Patent Application
20080096785
Numerous steps are involved in the fabrication of microelectronic structures. Within the manufacturing scheme of fabricating integrated circuits, selective etching of semiconductor surfaces is sometimes required. Historically, a number of vastly different types of etching processes, to selectively remove material have been successfully utilized to varying degrees. Moreover, the selective etching of different layers, within the microelectronic structure, is considered a critical and crucial step in the integrated circuit fabrication process.
In the manufacture of semiconductors and semiconductor microcircuits, it is frequently necessary to coat substrate materials with a polymeric organic substance. Examples of some substrate materials includes titanium, copper, silicon dioxide coated silicon wafer which may further include metallic elements of titanium, copper, and the like. Typically, the polymeric organic substance is a photoresist material. This is a material which will form an etch mask upon development after exposure to light. In subsequent processing steps, at least a portion of the photoresist is removed from the surface of the substrate.
One common method of removing photoresist from a substrate is by wet chemical means. The wet chemical compositions formulated to remove the photoresist from the substrate should do so without corroding, dissolving, and/or dulling the surface of any metallic circuitry; chemically altering the inorganic substrate; and/or attacking the substrate itself. Another method of removing photoresist is by a dry ash method where the photoresist is removed by plasma aching using either oxygen or forming gas such as hydrogen. The residues or by-products may be the photoresist itself or a combination of the photoresist, underlying substrate and/or etch gases. These residues or by-products are often referred to as sidewall polymers, veils or fences.
The purpose of stripping and/or cleaning compositions is to remove these residues or by-products from the surface of the substrate of the semiconductor device without corroding, dissolving or dulling the exposed surface of the substrate, after the termination of the etching step.
The use of acetals as casting solvents for blends for film casting has been described. Wanat et al (U.S. Pat. No. 6,911,293 B2) described a photoresist composition comprising a film forming resin, photoactive compound or photoacid generator and organic solvent selected from a list of acetals and ketals. However, the Wanat invention does not teach the use of acetal solvents as a stripping and/or cleaning composition.
Ikemoto and Kojiro (US 2004/0009883 A1) describe a resist stripping formulation that contains a fluorine compound, a mixed solvent of an amide solvent and an ether solvent and water. Examples shown are containing diethlene glycol monomethyl ether, N,N-dimethylacetamide (DMAC), ammonium fluoride and water. Dioxolane and trioxane were included in the examples of ether solvents provided in the description of the invention.
Doyle et al (U.S. Pat. No. 6,689,734 B2) described cleaning formulations that have additions of some agents to the mono brominated hydrocarbon compounds with highly fluorinated compounds. Those agents are one or more of the following materials: alcohols, esters, ethers, cyclic ethers, ketones, alkanes, terpenes, dibasic esters, glycol ethers, pyrollidones, or low or non ozone depleting chlorinated and chlorinated/fluorinated hydrocarbons. 1,4 dioxane and 1,3 dioxolane were among the cyclic ether group for the agents.
The formulation disclosed in the present invention is capable of removing post-etched organic and inorganic residue and photoresist from semiconductor substrates.
In one respect, the present invention provides a formulation for removing post-etched organic and inorganic residue and photoresist from semiconductor substrates, comprising: an acetal or a ketal solvent, water, a polyhydric alcohol, and a pH adjuster to adjust the formulation having a pH at least 7 or higher.
In another respect, the present invention provides a formulation for removing post-etched organic and inorganic residue and photoresist from semiconductor substrates, comprising: from 20 to 55% by weight of Glycol ether; from 10 to 55% by weight of Tetramethoxypropane; from 1 to 15% by weight of Tetramethylammonium hydroxide; from 0.5 to 5% by weight of Tolyltriazole; from 5 to 25% by weight of Propylene glycol, and from 40 to 60% by weight of Water
In yet another respect, the present invention provides a method for removing post-etched organic and inorganic residue and photoresist from semiconductor substrates, comprising: contacting the substrate with a formulation comprising an acetal or a ketal solvent, water, a polyhydric alcohol, and a pH adjuster to adjust the formulation having a p at least 7 or higher.
The present invention provides a composition whose components are present in amounts that effectively remove residue from a substrate such as, for example, a semiconductor substrate. In applications concerning semiconductor substrates, such residues include, for example, photoresists (hardened or otherwise), gap fill, bottom antireflective coating (BARC) and other polymeric materials (e.g., C—F-containing polymers, low and high molecular weight polymers) and/or processing residues such as the residues generated by etching and ashing processes, inorganic compounds such as metal oxides, ceramic particles from chemical mechanical planarization (CMP) slurries and other inorganic etch residues, metal containing compounds such as, for example, organometallic residues and metal organic compounds. In one embodiment, compositions according to the present invention are particularly effective at removing silicon-containing BARC residues from a semiconductor substrate.
