With the ongoing miniaturization, e.g. in the semiconductor industry, the need for metal- or semimetal-containing materials with fine structures increases while the requirements of the quality of such materials become stricter. Thin metal- or semimetal-containing materials serve different purposes such as dielectrics, conducting features, capping, or separation of fine structures. Classical etching processes are wet chemical processes. These processes have the drawback that very fine structures can often not be reached. Also, process control, e.g. with regard to the thickness of material which is removed, is limited. Vapor-based technologies, in particular atomic layer etching, overcome these limitations.

US 2015 / 0 270 140 A1 discloses a process for etching a metal- or semimetal-containing material including halogenation of the surface by a plasma including a halide-containing compound

US 8 608 973 discloses a process for etching a metal- or semimetal-containing material including halogenation of the surface by a plasma including PF3 or COF2.

However, the known methods are not sufficiently reliable to only halogenate the topmost atomic layer only which is the key to high control over the etch process. In particular when halogenating uneven surfaces, plasmas tend to halogenate the more exposed surfaces stronger than the less exposed surfaces.

It was an object of the present invention to provide a process for etching metal- or semimetal- containing materials with increased control of the amount of removed material independent of the surface topology. The process was aimed to be fast, easy to handle and applicable to a broad variety of different metals.

These objects were achieved by a process for etching a metal- or semimetal-containing material comprising bringing a metal- or semimetal-containing material in contact with an organic compound of general formula (I), (II) or (III) in the gaseous phase

(I) (III) wherein R is hydrogen, an alkyl, an alkenyl or an aryl group,

A is C, S, S=0, P-X or P-R, E is C bearing two further organic groups including hydrogen or N bearing one further organic group including hydrogen,

X is CI or Br. The present invention further relates to the use of an organic compound of general formula (I), (II) or (III) for an etching process.

Preferred embodiments of the present invention can be found in the description and the claims. Combinations of different embodiments fall within the scope of the present invention.

The metal- or semimetal-containing material can contain any metal or semimetal including Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os Ir, Pt, Au. Transition metals or silicon are preferred, in particular Ti, Fe, Co, Ni, Ru, Pd, Ta, W, Pt. Preferably, the metal- or semimetal-containing material contains at least 50 at-% metal and/or semimetal, more preferably at least 70 at-%, even more preferably at least 90 at-%, in particular at least 99 at-%. "At-%" means as typical in the field that all metals and/or semimetal atoms contained in the material together represent the given percentage of total atoms in the material. According to the present invention the metal- or semimetal-containing material is brought in contact with an organic compound of general formula (I), (II) or (III) in the gaseous phase. R is hydrogen, an alkyl, an alkenyl or an aryl group.

An alkyl group can be linear or branched. Examples for a linear alkyl group are methyl, ethyl, n- propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl. Examples for a branched alkyl group are iso-propyl, iso-butyl, sec-butyl, tert-butyl, 2-methyl-pentyl, 2-ethyl-hexyl, cyclo- propyl, cyclohexyl, indanyl, norbornyl. Preferably, the alkyl group is a Ci to Cs alkyl group, more preferably a Ci to C6 alkyl group, in particular a Ci to C ₄ alkyl group, such as methyl, ethyl, iso- propyl or tert-butyl. Alkyl groups can be substituted, for example by halogens such as F, CI, Br, I, in particular F; by hydroxyl groups; by ether groups; or by amines such as dialkylamines.

