WO2008023858A1

WO2008023858A1 - Manufacturing methods of fine cerium oxide particles and its slurry for shallow trench isolation process of semiconductor

Info

Publication number: WO2008023858A1
Application number: PCT/KR2006/003367
Authority: WO
Inventors: Ho-Seong Nam; Gui-Ryong Ahn; Jin-Seo Lee; Man-Woo Jung; Soon-Young Soh; Joo-Hyeong Lee; Young-Sik Hahn; Wan-Jae Myeong
Original assignee: Hanwha Chemical Corporation
Priority date: 2006-08-25
Filing date: 2006-08-25
Publication date: 2008-02-28

Abstract

The present invention relates to manufacturing methods of fine cerium oxide particles and its slurry for shallow trench isolation process of semiconductor. To increase of the removal selectivity, an aqueous solution of additives consists of polyacrylic acid and amine compounds is added the cerium oxide slurry. The polishing slurry have a high particle stability and removal selectivity, and also less scratches after chemical mechanical polishing of semiconductor.

Description

MANUFACTURING METHODS OF FINE CERIUM OXIDE PARTICLES AND ITS SLURRY FOR SHALLOW TRENCH ISOLATION PROCESS OF SEMICONDUCTOR

[Technical Field] The present invention relates to chemical mechanical polishing slurry for semiconductor trench isolation employing cerium oxide (ceria) which is useful for the selective removal of silicon oxide to silicon nitride layer.

[Background Art]

During recent years, miniaturization and high integration of elements have been further accelerated with development of semiconductor techniques. In case of memory semiconductor, the position of the capacitor is changed from CUB (capacitor under bit line) to COB (capacitor over bit line) in order to increase the capacity of a capacitor, as the integrity increases, and the shape of the capacitor is changed to cylinder structure. In a logic chip, since successive stacking stages are involved as using multi-layered wiring, surface step-height occurs in the wafer after such stages, which cause a lot of problems in subsequent processes. In order to eliminate such problems, planarization is performed by incorporating a chemical mechanical polishing ( ^λCMP' ) process.

One of the processes employing chemical mechanical polishing processes is shallow trench isolation. Shallow trench isolation is a process to isolate the active region during the process for preparing a semiconductor element. It is a technique which comprises depositing silicon oxide layer and silicon nitride layer on a silicon, forming a trench up to the silicon by means of etching, and gap-filling the silicon oxide layer, and planarizing it via chemical mechanical polishing to ensure activated region. However, as gap-filling of silicon oxide layer is performed on the trench and then chemical mechanical polishing is carried out, the silicon oxide layer and silicon nitride layer are exposed. If a slurry having the lower ratio of selective removal is employed, the larger amount of silicon nitride layer will be removed. The ratio of selective removal herein refers to ratio of the rate of removing silicon nitride layer to silicon oxide layer. Loss of silicon nitride layer results in change of thickness of the field oxide and reduces over-polishing margin. Thus the invention relates to a process for preparing slurry having high ratio of selective removal by using ceria as an abrasive, and additives to lower the removing rate of silicon nitride .

The processes which can prepare cerium oxide ultra- microparticles used as an abrasive include, depending on the phase where the reaction proceeds, gaseous processes, liquid processes and solid processes.

Gaseous processes comprise vaporizing cerium metal or a metal precursor and reacting it with oxygen or the like. Gaseous processes include various processes, depending on the manner of vaporization or reaction, such as flame combustion pyrolysis, laser vaporization, plasma vaporization, and spray pyrolysis. Though the technique is advantageous in that it may involve simple processes and give uniform and minute particles, it is disadvantageous in that the price of the particle to be prepared will be expensive because excessive energy for preparation is required, cost of device is high, and the productivity is not high.

A representative method of the solid processes is calcination, being a traditional process for preparing metal oxides, in which cerium carbonate as a precursor is subjected to pyrolysis and oxidation in a furnace at a high temperature to give cerium oxide, which is then crystallized for a long period and again pulverized into minute particles. For the stage of pulverizing into minute particles, a bead mill is essentially used but it is disadvantageous in that the impurities are difficult to be controlled by the beads.

International Patent Laid-Open WO 99/31195 and Japanese Patent Laid-Open No. 1998-106993, Japanese Patent Laid-Open No. 1998-154672 and Japanese Patent Laid-Open No. 2000-160136 employs, as a method for preparing cerium oxide particles for planarization of a semiconductor, a process in which cerium carbonate as raw material is heated in a calcining furnace at a high temperature for a long period, and the product obtained by dry pulverization, having the size of micrometer unit, and thereafter using high speed jet milling by bead mill in a solution, which is then filtered to provide final CMP slurry. However, this process is disadvantageous in that the reaction has to be carried out at a high temperature for a long period, impurities are likely to be incorporated during the stages of pulverization and high speed milling, and excessive energy consumption and production time are required. Further, the process has limitation in controlling the particle diameter in making the primary particles into ultra-microparticles, so that the process cannot avoid remnant large particle of not less than 1 μm. Thus, the final slurry has to be inevitably filtered, and the loss of particles cannot be avoided. In the meanwhile, according to a mechano-chemical process (MCP) , the surface of precursors such as cerium chloride is activated (by means of high temperature, or the like) by- mechanical stimulation with high speed and high energy (for example, high speed ball-milling) to drive the reaction. The mechano-chemical process is disadvantageous in that it cannot avoid incorporation of impurities from balls and/or vessel; washing out alkaline metal salts added in excess amount as a process additive is very difficult; and it requires a long reaction time, a calcination stage and very high cost for substantial production.

The proposed processes for preparing cerium oxide ultra- microparticles for planarization of semiconductor by using liquid process, are a process which comprises milling tri-valent nonaqueous cerium compound (cerium carbonate) dispersed in water, oxidizing the resultant substance and performing hydrothermal treatment [International Patent Laid-Open WO 97/29510] ; a process which comprises oxidizing tri-valent water-soluble cerium compound (cerium nitrate) by using an oxidant and performing hydrothermal treatment; and a process which comprises making a tetra-valent water-soluble cerium compound (cerium nitrate ammonium salt) alkaline to give cerium hydroxide, and performing hydrothermal treatment to obtain cerium oxide.