The residues are typically present in a substrate that may include metal, silicon, silicate and/or interlevel dielectric materials such as, for example, deposited silicon oxides and derivatized silicon oxides such as HSQ, MSQ, FOX, TEOS and spin-on glass, chemical vapor deposited dielectric materials, low-k materials and/or high-k materials such as hafnium silicate, hafnium oxide, barium strontium titanate (BST), TiO2, TaO5, wherein both the residues and the metal, silicon, silicide, interlevel dielectric materials, low-k and/or high-k materials will come in contact with the cleaning composition. The compositions according to the present invention are compatible with such materials and, therefore, can be employed to selectively remove residues such as, for example, those described above, without significantly attacking the metal, silicon, silicon dioxide, interlevel dielectric materials, low-k and/or high-k materials. In certain embodiments, the substrate may contain a metal, such as, but not limited to, copper, cobalt, copper alloy, titanium, titanium nitride, tantalum, tantalum nitride, tungsten, and/or titanium/tungsten alloys.
This invention describes a formulation comprising of acetal or ketal as a solvent, water, a polyhydric alcohol and a pH adjuster to adjust the formulations having a pH at least 7 or higher. Formulations in this invention can optionally contain water-soluble organic solvents as co-solvent. The formulations in this invention can be used to remove post-etched organic and inorganic residue as well as polymeric residues from semiconductor substrates.
This invention describes formulations with compositions containing an acetal or a ketal with general formula I or II or the combination of both:
Where n≧1 and R1, R2, R3, R4 and R5 are each independently H, alkyl, or phenyl
More specifically, this invention describes a semi-aqueous stripping composition comprising of an acetal or ketal of types I or II or combinations of both, polyhydric alcohol, high pH adjuster and base water. The pH of the composition is at least 7 or higher.
In this formulation, the range of the acetal or ketal solvent is about 0.01% to 90.00% by weight, the range of the polyol is about 1% to 80% by weight, the range of the water is 1% to 80% by weight, and the range of pH adjuster is about 0.1 to 50% by weight. The preferred range of the acetal or ketal solvent is about 5% to 55.00% by weight, the range of the polyol is about 3% to 40% by weight, the range of the water is 5% to 60% by weight, and the range of pH adjuster is about 0.1 to 15% by weight.
Preferred acetal or ketal solvents for such formulations are tetramethoxypropane, tetramethoxyethane, malonaldehyde bis(methyl acetal), phenylacetaldehyde dimethyl acetal, benzaldehyde dimethyl acetal, phenylacetaldehyde ethylene acetal, chloroacetaldehyde dimethyl acetal, Chloroacetaldehyde diethyl acetal, 1,3-dioxolane, trioxane, and mixtures thereof.
Preferred polyhydric alcohols for such formulations are ethylene glycol, propylene glycol, glycerol, butanediol, pentanediol and mixtures thereof.
Preferred pH adjusters for such formulations are Tetrabutylammonium hydroxide (TBAH), Tetramethylammonium hydroxide (TMAH), Tetramethoxypropane (aka malonaldehyde bis(methyl acetal) (TMP), Potassium hydroxide (KOH), Benzyltrimethylammonium hydroxide (BzTMAH). The pH adjuster also functions to assist in the removal of organic and inorganic residues.
Non-limiting examples of water include deionized (DI) water, ultra pure water, distilled water, doubly distilled water, or deionized water having a low metal content. Preferably, the water in the composition comprises DI water. In the present invention, water functions in various ways such as, for example, as a solvent to dissolve one or more solid components of the composition, as a carrier of the components, as an aid in the removal of the residue, as a viscosity modifier of the composition, and as a diluent.
Formulations in these compositions can also contain other organic solvents as co-solvents. The organic solvent is selected from the group consisting of Tetrahydrofurfuryl alcohol, glycol ether, and mixtures thereof. These formulations are restricted to cases where pH is at least 7 or higher.
The formulations in this invention can contain ammonium and quaternary ammonium fluoride. If employed, the ammonium and quaternary ammonium fluoride functions to assist in the removal of organic and inorganic residues. Preferred ammonium and quaternary ammonium fluoride are Tetrabutylammonium fluoride, Tetrapropylammonium hydroxide, Tetraethylammonium hydroxide, Tetramethylammonium fluoride, Ammonium hydroxide, and mixtures thereof. These formulations are restricted to cases where pH is at least 7 or higher.
The use of a corrosion inhibitor is optional in this invention. Examples of the corrosion inhibitor are tolyltriazole, benzotriazole, catechol, gallic acid and mixtures thereof. These formulations are restricted to cases where pH is at least 7 or higher.
Formulations containing the acetals or ketals have proved to be effective in removal of both pre- and post-etched photoresist, etched residues and post-etch polymeric residues. Care was taken to be sure that pH of the composition was at least 7 or higher as compositions with pH lower than 7 could pose shelf-life issues.
The cleaning composition of the present invention is typically prepared by mixing the components together in a vessel at room temperature until all solids have dissolved in the aqueous-based medium.
