EP1364563A1

EP1364563A1 - Method for making a multilevel circuitry comprising conductor tracks and micro-vias

Info

Publication number: EP1364563A1
Application number: EP01995753A
Authority: EP
Inventors: Robert Cassat; Vincent Lorentz
Original assignee: Kermel SNC
Current assignee: Kermel SNC
Priority date: 2000-12-29
Filing date: 2001-12-24
Publication date: 2003-11-26
Also published as: CA2433222A1; BR0116760A; FR2819144A1; US20040067447A1; WO2002054844A1; CN1488235A; FR2819144B1; MXPA03005841A

Abstract

The invention concerns a method for making an multilevel interconnection circuitry comprising conductor tracks and micro-vias. The method for producing at least one of the levels comprises the following steps: a) on a substrate including at its surface metallizable and/or potentially metallizable parts (102), forming a first insulating photosensitive resin layer (103) comprising a compound capable of inducing subsequent metallization; b) exposing and revealing the first layer (103) so as to selectively uncover the metallizable and/or potentially metallizable parts (102) of the substrate; c) forming, by metallization, metal conductor tracks (111) and micro-vias (110) at the surface of the first insulating photosensitive resin layer (113) and of the parts uncovered during step b), by providing a second photosensitive resin layer (105) forming a selective protection, the second photosensitive resin layer (105) being eliminated.

Description

Method for manufacturing a circuitry with several levels comprising tracks and microtraverses.

The invention relates to an improved method for producing interconnection circuitry at several levels comprising tracks, conductive microtransverses, and possibly pads.

In the context of the invention, the term “micro crossings” means the microconnections passing right through the thickness of a layer of dielectric. Microtraverses are commonly known as microvias in the art. In the field of electronics, there is a trend towards optimal miniaturization of products as well as an increase in performance in terms of speed. These trends are accentuated by the increasing use of surface connection components such as BGA CGA, CSP or other Flip Chip.

Integration densification is desirable in three dimensions: both in an axial direction by successive stacking of increasingly thin dielectric / copper layers to obtain a multilayer, than in the plane perpendicular to this direction by bringing tracks together. and increasingly fine pastilles.

The process of the invention meets these requirements by ensuring the development of "fine line" circuitry characterized by widths of tracks and interpenetrators less than 100 μm and diameters of holes or crossings less than 100 μm.

This method also ensures excellent adhesion of the metal layers to the dielectric substrate, and limits the inaccuracies due to the successive stacking of the layers.

The method of the invention is also economically advantageous insofar as it allows the implementation of a small number of steps.

According to a first of its aspects, the invention provides a method of forming conductive tracks and microtravers in a dielectric covering a first level of circuitry or a first metallized layer, without deterioration of said first level of circuitry or of said first metallized layer. For the manufacture of circuitry comprising conductive microwires, the process described in US Pat. No. 5,260,170 is known. This process comprises the following steps:

1. Application on a substrate of a first layer of photosensitive resin comprising an electrochemical metallization catalyst 2. Insolation and revelation in order to discover certain parts of the substrate

3. Application of a second layer of photosensitive resin not comprising a metallization catalyst 4. Insolation and revelation in order to discover certain parts of the first layer and of the substrate

5. Electrochemical metallization

Steps 3, 4, 5, 5 make it possible to form tracks and micro-crossings, the second layer of photosensitive resin constituting selective protection. This layer is not removed.

The process can be repeated several times in order to obtain circuitry with several layers, the last surface obtained serving as a substrate.

The circuitry obtained according to the method described above has poor flatness, which affects their accuracy. This defect may be due to phenomena of swelling of the photosensitive resin in contact with solutions used for different treatments such as activation of the catalyst or metallization. It may also be due to too much overlapping of layers.

The invention provides an improved method of manufacturing circuitry, in particular allowing better flatness to be obtained. The method also has the advantage of being more reliable, by reducing the rate of circuitry which would be non-compliant due to inaccuracies in the superposition of the layers and the positioning of the microtravers.

To this end, the invention provides a method of manufacturing interconnection circuitry at several levels comprising tracks and metal microtravers, comprising the following steps for producing at least one level: a) On a substrate having on its surface metallizable and / or potentially metallizable parts, formation of a first layer of insulating photosensitive resin comprising a compound capable of inducing a subsequent metallization b) exposure and revelation of the first layer so as to selectively uncover metallizable parts and / or potentially metallisable of the substrate c) formation, by metallization, of metal tracks and microstreams on the surface of the first layer of insulating photosensitive resin and of the parts discovered during step b), with the use of a second photoresist layer forming selective protection, characterized in that the method comprises, for the achievement of the level considered, a step during which the second layer of photosensitive resin is eliminated. The circuitry is obtained by forming layers and / or depositing layers of materials of different natures, on defined parts. We thus realize tracks metallic, metallic micro-crossings, possibly metallic pellets, separated in places and supported by layers of an insulating material.

The tracks, microtraverses and pads form an interconnection circuit.

The tracks are parts of circuitry positioned on the surface of an insulating material. They are generally in the form of lines of reduced thickness.

The circuitry according to the invention comprises several levels of circuitry.

Each level of circuitry corresponds to a set of tracks on the surface of an insulating material. The circuitry levels are therefore separated by a layer of insulating material, with in places metallic connections between the levels. These metallic connections between two or more levels are called micro-crossings. Such structures, and such terms are known to those skilled in the art.

The manufacture of the circuitry, for at least one of the levels, includes steps a), b), c), with elimination of the second layer for this level.

