TWI388653B - Grinding method for grinding - Google Patents

Description

Regeneration method of polishing slurry

The present invention relates to a method of regenerating a polishing slurry for regenerating a used slurry used in a semiconductor wafer polishing step.

In the polishing step of the semiconductor wafer, it is generally roughly classified into a rough polishing step and a finishing polishing step according to the established surface roughness.

In the finishing grinding step, since it is necessary to establish a very small surface roughness, it is generally convenient to perform grinding with an ammonia-base colloidal ceria slurry to which a water-soluble polymer such as ethyl cellulose is added.

It is known that the colloidal ceria slurry used in the finishing grinding step may have metal contamination from a member constituting the polishing device, or may contain a large amount of coagulated cerium oxide solid in the slurry. And will therefore be discarded.

However, from the viewpoint of environmental protection, it is preferable to reuse such waste slurry. Therefore, there has been proposed a method for regenerating a slurry for polishing as described below.

For example, Patent Document 1 proposes a method in which coarse particles in a CMP (Chemical Mechanical Polishing) slurry are filtered by a filter, and then the slurry is concentrated by centrifugal separation or the like to regenerate the slurry.

Further, Patent Document 2 proposes to use agglomerated abrasive grains in a slurry, perform ultrasonication using ultrasonic waves, and perform separation of the agglomerated abrasive grains and non-agglomerated abrasive grains by adjusting the temperature of the polishing slurry. Pulp recovery side law.

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-170793 (Patent Document 2) Japanese Patent Laid-Open Publication No. 2004-63858

However, the method described in each of the above patent documents is insufficient in terms of recovering and recycling the colloidal ceria slurry, and the following problems are caused.

That is, the ammonia contained in the colloidal cerium oxide slurry is a volatile substance, and the pH value is changed at the time of recovery, and there is a problem that it cannot be directly reused.

Further, the water-soluble polymer in the slurry tends to aggregate into a gel form, and even if filtration or the like is applied by a filter, a problem that a plug is formed in the filter occurs.

Furthermore, the finishing polishing step is a final step in the semiconductor wafer fabrication step, and it will be necessary to pay close attention to the problem of metal contamination.

Therefore, although the method described in each of the above patent documents can solve any of the problems, it is impossible to completely solve the problems.

It is an object of the present invention to provide a reusable slurry that can be used in a polishing step (especially a finishing polishing step) of a semiconductor wafer, which can greatly reduce the amount of slurry used, thereby reducing semiconductor wafer fabrication. A method of regenerating a slurry for polishing.

The method for regenerating the polishing slurry of the present invention is a method for regenerating a polishing slurry comprising colloidal cerium oxide and using the used polishing slurry used in the semiconductor wafer polishing step, characterized in that The method comprises the steps of: adding a dispersing agent to the recovered used pulp, and suppressing the gelation of the used slurry; and performing ultrasonic irradiation on the used slurry added with the dispersing agent to make the gelled slurry and the agglomerated two a step of dispersing cerium oxide; and a step of removing the foreign matter in the used slurry after the ultrasonic irradiation by a filter.

The dispersant may be any of (1) a salt, (2) a polarized molecule, and (3) a pH stabilizer.

(1) Salt: may be selected from cations selected from Li ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , NH ⁴⁺ , and selected from CO ₃ ^2- , Cl ^- , SO ₄ ^2- , S ^2- All salts of an anion combination of F ^- , NO ³ , PO ₄ ^3- , CH ₃ COO ^- , OH ^- .

(2) Polarized molecules: those containing ammonia, alcohols, sugars, and ethers may be used.

(3) pH stabilizer: such as ammonia, KOH, NaOH can be used.

According to the present invention, in addition to adding a dispersing agent to the used slurry to suppress gelation of the slurry, the gelled slurry and the condensed cerium oxide are dispersed by ultrasonic irradiation, and the foreign matter is removed by the filter. The foreign matter removal by the filter can be efficiently performed, and the gelled condensed cerium oxide can be captured by the filter to prevent the cerium dioxide in the slurry from being reduced, and the used slurry can be appropriately used. Reuse.

