JP2005268667A - Polishing composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing composition capable of suppressing a remarkable reduction of a polishing speed resulting from a clogging of a polishing pad. <P>SOLUTION: This polishing composition is used for polishing a substrate by means of the polishing pad, and contains colloidal silica. A particle diameter of the colloidal silica is expressed by an average primary particle diameter calculated on the basis of BET modulus and an average secondary particle diameter measured on the basis of a laser beam diffraction modulus. When the average primary particle diameter is expressed by D<SB>SA</SB>and the average secondary particle diameter is expressed by D<SB>N4</SB>, a relation that D<SB>SA</SB>is equal to or smaller than D<SB>N4</SB>is established between D<SB>SA</SB>and D<SB>N4</SB>. Furthermore, D<SB>N4</SB>is 30 nm or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polishing composition used for polishing a substrate with a polishing pad.

In general, in polishing a substrate such as a silicon wafer, it is important to improve the manufacturing efficiency in order to respond to the recent increase in demand as well as the improvement in surface quality due to higher performance and higher integration density of semiconductor devices. It is said that. In order to respond to this problem, for example, in Patent Document 1, in order to improve the polishing rate (polishing efficiency), a contrivance has been made for the polishing composition. Specifically, a silicon wafer and a polishing pad fixed to a ceramic block using a polishing composition comprising 10 to 80% by weight of colloidal silica or silica gel and piperazine based on the silica sol or silica gel based on SiO _2. The surface of the silicon wafer is mirror-polished chemically and mechanically.
Japanese Patent Laid-Open No. 5-154760

  However, in the polishing of the substrate, when the polishing is repeatedly performed using the polishing pad, the polishing pad is clogged, and the polishing amount (polishing rate) per unit time is reduced. Therefore, in order to maintain a practical polishing rate sufficient to improve manufacturing efficiency, it is necessary to reduce clogging of the polishing pad.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a polishing composition capable of suppressing a significant decrease in polishing rate due to clogging of a polishing pad. .

In order to achieve the above object, the invention described in claim 1 is a polishing composition used for polishing a substrate with a polishing pad and containing colloidal silica, wherein the colloidal silica is based on a BET method. the average primary particle size calculated Te expressed in D _SA, when the average secondary particle diameter measured based on the laser diffraction method was expressed in D _N4, between D _SA and D _N4, D _SA ≦ D _The gist is that the relationship of _N4 is established and _DN4 is 30 nm or less.

The invention described in claim 2 is summarized in that, in the invention described in claim 1, _DSA is 20 nm or less.
The gist of the invention described in claim 3 is that, in the invention described in claim 1 or 2, the relationship of D _N4 ≦ 3 × D _SA is established between D _SA and D _N4 .

  ADVANTAGE OF THE INVENTION According to this invention, the polishing composition which can suppress the remarkable fall of the polishing rate resulting from clogging of a polishing pad can be provided.

Hereinafter, an embodiment in which the present invention is embodied in a polishing composition for a silicon wafer used as a substrate of a semiconductor device will be described.
The silicon wafer is formed from single crystal silicon, and is manufactured through a step of cutting the silicon wafer from the silicon single crystal ingot, a step of lapping and etching the surface, and a step of polishing the surface into a mirror state. The polishing pad and the polishing composition are used in the step of polishing the surface of the silicon wafer. A polishing pad consists of porous bodies, such as a nonwoven fabric, a foam, and a suede. The silicon wafer is polished by bringing the polishing pad into contact with the wafer surface and sliding the wafer surface and the polishing pad relative to each other while supplying the polishing composition to the contact portion. When polishing is repeated, particles in the polishing composition, polishing pad debris, wafer scraps, etc. clog the polishing pad, the polishing rate is significantly reduced, and complicated dressing, pad replacement, etc. Since work is required, manufacturing efficiency is reduced. Therefore, in this embodiment, the polishing composition is prepared so as to reduce clogging of the polishing pad and to suppress a decrease in polishing rate due to repeated polishing.

  The polishing composition contains colloidal silica as an essential component. Colloidal silica is a slurry substance and contains a dispersion medium. As the dispersion medium, an organic solvent such as alcohol, water, a surfactant, and the like can be used as long as they are liquid. However, from the viewpoint that impurities are not included in the colloidal silica as much as possible, impurities are filtered by a filter. Water such as ion exchange water and distilled water is preferred.

Colloidal silica plays a role of polishing a silicon wafer by a mechanical polishing action. The particle diameter of the colloidal silica is indicated by an average primary particle diameter and an average secondary particle diameter. The average primary particle size, specific surface area measured by the specific surface area measurement method of the powder by the gas adsorption (BET method), is calculated from the particle density, represented by D _SA. The average secondary particle diameter is measured by a laser light diffraction method and is expressed as _DN4 . That is, _DSA is an average value of the particle diameter of primary particles, and _DN4 is an average value of the particle diameter of secondary particles. Here, the primary particles indicate dispersed particles (single particles) of the solid content of silicon dioxide in colloidal silica, and the secondary particles indicate particles in which the primary particles are aggregated (aggregated particles). ing.

