T 1897/16 05-02-2021

1. The patent

The invention of the patent concerns a power supply device for plasma processing. In plasma processing, arcs may occur. Arc events may lead to damages in the target or to a poor quality of the processed surfaces. Thus, when an arc event occurs, the supply of power to the plasma processing chamber is interrupted. In this case, the energy which is stored e. g. in the cables to the plasma processing chamber when the supply of power is interrupted is supplied to the plasma, prolonging the quenching of the arc. The patent proposes to handle arc events in a more efficient way by providing a recovery energy circuit for feeding at least a part of the energy stored in the cables back to the power supply circuit.

2. Prior art

Document D5 also concerns a power supply for plasma applications and the fast extinction of arcs. When an arc is detected in the plasma, a large amount of the energy stored in the cables (lead inductance) is transferred into a capacitor C, arranged, according to the figures, outside the power supply unit 5. The capacitor is discharged by means of a discharging circuit which can either dissipate the energy in a resistor or feed it back to the power supply unit.

3. Admissibility of the appeals

3.1 Admissibility of the opponent's appeal

The appeal of the opponent is admissible; this was not challenged by the proprietor.

3.2 Admissibility of the proprietor's appeal (see sections XII. (a) and XIII. (a) above)

The reasoning of the Opposition Division with respect to lack of inventive step concerning the former auxiliary request 1, which corresponds essentially to the present main request, is based on the embodiment of figure 6 of D5 (see point 18 of the Reasons).

The proprietor argues that the circuit shown in figure 6 was not an enabling configuration and thus did not form part of the prior art and could not be considered as closest prior art (grounds of appeal of the proprietor, point 2.5, second paragraph).

Thereby, contrary to the opponent's submissions, the proprietor does provide a reason why the Opposition Division's choice of the closest prior art was wrong and why they use a different prior art.

The proprietor's grounds of appeal thus relate to the reasoning of the Opposition Division with respect to lack of inventive step and indicate rea­sons for setting aside the impugned decision according to Rule 99(2) EPC. Consequently, the appeal of the proprietor is admissible.

4. Article 84 EPC (see sections XII. (b) and XIII. (b) above)

4.1 If - hypothetically - feature (1i) referred to "the" input terminals, the skilled person might be led to consider that the first and second input terminals mentioned should indeed be the input terminals by means of which the power supply circuit is connected to the mains supply (AC input 11, see figure 1), as submitted by the opponent.

However, feature (1i) defines in fact that the capacitor is connected to "a" first and "a" second input terminal of the power supply circuit. Since the indefinite article "a" is used, the skilled person would understand that the input terminals referred to could be any electrical terminals used by the power supply circuit as any input. In the present case, the input provided to the first and second terminals of the power supply circuit is the energy fed back by the recovery circuit and not necessarily the AC input provided by the mains supply, in line with the submissions of the proprietor.

It follows therefrom that feature (1i) is broad in that it does not specify the position of the capacitor in the power supply circuit or its role during standard operation of the power supply circuit, as acknowledged by the proprietor. It is, however, clear because it does not create any doubt whether a given power supply device would fall under the subject-matter for which protection is sought.

4.2 Moreover, the Board agrees with the proprietor in that the expression "in use" in feature (1h) meant that the effect defined in that feature (the closing of the first switch leading to the power of the power supply circuit being supplied again to the plasma processing chamber) occurs when the claimed power supply device is in use.

4.3 Therefore, claim 1 of the main request is clear (Article 84 EPC).

5. Main request, Article 56 EPC

5.1 Closest state of the art (see sections XII. (c) and XIII. (c) above)

Both the proprietor and the opponent regarded D5 as representing the closest state of the art, in agreement with the contested decision.

Both D5 and the patent are directed at a power supply device for plasma application. They also have many essential features in common. Further, both D5 and the patent concern the same problem, namely, removing energy when an arc event occurs. The Board thus sees no reason to disagree with the parties on this point.

It was, however, a point of dispute whether figure 6 of this document and the corresponding description represented an enabling disclosure and could be used to represent the closest prior art or not.

