Patent Application
20140076356
The present invention relates to the composition of a cleaning formulation dedicated to the complete and selective stripping of photoresists of all thicknesses used in microelectronic component integration processes (metal interconnections, copper pillars, TSV). Said solution is optimized to strip and/or dissolve the polymer matrix, which constitutes the resin, while ensuring and protecting the physicochemical integrity of exposed materials such as metal interconnections (copper, aluminum), dielectrics (SiO2, MSQ, etc.) and diffusion and adhesion barriers (TiN, Ti, Ta, TaN, etc.).
The fabrication of integrated circuits involves a consequent number of steps, a large percentage of which comprise successive series of depositions of electroconductive, resistant and/or semiconductor layers, uniform masking of the surface by photopolymers, exposure and development of the resin. The primary function of the photopolymer is to protect certain zones while selectively exposing others. It can thus be envisaged on these surfaces of exposed material to subsequently undertake steps of wet and/or dry selective deposition and/or etching. These selective and successive steps make it possible to construct a three-dimensional network whose complexity and multiplicity will define the final functionality of the microelectronic elements (flash memory, microchips, connectors, decoders, analog converters, graphics cards, etc.). Nevertheless, after all these fabrication steps, resin present on the surface must be stripped completely in order to ensure optimal surface quality, devoid of all residual debris which can cause defects and changes in the quality and performance of subsequent integration steps. Additionally, in a number of cases, these resins must be stripped while materials that are vulnerable from an electrochemical point of view remain exposed. The materials most likely to sustain chemical attack or corrosion during the resin stripping process are metals such as aluminum and copper, used specifically for intra- and inter-level connections (interconnections, pillars, TSV).
In order to ensure the optimal and maximal operation of the microelectronic component, a resin stripping formulation must be highly effective and have properties not only of polymer matrix dissolution but also of compatibility with materials comprising the microelectronic circuit.
Among the many resin stripping chemicals available on the market, mention can be made of:
This great diversity of resin stripping solutions is in harmony with the immense variety of resins used in the fabrication of electronic components. In the case of applications requiring the formation of complex structures deposited on a substrate, the thickness of the resin to be removed can vary from 1 to 300 microns. During this study, none of the chemical approaches cited above were effective in completely dissolving semi-novolac resins at temperatures between 40 and 100° C. However, professionals increasingly require that resin stripping solutions be effective at temperatures below 100° C., advantageously below 75° C. It is furthermore required that resin is completely dissolved in solutions in order to enable the recirculation of said solutions without premature clogging of the particulate filters typically installed in equipment dedicated to this operation.
The object of the present invention is the formulation of a chemical containing as a principal solvent, an ether and/or polyether solvent, an acid and, optionally, surfactants, enabling the stripping by complete dissolution of photoresists, at temperatures between 40 and 100° C. while ensuring total compatibility with exposed materials/metals (
The invention thus relates to a formulation for the stripping by dissolution, advantageously by complete dissolution, of photoresists, comprising as a principal solvent, an ether and/or polyether solvent, and an acid.
In the context of the present invention, the expression “complete dissolution” means that visually, after analysis by scanning electron microscopy (SEM), no more resin is observed on the substrate. The substrate is most often a silicon wafer comprising interconnections of metal (copper, aluminum), dielectrics (SiO2, MSQ, etc.) and diffusion and adhesion barriers (TiN, Ti, Ta, TaN, etc.).
In the context of the present invention, the expression “total compatibility” means that the substrate is not damaged by the implementation of the method of the invention. In particular, no substrate corrosion is observed.
The inventive formulation advantageously enables the stripping by complete dissolution of positive or negative photoresists (g and/or i and/or h), more particularly semi-novolac resins. The photoresist will generally comprise one or more photosensitive compounds (diazonaphthoquinone (DNQ), for example) and polymers of semi-novolac resins (structural monomers: styrene, cresol-formaldehyde).
