T 0114/99 05-05-2003

Reasons for the Decision

1. The appeal meets the requirements of Articles 106 to 108 and Rule 64 EPC and is therefore admissible.

Furthermore, for the reasons given below, the appeal is allowable, since the application documents according to the main request meet the requirements of the EPC.

2. Amendments and clarity - main request:

Claim 1 is based on claim 1 as filed together with the features disclosed in conjunction with Figures 1 to 3 of the application as filed. Regarding the lower limit of 380°C for the second temperature, it is disclosed on page 8, second paragraph of the application as filed that temperatures "a little below 400 °C can be used", and the value 380°C is disclosed in claim 6 as filed. The expression (0.7 x T) - 250 Å/s for the upper limit of the deposition rate is disclosed in Figure 3 and claim 16 as filed.

Independent claim 9 is based on claims 15 and 16 as filed together with the feature disclose on page 6, last paragraph of the application as filed.

Dependent claims 2 to 8 and 10 to 12, and 17 are based on claims 6 to 12, 17, 19, 4, 10 as filed, respectively. Claims 13, 14 and 15, 16 are based on the disclosure on page 9, second paragraph and page 6, last paragraph of the application as filed, respectively. Claims 18 and 19 are based on the embodiments of Figure 4(b) and (c).

Therefore, in the Board's judgement, the requirements of Article 123(2) EPC are met by the claims according to the main request. The Board is furthermore satisfied that the claims according to the main request meet the requirements of Article 84 EPC. In particular, the Board accepts the appellant's submissions that in the present case, it is justified to maintain the two independent claims 1 and 9 of the same category under Rule 29(2)(c) EPC.

3. Inventive step - main request:

3.1. Document D1 was considered the closest prior art in the decision under appeal. It discloses a method of filling via holes for ULSI with aluminum using sputtering. A refractory metal barrier layer is first deposited in the via hole in order to better control the aluminum deposition (cf. page 76, right hand column, last paragraph to page 77, left hand column, second paragraph; Figure 6(b)). The initial deposition of aluminum is carried out at a low temperature of the substrate to form a thin nucleating layer. After the nucleating layer is formed, the substrate is heated up during deposition to a temperature of about 450°C, and the remainder of the aluminum layer is formed at the higher temperature.

3.2. Document D2 is concerned with the deposition of aluminum using evaporation on substrate surface having a single step (cf. abstract). In order to obtain a good step coverage even when part of the step is shadowed from the evaporation source, it is taught in document D2 that the deposition rate should be reduced at the initial stage in order to form a stable nucleating layer on the step (cf. page 9, line 18 to page 10, line 5). After that the nucleating layer has been formed, it is not necessary to keep the deposition rate low and the final deposition rate is at least twice the initial deposition rate (cf. page 10, lines 11 to 13). The initial deposition rate is about 0.4 to 0.6 nm/s (cf. claim 3), and the higher deposition rate is about 1.5. nm/s (cf. page 10, lines 33 to 36; Figure 6). Both the deposition steps are carried out at a temperature between room temperature and 400°C, preferably about 300°C (cf. page 9, lines 18 to 20).

3.2.1. Thus, the Board agrees with the appellant's assessment of document D2 that the deposition rate of aluminum is reduced only at the first stage of the deposition process. In the decision under appeal, on the other hand, it was inferred from document D2 that the deposition rate had to be controlled at any given temperature (cf. items V(d) and VI(c) above).

3.3. From the above discussion it follows that document D1 represents the closest prior art, since it relates to deposition of aluminum in a via hole. The method of claim 1 according to the main request differs from that of document D1 in that (i) numerical temperature ranges are specified for the initial and final deposition temperatures; and (ii) the final deposition rate is less than 0.7*T-250 Å/s, where T is the deposition temperature, whereas document D1 does not mention any specific deposition rate.

3.4. As discussed in the decision under appeal, the method of document D1 has the disadvantage that it is increasingly difficult to fill via holes reliably as the aspect ratio (the ratio of depth over width of the via hole) is increased, since sputtering methods, such as the method of document D1, tend to create large aluminum grains on the upper surface of the insulating layer which may block the via before it is completely filled (cf. page 1, last paragraph, and item VI(a) above).

The appellants have discovered that when the final deposition rate is less than the empirical value 0.7*T-250 Å/s depending on the temperature T of the integrated circuit, the above-mentioned aggregation of aluminum at the opening of a via hole is avoided, and the via hole can be filled without voids. Thus, the claimed method, which specifies the limit of 0.7*T-250 Å/s for the final deposition rate, provides a method of filling via holes reliably without forsaking speed.

