JP4849660B2 - Slurry regeneration method - Google Patents

Description

  The present invention relates to a method for regenerating a slurry used for chemical mechanical polishing.

  Wafers such as semiconductor devices and electronic components are subjected to various processes such as cutting and polishing in the course of manufacturing. 2. Description of the Related Art In recent years, with the reduction in design rules for semiconductor integrated circuits, chemical mechanical polishing (CMP) has been frequently used in planarization processes for interlayer films and the like. Polishing of a wafer by CMP is performed by holding a wafer by a wafer holding head, pressing the wafer against a rotating polishing surface plate with a predetermined pressure, and a chemical abrasive (hereinafter referred to as “slurry”) between the polishing surface plate and the wafer. For example).

  Usually, in CMP, the polishing properties deteriorate, especially the increase in microscratches, such as polishing particles from reaction products, polishing pads, or agglomeration due to a decrease in zeta potential. In many cases, they are discarded without being reused. However, in recent years, it is strongly desired to reuse the slurry in consideration of environmental pollution and further cost reduction requirements.

Against this background, a slurry regeneration method that detects the pH value and zeta potential of used slurry and adjusts the used slurry to the optimum pH value and zeta potential by adding additives based on the detected value is proposed. (For example, refer to Patent Document 1).
JP 2000-158343 A

  However, in the regeneration method described in Patent Document 1, it is necessary to add a large amount of additive to the used slurry, and a sufficient cost reduction cannot be expected. Further, in CMP polishing of a wafer having a metal film such as tungsten, it is difficult to adjust the zeta potential because removal of metal components eluted in the slurry or impurities such as mixed metal debris is insufficient.

  The present invention has been made in view of such circumstances, and provides a slurry regeneration method for regenerating used slurry to a polishing quality similar to that of unused slurry by a low-cost and simple method. It is aimed.

In order to achieve the above object, according to the present invention, the invention according to claim 1 includes a step of storing a used slurry containing impurities whose zeta potential has changed due to inclusion of impurities in a recovery tank; The step of removing impurities by passing the used slurry stationary in the tank through the primary filter, and the used slurry passing through the primary filter being passed through the metal removal filter. And a step of removing impurities smaller than impurities removed by the primary filter by passing the used slurry that has passed through the metal removal filter through a secondary filter. When, wherein the spent slurry that has passed through the secondary filter particle number is measured by being passed through the particle counter, including the spent slurry The use that has passed through the secondary filter from the step of being stored in a recovery tank until the number of particles having a predetermined size or more is equal to or less than the number of particles having a predetermined size or more included in unused slurry. The step of repeating up to the step of measuring the number of particles of the used slurry, and the used number of particles having a predetermined size or more included in the unused slurry is equal to or less than the number of particles of the predetermined size or more included in the unused slurry. When the used slurry does not reach the predetermined pH value, the recovery tank is used until the used slurry reaches the predetermined pH value. a step of repeating the steps until the pH value is measured from the process is stored in a step of adjusting agent is added to the spent slurry that has passed through the pH measuring device, the use of the adjusting agent is added In the slurry regeneration method in which the zeta potential of the used slurry is measured, the zeta potential of the used slurry is the same as the zeta potential of the unused slurry. Until the zeta potential is reached, the process from returning to the recovery tank to the process of measuring the zeta potential is repeated.

  According to the invention of claim 1, the zeta potential is changed due to impurities mixed in while passing through the piping path or used for polishing and containing impurities such as pad scraps, metal eluates and metal scraps. The deteriorated slurry passes through the metal removal filter.

  As a result, impurities are removed from the slurry containing impurities, and the zeta potential that has changed to near the isoelectric point is restored to the same state as the unused slurry before containing impurities, and the processing rate, scratches, surface roughness The processing quality such as this is improved to the same level as that of unused slurry.

