Method for improved selective etching of silicon nitride over silicon oxide

Abstract

The present invention pertains to a method for selectively etching silicon nitride in the presence of silicon oxide.

Description

[0001] METHOD FOR IMPROVED SELECTIVE ETCHING OF SILICON NITRIDE OVER SILICON OXIDE

[0002] The present invention pertains to a method for selectively etching silicon nitride in the presence of silicon oxide.

[0003] BACKGROUND OF THE INVENTION

[0004] 3D memory devices are fabricated by vertically stacking multiple conductive silicon and insulating silicon dioxide layers alternatively. One of the fabrication steps involves selectively etching a sacrificial SiNx layer with an acidic etchant solution containing a variety of additives such as silanes, silicic acids, or unfunctionalized colloidal silica.

[0005] The additives are generally included to improve the selectivity of the etching process for the sacrificial SiNx layer. A high selectivity in etching is required to repeatedly remove vertical stacks of materials while maintaining the architecture of the chip. High selectivity is particularly needed for advanced chips that utilise multiply stacked architectures.

[0006] In the art, various attempts to use silicon oxide and / or silanes in etching formulations for above-described purpose have been reported. However, none of these approaches has been established in the industrial manufacturing to date.

[0007] US 2022 / 0228062 describes an etching composition that includes (A) phosphoric acid and (B) a mixture that includes (i) a silicon-containing compound and (ii) an aqueous solvent. The etching composition is for the selective removal of silicon nitride over silicon oxide.

[0008] US 2020 / 0377794 relates to an etchant composition that includes phosphoric acid and a silane compound having a specific formula, the etchant composition being for selectively removing a nitride film while minimizing an etching rate of an oxide film.

[0009] US 10781371 also describes an etchant composition that includes phosphoric acid and a silane compound of a specified formula. The etchant composition is again mentioned as being for selectively removing a nitride film while minimizing an etching rate of an oxide film.

[0010] US 2019 / 0074188 relates to compositions and methods for wet-etching a microelectronic device substrate that includes silicon nitride; the compositions including phosphoric acid, hexafluorosilicic acid, and an amino alkoxy silane.

[0011] WO 2017 / 091572 describes a composition and process for selectively removing p-doped polysilicon (e.g., boron-doped polysilicon) relative to silicon nitride from a microelectronic device having said material thereon. US 2021 / 0054287 relates to a composition and method for removing silicon nitride from a microelectronic device, the composition comprising (A) at least one compound selected from tetraalky Idisiloxane-silyldia- mines; 1 ,3 bis(n-aminoalky) tetraalkylsiloxanes, and O-phosphorylethanolamine, (B) phosphoric acid; and (C) a solvent comprising water.

[0012] US 8940182 describes an etching composition and method, the composition including phosphoric acid, ammonium ions and a silicon compound. The silicon compound includes a silicon atom, an atomic group having an amino group combined with the silicon atom, and at least two oxygen atoms combined with the silicon atom.

[0013] US 2022 / 0208553 relates to a composition for selective removal metal oxide hard masks such as zirconium oxide and hafnium oxide in the presence of other materials such as polysilicon, silicon dioxide, silicon nitride, and tungsten. The composition comprises water; a fluoride compound chosen from ammonium fluoride, ammonium bifluoride, and hexafluorosilicic acid; one or more acids; one or more corrosion inhibitors; and a water-soluble component chosen from alcohols, glycols, glycol ethers, ammonium halides, and amines; the composition having a pH of about -2 to 6.

[0014] JP 2021-015970 relates to a silicon nitride film etching solution for improving the etching selectivity of a silicon nitride film to a silicon oxide film, and a manufacturing method of a semiconductor device using silica having an amino acid-based, thioester-based, or ester-based group between the colloidal silica particles.

[0015] JP 2021-086943 describes the use of a composition of a silicon compound and phosphoric acid for selectively etching silicon nitride over silicon oxide.

[0016] US 2020 / 0308485 relates to an etching solution used for etching of silicon nitride. The etching solution includes: phosphoric acid; tetrafluoroboric acid; a silicon compound; water; and at least one of sulfuric acid and an ionic liquid. The silicon compound optionally comprises silica (claim 3, para 31).

[0017] US 2020 / 0216758 reports an etchant composition and a method of fabricating a semiconductor device, the composition including an inorganic acid; about 0.01 parts by weight to about 0.5 parts by weight of colloidal silica; about 0.01 parts by weight to about 30 parts by weight of an ammonium-based additive; and about 20 parts by weight to about 50 parts by weight of a solvent, all parts by weight being based on 100 parts by weight of the inorganic acid.

