JP7173879B2 - Polishing composition and polishing system - Google Patents

Description

The present invention relates to polishing compositions and polishing systems.

2. Description of the Related Art In recent years, along with multi-layer wiring on the surface of a semiconductor substrate, a so-called chemical mechanical polishing (CMP) technique for polishing and flattening a semiconductor substrate has been used when manufacturing devices. CMP planarizes the surface of an object to be polished (object to be polished) such as a semiconductor substrate using a polishing composition (slurry) containing abrasive grains such as silica, alumina, and ceria, anticorrosive agents, and surfactants. The object to be polished (object to be polished) is silicon, polysilicon, silicon oxide (silicon oxide), silicon nitride, wiring, plugs and the like made of metal or the like.

A general method of CMP involves attaching a polishing pad to a circular polishing surface plate (platen), soaking the surface of the polishing pad with an abrasive, pressing the surface of the substrate on which the wiring layer is formed, and pressing the surface of the substrate on which the wiring layer is formed. A polishing surface plate is rotated while pressure (polishing pressure) is applied, and the wiring layer is removed by mechanical friction between the abrasive and the wiring layer. For example, Patent Document 1 describes a CMP technique for silicon oxide (TEOS film).

JP-A-2003-142435

In recent years, the use of high dielectric constant materials as materials for semiconductor substrates has been studied. Along with this, the demand for CMP technology for high dielectric constant materials is increasing.

Accordingly, an object of the present invention is to provide a polishing composition capable of polishing a high dielectric constant layer at a high polishing rate.

The present inventors have discovered a polishing composition used for polishing an object having a high dielectric constant layer, the polishing composition containing abrasive grains and water and having a pH of less than 5.0. where X is the zeta potential of the abrasive grains in the polishing composition and Y [mV] is the zeta potential of the high dielectric constant layer being polished using the polishing composition, and X is negative. , Y is positive, and YX≧90.

According to the polishing composition of the present invention, a high dielectric constant layer can be polished at a high polishing rate.

The present invention provides a polishing composition used for polishing an object having a high dielectric constant layer, the polishing composition containing abrasive grains and water and having a pH of less than 5.0, When the zeta potential of the abrasive grains in the polishing composition is X [mV] and the zeta potential of the high dielectric layer being polished with the polishing composition is Y [mV], X is negative. , Y is positive, and Y−X≧90. According to the polishing composition, a high dielectric constant layer can be polished at a high polishing rate.

When X is negative, Y is positive, and YX≧90, when polishing an object to be polished using the polishing composition, the abrasive grains contained in the polishing composition and the object to be polished A sufficient electrostatic interaction works with the high dielectric constant layer of the object. Therefore, it is considered that the contact frequency of the abrasive grains with the high dielectric constant layer increases, and the high dielectric constant layer can be polished at a high polishing rate.

The above mechanism is based on speculation, and the present invention is not limited to the above mechanism.

Embodiments of the present invention will be described below. In addition, the present invention is not limited only to the following embodiments.

In this specification, unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (20 to 25° C.)/relative humidity of 40 to 50% RH. In this specification, the range "x to y" includes x and y and means "x or more and y or less".

<Method for measuring zeta potential>
The zeta potential X [mV] of the abrasive grains in the polishing composition is determined by subjecting the polishing composition to ELS-Z2 manufactured by Otsuka Electronics Co., Ltd., and using a flow cell at a measurement temperature of 25 ° C. using a laser Doppler method (electrophoretic light scattering measurement method) and analyzing the obtained data with the Smoluchowski formula.

The zeta potential Y [mV] of the high dielectric constant layer during polishing using the polishing composition was measured by subjecting the silicon wafer on which the high dielectric constant layer was deposited to ELS-Z2 manufactured by Otsuka Electronics Co., Ltd., and using the laser Doppler method ( It is obtained by measuring by electrophoretic light scattering measurement method). Specifically, a silicon wafer having a high dielectric constant layer formed thereon is attached to the upper surface of a flat plate sample cell unit (manufactured by Otsuka Electronics Co., Ltd.) at a measurement temperature of 25°C. A cell is filled with a polishing composition (abrasive grains whose zeta potential is known by the above measurement as monitor particles), the monitor particles are subjected to electrophoresis, and the electrical mobility of the monitor particles is measured at seven points between the upper and lower surfaces of the cell. do. The zeta potential Y
[mV] is calculated.

