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Title:
POWER CONVERTER UNIT, PLASMA PROCESSING EQUIPMENT AND METHOD OF CONTROLLING SEVERAL PLASMA PROCESSES
Document Type and Number:
WIPO Patent Application WO/2018/197696
Kind Code:
A1
Abstract:
Power converter unit (1, 1') capable to convert an electrical input power into a bipolar output power and to deliver this output power to at least two independent plasma processing chambers (9a, 9b,.. 9n), the unit (1, 1') comprising: - one power input port (2) for connection to an electrical power delivering grid (7), - at least two, preferably more than two, power output ports (3a, 3b,.. 3n) each for connection to one of the plasma process chambers (9a, 9b,.. 9n), - a control device (4) configured to control the unit (1, 1') to deliver the bipolar output power to the power output ports (3a, 3b,.. 3n), using control parameters of at least one of: power, voltage, current, excitation frequency, or threshold for protective measures, such the control device (4) comprising a virtual power supply (24a, 24b,.. 24n) for every output port (3a, 3b,.. 3n), every virtual power supply (24a, 24b,.. 24n) comprising a separate complete set of all fixed and time varying parameters and internal states associated with the operation of every individual output port (3a, 3b,.. 3n) is kept in the control device (4).

Inventors:
ENGELSTAEDTER, Jan Peter (Talhauser Strasse 20, Ebringen, 79285, DE)
RUDA, Krzysztof (ul. Kocjana 1/92, 01-473 Warsaw, 01-473, PL)
SWIATNICKI, Jakub (ul. Laska 52/35, 98-220 Zdunska Wola, 98-220, PL)
Application Number:
EP2018/060939
Publication Date:
November 01, 2018
Filing Date:
April 27, 2018
Export Citation:
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Assignee:
TRUMPF HÜTTINGER GMBH + CO. KG (Bötzinger Strasse 80, Freiburg, 79111, DE)
International Classes:
H01J37/32; C23C14/34; H01J37/34; H02J3/36; H02M7/00
Foreign References:
US20070045111A12007-03-01
US5777863A1998-07-07
US20110036707A12011-02-17
DE19702187A11998-07-30
US20140357064A12014-12-04
US20060156979A12006-07-20
US20050034667A12005-02-17
US7396759B12008-07-08
US6756318B22004-06-29
US6495392B22002-12-17
US6271053B12001-08-07
US6620299B12003-09-16
Attorney, Agent or Firm:
TRUMPF PATENTABTEILUNG (TRUMPF GmbH & Co. KG, TH501 Patente und LizenzenJohann-Maus-Strasse 2, Ditzingen, 71254, DE)
Download PDF:
Claims:
Claims

1. Power converter unit (1, 1') capable to convert an electrical input power into a bipolar output power and to deliver this output power to at least two independent plasma processing chambers (9a, 9b . . 9n), the unit (1, 1') comprising :

one power input port (2) for connection to an electrical power delivering grid (7),

at least two, preferably more than two, power output ports (3a, 3b, . . 3n) each for connection to one of the plasma process chambers (9a, 9b, . . . 9n),

a control device (4) configured to control the unit (1, 1') to deliver the bipolar output power to the power output ports (3a, 3b, . . 3n), using control parameters of at least one of:

power, voltage, current, excitation frequency, or threshold for protec- tive measures,

the control device (4) comprising a virtual power supply (24a, 24b, . . 24n) for every output port (3a, 3b, . . 3n), every virtual power supply (24a, 24b, . . 24n) comprising a separate complete set of all fixed and time varying parameters and internal states associated with the operation of every individual output port (3a, 3b, . . 3n) is kept in the control device (4).

2. Unit (1,1') of claim 1 where the unit (1, 1') comprises a first power converter stage (5) configured to convert the input power to an interme- diate power, preferable to DC link power.

3. Unit (1, 1') of one of the proceeding claims where the unit (1, 1') comprises at least one further power converter stage (6, 6a, 6b, . . 6n) configured to convert the intermediate power from the first power con- verter stage (5) to the bipolar output power.

4. Unit (1') of one of the proceeding claims where the unit (1') comprises at least two further power converter stages (6a, 6b, . . 6n) configured to convert the intermediate power from the first power converter stage (5) to several bipolar output power signals and lead these powers to the power output ports (3a, 3b . . 3n). 5. Unit (1, 1') of one of the proceeding claims where the unit (1, 1') comprises switching means (8a, 8b, . . . 8n) between the power converter stage(s) (5, 6, 6a, 6b, . . .6n) and the output ports (3a, 3b, . . 3n).

