Cleaning solvents are used throughout industry. These solvents are made from various organic and inorganic materials forming compositions differing in functionality and effectiveness. In order for cleaning solvents to be effective, the cleaning solvent, the material to be removed, and the surrounding material or substrate must be examined to insure that the material or residue to be removed can be dissolved, solvated, or removed by the cleaning solvent without damaging the surrounding materials. Several factors, such as pH, polarity, chemical reactivity, and chemical compatibility must be considered when selecting a cleaning solvent. Other factors must also be considered when utilizing cleaning solvents, such as environmental regulations, safety concerns, and cost.
Choline and other solvents have been utilized for a variety of processes in industry. These choline compositions have been used, for example, in the microprocessor industry, and the automotive industry. In these and other industries, there have been problems associated with the use of choline compounds and choline derivative compounds.
In the microprocessor industry, various materials are utilized throughout a device. Typically, many of the base structures are made of silicon or quartzware (e.g. silicon dioxide). Also present in this industry are metal products such as copper, aluminum, gold, and silver. The process of building these intricate structures is often so small that mechanical means of construction cannot be utilized. A photolithographic process is often used to construct the pattern on the microcircuit. This process utilizes photoresist materials on an insulating film or a conductive metal film (such as an oxide film, a copper film, or aluminum alloy film), coated on a substrate, to create the pattern on the microcircuit. These photoresists are used as masking materials to delineate patterns onto a substrate so that the patterns can be subsequently etched or otherwise defined into the substrate. A spin station is used to apply the photoresist on the surface of the wafer by dispensing the photoresist on the wafer. The spin station includes a member such as a spin chuck for holding and rotating the wafer and a spindle connected to a motor for rotating the spin chuck. The spin station also includes a catch cup and a dispensing member for applying the photoresist to the wafer. During the spin-coating process, the spinning of the chuck quickly rotates the wafer, which spreads the photoresist across the surface of the wafer and rids the excess photoresist off the wafer. The final steps in preparing the substrate then involve removing the unexposed resist material and any etching residue, if etching was used, from the substrate. It is critical that all of the photoresist, flux and other debris and residue be removed to provide a wafer having sufficient integrity for subsequent use of the wafer in microcircuitry.
Additionally, plasma etching, reactive ion etching, or ion milling are also used to define the pattern in a substrate. During such etching processing, an organometallic by-product compound can be formed on the sidewall of the substrate material. A recently developed technique effective for photoresist removal is plasma oxidation, also known as plasma ashing. However, while this process is effective for removing a photoresist, it is not effective for removing the organometallic polymer formed on the sidewall of the substrate during the etching process.
Polyimides are also used in microelectronics as fabrication aids, passivants, and inter-level insulators. The use of a polyimide as a fabrication aid includes application of the polyimide as a photoresist, planarization layer in a multi-level photoresist scheme and as an ion implant mask. In these applications, the polymer is applied to a wafer or substrate, subsequently cured or patterned by a suitable method and removed after use. Many conventional strippers are not sufficiently effective in removing the polyimide layer once the polyimide has been subjected to curing. The removal of such polyimides is normally accomplished by boiling the substrate in hydrazine or in oxygen plasma.
The catch cups of the photolithographic process must also be cleaned. Clean air is directed through the spin station to control the temperature and humidity of the environment in the catch cup. Because the photoresist typically includes a high concentration of volatile solvents, the photoresist will quickly dry and adhere to the inner walls of the catch cup before it can drain from the bottom of the catch cup. The resist will deposit on the inner walls of the top, the bottom, and the shield of the catch cup. After even a few processing cycles, excessive amounts of photoresist can begin to accumulate on the inner walls of the catch cup. This build up of photoresist on the inner walls of the catch cup can alter the desired air flow characteristics around the wafer and can lead to wafer contamination and poor coating uniformity.
