WO2005035688A1

WO2005035688A1 - Abrasive for chemical mechanical polishing and method for producing the same

Info

Publication number: WO2005035688A1
Application number: PCT/KR2004/002584
Authority: WO
Inventors: Su-Chul Chung; Seung-Ho Lee; Hyung-Mi Lim; Dae-Sun Ryu; Gyong-Beum Ko; Jong-Dai Park
Original assignee: Dongjin Semichem Co Ltd; Korea Institute of Ceramic Engineering and Technology KICET
Current assignee: Dongjin Semichem Co Ltd; Korea Institute of Ceramic Engineering and Technology KICET
Priority date: 2003-10-10
Filing date: 2004-10-09
Publication date: 2005-04-21
Anticipated expiration: 2006-04-10
Also published as: TW200521215A; KR20050034913A; KR100574225B1; TWI265193B

Abstract

An abrasive for chemical mechanical polishing, which is produced by hydrothermally treating a ceria particle coated silica, is disclosed. The abrasive for chemical mechanical polishing includes a silica core, a first shell for coating the silica core; and a second shell for coating the first shell, wherein the first shell is made of ceria particles and the second shell is made of silica particles. The method for producing an abrasive for chemical mechanical polishing comprises the steps of: (a) preparing ceria particle suspension by mixing aqueous ammonia and aqueous cerous nitrate solution and stirring the solution; (b) preparing core/shell particles by adding colloidal silica slurry into the prepared ceria particle suspension and stirring the suspension; (c) washing the suspension; and (d) hydrothermally treating the washed suspension.

Description

Description ABRASIVE FOR CHEMICAL MECHANICAL POLISHING AND METHOD FOR PRODUCING THE SAME Technical Field

[1] This invention relates to an abrasive for chemical mechanical polishing (CMP) and a method for producing the same. More particularly, this invention relates to an abrasive for CMP which is produced by hydrothermally treating a ceria particle coated silica. The abrasive includes a silica core, the first shell for coating the silica core, and the second shell for coating the first shell, wherein the first shell is made of ceria particles and the second shell is made of silica.

[2] Background Art

[3] Nowadays, as the degree of integration of an integrated circuit (TQ continues to rise, the global planarization of a semiconductor wafer become an important process in producing the integrated circuit. Large scale integrated semiconductor device, such as microprocessor or DRAM, is manufactured by forming various patterns of conductor materials and insulator materials, and generally has a multilayer structure. Before forming a new pattern layer, the surface of the former pattern layer should be planarized to properly form the multilayer structure. The global planarization is also important for minimizing a feature size and for a multilevel interconnection.

[4]

[5] One of the effective and widely used global planarization techniques is a chemical mechanical polishing (CMP) process, which performs the chemical polishing and the mechanical polishing simultaneously. The CMP process is relatively simple, and the planarizing area of the CMP process is greater than that of other planarization techniques by 100 to 1,000 times. The slurry useful for the CMP process includes metallic oxide abrasive, oxidizer, deionized water and various additives. Exemplary metallic oxide abrasive includes silica (SiO ), aluminum oxide (Al O ), ceria (CeO ), 2 2 3 2 zirconia (ZO ), or so on. The silica is widely used as the metallic oxide abrasive 2 because it is commercially available and inexpensive. Furthermore, in case of using the silica, serious contamination of semiconductor can be avoided since the material for forming an insulating layer of a semiconductor is SiO . Ifcwever, in case of using the 2 silica, the removal (polishing) rate is not satisfactory, and the selectivity of SiO layer 2 and Si N layer is not satisfactory, for example, in shallow trench isolation (STI) 3 4 process.

