Patent Grant
7192910
The present invention generally relates to compositions useful for etching various types of silicon oxide and oxynitrides. The compositions are also useful for cleaning residues from semiconductor substrates.
Selective etching and cleaning solutions for dielectric antireflective coatings (DARC), pre-metal contacts comprised of undoped tetraethylorthosilicate (TEOS) and thermal oxides, and doped phospho- and boro-phospho-silicate glasses (PSG & BPSG) and low-k dielectric/copper interconnect structures are important to device design and manufacturing for the most advanced semiconductor technologies. Such process chemicals enable processing advances such as reduction of critical dimension and lower resistivity and capacitance contacts and interconnect.
DARC films, and more generally antireflective coatings (ARC's), are used to minimize undesirable surface layer reflections during photolithography and in so doing provide better pattern definition. DARC films are also employed in Advanced Patterning Technology with amorphous carbon films to extend and enhance existing photolithography to pattern smaller geometry structures. However, it is generally necessary to selectively remove these films after photolithography or plasma etch by either a wet chemical or plasma method.
Both undoped and doped silicon oxides are used as dielectric materials in pre-metal contacts down to doped silicon, polysilicon, and suicides. After plasma etch to open the contact, a contact clean chemistry is applied to selectively remove residues and provide a clean and conductive contact surface while maintaining the contact profile and critical dimension.
Additionally, compositions for removing photoresist and etch residues following plasma etch and ash processes are crucial for optimum electrical performance, reliability, and yield in integrated circuit manufacturing. Back end of line (BEOL) cleaning chemicals need to be capable of cleaning organic, organometallic, and inorganic post etch and post ash residues from copper and aluminum interconnect while not etching the interconnect metal or altering silicon dioxide or low-k dielectrics and their associated materials.
Presently, aqueous and non-aqueous fluoride formulations are used in selective etching and cleaning applications. These compositions are generally comprised of a fluoride component, additives, and a solvent, in many instances water. In selective etch applications, etch rates of many fluoride containing compositions are generally high, requiring very short process times. In addition, the varying stoichiometry of the films to be etched may result in a non-uniform etch that manifests as small islands of film remaining on the substrate surface as depicted in
Fluoride chemistries, particularly HF/NH4F buffered oxide etch (BOE) and dilute HF, are also widely used for pre-metal contact cleaning. The high silicon oxide etch rates and narrow selectivity properties limit their use in applications where contact CD is below 0.18 μm, aspect ratio is greater than 10:1, and contact architecture uses complex material stacks as depicted in
Formulations containing various amounts and types of fluoride additives have been used for BEOL cleans particularly when interconnect features are comprised of copper, low-k dielectric and associated materials as depicted in
It has been found that formulations containing quaternary ammonium, phosphonium, and/or sulfonium fluoride salt, a relatively low water content, and a pH of 2–9 would be most compatible with silicon dioxide, low-k and porous low-k dielectrics, associated cap, barrier and etch stop materials, and metals such as copper and aluminum, which are used to construct interconnect features in integrated circuit manufacturing. Furthermore, it has been found that such formulations have high cleaning activity on post plasma etch and ash residues.
A cleaning or etching solution can be formulated by combining the following components in the amounts indicated below (by weight of the final composition):
(1) 0.1–20% by weight of a fluoride salt (preferably a quaternary ammonium, phosphonium or sulfonium);
(2) 0–5% by weight of a quaternary ammonium or phosphonium salt;
(3) 0.1–5% by weight of a pH adjusting acid (e.g., mineral acid, carboxylic acid, sulfonic acid);
(4) 0–99.8% by weight of an organic solvent (e.g., alcohols, amides, ethers); and
(5) 0–99.8% by weight of water.
In certain embodiments, the fluoride salt is present in an amount of 1–10%, water is present in an amount less than 5%, and the organic solvent makes up more than 80% of the total composition. The pH of the composition is preferably between about 2 and about 9.
