UV-curable organopolysiloxane compositions and negative photoresists comprised thereof

Substrates, e.g., silicon wafers, coated with a UV-curable organopolysiloxane composition including a crosslinking catalyst therefor (e.g., a platinum group metal compound) and an amount of a crosslinking inhibitor (e.g., an azodicarboxylate) which is effective at ambient temperature, but ineffective to prevent crosslinking on exposure of the composition to ultraviolet radiation, are well adapted for the imaging of negative intelligence patterns thereon.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to a UV-crosslinkable organopolysiloxane 
composition and to the use thereof as a negative resist especially adapted 
for microlithography applications. 
2. Description of the Prior Art: 
Significant progress has been made in recent years, both in the size 
reduction and in the cost reduction of electronic components, by virtue of 
the advances made in the technology of production of microelectronic 
circuits, for example, in the field of microlithography. 
In general, the microlithography process includes: 
(a) the application of "a resist", a film of radiation-sensitive polymeric 
material to one of the face surfaces of the substrate, 
(b) the exposure of certain areas of the film to ultraviolet light, an 
electron beam, X-rays, and the like, for example, and 
(c) development of the film with a solvent to remove the soluble portions 
thereof. 
Insofar as the polymeric materials, the "resists", are concerned, these are 
commonly divided into two categories, according to their behavior when 
subjected to irradiation. 
Some resins are characterized by an increased solubility after irradiation 
and produce a hollow image: these resins are referred to as positive. The 
others become insoluble in a solvent for post-irradiation development and 
they produce a relief image; these resins are referred to as negative. 
In each case, the resist portion which remains on the substrate is employed 
as a protective coating to permit selective etching or any other treatment 
of the uncoated areas of the substrate. 
Substrate etching may be performed by conventional chemical attack or by a 
plasma. Plasma etching generally makes it possible to obtain finer 
resolution than that obtained by chemical attack, and, in addition, makes 
it possible to eliminate contamination and handling problems which are 
inherent in chemical agents. However, many resins cannot withstand plasma 
discharge and are themselves eroded along with the substrate, and this 
unavoidably gives rise to a loss in image resolution. 
In parallel with these approaches, it will be appreciated that the growing 
complexity and miniaturization of integrated circuits expose the 
limitations of the technologies which rely on only one resist layer or 
level. Thus, in various earlier investigations reported, for example, in 
Solid State Technology, pages 130-135 (Aug., 1985), it has been proposed 
to solve, at least partially, the problems presented by the topography and 
the reflection of a substrate such as a silicon wafer, by using a 
plurality of resist layers or levels. 
Thus, it has been proposed to deposit a first, relatively thick layer of a 
polymeric material, referred to as a flattening layer, and to coat this 
first thickness with a thin radiation-sensitive, plasma-resistant layer of 
a silicon-containing polymer. 
There exists, therefore, serious need in this art for polymeric materials 
having enhanced radiation sensitivity for producing repeat patterns with 
higher resolution, in response to the demand for increasingly 
sophisticated circuitry. 
Understandably, this research is carried out in parallel with the emergence 
of the newer technologies. 
As will be seen later, the present invention relates more particularly to 
the field of negative resists, that is to say, those polymeric 
compositions or materials which are rendered or become insoluble in a 
development solvent after exposure to light, especially to ultraviolet 
(UV) radiation. 
There already exist in this art known systems in which an initiator of 
chemical reactions, reactions which involve either the principal chain or 
the side groups of a polymer and which produce a profound change in the 
solubility and/or in the plasma-etching resistance of this polymer, is 
activated under the influence of UV-radiation. 
Thus, U.S. Pat. No. 3,984,253 describes the sensitization of a 
polyphthalaldehyde to UV-radiation, to an electron beam, or to X-rays, by 
the introduction of acid-generating compounds such as diazonium salts in 
order to produce a positive image. 
There is another known system (cf. U.S. Pat. No. 4,491,628) in which an 
acid is generated by irradiation, and the acid generated in such manner is 
used to cleave labile pendent acid groups on the side chains of a polymer. 
The irradiated portions differ from the unexposed portions in their 
polarity and their solubility; they can, therefore, be selectively removed 
using alkaline development treatments or polar solvents. The unexposed 
portions may be selectively removed using a nonpolar solvent. However, 
most of the compositions which can be used for this purpose form, after 
development, solid layers which do not withstand plasma. Furthermore, the 
choice of the solvents employed for development is very critical. 