In the present invention, it is preferable that YX≧92. Also, the upper limit of YX is not particularly limited, but YX≦150, for example. The YX value can be controlled within a desired range by, for example, adjusting the amount of an electrical conductivity modifier to be added, which will be described later. Specifically, when the amount of the electrical conductivity modifier added is increased, each of X and Y approaches zero, so the value of YX decreases. Also, the YX value can be controlled within a desired range by using, for example, an acid described later as a pH adjuster.

<Object to be polished>
[High dielectric constant layer]
A polishing object according to the present invention has a high dielectric constant layer (a layer containing a high dielectric constant material as a main component). Here, the "layer containing a high dielectric constant material as a main component" means that the content of the high dielectric constant material in the layer is, for example, 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. , Still more preferably 95% by mass or more, particularly preferably 98% by mass or more (upper limit: 100% by mass).

A high dielectric constant material refers to a material having a dielectric constant higher than that of silicon oxide (SiO ₂ , dielectric constant 3.9), more specifically, a material having a dielectric constant of 5.0 or more. The high dielectric constant materials may be used singly or in combination of two or more. The dielectric constant is a value obtained by a mercury probe method.

Examples of materials having a dielectric constant of 5.0 or more include aluminum oxide (AlOx, dielectric constant 9 to 10), magnesium oxide (MgOx, dielectric constant 9 to 10), gallium oxide (GaOx, dielectric constant 9-10), hafnium oxide (HfOx, dielectric constant 20-30), lanthanum oxide (LaOx, dielectric constant 20-30), zirconium oxide (ZrOx, dielectric constant 20-30), cerium oxide (CeOx, dielectric constant dielectric constant of about 20) and titanium oxide (TiOx, relative dielectric constant of about 100). Since the metal oxide satisfies a positive zeta potential at a pH of less than 5.0, the parameter Y can be positive when the high dielectric constant layer contains the metal oxide as a main component. The said metal oxide may be used individually by 1 type, and may use 2 or more types together.

The metal oxide may be either crystalline or amorphous, but is preferably amorphous from the viewpoint of suppressing the occurrence of leakage current due to grain boundaries. Accordingly, in one embodiment of the invention, the high dielectric constant layer comprises an amorphous metal oxide. Note that "the high dielectric constant layer contains an amorphous metal oxide" means that in an X-ray diffraction pattern of a high dielectric constant layer containing a metal oxide, the half width of the maximum peak derived from the crystal structure of the metal oxide is is 1° or more.

The X-ray diffraction image can be specifically obtained using the following equipment and conditions:
X-ray diffractometer: Rigaku Corporation Model: SmartLab
Measurement method: XRD method (2θ/ω scan)
X-ray generator: Anticathode Cu
: Output 45kV 200mA
Detector: Semiconductor detector Incident optics: Parallel beam method (Scott collimation)
Solar slit: Incident side 5.0°
: Light receiving side 5.0°
Slit: incident side IS = 1 (mm)
: Longitudinal limit 5 (mm)
: Light receiving side RS1=1 RS2=1.1 (mm)
Scanning conditions: scanning axis 2θ/ω
: Scanning mode Continuous scanning
: Scanning range 20-90°
: Step width 0.02°
: Scanning speed 2°/min.

The high dielectric constant layer can be formed by a known method such as a vapor deposition method, a sputtering method, a plasma CVD method, a sol-gel method, or the like.

[Low dielectric constant layer]
The polishing composition of the present invention may further have a low dielectric constant layer (a layer containing a low dielectric constant material as a main component) in addition to the high dielectric constant layer. Here, the "layer containing a low dielectric constant material as a main component" means that the content of the low dielectric constant material in the layer is, for example, 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. , Still more preferably 95% by mass or more, particularly preferably 98% by mass or more (upper limit: 100% by mass).

