Photosensitive composition developable by aqueous base solutions

The present invention relates to the field of microelectronics and is intended to improve the characteristics and extend the functionality of thick-layer hybrid chip elements (conductors, resistors, capacitors), multi-layer circuit boards and special purpose products (temperature, humidity, gas sensors, etc.).

A characteristic feature of the stormy development of modern microelectronics is the ever-increasing miniaturization of products, the use of new materials and technologies. There is a growing demand for well-known classical technologies, including thin-layer technology, which, thanks to its simplicity and high performance, has gained a firm foothold in modern hybrid microelectronics and is not about to lose ground.

The essence of the thin-layer technology is the application of special multicomponent compositions called pastes to stencils on ceramic substrates and their subsequent heat treatment at high temperatures (600-1000 ° C). The paste, in turn, is a powder dispersion of very fine inorganic components in an inert organic medium that provides the required viscosity, theological and thixotropic properties of the entire composition. During the heat treatment, the organic medium burns and the ceramic substrate retains the hybrid chip elements formed by stencil printing. Depending on the composition of the inorganic components of the paste and their relation, this method is used to form conductors, resistors, capacitors, insulating layers, to produce multi-layer switchboards and other products. The main disadvantage of thick-film technology lies in the principle of stencil printing. Despite the great advances in this field, screen printing is virtually impossible to form conductors thinner than 100 microns, to obtain gaps between conductors narrower than 100 microns, or to have apertures less than 200 microns in insulating layers. The limit values ​​indicated in mass production conditions are much higher. Therefore, looking at the benefits of thin-film technology, it is very important to look for ways to increase its resolution. One such option is to disperse the powder of the inorganic components of the paste in a photosensitive organic medium. By irradiating a layer of such a paste on a ceramic substrate with high intensity ultraviolet light through a photocell whose transparent areas of radiation correspond to the future distribution of film elements, photopolymerization of organic media takes place in the exposed areas. The exposed areas of such a photosensitive paste, unlike non-irradiated ones, lose solubility and remain on the ceramic substrate when exposed to the appropriate solvent. The following technological operation (heat treatment) is no different from the conventional one. Thus, replacing screen printing with a photochemical process significantly increases the resolution of the thin-film technology. The first photopolymer composition of this type (paste) was patented in 1975. (U.S. Patent No. 3,877,950). This patent describes a composition comprising:

(1) gold powder with a particle size of 0.4 microns to 4 microns;

2) glass powder, which provides gold adherence to the ceramic;

3) an inert organic polymer (polymethyl methacrylate, polyethyl acrylate or a mixture thereof);

4) photoinitiation systems;

5) a polyfunctional monomer;

6) organic solvent.

The polymer, the components of the photoinitiation system and the polyfunctional monomer are dissolved in an organic solvent.

When dispersed in the thus prepared photosensitive medium, the gold and glass miheli. The resulting photosensitive paste is applied to a ceramic substrate through a thin mesh, dried, exposed to ultraviolet light via a photoconductor, washed unexposed areas with a pressurized tetrachloroethylene stream and heat treated at the substrate with a high temperature in a conveyor oven.

One of the disadvantages of this composition is the use of a non-organic and health-damaging organic solvent, tetrachlorethylene, to remove unexposed paste from the ceramic substrate, known as a developer.

This deficiency is not found in photosensitive gold conductors (US Patent No. 5032478) and silver conductors (US Patent No. 5049480) developed in aqueous solutions of 0.8% sodium carbonate.

According to the composition and the result obtained, they are closest to the patented photopolymer composition. The inventions of the two cited patents have identical definitions except for the first claim, which refers to either gold or silver powders, so that the two analogues referred to may be considered together. The photopolymeric compositions described in the analogs consist of:

1) gold (or silver) powder with a reference surface of less than 20 m²/ g and at least 80% gold (or silver) particle size in the range 0.5 to 10 microns and

2. glass powder (melting point between 500 ° C and 825 ° C) with a reference surface not exceeding 10 m²/ g and at least 90% of the glass particles are less than 10 microns dispersed in an organic binder consisting of

3) an organic polymer;

4) photoinitiation systems;

5) polyfunctional monomer and

6) organic media in which

(a) the organic polymer is a copolymer of alkyl acrylates, alkyl methacrylates, styrene or a mixture thereof and an unsaturated carboxylic acid (acrylic, methacrylic) with a molecular weight of less than 50000 and a content of comonomer with free carboxyl groups of 15% or more; aqueous disodium trioxocarbonate solution;

(b) the photoinitiation system consists of benzophenone and Michler's ketone;

c) the polyfunctional monomer is trimethylolpropane triacrylate or polyoxyethylated trimethylolpropane triacrylate;

d) the organic medium comprises an organic solvent (carbitol acetate or βterpineol) and other organic components which are (or may be) incorporated in the composition (plasticizers, dispersants, thermal polymerization inhibitors, adhesion promoters, pigments, etc.).