According to the invention, the layers of insulating material separating the circuitry levels consist of insulating photosensitive resin, comprising a compound capable of inducing subsequent metallization. This layer is called "first layer". The micro-crossings establishing a metallic connection between the levels through this layer are positioned where parts of the first layer have been eliminated by exposure and revelation. We often talk about "photovia". During step a) a first layer of photosensitive resin is formed on the surface of a substrate having metallizable and / or potentially metallizable parts.

By potentially metallizable surface is meant a surface portion which cannot be directly metallized by electrolytic and / or electrochemical means, but which can be metallized after having undergone an adequate treatment. It may for example be a part of the resin surface, photosensitive or not, insulating, comprising a compound capable of inducing subsequent metallization. It may in particular be a part of a layer having served as the first insulating photosensitive resin layer when a lower level is produced. By metallizable surface part is meant a surface which can be directly metallized by electrolytic and / or electrochemical means. It may for example be a metal part, for example tracks, pellets or microtraverses on the surface of the substrate.

The tracks and microtraverses are formed by metallization on the surface of the first layer of photosensitive resin and of the parts of the substrate discovered during step b). The metal parts formed on the surface of the parts discovered during step b) correspond to microtravers. For the formation of tracks and micro-crossings, selective protection is carried out by using a second layer of photosensitive resin. The methods of forming metallic interconnects with selective protection by a layer of photosensitive resin are known to those skilled in the art. We cite in particular the pattern type processes, the panel type processes. For the method according to the invention, the metallization on the parts of the first layer of photosensitive resin is made possible thanks to the compound capable of inducing a subsequent metallization included in said resin, and possibly with an adequate treatment preceding the metallization. According to the invention, the layer of photosensitive resin (second layer of photosensitive resin) used to form the selective protection is eliminated during the process.

The elimination of the second layer of photosensitive resin, for an intermediate level of circuitry, allows an improvement in the flatness. By intermediate level is meant a level which will not be the last and which will serve as a lower level during the formation of an upper layer. It also makes it possible to leave available, on certain parts, an insulating photosensitive resin surface comprising a compound capable of inducing subsequent metallization. In the event of imprecision during the manufacture of a higher level of circuitry or in the positioning of the microtraverses, metallization and obtaining a contact remain possible with very good cohesion, which is not the case if the second layer of photosensitive resin is not removed.

The substrate may be a lower level of circuitry produced according to the method of the invention, or according to another method. In the case where the substrate is a lower level of circuitry produced according to the method of the invention, the metallizable parts are parts of lower level circuitry, in particular tracks and / or micro-crossings, and the potentially metallizable parts are parts non-metallized of the first layer of insulating photosensitive resin used during the production of the lower level. The substrate can also be a printed circuit on one or more levels on rigid or flexible support, possibly with conductive crossings. For the support, it may for example be an injected insulating material or a conventional composite material in the field of printed circuits. Mention is made, for example, of epoxy / glass fiber-based supports. It may be a dielectric material comprising a sheet of nonwoven fibers or a paper, impregnated with dielectric resin. The presence of the web or paper ensures good uniformity of the thermal expansion coefficients (CTE). In a particularly advantageous manner, the support is a sheet made up of nonwoven aramid fibers (commercial aromatic polyamide) pre-impregnated with an epoxy resin, a polyimide resin or a mixture of these resins. More preferably, these aramid fibers (which are preferably meta-aramid, para-aramid fibers or a mixture of such fibers) are pre-impregnated with functionalized polyimide-amide resin (with chemical units which can be crosslinked when hot). This functionalization can be obtained with double bonds or maleimide groups as defined in patent EP 0 336 856 or US 4 927 900. Advantageously, the sheet comprises from 35 to 60% by weight of dielectric resin, preferably from 44 to 55 % by weight, better still from 40 to 50% by weight, for example 47% by weight.

For example, the thickness of the sheet varies between 10 and 70 μm, preferably between 15 and 50 μm, better still between 20 and 40 μm.

Its grammage generally varies between 10 and 50 g / m ² , better still between 15 and 40 g / m ² . It is specified that the circuitry obtained by the method according to the invention can be carried out on one or two faces.

During step a), a first layer of insulating photosensitive resin is formed on a substrate.

The first layer of insulating photosensitive resin comprises a compound capable of inducing subsequent metallization. They are preferably particles of a metal oxide. The metal oxide is chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn, and their mixtures. Particular preference is given to cuprous oxide Cu ₂ O. The resin may also include inert non-conductive fillers.

As regards the metal oxide, it must be in the form of particles of small dimensions; the particle size is generally between 0.1 and 5 μm.

The resin can be chosen from negative or positive photosensitive resins. It is advantageously applied to the substrate or the lower circuit level in the form of a solution in a solvent and / or in the form of a fluid, not crosslinked, in stage A. As an example of resin, the Probimer range marketed by Vantico. The compound capable of inducing a subsequent metallization is in principle introduced into these resins before formation of the layer.

The thickness of the resin is such that the insulation between two layers of conductive material is sufficient. It is advantageously less than 100 μm, for example between 10 and 20 μm, preferably between 20 and 40 μm. The dielectric permittivity of the layer is advantageously less than 5.

The compound capable of inducing a subsequent metallization makes it possible to achieve metallization after a treatment, for example by a treatment leading to the formation of an undercoat. Treatments that can be implemented will be described later.

During step b), the first layer of resin is exposed and then revealed. Depending on the nature of the resin, positive or negative, the parts eliminated during the revelation operation are the exposed or non-isolated parts.

The operations of insolation and revealing of a layer of photosensitive resin, in order to discover parts of the underlying layers, are known to those skilled in the art. Two techniques known from the state of the art are perfectly suitable. The first consists in exposing the resin layer, using a predetermined mask.

