The invention relates to a method of synthesizing a crystalline material, and to the material obtained thereby.
More particularly, the invention concerns a method of synthesizing a crystalline material, comprising the steps of:
a) producing seeds of a catalyst adapted to dissolve carbon on a substrate constituted by a first material;
b) growing carbon nanotubes from the seeds; and
c) producing a layer of a second material comprising at least one monocrystalline region orientated from a seed.
The method of the invention can produce a layer of silicon which is at least partially crystalline, such as polycrystalline silicon, on an amorphous substrate such as glass. In this case in particular, the product obtained by the method of the invention is particularly advantageous for electronics applications such as the fabrication of flat screens.
To optimize the orientation of monocrystalline domains with respect to each other, during step b), the seeds are orientated in a magnetic field.
The method of the invention may also comprise one or more of the following dispositions:
the first material is an amorphous material;
the catalyst comprises a transition metal;
the second material is silicon;
step c) comprises the following sub-steps:
step a) comprises the following sub-steps:
a1), during which studs of catalyst are produced on the substrate; then
step a) comprises the following sub-steps:
a′1), during which a thin film constituted by catalyst is deposited on the substrate; then
step a) comprises the following sub-steps:
a magnetic field is applied during steps a2), a′2) or a″2) to orientate the seeds;
step a) comprises the following sub-steps:
In another aspect, the invention provides a material comprising:
a substrate constituted by a first material extending essentially in a plane;
carbon nanotubes extending longitudinally essentially perpendicular to the plane of the substrate between a free end and an end which is fixed to the substrate;
seeds of a catalyst substantially located near the free end of carbon nanotubes; and
at least one domain of a second crystalline material orientated from at least one seed.
The above characteristics and others become more apparent from the following description of two particular implementations of the invention, given by way of non-limiting example.
The description is made with reference to the accompanying drawings, in which:
A first, non-limiting implementation of the method of the invention is described below with reference to FIGS. 1 to 6.
In this example, the method of the invention is applied to the production, on a substrate 2 of a first material, in this case glass, of a layer of a second material, in this case polycrystalline silicon (see
In this example, the method comprises:
a step a1), during which studs 4 are produced on a substrate 2;
a step a2), during which the substrate 2 and the studs 4 are annealed to form seeds 6;
a step b) of growing carbon nanotubes 8 from the seeds 6;
a step c1), during which a layer of amorphous silicon 10 is deposited on the substrate 2, the seeds 6, and the carbon nanotubes 8; and
a step c2), during which the substrate 2, on which the amorphous silicon layer 10 has been deposited, is annealed to crystallize the silicon in the solid phase and obtain grains 11 of orientated silicon.
The studs 4 are constituted by a catalyst, in this case a metal, typically a transition metal, which catalyzes the growth of carbon nanotubes 8. It may be iron, cobalt, nickel, platinum, etc.
To form the studs 4, a thin layer, for example of iron, is deposited on the substrate 2 during step a1) and is then etched by conventional lithographic methods to form an array of studs 4. Said studs are typically spaced 2 micrometers (μm) to 3 μm apart.
During step a2), the thin layer of iron is annealed at 650° C.-750° C. in a reducing atmosphere.
In a variation, a thin layer, 10 nanometers (nm) thick, of catalyst is deposited on the substrate 2, and the whole is annealed.
During step b), carbon nanotubes 8 are grown from the seeds 6 by purely thermal chemical vapor deposition (CVD) at 850° C.-1000° C. or by plasma enhanced chemical vapor deposition (PECVD), at 600° C.-700° C. For that growth method, reference should be made, for example, to the article by M. Meyyappan et al, Plasma Sources Sci Technol, No 12, page 205 (2003).
As shown in
In this case, after growth, the orientation of the seed 2 with respect to the axis of the carbon nanotube 8 is not random (see M. Audier et al, J. Cryst. Growth No 55, page 549 (1981)).
In particular, as shown in
As shown in
In order to perfect the orientation of the metallic seeds in the plane of substrate 2, a magnetic field which is judiciously orientated in the plane of substrate 2 may be applied during step a2) of forming the seeds 6, or during step b) of growing the carbon nanotubes 8 from the seeds 6.
During step c1), a thin layer of amorphous silicon 10 is deposited on the array of carbon nanotubes 8 at the tops of which the seeds 6 are orientated. This step c1) is carried out under conditions which are known to the skilled person, by PECVD or LPCVD (low pressure chemical vapor deposition), by decomposition of SiH4 or Si2H6, at a temperature in the range 200° C. to 600° C.
During step c2), the layer of amorphous silicon 10 is crystallized in the solid phase in a controlled atmosphere furnace at a temperature which is typically in the range 450° C. to 550° C. A layer of polycrystalline silicon is thus obtained which is highly textured and has a surface orientation corresponding to the orientation of the seeds 6 at the tops of the carbon nanotubes 8. Solid phase silicon epitaxy takes place on the seeds 6. Since these seeds 6 have the same orientation, a final thin layer of highly textured polycrystalline 12 or even monocrystalline silicon is obtained on an amorphous substrate 2.
Growth and solid phase epitaxy of silicon on the seeds 6 are shown in
A second example, also non-limiting, of the method of the invention is described below with reference to
As shown in
During a step a″1), metal ions are implanted in the thin layer 30. The metal ions correspond to the catalyst selected to form seeds 6.
During a step a″2), an anneal is carried out at about 600° C. of the substrate 2 and of the thin layer 30 that has undergone ionic implantation. During said anneal, the metal atoms precipitate out. The spacing and size of the precipitates 31 may be adjusted as a function of the implantation dose during step a″1). Typically, doses of the order of 1017 to 1018 ions per cm2 are used.
During a step a″3), chemical attack of the thin layer 30 of dielectric is carried out to “expose” the metallic precipitates 31. The emergent portions of the metallic precipitates 31 constitute the seeds 6 from which growth of a carbon nanotube 8 and then deposition of amorphous silicon then its crystallization can be carried out following steps b), c1) and c2) of the first example of the method of the invention as described above.
A third example, again non-limiting, of implementing the method of the invention is described below with reference to
As shown in
During a step a″′1)
patterns are produced in the resin 40, for example by photolithography, such that the resin 40 masks the thin layer 30 except in certain zones where the thin layer 30 is exposed; and
the thin layer 30 is etched down to the substrate 2 at the exposed zones to form pits 41.
During a step a″′2), a metal catalyst 44 selected to form the seeds 6 is deposited.
During a step a″′3), the resin 40 is dissolved. The catalyst 44 present on the resin is thus also eliminated during said operation.
During a step a″′4), an anneal is carried out at about 600° C. of the substrate 2, the thin layer 30, and the catalyst 44 present at the bottoms of the pits 41. During said anneal, the catalyst forms seeds 6 in the form of nanoparticles.
A step b″′ is then carried out of growing carbon nanotubes 8 from the seeds 6 in a manner analogous to step b) described above, in order to orientate the seeds 6.
Finally, a step c″′1) is carried out of depositing a layer of amorphous silicon 10, then a step c″′2) (not shown) is carried out of crystallizing the layer of amorphous silicon 10, respectively analogous to steps c1) and c2) described above.
Number | Date | Country | Kind |
---|---|---|---|
03/07849 | Jun 2003 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FR04/01634 | 6/25/2004 | WO | 12/21/2005 |