It is also known to this art that the polysiloxanes are among the foremost 
polymers envisaged for the preparation of two-layer resists. However, 
these dimethylsiloxane, methylphenylsiloxane and/or methylvinylsiloxane 
copolymers are sensitive to near UV-radiation only insofar as care has 
been taken to incorporate sensitive groups into their structure, for 
example, acrylic or methacrylic groups. Furthermore, incorporation of such 
functional groups in the polymer structure is difficult to carry out. 
It has also been proposed (cf. JA 60/057,833) to use, as a resist capable 
of withstanding an oxygen plasma, polysiloxanes having what is known as a 
"ladder" structure of the formula: 
##STR1## 
in which l, m and n are positive integers which may be zero, provided, 
however, that l and m are not zero simultaneously. 
Notwithstanding the fact that these polymers are relatively difficult to 
synthesize, they also constitute part of a system in which a direct 
photosensitization, involving substantially pure photochemistry, occurs, 
that is to say, each photon activates a pendent chemical moiety on the 
principal chain of the polymer, and this implies that the degree of 
crosslinking or chain scission which is detected, depending on each 
particular case, is directly proportional to the amount of light energy 
which is applied. 
SUMMARY OF THE INVENTION 
Contrariwise, in the system according to the present invention, 
photosensitization is carried out in an "indirect" manner, namely, a 
photon initiates catalytic activity. Crosslinking then occurs using 
quantities of applied energy which are much lower vis-a-vis the known 
systems. In view of such chemical amplification, the compositions 
according to this invention are highly sensitive to UV and permit an 
increase in production rates. In addition, the utilization of 
organosilicon compounds imparts resistance to plasma etching. 
From another standpoint, the system/composition according to the present 
invention entails a reaction which is, per se, well known to this art, 
namely, the hydrosilylation reaction of polymeric or other materials 
comprising Si-alkenyl groups, a reaction which is selective, fast and of 
high yield, and which has never been employed for this purpose, insofar as 
applicants are aware. Hydrosilylation involves the reaction of an 
organosilicon compound containing at least one silicon atom bonded to a 
hydrogen atom with a compound containing at least one silicon atom bonded 
to a carbon atom of a group containing alkenyl unsaturation, without the 
formation of any coproduct. 
Briefly, the present invention features, as a negative resist, a 
film-forming organopolysiloxane composition capable of being crosslinked 
by hydrosilylation in the presence of a catalyst derived from a platinum 
group metal, the activity of the catalyst being reversibly blocked by an 
inhibitor. The catalytic activity is produced essentially by exposing the 
subject composition to ultraviolet light. The composition according to 
this invention thus comprises: 
(1) at least one organopolysiloxane containing, per molecule, at least x 
hydrocarbon groups containing alkenyl unsaturation and bonded to a silicon 
atom, with x being greater than or equal to two; 
(2) at least one organohydropolysiloxane containing, per molecule, at least 
y hydrogen atoms bonded to a silicon atom, with y being greater than or 
equal to two, and with (x+y) being less than five, with the proviso that 
the Si-H and Si-alkenyl groups may be borne by the same molecule; 
(3) a catalytically effective amount of a platinum group metal compound; 
(4) an amount of at least one azodicarboxylate which is effective in 
inhibiting the formation of a gel at ambient temperature, but in 
insufficient amount to prevent crosslinking on exposure to ultraviolet 
rays; and 
(5) an organic solvent, if appropriate. 
The present invention also features a substrate comprising at least one 
face surface coated with a uniform adherent film, having a thickness of 
from about 0.1 to 3 micrometers, formed from the above composition, and to 
the imaging of such substrate with a pattern of intelligence. 