Above, before the step of adding a dispersing agent, it is preferable to use the above-mentioned used The pH of the slurry is measured, and a step of replenishing the lye to adjust the pH of the used slurry is performed.

Among them, for the lye to adjust the pH, for example, ammonia water or the like can be used.

According to the present invention, the aggregation of the slurry and the cohered cerium oxide can be further prevented by adjusting the pH value in advance.

In the present invention, before the step of adding the dispersing agent, it is preferred to carry out the measurement of the viscosity of the above-mentioned used slurry, and to carry out the step of adjusting the viscosity of the used slurry by replenishing the water-soluble polymer.

Here, as the water-soluble polymer for adjusting the viscosity, for example, ethyl cellulose, ethylene glycol or the like can be used.

According to the present invention, by replenishing the water-soluble polymer, the viscosity of the used slurry can be appropriately adjusted, and a suitable slurry which can be reused can be obtained.

In the present invention, it is preferred to carry out the temperature measurement of the above-mentioned used slurry before the step of adding the dispersant, and to carry out the step of adjusting the temperature of the used slurry by means of a heat exchanger.

According to the present invention, the gelled substance in the used slurry can be dispersed under optimum temperature conditions by performing temperature adjustment of the used slurry before the addition of the dispersant.

In the present invention, after the ultrasonic polishing using the above-mentioned polishing slurry, it is preferred to carry out the step of removing the metal ions in the used polishing slurry.

Here, as a method of removing metal ions, a method of adding a chelating agent to used ceria may be employed.

The chelating agent is composed of an organic amine carboxylate, and for example, EDTA (Ethylene Diamine Tetraacetic Acid, ethylenediaminetetrachloride) can be used. Sodium acetate), DTPA (Diethlene Triamine Pentaacetic Acid), NTA (Nitrilo Triacetic Acid), and the like.

According to the present invention, since the metal ions mixed in the polishing slurry during polishing can be removed, when the semiconductor wafer polishing is performed using the used slurry, the semiconductor wafer can be prevented from being contaminated by metal ions.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a view showing a polishing slurry regenerating apparatus 1 according to an embodiment of the present invention. The regenerating apparatus 1 recovers the used polishing slurry used in the finishing mill 2, and grinds the collected polishing slurry. After adjusting the pH value, specific gravity, and viscosity of the slurry, the metallic foreign matter is removed and regenerated, and is regenerated into the polishing slurry for the finishing mill 2.

The regeneration device 1 includes a multi-stage lamination tank 3, a heat exchanger 4, a storage tank 5, and a foreign matter filtration filter 6.

The multi-stage lamination tank 3 has a function of a sedimentation separation means for removing a large solid cerium oxide in the recovered slurry, which is removed by precipitation separation, and the inside of the tank is partitioned into a plurality of treatment tanks by using a plurality of composite rafts 31 of different heights. .

The plurality of jaws 31 are sequentially lowered from the side of the supply of the recovered slurry toward the side surface 32 where the discharge port is formed. Then, if the used slurry is supplied to the initial treatment tank and overflows in the treatment tank, the overflow portion will flow into the adjacent treatment tank, repeat in this order, and finally discharge from the discharge port. .

In each treatment tank, the large specific gravity is larger than that of the large cerium oxide solid used in the slurry, and the used supernatant portion of the smaller specific gravity is poured into the adjacent treatment tank, by repeating In this step, the large cerium oxide solids separate the precipitate and are removed from the used slurry.

The heat exchanger 4 is connected to the rear stage of the multi-stage lamination tank 3 via a pipe, and the used slurry discharged from the multi-stage lamination tank 3 is cooled, and the temperature is adjusted to be separated by a material having good thermal conductivity: The used slurry flow path formed at the discharge port below the multi-stage lamination tank 3 and the flow path for circulating the cooling water are subjected to heat exchange between the used slurry and the cooling water, and the temperature at which the slurry is used is performed. Adjustment. Further, the heat exchanger 4 may be in various forms as long as heat exchange can be performed between the liquid and the liquid, and for example, a plate heat exchanger, a double tube type heat exchanger, and a multi-tube type can be employed. Heat exchangers, etc.