[6]

[7] Ceria abrasive has been used in polishing a glass lens, and the slurry including the ceria abrasive has the removal rate which is 3 to 4 times faster than the slurry including the silica abrasive, and also shows high removal rate in neutral solution. H)wever, the ceria abrasive is expensive, has irregular shapes and sizes, and is liable to be aggregated. Thus, the slurry including the ceria abrasive has drawbacks in that the wafer can be scratched in the polishing process, and degree of the planarization of the wafer decreases. In addition, the Haymaker constant, which represents the attractive force between particles, of the ceria abrasive is 27.7, which is greater than that of silica (5.99) and aluminum oxide (15.4). Therefore, when the size of the ceria particles increases, the repulsive power between particles and the dispersibility of the ceria particles decrease, which results in the high possibility of abrasive aggregation and precipitation.

[8]

[9] To solve these problems, U.S. patent publication No. 2002-95873, titled Aqueous dispersions, process for their production, and their use, discloses alkaline treated silica abrasive having average particle size of less than lOOnm, and U.S. patent No. 6,328,944, titled Doped, pyrogenically prepared oxides, discloses oxides of metals and/or non-metals which are doped with one or more doping components such as a metal, a non-metal, or an oxide and/or a salt of a metal and/or a non-metal. However, the abrasives are not uniform in their particle sizes, and the slurry including such abrasives is not satisfactory in removal rate and may produce scratches on the polished wafer. U.S. patent publication No. 2003-92271, titled Shallow trench isolation polishing using mixed abrasive slurries, discloses abrasive slurry including two or more inorganic metallic oxides. The abrasive is also not uniform in their particle sizes, which may result in the scratch formation on the polished wafer. In addition, when the mixture of colloidal silica and ceria is used, the removal rate in CMP is not satisfactory. Korean patent Laid-open No. 10-2003-0017352, titled Polishing composition comprising silica-coated ceria powder, discloses a ceria abrasive having improved stability. However, the abrasive is also not uniform in their particle sizes and shapes. Therefore, the abrasive and the slurry flow irregularly in polishing process, and the contacts between an abrasive pad, a wafer and an abrasive are also irregular, which may result in the irregular polishing of a wafer.

[10] [11] To solve these problems, the present inventors have prepared an abrasive for CMP by coating ceria particles on colloidal silica sol in solution state. The abrasive has uniform sizes and shapes, and the slurry including the same has better removal rate and the scratch formation is suppressed. However, the slurry including such abrasive is unstable, and liable to be aggregated and precipitated in neutral solvent, especially when pH is more than 4. Furthermore, there is a drawback in that particle aggregation also occurs when heating amorphous ceria hydroxide to produce crystalline ceria particles coated on the silica sol.

[12] Disclosure of Invention Technical Problem

[13] Therefore, it is an object of the present invention to provide an abrasive for CMP having improved polishing rate and stability at wide pH range, and suitable for long- term storage. It is other object of the present invention to provide an abrasive for CMP having regular particle sizes and shapes and capable of being uniformly dispersed in a solvent without aggregation. It is another object of the present invention to provide an abrasive for CMP capable of improving the degree of planarization of wafer, and for producing a polished surface having fewer defects and scratches. It is yet another object of the present invention to provide an abrasive for CMP which is inexpensive. It is yet another object of the present invention to provide a method for producing an abrasive for CMP which can be mass-produced by relatively simple processes.

[14] Technical Solution

[15] To accomplish these objects, the present invention provides an abrasive for CMP comprising a silica core, the first shell for coating the silica core, and the second shell for coating the first shell, wherein the first shell is made of ceria particles and the second shell is made of silica particles. Preferably, the second shell is produced by hydrothermally treating the ceria particle coated silica core. The present invention also provides a method for producing an abrasive for CMP which comprises the steps of: (a) preparing ceria particle suspension by mixing aqueous ammonia and aqueous cerous nitrate solution and stirring the solution; (b) preparing core/shell particles by adding colloidal silica slurry into the prepared ceria particle suspension and stirring the suspension; (c) washing the suspension; and (d) hydrothermally treating the washed suspension. [16] Brief Description of the Drawings

