LT4534B - Photosensitive composition developable by aqueous base solutions - Google Patents

Abstract

This invention belongs to the field of microelectronics and is intended for application of thick layer technology and expansion of its potentialities. The composition presented consists of (in mass percentage): fine inorganic aggregate powder (100.0), polymer (9-36), photo-initiator (0.5-3.5), organic disulphide (0.2-2.0), inhibitor of thermal polymerisation (0.01-0.35) and organic solvent (5.5-21.5). This composition is painted over a thin net on ceramic plates, dried, exposed through photo-pattern to ultraviolet rays, areas not exposed to light are washed with a 0.5 % monoethanolamine solution, and the picture remaining on the plate is thermally processed at a temperature of 850 degrees Celsius. The aim of the invention is to increase the resolution of the composition and eliminate its sensitivity to visible light and oxygen in the air. The point of trying to solve this problem is as follows: a polymer, which forms a film and ensures solubility in the water base solutions, is photochemically active, its spatial polymerisation is effectively initiated by the photo-initiator, the one insensitive to a visible part of the spectrum, while side-chains of the polymer with alkyl groups and organic disulphide added in addition neutralize the inhibition effect of oxygen, and it ensures higher resolution of the composition.

Description

The present invention relates to the field of microelectronics and is intended to improve the performance and functional capabilities of high-density hybrid chip elements (conductors, resistors, capacitors), multilayer 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 them.

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 media 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 relationship, 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 great advances in this area, screen printing is virtually impossible to form conductors thinner than 100 microns, to obtain a gap between conductors narrower than 100 microns, or to have apertures less than 200 microns in insulating layers. The thresholds for mass production 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 radiation zones correspond to the future distribution of the film elements, photopolymerization of the organic medium takes place in the illuminated 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 ensures gold adherence to ceramics;

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 tetrachlorethylene stream, and heat treated at the substrate with 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 photopolymeric composition. The inventions of the two cited patents have the same definitions except for the first claim, which refers to either gold or silver powder, so that the two analogs mentioned can be considered together. The photopolymer compositions described in the analogs consist of:

(1) gold powder (or silver) with a reference surface area less than 20 m ² / g and at least 80% gold (or silver) particle size within the range of 0.5 to 10 microns; and

2. glass powder (melting point between 500 ° C and 825 ° C) with a reference surface area not exceeding 10 m ² / g and at least 90% of the glass particles being 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 50,000 and a content of comonomer with free carboxyl groups of 15% or more. aqueous disodium trioxocarbonate solution;

b) the photoinitiation system comprises 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 the inorganic components. The best results are obtained with the following ratio of components in parts by weight:

Table

Components Silver paste Gold paste Silver powder 70.8 - Gold powder - 78.0 Glass powder 5.3 4.6 Organic binder 17.1 13.0 Trimethylolpropane Triacrylate 1.0 0.8 Polyoxyethylated trimethylolpropane triacrylate 4.2 3.4

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 photosensitive compositions described herein 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 the three-dimensional structure resulting from the photopolymerization of polyfunctional monomers. 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 examples provided in the analogs, from 0.6 g to 0.65 g of polyfunctional monomers per gram of polymer, the polymer also 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 also does not exhibit high efficiency compared to other known photoinitiators.

3) The compositions are sensitive to the inhibitory effects of oxygen and should 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 forming by a thin-film technology that is insensitive to visible spectrum and inhibitory oxygen, exhibiting high photopolymerization rates and higher resolution. This object is solved by the patentable composition according to the general part of claim 1, wherein the organic polymer-based polymer is photochemically active, i. not only serves as a film-forming and solubility component in aqueous base solutions, but is also a large molecular polyfunctional monomer whose photopolymerization is efficiently initiated by a photo-insensitive photoinitiator, and the polymer side chains with allyl groups and additionally an organic disulfide added to the organic medium effect of oxygen at the following ratio of components, by mass:

powder of inorganic filler 100.00 polymer 9am - 36.00 photoinitiator 0.50 - 3.50 organic disulfide 0.20 - 2am inhibitor of thermal polymerization 0.01 - 0.35 an organic solvent 5.50 - 21.50

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 carried out in diffused daylight or under normal artificial light.

In addition, the exposure process is greatly 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 the presentation of 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 area 5 m ² / g, particle size 0.1 micron to 2.0 micron, 50% by weight of particles less than 1.0 micron.

4) Platinum powder with irregularly shaped particles. Spherical surface 0.4 m ² / g, particle size 0.5 microns to 4.0 microns, 50 wt% particles smaller than 2.0 microns.

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

CdO 9.8 CuO - 15.9 Well, how about - 14.3 B2O3 - 27.0 SiO ₂ - June 31 B12O3 1.4

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

sio ₂ - 33.4 Ai ₂ 0 ₃ 2.6 PbO - 41.3 b ₂ o ₃ S.O. ZnO -. 14.7

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

SiO ₂ - 57.6 PbO - July 26 B ₂ O; 1.4 Al ₂ O; 5.6 BaO 3.8 CuO 3.5 K ₂ O 1.4

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 vibrocouples. The smallest fraction of the powders filtered off, 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 a photosensitive organic substrate based 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 the inert base 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 of components) were synthesized.

