T 0042/97 22-05-2001

Reasons for the Decision

1. The appeal is admissible.

2. Novelty

2.1. Present claim 1 concerns a method for cleaning a semiconductor product of particles accumulated on its surface as well as of metallic and organic contamination, characterized in that the washing of the semiconductor product is carried out with an acid-water solution, with a dilution ratio between 1:106 - 1:103 advantageously between 1:105 - 1: 104.

In accordance with the usual interpretation of the term "for", in the expression "A method for cleaning a semiconductor product", the claimed method is suitable for cleaning a semiconductor product of particles accumulated on its surface as well as of metallic and organic contamination, characterized in that the washing of the semiconductor product is carried out with an acid-water solution, with a dilution ratio between 1:106 - 1:103 advantageously between 1:105 - 1: 104.

According to dependent claim 6, the employed acid is hydrofluoric acid (HF).

2.2. Three methods are known from document D1 (see the whole document; see in particular page 676, right-hand column, second paragraph, second to third line); each of these methods comprises a treatment of the semiconductor product, which is carried out with an HF-water solution and which is part of a wet cleaning procedure.

Document D1 (see page 676, right-hand column, first and second paragraph) is presented as a study in order to examine the cause of polycrystal growth in more detail whereby residual elements, mentioned as interface impurities, at the interface between grown films and HF-treated substrates are measured by spectrometry. It is thus derivable from document D1 (see the sentence bridging pages 676 and 677) that the results of the measurements of the interface impurities and the growth of an epitaxial layer on the HF-treated substrate, as opposed to polycrystalline growth, are an indication for an efficient treatment.

It is to be noted in this respect that it is generally known to people skilled in the art that particles accumulated on the surface of a substrate are detrimental to the epitaxial growth of e.g. silicon on such a substrate and can result in the growth of inter alia a polycrystalline layer.

2.2.1. In a first wet cleaning procedure of document D1, a silicon substrate was dipped in a 5% HF acid for 22. seconds. Silicon films were then grown on a 5% HF treated substrate and were found to be epitaxial. Also, impurities such as carbon, oxygen, fluorine and chlorine could not be detected at the interface of the deposited silicon film and the 5% HF treated substrate (see page 676, right-hand column, Figure 1(b)).

Therefore, a 5% HF acid clean results in desorption of contaminants from the HF-treated surface and, at least with respect to the epitaxial growth following the HF treatment of substrates, as giving "good results" in the sense of document D1 (see the sentence bridging pages 676 and 677 and the last sentence of the document and of the abstract).

However, there is no indication whatsoever in document D1 concerning cleaning a semiconductor product of metallic contamination, i.e., it is not derivable from the document that this known method is suitable for cleaning a semiconductor product of particles accumulated on its surface as well as of metallic and organic contamination.

It is to be noted in this respect that in the method of the present application (see in particular page 3, second paragraph; see also page 4, second paragraph and page 6, Example 4) (i) particle contents for particles larger than 0.3 µm, (ii) lifetime (which can reveal metallic impurities such as copper) and (iii) iron content are measured and the measurement results are shown.

In any case, a 5% HF solution is outside the range of dilution ratios of 1:106 - 1:103 of present claim 1.

Therefore, the cleaning method employing 5% HF acid solution does not anticipate the subject-matter of present claim 1, and this has not been contended either in the decision under appeal.

2.2.2. Document D1 (see the whole document) also discloses a treatment of the semiconductor product, which is carried out with an HF-water solution with a 49% HF concentration.

It is derivable from document D1 (see the last paragraph of the document; see also Figure 1(a) and the corresponding text) that impurities such as carbon, oxygen, fluorine and chlorine, which were measured at the interface between low-temperature (900 C) deposited silicon films and 49% HF-treated substrates were detected, and in this case the Si films which were grown were in the form of polycrystalline films.

Thus, at least with respect to the epitaxial growth following the HF treatment of substrates, an HF concentration of 49% can be derived as giving inadequate results in the sense of document D1 (see the sentence bridging pages 676 and 677).

