Alkene ligand precursor and synthesis method

Abstract: A metal(hfac), alkene ligand precursor has been provided. The alkene ligand includes double bonded carbon atoms, with first and second bonds to the first carbon atom, and third and fourth bonds to the second carbon atom. The first, second, third, and fourth bonds are selected from a the group consisting of H, C 1 to C 8 alkyl, C 1 to C 8 haloalkyl, and C 1 to C 8 alkoxyl. As a general class, these precursors are capable of high metal deposition rates and high volatility, despite being stable in the liquid phase at low temperatures. Copper deposited with this precursor has low resistivity and high adhesive characteristics. A synthesis method has been provided which produces a high yield of the above-described alkene ligand class of metal precursors.

Description: This invention relates generally to integrated circuit processes and fabrication, and more particularly, to a precursor and synthesis method, having an alkene ligand, which improves volatility, and which is capable of depositing copper at high deposition rates, low resistivity, and with good adhesion on selected integrated circuit surfaces. The demand for progressively smaller, less expensive, and more powerful electronic products, in turn, fuels the need for smaller geometry integrated circuits (ICs) on larger substrates. It also creates a demand for a denser packaging of circuits onto IC substrates. The desire for smaller geometry IC circuits requires that the interconnections between components and dielectric layers be as small as possible. Therefore, research continues into reducing the width of via interconnects and connecting lines. The conductivity of the interconnects is reduced as the area of the interconnecting surfaces is reduced, and the resulting increase in interconnect resistivity has become an obstacle in IC design. Conductors having high resistivity create conduction paths with high impedance and large propagation delays. These problems result in unreliable signal timing, unreliable voltage levels, and lengthy signal delays between components in the IC. Propagation discontinuities also result from intersecting conduction surfaces that are poorly connected, or from the joining of conductors having highly different impedance characteristics. There is a need for interconnects and vias to have both low resistivity, and the ability to withstand process environments of volatile ingredients. Aluminum and tungsten metals are often used in the production of integrated circuits for making interconnections or vias between electrically active areas. These metals are popular because they are easy to use in a production environment, unlike copper which requires special handling. Copper (Cu) would appear to be a natural choice to replace aluminum in the effort to reduce the size of lines and vias in an electrical circuit. The conductivity of copper is approximately twice that of aluminum and over three times that of tungsten. As a result, the same current can be carried through a copper line having nearly half the width of an aluminum line. The electromigration characteristics of copper are also much superior to those of aluminum. Aluminum is approximately ten times more susceptible than copper to degradation and breakage due to electromigration. As a result, a copper line, even one having a much smaller cross-section than an aluminum line, is better able to maintain electrical integrity. There have been problems associated with the use of copper, however, in IC processing. Copper pollutes many of the materials used in IC processes and, therefore barriers are typically erected to prevent copper from migrating. Elements of copper migrating into these semiconductor regions can dramatically alter the conduction characteristics of associated transistors. Another problem with the use of copper is the relatively high temperature needed to deposit it on, or removing it from, an IC surface. These high temperatures can damage associated IC structures and photoresist masks. It is also a problem to deposit copper onto a substrate, or in a via hole, using the conventional processes for the deposition of aluminum when the geometries of the selected IC features are small. That is, new deposition processes have been developed for use with copper, instead of aluminum, in the lines and interconnects of an IC interlevel dielectric. It is impractical to sputter metal, either aluminum or copper, to fill small diameter