T 1034/01 29-01-2004

Reasons for the Decision

1. The appeal is admissible.

2. Late filed documents and abuse of procedure

2.1. Document E7 was filed by the appellant one week before the oral proceedings before the Opposition Division. The respondent objected to the introduction of document E7 into the proceedings at such a late stage, since this document was already mentioned in the European Search Report and there were no apparent reasons which could have hindered the appellant to file the document in time. Such a behaviour amounts to an abuse of the procedure.

2.2. In this connection, although the Board concurs with the respondent that the parties should submit all the facts, evidence and arguments relevant to their case as early and completely as possible (cf. T 951/91, OJ 1995, 202), particularly when such an evidence was already known to the party concerned, in the present case it can hardly be assumed that the introduction of document E7 took the respondent by surprise, since he had been made aware of the existence of this state of the art document by the European Search Report. Moreover, there is no evidence that the late filing of document E7 was deliberately done for tactical reasons amounting to an abuse of procedure (cf. T 1019/92).

2.3. The circumstances in the present appeal proceedings are quite different from the proceedings before the Opposition Division where little time was left to consider document E7 in detail. Nevertheless, the Opposition Division discussed the validity of the priority date of the patent, found it to be valid and concluded therefrom that document E7, being part of the state of the art under Article 54(3) EPC, was not relevant for assessing the novelty of the subject-matter claimed in the contested patent, since it did not unequivocally disclose a planar coil.

The filing of document E7 was done on 6 March 2001, ie nearly three years before the oral proceedings before the Board. The parties and the Board had, therefore, sufficient time to assess its relevance.

2.4. Document E8 was submitted with the statement of grounds of appeal. Its disclosure merely reinforces the line of attack to the patent made before the Opposition Division, namely that the use of silicon as a scavenger for fluorine was known in the state of the art. Its filing, therefore, has to be considered as the normal behaviour of a losing party and cannot be regarded as an abuse of procedure (cf. T 113/96).

2.5. The Board considers, moreover that the disclosures of documents E7 and E8 are prima facie highly relevant for assessing the novelty and inventive step of the subject-matter of the claims.

2.6. For the above mentioned reasons, the Board allows the introduction of documents E7 and E8 into the proceedings.

3. Remittal to the department of first instance

3.1. The respondent requested that the case be remitted to the department of first instance in the event that document E7 is allowed, since this would define a factual framework different from the one which has been considered by the first instance for reaching its decision.

3.2. As already mentioned, the Opposition Division considered the disclosure of document E7 and found it to be of no relevance for the subject-matter according to the claims of the contested patent. It also decided that the priority right of the patent in suit was valid and that document E7 belonged to the state of the art under Article 54(3) EPC. There is thus no justification for remittal for reconsideration of the same issue, ie. the relevance of document E7. Moreover, contrary to the respondent's argument the factual framework of the case remains unchanged, since the Opposition Division correctly assessed first the disclosure of document E7 before deciding not to allow it under Article 114(2) EPC

3.3. For these reasons, the Board decides not to remit the case to the department of first instance.

4. Priority

Claim 1 as amended during the oral proceedings before the Board comprises all the features of claim 1 of the priority document (US Serial No. 07/984 045) and, therefore, overcomes all the objections raised by the appellant in respect of the claimed priority.

For this reason, the priority date of 1 December 1992 can be allowed for the contested patent.

5. Relevance of Document E7

5.1. As correctly pointed out by the respondent, document E7 claims two priority dates of US patent applications US1 and US2 which are both continuations-in-part of previous US patent application US3. The filing date of application US3 is, however, more than twelve months before the filing date of the European patent application E7. The respondent submitted, therefore, that document E7 was not entitled to the claimed priority dates, since documents US1 and US2 were not the 'first application' for the same invention as required by Article 87(1) EPC.

5.2. The question whether document E7 has a priority date earlier than the priority date of the contested patent and, consequently, whether the document belongs to the state of the art according to Article 54(3) EPC, does not need to be considered here, as the Board comes to the same conclusion as the Opposition Division that document E7 does not disclose unambiguously an apparatus for etching oxides comprising an electrically conductive planar coil, as will be shown below.

Document E7 discloses in the embodiments illustrated in Figures 1 and 2 an apparatus for etching oxides comprising a RF antenna 30 in the form of a multiple turn, cylindrical coil. Preferably, the coil surrounds a dome of the chamber for inductively coupling the high frequency electromagnetic energy into the chamber to form the plasma (cf. page 5, lines 33 and 43 to 44). It is further stated that the antenna may be formed by at least one turn or coil (cf. page 8, line 10). The appellant relied on this statement to establish that document E7 discloses a planar coil as specified in claim 1 of the patent in suit.

The Board, however, cannot follow the appellant's argument, since it is the established case law of the Boards of Appeal that for an invention to lack novelty its subject-matter has to be clearly and directly derivable from the prior art (cf. T 465/92, OJ 1996, 32; T 511/92).

Although document E7 discloses that a one turn coil can be used as antenna, it is not directly derivable that this coil necessarily lies in a plane. On the contrary, in the present case, it would be reasonable to form the one turn coil in the shape of a one turn helix, since, as pointed out by the respondent, with this shape the coupling of RF energy into a large volume can be accomplished. It is the consistent teaching of document E7 that the plasma is formed in the source region 16A, ie a volume overlying the processing region 16B in which the substrate to be treated is located (cf. Figures 1 and 2; page 8, lines 38 to 44; page 16, lines 31 to 32; page 23, lines 27 to 30). Creation of a plasma in a volume is, however, difficult if a one turn planar coil is used as antenna.