The resin can be positive or negative. As examples of negative resins, mention may be made of the commercial resins AZ®15nXT, AZ®nLOF2070, HNR80, KMPR1000, SC100, Nano™SU8, ma-N405, JSR-THB serie, NR5 serie, AZ®125nXT. As examples of positive resins, mention may be made of the commercial resins AZ®40XT, HPR500, OIR906, OIR620, micropositS1800, PR1 série, Megaposit™SPR™220 serie, AZ®9260, AZ®4562, AZ®4533, AZ®4999.
The inventive formulation comprises, as a principal solvent, at least one ether and/or polyether solvent, optionally polyfunctionalized. The term “polyfunctionalized” refers to any chemical compound comprising within its molecule at least two distinct functional groups, for example ether/alcohol, ether/ester, ether/amine, ether/amide, amine/alcohol, ether/ether.
The principal solvent used in the present invention advantageously has a dielectric constant between 2 and 7 and a dipole moment less than 2.
The term “ether solvent” refers to any solvent of the form R—O—R′, wherein R and R′ are carbon chains. The chains R and R′ can be aliphatic or aromatic, linear or branched, and optionally substituted. R and R′ can be joined to form a ring.
According to an advantageous embodiment of the invention, R and R′ represent, independently of one another, a linear or branched C1-C8 alkyl radical, advantageously a linear or branched C1-C4 alkyl radical, more advantageously a linear or branched C1-C4 alkyl radical, or a phenyl radical. R and/or R′, advantageously only one of the two, is optionally substituted by one or more groups selected independently from the groups comprising —OH, —(CH2)n—OH, wherein n is an integer varying from 1 to 4, and —O(CO)—(CH2)m—CH3, wherein m is an integer varying from 0 to 3. R and R′ can be joined to form an aliphatic ring, optionally substituted by one or more groups selected from the group defined above.
“Polyether solvent” refers to any solvent that contains at least two ether functional groups.
According to a first embodiment, the polyether is of formula A-(O—B)p—O-D wherein:
More advantageously, the polyether is of formula A-(O—B)p—O-D wherein:
Still more advantageously, the polyether is of formula A-(O—B)p—O-D:
More advantageously, D represents the same radical as A.
The polyether can also be a dibasic ester (DBE) of formula A-(O—B)q—O-D wherein:
According to a second embodiment, the polyether is of formula CH2—O—(CH2CH2O)r—OCH3 wherein r is an integer varying from 1 to 10.
The preferred solvents are selected from the group comprising linear or branched aliphatic ethers, cyclic ethers, aromatic ethers, glycol ethers, in particular glycol mono- or di-ethers, ethoxylated ethers and esters and polyfunctional ester ethers.
As examples of solvents, mention may be made of: carbitol (diethylene glycol monoethyl ether), dipropylene glycol monomethyl ether (DPGME), propylal (dipropoxymethane), butylal (dibutoxymethane), 2,5,7,10-tetraoxaundecane, 2-ethylhexylal, dioxolane (1,3-dioxacyclopentane), 5-hydroxy-1,3-dioxane, 4-hydroxymethyl-1,3-dioxolane, tetrahydrofurfuryl alcohol, butyl diglycol, ethylethoxypropylene, diglyme (bis(2-methoxyethyl)ether), propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, anisole, β-diethylaminoethyl ethers, ethylene glycol phenyl ether, ethylene glycol n-butyl ether acetate, ethylene glycol ethyl ether acetate, polyglyme, ethylene glycol ethyl ether, dibasic ester (DBE) and dimethyl diethylene glycol ether.
More generally, mention may also be made of the following glycol ethers: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monobenzyl ether, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol dimethyl ether, propylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol mono tert-butyl ether, dipropylene glycol diisopropyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol phenyl ether, ethylene glycol n-butyl ether acetate, ethylene glycol ethyl ether acetate, and mixtures thereof, in particular in pairs.
According to an advantageous embodiment of the invention, the solvent is selected from the group comprising methylal, ethylal, propylal, butylal, dioxolane, glycerol formal, TOU, 2-ethylhexylal, and mixtures thereof, in particular in pairs. TOU is particularly preferred.