The storage tank 5 is connected to the rear stage of the heat exchanger 4 via a pipe, and is stored in the used slurry subjected to temperature adjustment by the heat exchanger 4, and is subjected to adjustment of the state in which the slurry is used, in the storage tank 5. In order to measure the temperature, viscosity, specific gravity, and pH value of the used slurry stored therein, a thermometer 51, a viscometer 52, a hydrometer 53, and a pH meter 54 are provided.

Further, an ultrasonic oscillating device is disposed at the bottom of the storage tank 5.

The ultrasonic oscillating device irradiates the used slurry inside the storage tank 5 with ultrasonic waves, and by superimposing the used slurry, the gelled slurry and the condensed cerium oxide are dispersed. In addition, when ultrasonic waves of MHz units are used for the ultrasonic waves applied by the polishing slurry, the condensed cerium oxide cannot be formed due to the influence of the water-soluble polymer agent or the like. Disperse, and thus preferably ultrasonic waves in kHz units.

The foreign matter filtration filter 6 is connected to the rear stage of the storage tank 5 via a pipe, and foreign matter such as a large solid cerium oxide material in the slurry is used and captured by filtration. The foreign matter filtration filter 6 is configured by a filter such as a depth filter or a membrane filter disposed in a flow path in which the slurry is used.

Next, the operation of the above-described reproducing apparatus 1 will be described based on the flowchart shown in Fig. 2 .

When the used slurry is recovered from the finishing mill 2 (step S1), the recovered used slurry is supplied to the multi-stage lamination tank 3 of the regenerating apparatus 1, and precipitation separation is performed inside each treatment tank. The large cerium oxide solid is subjected to precipitation removal (step S2).

Next, the used slurry is removed from the solid cerium oxide solids, the cooling water in the heat exchanger 4 is circulated, and the used slurry is adjusted to an appropriate temperature (step S3), and then supplied to the storage tank 5. . Further, the liquid temperature is adjusted in the range of about 20 ° C to 30 ° C based on the value measured by the thermometer 51 in the storage tank 5.

The specific gravity, viscosity, and pH adjustment of the used slurry supplied to the storage tank 5 are sequentially performed.

The specific gravity adjustment is performed by adding the raw liquid of the colloidal ceria slurry to the storage tank 5 based on the measured value of the hydrometer 53 (step S4). In addition, the specific gravity adjustment is carried out in the range of 1.010 to 1.020.

The viscosity adjustment is carried out by adding a water-soluble polymer such as ethyl cellulose to the storage tank 5 based on the measured value of the viscosity meter 52 (step S5). In addition, the viscosity adjustment is between 0.004 and 0.01 Pa. s (will 4~10cP Implemented within the range of converted values).

The pH adjustment is performed by adding ammonia water to the storage tank 5 based on the measured value of the pH meter 54 (step S6). Further, the pH value is in the range of pH 10 to pH 11. The reason is that if the pH is too low, the polishing rate will decrease. Conversely, if it is too high, the cerium oxide will dissolve.

When the above adjustment is completed, any one of the salt, the polarizing molecule, and the pH stabilizer is added as a dispersing agent, and aggregation of the used slurry is suppressed (step S7), and the ultrasonic oscillating device is operated. On the other hand, when the ultrasonic wave is applied to the used slurry, the gelled slurry and the condensed cerium oxide are dispersed (step S8). Further, as the specific dispersant, KCl, NH ₄ HCO ₃ or the like can be used as the salt.

Finally, the used slurry irradiated with the ultrasonic wave is filtered by the foreign matter filter 6 to remove the foreign matter (step S9), and the regenerated polishing slurry is recovered from the branch pipe and supplied again. The finishing mill 2 is used.

[Examples]

Next, an embodiment of the present invention will be described. Further, the present invention is not limited to this.

