KR20040095118A - Chemical mechanical polishing slurry for shallow trench isolation - Google Patents

Abstract

PURPOSE: A chemical-mechanical polishing slurry for shallow trench isolation is provided to improve polishing selectivity in a silicon oxide film, polishing rate and dispersion stability of polishing grains. CONSTITUTION: The chemical-mechanical polishing slurry for shallow trench isolation comprises deionized water, a polishing grain, a pH controlling agent, a carboxylic acid-based polymeric compound and a phosphate ester type compound, wherein based on 100pts.wt of an aqueous slurry of the deionized water, the polishing grains and the pH controlling agent, 0.001-5pts.wt of the carboxylic acid-based polymeric compound is used, and 0.001-1pts.wt of the phosphate ester type compound is used, wherein the polishing grain is ceria, alumina, silica and titania.

Description

Chemical mechanical polishing slurry for shallow trench isolation

FIELD OF THE INVENTION The present invention relates to chemical mechanical polishing slurries for the isolation of shallow trench elements, and more particularly to chemical mechanical polishing slurries useful for the selective removal of silicon oxide films used in semiconductor devices, particularly shallow trench device isolation.

In recent years, with the development of semiconductor technology, the miniaturization and high integration of devices have been accelerated. In the case of a memory semiconductor, as the degree of integration increases, the position of the capacitor is changed from the CUB (Capacitor Under Bit line) to the COB (Capacitor Over Bit line) in order to increase the capacity of the capacitor. Since the process is changed to a "cylinder" structure and a stacking process is continuously performed by using multi-layered wiring in a logic chip, a surface step occurs in the wafer after such a process. This surface step causes many problems in subsequent processes. In order to eliminate these problems, a chemical-mechanical polishing (CMP) process is introduced and planarized.

One process in which a chemical mechanical polishing process is used is shallow trench isolation. Shallow trench device isolation is a method of separating active regions during semiconductor device fabrication. It deposits a silicon oxide film and a silicon nitride film on the silicon, forms a trench to the silicon through etching, and then gap-fills the silicon oxide film, and then planarizes it by chemical mechanical polishing to secure a desired active region. It is a technique to do. However, the silicon oxide film and the silicon nitride film are exposed by chemical mechanical polishing after the silicon oxide film gap-fill in the trench. In this case, the use of a slurry having a low removal selectivity will increase the removal amount of the silicon nitride film. Here, the removal selectivity means the removal rate ratio of the silicon nitride film to the removal rate of the silicon oxide film. Loss of silicon nitride causes variation in the thickness of the field oxide and reduces the over-polishing margin.

According to US Pat. No. 5,738,800 to Hosali et al., A CMP slurry is a complexing agent having at least two functional groups having an aqueous medium, abrasive particles, a surfactant, and separable both complexed with a silicon oxide film and a silicon nitride film, respectively. It includes. According to this patent, surfactants used with complexing agents in CMP slurries do not perform the function of conventional surfactants (i.e. stabilization of the particulate dispersion) but affect the rate of removal of the silicon nitride film from the composite surface. It is believed to be. The interaction chemistry between the surfactant and the complexing agent has not been described. According to this patent, the slurry composition shows better selectivity than conventional CMP slurries, but only within a narrow pH range (about 6 to about 7).

US Pat. No. 5,759,917 to Grover et al. Discloses a CMP slurry for selectively polishing an overfilled silicon oxide film prior to the silicon nitride film anti-polishing layer during fabrication of integrated circuits and semiconductors. According to Grover et al. CMP slurries include carboxylic acids, salts, and cerium compounds that are soluble at a pH in the range of about 3-11. According to this patent, removal selectivity of silicon nitride film to silicon oxide film of about 5 to about 100 can be obtained, but the highest reported selectivity in the examples was 34.89 and substantially less than 20 in most examples. .

Korean Patent Application No. 2000-074748 discloses a carboxylic acid functional group and a second functional group selected from amines and halides for use in selectively removing a silicon oxide film in preference to a silicon nitride film from the surface of a product by chemical-mechanical polishing. An aqueous slurry comprising both an organic compound (amino acid) and abrasive particles having both is disclosed, but the removal selectivity tends to be low.

