U.S. patent application number 14/445511 was filed with the patent office on 2015-02-19 for method for producing a metal layer on a surface.
This patent application is currently assigned to COMMISSARIAT A L'ENERGIE ATOMIQUE ET AUX ENE ALT. The applicant listed for this patent is Commissariat A L'energie Atomique Et Aux Ene Alt. Invention is credited to Xavier BAILLIN, Didier GASPURATTO.
Application Number | 20150050428 14/445511 |
Document ID | / |
Family ID | 49753300 |
Filed Date | 2015-02-19 |
United States Patent
Application |
20150050428 |
Kind Code |
A1 |
BAILLIN; Xavier ; et
al. |
February 19, 2015 |
METHOD FOR PRODUCING A METAL LAYER ON A SURFACE
Abstract
The invention concerns a method for producing a metal coating on
a portion of the surface of a substrate of a microelectronic
device, wherein it comprises, using a modified nucleic acid strand
comprising a nucleic acid strand structure, at least one metal
nanoparticle and/or a metal atom and at least one chemical
function, at least one step of fixing the chemical function of the
at least one modified nucleic acid strand on the portion of the
surface of the substrate.
Inventors: |
BAILLIN; Xavier; (Crolles,
FR) ; GASPURATTO; Didier; (Notre Dame de Mesage,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Commissariat A L'energie Atomique Et Aux Ene Alt |
Paris |
|
FR |
|
|
Assignee: |
COMMISSARIAT A L'ENERGIE ATOMIQUE
ET AUX ENE ALT
Paris
FR
|
Family ID: |
49753300 |
Appl. No.: |
14/445511 |
Filed: |
July 29, 2014 |
Current U.S.
Class: |
427/550 ;
427/123; 427/125; 427/553 |
Current CPC
Class: |
C23C 18/04 20130101;
C23C 18/1608 20130101; C23C 18/1893 20130101; H01L 21/76874
20130101; C23C 18/02 20130101; C23C 18/2086 20130101; H01L 21/76841
20130101; H01L 21/288 20130101; C23C 18/08 20130101; C23C 18/10
20130101; C23C 18/1612 20130101; H01L 21/76898 20130101; C23C
18/1653 20130101 |
Class at
Publication: |
427/550 ;
427/123; 427/125; 427/553 |
International
Class: |
C23C 18/08 20060101
C23C018/08; C23C 18/02 20060101 C23C018/02; C23C 18/10 20060101
C23C018/10; C23C 18/04 20060101 C23C018/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2013 |
FR |
13 57547 |
Claims
1. A method for producing a metal-based coating on at least one
portion of the surface of a substrate of a microelectronic device,
wherein it comprises: using a modified nucleic acid strand
comprising a nucleic acid strand structure, at least one
metal-based nanoparticle and/or a metal atom and at least one
chemical function, at least one step of fixing the modified nucleic
acid strand to the portion of the surface of the substrate; said
portion of the surface of the substrate being a three-dimensional
surface in the form of a cavity.
2. The method according to claim 1, wherein the step of fixing the
modified nucleic acid strand is performed by means of the chemical
function.
3. The method according to claim 1, wherein the method comprises a
step of at least partial destruction of the nucleic acid strand
structure and/or of the chemical function.
4. The method according to claim 3, wherein the step of at least
partial destruction of the nucleic acid strand structure and/or of
the chemical function comprises a heating step configured so as to
partially or completely destroy the structure of the nucleic acid
strand and/or of the chemical function.
5. The method according to claim 1, wherein the cavity has a depth
greater than its width.
6. The method according to claim 1, wherein the step of fixing the
at least one modified nucleic acid strand on the portion of the
surface of the substrate is obtained by putting the surface of the
substrate in contact with a bath comprising at least one modified
nucleic acid strand.
7. The method according to claim 1, wherein the portion of the
surface of the substrate comprises a chemical group configured so
as to interact with the chemical function fixed on the structure of
the at least one nucleic acid strand.
8. The method according to claim 1, comprising several steps of
fixing modified nucleic acid strands.
9. The method according to claim 8, wherein the modified nucleic
acid strands are identical or different through the structure of
their respective strands and/or through their respective chemical
functions and/or through the nature and/or dimensions of the
metal-based nanoparticles and/or the metal atoms.
10. The method according to claim 8, comprising, after the steps of
fixing modified nucleic acid strands, a single step of destruction
of the nucleic acid strand structures.
11. The method according to claim 1, comprising, prior to said at
least one step of fixing the at least one modified nucleic acid
strand on the portion of the surface of the substrate, a step of
deposition of a grafting layer on at least the portion of the
surface of the substrate.
12. The method according to claim 1, wherein the portion of the
surface of the substrate or the grafting layer comprises a
hydrophilic or hydrophobic material.
13. The method according to claim 1, wherein the chemical function
is a group of hydrophilic or hydrophobic atoms.
14. The method according to claim 1, wherein the metal-based
coating forms part of a via.
15. The method according to claim 1, wherein the metal atom is
chosen from copper, nickel, aluminium, palladium, gold or
silver.
16. The method according to claim 1, wherein the metal-based
nanoparticle is chosen from a metal, a metal oxide, a metal nitride
or a metal carbide.