The argument of the proprietor that the capacitor C shown in figure 6 of D5 would be charged in the wrong direction when switch SS was closed is based on the particular connection of diode D2 shown in figure 6, in which its cathode is connected to capacitor C, diode D3 and switch SS, while its anode is connected only to the plasma chamber. In this configuration, current from the current source or capacitor C (when pre-charged by the current source) could in principle pass through switch SS without being blocked by diode D2.

However, the Board concurs with the opponent that this possible flaw in the disclosure of figure 6 of D5 concerns the transfer of energy to capacitor C and does not directly affect the discharge of energy stored therein by transfer into the power supply unit.

In addition, as pointed out by the opponent in their letter dated 6 October 2017 (page 3, point 2.3.4.2 and footnote 1), each part of any document has to be construed in the context of the document as a whole according to the Case Law of the Boards of Appeal of the EPO (9th edition 2019, section I.C.4.1).

In the present case, in all the embodiments of D5 other than the one shown in figure 6 (i. e. in figures 1 to 5), diode D2 is arranged such that current provided by the pre-charged capacitor C cannot flow through switch SS when the latter is closed. In particular, in the embodiments which are most similar to the one shown in figure 6, that is, the embodiments where switch SS is arranged on the negative side of the power supply unit 5 and where the discharging circuit 7.2 is explicitly shown (figures 2 and 5), diode D2 is arranged with its anode not only connected to the plasma chamber, but also to switch SS, thereby blocking any current from pre-charged capacitor C through switch SS.

In the context of D5 as a whole, the skilled person would thus realize that figure 6 contained an error and that diode D2 in that figure should in fact be connected in a similar manner as in the embodiments shown in figures 2 and 5. They would thereby know that diode D2 was to be connected to switch SS with its anode side, as suggested by the opponent.

The Board notes that this latter arrangement would then also be in agreement with figure 7 of D5, in which the switch SS is connected to the anode of D2.

The Board thus considers that the embodiment of figure 6 of D5 is disclosed in an enabling manner in the context of D5 as a whole, contrary to the submissions of the proprietor. It is therefore suitable as closest prior art in the present case.

5.2 Disclosure of D5 (see sections XII. (d) and XIII. (d) above)

In the words of claim 1 of the main request, the embodiment of figure 6 of D5 discloses:

(1a) A power supply device for plasma processing (page 11, lines 1 to 4), wherein electric arcs may occur (page 2, lines 11 to 16 and 24 to 26), comprising

(1b) a power supply circuit (power supply unit 5, see figures) designed to generate a DC voltage across a negative and a positive output terminal (outputs 4.2, 4.1, see page 11, lines 1 to 12 and figures),

(1c) the output terminals being for connection to a plasma processing chamber (plasma chamber 2, see figures) by means of conductors (leads 3.2, 3.1, see page 11, lines 1 to 12 and figures),

(1d) a first switch (serial switch SS, see figures) connected between the power supply circuit and one of the output terminals for interrupting the power supply to the plasma processing chamber in case of the occurrence of an arc (page 13, lines 1 to 4), and

(1e) a recovery energy circuit (discharging circuit 7.2, see figure 6) connected to the output terminals (outputs 4.2, 4.1) and to the power supply circuit (power supply unit 5),

(1f) the recovery energy circuit (discharging circuit 7.2) serving for feeding at least partially the energy which is stored in the conductors (leads 3.2, 3.1) when the first switch (serial switch SS) is actuated to interrupt the power supply to the plasma processing chamber (plasma chamber 2) back to the power supply circuit (see page 7, lines 10 to 12; page 9, lines 4 to 6 and page 21, lines 7 to 11),

(1g) which is configured to reuse the energy fed back by the recovery energy circuit (discharging circuit 7.2) for the power supplied to the plasma processing chamber (see page 21, lines 9 to 11, "energy is actually 'recycled'").

This was not disputed by the parties.

The Board shares the opinion of the opponent that a DC power supply, like the one disclosed in D5, implicitly comprises capacitors and that thereby the power supply unit 5 of D5 implicitly discloses (at least one) capacitor.