6. Unit (1, 1') of one of the proceeding claims where the switching means (8a, 8b, . . . 8n) are controlled by the control device (4).

7. Unit (1, 1') of one of the proceeding claims where the control device (4) is configured to control the power converter stages (5, 6, 6a, 6b, . . .6n) and/or the switching means (8a, 8b, . . 8n) such that, in use, the unit (1, 1') delivers at a first time T31 a first output power signal at the first output power port (3a) for a first time frame (T31-T32) and at a second time T41 a second power signal at a second output power port (3b, . . 3n) for a second time frame (T41-T42), where the first time (T31) is different from the second time (T41) and/or the first time frame (T31-T32) is dif- ferent from the second time frame (T41-T42).

8. Unit (1, 1') of one of the proceeding claims where the control device (4) is configured to activate a switching means (8a, 8b, . . . 8n) from a closed status into an open status only when the absolute value of current through the switch is lower than one ampere, preferably zero.

9. Unit (1, 1') of one of the proceeding claims where the control device (4) is configured to activate a switching means (8a, 8b, . . . 8n) from an open status into an closed status only when the absolute value of voltage along the open switch is lower than 20 volts, preferably zero.

10. Unit (1, 1') of one of the proceeding claims where at least one of the power converter stages (5, 6, 6a, 6b, . . .6n) comprises a bridge circuit, preferably a full bridge circuit.

11. Unit (Ι, Ι') of one of the proceeding claims where the unit comprises a cabinet (10) encompassing all other parts of the unit (1,1') and where preferably the input port (2) is directly connected to the cabinet (10), and where more preferably the output ports ( 3a, 3b, . . . 3n) are directly connected to the cabinet (10).

12. Plasma processing equipment (19, 19') comprising :

two, preferably more than two, plasma processing chambers (9a, 9b, . . 9n)

one power converter unit (1, 1') of one of the proceeding claims, and- each plasma processing chamber (9a, 9b, . . 9n) is connected to the one of the power output ports ( 3a, 3b, . . . 3n) of the power converter unit (1,1'), and preferably a control (17) external from the power con- verter unit (1, 1').

13. Plasma processing equipment (19, 19') of claim 12 where at least one of the plasma processing chambers, preferably both, more preferably all plasma processing chambers are configured to process in use a PECVD process.

14. Method of controlling several plasma processes in several plasma processing chambers (9a, 9b, . . . 9n) with a control device (4) by converting an electrical input power into a bipolar output power and deliver this output power to the plasma processing chambers (9a, 9b . . 9n), where the control device (4) controls a power converter unit (1, 1') to deliver the bipolar output power to the power output ports (3a, 3b, . . 3n), using control parameters of at least one of: power, voltage, current, excitation frequency, or threshold for protective measures, by establishing a virtual power supply (24a, 24b, . . 24n) for every output port (3a, 3b, . . 3n), every virtual power supply (24a, 24b, . . 24n) comprising a separate complete set of all fixed and time varying parameters and internal states associated with the operation of every individual output port (3a, 3b, . . n) is kept in the control device (4).

Description:
Power converter unit, plasma processing equipment and method of controlling several plasma processes

The invention is dedicated to a power converter unit, plasma processing equipment and method of controlling several plasma processes.

Many plasma processing equipments employ multiple independent plasma processing chambers where plasma processing is performed in parallel. Such plasma process equipment is known from US 2014/0357064A1, US 2006/0156979A1, US2005/0034667A1, US 7,396,759B1,

US 6,756,318B2, US 6,495,392B2, US 6,271, 053B1. To this purpose these equipments employ multiple independent power supplies connected to the individual chambers. In many instances the power delivered to all chambers is always less than the sum of the rated power installed on the machine through all independent power supplies. This excess in installed power creates high installation cost.

It is an object of this invention to reduce the excess costs.

The object is solved by a power converter unit according to claim 1 and by a plasma processing equipment according to claim 12 as well as by a method according to claim 14. Further independent or preferred aspects of the invention are covered by the dependant claims and the description.