Since primary particles are aggregated to form secondary particles, it is essential that a relationship of D _SA ≦ D _N4 is established between D _SA and D _N4 . Further, from the viewpoint of suppressing excessive aggregation of primary particles, it is preferable that a relationship of D _N4 ≦ (3 × D _SA ) is established between D _SA and D _N4 . DN ₄ is essentially 30 nm or less, preferably 25 nm or less, and more preferably 20 nm or less, from the viewpoint of sufficiently achieving clogging reduction of the polishing pad. Further, D _SA, from the viewpoint of sufficiently achieving clogging reduction of the polishing pad is preferably 20nm or less, more preferably 15 nm or less, and most preferably 10 nm. On the other hand, from the viewpoint of obtaining a practical polishing rate, D _N4 is preferably more than 5 nm, D _SA is preferably at least 3 nm. The practical polishing rate refers to a polishing rate at which polishing of a silicon wafer can be completed in a time that does not hinder manufacturing efficiency.

The content of the silicon dioxide (SiO ₂ ) solid content of the colloidal silica in the polishing composition is preferably 50% by mass or less, more preferably 30% by mass or less from the viewpoint of sufficiently achieving clogging reduction of the polishing pad. Preferably, 20 mass% or less is the most preferable. On the other hand, from the viewpoint of obtaining a practical polishing rate, the content of the SiO ₂ solid content of colloidal silica is preferably 0.1% by mass or more, more preferably 1% by mass or more, and most preferably 10% by mass or more. Colloidal silica may contain metal impurities such as iron, nickel, copper, calcium, chromium, zinc, or their hydroxides, oxides, etc., and these metal impurities adhere to the wafer surface and are subjected to subsequent heat treatment. Therefore, it may be diffused into the wafer and affect the electrical characteristics. From the viewpoint of suppressing the influence on the electrical characteristics of the silicon wafer, the content of the metal impurities in the dispersion (water) in which the content of colloidal silica is 20% by mass is preferably 300 ppm or less, more preferably 100 ppm or less. 0.3 ppm or less is most preferable.

  In the case of a polishing composition for polishing a silicon wafer, at least one of an alkali compound and a chelating agent may be contained in addition to colloidal silica. When the polishing composition contains an additive other than colloidal silica, the dispersion medium can be allowed to act as a solvent for the additive.

  The alkali compound acts as a polishing accelerator that assists the mechanical polishing by a chemical polishing action by corrosion or etching and promotes the polishing. Examples of the alkali compound include potassium hydroxide, sodium hydroxide, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate and other inorganic alkali compounds, ammonia, tetramethyl ammonium hydroxide, ammonium hydrogen carbonate, ammonium carbonate and other ammonium salts. , Anhydrous piperazine, piperazine hexahydrate, 1- (2-aminoethyl) piperazine, N-methylpiperazine, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β -Aminoethyl) Amine such as ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine and the like. These alkali compounds are contained alone or in combination of two or more in the polishing composition. In addition, potassium hydroxide, sodium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, ammonia, tetramethylammonium hydroxide, ammonium bicarbonate, ammonium carbonate, anhydrous piperazine, piperazine hexahydrate, 1 -(2-Aminoethyl) piperazine or N-methylpiperazine is preferable from the viewpoint of increasing the polishing rate by a strong chemical polishing action. Some alkali compounds chelate bond with the metal impurities, but due to the weak binding force, the metal impurities are released when the silicon wafer is chemically polished. There is something that can be contaminated. For this reason, potassium hydroxide, sodium hydroxide, ammonia, or tetramethylammonium hydroxide is more preferable from the viewpoint of suppressing the contamination of the silicon wafer without forming complex ions with the metal impurities.

  The content of the alkali compound in the polishing composition is preferably 10% by mass or less from the viewpoint of suppressing gelation of the polishing composition or suppressing surface roughness of the silicon wafer due to the etching force of the alkali compound. 8 mass% or less is more preferable, and 5 mass% or less is the most preferable. On the other hand, from the viewpoint of maintaining the promoting action of polishing, the content of the alkali compound is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and most preferably 0.5% by mass or more.

