The present invention relates to a method for manufacturing
a mold tool to be used for forming a structured nano scale pattern on an object,
and which has an anti-adhesive layer with regard to the object.
The invention also relates to a mold tool to be used for
forming a structured nano scale pattern on an object and has an anti-adhesive layer
with regard to the object.
The present invention also relates to a storage medium
such as a CD or DVD or a hard disc.
A stamp is often used for the replication of nano scale
structures. The stamp imprints a pattern on a plate coated with a layer of a suitable
polymer, such as a thermoplastic. In order to avoid that the polymer sticks to the
surface of the stamp and contaminates said surface when the stamp is released from
the coated plate after the imprint process, it is necessary to provide an anti-adhesive
interface surface between the pattern equipped stamp and the polymer. Such an adhesion
can also damage the replicated pattern on the plate. A successful imprint thus requires
the stamp to be chemically and mechanically stable and to have a low adhesion to
R.W. Jaszewski et al describes in Microelectronic Engineering
35 (1997) 381-384 that the surface of the stamp can be covered with an ultra-thin,
anti-adhesive, layer of PTSE (polytetrafluorethene). The layer is precipitated either
by means of plasma polymerisation or ion sputtering from a plasma. The quality of
the stamp is reduced when the stamp is used for repeated hobbing according to Jaszewski
et al. The layer is obviously not stable enough.
WO 01/53889 describes one way to fasten a monomolecular,
anti-adhesive layer on a metal stamp. This method requires that the monomolecular
layer comprises a mercapto group capable to bond with the metal stamp and form a
The above mentioned monomolecular layer is however specifically
adapted to a particular surface and requires that the monomolecular layer comprises
a mercapto group capable of bonding with the metal stamp and form a metal sulphide.
In some applications the monomolecular layer does not have a sufficient adhesion
to the surface of the stamp and the respective surface of the form. This may on
one hand lead to that the monomolecular layer comes loose from the stamp wherein
the stamp must be repaired or discarded and on the other hand lead to that an object,
such as a DVD, to which a pattern shall be copied, gets damaged during the transition
of the pattern because of adhesion to the stamp.
WO00/00868 relates to various coatings, less than and approaching
monomolecular coatings, of persistent release materials comprising compounds of
the formula: RELEASE-M(X)>n-1<- RELEASE-M(X)>n-m-1< Q>m'< or RELEASE-M(OR)>n-1<-,
wherein RELEASE is a molecular chain of from 4 to 20 atoms in length, M is a metal
atom, semiconductor atom, or semimetal atom; X is halogen or cyano, especially Cl,
F, or Br; Q is hydrogen or alkyl group; R is hydrogen, alkyl or phenyl, preferably
hydrogen or alkyl of 1 to 4 carbon atoms. The coating usable for application on
a mold having a structured pattern, for use in a lithographic method and apparatus
for creating sub-25nm patterns on a substrate, in which the mold is pressed into
a thin film carried on the substrate.
US6,380,101 discloses a method of microcontact printing
to pattern a self-assembled monolayer (SAM) of an alkanephosphonic acid on a film
of indium zinc oxide (IZO). The SAM is robust enough to protect the underlying IZO
from wet chemical etching, and thus defines a pattern of IZO on the substrate. In
the microcontact printing process, a patterned, elastomeric stamp is inked with
a solution of octadecylphosphonic acid and brought into conformal contact with the
IZO surface. A SAM of alkanesulfonic acid forms where the stamp and the surface
make contact; the rest remains underivatized. The stamp is then removed from the
surface. Etching the sample in aqueous oxalic acid removes the unprotected areas,
while the areas protected by the SAM remain in place.
Summary of the invention
The object of the present invention is to eliminate or
alleviate the above mentioned drawbacks and to provide a method of manufacturing
a mold tool having an anti-adhesive layer which is stable and has good anti-adhesive
characteristics. The object is obtained according to the invention by a method of
manufacturing a mold tool according to claim 1.
Another object of the present invention is to provide a
mold tool having an anti-adhesive layer, which is stable and has good anti-adhesive
characteristics. This object is obtained by means of a mold tool according to claim
Further advantages and features of the invention are apparent
from the description below and the following claims.
Brief descriptions of the drawings
The invention will now be described in more detail by way
of non-limiting examples, with reference to the accompanying drawings.
Detailed description of preferred embodiments
- Fig. 1 is a cross-section showing a portion of a nickellic stamp equipped with
a metal layer to be used for imprint of DVDs.
- Fig. 2 is an enlargement of the portion II shown in Fig. 1 and shows the metal
layer with an anti-adhesive layer attached thereon.
An illustrative, non-limiting example of a structured nano
scale pattern transfer is nano hobbing lithography, also called nano-imprint lithography,
which is a technique for mass production of nano structures. A mold tool in form
of a stamp is provided with a nano scale pattern on its surface. The stamp is heated
and pressed towards a substrate having a polymer layer wherein the pattern is transferred
to the polymer layer. Nano imprint is further described in WO 01/69317 and US 5,772,905.