[17] A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:

[18] Fig. 1 is a diagram for illustrating a method for producing an abrasive for CMP according to an embodiment of the present invention;

[19] Fig. 2 is a diagram for illustrating a method for producing an abrasive for CMP according to other embodiment of the present invention;

[20] Fig. 3 shows TEM photographs before and after hydrothermally treating core/shell particles;

[21] Fig. 4 is a graph showing Zeta potential changes of the slurry including core/shell particle with respect to pH variation before and after the hydrothermal treatment; and

[22] Fig. 5 shows XRD graphs of the core/shell particle before and after the hydrothermal treatment.

[23] Mode for the Invention

[24] The abrasive for CMP according to the present invention comprises a silica core, the first shell for coating the silica core, and the second shell for coating the first shell. The first shell is made of ceria particles. To produce the first shell, 5 to 30 weight parts of ceria particles is uniformly coated on the 100 weight parts of the silica core. When the size of the silica core is about 400nm, the preferable amount of ceria particles is about 30 weight parts based on 100 weight parts of the silica core. On the contrary, when the size of the silica core is about lOOnm, the preferable amount of ceria particles is about 5 weight parts based on 100 weight parts of the silica core. The silica core useful in this invention is uniform colloidal silica having a spherical shape and a diameter of preferably 20 to 400 nm, and more preferably 100 to 400nm. The ceria particles coated on the silica core preferably have crystalline structure and sizes of 5 to 20nm. Preferably, the ceria particles are uniformly coated on the silica core without aggregation to form uniform abrasive particles. Hereinafter, the ceria particles coated silica core is called as core/shell particle.

[25]

[26] The core/shell particle is hydrothermally treated to form the second shell on the surface of the core/shell particle. The second shell is made of silica particles and has the thickness of less than 2nm, preferably 0.01 to 2nm, and more preferably 0.1 to 2nm. When the thickness of the second shells is less than 1 nm, the removal rate increase, but when the thickness of the second shells is more than 2 nm, the removal rate decrease. By hydrothermally treating the core/shell particle, the cohesive force between silica core and ceria particles increases, the number of ceria particles on the silica core and the crystallinity of the ceria particles increases, and the silica particles is coated on the core/shell particle to improve the removal rate and the stability of the slurry. The size of the abrasive for CMP according to the present invention is preferably about 50 to 500nm, and more preferably about 100 to 300 nm. When the size of the abrasive is less than 50nm, the stability of the abrasive increases but the removal rate decrease. On the contrary, when the size of the abrasive is more than 500nm, the stability of the abrasive decrease.

[27]

[28] Hereinafter, the method for producing an abrasive for CMP of this invention will be described. Fig. 1 is a diagram for illustrating a method for producing an abrasive for CMP according to an embodiment of the present invention. As shown in Fig. 1, the method for producing an abrasive for CMP includes the steps of: (a) preparing ceria particle suspension by mixing aqueous ammonia and aqueous cerous nitrate solution and stirring the solution; (b) preparing core/shell particles by adding colloidal silica slurry into the prepared ceria particle suspension and stirring the suspension; (c) washing the suspension preferably before or after centrifuging and/or filtering the stined suspension to remove excess salt in the suspension; and (d) hydrothermally treating the washed suspension. For example, 300m£ of 0.2M aqueous ammonia is added into 200 mil of 0.2M aqueous cerous nitrate solution, and the solution is stined at the temperature of 80 to 100°C to prepare suspension including ceria particles having the sizes of 5 to 20nm. While maintaining the temperature of the suspension at 80 to 100°C, colloidal silica slurry is added into the prepared ceria particle suspension. The colloidal silica slurry includes spherical silica particles of uniform size, and the preferable amount of the solid particles is 5g. The suspension is stined for about 2 hours to produce core/shell particles, which comprise silica core and ceria particles uniformly coated on the silica core. Then water is added into the stined suspension, and the suspension is centrifuged and/or filtered to remove excess salt in the suspension. The washed suspension is hydrothermally treated in an auto-clave at the temperature of 100 to 350°C for more than 30 minutes, and preferably 30 minutes to 2 hours to produce silica coated core/shell particles. [29]