The second technique is the LDI technique called direct photosensitive resin exposure (Laser Direct Imaging).

This technique is advantageous economically since it does not require the use of a mask. According to this second technique, the photosensitive resin is selectively exposed, pixel by pixel, by a laser beam scanning the surface of the dielectric coated with photosensitive resin.

The solubilizable parts of the resin are then removed in the same way as for the conventional technique using positive and negative photosensitive resins.

For the implementation of this second technique, two types of laser are for example suitable: a laser operating in the infrared (thermal LDI), a UV laser operating in the wavelength range 330-370 nm (LDI- UV).

Step c) itself comprises several steps. There are several embodiments of step c), corresponding to sequences of different steps. Three sequences corresponding to different particular embodiments will be exposed later.

During step c), a second layer of photosensitive resin is used. The resin of the second layer, advantageously, does not contain any compound capable of inducing subsequent metallization.

The resin for the second layer can be chosen from positive or negative photosensitive resins. The layer can be formed by application in the form of a solution in a solvent and / or in the form of a non-crosslinked fluid in stage A. As an example of resin, mention is made of the Probimer range sold by the company Vantico.

The layers of photosensitive resins, in particular the first, may optionally include other non-conductive and inert compounds, such as powdery mineral fillers. They may, for example, be particles of calcium carbonate. The presence of such fillers, in particular in the first layer, can make it possible to improve the cohesion of the metallic layers formed and to improve their adhesion. The particle size of the fillers is chosen so as to be compatible with the process for applying the resins.

The second layer, during step c), is exposed and then revealed so as to discover certain parts of the first layer and / or of the substrate and / or certain parts of metal layer formed before the formation of the second layer. The nature of the parts discovered may vary depending on the particular embodiments that will be implemented. Embodiments will be described below. For example are discovered for a first embodiment certain parts of the first layer and the parts discovered during step b) of the substrate, and, for other embodiments, certain parts of a metal layer formed on the entire surface of the first layer. Depending on the nature of the resin, positive or negative, the parts eliminated during the revelation operation are the insulated or non-insulated parts.

The exposure and development of the second layer of photosensitive resin can be carried out according to the methods which have been described for the first layer of photosensitive resin. The tracks and microtraverses are formed by metallization on all or part of surfaces not protected by the second layer of photosensitive resin, either before application of the latter, or after elimination of certain parts of the latter. Metallization can be carried out electrochemically (without current) and / or electrolytically (with current). The latter route is more particularly preferred since it is faster. It can also be carried out in an acid medium, which avoids swelling of the photosensitive layers, thus improves the positioning accuracy of the various exposures and revelations, and improves the reliability and longevity of the circuitry. For metallization by electrolytic means, it is advantageous to operate at increasing intensity. The metal is preferably copper. Electrochemical metallization (without current) is a known technique which is described in "Encyclopedia of Polymer Science and Technology, 1968, vol. 8, 658-661".

Likewise, electrolytic metallization (with current) is a conventional technique also described in Encyclopedia of Polymer Science, 661-663. According to a particularly preferred embodiment of the invention, the metallization, whether electrochemical or electrolytic, is continued until a metallic layer is obtained having a thickness of at least 5 μm, preferably a thickness of between 10 and 20 μm.

Step c) advantageously comprises before metallization a step of forming a sub-layer capable of being metallized. Such an underlayer is formed on the surface of the first layer of photosensitive resin, or on the surface of exposed parts of the first layer with selective protection of the other parts by the second layer. The under layers formed are, depending on the case, continuous or discontinuous, and lend themselves, or not, directly to metallizations by electrolytic means. However, they are still suitable for electrochemical metallizations. In this case the electrochemical deposition of metal is catalyzed by the under layer, and the metallization is equivalent to those using Palladium or Platinum.

Two modes are preferred for the embodiment for obtaining a sub-layer capable of being metallized.

According to a first embodiment of the under layer, the compound capable of inducing a subsequent metallization is chosen from the metal oxides, mentioned above, and the under layer is formed by bringing the first layer or exposed parts of it into contact. the first layer with a solution of a noble metal salt capable of being reduced by oxide particles.

During this step other layers can be brought into contact with the solution. It has no useful effect on them. A continuous sublayer of the noble metal is thus formed on the exposed surface of the first layer. The resistivity of the sub-layer is between 10 ⁶ and 10 ³ Ω / D. It is preferably less than 10 ³ Ω / D. This allows electrochemical metallization, preferably at increasing intensity. It is indicated for information that the cohesion of the under layer is all the better the higher the concentration of oxide particles.

As solutions of preferred noble metal salts, mention is made of solutions of salts of Au, Ag, Rh, Pd, Cs, Ir, Pt, with a counter ion chosen from Cl ^" , NO ^" ₃ , CH ₃ COO ^" . The contacting can be carried out by soaking in the solution, spraying, passing a roller.The noble metal salt solution is generally acidic, with a pH of between 0.5 and 3.5, preferably between 1 , 5 and 2.5 The pH can be controlled by adding acid. This treatment in an acid medium also makes it possible to limit swelling of the resin layers which takes place in basic medium. This first mode of circuitry is therefore obtained having excellent definition and excellent flatness. It is mentioned that treatment with an acid solution of noble metal salts may be preceded by rinsing with an acid solution, for example acetic acid, in the case where the first layer of photosensitive resin comprises carbonate particles of calcium. This rinsing makes it possible to increase the roughness of the surface, the calcium carbonate particles present on the surface being dissolved, and thus to improve the adhesion of the metallic deposits.

