Process for fabricating a device

The invention is directed to a process for fabricating an integrated circuit. An imaging layer is deposited on a substrate. The imaging layer is an energy sensitive resist material. The energy sensitive resist material contains moieties that preferentially bind to refractory material. A latent image of a pattern is introduced into the imaging layer by patternwise exposing the imaging layer to energy. The patternwise exposure introduces a selectivity into the resist material that is exploited to bind refractory material preferentially to either the exposed resist material or the unexposed resist material, but not both. The refractory material forms an etch mask over the resist material to which it preferentially binds. This etch mask is then used to transfer a pattern that corresponds to the latent image into the substrate.

FIELD OF THE INVENTION 
The invention is directed to the fabrication of integrated circuits and the 
like devices, and in particular, fabrication using lithographic processes. 
ART BACKGROUND 
Design rules for integrated circuit fabrication are becoming increasingly 
fine. Design rules of 0.5 .mu.m are being replaced by design rules that 
are less than 0.5 .mu.m. These increasingly fine design rules require 
processes which can delineate features in the integrated circuit with the 
required accuracy. 
Lithographic processes are used during the fabrication of integrated 
circuits. A lithographic process employs energy that is introduced onto 
selected portions of an energy sensitive resist material (imaging layer) 
overlying a substrate. One way in which energy is introduced into selected 
portions of the resist is through openings in a mask substrate interposed 
between the energy source and the resist material. These openings in the 
mask substrate define the pattern. The pattern is transferred into the 
resist material by the energy that is permitted to pass through the 
openings in the mask substrate and into the resist. Thus, it is an image 
of the pattern defined by the mask substrate that is transferred into the 
resist material. 
After the image is transferred into the resist material, the resist 
material is developed to form a pattern. The pattern is then transferred 
by etching into the substrate underlying the resist material. Once the 
pattern is incorporated into the substrate, it becomes a feature of the 
integrated circuit. 
The energy used to expose the resist material, the composition of the 
resist material, the thickness of the resist material, and many other 
factors affect the ability of a lithographic process to delineate a 
feature in a substrate. The smaller the design rule, the more precisely 
the feature must be delineated. 
Current lithographic processes use solution-developed resist materials. 
However, as design rules decrease to 0.25 .mu.m, 0.18 .mu.m, and smaller, 
lithographic processes that use dry-developed resists are becoming more 
attractive. Although lithographic processes that use dry-developed resists 
usually have more processing steps, these processes offer certain 
advantages when used for fabricating devices subject to these smaller 
design rules. These advantages include minimized linewidth variations over 
topography and enhanced depth of focus. Processes that utilize 
dry-developed resists offer these advantages because the image is 
transferred into the surface of the imaging layer, not throughout its 
entire thickness. Thus, the active region in which the image is focussed 
is not necessarily the entire thickness of the imaging layer. A thinner 
lithographically active region is advantageous because it is easier to 
precisely introduce the image into a thinner region. 
Processes that use these dry-developed resists are referred to as 
surface-imaging lithographic processes. The processes are so named because 
they permit the image to be introduced near the surface of the resist. 
Surface-imaging lithographic processes also provide the promise of higher 
resolution patterns and the elimination of the need for an antireflective 
coating. 
Because the dry-developed resists have a thinner lithographically active 
region, they must also have greater development selectivity between the 
exposed and unexposed regions of the resist layer than thicker 
conventional resists. Consequently, surface-imaging lithographic processes 
which introduce the requisite etch selectivity into the dry-developed 
resists used in these processes are being investigated. 
SUMMARY OF THE INVENTION 
In the process of the present invention, the etch selectivity between the 
exposed and unexposed areas of the resist material used in the 
surface-imaging lithographic process is provided by forming self-assembled 
layers of refractory material on either the exposed or unexposed areas of 
the resist material, but not both. Depositing these layers of refractory 
material on one of the two areas of the resist material provides 
sufficient etch selectivity between the two areas to permit a pattern to 
be developed in the substrate beneath the surface-imaging resist material. 
In the present lithographic process, an imaging layer is first deposited on 
a substrate. In a surface-imaging process, a latent image is transferred 
into the surface of this imaging layer and not throughout the thickness of 
the imaging layer. The term "imaging layer," when used, refers to the 
entire layer and not just that portion of the layer into which the latent 
image is transferred. The imaging layer contains an energy sensitive 
polymeric resist material. 