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

Styrene 24.0 Butyl methacrylate 17.5 Acrylic acid 36.0 Methacrylic acid 42.5 Glycidyl Methacrylate - 30.0 Glycidyl acrylate 30.0 Allyl glycidine ether 10.0 Allyl glycidine ether - 10.0

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 action of oxygen, but do not permanently eliminate it.

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

Ri-CH ₂ -S-S-CH ₂ -R ₂ described in EP no. 0028749, G03C 1/68, May 20, 1981, wherein R _x and R ₂ are the same or different alkyl, cycloalkyl, aryl, arylalkyl or carbamoylalkyl radicals.

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

3) Photoinitiator.

At present, there are many organic compounds known to be thermally stable but which generate free radicals by one or the other 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 the 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 (a 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

Components Organic medium I II III IV Polymer A 100 - - - Polymer B - 100 100 100 2,6-Dimethoxybenzoyl diphenylphosphine 7.5 7.5 7.5 - Didodecyldisulfide 5.0 - 5.0 5.0 2,6-di-tert-butyl-1,4-cresol 0.5 0.5 0.5 0.5 Benzyl alcohol 60 60 60 60 Benzophenone - - - 12th Michler's ketone - - - 12th

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 way 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 through a special photo template to evaluate the properties (resolution, specific resistivity, adhesion, etc.) of the compositions under investigation and of 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 focusing, i.e. flushing unexposed areas of the composition layer from the substrate.

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 over a wide range, and the nozzle duration 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 machine for 2-3 seconds with distilled water and then dried for 10-15 seconds at the same rotation 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.

Comparison of the results of the tests of compositions Nos. 2,3,4 and 5, which differ only in the composition of the organic medium, leads to the following conclusions:

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 times (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.

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

Claims (14)

DEFINITION OF INVENTION CLAIMS 1. A photosensitive aqueous base solution formulation for the formation of film elements by a thin-layer technology consisting of a fine inorganic filler powder dispersed in a photosensitive organic medium comprising a film-forming polymer, a photoinitiator, a thermoplastic organic solvent, an organic solvent, does not contain a polyfunctional monomer and is based on a polymer which is photochemically active and additionally contains, in a proportion by weight, an organic disulphide in an organic medium in the following proportions: inorganic filler powder polymer 100.00 9am - 36.00 photoinitiator 0.50 - 3.50 organic disulfide 0.20 - 2am inhibitor of thermal polymerization 0.01 - 0.35 an organic solvent 5.50 - 21.50 2. The composition of claim 1, wherein the film-forming polymer is alkyl acrylates or alkyl methacrylates having an alkyl radical of 1 to 12 carbon atoms, cycloalkyl (meth) acrylates, arylalkyl (meth) acrylates, styrene, acrylonitrile or a mixture thereof and unsaturated a copolymer of carboxylic acids with a portion of the free carboxylic groups esterified with 2,3-epoxypropyl (meth) acrylate and allylglycidine ether. 3. The composition of claim 2, wherein the film-forming polymer is a copolymer of styrene and acrylic acid containing 15% by weight of non-esterified acrylic acid, 15% by weight of acrylic acid esterified with 2,3-epoxypropyl methacrylate and 6% by weight of allyl glycidine ether. 4. The composition of claim 2, wherein the film-forming polymer is a copolymer of butyl methacrylate and methacrylic acid containing 15 wt% non-esterified methacrylic acid, 20 wt% methacrylic acid esterified with 2,3-epoxypropyl methacrylate and 7.5 wt% allyl . 5. The composition of claim 1, wherein the photoinitiator is 2,6-dimethoxybenzoyl diphenylphosphine. 6. The composition of claim 1, wherein the organic solvent is benzyl alcohol. 7. The composition of claim 1, wherein the disulfide additionally added to the organic medium is didodecyldisulfide. 8. The composition of claim 1, wherein the inhibitor of thermal polymerization is 2,6-di-tert-butyl-1,4-cresol. 9. The composition of claim 1, wherein the inorganic filler is a mixture of gold and glass powder in which 1 to 4 parts by weight of glass is contained per 100 parts by weight of gold. 10. The composition of claim 1, wherein the inorganic filler is a mixture of silver and glass powder, wherein 100 parts by weight of silver contains from 1 to 3 parts by weight of glass. 11. The composition of claim 1 further comprising. that the inorganic filler consists of a mixture of silver, palladium and glass powder containing 85 parts by weight of silver per 15 parts by weight of palladium and a glass content of 3-5% by weight based on the total weight of silver and palladium powder. 12. The composition of claim 1, wherein the inorganic filler is a crystallization powder. 13. The composition of claim 1, wherein the inorganic filler is a mixture of platinum and glass powder containing 55% K by weight platinum and 45% by weight glass. 14. The composition of claim 1, wherein the inorganic filler is a mixture of ruthenium oxide and glass powder containing 60% by weight of ruthenium oxide and 40% by weight of glass.