For the first mode of forming a sublayer, the metal oxide particles are preferably chosen from MnO, NiO, Cu ₂ O, SnO, and are preferably contained in the first layer up to 2.5- 90% by weight, even more preferably up to 10-30%. The preferred metal oxide is cuprous oxide Cu ₂ O. The solution advantageously comprises at least 10 ^"5 mol / L of noble metal salt, preferably between 0.0005 and 0.005 mol / L. An undercoat is obtained of noble metal continuous and of thickness less than 1 μm. The under layer obtained has excellent uniformity, which improves the quality of the connections obtained after metallization. As salts which can be used, mention may be made of AuBr ₃ (HAuBr), AuCI ₃ (HAuCI ₄ ) or CI ₆ , silver acetate, silver benzoate, AgBrO ₃ , AgCIO ₄ , AgOCN, AgNO ₃ , Ag ₂ SO ₄ , RuCI ₄ .5H ₂ O, RhCI ₃ .H ₂ O, Rh (NO ₃ ) ₂ .2H ₂ O, Rh ₂ (SO ₄ ) ₃ .4H ₂ O, Pd (CH ₃ COO) ₂ , Rh ₂ (SO ₄ ) ₃ .12H ₂ O, Rh ₂ (SO ₄₎ ₃ .15H ₂ O, PdCl _2, PdCl ₂ .2H ₂ O, SODP ₄ SODP ₄ .2H ₂ O, Pd (CH ₃ COO) _2, OSCI ₄ OSCI ₃ OSCI ₃ .3H ₂ O, Osl ₄ , lrBr ₃ 4H ₂ O, lrCI ₂ , lrCI ₄ , Ir0 ₂ , PtBr ₄ , H ₂ PtCI ₆ 6H2O, PtCI ₄ , PtCI ₃ , Pt (SO ₄ ) ₂ .4H ₂ O or Pt (COCI ₂ ) CI ₂ , and cor complexes respondent as NaAuCI ₄₎ (NH ₄ ) ₂ PdCI ₄ , (NH4) ₂ PdCI ₆ , K ₂ PdCI ₆ or KAuCI ₄ . The undercoat obtained is particularly suitable for electrolytic metallization. One can for example implement an electrolytic metallization with increasing intensity.

The formation of the under layer in the context of the first mode, can in particular comprise the following operations:

- updating of the metal oxide particles included in the first layer of photosensitive resin. This operation is preferably carried out by alkaline attack

(for example with a solution of soda or potash in an alcoholic medium) then rinsing with water, possibly under utra-sounds in order to remove the loose oxide particles.

- In the event that the first layer of photosensitive resin contains inert fillers such as calcium carbonate, creation of a slight surface roughness by acid attack. This operation is preferably distinct from the operation of forming the metal underlayer.

Formation of a continuous metallic sublayer of noble metal by contacting with an aqueous, acidic solution of noble metal salt. As an indication, it should be noted that the sublayer obtained is generally monoatomic, the noble metal acting as a barrier to the continuation of the redox reaction. The layer is continuous because part of the metal oxide particles release ions by dissolution. These ions react in an aqueous medium with the noble metal salt, causing the reduction of this metal, which is deposited thus filling the inter-particle spaces. The reaction is all the more efficient and economical as the aqueous medium of noble metal salt is more confined. For this reason, it is preferred to carry out the reaction in a thin layer, that is to say by immersion in the solution comprising the noble metal salt, and withdrawal immediately afterwards. The reaction then takes place in the layer of aqueous solution entrained with the object. According to a second embodiment of the sublayer, the compound capable of inducing a subsequent metallization is chosen from the metal oxides mentioned above, and the sublayer is formed by bringing the first layer or exposed parts of it into contact. the first layer with a reducing agent capable of reducing the oxide particles.

During this step other layers can be brought into contact with the reducing agent; it has no useful action on them. There is thus formed on the surface of the first layer a sublayer of a reduced form and conductive of the metal oxide.

In the context of the second mode of formation of the sublayer, the preferred metal oxide is cuprous oxide Cu ₂ O. The first layer advantageously comprises, according to this mode, from 10 to 90% by weight of metal oxide, preferably from 25 to 90%. In a variant, it comprises less than 10% of cuprous oxide. The underlayer formed is, depending on the case, continuous or discontinuous and has a surface resistivity of between 0.01 and 10 ⁶ Ω / D.

The surface resistivity that it is possible to achieve for the sub-layer depends on the composition of the first layer of photosensitive resin. It is indicated for information that the cohesion of the under layer is all the better as the concentration of the oxide particles is important.

When the first layer of photosensitive resin consists of 10 to 90% by weight of metal oxide; from 0 to 50% by weight of inert and non-conductive filler (s); and from 10 to 90% by weight of polymer resin, the reduction is advantageously continued until a surface resistivity of 0.01 to 10 ³ Ω / D is obtained. We generally obtain a continuous sublayer. The continuity and the resistivities achieved allow in particular to implement electrolytic metallizations directly on the undercoat. One can for example implement an electrolytic metallization with increasing intensity. When the first layer of photosensitive resin consists of less than

10% by weight of metal oxide; from 0 to 50% by weight of inert filler (s) and not conductor (s); and from 50 to 90% by weight of polymer resin, the reduction is advantageously continued until a surface resistivity greater than 10 ⁶ Ω / D is obtained. In this case the sub-layer may have discontinuities.

The continuous or discontinuous sub-layer also catalyzes the subsequent metal deposit while being perfectly compatible with it.

This step contributes more precisely to improving the adhesion of the subsequent metallic deposit by preventing any break in the electrical conduction at the level of the metallized bushings.