An alkenyl group contains at least one carbon-carbon double bond. The double bond can include the carbon atom with which the alkenyl group is bound to the rest of the molecule, or it can be placed further away from the place where the alkenyl group is bound to the rest of the molecule, preferably it is placed further away from the place where the alkenyl group is bound to the rest of the molecule. Alkenyl groups can be linear or branched. Examples for linear alkenyl groups in which the double bond includes the carbon atom with which the alkenyl group is bound to the rest of the molecule include 1-ethenyl, 1 -propenyl, 1-n-butenyl, 1 -n-pentenyl, 1 -n- hexenyl, 1 -n-heptenyl, 1 -n-octenyl. Examples for linear alkenyl groups in which the double bond is placed further away from the place where alkenyl group is bound to the rest of the molecule include 1-n-propen-3-yl, 2-buten-1-yl, 1-buten-3-yl, 1-buten-4-yl, 1 -hexen-6-yl. Examples for branched alkenyl groups in which the double bond includes the carbon atom with which alkenyl group is bound to the rest of the molecule include 1 -propen-2-yl, 1-n-buten-2-yl, 2-buten-2-yl, cyclopenten-1-yl, cyclohexen-1-yl. Examples for branched alkenyl groups in which the double bond is placed further away from the place where alkenyl group is bound to the rest of the molecule include 2-methyl-1 -buten-4-yl, cyclopenten-3-yl, cyclohexene-3-yl. Examples for an alkenyl group with more than one double bonds include 1 ,3-butadien-1 -yl, 1 ,3-butadien-2-yl, cylopenta- dien-5-yl.

Aryl groups include aromatic hydrocarbons such as phenyl, naphthalyl, anthrancenyl, phenan- threnyl groups and heteroaromatic groups such as pyrryl, furanyl, thienyl, pyridinyl, quinoyl, benzofuryl, benzothiophenyl, thienothienyl. Several of these groups or combinations of these groups are also possible like biphenyl, thienophenyl or furanylthienyl. Aryl groups can be substituted for example by halogens like fluoride, chloride, bromide, iodide; by pseudohalogens like cyanide, cyanate, thiocyanate; by alcohols; alkyl chains or alkoxy chains. Aromatic hydrocarbons are preferred, phenyl is more preferred.

In the compound of general formula (I) and (II) A stands for C, S, S=0, P-X or P-R, preferably C, S, or P-X, in particular C.

In the compound of general formula (I) E stands for C bearing two further organic groups includ- ing hydrogen or N bearing one further organic group including hydrogen. An organic group is any group which contains carbon, hydrogen, oxygen, nitrogen, sulfur and/or phosphor. Preferably, an organic group is hydrogen, an alkyl group, an alkenyl group, an alkoxy group, an acyl group, an acyl oxy group, an ester group, an amide group, an amine group, an aryl group or an aryloxy group. The definitions for alkyl, alkenyl and aryl as described above apply also for E. If E is C bearing two further organic groups, these can be the same or different to each other, preferably one of these groups is hydrogen.

Preferably, the compound of general formula (I) is a compound of general formula (la).

The two A can be the same or different to each other, preferably they are the same, in particular both A are C. The two R can be the same or different to each other, preferably they are the same. Some preferred examples of general formula (la) are given below.

Also preferably, the compound of general formula (I) is a compound of general formula (lb) or (lc).

(lb) (lc) The four R can be the same or different to each other. The same definitions for R as described above apply. Some preferred examples are shown below.

lb-1 lb-2 lc-1 lc-2 Some preferred examples of the compound of general formula (II) are shown below.

11-1

-10

Some preferred examples of the compound of general formula (III) are shown below.

111-7 111-8 111-9 111-10 111-11 111-12 Preferably, the compound of general formula (III) is a compound of general formula (Ilia), (lllb) or (lllc).

(Ilia) (lllb) (lllc)

The two or three R can be the same or different to each other. The same definitions for R as de scribed above apply. Some preferred examples are shown below.

Preferably the molecular weight of the organic compound of general formula (I), (II) or (III) is not more than 1000 g/mol, more preferred not more than 800 g/mol, in particular not more than 600 g/mol. The compound of general formula (I), (II), or (III) is in the vapor phase when brought in contact with the surface of the metal- or semimetal-containing material. It can be used as pristine compound or mixed with an inert gas, for example He, Ne, or Ar. Typically, a halogenation reaction occurs producing partially or fully halogenated metal and/or semimetal atoms. The reaction usually takes between 1 s and 1 min, for example 5 to 20 s. The pressure of the vapor phase during the halogenation reaction is typically 1 to 100 mbar, preferably 2 to 50 mbar, such as 5 to 20 mbar.

