KR20070073411A - Method for preparing cerium oxide for polishing of a semiconductor thin film - Google Patents

Abstract

A method for manufacturing a cerium oxide for polishing a semiconductor thin film is provided to polish effectively a high stepped part of the semiconductor thin film by increasing the number of polishing particles in a polishing process. A method for manufacturing a cerium oxide includes a process for baking a precursor of the cerium oxide and a lipid-containing material within a receptacle for shielding external air. The baking process for the precursor of the cerium oxide is performed at the temperature of 600 to 1000 degrees centigrade. The lipid-containing material corresponds to 0.05 to 20 weight percent on the basis of weight percent of the precursor of the cerium oxide.

Description

Method for manufacturing cerium oxide for semiconductor thin film polishing {METHOD FOR PREPARING CERIUM OXIDE FOR POLISHING OF A SEMICONDUCTOR THIN FILM}

1 is a photograph of the cerium oxide particles prepared in Example 1 according to the present invention with a transmission electron microscope (TEM),

2A and 2B are schematic views of a patterned wafer used in evaluating step removal force, which is a kind of polishing property, in which FIG. 2A corresponds to a top view and FIG. 2B corresponds to a sectional view.

The present invention relates to a method for producing a cerium oxide for polishing a semiconductor thin film, a cerium oxide prepared by the method and a polishing slurry comprising the same.

During chemical mechanical polishing (CMP) of semiconductor thin films, cerium oxide aqueous slurry, which is a slurry made by dispersing cerium oxide in an aqueous suspension, is mainly used.In recent years, as the wiring of semiconductor processes has become increasingly finer and the spacing between chips decreases, Slurry is required to reduce the frequency and size of scratches. Therefore, many efforts have been made to reduce the occurrence of scratches in the polished film by reducing the particle size of cerium oxide.

However, when the average particle diameter of the cerium oxide abrasive grains is reduced to reduce scratches, a decrease in the amount of polishing reduces production, increases the consumption of the polishing slurry, and deteriorates the flatness of the entire surface of the wafer.

Therefore, in order to compensate for this problem when polishing a semiconductor thin film having a large step pattern, polishing is performed for a predetermined time by using a silica slurry having a higher polishing rate than a cerium oxide slurry to remove the step, and subsequently polishing with a cerium oxide slurry. The method of carrying out was studied. However, even in this case, although the problem can be solved in terms of the consumption amount of the cerium oxide slurry, unlike the ceria slurry, in the case of the silica slurry, the gelled particles are re-dispersed by distilled water or the like and adhere to the pad or the polisher site. Since the cerium oxide slurry is used after the pad is replaced, the grinding machine may not be operated to replace the pad, thus adversely affecting productivity.

On the other hand, cerium oxide is usually produced in large quantities by firing the cerium oxide precursor at a high temperature, wherein the cerium oxide particles are grown as crystals as the cerium oxide precursor is oxidized and the gas is released, and the size thereof is generally proportional to the firing temperature. do. When the cerium oxide thus prepared is dispersed in water to prepare the polishing slurry, the primary particles are separated by being separated alone, and the secondary particles dispersed by 2 to 5 aggregates are mixed. The type of dispersion of these particles depends on the dispersing agent and the method of dispersing the slurry, but a large number of crystals are agglomerated to form secondary particles rather than when each of the crystals are dispersed.

Therefore, in order to avoid scratches on the polished film during polishing, when a certain pressure is applied to the particles, the crystals and the aggregated portions of the secondary particles must be broken to avoid serious scratches, that is, scratches on the polished film. However, in the case of the cerium oxide produced so far, the secondary particles were difficult to be easily broken due to the pressure during polishing.

Accordingly, an object of the present invention is to provide a method for producing cerium oxide, which can reduce the occurrence of scratches on a polished film while showing a high polishing amount, of a cerium oxide prepared by the method and a semiconductor thin film having a large step pattern including the same. It is to provide a polishing slurry suitable for polishing.

In accordance with the above object, the present invention provides a method for producing a cerium oxide for polishing a semiconductor thin film, comprising firing a cerium oxide precursor together with a lipid-containing material in a vessel in which external air is blocked from entering.

Hereinafter, the present invention will be described in detail.

The method for producing cerium oxide according to the present invention is characterized in that during firing of the cerium oxide precursor, firing is performed while blocking the inflow of external air after adding the lipid-containing material.