[30] When the temperature of steps (a) and (b) is less than 80°C, it takes long time to produce the ceria particles and to coat the ceria particles on the silica core, and therefore it is economically unfavorable. On the contrary, when the temperature is more than 100°C, it is difficult to control the coating speed. The preferable pH of the washed suspension is 3.0 to 4.0, and more preferably 3.5 to 3.9. When the pH is less than 3.0, or the pH is more than 4.0, the suspension is liable to be unstable.

[31] [32] The amounts of SiO and CeO in the solid particles before and after the hy- 2 2 drothermal treatment were measured by wet and inductively coupled plasma (ICP), and the results are set forth in Table 1. As shown in Table 1, the amount of ceria increases after the hydrothermal treatment.

[33] Table 1

[34] In order to confirm the coating of silica by the hydrothermal treatment, surfaces of the solid particles were observed with high-resolution transmission electron microscope (HR-TEM, Jeol ltd., Model: JEM-4010, TEM 400 KV) and with conventional TEM before and after the hydrothermal treatment, and the results are set forth in Fig. 3. As shown in Fig.3, silica was coated on the ceria particle shell with the thickness of about 0.5 nm after the hydrothermal treatment. While changing the pH of the slurry including the core/shell particle, the Zeta potential of the slurry were measured with ELS-8000 (Otsuka Electronics Co., Ltd.) before and after the hydrothermal treatment, and the results are set forth in Fig. 4. As shown in Fig. 4, the Zeta potential change before the hydrothermal treatment is similar with that of the ceria particle, but the Zeta potential change after the hydrothermal treatment is similar with that of the silica sol, and the IEP (Isoelectric Point) was about 2. Therefore, it is confirmed that silica layer was formed on the surface of the core/shell particle by the hydrothermal treatment. In addition, the XRD peak of the solid particles before and after the hydrothermal treatment are set forth in upper part of Fig. 5. After the hydrothermal treatment, the full width at half maximum decreases, which means that the crystalline size of particle increases.

[35]

[36] Fig. 2 is a diagram for illustrating a method for producing an abrasive for CMP according to other embodiment of the present invention. As shown in Fig. 2, the method for producing an abrasive for CMP includes the steps of: (a) preparing a suspension including silica on which ceria particles are electrostatically coated by mixing silica sol and ceria sol; and (b) hydrothermally treating the suspension. Preferably, the ceria sol includes ceria particles having the sizes of 5 to 20nm. For example, 5 m£ of 20svt% acidic ceria sol (CeO -NIT, U.S.A., Nyacol Inc.) and 300 m£ 2 of 4wt% spherical silica sol are added into 300 mil beaker and stined with magnetic stiner for about 1-2 hours preferably at room temperature. Then, the mixed slurry is hydrothermally treated in an auto-clave at the temperature of 100 to 350 °C for more than 30 minutes, and preferably 30 minutes to 2 hours to produce silica coated core/ shell particles. The ceria in the core/shell particles are chemically bound to the silica core. Preferably, the hydrothermally treated slurry is centrifuged and/or filtered to remove the silica particle not coated with ceria particles. The Zeta potentials of the slurry before and after the hydrothermal treatment were measured as previously described, and the results were similar as shown in Fig. 4. The X-ray diffractions of the solid particles before and after the hydrothermal treatment are also set forth in lower part of Fig. 5, which confirms the crystalline size of the particle increases after the hydrothermal treatment.