vias, since the gap filling capability is poor. To deposit copper, first, a physical vapor deposition (PVD), and then, a chemical vapor deposition (CVD) technique, have been developed by the industry. With the PVD technique, an IC surface is exposed to a copper vapor, and copper is caused to condense on the surfaces. The technique is not selective with regard to surfaces. When copper is to be deposited on a metallic surface, adjoining non-conductive surfaces must either be masked or etched clean in a subsequent process step. As mentioned earlier, photoresist masks and some other adjoining IC structures are potentially damaged at the high temperatures at which copper is processed. The CVD technique is an improvement over PVD because it is more selective as to which surfaces copper is deposited on. The CVD technique is selective because it is designed to rely on a chemical reaction between the metallic surface and the copper vapor to cause the deposition of copper on the metallic surface. In a typical CVD process, copper is combined with a ligand, or organic compound, to help insure that the copper compound becomes volatile, and eventually decomposes, at consistent temperatures. That is, copper becomes an element in a compound that is vaporized into a gas, and later deposited as a solid when the gas decomposes. Selected surfaces of an integrated circuit, such as diffusion barrier material, are exposed to the copper gas, or precursor, in an elevated temperature environment. When the copper gas compound decomposes, copper is left behind on the selected surface. Several copper gas compounds are available for use with the CVD process. It is generally accepted that the configuration of the copper gas compound, at least partially, affects the ability of the copper to be deposited on to the selected surface. Copper metal thin films have been prepared via chemical vapor deposition by using many different kinds of copper precursors. In 1990, D. B. Beach et al. Chem. Mater. (2) 216 (1990) obtained pure copper films via CVD by using (η 5 -C 5 H 5 )Cu(PMe 3 ), and later, in 1992, H. K. Shin et al., Chem. Mater. (4) 788 (1992) declared the same results by using (hfac)Cu(PR 3 ) n (R = methyl and ethyl and n = 1 and 2). However, these copper precursors are solids, which can not be used in the liquid delivery system for copper thin film CVD processing. Furthermore, the copper films often contain contamination of carbon and phosphorus, which can not be used as interconnectors in microprocessors. Cu 2+ (hfac) 2 , or copper (II) hexafluoroacetylacetonate, precursors have previously been used to apply CVD copper to IC substrates and surfaces. However, these Cu 2+ precursors are notable for leaving contaminates in the deposited copper, and for the relatively high temperatures that must be used to decompose the precursor into copper. The studies of copper precursors conducted in the early of 1990's were concentrated on the evaluation of a series of copper(I) fluorinated β-diketonate complexes, which have been proven to be very promising sources for the use in the chemical vapor deposition of copper metal thin films. Copper(I) fluorinated β-diketonate complexes were first synthesized by Gerald Doyle, U.S. Pat. No. 4,385,005 (1983) and 4,425,281 (1984), in which he presented the synthesis method and their application in the separation of unsaturated organic hydrocarbons. In the U.S. Pat. No. 5,096,737 (1992), Thomas H. Baum, et at., claimed the application of these copper(I) fluorinated β-diketonate complexes as copper precursors for CVD copper thin film preparation. Copper thin films have been prepared via chemical vapor deposition using these precursors. Among several liquid copper precursors, 1,5-dimethyl 1,5-cyclooctadiene copper(I) hexafluoroacetylacetonate mixed with 1,6-dimethyl 1,5-cyclooctadiene copper(I) hexafluoroacetylacetonate ((DMCOD)Cu(hfac)) and hexyne copper(I) hexafluoroacetylacetonate (HYN)Cu(hfac)) were evaluated in detail. The copper thin films deposited using (DMCOD)Cu(hfac) have very good adhesion to metal or metal nitride substrates, but a high resistivity (2.5 µΩ·cm) and a low deposition rate. (HYN)Cu(hfac) copper film has poor adhesion to a TiN substrate, and high resistivity (∼ 2.1 µΩ·cm). Another compound, butyne copper(I)(hfac), ((BUY)Cu(hfac)), gives a copper film with low resistivity (1.93 µΩ cm), but has poor adhesion and is relatively expensive. Also, the compound is a solid and, therefore, difficult to use in a