Low dielectric constant materials include silicon oxide (SiO ₂ , dielectric constant 3.9) and materials with a dielectric constant lower than that of silicon oxide (specifically, materials with a dielectric constant of 3.5 or less). Point. Examples of materials having a dielectric constant of 3.5 or less include carbon-containing silicon oxide (SiOC) and fluorine-containing silicon oxide (SiOF). The low dielectric constant materials may be used singly or in combination of two or more.

The low dielectric constant layer can be formed by a known method such as a CVD method using TEOS or the like as a starting material.

When the high dielectric constant layer and the low dielectric constant layer are polished at the same time, the polishing rate ratio (selection ratio) of the high dielectric constant layer to the low dielectric constant layer is preferably as low as possible from the viewpoint of suppressing the step between both layers.

<Polishing composition>
[Abrasive]
Abrasive grains used in the polishing composition of the present invention exhibit a negative zeta potential at a pH of less than 5.0 (that is, the above parameter X becomes negative), and are obtained by immobilizing an organic acid on silica. (hereinafter also referred to as organic acid-fixed silica) is preferred. As silica, colloidal silica is preferable from the viewpoint of suppressing the occurrence of polishing scratches.

Here, colloidal silica can be produced, for example, by a sol-gel method. Colloidal silica produced by the sol-gel method is preferable because it contains a small amount of corrosive ions such as metal impurities and chloride ions that are diffusible in semiconductors. The production of colloidal silica by the sol-gel method can be performed using a conventionally known method. Specifically, a hydrolyzable silicon compound (for example, alkoxysilane or a derivative thereof) is used as a raw material, and a hydrolysis/condensation reaction is performed. Colloidal silica can be obtained by performing.

The immobilization of the organic acid cannot be achieved simply by allowing the silica and the organic acid to coexist. For example, if sulfonic acid, which is a kind of organic acid, is immobilized on silica, for example, "Sulfonic acid-functionalized silica through of thiol groups", Chem. Commun. 246-247 (2003). Specifically, sulfonic acid is immobilized on the surface by coupling a silane coupling agent having a thiol group such as 3-mercaptopropyltrimethoxysilane to silica and then oxidizing the thiol group with hydrogen peroxide. silica can be obtained.

Alternatively, if a carboxylic acid, which is a kind of organic acid, is immobilized on silica, for example, see "Novel Silane Coupling Agents Containing a Photolabile 2-Nitrobenzyl Ester for Introduction of a Carboxy Group on the Surface of the Silicon Gastry," for example. , 3, 228-229 (2000). Specifically, silica having a carboxylic acid immobilized on its surface can be obtained by coupling a silane coupling agent containing a photoreactive 2-nitrobenzyl ester to silica and then irradiating with light.

In the polishing composition of the present invention, the lower limit of the average primary particle size of abrasive grains is preferably 5 nm or more, more preferably 7 nm or more, and even more preferably 10 nm or more. In the polishing composition of the present invention, the upper limit of the average primary particle size of abrasive grains is preferably 120 nm or less, more preferably 80 nm or less, and even more preferably 50 nm or less. Within such a range, defects such as scratches can be suppressed on the surface of the object to be polished after polishing with the polishing composition. The average primary particle size of the abrasive grains is calculated based on the specific surface area of the abrasive grains measured by the BET method, for example.

In the polishing composition of the present invention, the lower limit of the average secondary particle size of the abrasive grains is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more. In the polishing composition of the present invention, the upper limit of the average primary particle size of abrasive grains is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less. Within such a range, defects such as scratches can be suppressed on the surface of the object to be polished after polishing with the polishing composition. The average primary particle size of abrasive grains can be measured by, for example, a dynamic light scattering method typified by a laser diffraction scattering method.

The average degree of association of abrasive grains is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.5 or less. As the average degree of association of abrasive grains becomes smaller, it is easier to obtain a polished surface with fewer surface defects by polishing an object to be polished using the polishing composition. Further, the average association degree of abrasive grains is preferably 1.0 or more, more preferably 1.2 or more. As the average degree of association of abrasive grains increases, there is an advantage that the removal rate of the object to be polished by the polishing composition increases. The average degree of association of abrasive grains is obtained by dividing the average secondary particle diameter value of the abrasive grains by the average primary particle diameter value.