Typically, cleaning the catch cups has been by removing the catch cup from the spin station and manually applied cleaning fluids to the contaminated inner surfaces of the catch cup. Another method of cleaning the catch cups involves a system having two rotating catch cups; one of the catch cups actively catches excess photoresist while a cleaning solvent is dispensed on the contaminated walls of the second catch cup. The solvents used in these processes often poses a safety concern, as they may be health or environmental hazards. These hazards increase overall costs of cleaning by increasing materials handling costs and safety equipment costs.
Traditionally, the photoresist material was used to create interconnects made of aluminum or aluminum alloys isolated by dielectric material, for example silicon dioxide. More recently developed interconnects use copper as the conducting material and low-k dielectric material (a dielectric, having a dielectric constant, ε, smaller than the dielectric constant of silicon dioxide). To integrate copper and eventually aluminum, the pattern is transferred from the photoresist through the dielectric. The gaps are then filled up by the conducting layer. This process is called damascene and can integrate either one level of interconnect only (single damascene) or both the horizontal interconnects and the vertical interconnects called vias (dual damascene). Vias always open atop the underlying metal lines and good cleanliness of the via is required in order to minimize electrical resistance along the interconnect.
Various processes have been developed to build those structures, as disclosed, for example, in U.S. Pat. Nos. 5,739,579; 5,635,423; 5,705,430; and 5,686,354, which can include optional layers into the dielectric stack but all those processes have in common:    that the via needs to be cleaned from all post etch residues, without damaging the metal, before the second metal layer can be deposited,    that the whole dielectric material needs to be cleaned from copper compounds back-sputtered onto the sidewall and top surface on the underlying copper during the final part of the etching, called “opening”.    that the transfer of the wafer from the etching chamber to the ambient air for further processing creates oxidized copper compounds CuO or Cu2O that need to be cleaned to minimize the via resistance.
It has been described previously to clean materials used in the semiconductor industry by including a small amount (generally between 1% and 5% weight) of choline and other compounds to remove or avoid adsorption of metal impurities (U.S. Pat. Nos. 4,239,661 and 4,339,340, and Japanese Patent Nos. 6-163495, 6-041773, 2-275631, and 1-191450). Choline base is also well known for its use as developer of positive working photoresist (U.S. Pat. Nos. 4,294,911 and 4,464,461). It has also been recognized that choline base can act as a etching agent of metal for thin film layer definition (Japanese Patent No. 62-281332 and U.S. Pat. No. 4,172,005) and that adding choline atoms into an etching chamber when etching copper helps to lower the process temperature and hence minimize copper oxidation. U.S. Pat. No. 5,846,695 discloses aqueous solutions of quaternary ammonium hydroxides, including choline, in combination with nucleophilic amines and sugar and/or sugar alcohols, for removal of photoresist and photoresist residues in integrated circuit fabrication.
During the formation and utilization of these wares, excess coatings and/or flux from the manufacturing process can remain on the quartzware. In electronic applications the effectiveness of the production cleaning process can directly affect the reliability of the finished device. For example, a clean surface is necessary to ensure good bonding and coating, chemical contaminants can cause corrosion, and particulate matter may provide conductance paths resulting in current leakage or electrical short circuits. These are usually time related failure mechanisms that occur after the device has been put into use. The removal of these fluxes has posed a lasting difficulty for the microprocessor industry for many reasons, including the presence of various types of materials all having different reactivities and tolerances for chemical solvents. The removal of solder-flux from printed circuit boards is essentially one of washing the board with either an organic-solvent or water based cleaning solution. With the increasing limitations on organic-solvent-systems that are imposed by environmental considerations, the water-based-systems are starting to dominate flux-removal processes. Whichever process is used, it is generally involves a dissolving/dilution/flushing process where the flux is dissolved and dispersed within the flushing-solvent through the action of one or more surface-active agents.