According to the present invention, a cerium oxide precursor such as cerium carbonate, cerium hydroxide, cerium nitride, cerium chloride, cerium acetate, and the like is placed in a container such as a crucible together with a lipid-containing material and covered with a lid to block the atmosphere inside the container from outside air. The desired cerium oxide powder may be prepared by firing at 600 to 1000 ° C. for 30 minutes to 8 hours and then milling in a conventional grinding process.

The lipid-containing material added to the cerium oxide precursor can be used in an amount of 0.05 to 20% by weight, preferably 0.1 to 10% by weight, based on the weight of the cerium oxide precursor, and representative examples thereof are stearic acid, oleic acid and glycerol. , Lecithin, triglycerol, wax and mixtures thereof.

Since the lipid-containing material is carbonized at a temperature of 550 ° C. or higher, the firing temperature is preferably controlled in the range of 600 to 1000 ° C. to appropriately grow the cerium oxide particles and induce carbonization of the lipid-containing material. Upon firing the cerium oxide precursor, the lipid-containing material is thermally decomposed into carbon dioxide and water to increase the gas partial pressure in the vessel (crucible), and as the pressure in the vessel increases, the rate at which the cerium oxide precursor is oxidized is slowed. As the oxidation rate of the cerium oxide precursor is slowed, the gas is discharged into the fine pores, and the gas is gradually released while the pores remain without collapse. If calcination is carried out in a state of rapid heating or high oxygen partial pressure, the cerium oxide precursor undergoes a phase transition, and the oxidation reaction is accelerated, the gas is rapidly discharged and the fine pores are collapsed. As a result, cerium oxide grows. When using the cerium oxide particles thus prepared, it is difficult to achieve scratch reduction in a fine pattern of 90 nm or less.

In the present invention, the firing process should be carried out to close the contact with the outside air by covering the lid of the container containing the cerium oxide precursor and the lipid-containing material in order to induce uniform growth of the cerium oxide particles. When the container is opened and calcined, the gas partial pressure inside the vessel does not increase, and thus fine pores are not formed in the cerium oxide particles produced, and the lipid-containing material is formed even after firing after adding the lipid-containing material. The same result is obtained when no addition is made.

The cerium oxide particles obtained through the firing process have a size of 10 to 100 µm, and the cerium oxide particles are composed of crystals having a particle diameter of 50 to 90 nm.

Furthermore, these cerium oxide particles can be finely divided into smaller sizes by milling through conventional grinding processes such as ball milling. Lipid-containing materials added during firing are all removed during the firing process, so this is not a problem at all during the milling process.

The cerium oxide powder of the present invention obtained through the above-described firing and milling process has a crystal size of 20 to 60 nm and a specific surface area (BET value) of 1 to 10 m ² / g. In addition, as calculated from the obtained BET value, the cerium oxide powder of the present invention has a micropore volume of 0.04 to 0.1 cm ³ / g and a density of 6.0 to 7.2 g / cm ³ . In this case, when the density of the cerium oxide powder is less than 6.0 g / cm ³ , the polishing amount is likely to decrease, and when the cerium oxide powder exceeds 7.2 g / cm ³ , the polishing amount is high, but an increase in scratch is expected, which is not preferable.

According to the present invention, the cerium oxide polishing slurry according to the present invention can be produced by dispersing the cerium oxide powder thus obtained in distilled water. In this case, the polishing slurry may include cerium oxide powder in an amount of 0.5 to 20% by weight based on the total weight, and the dispersion may be performed according to a conventional method and is not particularly limited.

The cerium oxide particles in the polishing slurry have an average primary particle diameter of 20 to 60 nm and an average secondary particle diameter of 200 to 1000 nm, preferably 250 to 500 nm. When the slurry is prepared using the cerium oxide particles prepared by uniformly mixing the lipid components during firing and firing as in the present invention, the density is relatively low compared to the particle size, so that the number of particles is relatively high at the same size and concentration, When the particles reach a certain pressure during polishing, they can easily collapse and reduce scratches on the polished finish. In addition, when compared to a slurry composed of secondary particles having a particle diameter smaller than 200 nm, the secondary particles having a particle diameter in the range of 200 to 1000 nm have a high speed of spreading the slurry throughout the pad by centrifugal force as the pad rotates, The space between the wafer and the wafer is wide, and the slurry flows actively. As such, when the slurry flows quickly, uniform polishing is possible on the entire wafer, and even when the particles of the slurry are trapped in the constricted portion due to the step, the particles can easily come out, thereby improving the step removal force.