  As described above, according to the slurry regeneration method of the present invention, impurities can be removed from a slurry in which the zeta potential is changed due to contamination or by using impurities by a low-cost and simple mechanism using a filter. By removing the slurry, the zeta potential can be recovered to regenerate the slurry containing impurities to the same polishing quality as that of the unused slurry.

  Hereinafter, preferred embodiments of a slurry regeneration method according to the present invention will be described in detail with reference to the accompanying drawings.

  First, the configuration of a regenerator that performs the slurry regenerating method according to the present invention will be described. FIG. 1 is a conceptual diagram of a playback device.

  As shown in FIG. 1, the regeneration apparatus 1 includes a recovery tank 11, a pump 12, a metal removal filter 13, a primary filter 14, a secondary filter 18, a regeneration slurry tank 15, a particle counter 16, a pH measuring device 17, and a valve A. , B and C, and the used slurry US containing impurities discharged from the CMP polishing apparatus 2 is regenerated.

  The CMP polishing apparatus 2 holds a wafer having a metal film such as tungsten with a rotating polishing head 22 and presses the wafer against the rotating polishing pad 21 while supplying the slurry S onto the polishing pad 21 from the slurry supply pipe 24. Then, chemical mechanical polishing is performed. As the slurry S, a slurry in which silica abrasive grains are dispersed in an usually acidic solution is used.

  A plurality of slurry collection boxes 23 for collecting used slurry US are provided around the polishing pad 21 to collect used slurry US scattered from the polishing pad 21 rotating during polishing.

  In the recovery tank 11, the used slurry US recovered in the slurry recovery box 23 is collected, and the collected used slurry US is allowed to stand for a predetermined period of time, and the H2O2 contained in the used slurry US is decomposed. .

  The used slurry US after the decomposition of H 2 O 2 is conveyed by the pump 12. A tube pump is used as the pump 12.

  The primary filter 14 separates impurities of about 10 μm or more, such as fine polishing scraps generated from the polishing pad 21 and aggregated coarse polishing abrasive grains, from the used slurry US that has been conveyed.

  The metal removal filter 13 is a filter that removes impurities such as metal components eluted in the used slurry US or mixed metal scraps, and is formed of a material that performs an ion exchange reaction or a chelate reaction. For example, Metolate manufactured by Nomura Micro Science Co., Ltd. can be suitably used.

  The secondary filter 18 removes impurities such as coarse particles that could not be removed by the primary filter 14 or the metal removal filter 13.

  The particle counter 16 measures the particle size and the number of particles in the used slurry US that has passed to the secondary filter 18. As the particle counter 16, for example, KS-71 manufactured by Rion Co., Ltd. is used.

  The regenerated slurry tank 15 passes through the primary filter 14, the metal removal filter 13, and the secondary filter 18, and as a result of measurement by the particle counter 16, the number of particles having a size of 3 μm or more and 5 μm or more is unused. The used slurry US having a pH value changed to a predetermined value is stored.

  The pH measuring device 17 measures the pH value of the used slurry US passed to the secondary filter 18 or the used slurry US stored in the regenerated slurry tank 15. As a result of measuring the pH value of the used slurry US stored in the regenerated slurry tank 15, if the pH value is not suitable for the pH value of the regenerated slurry, a regulator is supplied by a supply device (not shown) to adjust the pH. The value is adjusted and returned to the CMP polishing apparatus 2 from the regenerated slurry tank 15 as a regenerated slurry RS.

  The supply amount and the supply speed of the used slurry US to the recovery tank 11, the primary filter 14, the metal removal filter 13, the secondary filter 18, and the regeneration slurry tank 15 are provided in each apparatus or a pipe connecting the filters. Performed by the valves A, B, and C and the pump 12.

  The used slurry is regenerated by the regenerator configured as described above.

  In addition, when a slurry in which impurities are mixed in due to some influence when not in use and contaminated and the zeta potential has changed is regenerated, it can be regenerated by a regenerator having a similar configuration. When it is not necessary to stand and decompose H 2 O 2, the recovery tank 11 is not necessary for the above configuration, and slurry containing impurities is directly supplied to the primary filter 14.