17. The method according to claim 1, comprising, prior to the step
of fixing the at least one modified nucleic acid strand on the
portion of the surface of the substrate, a step of irradiating, by
ultraviolet radiation, the portion of the surface of the substrate
intended to receive the metal-based coating.
18. The method according to claim 1, comprising, prior to the step
of fixing the at least one modified nucleic acid strand on the
portion of the surface of the substrate, a step of irradiating, by
ultraviolet rays, the entire surface of the substrate except for
the portion of the surface intended to receive the metal-based
coating.
19. A The method according to claim 1, comprising the use of at
least one nanoparticle with a diameter of between 1 nanometre and
100 nanometres.
20. Use of at least one modified nucleic acid strand comprising a
nucleic acid strand structure, at least one metal-based
nanoparticle and/or a metal atom said structure being configured so
as to form a metal-based coating on a three-dimensional portion of
the surface of a substrate, said portion being a cavity.
21. Use according to claim 21, wherein the modified nucleic acid
strand comprises at least one metal-based nanoparticle, said metal
being a ferromagnetic metal, said nanoparticle being configured so
as to form, under the action of a magnetic field, a coating based
on ferromagnetic metal on a portion of the surface of a
substrate.
22. Use according to claim 21, wherein: at least one first modified
nucleic acid strand comprising at least one first metal-based
nanoparticle and/or one first metal atom, and at least one second
modified nucleic acid strand comprising at least one second
metal-based nanoparticle and/or one second metal atom, are
configured so that the first and/or second nanoparticle and the
first and/or second metal atom form a coating based on a metal
alloy or a composite on a portion of the surface of a
substrate.
23. Use according to claim 21, wherein: at least one first modified
nucleic acid strand comprising at least one first nanoparticle
based on a first metal, and at least one second modified nucleic
acid strand comprising at least one second nanoparticle based on
one second metal, are configured so that the first and second
nanoparticles form a dual-layer coating composed of a deposit based
on a first metal of the first nanoparticle covered by a deposit of
the second metal of the second nanoparticle on a portion of the
surface of a substrate.
24. Use according to claim 21, comprising the use of a nanoparticle
having a diameter of between 1 nanometre and 100 nanometres.
25. The method according to claim 9, wherein the modified nucleic
acid strands are different through the structure of their
respective strands and/or through their respective chemical
functions and/or through the nature and/or dimensions of the
metal-based nanoparticles and/or the metal atoms.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a microelectronic device.
It concerns in particular the production of a metal-based coating
on a surface, in particular three-dimensional, of a substrate.
TECHNOLOGICAL BACKGROUND
[0002] Three-dimensional (3D) integration is becoming a method of
exploration that is very much followed in microelectronics. It
makes it possible in particular to assemble chips together on a
vertical axis thus assisting the production of ever more compact
and high-performance components; the length of the interconnections
being reduced compared with a conventional assembly. It is
consequently necessary, for this three-dimensional technology, to
master the step of deposition of 3D materials such as the
insulators or metals.
[0003] Furthermore, through electrical connections, more commonly
referred to by the English acronyms "TSV", standing for
"through-silicon vias", when the substrate is made from silicon,
"TGV", standing for "through-glass vias", when the substrate is
made form glass, or "TPV", standing for "through-polymer vias",
when the substrate is made from polymer, are used in
microelectronic components in order to connect one face of a
component to its opposite face.
[0004] Because of the increase in density of electrical
connections, it is becoming essential to reduce their dimension in
the plane, and in particular their diameter (of around a few
microns), while keeping a depth of around a hundred microns. The
steps of deposition of insulators and conductive materials are
therefore becoming key technical points.
[0005] The etching of a substrate when it is made from silicon is
generally carried out by deep reactive ion etching (DRIE). The
insulation of the walls of a via is obtained by deposition of an
insulator (for example silicon dioxide SiO.sub.2), generally by the
chemical vapour deposition (CVD) method. Depending on the maximum
temperature acceptable for the substrate, several methods exist in
a temperature range lying between 150.degree. C. and 400.degree. C.
If the substrate so permits, a thermal oxidation can be envisaged
(temperature above 800.degree. C. for example). The deposition of
the metal conductor takes place in three steps: the first consists
of depositing an attachment layer on the insulator (for example
titanium on SiO.sub.2), the second of depositing a
diffusion-barrier layer (nickel or titanium nitride for example),
the third of depositing a layer of metal (copper or gold for
example) that will serve as a seed layer or for the growth of a
deposition by electrodeposition (copper for example).
[0006] The entire problem, when the shape factor (the depth of the
via with respect to the diameter of the via, also referred to as
aspect ratio--AR) increases, is finding solutions for obtaining a
conforming deposition, that is to say one covering the walls of the
via uniformly.
[0007] Furthermore, the layers formed by these traditional
deposition techniques are not conforming, and therefore do not have
a uniform thickness at every point on the surface of the substrate.
The sides of the trenches and vias may in particular be covered
with an insufficient thickness of the layer, then causing imperfect
subsequent filling having defects in the material (referred to as
voids). In addition, the layers produced on the sides of the
patterns have by nature an appearance different from that deposited
on the flat surface of the substrate (top and bottom of the
trenches and vias). This may lead to impaired reliability
performances, such as resistance to electromigration. In other
words, the defect in conformity is revealed not only by differences
in thickness; defects of continuity and adhesion of the layer on
the sides of the trenches and vias may also result therefrom.