The organic binder is prepared by dissolving the polymer, photoinitiators, and thermal polymerization inhibitor in an organic solvent. From the examples given in the analogues, the best results are obtained with the following ratio of components,% by weight:

^c/ c Copolymer of methyl methacrylate and 50.00% methacrylic acid (M = 10000)

Carbitol acetate 42.38

Benzophenone 5.94

Michler’s Ketone 1.00

2,6-di-tert-butyl-4-methylphenol 0.68

Gold (or silver) conductive pastes are prepared by mixing an organic binder and a polyfunctional monomer (or a mixture thereof) with a powder of inorganic components. The best results are obtained with the following ratio of components in parts by weight:

Table

<td>Components</td><td>Silver paste</td><td>Gold paste</td>

<td>Silver powder</td><td> 70.8</td><td> -</td>

<td>Gold powder</td><td> -</td><td> 78.0</td>

<td>Glass powder</td><td> 5.3</td><td> 4.6</td>

<td>Organic binder</td><td> 17.1</td><td> 13.0</td>

<td>Trimethylolpropane Triacrylate</td><td> 1.0</td><td> 0.8</td>

<td>Polyoxyethylated trimethylolpropane triacrylate</td><td> 4.2</td><td> 3.4</td>

The paste is then applied through a fine mesh over the ceramic substrates and dried at 75-100 ° C. The dry film thickness of photosensitive pastes ranges from 16 microns to 20 microns.

Organic solvent and paste preparation, paste lubrication and drying operations are performed under yellow light since the pastes are sensitive to the visible part of the spectrum.

Exposure to ultraviolet rays is done in special devices by flushing a nitrogen chamber containing a ceramic substrate with a layer of photosensitive paste and a photographic template and then vacuuming it. This is because the pastes are sensitive to the inhibitory action of airborne oxygen and their photopolymerization in air does not occur or is very slow.

The unexposed areas of the paste layer are washed from the ceramic substrate by spraying with a pressurized aqueous solution of 0.8% disodium trioxocarbonate and the remaining paste is burnt at 900 ° C in a conveyor oven.

The examples provided show that the light-sensitive compositions described (pastes) allow the formation of 25 micron gold and silver conductors with a surface square impedance of 4.4 mOm / kv and 2.7 mOm / kv respectively.

The photosensitive compositions described in the analogues have a number of disadvantages:

1) The organic binder-based copolymers are photochemically inert and their macromolecules are purely mechanically fixed in a three-dimensional three-dimensional structure resulting from photo-polymerization of polyfunctional monomers. The selective loss of solubility in illuminated areas in the system is only possible with an inert polymer-polyfunctional monomer at sufficiently high monomer contents. In the analogous examples, 1 g of polymer contains 0.6 g to 0.65 g of polyfunctional monomers, but again, the polymer swells during development.

2) The compositions are sensitive to the visible part of the spectrum, which complicates their work and creates special requirements for indoor lighting. The undesirable sensitivity to the visible part of the spectrum is determined by the benzophenone-Michler ketone photoinitiation system, which is also not very effective compared to other known photoinitiators.

3) The compositions are sensitive to the inhibitory effects of oxygen and need to be exposed in an inert atmosphere or vacuum using special sophisticated devices.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a more photosensitive composition based on aqueous base solutions for film formation using a thin-layer technology that is insensitive to the visible spectrum and inhibitory to oxygen, having a high photopolymerization rate and higher resolution. This problem is solved by the patentable composition according to the general part of claim 1, wherein the organic polymer-based polymer is photochemically active, i. In addition to its role as a film-forming and water-soluble component, it is also a large-molecule polyfunctional monomer whose photopolymerization is effectively initiated by a photo-insensitive photoinitiator, and the polymer side chains with allyl groups and additionally organic the effect of oxygen at the following ratio of components to parts by weight:

<td>powder of inorganic filler</td><td></td><td> 100.00</td>

<td>polymer</td><td> 9.00</td><td> - 36.00</td>

<td>photoinitiator</td><td> 0.50</td><td> - 3.50</td>

<td>organic disulfide</td><td> 0.20</td><td> - 2.00</td>

<td>inhibitor of thermal polymerization</td><td> 0.01</td><td> - 0.35</td>

<td>an organic solvent</td><td> 5.50</td><td> - 21.50</td>

Advantages of the patented composition are that all technological operations (preparation of photosensitive organic media, mixing with powder of inorganic filler, application of the resulting composition on ceramic substrates and drying) can be performed in diffused daylight or under normal artificial light.