Those processes are carried out batch-wise, so that the amount of production is restricted, and the stages of isolating the particles prepared from the solution, washing and drying are inevitable because the reaction product contains a large amount of waste acid and waste alkaline substances after the reaction, thereby the process for preparation is complicated and the product cannot be manufactured in a large scale. Further, it is disadvantageous in that the particles prepared have large size and broad particle size distribution.

Supercritical hydrothermal synthesis, one of the hydrothermal processes, has been intensively studied by Aziri (Japan) or the like and reviewed in Ind. Eng. Chem. Res. Vol. 39, 4901-4907 (2000) . It is known that ultra-microparticles having nanosize can be easily obtained by reacting water soluble cerium salt under a supercritical water condition (T_C≥374^°C & P_c≥22.4 MPa)

International Patent Laid-Open WO 87/04421 and USP 5,635,154 propose processes for preparing metal oxide ultra- microparticles by means of supercritical hydrothermal synthesis in a batch process and continuous process, respectively. The batch process is disadvantageous in that control of particle diameter is difficult owing to relatively long reaction time (dozens of minutes or longer) and broad particle size distribution.

In case of the ceria concentrate prepared by continuous supercritical hydrothermal process according to Korean Patent Application No. 2003-32574 (Cerium oxide ultra-microparticle concentrate for chemical mechanical polishing and process for preparing thereof) filed by the present Applicant, it is easy to control the primary ceria particle size, but it is difficult to obtain a stable aqueous ceria solution owing to precipitation of ceria during the storage in a long period, and to be employed as a slurry solution for semiconductor owing to alteration of the physical propertis such as agglomeration or aggregation of particles, or the like.

[Disclosure] [Technical Problem] The object of the present invention is to provide a process for preparing a chemical mechanical cerium oxide polishing composition for semiconductor, in which cerium oxide of nanometer size is prepared by supercritical hydrothermal synthesis, and a mixture consisting of the cerium oxide abrasive particles thus prepared, a dispersant and deionized water is dispersed by using a high pressure dispersion equipment, to obtain a chemical mechanical cerium oxide polishing composition for semiconductor having narrow particle size distribution without agglomeration or aggregation, having small size of secondary particle size, and not more than 10 ppm of alkaline metal and alkaline earth metal, respectively, not more than 10 ppm of transition metal and other impurities, respectively, and not more than 10 ppm of ionic impurities, respectively.

Another object of the present invention is to provide a process for preparing abrasive slurry wherein additives including polycarboxylic acid polymer, nitrogen-containing organocyclic compound and amine compound, and a pH adjusting agent, if required, are added to the cerium oxide abrasive composition, as an aqueous solution of additives for raising the ratio of selective removal, and a slurry prepared according to the process described above.

In addition, the object of the present invention is to provide chemical mechanical polishing slurry having high ratio of selective removal and excellent planarity, to be applied to shallow trench isolation by using a mixture of said cerium oxide abrasive composition with the aqueous solution of additives.

Cerium oxide particles employed to achieve the object of the present invention is the cerium oxide ultra-microparticles disclosed by the present Applicant in Korean Patent Application No. 2003-32574. When preparing the cerium oxide ultra- microparticles by means of supercritical hydrothermal synthesis, ammonia-containing substance (such as aqueous ammonia) is also injected to the reactor, so that nitrate by-product can be decomposed simultaneously with the reaction in the same synthetic device to obtain cerium oxide slurry of high purity. In addition, by establishing a concentrating tank equipped with a metal filter at the latter end of the reactor, concentrates of cerium oxide ultra-microparticles having high purity can be obtained in a variety of concentration substantially free of nitric acid byproduct or impurities. CMP slurry for planarization of semiconductor can be easily prepared by simply diluting the concentrate and adding some additives. The present invention has been completed on the basis of the findings described above.

[Technical Solution]

The present invention relates to a process for preparing chemical mechanical polishing slurry for shallow trench isolation, and a slurry composition prepared therefrom.

As described above, the chemical mechanical polishing slurry according to the present invention comprises cerium oxide abrasive composition and an aqueous solution of additives (to which deionized water or pH adjusting agent may be further added) , and the cerium oxide abrasive composition is prepared by employing cerium oxide ultra-microparticles prepared via a process for preparing cerium oxide ultra-microparticles having the size of nanometer order.

The process for preparing shallow trench polishing slurry for semiconductor according to the present invention comprises the steps of a) preparing a mixture by mixing cerium oxide ultra- microparticles, deionized water and dispersant; b) filtering the mixture through a filter; c) dispersing the filtered mixture under high pressure; d) filtering the dispersed mixture through a filter to prepare an abrasive composition; and e) mixing from 50 to 300 parts by weight of aqueous solution of additives to 100 parts by weight of the abrasive composition.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

The process for preparing chemical mechanical polishing cerium oxide ultra-microparticle according to the present invention is based on the disclosure of Korean Patent Application No. 2003-32574 filed by the present Applicant, and comprises the steps of: a) reacting pre-heated and pre-pressurized deionized water, a solution of metal salt containing from

0.01 to 20% by weight of cerium salt based on the total reactant, and ammonia-containing fluid in a continuous reactor at a temperature from 250 to

700^°C under a reaction pressure from 180 to 550 bar for 0.01 second to 10 minutes to obtain a solution containing cerium oxide ultra- microparticles; and b) concentrating the solution containing cerium oxide ultra-microparticles in a concentrating tank equipped with a filter having pore size of 0.01 to

10 μm.

The CMP cerium oxide ultra-microparticles prepared according to said process are characterized in that they have not more than 10 ppm of alkali metal and alkaline earth metal content, respectively, not more than 10 ppm of transition metal and other impurities, respectively, and not more than 10 ppm of ionic impurities, respectively.