The formation of the under layer in the context of the second mode, can in particular comprise the following operations:

- updating of the metal oxide particles included in the first layer of photosensitive resin. This operation is preferably carried out by alkaline attack (for example by a solution of soda or potassium hydroxide in hydroalcoholic medium) then rinsing with water, possibly under utra-sounds in order to remove the loose particles of oxide.

- In the event that the first layer of photosensitive resin contains inert fillers such as calcium carbonate, creation of a slight surface roughness by acid attack. This operation is preferably distinct from the operation of forming the metal underlayer. - Formation of a metal undercoat by contacting with an aqueous solution comprising a reducing agent. The formation of the sublayer is preferably carried out in a thin layer, by immersion in an aqueous solution comprising the reducing agent, and immediate removal, according to a principle analogous to that described above. As an indication, it is specified that when the metal oxide is a cuprous oxide, part of the copper is reduced to the CuH state, a state in which the copper acts as a catalyst for the formation of the sublayer. If there is an excess of CuH, the latter transforms slowly into copper metal at room temperature, with diffusion of the hydrogen towards the outside. In the following, the presence of this transient hydride is no longer mentioned and reference is simply made to a metallic layer.

For the implementation of the reduction, a person skilled in the art can select any of the reducing agents capable of reducing the metal oxide to a metal of oxidation state 0.

Obtaining the desired resistivity values during this step will depend on the one hand on the proportions and on the nature of the metal oxide included in the matrix. polymer forming dielectric and on the other hand, the importance of the reduction carried out, and in particular the type of reducing agent used as well as the step of preliminary pickling.

Depending on the type of reducing agent used and on the nature of the metal oxide to be reduced, the nature of the metal layer deposited varies. According to a preferred embodiment of the invention, the reducing agent is a borohydride.

The action of borohydrides is described more precisely below in the case where the metal oxide is a cuprous oxide.

By the action of a borohydride Cu ₂ O is reduced to metallic copper. By using this type of reducing agent, the layer formed on the surface of the dielectric is a continuous or discontinuous metallic layer of copper.

Usable borohydrides include substituted borohydrides as well as unsubstituted borohydrides. Substituted borohydrides in which at most three hydrogen atoms of the borohydride ion have been replaced by substituents which are inert under the reduction conditions, for example alkyl radicals, aryl radicals, aikoxy radicals, can be used. Preferably alkali borohydrides are used in which the alkaline part consists of sodium or potassium. Typical examples of suitable compounds are: sodium borohydride, potassium borohydride, sodium diethylborohydride, potassium triphenylborohydride. The reducing treatment is carried out in a simple manner by bringing the surface of the dielectric into contact with a solution of the borohydride in water or in a mixture of water and an inert polar solvent such as, for example, a lower aliphatic alcohol.

Preference is given to purely borohydride solutions. The concentration of these solutions can vary within wide limits and is preferably between 0.05 and 1% (by weight of active hydrogen of the borohydride in the solution). The reducing treatment can be carried out at elevated temperature, however it is preferred to carry it out at a temperature close to room temperature, for example between 15 and 30 ° C. Regarding the course of the reaction, it should be noted that it gives birth of B (OH) ₃ and of OH ions ^" which have the effect of inducing an increase in the pH of the medium during the reduction. However, at high pH values, for example greater than 13, the reduction is slowed down so that it can be advantageous to operate in a buffered medium in order to have a well-fixed reduction speed.

It is by playing mainly on the duration of the treatment that it is possible to easily control the extent of the reduction made. To obtain a resistivity corresponding to the desired values, the duration of the treatment which is necessary is generally quite short and, depending on the proportions of oxide included in the dielectric, it is usually between approximately one minute and fifteen minutes. For a given treatment time, it is possible to act further on the reduction speed by adding various accelerators to the medium such as boric acid, oxalic acid, citric acid, acid tartaric or metal chlorides such as cobalt-ll, nickel-ll, manganese-ll, copper-II chloride. It is also possible to act on the quantity of borohydride used, so as to control the extent of the reduction. A preferred procedure consists in soaking the substrate to be reduced in a more or less viscous borohydride solution, then in removing the substrate to allow the reduction operation to be carried out in air. The quantity of borohydride ions, BH ₄ ^" , consumed depends on the viscosity. BH ₄ ^" therefore reacts in a thin layer on the surface to be reduced. This process also has the advantage of not polluting the initial bath, nor of destabilizing it.

The exact and precise conditions for the reduction by the borohydride are as described in EP 82 094. It should however be understood that, in the context of the invention, only a surface part of the dielectric must be reduced. The metallizations on the under layer are carried out as mentioned previously.

During the realization of the circuit level, the photosensitive resin layer is eliminated. This operation can be implemented at various stages depending on the embodiment. The elimination can be carried out by dissolution or stripping. The techniques for completely removing a layer of photosensitive resin are known. The removal is all the easier since the second layer of photosensitive resin is not in an advanced curing state. It is preferably, when it is eliminated, at stage A.

The method can comprise a treatment step intended to place the first layer of insulating photosensitive resin in an advanced state of hardening, for example in stage B. The treatment can for example consist of baking. It is preferably implemented after the elimination of the second layer of photosensitive resin. The treatment gives the circuitry a greater stability, in particular a greater dimensional stability, and thus makes it possible to improve the precision of placement of the exposures and revelations. It also limits the swelling phenomena of the resins in contact with the solutions used during the various treatments.

The method is particularly suitable for producing printed circuits and multilayer modules with high integration density.