The stamp according to the present invention can also be used in other imprint processes
and with or without heating before pressing.
Another example of nano scale pattern transfer is the manufacturing
of CDs and DVDs. The method for manufacturing CDs is described e.g. in "The compact
disc handbook" by C. Pohlmann, second edition, A-R Editions Inc., ISBN 0-89579-300-8,
p. 277. This manufacturing method makes use of a mold in which a board of polycarbonate
is molded. A mold tool in form of a nickellic stamp with a pattern is inserted into
a wall in the mold to form a desired pattern on the CD or DVD.
The wording "nano scale" shall not be interpreted as to
only concern structures in the submicrometer field, e.g. structures with a size
of 1-1000 nm. A stamp often has a pattern with structures in both the submicrometer
field and structures with a size up to 100 micrometer and larger, such as up to
approximately 5 mm. The present invention is suitable for stamps comprising structures
in the submicrometer range and/or ranging between 1-100 micrometer. The invention
gives the most efficient result for structures in the submicrometer range since
these are relatively sensitive to adhesion when the stamp is released.
The wording "monomolecular layer" shall in this description
be interpreted as a layer having a thickness corresponding to the length of one
molecule. The molecule being integral part of the monomolecular layer is in the
present invention elongated and is chemically bonded in one end with a surface.
The molecules bonded with the surface have no or only a very low tendency to adhere,
chemically or physically, to other molecules or other surfaces.
A stamp to be used for forming a nano scale pattern, which
has a very stable and durable anti-adhesive layer, is provided by the present invention.
The wording "forming of pattern" can, when used in the present application, mean
that the stamp is used for imprinting a pattern into an object, or that the stamp
is used as a wall in a mold in which an object, to obtain the pattern, is molded.
In a first step a stamp blank, the surface of which has
been provided with a structured pattern in a known manner, e.g. by etching or molding
in a mold having a pattern, is used. Suitable materials for the stamp blank are
e.g. nickel, chromium, silicon, silicon dioxide, silicon carbide, tungsten oxide,
diamond, different polymers, semi-conducting materials, such as GaAs, InP, GaInP,
GaInAs, ZnS, and mixtures of these materials. Particularly preferred materials for
the manufacturing of a stamp are silicon and nickel, since these materials are easily
patterned and have high hardness and are durable. The stamp blank may also comprise
a layer of nickel, which has been applied on a base plate of silicon.
The patterned surface of the stamp blank is washed after
the patterning, preferably with one or more suitable organical solvents, and dried.
After the wash a thin metal layer is applied on the patterned
surface of the stamp blank. The metal layer can preferably be applied by using methods
known from other technical fields for the application of thin metal layers on surfaces.
Different precipitation methods of metal layers are described e.g. in "Handbook
of deposition technologies for films and coatings: Science, technology and applications",
edited by Rointan F. Bunshah, second ed., Noyes Publications, Westwood, NJ, USA
1994, ISBN 0-8155-1337-2. The preferred methods for the present invention are coating
with evaporated metal in vacuum, which is described in chapter 4 in the above handbook,
and sputtering, which is described in chapter 5 in the above handbook. The thickness
of the metal layer can be measured by using the methods described in chapter 4 and
5, respectively, in the above handbook.
In case the stamp is being coated with evaporated metal
in vacuum, the patterned stamp blank is preferably placed on a rotating plate in
an oven, which is evacuated to a pressure of e.g. 1-100 mPa. The stamp blank preferably
has a temperature close to room temperature. The oven is thereafter fed with evaporated
metal, which condenses on the surface of the stamp blank forming a thin layer. The
rotation of the stamp blank during the coating makes the thickness of the layer
substantially equal on all portions of the pattern of the stamp blank. The thickness
of the metal layer is measured during the coating by using a calibrated, vibrating
crystal positioned inside the oven. A metal layer will be deposited also on the
crystal, which then obtains a different frequency. The difference in frequency is
used as a measure of the thickness of the metal layer.
In case of the metal layer being deposited by means of
sputtering, e.g. magnetron sputtering, the stamp blank and a solid piece of the
metal forming the layer are placed in a chamber comprising an inert gas, such as
argon, at a very low pressure, such as 1-100 mPa. The inert gas is ionised and a
magnetron sends inert gas ions, in this case argon ions, towards the metal piece.
The argon ions knock out atoms from the surface of the metal piece, which in turn
are precipitated on the surface of the stamp blank. When the precipitated metal
layer on the surface of the stamp has become thick enough the deposition is concluded
and the thereby formed stamp is taken out of the oven and the chamber respectively.
