Composition for chemical mechanical polishing

[0002] 1. Field of the Invention

[0003] The present invention relates to a polishing composition which can be used in the semiconductor industry. More particularly, the present invention relates to use of Al₂O₃/SiO₂composite particles as an essential abrasive so as to improve the removal rate without causing microscratches.

[0004] 2. Description of the Prior Art

[0005] Nowadays, the increase in the density of integrated circuits makes their producers aware of the importance of the global planarization of wafers. Under the circumstance, intensive and extensive attention has been given to CMP (Chemical Mechanical Polishing) as a planarization method.

[0006] Typically, highly integrated semiconductor devices are manufactured by alternately depositing conducting materials and insulating materials and thus forming patterns. If a surface is not flat, it is very difficult to form a new pattern on the surface. To highly integrate semiconductor devices, it is required to minimize feature sizes and to perform multilevel interconnections. Global planarization is one of the most important prerequisites to achieve this.

[0007] As the structures of microprocessors and DRAMs become multileveled, for instance, as the metal layer for the third generation version of 64 MDRAM becomes of a triply structure, problems may occur owing to the process complexity if the films are deposited onto the layers which are not flat. Particularly as for the photolithography process, when it is carried out over a non-planar layer, an incident light will reflect diffusely, which will result in an imprecise photoresist pattern. Thus, there remains a need to make the structure between layers simpler. For this, the surface is planarized by polishing unnecessarily deposited parts thereon, so as to effectively deposit more film layers.

[0008] Of the planarization methods ever known, CMP is the most effective. The other planarization methods which have been developed thus far, such as SOG/Etch Back/ECR Depo & Etch, are very complicated in process procedure, requiring 2-5 process steps, but the CMP process can be finished simply by polishing and cleaning.

[0009] Conventional polishing compositions or slurries for use in semiconductor CMP processes commonly comprise metallic oxide. According to the materials to be polished, the conventional polishing compositions or slurries can be largely classified into three kinds: polishing compositions for monosilicon, for insulating layers, and for metal lines and plugs.

[0010] Abrasives which are most extensively used in the semiconductor CMP process are silica (SiO₂), alumina (Al₂O₃), ceria (CeO₂), zirconia (ZrO₂), and titania (TiO₂), which can be produced by a fuming or a sol-gel method, as described in U.S. Pat. Nos. 4,959,113, 5,354,490, and 5,516,346 and WO 97/40,030. There has recently been reported a composition or a slurry comprising mangania (Mn₂O₃) (European Pat. No. 816,457) or a silicon nitride (SiN) (European Pat. No. 786,504). These metal oxides are independently used in the patent references and determine the properties and performance of their polishing slurries. With a relatively unstable dispersed state under an acidic condition, for example, a polishing slurry comprising silica causes less microscratches compared with a polishing slurry comprising alumina, but shows a low removal rate against barrier material when being applied as a metal slurry. On the other hand, a polishing slurry comprising alumina is advantageous in terms of being more stable in a dispersed state compared with a polishing slurry comprising silica and high in the removal rate against barrier materials, but suffers from a serious disadvantage of causing a quantity of microscratches after polishing.

[0011] Improved as they are to some extent in physical properties and polishing performance, recently developed polishing slurries comprising ceria, zirconia, titania, mangania or silicon nitride have not yet been stably established in the production processes on a commercial scale and are expensive compared with ones comprising silica or alumina.

[0012] Also, there have been reported attempts to use two or more metal oxides in combination with the aim of improving polishing performances. For example, U.S. Pat. No. 5,084,071 discloses that the presence of alumina (Al₂O₃) particles brings the slurry comprising silica as a main abrasive to an improved level of polishing reproductivity. Another combined polishing slurry can be referred to WO 97/13889, which discloses the uses of alumina (a type) in combination with a relatively soft metal oxide. Such composite polishing slurries exhibit better results in removal rate and selectivity than do the polishing slurries comprising single metal oxides, but have much to be improved. For example, when a great quantity of alumina (a type) coexists with a small quantity of silica in a polishing slurry, the oxide particles are in a simple mixed state so that poor dispersion stability appears on the slurry, giving rise to particle coagulation during storage. In result, the polishing slurry suffers sedimentation.

[0013] Leading to the present invention, the intensive and thorough research on a polishing composition, repeated by the present inventors, resulted in the finding that fine Al₂O₃/SiO₂composite particles increase a removal rate on semiconductor wafers as well as are superior in polishing selectivity without causing microscratches after polishing.

[0014] Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a polishing composition which is superior in removal rate and polishing selectivity and free of causing microscratches.

[0015] In accordance with the present invention, there is provided a polishing composition comprising fine Al₂O₃/SiO₂composite-based metal oxide particles, deionized water and additives.