In the polishing composition of the present invention, the lower limit of the content of abrasive grains is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and 0.1% by mass or more. It is even more preferable to have In addition, the upper limit of the content of abrasive grains in the polishing composition of the present invention is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less. It is preferably 1% by mass or less, even more preferably 0.4% by mass or less, and particularly preferably 0.4% by mass or less. When the upper limit is such, the occurrence of surface defects on the surface of the object to be polished after polishing with the polishing composition can be further suppressed.

[water]
The polishing composition according to the present invention contains water as a dispersion medium or solvent. Water preferably contains as few impurities as possible from the viewpoint of contamination of the object to be washed and inhibition of the action of other components. As such water, for example, water having a total content of transition metal ions of 100 ppb or less is preferable. Here, the purity of water can be increased by, for example, removal of impurity ions using an ion exchange resin, removal of foreign matter using a filter, distillation, or other operations. Specifically, as water, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, distilled water, or the like.

[pH of Polishing Composition]
The pH of the polishing composition of the present invention is less than 5.0. When the pH is 5.0 or more, the zeta potential of the high dielectric constant layer is lowered, and the zeta potential difference (that is, Y−X) with the abrasive grains is reduced. This is not preferable (see Comparative Example 6 below). On the other hand, the lower limit of pH of the polishing composition is preferably 2.0 or higher, more preferably 3.0 or higher, and particularly preferably 4.0 or higher. When the pH is equal to or higher than the lower limit pH, the polishing rate for the low dielectric layer can be improved while maintaining the polishing rate for the high dielectric layer. As a result, the selection ratio of the high dielectric layer to the low dielectric layer can be reduced. Therefore, it can be advantageous in simultaneous polishing of a high dielectric constant layer and a low dielectric constant layer.

The pH of the polishing composition was measured using a pH meter (for example, a glass electrode type hydrogen ion concentration indicator (model number: F-23) manufactured by Horiba, Ltd.) and a standard buffer (phthalate pH buffer). Solution pH: 4.01 (25°C), neutral phosphate pH buffer pH: 6.86 (25°C), carbonate pH buffer pH: 10.01 (25°C)) After that, the glass electrode is placed in the polishing composition, and after 2 minutes or more have passed and the value is stabilized, it can be grasped by measuring the value.

The pH of the polishing composition according to the present invention can be adjusted by adding an appropriate amount of pH adjuster, if necessary. The pH adjuster may be either an acid or an alkali, and may be either an inorganic compound or an organic compound. The pH adjusters may be used alone or in combination of two or more.

(pH adjuster)
A known acid or base can be used as the pH adjuster. In particular, since the polishing composition of the present invention has a pH of less than 5.0, an acid is preferably used as a pH adjuster. Therefore, the polishing composition according to one embodiment of the invention further comprises an acid.

Acids that can be used as pH adjusters include, for example, inorganic acids such as sulfuric acid, nitric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid and phosphoric acid; -methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid Carboxylic acids such as acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, and lactic acid, and methanesulfonic acid , organic sulfonic acids such as ethanesulfonic acid and isethionic acid.

Among them, an acid having 1 or 2 oxoacid groups and an integer of 0 or more and 2 or less hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups) is preferable. By using such an acid as a pH adjuster, the decrease in the zeta potential Y can be suppressed, and the YX can be controlled within a desired range. Therefore, it is possible to obtain a polishing composition having an excellent polishing rate for a high dielectric constant layer.

Here, "oxoacid group" refers to a group having a structure in which a hydrogen atom that can be dissociated as a proton is bonded to an oxygen atom. Examples of oxoacids include a carboxyl group (--COOH), a phosphate group (--OP(O)(OH) ₂ ), a phosphonic acid group (--P(O)(OH) ₂ ), a sulfate group (--OS( O) ₂ (OH)), sulfonic acid group (-S(O) ₂ (OH)), and the like.

Examples of the acid having 1 or 2 oxoacid groups and an integer of 0 to 2 hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups) include formic acid, acetic acid, propionic acid, butyric acid, Valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethyl carboxylic acids such as hexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, and lactic acid; and organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid and isethionic acid.