The power converter unit is capable to convert an electrical input power into a bipolar output power and to deliver this output power to at least two independent plasma processing chambers, the unit comprises:

- one power input port for connection to an electrical power delivering grid,

- at least two, preferably more than two, power output ports, each for connection to one of the plasma process chambers,

- a control device configured to control the unit to deliver the bipolar output power to the power output ports, using control parameters of at least one of: power, voltage, current, excitation frequency, or threshold for protective measures,

such that at least one of the control parameters at a first power output port is different from the corresponding control parameter at a different power output port. In this way one single power converter unit with a given maximum power capability may be used instead of several of them.

With bipolar output power in this disclosure is meant an output power with an alternating current, where the current changes its direction with a fre- quency which may excite the plasma process (exciting frequency).

Control parameters may be measured values or set values of the mentioned parameters. The measured and set values may be absolute, actual, effective such as root mean square (rms), or extreme such as maximum or minimum values.

The input power may be an electrical power delivered from an AC power grid . It may be also a DC power line.

The control device may comprise a microcontroller with a software program running on it when the power unit is in use. The control device may have several interfaces, such as data connections to external components, monitors, keyboards, connectable with wires or wireless.

The control device may have a computing part and a memory part. The memory part may be divided for several purposes such as monitor memory, ram, data memory, program memory. A threshold value may be a value used for detecting ignition or breakdown of the plasma . It may be specified for each output port differently and changing in time. The bipolar output power may be a power value more than 1 kW, preferably more than 10 kW.

The bipolar output power may be of a frequency more than 1 kHz, preferably more than 10 kHz, preferably more than 50 kHz.

In a further aspect, the power converter unit may comprise a first power converter stage configured to convert the input power to an intermediate power, preferable to DC link power. In a further aspect, the power converter unit may comprise at least one further power converter stage configured to convert the intermediate power from the first power converter stage to the bipolar output power.

In a further aspect, the power converter unit may comprise at least two further power converter stages configured to convert the intermediate power from the first power converter stage to several bipolar output power signals and lead these powers to the power output ports.

In a further aspect, the power converter unit may comprise switching means between the power converter stage(s) and the output ports.

In a further aspect, the switching means are controlled by the control device. Switching means to switch between electrodes in only one plasma chamber are described in US 6,620,299 Bl .

In a further aspect, the control device may be configured to control the power converter stages and/or the switching means such that, in use, the unit delivers at a first time a first output power signal at the first output power port for a first time frame and at a second time a second power signal at the second output power port for a second time frame, where the first time is different from the second time and/or the first time frame is different from the second time frame.

In a further aspect, the switching means are configured to lead current into two opposite directions.

In a further aspect, the control device may be configured to activate a switching means from a closed status into an open status only when the absolute value of current through the switch is lower than one ampere, preferably zero.

In a further aspect, the control device may be configured to activate a switching means from an open status into a closed status only when the absolute value of voltage along the open switch is lower than 20 volts, preferably zero.

In a further aspect, at least one of the power converter stages comprises a bridge circuit, preferably a full bridge circuit.

One bridge circuit may be a rectifier bridge circuit capable of rectifying an AC power. One bridge circuit may be a bipolar output power generating switching bridge circuit.

In a further aspect, the power converter unit may comprise a cabinet encompassing all other parts of the unit.

In a further aspect, the input port may be directly connected to the cabinet. In a further aspect, the output ports may be directly connected to the cabinet.

In a further aspect, a plasma processing equipment may comprise :

- two, preferably more than two, plasma processing chambers,

- one electrical power converter unit as described above.

Each plasma processing chamber may be connected to one of the power output ports of the power converter unit.

In a further aspect, at least one of the plasma processing chambers, preferably all plasma processing chambers, may be configured to process, in use, a plasma vapor deposition (PVD) process. At least one of the plasma processing chambers, preferably all plasma processing chambers may be configured to process, in use, a plasma enhanced chemical vapor deposition (PECVD) process.

At least one of the plasma processing chambers, preferably all plasma processing chambers, may be configured to process, in use, an atomic layer deposition (ALD) process.

At least one of the plasma processing chambers, preferably all plasma processing chambers, may be configured to process, in use a plasma etching process.

The object is also solved by a method of controlling several plasma processes in several plasma processing chambers with a control device by converting an electrical input power into a bipolar output power and deliver this output power to the plasma processing chambers, where the control device controls a power converter unit to deliver the bipolar output power to the power output ports, using control parameters of at least one of: power, voltage, current, excitation frequency, or threshold for protective measures,

by establishing a virtual power supply for every output port, every virtual power supply comprising a separate complete set of all fixed and time varying parameters and internal states associated with the operation of every individual output port is kept in the control device.