Other details and advantages of the invention will appear more clearly in the light of the particular embodiments given below. More specifically, three embodiments are presented, illustrated by figures representing sectional views. schematic cross-sections of the circuitry produced by a method according to the invention, at the various stages thereof.

Figures 1a) to 1g) show the circuitry at the various stages of the method according to the first embodiment. Figures 2a) to 2h) show the circuitry at the various stages of the method according to the second embodiment.

Figures 3a) to 3i) show the circuitry at the various stages of the method according to the third embodiment.

Figures 4a) to 4c) show circuitry at several levels at different stages of the process.

According to a first embodiment, the method comprises the following steps: ai) on a substrate 101 having metallizable parts 102 and / or potentially metallizable parts, forming a first layer 103 of insulating photosensitive resin comprising oxide particles metallic, the oxide being chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn and their mixtures and, where appropriate, one or more other non-conductive and inert fillers b1) exposure and revelation of the first layer so as to selectively discover metallizable and / or potentially metallizable parts of the substrate, d) formation on the first layer and on the exposed portions of the substrate of a second layer 105 of photosensitive resin, intended to form a selective protection, this second layer not comprising metal oxide particles d1) exposure and revelation of the second layer so as to selectively discover certain parts of the first layer or certain parts of the substrate e1) formation of an under layer 107 capable of being metallized either by contacting with a solution of a noble metal salt capable of being reduced by the particles d metal oxide, either by contacting with a reducing agent capable of reducing the particles of metal oxide, f1) electrochemical and / or electrolytic metallization in order to deposit a metal layer 108 on the exposed parts of the first layer and of the substrate g1) elimination of the second layer of photosensitive resin The first embodiment corresponds to metallization according to a process of the pattern type. For the first embodiment, the elimination of the second layer of photosensitive resin is carried out in step g1). Steps ai) and b1) are in accordance with steps a) and b). The compound in the first layer of insulating photosensitive resin, capable of inducing a subsequent metallization, is a metal oxide chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sn. Step c) of forming tracks and microtraverses is a sequence of steps comprising steps d), d1), e1), f1), g1).

The procedures for implementing each step have been detailed previously. During the process according to the first embodiment, in step b1) a photovoltaic film 104 is formed, that is to say a passage through an insulating photosensitive resin leading to a metallizable part 102 and / or a potentially metallizable part. During step d1) selective protection is obtained by making a crossing 106 at the level of the photovia 104, so as to uncover the metallizable portion 102 and by making a crossing 107 at a portion of the first layer of resin photosensitive. During step e1), a sub-layer capable of being metallized 107 is formed according to one of the two given modes, preferably the first, using noble metal salts in an acid medium. In step f 1), metallization is carried out, preferably by electrolytic means. Metallic interconnections 109 are obtained, which will in particular constitute tracks and micro-crossings. In step g1), the second layer of photosensitive resin is eliminated. The surface of the circuitry obtained includes:

- the first layer of photosensitive resin 113

- portions of tracks 1 11 on the surface of the first layer, which are not in contact with the substrate - microtravers 110 in contact with the substrate portions of tracks 112 on the surface of the first layer, in contact with the microtraversée. According to a second embodiment, the method comprises the following steps: a2) on a substrate 201 having metallizable parts 202 and / or potentially metallizable parts, forming a first layer 203 of insulating photosensitive resin comprising oxide particles metallic, the oxide being chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn and their mixtures and, where appropriate, one or more other non-conductive and inert fillers b2) exposure and revelation of the first layer so as to selectively discover metallizable and / or potentially metallizable parts of the substrate, c2) formation of an under layer 205 capable of being metallized on the surface of the first layer of photosensitive resin and exposed parts of the substrate,

- either by contacting with a solution of a noble metal salt capable of being reduced by the metal oxide particles, - or by contacting with a reducing agent capable of reducing the metal oxide particles, d2) electrochemical and / or electrolytic metallization in order to deposit a metallic layer 206 on the first layer and on the exposed parts of the substrate e2) formation of a second layer 207 of photosensitive resin on the metallized surface, f2) exposure and revelation of the second layer selectively uncovering certain parts of the metal layer g2) elimination of the metal layer at the level of the parts discovered during step f2) h2) elimination of the second layer of photosensitive resin The second embodiment corresponds to metallization according to a panel type process.

For the second embodiment, the elimination of the second layer of photosensitive resin is carried out in step h2). Steps a2) and b2) comply with steps a) and b). The compound in the first insulating photosensitive resin layer, capable of inducing a subsequent metallization, is a metal oxide chosen from Cu, Co, Cr, Ni, Pb, Sn oxides. Step c) of forming tracks and microtraverses is a sequence of steps comprising steps c2), d2), e2), f2), g2), h2).

The procedures for implementing each step have been detailed previously. During the method according to the second embodiment, a photovia is formed in step b2), that is to say a passage in an insulating photosensitive resin leading to a metallizable part 202 and / or a potentially metallizable part. During step c2), a sub-layer capable of being metallized 205 is formed over the entire available surface of the first layer, according to one of the two given modes, preferably the first, using noble metals in an acid medium. During step d2) metallization is carried out, in order to obtain a continuous metallic layer 206 over the entire available surface. The metallization is preferably carried out electrolytically in an acid medium. During step f2) selective protection is obtained by making crossings 208 in the second layer, so that the second layer of photosensitive resin remains present on the surface of the metal layer in places. Second layer protections 209 thus remain at the crossing 204 and a second layer protection 210 on a part where there is no crossing in the first layer.