The metal layer shall thereafter be oxidised. The oxidation
can either take place spontaneously or be achieved by suitable treatment depending
on the metal in question. Spontaneous oxidation can take place by contact with surrounding
air, filtered surrounding air, pure oxygen gas or a mixture of oxygen gas and nitrogen
gas. A suitable treatment may consist of treating the metal with an oxygen plasma
or anodically. Treating a metal surface with an oxygen plasma is described for instance
in the above-mentioned "Handbook of deposition technologies...", chapter "Surface
preparation for film and coating deposition processes", pages 82-130, especially
on pages 108-120.
The metal being an integral part of the metal layer must
be such that it forms chemically and mechanically stable oxides, to which an anti-adhesive
layer can be bonded, when said metal oxidises. The wording "chemically stable" in
this description means that the oxidation number of the oxidised metal must not
change at the different pressures, temperatures and chemical conditions present
during the manufacturing of the anti-adhesive layer on one hand nor during use of
the stamp for nano-imprint lithography or molding on the other. The wording "mechanically
stable" means in this description that the oxidised metal must not come loose from
the stamp blank or in another way change its form at those pressures and temperatures
being present during the manufacturing of the anti-adhesive layer on one hand nor
during the use of the stamp for nano-imprint lithography or molding on the other.
The metal should have a stable oxidation number. Metals
with a preferred oxidation number substantially only form one type of oxide with
a chemically stable oxidation number, which is not altered during the manufacturing
of the anti-adhesive layer or during use of the stamp for nano-imprint lithography
or during molding of objects with structured nano scale patterns. Some metals may
have a catalytical effect, which seems to have an oxidational effect on carbon chains
in the anti-adhesive layer at those conditions being present during the above-mentioned
use. Examples of metals with probable catalytical effect are platina, Pa, and palladium,
Pd, but also to some extent other metals such as nickel, Ni. An indication of this
is disclosed in "Preparation of novel Raney-Ni catalysts and characterization by
XRD, SEM and XPS", Hao Lei et al, Applied Catalysis A: General 214 (2001) 69-76.
Raney-nickel is a sponge-like nickel material having a catalytic effect and can
among other things break down hydrocarbon compounds. A structured nanoscale nickel
surface can be regarded to have some similarities with Raney-nickel and may therefore
have a breakdown effect on a monomolecular layer. The risk is therefore considerable
that a monomolecular layer bonded with e.g. a stamp having a nickel surface comes
loose from the nickel surface. When a stamp blank is manufactured of many different
materials, e.g. a stamp blank manufactured of a metal alloy or a stamp blank manufactured
of many different materials, the metal layer will provide the effect that the surface
layer gets the same and furthermore predictable characteristics throughout the entire
surface of the stamp.
Another important characteristic of the metal layer is
that it must have a good adhesive characteristic to the material of the stamp blank
The formed oxide should have good resistance so as to withstand
repeated stamping. Even more preferable is that the oxide is so hard that a hard
surface layer is formed which is durable and pressure resistant. The hardness of
the oxide layer is preferably at least 4 on Moh's scale, even more preferable at
Metals being specifically suitable for deposition of the
surface of the stamp blank are titanium, Ti, zirkonium, Zr, niobium, Nb, tantalum,
Ta and aluminium, Al. The monomolecular layer seems to have best adherence with
the metal layer if the bond between the molecules and the metal layer has a substantially
covalent structure. B.F. Levine has in Phys, Rev B 7, 2591, (1973) made measurements
of Phillips-ionicity. According to these measurements the ionicity for NiO is 0,841,
for Al2O3 0,796 and for TiO2 0,686. A possible
interpretation of these results is that TiO2 has the least ionic characteristic
and could therefore give rise to bonds with a more covalent characteristic than
NiO. Thus, this could also be an explanation of why a nickel surface is not completely
suitable to maintain a monomolecular layer.
Titanium forms stable titanium oxide during contact with
surrounding air, which can be in form of TiO2 and/or TiO(OH)2
in different mutual relationships depending on humidity, temperature etc. When the
layer of titanium has become dry, as is the case for the below described bonding
of an anti-adhesive layer, there is almost only TiO2 in the titanium
dioxide. After a short contact with the surrounding air there is almost only quadrivalent,
Ti+IV and thus forms a stable oxide, being substantially covalent regarding
the bonding characteristic. Zirkonium, Zr, forms in a similar manner stable zirkonium
oxide, which can be represented by ZrO2 in which zirkonium has the completely
outweighing oxidation number +IV. Niobium, Nb, forms stable Nb2O5
during contact with surrounding air. Tantalum, Ta, forms stable Ta2O5
during contact with surrounding air. Tantalum and niobium have in these oxides the
oxidation number +V, respectively. Aluminium forms stable aluminium oxide during
contact with surrounding air, said aluminium oxide is presumed to be in the form
of Al2O3 in which the aluminium is trivalent, Al+III.
The metal should form covalent oxides since this often means that the oxide layer
gets harder than is the case for ionical oxides. Titanium and aluminium are therefore
particularly suitable metals.