In a further aspect of the method the control device controls a power converter unit such that at least one of the control parameters at a first plasma chamber is different from the corresponding control parameter at a different plasma chamber.

In a further aspect of the method the full set of desired values may be obtained via a interface connection, preferable from a control external from the power converter unit, where this external control controls also the plasma process in the plasma chambers.

In a further aspect of the method the calculation may comprise the calculation of the maximum desired power at all times and the comparism to the maximum power rating of the power converter unit.

In a further aspect of the method an error message mayl be given, in the case that the outcome of the calculation is, that there is no way of possible delivery the desired value to every for the output ports.

In a further aspect of the method may be given one or more options of changing the process with a new set of desired values in the case that the outcome of the calculation is, that there is no way of possible delivery the desired value to every for the output ports.

In a further aspect of the method the control device may control the power converter unit such that at least one of the control parameters at a first plasma chamber is different from the corresponding control parameter at a different plasma chamber. Plasma processes in the different plasma chambers may be different or the same. They may be the same but in a different status, which means for example plasma process in a first plasma chamber is in a PECVD status where plasma process in a other plasma chamber at the beginning cleaning status, and the same PECVD status will be worked later, when plasma process in a first plasma chamber may be in a etching status. All these processes may be worked out simultaneously or in a time multi- plexed manner or in a combination.

In the figures some examples of the invention are shown schematically and described in more detail in the following description. The figures show: Fig . 1 a first plasma processing equipment wit a power converter unit according to the invention;

Fig . 2 a second plasma processing equipment wit a second power converter unit according to the invention;

Fig . 3 timing diagrams of output power at a first output power port;

Fig . 4 timing diagrams of output power at a second output power port;

Fig . 5 a rectifier bridge circuit;

Fig . 6 a bipolar power converting bridge; Fig . 7 a first embodiment of a switching means;

Fig . 8 a second embodiment of a switching means. In Fig. 1 a first plasma processing equipment 19 wit a first power converter unit 1 is shown. The plasma processing equipment 19 comprises plasma processing chambers 9a, 9b . . 9n. each connected to a power output port 3a, 3b, . . 3n.

The power converter unit 1 comprises a power input port 2 for connection to an electrical power delivering grid 7.

The power converter unit 1 further comprises a first power converter stage 5 configured to convert the input power at the input power port 2 to an intermediate power, preferably to DC link power 12. Also several first power converter stages 5 configured to convert the input power at the input power port 2 to an intermediate power, preferably to DC link power 12 may be part of the power converter unit 1 and, preferably connected in parallel .

The power converter unit 1 further comprises one further power con- verter stage 6 connected downstream to the first power converter stage 5 configured to convert the intermediate power from the first power converter stage to the bipolar output power.

In between the power converter stage 5 and the further power converter stage 6 may be implemented an energy saving element such as an in- ductor or a capacitor for smoothing the current or voltage respectively.

The power converter unit 1 further comprises several switching means 8a, 8b, . . . 8n between the power converter stage 6 and the output ports 3a, 3b, . . 3n.

The power converter unit 1 further comprises a control device 4 config- ured to control the power converter unit 1 to deliver the bipolar output power to the power output ports 3a, 3b, . . 3n, using control parameters of at least one of: power, voltage, current, excitation frequency, or threshold for protective measures, such that at least one of the control parameters at a first power output port 3a is different from the corre- sponding control parameter at a different power output port 3b, . . . 3n.

In this example the control device 4 has connections to the power converter stages 5, 6 and the switching means 8a, 8b, . . . 8n. Some of these connections may be optional such for example the connection to the power converter stages 5. The control device 4 may be configured to activate a switching means 8a, 8b, . . . 8n from a closed status into an open status only when the absolute value of current through the switch is lower than one ampere, preferably zero. This has the advantage that switching means may be used which need not to be designed to switch higher cur- rents. This makes the unit even less expensive.

The control device 4 may also be configured to activate a switching means 8a, 8b, . . . 8n from an open status into an closed status only when the absolute value of voltage along the open switch is lower than 20 volts, preferably zero. This has the advantage that switching means may be used which need not to be designed to switch higher voltages. This makes the unit even less expensive.

