| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 10.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 24.10.00 |
| PATENT TITLE |
Planarization fluid composition including chelating agents |
| PATENT ABSTRACT |
A planarization method including the provision of a wafer having a wafer surface. A pad is positioned for contact with the wafer surface and the wafer surface is planarized using the pad and a fluid composition that includes a chelating agent. The chelating agent is a water soluble multidentate chelating agent, preferably a water soluble bidentate ionic chelating agent, and more preferably 1,2-ethylenediphosphonic acid (EDP). A fluid composition for use in planarization of a surface of a wafer includes a chemically interactive component that interacts with the surface of the wafer and a chelating agent for reducing the metal ion contamination of the wafer during planarization. The chelating agent may be one of a water soluble multidentate chelating agent, preferably a water soluble bidentate ionic chelating agent, and more preferably 1,2-ethylenediphosphonic acid (EDP). Further, the fluid composition may include an abrasive component. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 26.02.99 |
| PATENT REFERENCES CITED |
Akiya et al., "This-Oxide Dielectric Strength Improvement by Adding a Phosphonic Acid Chelating Agent into NH-4-OH-H-O- Sollution," J. Electrochem. Soc., 141(10), L139-L142 (1994). Ernsberger, "Attach of Glass by Chelating Agents," Journal of the American Ceramic Society, 42(8), 373-375 (1959). Fang et al., "Determination of the Composition of Viscour Liquid Film on Electropolishing Copper Surface by XPS and AES," J. Elect. Soc., 136(12), 3800-3803 (1989). |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A fluid composition for use in planarization of a surface of a wafer, the fluid composition comprising: a chemically interactive component that interacts with the surface of the wafer during planarization; and a chelating agent for reducing the ion contamination of the wafer during planarization, wherein the chelating agent is 1,2-ethylenediphosphonic acid (EDP). 2. The fluid composition according to claim 1, wherein the EDP of the fluid composition is of an amount less than about 0.5% by weight of the total weight of the fluid composition. 3. The fluid composition according to claim 2, wherein the EDP of the fluid composition is of an amount less than about 0.1% by weight of the total weight of the fluid composition. 4. A fluid composition for use in planarization of a surface of a wafer, the surface including oxide material, the fluid composition comprising: a chemically interactive component that interacts with the surface of the wafer during planarization; and a chelating agent for reducing the ion contamination of the wafer during planarization, wherein the chelating agent reduces a concentration of uncomplexed metal ions for at least one metal of a plurality of metals with respect to the wafer after a planarization process as compared to the concentration of uncomplexed metal ions for the at least one metal when the chelating agent is not used in the fluid composition in a planarization process for the wafer surface while maintaining substantially a same or greater planarization rate for the oxide material when the chelating agent is used compared to a planarization rate for the oxide material when the chelating agent is not used. 5. The fluid composition according to claim 4, wherein the chelating agent is 1,2-ethylenediphosphonic acid (EDP). 6. A fluid composition for use in planarization of a surface of a wafer, the fluid composition comprising: a chemically interactive component that interacts with the surface of the wafer during planarization; an abrasive component; and a chelating agent for reducing the ion contamination of the wafer during planarization, wherein the chelating agent is 1,2-ethylenediphosphonic acid (EDP). 7. The fluid composition according to claim 6, wherein the EDP of the fluid composition is of an amount less than about 0.5% by weight of the total weight of the fluid composition. 8. The fluid composition according to claim 7, wherein the EDP of the fluid composition is of an amount less than about 0.1% by weight of the total weight of the fluid composition. 9. The fluid composition according to claim 6, wherein the chelating agent reduces a concentration of uncomplexed metal ions for at least one metal of a plurality of metals with respect to the wafer after a planarization process as compared to the concentration of uncomplexed metal ions for the at least one metal when the chelating agent is not used in the fluid composition in a planarization process for the wafer surface while maintaining substantially a same or greater planarization rate when the chelating agent is used compared to a planarization rate when the chelating agent is not used. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention pertains to planarization fluid compositions and planarization methods in the fabrication of semiconductor devices. More particularly, the present invention is directed to the use of chelating agents in such fluid compositions and methods. BACKGROUND OF THE INVENTION A large fraction of yield losses in wafer fabrication or processing of semiconductor devices is attributed to microcontamination. Contaminants can be organic or inorganic particles, films or molecular compounds, ionic materials, or atomic species. Examples of ionic contaminants are sodium, potassium, lithium, calcium, boron, manganese, sodium, titanium, zirconium, aluminum, sulfur and magnesium. Other damaging elemental impurities include heavy metals, for example, such as iron, copper, nickel, and gold. The presence of contaminants during wafer processing has become particularly problematic in high density, large scale integration (LSI) technology. For example, contaminants can cause a device to fail by improperly defining patterns, creating unpredictable surface topography, inducing leakage currents through insulating layers, or accelerating device wearout. Silicon wafers may be exposed to metallic or semimetallic contaminants during, for example, chemical mechanical planarization or polishing (CMP) or during other cleaning operations. CMP may, for example, involve holding or rotating a wafer of semiconductor material against a wetted polishing surface under controlled chemical fluid (i.e. slurry), pressure, and temperature conditions. The fluid typically consists of an abrasive component such as alumina or silica (unless it is utilized with a pad including an abrasive component) and a chemical etchant that chemically interacts with the surface. Generally, such fluid or slurries are quite pure; however, they are not free of contaminants such as the ionic contaminants listed above. Chemical-mechanical planarization or polishing may be used to produce a surface with the desired end point or thickness. However, metal ions create contamination problems. For example, such contaminants may diffuse into the surface of the wafer and down fracture paths. It has been reported that phosphonic acid chelating agents added to SC-1 wet cleaning solution (a mixture of NH.sub.4 OH, H.sub.2 O.sub.2, and H.sub.2 O) of an RCA clean commonly used to remove particles and organic contaminants on silicon surfaces, reduces certain metallic contamination deposition on a silicon wafer. This conclusion was reached in the article entitled "Thin-Oxide Dielectric Strength Improvement by Adding a Phosphonic Acid Chelating Agent into NH.sub.4 OH--H.sub.2 O.sub.2 Solution" by Akiya et al., J Electrochem. Soc., Vol.141, No. 10, October 1994. However, such wet cleaning procedures are performed after CMP processing and contamination may have already caused significant contamination problems to the wafer during the CMP process. For the above reasons, improvements in the CMP process to reduce metal ion contamination of the wafer being processed are needed. The present invention as described below provides such improvements and overcomes the problems described above and those problems which will become apparent to one skilled in the art from the detailed description below. A fluid composition for use in planarization of a surface of a wafer in accordance with the present invention includes a chemically interactive component that interacts with the surface of the wafer during planarization and a chelating agent for reducing the metal ion contamination of the wafer during planarization. The chelating agent may be one of any water soluble multidentate chelating agent, preferably a water soluble bidentate ionic chelating agent, and more preferably 1,2-ethylenediphosphonic acid (EDP). In one embodiment, the fluid composition also includes an abrasive component. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A and 1B are cross-sectional illustrations of a part of a wafer before and after a planarization process has been performed in accordance with the present invention; FIG. 2 is a general diagrammatical illustration of a chemical-mechanical polishing or planarization apparatus utilized in accordance with the present invention; FIG. 3 is an enlarged view of a portion of the dashed circle area of FIG. 2; FIG. 4A-4D illustrate spectrographic concentrations of the metal ions Mg, K, Ca, and Na, respectively, for various wafers tested; FIG. 5A-5C illustrate spectrographic concentrations of the metal ions Mg, Ca, and Na, respectively, for various wafers tested; FIG. 6A-6C illustrate spectrographic concentrations of the metal ions Mg, Ca, and Na, respectively, for various wafers tested; FIG. 7A-7C illustrate spectrographic concentrations of the metal ions Mg, Ca, and Na, respectively, for various wafers tested; and FIG. 8A-8C illustrate spectrographic concentrations of the metal ions Mg, Ca, and Na, respectively, for various wafers tested. DETAILED DESCRIPTION OF THE EMBODIMENTS The present invention is directed to methods of planarization and in particular to planarization using a fluid composition including a quantity of a chelating agent. The fluid composition of the present invention, including the chelating agent is used in planarizing or polishing wafers being fabricated to reduce the amount of metal ion contaminants left on the wafer after the CMP process is completed. The target metal ion contaminants of which the present invention is beneficial in reducing, include, for example: the