liquid delivery system. The invention of copper(I)(hfac) stabilized with a series of trialkylvinylsilane (John A. T. Norman et al., U.S. Pat. No. 5,085,731 (1992)) improved the properties of copper thin films. Copper films deposited using a liquid copper precursor, (hfac)Cu(TMVS), where TMVS = trimethylvinylsilane, have low resistivities and reasonably adhesion to substrates. This precursor is useful because it can be used at relatively low temperatures, approximately 200°C. This liquid copper precursor has been used for the preparation of copper metal thin films via CVD for some time, but there are still some drawbacks: stability, the adhesion of copper films, and cost for the trimethylvinylsilane stabilizer. Also, the precursor is not especially stable, and can have a relatively short shelf life if not refrigerated. Various ingredients have been added to (hfac)Cu(tmvs) to improve its adhesiveness, temperature stability, and the rate at which it can be deposited on an IC surface. U.S. Patent 5,744,192, entitled "Method Of Using Water To Increase The Conductivity Of Copper Deposited With Cu(HFAC)TMVS", invented by Nguyen et al., discloses a precursor and method of improving the electrical conductivity of Cu deposited with (hfac)Cu(tmvs). It is generally acknowledged in the industry that (hfac)Cu(tmvs) becomes unstable, and begins to decompose, above 35° C. Use of a (hfac)Cu(tmvs) precursor stored at this temperature leads to undesirable process results. The effectivity of (hfac)Cu(tmvs) stored at temperatures lower than 35° C is also unpredictable. A "fresh" batch of precursor, or precursor stored at temperatures well below room temperature, is used to guarantee predictable processes. A Cu precursor comprising a ligand of alkyl and alkyl groups is disclosed in U.S. Patent 5,767,301, entitled "Precursor with (Alkyloxy)(Alkyl)silylolefin Ligands to Deposit Copper", invented by Senzaki et al. The disclosed precursor describes alkyl groups bonded to the silicon atom of the ligand with alkoxyl groups. However, the search continues for even more effective copper precursors. As mentioned by Norman et al. in US Patent 5,085,731 (col. 9, line 28 to col. 10, line 31), precursors have been made with simple linear olefins such as 1-hexene. Disproportionation occurred when a distillation of such precursors was attempted. Norman et al. conclude that silylolefin compounds are necessary for the synthesis of isolable volatile liquid precursors, and that comparable hydrocarbons, such as 1-hexene, would not be suitable as precursors in atmospheric pressure or low pressure CVD (LPCVD) processes. However, H-K Shin, et al., in "MOCVD of Copper from the Solution of New and Liquid Precursor", Abstract, Mat. Res. Soc. Symp. Proc. Vol. 514, 1998 Material Research Society, pp. 301, claim the fabrication of (hfac)(Cu)(l-pentene), although a large (greater than 10%) excess of free 1-pentene is apparently required to stabilise the precursor. Doyle et al (CA, 102 , 21, no. 185204 and Organometallics (1985), 4(5), 830-5) describe the reaction of Ag 2 O with hfac and various alkenes (L), including 1-decene, to give AgL (hfac). Also, Zhuang et al (EPA 10 00 947) describe the preparation of (hfac)Cu(2-methyl-1-butene) but were unable to achieve product yields much above 78%, based on hfac. Additionally, Shin (EPA 09 89 133) describes (hfac)Cu(1-pentene) but states that this compound is thermally unstable and requires 20 to 50% 1-pentene to achieve stability. It would be advantageous if a copper precursor was found that effectively deposits copper with low resistivity and good adhesion properties. It would be further advantageous if this precursor was inexpensive to synthesize. It would be advantageous if a method were found of making a Cu(hfac) precursor stable over a wider range of temperatures, and to provide that the precursor remain in liquid phase during storage. It would be advantageous if a precursor could be developed which encouraged a stable Cu +1 (hfac) bond without the use of silylolefins directly bonded to olefinic double bonds. Further, it would minimize silicon contamination if a precursor could be developed without the use of silylolefin groups, at all. It would be advantageous if a metal precursor could be developed which made use of alkene ligands to stabilize the precursor. Accordingly, a volatile metal (M) precursor compound for the chemical vapor deposition (CVD) of metal, such as copper, silver, and iridium to selected surfaces