The compositions of the present invention have been found to be useful in various semiconductor cleaning and etching processes. For example, the compositions can be used after patterning a semiconductor substrate that includes a dielectric antireflective coating (DARC). The compositions can be used to selectively etch the DARC after it has been applied to the substrate. The etching composition is formulated to remove the DARC at a greater rate than it etches other layers on the substrate (e.g., amorphous carbon, BPSG, etc.).
The compositions of the present invention have also been found to be useful in pre-deposition and contact cleaning applications. For example, the compositions can be used to etch doped and undoped oxide layers with a 1:1 selectivity. Alternately, the compositions can be used to selectively etch these oxide layers such that the undoped oxide is removed at a rate that is between 2 and 10 times as fast as the rate at which the doped oxide is removed. The contact material can be a pre-metal contact material such as doped silicon, polysilicon, or silicide, or it can be a metal contact such as Cu or AlCu.
These compositions can also be used to remove the residue that is typically formed on contacts, vias, and metal lines when a dielectric or stack of dielectrics is etched to expose contact material. In this case, the cleaning formulation removes the post-etch residue while having little or no effect on the surrounding dielectric and/or metal.
References are made to the following description taken in connection with the accompanying drawings, in which:
Various etching and cleaning compositions containing quaternary ammonium, phosphonium, or sulfonium fluoride formulations have been formulated to obtain improved etch rate, etch selectivity, etch uniformity and cleaning criteria on a variety of substrates.
The compositions preferably include a fluorine-containing compound such as a fluoride salt (e.g., a salt containing any type of fluoride, hydrogen fluoride, difluoride, etc.) as an active agent. The fluorine-containing compound can be a quaternary ammonium salt, a phosphonium salt, or a sulfonium salt, (i.e., more generally an “onium” salt), or it can be a salt that includes two or more quaternary onium groups linked together by one or more carbon-containing groups (e.g., “di-quats”, “tri-quats”, “tetraquats”, etc.). The fluorine-containing compound preferably makes up between about 0.1% to about 20% by weight of the composition, more preferably between about 1% and about 10% by weight, and more preferably still between about 2% and about 7% by weight.
The composition may further include a pH adjusting acid such as a mineral acid, carboxylic acid, dicarboxylic acid, sulfonic acid, or combination thereof. The acid preferably makes up between about 0.1% to about 5% by weight of the composition, more preferably between about 0.1% and about 1% by weight, and more preferably still between about 0.1% and about 0.5% by weight. The resulting pH of the solution is typically between about 2 and about 9 and is preferably acidic. In some embodiments, the pH is between about 2 and about 7, and more preferably between about 2 and about 4.
The composition may further include an organic solvent such as an alcohol, amide, ether, or combination thereof. The solvent preferably makes up between about 1% to about 99.8% by weight of the composition, more preferably greater than about 80% by weight, and more preferably still greater than about 90% by weight.
The composition can also include water either as the primary solvent or in combination with an organic solvent. The composition may optionally be substantially anhydrous. It has been found that compositions having a very small water content are particularly suitable for certain semiconductor etching and cleaning applications, and the compositions used in these applications preferably have a water content of less than about 5% by weight, more preferably between about 0.5% and about 4%, and more preferably still between 1 and 3%.
The composition can optionally include a quaternary ammonium salt, a sulfonium salt, or a phosphonium salt in addition to the fluorine-containing compound. If present, this salt preferably makes up less than about 5% of the composition by weight, more preferably less than about 4% of the solution, and more preferably still between about 1% and about 3%.