[0018] US 2015 / 0111390 is directed at a method of selectively removing silicon nitride including: providing a wafer having silicon nitride on a surface of the wafer; providing a mixture of phosphoric acid and a silicon- containing material; and delivering the mixture to the surface of the wafer to remove the silicon nitride.

[0019] CN112216607 concerns a silicon nitride film etching solution comprising two different types of silica particles. JP 2020-205320 proposes an additive for a silicon nitride etching solution, which contains an organic alkali silicate and water, and has a content of Na, K, Ca, Cr, Fe, and Cu of 1 mg / L or less.

[0020] While silanes or oligomers and polymers derived therefrom have also been used in the prior art, the compatibility of such compounds in the etching solutions remains a largely unresolved issue. For example, etching solutions that contain phosphoric acid require compatibility between this acid and the additive silanes. Many of such etching solutions are of poor stability and / or suffer from insufficient processability properties because the etching solutions are too viscous or inhomogeneous. It is fairly common that such etching solutions comprising silanes become more viscous over time, even to a point where they become unprocessable, or that the etching solution suffers from precipitation. This precipitation can involve the generation of insoluble post-etch residues on the substrate surface as a result of complex reactions among the chemicals that are present. Improvements in selectivity in order to minimise loss of yield are also sought.

[0021] OBJECTIVE OF THE INVENTION

[0022] It is therefore the objective of the present invention to overcome the shortcomings of the prior art. It is a further objective of the present invention to provide a method for selectively etching silicon nitride in the presence of silicon oxide.

[0023] SUMMARY OF THE INVENTION

[0024] The aforementioned objectives are solved by the method according to the invention for selectively etching silicon nitride in the presence of silicon oxide, comprising the method steps:

[0025] P1) providing a substrate having at least one surface;

[0026] P2) treating the at least one surface of the substrate with a pretreatment composition, the pretreatment composition comprising at least one pretreatment compound wherein the at least one pretreatment compound is selected from the group consisting of:

[0027] - one or more silanes according to formula (X):

[0028] RX1

[0029] Rx2o-Si-ORX2(X)

[0030] ORX2wherein

[0031] RX1is an organofunctional radical; and each RX2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and

[0032] - one or more siloxanes comprising at least one building block according to formula (Y): wherein

[0033] RY1is an amino-functional alkyl group; each RY2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and y is selected from 0, 1 and 2; and optionally, at least one building block according to formula (Z) (in addition to the at least one building block according to formula (Y)):

[0034] RZ1

[0035] SiO[(3.Z) / 2] (Z)

[0036] (ORZ2)Zwherein

[0037] RZ1is selected from the group consisting of alkyl group and alkenyl group, preferably a C1 -C4- alkyl group, more preferably a methyl group, n-propyl group or a / so-butyl group, even more preferably a / so-butyl group; each RZ2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group, preferably selected from the group consisting of hydrogen and methyl group, more preferably RZ2is hydrogen; and z is selected from 0, 1 and 2; optionally, P3) rinsing the substrate, preferably with water; and

[0038] P4) treating the at least one surface of the substrate with an etching composition, the etching composition comprising at least one acid.

[0039] The method according to the invention surprisingly allows for very selective etchings of silicon nitride over silicon oxide. Using the inventive method, it is now possible to selectively remove silicon nitride in the presence of silicon oxide.

[0040] The method according to the invention advantageously allows for an improved ease of cleaning after its use, resulting in overall cleaner processing.

[0041] The method according to the invention allows for a higher etch rate of silicon nitride compared to prior art solutions.

[0042] Preferred embodiments solving the above-described objectives particularly well are described in the following description and in the dependent claims.

[0043] DETAILED DESCRIPTION OF THE INVENTION

[0044] Percentages throughout this specification are weight-percentages (wt.-% or weight-%) unless stated otherwise. Yields are given as percentage of the theoretical yield. Concentrations given in this specification refer to the mass of the entire solutions, dispersions or compositions unless stated otherwise. Room temperature means 20 °C. Standard pressure means 1013 mbar. Experiments were conducted at room temperature and standard pressure unless stated differently hereinafter. “At least one” in the context of the present invention means one or more than one, for example two. The term "alkyl" according to the present invention comprises branched or unbranched alkyl groups comprising cyclic and / or non-cyclic structural elements, wherein cyclic structural elements of the alkyl groups naturally require at least three carbon atoms. C1-CX-alkyl in this specification and in the claims refers to alkyl groups having 1 to X carbon atoms (X being an integer). C1 -C18-alkyl for example includes, among others, methyl, ethyl, n-propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, secpentyl, tert-pentyl, neo-pentyl, hexyl, heptyl and octyl, hexadecyl and octadecyl. The alkyl group is typically not substituted unless specified differently hereinafter.

