Patent Application
20230340370
The present invention relates to a composition, its use and a process for removing post-etch residues in the presence of a layer comprising silicon and a dielectric layer comprising a silicon oxide.
Steps of preparing certain microelectronic devices, e.g., integrated circuits, may include removing oxide residues remaining within the recessed patterns opened by etching a layer of amorphous silicon. The patterns in this amorphous silicon layer are usually prepared by dry etching through a photomask that is afterwards removed by ashing. After these dry etching and ashing steps oxide residues remain on the surface and particularly within the patterns of the amorphous silicon layer that need to be removed to avoid any significant impact on the electrical integrity of the integrated circuit.
The main task here is to effectively remove the oxide residues without impacting the amorphous silicon layer itself and a dielectric layer, e.g. a dielectric layer prepared from tetraethyl orthosilicate and therefore often named “TEOS” in the industry, below the amorphous silicon.
For oxide residue removal usually compositions comprising hydrofluoric acid (HF) are used but such compositions show either a good oxide residue removal rate or a low etching rate of the TEOS layer, i.e. the selectivity for oxide residues against TEOS is rather low.
WO 02/004233 A1 discloses a composition for the stripping of photoresist and the cleaning of residues from substrates, and for silicon oxide etch, comprising from 0.01 to 10 % by weight of one or more fluoride compounds, from 10 to 95 % by weight of a sulfoxide or sulfone solvent, and from about 20 to 50 % by weight water. However, this composition is unable to effectively remove thermal oxide residues.
WO 2010/113616 discloses a solution for etching a silicon oxide film, the solution containing hydrofluoric acid, ammonium fluoride, an acid having a pKa higher than that of hydrofluoric acid, a base having a pKa higher than that of ammonia, and water.
WO 2005/057281 A2 discloses an aqueous-based composition and process for removing photoresist, bottom anti-reflective coating (BARC) material, and/or gap fill material from a substrate having such material(s) thereon. The aqueous-based composition includes a fluoride source, at least one organic amine, at least one organic solvent, water, and optionally a chelating agent and/or surfactant.
However, the state-of-the-art solutions are not able to fulfil all requirements since they have at least one of the following deficiencies:
It is therefore an object of the present invention to ensure a good etch-residue removal rate in combination with a low dielectric etching rate, particularly TEOS etching rate. Furthermore, it is an object of the invention to develop a composition that shows an increased etch-residue to dielectric selectivity.
It has now been found that the use of an aqueous composition comprising HF, an ammonium fluoride, and a particular solvent is capable of removing post-etch residues comprising silicon oxide against elemental silicon and a dielectric material, particularly against amorphous silicon and TEOS.
Therefore, one embodiment of the present invention is a composition for removing post-etch residues in the presence of a layer comprising silicon and a dielectric layer comprising a silicon oxide, the composition comprising or essentially consisting of:
It was particularly surprising that the etching composition according to the invention is suited to allow for a controlled and selective etching of oxidic post-etch-residues while at the same time not or not significantly compromising silicon containing layers and dielectric layers comprising silicon oxide.
It should be emphasized that the compounds in the composition according to the invention may react to form other compounds, particularly component (a), HF, may react with optional component (e), an ammonium compound, if it is ammonia. In this case, depending on the ratio of components (a) and (e), HF may be reduced or even completely neutralized, and additional ammonium fluoride is formed. Therefore, the composition also covers reaction products of the compounds (a) to (e) above.
Another embodiment of the present invention is the use of the compositions described herein for removing post-etch residues in the presence of a layer comprising silicon and a dielectric layer comprising a silicon oxide.
Yet another embodiment of the present invention is a process of removing post-etch residues in the presence of a silicon layer comprising silicon and a dielectric layer comprising a silicon oxide, the process comprising:
The purpose of the composition is etching silicon oxide residues against an elemental silicon layer and, in particular, a silicon oxide containing dielectric layer. Since both the post-etch residues and the dielectric layer comprise or consist of a silicon oxide, it is particularly challenging to get high etch rates for the silicon oxide residues and sufficiently low etch rates for the dielectric layer, particularly if the dielectric layer comprises or consists of TEOS.