Exemplary fluorine-containing compounds and salts suitable for use in the compositions of the present invention include Tetramethylammonium Fluoride, Tetrabutylammonium Fluoride, Methyltriphenylammonium Fluoride, Phenyltrimethylammonium Fluoride, Benzyltrimethylammonium Fluoride, Methtyltriethanolammonium Fluoride, Tetrabutylphosphonium Fluoride, Methyltriphenylphosphonium Fluoride, Trihexyltetradecylphosphonium Fluoride, Tributyltetradecylphosphonium Fluoride, Methyltriethanolammonium Hexafluorophosphate, Methyltriethanolammonium Tetrafluoroborate, Methyltriethanolammonium Dihydrogen Fluoride, Tetrabutylphosphonium Hexafluorophosphate, Tetrabutylphosphonium Tetrafluoroborate, Tetrabutylphosphonium Hydrogen Difluoride, Tetrabutylphosphonium Dihydrogen Trifluoride, [(CH3)3NCH2CH(OH)CH2N(CH3)3]2+ [F-]2, Betaine Hydrofluoride, 1-Butyl-3-methylimidazolium Fluoride, Trimethylsulfonium Fluoride, Trimethylsulfoxonium Fluoride, trimethyl (2,3-dihydroxypropyl) ammonium fluoride, [(C6H5)CH2N(CH3)2CH2CH(OH)CH2N(CH3)2CH2CH(OH)CH2N(CH3)2CH2NCH2(C6H5)]4+[F-]4, and [(CH3)3NCH2CH(OH)CH20H]+[F-], Hexamethonium difluoride. These compounds are merely examples, and the skilled artisan will understand (with the benefit of this Specification) that additional fluoride-containing compounds can be used in the present invention.
In one embodiment, the fluorine-containing compound is an alkanol quaterary ammonium fluoride. As used herein, an “alkanol group” is an akyl chain containing one or more hydroxy groups. Each alkanol group may be a hydroxylethyl, hydroxylbutyl, hydroxypropyl, 2,3 dihydroxypropyl etc. The alkanol quaternary ammonium fluoride can contains 1, 2, or 3 alkyl groups along with 3, 2, or 1 alkanol groups, respectively. The alkanol group may contain the hydroxy substituent(s) on the alpha, beta, gamma, etc., carbon position. In addition, alkanol or alkyl groups may bridge between adjacent quaternary ammonium cations to give diquats, triquats and multiquats. It is also envisioned that alkoxy groups could be acceptable in place of the hydroxy groups to give analogous alkoxy substituted quaternary ammonium or phosphonium fluorides.
Exemplary quaternary ammonium, sulfonium, and phosphonium salts that may optionally be included in the compositions in addition to the fluorine-containing compound include Tetramethylammonium Acetate, Tetrabutylammonium Chloride, Benzyltrimethylammonium Methanesulfonate, Methtyltriethanolammonium Benzoate, Tetrabutylphosphonium Salicylate, Trihexyltetradecylphosphonium Chloride, Tributyltetradecylphosphonium Fluoride, Methyltriethanolammonium Dihydrogen Phosphate, Methyltriethanolammonium Nitrate, Methyltriethanolammonium Sulfate, Tetrabutylphosphonium Phthalate, Tetrabutylphosphonium Acetate, Tetrabutylphosphonium Oxalate, Tetrabutylphosphonium Malonate, [(CH3)3NCH2CH(OH)CH2N(CH3)3]2+Diacetate, Betaine, and 1-Butyl-3-methylimidazolium Acetate.
Exemplary pH adjusting acids that may be included in the compositions include Hydrofluoric acid, Hydrochloric Acid, Nitric Acid, Sulfuric Acid, Phosphoric Acid, Hydrobromic Acid, Perchloric Acid, Methanesulfonic Acid, Acetic Acid, Benzoic Acid, Octanoic Acid, Oxalic Acid, Salicylic Acid, Malonic Acid, Fluoroboric Acid, Hexafluorophosphoric Acid, Phenylphosphonic Acid, and Phytic Acid.