In some cases it is appropriate to remove possible oxide
from the surface of the stamp blank by treatment in a reducing environment before
the metal layer is applied on this surface in order to achieve the best possible
adhesion. It seems, however, that some metals, e.g. titanium and aluminium, can
react with the oxygen of the oxide of the stamp blank and form a metal layer which
has good adhesion to the surface of the stamp blank even if the surface of the stamp
blank is not free from oxide when the metal layer is applied.
The thickness of the metal layer should be such that a
homogenous and stable oxide layer is formed on the surface of the metal layer while
the metal layer is attached to the underlying stamp blank in a stable way. A metal
layer being too thick could effect the pattern of the stamp blank so that the desired
result would not be obtained when imprinting with the prepared stamp. It is, however,
often possible to take into consideration that a metal layer of a certain thickness
is to be precipitated on the stamp blank and adapt the structures of the stamp blank
in accordance with said precipitation when forming the surface of the stamp blank.
Another reason why the metal layer should not be too thick is that cracks may arise
in the metal layer during heating of the stamp if the stamp blank and the metal
layer do not have the same coefficient of thermal expansion. Since the stamp is
heated during the nano imprint process and the molding process, respectively, a
thick metal layer and a difference regarding the coefficient of thermal expansion
resulting in the formation of cracks would effect the useful life of the stamp negatively.
The metal layer has a suitable thickness of 1-300 nm, more preferably 1-100 nm and
2-20 nm is most preferred.
It is suitable for some stamp blanks that the metal layer
has such a thickness that it in the interface towards the surface of the stamp blank
also after the oxidation is present in metallic form in order to provide good adhesion
to said stamp blank. If the metal layer is too thin atoms of oxygen can roam through
the metal layer down to the stamp blank and oxidise the same, which in some cases
is negative for the adhesion of the metal layer to the surface of the stamp blank.
In the case of e.g. titanium dioxide it has been shown that the titanium dioxide
layer obtains a thickness of about 5 nm after oxidation in surrounding air according
to the above. When the metal layer is a titanium layer it is often appropriate for
the titanium layer to have a thickness exceeding 5 nm, preferably about 10 nm. A
layer of aluminium oxide formed by oxidation in surrounding air has a thickness
of at least about 2 nm. A layer of aluminium oxide has therefore a total appropriate
thickness of at least about 5 nm.
In other cases, such as when a layer of titanium or aluminium
is applied on a stamp blank of nickel, also the oxide, titanium dioxide or aluminium
oxide in said case, will have a good enough adhesion to the stamp blank. In case
of a titanium layer on a nickellic stamp blank the minimum thickness of the titanium
layer is thus determined by the thickness required for the formed titanium dioxide
layer to be durable enough and to cover the entire surface of the stamp blank. In
case of a stamp blank of nickel the layer of titanium or aluminium should have a
thickness of at least about 2 nm.
An anti-adhesive layer is thereafter attached to the oxidised
metal layer. In a preferred embodiment of the invention a first and second reagent
is used. The first reagent is bonded with the metal layer at a first reaction, wherein
the second reagent is bonded to the first reagent at a second reaction. The reason
for this embodiment to be preferred is that it is quite a simple task to find commercial
compounds suitable to be used as a first and second reagent, respectively.
A first reagent to be used during the manufacturing of
the stamp has at least two functional groups according to the invention. A first
functional group has the purpose to bond with the surface of the metal layer. An
example of such a first functional group is a silane group with the chemical formula
(BO)3-nR'nSi-.The silane group can bond with the metal layer
by means of a group B 1 on the surface of the metal layer, wherein B 1 usually is
a M-O- or a M-OH where M is a metal atom comprised in the metal layer. In this application
the wording "silane group" also means the above-mentioned group after being bonded
with the stamp. The silane group may comprise n aliphatical groups R'and 3-n reactive
bonding groups B0, where n=0, 1 or 2. B0 is suitably a group capable of hydrolysis.
Suitable reactive bonding groups B0 are chlorine (C1) or alcoxi groups, preferably
C1-4alcoxi groups, more preferably C1-2 alcoxi groups, such
as ethoxy groups (EtO), methoxy groups (MeO). The aliphatic groups R' are preferably,
to the extent they are present at all, short saturated aliphatical groups, preferably
C1-4 alkylical groups, even more preferable C1-2 alkylical
groups, such as ethyl groups and methyl groups. When n=1 or 2 and R' is a methyl
group a smaller bonding area is obtained, e.g. the monomolecular layer can be packed
with a higher density. The strongest bond with the surface is however obtained when
n=0, e.g. when the silane group has three reactive bonding groups B0. An example
of such a suitable first functional group is thus:
Another example of a suitable first functional group is
a phosphate group, - H2PO4.
