, maximum and minimum input values and phase of each pulse could also be varied according to the present invention. A feedback controller able to control in open loop or closed loop mode the totality or any one of the pulses is also part of the present invention. This invention also relates to the use of such devices with or without feedback plasma process control. This invention also relates to any deposition method or surface modification method. This invention also relates to any vacuum and non-vacuum deposition technique. This invention relates to any Physical Vapour Deposition and Reactive Vapour Deposition. This invention also relates to Chemical Vapour Deposition and Plasma Assisted Chemical Vapour Deposition. This invention also relates to plasma and non-plasma deposition methods. This invention also relates to Atomic Layer Deposition. This invention also relates to Ion Beam Assisted Deposition. This invention also relates to any Ion Bombardment treatment. The present invention relates to the use of the device in different system application such as web, glass, display, decorative, optical, semiconductor, ferroelectric, photovoltaic, thermal solar, inline, batch or cluster coaters.

Suitably, the evaporation chamber comprises a heating element arranged to heat, and thus, evaporate a material. A vacuum system may be used to at least partially evacuate the evaporation chamber to facilitate the evaporation of the material. The vacuum system, where provided, may communicate directly with the interior of the evaporation chamber, or it may communicate therewith via the delivery system.

The delivery system suitably comprises a tube extending from the conduit, which can be arranged, in use, to extend into the process chamber of a deposition apparatus, such as a magnetron sputtering apparatus. Suitably, the delivery system comprises an elongate, perforated tube, whereby cracked gasses from the cracker valve can enter the process chamber via the perforations. The perforations may take any form, although through apertures, one or more slotted apertures in a side wall of the tube may be employed. In alternative embodiments of the invention, the delivery system comprises a porous element having an open-porous structure though which gasses can permeate, or be forced under the action of a pressure or vacuum on either side thereof. Additionally or alternatively, a reticulated, mesh or grille-type structure may be used.

The high temperature heating element is suitably located in the conduit downstream of the flow controller. Such an arrangement means that cracked (i.e. reactive) gasses are less likely to enter the evaporation chamber and cause damage thereto, or to react with the feedstock material.

The on/off valve may be of any suitable type. The on/off valve has just two nominal settings, namely: fully-on and fully-off. Nevertheless, the valve will naturally adopt positions falling between the fully-on and fully-off positions during switching thereof, but the on/off valve cannot, for example, be "set" to a position falling between these two settings, e.g. 25% open.

An electrically-actuated, high frequency on/off valve is suitably used. In an embodiment of the invention, the on/off valve comprises a piezoelectrically-controlled on/off valve.

The controller is operatively connected to the on/off valve for controlling its on/off state. The controller suitably comprises a PWM controller whereby the on time and off time of the on/off valve can be selected automatically. Thus, for a 50% setting, the on time of the on/off valve is substantially equal to the off time, whereas for a 75% setting, the on time is three times greater than the off time. The on and off times can be of any suitable duration, although it will be appreciated that short on and off times are preferred in a dynamic system where the process parameters are apt to change quickly. Higher frequency operation of the on/off valve thus increases the responsiveness and/or resolution of the flow controller.

The controller suitably comprises a computer for calculating the desired on and off times for the on/off valve. The controller suitably comprises a feedback control system that monitors sensor inputs from a system comprising the cracker valve, and which dynamically amends the on and off times of the on/off valve to maintain the system or process within desired operating parameters. It will be appreciated that the on/off valve could be operated in continuous or pulsed mode or a combination of those modes. Pulsed frequencies of vapour in the process of the present invention could be, although not exclusively, from 1 Hz to 100 kHz. Different pulsed packages are also part of the present invention. The frequency (or period), time on/off, amplitude, maximum and minimum input values and phase of each pulse could also be varied according to the present invention.

A feedback controller may be used to control in open, or closed, loop mode the totality or any one of the pulses is also part of the present invention.

This invention is particularly relevant to AC dual magnetron sputtering using planar or cylindrical targets. In addition, the invention may be employed in non-AC sputtering applications such as RF, DC, DC pulsed power, complex power wave forms or high intensity pulsed power, such as HIPIMS (High Power Impulse Magnetron Sputtering) technology for single or plurality of plasma sources. This invention also relates to the use of magnetron sputtering sources, hollow cathodes and diode discharges in those reactive gas pulse discharges. This invention also relates to non-reactive and reactive deposition methods. This invention also relates to plasma and non-plasma deposition methods. This invention also relates to thermal evaporation, electron beam evaporation, laser ablation and cathodic arc, or combination. This invention also relates to Atomic Layer Deposition. This invention also relates to Ion Beam Assisted Deposition. This invention also relates to any Ion Bombardment treatment. This invention also relates to any Physical Vapour Deposition and Reactive Vapour Deposition. This invention also relates to Chemical Vapour Deposition and Plasma Assisted Chemical Vapour Deposition.