[0008] These drawbacks make it very tricky to use PVD technology in
the advanced generations of integrated circuits where the
transverse dimensions of the trenches and vias are very small
(around a few tens of nanometres) and where the aspect ratios may
be high. With regard to physical vapour deposition, the method
reaches its limits with an aspect ratio of around 10 to 1 (denoted
10:1). Metallic deposition by CVD also finds limits in the aspect
ratio, but especially in the technological cost. Likewise, atomic
layer deposition is an expensive alternative (slow process)
compared with chemical vapour deposition. The solution therefore at
the present time seems to lie in wet methods, which are the best
suited for meeting the specification: aspect ratio and cost.
[0009] In this context, solutions through the deposition of a layer
in a liquid medium have an advantage by involving a method by
electrografting of an organic precursor on a conductive or
semiconductive substrate. It is then possible to produce a stack of
layers by successive deposition of an isolation layer, then a
diffusion-barrier layer followed by a seed layer. Electrografting
consists of a method of wet deposition based on the initiation and
then electro-induced polymerisation of electroactive monomers. The
document FR-A-2933425 describes a method for producing an
electrically insulating film by electrografting as well as the
deposition of a copper diffusion barrier. These methods make it
possible to obtain conforming films, with a thickness of between a
few nanometres and 500 nanometres for aspect ratios that may be as
much as 20:1. The method described in the document FR-A-2933425
consists of depositing an organic film by electrografting on a
conductive or semiconductive surface. The electrografting is
obtained by immersing the conductive or semiconductive surface in a
solution containing the organic precursor or precursors and
applying an electrical potential to said surface.
[0010] One object of the present invention is to propose an
alternative deposition method that will be able to be used, for
example, for producing a through via the aspect ratio of which may
be as much as, for example, 50:1.
[0011] Moreover, it may be particularly advantageous to propose a
solution for being able to lay down at least one monolayer of
nanoparticles with geometric shapes, for example, in three
dimensions.
[0012] It would also be advantageous to propose a method for
forming a uniform and homogeneous coating on a surface, and for
example three-dimensional, while making it possible to obtain a
high aspect ratio such as 50:1.
[0013] The present invention sets out to afford a solution for
achieving at least one of these objectives.
SUMMARY OF THE INVENTION
[0014] The invention concerns, according to one aspect of
embodiments, a method for producing a metal-based coating on at
least a portion of the surface of a substrate of a microelectronic
device, characterised in that it comprises, using a modified
nucleic acid strand comprising a nucleic acid strand structure, at
least one metal-based nanoparticle and/or a metal atom and/or a
chemical function, and at least one step of fixing the modified
nucleic acid strand to the portion of the surface of the substrate
by means of at least one chemical function.
[0015] According to the invention, the concept of "microdevice"
includes that of "nanodevice". Moreover, nucleic acid strand means
both a single strand and a double strand.
[0016] Because it is possible to synthesise nucleic acid that will
comprise, within a double strand, a metal atom or a chain of metal
atoms that may be of different chemical natures, or at the end of a
single strand a metal-based nanoparticle, it therefore appears
possible to produce metal-based depositions using this metallised
nucleic acid within it and/or on the periphery.
[0017] The method thus involves precursors obtained from modified
nucleic acid strands. It is therefore a wet method that will make
it possible to coat the walls for example of a cavity (in
particular of a via) and/or of a relief (in particular of a pad),
for example, by precursors of nanometric size present on the
modified nucleic acid strands. In a particularly advantageous
manner, these will make it possible, for example, to produce
insulating layers, a diffusion barrier and the metal seed layer for
a chemical (electroless) deposition, which will then be able to be
followed by a conventional electrochemical deposition (ECD). The
method involves nucleic acid strands comprising both nanoparticles
and/or atoms as well as at least one chemical function that will
make it possible to graft the strand onto the three-dimensional
surface. Advantageously, the invention will apply not only to
three-dimensional surfaces but also for example to two-dimensional
surfaces.
[0018] Advantageously, the method makes it possible to coat at
least one monolayer of nanoparticles of geometric shapes, for
example, in three dimensions.
[0019] Advantageously, the invention makes it possible to obtain a
high aspect ratio.
[0020] Furthermore, the invention does not necessarily require the
external action of an electrical field. Nevertheless, according to
a particular embodiment, it is possible advantageously to use an
external magnetic field when the nanoparticle or the metal atom is
magnetic, such as for example iron (Fe), cobalt (Co) or nickel
(Ni).
[0021] The invention also concerns, according to other aspects, the
use of at least one modified nucleic acid strand comprising a
nucleic acid strand (or skeleton), at least one metal-based
nanoparticle and/or a metal atom, configured to form a metal-based
coating on at least a portion of the surface of a substrate.
BRIEF INTRODUCTION OF THE FIGURES
[0022] Other features, aims and advantages of the present invention
will emerge more clearly from the detailed description of
embodiments thereof which are illustrated by the following
accompanying drawings, in which:
[0023] FIG. 1 illustrates a schematic view of a modified nucleic
acid double strand of the DNA type on which, at the periphery of
the double strand, and in particular on the structure of the
strand, an atom or nanoparticle has previously been grafted.
[0024] FIG. 2 illustrates a schematic view of a modified nucleic
acid double strand on which, on a structure of the strand, between
two bases, an atom or a nanoparticle has previously been
grafted.