Compositions disclosed herein are compatible with substrates containing low-k films such as HSQ (FOx), MSQ, SiLK, etc. including those low-k films containing a fluoride. The compositions are also effective in stripping photoresists including positive and negative photoresists and plasma etch residues such as organic residues, organometallic residues, inorganic residues, metallic oxides, or photoresist complexes at low temperatures with very low corrosion of copper, and/or titanium containing substrates. Moreover, the compositions are compatible with a variety of metal, silicon, silicon dioxide, interlevel dielectric materials, low-k and/or high-k materials.
During the manufacturing process, a photoresist layer is coated on the substrate. Using a photolithographic process, a pattern is defined on the photoresist layer. The patterned photoresist layer is thus subjected to plasma etch by which the pattern is transferred to the substrate. Etch residues are generated in the etch stage. Some of the substrates used in this invention are ashed while some are not ashed. When the substrates are ashed, the main residues to be cleaned are etchant residues. If the substrates are not ashed, then the main residues to be cleaned or stripped are both etch residues and photoresists.
The method described herein may be conducted by contacting a substrate having a metal, organic or metal-organic polymer, inorganic salt, oxide, hydroxide, or complex or combination thereof present as a film or residue, with the described composition. The actual conditions, e.g., temperature, time, etc., depend on the nature and the thickness of the material to be removed. In general, the substrate is contacted or dipped into a vessel containing the composition at a temperature ranging from 20° C. to 85° C., or from 20° C. to 60° C., or from 20° C. and 40° C. Typical time periods for exposure of the substrate to the composition may range from, for example, 0.1 to 60 minutes, or 1 to 30 minutes, or 1 to 15 minutes. After contact with the composition, the substrate may be rinsed and then dried. Drying is typically carried out under an inert atmosphere. In certain embodiments, a deionized water rinse or rinse containing deionized water with other additives may be employed before, during, and/or after contacting the substrate with the composition described herein. However, the composition can be used in any method known in the art that utilizes a cleaning fluid for the removal of photoresist, ash or etch residues and/or residues.
It will be appreciated by those skilled in the art that the composition of the present invention may be modified to achieve optimum cleaning without damaging the substrate so that high throughput cleaning can be maintained in the manufacturing process. For example, one skilled in the art would appreciate that, for example, modifications to the amounts of some or all of the components may be made depending upon the composition of the substrate being cleaned, the nature of the residue to be removed, and the particular process parameters used.
Although the present invention has been principally described in connection with cleaning semiconductor substrates, the cleaning compositions of the invention can be employed to clean any substrate that includes organic and inorganic residues.
The following examples are provided for the purpose of further illustrating the present invention but are by no means intended to limit the same.
In the following examples, all amounts are given in weight percent and add up to 100 weight percent. The compositions disclosed herein were prepared by mixing the components together in a vessel at room temperature until all solids have dissolved. Examples of certain compositions disclosed herein are set forth in Table I.
The following are the acronyms used in Table I:
Each substrate used in the present Examples comprised three layers. The first (i.e., the bottom layer) was an ILD material comprising BLACK DIAMOND II™. The next layer was a silicon-containing BARC (193 nm) and the top layer was a photoresist (193 nm). The substrates were then subjected to plasma etching
Cleaning tests were run using 305 mL of the cleaning compositions in a 400 mL beaker with a ½″ round Teflon stir bar set at 600 rpm. The cleaning compositions were heated to the desired temperature indicated below on a hot plate if necessary. Wafer segments approximately ½″×½″ in size were immersed in the compositions under the following set of conditions.
10 minutes @ 25° C.
20 minutes @ 25° C.
10 minutes @ 35° C.
20 minutes @ 35° C.
The segments were then rinsed for 3 minutes in a DI water overflow bath and subsequently dried using filtered nitrogen. They were then analyzed for cleanliness using SEM microscopy.
✓ = successful
✓− = partially successful
X = unsuccessful
NT = not tested
Table II illustrates the effectiveness of compositions according to the present invention at removing a BARC residue and a photoresist residue.
Coupons of blanket Cu, Co, and W wafers were measured for metal layer thickness by measuring the resistivity of the layer by employing a ResMap™ model 273 resistivity instrument from Creative Design Engineering, Inc. The coupons were then immersed in the composition at the desired temperature for up to one hour. Periodically the coupons were removed from the composition, rinsed with de-ionized water and dried and the thickness of the metal layer was again measured. A graph of the change in thickness as a function of immersion time was made and the etch rate in Angstroms/min was determined from the slope of the curve.
NT = not tested
Table III illustrates the effectiveness of certain of the compositions according to the present invention at selectively removing residue without significantly etching the metal substrate.
The foregoing examples and description of the preferred embodiments should be taken as illustrating, rather than as limiting the present invention as defined by the claims. As will be readily appreciated, numerous variations and combinations of the features set forth above can be utilized without departing from the present invention as set forth in the claims. Such variations are not regarded as a departure from the spirit and scope of the invention, and all such variations are intended to be included within the scope of the following claims.
This application claims the benefit of priority under 35 U.S.C. § 119(e) to earlier filed U.S. patent application Ser. No. 60/852,758, filed on 19 Oct. 2006, the disclosure of which is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60852758 | Oct 2006 | US |