This invention relates to the use of the device in different system application such as web, glass, display, decorative, optical, semiconductor, ferroelectric, photovoltaic, thermal solar, inline, batch or cluster coaters. This invention also relates to any vacuum and non- vacuum deposition technique. This invention also relates to any deposition method or surface modification method.

The invention will be further described by way of example only with reference to the following figure in which:

Figure 1 is a schematic diagram of a known cracker valve;

Figure la is a schematic diagram of a cracker valve in accordance with the invention;

Figure 2 is a schematic cross-section of a dual magnetron sputtering apparatus fitted with a number of cracker valves in accordance with the invention;

Figure 3 is a schematic cross-section of a tubular magnetron sputtering apparatus fitted with a number of cracker valves in accordance with the invention;

Figure 4 is a schematic cross-section of an evaporator apparatus fitted with a number of cracker valves in accordance with the invention;

Figure 5 is a system diagram for a controller of the cracker valve of the invention;

Figures 6 and 7 are graphs of reactive gas input versus time;

Figure 8 shows a single Reactive Gas/Vapour input via pulsed cracker valves following different gas pulse packages according to the present invention;

Figure 9 are experimental results corresponding to Figure 8;

Figure 10 shows a single Reactive Gas/Vapour input via pulsed cracker valves following different gas pulse packages according to the present invention;

Figure 11 shows a single Reactive Gas/Vapour input via pulsed cracker valves following different gas pulse packages according to the present invention;

Figure 12 shows a process hysteresis ramp according to the present invention;

Figure 13 shows a plurality of process hysteresis ramps according to the present invention; and Figure 14 shows a process feedback control in closed loop according to the present invention.

Referring now to the drawings:

Figure 1 shows a schematic of a typical cracker valve 1 as described in the patent ES 2067381. Material in reservoir 3 is heated up at a controlled temperature via different elements and features 4 creating a constant vapour pressure. A needle valve 5 is able to open the access of the vapour into a high temperature element 7 by controlling the opening closing movements 6. The high temperature element then cracks the vapour prior to its release into the process system/chamber 2. Another possible embodiment of the cracker valve could be described by Patent Application GB1208438.0. Other cracker valve embodiments are also possible.

Figure la shows a similar cracker valve 1, albeit in accordance with the invention. In Figure la, the needle valve 5 of Figure 1 has been replaced by an on/off control valve 58, which is actuated by a controller 50. The controller 50 is operatively connected to, and is adapted, in use, to control the on/off control valve 58. The controller 50 also receives inputs from a sensor 52 located within a process chamber 56 of a system to which the cracker valve 1 is connected. A user interface 54 is provided for setting the controller, for example, for setting a set point of the process via a GUI, whereupon the controller 50 monitors the sensed 52 value and adjusts the operation of the on/off valve, via a feedback control loop, to bring the process within the chamber 56 within the user-defined parameters.

Figure 2 shows an application of the cracker valve technology in combination with magnetron sputtering according to the present invention. Gas/vapour injection elements 18a,b,c could be a combination of cracker valves and other gas injection methods. In this figure a dual rotatable magnetron sputtering of targets 10a,b are operated in AC dual sputtering mode by suitable power means 8. Targets 10a and 10b will be generally rotating in a particular direction, respectively 17a and 17b. Magnetic field and electrical potential will enable a plasma discharge 19 where the electrons 13 will move from cathode to anode in an alternating fashion 14. Some degree of plasma confinement is given by suitable magnetic field lines 15,16. Electrons collisions will produce ionisation. Gas/Vapour injection elements 18a,b,c could introduce a mixture of inert gases such as Ar, and reactive gases, such as 0₂, N₂, H₂, and reactive vapours such as H₂0, NH₃, CH₃OH, and sublimated reactive vapours such as S, Se, Te. Reactive vapours will usually be, although not exclusively, injected via cracker valves. Reactive vapours will react with material sputtered from targets 10a, b and the reactive deposition will produce a deposit on substrate 20. The rotation 17a,b of targets 10a,b enables to maintain a clean sputtering surface even in reactive sputtering conditions when reactive vapours are being injected.