is provided. The precursor compound comprises a M +1 (hexafluoroacetylacetonate) and an alkene ligand. The alkene ligand 2, 4, 4-trimethyl-1-pentene. In one alternative the compound includes an additive to create a precursor blend. Then, the precursor blend comprises less than approximately 10% alkene, as measured by weight ratio of the precursor compound, to facilitate a stable liquid phase precursor. A method for synthesizing a copper(hfac) alkene ligand precursor is also provided. The method comprises the steps of: a) forming a uniformly mixed solution of Cu 2 O in a solvent, such as dichloromethane and tetrahydrofuran (THF); b) introducing 2,4,4-trimethyl-1-pentene ligand to the solution of Step a), and forming a uniformly mixed solution; c) introducing hexafluoroacetylacetone (hfac) to the solution of Step b), and forming a uniformly mixed solution; f) filtering the solution to remove solid materials, whereby any excess Cu 2 O is removed; e) removing the solvent from the solution; and f) filtering to remove the solid material, whereby a liquid phase precursor is formed. In one example, Step a) includes the Cu 2 O being, in proportion, 0.310 mol, Step b) includes 2,4,4-trimethyl-1-pentene being, in proportion, 0.48 mol, and Step c) includes the hfac being, in proportion, 0.48 mol.In one aspect of the invention, a further step follows Step f), g) adding less than approximately 10%, by weight ratio, of the alkene to the solution, whereby the liquid phase stability of the precursor is improved. Approximately 4.7 % alkene additive is added in some aspects of the invention. The invention is described below in greater detail with reference to the accompanying drawings, in which : Fig. 1 is a schematic representation of a 2, 4, 4-trimethyl-1-pentene ligand; Fig. 2 is a schematic representation of a Cu precursor with the 2, 4, 4-trimethyl-1-pentene ligand of Fig. 1; and Fig. 3 illustrates steps in a method for synthesizing the copper(hfac) alkene ligand precursor. The alkene metal precursor is inexpensive to synthesize. Compared to trimethylvinylsilane, which costs approximately $180 per 100 g, the general class of alkene ligands are inexpensive. Many alkene precursors are stable at room temperature for easy storage and handing. Despite retaining liquid phase at room temperature, many alkene ligand precursors are highly volatile at higher temperatures. Therefore, no decomposition occurs in the CVD liquid delivery line and vaporizer, which requires precursor stability at 90 degrees C, under vacuum, for four minutes. Further, many alkene ligand precursors have excellent adhesion to metal and metal nitride substrates, such as W, Ti, TiN, Ta, TaN, Al, Pt, WN, and similar barrier materials. The copper deposited with many of these precursors has low resistivity (< 1.9 µΩ·cm), high electromigration resistance, and excellent conformality to severe surface morphology. Fig. 1 is a schematic representation of a 2, 4, 4-trimethyl-1-pentene ligand. Fig. 2 is a schematic representation of a Cu precursor with 2, 4, 4-trimethyl-1-pentene ligand of Fig. 1. In one aspect of the invention, metal precursor 10 includes an additive to create a precursor blend, and in which the precursor blend comprises less than approximately 10% alkene, as measured by weight ratio of the precursor compound, to facilitate a stable liquid phase precursor. Alternately, the volatile metal (M) precursor compound of the present invention is described by the following structural formula: ((R 1 )(R 2 )C=C(R 3 )(R 4 ))M +1 (hfac) in which R 1 , R 2 , R 3 , and R 4 are selected from the group consisting of H, C 1 to C 8 alkyl, C 1 to C 8 haloalkyl, and C 1 to C 8 alkoxyl, whereby a stable alkene ligand precursor capable of high metal deposition rates is formed. As above, R 1 , R 2 , R 3 , and R 4 vary independently from each other. When R 1 is H, R 2 is H, R 3 is CH 3 , and R 4 is CH 2 C(CH 3 ) 3 , a 2, 4, 4-trimethyl-1-pentene ligand is formed. When R 1 is H, R 2 is H, R 3 is H, and R 4 is C(CH 3 ) 3 , a 3, 3-dimethyl-1-butene ligand is formed. When R 1 is H, R 2 is H, R 3 is CH 3 , and R 4 is CH(CH 3 ) 2 , a 2, 3-dimethyl-1-butene ligand is formed. When R 1 is H, R 2 is CH 3 , R 3 is CH 3 , and R 4 is CH 3 , a 2-methyl-2-butene ligand is formed. When R 1 is H, R 2 is H, R 3 is H, and R 4 is CH 2 (CH 2 ) 2 CH 3 , a 1-hexene ligand is formed. When R 1 is H, R 2 is H, R 3 is H, and R 4 is CH 2 CH 2 CH 3 , a 1-pentene ligand is formed. In some aspects of the invention, the