Cerium oxide ultra-microparticles according to the present invention is synthesized as ultra-microparticles having the size from 1 to 1000 nm by continuous reaction of deionized water, water-soluble cerium salt and ammonia-containing fluid in a continuous reactor under the condition of reaction temperature from 250 to 700^°C and reaction pressure from 180 to 550 bar, simultaneously with the nitrogen containing by-products being decomposed to drastically reduce the amount of nitrogen- containing compound in the waste liquid of the synthetic process. Further, the reaction mixture of high purity, substantially free of nitrogen compound, is concentrated in a concentrating tank to obtain the concentrate of cerium oxide ultra-microparticles, or dried to obtain powder.

In the process of the present invention, cerium salts employed include cerium nitrate, ammonium cerium nitrate or a mixture thereof. In addition, at least one water-soluble metal nitrate (hereinafter, referred to as "metal salt") other than cerium nitrate may be admixed.

The metal of said aqueous solution of metal salts is not specifically restricted as long as it is water-soluble, and the metal (s) employed is (are) at least one metal (s) selected from the group consisting of transition metals including Group IA, IB, HA, HB, IHA, IHB, IVA, IVB, VA, VB, VIA, VIB, VIIB, VIII of the Periodic Table and lanthanides and actinides, and combination thereof. More specifically, the metal (s) is (are) at least one selected from the group consisting of zinc, cobalt, nickel, copper, iron, aluminum, titanium, barium and manganese.

According to the present invention, the concentration of the aqueous solution of cerium salt, or mixed aqueous solution of cerium salt and at least one other metal salt is not specifically restricted. The final concentration after being mixed with preheated and pre-pressurized deionized water is from 0.01 to 20% by- weight, preferably from 0.05 to 10% by weight. If the concentration of the solution of cerium salt, or the mixed solution of cerium salt and at least one other metal salt is less than 0.1% by weight, the solution is too dilute to be economic, while if it is more than 20% by weight, the concentration is too high to result in high viscosity of the synthesized liquid to inhibit fluent flow, thereby affecting the quality of the product. According to the present invention, the ammonia-containing fluid is aqueous ammonia, ammonia or an aqueous solution of ammonium salt such as ammonium carbamate, and the concentration (molar ratio) is from 0.5 to 3.0, preferably from 0.8 to 2.0 relative to the total amount of the by-product nitrogen compound generated from cerium salt or other metal salt in the reaction mixture after final mixing. If the molar ratio of ammonia to the nitrogen compound is less than 0.5, degradation of the nitrogen compound is not sufficient, while if it is more than 3.0, the problem of excessively high ammonia content in the waste fluid occurs .

According to the present invention, the reaction is carried out at a temperature of 250^°C or higher, under a reaction pressure of 180 bar or more, preferably at a temperature from 250 to 700^°C under a reaction pressure from 180 to 550 bar, more preferably at a temperature from 300 to 550^°C under a reaction pressure from 200 to 400 bar. If the reaction temperature is lower than 250^°C or the reaction pressure is less than 180 bar, the size of particles synthesized becomes large, and degradation of nitrogen-containing by-products is not sufficient. Further, if the temperature and pressure is excessively high, the process becomes less economic, and cerium oxide microparticles may be redissolved. Since uniform particle size can be obtained as the complete mixing is achieved in a shorter time, the mixer should be designed to be tailored for desired particle size distribution, and the temperature and pressure should be appropriately adjusted along with injection rate of the fluid, location of injection and injection concentration, or the like.

As the reactor employed in the present invention, preferable is a continuous reactor which can control the reaction time short, rather than batch-type or semi-batch type having longer reaction time. Though any type of the reactor can be employed including tube type, cylinder type, square type, sphere type or the like, a tube type reactor is more preferable among them. In some cases, a reactor equipped with internal structure to facilitate complete mixing of the fluid inside the reactor can be used. Reaction time depends on the situation, but usually from 0.01 second to 10 minutes, preferably from 0.1 second to 2 minutes .

According to the present invention, it is preferable that deionized water is pressurized and heated to a certain pressure and temperature or higher, to provide sufficient pressure and temperature to eventually cause synthesis of cerium oxide, as being mixed with the aqueous solution of cerium salt and the ammonia-containing fluid. Deionized water and the ammonia- containing fluid may be mixed first and preheat and/or pre- pressurized, and then reacted with said cerium salt or a mixed aqueous solution of cerium salt and at least one other metal salt. Alternatively, deionized water and aqueous solution of cerium salt may be mixed first to be preheated and pre-pressurized, and then reacted with said ammonia-containing fluid. Or, cerium salt and the ammonia-containing fluid may be firstly mixed, and then mixed with preheated and/or pre-pressurized deionized water to carry out the reaction. In the meanwhile, in order to control the size, shape, physical properties or the like of the finally produced particles or to adjust the synthetic rate, 0.1 to 20 moles (based on 1 mole of the cerium salt) of an alkaline solution such as that of potassium hydroxide or an acidic solution such as sulfuric acid may be added, before or during the reaction according to the present invention, if required. If necessary, a reductant such as hydrogen, or an oxidant such as oxygen or hydrogen peroxide may be added in an amount of 0.1 to 20 moles based on 1 mole of the cerium salt, before or during the reaction according to the present invention.

The volume of the concentrating tank for concentrating the reaction mixture thus obtained is not specifically restricted. The material of the filter equipped inside the tank is not specifically restricted, but a metal sintered filter having the pore size from 0.01 to 10 μm, preferably from 0.1 to 5.0 μm is appropriately used. If the pore size of the filter is less than 0.01 μm, filter is clogged by particles during the operation to rapidly increase the pressure difference between before and after filtering, so that concentrating to a proper concentration with smooth operation becomes difficult. If it is larger than 10.0 μm, efficient concentration cannot be achieved because significant number of the cerium oxide ultra-microparticles are passed through the filter. If required, washing step by using deionized water or other fluid is added in the concentrating tank.

According to the present invention, the reaction mixture is recovered by concentrating it by from 1 to 50% by weight, preferably from 1 to 30% by weight. The solid/liquid mixed concentrate may be used as it is, or prepared as powder to be used.