The polymeric resist material in the imaging layer has certain moieties 
attached thereto. These moieties are referred to as reactive groups when 
they are susceptible to reaction with other moieties under certain 
conditions. In some instances, the resist material has certain moieties 
attached thereto which, when irradiated, become the desired reactive 
group. In other instances, radiation causes a moiety with a desired 
reactivity to change into a moiety that does not have the requisite 
reactivity. 
The reactive groups are selected for their susceptibility to react with a 
reagent containing a refractory material, a ligand for a refractory 
material, a host for a refractory material, etc. Such reaction binds the 
refractory material to the polymeric resist material. The polymeric resist 
material is energy sensitive. When the polymeric resist material is 
exposed to energy, it becomes chemically distinct from the polymeric 
resist material that is not exposed to energy. The chemical distinctness 
between the polymeric resist material that is exposed to energy and the 
polymeric resist material that is not exposed to energy is exploited to 
introduce a selectivity between the unexposed and exposed polymeric resist 
material. In the process of the present invention, the unexposed polymeric 
resist material is chemically distinct from the exposed polymeric resist 
because the reactive groups described above are present in substantially 
greater numbers in one of either the exposed portion or the unexposed 
portion of the polymeric resist material than in the other portion. When 
the polymeric resist material is contacted with the refractory material, 
more of the refractory material binds to the polymeric resist material 
with the greater concentrations of reactive groups. Etch selectivity is 
provided because the portion of the polymeric resist material with the 
greater concentration of refractory material bound thereto is more etch 
resistant than the other portion of the polymeric resist material. 
Radiation induces the desired chemical change in the polymeric resist 
material either directly or via a photogenerated catalyst in the imaging 
layer. The chemical change renders the resist material susceptible to 
binding a refractory material if it was not so susceptible prior to its 
being exposed to radiation. In the alternative, radiation will passivate 
the resist material, thereby rendering it not susceptible to binding the 
refractory material to the resist material. In certain instances, heat is 
used in conjunction with radiation to either activate or passivate resist 
material for the desired reaction. 
The imaging layer is patternwise exposed to radiation. Patternwise exposure 
means that a certain portion of the resist material in the imaging layer 
is exposed to radiation while another portion of the resist material is 
not exposed to radiation. This patternwise exposure introduces a latent 
image into the resist material. 
The layer of refractory material is then assembled onto either the exposed 
or the unexposed area of the resist material. The refractory material is 
provided in a form that facilitates binding with the reactive groups on 
the resist polymer in the desired area of the resist. Refractory materials 
such as aluminum, chromium, iron, cobalt, nickel, zirconium, molybdenum, 
tungsten, bismuth, antimony, and ions and clusters of these elements are 
contemplated as suitable refractory materials for binding to the polymer 
surface. 
In one example, zirconium, is bound to the resist material in one of either 
the exposed or the unexposed portions of the resist material. The imaging 
layer is contacted with a solution of zirconium oxychloride dissolved in a 
polar solvent such as water, methanol or ethanol. The solution is applied 
onto the imaging layer by any suitable technique such as puddling, 
immersion, or spraying. 
To introduce the desired etch selectivity into the resist, multiple 
applications of the refractory material are contemplated. The multiple 
applications of refractory material are linked together by applying a 
reactant which links succeeding applications of the refractory material 
together. Pyrophosphoric acid (H.sub.4 P.sub.2 O.sub.7) is an example of 
such a reactant. Pyrophosphoric acid is advantageous for binding 
transition metals together. 
In the above example, succeeding applications of zirconium are bound 
together by introducing an aqueous solution of pyrophosphoric acid into 
contact with the imaging layer between the succeeding applications of the 
zirconium oxychloride solution. Each application of zirconium oxychloride 
followed by an application of pyrophosphoric acid is a cycle that deposits 
zirconium on the desired area of the resist. It is advantageous for the 
cycle to be repeated at least 30 times, which provides sufficient 
zirconium on the desired area of the resist to introduce the desired 
degree of selectivity into the resist. 