Figure 3 shows another application configuration of the present invention where a single rotatable cathode where a cylindrical target 10 is rotating in a particular direction 17. A suitable magnetic field created by magnetic cathode means 21 will enable a plasma discharge 19a on the target cathode zone when a suitable power is applied in suitable sub- atmospheric pressure conditions. Plasma 19b is guided towards the corresponding anode 23, in this particular case a magnetically and electrically guided anode where by suitable magnetic means 22 situated in the anode will form a guiding magnetic field when liking with cathode magnetic means 21. Gas/Vapour injection elements 18a,b could introduce a mixture of inert gases such as Ar, and reactive gases, such as 0₂, N₂, H₂, and reactive vapours such as H₂0, NH₃, CH3OH, and sublimated reactive vapours such as S, Se, Te. Reactive vapours will usually be, although not exclusively, injected via cracker valves. Reactive vapours will react with material sputtered from target 10 and the reactive deposition will produce a deposit on substrate 20. The rotation 17 of target 10 enables to maintain a clean sputtering surface even in reactive sputtering conditions when reactive vapours are being injected. Anode elements 23 would need protection 24 from deposit contamination in order to maintain electron conductivity during the process.

Figure 4 shows an application of the cracker valve technology in combination with any evaporation method according to the present invention. Gas/vapour injection elements 18aa,bb,cc could be a combination of cracker valves and other gas injection methods. In this figure materials 25a,b are being evaporated from crucibles 26a,b where energy means 27a,b which would produce suitable temperature in order to produce respective vapours 25aa and 25bb. Energy means could be thermal, such or electron beam or laser beam for example. Other energy means or combinations are also possible. Gas/Vapour injection elements 18a,b,c could introduce a mixture of inert gases such as Ar, and reactive gases, such as 0₂, N₂, H₂, and reactive vapours such as H₂0, NH₃, CH₃OH, and sublimated reactive vapours such as S, Se, Te. Reactive vapours will usually be, although not exclusively, injected via cracker valves. Reactive vapours will react with thermally evaporated material 25aa,bb and the reactive deposition will produce a deposit on substrate 20.

Figure 5 shows a process feedback control block diagram according to the present invention. Process controller 31 via suitable sensors 30 and algorithms is able to act or command actions via Cracker Valves 1 and any other suitable system actuators 29 on a Process/System 28. The Process Controller 1 could command open loop control actions or closed loop control actions maintaining the Process/System 28 in a desirable process window of operation.

Figure 6 shows Reactive Gas/Vapour input via cracker valves according to the present invention. Different vapours or vapour time profile 32,33,34 could be introduced. Vapours could be of the same or different nature. Vapours could share the same cracker element of could be introduced via different cracker elements. In the present figure the input profile of the injection follows a continuous flow curve. Figure 7 shows Reactive Gas/Vapour input via pulsed cracker valves according to the present invention. Different vapours and/or vapour pulses 37,38, 39, 37b, 38b, 39b could be introduced (list not all inclusive). Vapours could be of the same or different nature. Vapours could share the same cracker element of could be introduced via different cracker elements. In the present figure the input profile of the injection is being pulsed. Pulses of vapours 37,38,39 could be repeated with a particular frequency, marking a reactive flow period Tp, 35. In that period Tp there could also be a time off 36 where no vapour is introduced. In addition, the different vapours pulses could vary in amplitude and frequency and phase and time off for each pulse as in 37b, 38b and 39b with respect to 37, 38 and 39 respectively. Also the minimum flow during a time off could be adjusted to a value different from zero. This minimum flow value could also vary during the process.

Figure 8 shows a single Reactive Gas/Vapour input via pulsed cracker valves following different gas pulse packages according to the present invention. Several of these pulse packages could coexist within the same system operating at the same or different frequencies, amplitudes and phases. Also according to the present invention the pulse packages could inject the same or different type of vapour. Figure 8(a) shows a regular time on/off pulse where the amplitude, frequency and time on/off are maintained constant. Figure 8(b) shows pulses with the same time on and different time off. Figure 8(c) shows pulses where both, the time on and time on and time off are changed. Figure 8(d) shows pulses where time on, time off and frequency are being changed.