(Experimental Example 1)

The slurry was diluted to 20 times with water, and after 500 minutes of polishing, the used slurry was subjected to ultrasonic irradiation, and then the foreign matter was removed by the foreign matter filter 6 to obtain a regenerated slurry.

(Experimental Example 2)

For the same used slurry as in Experimental Example 1, the dispersion was added. After the ammonia water of the agent is applied, ultrasonic irradiation is performed, and the foreign matter is removed by the foreign matter filter 6 to obtain a regenerated slurry.

(Experimental Example 3)

With respect to the same used slurry as in Experimental Example 1, after the KCl water of the dispersing agent was added, ultrasonic irradiation was performed, and the foreign matter was removed by the foreign matter filter 6 to obtain a regenerated slurry.

(Experimental Example 4)

The stock solution of the colloidal cerium oxide slurry was diluted 20 times with water to obtain a slurry.

(Experimental Example 5)

The same slurry as that used in Experimental Example 1 was directly used, and it was used as a regenerated slurry.

■1. Relevant polished semiconductor wafer quality

Using the polishing slurry of Experimental Example 1 to Experimental Example 5, a semiconductor wafer having a diameter of 150 mm was polished, and the surface quality of each of the polished semiconductor wafers was evaluated. The polishing conditions were set such that the polishing pad was PORIMEX, the number of revolutions of the stage was 50 rpm, the number of revolutions of the polishing head was 70 rpm, the pressure was 80 g/cm ² , and the polishing time was 30 minutes.

The quality assessment program evaluates the grinding rate, micro-roughness, and number of defects.

The micro-roughness-related short wavelength is expressed by an index when the value measured in Experimental Example 4 is set to 100 by a particle counter (KLA-Tencor SP1) after grinding for 30 minutes. On the other hand, the relevant long wavelength is obtained by averaging the rms at three places near the center of the wafer after grinding for 30 minutes. The index is expressed in accordance with the index when Experimental Example 4 is set to 100.

The number of defects counts the number of defects in the polished surface of a wafer after grinding for 30 minutes.

The results are shown in Table 1.

Regarding the polishing rate, it was confirmed that the polishing rate was comprehensively improved by performing ultrasonic irradiation, and in particular, in the case where the dispersing agent composed of KCl water was added in Experimental Example 3, the polishing rate was greatly increased. On the other hand, in the case of Experimental Example 4, since the stock solution was diluted only with water, the dispersibility of the water-soluble polymer was poor, and partial aggregation occurred on the polished surface during polishing to form a protective film-like action, and thus the polishing rate was estimated. Will decrease.

Regarding the short-wavelength micro-roughness, it was found that any of Experimental Example 1 to Experimental Example 3 was the same as the turbidity degree of Experimental Example 4 in which the stock solution was diluted. In the case of the related experimental example 5, the ultrasonic wave was not applied at all, and the filtration was observed, and it was found that the turbidity was greatly lowered.

Regarding the long-wavelength micro-roughness, it was confirmed that any of Experimental Example 1 to Experimental Example 3 had the same degree of roughness as Experimental Example 4, and similarly, in the case of Experimental Example 5, it was found that the roughness would become large. .

Regarding the number of related defects, it was found that any of Experimental Examples 1 to 3 was the same number of defects as Experimental Example 4, and in Experimental Example 5, the number of defects was greatly increased.

From the above, it can be confirmed that, as in Experimental Example 5, even if the recovered used slurry diameter is directly used for the polishing, the polishing rate, the micro roughness, and the number of defects cannot be reused for the experimental example 4 in which the stock solution is diluted. The degree of grinding, but with the addition of ultrasonic irradiation and dispersing agent, these values will be greatly improved, and the used slurry can be used as a regenerated slurry.

■2. Relevant filtration by the foreign matter filter 6

With respect to the polishing slurry of Experimental Example 1 to Experimental Example 5, the filter size of the foreign matter filtration filter 6 was changed, and it was confirmed to what extent the filter sieve pores were fine. The results are shown in Table 2.