The coated substrate is immersed in the zirconium oxychloride solution for 
a length of time that permits the metal to deposit on the desired discrete 
areas of the imaging layer. A suitable length of time is about 2 minutes 
to about 5 minutes. The coated substrate is then rinsed in a polar solvent 
such as water to remove any unbound zirconium oxychloride from the surface 
of the coated substrate. The coated substrate is then preferably immersed 
in an aqueous solution of pyrophosphoric acid for a length of time that is 
sufficient to permit the pyrophosphate to bind to the zirconium previously 
bound to the polymer. The coated substrate is then rinsed to remove the 
excess pyrophosphoric acid before the next deposition cycle is commenced. 
The pattern formed by exposing the polymeric resist to energy and 
depositing refractory material on the polymeric resist as described above 
is then developed by reactive ion etching (RIE). Other suitable means for 
etching the pattern in the resist are contemplated, however, and these 
methods are known to those skilled in the art. If RIE is the method chosen 
for etching the pattern, then the gaseous plasma used for the etch is 
preferably an oxygen plasma. The pattern is then transferred into the 
substrate using conventional means. 
DETAILED DESCRIPTION 
The process of the present invention is directed to processes for device 
fabrication using surface imaging lithography. In surface imaging 
lithography an image is transferred into the near-surface portion of the 
imaging layer. The image is developed, after which it is transferred into 
the substrate on which the layers are deposited. The imaging layer has a 
thickness of about 0.1 microns to about 1 micron. 
These thin imaging layers are made of polymeric resist materials that are 
energy sensitive. Exposing discrete areas of the imaging layer to 
radiation, e.g. light or discrete particles, induces a chemical change in 
polymeric resist material in the exposed areas. This chemical change is 
exploited to develop a pattern from the image defined by the exposed and 
the unexposed areas of the imaging layer. 
The imaging layer is deposited on a substrate, after which the imaging 
layer is patternwise exposed to radiation. The patternwise exposure 
provides two discrete areas in the resist, the unexposed area and the 
exposed area. The two discrete areas together define a latent image of the 
pattern introduced into the resist by the patternwise exposure. 
Numerous conventional resist polymers are contemplated as suitable in the 
process of the present invention. These resist polymers include phenolic 
resins, which are thermosetting resins that are the condensation product 
of phenol or substituted phenols with aldehydes such as formaldehyde, 
acetaldehyde and furfural. Resist polymers with amide functional groups 
pendant to the polymer backbone are also contemplated. Poly(acrylamide) is 
one example of such a resist polymer. Resist polymers with carboxyl groups 
that are pendant to the polymer backbone are also contemplated. The 
carboxyl groups are either pendant to the resist polymer when the resist 
material that contains the polymer is applied to the substrate or they are 
generated during the lithographic process by irradiation or post exposure 
processing. Examples of suitable resist polymers that contain carboxyl 
functional groups are polyacrylic acid, poly(itaconic acid), polymers that 
contain fumaric acid, or maleic acid and their associated ester 
precursors. Resist polymers that have phosphonate or phosphate groups 
pendant to the polymer backbone or attached to groups pendant to the 
polymer backbone are also contemplated as useful in the process of the 
present invention. These polymers are described in U.S. application of 
Houlihan-Katz-Schilling 9-7-6, which is filed concurrently herewith and is 
hereby incorporated by reference. 
The resist polymers described above are combined with other materials to 
form a resist material. The resist material so formed is applied as an 
imaging layer onto a substrate using conventional methods for depositing 
such materials that are well known to those skilled in the art. The 
imaging layer is then patternwise exposed to radiation. The patternwise 
exposure introduces a latent image into the imaging layer. Preferably, the 
wavelength of the radiation used to expose the imaging layer is 193 nm, 
although other wavelengths of radiation such as soft x-ray (5 nm to 40 nm) 
and other radiation types such as electron radiation and ion radiation are 
also contemplated. 
The process of the present invention contemplates binding a refractory 
material onto the imaging layer. The refractory material is intended to 
function as an etch mask which enables the latent image introduced into 
the imaging layer to be developed and transferred into the substrate. 
Therefore, in order for the refractory material to perform its desired 
function, it must be deposited on the imaging layer in a manner that 
conforms to the latent image. This selective deposition is accomplished by 
providing the functional groups described above on the resist polymers in 
the imaging layer. However, these functional groups will bind to the 
refractory material only in one of either the area of the resist material 
that is exposed to radiation, or the area of the resist that is not 
exposed to radiation. It is contemplated that this selective reactivity 
will be introduced into the resist material in a number of different ways. 