As schematically shown in
At least two etchants are present in the etching composition according to the invention, hydrogen fluoride and an ammonium fluoride of formula NRE4F.
Hydrogen fluoride may be used in an amount of from about 0.005 to about 0.3 % by weight, preferably of from about 0.008 to about 0.2 % by weight, more preferably of from about 0.01 to about 0.1 % by weight, most preferably of from about 0.01 to about 0.05 % by weight, based on the total weight of the composition.
Hydrogen fluoride may be present in the etching composition in an amount of from about 0.01 to about 0.6 mol/l, preferably of from about 0.01 to about 0.5 mol/l, more preferably of from about 0.015 to about 0.3 mol/l, most preferably of from about 0.02 to about 0.15 mol/l.
The ammonium fluoride NRE4F is present in an amount of from about 0.01 to about 1 % by weight, preferably from about 0.1 to about 0.8 % by weight, most preferably from about 0.2 to about 0.6 % by weight.
RE may be H or a C1 to C4 alkyl group, preferably H, methyl, ethyl or propyl, more preferably H, methyl or ethyl, even more preferably H or methyl, most preferably H.
In a preferred embodiment the etchant comprises a combination of NH4F and N(CH3)4F, preferably in a mass ratio of from 0.05 to 1, particularly from 0.1 to 0.5.
The etching compositions according to the invention comprising a combination of hydrogen fluoride and ammonium fluoride as the etchant have shown a stable and reproducible controlled selective etch rate for etching oxide residues in the presence of a dielectric layer, particularly a TEOS layer.
Most preferably the etchant consists of a combination of hydrogen fluoride and ammonium fluoride NRE4F, i.e. no further etchants besides hydrogen fluoride and ammonium fluoride NRE4F are present in the etching composition.
In a preferred embodiment the etchant consists of a combination of hydrogen fluoride and ammonium fluoride in a mass ratio of from 0.005 to 1, preferably of from 0.01 to 0.5, most preferably of from 0.02 to 0.2.
Compositions according to the invention comprising the etchant in the here defined preferred total amounts have shown a superior balance of acceptable etch rate, in particular for etch residues comprising silicon oxide, and etch rate selectivity, in particular in the presence of a layer comprising or consisting of a dielectric, such as but not limited to TEOS.
The etching composition according to the invention further comprises from about 5 to about 30 % by weight of an organic solvent selected from a sulfoxide and a sulfone.
Preferably the organic solvent may be present in the etching composition in an amount of from about 8 to about 27 % by weight, more preferably of from about 10 to about 25 % by weight, even more preferably of from about 12 to about 23 % by weight, most preferably from about 15 to about 20 % by weight.
Preferred sulfoxides are compounds of formula
wherein RS1 and RS2 are independently selected from a C1 to C4 alkyl or RS1 and RS2 together form an C4 or C5 alkanediyl group to form 5 or 6 membered saturated cyclic ring system.
Suitable sulfoxide solvents include the following and mixtures thereof: Dimethyl sulfoxide (DMSO), dipropylsulfoxide, diethylsulfoxide, methylethylsulfoxide, diphenylsulfoxide, methylphenylsulfoxide, 1, 1′-dihydroxyphenyl sulfoxide and the like.
Preferred sulfones are compounds of formula
wherein RS3 and RS4 are independently selected from a C1 to C4 alkyl or RS3 and RS4 together form an C4 or C5 alkanediyl group to form 5 or 6 membered saturated cyclic ring system.
Suitable sulfone solvents include the following and mixtures thereof dimethylsulfone, diethylsulfone, 2,3,4,5-tetrahydrothiophene-1,1-dioxide (also referred to as sulfolane) and the like.