The first reagent has a second functional group X1, preferably
chosen so as to not react or only to a limited extent react with the surface of
the metal layer. Such a functional group has the advantage that a homogeneous monomolecular
layer having a well-defined group at one end is obtained when the surface of the
metal layer is treated with the first reagent. A suitable group X 1 is thus a group,
which can not be hydrolysed. In addition, the group X1 should not react with the
first functional group. Suitable groups of X1 are e.g. -SH, NH2, and
-OH. When X1 is a NH2-group or an -OH-group then B0 must not be chlorine,
since this would cause undesirable reactions of polymerisation.
The first and second functional groups of the first reagent
are advisably attached to opposite ends of a carbon compound R1. Such a carbon compound
R1 is preferably a carbon chain, lacking branches or having only short branches,
which advisably have a length of 1-6 carbon atoms, more preferably 1-3 carbon atoms.
The carbon chain is advisably a saturated, aliphatical carbon chain. Non-saturated
carbon chains may participate in undesirable side reactions and heavily branched
or cyclic compounds occupy an unnecessary amount of space on the surface of the
stamp, thereby reducing the density of the anti-adhesive functionality on this surface.
The second functional group X1 may effect the electron
density in the nearest positioned atoms in the molecule, which can give rise to
undesirable effects on the first functional group. It is therefore advisable that
the R1 group is designed so as to "isolate" the group X1 from the first functional
group from an electron density point of view. In case of aliphatical, saturated
carbon chains the CH2-group being closest to X1 is strongly effected,
the next-coming CH2-group effected to some extent while the third CH2-group
is substantially unaffected by X1. The group R1 is advisably not substituted in
order not to effect the first and second functional groups in a negative way. R1
has thus advisably a length from the first to the second functional group of 1-10
carbon atoms, preferably 2-5 carbon atoms and most preferably 3 carbon atoms.
It is preferable to choose a first reagent that fulfils
the above-described criteria and which is commercially available. Example of a preferred
first reagent is thus mercaptopropyltriethoxysilane:
The second reagent comprises a first portion X2, supposed
to bond with the X1-group of the first reagent, and a second portion R2, having
an anti-adhesive functionality.
The group X2 can be chosen in order to be suitable for
reacting with the X1-group present in the first reagent. The reaction shall result
in a bond being strong enough to maintain the anti-adhesive functionality at the
surface of the stamp. The bond, which is formed between X1 and X2, is, however,
weaker than the rest of the bonds in the monomolecular layer. A possible break in
the molecule chain will then take place at a predictable position, e.g. between
X1 and X2. Examples of suitable combinations of X1 and X2 are: X1 = -SH-group and
X2 = -SH-group, which can form a sulphur bridge, X1 = NH2-group and X2
= Cl- (C=O)-, which can form a peptide bond, and X1= -OH and X2= HO- (C=O)-, which
can form an ester. Particularly preferable is that both X1 and X2 are -SH-groups,
since these form a bond strong enough to maintain the anti-adhesive functionality,
but is weaker than e.g. bonds between carbon atoms in the molecule chain, between
carbon atoms and sulphur atoms and between a silane group and the surface of the
The group R2 preferably comprises fluorine atoms, which
give the desired anti-adhesive functionality. Particularly advisable is that R2
has a free end group, comprising a carbon atom to which one or several fluorine
atoms are bonded. The R2-group is preferably a fluorinated, aliphatical, saturated
carbon chain. Unsaturated carbon chains can participate in undesirable side reactions
and heavily branched or cyclical compounds occupy an unnecessary large amount of
space, which reduces the density of the anti-adhesive functionality.
The fluorine atoms will effect the electron density in
the nearest positioned atoms in the molecule, which can give undesirable effects
for the bond between X2 and X1. It is therefore advisable that the R2-group is formed
in such a way that it "isolates" the X2-group from the fluorine atoms from an electron
density point of view. In case of aliphatical, saturated carbon chains the CH2-group
being closest to a carbon atom, which is substituted with fluorine, is strongly
effected, while the next-coming CH2-group is almost unaffected. The R2-group
has advisably at least 1 and preferably 2 CH2-groups in line nearest
the X2-group. In case of longer chains of CH2-groups the risk of breakage
increases. The number of CH2-groups in line should thus not be more than
R2 has preferably at least one perfluorated carbon atom.
This carbon atom is preferably the end group of the R2-group, e.g. a CF3-group.
Additional perfluorated carbon atoms give a better anti-adhesive functionality.
Very long carbon chains increase the risk of breakage of the chain and also makes
the anti-adhesive layer less stable, when the carbon chains can change their angle
in relation to the surface. R2 has thus advisably 1-12 perfluorated carbon atoms,
preferably 2-8 perfluorated carbon atoms and most preferably 3-6 perfluorated carbon
It is suitable to choose a second reagent that fulfils
the above-described criteria and which is commercially available. Examples of such
preferred second reagents are thus 1H, 1H, 2H, 2H-perfluorooctanethiol:
SH - (CH2)2
- (CF2)5 - CF3
The oxidised metal layer is washed e.g. by using 1-4 organical
solvents, e.g. trichloroethylene, ethanol, acetone and isopropanol, after each other.