However, the Board concurs with the proprietor that the power supply unit 5 of D5 does not directly and unambiguously disclose a particular capacitor connected to the output terminals of the power supply unit 5 for storing energy fed back when the switch SS is opened, as defined in the first part of feature (1h). Hence, the lines and terminals connecting such a particular capacitor as defined in features (1i) and (1j ii) are not directly and unambiguously disclosed in D5, either.

Consequently, contrary to the submissions of the opponent, D5 does not disclose all of features (1h), (1i) and (1j ii). However, D5 discloses the following features:

(1h part b) wherein, in use, closing the first switch SS has the effect that the power of the power supply circuit (power supply unit 5) is supplied again to the plasma processing chamber (plasma chamber 2) (in view of the arrangement of serial switch SS in all figures 1 to 6, it is a requirement that it be closed before power can be supplied again to the plasma chamber 2),

(1j i) the recovery energy circuit (discharging circuit 7.2) being connected by a first line to the negative output terminal (output 4.2) (via diode D2), by a second line to the positive output terminal (output 4.1) (via the line connecting the positive output terminal of the power supply unit 5 to the output 4.1).

5.3 Distinguishing features

The subject-matter of claim 1 of the main request thus differs from the embodiment of figure 6 of D5 in that

(1h part a) the power supply circuit comprises a capacitor for storing at least partially the energy fed back,

(1i) the capacitor being connected to a first input terminal of the power supply circuit and a second input terminal of the power supply circuit, and

(1j ii) the recovery circuit being connected by a third line to the first input terminal and by a fourth line to the second input terminal.

The Board notes that neither the position of the capacitor within the power supply circuit nor the role of the capacitor with respect to the normal operation of the power supply circuit are defined in the claims (see the section on Article 84 EPC above).

The capacitor defined in the distinguishing features could thus be any capacitor that is either already present in the power supply circuit or is an additional capacitor provided only for the purpose of storing the energy fed back (see also point 18.11 of the contested decision).

5.4 Obviousness (see sections XII. (e) and XIII. (e) above)

As discussed above, the capacitor in which the energy fed back is stored could be any capacitor at any position within the power supply circuit, as acknowledged by the proprietor during the discussion relating to Article 84 EPC. This capacitor as claimed is thus not necessarily directly involved in providing power to the output terminals during normal operation of the power supply circuit.

Thereby, the Board does not believe that storing the energy fed back in a capacitor within the power supply circuit as claimed achieves, in itself, the technical effect that the energy fed back is immediately discharged to the plasma chamber when switch 25 is closed, contrary to the submission of the proprietor.

To achieve that technical effect alleged by the proprietor, at least the role of the capacitor in providing power to the output terminals during the normal operation of the power supply would have to be defined in claim 1, e. g. by claiming that the capacitor for storing the energy fed back is the main reservoir capacitor of the power supply circuit as shown in figure 1 of the contested patent.

However, nothing of the sort is defined in claim 1 which is formulated in very general terms with respect to the capacitor mentioned.

In line with the submissions of both the opponent and the proprietor, D5 discloses the general idea that the excess energy stored in the leads is fed "into the power supply unit 5 such that energy is actually 'recycled'" (page 21, lines 9 to 11), whereby it has to be stored within the power supply unit 5, but fails to mention any details relating to how this was done. Only an arrow from the discharging circuit 7.2 to the power supply unit 5 is shown in figure 6.

This is reflected by the distinguishing features (1h part a), (1i) and (1j ii). Consequently, the technical effect of these features is to define one particular way of storing the energy fed back by the recovery circuit to the power supply circuit.

Thereby, the skilled person starting from D5 would be faced with the objective technical problem of implementing the general idea disclosed in D5, or - figuratively speaking - implementing the "arrow" from the discharging circuit 7.2 to the power supply unit 5 according to the proprietor's submission. That is, they would have had to find a way to transmit the energy to and store it in the power supply unit 5.

Contrary to the proprietor's submission, the skilled person would not have considered an energy storage outside of the power supply unit 5 or a direct connection to the output terminals thereof, since D5 gives the instruction to feed the excessive energy into the power supply unit 5.