In addition, the exposure process is significantly simplified, since no special measures are required to avoid contact of the surface of the composition with airborne oxygen. During photopolymerization, linear polymer macromolecules having side chains with acrylic and allyl groups form a dense spatial structure, rendering the polymer completely insoluble in aqueous base solutions upon illumination. This makes it possible to increase the resolution of the composition, and the use of a photoinitiator of the acylphosphine class allows a shorter exposure time of the composition.

The invention is further described by the specification of the components of the inorganic filler and organic media mentioned in the definition of the invention and by providing examples with experimental results.

A. Inorganic Components

1) Gold powder with spherical particles. Specific surface area 0.33 m ”/ g, particle size 0.5 microns to 2.0 microns, 90% by weight of particles less than 1.85 microns.

2) Silver powder with irregularly shaped particles. Specific surface area 0.8 m / g, particle size 0.2 microns to 2.0 microns, 50 wt% particles smaller than 1.5 microns.

3) Palladium powder with irregularly shaped particles. Specific surface 5 m²/ g, particle size from 0.1 micron to 2.0 micron, 50% by weight of the particles are smaller than 1.0 micron.

4) Platinum powder with irregularly shaped particles. Spherical surface 0.4 m²/ g, with a particle size of 0.5 microns to 4.0 microns, 50% by weight of the particles are smaller than 2.0 microns.

5) Glass No. 1, melting point 710-720 ° C, at the following component ratio, mole%:

<td>CdO</td><td> 9.8</td>

<td>CuO</td><td> - 15.9</td>

<td>Well, how about</td><td> - 14.3</td>

<td>B2O3</td><td> - 27.0</td>

<td>SiO₂</td><td> - 31.6</td>

<td>B12O3</td><td> 1.4</td>

6) Glass No. 2, melting point 660-680 ° C, with the following component ratio, mole%:

<td>sio₂</td><td> - 33.4</td>

<td>Oh₂0₃</td><td> 2.6</td>

<td>PbO</td><td> - 41.3</td>

<td>b₂o₃</td><td>SO</td>

<td>ZnO</td><td> -. 14.7</td>

7) Glass No. 3, melting point 780-795 ° C, at the following component ratio: mole%:

<td>SiO₂</td><td> - 57.6</td>

<td>PbO</td><td> - 26.7</td>

<td>B₂O;</td><td> 1.4</td>

<td>AI₂0;</td><td> 5.6</td>

<td>BaO</td><td> 3.8</td>

<td>CuO</td><td> 3.5</td>

<td>K₂O</td><td> 1.4</td>

8) Glass No. 4 - special crystallizing glass for interlayer insulation, crystallization temperature 850 ° C.

All glasses were wet milled on a Fritsh planetary mill in agate drums for 20 hours, and the resulting slurry was fractionated with the same firm's vibrosols. The smallest fraction of the powder filtered, washed with acetone and dried in vacuo at 50 ° C was used for the experiments. Specific powder surface 6-8 m ^ / g. 50% by weight of particles smaller than 1.5 microns.

9) Ruthenium oxide powder was obtained by thermal decomposition of ruthenium (IV) hydroxychloride. The powder has a specific surface area of ​​10 µm / g, 50% by weight of particles smaller than 1.0 micron.

B. Organic Components

1) Polymers.

The patented composition has a number of requirements for the photosensitive organic substrate polymer. It must be soluble in aqueous base solutions, form a non-stick film at room temperature, provide the required viscosity of the entire composition, actively participate in photoinitiated radical polymerization in an oxygen-containing environment, and terminate at the lowest possible temperature.

Copolymers of acrylic or vinyl monomers and unsaturated carboxylic acids (acrylic, methacrylic) having a molecular weight of 10,000 to 20,000 and an unsaturated carboxylic acid content of 15 to 30% by weight have been found to meet these requirements best.

Oxygen is known to be a very active inhibitor of free radical processes, but its influence decreases with increasing molecular weight of acrylic monomers.

It is also known that the polymerization of allyl monomers by other mechanisms is unaffected by oxygen.