In the example bipolar transistors 81, 82, 91, 92 are used as shown in Fig . 7 and 8. These bipolar transistors are much cheaper than MOSFETs. The bipolar transistors 81, 82, 91, 92 may be IGBTs, this is a low cost transistor for leading high currents with low loss of energy. This makes the unit 1 even less expensive, due to no need of expensive cooling devices.

In Fig. 7 and 8 additional diodes 83, 84, 93, 94 are connected for leading current into the wanted direction and blocking current into unwanted direction.

The first power converter stage 5 may comprise a rectifier circuit, preferably a bridge rectifier circuit 50 as shown in Fig. 5. Four rectifying diodes 52, 53, 54, 55 are connected in a bridge circuit in order to rectify AC power from the first port 51 to the second port 56. At the first port 51 may be additionally connected at least one of the following : a filter, an overvoltage protection circuit, an overcurrent protection circuit. A filter may comprise one or several of energy saving elements such as capacitors or inductivities.

The second power converter stage 6 may comprise a switching bridge, preferably a full switching bridge 60 as shown in Fig. 6. This full bridge switching bridge 60 comprises four switching means 62, 63, 64, 65. These switching means may be transistors, bipolar transistors, IGBTs and most preferably MOSFETs. A filter circuit comprising one or several energy saving elements such as a capacitor 61 and/or inductivities 66, 67 may be at the input of the second power converter stage 6. The full bridge switching bridge 60 may further comprise some diodes in the shown manner.

The power converter unit 1 may comprise a cabinet 10 encompassing all other parts of the unit 1. It may be of metal and therefore a good pro- tection against electromagnetical disturbing waves. The input port 2 may be directly connected to the cabinet 10. The output ports 3a, 3b, . . . 3n may also be directly connected to the cabinet (10).

In one power converter unit 1 the current leading capability of all of the switching means 8a, 8b . . . 8n together may be higher than the maxi- mum power delivery possibilities of all the power converter stages 5 together.

In Fig. 2 a second plasma processing equipment 19' with a second power converter unit 1' is shown. The second power converter unit 1' is an alternative to the first power converter unit 1 as shown in Fig . 1. All ele- ments which are the same as in Fig. 1 have the same reference numbers. The power converter unit 1' as shown in Fig . 2 comprises instead of the switching means 8a, 8b, . . . 8n several power converter stages 6a, 6b, . . 6n configured to convert the intermediate power 12 from the first power converter stage 5 to several bipolar output power signals and lead these powers to the power output ports 3a, 3b . . 3n. All power converter stages 6a, 6b, . . 6n are controllable by the control device 4. All power converter stages 6a, 6b, . . 6n may comprise full bridges 60 and filter elements 61, 66, 67 as shown in Fig . 6.

Measuring sensors for detecting voltage, current, frequency or power may be connected at the output ports 3a, 3b, . . 3n (not shown).

Also several first power converter stages 5 configured to convert the input power at the input power port 2 to an intermediate power, preferably to DC link power 12 may be part of the power converter unit 1 and, preferably connected in parallel.

Fig . 3 shows a timing diagram of output power at a first output power port 3a. The axis t is the time axis and the axis S30 may be for example the voltage, current or power axis. As the axis S30 is for the actual values of these parameters, the axis S31 is for an effective value of these parameters. In the first diagram of Fig . 3 with the S30 axis the bipolar signal is shown in two signal sequences 31, 32. The signal sequence 31 has an excitation frequency with a period of 2/11 of the time frame which begins at time point T31 and ends at time point T32. The signal sequence 32 has an excitation frequency with a period of 2/11 of the time frame which begins at time point T33 and ends at time point T34. In this example these frequencies are the same, but it is possible that these frequencies may be different. In the second diagram of Fig. 3 with the S31 axis the effective values of the two signal sequences 31, 32 are shown in two signal sequences 33, 34. Two threshold lines 35, 36 are also shown in this diagram. They may be used to detect a plasma breakdown such as an arc or an ignition of the plasma, when the effective value of one of the parameters power, voltage or current exceeds such a threshold .

In one power converter unit 1' the current leading capability of all of the power converter stages 6a, 6b, 6n together may be higher than the maximum power delivery possibilities of all the power converter stages 5 together.