alkali metals such as sodium (Na), potassium (K) and Lithium (Li); alkaline earth metals such as magnesium (Mg) and calcium (Ca); heavy metals such as iron (Fe), nickel (Ni), and zinc (Zn); and any other metal ion contaminants including, for example, aluminum (Al), chromium (Cr), manganese (Mn), titanium (Ti), boron (B), zirconium (Zr), and copper (Cu), any other metallic ion or any other contaminant that would form a ligand forming complex. FIG. 1A illustrates a portion of a wafer 10 prior to planarization by chemical-mechanical polishing (CMP) in accordance with the present invention. The wafer portion 10 includes a substrate 26 having junctions 20 formed thereon. Isolation areas 24 are also formed on substrate 26 with polysilicon 22 deposited thereon. Over these elements formed on substrate 26, a film of borophosphosilicate glass (BPSG) 12 is formed, and, such as by reflow, the glass 12 conformably covers steps, fills gaps between polysilicon lines, and forms an upper surface having different heights such as at areas 14, 16, and 18. The nonplanar upper surface 13 of BPSG film 12 is the surface having non-uniformities which can be reduced or eliminated when subjected to planarization in accordance with the present invention with reduced metal ion contamination to the wafer. FIG. 1A is shown only to illustrate a surface having nonuniformities in need of planarization for the fabrication of semiconductor devices. Other surfaces, including but not limited to other dielectrics, polysilicon, oxide filled trenches, various metal films, other doped oxides, spin on glasses, or any other fabricated surface which may require planarization as is known to one skilled in the art may benefit from the present invention. Therefore, the present invention is not limited to the planarization of any particular surface, but is limited only in accordance with the invention as described in the accompanying claims. FIG. 1B illustrates the wafer portion 10 shown in FIG. 1A after the upper surface 13 of the BPSG film 12 has been planarized in accordance with the present invention. The resulting wafer 10 includes an upper surface 28 planarized or polished such that the thickness of the wafer 10 is substantially uniform across the entire wafer 10. As will be described further below, the present invention provides for a uniformly thick wafer with reduced metal ion contamination. The reduced metal ion contamination of the wafer using a fluid composition including a chelating agent as described herein is shown by the reduced ion concentration levels as reported in the Examples herein. The present invention is not limited to use with nonplanar surfaces, such as that shown in FIG. 1A. The present invention is also beneficial for use with substantially planar surfaces such as the surface 28 shown in FIG. 1B. For example, the slurry and method of planarization in accordance with the present invention is beneficial during the whole planarization process. As such, the benefits are applicable to both nonplanar and planar surfaces and furthermore through the entire planarization process. FIG. 2 is a diagrammatical illustration showing one embodiment of a CMP process for planarization of surfaces of semiconductor wafers in accordance with the present invention. As shown in FIG. 2, the present invention utilizes a planarization assembly 29 such as Model 372 or Model 472 available from IPEC/Westech. Other planarization assemblies or units for performing CMP methods are readily available and are clearly contemplated by the scope of the present invention as described in the accompanying claims. For example, the planarization process may be performed with the apparatus described in U.S. Pat. No. 5,421,729, entitled "Apparatus For Planarizing Semiconductor Wafers, and a Polishing Pad for a Planarization Apparatus" and herein incorporated by reference; U.S. Pat. No. 4,193,226 entitled "Polishing Apparatus" and herein incorporated by reference; U.S. Pat. No. 4,811,522 entitled "Counterbalanced Polishing Apparatus" and herein incorporated by reference; and any other planarization assembly as known to those skilled in the art. Various other embodiments of planarization assemblies are known and available for use with the present invention. For example, some planarization units do not use rotating platens and rotating wafer holders. The present invention is inclusive of all planarization units for which the present invention provides benefit. The general illustrative planarization assembly, as shown in FIG. 2, for performing CMP in accordance with the present invention, includes a rotating wafer holder 30 that holds wafer 32 of which wafer portion 10 is a part thereof. A fluid composition 34 in accordance with the present invention is introduced atop a polishing pad 38. The polishing pad 38 is located on a rotating table platen 36. The polishing pad 38 is applied to the surface 12 of wafer 10 in the presence of the fluid composition 34 at a certain pressure to perform the planarization as is shown in the detail drawing of FIG. 3. The pressure applied is represented in FIG. 2 by the arrow mark "P"; this pressure P represents both down force pressure and backside pressure applied per a