T 0850/93 (Single crystal growth/CANON I) 18-12-1995

I. European patent application No. 87 302 788.2 (publication No. 0 240 309) was refused by a decision of the Examining Division.

II. The reason given for the refusal was that the subject- matter of Claims 1 of the main, first and second auxiliary requests filed on 2 March 1993 does not meet the requirements of Articles 52(1) and 56 EPC having regard to documents:

D1: Solid State Technology, vol. 27, No. 9, September 1984, pages 239 to 243;

D5: US-A-3 620 833; and

D8: Philips Technical Review, vol. 41, No. 2, 1983/84, pages 60 to 69.

The reasons for the refusal can be summarised as follows:

(a) In respect of Claim 1 of each of the main and first auxiliary requests, document D5 is the most relevant prior art. In particular, a skilled person would derive from document D5, Figures 3 to 4 and column 2, lines 33 to 36, that under selected conditions of deposition a relatively small size of the nucleation sites (formed by imprinting a nucleating agent on a SiO2 surface or by making indentations or by selective damage of the SiO2 layer) supports the formation and growth of a single nucleus only, since otherwise two or more crystals or no crystals at all would have developed on at least some of the nucleation sites which have a larger nucleation density than the remainder of the SiO2 layer. Document D8, in particular Figure 10 and page 64, right column, last paragraph discloses that the nucleation density of Si is much greater on Si3N4 than on SiO2 and that this difference increases with lower deposition temperatures. This teaching in document D8 is a clear incentive to the skilled person to use Si3N4 as a nucleating agent on SiO2 in the method disclosed in document D5. In such use a skilled person can either provide (a) a patterned Si3N4 layer (spots) on SiO2 or (b) a patterned SiO2-layer forming windows on Si3N4. Since a combination of SiO2 and Si3N4 layers is generally known from the well-established LOCOS technique, selection of alternative (b) and arriving thereby at the subject-mater of Claim 1 of the main request does not demand inventive action from the skilled person.

Claim 1 of the first auxiliary request specifies that the nucleating agent (i.e. the material of the deposition surface areas) is amorphous. Since Si3N4 deposits are normally amorphous, also the subject- matter of Claim 1 of the first auxiliary request is obvious in view of documents D5 and D8.

(b) With regard to Claim 1 of the second auxiliary request, document D1 is considered to be the most relevant prior art. Claim 1 of this request differs from the disclosure in document D1 in that the deposition surface areas exposed through windows in a SiO2 layer are of polycrystalline silicon rather than of monocrystalline silicon. It would be obvious to a skilled person to replace the monocrystalline silicon substrate in the method according to document D1 by a polycrystalline one, if the circumstances require this and to select the window size so that at the most one complete single crystalline grain of the polycrystalline substrate is exposed.

III. The Appellant lodged an appeal against this decision. In the Statement of Grounds of Appeal the Appellant filed a new main request based on a set of claims containing a main Claim 1 which is based on Claims 1 and 2 of his former main request, and four auxiliary requests. Furthermore, he requested oral proceedings as an auxiliary request. In support of his arguments the Appellant filed the following documents:

D9: Applied Physics Letters, vol. 52, No. 15, 1988, pages 1231 to 1233;

D10: Applied Physics Letters, vol. 55, No. 7, 1989, pages 636 to 638;

D11: Applied Physics Letters, vol. 55, No. 11, 1989, pages 1071 to 1073;

D12: Applied Surface Science, vol. 41/42, 1989, pages 638 to 642.

IV. In a communication pursuant to Article 110(2) EPC dated 5. December 1994 the Board informed the Appellant of its provisional view that Claim 1 of the Appellant's main request may be regarded as obvious in view of the two embodiments disclosed in document D5, column 2, lines 10 to 36 and column 3, lines 37 to 46 respectively. On the basis of the Appellant's submissions explaining the gist of the present invention, the Board proposed amendments to Claim 1 of the main request in order to overcome the objection under Article 56 EPC. In particular a more specific definition was suggested in Claim 1 of the materials of the deposition area surface, and of the deposited material which may epitaxially grow on the former. Amendments were also suggested with a view to meeting objections under Articles 84 and 123(2) EPC and Rules 29(1) and 27(1)(b) and (c) EPC.

V. In reply to the Board's communication the Appellant filed on 10 February 1995 an amended main request and cited the following document

D13: Charles Kittel: "Introduction to Solid State Physics" 3rd edition, 1967, John Wiley and Sons Inc. New York) pages 609 and 610.