Thus, in the present invention, the above problems can be solved by adding a carboxylic acid polymer compound and a phosphate ester compound, which is a silicon oxide film hydration accelerator, to increase the removal selectivity to the polishing slurry, and the present invention has been completed based on this.

Accordingly, it is an object of the present invention to provide a chemical mechanical polishing slurry having a high removal selectivity and an excellent removal rate for shallow trench device isolation.

The chemical mechanical polishing slurry according to the present invention for achieving the above object is a shallow chemical device for chemical trench polishing slurry separation device comprising deionized water, abrasive particles and pH controller, the slurry is an aqueous solution consisting of deionized water and abrasive particles 0.001 to 5 parts by weight of a carboxylic acid polymer compound and 0.001 to 1 part by weight of a phosphate ester compound based on 100 parts by weight of the slurry.

1 is a graph showing the change in the zeta potential of the surface of the semiconductor substrates with the pH change when the carboxylic acid polymer is added to the chemical mechanical polishing slurry according to the present invention and when the carboxylic acid polymer is not added.

FIG. 2A is a SEM photograph showing the extent of abrasive particles adsorbed on the surface of a silicon nitride film of a chemical mechanical polishing slurry without addition of a carboxylic acid polymer,

Figure 2b is a SEM photograph showing the extent of the abrasive particles adsorbed on the surface of the silicon nitride film of the chemical mechanical polishing slurry to which the carboxylic acid polymer is added according to the present invention.

3 is a graph showing scattering intensity distribution of ceria particles with and without addition of a carboxylic acid polymer to the chemical mechanical polishing slurry according to the present invention.

Looking at the present invention in more detail as follows.

As described above, the chemical mechanical polishing slurry according to the present invention is deionized water, abrasive particles, pH controller, a carboxylic acid polymer compound for increasing the removal selectivity, and a phosphate ester which is a silicon oxide hydration accelerator ( phosphate ester) compounds.

The deionized water used in the present invention has mostly removed impurities such as ions, fine particles, and organic matter, and the resistivity of the deionized water is preferably about 5 to 18 ㏁cm. The amount of deionized water used is preferably 70 to 99.99% by weight based on the aqueous slurry composed of deionized water and abrasive particles.

The abrasive particles used in the aqueous slurry according to the present invention perform a mechanical polishing function. The abrasive particles used in the aqueous slurry may include any one or a mixture of various abrasive particles commonly used in CMP slurries. Examples of suitable abrasive particles are alumina, ceria, copper oxide, tin oxide, nickel oxide, manganese oxide, silica, silicon carbide, silicon nitride, tin oxide, titania, titanium carbide, tungsten oxide, yttria, and zirconia, and combinations thereof It includes. Preferred abrasive particles for the present invention are at least one selected from the group consisting of ceria, alumina, silica and titania.

The abrasive particles preferably have an average size in the range of about 0.02 to about 1.0 micrometers, with a maximum size of about 10 micrometers. The particle size is not critical by itself, but it will be understood that if the particles are too small, the polishing rate of the slurry may be unacceptably slow. On the other hand, it will be understood that if the particles are too large, unacceptable scratches may occur on the surface of the particles to be polished. The abrasive particles may be present in an amount of 0.01 to 30% by weight of the slurry, with 0.5 to 10% by weight being the optimal range.

According to the present invention, the carboxylic acid polymer compound for increasing the removal selectivity is adsorbed on the silicon nitride film to bring about a change in the surface zeta potential. This can reduce the removal rate of the silicon nitride film by reducing the number of contact sites between the silicon nitride film and the abrasive particles. In addition, the use of a polymer may further reduce the removal rate by forming a steric barrier as well as reducing the surface zeta potential of the silicon nitride film.