planarization assembly, such as an assembly available from IPEC/Westech. The rotating elements 30, 36 are rotated and moved by motors or drive means (not shown) as is readily known to those skilled in the art. Wafer holder 30 rotates wafer 32 at a selected velocity about an axis 33 and moves wafer 32 under controlled pressure P across pad 38. The wafer 32 contacts the pad 38 as it is moved. The area of the pad 38 which comes into contact with the surface 12 of the wafer 32 varies as the wafer 32 is moved in a predetermined pattern as is known to those skilled in the art. A chemical supply system (not shown) introduces a fluid composition 34 atop the pad 38 at a specified flow rate. The fluid composition 34 may be introduced at various locations about the pad without affecting the benefits of the present invention. For example, the fluid composition 34 may be introduced from above the pad 38, such as by drip, spray, or other dispensing means and further may be introduced from beside the rotating table 36 by spraying or other dispensing means. The rotating table 36 is rotated at a selected velocity and is rotated in the same direction as the wafer holder 30. The surface 12 of the wafer 32 is held in juxtaposition relative to the pad 38 so that the pad 38 can planarize or polish surface 12. The fluid composition and the pad pressure primarily determine the polishing rate or rate of removal of the surface material. To alleviate metallic contamination during the planarization process, the present invention performs planarization in the presence of the fluid composition including a chelating agent. The chelating agent contains donor atoms that combine by coordinate bonding with a metal ion to form a chelating complex, or simply a chelate. The fluid composition in accordance with the present invention includes a fluid component and a chelating agent. The fluid composition may include a conventional slurry component generally including an abrasive component and a component that chemically interacts with the surface 12. For example, a typical oxide polishing slurry may consist of a colloidal suspension of oxide particles, with an average size of, for example 120 nm, in an alkali solution having a pH greater than or equal to 9. Ceria (CeO.sub.2) suspensions may also be used when appropriate, particularly where large amounts of SiO.sub.2 must be removed. Ceria acts as both the chemical and mechanical agent in the slurry. Other abrasive components of the slurry component may include, but are not limited to, alumina (Al.sub.3 O.sub.2), silica, zirconium oxide (ZnO.sub.2), titania (TiO.sub.2), or any other abrasive used in conventional planarization slurries as is known to one skilled in the art. Several slurry solutions presently available include ILD1300, an aqueous fumed silica slurry including amorphous silica and ammonium hydroxide, available from Rodel, Inc., Newark, Del., and SC-1, a colloidal fumed silica aqueous slurry including amorphous silicon dioxide, DI water, and potassium hydroxide, available from Cabot Corp. Tuscola, Ill. under the trade designation CAB-O-SPERSE SC-1. General characteristics of suitable conventional slurry components utilized in conjunction with the present invention include that the hardness of the polishing particles or abrasive component should be about the same hardness as the hardness of the film being polished to avoid damaging the film. In addition, the particles should be uniform and the solution free of metallic contaminants. Further, for example, conventional planarization slurries having a pH greater than about 9 are used for oxide polishing processes and those less than a pH of about 4 are used in polishing processes of, for example, tungsten. The conventional slurry used is dependant upon the type of surface being polished. The present invention may also be utilized with planarization units using pads including abrasive components wherein the fluid composition includes the chelating agent and a fluid component that chemically interacts with the surface. Therefore, the slurry including an abrasive component is not needed as the abrasive component of a slurry is provided by the pad that has an abrasive component at a surface thereof. The chemical interacting fluid component however, would still be required. The fluid chemically interacting component may include, for example, ammonium hydroxide or any alkali solution having a pH greater than or equal to 9. A suitable chelating agent may be any water soluble multidentate molecular ligand (having two or more donor atoms in the molecule) capable of occupying more than one position in the coordination sphere of a metal ion to form a cyclic structure, referred to as the chelating complex or the chelate. For example, the chelating agents may have donor atoms that may include N, O, S, P, As, and Se and most of the donor atoms are contained in linear or branched-chain structures, separated by suitable numbers of other atoms to allow the formation of the chelate structure with the metal. Such multidentate chelating agents include, for example, ethylenediaminetetracetic acid (EDTA), and trimethylenetetramene (trien). Preferably, the chelating agents are bidentate ionic groups, either