The skilled person might also have thought of using an inductor in the power supply unit 5 to store the energy fed back, as submitted by the proprietor. However, as submitted by the opponent, using a capacitor is one of the- if not the- most obvious way of storing DC energy. The skilled person, using their common general knowledge, would thus have chosen a capacitor in the power supply unit for that purpose as a matter of routine practice depending on the circumstances without the exercise of inventive skills (see also the contested decision, point 18.11 of the Reasons) and without hindsight, contrary to the submission of the proprietor.

The Board notes that the capacitor chosen in that manner by the skilled person would not necessarily be a reservoir capacitor of the power supply unit 5. This is, however, not required by claim 1 of the main request. Instead - in accordance with the proprietor's submissions - the capacitor mentioned therein can be any capacitor in the power supply circuit (see the submissions with respect to Article 84 EPC).

Once having chosen a capacitor for storing the energy fed back, the skilled person would have inevitably used two lines to connect it to the discharging circuit 7.2. Each of these lines would have had a connection point at the housing of the power supply unit 5. These connection points can be considered to correspond to the first and second input terminals of feature (1i), while the lines connecting the connection points to the chosen capacitor can be considered to correspond to the third and fourth lines of feature (1j ii).

Thereby, starting from the embodiment represented by figure 6 of D5, the skilled person would have arrived at the subject-matter of claim 1 of the main request using their common general knowledge without the involvement of an inventive step under Article 56 EPC.

This finding of the Board corresponds to the conclusion of the Opposition Division set out in points 18.11 and 18.13 of the Reasons in the contested decision.

6. Auxiliary request 1 (see sections XII. (f) and XIII. (f) above)

As set out above with respect to feature (1j i), the discharging circuit 7.2 of figure 6 of D5 is connected by diode D2 to the negative output terminal 4.2. The Board notes that irrespective of whether diode D2 is connected with its anode or its cathode to switch SS, energy fed back to capacitor C would have to pass diode D2, contrary to the submission of the proprietor that diode D2 was not used for feeding back energy.

Thus, D5 also discloses feature (1j i').

The Board accepts that page 6, lines 13 to 15 of D5 mentions that the power supply must be interrupted, as submitted by the proprietor. However, as noted by the opponent, in the general description of the operation of the power supply device on page 13, lines 8 to 27, this requirement is not mentioned and on page 19, lines 12 to 14 relating to figure 5, interrupting the power supply is presented as optional. The interruption of the power supply is thus not presented as mandatory throughout D5 in a consistent manner.

Irrespective thereof, interrupting the power supply circuit is not excluded by the wording of claim 1 of auxiliary request 1. Thereby, even if such an interruption were required in the embodiments of D5, it would be of no consequence for the establishment of the distinguishing features of claim 1 of auxiliary request 1 vis-à-vis D5. The same holds for switch DS which has to be closed according to D5 in order to discharge capacitor C, as noted by the proprietor. The presence of such a switch is not excluded by the wording of claim 1 of auxiliary request 1.

In view of the above, the subject-matter of claim 1 of auxiliary request 1 differs from D5 by features (1h part a), (1i) and (1j ii').

With respect to claim 1 of the main request, claim 1 of auxiliary request 1 thereby differs from D5 additionally in that the connection of the recovery energy circuit to the first input terminal by the third line comprises a diode.

The Board notes that the technical effect of immediate feedback of the excess power to the power supply without having to shut down the power supply alleged by the proprietor might be achieved by the complete circuit shown for example in figure 1. It is, however, not achieved by the distinguishing features of claim 1 as set out above, which only concern the type of element in which the energy is stored in the power supply circuit and connections therefore in a very general manner.

Instead, the technical effect of the additional distinguishing feature is that the current can flow only in one direction to the capacitor, as submitted by the opponent. The Board further agrees with the opponent that in the context of using a transformer to charge a capacitor, a conversion from alternating current to directed current is required. D17 (figure 6.46, upper left corner) and D18 (page 535) cited by the opponent show examples of such conversions using diodes and the Board is not aware of any practical implementation of such a conversion without using at least one diode.