Existing cleaning compositions used in the semiconductor industry are not suitable for the following reasons:    amine containing products are not compatible with copper and dissolve the metal at the exposed areas;    dilute hydrofluoric acid solutions (DHF) remove the sidewall polymer and CuO compounds by aggressively attacking the sidewall of the dielectric and hence change the designed dimensions of the device. Furthermore those solutions are ineffective for cleaning Cu2O or CFx compounds.
Optionally the photoresist might or might not be removed before the copper is exposed. Using traditional photoresist removal techniques is not ideal for the following reasons:    an oxygen plasma step will oxidize the copper to the CuO and Cu2O states, which will increase the via resistance,    an oxygen plasma step will be detrimental to organic dielectric material, if used, by etching the material in an uncontrolled manner.    a traditional solvent used to remove photoresist such as, for example, products containing N-methyl pyrrolidone, might require an extra cure step to recover the dielectric constant and properties of an organic dielectric.
Copper has been chosen because it is a relatively inexpensive metal with better conductivity (ρ=1.7 Ω·cm) than aluminum (ρ=2.7 Ω·cm). However the main drawbacks of this material are first its high diffusivity into silicon, introducing risk of a killing defect in the front end device, and second the difficulty to dry etch it and integrate it in traditional processes. In addition, copper does not form an oxide passivation layer under ambient conditions (as aluminum does), making this metal very difficult to work with.
On the gap-fill side, the industry's choice of low-k dielectric material has not yet emerged, though various candidates have been suggested. It has been shown that a general trend to achieve lower dielectric constant is to use material with less silicon and more carbon. There is then a logical evolution from the inorganic materials (such as SiO2 [ε=4], SiOF [ε=3.5]) to silsesquioxane types of material (such as HSQ, MSQ [3.0<ε<3.5]), towards organic material, such as benzyl cyclobutane (BCB) or silicon low k (SiLK) [ε=2.7]), with the ultimate low-k value being reached with air gaps.
We have seen over the past few years, the emergence of the damascene type of structure in which the design is etched into a dielectric layer, which is then filled with conducting wires and planarized. Dual damascene structures have the advantage of incorporating both lines and vias in one deposition step; this reduces the number of process steps and is therefore cost effective. However the main reason for the emergence of such structures nowadays is the fact that this is the easiest way to introduce copper.
Variations of the dual damascene structure exist, incorporating a series of layers for process purposes such as anti-reflective coatings, adhesion promoters, moisture barriers, diffusion barriers, polishing stops, buried etch mask and so on. The choice of whether those have to be used or not and what material (SiOxNy or SixNy) should be used for them often depend upon the final choice of the low-k material.
Known photoresist stripper compositions containing a combination of a polar solvent and an amine compound include:
1. U.S. Pat. No. 4,403,029 describes alkaline/solvent mixtures useful as photoresist strippers, but not necessarily cleaners, that include dimethylacetamide or dimethylformamide and alkanolamines.
2. U.S. Pat. Nos. 4,428,871, 4,401,747, and 4,395,479 describe cleaners containing 2-pyrrolidone, dialkylsulfone and alkanolamines.
3. U.S. Pat. No. 4,744,834 describes cleaners containing 2-pyrrolidone and tetramethylammonium hydroxide. Such stripping compositions, however, have only proven successful in cleaning “sidewall polymer” from the contact openings and metal line etching in simple microcircuit manufacturing involving a single layer of metal when the metal structure involves mainly Al—Si or Al—Si—Cu and the residue that contains only an organometallic compound with aluminum.
4. U.S. Pat. No. 4,617,251 teaches a positive photoresist stripping composition containing (A) selected amine compound (e.g., 2-(2-aminoethoxy)-ethanol; 2-(2-aminoethylamino)-ethanol; and mixtures thereof) and (B) selected polar solvents (e.g., N-methyl-2-pyrolidinone, tetrahydrofurfuryl alcohol, isophorone, dimethyl sulfoxide, dimethyl adipate, dimethyl glutarate, sulfolane, gamma-butyrolactone, N,N-dimethylacetamide and mixtures thereof). The reference further teaches that water as well as dyes or colorants, wetting agents, surfactants and antifoamers may be added into this composition.