The desired selectivity is introduced into an imaging layer by "protecting" 
the reactive functional group in the resist polymer. A functional group is 
protected when another moiety is attached to it which prevents the 
functional group from reacting. Once the protecting moiety is removed, the 
functional group is free to react. The protecting moieties are removed 
under conditions which strip the moieties from the polymer but do not 
otherwise substantially effect the polymer. 
Typically, the moieties are stripped from the polymer in the presence of 
acid. Moieties stripped from the polymer under acidic conditions are 
commonly referred to as being acid labile. By adding a photoacid generator 
(PAG) to the resist polymer, the acid is generated only in those portions 
of the imaging layer that are exposed to radiation. Suitable PAGs are 
disclosed in U.S. Pat. No. 4,996,136, which is hereby incorporated by 
reference. Removing the protecting groups renders the deprotected moieties 
susceptible to binding the refractory material. 
The desired selectivity is also introduced into the imaging layer by 
oxidizing certain areas of the resist which correspond to the latent image 
introduced into the imaging layer. For example, phenolic polymers do not 
directly bind to positive transition metal ions such as zirconium. 
However, if the phenolic polymer is subjected to photolysis at 193 nm in 
air, the hydroxyl moieties in the phenolic polymer undergo oxidation, and 
carboxylic acid moieties are formed on the polymer. Sufficient carboxylic 
acids are not formed on polymers that are less easily oxidized than phenol 
under the same conditions. 
In the polymers described above, carboxylic acid functional groups (--COOH) 
are contemplated as suitable for binding the refractory material to the 
imaging layer. These functional groups are provided on the phenolic resin 
polymers in the manner described above. These functional groups are also 
generated on the resist polymer after the resist polymer has been exposed 
to radiation and baked. For example, 
poly(tetrahydropyranyl-4-styrenecarboxylate) is a resist polymer wherein 
the carboxyl functionality is masked by a tetrahydropyranyl moiety and 
removed by acid generated from a PAG when the polymer is exposed to 
radiation. After the t-hydropyranyl moiety is removed, the carboxyl moiety 
will bind to the refractory material. Another example of this type of 
polymer is the bis-(tetrahydropyranyl ester) of poly(itaconic acid). 
Another example of a resist polymer with carboxyl functional groups that 
bind refractory metal to the polymer is poly(acrylic acid) (PAA). Also, 
carboxylic acid moieties are generated on certain polymers by photolysis 
of phenolic moieties as described above and by cleaving the 
tetrahydropyranyl and t-butyl groups from poly(tetrahydropyranyl acrylate) 
and poly(t-butyl acrylate), respectively in the presence of a PAG. 
Amides are another functional group used to bind refractory metals to the 
polymers in the present invention. Similar to the deprotection mechanisms 
described generally above, a polymer with amide groups attached to the 
polymer backbone is incorporated into a resist material. For example, a 
resist material containing poly(methacrylamide) is applied as an imaging 
layer onto a substrate. A latent image is introduced into the imaging 
layer by a patternwise exposure to 193 nm radiation, which oxidizes the 
amide side chain to provide methacrylic acid side chains on the polymer. 
These methacrylic side chains do not bind zirconium or other refractory 
materials because the side chain is oriented such that the methyl group is 
at the surface. The amide functional groups in the areas of the imaging 
layer that were unexposed to radiation are not so oxidized and are then 
able to bind refractory metal to the polymer. Therefore, the ability of 
the polyamide to bind to the refractory material is destroyed by exposing 
the polyamide to radiation. 
Imide-containing polymers are also contemplated for use in the present 
process. The imide functional group in the resist polymer does not bind to 
refractory materials. Upon photooxidation, carboxylic acid groups are 
formed. Amine-based polymers such as poly(ethyleneimine) that have 
acid-sensitive t-butoxycarbonyl groups pendant to the amine moiety which 
mask the amine functionality are also contemplated to be used in the 
process of the present invention. When the polymer is irradiated in the 
presence of PAG, the t-butoxycarbonyl groups are stripped from the amine 
moieties. The free amine moieties are then able to bind with the 
refractory material. 
A deprotection mechanism as described above is also used when resist 
materials with polymers having pendant phosphonate or phosphate groups are 
used. Acid labile or photolabile groups are attached to the phosphate or 
phosphonate groups. The acid labile groups or photolabile groups are 
stripped from the polymer under certain conditions which depend upon the 
specific acid labile or photolabile group and the polymer to which these 
groups are bound. The unprotected phosphonate or phosphate groups are then 
free to bind to a refractory material. 