The carboxylic acid polymer-based compound is poly (acrylic acid), poly (methacrylic acid), poly (ethylene-co-acrylic) (ploy (ethylene-co-acrylic) acid)) and poly (ethylene-co-methacrylic acid) (poly (ethylene-co-methacrylic acid)) and at least one selected from the group consisting of carboxylic acid polymer compound to easily dissolve in the slurry, It is preferable to have a molecular weight of 1,250,000, and if the molecular weight is less than 1,000, the steric hindrance effect is inferior, and if it exceeds 1,250,000, there is a problem of causing agglomeration of abrasive particles. The amount of the carboxylic acid polymer-based compound added is preferably in the range of 0.001 to 5 parts by weight based on 100 parts by weight of the aqueous slurry composed of deionized water and abrasive particles. If it exceeds the portion, there is a tendency that complete dissolution of the carboxylic acid polymer compound does not occur.

In addition, according to the present invention, chemical bonds are formed between the abrasive particles and the silicon oxide film hydrated with deionized water during chemical mechanical polishing. Then, the hydrated silicon oxide film chemically bonded to the abrasive particles by the physical force of the polishing pad is removed from the surface. When the phosphate ester compound, which is a silicon oxide film hydration accelerator, is added to the slurry, the phosphate ester compound is adsorbed onto the silicon oxide film surface to improve the hydration rate of the upper layer of the silicon oxide film. This facilitates chemical bonding with the abrasive particles, resulting in an improvement in the removal rate of the silicon oxide film.

Preferred phosphate ester compounds of the present invention are represented by Formula 1, and at least one of the following phosphate ester compounds is selected. On the other hand, the amount of the compound is added in the range of 0.001 to 1 parts by weight based on 100 parts by weight of the aqueous slurry composed of deionized water and abrasive particles. If the added amount is less than 0.001 part by weight, there is no addition effect. If the added amount exceeds 1 part by weight, foaming tends to occur, and thus an additional antifoaming agent is required.

Wherein R is alkyl having 6 to 18 carbon atoms, x is 1 or 2, and y is 1 or 2;

On the other hand, the pH of the slurry is preferably 4 to 10, the pH controller may be an acidic solution such as HCl, H ₂ SO ₄ , HNO ₃ and basic solutions such as KOH, NaOH, NH ₄ OH.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to the following examples.

Example 1

After dipping the silicon oxide film and the silicon nitride film in deionized water to which 1 wt% of poly (acrylic acid) having a molecular weight of 2000 was added, the change in the surface zeta potential was examined, and the results are shown in FIG. 1. As shown in Fig. 1, the surface zeta potential of the silicon nitride film was greatly reduced. From this, it was confirmed that the polyacrylic acid was well adsorbed onto the silicon nitride film.

Example 2

1 wt% of ceria particles having an average particle diameter of 200 nm were dispersed in 97.999 wt% of deionized water to form an aqueous slurry. 1 weight% of poly (acrylic acid) having a molecular weight of 2000 was included based on 100 parts by weight of the slurry. The pH was adjusted to 7 by adding a sufficient amount of 0.001% by weight KOH solution.

A blanket silicon wafer (6 inch diameter) with a 1.0 micron silicon oxide film layer applied by TEOS precursor chemical vapor deposition was polished into the slurry using a Straussbau 6CA polisher and a Rodel IC1400 K-grooved pad. Polishing conditions include a dropping pressure of 4 psi; Back pressure of 0 psi; Table speed of 60 rpm; Quill speed of 60 rpm; temperature of 20 ° C .; And a slurry flow rate of 150 cc / min. The amount of silicon oxide film removed from the surface of the silicon wafer by CMP was measured with an optical interferometer, and the removal rate was measured as the thickness of the silicon oxide film removed per minute.

A blanket silicon wafer (6 inch diameter) with a 0.3 micron silicon nitride film layer applied by low pressure chemical vapor deposition was polished with the slurry. The amount of silicon oxide film removed from the surface of the silicon wafer by CMP was measured with an optical interferometer, and the removal rate was measured as the thickness of the silicon nitride film removed per minute. Polishing rates and selectivity of silicon nitride to silicon dioxide are shown in Table 1 below.

