T 0582/04 (Dielectric film/ALLIEDSIGNAL) 15-12-2005

Reasons for the Decision

1. The appeal is admissible.

2. Admissibility of the first to fourth auxiliary requests submitted during the oral proceedings

2.1 The appellant submitted at the start of the oral proceedings new first to fourth auxiliary requests. Claim 1 of all these requests was directed to a method of making a dielectric film on a substrate and comprised features that were not present in any of the original claims and were taken from the description. It was therefore uncertain if these features had been considered when drawing up the search report. To examine the amended claims, it would have been necessary to remit the case to the department of first instance.

2.2 Article 10b(3) RPBA states, however, that "Amendments sought to be made after oral proceedings have been arranged shall not be admitted if they raise issues which the Board or the other party or parties cannot reasonably be expected to deal with without adjournment of the oral proceedings".

2.3 The board decided therefore not to admit these requests into the proceedings.

3. A new request comprising a single claim was then submitted by the appellant, replacing his previous requests.

4. Amendments

4.1 This claim is based on a combination of original claims 15, 19 and 20. Moreover, the two baking steps at successively higher temperatures were disclosed inter alia in original method claims 2 and 3, while films with a dielectric constant of less than 3 were disclosed inter alia on page 4, lines 4 to 5.

The description has been adapted to the claim.

For these reasons, the board is satisfied that the requirement of Article 123(2) EPC is met.

4.2 The dielectric film specified in the claim is defined partly by product parameters including thickness variation and dielectric constant and partly by the steps of the method by which it is obtainable. According to the jurisprudence of the EPO Boards of Appeal this claim form is justified if the product itself is novel and if there is no other information available in the application to define the product by reference to its composition, structure or other testable parameters (cf T 150/82, OJ 1984, 309).

In the present case the dielectric film consists of a polymer having the general formula given in the claim. It is, however, difficult to characterize polymers, as these materials possess a wide range in molecular weight and chain lengths and vary considerable from each other depending on their specific fabrication method. In the view of the board, therefore, the most suitable way of characterizing the polymer forming the dielectric film is by the method by which it is obtainable, as done in the claim.

5. Novelty (Article 54 EPC)

5.1 Document D1, the closest state of the art, discloses dielectric films formed from a solution containing an organohydridosiloxane resin which corresponds to the formula of the claim. To obtain the dielectric film, the solution is spin-coated on a substrate and cured by a heat treatment at 380 to 450ºC. Films having dielectric constants of less than 3 and a thickness of about 400 nm were obtained (cf page 3, line 17 to page 4, line 9; page 28, lines 8 to 19; page 29, Table 1). The thickness variation of the films is however not disclosed in D1.

5.2 The dielectric films according to the claim differ therefore from the ones disclosed in document D1 in that they have a thickness variation over a single substrate of less than 1% and that the method by which these films are obtainable comprises baking the resin coated substrates at least two times at successively higher temperatures.

5.3 It has been argued by the appellant that a thickness variation of less than 1% was previously not attainable. Document D5, a copy of a web page from a research group of the University of Köln submitted by the appellant during the oral proceedings, discloses that the chemical mechanical polishing method (CMP) was introduced in the 80's by IBM. This method enabled perfectly planar surfaces to be achieved, a key feature in the fabrication of VLSI integrated circuits. The document further discloses that with CMP a planarity of about ± 20 nm was attainable (cf bottom of page 3 and page 7, last paragraph).

5.4 The present application discloses however dielectric films with a thickness between about 300 and 700 nm and having a thickness variation of less than 1% (cf eg Table 7). This implies a thickness variation in the range of 3 to 7 nm, a value well below the one disclosed in D5.

5.5 The board is therefore satisfied that, absent evidence to the contrary, document D1 does not even implicitly disclose a thickness variation of less than 1%.

5.6 Documents D2 and D4, on the other hand, disclose neither dielectric films obtained from an organohydridosiloxane resin nor the thickness variation of these films.

5.7 It follows from the above that the dielectric film of the claim is new.

6. Inventive step (Article 56 EPC)

6.1 The board agrees with the appellant that, having regard to the differences indicated in point 5.2 above, the objective technical problem addressed by the invention is to provide low dielectric constant films having a high degree of planarity.

6.2 Document D4 discloses spin-coating a solution of siloxane in alcohol on a substrate, baking the substrate at three successively higher temperatures (100ºC, 160ºC and 250ºC) and then curing it in an inert atmosphere at about 420ºC. The cured dielectric film had typically a thickness of about 300 nm. Although neither the thickness variation nor the planarity of these films is explicitly disclosed, it is stated that the upper surface of the films is essentially planar. However, although the overall thickness of the layer is uniform across the semiconductor wafer, it tended to be slightly thinner towards the edge. After the film had been cured, the wafer was mounted in an RIE tool for a planarization etchback (cf column 3, line 62 to column 4, line 11; column 4, lines 19 to 23; column 4, lines 24 to 25).

6.3 A 1% thickness variation for the typically 300 nm thick films disclosed in document D4 would be about ±3 nm. This value is well below the ±20 nm disclosed in D5 for the CMP method disclosed therein which enabled 'perfectly planar' surfaces to be obtained. Moreover, the mention in document D4 that the films were merely 'essentially planar' and that they were slightly thinner towards the edge suggests strongly that such an extreme degree of planarity was not achieved and even not required, since the films thus obtained were etched back by RIE. For this application the planarity required had to be sufficient to allow the RIE process to start, but not necessarily a planarity of about ±3 nm.

6.4 The board concludes therefore that document D4 does not disclose a way of obtaining dielectric films having a thickness variation of less than 1%. The person skilled in the art would not have considered its disclosure as relevant for solving the problem posed at point 6.1 above.

6.5 Consequently, the board judges that the dielectric film according to the claim involves an inventive step within the meaning of Article 56 EPC.