Polymers which have more than one functional group which will bind to a 
refractory material per repeat unit of the polymer are also contemplated 
for use as polymeric resist materials for use in the present process. 
These polymers include the poly(itaconates), which have two carboxyl 
groups per repeating unit and the poly( styrene dicarboxylates). 
These poly(itaconates) are represented by the general structure: 
##STR1## 
R is representative of the protective groups described generally above. 
Typically, these groups are stripped from the polymer when it is exposed 
to radiation (photolabile) or in the presence of acid (acid labile). 
A styrene polymer which has multiple carboxyl groups per repeating unit, 
poly(styrene-3,4,-dicarboxylic anhydride) or other protected diester 
thereof, is also contemplated as a resist polymer in the process of the 
present invention. Other polymers include copolymers of methyl vinyl ether 
and fumarate or maleate esters. The maleate and fumarate esters also 
contain multiple carboxyl groups per repeating unit. These polymers are 
represented by the general formula: 
##STR2## 
wherein the description of R is the same as in the previous paragraph. 
If a surface carboxyl or other functional group on the polymer is reacted 
with a branched binding enhancer having multiple binding groups, it is 
possible to bind more refractory metal to the surface of the imaging 
layer. This branched binding group is depicted by the structure --A--Y 
(R--Z).sub.n in which A is a reactive group bound via a covalent, ionic, 
or coordinating bond to the polymer surface. Y is a central atom or 
anchoring group to which the branched functional groups are attached. The 
branching groups (R--Z) are tethered to Y via a bond between Y and R. The 
terminal group Z is selected from those above-enumerated functional groups 
that have a strong binding attraction to the refractory material which is 
bound to the polymer surface to introduce the desired etching selectivity 
into the imaging layer. Examples of such branched binding groups are 
##STR3## 
In these groups NH.sub.2 is the anchoring group (A) and the 
tetrasubstituted carbon is tethering group (Y). The branching groups 
(R--Z) are alkanecarboxylic acid or alkaneamide moieties that strongly 
bind with the refractory material. 
These branched binding groups are derived from nitromethane. One skilled in 
the art will recognize how to incorporate these reactive groups into the 
previously described resist polymers. 
Not only must the resist polymer have functional groups that bind the 
refractory material to the polymer surface, the functional groups must be 
oriented on the polymer such that they are in a position to bind to the 
refractory material. For example, the x-ray photoelectron spectroscopy 
(XPS) spectra at 20.degree. of two resist polymers, poly(methacrylic acid) 
(PMAA) and poly(acrylic acid) (PAA) showed that PMAA had a higher carbon 
concentration on its surface than indicated by its stoichiometry. PAA was 
observed to have a surface carbon concentration that was consistent with 
its stoichiometry. PMAA was observed not to bind the refractory material, 
although it has almost as many carboxyl groups per molecule as PAA, which 
was observed to bind Zr quite well. A contemplated explanation for this 
observation is that the methyl groups on the PMAA are oriented toward the 
polymer surface to minimize surface energy, and the carboxyl groups are 
oriented away from the polymer surface. PAA has no methyl groups and, 
therefore, more of its carboxyl groups are oriented toward the polymer 
surface. Thus, not only must the resist polymers have suitable functional 
groups, those functional groups preferably are oriented toward the polymer 
surface and are available to bind to the refractory material. 
The layer of refractory material is then assembled onto either the exposed 
or the unexposed area of the resist material. The refractory material is 
provided in a form that facilitates binding the refractory material to the 
functional groups on the resist polymer. Refractory materials such as 
aluminum, chromium, iron, cobalt, nickel, zirconium, molybdenum, tungsten, 
bismuth, antimony, and ions and clusters of these elements are 
contemplated as suitable refractory materials for binding to the polymer 
surface. Zirconium has been found to be advantageous. The process also 
contemplates binding metal-containing clusters such as phosphotungstate 
P.sub.2 W.sub.18 O.sub.62.sup.-6, a hexanion, and phosphomolybdate, 
P.sub.2 Mo.sub.18 O.sub.62.sup.-6 to the desired portion of the imaging 
layer. The process of the present invention further contemplates binding 
metal oxide clusters such as Ti.sub.16 O.sub.16 (OC.sub.2 H.sub.5).sub.32, 
Mo.sub.6 Cl.sub.8 (CF.sub.3 SO.sub.3).sub.6, and Zn.sub.4 O[(CO).sub.9 
Co.sub.3 CCOO].sub.6 to the desired portion of the imaging layer. 