The cerium oxide ultramicroparticles according to the present invention has high purity with containing cerium oxide as the main component, and has the half width of main peak (FWHM) in terms of crystalline particle diameter by X-ray diffraction of 0.016 to 3.5°, the calculated value of the crystallite according to Scherrer Equation of 1 to 1000 nm, mean particle diameter of primary particles according to SEM or TEM image analysis of 1 to 1000 nm, specific surface area by BET method of 2 to 200 m²/g, and TREO (total rare-earth oxide) of 99% or more and CeO₂/TREO of 95% or more, from the viewpoint of the purity.

In addition, said solid/liquid mixed concentrate preferably has not more than 10 ppm of alkaline metal and alkaline earth metal, respectively, not more than 10 ppm of transition metal and other impurities containing the elements such as radioactive isotopes, respectively, and not more than 10 ppm of anionic components such as nitrate, nitrite, sulfate and chloride ion and cationic components such as ammonium and sodium, respectively.

To the cerium oxide ultra-microparticles obtained according to the present invention as described above, added is a dispersing additive, to form a dispersion which can prevent agglomeration and aggregation of cerium oxide particles by using a high pressure dispersing device of collision mode, to prepare cerium oxide abrasive composition and chemical mechanical polishing slurry using the same.

The process for preparing the chemical mechanical polishing slurry according to the present invention comprises the steps of a) preparing a mixture by mixing cerium oxide ultra- microparticles, deionized water and dispersant; b) filtering the mixture through a filter; c) dispersing the filtered mixture under high pressure; d) filtering the dispersed mixture through a filter to prepare an abrasive composition; and e) mixing from 50 to 300 parts by weight of aqueous solution of additives to 100 parts by weight of the abrasive composition. Said cerium oxide ultra-microparticles are prepared according to the process for preparation described above, and the mixed ratio of the cerium oxide ultra-microparticles can be employed in an amount of 0.01 to 30% by weight, preferably from 0.5 to 10% by weight of the mixed solution in step a) . As the dispersant for dispersing the abrasive particles, a polymeric dispersant, a water-soluble anionic surfactant, a water-soluble non-ionic surfactant, or a water-soluble cationic surfactant may be employed. The content of alkali metal such as sodium (Na) and potassium (K) and halogen ion of the surfactant is preferably adjusted to 10 ppm or less. The polymeric dispersant employed in the present invention is one or more polycarboxylic ammonium salt(s), selected from the group consisting of polyacrylic acid ammonium salt, polymethacrylic acid ammonium salt, polyacrylic acid amine salt, polymethacrylic acid amine salt, poly (ethylene-co-acrylic acid) ammonium salt, poly (ethylene-co-acrylic acid) amine salt, poly (ethylene-co- methacrylic acid) ammonium salt and poly (ethylene-co-methacrylic acid) amine salt. The amount of surfactant used is from 0.1 to 10% by weight, preferably from 0.5 to 8% by weight based on the abrasive particles.

In order to prevent agglomeration of secondary agglomerated cerium oxide particles, dispersing process under high pressure was employed. Dispersion was carried out in a colliding manner through minute passage under a dispersing pressure from 50 to 200 MPa, preferably from 80 to 120 MPa. In order to reduce the width of distribution and decrease the mean particle size, the dispersing step is preferably carried out from once to ten times. The prefilter employed in step b) , having from 1 to 50 μm of pore size, removes large particles through said prefiltering, while the final filter employed in step d) , having from 0.5 to 5 μm of pore size, removes particles of medium size.

The measurement of size and distribution was carried out by using LA-910 instrument from Horiba. The median particle size was taken as the size located in the middle of the size distribution in terms of volume percentage of each particle (D₅o), and the maximum particle size was taken as the highest value (Dioo) as can be shown from the results of measurement by using Horiba instrument in Figs. 1 and 2. Distribution of the particles dispersed in the cerium oxide abrasive composition prepared according to the present invention shows mean particle diameter of from 100 to 700 nm, preferably from 150 to 400 nm, with the maximum particle size of 1.20 μm or less, as can be seen from Figs. 1 and 3. The zeta potential of the cerium oxide abrasive composition was -30 mV or less.

Said aqueous solution of additives for raising the ratio of selective removal of the slurry, consists of polycarboxylic acid polymer as an acidic additive, nitrogen-containing organocyclic compound as a basic additive, an amine compound and deionized water. In addition, solutions of hydrochloric acid, sulfuric acid, nitric acid, and basic solution such as that of potassium hydroxide or ammonia may be added as a pH modifier to the solution.

The aqeous solution of additives combines to the surface of abrasion of silicon nitride layer to induce steric hindrance and prevent the approach of abrasive particles, thereby serving to selectively intervene the rate of abrasion. For example, since the oxide layer has negative surface charge while the nitride layer positive at the pH range from 6 to 8, use of anionic additive can drop the abrasion rate of the nitride layer by- adsorption of the additives on the nitride layer. Said composition of additives selectively consists of acidic polycarboxylic acid polymer, basic nitrogen-containing organocylclic compound and amine compounds.

Said polycarboxylic acid polymer, being a poly (meth) acrylic acid homopolymer or copolymer, is an anionic compound having excellent adsorption to the nitride layer having positive surface charge. Preferably, it is one or more polymer (s) selected from the group consisting of poly (acrylic acid), poly (methacrylic acid), poly (ethylene-co-acrylic acid) and poly (ethylene-co- methacrylic acid). The molecular weight is preferably from 1,000 to 1,250,000, in order to be readily dissolved in an aqueous solution. If the molecular weight is less than 1,000, the effect of steric hindrance is not sufficient, while it is more than 1,250,000, the problem of agglomeration of the abrasive particles occurs. The amount of said carboxylic acid polymer compound added is preferably in a range from 0.001 to 5% by weight based on total aqueous solution of additives (which consists of additives and deionized water) . If the amount is less than 0.001% by weight, no effect of addition reveals, while if it is more than 5% by weight, the carboxylic acid polymer compound is not likely to be dissolved completely.

The nitrogen-containing organocyclic compound plays a role to enhance adsorption between the acrylic acid compound and the nitride layer to reduce the abrasion rate of the nitride, and increase the ratio of selection.