[0045] The term "alkanediyl" is the corresponding group having two free valences (bonding sites). Sometimes, it is referred to as "alkylene" in the art. Said residues according to the present invention comprise cyclic and / or non-cyclic structural elements and can be linear and / or branched. C1 -C4-alkanediyl for example includes, among others, methane-1 ,1-diyl, ethane-1 ,2-diyl, ethane-1 ,1-diyl, propane-1 ,3-diyl, propane-1 ,2- diyl, propane-1 ,1-diyl, butane-1 ,4-diyl, butane-1 ,3-diyl, butane-1 ,2-diyl, butane-1 ,1-diyl, butane-2,3-diyl. Usually, unless specified differently hereinafter, the alkanediyl group in not substituted.

[0046] The "alkenyl" is an unsaturated alkyl group comprising at least one olefinic ( / .e. a C=C-double) bond. Above-described details and preferences for the alkyl groups apply to alkenyl groups mutatis mutandis.

[0047] The term "aryl" according to the invention refers to ring-shaped aromatic hydrocarbon residues, for example phenyl or naphthyl. The aryl group is typically not substituted unless specified differently hereinafter.

[0048] The term "alkaryl" according to the invention refers to hydrocarbon groups comprising at least one aryl and at least one alkyl group such as benzyl and p-tolyl. The bonding of such an alkaryl group to other moieties may occur via the alkyl or the aryl group of the alkaryl group. Above-described details and preferences for the alkyl and aryl groups apply for alkaryl groups mutatis mutandis.

[0049] If more than one residue - being it an atom, a group of atoms or entire building blocks - is to be selected from a given group, each of the residues is selected independently from each other unless stated otherwise hereinafter, meaning they can be selected to be the same members or different members of said group. The bonding sites in some chemical formulae herein may be emphasized by a wavy line (“^vw>“) as it is customary in the art.

[0050] Embodiments and preferences described for one aspect of the present invention apply mutatis mutandis to all the other aspects thereof unless technically unfeasible or stated otherwise. The repetition is omitted to improve the conciseness of the specification.

[0051] The method according to the invention is for selectively etching silicon nitride in the presence of silicon oxide, and comprises the method steps:

[0052] P1) providing a substrate having at least one surface;

[0053] P2) treating the at least one surface of the substrate with a pretreatment composition, the pretreatment composition comprising at least one pretreatment compound wherein the at least one pretreatment compound is selected from the group consisting of: - one or more silanes according to formula (X):

[0054] RX1

[0055] RX2O-Si-ORX2(X)

[0056] ORX2wherein

[0057] RX1is an organofunctional radical; and each RX2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and

[0058] - one or more siloxanes comprising at least one building block according to formula (Y): wherein

[0059] RY1is an amino-functional alkyl group; each RY2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and y is selected from 0, 1 and 2; and optionally, at least one building block according to formula (Z) (in addition to the at least one building block according to formula (Y)):

[0060] RZ1

[0061] SiO[(3.Z) / 2] (Z)

[0062] (ORZ2)Zwherein

[0063] RZ1is selected from the group consisting of alkyl group and alkenyl group, preferably a C1 -C4- alkyl group, more preferably a methyl group, n-propyl group or a / so-butyl group, even more preferably a / so-butyl group; each RZ2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group, preferably selected from the group consisting of hydrogen and methyl group, more preferably RZ2is hydrogen; and z is selected from 0, 1 and 2; optionally, P3) rinsing the substrate, preferably with water; and

[0064] P4) treating the at least one surface of the substrate with an etching composition, the etching composition comprising at least one acid.

[0065] Preferably, the at least one pretreatment compound is one or more silanes according to formula (X) as defined herein. The substrate is preferably a semiconductor substrate. The semiconductor substrate is preferably selected from the group consisting of sensors, memory device substrates, logic device substrates, and semiconductor packaging material. Preferable sensors are MEMS (micro-electromechanical systems). Memory logic device substrates are inter alia RAMs such as CBRAM, ReRAM, PCM, FeRAM and Memory (NAND and DRAM). Semiconductor packaging material in the context of the present invention are - among others - IC substrates and printed circuit boards.

[0066] In the method according to the invention, it is preferred that the silicon nitride and silicon oxide are present on the surface of the substrate.