The halogenation reaction rate on the surface can be increased by increasing of the temperature, such as to 50 °C or to 300 °C, preferably 100 °C to 200 °C.

Preferably, after completion of the halogenation reaction, any residual vapor is removed by purging with an inert gas, for example nitrogen, helium, or argon. Alternatively, the residual vapor can be removed by high vacuum, such as lowering the pressure to 0.1 to 10 ^-6 mbar. The compound of general formula (I), (II), or (III) is used in the process according to the present invention is preferably used at high purity to achieve the best results. High purity means that the substance employed contains at least 90 wt.-% of the organic compound, preferably at least 95 wt.-%, more preferably at least 98 wt.-%, in particular at least 99 wt.-%. The purity can be determined by elemental analysis according to DIN 51721 (Prufung fester Brennstoffe - Bestimmung des Gehaltes an Kohlenstoff und Wasserstoff - Verfahren nach Radmacher-Hoverath, August 2001 ).

Preferably, after the metal- or semimetal-containing material is brought in contact with a compound of general formula (I), (II), or (III), the metal- or semimetal-containing material is brought in contact with a coordinating compound, i.e. a compound which can form a coordinative bond with the metal or semimetal in the metal- or semimetal-containing material. The coordinating compound is preferably able to convert the halogenated metal or semimetal atoms of the metal or semimetal in the metal- or semimetal-containing material into a volatile complex. In this way, the halogenated metal or semimetal compounds can be removed while the non-halogenated metal or semimetal atoms remain in the metal- or semimetal-containing material. In this case the complexation and removal reaction is self-limiting. Preferably, the metal- or semimetal-containing material is brought in contact with a coordinating compound in the gaseous state.

Various coordinating compounds can be employed including amines, phosphanes, hydrogen, NO, CO, and ethylene. Preferably, the coordinating compound contains at least one nitrogen, oxygen, or phosphor atom which can coordinate a metal or semimetal. Examples for coordinating compounds containing a nitrogen atom which can coordinated a metal or semimetal include amines like trimethylamine, triphenylamine, dimethylamino-iso-pro- panol. Preferably, the coordinating compound contains two or more nitrogen atoms including ethylenediamine derivatives like Ν,Ν,Ν',Ν'-tetramethylethylenediamine or N,N,N',N",N"-pen- tamethyldiethylenetriamine; imines like 2,4-pentandione-N-alkylimines, 2,4-pentandione-N-iso- propylimine, glyoxal-N,N'-bis-isopropyl-diimine, glyoxal-N,N'-bis-tert-butyl-diimine or 2,4-pen- tanedione-diimine; diketiminates such as N,N'-2,4-pentanediketiminate; iminopyrroles including pyrrol-2-carbald-alkylimines such as pyrrol-2-carbald-ethylimine, pyrrol-2-carbald-iso-propy- limine or pyrrol-2-carbald-tert-butylimine as well as pyrrol-2,5-biscarbald-alkyldiimines such as pyrrol-2,5-biscarbald-tert-butyldiimine; amidinates such as acetamidine or N,N'-bis-iso-propyla- cetamidine; guanidinates such as guanidine; aminoimines such as 2-N-tert-butylamino-2- methylpropanal-N-tertbuylimine; amides such as formamide or acetamide.

Examples for coordinating compounds containing an oxygen atom which can coordinated a metal or semimetal include alkanolates, tetrahydrofurane, acetylacetonate, or 1 ,1 ,1 , 5,5, 5-pen- tafluoroacetylacetone. Other suitable examples for coordinating compounds contain both a nitrogen and an oxygen atom which both coordinate to M including dimethylamino-iso-propanol, formamide, acetamide, 2,4-pentandione-N-alkylimines such as 2,4-pentandione-N-iso-propy- limine.