The stamp is thereafter treated with the first reagent. This first treatment can
be performed either in a liquid phase or in a gas phase.
At a first treatment in a liquid phase the stamp is placed
in a vessel for about 1-5 h, comprising about 0,1-1 % of the first reagent in an
organical solvent, advisably an alkane not comprising water at room temperature.
The stamp is thereafter washed advisably by using a series of 1-4 organical solvents
similar to those mentioned above in order to remove such compounds which are not
covalently bonded with the surface.
In a first treatment in a gas phase the stamp is placed
in an oven having a nitrogen atmosphere comprising no water and a temperature of
about 50-250°C, preferably about 150-220°C, and having a pressure at which
the first reagent is present in a gas phase, usually a pressure of about 0.5-20
kPa, preferably about 1-3 kPa. The precise combination of temperature and pressure
is chosen so that the first reagent will certainly be present in a gas phase. The
first reagent is thereafter conveyed into the oven, e.g. by using a syringe, where
it is evaporated and is left to react with the stamp for about 0.5-10 h. The stamp
is thereafter removed from the oven and is left to cool down and is thereafter washed
with a series of organical solvents according to the description above.
The gas phase reaction is much more complicated to perform
than the relatively simple liquid phase reaction. The gas phase reaction, however,
often gives a much more homogenous monolayer on the surface of the stamp and is
therefore to prefer in many cases.
In case of a stamp blank having a metal layer of titanium
and the above-mentioned preferred first reagent can thus the following result be
obtained after the first treatment:
The bond between the metal layer and the actual structure
of the silane group and the residue product, ethane of ethanol in the above example,
may be effected to some extent depending on the original structure of the surface.
The bond between the titanium surface and the silane group is assumed to look like
(Ti)3Si or (Ti-O)3Si, but the precise appearance is not completely
established. The above formulas thereby intend to denote a silane group bonded with
a metal surface independently of the precise appearance of the actual bond.
The washed stamp is thereafter treated with the second
reagent. This second treatment can be carried out either in a liquid phase or in
a gas phase.
In a second treatment being carried out in a liquid phase
the stamp is placed in a vessel comprising a suitable solvent, e.g. an alkane comprising
no water, with about 0.1-5 % of the second reagent at room temperature. The reaction
is left to proceed for about 6-24 h and the stamp is thereafter taken up and made
clean by inserting it in one or several baths in a suitable, organical solvent,
e.g. the above-mentioned alkane. The stamp is thereafter dried and then ready to
use for nano imprinting.
In a second treatment being carried out in a gas phase
the stamp is placed in an oven with a nitrogen atmosphere comprising no water and
having a temperature of about 50-200°C, preferably about 70-120°C. The
oven is evacuated to a low pressure, suitably about 1-20 kPa, even more preferably
about 5-10 kPa. The precise combination of temperature and pressure is chosen in
such a way so that the second reagent for certain will be present in a gas phase.
The second reagent is then conveyed into the oven, e.g. by using a syringe, where
it is evaporated and reacts for about 1-10 h with the mono layer on the surface
of the stamp. The stamp is removed from the oven, is left to cool down and is thereafter
made clean in the same way as described above and is thereafter ready to use for
At the second treatment, the surface of the stamp is covered
with a monomolecular layer from the beginning. Therefore, a gas phase reaction does
usually not give any advantage regarding the homogeneity of the layer. The reaction
in a liquid phase is much less complicated to perform and is therefore normally
to prefer at the second treatment. In case of very small nano structures a gas phase
reaction is sometimes required to obtain a resulting layer having a thickness being
homogeneous enough, after the reaction.
In a reaction between the above described product after
the first treatment and the above described preferred second reagents can thus the
following result be obtained after the second treatment when the X1- and X2-groups
have reacted and formed a group Q in form of S-S:
When the first functional group is a phosphate group in
stead of a silane group can e.g. a first reagent in form of a mercaptopropylphosporic
acid be used:
When the first reagent has been attached to the metal layer
according to any of the above described procedures, the above-mentioned second reagent
1H, 1H, 2H, 2H-perfluorooctanethiol can be used in a second treatment as described
above in order to obtain the following anti-adhesive layer on the surface of the
metal layer (Me in the formula below denotes a simple metal, such as Ti):
One way to attach a phosphate group to a metal oxide is
described in "Surface Modifications for optical Biosensor Applications" by Rolf
Hofer, Diss. ETH No. 13873, Zürich 2000. According to this document the metal
oxide is treated with an organical solvent comprising phosphate groups, wherein
the phosphate groups are chemically bonded with the metal oxide.