  In the present embodiment, the primary filter 14 and the secondary filter 18 are provided before and after the metal removal filter 13, respectively, but the present invention is not limited thereto, and only the primary filter 14 or only the secondary filter 18 is provided. It may be a configuration.

  Next, the slurry regeneration method according to the present invention will be described. FIG. 2 is a flowchart showing the procedure of the slurry regeneration method.

  In the slurry regeneration method of the present invention, first, a used slurry containing impurities scattered from the polishing pad 21 during polishing is obtained by a plurality of slurry recovery boxes 23 provided around the polishing pad 21 of the CMP polishing apparatus 2 shown in FIG. US is collected (step S1).

  The used slurry US collected in the slurry collection box 23 is collected manually or automatically in the collection tank 11 and is allowed to stand for a predetermined period (step S2).

  At this time, the used slurry US used for polishing a wafer having a tungsten metal film contains H2O2 added to make the slurry acidic, and tungsten metal components and debris eluted during polishing. It is. As shown in the table of FIG. 3, H2O2 is gradually decomposed and lowered in concentration by the action of tungsten.

  When the H2O2 concentration in the used slurry US becomes almost zero, the valve A and the valve B are opened, the pump 12 is operated, and the used slurry US in the recovery tank 11 is conveyed to pass the primary filter 14. Pass (step S3).

  As a result, impurities of about 10 μm or more such as fine polishing debris generated from the polishing pad 21 mixed in the used slurry US and aggregated coarse abrasive grains are separated.

  The used slurry US that has passed through the primary filter 14 then passes through the metal removal filter 13 (step S4).

  From the used slurry US that has passed through the metal removal filter 13, metal components, mixed metal scraps, and the like are removed by a fiber material that performs an ion exchange reaction or a chelate reaction in the metal removal filter.

  The used slurry US that has passed through the metal removal filter 13 passes through the secondary filter 18 to remove coarse particles that could not be removed by the preceding filter (step S5).

  The used slurry US that has passed through the secondary filter 18 is measured by the particle counter 16 for the number of particles of 3 μm or more and the number of particles of 5 μm or more (step S6).

  At this time, if the number of particles of 3 μm or more and the number of particles of 5 μm or more are equal to or less than the unused slurry as a result of measurement by the particle counter 16, the process proceeds to the next determination. If there are more unused slurries, the used slurry US after passing through the secondary filter 18 is circulated to the recovery tank 11 and again passes through the primary filter 14, the metal removal filter 13, and the secondary filter 18. (Decision E1).

  As a result, as shown in FIG. 4, the number of particles of 3 μm or more and 5 μm or more in the used slurry US decreases to the same level or less as the unused slurry with the processing time.

  When the number of particles of the used slurry US decreases to the same level as that of the unused slurry, the pH value of the used slurry US after passing through the secondary filter 18 is measured by the pH measuring device 17.

  At this time, when the pH value is about 5.5 to 6.0, the process proceeds to the next step. If it is not about 5.5 to 6.0, the used slurry US after passing through the secondary filter 18 is circulated to the recovery tank 11, and the primary filter 14, the metal removal filter 13, and the secondary filter 18 are again connected. Pass (determination E2).

  When the pH value of the used slurry US after passing through the secondary filter 18 becomes about 5.5 to 6.0, the valve B is closed and the valve C is opened to recycle the used slurry US. It is transported to 15 and stored (step S7).

  The used slurry US in the regenerated slurry tank is measured for pH value by the pH measuring device 17, and the pH value is adjusted by adding a regulator based on the measured value. The used slurry US is adjusted to a pH value to become a regenerated slurry RU (step S8).

  In general, in polishing a wafer having a tungsten metal film, the slurry is preferably acidic, and a pH value is adjusted to be acidic by adding a regulator such as H 2 O 2, NaOH, or HNO 3.