The technical problem addressed by the application in suit therefore relates to finding a method of reliably filling via holes completely with aluminum also for via holes having a large aspect ratio (cf. the application as filed, page 2, first paragraph; page 3, last paragraph to page 4, third paragraph).

3.4.1. In the decision under appeal, the problem addressed by the application in suit was considered to relate to improving electromigration resistance and improving via hole filling (cf. item V(c) above). As discussed in the application as filed, poor electromigration resistance is caused by uneven thickness of the aluminum layer in the via holes (cf. application as filed, page 2, second paragraph). Therefore, the problem as formulated above is consistent with that stated in the decision under appeal.

3.5. Contrary to the findings in the decision under appeal regarding the disclosure of document D2, however, the Board agrees with the appellant that document D2 teaches that it is not necessary to reduce the deposition rate once the formation of the nucleating layer is completed. Therefore, a skilled person seeking to improve the method of document D1 would not be led towards the claimed invention by the teaching of document D2.

3.6. For the above reasons, in the Board's judgement, the subject matter of claim 1 according to the main request involves an inventive step within the meaning of Article 56 EPC.

3.7. The method of independent claim 9 according to the main request differs from that of document D1 in the same features (i) and (ii) referred to under item 3.3 above. Thus, the subject matter of independent claim 9 involves an inventive step within the meaning of Article 56 EPC for same reasons as for claim 1.

4. Substantial procedural violation and reimbursement of the appeal fee

The appellant has requested reimbursement of the appeal fee for the reason that the examining division committed a substantial procedural violation (Rule 67 EPC). Essentially, the appellant argued that his right to be heard under Article 113(1) EPC was violated for the following reasons:

(i) The representative was only made aware of a new inventive step objection based on documents D1 and D2 during the oral proceedings and was given only 25 min to consider the objection. This short time was clearly inadequate for presenting comments on the complicated mathematical analysis disclosed in document D2.

(ii) Document D2 was cited in the first official communication, but without the complex arguments raised in the oral proceedings. The appellant was furthermore led to believe from the communication accompanying the summons to the oral proceedings that the inventive step objection involving document D2 would be dropped once the claimed methods comprised the step of forming a barrier layer.

(iii) In view of the complexity of document D2, the EPO should have alerted the representative in response to the new claims filed before the oral proceedings that document D2 would be discussed in detail.

4.1. From the appellant's own submissions, it is evident that the new arguments based on document D2, which was already considered in the assessment of inventive step in the written proceedings, were presented by the examining division during the oral proceedings. The appellant contends that the time given to him (25 minutes) to study the complicated mathematical analysis disclosed in document D2 was not adequate to respond to the new arguments. In the minutes of the oral proceedings, however, there is no record of any request from the appellant for more time to study document D2, nor is there any record of rejection of such a request. Under these circumstances, an implicit assumption on the part of the examining division that about half an hour was enough to study a document which already formed part of the written proceedings, was in the Board's view justified.

It therefore appears that the examining division was entitled to conclude that the matter had been sufficiently discussed and that a decision could be taken (cf. T 248/92, reasons, 2, and T 484/89, reasons, 2.1, both cited in "Case Law of the Boards of Appeal of the EPO", 4th Edition, Chapter VI.B.2, page 265).

4.2. Regarding grounds (ii) and (iii) above, the Board notes that the purpose of the communication under Rule 71a(1) EPC is to draw attention to the points which in the examining division's opinion need to be discussed during the oral proceedings. Such a communication can, however, only deal with points which appear relevant having regard to the requests being on file at the time when the summons for oral proceedings are issued. In the present case, the appellant filed new claims giving rise to a further examination which may raise new issues. It is also noted that although the final date under Rule 71a(1) EPC for making written submissions and amendments was 24 February 1998, the appellant nevertheless filed two sets of claims (A and B) on Wednesday 18 March 1998 for the oral proceedings scheduled for Monday 23 March 1998.

Considering the late filing of the new claims by the appellant, further discussion of document D2 during the oral proceedings was completely justified and even necessary.

4.3. The case T 783/89 referred to by the appellant related to the introduction of a new claim containing substantial amendments, whereby the time given to the opponents to study the amendments was not considered to be sufficient by the Board. In the present case, the appellant was himself responsible for the late filing of the new claims and, moreover, document D2 already formed part of the written proceedings so that the appellant could be reasonably expected to be aware of its content and to be prepared that his amended claims would be discussed in the oral proceedings in the light of the overall content of document D2. The circumstances of T 783/89 are therefore not comparable to the present case.

4.4. Therefore, the Board finds that the decision of the examining division has not been in violation of Article 113(1) EPC. Hence, the request for reimbursement of the appeal fee is rejected.