[0067] RX1is preferably selected from the group consisting of an alkyl group, alkylsulfonic group, polyfluoroalkyl group, aminoalkyl group, aryl group. The aryl group of RX1is preferably a phenyl group. The alkyl group of RX1is preferably a C1 -C4-alkyl group, more preferably a methyl group. More preferably, RX1is selected from the group consisting of phenyl group and C1 -C4-alkyl group. Even more preferably, RX1is a phenyl group.

[0068] In the one or more silanes according to formula (X), each RX2is preferably selected from the group consisting of a methyl group and an ethyl group. More preferably, each RX2is an ethyl group.

[0069] Particularly preferably, the one or more silanes according to formula (X) is represented by formula (1 a): wherein each RX2is independently selected from the group consisting of methyl group and ethyl group. More preferably, each RX2is an ethyl group.

[0070] RY1is preferably selected from the group consisting

[0071] In some embodiments, the at least one pretreatment compound is a siloxane comprising at least one building block according to formula (Y) wherein RY1is preferably selected from the group consisting of , especially RY1is , and at least one building block according to formula (Z) wherein RZ1represents a

[0072] C1-C4-alkyl group. In some embodiments, the one or more siloxanes comprising at least one building block according to formula (Y) additionally comprises at least one building block according to formula (Z).

[0073] The numerical ratio of the at least one building block according to formula (Y) to the at least one building block according to formula (Z) preferably ranges from 0.1 to 10, more preferably from 0.5 to 5, even more preferably from 1 to 1 .

[0074] The at least one building block according to formula (Y) and - if contained in the pretreatment compound - the at least one building block according to formula (Z) preferably make up for at least 50 weight-%, more preferably 75 weight-%, even more preferably 90 weight-%, of the pretreatment compound.

[0075] Preferably, the one or more siloxanes is an oligomer or a polymer. An improved crosslinking density of the film obtained from the pretreatment compound can then be obtained if the one or more siloxanes is an oligomer or a polymer. An oligomer according to the invention may comprise (in total) 2 to 4 building blocks according to formulae (Y) and (optionally) (Z), a polymer may comprises (in total) at least 5 building blocks according to formulae (Y) and (optionally) (Z). A non-limiting example of an oligomer comprising one building block according to formula (Y) and one building block according to formula (Z) is depicted hereinafter:

[0076] Oligomers and polymers usually comprise one or more linear, branched and cyclic structures (said structures being formed by the building blocks according to formula (Y) and / or (Z)). The building blocks described herein can also be understood as structural repeating units if more than one building blocks according to formula (Y) and optionally (Z) is comprised by the pretreatment compound.

[0077] As used conventionally in the art, the Rg-SiO<4-g / 2) nomenclature shall be understood that the depicted silicon atom carries 4-g oxygen atoms (g being an integer ranging from 0 to 4) and g residues R. The oxygen atoms are bound by a single bond to the silicon atom and thus have another substituent such as a silicon atom of a unity named above. In the case of the present invention, the other silicon atom is preferably one of a building block according to formula (Y) or (Z). If g is 3, a M-unit is present. If g is 2, a D-unit is present. If g is 1 , a T-unit is present. If g is 0, a Q-unit is present. This nomenclature is known to the person skilled in the art, e.g. from W. Noll, Chemie und Technologie der Silicone, Verlag Chemie, Weinheim Bergstr.,1960, p. 2 et seqq.

[0078] The pretreatment composition preferably comprises at least one solvent, the at least one solvent preferably being selected from the group consisting of water, alcohols, glycols and mixtures of the aforementioned, the at least one solvent most preferably being water. The pretreatment composition preferably comprises the at least one pretreatment compound in an amount of 0.1 to 20 wt.-%, preferably 1 to 15 wt.-%, more preferably 5 to 12 wt.-%, based on the total weight of the pre-treatment composition.

[0079] In the method according to the invention, the etching composition comprises at least one acid. The at least one acid can be an inorganic or an organic acid. As an organic acid, methane sulfonic acid is preferred. The at least one acid is preferably an inorganic acid. The at least one acid is preferably selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypo- phosphorous acid, nitric acid, methane sulfonic acid and mixtures of the aforementioned. The at least one acid is more preferably selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, nitric acid, and mixtures of the aforementioned. Most preferably, the at least one acid is phosphoric acid.

[0080] The etching composition preferably comprises the at least one acid in an amount ranging from 20.0 to 99.9 wt.-%, more preferably from 30.0 to 90.0 wt.-%, even more preferably from 40.0 to 85.0 wt.-%, based on the total weight of the composition.