[0025] FIGS. 3A and 3B are schematic representations of a modified
single nucleic acid strand on which, at a first end of the strand,
a nanoparticle and, at the other end, a chemical function have
previously been grafted.
[0026] FIG. 4 illustrates the step of forming an interconnection
pattern on the substrate.
[0027] FIG. 5 illustrates the step of treating the
three-dimensional surface of the substrate.
[0028] FIG. 6 illustrates a step of grafting at least one modified
nucleic acid strand, comprising the structure of the strand, at
least one atom or a nanoparticle and a chemical function.
[0029] FIG. 7 illustrates a heating step configured to partially or
totally destroy the structure of the modified nucleic acid
strand.
[0030] FIG. 8 illustrates the step of making an electrochemical
deposition on the coating.
[0031] FIGS. 9A and 9B illustrate an example of a three-dimensional
surface on which the coating according to the present invention can
be produced while ensuring uniformity of the layer and distribution
over the entire surface.
[0032] FIG. 10A illustrates an example of a three-dimensional
surface of a substrate on which a cavity has previously been
produced. The sides of the cavity are covered with a hydrophilic or
hydrophobic film enabling the modified nucleic acid strands to be
fixed.
[0033] FIG. 10B illustrates an example of a three-dimensional
surface of a substrate on which a cavity has previously been
produced. Following irradiation by ultraviolet rays, only the sides
of the cavity protected from the rays are covered with modified
nucleic acid strands.
[0034] The drawings are given by way of examples and are not
limitative of the invention. They constitute schematic outline
representations intended to facilitate understanding of the
invention and are not necessarily to the scale of practical
applications. In particular, the relative thicknesses of the
various layers and films are not representative of reality.
DETAILED DESCRIPTION
[0035] In the context of the present invention, the term "on" does
not necessarily mean "in contact with". Thus, for example, the
deposition of a layer on another layer does not necessarily mean
that the two layers are directly in contact with each other but
means that one of the layers at least partially covers the other
while either being directly in contact therewith or being separated
therefrom by a film, yet another layer or another element.
[0036] Before beginning a detailed review of embodiments of the
invention, optional features, which may optionally be used in
combination or alternatively, are stated below: [0037] The step of
fixing a modified nucleic acid strand is performed by means of the
chemical function. [0038] At the end of the step of fixing the
chemical function, a step of at least partial destruction of the
nucleic acid strand structure (or skeleton) and the chemical
function. [0039] The step of at least partial destruction of the
nucleic acid strand structure and/or of the chemical function
comprises a heating step configured so as to partially or totally
destroy the nucleic acid strand structure and/or the chemical
function. [0040] The at least one surface portion of the substrate
is a three-dimensional surface. [0041] Said surface portion is
chosen from a cavity and/or a relief. [0042] Said surface portion
is a cavity and the cavity has a depth greater than its width.
[0043] The step of fixing the at least one modified nucleic acid
strand on the portion of the surface of the substrate is obtained
by putting the surface of the substrate in contact with a bath
comprising at least one modified nucleic acid strand. [0044] The
portion of the surface of the substrate comprises a chemical group
configured so as to interact with the chemical function fixed on
the structure of the at least one modified nucleic acid strand.
[0045] Several steps of fixing modified nucleic acid strands are
performed. [0046] The modified nucleic acid strands are identical
or different through the structure of their respective strands
and/or through their respective chemical functions and/or through
the nature and/or dimensions of the metal-based nanoparticles
and/or metal atoms. Advantageously, the modified nucleic acid
strands have variable natures. [0047] After the steps of fixing the
modified nucleic acid strands, a single step of destruction of the
nucleic acid strand structures is performed. [0048] Prior to said
at least one step of fixing the chemical function of the at least
one modified nucleic acid strand on the portion of the surface of
the substrate, a step of deposition of a grafting layer on at least
the portion of the surface of the substrate. [0049] The grafting
layer is deposited over the entire surface of the substrate. [0050]
The portion of the surface of the substrate or the grafting layer
comprises a first chemical group or a hydrophilic or hydrophobic
material. [0051] The chemical function comprises a second
hydrophilic or hydrophobic chemical group. [0052] The metal-based
coating forms part of a via. [0053] The metal atom is chosen from
copper, nickel, aluminium, palladium, gold or silver. [0054] The
metal nanoparticle is chosen from a metal, a metal oxide, a metal
nitride or a metal carbide. [0055] Prior to the step of fixing the
chemical function of at least one modified nucleic acid strand on
the portion of the surface of the substrate, a step of irradiation
by ultraviolet rays of the portion of the surface of the substrate
intended to receive the metal-based coating. [0056] Prior to the
step of fixing the chemical function of at least one modified
nucleic acid strand on the portion of the surface of the substrate,
a step of irradiation by ultraviolet rays of the entire surface of
the substrate, except for the portion intended to receive the
metal-based coating. [0057] At least one nanoparticle based on
ferromagnetic metal is configured so as to form, under the action
of a magnetic field, a coating based on ferromagnetic metal on a
portion of the surface of a substrate. [0058] At least one first
modified nucleic acid strand comprising at least one first
metal-based nanoparticle and/or a first metal atom and at least one
second modified nucleic acid strand comprising at least one second
metal-based nanoparticle and/or a second metal atom, are configured
so that the first and/or second nanoparticle and the first and/or
second metallic atom form a coating based on a metal alloy or a
composite on a portion of the surface of a substrate.