Zirconium oxychloride reacts with the functional groups on the resist 
polymer to bind the metal to the polymer. Although zirconium oxychloride 
is mentioned specifically, solutions in which a zirconium salt is soluble 
at a pH of about 3 are contemplated suitable sources of zirconium for the 
process of the present invention. Zirconium salts such as zirconium 
nitrate and zirconium chloride are additional examples of suitable 
zirconium salts. The zirconium oxychloride is dissolved in a polar solvent 
such as water, methanol or ethanol. The concentration of zirconium 
oxychloride in the solution is about 0.001M to about 0.1M. It is 
advantageous if the concentration of the zirconium is about 0.005M to 
about 0.007M. 
The solution is then applied onto the imaging layer by any suitable 
technique. The coated substrate is immersed in the zirconium oxychloride 
solution. The zirconium oxychloride is also puddled onto the imaging 
layer. The imaging layer is placed in contact with the zirconium 
oxychloride solution for a length of time that is sufficient for zirconium 
to bind to the desired discrete areas of the imaging layer. If an 
immersion technique is used, the coated substrate is immersed in the 
zirconium oxychloride solution for about 2 to about 5 minutes. 
Refractory material is assembled on the polymeric resist material via 
successive applications. A reactant is used to bind succeeding 
applications of the refractory material together. The reactant binds 
succeeding applications together because it is capable of binding to two 
or more atoms or molecules of refractory metal. For example if X is a 
molecule of refractory material and Y is a molecule of the reactant, Y 
forms the link --X--Y--X-- between two atoms or molecules of refractory 
material. An example of a material is a polyphosphoric acid such as 
pyrophosphoric acid. Coated substrate with the imaging layer thereon is 
deposited in an aqueous solution of pyrophosphoric acid between succeeding 
applications of a solution containing a refractory material such as the 
previously mentioned zirconium oxychloride. The coated substrate is 
immersed in an aqueous solution of pyrophosphoric acid for about 2 to 
about 5 minutes which is sufficient for the phosphate to bind to the 
zirconium previously bound to the polymer. The concentration of 
pyrophosphoric acid in the aqueous solution is about 0.005M to about 
0.007M. This cycle is repeated 30 times to introduce the desired etch 
selectivity into the resist. 
The coated substrate is preferably rinsed in a polar solvent after being 
immersed in solutions of zirconium oxychloride and pyrophosphoric acid. 
Such rinsing removes unbound traces of these reactants from the surface of 
the polymeric resist material but does not dissolve the polymer in the 
imaging layer. Thus, these unbound traces are prevented from accumulating 
on the surface of the polymeric resist material and interfering with the 
process of binding the refractory materials to the polymer surface. 
After the desired amount of refractory material has been deposited on the 
substrate, the image in the polymeric resist is developed into a pattern. 
The pattern is preferably developed by plasma ion etching (RIE), although 
other suitable means for etching the pattern in the resist are 
contemplated, such as electron cyclotron resonance (ECR), electron 
stimulated etching, or ion stimulated etching. If RIE is the method chosen 
for etching the pattern, then the gaseous plasma used for the etch is 
preferably an oxygen plasma. The pattern is then transferred into the 
substrate using conventional means. Typically, in a helicon source etcher, 
O.sub.2 RIE is conducted at 50.degree. C. to -100.degree. C. and 1-3 mTorr 
of O.sub.2 at 100-300 sccm with a source power of 1000-2500 W and an RF 
bias of -20 V to 150 V. 
The refractory material assembled on the polymer surface is so assembled in 
an anisotropic manner accompanied by less linewidth loss and less 
linewidth variation. Anisotropic assembly of the refractory mask permits 
steeper wall profiles during pattern development. Anisotropy is provided 
in the process of the present invention by the vertical assembly of 
molecular units on the polymer surface. Preferential bonding in the 
vertical direction also promotes anisotropy. 
The following examples are intended to illustrate specific embodiments of 
the present invention and are not intended to limit the invention defined 
by the claims.