Thus, the Board holds that once the skilled person starting from D5 had chosen a capacitor in the power supply unit 5 to store the energy to be recycled, the use of at least one diode in the line between the secondary winding of the transformer shown in figure 6 of D5 and the capacitor was mandatory and therefore a "one-way street" situation, contrary to the finding of the Opposition Division in points 21.11 and 21.12 of the Reasons of the contested decision.

Thereby, the Board considers that the presence of at least one diode between the secondary winding of the transformer and the capacitor is a direct consequence of the choice of a capacitor as energy storage device. The skilled person would then place this (at least one) diode in the third or the fourth line or between the first or the second terminal and the capacitor as a matter of routine practice depending on the circumstances, without the exercise of inventive skills.

Thus, the skilled person would have arrived at the subject-matter of claim 1 of auxiliary request 1 without the involvement of an inventive step under Article 56 EPC starting from the embodiment represented in figure 6 of D5 and using their common general knowledge by choosing a capacitor as energy storage device.

7. Auxiliary request 2 (see sections XII. (g) and XIII. (g) above)

The symbol shown in the discharging circuit 7.2 of figure 6 of D5 is a transformer symbol showing a primary and a secondary winding. On the other hand, the description of D5 refers to a "converter" (page 21, lines 7 to 9). According to the proprietor this rendered the disclosure of D5 inconsistent.

However, as submitted by the opponent, a standard way of implementing a DC-DC converter is by means of using a switching circuit, a transformer, and a rectifier. That is, a converter may well comprise a transformer. The Board thus does not see any contradiction between the transformer symbol in figure 6 and the corresponding part of the description of D5 mentioning a converter.

Thereby, D5 also discloses that the discharging circuit comprises a transformer and thereby feature (1j 0).

The argument of the proprietor that D5 did not disclose any diode connected to the transformer and that instead switches were provided whose timing had to be controlled is not fully accepted by the Board.

The Board shares the opinion of the proprietor to the extent that figure 6 of D5 does not show explicitly any diode connected to the secondary winding of the transformer, i. e. between the discharging circuit 7.2 and the power supply unit. D5 thus does not disclose (1j ii'').

However, no switch is disclosed between discharging circuit 7.2 and the power supply unit 5. Moreover, switch DS present in the discharging circuit 7.2 is not provided instead of a diode, but in addition to diode D2 and has a different purpose than diode D2.

Further, as submitted by the oppo­nent, the claim does not require a direct connection and the line connecting the negative output terminal 4.2 to the discharging circuit 7.2 via diode D2 must inevitably, at least in an indirect manner, be connected to the primary, i. e. input, winding of the transformer via switch DS. In the same manner, the line connecting the positive output terminal 4.1 to the discharging circuit 7.2 must inevitably be connected to the primary winding of the transformer as well.

Therefore, D5 also discloses feature (1j i'').

Claim 1 of auxiliary request 2 thereby differs from figure 6 of D5 by feature (1h part a), (1i) and (1j ii'').

Emphasizing what is set out above in relation to auxiliary request 1, the technical effect of immediate automatic feed back of the energy stored in the cables in the case of an arc to the power supply without having to shut the power supply down alleged by the proprietor might be achieved by the complete circuit shown for example in figure 1. It is, however, not achieved by the distinguishing features of claim 1 of auxiliary request 2 vis-à-vis D5 as defined above, which only concern the type of element in which the energy is stored in the power supply circuit and connections therefore in a very general manner.

Instead, the distinguishing features defined above correspond, with the exception of explicitly mentioning the secondary winding of the transformer, to the features distinguishing claim 1 of auxiliary request 1 from D5.

The secondary winding of the transformer was however already considered when discussing lack of inventive step with respect to auxiliary request 1 above.

Thus, the subject-matter of claim 1 of auxiliary request 2 is not inventive under Article 56 EPC in view of D5 combined with the common general knowledge for the same reasons as those set out above for claim 1 of auxiliary request 1.

8. Auxiliary request 3

Claim 1 of auxiliary request 3 is identical to claim 1 of auxiliary request 2. Auxiliary request 3 thus does not fulfill the requirements of Article 56 EPC for the same reasons as set out above for auxiliary request 2.