Examples for coordinating compounds containing a phosphor atom which can coordinated a metal or semimetal include phosphane or trisubstituted phosphanes including trihalogenphos- phanes, trialkylphosphanes, dialkylarylphosphanes, alkyl-diarylphosphanes or tri- arylphosphanes, wherein the alkyl or the aryl groups can be the same or different to each other if more than one alkyl or aryl group is present. Examples include trifluoro phosphane, trimethyl phosphane, trimethoxyphosphane, methyl-dimethoxy phosphane, tri-tertbutyl phosphane, tricy- clohexyl phosphane, di-isopropyl-tert-butyl phosphane, dimethyl-tert-butyl phosphane, triphenyl phosphane, and tritolylphosphane. Preferably, the coordinating compound contains two or more phosphor atoms. Such compounds include diphosphinoethanes such as 1 ,2-bis(dieth- ylphosphino)ethane.

Preferably, the coordinating compound contains a group which is capable of forming a volatile compound with a halogen atom, for example groups containing Si, B, Sn or Ge. In this way, the removal of such a volatile compound is another driving force to form a coordinative bond to the metal or semimetal in the metal- or semimetal-containing material. Preferred examples include silylated amines such as N,N-dimethyl-N-trimethylsilylamine; silylated alcohols such as meth- oxy-trimethylsilane; silylated carboxylates such as trimethylsilyl acetate; silylated diamines such as N,N'-bis(trimethylsilyl)-N,N'-di-tertbutyl-ethen-1 ,2-diamine; diketiminates of Sn or Ge; amidinates of Sn or Ge; or borylated cyclopentadiene such as cyclopentadiene-boron-dichloride.

Preferably, after the metal- or semimetal-containing material is brought in contact with the coordinating compound, any residual excess coordinating compound is removed by purging with an inert gas, for example nitrogen, helium, or argon. Alternatively, the excess coordinating compound can be removed by high vacuum, such as lowering the pressure to 0.1 to 10 ^-6 mbar.

In some cases it is preferable to bring the halogenated metal- or semimetal-containing material in contact with an organic solvent prior to bringing it in contact with a coordinating compound. Preferably, the solvent is in the vapor phase when being brought in contact with the metal- or semimetal-containing material. Preferably, the pressure of the solvent vapor is 1 to 100 mbar, more preferably 2 to 50 mbar, in particular 5 to 20 mbar. Organic solvents include alcohols like methanol, ethanol or isopropanol; ethers like dimethylether, diethylether or tetrahydrofurane; es- ters like methyl formiate, ethyl formiate, methyl acetate, ethyl actetate; aldehydes like formaldehyde or acetaldehyde; ketones like acetone or methyl ethyl ketone; acids like formic acid or acetic acid; amines like trimethyl amine, triethylamine, dimethyl-isopropylamine; amides like N,N- dimethylformamide or N,N-dimethylacetamide. Preferably, after bringing the metal- or semimetal-containing material in contact with an organic solvent, any residual solvent vapor is removed by purging with an inert gas, for example nitrogen, helium, or argon. Alternatively, the residual vapor can be removed by high vacuum, such as lowering the pressure to 0.1 to 10 ^"6 mbar. Preferably, the sequence including bringing the metal- or semimetal-containing material in contact with a compound of general formula (I), (II), or (III) and then bringing it in contact with a coordinating compound is performed at least twice, more preferably at least five times, in particular at least 10 times.

A process containing multiple of said sequence is often referred to as atomic layer etching (ALE). ALE can be employed in the semiconductor manufacturing process, in particular when sub-10 nm technologies are involved. ALE is often combined with passivating layers, such as photocured resins which are irradiated through shadow masks, in order to selectively etch metals or semimetals only in particular areas for building up complex structures.