It is also to be noted that related compositions wherein the x+y value is 
equal to or greater than 5 are disclosed in U.S. Pat. No. 4,640,939. Such 
systems with these higher values are indicated for their anti-stick 
characteristics. However, in contrast to the systems of the instant 
invention, these prior art systems with the presence of this feature along 
with certain solubility limitations and limitations in certain other 
desired photoresist properties stemming from the lengthened siloxane 
chains are not readily applicable for such photoresist utility.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
More particularly according to the present invention, the first component 
of the subject composition is advantageously an organopolysiloxane 
containing, per molecule, at least x hydrocarbon groups containing alkenyl 
unsaturation and bonded to a silicon atom, with x being greater than or 
equal to two. This component may be "substantially linear", that is to 
say, it may be a polymer or a copolymer containing a straight or partly 
branched chain. The groups containing alkenyl, preferably vinyl, 
unsaturation, may be located at the end of the polymer chain and/or within 
the chain itself. This first component advantageously has a viscosity of 
from approximately 50 to 100,000 mPa.s at 25.degree. C. It may be a 
diorganopolysiloxane containing from 1.9 to 2.1 organic radicals per 
silicon atom. The organic radicals (other than the radicals containing 
alkenyl unsaturation) may be of any type, to the extent that these 
radicals are devoid of aliphatic unsaturation and have no detrimental 
influence on the catalytic activity of the constituent (3) of the 
composition. Exemplary of such radicals, representative are methyl, ethyl, 
phenyl and 3,3,3-trifluoropropyl radicals. These compounds are well known 
and are described, in particular, in U.S. Pat. Nos. 3,220,972, 3,344,111 
and 3,434,366. 
Up to 80% by weight of this polymer may be replaced by a resinous product 
which is an organopolysiloxane copolymer essentially consisting of 
trimethylsiloxane, methylvinylsiloxane and SiO.sub.2 recurring units, in 
which from 2.5 to 10 mol % of the silicon atoms bear a vinyl group and in 
which the molar ratio of trimethylsiloxane groups to SiO.sub.2 groups 
ranges from 0.5 to 1. Such resinous copolymers which are useful according 
to the present invention are described in U.S. Pat. Nos. 3,284,406 and 
3,436,366. 
The composition may also contain a cycloorganosiloxane compound containing 
vinyl and methyl groups in the form of a tetramer, such as 
1,3,5,7-tetramethyl-1,3-5,7-tetravinylcyclotetrasiloxane. 
Component (2) is an organohydropolysiloxane containing, per molecule, at 
least y hydrogen atoms bonded to a silicon atom, y being greater than or 
equal to two. This component, which may be linear or cyclic, 
advantageously has a viscosity of from 10 to 100,000 mPa.s at 25.degree. 
C. 
The amount by weight of hydrogen atoms bonded to silicon does not exceed 
1.67 and preferably ranges from 0.1 to 1.6% in the case of polymers 
containing only SiH and Si-CH.sub.3 groups. 
The valencies of the silicon which are not satisfied by hydrogen atoms and 
oxygen atoms are preferably satisfied by methyl, ethyl and/or phenyl 
groups. 
The SiH groups may be located within the polymer chain or at the ends 
thereof, or within as well as at the chain ends of the 
organohydropolysiloxanes. 
Representative are, for example, the polymethylhydrosiloxanes having 
trimethylsiloxyl end groups, polydimethylpolymethylhydrosiloxane 
copolymers having trimethylsiloxyl end groups, and 
polydimethylpolymethylhydrosiloxane copolymers having hydrodimethylsiloxyl 
end groups. 
The compounds (2) are per se well known to this art and are described, for 
example, in U.S. Pat. Nos. 3,220,972, 3,341,111, 3,436,366 and 3,697,473. 
Up to 80% by weight of this polymer may be replaced by a resinous product 
which is an organopolysiloxane bearing mono-, di- or trifunctional 
siloxane recurring units, some of which bearing SiH groups; examples of 
such recurring units correspond to the following formulae: 
RHSiO, HSiO.sub.1.5, HSiO.sub.0.5, in which R denotes a methyl, ethyl, 
n-propyl, phenyl or 3,3,3-trifluoropropyl radical. 
Hydrogenated resins, such as those described, in particular, in U.S. Pat. 
Nos. 3,284,406 and 3,486,366, may be employed for this purpose. 
The composition of this invention may also contain a cycloorganosiloxane 
compound bearing methyl groups and hydrogen atoms on silicon atoms in the 
form of a tetramer, such as 
1,3,5,7-tetramethyl-1,3,5,7-tetrahydrocyclotetrasiloxane. 
In general, the total amount of resin may constitute up to 80% by weight of 
the solids content of the composition, provided, however, that it remains 
soluble in the organic solvents. 
As indicated above, the SiH and Si-vinyl groups may be borne by a copolymer 
constituting a single polysiloxane. 
The sum of the number of groups containing (alkenyl, preferably vinyl) 
unsaturation per molecule of compound (1) and of the number of SiH groups 
per molecule of compound (2) should be less than 5 such as to produce a 
crosslinked polymer during the crosslinking of the organopolysiloxane 
composition. 