compound includes a 1-pentene ligand additive to create a metal precursor blend. The alkene additive has the following structural formula: H 2 C=CH(CH 2 CH 2 CH 3 ). The alkene is typically less than approximately 10% by weight ratio of the precursor blend, and is preferably about 4.7%. Fig. 3 illustrates steps in a method for synthesizing the copper(hfac) alkene ligand precursor. Although the method expressly discusses the synthesis of a copper precursor, the general method is applicable for the synthesis of iridium and silver precursors. Step 100 provides copper oxide (Cu 2 O), or the oxide of the metal to be used. Step 102 forms a uniformly mixed solution of Cu 2 O in a solvent. Step 102 includes using a solvent selected from the group consisting of dichloromethane and tetrahydrofuran (THF). Dichloromethane, especially, has been found to be an effective solvent. Step 104 introduces the alkene ligand to the solution of Step 102, forming a uniformly mixed solution. Step 106 introduces hexafluoroacetylacetone (hfac) to the solution of Step 104, forming a uniformly mixed solution. Step 108 filters the solution to remove solid materials, whereby any excess Cu 2 O is removed. Typically, Step 108 includes using celite to filter the solution, removing solid material larger than approximately 10 µm. Step 110 removes the solvent from the solution. Step 112 filters to remove the solid material. Step 112 typically includes filtering solid material having a size greater than approximately 1 µm. Step 114 a a product, where a liquid phase alkene ligand precursor is formed. In one aspect of the invention, Step 102 includes the Cu 2 O being, in proportion, 0.310 mol, Step 104 includes 2,4,4-trimethyl-1-pentene being, in proportion, 0.48 mol, and Step 106 includes the hfac being, in proportion, 0.48 mol. In one aspect of the invention, a further step follows Step 112. Step 112a adds less than approximately 10%, by weight ratio, of the alkene ligand to the solution, whereby the liquid phase stability of the precursor is improved. In one aspect of the invention, Step 112a includes adding approximately 4.7% alkene additive. All manipulations were carried out in an air-free dry glovebox or by using standard Schlenk techniques. Solvents were purified before synthesis. Dichloromethane was refluxed and distilled over calcium hydride under an atmosphere of nitrogen prior to use. 2,4,4-Trimethyl-1-pentene and Cu 2 O were purchased from Aldrich, and 1,1,1,5,5,5-hexafluoroacetylacetone, from Strem, and they were used directly without any purification. The synthesis procedure of organometallic copper(I) complexes was firstly described by Doyle in U.S. Pat. No. 4,385,005, in which copper monoxide reacted with unsaturated organic hydrocarbon and 1,1,1,5,5,5-hexafluoroacetylacetone in dichloromethane or THF. The reaction is described by the following equation: where L is an unsaturated organic hydrocarbon ligand. The synthesized alkene copper(I)(hfac) product is not stable at room temperature for long periods of time. To solve this problem, less than 10% extra organic stabilizing ligand (by product weight) was added into the product for the compound stabilization. After one month, no solid precipitation or decomposition was observed in these stabilized products. The following Example illustrates the invention. Synthesis Example In the synthesis of (2,4,4-trimethyl-1-pentene)Cu(hfac), Cu 2 O (44.7 g, 0.31 mol) was added into a 500 ml round bottom flask equipped with CH 2 Cl 2 (150 mL) and a stirring bar. The color of the solution was red. To this Cu 2 O dichloromethane solution, 2,4,4-trimethyl-1-pentene (76 mL, 0.48 mol) was added and stirred at room temperature for five minutes. Then 1,1,1,5,5,5-hexafluoroacetylacetone (100 g, 0.48 mol) was added with stirring. The addition of 1,1,1,5,5,5-hexafluoroacetylacetone was completed within 2 minutes, during which the color of the solution began to gradually change to green, after about 1 minute. After addition, the solution was continually stirred for another 5 minutes, and then filtered through celite (10-25 µm filter size). The green filtrate was stripped under vacuum for two hours and then heated to 35° C under vacuum for another half-hour stripping. During the stripping, some crystals were precipitated, and then dissolved by strong stirring. This produced a green liquid organometallic copper compound, which was then filtered through a fine filter (1 µm) to give 144.4 gram product (yield: 78.5% based