Figure 9 shows experimental results for the Se flux introduced by a cracker valve operating at different frequencies and different time on (aperture time).

Figure 10 shows a single Reactive Gas/Vapour input via pulsed cracker valves following different gas pulse packages according to the present invention. Several of these pulse packages could coexist within the same system operating at the same or different frequencies, amplitudes and phases. Also according to the present invention the pulse packages could inject the same or different type of vapour. Figure 10(a) shows a regular time on/off pulse where the frequency and time on/off are maintained constant, while the amplitude is varying. Figure 10(b) shows pulses where time on, time off and frequency are being changed as well as the amplitude of the vapour input. Both (a) and (b) figures show a variable maximum vapour flux input.

Figure 11 shows a single Reactive Gas/Vapour input via pulsed cracker valves following different gas pulse packages according to the present invention. Several of these pulse packages could coexist within the same system operating at the same or different frequencies, amplitudes and phases. Also according to the present invention the pulse packages could inject the same or different type of vapour. Figure 11(a) shows a regular time on/off pulse where the frequency and time on/off are maintained constant, while the amplitude is varying. Figure 11(b) shows pulses where time on, time off and frequency are being changed as well as the amplitude of the vapour input. Both (a) and (b) figures show a variable maximum and a variable minimum vapour flux input.

Figure 12 shows a process hysteresis ramp according to the present invention. This particular example is a dual magnetron sputtering of copper targets. The Reactive vapour in this particular case is sulphur. A suitable sensor 40a, in this case one of the spectral line of the plasma emission of copper during sputtering, is chosen. The actuation 41 on the cracker valve is the frequency. A hysteresis ramp up/down cycle is used in order to track the sensor response 40 during the actuator 41 cycle. When there is no injection the sputtering is of Cu, also know as metal mode. When the flux of S the target become covered and saturated on S, also know as poisoning mode. During the actuator cycle ramp the target poisons and de- poisons, returning to the metal status. Figure 13 shows a process with multiple hysteresis ramps according to the present invention. The purpose of the multiple hysteresis ramps is process conditioning. This particular example is a dual magnetron sputtering of copper planar targets. The Reactive vapour in this particular case is sulphur. A suitable sensor 40a, in this case one of the spectral line of the plasma emission of copper during sputtering, is chosen. The actuation 41 on the cracker valve is the frequency. Hysteresis ramp up/down cycles are used in order to track the sensor response 40 during the actuator 41 cycles. When there is no injection the sputtering is of Cu, also know as metal mode. When the flux of S the target become covered and saturated on S, also know as poisoning mode. During each of the actuator cycle ramp the target poisons but it cannot fully de-poison until the last ramp. There is not enough time for the target/process to return to the metal status.

Figure 14 shows a process feedback control in closed loop according to the present invention. This particular example is a dual magnetron sputtering of copper planar targets. The Reactive vapour in this particular case is sulphur. A suitable sensor 40a, in this case one of the spectral line of the plasma emission of copper during sputtering, is chosen. The actuation 41 on the cracker valve is the frequency. A feedback closed loop is established and the actuator, acting on the cracker valve, changes values in order to maintain certain specific setpoint on the process sensor. Changes in setpoints demand changes in the actuation. The present figure shows how the setpoint can be met by suitable process actuation on the cracker valve.

By controlling the addition of one or more gasses into a deposition system by pulsing, the dynamics of the chemical reactions of each gas, or the overall composition of a mixture of gasses, can be more accurately, and reproducibly controlled.

Claims

Claims:

1. A cracker valve comprising an evaporation chamber, a delivery system and a conduit in fluid communication with the evaporation chamber and the delivery system, a high temperature heating element located in the conduit and a flow controller for controlling the flux of a gas into the delivery system, characterised in that the flow controller comprises an on/off valve and a controller for controlling the on/off state of the valve and wherein the flow controller is operatively connected to the on/off valve for controlling its on/off state and comprises a pulsed controller whereby the on time and off time of the on/off valve can be selected automatically.

2. The cracker valve of claim 1, wherein the pulsed controller comprises any one or more of the group comprising: a pulse width modulated (PWM) controller; a pulse frequency modulated (PFM) controller; a pulse amplitude modulated (PAM) controller; and a pulse code modulation (PCM) controller.

3. The cracker valve of claim 1 or claim 2, wherein the flow controller comprises a computer for calculating the desired on and off times for the on/off valve.