[0081] In some embodiments, the etching composition comprises at least one silicon compound. The at least one silicon compound is preferably selected from the group consisting of:

[0082] - one or more silanes according to formula (1):

[0083] R11

[0084] R22O— Si— OR22(1)

[0085] OR22wherein

[0086] R11is an organofunctional radical, R11is preferably selected from the group consisting of alkyl group, alkylsulfonic group, polyfluoroalkyl group, aminoalkyl group, aryl group, R11is more preferably selected from the group consisting of C1-C4-alkyl group and phenyl group, R11is most preferably a phenyl group; and each R22is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and

[0087] - one or more siloxanes comprising at least one building block according to formula (2): wherein

[0088] R21is an amino-functional alkyl group; each R22is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and s is selected from 0, 1 and 2; and optionally, at least one building block according to formula (3) (in addition to the at least one building block according to formula (2)):

[0089] R31

[0090] I .

[0091] SiO[(3-t) / 2] (3)

[0092] (OR32)twherein

[0093] R31is selected from the group consisting of alkyl group and alkenyl group, preferably a C1 -C4- alkyl group, more preferably a methyl group, n-propyl group or a / so-butyl group, even more preferably a / so-butyl group; each R32is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group, preferably selected from the group consisting of hydrogen and methyl group, more preferably R32is hydrogen; and t is selected from 0, 1 and 2.

[0094] More preferably, when the etching composition comprises at least one silicon compound, the at least one silicon compound is preferably selected from the group consisting of:

[0095] - one or more silanes according to formula (1):

[0096] R11

[0097] R22O— Si— OR22(1)

[0098] OR22wherein

[0099] R11is an organofunctional radical, R11is preferably selected from the group consisting of alkyl group, alkylsulfonic group, polyfluoroalkyl group, aminoalkyl group, aryl group, R11is more preferably selected from the group consisting of C1-C4-alkyl group and phenyl group, R11is most preferably a phenyl group; and each R22is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and

[0100] - one or more siloxanes comprising at least one building block according to formula (2): wherein

[0101] R21is an amino-functional alkyl group; each R22is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and s is selected from 0, 1 and 2.

[0102] The etching composition preferably comprises at least one surfactant, at least one solvent, at least one fluorine compound, and optionally, at least one polysilicon corrosion inhibitor. The composition according to the invention preferably comprises at least one surfactant. Preferable surfactants are (water-soluble) nonionic surfactants. The at least one surfactant is more preferably selected from the group consisting of polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene C2-C22- alcohol ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbit tetraoleate, polyethylene glycol onolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene alkylamine, polyoxyethylene hardened castor oil, alkylalkanolamide and mixtures thereof. Such surfactants are commercially available under the trade names Dynols and Surfynols.

[0103] Preferably, the composition according to the invention comprises the at least one surfactant in an amount ranging from 0.001 to 5 wt.-%, more preferably from 0.01 to 2.5 wt.-%, even more preferably from 0.1 to 1 wt.-%, based on the total weight of the composition according to the invention.

[0104] The composition according to the invention preferably comprises at least one solvent. The at least one solvent is preferably selected from the group consisting of water, alcohols, glycols and mixtures of the aforementioned.

[0105] Preferably, the composition according to the invention comprises the at least one solvent in an amount ranging from 0.1 to 50 wt.-%, more preferably from 1 to 30 wt.-%, even more preferably from 10 to 30 wt.- %, based on the total weight of the composition according to the invention.

[0106] The composition according to the invention preferably comprises at least one fluorine compound. The at least one fluorine compound is preferably selected from the group consisting of ammonium fluoride, tetra(C1-C6-alkyl)ammonium floride, hexafluorosilicic acid, ammonium tetrafluoroborate, tetra(C1 -C6-al- kyl)ammonium fluoride and tetrafluoroboric acid.

[0107] Preferably, the composition according to the invention comprises the at least one fluorine compound in an amount ranging from 0.0002 to 5 wt.-%, more preferably from 0.0005 to 2 wt.-%, even more preferably from 0.01 to 1 wt.-%, based on the total weight of the composition according to the invention.