In step g2) parts of the metal layer are removed, those which were discovered during step f2). This elimination can be carried out by etching or by dissolution, according to methods known per se. The eliminated parts are generally the parts of the metallic layer which are not in contact with the parts discovered during step b2) before metallization. The elimination is preferably carried out by etching, preferably in an acid medium.

After elimination of the second layer of photosensitive resin in step h2), the surface of the circuitry obtained comprises: - the first layer of photosensitive resin 214

- portions of tracks 212 on the surface of the first layer, which are not in contact with the substrate

- 211 micro-crossings in contact with the substrate

- Parts of the tracks 213 on the surface of the first layer, in contact with the microscross.

According to a third embodiment, the method comprises the following steps: a3) on a substrate 301 having metallizable parts 302 and / or potentially metallizable parts, forming a first layer 303 of insulating photosensitive resin comprising oxide particles metallic, the oxide being chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn and their mixtures and, where appropriate, one or more other non-conductive and inert fillers b3) exposure and revelation of the first layer so as to selectively discover metallizable and / or potentially metallizable parts of the substrate, c3) formation of an under layer 305 capable of being metallized on the surface of the first layer of the photosensitive resin and exposed parts of the substrate,

- either by contacting with a solution of a noble metal salt capable of being reduced by the metal oxide particles,

- Either by contacting with a reducing agent capable of reducing the metal oxide particles, d3) if necessary, electrochemical and / or electrolytic metallization in order to deposit a metallic layer 306 on the first layer and on the exposed parts of the substrate e3) formation of a second layer 207 of photosensitive resin on the metallized surface, this second layer not comprising metal oxide particles f3) exposure and revelation of the second layer so as to selectively discover certain parts of the metal layer g3) reinforcement of the metal layer by metallization at the parts discovered during step f3) h3) elimination of the second layer of photosensitive resin, so as to discover the metal layer, reinforced on certain parts i3) etching of the metal layer, so as to eliminate the entire layer on the parts which have not been reinforced. The third embodiment corresponds to metallization according to a panel type process with patern reinforcement. For the third embodiment, the elimination of the second layer of photosensitive resin is carried out in step h3). Steps a3) and b3) comply with steps a) and b). The compound in the first insulating photosensitive resin layer, capable of inducing a subsequent metallization, is a metal oxide chosen from Cu, Co, Cr, Ni, Pb, Sn oxides. Step c) of forming tracks and microtraverses is a sequence of steps comprising steps c3), d3), e3), f3), g3), h3), i3).

The procedures for implementing each step have been detailed previously. During the method according to the third embodiment, in step b3) a photovoltaic 304 is formed, that is to say a passage through an insulating photosensitive resin leading to a metallizable part 302 or potentially metallizable. During step c3), a sub-layer capable of being metallized 305 is formed over the entire available surface of the first layer, according to one of the two modes given, preferably the first, using noble metals in an acid medium. During a step d3) metallization can be carried out, in order to obtain a continuous metallic layer 306 over the entire available surface. By step f3) selective protection is obtained by making a crossing 308 so as to discover the metal layer at the level of the photovia 304, and a crossing 309 is obtained so as to discover the metal layer at a part of the first layer where there is no photovia.

In step g3) the parts of the metal layer discovered during step f3) are reinforced, that is to say at the crossings 308 and 309. The reinforcement 310 may consist of a simple metallic deposit, easily engraved, for example of the same nature as the metal layer, and preferably obtained by electrolytic metallization. The thickness of the metal layer on the reinforced parts is greater than on the non-reinforced parts. The reinforcement can also be made of a metal material which is difficult to etch such as gold.

After removal of the photosensitive resin layer in step h3), the metal layer is etched during a step i3), so as to remove the entire metallic layer on the parts which have not been reinforced, and to leave a metallic deposit at the level of the parts which have been reinforced. One proceeds for example by differential etching. Etching is for example carried out in an acid medium. The surface of the circuitry obtained includes:

- the first layer of photosensitive resin 314 - portions of tracks 312 on the surface of the first layer, which are not in contact with the substrate

- micro-crossings 311 in contact with the substrate

- Parts of the tracks 313 on the surface of the first layer, in contact with the microscross.

The level of circuitry obtained can support another level of circuitry, obtained according to sequences of similar steps. An exemplary embodiment of a second level of circuitry is given below, illustrated by FIGS. 4a to 4c.

In this example, the method is analogous to the first embodiment.

During a step a4) a first layer of photosensitive resin is formed on the surface of a circuit level obtained by one of the embodiments described above, having the layer 401 of insulating photosensitive resin comprising particles of metal oxide of the previous circuit level (said lower level), and having tracks and microtraverses 402, 403.

During a step b4), the first layer of resin is exposed and revealed so as to form photovoltaics 406, 407 opening onto a track part or onto microtraverse 402, 403 and if necessary on a potentially metallizable part 405 consisting of part of the first layer of the lower level (the second layer of the lower level has been eliminated).

During steps c4) and d4), a second layer of photosensitive resin is deposited, it is exposed and revealed so as to form a selective protection.

During a step e4), a sub-layer capable of being metallized is formed as described above. The sub-layer is also formed on the unprotected surfaces of the first layer and on the potentially metallizable surface 405.

During a step f4), metallized. Tracks and microtraverses 410, 411, 412 are formed.

During a step g4), the second layer of photosensitive resin is eliminated.

Claims

1. A method of manufacturing a multi-level interconnection circuit comprising metal tracks and microtravers, comprising the following steps for producing at least one level: a) On a substrate having on its surface metallizable parts and / or potentially metallizable, formation of a first layer of insulating photosensitive resin comprising a compound capable of inducing a subsequent metallization b) exposure and revelation of the first layer so as to selectively discover metallizable and / or potentially metallizable parts of the substrate c ) formation, by metallization, of metal tracks and micro-crossings on the surface of the first layer of insulating photosensitive resin and of the parts discovered during step b), with the use of a second layer of photosensitive resin forming a protection selective, characterized in that the method comprises, for the achievement of the level considered, a step during which the second layer of photosensitive resin is eliminated.