Using these long-known principles and esterification of a portion of the free carboxy group glycidyl acrylate or glycidyl methacrylate and allyl glyceride ether of an inert basic copolymer, polymers with high photochemical activity and low sensitivity to the inhibitory effect of oxygen were synthesized.

The basic copolymers according to claims 3 and 4 were synthesized according to a general procedure by dropwise addition of a monomer mixture with a dissolved thermal polymerization initiator to a stirred boiling isopropyl alcohol and continued the reaction under an inert atmosphere for 18 hours. Thereafter, a polymerization inhibitor and a catalyst (tertiary amine or quaternary ammonium base) are added to the polymer solution, the mixture of glycidic monomers is added dropwise and the reaction is continued at the boiling point of the solvent for 6 hours. The reaction mixture was cooled, diluted with iso-propyl alcohol and. with vigorous stirring, pour into ten times the volume of water.

The polymer flakes were filtered, washed on the filter with water and dried at 40 ° C under vacuum for 24 hours. According to this procedure, polymers conditionally named polymers A and B (content by weight%) were synthesized.

Polymer A (M = 15000) Polymer B (M = 15000)

<td>Styrene</td><td> 24.0</td><td>Butyl methacrylate</td><td> 17.5</td>

<td>Acrylic acid</td><td> 36.0</td><td>Methacrylic acid</td><td> 42.5</td>

<td>Glycidyl Methacrylate -</td><td> 30.0</td><td>Glycidyl acrylate</td><td> 30.0</td>

<td>Allyl glycidine ether</td><td> 10.0</td><td>Allyl glycidine ether -</td><td> 10.0</td>

2) Organic disulfide.

The patented composition describes polymers having side chains with acrylic and allyl groups significantly reduce the sensitivity of the organic medium to the inhibitory effect of oxygen, but do not permanently eliminate it.

It is known .. that the effects of oxygen are neutralized by organic disulfides of the general formula

Ri - CH₂ - S - S - CH₂ - R₂ , described in EP no. 0028749, G03C 1/68, 20.05.1981, in which R_x and R₂ are the same or different alkyl, cycloalkyl, aryl, arylalkyl or carbamoylalkyl radicals.

The didodecyldisulfide used in the patented composition was synthesized by oxidation of dodecylmercaptan with iron (III) chloride in an organic solvent. Colorless needles were obtained in the form of needles with a melting point of 45 ° C.

3) Photoinitiator.

At present many organic compounds are known which are thermally stable but which generate free radicals by one or another mechanism by absorbing light · in the ultraviolet or visible part of the spectrum. Mention may be made of anthraquinone, phenanthrenquinone and other multinuclear quinone derivatives, λ-dicctones and their dialkyl ketals, acyloins and their ethers, acridine, quinoxaline, oxazine, thioxanthone derivatives and many other organic classes}.

One of the most effective photoinitiators currently known is the acylphosphine class of compounds described in EP 0040721. CO7F 9/50, 12.12.1981.

The 2,6-dimethoxybenzoyl diphenylphosphine used in the patented composition was synthesized according to the following procedure:

In a four-flask flask fitted with an air-tight stirrer, reflux condenser, a dropping funnel and a bubbling tube, purge air with dry argon and dissolve 46.5 g of diphenylphosphine and 25 g of triethylamine in 500 ml of anhydrous diethyl ether.

50 g of 2,6-dimethoxybenzoyl chloride solution in 100 ml of dry diethyl ether are added dropwise while stirring and maintaining the temperature at 20 ° C. The reaction mixture is refluxed for 5 hours, then cooled, the resulting triethylamine hydrochloride is filtered off and the filtrate is evaporated on a rotary evaporator. The residue is purified by column chromatography over silica gel, eluting with toluene / ether (2: 1).

Yield: 17 g (10% of theory). Melting point 113-115 ° C λ max = 336 nm.

Calculated,%: C 72.0 H 5.43 P 8.86

Found,%: C 71.7 H 5.4 P 8.7

4) Solvent

The photosensitive composition of the organic solvent must dissolve all the organic components well, be low volatile at room temperature and evaporate sufficiently quickly at 80-100 ° C. The most commonly used solvents are terpenes (α and β-terpineol), carbitol acetate, butylcarbitol acetate, higher alcohol esters. Benzyl alcohol has been found to be the most suitable solvent for the patented composition.

5) The thermal polymerization inhibitor must ensure stability of the whole composition, especially during drying. 2,6di-tert-butyl-1,4-cresol has been found to be the most suitable inhibitor.