EXAMPLE 1: ASSEMBLY OF REFRACTORY MATERIAL ON A BILAYER RESIST 
A layer of a photoresist material (SPR-1811; obtained from the Shipley Co. 
in Newton, Mass.) was spin-coated at 2000 rpm onto a silicon wafer (5 inch 
diameter). The coated wafer was heated to a temperature of 210.degree. C. 
and held at that temperature for 5 minutes, which crosslinked the 
photoresist material. The thickness of the layer of crosslinked 
photoresist on the substrate was 870 nm. 
A solution of poly(vinyl phenol) (10 percent by weight) in cyclopentanone 
was spin coated at 1000 rpm onto the coated substrate. The poly(vinyl 
phenol) had a molecular weight of 7000 g/mole and was obtained from 
Polysciences, Inc. of Warminster, Pa. The coated substrate was then heated 
to 108.degree. C. and held at that temperature for 4 minutes. 
The bilayer-resist-coated-wafer was then patternwise exposed using 
radiation with a wavelength of 193 nm. The radiation source was a Lambda 
Physik Argon-Fluoride (ArF)excimer laser at a fluence of 100 
microwatt/cm.sup.2 /pulse. Forty regions of the bilayer resist coating 
were exposed to radiation dosages of about 2.5 mJ/cm.sup.2 to about 102.5 
mJ/cm.sup.2. Each region had a size of about 5 mm by about 5 min. 
The exposed, bilayer-resist-coated wafer was then immersed in a solution 
0.005M of zirconium oxychloride, ZrOCl.sub.2, for 2 minutes. The solution 
was at a temperature of about 23.degree. C. The 
bilayer-resist-coated-wafer was rinsed by dipping the coated wafer in 
deionized water for 2 minutes. 
The coated wafer was then immersed in an aqueous solution of pyrophosphoric 
acid (0.005M) for 2 minutes, after which the coated wafer was again 
immersed in deionized water for 2 minutes. The four step cycle (immerse in 
ZrOCl.sub.2 /rinse/immerse in pyrophosphoric acid/rinse) was repeated 
another 29 times for a total of 30 cycles. In this manner zirconium was 
selectively self-assembled on top of the exposed regions of the resist 
material. This self-assembly was confirmed by x-ray photoelectron 
spectroscopy and x-ray fluorescence measurements. 
The coated wafer was then loaded into a Model 5410 Lucas- Signatone, Inc. 
plasma etching machine having source and bias 13.56 mHz RF power supplies. 
The coated wafer was etched in an oxygen plasma at a pressure of 2 mTorr 
and an O.sub.2 flow rate of 85 sccm at 25.degree. C. The etcher had a 
sample bias power of 120 W and a bias voltage of -65 V. The sample was 
etched for 50 seconds. Negative tone full thickness patterns were obtained 
at a dosage of about 85 mJ/cm.sup.2 with good contrast. 
EXAMPLE 2: ASSEMBLY OF A MULTILAYER REFRACTORY MATERIAL ON A BILAYER RESIST 
A bilayer film of a hardened resist (SPR-1811, obtained from the Shipley 
Co.) was deposited on a silicon substrate and hardened as described in 
Example 1. The resulting film was 870 nm thick. The film was overcoated 
with a solution of resorcinol novolac resin (SD-562A which was obtained 
from the Borden Chemical Co. in Louisville, Ky.). The resorcinol novolac 
resin was in a solution of cyclopentanone that contained 15 percent by 
weight resorcinol novolac resin. The solution of resorcinol novolac resin 
was spin coated onto the coated wafer at 1000 rpm, after which the coated 
substrate was heated to a temperature of 108.degree. C. and held at that 
temperature for about 2 minutes. The resorcinol novolac resin layer was 
640 nm thick. 
The bilayer coated wafer was then exposed to radiation as described in 
Example 1. The exposed, coated wafer was then immersed in successive 
solutions of ZrOCl.sub.2 and pyrophosphoric acid. The coated wafer was 
rinsed after being immersed in these solutions as described in Example 1. 
The coated wafer was then etched as described in Example 1, except that 
the coating was etched for 55 seconds. Full thickness negative tone 
patterns were obtained at an energy dosage of 20 mJ/cm.sup.2. The contrast 
was observed to be higher than the contrast observed in the poly(vinyl 
phenol) resist material used in Example 1.