According to another embodiment, the principal solvent comprises advantageously two ethers such as defined above. In particular, the principal solvent is a mixture of:
The use of this solvent mixture makes it possible to obtain formulations having both excellent properties of dissolution of photoresists, in particular semi-novolac resins, and a suitably low cost. Indeed, glycol ethers are most generally of low or reasonable cost. The other solvent, although more expensive, makes it possible to improve dissolution properties.
Without wanting to be bound by one such theory, the Inventors believe that the use of a solvent such as defined above enables, on the one hand, the expansion/swelling of the resin and, on the other hand, the dissolution of polymer fragments of the resin.
The principal solvent goes into the inventive formulation in proportions between 50% and 99.99% by mass, in relation to the weight of the formulation, advantageously between 75% and 99.99% by mass.
In addition to this principal solvent, the formulation can comprise non-ether solvents. This non-ether solvent is easily hydrolysable, and in particular it is selected from dimethylacetamide (DMAC), N-methylpyrrolidinone (NMP), dimethylsulfoxide (DMSO), dimethylformamide, N-methylformamide, formamide, dimethyl-2-piperidone (DMPD), alcohols and mixtures thereof, in particular DMSO, alcohols and mixtures thereof.
As examples of alcohols, notable mention may be made of propylene glycol, glycol, benzyl alcohol and amino alcohols.
In a preferred embodiment, the non-ether solvent is DMSO.
The fraction of non-ether solvent varies in proportions between 0% and 50% by total mass of the solvent (principal solvent+non-ether solvent)
In a preferred embodiment of the invention, the fraction of non-ether solvent is less than 10% by mass of the total weight of solvents, more advantageously 0%.
The total solvent content in the formulation varies advantageously in proportions between 75% and 99.99% by mass in relation to the weight of the formulation.
The inventive formulation comprises an acid. “Acid” refers to any compound that has the definition of a Lewis acid or a Brönsted acid.
In the context of the present invention, the acid must be completely soluble in the solvent or solvent mixture used in the formulation. The expression “completely soluble” means that more than 95% of the acid is solubilized in the solvent or solvent mixture, advantageously more than 99%, even more advantageously more than 99.5% (the percentages are expressed in moles in relation to the total number of moles of the acid).
The photopolymer breakdown step is essential to the mechanism by which the resin is solubilized by the solvent. This fundamental step is enabled by the presence of acid in the formulation.
This acid can be mineral (phosphoric acid, sulfuric acid, etc.) or organic (carboxylic acid, phosphonic acid, etc.).
According to an advantageous embodiment of the invention, the acid is selected from the group comprising
The acid is more particularly selected from the group comprising itaconic acid, acrylic acid, methacrylic acid, salicylic acid, etidronic acid (60% in particular), nitro-benzoic acid, oxalic acid, phosphoric acid, sulfuric acid, formic acid, and mixtures thereof, in particular in pairs. Oxalic acid is particularly preferred.
In addition to these preferred acids, the formulation can also comprise methanesulfonic acid.
The proportion by mass of acid in in the formulation will be adjusted according to the molecular weight and strength of the acid or the acids selected (pKa equivalent to the solvent).
The acid concentration in the formulation is advantageously between 0.01% and 25% by mass in relation to the total weight of the formulation, advantageously between 0.1% and 25% by mass.
In one embodiment of the invention, the acid is methanesulfonic acid, alone or in mixture with the above quoted acids. In such an embodiment, the solvent is not alcohol, meaning that the formulation is free of alcohol. Advantageously, in the same embodiment, the acid concentration in the formulation is between 0.01 and 10% by mass, 10% being excluded, in relation to the total weight of the formulation, more advantageously between 0.1 and 10% by mass, 10% being excluded, even more advantageously between 0.1 and 5% by mass.
In one embodiment of the invention, the inventive formulation also comprises one or more surfactants.