In another embodiment the anti-adhesive layer is formed
by directly attaching a ready molecule chain on the surface of the stamp, e.g. a
molecule chain comprising a group capable of bonding with the surface of the stamp
and at least a fluorine-comprising group. A ready molecule chain means that the
anti-adhesive layer is attached to the surface of the stamp in a single step, which
facilitates the practical operation. Attaching a complete ready molecule chain in
one single step is carried out in substantially the same way and under the same
conditions as have been described above for the first treatment. The resulting anti-adhesive
layer can in a metal layer of titanium e.g. obtain the following appearance:
A suitable manufacturing process for a stamp can thus comprise
the following steps:
- a) a nickellic stamp blank is provided with a nano pattern on its surface in
a known way
- b) the stamp blank is washed in a known way with a mixture comprising 15 vol-%
NH3, 70 vol-% H2O and 15 vol-% H2O2
and is thereafter dried
- c) the stamp blank is placed in a vacuum oven, wherein evaporated metal is furnished
and precipitated on the surface of the stamp
- d) the stamp thereby equipped with a metal layer is taken out of the oven, wherein
the surface of the metal layer is brought to oxidise by contact with filtered surrounding
- e) the oxidised metal layer of the stamp is provided with an anti-adhesive layer
by a reaction in one or several steps
- f) the stamp is washed in a known way using a series of organical solvents,
thereafter dried and is then ready for use e.g. for nano-imprint lithography or
for molding objects with nano patterns.
There are also other ways to manufacture a stamp according
to the invention. One possibility is to use a molecule, which has a carboxyl group
as a first functional group instead of the above-mentioned phosphate- and silane
groups. The carboxyl group, however, does not bond with an oxidised metal layer
of aluminium or titanium in a stable enough way. If the surface of the metal layer
on the other hand is treated with a thin layer (corresponding to a single or a couple
of atom layers) of zirconium oxide the bond of the carboxyl groups will become very
good and a strong anti-adhesive layer can be obtained. A layer of zirconium oxide
can also be used in order to strengthen the bond of phosphate groups on a metal
layer of TiO2 or Al2O3. A layer of zirconium oxide
can for instance be precipitated on the metal layer of TiO2 or Al2O3
by putting the stamp in a reaction chamber being evacuated down to 0.013 Pa. Distilled
(t-butyl-O)4 Zr is furnished to the reactor. When a zirconium layer with
a desired thickness has been obtained on the stamp the stamp is taken out from the
reactor, it is washed and treated as described above with a suitable reagent for
the formation of an anti-adhesive layer.
Another possibility to manufacture a stamp according to
the invention is to treat the oxidised metal layer with a super critical liquid
comprising a suitable molecule, e.g. any of the above described reagents, in a solution.
Such a liquid is super critical CO2. The low viscosity and the high rate
of diffusion of super critical CO2 makes it easy for the reagent to be
transported into the structured nano scaled patterns of the stamp and bond with
the oxidised metal layer. For instance can a large surplus of a suitable molecule,
e.g. any of the described reagents, be dissolved in a pressure reactor with super
critical CO2 at a pressure of 7500 psi (500 bar) and a temperature of
150°C. The stamp is placed in the pressure reactor for a few minutes. The stamp
equipped with a monemolecular layer is thereafter taken out of the pressure reactor
and washed in a following step using a suitable solvent.
A less preferable possibility is to dip the stamp equipped
with the oxidised metal layer in a solution comprising a suitable molecule, e.g.
any of the above described reagents. A solvent that can be used is tetrahydrofurane
(THF). Dipping into a solvent is however very sensitive to possible residues of
water in the solvent and the risk is quite extensive that the anti-adhesive layer
will not get the desired quality. The consumption of reagents often gets quite large.
The anti-adhesive layer is advisably monomolecular. However,
in some cases, a layer can be used having a certain polymerisation on the surface
of the layer.
Detailed description of a preferred embodiment
Fig. 1 shows a stamp 1 to be used for nano-imprint lithography.
The stamp 1 has a stamp blank 2 of nickel. The stamp blank 2 has been manufactured
by electroplating of a structured silicon disk and thereby obtained a number of
protrusions, in Fig. 1 schematically shown as one protrusion having a height HU
of about 200 nm and a width BU of about 200 nm. A titanium layer 6 has been applied
on the surface 8 of the stamp blank 2 by the above-described evaporation in vacuum.
The titanium layer 6 has a total thickness HT of 10 nm. The titanium layer 6 has
formed an oxide film 10 when in contact with the filtered surrounding air, as is
best seen in Fig. 2. The oxide film 10 has a thickness HO of about 5 nm. Under the
oxide film 10 titanium is still present in a metallic form and forms a metallical
layer 12, which holds the titanium layer 6 to the surface 8 of the stamp.