  The chelating agent forms complex ions with the metal impurities and captures them to suppress contamination of the silicon wafer. Chelating agents include nitrilotriacetic acid, ethylenediaminetetraacetic acid, hydroxyethylenediaminetetraacetic acid, propanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, ethylenediaminetetraethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, ethylenediaminetetrakismethylenephosphonic acid, Acids such as diethylenetriaminepentaethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, triethylenetetraminehexaethylenephosphonic acid, triethylenetetraminehexamethylenephosphonic acid, propanediaminetetraethylenephosphonic acidpropanediaminetetramethylenephosphonic acid, and ammonium of these acids It is at least one selected from the group consisting of salts such as salts, potassium salts, sodium salts and lithium salts.

  The content of the chelating agent in the polishing composition is preferably 6% by mass or less, more preferably 3% by mass or less, and most preferably 1% by mass or less from the viewpoint of suppressing gelation of the polishing composition. On the other hand, the content of the chelating agent is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and most preferably 0.01% by mass or more from the viewpoint of maintaining the capturing action of metal impurities.

The effects exhibited by the above embodiment will be described below.
· D between the _SA and D _N4, since the relation of _{D SA ≦ D N4 ≦ (3} × D SA) is established, reduce the primary particle size, and secondary particle size may be obtained subdued abrasive grains small Therefore, the clogging of the polishing pad can be sufficiently reduced. Therefore, when the polishing is repeatedly performed, it is possible to reliably suppress a significant decrease in the polishing rate due to clogging of the polishing pad.

In addition, the said embodiment can also be changed and comprised as follows.
-You may add additives other than an alkali compound and a chelating agent to polishing composition. Examples of the additive include preservatives and surfactants. In particular, since the particle surface of colloidal silica is negatively charged, the anionic surfactant exhibits a function as a dispersant for colloidal silica and can be expected to further suppress clogging of the polishing pad.

-You may dilute and use polishing composition. The dilution factor is preferably 50 times or less, preferably 40 times or less, when the concentration of SiO ₂ solid content of colloidal silica in the polishing composition is 0.1 to 50% by mass from the viewpoint of obtaining a practical polishing rate. Is more preferable, and 25 times or less is most preferable.

  The substrate is not limited to a silicon wafer, and any substrate can be used as long as it is polished using a polishing composition containing colloidal silica and a polishing pad. As such a substrate, for example, a semiconductor device having a wiring structure made of copper, aluminum, or an alloy thereof, a semiconductor substrate such as silicon-germanium, a compound semiconductor substrate such as gallium-arsenic, indium-phosphorus, lithium tantalate, Examples thereof include oxide substrates made of lithium niobate, sapphire, and the like, aluminum substrates and glass substrates used for magnetic recording media for hard disk drives and the like, glass substrates and resin substrates used for liquid crystal displays, organic EL displays and the like.

Next, the present invention will be described more specifically with reference to examples and comparative examples.
Colloidal silica, an alkali compound and a chelating agent shown in Table 1 are mixed with ion-exchanged water to prepare polishing compositions of Examples 1 to 16 and Comparative Examples 1 to 7, and the dilution ratio thereof is 20 times. Polishing was performed under the following polishing conditions using a polishing liquid obtained by diluting with ion exchange water. Table 1 shows the evaluation results of the polishing rate and the rate of rate reduction shown below.

<Polishing conditions> Polishing apparatus: single-side polishing machine (SPM-15; manufactured by Fujikoshi Machine Industry Co., Ltd., 4 ceramic plates), object to be polished: 6-inch silicon wafer (p-type, crystal orientation <100>, silicon wafer Resistivity 0.1 Ω · cm or more and less than 100 Ω · cm), polishing condition of the object to be polished: a load in which polishing of the same silicon wafer is repeated under the condition that four silicon wafers are fixed with wax per ceramic plate : 31.5 kPa, surface plate rotation speed: 60 min ⁻¹ (60 rpm), ceramic plate rotation speed: 120 min ⁻¹ (120 rpm), polishing pad: Suba800 (manufactured by Rodel) without any dressing, for polishing usage of the composition: recycling, polishing time the feed rate as per minute 0.008m ³ (8L): 1 per batch 15 Holding the temperature of the composition: 40 ° C..

  <Polishing rate> The thickness at the center of the wafer was measured before and after polishing, and the polishing rate was calculated by dividing the difference in thickness before and after polishing by the polishing time (15 minutes). The polishing rate was calculated for each batch, and Table 1 shows the polishing rates calculated for the fifth, tenth, and fifteenth batches.

  <Speed maintenance ratio> Percentage of polishing rate of 10th batch with respect to polishing rate of 5th batch of silicon wafer ((polishing rate of 10th batch / polishing rate of 5th batch) × 100) and polishing rate of 5th batch The percentage of the polishing rate of the 15th batch with respect to (polishing rate of the 15th batch / polishing rate of the 5th batch) × 100) was calculated, and the rate maintenance rate was obtained.