The solubilization rate of the resin can also be dependent on the surface tension at the polymer-substrate and resin-solution interface. It turns out that the presence of a surfactant can decrease resin-substrate and solution-resin interactions and prevent deposition of organic residues on the surface (front and back side of the plate) due to the surfactant's wetting, dispersing, detergent and emulsifying properties. Moreover, surfactants improve the solubilization of hydrophilic compounds in organic solvent. The preferred surfactants are, for example: ethoxylated and propoxylated fatty alcohols, ethoxylated terpenes, ethoxylated alkylphenols, ethoxy cetyl-oleyl alcohol, ethoxylated lauryl alcohol, ethoxylated isodecyl alcohol with a hydrophilic-lipophilic balance (HLB) value between 4 and 10. The quantity of surfactant, when present, is established between 0.01% and 15% by mass in relation to the total weight of the formulation.
In a preferred embodiment of the invention, the inventive formulation does not comprise a surfactant.
According to an advantageous embodiment, the inventive formulation is principally an organic solution. Indeed, the quantity of water added to the formulation is less than 1% by mass in relation to the total weight of the formulation, more advantageously it is zero. Advantageously, the formulation contains only water provided by the components used. The Inventors believe that the metal compatibility of the resin stripping solution is made possible by the very small quantity of water present in the medium (<1% by mass in relation to the total weight of the formulation), preventing/limiting metal dissociation and oxidation.
For cleaning processes that require working at high temperature (>70° C.) and for long process times (>30 min), corrosion inhibitors could be added to the composition in order to guarantee complete compatibility of the metal elements. Such inhibitors will be selected, according to the metals to be protected, from inhibitors known by those persons skilled in the art such as triazole and derivatives, polyhydroxyl benzene and derivatives, phosphonate and derivatives, which can go into the composition in proportions between 0.01% and 2% by mass in relation to the total weight of the formulation. It has nevertheless been noted, in a surprising manner, that the presence of a corrosion inhibitor was most often not required, in particular when the acid used is oxalic acid, alone or in mixture with methanesulfonic acid. Preferentially, the inventive formulation does not comprise a corrosion inhibitor.
Contacting is carried out advantageously by immersion and/or spraying.
In the case of applications requiring the formation of complex structures deposited on a substrate, the thickness of the resin to be removed can vary from 1 to 300 microns.
The contacting step is advantageously implemented at temperatures between 40 and 100° C. advantageously between 40 and 75° C., for a period of contact advantageously between 20 s and 60 min, advantageously between 20 s and 30 min, more advantageously between 20 s and 10 min.
The method of the invention enables complete dissolution of the resin, advantageously without having to repeat the contacting step.
The method of the invention comprises advantageously, following the contacting step, a substrate rinsing step. In one embodiment, the substrate is either cleaned directly with water or first with a solvent (isopropanol or acetone) and then with water. In most cases, since the inventive formulation is soluble in water, rinsing with water suffices. The duration of the rinsing step is most often less than 15 min, with 5 min being sufficient. The use of ultrasound is not necessary. Next, the substrate is dried.
Traditional batch equipment is well suited to the implementation of the method of the invention.
The examples that follow illustrate the present invention but do not limit it in any way.
A copper substrate coated with AZ® 15nXT resin is placed in a beaker comprising either a formulation of the invention (as described in Example 1H), or a formulation containing DMSO/TMAH (tetra methyl ammonium hydroxide), or a formulation containing NMP(N-methyl-2-pyrrolidone).
The resin is completely dissolved after 20 min of soaking at 60° C. in the inventive formulation. An SEM analysis of the substrate shows no resin residue on the surface or attack on the metal. The residual liquid in the beaker does not comprise solid residues, which facilitates recycling of the solution.
In formulations containing DMSO/TMAH or NMP, insoluble residues are observed in the beaker after 3 hours of soaking.
The formulation of Example 1H was used to strip the resins AZ® 40XT and AZ® nLOF 2070:
The coated wafers were treated by immersion in the following formulation:
The wafers are then rinsed with water and then dried.
An SEM analysis of the substrate shows no resin residue on the surface or attacks on the metal.
The compatibility of the formulation of Example 1H was verified by immersion of various metals in the formulation at 65° C. for 20 min. The results are summarized in the following table:
Very high compatibility of the formulation with metals is thus noted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11/01779 | Jun 2011 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/061037 | 6/11/2012 | WO | 00 | 11/21/2013 |