[0016] The polishing composition of the present invention is suitable for use in polishing various industrial products, including semiconductors, photomasks, glassdiscs, and synthetic resins, especially, in surface planarization of device wafers. In detail, with superiority in removal rate and polishing selectivity for thin films and low incidence of microscratches after polishing, the polishing composition of the present invention can find numerous applications in CMP fields, especially in highly integrated device fabrication fields, including the polishing of silicon, interlayer insulating films, metal lines and plug, and barrier materials.

[0017] The present invention contemplates use of an Al₂O₃/SiO₂composite as an essential metal oxide ingredient of a CMP composition suitable for use in fabricating semiconductor devices.

[0018] The Al₂O₃/SiO₂composite, a feature of the present invention, can be prepared from AlCl₃and SiCl₄by a Co-Fuming method as follows: ${\mathrm{AlCl}}_3+{\mathrm{SiCl}}_4\stackrel{\mathrm{air}}{\underset{\mathrm{Heat}\left(\ge 1000°C.\right)}{\to }}{\mathrm{Al}}_2{O}_3/{\mathrm{SiO}}_2+\mathrm{HCl}.$

[0019] The metal oxide particles thus obtained are not in a simple mixed state of Al₂O₃and SiO₂, but in a composite state in which Al₂O₃is linked to SiO₂. The composite shows characteristic phisycal properties which are quite different from a simple mixture of the two components. Physical properties of the Al₂O₃/SiO₂composite based on ‘VP MOX 90’, a brand name of Degussa, Germany, are summarized in Table 1, below.

[0020] Physical properties of Al₂O₃/SiO₂(based on VP MOX 90)

[0021] The contents of each component in the composite can be controlled depending on fed amount and reaction condition. In a typical Co-Fuming method, a composite comprising 67±15 wt % of Al₂O₃and 33±15 wt % of SiO₂is obtained, which is preferable for the present invention.

[0022] Any of the conventional dispersion methods, such as high speed milling with a dyno-mill or ball mill and use of a high shear mixer, is available to prepare a dispersion of Al₂O₃/SiO₂for use in a polishing composition. More efficient than conventional methods is the method using a microfluidizer, disclosed in Korean Pat. Appl'n No. 98-39212 filed by the present inventors.

[0023] For use in a polishing dispersion slurry, the Al₂O₃/SiO₂composite is in primary particle size between 10 and 100 nm and preferably between 20 and 60 nm as measured in BET. For example, when the primary particle size is smaller than 10 nm, a sharp decrease occures in the removal rate, deteriorating the throughput. On the other hand, when the primary particle size is larger than 100 nm, an increased removal rate is obtained, but difficulty is imposed on the dispersion of the particles. What is worse, a quantity of large particles are feasible to cause a significant quantity of microscratches.

[0024] The metal oxides in an aqueous dispersion form secondary particles, which preferably range, in mean size, from 10 to 500 nm. Particles larger than 500 nm in size negatively affect the dispersion stability such that the aqueous dispersion suffers sedimentation after being allowed for stand for one week at room temperature. Thus, a stirring process is additionally conducted just before a CMP process.

[0025] To be used in the dispersion slurry, the Al₂O₃/SiO₂composite of the present invention also should meet a specific surface area requirement which is in the range of 20-200 m²/g.

[0026] As for the solid content of the Al₂O₃/SiO₂, it is on the order of 1-50% by weight based on the total weight of the polishing composition and preferably on the order of 1-25% by weight. For example, if the solid content of Al₂O₃/SiO₂is below 1% by weight, desired effects cannot be obtained. The solid content of Al₂O₃/SiO₂may be further confined to a narrower range depending on the surfaces to be polished. When applied in a CMP process for semiconductor device fabrication, the polishing composition using the Al₂O₃/SiO₂as a main abrasive more preferably has a solid content of 1-5% by weight for monosilicon, 5-15% by weight for interlayer insulating films, and 3-7% by weight for metal lines, plugs, and barrier materials.

[0027] In accordance with the present invention, the polishing dispersion may be further supplemented with additives depending on the substrates to be polished. For instance, the dispersion may be added with bases such as KOH for polishing monosilicons and interlayer insulating films and with oxidizing agents or other appropriate agents for polishing metal surface such as W and Cu, and barrier materials such as Ti/TiN and Ta/TaN. Examples of available bases include KOH, NH₄OH, and R₄NOH. Acids also can be added, which can be exemplified by H₃PO₄, CH₃COOH, HCl, HF and so on. Available as such supplementary oxidizing agents are H₂O₂, KIO₃, HNO₃, H₃PO₄, K₂Fe(CN)₆, Na₂Cr₂O₇, KOCl, Fe(NO₃)₂, NH₂OH, and DMSO. Divalent acids, such as oxalic acid, malonic acid and succinic acid can be used as additives for the polishing composition of the present invention. In order to improve polishing selectivity for metal surfaces, potassium hydrogen phthalate may be used. 2-pyrrolidinone may be added to enhance a moisturizing effect, thereby preventing the aggregation and agglomeration of the abrasive particles. These additives may be used alone or in combination. The addition order of the additives is not particularly limited. They may be added before or after the dispersion of the Al₂O₃/SiO₂composite in deionized water. Preferably, the polishing composition of the present invention is essentially composed, by weight, of 1-50% of the Al₂O₃/SiO₂composite, 1-10% of the additives, and 40-98% of deionized water.

