Method and device for regenerating etching solution

Abstract

To provide a reproduction technique capable of efficiently removing a silicon compound in an etchant.SOLUTION: A reproduction method is a method for reproducing an etchant containing phosphoric acid as a main component from a used state for an object containing silicon nitride as a main component and includes a first temperature adjustment step, a second temperature adjustment step, and a removal step. In the first temperature adjustment step, the temperature of the etchant is increased, thereby cutting a part of a chemical bond in the phosphoric acid (SinOn-1(OH)2n+2) existing in the etchant, such that the number of non-bonded hands in the phosphoric acid is increased. After the first temperature adjustment step, the temperature of the etchant is decreased in the second temperature adjustment step, such that the phosphoric acid existing in the etchant is grown by bonding the non-bonded hands with the other phosphoric acid. In the removal step, the phosphoric acid grown in the second temperature adjustment step is removed from the etchant.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for regenerating an etching solution containing phosphoric acid as a main component after it has been used on an object containing silicon nitride as a main component. [Background technology]

[0002] Etching solutions containing phosphoric acid as a main component are used in an etching process for removing silicon nitride films on semiconductor wafers during the manufacturing process of semiconductor devices. In this etching process, non-volatile silicon compounds generated by the removal of the silicon nitride film are accumulated in the etching solution, which increases the silicon concentration in the etching solution. If the etching solution with an increased silicon concentration is continued to be used as is, problems such as a decrease in the etching rate for silicon nitride films will occur. In addition, if the silicon concentration in the etching solution exceeds the saturation concentration, the silicon compounds in the etching solution will gel and precipitate, which can cause problems such as contamination of the substrate surface and clogging of the filter installed in the circulation path of the etching solution.

[0003] In order to solve the above problems, a method has been conventionally used in which the silicon concentration in the etching solution is adjusted to a predetermined concentration or less by replacing a part or all of the etching solution used in the etching process with a new one (generally an unused etching solution).

[0004] On the other hand, in the method of replacing the etching solution as described above, a new etching solution is required, and a large amount of waste liquid is generated by the replacement. Therefore, from the viewpoint of cost reduction and environmental consideration, a technology for regenerating the etching solution has been proposed. As an example, Patent Document 1 proposes a technology in which silicon compounds are precipitated in the etching solution by adding water to the etching solution or cooling the etching solution, and the precipitated silicon compounds are removed with a filter. As another example, Patent Document 2 proposes a technology in which silicon compounds are grown in the etching solution by slowly cooling the etching solution, and the grown silicon compounds are removed with a filter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3788985 [Patent Document 2] Patent No. 5829444 Summary of the Invention [Problem to be solved by the invention]

[0006] When removing silicon compounds with a filter as in the above-mentioned Patent Documents 1 and 2, it is necessary to grow the silicon compounds in the etching solution to a size that can be removed with the filter. However, even if water is added or cooling is performed as in Patent Document 1, the silicon compounds do not necessarily grow. In addition, when slow cooling is performed as in Patent Document 2, the growth of silicon compounds may be expected, but it takes a long time to grow them to a size that can be removed with a filter, which is not very efficient.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a regeneration technique capable of efficiently removing silicon compounds from an etching solution. [Means for solving the problem]

[0008] The method for regenerating an etching solution according to the present invention is a method for regenerating an etching solution mainly composed of phosphoric acid from a state after it has been used on an object mainly composed of silicon nitride, and includes a first temperature control step, a second temperature control step, and a removal step. In the first temperature control step, the temperature of the etching solution is increased to remove silicic acid (Si n O n-1 (OH) 2n+2 ) is broken, thereby increasing the number of dangling bonds in the silicic acid. After the first temperature adjustment step, the temperature of the etching solution is lowered in the second temperature adjustment step, so that the silicic acid present in the etching solution grows by bonding between the dangling bonds with other silicic acid. In the removal step, the silicic acid grown in the second temperature adjustment step is removed from the etching solution.