acidic or base, such as, for example, 1,2-ethylenediphosphonic acid (EDP). Most preferably, the chelating agent is EDP available from Lancaster Synthesis Ltd., Windham, NH. Also preferably, the chelating agent is one that forms a chelate or chelating complex that has a large conditional formation or stability constant K.sub.f with regard to the various metals of greatest concern during planarization. Each chelating agent has a K.sub.f that is different with respect to each metal. The formation constant is the equilibrium constant for the formation of the chelate complex from the solvated metal ion and the ligand in its fuilly dissociated form. Many parameters influence stability, including the size and number of chelate rings formed between the ligand and metal ion, substituents on the chelate rings, and the nature of the metal ions and donor atoms of the chelating agent. Suitable chelating agents are agents which have sufficiently high formation constants with respect to particular metal ions such as those known to be at the surface of the wafer during the use of a slurry for planarization. With the use of such chelating agents having high formation constants for these particular metal ions, the concentration of uncomplexed metal ions can be reduced to prevent contamination of the wafer during planarization. Two or more metal ions may be buffered at different concentrations by a single chelating agent, because as discussed above, the single chelating agent will typically have different stability or formation constants for different metals. Because the formation constants are different with respect to different metal ions for a single chelating agent, preferable ranges for K.sub.f are given with respect to the metal ions of greatest concern. Preferably, the chelating agents have a K.sub.f greater than 3 for such metal ions of greatest concern. Particularly, the metal ions of greatest concern include Na, K, Li, Mg, Ca, Fe, Zn, and Al. For example, EDTA has a K.sub.f of 8.7 with respect to Mg, a K.sub.f of 10.7 with respect to Ca, a K.sub.f of 14.3 with respect to Fe(+2), a K.sub.f of 25.1 with respect to Fe(+3), a K.sub.f of 16.5 with respect to Zn, and a K.sub.f of 18.8 with respect to Cu. Further, for example, trien has a K.sub.f of 4.9 with respect to Mg, a K.sub.f of 7.8 with respect to Fe(+2). a K.sub.f of 12.1 with respect to Zn, and a K.sub.f of 20.4 with respect to Cu. The benefits of using the chelating agent are not affected by the type or material of the polishing pad utilized. For example, the fluid composition may be utilized with any known and appropriate polishing pad as would be known to one skilled in the art because the choice of pads is application dependant. For example, suitable pads may include pads such as Model No. IC 1000, Model No. IC 60 and Polytech pads, all available from Rodel, Inc., Scottsdale, Arizona. The polishing pad 38 may include one or more pads; may be of specific shape, i.e. circular, oval, or rectangular; may be of a nonuniform shape; and may be of any particular hardness depending on the particular application. Further, as described above, the pads may be pads that include an abrasive component at a surface thereof for planarization. Metal ion contamination of wafers occurs in several different modes. For example, metal ions in the slurries may bulk diffuse into a surface of a wafer. Alternatively, metal ions may diffuse down fracture paths of the wafer. The chelating agent, such as 1,2-ethylenediphosphonic acid (EDP), is added to the conventional abrasive slurry, or to a fluid component for use with a pad that includes an abrasive component, to reduce the amount of metal ion contamination to the wafer. The chelating agent bonds to the metal ions and reduces the migration of metal contaminants into the wafer surface. The combination of the metal ion and chelating agent are slow to diffuse into the silicon wafer surface. The amount of chelating agent used in the fluid composition is of an amount effective to reduce the concentration of metal ions in the fluid composition without impeding the polishing or planarization rate. Preferably, the chelating agent is present in an amount of about parts per billion (ppb) to about 5% by weight, more preferably about parts per million (ppm) to about 1% by weight, based upon the total weight of the fluid composition. As shown in the Examples below, the chelating agent EDP is present in the slurry in the amount of 2 grams to 5000 ml of slurry and in the amount of 0.2 grams to 2 gallons of the slurry. The use of chelating agents for planarization is beneficial for the reduction of ion concentration as shown by the data of the Examples below. Benefits of the process shown include the concentration reduction of uncomplexed metal ions for at least one type of metal whenever the slurry with EDP is used. Preferably, concentration reduction with respect to more than one type of metal is desired; however, the reduction of just one metal is beneficial. Further, although it is preferable to obtain a high percentage reductions for at least one metal, even the slightest reduction of uncomplexed metal ions is beneficial. |
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