  The regenerated slurry RS is measured for zeta potential after the pH value is adjusted. At this time, when the zeta potential is not 1 mV or more, the regenerated slurry RS is returned to the recovery tank 11 again, and again passes through the primary filter 14, the metal removal filter 13, and the secondary filter 18, and the number of particles and the pH value are confirmed. (Determination E3).

  As shown in FIG. 5, the regenerated slurry RS processed by the primary filter 14, the metal removal filter 13, and the secondary filter 18 and adjusted in pH value has a zeta potential higher than that of the unprocessed used slurry US. Will increase. As a result, the number of scratches of the wafer having the tungsten metal film polished with the regenerated slurry is the same as that obtained when the unused slurry is used, as shown in FIG. Also in the difference in microroughness, as shown in FIG. 7, a polishing result similar to that obtained when an unused slurry is used is obtained, which is improved from the used slurry US before processing.

  The regenerated slurry RS for which all the processes have been completed is supplied again to the CMP polishing apparatus 2 and used as a polishing slurry (step S9).

  As described above, according to the slurry regeneration method according to the present invention, impurities can be removed from a slurry in which impurities are contained and zeta potential has changed due to being used for contamination or polishing by a low-cost and simple mechanism using a filter. Removal is performed to restore the zeta potential of the slurry containing the impurities. As a result, the regenerated slurry can be used with the same polishing quality as that of the unused slurry, and it is possible to regenerate high-quality slurry in response to environmental pollution countermeasures and cost reduction requirements.

The conceptual diagram of the slurry reproduction | regeneration apparatus concerning this invention. The flowchart which showed the procedure of the reproduction | regeneration method of a slurry. The chart which showed the relation between the standing time of slurry and the concentration of H2O2. A chart showing the number of particles in the slurry after passing through the filter. A chart comparing differences in zeta potential. A chart comparing the number of scratches. Chart comparing surface microroughness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Regenerating apparatus, 2 ... CMP polisher, 11 ... Recovery tank, 12 ... Pump, 13 ... Metal removal filter, 14 ... Primary filter, 15 ... Regenerated slurry tank, 16 ... Particle counter, 17 ... pH measuring device, 18 ... secondary filter, 21 ... polishing pad, 22 ... polishing head, 23 ... slurry recovery box, 24 ... slurry supply pipe, A, B, C ... valve, RS ... recycled slurry, US ... used slurry (contains impurities) Slurry)

Claims (1)

A used slurry containing impurities whose zeta potential has changed due to the inclusion of impurities is stored in a recovery tank and allowed to stand;
A step of removing impurities by passing the used slurry placed in the recovery tank through a primary filter;
The metal component is removed by passing the used slurry that has passed through the primary filter through a metal removal filter;
A step of removing impurities smaller than impurities removed by the primary filter by passing the used slurry that has passed through the metal removal filter through a secondary filter;
The used slurry that has passed through the secondary filter is passed through a particle counter, whereby the number of particles is measured, and the number of particles of a predetermined size or more contained in the used slurry is converted into unused slurry. Repeating the steps from storing in the recovery tank until measuring the number of particles of the used slurry that has passed through the secondary filter until the number of particles not less than the predetermined size is included,
The used slurry in which the number of particles greater than or equal to the predetermined size included is equal to or less than the number of particles greater than or equal to the predetermined size included in the unused slurry is passed through a pH measuring device, and thus the pH value If the used slurry does not reach the predetermined pH value, the process from storing in the recovery tank to the step of measuring the pH value until the used slurry reaches the predetermined pH value. Repeating the process;
A step of adding a regulator to the used slurry that has passed through the pH meter;
In the slurry regeneration method, the step of measuring the zeta potential of the used slurry to which the adjusting agent has been added is performed.
In the step of measuring the zeta potential, from the step of returning to the recovery tank to the step of measuring the zeta potential until the zeta potential of the used slurry becomes the same zeta potential as that of the unused slurry. A slurry regeneration method characterized by repeating.

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