[0009] The etching solution regeneration device according to the present invention is a device for regenerating an etching solution mainly composed of phosphoric acid from a state after it has been used on an object mainly composed of silicon nitride, and includes a first temperature control unit, a second temperature control unit, and a removal unit. The first temperature control unit removes silicic acid (Si n O n-1 (OH) 2n+2 ) and thereby increase the number of dangling bonds in the silicic acid. The second temperature control unit lowers the temperature of the etching solution after temperature control by the first temperature control unit, thereby growing the silicic acid present in the etching solution by bonding the dangling bonds between other silicic acid. The removal unit removes the silicic acid grown by temperature control by the second temperature control unit from the etching solution.

[0010] According to the above-mentioned regeneration method or regeneration device, even if the temperature control process is performed for a relatively short time, the temperature of the etching solution is raised to activate the silicic acid into an unstable state having dangling bonds, and then the temperature of the etching solution is lowered to allow the activated silicic acid to condense with the dangling bonds and grow further. Therefore, the silicic acid in the etching solution is easily grown to a size that can be removed by a removal means (such as a filter). In this way, according to the above-mentioned regeneration technology, it is possible to efficiently grow the silicic acid in the etching solution to a size that can be removed by a removal means (such as a filter). Effect of the Invention

[0011] According to the present invention, it becomes possible to efficiently remove silicon compounds from an etching solution. [Brief description of the drawings]

[0012] [Figure 1] 4 is a flowchart showing a method for regenerating an etching solution according to an embodiment. [Diagram 2] FIG. 1 is a conceptual diagram showing an example of a playback device capable of implementing a playback method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] FIG. 1 is a flow chart showing a method for regenerating an etching solution according to an embodiment. As shown in this figure, in the regeneration method of this embodiment, a pretreatment step, a first temperature adjustment step, a second temperature adjustment step, and a removal step are performed in this order. Here, the etching solution is an etching solution whose main component is phosphoric acid (H3PO4). The regeneration method of this embodiment is a method for regenerating such an etching solution from a state after use on an object whose main component is silicon nitride (for example, after use in an etching process for removing a silicon nitride film on a semiconductor wafer). Specifically, the etching solution after use accumulates silicon compounds (H2SiP2O8, Si(OH)4, etc.) in the solution, resulting in an increased silicon concentration. Therefore, in the regeneration method of this embodiment, the etching solution is regenerated by efficiently removing the silicon compounds in the solution from such a state. Hereinafter, each step performed in the regeneration method of this embodiment will be specifically described.

[0014] <Pretreatment process> In the pretreatment process, the used etching solution is hydrated (water (H2O) is added) to increase the proportion of silicic acid (Si(OH)4) in the silicon compounds in the etching solution. Specifically, H2SiP2O8 present in the etching solution is reacted with water to change to silicic acid, which precipitates in the etching solution (H2SiP2O8 + 3H2O → Si(OH)4 + H4P2O7). As an example, the etching solution is diluted with water so that the phosphoric acid concentration becomes a predetermined concentration of 50% to 80% by weight.

[0015] In the pretreatment step, the etching solution is cooled to condense the silicic acids present in the etching solution (condensation reaction). Specifically, by cooling the etching solution, the silicic acids present in the etching solution grow by bonding with other silicic acids through dangling bonds (nSi(OH)4 → Si n O n-1 (OH) 2n+2 +(n-1)H2O). As an example, the etching solution is cooled to a predetermined temperature of 20°C or more and 80°C or less.

[0016] In addition, the pretreatment step is not limited to the case where both the treatments of adding water and cooling the etching solution are performed, and may be appropriately changed to the case where only one of the treatments is performed, as long as silicic acid can be precipitated in the etching solution and the silicic acid can be grown to a certain extent by a condensation reaction. In addition, the addition of water to the etching solution is not limited to before the first temperature adjustment step described below, and may be performed at any timing before the removal step.