Item Control Example 2 Carboxylic acid polymer compound (weight part) 0 One Slurry pH 7 7 HDP-oxide removal rate (제거 / min) 3200 2000 Silicon Nitride Removal Rate (Å / min) 1000 100 Selectivity 3.2: 1 20: 1

From Table 1, the slurry of the present invention shows a polishing result with improved removal selectivity. In addition, Figure 2 shows the distribution of the abrasive particles adsorbed after immersing the silicon nitride film in a slurry to which 1% by weight of the carboxylic acid polymer compound is added according to the control and Example 2. It can be seen from FIG. 2 that the removal rate of the silicon nitride film is reduced by less adsorption of ceria particles. However, the desired selectivity ratio could not be obtained by adding only the carboxylic acid polymer compound, and the removal rate of the silicon oxide film was too low. In order to increase the removal rate of the silicon oxide film, a phosphate ester compound was added.

Example 3

1 wt% of ceria particles having an average particle diameter of 200 nm were dispersed in 97.949 wt% of deionized water to form an aqueous slurry. 1% by weight of poly (acrylic acid) having a molecular weight of 2000 and 0.05% by weight of a phosphate ester compound represented by Chemical Formula 1 (Gafac, Re-610) based on 100 parts by weight of the slurry. The pH was adjusted to 7 by adding a sufficient amount of 0.001% by weight KOH solution. Polishing was performed under the conditions described in Example 2. Polishing rates and selectivity of silicon nitride to silicon dioxide are shown in Table 2 below.

Item Control Example 3 Carboxylic acid polymer compound (weight part) 0 One Phosphate ester compound (weight part) 0 0.05 Slurry pH 7 7 HDP-oxide removal rate (제거 / min) 3200 3400 Silicon Nitride Removal Rate (Å / min) 1000 110 Selectivity 3.2: 1 31: 1

It can be seen from Table 2 that the removal rate and removal selectivity of the silicon oxide film are significantly improved by adding the phosphate ester compound.

Example 4

1% by weight of ceria particles were dispersed in 97.999% by weight of deionized water to form an aqueous slurry. 1 weight% of poly (acrylic acid) having a molecular weight of 2000 was added to 100 parts by weight of the slurry, and then a sufficient amount of 0.001% by weight of a KOH solution was added to adjust the pH to 7. The distribution of ceria primary particles with and without poly (acrylic acid) addition and zeta potential of the slurry were measured using an ELS-8000 (Otsuka Electronics) instrument. Zeta potential of the slurry with or without poly (acrylic acid) addition is shown in Table 3 below.

Item Control Example 4 Carboxylic acid polymer compound (weight part) 0 One Zeta Potential of Slurry (mV) -10.78 -56.87

It can be seen from FIG. 3 that when poly (acrylic acid) is added, a narrow distribution of ceria primary particles is shown, which improves dispersion stability of ceria particles.

As described above, the chemical mechanical polishing slurry according to the present invention is added with a phosphate ester compound, which is a silicon oxide film hydration accelerator, in the state of containing a carboxylic acid polymer compound to increase the removal selectivity. A chemical mechanical polishing slurry can be provided with significantly improved removal selectivity. In addition, when the carboxylic acid polymer compound is added, not only does the removal selectivity of the oxide to the silicon nitride film be improved, but also the dispersion stability of the ceria particles is improved.

Claims (5)

In the chemical mechanical polishing slurry for separating shallow trench elements comprising deionized water, abrasive particles and pH controller, Separating the shallow trench, characterized in that the slurry further comprises 0.001 to 5 parts by weight of the carboxylic acid polymer compound, and 0.001 to 1 part by weight of the phosphate ester compound based on 100 parts by weight of the aqueous slurry composed of deionized water and abrasive particles. Chemical mechanical polishing slurry. The slurry of claim 1, wherein the abrasive particles are at least one selected from the group consisting of ceria, alumina, silica, and titania. The method of claim 1, wherein the carboxylic acid polymer compound is one selected from the group consisting of poly (acrylic acid), poly (methacrylic acid), poly (ethylene-co-acrylic acid), and poly (ethylene-co-methacrylic acid). Slurry characterized in that selected above. The slurry according to claim 1 or 3, wherein the carboxylic acid polymer compound has a molecular weight of 1,000 to 1,250,000. The slurry of claim 1, wherein the phosphate ester compound is represented by the following Chemical Formula 1. Formula 1 Wherein R is alkyl having 6 to 18 carbon atoms, x is 1 or 2, and y is 1 or 2;