4. The cracker valve of any preceding claim, wherein the flow controller comprises a feedback control system that monitors sensor inputs from a system comprising the cracker valve, and which dynamically amends the on and off times of the on/off valve to maintain the system or process within desired operating parameters.

5. The cracker valve of any preceding claim, wherein the flow controller is adapted to operate the on/off valve in continuous or pulsed mode or a combination of continuous and pulsed modes.

6. The cracker valve of any preceding claim, wherein the flow controller is adapted to actuate the on/off valve at pulsed frequencies from 1 Hz to 100 kHz.

7. The cracker valve of any preceding claim, wherein the flow controller is adapted to actuate the on/off valve at any desired frequency, on time, off time, amplitude, maximum and minimum input values and phase.

8. A deposition system comprising a process chamber and one or more cracker valves according to any preceding claim, in which the delivery system or systems of the cracker valve or valves communicates with the interior of the process chamber.

9. A deposition system according to claim 8, wherein the deposition apparatus comprises any one or more of the group comprising: an AC dual magnetron sputtering apparatus using planar or cylindrical targets; a non-AC sputtering apparatus; an F, DC, DC pulsed power, complex power wave forms or high intensity pulsed power, such as HIPIMS (High Power Impulse Magnetron Sputtering) sputtering apparatus; a magnetron sputtering source; a non-reactive deposition apparatus; a reactive deposition apparatus; a plasma deposition apparatus; a non-plasma deposition apparatus; a thermal evaporation apparatus; electron beam evaporation apparatus; a laser ablation apparatus; a cathodic arc deposition apparatus; an Atomic Layer Deposition apparatus; an Ion Beam Assisted Deposition apparatus; an Ion Bombardment treatment apparatus; a Physical Vapour Deposition apparatus; a Reactive Vapour Deposition apparatus; a Chemical Vapour Deposition apparatus; and a Plasma Assisted Chemical Vapour Deposition apparatus.

10. The deposition apparatus of claims 8 or 9, adapted for use in web, glass, display, decorative, optical, semiconductor, ferroelectric, photovoltaic, thermal solar, inline, batch or cluster coating applications.

11. A method of controlling a cracker valve comprising an evaporation chamber, a delivery system and a conduit in fluid communication with the evaporation chamber and the delivery system, a high temperature heating element located in the conduit and an on/off valve for controlling the flux of a gas into the delivery system, the method being characterised by pulsing the on/off valve to control the flux of gas into the delivery system.

12. The method of claim 11, wherein controlling the flux of gas into the delivery system comprises any one or more of the group comprising: varying the pulse width; varying the pulse frequency; varying the pulse amplitude; and using pulse code modulation.

13. The method of claim 11 or claim 12, further comprising monitoring a process parameter that depends on the flux of gas and adjusting the pulsing via a process feedback control loop to maintain the monitored process parameter within desired upper and lower threshold values.

14. The method of claim 13, wherein the feedback control loop comprises an algorithm and wherein the pulsed controller is operatively connected to one or more further controllers for controlling other process parameters, and wherein the pulsed controller and the further controller or controllers are configured to vary the process parameters to maintain the process/system in a desired process window of operation.

15. The method of any of claims 11 to 14, comprising controlling a plurality of cracker valves operatively connected to a system.

16. The method of claim 15, wherein the plurality of cracker valves are adapted to deliver different gasses into the system, and wherein the method is configured to automatically control the quantity and composition of gasses entering the system.

17. The method of claim 15 or claim 16, wherein the pulsing of the on/off valves of each cracker valve are controlled independently.

18. The method of any of claims 11 to 17, wherein the pulsing is configured to perform a process hysteresis ramp in which the flux of gas is ramped up until a sensor detects that the process has become saturated, and then down until the sensor detects that the process has become de-saturated.

19. The method of any of claims 11 to 18, wherein the pulsing is configured to perform a series of process hysteresis ramps in which the flux of gas is ramped up and down until a sensor detects that the process has become saturated, and then down.

20. The cracker valve or method of any preceding claim, wherein the on/off valve has two nominal settings, namely: fully-on and fully-off.

21. The cracker valve or method of any preceding claim, wherein the on/off valve comprises an electrically-actuated, high frequency on/off valve.

22. The cracker valve or method of any preceding claim, wherein the on/off valve comprises a piezoelectrically-controlled on/off valve.

23. The cracker valve or method of any of claims 1 to 21, wherein the on/off valve comprises a solenoid-controlled on/off valve.