As seen from Table 2, Experimental Example 4 (diluted solution of the stock solution), Experimental Example 5 (untreated used slurry), even with a filter having a filter size of 20 μm, the plug condition was quite severe and filtration was impossible.

In the case of performing ultrasonic irradiation in Experimental Example 1, although a filter having a filter size of 20 μm was able to be filtered, a filter having a filter size of 10 μm or 5 μm having a fine mesh opening would still have a plug condition.

On the other hand, in Experimental Example 2 (ammonia addition + ultrasonic) and Experimental Example 3 (KCl water addition + ultrasonic), even a filter having a filter size of 5 μm can be filtered, and it is confirmed that the filter can be used to capture 1 ~10 μm grade cerium oxide solids (dry cerium oxide).

Next, in the relevant Experimental Example 1 to Experimental Example 3, it was confirmed by the foreign matter filtration filter 6, to what extent the cerium oxide solid matter can be captured. In the experiment, each slurry was continuously circulated and subjected to filtration for 300 minutes, and evaluation was performed by measuring the number of filtered ceria having a size of 3 μm after filtration. The results are shown in Table 3. In addition, the filtration of each slurry is a filter of a filter size that is sustainable and well filtered. Specifically, in Experimental Example 1, a filter having a filter size of 20 μm was used, in Experimental Example 2, a filter having a filter size of 10 μm, and in Experimental Example 3, a filter having a filter size of 5 μm was used.

As is apparent from Table 3, after the addition of the dispersant, after the ultrasonic irradiation, if the foreign matter filter 6 is used for filtration, the dry cerium oxide in the slurry can be greatly reduced. Incidentally, the number of dried cerium oxide in the slurry of Experimental Example 5 was measured, and it was found that there were about 6,000 to 8,000 dry cerium oxide, and it was found that the number of dry cerium oxide was greatly reduced.

■3. Confirmation of dispersion effect

The dispersion effect by the ultrasonic irradiation and the addition of the dispersant was confirmed by measuring the average particle diameter of the cerium oxide microparticles in the slurry and the dielectric potential of the slurry. In addition to the above-mentioned Experimental Example 1 and Experimental Example 3 to Experimental Example 5, in addition to the comparison of different dispersing agents, the following Experimental Example 6 was added. Further, the dielectric potential refers to the charged state of the surface of the cerium oxide, and the larger the value, the better the dispersion state.

(Experimental Example 6)

For the same polishing slurry as in Experimental Example 1, after the methanol of the dispersing agent was added, ultrasonic irradiation was performed to obtain a regenerated slurry.

The results are shown in Table 4.

In Experimental Example 5 (untreated used slurry), the intervening potential was greatly lowered and the dispersibility of the slurry was poor as compared with Experimental Example 4 (diluted solution of the stock solution). On the other hand, the dielectric potential of Experimental Example 1 (ultrasonic irradiation) was restored to the extent of Experimental Example 4, and it was confirmed that the dispersibility of the slurry was greatly improved.

Further, in the case of Experimental Example 6 (methanol addition + ultrasonic wave), it was confirmed that the dispersibility was slightly improved as compared with Experimental Example 1.

The dielectric potential of Experimental Example 3 (KCl water + ultrasonic wave) was greatly improved compared with other experimental examples, and it was confirmed that by adding KCl water as a dispersing agent, the dispersibility was excellent, and the average particle diameter was also improved. In the case of being smaller than the other experimental examples, it was confirmed that the method of Experimental Example 3 was used for regeneration. The slurry will be suitable for grinding.

■4. Differences in dispersion effect achieved with different dispersants

Next, with respect to the used slurry of Example 1, the difference in the degree of aggregation at the time of adding a different dispersing agent was compared. The result is shown in Figure 3. Further, FIG. 3, "Ref" refers to the use of any excessive slurry was not added, "KCl" means a dispersant by adding KCl, 'NH ₄ HCO _3' means a dispersant was added NH ₄ HCO ₃ . Further, when the amount of the dispersant added by the salt is 20 times that of the slurry diluted with water, 0.01 mol/L to 0.001 mol/L is preferably added.