[0108] The composition according to the invention preferably comprises at least one polysilicon corrosion inhibitor. The at least one polysilicon corrosion inhibitor is preferably selected from the group consisting of linear and branched C8-C16-alkylbenzenesulfonic acids. More preferably, the at least one polysilicon corrosion inhibitor is selected from the group consisting of octylbenzenesulfonic acid, nonylalkylbenzenesulfonic acid, decylbenzesulfonic acid, undecylbenzenesulfonic acid, dodecylbenzenesulfonic acid, tridecylbenzenesulfonic acid, tetradecylbenzenesulfonic acid, tetradecylbenzenesulfonic acid, pentade- cylbenzenesulfonic acid, hexadecylbenzenesulfonic acid, heptadecylbenzesulfonic acid, octadecylbenzenesulfonic acid. As an alternative to aforementioned C8-C16-alkylbenzenesulfonic acids, C6-C16-al- kyldiphenyl sulfide disulfonic acids, and C6-C16-alkyldiphenylamine disulfonic acids may be used.

[0109] Preferably, the composition according to the invention comprises the at least one polysilicon corrosion inhibitor in an amount ranging from 0.001 to 5 wt.-%, more preferably from 0.01 to 2 wt.-%, even more preferably from 0.02 to 0.08 wt.-%, based on the total weight of the composition according to the invention.

[0110] The temperature of the etching composition in method step P4 preferably ranges from 100 to 200 °C, more preferably from 120 to 180 °C, even more preferably from 140 to 170 °C.

[0111] The pretreatment composition according to the invention can be prepared by standard means known to the person skilled in the art. It is preferably prepared by mixing the components of the composition using standard equipment such as stirrers and suitable vessels.

[0112] The duration of the method of the invention is not further limited and person skilled in the art can select suitable durations based on routine experiments. Generally, durations of method step P2 ranging from 1 hr to 48 hr, preferably from 12 hr to 36 hr, more preferably from 18 hr to 30 hr, have proven useful. Similarly, durations of method step P4 ranging from 1 s to 360 min, preferably from 30 s to 240 min, more preferably from 1 min to 120 min, have proven useful.

[0113] The method of the invention optionally comprises, after step P4, step P5 of rinsing the substrate, preferably with water. Method steps P3 and P5 aim to remove any residual components of the comprising according to the invention, in particular the acid (in step P5), from the surface of the substrate. Method steps P3 and P5 reduce the risk of derogation of any residual components on the surface of the substrate during subsequent manufacturing steps.

[0114] In method steps P3 and P5, the water is preferably deionized. The temperature of the water in method step P3 preferably ranges from 5 to 50 °C, more preferably from 10 to 30 °C. The duration of method step P3 preferably ranges from 1 s to 120 s, preferably from 5 to 30 s.

[0115] The invention will now be illustrated by reference to the following non-limiting examples.

[0116] This invention will be further described by reference to the following Figures which are not intended to limit the scope of the invention claimed, in which:

[0117] Figure 1 shows a graph of normalized etch rates for SiOx and SiNx for Examples 1 , 4, 2, 5 and 3, as well as a control sample using 85% phosphoric acid only, and

[0118] Figure 2 shows a Scanning Electron Microscopy (SEM) image of a cross-section of the wafer of Example 2 after etching. EXAMPLES

[0119] Commercial products were used as described in the technical datasheet available on the date of filing of this specification unless stated otherwise hereinafter. The most recent versions of standards were used unless stated differently hereinafter.

[0120] The following silanes and siloxanes were used throughout the experiments: a. phenyltriethoxysilane (as Dynasylan 9165, hereinafter 9165) b. a siloxane prepared as described in example 1 of US 10,259,832, i.e. an aqueous oligomeric aminosilane hydrolysate (as Hydrosil 1 153, hereinafter 1153) c. a siloxane prepared as described in example 5 of US 5,629,400, i.e. an aqueous oligomeric aminoal- kylfunctional silane hydrolysate (as Hydrosil 2909, hereinafter 2909)

[0121] The following examples compare methods of etching a substrate that comprises silicon oxide and silicon nitride. Three different methods were tested, (i) treating the substrate with an etching composition to which a silane had been added, without any pretreatment step, and the inventive methods of (ii) treating the substrate with a pretreatment composition comprising a silane, followed by treating the substrate with an etching composition without any added silane, and (iii) treating the substrate with a pretreatment composition comprising a silane, followed by treating the substrate with an etching composition to which a silane had been added.