[37]

[38] In the present invention, the first shell, namely the ceria particles, can also be coated on the silica core by a chemical vapor deposition (CVD), but the preferable coating method is the previously described solution phase reaction. The pH of the slurry including the abrasive of the present invention is important for abrasive dispersion, and the preferable pH of the slurry is 2 to 10, and more preferably 4 to 9. The surface of the abrasive is electrically charged, and the magnitude and type (positive or negative) of the charge depend on the pH of the slurry. The Zeta potential of the abrasive of the present invention decreases as the pH increases, and has (-) value when the pH of the slurry is more than 2. Therefore, when the pH is more than 2, the silica abrasive can be uniformed dispersed due to the electrostatic repulsion. However, when the pH is more than 10, the silica coated on the ceria and the silica core can be dissolved to form silicate, and the ceria particles can be separated from the silica, which may decrease the polishing efficiency of the slurry. [39]

[40] Hereinafter, the preferable examples are provided for better understanding of the present invention. However, the present invention is not limited to the following examples.

[41]

[42] [Comparative Example 1]

[43] 300mH of 0.2M aqueous ammonia was added into 200 mil of 0.2M aqueous cerous nitrate solution which was preheated to 93°C, and the solution was stined to prepare a suspension. While maintaining the temperature of the suspension at 93°C, colloidal silica slurry was added into the suspension and the suspension was stined for 2 hours. The average size of the silica particles in the silica slurry was 300nm, and the amount of the solid particles in the silica slurry was 5g. After completion of the stirring, the suspension was centrifuged and filtered, and then the produced slurry was washed so that the pH of the slurry became 3.7. The obtained slurry was dispersed in water with supersonic wave to produce polishing slurry of pH 4.0 and having the abrasive concentration of 1 weight%.

[44]

[45] [Example 1]

[45] 300mH of 0.2M aqueous ammonia was added into 200 mil of 0.2M aqueous cerous nitrate solution which was preheated to 93°C, and the solution was stined to prepare a suspension. While maintaining the temperature of the suspension at 93°C, colloidal silica slurry was added into the suspension and the suspension was stined for 2 hours. The average size of the silica particles in the silica slurry was 300nm, and the amount of the solid particles in the silica slurry was 5g. After completion of the stirring, the suspension was centrifuged and filtered, and then the produced slurry was washed so that the pH of the slurry became 3.7. The washed slurry was hydrothermally treated in an auto-clave at the temperature of 150 °C for 1 hour. The obtained slurry was dispersed in water with supersonic wave to produce polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight%.

[47]

[48] [Example 2]

[49] Except for performing the hydrothermal treatment at 190°C, the polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight% was prepared in the same manner as described in Example 1.

[50] [51] [Example 3]

[52] Except for performing the hydrothermal treatment at 190°C, and washing the slurry so that the pH of the slurry became 3.9, the polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight% was prepared in the same manner as described in Example 1.

[53] [54] [Example 4] [55] Except for performing the hydrothermal treatment at 200°C, the polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight% was prepared in the same manner as described in Example 3.

[56] [57] The reaction conditions of Examples 1-4 and Comparative Example 1, and the removal rate of each slurry are set forth in the following Table 2.

[58] Table 2

[59] * HDP layer: high density passivation layer [60] As shown in Table 2, the hydrothermally treated slurries prepared in Examples 1-4 have more desirable removal rate with compared to that prepared in Comparative Example 1.

[61] [62] [Comparative Example 2] [63] 5 M of 20svt% acidic ceria sol (CeO -NIT, U.S.A., Nyacol Inc.) and 300 M of 2 4wt% spherical silica sol were added into 300 mil beaker and stined with magnetic stiner for about 2 hours. The average size of the ceria particles was lOnm, and the average size of the silica particles was 300nm. The obtained slurry was dispersed in water with supersonic wave to produce polishing slurry of pH 4.0 and having the abrasive concentration of 1 weight%.