The polishing slurry of the present invention may include a dispersant to improve the particle stability of the abrasive particles and to have a stable dispersion for a long time. The dispersant is preferably selected in consideration of the surface potential value of cerium oxide in water, but there is no particular limitation. Dispersion of cerium oxide is usually in the range of pH 3 to 9, wherein the surface potential value of cerium oxide has a positive value, an anionic organic compound can be preferably used as the dispersant. Specific examples of the dispersant usable in the present invention include polyacrylic acid, polyvinyl sulfuric acid, polymethacrylic acid, polyacrylamide, polyarylamine and salts thereof. The dispersant preferably has a weight average molecular weight of 250,000 or less, and when the molecular weight exceeds 250,000, the viscosity of the slurry is increased, so that the flowability is not good, so that the flow rate may not be maintained, which may cause problems in the process. The dispersant is preferably added in an amount of 0.1 to 10% by weight based on the dry weight of the cerium oxide powder, if less than 0.1% by weight it is difficult to secure the dispersion stability of the slurry, if more than 10% by weight of oxidation It does not adsorb | suck to a cerium surface and remains in a slurry liquid, and long-term stability is easy to be inhibited.

As described above, the cerium oxide polishing slurry according to the present invention has a low frequency of scratches and a large size of the abrasive grains, so that the abrasive grains are not recessed in the pattern region. Since the number of abrasive particles participating in polishing increases as they are easily broken, it can be usefully used for polishing a semiconductor thin film having a large step difference pattern.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention, and the content of the present invention is not limited by the following examples.

Example 1

20 kg of cerium carbonate and 200 g of stearic acid were mixed in a stirrer for 10 minutes, and then the mixed powder was placed in an alumina crucible, covered with a lid, and calcined at 750 ° C. for 4 hours. The powder and salt obtained by baking were mixed at a mass ratio of 5: 5, put in a ball mill, and then milled at 100 rpm for 60 minutes. The milled powder was washed with distilled water to remove salt from the powder to obtain cerium oxide powder. The photograph which observed the cerium oxide powder obtained after baking with the scanning electron microscope (SEM) is shown in FIG.

Polymethacrylammonium salt (average molecular weight 16,000) was added to the obtained cerium oxide powder in an amount of 5% by weight relative to the cerium oxide powder, and a predetermined amount of distilled water was added thereto, followed by stirring for 30 minutes. The resulting slurry was dispersed at a pressure of 150 MPa using a high-pressure impact disperser, and then aggregated 0.8 μm or more particles were removed using a cyclone, and a microless 3 μm depth type filter was used. Finally, large particles were removed. Thereafter, a predetermined amount of distilled water was added to prepare a cerium oxide slurry containing cerium oxide at a concentration of 5% by weight.

Example 2

A cerium oxide slurry was prepared in the same manner as in Example 1, except that cerium hydroxide was used instead of cerium carbonate.

Example 3

A cerium oxide slurry was prepared in the same manner as in Example 1, except that glycerol was used instead of stearic acid.

Example 4

A cerium oxide slurry was prepared in the same manner as in Example 1, except that oleic acid was used instead of stearic acid.

Example 5

A cerium oxide slurry was prepared in the same manner as in Example 1 except that firing was performed at 900 ° C.

Comparative Example 1

A cerium oxide slurry was prepared in the same manner as in Example 1 except that stearic acid was not used.

Comparative Example 2

A cerium oxide slurry was prepared in the same manner as in Example 1, except that the crucible lid was not covered.

Comparative Example 3

A cerium oxide slurry was prepared in the same manner as in Example 1 except that firing was performed at 500 ° C.

Measurement of Properties of Cerium Oxide Particles in Slurries

For each of the cerium oxide slurries obtained in Examples 1 to 5 and Comparative Examples 1 to 3, an average particle diameter of crystal grains (primary particles) was determined by X-ray diffraction (XRD) analysis. The average particle diameter of the secondary particles was measured using LA910 as a particle size distribution analyzer, and the specific surface area of the cerium oxide particles was measured by BET (Micromeritics Tristar), and the density and pores were measured therefrom. 1 is shown.

Evaluation of Polishing Properties of Slurry

First, on an 8-inch silicon wafer, PE-CVD (plasma enhanced-chemical vapor deposition) method using TEOS (tetraethyl orthosilicate), ie, a thickness of 10,000Å by PE-TEOS process A silicon film was formed into a film, and the to-be-finished film was produced.