[0122] To prepare the etching composition, 1.2 g of either silane 1 153 (Example 1) or 2909 (Example 4) was placed in 3.8 g of 85 % phosphoric acid (giving a concentration of silane of 10%w / w). The solution was heated to 160 °C. An area of 1x1 cm2of a 1 x 3 cm2wafer strip was then placed in the etching solution for 1 hr. Afterwards, the wafer was removed from the etching solution, then submerged in water to remove any residual etching solution. with silane

[0123] A pretreatment composition was prepared by adding 1 g of either silane 9165 (Example 2), 2909 (Example 5) or 1 153 (Example 7) to 9 g of deionized water. The wafer was placed into the resulting solution for 24 hr at 20 °C. Afterwards, the wafer was removed from the silane solution and washed with deionized water.

[0124] To prepare the etching solution, 5 g of 85 % phosphoric acid was placed in a 20 ml vial. The vial was then heated to 160 °C. The pre-treated wafer with dimensions 1x1 cm was placed in the etching solution for 1 hr. Afterwards, the wafer was removed from the etching solution, then submerged in water to remove any residual etching solution

[0125] 3, 6 and 8: substrate with silane, followed silane in A pretreatment composition was prepared by adding 1 g of either silane 9165 (Example 3), 2909 (Example 6) or 1 153 (Example 8) to 9 g of deionized water. The wafer was placed into the resulting solution for 24 hr at 20 °C. Afterwards, the wafer was removed from the silane solution and washed with deionized water.

[0126] To prepare the etching composition, 1.2 g of silane 1153 (Examples 3, 6 and 8) was placed in 3.8 g of 85 % phosphoric acid (concentration of silane is 10%). The solution was heated to 160 °C. An area of 1x1 cm2of a 1 x 3 cm2wafer strip was then placed in the etching solution for 1 hr. Afterwards, the wafer was removed from the etching solution, then submerged in water to remove any residual etching solution.

[0127] The etch rates for SiOx and SiNx were measured using Scanning Electron Microscopy (SEM). The measurement was taken after 1 hr of etching. The equipment used was a Hitachi S-4800 Field Emission Scanning Electron Microscope (FE-SEM). This uses a cold-field emission gun for high resolution imaging and an upper secondary electron detector. The upper detector is a through-the-lens detector, providing ultra- high surface resolution, and uses a Si-Li crystal and ultra-thin window, allowing elements from carbon and above to be characterized qualitatively. An anti-contamination trap was used in order to improve image quality. The sample was cleaved by scoring with a diamond tip scribe and snapping over a fulcrum point. The fractured piece was mounted in a cross-sectional holder and placed in the instrument as quickly as possible. Analysis was performed at a 1 kV accelerating voltage in ultra-high resolution imaging mode.

[0128] The extraction voltage was set at either 7 or 10 pA. Images were collected with the upper secondary electron detector and were typically acquired using frame averaging. Measurements were performed using Quartz PCI software, which provides the thickness of each wafer.

[0129] The normalized silicon oxide etch rate (referred to as “Normalized SiOx etch rate” in below tables) was measured as follows: [thickness difference of silicon oxide per unit time with silane] / [thickness difference of silicon oxide per unit time without silane].

[0130] The normalized silicon nitride etch rate (referred to as “Normalized SiNx etch rate” in below tables) was measured as follows: [thickness difference of silicon nitride per unit time with silane] / [ thickness difference of silicon nitride per unit time without silane].

[0131] The selectivity ratios (SiNx / SiOx) in below tables are the quotient of the normalized silicon nitride etch rate by the normalized silicon oxide etch rate.

[0132] The selectivity differences (|SiNx| - |SiOx|) are calculated by subtracting the absolute value of the normalized silicon oxide etch rate from the absolute value of the normalized silicon nitride etch rate.

[0133] Table 1

[0134] * Not of the invention

[0135] The normalized etch rates for SiOx and SiNx for Examples 1 , 4, 2, 5 and 3, as well as a control sample using 85% phosphoric acid only, are depicted in Figure 1 . A normalized rate of 1 means the etch rate with silane is the same as that without any silane. A normalized rate >1 means accelerated etching due to silane, and <1 means inhibited etching due to silane; <0 indicates deposition instead of etching.

[0136] An SEM image of a cross-section of the wafer of Example X after etching is shown in Figure 2.