Preferable nitrogen-containing organocylclic compound according to the present invention is one or more compound (s) selected from the group consisting of 1, 3, 5-triazine, 1,3,5- triazine-2, 4, 6-triol (cyanuric acid), 1, 3, 5-triazine-2, 4, 6- trichloride (cyanuric chloride), 1, 3, 5-triazine-2, 4, 6- trithiol (trithiocyanuric acid), 1, 3, 5-triazine-2, 4, 6-trithiol sodium salt, 1, 3, 5-triazine-2, 4, 7-trithiol trisodium salt nonahydrate, 3,5, 7-triamino-s-triazolo [4,3-a]-s-triazine, 1,3,5- triacryloylhexahydro-1, 3, 5-triazine, 2, 4, 6-triaryloxy-l, 3, 5- triazine, triallyl-1, 3, 5-triazine-2, 4, 6- (IH, 3H, 5H) -trione, 5- azacytidine, 5-azacytosine, 4-amino-l-β-D-arabinofuranosyl-l, 3, 5- triazine-2 (IH) -one, cyanuric fluoride, 2-chloro-4, 6-dimethoxy- 1, 3, 5-triazine, 2, 4, 6-triallyloxy-l, 3, 5-triazine, 2,4,6- triphenyl-1, 3, 5-triazine, 2-chloro-4, 6-diamino-l, 3, 5-triazine, melamine, 2, 4, 6-tri (2-pyridyl) -1, 3, 5-triazine, 2, 4, 6-tris (I' - aziridinyl) -1,3, 5-triazine, l,2,4-triazine-3,5(2H,4H) -dione ( 6- azurasyl) , 6-aza-2-thymine, 6-aza-2-thiothymine, 6-aza-2- thiouridine, 6-azauracil, 3-amino-5, 6-dimethyl-l, 2, 4-triazine, 3-

(2-pyridyl) -5, 6-diphenyl-l, 2, 4-triazine, 3- (2-pyridyl) -5, β-bis (5- sulfo-2-furyl) -1, 2, 4-triazinedisodium salt trihydrate, 3- (2- pyridyl) -5, 6-diphenyl-l, 2,4-triazine-p,p' -disulfonic acid monosodium salt hydrate and 5, 6-di-2-furyl-3- (2-pyridyl) -1, 2, 4- triazine. The amount added is preferably in the range from 0.001 to 4% by weight relative to the aqueous solution of additives, which consists of deionized water and additives. If the amount is less than 0.001% by weight, no effect of addition occurs, while if it is more than 4% by weight, the abrasion rate of silicon oxide layer is also decreased to reduce the ratio of selection.

Further, according to the present invention, chemical bonds are formed between the silicon oxide layer hydrated with deionized water during the chemical mechanical polishing and the abrasive particles. Then, the hydrated silicon oxide layer having chemical bonds with the abrasive particles is removed from the surface by means of physical force of the abrasive pad. If an amine compound as a hydration accelerator of silicon oxide layer is added to the slurry, it is adsorbed onto the surface of the silicon oxide layer to enhance the hydration rate of the upper layer of the silicon oxide layer. By this way, chemical bonds with the abrasive particles can be easily achieved to result in improvement of rate of removing the silicon oxide layer. Preferable amine compound according to the present invention is one or more compound (s) selected from the group consisting of tetramethylammonium hydroxide, tetramethylammonium hydroxide pentahydrate, tetramethylammonium fluoride, tetramethylammonium fluoride tetrahydrate, tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, tetramethylammonium nitrate, tetramethylammonium sulfate hydrate, tetramethylammonium acetate, tetramethylammonium carbonate, tetramethylammonium formate, tetramethylammonium silicate, tetramethylammonium tetrafluoroborate, tetramethylammonium thioacetate, tetramethylammonium triacetoxyborohydride, tetramethylammonium borohydride, tetramethylammonium (1- hydroxyethylidine) pentacarbonylchromium, tetramethylammonium hexafluorophosphate, tetramethylammonium hydrogenphthalate and tetramethylammonium hydrogensulfate . The amount of said compound (s) used is in the range from 0.001 to 3% by weight relative to the entire aqueous solution of additives. If the amount is less than 0.001% by weight, no effect of addition occurs, while if it is more than 3% by weight, the aqueous solution of additives becomes alkaline, so that the pH range becomes out of the range from pH 6 to 8, when used in a mixture with the aqueous abrasive solution, becoming difficult to provide the property of selective abrasion. Since pH of the prepared solution plays a very important role to dispersion of the particles, hydrochloric acid, sulfuric acid, nitric acid and basic solution of potassium hydroxide, ammonia or the like are used to further adjust the pH. In the meanwhile, said abrasive composition and aqueous solution of additives are employed together with an appropriate amount of deionized water depending their abrasive properties, and the aqueous solution of additives is employed in an amount from 50 to 300 parts by weight, and deionized water from 0 to 500 parts by weight, on the basis of 100 parts by weight of the aqueous abrasive solution.

[Brief Description of Drawings] Fig. 1 is a graph showing particle distribution of cerium oxide abrasive composition prepared in Example 1 by using the cerium oxide ultra-microparticles prepared according to Preparation Example 1.

Fig. 2 is a graph showing particle distribution of cerium oxide abrasive composition prepared in Example 1 by using the cerium oxide ultra-microparticles prepared according to Preparation Example 2.

Fig. 3 is a graph showing particle distribution of cerium oxide abrasive composition prepared in Comparative Example 1 by using the cerium oxide ultra-microparticles prepared according to Preparation Example 1.

Fig. 4 is a graph showing particle distribution of cerium oxide abrasive composition prepared in Comparative Example 1 by using the cerium oxide ultra-microparticles prepared according to Preparation Example 2.

[Mode for Invention]

The present invention is further described by the following examples, which are provided for illustration only and are not intended to be limiting in any way.