Advantageously, a compound in the invention is, for example, a
mixture of metal and metal oxide, carbide and/or nitride. [0059] At
least one first modified nucleic acid strand comprising at least
one first nanoparticle based on a first metal and at least one
second modified nucleic acid strand comprising at least one second
nanoparticle based on a second metal are configured so that the
first and second nanoparticles form a dual-layer coating composed
of a deposition based on the first metal of the first nanoparticle
covered by a deposition of the second metal of the second
nanoparticle on a portion of the surface of a substrate.
[0060] An advantageous non-limitative aspect is to allow
depositions in cavities, optionally with high aspect ratios (for
example 50) using: [0061] A deposition solution, that is to say a
deposition by liquid method; [0062] A template produced from a
nucleic acid strand, this template having a nanometric size; [0063]
A chemical function for grafting the template onto the required
surface.
[0064] FIG. 1 illustrates a schematic view of a modified nucleic
acid double strand 100 on which a nanoparticle 20 comprising a
metal compound has previously been grafted, at the periphery of the
double strand, on the structure of the nucleic acid strand. Metal
means something that comprises at least one metal. This strand
represents a nucleic acid of the DNA or RNA type or an analogue of
nucleic acid. Analogue of nucleic acid means an acid composed of a
skeleton (or polymer or strand) formed by an alternation of
phosphates and sugars, bases 10 nitrogenated by means of sugar, at
the rate of one base 10 per sugar, being connected to said
skeleton. The term "metallization" of the nucleic acid strand 100
is used when a nanoparticle 20 comprising a metal compound is
grafted at the periphery or end of the structure of the strand. The
pitch of the strand is around 3 nanometres and, in this example,
comprises ten pairs of bases 10. The envelope surrounding the
nucleic acid strand 100 is notional. The nanoparticle 20 is
preferably chosen from a metal, a metal oxide, a nitride or a metal
carbide. By way of example, metals such as Cu, Ag, Au, Ru or Pt can
be cited; oxides of the elements Si, Cu, Al, Zr, Ti, Fe and Zn;
nitrides of the elements Ti, Ta, Hf, Mo and Si; carbides of the
elements Si, Ti, Ta, W, Al or Fe. The nanoparticle 20 has a
diameter of between 1 nanometre and 100 nanometres.
[0065] FIG. 2 illustrates a schematic view of a modified nucleic
acid double strand 100 on which there has been inserted, on the
structure of the strand, an atom 40, comprising a metal compound,
between two bases 10. In this case the term "metallation" of the
nucleic acid strand 100 is used. The atom 40 is preferably chosen
from copper, nickel, aluminium, palladium, gold or silver. The
modified nucleic acid strand 100 within which an atom 40 has been
grafted on the structure of the strand is of smaller size compared
with a modified nucleic acid strand 100 having a grafted
nanoparticle 20 at the periphery. A chemical function 60, for
fixing the modified nucleic acid strand 100 on a specific
three-dimensional surface, has been grafted on the periphery of the
structure of the strand. According to one configuration, this
chemical function 60 is grafted onto the structure of a modified
nucleic acid strand 100 comprising one or more nanoparticles 20
grafted at the periphery of the structure of the strand. According
to another embodiment, a nucleic acid strand 100 comprises one or
more atoms 40 inserted in it and/or attached at the periphery of
the structure of the strand as well as a chemical function 60 for
attaching the strand to a specific three-dimensional surface of the
substrate 20. Preferably, a modified nucleic acid strand 100
comprises, on the structure thereof, one or more nanoparticles 20,
one or more atoms 40 and at least one chemical function 60.
[0066] The chemical function 60 is a chemical group (linker and/or
spacer) able firstly to be fixed to the modified nucleic acid
strand 100 and secondly to have a group of peripheral atoms having
either a hydrophilic property or a hydrophobic property. It may be
advantageous to have several chemical functions 60 per nucleic acid
strand 100 in order to facilitate the grafting onto the substrate
200 such as for example one chemical function 60 per end.
[0067] Moreover, hydrophilicity can be obtained by a chemical group
associated with the structure (or skeleton) of the nucleic acid
strand 100 or integrated therein (in other words the skeleton is
itself hydrophilic). The nucleic acid double strand 100 is
naturally hydrophilic at the periphery. Thus it is possible to use
this intrinsic property for grafting onto hydrophilic surfaces
without having to add a specific chemical function 60; the latter
is naturally integrated in the nucleic acid strand 100.
[0068] FIGS. 3A and 3B illustrate schematic views of a modified
nucleic acid single strand 100 on which there have previously been
grafted, at one of the ends thereof, on the structure of the
nucleic acid strand 100, a nanoparticle 20 comprising a metal
compound and at the other end a chemical function 60. The nucleic
acid strand 100 is provided with at least one nanoparticle 20
and/or one atom 40 as well as a chemical function 60 that will
enable the modified nucleic acid strand 100 to be grafted onto the
accepter surface.
[0069] FIGS. 4 to 8 illustrate an example embodiment showing the
concatenation of the technological step for integrating the
metal-based coating 30 on a three-dimensional surface of a
substrate 200 with a view to producing a through via. This example
is purely illustrative. In particular the three-dimensional surface
may comprise reliefs both in a peak and in a hollow on the surface
of the substrate 200.