Claims

Claims1 . A method for selectively etching silicon nitride in the presence of silicon oxide, comprising the method steps:P1) providing a substrate having at least one surface;P2) treating the at least one surface of the substrate with a pretreatment composition, the pretreatment composition comprising at least one pretreatment compound wherein the at least one pretreatment compound is selected from the group consisting of:- one or more silanes according to formula (X):RX1RX2O-Si-ORX2(X)ORX2whereinRX1is an organofunctional radical; and each RX2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and- one or more siloxanes comprising at least one building block according to formula (Y):whereinRY1is an amino-functional alkyl group; each RY2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and y is selected from 0, 1 and 2; and optionally, at least one building block according to formula (Z) (in addition to the at least one building block according to formula (Y)):RZ1SiO[(3-Z) / 2] (Z)(ORZ2)ZwhereinRZ1is selected from the group consisting of alkyl group and alkenyl group, preferably a C1 -C4- alkyl group, more preferably a methyl group, n-propyl group or a / so-butyl group, even more preferably a / so-butyl group; each RZ2is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group, preferably selected from the group consisting of hydrogen and methyl group, more preferably RZ2is hydrogen; andz is selected from 0, 1 and 2; optionally, P3) rinsing the substrate, preferably with water; andP4) treating the at least one surface of the substrate with an etching composition, the etching composition comprising at least one acid.

2. The method according to claim 1 characterized in that the substrate is a semiconductor substrate, preferably selected from the group consisting of sensors, memory device substrates, logic device substrates and semiconductor packaging material.

3. The method according to any one of claims 1 or 2 characterized in that the silicon nitride and silicon oxide are present on the surface of the substrate.

4. The method according to according to any one of the preceding claims characterized in that RX1is selected from the group consisting of alkyl group, alkylsulfonic group, polyfluoroalkyl group, aminoalkyl group, aryl group, RX1is preferably selected from the group consisting of C1-C4-alkyl group and phenyl group, RX1is most preferably a phenyl group.

5. The method according to any one of the preceding claims characterized in that RY1is selected from the group consisting,6. The method according to any one of the preceding claims characterized in that the at least one pretreatment compound is a siloxane comprising at least one building block according to formula (Y) wherein RY1is selected from the group consisting ofleast one building block according to formula (Z) wherein RZ1represents a C1-C4-alkyl group.

7. The method according to any one of the preceding claims characterized in that the pretreatment composition comprises at least one solvent, the at least one solvent being preferably selected from the group consisting of water, alcohols, glycols and mixtures of the aforementioned, the at least one solvent being most preferably water.

8. The method according to any one of the preceding claims characterized in that the pretreatment composition comprises the at least one pretreatment compound in an amount of 0.1 to 20 wt.-%,preferably 0.5 to 15 wt.-%, more preferably 1 to 10 wt.-%, based on the total weight of the pretreatment composition.

9. The method according to any one of the preceding claims characterized in that the at least one acid is selected from the group consisting of sulfuric acid, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, nitric acid, methane sulfonic acid and mixtures of the aforementioned; the at least one acid is most preferably phosphoric acid.

10. The method according to any one of the preceding claims characterized in that the etching composition comprises the at least one acid in an amount ranging from 20.0 to 99.9 wt.-%, preferably from 30.0 to 90.0 wt.-%, more preferably from 40.0 to 85.0 wt.-%, based on the total weight of the composition.11 . The method according to any one of the preceding claims characterized in that the etching composition comprises at least one silicon compound.

12. The method according to claim 11 characterized in that the at least one silicon compound wherein the at least one silicon compound is selected from the group consisting of- one or more silanes according to formula (1):R11R22O- Si— OR22(1)OR22whereinR11is an organofunctional radical, R11is preferably selected from the group consisting of alkyl group, alkylsulfonic group, polyfluoroalkyl group, aminoalkyl group, aryl group, R11is more preferably selected from the group consisting of C1-C4-alkyl group and phenyl group, R11is most preferably a phenyl group; and each R22is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and- one or more siloxanes comprising at least one building block according to formula (2):whereinR21is an amino-functional alkyl group; each R22is independently selected from the group consisting of hydrogen and C1 -C4-alkyl group; and s is selected from 0, 1 and 2; and optionally, at least one building block according to formula (3) (in addition to the at least one building block according to formula (2)):whereinR31is selected from the group consisting of alkyl group and alkenyl group, preferably a C1 -C4- alkyl group, more preferably a methyl group, n-propyl group or a / so-butyl group, even more preferably a / so-butyl group; each R32is independently selected from the group consisting of hydrogen and C1-C4-alkyl group, preferably selected from the group consisting of hydrogen and methyl group, more preferably R32is hydrogen; and t is selected from 0, 1 and 2.

13. The method according to any one of the preceding claims characterized in that the etching composition comprises at least one surfactant, at least one solvent, at least one fluorine compound, and optionally, at least one polysilicon corrosion inhibitor.

14. The method according to any one of the preceding claims that the temperature of the etching compo- sition in method step P4 ranges from 100 to 200 °C, preferably from 140 to 170 °C.

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