On the surface 14 of the oxide film 10 exposed to the surroundings
there is a monomolecular anti-adhesive layer, in Fig. 2 schematically illustrated
as 16. The anti-adhesive layer 16 has been manufactured by means of the above first
and second treatments. Each molecule 18 in the anti-adhesive layer 16 thus comprises
a silane group 20, bonded with the oxide film 10, and a group comprising fluorine,
in Fig. 2 schematically illustrated as 22.
When the stamp 1 is used to imprint a pattern in a DVD
blank 24 of polycarbonate both the stamp 1 as well as the DVD blank 24 are heated,
wherein the protrusions 4 are pressed into the soft blank 24. The fluoronized alkyl
groups 22 do not attach to the stamp 24 and give thus the effect that the stamp
1 after the imprint process can be released from the blank 24 quite easily without
sticking to it.
It is understood that many modifications of the above-described
embodiment are possible within the scope of the invention as defined by the following
claims. Thus the method and the mold tool can be used for the manufacturing of a
wide range of nano scale structures. The mold tool can either be pressed into a
substrate on an object or be used as an integral part of a mold in which a structured
nano scale pattern is to be molded. Integrated circuits, micro scale devices, magnetic
storage media and optical storage media constitute non-limiting examples of such
objects. Examples of optical storage media are, in addition to the above-mentioned
CDs and DVDs, also future generations optical storage media. These storing media
are expected to have much smaller structures than for instance DVDs and will thus
require less adhesion between the mold tool and for instance a polymer on the surface
of the medium.
A stamp blank of nickel was used to make a stamp blank,
which stamp blank was produced by electro-plating of a structured silicon disc for
forming a structured nano scale pattern suitable for the production of optical storage
media, such as CDs and DVDs. The pattern had protrusions with a typical width of
200-600 nm and a height of 150 nm. The stamp blank was washed with a mixture comprising
15 vol-% NH3, 70 vol-% H2O and 15 vol-% H2O2.
The stamp blank was thereafter placed in an oven, which was evacuated to a pressure
of 0.013 Pa. The oven was thereafter furnished with evaporated titanium during measurement
of the thickness of the titanium layer on the stamp blank. When the layer had a
thickness of about 10 nm the treatment was stopped and the stamp equipped with a
titanium layer was taken out of the oven. When the stamp was taken out into the
air of the room an almost immediate oxidation of the surface of the titanium layer
The stamp was thereafter washed with organical washing
means in three steps comprising substances in the following order trichloroethylene,
acetone and isopropanol. Each step had a duration of about 1 minute. The stamp was
thereafter dried in nitrogen atmosphere.
The stamp was thereafter brought into a so-called glove
box filled with nitrogen gas at atmospheric pressure. The concentration of both
oxygen gas, O2, as well as vapor, H2O, was under 1 ppm in
the glove box. The stamp was placed in a petri dish, which had a volume of 20 ml.
The petri dish had been passivated beforehand by treatment with dimethyl-dichloro-silane
(10 % solution in dichloro methane) in order not to react with the furnished reagent.
The petri dish was placed on a heating plate in the glove box, wherein a temperature
of 250°C was tuned in for the heat plate. 10 µl of tridecafluoro-(1,1,2,2)-tetrahydrooctyl-trichloro
silane (also called F13-TCS), was injected into the petri dish, evaporated
and was thereafter left to react with the stamp during 2 hours. The stamp was thereafter
taken out of the oven, was left to cool down, was washed with hexane in three consecutive
baths and was thereafter dried with nitrogen gas.
The stamp was thereafter used for nano-imprint lithography
for transferring a pattern to a plate covered with a layer of thermoplastic. No
adhesion of thermoplastic to the stamp could be detected.
A stamp was equipped with a titanium layer and was washed
in accordance with Example 1. The washed stamp was brought into a glass reactor
(standard glass reactor from Schott GmbH, DE), which had been passivated beforehand
by using dimethyl-dichloro silane according to the description above. Pure nitrogen
gas (99.99 %) was furnished through one of the reactor openings and was left to
flush through the reactor, wherein nitrogen gas and remaining air were flushed out
through another opening. After flushing for 10 minutes the reactor was evacuated
to a pressure of <100 Pa in order to further decrease the amount of oxygen and
water steam. The evacuated reactor was heated to 250°C in a heat bath and thereafter
10 µl F13-TCS was furnished through an inlet. The stamp was taken
out from the reactor after 2 hours and was after the corresponding wash according
to the one in Example 1 ready to use.
A stamp was provided with a titanium layer and washed according
to Example 1. The washed stamp was placed in a cup. The cup comprised a huge surplus
of F13-TCS in water free hexane. After 16 hours at 50°C the stamp
was taken out and washed with hexane in three consecutive baths and was thereafter
dried with nitrogen gas.
In trials with nano-imprint lithography similar to the
trials in Example 1 some deformation of the thermoplastic of the structure of the
plate could be observed. This implies that the anti-adhesive layer did not become
completely smooth, probably due to some polymerisation caused by water residues.