on hfac, and the theoretical yield based on hfac is 184.0 gram.). The pure compound experiences partial decomposition over one or two days. To the partial decomposed compound, some red solid precipitates were seen on the bottom of glass vial or on the glass wall. To prevent the decomposition, 2,4,4-trimethyl-1-pentene (0.205 g) was introduced into the pure compound (4.027 g, and total of 4.232 g) and the mixture contained 4.844% free 2,4,4-trimethyl-1-pentene. After one month, no crystal or solid precipitate was observed in this stabilized compound. The proton NMR structural analysis was carried out on a 300 MHz NMR instrument. The sample contained 2.4% (weight percentage) free 2,4,4-trimehtyl-1-pentene. The results are as follows: 1 H NMR (CD 2 Cl 2 ) δ 0.67 (s, 9, CH 2 =C(CH 3 )CH 2 C(C H 3 ) 3 ), 1.41 (s, 3, CH 2 =C(C H 3 )CH 2 C(CH 3 ) 3 ), 1.67 (s, 2, CH 2 =C(CH 3 )C H 2 C(CH 3 ) 3 ), 3.73 ( cis to H) (s, 1, C H 2 =C(CH 3 )CH 2 C(CH 3 ) 3 ), 3.83 ( trans to H) (s, 1, C H 2 =C(CH 3 )CH 2 C(CH 3 ) 3 ), 6.17 (s, 1, CF 2 C(O)C H C(O)CF 3 ). The results of copper metal thin films deposition via CVD using this volatile liquid precursory was very good. The copper thin films have shown good adhesion to metal and metal nitride substrates, low resistivity (1.8 µΩ·cm), and also very good reproducibility. A new and improved copper precursor, and synthesis method for the copper precursor, has been disclosed above. The alkene ligand precursors, as a general class, are stable at low temperatures, and sufficiently volatile at higher temperatures. Copper deposited with the precursor has low resistivity and high adhesive characteristics. Finally, the precursor is inexpensive to make. A synthesis method has been disclosed which produces a high yield of the above-described precursor.

Claims: A volatile metal precursor compound for the chemical vapor deposition (CVD) of metal (M) onto selected surfaces, the precursor compound comprising: M -1 (hexafluoroacetylacetonate); and an alkene ligand, characterized in that the alkene ligand is 2,4,4-trimethyl-1-pentene. A metal precursor according to claim 1, wherein the metal (M) is selected from copper, silver and iridium. A volatile metal precursor biend for the chemical vapor deposition (CVD) of metal (M) onto selected surfaces, comprising a precursor compound according to claim 1 or claim 2; and M -1 (hexafluoroacetylacetonate); and less than 10% by weight, based on the precursor compound, of 2,4,4-trimethyl-1-pentene. A method for synthesizing a copper precursor compound comprising the steps of: (a) forming a uniformly mixed solution of Cu 2 O in a solvent; (b) introducing an alkene to the solution of step (a), and forming a uniformly mixed solution; (c) introducing hexafluoroacetylacetone (hfac) to the solution of step (b), and forming a uniformly mixed solution; (d) filtering the solution of step (c) to remove solid materials, whereby any excess Cu 2 O is removed; (e) removing the solvent from the solution of step (d); and (f) filtering the residue obtained in step (e) to remove the solid material, whereby a liquid phase copper precursor compound is formed, characterized in that the alkene in step (b) is 2,4,4-trimethyl-1-pentene. A method according to claim 4, wherein Cu 2 O, 2,4,4-trimethyl-1-pentene and hfac are used in steps (a), (b) and (c) in molar proportions of 0.310, 0.48 and 0.48. A method according to claim 4 or claim 5, wherein step (d) includes removing solid material larger than approximately 10 µm. A method according to claim 6, wherein celite is used to filter the solution. A method according to any one or claims 4 to 7, wherein the solvent in step (a) is selected from dichloromethane and tetrahydrofuran (THF). A method according to any one of claims 4 to 8, wherein step (f) includes removing solid material larger than approximately 1µm. A method according to any one of claims 4 to 9, including also the further step, following step (f), of: (g) adding up to 10% by weight of 2,4,4-trimethyl-1-pentene, based on the precursor compound. A method according to claim 10, wherein step (g) includes adding approximately 4.7% alkene.

Inventors: BARROWCLIFF ROBERT, CHARNESKI LAWRENCE J, EVANS DAVID R, HSU SHENG TENG, NGUYEN TUE, ZHUANG WEI-WEI, BARROWCLIFF, ROBERT, CHARNESKI, LAWRENCE J., EVANS, DAVID R., HSU, SHENG TENG, NGUYEN, TUE, ZHUANG, WEI-WEI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1999
Main classification: C07F1
IPC codes: C07C11, C07F1, C07C49, C23C16