[Preparation Example 1] Preparation of cerium oxide particles

Deionized water was preheated by heating and pressurizing at 400^°C under 240 bar with pumping through a tube having 9/16 inch of external diameter at a rate of 294.0 kg/hr. A solution of 21.0% by weight of cerium nitrate was pumped through a tube having 1/4 inch of external diameter at a rate of 24.5 kg/hr up to the pressure of 240 bar. A solution containing aqueous ammonia and nitric acid (by-product from cerium nitrate) in a molar ratio of 1.7:1 was pumped through a tube having 1/4 inch of external diameter at a rate of 24.5 kg/hr up to the pressure of 240 bar. The aqueous cerium nitrate solution, aqueous ammonia and preheated deionized water were mixed in a mixer under pressurized condition while maintaining the temperature at 383^°C, to carry out the reaction. At the latter end of a heat exchanger for cooling the hot reaction solution in the reaction device, two concentrating tanks each equipped with sintered filter having 0.5 μm of pore size are established and operated alternately. From each concentrating tank, 140 kg of concentrate was obtained after operating 4 hours, of which the concentration was 11.6% by weight. The concentrate was spray-dried to obtain powder. As the half value width of the main peak from powder X-ray diffraction was applied to Scherrer Equation, the powder was cerium oxide having about 30 nm of mean crystal size. Specific surface area according to BET was 13.41 m²/g. The impurities existing in said concentrate, as a result from analysis via ICP-MS, contained not more than 1 ppm of total content of alkali metal and alkaline earth metal, less than 1 ppm of other elements such as transition metal, respectively, and less than 5 ppm of total amount of lanthanides other than cerium. When the solution excluding any particles is analyzed by Ion Chromatography (IC), NO^3" concentration was 1.8 ppm, NO^2" concentration 0.2 ppm, NH⁴⁺ concentration 5.0 ppm, with no other ions detected.

[Preparation Example 2] Preparation of cerium oxide particles

Deionized water was preheated by heating and pressurizing at 400^°C under 240 bar with pumping through a tube having 1.0 inch of external diameter at a rate of 294.0 kg/hr. A solution of 21.0% by weight of cerium nitrate was pumped through a tube having 1/4 inch of external diameter at a rate of 24.5 kg/hr up to the pressure of 250 bar. A solution containing aqueous ammonia and nitric acid (by-product from cerium nitrate) in a molar ratio of 1.3:1 was pumped through a tube having 1/4 inch of external diameter at a rate of 24.5 kg/hr up to the pressure of 250 bar. The aqueous cerium nitrate solution, aqueous ammonia and preheated deionized water were mixed in a mixer under pressurized condition while maintaining the temperature at 386^°C, to carry out the reaction. At the latter end of a heat exchanger for cooling the hot reaction solution in the reaction device, two concentrating tanks each equipped with sintered filter having 0.5 μm of pore size are established and operated alternately. From each concentrating tank, 140 kg of concentrate was obtained after operating 4 hours, of which the concentration was 11.6% by weight. The concentrate was spray-dried to obtain a powdery sample. As the half value width of the main peak from powder X-ray diffraction was applied to Scherrer Equation, the powder was cerium oxide having about 45.0 nm of mean crystal size. Specific surface area according to BET was 5.91 m²/g.

The impurities existing in said concentrate, as a result from analysis via ICP-MS, contained not more than 1 ppm of total content of alkali metal and alkaline earth metal, less than total 1 ppm of other elements such as transition metal (most of them have the content below the detection limit), and less than 5.0 ppm of total amount of lanthanides other than cerium. When the solution excluding any particles is analyzed by Ion Chromatography (IC), NO^3" concentration was 0.5 ppm, NO^2~ concentration 0.1 ppm, NH⁴⁺ concentration 3.5 ppm, with no other ions detected.

[Example 1] Preparation of abrasive composition by using cerium oxide

In order to prepare cerium oxide slurry by using the two types of powdery samples prepared in Preparation Examples 1 and 2, 376 kg of ultra-pure water was charged into a container for ceria premixing, and 1.92 kg of solution of polyacrylic acid ammonium salt (solid content: 1.0% by weight) was slowly introduced to give a mixture. In the mixing tank equipped with a homogenizer of linear velocity of 3.7 m/s circulated in an internal circulating manner, the two types of samples prepared in Preparation Example 1 and 2 were introduced over 10 minutes through an input for cerium oxide aspirated in vacuo with stirring at 3500 rpm, to prepare mixed cerium oxide solution after stirring for 30 minutes. From the cerium oxide prepared in Preparation Example 1 and 2, premixed solution of cerium oxide 1 and 2 were prepared. The mixed solution of cerium oxide prepared was passed through a prefilter to filter off the large particles. After filtration, high pressure dispersion process was performed in order to prevent agglomeration of secondary agglomerated cerium oxide particles. Dispersion was carried out in a colliding manner through minute passage under 100 MPa of dispersing pressure. After dispersing, a cerium oxide abrasive composition for semiconductor having narrow and uniform particle distribution was obtained through a final filter having 1 micron size, for each cerium oxide prepared from Preparation Example 1 and 2 as chemical mechanical cerium oxide polishing composition 1 and 2.

LA-910 instrument from Horiba was employed. As shown in Fig. 1, the results of measurement using Horiba equipment, the median particle size was taken as the size located in the middle of the size distribution in terms of volume percentage of each particle (D₅o) , and the maximum particle size was taken as the highest value (Dioo). Zeta potential was measured by using ELS 8000 instrument from Otsuka. The results are shown in Table 1.

[Comparative Example 1] Preparation of abrasive composition by using cerium oxide

In order to prepare cerium oxide slurry by using the two types of powdery samples prepared in Preparation Examples 1 and 2, 376 kg of ultra-pure water was charged into a container for ceria premixing, and 1.92 kg of solution of polyacrylic acid ammonium salt (solid content: 1.0% by weight) was slowly introduced to give a mixture. In the mixing tank equipped with a homogenizer of linear velocity of 3.7 m/s circulated in an internal circulating manner, the two types of samples prepared in Preparation Example 1 and 2 were introduced over 10 minutes through an input for cerium oxide aspirated in vacuo with stirring at 3500 rpm, to prepare premixed cerium oxide abrasive composition after stirring for 30 minutes. From the cerium oxide prepared in Preparation Example 1 and 2, abrasive composition 1 and 2 were prepared.