The ratio of the number of SiH groups to vinyl groups is generally greater 
than 0.4 and generally less than 2 and preferably ranges from 0.7 to 1.4. 
As the catalyst (3), complexes of a platinum group metal are advantageously 
used, particularly the platinumolefin complexes described in U.S. Pat. 
Nos. 3,159,601 and 3,159,662, the reaction products of platinum compounds 
with alcohols, aldehydes and ethers, described in U.S. Pat. No. 3,220,972, 
the platinum-vinylsiloxane catalysts described in French Patent No. 
1,313,846 and the patent of addition thereto, No. 88,676, and French 
Patent No. 1,480,409, as well as the complexes described in U.S. Pat. Nos. 
3,715,334, 3,775,452 and 3,814,730, or a rhodium catalyst such as 
described in U.S. Pat. Nos. 3,296,291 and 3,928,629. 
The preferred platinum group metals are platinum and rhodium; although less 
active, ruthenium, being less expensive, can also be used. 
Particularly interesting results are obtained using platinum-vinylsiloxane 
complexes, especially the 1,3-divinyl-1,1,3,3-tetramethyldisiloxane 
complex and platinum-methylvinylcyclotetrasiloxane complexes, in 
particular the 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane 
platinum complex. 
The azodicarboxylates used as the inhibitors (4) in the composition of the 
invention are characterized in that they contain the group: 
##STR2## 
with each carboxyl group being bonded to an organic radical without 
detrimental effect on the catalytic activity of the compound (3), and in 
that they are liquid at 25.degree. C. or, if they are solid at this 
temperature, in that they are soluble in an organic solvent which is 
compatible with the organopolysiloxane compositions. 
These inhibitors (4) preferably have one or the other of the formulae (I) 
and (II) below: 
EQU R.sub.1 OOC--N.dbd.N--COOR.sub.2 (I) 
in which R.sub.1 and R.sub.2, which are identical or different, denote a 
linear or branched chain alkyl radical containing from 1 to 12 carbon 
atoms, preferably from 1 to 4 carbon atoms. 
The compounds having the formula (I) are, for the most part, known 
compounds, the preparation of which is described, in particular, by Ingold 
and Weaver, J. Chem. Soc., 127, pp. 378-387, wherein the synthesis of 
ethyl azodicarboxylate is more particularly described. 
EQU R'.sub.1 OOC--N.dbd.N--R--OOC--N.dbd.N--COOR'.sub.2 (II) 
in which R'.sub.1 and R'.sub.2 have the definitions of R.sub.1 and R.sub.2 
and --R-- is an alkylene radical of the formula--CH.sub.2).sub.n -- with n 
being an integer from 1 to 12, or a radical: 
EQU --CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 -- 
The synthesis of these compounds is described by Norman Rabjohn, Journal of 
the American Chemical Society, 70, pp. 1181-1183 (Mar., 1948). 
Ethyl azodicarboxylate and methyl azodicarboxylate are more especially 
preferred. 
The amount of the complex of catalyst (3) and inhibitor (4) to be added is 
a function especially of the compositions and of the type of catalyst. As 
a general rule, the catalyst content ranges from approximately 5 to 1000 
ppm, preferably from 10 to 100 ppm (calculated as the weight of precious 
metal and related to the polysiloxanes). 
Very small amounts of inhibitors according to the invention have been found 
suited to increase the stability of the subject compositions and of a film 
made from these compositions when stored at typical ambient temperature, 
that is to say, below approximately 45.degree. C. without, nevertheless, 
affecting the cure time of a film formed using a composition of this kind 
and exposed to ultraviolet radiation. Furthermore, it is important to note 
that a film formed using a composition of this type may be dried at a 
temperature which may reach 50.degree. C. for 1 hour without its 
solubility being altered. 
The composition according to the invention may also contain a greater or 
lesser amount of an organic solvent (5) which may represent up to 95% by 
weight of the composition and, preferably, at most 80%. 
A volatile organic solvent can then be used which is compatible with the 
composition, for example, an alkane, petroleum cuts containing paraffinic 
compounds, toluene, heptane, xylene, isopropanol methyl isobutyl ketone, 
tetrahydrofuran, chlorobenzene, chloroform, 1,1,1-trichloroethane, and 
monoethylene glycol and methylene glycol derivatives. 