In any case, an HF concentration of 49% (i.e. 49 x 10-2), as in this other known method, is outside the range of dilution ratios between 1:106 - 1:103 of present claim 1, and this has not been disputed either.

2.2.3. Document D1 also discloses washing of a semiconductor product with an acid-water solution, with a dilution ratio of 0.05%, which indeed falls within the range of 1:106 - 1:103 specified in the claim.

The appellant has submitted that since it is specified in the last paragraph of document D1 that it was found that there were impurities, such as carbon, oxygen, fluorine, and chlorine at the interface between low-temperature (900 C) deposited silicon and 49% and 0.05% acid treated surface and since it was derivable from the document that this was detrimental to epitaxial growth of silicon films, this was to be interpreted by the person skilled in the art as meaning that this particular method of document D1 is not suitable for cleaning a semiconductor product of particles accumulated on its surface as well as of metallic and organic contamination.

The following is to be noted in this respect:

It is derivable from document D1 that the three disclosed methods differ only in the concentration of the HF solution and that the measured concentrations of residual elements (shown in Figures 1(a) to 1(c)) and the form of the deposited silicon film, i.e. epitaxial or polycrystalline, is dependent on the concentration of HF solution. It is also directly and unambiguously derivable that the treatment with a 0.05% or with a 49% HF solution does not result in the removal of the contaminants, and that removal of contaminants is obtained only with the 5% HF concentration.

Moreover, there is no derivable definite teaching from document D1 about removal of impurities or desorption of contaminants following a 0.05% or a 49% acid treatment.

It is also to be noted that there is no information derivable from document D1 about removal of metallic contamination.

2.2.3.1. Therefore, the appellant's argument that document D1 does not give the person skilled in the art a technical teaching to use a 0.05% HF solution as cleaning liquid and that, consequently, the document does not anticipate the presently claimed method, is convincing.

The further prior art documents are less relevant.

Therefore, the subject-matter of present claim 1 does not form part of the state of the art and, consequently, it is new in the sense of Article 54 EPC.

3. Inventive step

3.1. As set forth here above, the relevant teaching from document D1 is that impurities such as carbon, oxygen, fluorine and chlorine, could not be detected at the interface between low-temperature (900 C) deposited silicon films and 5% HF-treated substrates, that in this case Si films were grown epitaxially, and that this is to be understood as being the result of desorption of contaminants from the treated surface of the semiconductor substrate. Removal of contaminants by the treatment with a 0.05% acid solution is not derivable from the document.

3.2. As convincingly argued in the statement setting out the grounds of appeal (see page 4, second paragraph), starting from document D1, with "good results" for the 5% HF-solution and "bad results" for the 0.05% HF-solution, and taking into account that it is generally known that very highly diluted acid solutions are less effective for obtaining good cleaning results, it was surprising to choose a very highly diluted acid solution for obtaining good cleaning results, as has been done in the invention.

The further prior art documents are less relevant.

3.3. Therefore, the subject-matter of present claim 1 involves an inventive step in the sense of Article 56 EPC, so that a European patent can be granted on this basis (Art. 52(1) and 97(2) EPC).

4. Reimbursement of the appeal fee

It is the established case law of the boards of appeal (see e.g. T 182/90 OJ 1994, 641; cf. point 4 of the reasons) that it was not a substantial procedural violation within the meaning of Rule 67 EPC if a request to have an interview with the primary examiner was ignored; it was at the examiner's discretion to decide whether to conduct such informal discussions in accordance with the Guidelines, bearing in mind the particular circumstances of the case (see Guidelines, C-VI, 4.4 and 6, and T 300/89, OJ 1991, 480; cf. in particular point 9.2 of the reasons).

In support of his contention that Article 113 EPC has been violated, the appellant has not provided any argument that in the present case the decision of the examining division was based on grounds or evidence on which he had not had an opportunity to present his comments.

The fact that the applicant had no chance to learn the evaluation of the applicant's arguments by the examiner before the decision is not relevant in the present case since, as set forth here above, there is no indication that the decision of the examining division was based on grounds or evidence on which he had not had an opportunity to present his comments.

Therefore, the appellant's request for reimbursement of the appeal fee is rejected (Rule 67 EPC).