Among acids in which the number of oxoacid groups is 1 or 2 and the number of hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups) is an integer of 0 or more and 2 or less, From the point of view, an acid in which the total number of oxoacid groups and hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups) is 1 or 2 is more preferable. Preferred such acids are, for example, maleic acid, succinic acid, acetic acid, or lactic acid. Thus, in one embodiment of the invention the acid is at least one selected from the group consisting of maleic acid, succinic acid, acetic acid and lactic acid. Furthermore, among these acids, an acid having two oxoacid groups is more preferable from the viewpoint of reducing the selection ratio of the high dielectric constant layer to the low dielectric constant layer.

Bases that can be used as pH adjusters include, for example, alkali metal hydroxides or salts, Group 2 element hydroxides or salts, quaternary ammonium hydroxides or salts thereof, ammonia, and amines. Specific examples of alkali metals include potassium and sodium.

The amount of the pH adjuster to be added is not particularly limited, and may be adjusted appropriately so that the pH of the polishing composition is within the desired range. Adjusting is preferred.

[Electrical conductivity of polishing composition]
The upper limit of the electrical conductivity of the polishing composition of the present invention is preferably 4.0 mS/cm or less, more preferably 2.0 mS/cm or less, from the viewpoint of suppressing a decrease in the polishing rate of the high dielectric layer. , more preferably 1.0 mS/cm or less, and particularly preferably 0.5 mS/cm or less. The lower limit of the electrical conductivity of the polishing composition of the present invention is preferably 0.1 mS/cm or more, more preferably 0.2 mS/cm or more, from the viewpoint of improving the polishing rate of the low dielectric constant layer. , more preferably 0.3 mS/cm or more, and particularly preferably 0.4 mS/cm or more. That is, within the above range, the polishing rate for the low dielectric layer can be improved while maintaining the polishing rate for the high dielectric layer. As a result, the selection ratio of the high dielectric layer to the low dielectric layer can be reduced. Therefore, it can be advantageous in simultaneous polishing of a high dielectric constant layer and a low dielectric constant layer. The electrical conductivity of the polishing composition is a value measured by a desktop electrical conductivity meter (manufactured by Horiba, Ltd., model number: DS-71).

(Electrical conductivity modifier)
Electrical conductivity can be controlled, for example, by adding an electrical conductivity modifier to the polishing composition. Although there are no particular restrictions on the electrical conductivity adjuster, salt compounds are preferred.

Salt compounds include, for example, acid salts, base salts, etc. Examples include potassium nitrate, ammonium nitrate, potassium hydrogen carbonate, ammonium carbonate, ammonium hydrogen carbonate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium sulfate, Examples thereof include potassium chloride, sodium chloride, potassium bromide, potassium iodide, ammonium citrate, potassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide and tetraethylammonium hydroxide, among which ammonium sulfate is preferred. A salt compound may be used individually by 1 type, and may use 2 or more types together.

The upper limit of the content of the electrical conductivity modifier is preferably less than 0.3% by mass with respect to the total mass of the polishing composition, from the viewpoint of suppressing a decrease in the polishing rate of the high dielectric layer, and more It is preferably less than 0.2% by weight, even more preferably less than 0.1% by weight, and less than 0.05% by weight. In addition, the lower limit of the content of the electrical conductivity modifier is preferably 0.001% by mass or more with respect to the total mass of the polishing composition, from the viewpoint of improving the polishing rate of the low dielectric constant layer. It is preferably 0.005% by mass or more, still more preferably 0.01% by mass or more, and particularly preferably 0.02% by mass or more. Therefore, within the above range, the polishing rate for the low dielectric layer can be improved while maintaining the polishing rate for the high dielectric layer. As a result, the selection ratio of the high dielectric layer to the low dielectric layer can be reduced. Therefore, it can be advantageous in simultaneous polishing of a high dielectric constant layer and a low dielectric constant layer.

[Other additives]
The polishing composition of the present invention contains known complexing agents, metal anticorrosive agents, preservatives, antifungal agents, reducing agents, nonionic surfactants, water-soluble polymers, as long as the effects of the present invention are not impaired. It may further contain an organic solvent or the like for dissolving a sparingly soluble organic substance.