5. U.S. Pat. No. 4,770,713 teaches a positive photoresist stripping composition containing (A) a selected amide (e.g., N,N-dimethyl acetamide; N-methyl acetamide; N,N-diethyl acetamide; N,N-dipropyl acetamide; N,N-dimethyl propionamide; N,N-diethyl butyramide and N-methyl-N-ethyl propionamide) and (B) selected amine compound (e.g., monoethanolamine, monopropanolamine, methyl-aminoethanol). The patent also teaches this stripper may optionally contain a water miscible nonionic detergent (e.g., alkylene oxide condensates, amides and semi-polar nonionics).
6. U.S. Pat. No. 4,824,763 teaches positive-working photoresist stripping composition containing (A) triamine (e.g., diethylene-triamine) and (B) a polar solvent (e.g., N-methyl-2-pyrrolidone, dimethylformamide, butyrolactone, aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons).
7. U.S. Pat. No. 4,904,571 teaches printed circuit board photoresist stripper composition containing (A) a solvent (e.g., water, alcohols, ethers, ketones, chlorinated hydrocarbons and aromatic hydrocarbons); (B) an alkaline compound dissolved in said solvent (e.g., primary amines, secondary amines, tertiary amines, cyclic amines, polyamines, quaternary ammonium amines, sulfoniumhydroxides, alkali hydroxides, alkali carbonates, alkali phosphates and alkali pyrophosphates); and (C) a borohydride compound dissolved in said solvent (e.g., sodium borohydride, lithium borohydride, dimethyl amine borone, trimethyl amine borone, pyridane borone, tert-butyl amine borone, triethyl amine borone, and morpholine borone).
8. U.S. Pat. No. 5,102,777 teaches a positive photoresist stripper composition comprising (A) a solvent (e.g., a pyrrolidone compound, a diethylene glycol monoalkyl ether, a sulfur oxide compound, a sulfolane compound or a mixture thereof); (B) an amine (e.g., alkanolamine); and (C) a fatty acid (e.g., capric acid, lauric acid, talmitric acid, caprylic acid, myristic acid, oleic acid, stearic acid, linoleic acid, linolic acid, buthylic acid, abietic acid, isooctoic acid, isohexadecanoic acid, isostearic acid, behenic acid, undecylenic acid, hydroxystearic acid, chipanodonic acid, arachidonic acid, oleostearic acid, and 2-ethylhexadecanilic acid).
9. U.S. Pat. No. 5,279,791 teaches a stripping composition for removing resists from substrates containing (A) hydroxylamine; (B) at least one alkanolamine; and optionally (C) at least one polar solvent.
10. U.S. Pat. No. 5,308,745 teaches an alkaline-containing photoresist stripping composition comprising (A) a stripping solvent (e.g., 2-pyrrolidinone, 1-methyl-2-pyrrolidinone, 1-ethyl-2-pyrrolidinone, 1-propyl-2-pyrrolidinone, 1-hydroxyethyl-2-pyrolidinone, 1-hydroxypropyl-2-pyrrolidinone, diethylene glycol monoalkyl ethers, dialkyl sulfones, dimethyl sulfoxide, tetrahydrothiophene-1,1-dioxides, polyethylene glycol, dimethylacetamide and dimethylformamide; (B) a nucleophilic amine (e.g., 1-amino-2-propanol, 2-(2-aminoethoxy) ethanol, 2-aminoethanol, 2-(2-aminoethylamino)-ethanol and 2-(2-aminoethylamino) ethylamine); and (C) a non-nitrogen containing weak acid (e.g., acetic acid, phthalic acid, 2-mercaptobenzoic acid, 2-mercaptoethanol, 1,3,5-trihydroxybenzene, pyrogallol, resorcinol, 4-tert-butylcatechol, carbonic acid and hydrofluoric acid).