From 0.1 and 50 parts of the compounds (2) and from 0.005 to 3 parts, 
preferably from 0.01 to 0.5 parts, by weight of the compound (4) are 
advantageously used per hundred parts by weight of the compound (1). 
The composition according to the invention may also include various 
additives to improve the properties thereof, especially adhesion. 
Without wishing to be bound by any particular scientific theory, the 
extremely advantageous properties of the inhibitor according to the 
invention may be explained as follows: 
The manner in which the inhibitor (4) according to the invention forms 
complexes with the catalyst is, in fact, completely different from other 
known inhibitors. Thus, when a .sup.195 Pt nuclear magnetic resonance 
(NMR) spectrum is obtained, a catalyst-inhibitor complex (for example, in 
the case where the inhibitor is methyl maleate, described in French Patent 
No. 2,456,767) shows a signal characteristic of the formation of a 
diamagnetic complex. 
However, a signal of this type in .sup.195 Pt NMR does not appear when the 
inhibitor (4) is an azodicarboxylic ester. On the other hand, a signal 
appears when a paramagnetic electron resonance (PER) spectrum is produced, 
which demonstrates the formation of a paramagnetic complex of platinum, 
while this signal does not appear in the case of known inhibitors, in 
particular methyl maleate. 
This paramagnetic complex becomes diamagnetic after UV irradiation, the 
platinum is activated and the azodicarboxylate is converted into the 
corresponding hydrazine. The paramagnetic complex is formed in the event 
of low degrees of oxidation of the platinum, and, more precisely, in the 
event of oxidation states of 0 and II in the catalytic compound (3) such 
as described above. 
The major advantage of the formation of this paramagnetic complex is that, 
in contrast to the diamagnetic complex, it is much more stable, especially 
at elevated temperatures. 
As a result, the pot or vat life of the compositions inhibited in this 
manner, as well as that of the films formed using these compositions under 
certain conditions, is longer. To destroy the paramagnetic complex and to 
activate the catalyst, it is necessary to convert the paramagnetic complex 
into a diamagnetic complex by subjecting a thin layer of the 
organopolysiloxane composition to UV irradiation. 
As those skilled in this art are well aware, organopolysiloxane 
compositions may have higher or lower viscosities. Some highly viscous or 
even pasty materials capable, where appropriate, of forming a more or less 
solid resin will have to be diluted in a solvent to reduce the viscosity 
to a value which is compatible with the intended end application. Some 
compositions are fluid even in the absence of a solvent, and these are 
capable of being stored for several days without an appreciable change in 
their viscosity. 
However, as above-indicated at the beginning of this specification, the 
present invention also features a substrate comprising at least one face 
surface coated with a uniform adherent film with a thickness of from about 
0.1 to 3 micrometers, formed from a composition of the above type, as well 
as the imaging of such substrates with a pattern of intelligence. 
In the present case, by "substrate" is more particularly intended plaques, 
wafers and components of plaques or wafers made of materials employed in 
the manufacture of electronic components or component carriers. 
Exemplary of such substrates, representative are wafers (or chips) of 
silicon coated or otherwise with a layer of oxide or nitride, ceramic 
plates and aluminum-coated plates; it is also possible to consider as a 
suitable substrate the same surfaces, coated with a first flattening 
layer, for example, of a novolak or of any other suitable polymeric 
material well known to this art. 
The process comprises the formation of a film which adheres to the surface 
using the composition described above, the irradiation of at least a 
portion of this film with ultraviolet radiation, which will cause the 
exposed area to cure, while the unirradiated area remains soluble in 
organic solvents which are compatible with polysiloxane compositions. 
Although certain compositions according to the invention have a relatively 
low viscosity in the absence of solvent (a viscosity or less than 5000 
mPa.s, measured at 25.degree. C.), in most cases the organopolysiloxane 
composition will be diluted in a suitable solvent in order to impart a 
viscosity thereto which is compatible with the deposition of a thin layer 
using a rotary plate-coating machine. If necessary, it will be filtered 
beforehand. 
Using predetermined speed of rotation of the plate-coating machine, of the 
nature of the solvent and of the viscosity of the composition, a thin 
layer will be deposited onto the substrate such that, after removal of the 
solvent at a temperature below 50.degree. C. and preferably below 
45.degree. C., there remains adhered a thin film having a thickness which 
generally ranges from about 0.1 to 3 micrometers, and preferably on the 
order of 1 to 2 micrometers, when a single layer is employed, and on the 
order of 1000 to 2000 angstroms, if a double or multiple layer is 
employed. 