However, when the high dielectric constant layer is a layer containing an amorphous metal oxide as a main component, polishing with a polishing composition containing an oxidizing agent may reduce the polishing rate of the high dielectric constant layer. Therefore, the polishing composition of the present invention preferably contains substantially no oxidizing agent. That is, in one preferred embodiment of the present invention, the high dielectric constant layer comprises an amorphous metal oxide and the polishing composition is substantially free of oxidizing agents. Specific examples of the oxidizing agent here include hydrogen peroxide (H ₂ O ₂ ), sodium persulfate, ammonium persulfate, sodium dichloroisocyanurate and the like. Here, "the polishing composition does not substantially contain an oxidizing agent" means that it does not contain an oxidizing agent at least intentionally. Therefore, a polishing composition that inevitably contains a small amount of oxidizing agent due to its raw material, manufacturing method, or the like can be included in the concept of a polishing composition that does not substantially contain an oxidizing agent. For example, the molar concentration of the oxidizing agent in the polishing composition is 0.0005 mol/L or less, preferably 0.0001 mol/L or less, more preferably 0.00001 mol/L or less, particularly preferably 0.000001 mol. /L or less.

<Polishing system>
The present invention is a polishing system comprising an object to be polished, a polishing pad and a polishing composition, wherein the polishing composition contains abrasive grains and water and has a pH of less than 5.0, and the polishing composition When the zeta potential of the abrasive grains inside is X [mV] and the zeta potential of the object being polished with the polishing composition is Y [mV], X is negative and Y is positive. and YX≧90, wherein the surface of the object to be polished is in contact with the polishing pad and the polishing composition.

Preferred embodiments of the object to be polished and the polishing composition that are applied to the polishing system of the present invention are the same as described above, so descriptions thereof will be omitted.

The polishing pad used in the polishing system of the present invention is not particularly limited, and for example, polyurethane foam type, non-woven fabric type, suede type, one containing abrasive grains, one containing no abrasive grains, etc. can be used.

The polishing system of the present invention may polish both surfaces of the object to be polished by bringing both surfaces of the object to be polished into contact with the polishing pad and the polishing composition, or polish only one surface of the object to be polished. Only one side of the object to be polished may be polished by bringing it into contact with the pad and the polishing composition.

In the polishing system of the present invention, a working slurry containing the above polishing composition is prepared. Then, the polishing composition is supplied to the object to be polished, and the object is polished by a conventional method. For example, an object to be polished is set in a general polishing apparatus, and the polishing composition is supplied to the surface of the object to be polished (surface to be polished) through the polishing pad of the polishing apparatus. Typically, while the polishing composition is continuously supplied, the polishing pad is pressed against the surface of the object to be polished, and the two are relatively moved (for example, rotationally moved). Polishing of the object to be polished is completed through such a polishing process.

As for the polishing conditions, for example, the rotation speed of the polishing platen is preferably 10 to 500 rpm. The pressure (polishing pressure) applied to the substrate having the object to be polished is preferably 0.5 to 10 psi (about 3 to 69 kPa). The method of supplying the polishing composition to the polishing pad is also not particularly limited, and, for example, a method of continuously supplying it using a pump or the like is adopted. The amount supplied is not limited, but it is preferred that the surface of the polishing pad is always covered with the polishing composition of the present invention.

The present invention will be described in more detail with the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. In the following examples, unless otherwise specified, the operations were carried out under the conditions of room temperature (25° C.)/relative humidity of 40 to 50% RH.

<Preparation of polishing composition>
Sulfonic acid-fixed colloidal silica (average primary particle diameter 35 nm, average secondary particle diameter 70 nm, average association degree 2.0) as abrasive grains, ammonium sulfate as electrical conductivity modifier, and POE lauryl sulfate as surfactant if necessary Ester ammonium and hydrogen peroxide as an oxidizing agent were added to water so that the content (relative to 100% by mass of the polishing composition) shown in Table 1 was obtained, and the mixture was stirred and mixed at room temperature (25° C.) for 30 minutes. , pH was adjusted to the pH shown in Tables 1-1 and 1-2 using the acid shown in Tables 1-1 and 1-2 as a pH adjuster to prepare each polishing composition.