Fig. 4 shows a timing diagram of output power at a different output power port 3b, . . 3n. The axis t is the time axis and the axis S40 may be for example the voltage, current or power axis. As the axis S40 is for the actual values of these parameters, the axis S41 is for an effective value of these parameters. In the first diagram of Fig. 4 with the S40 axis the bipolar signal is shown in two signal sequences 41, 42. The signal sequence 41 has an excitation frequency with a period of 1/7 of the time frame which begins at time point T41 and ends at time point T42. At time point T43 a second pulse 44 starts the end of which cannot be seen in this diagram . It may be seen out of this example that the frequencies of the signals 31, 32 and the signals 41, 42 are different, and the frequency of the signals 41, 42 is higher than the frequency of the signals 31, 32.

Additionally or alternatively to the exciting the frequency also power, voltage, current, or threshold for protective measures may be different between two different output ports 3a, 3b, . . 3n or at two different plasma chambers 9a, 9b, . . 9n. Two threshold lines 45, 46 are also shown in this diagram . They may be used to detect a plasma breakdown such as an arc or an ignition of the plasma, when the effective value of one of the parameters power, voltage or current exceeds such a threshold.

The invention works in a way of controlling several plasma processes in the several plasma processing chambers 9a, 9b, . . . 9n with the control device 4 by converting an electrical input power into a bipolar output power as shown in the signal sequences 31, 32, 41, 42 and deliver this output power to the plasma processing chambers 9a, 9b . . 9n. The control device 4 controls the power converter unit 1 to deliver the bipolar output power to the power output ports 3a, 3b, . . 3n, using control parameters of at least one of: power, voltage, current, excitation frequency, or threshold for protective measures.

For that the control device 4 may control the power converter stages 6, 6a, 6b, . . .6n and/or the switching means 8a, 8b, . .. 8n such that, in use, the unit 1 delivers at a first time T31 a first output power signal at the first output power port 3a for a first time frame T31-T32 and at a se- cond time T41 a second power signal at a second output power port 3b, . . 3n for a second time frame T41-T42, where the first time T31, T41 is different from the second time T32, T42 and/or the first time frame T31-T32 is different from the second time frame T41-T42. The control device 4 comprises virtual power supplies 24a, 24b, . . 24n. For the power converter unit 19 of Fig. 1, where the output power from one central converter stage 5,6 is routed to different output ports 3a, 3b, . . 3n in turn, the plasma processes driven from the different output ports 3a, 3b, . . 3n will in the general case impose different operating points in terms of power, impedance etc. With the use of virtual power supplies 24a, 24b, . . 24n a separate complete set of all fixed and time varying parameters and internal states associated with the operation of every individual output port 3a, 3b, . . 3n is kept in the control device 4. This means, for example, that when the active output ports 3a is switched from 3a to 3b, the control device 4 reinstates from memory the regulation state as it was present when the output power was last switched away from output 3b. This also means for example, that for a power supply with N outputs, there will be N individual sets of arc management parameters, or N sets of pulse frequency and duty cycle settings as controlled and synchronised by a sequence controller 14.

A sequence controller 14 is part of the control device 4. Its algorithm determines for every request to the power converter unit 1 to deliver out- put power to any of its output ports, or for a request to change one or more parameters of the output ports, whether this request lies in the possible area of operation. For a process as shown in Fig 3 and 4 with power delivered to output ports 3a, 3b, . . 3n, where the different output ports 3a, 3b, . . 3n are driven with different power levels, different pulse duty cycles and different pulse frequencies, the sequence controller ensures that:

• the pulse frequencies are integer multiples of each other, to avoid pulse overlaps (For plasma equipment 19' like in Fig. 2)

• for overlapping pulses the total requested output power and current do not exceed the possible maximum ((For plasma equipment 19' like in

Fig . 2)

• if possible maximums are exceeded at a limited period in the cycle, that a pattern is found without this limitation if possible (For plasma equipment 19' like in Fig . 2)

· the sum of the pulse on times plus the time to switch between outputs is smaller than the lowest frequency pulse cycle time (For plasma equipment 19 like in Fig . 1)

• a newly requested output pulse pattern on a particular output is activated at an appropriate time to fit into the pre existing active pulse pat- tern on the other outputs (For plasma equipment 19 like in Fig . 1)

• overall average power and current limits are not exceeded

• a warning is issued to the user if the requested sequence is outside the possible area

• a possible modified sequence is recommended to the user.