11. U.S. Pat. No. 5,334,332 teaches a photoresist resist stripping and cleaning composition comprising (A) hydroxylamine; (B) at least one alkanolamine; (C) water; (D) optionally, at least one polar solvent; and (E) optionally, a chelating reagent (e.g., thiophenol, ethylenediamine tetraacetic acid and 1,2-dihydroxybenzene) to reduce the surface metal contamination on wafers.
12. U.S. Pat. No. 5,399,464 teaches a stripping composition for removing positive organic photoresist from a substrate comprising (A) a triamine (e.g., diethylene triamine); (B) a nonpolar or polar organic solvent (e.g., N-methyl pyrrolidone).
13. U.S. Pat. No. 5,417,802 teaches a material useful for photoresist removal or post-metal etch clean up that comprises (A) primary or secondary amines; (B) solvents (e.g., dimethyl sulphoxide or dimethylacetylamide); and (C) organic ligands such as crown ethers or cyclodextrines).
14. Japanese Published Patent Application No. 63-208043, which was published to R. Ohtani (Kanto Chemical) on Aug. 29, 1988, teaches a positive-working photoresist stripper composition containing (A) 1,3-dimethyl-2-imidazolidinone; (B) a water-soluble organic amine [e.g., monoethanolamine, 2-(2-aminoethoxy)-ethanol, triethylene(tetramine)]. The application also teaches a surfactant may be added to the stripper.
15. Japanese Published Patent Application No. 64-081949, which was published to K. Matsumoto (Asahi Chemical) on Mar. 28, 1989, teaches a positive-working photoresist stripper composition containing (A) a solvent (e.g., gamma-butyrolactone, N-methyl-formamide, N,N-dimethylformamide, N,N-dimethyl-acetamide or N-methylpyrrolidone); (B) an amino alcohol (e.g., N-butyl-ethanolamine and N-ethyldiethanolamine); and (C) water.
16. Japanese Published Patent Application No. 4-350660, which was published to H. Goto (Texas Instruments, Japan and Kanto Chemical, Inc.) on Dec. 4, 1992, teaches a stripper for positive photoresists comprising (A) 1,3-dimethyl-2-imidazolidinone (DMI), (B) dimethylsulfoxide (DMSO) and (C) a water-soluble amine [e.g., monoethanolamine or 2-(2-amino-ethoxy)ethanol] wherein the amount of the water-soluble amine is 7–30% by weight.
17. Japanese Published Patent Application No. 1999-197523 describes a stripper composition for photoresist used in manufacture of liquid crystal display device that includes 5–15 weight % of alkanolamine, 35–55% sulfoxide or sulfone compound, and 35–55 wt. % glycol ether.
18. Japanese Published Patent Application No. 08087118 describes a stripper composition that includes 50–90 weight % of alkanolamine, and 50–10% dimethyl sulfoxide or N-methyl-2-pyrrolidone.
19. Japanese Published Patent Application No. 03227009 describes a stripper composition that includes ethanolamine and dimethyl sulfoxide.
20. Japanese Patent 07069619 describes a stripper composition that includes alkanolamine, dimethyl sulfoxide, and water.
21. U.S. Pat. No. 5,480,585 and the Japanese Patent Hei. 5-181753 disclose organic strippers comprising alkanolamine, sulfone compound or sulfoxide compound and a hydroxyl compound.
22. The Japanese Laid-open Patent 4-124668 discloses a photoresist stripping composition including an organic amine of 20–90% by weight, phosphoric ester surfactant of 0.1–20% by weight, 2-butyne-1,4-diol of 0.1–20% by weight, and the remainder glycolmonoalkylether and/or aprotic polar solvent.