[0028] As described above, the present invention is directed to a polishing composition comprising fine Al₂O₃/SiO₂composite particles, which can polish semiconductor wafers at high removal rates and show high selectivity for interlayer insulating films (SiO₂) without causing microscratches after polishing. Therefore, the present invention can be applied to the fabrication of highly integrated devices, such as shallow trench isolation (STI) processes.

[0029] In a 20 liter polyethylene vessel, 1.3 kg of Al₂O₃/SiO₂composite powder, such as that manufactured by Degussa, Germany, identified as VP MOX 90 and 8.6 kg of deionized water were pre-mixed at 1,000 rpm for 2 hours. The mixture was allowed to pass once through a dispersion chamber which was maintained at a pressure pulsation in a range of 18,000±1800 psi. After being filtered through a 5 μm depth filter, the sample thus dispersed was found to be 10-400 nm in particle size distribution and 180 nm in mean particle size as measured by a grain size analyzer, such as that manufactured by Malvern, identified as Zetasizer.

[0030] Five liters of the Al₂O₃/SiO₂composite dispersion prepared above was adjusted to 11.0 in pH by the addition of an appropriate amount of a 20%-KOH solution. Under the following polishing conditions, this polishing composition was used to polish a six-inch monosilicon wafer for two minutes. The removal rate and WIWNU (Within Wafer Non-Uniformity) were evaluated from the thickness of the sample left. The number of microscratches was measured by a wafer defect inspection system (KLA TENCOR).

[0031] Polishing Conditions

[0032] Polisher: 6EC (Strasbaugh)

[0033] Conditions

[0034] Pad type: IC100/Suba IV Stacked (Rodel)

[0035] Platen Speed: 90 rpm

[0036] Quill Speed: 30 rpm

[0037] Pressure: 8 psi

[0038] Back Pressure: 0 psi

[0039] Temp.: 25° C.

[0040] Slurry Flow: 150 ml/min.

[0041] The same procedure as in Example I was repeated, except that an interlayer insulating film (SiO₂) and an SiN film were independently used instead of the monosilicon substrate.

[0042] Five liters of the Al₂O₃/SiO₂composite dispersion slurry prepared above was diluted with five liters of deionized water to control the solid content into 6.5% by weight, and the dispersion was adjusted to 3 in pH by the addition of 0.4 liters of 50%-H₂O₂as an oxidizing agent and then with H₂SO₄and HNO₃. Using six-inch wafers on which W and SiO₂were respectively deposited, the polishing performance of the polishing composition was evaluated as in Example I.

[0043] Five liters of the Al₂O₃/SiO₂composite dispersion slurry prepared above was diluted with five liters of deionized water to control the solid content into 6.5% by weight, and the dispersion was adjusted to 6.5 in pH by the addition of 0.4 liters of 50%-H₂O₂as an oxidizing agent and then with H₂SO₄, HNO₃and ammonia. Using six-inch wafers on which Cu and SiO₂were respectively deposited, the polishing performance of the polishing composition was evaluated as in Example I.

[0044] Polishing slurries were prepared and evaluated for polishing performance in the same manner as in Example I, except that the following metal oxide materials were used instead of the Al₂O₃/SiO₂composite dispersion.

[0045] Al₂O₃dispersion slurry: particle size distribution 10-720 nm, mean size: 255 nm

[0046] SiO₂dispersion slurry: particle size distribution 10-400 nm, mean size: 175 nm

[0047] CeO₂dispersion slurry: particle size distribution 10-1100 nm, mean size: 450 nm

[0048] Polishing slurries were prepared and evaluated for polishing performance in the same manner as in Example II, except that the following metal oxide materials were used instead of the Al₂O₃/SiO₂composite dispersion.

[0049] Polishing slurries were prepared and evaluated for polishing performance in the same manner as in Example III, except that the following metal oxide materials were used instead of the Al₂O₃/SiO₂composite dispersion.

[0050] Polishing slurries were prepared and evaluated for polishing performance in the same manner as in Example IV, except that the following metal oxide materials were used instead of the Al₂O₃/SiO₂composite dispersion.

[0051] As described hereinbefore, the polishing composition of the present invention is superior in removal rate and free of causing microscratches after polishing and suitable for use in the global planarization of device wafer surfaces.