5.3. For the above mentioned reasons, the Board concludes that document E7 does not disclose an apparatus according to claim 1 of the patent in suit. It is, therefore, not necessary to determine the validity of the claimed priority date of document E7.

6. Inventive step

6.1. It is common ground that document E1 represents the closest state of the art. This document discloses an apparatus for producing a magnetically-coupled planar plasma having all the features specified in the preamble of claim 1 of the contested patent (cf. column 3, lines 19 to 43; column 5, lines 33 to 53; column 6, lines 11 to 13; Figures 1 and 2).

6.2. The apparatus according to claim 1 differs, therefore, from the disclosure of document E1 in that a fluorine scavenger is provided in or near the plasma and that the scavenger is:

(i) an article of silicon mounted between the dielectric window and the substrate support, generally parallel thereto,

(ii) a silicon-containing gas,

(iii) an article of graphite, or

(iv) a carbon-rich gas.

6.3. According to the patent in suit, the provision of a fluorine scavenger improves the selectivity of etching oxide films or layers and gives improved anisotropy and etch rate (cf. page 2, lines 47 to 48 and lines 52 to 54).

When the fluorohydrocarbon gas present within the apparatus chamber is exposed to the plasma, various fragments are generated, including e.g. F, CF and CF2 radicals. The free fluorine etches oxides, but other species form C-F polymers that can deposit onto the sidewalls of the etched via and also act to protect underlying and overlying layers from being etched. However, this polymer is attacked by oxygen and also by free fluorine radicals, reducing thus the etch selectivity between the oxide and the other layers. The provision of a fluorine scavenger, however, reduces the amount of free fluorine radicals, thus reducing the attack of the substrate by free fluorine (cf. page 3, lines 46 to 54 of the contested patent).

The objective problem addressed by the invention having regard to document E1 corresponds, therefore, to the one originally stated in the contested patent.

6.4. Document E8 discloses, however, a plasma-etch apparatus wherein the mounting base (17) for a substrate is a piece of single crystal silicon. The base consumes the free fluorine radicals present in the plasma which come close to the periphery of the mounting base by reaction with the silicon to form SiF4 (cf. page 4, 3rd paragraph). It is further disclosed in document E8 that other materials may be used instead of silicon as long as they consume the free radicals in the plasma. As examples of these materials SiC is inter alia mentioned (cf. page 7, end of the 3rd paragraph and claims 1 and 6).

6.5. Document E3, on the other hand, discloses the use in a plasma-etch apparatus of a heating plate 12 made of SiC which reacts with the free fluorine radicals of the reaction gas producing the stable gases CF4 and SiF4 which are discharged by the pumping system (cf. page 8, 2nd paragraph). The heating plate is placed above and facing the substrate support 6 (cf. Figure 1 and page 5, 3rd paragraph). The removal of the fluorine radicals from the reaction gas not only reduces the adhesion of the products of the plasma-etch process to the walls of the apparatus, but also greatly improves the etching selectivity between Si and SiO2 (cf. last three lines on page 3; page 4, 2nd paragraph; page 6, 2nd paragraph).

6.6. From the teachings of documents E3 and E8 the skilled person learns that a fluorine scavenger can be made of different materials as long as they consume the fluorine radicals. The possible materials comprise inter alia Si and SiC, although a source of carbon would also react with the fluorine radicals producing CF4. Moreover, the location of the scavenger can be below the substrate to be treated, as done in document E8, or above the substrate, as in document E3. It is, therefore, obvious for a skilled person to locate a fluorine scavenger made of silicon above the substrate to be treated, since by locating the scavenger above the substrate the scavenger's surface exposed to the plasma increases and the scavenging of free fluorine radicals is improved with respect to the apparatus disclosed in document E8 in which a portion of the scavenger is covered by the substrate and the scavenging action only takes place at the substrate's periphery.

Accordingly option (i) of claim 1, ie the use of an article of silicon as fluorine scavenger mounted between the window and the substrate, does not involve an inventive step having regard to the combined teaching of documents E1, E3 and E8. A finding of lack of inventive step with respect to one alternative of the invention as claimed, however, renders the whole claim including different alternatives not allowable. For this reason, it is not necessary to discuss the presence of an inventive step of the other options provided in claim 1.

The patent, moreover, does not disclose any technical effect that is achieved by locating the scavenger above the substrate when it is formed by an article of silicon that is not achieved by a scavenger formed by an article of graphite. Such a limitation in the claim renders the claimed subject-matter new with respect to the state of the art, but is hardly suitable to render it inventive.

6.7. The Board, moreover, does not concur with the respondent's argument that the teachings of documents E1, E3 and E8 cannot be combined with one another, since they are directed to different kinds of plasma-etch apparatus. Although it is true that these apparatus differ e.g. in the gas distribution system and the pressure ranges used, the skilled person learns from documents E3 and E8 that the presence of free fluorine radicals is the main cause for a poor etch selectivity of the oxide layers and that the free fluorine radicals have to be removed from the reaction gas. For the skilled person it is, in consequence, obvious to apply these teachings also to the plasma-etch apparatus disclosed in document E1.

6.8. For these reasons, in the Board's judgement, the apparatus according to claim 1 does not involve an inventive step in the sense of Article 56 EPC.