23. The Japanese Patent Laid-open Sho. 64-42653 discloses a photoresist stripping composition comprising over 50% by weight of dimethylsulfoxide (more desirably over 70% by weight), 1 to 50% by weight of a solvent selected among diethyleneglycolmonoalkylether, diethyleneglycoldialkylether, gamma-butyrolactone and 1,3-dimethyl-2-imidazoledione, and 0.1–5% by weight of nitrogen-including organic hydroxyl compound such as monoethanolamine. It states that the amount of dimethylsulfoxide less than 50% by weight causes great reduction in stripping force, while the amount of nitrogen-including organic hydroxyl compound solvent over 5% by weight corrodes the metal film such as aluminum.
Depending on the constituents of the compositions and the ratio thereof, the aforementioned stripping compositions exhibit greatly different characteristics in photoresist stripping force, metal corrosion properties, the complexities of a rinsing process following the stripping, environmental safety, workability and price. Several commercial products are now available to clean the photoresist and plasma etching residues left by plasma etching followed by oxygen ashing. For example, EKC 265™, available from EKC Technology, Inc., is a plasma etching cleaning solution composed of water, alkanolamine, catechol and hydroxylamine. Such a composition is disclosed in U.S. Pat. No. 5,279,771 to Lee.
Although these commercial products can dissolve photoresist and plasma-etching residues, the combination of water and alkanolamine contained therein can also attack the metallic layers deposited patternwise on the substrate. The addition of a corrosion inhibitor to these products can mitigate the unwanted attack on the metallic layers and oxide layers deposited on the substrate. However, even in the presence of a corrosion inhibitor, they may attack certain corrosion-sensitive metal layers such as copper, aluminum or aluminum alloys (e.g., Al—Cu—Si), titanium nitride, titanium tungsten and the like.
It is difficult to balance effective plasma etching residue removal and corrosion inhibition because chemical compositions of the plasma etching residues are generally similar to those of the metal layers or oxide layers on the substrate. The alkanolamine used in the prior art cleaning compositions was often times found to attack both the plasma etching residues and the substrate metal layers in the presence of water. Water is often added as a contaminant, for example from the atmosphere, from wet components, and the like, and may even be released from certain photoresist structures during dissolution. The problem of water-cleaning composition induced corrosion has resulted in manufacturers resorting to alcohol or other solvent, for example isopropyl alcohol, to remove the cleaner.
Moreover, if a post-cleaner rinse such as isopropyl alcohol was not used, the corrosion could be very severe. In addition, some types of the corrosion inhibitors have been found to retard plasma etching residue removal and other treatments. There is a need for strippers that are useful with corrosion-prone metal substrates, particularly for copper substrates, which do not corrode metal substrates in the presence of small quantities of water.
The stripping and cleaning compositions of the present invention remove photoresists without attacking the substrates themselves include metal substrates such as copper, aluminum, titanium/tungsten, aluminum/silicon, aluminum/silicon/copper; and substrates such as silicon oxide, silicon nitride, and gallium/arsenide, and plastic substrates such as polycarbonate. The requirement for a cleaning solution to remove all types of residue generated as a result of resist and etching of various types of metals, such as aluminum, aluminum/silicon/copper, titanium, titanium nitride, titanium/tungsten, tungsten, silicon oxide, polysilicon crystal, etc., presents a need for more effective cleaning chemistry in the processing area.
In addition to removing completely the resist material, particularly with the introduction of submicron process techniques to form wafers, there is a demand for cleaning technology for removing etching residue remaining following resist removal. Unfortunately, it has been found that no one cleaner is universal, in that it can clean the required materials without adversely affecting or hindering subsequent manufacturing operation or process steps involving the substrate. The requirement for a cleaning solution to remove photoresist and other residue of various types of metals, such as aluminum, aluminum/silicon/copper, titanium, titanium nitride, titanium/tungsten, tungsten, silicon oxide, polysilicon crystal, low-k materials, etc., presents a need for more effective cleaning chemistry in the processing area.