The solvent should be water miscible to provide a homogenous solution. The term “water-miscible organic solvent” in the context of the present invention preferably means that an organic solvent fulfilling this requirement is miscible with water at least in a 1:1 weight ratio at 20° C. and ambient pressure.
In a preferred embodiment the organic solvent is selected from the group consisting of DMSO, sulfolane and mixtures thereof. The most preferred organic solvent is DMSO.
To further enhance selectivity the composition according to the present invention comprises ammonia or a C4 to C20 aliphatic quaternized ammonium hydroxide compound in an amount of from 0.01 to 1 % by weight as an optional component.
In a first embodiment ammonia is added to the etching composition, preferably in the form of ammonia water.
Preferably ammonia may be added in an amount of from about 0.03 to 2 % by weight, more preferably from 0.05 to 1.5 % by weight, even more preferably from 0.1 to about 1 % by weight, most preferably from 0.15 to 0.5 % by weight.
Preferably the mass ratio of ammonia to the etchant, particularly HF, is of from 0.2 to 4, more preferably of from 0.5 to 2.
In a second embodiment a C4 to C20 quaternized aliphatic ammonium compound is added to the etching composition.
Such C4 to C20 quaternized aliphatic ammonium compounds comprise the following formula
wherein RA1 RA2, RA3, and RA4 are the same or different and independently selected from a C1 to C10 alkyl, wherein the sum of carbon atoms within RA1, RA2, RA3, and RA4 are 20 or less. Preferably RA1, RA2, RA3, and RA4 are independently selected from a C1 to C6 alkyl, most preferably from a C1 to C4 alkyl, and XA is a counter ion such as but not limited to sulfate, chloride and hydroxide, preferably hydroxide.
Preferred C4 to C20 quaternized aliphatic ammonium compound are selected from tetramethyl ammonium hydroxide (TMAH), tetraethyl ammonium hydroxide (TEAH).
The C4 to C20 quaternized aliphatic ammonium compound may be added in an amount of from about 0.03 to 2 % by weight, more preferably from 0.05 to 1.5 % by weight, even more preferably from 0.1 to about 1 % by weight, most preferably from 0.15 to 0.5 % by weight.
Preferably the molar ratio of the C4 to C20 quaternized aliphatic ammonium compound to the etchant, particularly HF, is of from 0.3 to 2, more preferably of from 0.5 to 1.
The composition may also further comprise one or more surfactants as an optional component.
Preferred surfactants are selected from the group consisting of
More preferred surfactants in compositions according to the invention are or comprise perfluorinated, N-substituted alkylsulfonamide ammonium salts.
Preferred surfactants in compositions according to the invention do not comprise metals or metal ions.
In a preferred embodiment the composition comprises a combination of anionic surfactant, preferably a C6 to C20 carboxylic acid or their salts, most preferably a C6 to C12 aliphatic carboxylic acid, and a cationic surfactant, preferably a C6 to C30 alkylamine or its salts, a C6 to C30 quaternary ammonium compound, most preferably a quaternary C6 to C30 alkyl ammonium compound.
The compositions according to the present inventions are water-based compositions, i.e. water forms the major part of at last 70% by weight of the composition. Preferably the amount of water present in the composition is 72 % by weight or more, more preferably 75 % by weight or more, even more preferably 78 % by weight or more, most preferably 80 % by weight or more.
In a preferred embodiment the pH of the etching composition is of from 1 to 7, particularly of from 2 to 6, most particularly from 3 to 5.
In a first particular embodiment the composition comprises or consists of
In a second particular embodiment the composition comprises or consists of
In a third particular embodiment the composition comprises or consists of
All percent, ppm or comparable values refer to the weight with respect to the total weight of the respective composition except where otherwise indicated. All % amounts of the components add to 100 % by weight in each case.
It will be appreciated that it is common practice to make concentrated forms of the compositions to be diluted prior to use. For example, the compositions may be manufactured in a more concentrated form and thereafter diluted with water, at least one oxidizing agent, or other components at the manufacturer, before use, and/or during use. Dilution ratios may be in a range from about 0.1 parts diluent to 1 parts composition concentrate to about 100 parts diluent to 1 part composition concentrate.