[0070] FIG. 4 illustrates the step of forming an interconnection
pattern on the substrate 200. The pattern is produced so as to form
a cavity in the substrate 200. Advantageously, the cavity has a
depth greater than its width. Depth means a dimension through the
thickness of the substrate 200. Width means a dimension
perpendicular to the thickness of the substrate 200. According to
one embodiment, the pattern forms a relief on the surface of the
substrate 200. The substrate 200, or at least the portion of the
substrate 200 in which the pattern is formed, is preferentially
chosen from a semiconductor material. The substrate 200 is
preferably made from silicon. It may be glass or polymer. For a
silicon substrate 200, the step of forming the interconnection
pattern may be performed by deep reactive ion etching using an
SiO.sub.2 mask for example. The etching of the substrate 200 to
form the interconnection pattern is preferably anisotropic. The
etching of the substrate 200 may be dry or wet.
[0071] FIG. 5 illustrates the step of treating the
three-dimensional surface of the substrate 200, or at least a
portion of the surface, in order to obtain, for example, a
hydrophilic/hydrophobic contrast. This step is optional since some
surfaces are naturally hydrophilic or hydrophobic. This is because
the surface of a silicon substrate 200 is for example naturally
hydrophobic while that of silicon oxide is naturally
hydrophilic.
[0072] For a substrate 200 not having a hydrophilic or hydrophobic
nature, a grafting layer 250 may be deposited on the substrate 200.
The grafting layer 250 may be deposited according to any type of
technique, for example chosen from chemical vapour deposition,
physical vapour deposition, atomic layer deposition or molecular
jet deposition. According to one embodiment, the grafting layer 250
comprises a hydrophilic material such as a metal oxide, such as for
example silicon dioxide (SiO.sub.2), titanium oxide (TiO.sub.2) or
aluminium oxide (Al.sub.2O.sub.3). According to another embodiment,
the grafting layer 250 comprises a hydrophobic material such as
hexamethyldisilazane (HMDS) normally used in microelectronics as a
promoter of the adhesion of photolithography resins, or a
fluorinated polymer such as the one used in a passivation layer in
the deep etching method of the DRIE type. Note that the compounds
in the family of organosilanes may be either hydrophilic or
hydrophobic. The thickness of the grafting layer 250 is
preferentially between a few tens of nanometres and 1 micron. When
its thickness is sufficient and the properties of the material so
permit, the grafting layer 250 may also serve as an electrical
insulation layer. The grafting layer 250 may be deposited over the
entire three-dimensional surface of the substrate 200. Preferably,
the grafting layer 250 is deposited selectively on the
three-dimensional surface of the substrate 200, that is to say on
only a portion of the three-dimensional surface where the modified
nucleic acid strands 100 must be deposited.
[0073] FIG. 6 illustrates a step of grafting, on the
three-dimensional surface of the substrate 200, at least one
modified nucleic acid strand 100, comprising at least one atom 40
and/or one nanoparticle 20 and at least one chemical function 60,
as described previously in FIGS. 1 and 2. It is possible, in
general terms, to define the chemical function 60 according to the
nature of the surface (insulator, metal, etc.) on which the
modified nucleic acid strand 100 will be deposited. The chemical
function 60 will be suited to the treatment of the surface of the
substrate 200. According to a configuration where the substrate 200
has a hydrophobic surface, the chemical function will be chosen
with a hydrophobic nature so as to interact and be fixed to the
three-dimensional surface of the substrate 200. According to
another embodiment where the substrate 200 has a hydrophilic
surface, the chemical function 60 will be chosen with a hydrophilic
nature so as to interact and be fixed to the three-dimensional
surface of the substrate 200.
[0074] According to an embodiment where the three-dimensional
surface of the substrate 200 comprises a plurality of portions with
different natures (that is to say either hydrophilic or
hydrophobic), the chemical function 60 will cooperate only with the
portion or portions of the surface having the same nature as it.
Thus the cooperation between a chemical function 60 and the
three-dimensional surface of the substrate 200 will take place
selectively on the chosen portion or portions.
[0075] The step of grafting, on the three-dimensional surface of
the substrate 200, at least one modified nucleic acid strand 100,
comprising at least one atom 40 and/or a nanoparticle 20 and at
least one chemical function 60, is obtained by putting the surface
of the substrate 200 in contact with a bath comprising at least one
modified nucleic acid strand 100. The bath is advantageously an
aqueous solution with a concentration of nucleic acid strands 100
of between approximately 10.sup.-12 and 10.sup.-6 moles/litre. The
substrate 200 is immersed in the bath at ambient temperature for
the time necessary, for a period for example of between one minute
and a few hours, for grafting at least one modified nucleic acid
strand 100 on the pretreated portions of the three-dimensional
surface of the substrate 200. According to the concentration of
nucleic acid strands 100 in the solution and the number of
nanoparticles 20 and/or atoms 40 inserted on the structure of the
nucleic acid strands 100, a thickness of metal-based coating 300 is
obtained, for example, between a minimum thickness that is around
the size of the nanoparticle 20 or the length or diameter of the
nucleic acid strands 200 to reach a maximum thickness of a few
hundreds of nanometres.