Following a telephone consultation between the Rapporteur and the Appellant's representative on 30 June 1995 wherein further amendments were discussed, the Appellant now requests that a patent be granted on the basis of the following main request:

Claims:

Claim 1 according to claim pages 53 to 55 filed on 10 February 1995;

Claims 2 to 32 according to:

claim pages 55 (renumbered into 55a), 58, 60. and 62 as approved on 10 February 1995; and

claim pages 56, 57, 59, 61, 63 to 66 filed on 15 September 1993.

Description:

Pages 1 to 7 filed on 10 February 1995 with the amendment on page 7 requested on 21. June 1995;

Original page 7 (renumbered into page 7a), lines 24 to 37;

Original pages 8 to 52 with the amendments on pages 8, 22, 26, 28 and 30 requested on 21 June 1995.

Drawings: Original sheet 1/15 to 15/15.

VI. Independent Claims 1, 24, 27, 28 and 29 read as follows:

"1. A method (Fig. 4; Fig. 6; Fig. 7; Fig. 9; Fig. 12) for producing on the surface of a substrate (4; 9; 10) one or more single crystals (7A; 7; 13A-1 and 13A-2) of a crystal-forming material, which method comprises:

establishing at a free surface of said substrate one or more deposition surface areas (6A; 9A; 12A-1 and 12A-2) having under chosen conditions of deposition a higher deposition rate than that of the adjacent deposition surface area or areas (5A; 11A and 11-1A), so that said crystal-forming material deposits selectively on said one or more deposition surface areas (6A; 9A; 12A-1, 12A-2), wherein the step of establishing said one or more deposition surface areas (6A; 9A; 12A-1 and 12A-2) and adjacent deposition surface area or areas (5A; 11A and 11-1A) comprises depositing a thin film (5; 11) of material which is to form said adjacent deposition surface area or areas (5A; 11A and 11- 1A) onto the surface of said substrate (4; 9; 10) and opening one or more windows in said thin film by photolithographic patterning (including x-ray lithography) or by patterning with an electron beam or ion beam whereby said one or more deposition surface areas (6A; 9A; 12A-1 and 12A-2) are exposed to said crystal-forming material via said corresponding one or more windows in said adjacent deposition surface area or areas (5A; 11A and 11- 1A); and

depositing said crystal-forming material on the exposed free surface (5A and 6A; 5A and 9A; 11A; 12A-1 and 12A-2) of said substrate (4; 9; 10) under said chosen conditions of deposition; characterised in that:

(a) said one or more deposition surface areas (6A; 9A; 12A-1 and 12A-2) have surface properties which exclude an epitaxial growth of a single crystal of said crystal-forming material on said one or more deposition surface areas;

(b) the difference in deposition rates arises because the surface properties of the deposition surface area or areas and of the adjacent surface area or areas are such that a higher number of nuclei form per unit area in the deposition surface area or areas than in the adjacent surface area or areas; and

(c) the or each exposed deposition surface area or areas is limited to such a size that under said chosen conditions of deposition said crystal-forming material forms on the or each deposition surface area one single nucleus of supra-critical size which grows into one single crystal (7A; 7; 13A-1 and 13A-2).

24. An article (Fig. 4(D), Fig. 5(B), Fig. 6(D), Fig. 7(D), Fig. 8(B), Fig. 9(C), Fig. 10(B), Fig. 11, Fig. 12(D)), produced by a method as claimed in Claim 1, which article comprises:

a substrate (4) having one or more amorphous or polycrystalline regions (6A);

a thin film or layer (5) above said substrate (4);

and

one or more single crystals (7A, 8) on said thin film or layer (5), which one or more single crystals (7A, 8) respectively are in contact with said one or more amorphous or polycrystalline regions (6A) via a corresponding one or more respective windows provided in said thin film or layer (5) which article does not include as thin film or layer (5) a thin film or layer of material convertible by change of crystalline state to single crystal material lattice matched to the one or more single crystals.

27. An article produced by a method as claimed in Claim 1, which article comprises:

a substrate (4);

a thin film or layer (5) above said substrate (4);

and

one or more single crystals (7A, 8) on said thin film or layer (5), which one or more single crystals (7A, 8) are in contact with a respective one or more regions (6A) of said substrate (4) via a respective one or more windows provided in said thin film or layer (5); and wherein

each respective substrate region (6A) is one of the metals copper, tungsten, tantalum, molybdenum, gold, titanium, aluminium or nickel;

said thin film or layer (5) is of iron or cobalt;

and

each of said single crystals (7A, 8) is of diamond.