The average primary particle size of the abrasive grains was calculated from the specific surface area of the abrasive grains measured by the BET method using "Flow Sorb II 2300" manufactured by Micromeritex and the density of the abrasive grains. Further, the pH of the polishing composition (liquid temperature: 25° C.) was confirmed with a pH meter (manufactured by HORIBA, Ltd., model number: LAQUA). In addition, the electrical conductivity of the polishing composition was measured with a desktop electrical conductivity meter (manufactured by HORIBA, Ltd., model number: DS-71).

<Measurement of zeta potential of abrasive grains>
Each polishing composition prepared above was subjected to ELS-Z2 manufactured by Otsuka Electronics Co., Ltd., and measurement was performed by a laser Doppler method (electrophoretic light scattering measurement method) using a flow cell at a measurement temperature of 25°C. The zeta potential X [mV] of the sulfonic acid-fixed colloidal silica in each polishing composition was calculated by analyzing the obtained data using the Smoluchowski formula.

<Zeta potential measurement of high dielectric constant layer>
The zeta potential Y [mV] of the high dielectric constant layer during polishing using the polishing composition was measured as follows. ELS-Z2 manufactured by Otsuka Electronics Co., Ltd. was used for silicon wafers (300 mm wafer cut into 15 x 35 mm) on which amorphous metal oxides (AlOx, MgOx, GaOx) were deposited with a thickness of 1000 Å as a high dielectric constant layer. Measurement was performed by the laser Doppler method (electrophoretic light scattering measurement method). Specifically, the silicon wafer was attached to the upper surface of a cell unit for flat plate samples (manufactured by Otsuka Electronics Co., Ltd.) under the condition of a measurement temperature of 25°C. Each polishing composition prepared above (using sulfonic acid-fixed colloidal silica having a known zeta potential by the above measurement as monitor particles) was filled in the cell, electrophoresis of the monitor particles was performed, and at seven points between the upper and lower surfaces of the cell Electromobility of monitor particles was measured. The zeta potential Y [mV] was calculated by analyzing the obtained electrical mobility data using the Mori-Okamoto equation and the Smoluchowski equation.

Table 1 shows the X, Y and YX values obtained using each polishing composition.

<Polishing Performance Evaluation>
Silicon wafer (300 mm wafer cut into 60 x 60 mm) on which amorphous metal oxides (AlOx, MgOx, GaOx) as high dielectric layers or SiO ₂ (TEOS) as low dielectric layers are deposited to a thickness of 1000 Å were prepared, and each wafer was polished under the following polishing conditions using the polishing composition obtained above, and the polishing rate was measured.

(polishing conditions)
Polishing machine: Desktop polishing machine Polishing pad: IC1010 pad (manufactured by Dow Chemical Company)
Pressure: 1.4 psi (about 10 kPa)
Platen (surface plate) rotation speed: 60 rpm
Head (carrier) rotation speed: 60 rpm
Flow rate of polishing composition: 100 ml/min
Polishing time: 15 sec.

(polishing rate)
The removal rate (RR) was calculated by the following formula.

The film thickness was determined by an optical interferometric film thickness measuring device (manufactured by KLA-Tencor Co., Ltd., model number: ASET-f5x), and was evaluated by dividing the difference in film thickness before and after polishing by the polishing time. . Table 2 shows the results.

The high dielectric constant layers (amorphous AlOx, MgOx, GaOx layers) used for the zeta potential measurement and polishing performance evaluation were deposited by a sputtering method. The half widths of the peaks (AlOx: around 2θ=51°, MgOx: around 2θ=43°, GaOx: around 2θ=27°) were all 3° or more.

As shown in Table 2, when YX≧90 (Examples 1 to 11), compared to when YX<90 (Comparative Examples 1 to 9), the high dielectric constant layer (amorphous (AlOx, MgOx, GaOx) were remarkably superior in polishing rate. This result suggests that the strength of the electrostatic interaction acting between the abrasive grains and the high dielectric layer greatly contributes to the polishing rate of the high dielectric layer.