LA-910 instrument from Horiba was employed. As shown in Fig. 2, the results of measurement using Horiba equipment, the median particle size was taken as the size located in the middle of the size distribution in terms of volume percentage of each particle (D₅₀) , and the maximum particle size was taken as the highest value (D100) • Zeta potential was measured by using ELS 8000 instrument from Otsuka. The results are shown in Table 1.

[Table 1] Particle size of cerium oxide abrasive composition (measured)

Comp. Ex. Ex. 1 Comp. Ex. 1 Ex. 1 1

Process for preparing Prep. Ex. Prep. Ex. Prep. Ex. 2 Prep. Ex. cerium oxide 1 1 2

[Example 2] Abrasion of silicon oxide layer and silicon nitride

To deionized water, added were 1.5% by weight of polyacrylic acid polymer, 2% by weight of triazine compound as a nitrogen-containing organocyclic compound and 1% by weight of tetramethylammonium hydroxide as a amine compound. In order to increase the selectivity, pH of the solution of additives was adjusted to pH 7 by using hydrochloric acid. Three hundred (300) parts by weight of the aqueous solution of additives and 300 parts by weight of deionized water were mixed with 100 parts by weight of the abrasive composition prepared in Example 1 and Comparative Example 1, respectively, to prepare slurry. By using the mixed slurry, a blanket silicon wafer (6 inch diameter) having 1.0 micron of silicon oxide film layer applied by using chemical vapor-deposition of TEOS precursor was abraded in a CMP abrasive equipment manufactured by GNP with Rodel SUVA IV pad. The abrasion condition was 3.5 psi of drop pressure; 60 rpm of table speed; and 60 rpm of head speed; 20^°C of temperature; and 150 cc/min of flow rate of slurry, for 1 minute. After abrasion and washing with deionized water, the amount of silicon oxide layer removed from the surface of the silicon wafer was measured by using an optical interferometer, to determine the removal rate expressed as the thickness of silicon oxide layer (A) per minute.

To examine the surface defect, the defect of surface after the chemical mechanical polishing was measured by using the

Surfscan device from KLA. The number of 6-in wafers wherein the size of defect was from 0.25 μm to 2.56 μm was counted and the results are shown in Table 2.

A blanket silicon wafer (6 inch diameter) having a silicon nitride film layer of 0.3 micron thickness applied by using low pressure chemical vapor-deposition was abraded by using the same slurry. After abrasion, the amount of silicon nitride layer removed from the surface of the silicon wafer was measured by using an optical interferometer, to determine the removal rate expressed as the thickness of silicon nitride (A) per minute. The abrasion rate and selectivity of silicon nitride layer to silicon oxide layer are shown in Table 2 below:

[Table 2] Evaluation of abrasion properties of slurry compositions

[industrial Applicability]

As described above, the present invention could provide chemical mechanical cerium oxide polishing solution for semiconductor having a small median particle size and maximum particle size, by employing a supercritical process, which enables production of high-purity product with easier controlling of the size of the primary particles of ultra-micro cerium oxide having nano size as compared to that of conventional technique, and by mixing dispersing additives to prevent the agglomeration or aggregation of particles in a high pressure dispersing device of collision mode.

By virtue of incorporating a nitrogen-containing organocyclic compound, a carboxylic acid polymer compound and an amine compound, the slurry shows suitable properties for use in shallow trench isolation, having high ratio of selection between silicon oxide layer and silicon nitride layer. The cerium oxide slurry in which median particles and large particles has been reduced by using high pressure dispersing stage is effective on noticeably reducing the defects such as scratch occurred after the semiconductor processing.

Claims

What is claimed is:

1. A process for preparing chemical mechanical polishing slurry for shallow trench for semiconductor, which comprises the steps of a) preparing a mixture by mixing cerium oxide ultra- microparticles, deionized water and dispersant; b) filtering the mixture through a filter; c) dispersing the filtered mixture under high pressure; d) filtering the dispersed mixture through a filter to prepare an abrasive composition; and e) mixing from 50 to 300 parts by weight of aqueous solution of additives to 100 parts by weight of the abrasive composition.

2. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein said cerium oxide ultra- microparticles are prepared by the steps of: a) reacting pre-heated and pre-pressurized deionized water, a solution of metal salt containing from 0.01 to 20% by- weight of cerium salt based on the total reactant, and ammonia-containing fluid in a continuous reactor at a temperature from 250 to 700^°C under a reaction pressure from 180 to 550 bar for 0.01 second to 10 minutes to obtain a solution containing cerium oxide ultra- microparticles; and b) concentrating the solution containing the cerium oxide ultra-microparticles in a concentrating tank equipped with a filter having pore size from 0.01 to 10 μm.

3. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein said aqueous solution of metal salt further comprises water-soluble metal nitrate salt containing at least one metal component (s) selected from the group consisting of zinc, cobalt, nickel, copper, iron, aluminum, titanium, barium and manganese.

4. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein said cerium salt is cerium nitrate, ammonium cerium nitrate or a combination thereof.

5. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein the molar ratio of ammonia concentration of said ammonia-containing fluid to the concentration of the nitrogen compound produced during the reaction of the aqueous solution of the metal salt is from 0.5 to 3.0.

6. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein said ultra-microparticles has the half width of main peak (FWHM) in terms of crystalline particle diameter by X-ray diffraction of 0.016 to 3.5°, the calculated value of the crystallite according to Scherrer Equation of 1 to 1000 rim, mean particle diameter of primary particles according to SEM or TEM image analysis of 1 to 1000 nm, specific surface area by BET method of 2 to 200 m²/g, TREO (total rare-earth oxide) of 99% or more, and CeO₂/TREO of 95% or more.

7. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein the solution containing cerium oxide ultra-microparticles are concentrated to 1 to 50% by weight during said concentrating step.

8. A process for preparing chemical mechanical polishing slurry according to claim 7, wherein the solution containing cerium oxide ultra-microparticles are concentrated to 1 to 30% by weight during said concentrating step.

9. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein the pore size of said filter is from 0.1 to 5 μm.

10. A process for preparing chemical mechanical polishing slurry according to claim 2, wherein said cerium oxide ultra- microparticles contain not more than 10 ppm of alkaline metal and alkaline earth metal, respectively, not more than 10 ppm of transition metal and other impurities, respectively, and not more than 10 ppm of ionic impurities, respectively.

11. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein the dispersant is one or more substance (s) selected from the group consisting of polyacrylic acid ammonium salt, polymethacrylic acid ammonium salt, polyacrylic acid amine salt, polymethacrylic acid amine salt, poly (ethylene-co-acrylic acid) ammonium salt, poly (ethylene-co-acrylic acid) amine salt, poly (ethylene-co- methacrylic acid) ammonium salt or poly (ethylene-co-methacrylic acid) amine salt.

12. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein the pore size of the filter in step b) is from 1 to 50 μm.

13. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein the dispersion step is carried out under a high pressure of 50 to 200 MPa.

14. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein the dispersion step is carried out by passing the mixture through minute passages repeatedly from once to 10 times.

15. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein the pore size of the filter in step d) is from 0.5 to 5 μm.

16. A process for preparing chemical mechanical polishing slurry according to claim 1, wherein the aqueous solution of additives consists of deionized water, from 0.001 to 5% by weight of poly (meth) acrylic acid polymer, from 0.001 to 4% by weight of nitrogen-containing organocyclic compound and from 0.001 to 3% by weight of amine compound.

17. A process for preparing chemical mechanical polishing slurry according to claim 16, wherein the poly (meth) acrylic acid polymer is one or more polymer (s) selected from the group consisting of poly (acrylic acid), poly (methacrylic acid), poly (ethylene-co-acrylic acid) and poly (ethylene-co-methacrylic acid) .

18. A process for preparing chemical mechanical polishing slurry according to claim 16, wherein the nitrogen-containing organocyclic compound is one or more compound (s) selected from the group consisting of 1, 3, 5-triazine, 1, 3, 5-triazine-2, 4, 6- triol (cyanuric acid), 1, 3, 5-triazine-2, 4, β-trichloride (cyanuric chloride) , 1,3, 5-triazine-2,^'4, 6-trithiol ( trithiocyanuric acid) , 1, 3, 5-triazine-2, 4, 6-trithiol sodium salt, 1, 3, 5-triazine-2, 4, 7- trithiol trisodium salt nonahydrate, 3, 5, 7-triamino-s- triazolo[4,3-a]-s-triazine, 1_/3, 5-triacryloylhexahydro-l, 3,5- triazine, 2, 4 , β-triaryloxy-1, 3, 5-triazine, triallyl-1, 3, 5- triazine-2, 4 , 6- ( IH, 3H, 5H) -trione, 5-azacytidine, 5-azacytosine, 4-amino-l-β-D-arabinofuranosyl-l, 3, 5-triazine-2 (IH) -one, cyanuric fluoride, 2-chloro-4, 6-dimethoxy-l, 3, 5-triazine, 2,4,6- triallyloxy-1, 3, 5-triazine, 2, 4, 6-triphenyl-l, 3, 5-triazine, 2- chloro-4, 6-diamino-l, 3, 5-triazine, melamine, 2,4,6-tri(2- pyridyl) -1,3, 5-triazine, 2,4,6-tris(l' -aziridinyl) -1,3, 5-triazine, 1, 2, 4-triazine-3, 5 (2H, 4H) -dione ( 6-azurasyl) , 6-aza-2-thymine, 6- aza-2-thiothymine, 6-aza-2-thiouridine, 6-azauracil, 3-amino-5, 6- dimethyl-1, 2, 4-triazine, 3- (2-pyridyl) -5, 6-diphenyl-l, 2, 4- triazine, 3- (2-pyridyl) -5, 6-bis (5-sulfo-2-furyl) -1,2, 4- triazinedisodium salt trihydrate, 3- (2-pyridyl) -5, 6-diphenyl- 1, 2, 4-triazine-p, p' -disulfonic acid monosodium salt hydrate and 5, 6-di-2-furyl-3- (2-pyridyl) -1,2, 4-triazine.

19. A process for preparing chemical mechanical polishing slurry according to claim 16, wherein the amine compound is one or more compound (s) selected from the group consisting of tetramethylammonium hydroxide, tetramethylammonium hydroxide pentahydrate, tetramethylammonium fluoride, tetramethylammonium fluoride tetrahydrate, tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, tetramethylammonium nitrate, tetramethylammonium sulfate hydrate, tetramethylammonium acetate, tetramethylammonium carbonate, tetramethylammonium formate, tetramethylammonium silicate, tetramethylammonium tetrafluoroborate, tetramethylammonium thioacetate, tetramethylammonium triacetoxyborohydride, tetramethylammonium borohydride, tetramethylammonium (1- hydroxyethylidine) pentacarbonylchromium, tetramethylammonium hexafluorophosphate, tetramethylammonium hydrogenphthalate and tetramethylammonium hydrogensulfate .

20. A process for preparing chemical mechanical polishing slurry according to any one of claims 1 to 19, wherein said chemical mechanical slurry further comprises deionized water in an amount up to 500 parts by weight relative to the abrasive composition.

21. A process for preparing chemical mechanical polishing slurry according to any one of claims 1 to 19, wherein said chemical mechanical polishing slurry comprises one or more pH adjusting agent selected from hydrochloric acid, sulfuric acid, nitric acid, KOH and ammonia, to make the pH in the range from 6 to 8.

22. Shallow trench polishing cerium oxide slurry for semiconductor having excellent property of reducing scratch, which is prepared in accordance with any one of claims 1 to 19.

23. Shallow trench polishing cerium oxide slurry for semiconductor having excellent property of reducing scratch, which is prepared in accordance with claim 20.

24. Shallow trench polishing cerium oxide slurry for semiconductor having excellent property of reducing scratch, which is prepared in accordance with claim 21.