The formation of the film using the composition of the invention can be 
effected onto a first layer, known as a flattening layer, such as a 
novolak (for example); the two layers may also be separated by at least 
one other layer of another polymeric material. 
Regions of the film are then selectively irradiated, for example, using UV 
radiation, through a mask. In this case, the wavelength ranges from 200 to 
400 nanometers and preferably on the order of 254 and 360 nanometers. 
After irradiation, the image is developed by dissolving the unirradiated 
areas of the film by spraying or soaking with an organic solvent, which 
may be the same as that used to dilute the original composition. 
It is then possible to rinse and/or to reheat the areas of the layer which 
remain on the substrate, if appropriate, and then to carry out an etching 
process using a chemical agent or a plasma. 
In order to further illustrate the present invention and the advantages 
thereof, the following specific examples are given, it being understood 
that same are intended only as illustrative and in nowise limitative. 
EXAMPLE 1: 
A silicone composition consisting of the following mixture was prepared: 
(i) 48% by weight of a polysiloxane resin containing approximately 2.8% by 
weight of vinyl groups bonded to silicon atoms; 
(ii) 43.3% by weight of a substantially linear polydimethylsiloxane polymer 
having dimethylvinylsiloxyl end groups, containing approximately 2.7% by 
weight of vinyl groups and having a viscosity of approximately 20 mPa.s at 
25.degree. C.; 
(iii) 2.3% of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane; and 
(iv) 6.4% of a polymethylhydrosiloxane fluid having trimethylsiloxyl end 
groups, containing approximately 1.5% by weight of hydrogen atoms bonded 
to silicon and having a viscosity of approximately 20 mPa.s at 25.degree. 
C. 
To this mixture was added 0.04% by weight of ethyl azodicarboxylate (EADC), 
i.e., 2.3 10.sup.-3 mole/kg of composition; the EADC diluted in toluene 
(concentration: 10 g of EADC per liter of solvent) was added dropwise to 
the vigorously stirred polysiloxane mixture. 
Similarly, 50 ppm of platinum (2.5 10.sup.-4 g-at of platinum per kg of 
composition) were added in the form of a complex prepared from 
chloroplatinic acid and 1,3-divinyl-1,1,4,4-tetramethyldisiloxane, as 
described in U.S. Pat. No. 3,824,730; a toluene solution of this complex 
was employed (solution concentration: 1 g of platinum per liter of 
solvent). 
The resultant composition was then spread out in a thin layer onto the 
surface of a water of monocrystalline silicon. 
Film deposition was carried out using a rotary plate-coating machine 
operating at 3000 revolutions/min. 
The toluene was then evaporated off by heating for one hour in an oven at 
50.degree. C. 
A part of the surface of the silicon wafer was protected with a cover which 
was opaque to UV radiation. 
The film was then exposed to UV irradiation for 5 min. This operation was 
carried out using a Tamarack Scientific Inc. instrument, model PRX 350-4, 
fitted with a 350W, HBO type mercury lamp. 
After development in toluene for 5 to 10 sec, it was found that an adherent 
polysiloxane film was coated onto the irradiated region, while no trace of 
silicone material could be detected in the unexposed region. 
EXAMPLES 2 AND 3: 
The procedure and the starting materials were identical to those described 
in Example 1. 
The concentrations of EADC and of platinum were simply modified, together 
with the times of exposure to the UV radiation. 
EXAMPLE 4: 
In this example, an alternative form of the hydrosiolylation catalyst was 
used, this being the product of the reaction of chloroplatinic acid with 
octanol, in accordance with the teaching of U.S. Pat. No. 3,220,972. 
The remaining constituents of the mixture, and the procedure followed, were 
identical to those of Examples 1, 2 and 3. The particular conditions, and 
the results obtained are reported in the Table below: 
TABLE 
______________________________________ 
Exposure 
EADC concentra- 
Platinum con- 
time (in 
Example 
tion (% by weight) 
centration (ppm) 
min) 
______________________________________ 
1 0.04 50 5 
2 0.1 77 30 
3 0.75 116 10 
4 0.1 54 32 
______________________________________ 
While the invention has been described in terms of various preferred 
embodiments, the skilled artisan will appreciate that various 
modifications, substitutions, omissions, and changes may be made without 
departing from the spirit thereof. Accordingly, it is intended that the 
scope of the present invention be limited solely by the scope of the 
following claims, including equivalents thereof.