The photosensitive organic medium is prepared by dissolving the remaining organic components in benzyl alcohol at 60 ° C. The viscous solution is passed through a dense stainless steel mesh and cooled.

In this way the organic media used in the following experiments were prepared in the following proportions by weight:

Table

<td rowspan="2">Components</td><td colspan="4">Organic medium</td>

<td>I</td><td>II</td><td>III</td><td>IV</td>

<td>Polymer A</td><td> 100</td><td> -</td><td> -</td><td> -</td>

<td>Polymer B</td><td> -</td><td> 100</td><td> 100</td><td> 100</td>

<td>2,6-Dimethoxybenzoyl diphenylphosphine</td><td> 7.5</td><td> 7.5</td><td> 7.5</td><td> -</td>

<td>Didodecyldisulfide</td><td> 5.0</td><td> - </td><td> 5.0</td><td> 5.0</td>

<td>2,6-di-tert-butyl-1,4-cresol</td><td> 0.5</td><td> 0.5</td><td> 0.5</td><td> 0.5</td>

<td>Benzyl alcohol</td><td> 60</td><td> 60</td><td> 60</td><td> 60</td>

<td>Benzophenone</td><td> -</td><td> -</td><td> -</td><td> 12</td>

<td>Michler's ketone</td><td> -</td><td> -</td><td> -</td><td> 12</td>

Note: Organic media IV uses the benzophenone / Michler ketone photoinitiation system described in the analogues to compare the efficacy of photoinitiators.

The photosensitive compositions according to claims 9-14 were prepared by mixing the powder of the inorganic components with the photosensitive organic medium. The initial mixing is done manually in an agate mortar, and the final mixing in a special three-shaft mixer which ensures an even distribution of the inorganic filler powder in the organic medium.

The photosensitive compositions prepared in this manner were applied over a stainless steel mesh (80 microns mesh, 40 microns mesh, 90x90 microns mesh) on alumina ceramic substrates using conventional technology.

The substrate compositions were dried for 10 minutes at 100 ° C in electric furnaces and then exposed to a special photo template to evaluate the properties (resolution, specific impedance, adhesion, etc.) of the compositions under investigation and the substrates formed therefrom.

The light source used in the exhibit is the Philips halogen 1000W HPA1000 halogen lamp with an emission spectrum concentrated in the 320-400 nm range. The optimum exposure time for each composition was determined experimentally by evaluating the results obtained by highlighting, i.e., flushing unexposed areas of the composition layer.

The clarification was performed on a special machine by spraying an aerosol of 0.5% aqueous solution of monoethanolamine on a rotating pad at 3000 rpm. The pressures of solution and compressed air delivered to the nozzle head can be adjusted within wide limits, n the duration of spraying can be adjusted in 0.1 second increments. Typical development times are between 2 and 5 seconds at a solution pressure of 1.5 bar and an air pressure of 2.5 bar. At the end of the development cycle, the rest of the composition on the substrate is washed in the same device for 2-3 seconds with distilled water and then dried for 10-15 seconds at the same speed.

The test structures produced in this way were heat treated in an electric conveyor furnace for a maximum of 850 ° C for 15 minutes.

The results of the experiments are shown in Table 3, the amounts of the components being given in parts by weight.

Comparing the results of the tests of compositions Nos. 2,3,4 and 5, which differ only in the composition of the organic medium, the following conclusions can be drawn:

1) The photochemical activity of polymers having side chains with acrylic groups (composition No. 4) is higher than that of polymers with side methacrylic groups (composition No. 2).

2) Using the same polymer, the organic disulfide additive completely neutralizes the inhibitory effect of oxygen and shortens the exposure time 3-fold (compositions 3 and 4).

3) The photoinitiator used in the patented composition is significantly more effective than the benzophenone / Michler ketone photoinitiation system described in the analogs (Compositions Nos. 4 and 5).

Compositions Nos. 1, 4 and 6 allow the formation of ultra-narrow conductors by the method of thick-layer technology, which significantly extends its capabilities and application range.

By using compositions No. 1 (or No. 5) and No. 8, alternating switching and insulating layers can be formed and multi-layer switching boards of extremely high degree of integration can be produced.

Compositions Nos. 7 and 9 can be used for the manufacture of miniature temperature sensors with high temperature resistance.

<img file="LT4534B_D0001.tif" />

Note: The resolution indicated for composition # 8 means that a 50x50 micron hole can be formed in the insulating layer.