Each cerium oxide slurry obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was diluted to a concentration of 1% by weight of cerium oxide and used as a polishing liquid. The grinder was an 8-inch CMP grinder, which was polished for 90 seconds using the IPEC472 device (Speedfam-IPEC) at a pressure of 4 psi. At this time, the cerium oxide slurry was supplied at a rate of 500 ml / min, the rotation speed of the upper plate wafer head was 28 rpm, and the rotation speed of the lower plate was 80 rpm. The pad used was an IC1000 / suba IV laminated pad manufactured by Rodel, USA.

Grinding amount and scratch evaluation

After polishing of the finish, the number of scratches was measured using AIT-XP, a scratch evaluation equipment of KLA-Tenco, USA, and the Derma-Wave Optipro 300 series (Therma-Wave), Therma-wave, USA The amount of polishing was measured from the film thickness before and after polishing using wave Optiprobe 300 series), and is shown in Table 1 below.

<Step clearance evaluation>

Evaluation of the step removal force measured the amount of polishing after one minute polishing of the patterned wafer as schematically shown in FIGS. 2A (top view) and FIG. 2B (section view).

From the above Table 1, the cerium oxide slurry prepared in Examples 1 to 5 of the present invention not only has a significantly low frequency of scratches at the time of polishing, but also has a considerably high level of polishing amount of at least 4000 Pa / min. In this case, the polishing amount was sufficient, but the scratch occurrence frequency was high, and in Comparative Example 3, it was confirmed that the polishing amount was insufficient because the average particle diameter was too small.

In addition, in the step removal force, the cerium oxide slurry prepared in Examples 1 to 5 of the present invention showed excellent performance, whereas in Comparative Example 3, the polishing amount was insufficient to polish compared to the case of polishing a wafer without a pattern. The amount was even lower.

As described above, the polishing slurry containing cerium oxide prepared according to the present invention has a low frequency of scratch generation, and has a large abrasive grain size, so that the abrasive grains are not recessed in the pattern region, and subjected to high pressure in the region. As the amount is increased and the aggregated secondary particles are easily broken, the number of abrasive particles participating in polishing increases, and thus, it can be usefully used for polishing a semiconductor thin film having a large step pattern.

Claims (14)

10. A method for producing cerium oxide, comprising calcining a cerium oxide precursor together with a lipid-containing material in a vessel where external air is blocked from entering. The method of claim 1, Firing is carried out at 600 to 1000 ° C., the method of producing cerium oxide. The method of claim 1, A process for producing cerium oxide, characterized in that the lipid-containing material is used in an amount of 0.05 to 20% by weight, based on the weight of the cerium oxide precursor. The method of claim 1, A process for producing cerium oxide, characterized in that the lipid-containing material is selected from the group consisting of stearic acid, oleic acid, glycerol, lecithin, triglycerol, waxes and mixtures thereof. The method of claim 1, A process for producing cerium oxide, characterized in that the cerium oxide precursor is selected from the group consisting of cerium carbonate, cerium hydroxide, cerium nitride, cerium chloride, cerium acetate and mixtures thereof. The method of claim 1, A method for producing cerium oxide, comprising performing milling following firing. Cerium oxide having a specific surface area of 1 to 10 m ² / g, prepared by the method of any one of claims 1 to 6. The method of claim 7, wherein Cerium oxide, characterized in that it has a micropore volume of 0.04 to 0.1 cm ³ / g and a density of 6.0 to 7.2 g / cm ³ . A polishing slurry comprising the cerium oxide of claim 7 as an abrasive. The method of claim 9, A cerium oxide having an average primary particle size of 20 to 60 nm and an average secondary particle size of 200 to 1000 nm. The method of claim 9, A polishing slurry comprising cerium oxide in an amount of 0.5 to 20% by weight based on the total weight. The method of claim 9, And a dispersant which is an anionic organic compound having an average molecular weight of 250,000 or less. The method of claim 12, And the dispersant is selected from the group consisting of polyacrylic acid, polyvinylsulfuric acid, polymethacrylic acid, polyacrylamide, polyarylamine and salts thereof. The method of claim 12, Polishing slurry, characterized in that the dispersant is included in the range of 0.1 to 10% by weight relative to the dry weight of cerium oxide.

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