[0017] Here, when removing silicic acid with a filter in the removal step as described below, it is necessary to grow the silicic acid in the etching solution to a size that can be removed with a filter (specifically, a size that can be filtered with a filter). However, although the above-mentioned water addition and cooling can grow silicic acid to a certain extent, it is not necessarily possible to sufficiently grow it to a size that can be removed with a filter. The present inventors believe that one of the reasons for this is that the silicic acid in the etching solution becomes stable before it grows large, making it difficult for a condensation reaction to occur. In addition, the present inventors believe that when the silicic acid is gradually cooled over a long period of time (i.e., when slow cooling is performed), the growth of silicon compounds may be expected, but it takes a long time to grow it to a size that can be removed with a filter, which is not very efficient.

[0018] Therefore, the inventors have made it possible to efficiently grow the silicic acid in the etching solution to a size that can be removed in the removal step by performing the first temperature adjustment step and the second temperature adjustment step described below.

[0019] <1st temperature control process> In the first temperature control step, the temperature of the etching solution is increased to oxidize the silicic acid (Si n O n-1 (OH) 2n+2), thereby increasing the number of dangling bonds in the silicic acid. Specifically, thermal energy is applied to silicic acid that has become stable before it has grown to a sufficient size, and some of the chemical bonds in the silicic acid are cut, activating it to an unstable state with dangling bonds (i.e., a state in which further growth is possible by bonding between the dangling bonds with other silicic acid). As an example, in the first temperature adjustment step, the temperature of the etching solution is raised to a predetermined temperature of 50°C or higher and 160°C or lower.

[0020] <Second temperature control process> In the second temperature control step, in order to grow the silicic acid activated in the first temperature control step, the etching solution after the first temperature control step is cooled again, so that the silicic acid present in the etching solution is condensed with itself (condensation reaction). Specifically, by lowering the temperature of the etching solution after the first temperature control step, the silicic acid activated in the first temperature control step (silicic acid in an unstable state having dangling bonds) is further grown by bonding between the dangling bonds with other silicic acid activated in the first temperature control step. As an example, in the second temperature control step, the temperature of the etching solution after the first temperature control step (for example, 50°C to 160°C) is lowered to a predetermined temperature of 45°C or less.

[0021] In the second temperature control step, it is sufficient to condense the silicic acids that have grown to a certain extent in the pretreatment step (conversely, there is no need for gradual growth), so there is no need to gradually cool the silicic acids over a period of time as in slow cooling, and the temperature of the etching solution after the first temperature control step can be reduced at a faster rate than if the etching solution was allowed to cool naturally.

[0022] <Removal process> In the removing step, the silicic acid grown in the second temperature adjusting step is removed from the etching solution. Specifically, the etching solution is passed through a filter, and the silicic acid in the etching solution is filtered through the filter.

[0023] According to this regeneration method, even if the temperature control process is performed for a relatively short time in the first temperature control step and the second temperature control step, the temperature of the etching solution is raised to activate the silicic acid into an unstable state having dangling bonds, and the activated silicic acid can be further grown by condensing the dangling bonds by bonding with each other by lowering the temperature of the etching solution. Therefore, the silicic acid in the etching solution is easily grown to a size that can be removed in the removal step. In this way, according to the above-mentioned regeneration method, it is possible to efficiently grow the silicic acid in the etching solution to a size that can be removed in the removal step, and as a result, it is possible to efficiently remove the silicon compound in the etching solution. Note that the first temperature control step and the second temperature control step are not limited to being performed once each, and may be repeatedly performed until the silicic acid present in the etching solution grows to a size that can be removed in the removal step. In addition, in the above-mentioned regeneration method, the first temperature control step and the second temperature control step may be performed once each or repeatedly without performing the pretreatment step.

[0024] FIG. 2 is a conceptual diagram showing an example of a regeneration device capable of carrying out the above-mentioned regeneration method. In the regeneration device shown in this figure, first, the used etching solution to be regenerated is supplied from a liquid supply unit 14 into a first treatment tank 1. Then, the regeneration device adds water to the etching solution in the first treatment tank 1 by supplying water from a water supply unit 15 into the first treatment tank 1, thereby precipitating silicic acid in the etching solution (H2SiP2O8+3H2O→Si(OH)4+H4P2O7). As an example, the regeneration device dilutes the etching solution in the first treatment tank 1 with water so that the phosphoric acid concentration is 50% by weight or more and 80% by weight or less.