Exemplary solvents that may be included in the compositions include water, Tetrahydrofurfuryl Alcohol, Benzyl Alcohol, Hexanol, 2-(2-methoxyethoxy)-ethanol, Dimethylacetamide, Bis-(2-methoxyethyl) Ether, Octanoic Acid, Diethyleneglycol mono butyl ether, Glyme (including diglymes and monoglymes), Dipropyleneglycol mono methyl ether, 2-butoxyethanol, 1-Cyclohexyl-2-pyrrolidinone, and 1-Hydroxyethyl-2-pyrrolidinone. The organic solvent is preferably partially water-soluble.
The composition preferably is substantially free of metal ions, including sodium ions, potassium ions, and free metal ions to prevent wafer contamination. The solution components (e.g., salts, organic solvent) are preferably purified using ion exchange to remove metal ions. The organic solvents may also be purified via distillation or ion exchange. High purity acids can be purchased commercially. After purification, the composition preferably has a free metal ion content of less than about 200 parts per billion (PPB), more preferably less than about 20 PPB, more preferably less than about 10 PPB, and more preferably still less than about 5 PPB.
These compositions can be used for a variety of selective and non-selective etching and cleaning applications including those depicted in
Application 1 (
Application 2 (
Application 3 (
Application 4 (
The high selectivity to undoped oxide etch formulations and the non-selective doped to undoped etch formulations can be used to clean plasma etched structures of varying architecture as depicted in
The composition used in Example 17 was formulated by the following steps:
(1) 7.33 g of HF (Air Products 48.9%; Lot 3067035P) was slowly added with stirring to 89.79 g of Tetrabutylphosphonium Hydroxide (Sachem 39.97%; Lot A30761012503). Heat was generated during this neutralization step.
(2) The resulting solution was diluted with diethyleneglycol monobutyl ether (ACROS; 99+%, <0.1% H20) to a final mass of 326.8 g. The resulting solution was approximately 18.3% water, 10.97% tetrabutyl phosphonium fluoride, 0.305% HF, and 70.42% diethyleneglycol monobutyl ether.
(3) The resulting solution was placed in a teflon coated round bottom flask and rotovaped at 85° C. @40 Torr (or better) until the water content dropped to 3.1% (total time 33 minutes).
(4) This solution, having a mass of 277.82 g, was diluted 3.6 fold (to 1000.14 g) with diethyleneglycol monobutyl ether, resulting in the formulation used in Example 1. The other formulations in Table 1 below were made in a similar manner.
The following films were tested using the compositions listed in Table 1 below:
(1) 6000 Å 3.0%×6.0% boron and phosphorus (BPSG) doped oxide;
(2) 1050 Å dielectric antireflective coating (DARC; SiOxNy);
(3) 2300 Å Plasma enhanced chemical vapor deposition (PECVD TEOS) oxide;
(4) 5000 Å 5.0% Phosphorus doped oxide (PSG); and
(5) 5000 Å Thermal oxide (THox);
The DARC, BPSG, PSG, TEOS etc. wafers were cleaved into 1″×1″ square pieces. The pieces were submerged into plastic beakers containing the etchant solutions at 25–70° C. The wafer pieces were processed for 10–30 min after which they were rinsed with isopropyl alcohol then DI water and blown dry with nitrogen. The film thicknesses before and after processing were determined by reflectometry using a NANOSPEC 210. The films were also examined by optical microscopy to assess uniformity of etch.
The results for etch rate, selectivity and film removal uniformity (DARC) are presented in Table 1. The results in Table 1 represent some of the preferred formulations based upon over 800 formulations tested. It is to be understood that formulations in Table 1 are merely examples of the present invention, which is not to be limited to the specific components or percentages in this description. One of ordinary skill will appreciate, with the benefit of this specification, that many other formulations could be made that fall within the scope of the invention described herein that contain only insubstantial variations to the illustrative embodiments found in Table 1. The metes and bounds of the invention are to be ascertained from the appended claims rather than from the specific illustrative embodiments set forth in this description.
The etching and selectivity characteristics of the formulation of Example 16 were studied versus process temperature, process time and water content. This data is presented in
This application claims priority to U.S. Provisional Application No. 60/515,065, filed Oct. 28, 2003.
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