It can be seen from Fig. 3 that even in the range of pH 9.8 to 10.1 in the usual use region, even if KCl has a sufficient effect of lowering the degree of aggregation, in the case of NH ₄ HCO ₃ , in a wide pH region exceeding this range, The effect of lowering the degree of aggregation was confirmed, and it was confirmed that it was extremely suitable as a dispersing agent.

1‧‧‧Regeneration device

2‧‧‧Finishing mill

3‧‧‧Multi-layer stacking trough

4‧‧‧ heat exchanger

5‧‧‧ storage tank

6‧‧‧ Foreign material filter

31‧‧‧堰板

32‧‧‧ side

51‧‧‧ thermometer

52‧‧‧Viscometer

53‧‧‧Specometer

54‧‧‧pH meter

Fig. 1 is a schematic structural view of a reproducing apparatus according to an embodiment of the present invention.

Fig. 2 is a flow chart showing the steps of the regeneration method of the above embodiment.

Figure 3 is a plot of the dispersion effect achieved by different dispersants.

S1‧‧‧Recycling

S2‧‧‧Precipitation removal

S3‧‧‧ liquid temperature adjustment

S4‧‧‧ proportion adjustment

S5‧‧‧ Viscosity adjustment

S6‧‧‧pH adjustment

S7‧‧‧ Dispersant addition

S8‧‧‧Supersonic irradiation

S9‧‧ Foreign body removal

Claims (9)

A method for regenerating a slurry for polishing, comprising a colloidal cerium oxide, and regenerating the used slurry used in the semiconductor wafer grinding step, characterized by comprising: using the used slurry after recycling Adding a dispersing agent and inhibiting the step of gelating the used slurry, wherein the dispersing agent is one of KCl and NH ₄ HCO ₃ , and the dispersing agent is added at a concentration of 0.01 to 0.001 mol/L; A step of supersonic irradiation using a slurry, a step of dispersing the gelled slurry and the agglomerated ceria, and a step of removing the foreign matter in the used slurry after the ultrasonic irradiation by a filter. The method for regenerating a polishing slurry according to claim 1, wherein before the step of adding the dispersing agent, the pH value of the used slurry is measured, and the lye is replenished to adjust the used slurry. The pH step, wherein the pH of the used slurry is adjusted to a pH of 9.8 to 11. The method for regenerating a polishing slurry according to claim 1 or 2, wherein the viscosity measurement of the used slurry is performed before the step of adding the dispersing agent, and the water-soluble polymer is added to adjust the use. The step of slurry viscosity is adjusted, and the viscosity of the used slurry is adjusted to be 0.004~0.01 Pa. s. Regeneration of polishing slurry as claimed in claim 1 or 2 a method, wherein, before the step of adding a dispersant, performing temperature measurement of the above-mentioned used slurry, and performing a step of adjusting a temperature of the used slurry by using a heat exchanger, wherein an adjustment range of the temperature of the used slurry is used It is 20~30 °C. The method for regenerating a polishing slurry according to the third aspect of the invention, wherein the temperature measurement of the used slurry is performed before the step of adding the dispersing agent, and the temperature of the used slurry is adjusted by using a heat exchanger. The step of adjusting the temperature of the used slurry is 20~30 °C. The method for regenerating a polishing slurry according to claim 1 or 2, wherein the step of removing the metal ions in the used slurry after performing the ultrasonic irradiation on the used slurry. The method for regenerating a polishing slurry according to the third aspect of the invention, wherein the step of removing the metal ions in the used slurry after performing the ultrasonic irradiation on the used slurry. The method for regenerating a polishing slurry according to the fourth aspect of the invention, wherein the step of removing the metal ions in the used slurry after performing the ultrasonic irradiation on the used slurry. The method for regenerating a polishing slurry according to claim 7 or 8, wherein the removal of metal ions in the used polishing slurry is carried out by adding a chelating agent to the used polishing slurry.