Furthermore, when maleic acid is used as the pH adjuster, when the polishing composition contains ammonium sulfate (Examples 1 to 4 and 6), compared to the case where it does not contain ammonium sulfate (Example 5), the high dielectric The polishing rate of the low dielectric constant layer (TEOS layer) was improved, and the selectivity of the high dielectric constant layer to the low dielectric constant layer was low, while the polishing rate of the dielectric constant layer was the same. From this result, it can be said that the form containing the electrical conductivity modifier is advantageous for simultaneous polishing of the high dielectric constant layer and the low dielectric constant layer.

Further, as can be seen from Examples 1, 7 to 11 and Comparative Examples 7 to 9, an acid having 1 or 2 oxoacid groups and an integer of 0 to 2 hydroxyl groups was used as a pH adjuster. When it was used, it was possible to control YX≧90, and the polishing rate of the high dielectric constant layer was excellent. Furthermore, when an acid having a total number of oxoacid groups and hydroxyl groups of 1 or 2 was used (Examples 1, 7 to 9), an acid having a total number of oxoacid groups and hydroxyl groups of 3 was used as a pH adjuster. The polishing rate of the high dielectric constant layer was further improved compared to the case of using as (Examples 10 and 11).

In addition, when compared under the same pH conditions, the polishing composition containing an oxidizing agent (Example 6) had a higher dielectric constant layer (especially an amorphous AlOx) polishing rate decreased. It is conceivable that the addition of the oxidizing agent increased the electrical conductivity of the polishing composition and prevented the electrostatic interaction between the abrasive grains and the high dielectric constant layer.

Claims (16)

A polishing composition used for polishing an object having a high dielectric constant layer,
The polishing composition contains abrasive grains and water and has a pH of less than 5.0,
When the zeta potential of the abrasive grains in the polishing composition is X [mV] and the zeta potential of the high dielectric layer being polished with the polishing composition is Y [mV], X is negative. , Y is positive, and Y−X≧90. 2. The polishing composition according to claim 1, which is substantially free of oxidizing agents. 3. The polishing composition according to claim 1, further comprising an acid. 4. The polishing according to claim 3, wherein the acid has 1 or 2 oxoacid groups and the number of hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups) is an integer of 0 or more and 2 or less. composition. 5. The polishing composition according to claim 4, wherein the acid has 1 or 2 total oxoacid groups and hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups). The polishing composition according to any one of claims 3 to 5, wherein the acid is at least one selected from the group consisting of maleic acid, succinic acid, acetic acid and lactic acid. The polishing composition according to any one of claims 1 to 6, wherein the high dielectric constant layer contains an amorphous metal oxide. The polishing composition according to any one of claims 1 to 7, wherein the object to be polished further comprises a low dielectric constant layer. A polishing system comprising a polishing object having a high dielectric constant layer, a polishing pad and a polishing composition,
The polishing composition contains abrasive grains and water and has a pH of less than 5.0,
When the zeta potential of the abrasive grains in the polishing composition is X [mV] and the zeta potential of the high dielectric layer being polished with the polishing composition is Y [mV], X is negative. , Y is positive and Y−X≧90,
A polishing system, wherein the surface of the object to be polished is contacted with the polishing pad and the polishing composition. 10. The polishing system of claim 9, wherein the polishing composition is substantially free of oxidants. 11. The polishing system of claim 9 or 10, wherein the polishing composition further comprises an acid. 12. The polishing according to claim 11, wherein the acid has 1 or 2 oxoacid groups and the number of hydroxyl groups (excluding the hydroxyl groups constituting the oxoacid groups) is an integer of 0 or more and 2 or less. system. 13. The polishing system according to claim 12, wherein the acid is an acid in which the total number of oxoacid groups and hydroxyl groups (excluding hydroxyl groups constituting oxoacid groups) is 1 or 2. The polishing system according to any one of claims 11 to 13, wherein the acid is at least one selected from the group consisting of maleic acid, succinic acid, acetic acid and lactic acid. The polishing system of any one of claims 9-14, wherein the high dielectric constant layer comprises an amorphous metal oxide. The polishing system according to any one of claims 9 to 15, wherein the object to be polished further includes a low dielectric constant layer.