The etching composition described herein may be advantageously used for removing post-etch residues in the presence of a silicon layer comprising silicon and a dielectric layer comprising a silicon oxide, particularly TEOS. It may also be advantageously used in a process for the manufacture of a semiconductor device comprising the step of removing silicon oxide residues from a surface of a microelectronic device relative to a silicon oxide based dielectric layer, particularly TEOS.
The etching composition described herein may be advantageously used in a process of removing post-etch residues in the presence of a silicon layer comprising silicon and a dielectric layer comprising a silicon oxide, the process comprising:
In a preferred embodiment before step (a) above further steps (a1) and (a2) are performed:
The application of the compositions according to the invention are described in more detail with respect to the structures depicted in
With respect to structure (A), the electronic device structure comprises a silicon layer onto which a patterned photoresist is located. Below the silicon layer there is a dielectric layer.
In structure (A) the silicon layer is opened by dry etching through the photomask. Afterwards, the photomask on top of the silicon layer is removed. The technology of dry etching of a silicon layer is well known in the art and not further described herein.
In many cases residues, particularly sidewall residues, comprising high amount of silicon oxide remain on the surface of the recessed feature. These need to be removed without damaging the silicon layer and particularly the underlying dielectric layer. This is particularly challenging if the dielectric layer is susceptible to fluoride etching like TEOS.
As used herein, “Silicon oxide residues” or “oxide residues” mean residues comprising silicon oxide usually received by dry etching of the layer comprising silicon and the thermal removal of the photomask, i.e. impure silicon oxide including other elements or oxides.
As used herein, “silicon layer” or “layer comprising silicon” means a layer that comprises elemental silicon. The silicon may be amorphous silicon (a-Si), polycrystalline silicon (poly-Si), crystalline silicon, or combinations thereof. Amorphous silicon is preferred.
“Dielectric layer” corresponds to a layer that comprises any sort of silicon oxide used for preparing a dielectric layer, such as but not limited to TEOS, thermal silicon oxide, or carbon doped oxides (CDO) deposited using commercially available precursors such as SiLK™, AURORA™, CORAL™ or BLACK DIAMOND™.
As used herein, the term “TEOS” corresponds to silicon oxide based dielectric materials made by decomposition of tetraethoxy orthosilicate.
As used herein, removing a first material without damaging a second material preferably means that upon applying a composition according to the invention to a substrate comprising or consisting of the first material, in this case SiOx, in the presence of one or more substrates comprising or consisting of the second material, in this case particularly a-Si or TEOS, the etch rate of said composition for etching the first material is such that the first material is removed and the etching of the second material sufficiently suppressed not to cause structural damages on the substrate, particularly over-etching of the dielectric material.
As used herein, the term “layer” means a part of a substrate that was separately disposed on the surface of a substrate and has a distinguishable composition with respect to adjacent layers.
All cited documents are incorporated herein by reference.
The following examples shall further illustrate the present invention without restricting the scope of this invention.
The following non-patterned coupons were used as model layers for etch rate determination:
The thermal SiO2 was used to represent the etch rate of the post-etch-residues due to its similarity to etch-residues on patterned substrates.
The following materials were used in electronic grade purity:
All amounts given for the compounds in the composition are absolute amounts, i.e. excluding water, in the overall mixture.
The raw materials were mixed with water according to the weight content described in table 1 at room temperature with no special order of mixing. The formulation was then cooled or heated to the described temperature.
The substrates were etched at 40° C. by dipping the respective coupons into the etching solution according to table 1, washed with water and dried with nitrogen blowing The etching rates were determined by Ellipsometry by comparing the layer thickness before and after etching. Ellipsometry was performed by using an M2000 Elipsometer from Woolam. The etch rates (in Å/min; 1 Å = 0.1 nm) are depicted in table 1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20192699.5 | Aug 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/072719 | 8/16/2021 | WO |