[0076] In order to increase the surface density of nanoparticles 20
and/or atoms 40 on the three-dimensional surface of the substrate
200, use will advantageously be made of a mixture of modified
nucleic acid strands 100 comprising strand structures (or
skeletons) with different lengths and/or sizes of nanoparticles 20
and/or atoms 40, or first the modified nucleic acid strands 100
will be grafted with the larger nanoparticles 20. According to
another embodiment, the modified nucleic acid strands 100
comprising atoms 40 will be grafted first, and then the modified
nucleic acid strands 100 comprising the nanoparticles 20, or vice
versa. Preferably, the bath comprises both modified nucleic acid
strands 100 provided with atoms 40 and modified nucleic acid
strands 100 provided with nanoparticles 20.
[0077] In a particular case, it is possible to choose a mixture of
a pair comprising at least a first modified nucleic acid strand 100
comprising a strand structure or a skeleton equipped with at least
one nanoparticle 20 based on a metal M1 and at least a second
modified nucleic acid strand 100 comprising a skeleton, which may
be of a different size from the first, equipped with at least one
nanoparticle 20 based on a metal M2. It is thus possible, using
this mixture, to deposit a composite material formed from
nanoparticles 20 M1 and M2. A composite in the invention is for
example a mixture of metal and metal oxide, carbide and/or nitride.
When M1 and M2 are metals, it is thus possible to form a metal
alloy. It is also possible to produce a metal alloy when the two
modified nucleic acid strands 100 comprise metal atoms 40
respectively M1 and M2. When M1 and M2 are for example and
respectively a metal and a metal compound of the oxide, nitride or
carbide type, it is possible to form a composite metal the physical
properties of which, such as for example electrical or thermal
conductivity and/or coefficient of expansion, are dependent on the
composition of material M1 and material M2.
[0078] In a variant, it is possible to choose M1 such that it is
for example associated with an oxide M1.sub.XO.sub.Y and M2 as a
metal, such that, in contact, the two materials react (under the
action of temperature, for example) in order to form a first metal
M1 and a second metal oxide M2.sub.ZO.sub.T (produced from the
second metal M2). Thus, therefore, when first modified nucleic acid
strands 100 comprising the metal M2 are first of all deposited, and
then second modified nucleic acid strands 100 comprising the metal
oxide M1.sub.XO.sub.Y, it will be possible to create a dual layer
composed of metal M1 on the insulator M2.sub.ZO.sub.T. According to
one example embodiment, copper will be chosen as the first metal M1
and aluminium as the second metal M2.
[0079] FIG. 7 illustrates a heating step configured to partially or
completely destroy the structure of the nucleic acid strand 100
and/or the chemical function 60 in order to promote the formation
of the coating 300 based on atoms 40 and/or nanoparticles 20 on the
three-dimensional surface of the substrate 200. The step of partial
or complete destruction of the structure of the nucleic acid strand
100 and/or of the chemical function 60 may be performed at low
temperature, preferably below 200.degree. C. In order to promote
the coalescence or aggregation of the metal-based nanoparticles 20
and/or metal atoms 40, an annealing can be carried out at a
temperature of between 200.degree. C. and 450.degree. C., or even
at a higher temperature compatible with the permissible thermal
budget and below approximately 800.degree. C. In order to densify
the metal-based coating 300, the step of grafting a modified
nucleic acid strand 100 and the heating step may be repeated.
[0080] According to an embodiment where it is then wished to
deposit a metal, a chemical (electroless) deposition is carried out
after the coating 300 obtained by the grafting of modified nucleic
acid strands 100. For example, gold could be deposited on gold
nanoparticles 20; the metal-based coating 300 being previously
formed from nanoparticles 20.
[0081] FIG. 8 illustrates the step of carrying out an
electrochemical deposition (ECD) on the metal-based coating
300.
[0082] FIG. 8 illustrates a view in section according to the prior
art of a through via of the TSV type filled in accordance with the
current methods. In the methods based on the use of a silicon
substrate 200, the succession of steps consisting of the production
of a through via comprises, at the end of the step of etching the
substrate 200, the step of depositing an insulator and the step of
depositing a layer that is a barrier to the diffusion of metal (for
example copper), a step consisting of covering and/or filling the
via with an electrical conductor (for example copper), generally by
electrodeposition. A chemical and mechanical polishing step may be
performed at the end of this concatenation with a view to
eliminating the excess metal on the surface of the substrate 200.
Thus the through via will emerge on a first face of the substrate
200 from which the etching of the cavity is performed. The through
via will be obtained after thinning of a second face of the
substrate 200, opposite to the first face.
[0083] FIGS. 9A and 9B illustrate an example of a three-dimensional
surface on which the metal-based coating 300 according to the
present invention can be produced while ensuring uniformity of the
layer and distribution over the entire three-dimensional surface of
the substrate 200. The majority of the traditional deposition
methods (of the CVD, ALD, PVD, etc. type) do not make it possible
to produce a uniform deposit on patterns. It proves to be actually
difficult to form a uniform coating on a three-dimensional surface
having hollow patterns and/or in relief. In a particularly
advantageous manner, the method according to the invention will
make it possible to produce a uniform metal-based coating 300
perfectly following the topography of the three-dimensional surface
of the substrate 200.
