T 0909/95 (Deposition of conductive layer for contacts/MOTOROLA INC) 02-10-1998

1. The appeal is admissible.

2. Added subject-matter (Article 123(2) EPC)

2.1. The present application is directed to a method of making a semiconductor device and more specifically to the deposition of conductive material onto an exposed surface of a semiconductor substrate to form electrical contacts to the substrate. This deposition is effected at elevated temperatures in the chamber (in the original claims named "wafer area") of a furnace.

According to the original description (cf. in particular page 2, lines 2 to 13; page 5, lines 3 to 21 and 29 to 33; and page 6, lines 5-13 and 25-33), the invention as filed is based on the following problem and solution principles :

- when forming the contact from a material such as polysilicon, the average grain size has a significant impact on the electrical characteristics of the deposited material;

- the grain size, in turn, is dependent on the temperature of deposition so that it is desirable to provide a specific temperature with narrow tolerance to all deposition locations within the furnace in order to obtain a consistent grain size, in particular when a plurality of substrates is treated in a single batch;

- it takes, however, a fairly long time (in the order of an hour) to heat the furnace to the required temperature of deposition and to obtain the requisite uniformity of temperature throughout the furnace;

- in the meantime, the exposed surface of the (monocrystalline) semiconductor substrate tends to become significantly oxidised, resulting in contact resistances which are undesirably high and vary widely;

- in order to avoid significant oxidation of the exposed substrate, but at the same time obtain deposited material of consistent grain size, the deposition is effected in two steps:

a first thin layer of the conductive material is deposited when the chamber/furnace is in principle at the requisite temperature level but has not yet reached the ideal uniformity of temperature throughout the chamber (i.e. when the temperature is in "a first temperature range") [the thin layer preventing or slowing down further oxidation], followed by the deposition of a thick layer of conductive material, once the requisite temperature uniformity has been obtained (i.e. when the temperature is in "a second, narrower temperature range").

It is further evident from the description (cf. figure 4; page 4, lines 26 to 33; and page 5, lines 29 to 33) that the uniformity of temperature (i.e. the "temperature ranges") is monitored by making use of temperature gauges distributed along the chamber/ furnace. Even the general summary of the invention as given on page 3, lines 9 to 17, referring to a stabilizing of the temperature, has to be interpreted in the light of the specific embodiment which exclusively concerns a method employing temperature measurement at a plurality of temperature measuring points.

In the most general definition, as given by original claim 1, the invention is defined as requiring the steps of "raising the temperature to all points within the wafer area to a first temperature range, said first temperature range including a first temperature", and "stabilizing the temperature to all points within the wafer area to a second temperature range, ..., said second temperature range including the first temperature" [emphasis added].

2.2. Claim 7 on file includes :

(a) the provision of a single temperature measuring point, by the feature "wherein a temperature measuring point is located near the chamber wall";

(b) the steps of "raising the temperature of the chamber such that the temperature of the temperature measuring point lies within a first temperature range" and "adjusting the temperature .. of the temperature measuring point such that ... [it] lies within a second temperature range"; and

(c) the requirement that the temperature during the first deposition step lies within the first chamber temperature range and outside the second chamber temperature range within which the second deposition step is performed.

2.3. Claim 7, thus, seeks protection for a method where spatial uniformity of temperature is not required and the deposition of material is carried out at temperatures measured at a single measuring point, whereas it is clear from point 2.1 above that the invention as disclosed is concerned exclusively with a method employing spatial uniformity of temperature (within a second temperature range) within the furnace during the second deposition step.

Moreover, since it is impossible to monitor a temperature distribution within a chamber/ furnace by using only a single temperature point at a fixed location, the definition given by claim 7 on file can only mean that the first deposition step is performed when the temperature observed at the temperature measuring point lies within a (predetermined) first temperature range. Thus, the claimed subject-matter would provide protection for any method in which the first deposition step is performed when the single temperature measuring point indicates a temperature which lies in the predetermined first range, regardless of which temperature might occur at that time at other points of the chamber/ furnace.

This is, however, in clear contrast to the original disclosure which requires (cf. for instance original claim 1) that all points of the chamber/ furnace lie within the first temperature range when the first deposition step is performed.

2.4. Although the appellant is in principle right that, for the purpose of having a basis of disclosure, claims need not (necessarily) be limited to specifically described embodiments, this does not apply in the present case, in which in fact none of the originally-filed claims mentions a single temperature measuring point.

In the present case, the only disclosure concerning the provision of a temperature measuring point is given by the description of the specific embodiment. From this description it is evident that a plurality of temperature measuring points is used to monitor the temperature variation or uniformity along the extension of the chamber/ furnace. Since it is impossible to establish or monitor the occurrence of a desired temperature variation or uniformity at various locations within the chamber at any given point of time from a single measuring point, the provision of more than one measuring point is apparently an indispensable feature for performing a method according to the invention as it is disclosed.

2.5. Further added subject-matter is introduced by claim 5 on file, in particular as far as this claim directly refers to claim 1.

The original disclosure (cf. page 5, lines 3 to 13 and 26. to 33) refers to the specific temperature ranges defined in claim 5 on file only in the context of the deposition of polysilicon. Thus, the additional features given in claim 5 have been disclosed only in combination with those given in present claims 2 and 3. In fact, it is not plausible that for any other conductive material the temperature ranges specified in claim 5 on file would be suitable.

2.6. For these reasons, the Board considers that claims 5 and 7 of the request on file introduce added subject-matter so that the application as amended does not comply with the requirements of Article 123(2) EPC.

3. Reimbursement of the appeal fee

3.1. Although the appellant may have reasons not to be fully satisfied by the course of events during the examination procedure, the Board does not consider that any procedural violation took place.

3.2. With regard to the applicant's complaint that, contrary to his request, he was not invited to an interview before a decision had been taken, it is to be noted that the EPC does not foresee an interview (with a member of the examining division) and that a request for an interview is clearly not a request for formal oral proceedings provided by Article 116 EPC (cf. decisions T 19/87 [OJ EPO 1988, 268] or T 98/88 ["Case law of the Boards of Appeal of the European Patent Office", 1996, page 194]).

There is no obligation upon an examiner or examining division to grant a request for an interview, in particular when, as set out in the "Guidelines for Examination in the European Patent Office" part C-VI, 6.1a, the examiner believes that no useful purpose would be served by such an interview.

In the present case, it is evident from the reasons in paragraph 4.3 of the decision under appeal that the examining division did not see any useful purpose in an interview.

3.3. Moreover, although the Board has no reason to doubt the applicant's account of the information given to him in the telephone conversations with the formalities officer, neither this information nor the course of the examination procedure actually deprived the applicant of any right in pursuing the application. In particular, since the application was refused on grounds or evidence which were communicated to the applicant, the applicant's right to be heard before the issue of an adverse decision was also respected in accordance with Article 113(1) EPC.

The degree to which the applicant was taken by surprise by the decision has to be judged in the light of the fact that the second communication ended with an unambiguous warning that the rejection of the application was to be envisaged.

3.4. According to Rule 67 EPC the appeal fee is to be reimbursed where the Board considers the appeal to be allowable, if reimbursement is equitable by reason of a substantial procedural violation.

In the present case, the Board considers neither the appeal to be allowable nor a substantial procedural violation to have been committed by the examining division. Accordingly the request for the refund of the appeal fee cannot be granted.