In addition, the value of the average primary particle diameter shown in the “D _SA ” column of Table 1 was calculated using the specific surface area measured with FlowSorbII2300 (manufactured by micromeritics). The value of the average secondary particle size shown in the “D _N4 ” column was measured by N4 Plus Submicron Particle Sizer (manufactured by Beckman Coulter, Inc.). "KOH" shown in the "first alkali compound" and "second alkali compound" columns is an abbreviation for potassium hydroxide, "TMAH" is tetramethylammonium hydroxide, and "PIZ" is an anhydrous piperazine. “TTHA” shown in the “chelating agent” column is an abbreviation for triethylenetetraminehexaacetic acid, “EDPTO” is an abbreviation for ethylenediaminetetrakismethylenesulfonic acid, and “DTPA” is an abbreviation for diethylenetriaminepentaacetic acid. “A” shown in the “Evaluation” column of “Polishing rate” is a polishing rate of 1.0 μm / min or more, “B” is less than 1.0 μm / min and 0.9 μm / min or more, and “C” is 0. Less than 9 μm / min, 0.8 μm / min or more, “D” represents less than 0.8 μm / min, 0.7 μm / min or more, and “E” represents less than 0.7 μm / min, 0.6 μm / min or more. “A” shown in the “Evaluation” column of “Speed maintenance rate” is a speed maintenance rate of 90% or more, “B” is less than 90% and 80% or more, “C” is less than 80% and 70% or more, “ "D" represents less than 70% and 60% or more. In the “Evaluation” column of “Polishing rate” and the “Evaluation” column of “Speed maintenance rate”, “x” markedly decreased before reaching the 10th or 15th batch. It represents that the subsequent polishing was not performed, and the rate maintenance rate was not evaluated.

As shown in Table 1 above, Examples 1 to 8 were evaluated to be very excellent in both the polishing rate and the rate maintenance rate as compared with Comparative Examples 1 to 5. From these results, it is clear that the polishing compositions of Examples 1 to 8 are less likely to clog the polishing pad and can suppress a decrease in polishing rate due to repeated polishing. Further, from the speed maintenance rate of Example 8 and Comparative Example 2, by reducing DN ₄ to 30 nm or less, a decrease in the polishing rate due to repeated polishing is suppressed, and from the speed maintenance rate of Example 8 and Comparative Example 1, D 4 _{As a result of SA} being 20 nm or less, the reduction in the polishing rate was further suppressed. About Example 9, it resulted in that the polishing rate of 15th batch fell by reducing the addition amount of colloidal silica. As for Examples 10 and 11, compared with Comparative Example 6, both the polishing rate and the rate maintenance rate were very excellent. In Examples 12 and 13, both the polishing rate and the rate maintenance rate were excellent compared to Comparative Example 7. About Example 3, 10 and Example 5, 11, it became a result that a rate maintenance factor improved by using potassium hydroxide as an alkali compound. As for Examples 3 and 14 to 16, the change in the addition amount of the alkali compound or the presence or absence of the addition of the chelating agent did not significantly affect the polishing rate and the rate maintenance rate.

Further, for Examples 3 and 8 and Comparative Example 3, the relationship between the number of polishings and the polishing rate is shown in the graph of FIG. As shown in FIG. 1, Comparative Example 3 has the least number of polishings capable of maintaining a polishing rate of 0.60 μm / min or more, and Example 8 can maintain a polishing rate of 0.60 μm / min or more as compared with Comparative Example 3. It can be seen that the number of polishing is large, and the number of polishings in Example 3 that can maintain a polishing rate of 0.60 μm / min or more is higher than that in Example 8. From this result, it is clear that the smaller the DN ₄ is, the less clogging occurs, and it is possible to suppress a significant decrease in the polishing rate even if the polishing is repeated.

Further, the technical idea that can be grasped from the embodiment will be described below.
(1) _DN4 is 5 nm or more, The polishing composition as described in any one of Claims 1-3. Thereby, a practical polishing rate for the substrate can be obtained.

(2) _DSA is 3 nm or more, Polishing composition as described in any one of Claims 1-3. Thereby, a more practical polishing rate for the substrate can be obtained.

The graph which shows the relationship between the frequency | count of grinding | polishing, and grinding | polishing speed.

Claims (3)

A polishing composition used for polishing a substrate with a polishing pad and containing colloidal silica,
The colloidal silica, when the average primary particle diameter calculated based on the BET method expressed by D _SA, an average secondary particle diameter measured based on the laser diffraction method was expressed in D _N4, D _SA and D _A polishing composition wherein a relationship of D _SA ≦ D _N4 is established between _N4 and D _N4 is 30 nm or less. The polishing composition according to claim 1, wherein _DSA is 20 nm or less. The polishing composition according to claim 1, wherein a relationship of D _N4 ≦ 3 × D _SA is established between D _SA and D _N4 .

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