[0084] In FIG. 9A, the modified nucleic acid strands 100,
comprising at least one nanoparticle 20 and/or one atom 40 and at
least one chemical function 60, are fixed on the pretreated
hydrophilic or hydrophobic portions of the surface of the substrate
200 or on the grafting layer 250 of the three-dimensional surface
of the substrate 200.
[0085] FIG. 9B illustrates the coating 300 obtained after grafting
of the modified nucleic acid strands 100 on the pretreated portions
of the three-dimensional surface of the substrate 200.
Advantageously, the metal-based coating 300 covers all the flanks
and angles of the three-dimensional surface of the substrate 200
with the same thickness and the same uniformity.
[0086] FIG. 10A illustrates an example of a three-dimensional
surface of a substrate 200 on which a cavity was previously
produced. The flanks of the cavity are covered with a hydrophilic
or hydrophobic film, that is to say with the grafting layer 250,
for fixing the modified nucleic acid strands 100 comprising at
least one nanoparticle 20 and/or at least one atom 40 and at least
one chemical function 60. Advantageously, at the end of the method
according to the invention, the metal-based coating 300 is
deposited on all the flanks of the cavity formed in the substrate
200.
[0087] FIG. 10B illustrates an example of a three-dimensional
surface of a substrate 200 on which a cavity has previously been
produced. In order to make a localised deposition on a selective
portion of the substrate 200, a mask may advantageously be produced
by the overhanging over the cavity formed in the substrate 200.
Following an irradiation by ultraviolet rays, only the flanks of
the cavity protected from the rays are covered with modified
nucleic acid strands 100. When a surface is exposed to an
ultraviolet radiation, it has a tendency to become hydrophilic.
Thus, according to an embodiment in which the three-dimensional
surface of the substrate 200 is naturally or pretreated so as to be
hydrophobic, the chemical functions 60 chosen with a hydrophobic
nature will come to be fixed on the hydrophobic portions of the
three-dimensional surface. The portions exposed to ultraviolet
radiation, which have become hydrophilic, will no longer be able to
cooperate with the chemical function 60 and, consequently, the
modified nucleic acid strands 100 will not be able to be deposited
on the exposed portions. Advantageously, this embodiment makes it
possible to effect a selective grafting under irradiation by
ultraviolet rays. According to another embodiment where the
three-dimensional surface of the substrate 200 is naturally or
pretreated so as to be hydrophobic and the chemical functions 60
chosen with a hydrophilic nature, some hydrophobic portions of the
surface of the substrate 200, after irradiation by ultraviolet
radiation, will become hydrophilic and will therefore be able to
interact with the also hydrophilic chemical functions 60.
[0088] The present invention makes it possible to produce a
metallic or insulating coating 300 on a three-dimensional surface
comprising monolayers of nanoparticles 200 based on metal and/or
metal atoms 40. One of the advantages of the present invention
consists of the use of a wet method for effecting the deposition,
promoting a uniform and continuous deposition on a
three-dimensional surface of the substrate 200.
[0089] It therefore appears that it is possible to deposit
nanoparticles 20 based on metal (gold, nickel, for example) or
insulating nanoparticles (SiO.sub.2, TiO.sub.2, for example) on a
hydrophilic surface or a hydrophobic surface. The technique appears
to be very versatile and could therefore make it possible to graft
any type of nanoparticle 20 on any type of surface with, in some
cases, the possibility of localising the deposit under ultraviolet
irradiation through a photolithography mask.
[0090] The size of the nucleic acid strands 100, of around one
nanometre, makes it possible, in a particularly advantageous
fashion, to penetrate cavities with a high aspect ratio. Because of
the size of the strand, it therefore appears possible to have a
nanometric template for positioning nanoparticles 20 or atoms 40 on
surfaces with relief and in particular through vias with a high
aspect ratio, approaching 50:1.
[0091] Particularly advantageously, it is possible, under the
action of a magnetic field, to selectively and in a directed
fashion deposit modified nucleic acid strands 100 comprising at
least one ferromagnetic nanoparticle 20. A ferromagnetic material,
when it is immersed in a magnetic field, generates a new magnetic
field within it. This phenomenon is more commonly called
magnetisation.
[0092] The method according to the present invention opens the door
to high-density three-dimensional integration. This invention makes
it possible to collectively effect 3D (or even 2D also) deposits on
substrates 200 of the silicon or silicon-oxide type or based on
silica. It makes it possible in particular to produce high-density
TSV through vias in substrates where it is necessary to
electrically connect the substrates to each other. It applies to
the manufacture of microelectronic systems. According to the
invention, microelectronics means all microelectronic and
nanoelectronic techniques. In addition to the applications for the
deposition of coatings or layers described above, the multilayer
structures according to the invention advantageously can be used in
the form of capacitances as energy accumulators or filtering
elements in many electronic products such as integrated electrical
supplies, signal amplifiers and radio-frequency (RF) circuit
filters and for all kinds of domestic applications, or for the
motor industry and the telecommunications industry where
miniaturisation brings advantages of reliability and cost
reduction. The devices that can be formed can fit in
microelectromechanical (MEMS) and/or optical systems.
[0093] The present invention is not limited to the embodiments
described above but extends to any embodiment covered by the
claims. The invention does not apply solely to a three-dimensional
surface but also to a two-dimensional surface.
* * * * *