It is therefore not necessary to discuss inventiveness of independent claim 2 of auxiliary request 3.

9. Revised versions of the main request and auxiliary requests 1 to 3

The conditionally filed revised versions of the main request and auxiliary requests 1 to 3 did not have to be considered since the condition (negative finding of the Board concerning sufficiency of disclosure of claim 12 of the main request) was not fulfilled.

In any case, since the independent claims of the revised versions of these requests are unchanged the same objections as for the main request and auxiliary requests 1 to 3 apply to them, as well.

10. Auxiliary request 4 (see sections XI. (h) and XII. (h) above)

According to Article 13(2) RPBA 2020, any amendments to a party's appeal made after notification of a summons to oral proceedings shall, in principle, not be taken into account unless there are exceptional circumstances, which have been justified with cogent reasons by the party concerned.

In the present case, both the proprietor and the opponent appealed the contested decision. The principle of "reformatio in peius" thus does not apply. The proprietor must have been aware thereof and thus of the possibility that the Board may revoke the patent in its entirety at the time of filing their grounds of appeal, since the opponent's notice of appeal had been filed two months earlier. Furthermore, the grounds of appeal of the opponent comprise arguments against auxiliary request 2, according to which the Opposition Division maintained the patent and which essentially corresponds to present auxiliary request 2. Claim 1 of auxiliary request 3 is identical to claim 1 of auxiliary request 2.

The proprietor must therefore have been aware of the possibility that the Board could come to a different conclusion than the Opposition Division with respect to present auxiliary requests 2 and 3. Consequently, they should have considered their strategy against the appeal of the opponent, including the possible filing of corresponding auxiliary requests with their reply to the grounds of appeal of the opponent.

For these reasons, the Board cannot consider the proprietor's "surprise" with respect to the adverse conclusion of the Board vis-à-vis claim 1 of both auxiliary requests 2 and 3 as an exceptional circumstance within the meaning of Article 13(2) RPBA 2020 justifying the filing of a new request at such an extremely late stage of the proceedings.

The representative of the proprietor expressed the view that the conclusion of the Board with respect to auxiliary requests 2 and 3 was surprising and shocking for a physicist. However, the conclusion was reached after an exchange of arguments between the parties. In the end the Board found the arguments of the opponent to be more convincing. The proprietor may strongly disagree with the Board, but that is not an exceptional circumstance either.

The technical problems at the beginning of the oral proceedings referred to by the proprietor essentially concerned the provision of the English interpretation channel and were solved immediately after they had been notified to the Board and before continuing the oral proceedings. No further technical problems occurred in the course of the rest of the oral proceedings. The proprietor has furthermore not explained how the alleged technical shortcomings could be causal for the need to file auxiliary request 4 only at the end of the oral proceedings rather than at an earlier stage of the appeal proceedings. The Board also notes that the proprietor only mentioned the alleged technical shortcomings after all the auxiliary requests on file had been discussed. Neither before the oral proceedings (which were also requested by the proprietor) nor during the discussions, the proprietor expressed concerns with using video-conference technology for conducting oral proceedings, including the use of a headset in order to facilitate the work of the interpreters.

Therefore, the Board does not consider these technical problems as exceptional circumstances within the meaning of Article 13(2) RPBA 2020, either.

Consequently, the Board decided that auxiliary request 4 was not to be taken into account under Article 13(2) RPBA 2020.

11. Summary / Conclusion

The subject-matter of claim 1 of the main request does not fulfill the requirements of Article 56 EPC. The same holds for claim 1 of auxiliary requests 1 to 3. Thereby, none of these requests is allowable. It is therefore not necessary to further elaborate on the other issues discussed for these requests during the written procedure and the oral proceedings. Furthermore, it was not necessary to consider the conditionally filed revised versions of the main request and auxiliary requests 1 to 3. Auxiliary request 4 is not taken into account pursuant to Article 13(2) RPBA 2020.

Due to the absence of any allowable request on file, the patent has to be revoked under Articles 101(3)(b) and 111(1) EPC.