[64]

[65] [Example 5] [66] 5 M of 20svt% acidic ceria sol (CeO -NIT, U.S.A., Nyacol Inc.) and 300 M of 2 4wt% spherical silica sol were added into 300 mil beaker and stined with magnetic stiner for about 2 hours. The average size of the ceria particles was lOnm, and the average size of the silica particles was 300nm. The stined slurry was hydrothermally treated in an auto-clave at the temperature of 150 °C for 1 hour. The obtained slurry was dispersed in water with supersonic wave to produce polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight%.

[67] [68] [Example 6] [69] Except for performing the hydrothermal treatment at 190C, the polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight% was prepared in the same manner as described in Example 5.

[70] [71] [Example 7] [72] Except for performing the hydrothermal treatment at 200C, the polishing slurry of pH 6.0 and having the abrasive concentration of 1 weight% was prepared in the same manner as described in Example 5.

[73] [74] The reaction conditions of Examples 5-7 and Comparative Example 2, and the removal rate of each slurry are set forth in the following Table 3.

[75] Table 3

[76] As shown in Table 3, the hydrothermally treated slurries prepared in Examples 5-7 have more desirable removal rate with compared to that prepared in Comparative Example 2.

[77] [78] The polishing conditions for measuring the removal rate in Tables 2 and 3 are set forth in following Table 4.

[79] Table 4

[80] While the present invention has been described with respect to certain prefened embodiments and examples only, other modifications and variations may be made without departing from the spirit and scope of the present invention as set forth in the following claims.

Claims

[1] An abrasive for chemical mechanical polishing comprising: a silica core, a first shell for coating the silica core; and a second shell for coating the first shell, wherein the first shell is made of ceria particles and the second shell is made of silica particles.

[2] The abrasive for chemical mechanical polishing according to claim 1, wherein the second shell is produced by hydrothermally treating the ceria particle coated silica core.

[3] The abrasive for chemical mechanical polishing according to claim 1, wherein the amount of ceria particles is 5 to 30 weight parts based on 100 weight parts of the silica core.

[4] The abrasive for chemical mechanical polishing according to claim 1, wherein the second shell has the thickness of less than 2nm.

[5] A method for producing an abrasive for chemical mechanical polishing comprising the steps of: (a) preparing ceria particle suspension by mixing aqueous ammonia and aqueous cerous nitrate solution and stirring the solution; (b) preparing core/shell particles by adding colloidal silica slurry into the prepared ceria particle suspension and stirring the suspension; (c) washing the suspension; and (d) hydrothermally treating the washed suspension.

[6] The method for producing an abrasive for chemical mechanical polishing according to claim 5, further comprising the step of centrifuging and or filtering the suspension before or after the washing step.

[7] The method for producing an abrasive for chemical mechanical polishing according to claim 5, wherein the step of preparing ceria particle suspension is carried out at the temperature of 80 to 100 °C.

[8] The method for producing an abrasive for chemical mechanical polishing according to claim 5, wherein the ceria particle suspension includes ceria particles having the sizes of 5 to 20nm.

[9] The method for producing an abrasive for chemical mechanical polishing according to claim 5, wherein the step of preparing core/shell particles is carried out at the temperature of 80 to 100 °C.

[10] The method for producing an abrasive for chemical mechanical polishing according to claim 5, wherein the step of hydrothermally treating is carried out at the temperature of 100 to 350 °C for more than 30 minutes.

[11] A method for producing an abrasive for chemical mechanical polishing comprising the steps of: (a) preparing a suspension including silica on which ceria particles are electrostatically coated by mixing silica sol and ceria sol; and (b) hydrothermally treating the suspension.

[12] The method for producing an abrasive for chemical mechanical polishing according to claim 11, wherein the ceria sol includes ceria particles having the sizes of 5 to 20nm.

[13] The method for producing an abrasive for chemical mechanical polishing according to claim 11, wherein the step of hydrothermally treating is carried out at the temperature of 100 to 350 °C for more than 30 minutes.