28. An article produced by a method as claimed in Claim 1, which article comprises:

a substrate (4);

a thin film or layer (5) above said substrate (4);

and

one or more single crystals (7A, 8) on said thin film or layer (5), which one or more single crystals (7A, 8) are in contact with a respective one or more regions (6A) of said substrate (4) via a respective one or more windows provided in said thin film or layer (5); and wherein:

each respective substrate region (6A) is one of the semiconductor materials silicon, germanium, gallium arsenide, indium phosphide or silicon carbide;

said thin film or layer (5) is of iron or cobalt;

and

each of said single crystals (7A, 8) is of diamond.

29. An article produced by a method as claimed in Claim 1, which article comprises:

a substrate (4);

a thin film or layer (5) above said substrate (4);

and

one or more single crystals (7A, 8) on said thin film or layer (5), which one or more single crystals (7A, 8) are in contact with a respective one or more regions (6A) of said substrate (4) via a respective one or more windows provided in said thin film or layer (5); and wherein

each respective substrate region (6A) is of silicon, tungsten silicide, platinum silicide or aluminium;

said thin film or layer (5) is of silicon oxide;

and

each of said single crystals (7A, 6) is of tungsten."

Claims 2 to 23 are dependent on Claim 1; and Claims 25, 26, 30, 31 and 32 are dependent on Claim 24.

VII. In support of his requests the Appellant made essentially the following submissions:

(a) The deposition of silicon through the windows in accordance with the "second embodiment" disclosed in document D5 at column 3, lines 18 to 46 does not proceed by a process that involves nucleation (i.e. the formation of fresh crystal nuclei), but instead involves the different phenomenon of continued growth of the existing crystal lattice of an existing material. The rate of growth of Si crystallites at random locations on the surface of the SiO2 layer is moderated by etching windows through the SiO2 which expose the underlying Si. There is then epitaxial growth of Si at the windows which competes with the nucleation and growth of Si on SiO2.

(b) The disclosure at column 1, lines 50 to column 2, line 60 in document D5 is so seriously deficient that the method of making the crystallites cannot be said to have been disclosed in such a way as to enable a skilled person to carry out the claimed invention, and therefore the claimed invention was not comprised in the state of the art within the meaning of Article 54(2) EPC. In particular, printing tools or indentation tools producing nucleation sites having diameters in the length of a micron range as disclosed in document D5 (see column 2, lines 35 and 36) are not described in sufficient detail and were not common general knowledge at the date of publication of document D5 or even subsequently. In the creation of deposition sites by electron bombardment, there is no disclosure of the practical conditions required and the results achieved and deposition of a single nucleus is not to be expected (see parallel case T 869/93). Moreover, the nucleation agents disclosed in document D5 would decompose at the silicon deposition temperatures. Crystallite regions 16 in the embodiment disclosed in Figures 8 to 13 of document D5 do not form in previously defined locations, so that actual randomly distributed locations have to be determined by scanning with a light beam and recording the resulting data in a computer (D5, column 3, lines 54 to 60).

(c) Document D5 does not teach to select the size of each deposition surface area in relation to the deposition conditions and the nucleation density so that only a single nucleus of crystal-forming material grows at each deposition site. The purpose of the windows in the Figures 8 to 13 embodiment of document D5 is to create sites where rapid epitaxial deposition of silicon reduces the formation of Si-crystallites on SiO2 outside the windows. A skilled person would not consider to reduce the size of these windows since this would slow down the epitaxial deposition and increase the packing density of Si-crystallites on SiO2.

(d) Consistent with document D13, document D8, (Figure 5 in conjunction with page 62) teaches that epitaxial growth of Si on Si takes place via surface diffusion of adsorbed atoms to a stable kink position at surface steps. At lower temperatures the diffusion of the atoms across the surface is less rapid, nucleation starts and gives rise to polycrystalline films. There is no disclosure in document D8 that a region with larger nucleation density determines the location of crystal growth. Although document D8 discloses values for the nucleation densities of SiO2 and Si3N4, the prior art does not hint at trying Si3N4 as nucleation site material (i.e. in the "deposition surface areas") which is surrounded by SiO2 as non-nucleation site material (i.e. in the "adjacent deposition surface areas").

(e) The epitaxial lateral overgrowth (ELO) process disclosed in document D1 does not proceed by selective nucleation to initiate the growth of new crystals but instead proceeds by further epitaxial growth from an exposed region of an existing single crystal. Document D1 is silent about the nucleation density of exposed silicon areas and contains no disclosure that the window size is a critical feature in forming a single crystal of silicon on an insulator (SOI).