2. Method according to claim 1 characterized in that the substrate is a lower level of circuitry, the metallizable parts being metal tracks or micro-crossings and the potentially metallizable parts being non-metallized parts having the first insulating photosensitive resin layer for the realization of a lower level.

3. Method according to claim 1 or 2 characterized in that the second layer of photosensitive resin does not include any compound capable of inducing subsequent metallization.

4. Method according to one of the preceding claims, characterized in that the compound capable of inducing a subsequent metallization consists of metal oxide particles chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn and their mixtures.

5. Method according to one of the preceding claims characterized in that the first resin layer comprises inert non-conductive fillers.

6. Method according to one of the preceding claims characterized in that the metallization is carried out on an under layer capable of being metallized, previously formed on the surface of the first layer of photosensitive resin or of exposed parts of the first layer of photosensitive resin .

7. Method according to claim 6 characterized in that the compound capable of inducing a subsequent metallization consists of metal oxide particles chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn and their mixtures and in that the sublayer is formed by bringing the first layer of photosensitive resin or parts of the first layer of photosensitive resin into contact with a solution of a noble metal salt capable of being reduced by the oxide particles .

8. Method according to claim 7 characterized in that the noble metal salt solution is an acid solution.

9. Method according to one of claims 6 or 7 characterized in that the noble metal salt is chosen from the salts of Au, Ag, Rh, Pd, Os, Ir, Pt, with a counter ion chosen from Cl ^" , NO ₃ ^" , CH ₃ COO ^" .

10. Method according to claim 6 characterized in that the compound capable of inducing a subsequent metallization consists of metal oxide particles chosen from the oxides of Cu, Co, Cr, Ni, Pb, Sb, Sn and their mixtures and in that the sublayer is formed by bringing the first layer of photosensitive resin or parts of the first layer of photosensitive resin into contact with a reducing agent capable of reducing the oxide particles.

11. Method according to one of claims 6 to 10 characterized in that the particles of the first layer of photosensitive resin are updated before the formation of the sub-layer capable of being metallized.

12. Method according to one of the preceding claims, characterized in that the metallization is carried out electrochemically and / or electrolytically.

13. Method according to one of the preceding claims, characterized in that the metallization is carried out electrolytically in an acid medium.

14. Method according to one of claims 7 to 13 characterized in that step c) comprises the following steps: d) formation on the first layer and on the exposed parts of the substrate of a second layer of photosensitive resin, intended to form selective protection, this second layer not comprising any compound capable of inducing a subsequent metallization d1) exposure and revelation of the second layer so as to selectively discover certain parts of the first layer and certain parts of the substrate e1) formation d '' a sub-layer capable of being metallized - either by bringing it into contact with a solution of a noble metal salt capable of being reduced by the metal oxide particles,

- Either by contacting with a reducing agent capable of reducing the metal oxide particles, f1) electrochemical and / or electrolytic metallization in order to deposit a metal layer on the exposed parts of the first layer and of the substrate g1) elimination of the second layer of photosensitive resin

15. Method according to one of claims 7 to 13 characterized in that step c) comprises the following steps: c2) formation of an under layer capable of being metallized on the surface of the first layer of the photosensitive resin and exposed parts of the substrate

- Either by contacting with a reducing agent capable of reducing the metal oxide particles, d2) electrochemical and / or electrolytic metallization in order to deposit a metal layer on the first layer and on the exposed parts of the substrate e2) formation on the metallized surface of a second layer of photosensitive resin, intended to form selective protection, f2) exposure and revelation of the second layer so as to selectively uncover certain parts of the metal layer g2) elimination of the metal layer at the level of the parts discovered during from step f2) h2) elimination of the second layer of photosensitive resin

16. Method according to claim 7 to 13 characterized in that step c) comprises the following steps: c3) formation of a sub-layer capable of being metallized on the surface of the first layer of the photosensitive resin and of the exposed parts of the substrate either by contacting with a solution of a noble metal salt capable of being reduced by the metal oxide particles, - either by contacting with a reducing agent capable of reducing the metal oxide particles, d3) if necessary, electrochemical and / or electrolytic metallization in order to deposit a metal layer on the first layer and on the exposed parts of the substrate e3) formation on the metal surface of a second layer of photosensitive resin, intended to form selective protection, this second layer comprising no compound capable of inducing a subsequent metallization f3) exposure and revelation of the second layer selectively uncovering certain parts of the metal layer g3) reinforcement of the layer m metallic by metallization at the parts discovered during step f3) h3) elimination of the second layer of photosensitive resin, so as to discover the metal layer, reinforced on certain parts i3) etching of the metal layer, so as to eliminate the entire layer on the parts which have not been reinforced.

17. Method according to one of the preceding claims characterized in that it comprises a step of treating the first layer of photosensitive resin so as to obtain a resin in stage B.

18. The method of claim 17 characterized in that the treatment step is a baking, implemented after the removal of the second layer of photosensitive resin.

19. Method according to one of the preceding claims, characterized in that the substrate is a rigid printed circuit comprising tracks on its surface.

20. Use of a method according to one of the preceding claims for the production of printed circuits and multilayer modules with high integration density.

21. Circuitry systems comprising tracks and microtraverses capable of being obtained by a method according to one of claims 1 to 19.