[0025] In addition, the regeneration device cools the etching solution in the first treatment tank 1 by sending it to the heat exchanger 11 using the liquid delivery pump 13, thereby lowering the temperature of the etching solution, and thereby condensing the silicic acids present in the etching solution (nSi(OH)4 → Si n O n-1 (OH) 2n+2+(n-1)H2O). As an example, the regenerating device cools the etching solution to a predetermined temperature of 20°C or more and 80°C or less. At this time, the regenerating device may circulate the etching solution through a path from the first processing tank 1 through the heat exchanger 11 and back to the first processing tank 1 until the temperature of the etching solution drops to the predetermined temperature.

[0026] As described above, the regeneration apparatus shown in FIG. 2 includes the water supply unit 15, the heat exchanger 11, the liquid delivery pump 13, the circulation path, and the like as a pretreatment unit for adding water to and cooling the etching liquid.

[0027] Next, the regeneration device sends the etching liquid (pre-treated etching liquid in this case) in the first treatment tank 1 to the heater 12 by the liquid delivery pump 13 to heat the etching liquid, thereby increasing the temperature of the etching liquid, and thereby oxidizing the silicic acid (Si n O n-1 (OH) 2n+2 ) is activated. As an example, the regeneration device increases the temperature of the etching solution to a predetermined temperature of 50° C. or more and 160° C. or less. At this time, the regeneration device may circulate the etching solution through a path that runs from the first processing tank 1 through the heater 12 and back to the first processing tank 1 until the temperature of the etching solution increases to the predetermined temperature.

[0028] As described above, the regeneration apparatus shown in FIG. 2 includes the heater 12, the liquid sending pump 13, the circulation path, and the like as a first temperature adjustment unit for increasing the temperature of the etching liquid.

[0029] Thereafter, the regeneration device uses the liquid feed pump 13 to send the etching solution (here, the etching solution after heating) in the first treatment tank 1 to the heat exchanger 11 to cool it again, thereby lowering the temperature of the etching solution, thereby condensing the silicic acid (activated silicic acid) present in the etching solution. As an example, the regeneration device lowers the temperature of the etching solution after heating (e.g., 50°C or higher and 160°C or lower) to a predetermined temperature of 45°C or lower. At this time, the regeneration device may circulate the etching solution through a route from the first treatment tank 1 through the heat exchanger 11 and back to the first treatment tank 1 until the temperature of the etching solution drops to the predetermined temperature.

[0030] In this manner, the regeneration apparatus shown in FIG. 2 includes the heat exchanger 11, the liquid sending pump 13, the circulation path, and the like as a second temperature adjustment unit for lowering the temperature of the etching liquid.

[0031] The etching solution obtained by these temperature adjustments is supplied to the second treatment tank 2 by the liquid supply pump 13. Then, the regeneration device passes the etching solution in the second treatment tank 2 through a filter 22 by the liquid supply pump 21, thereby filtering the silicic acid in the etching solution (silicic acid grown by the above-mentioned temperature adjustment) through the filter 22. At this time, the regeneration device may circulate the etching solution through a path that passes from the second treatment tank 2 through the filter 22 and returns to the second treatment tank 2.

[0032] In this manner, the regeneration device shown in FIG. 2 includes the filter 22, the liquid sending pump 21, the circulation path, and the like as a removal section for removing silicic acid from the etching solution.

[0033] Furthermore, the etching solution that has passed through the filter 22 is supplied to the third treatment tank 3 by the liquid supply pump 21. Then, the regeneration device heats the etching solution in the third treatment tank 3 with a heater 31 to evaporate water from the etching solution, thereby concentrating the etching solution to a phosphoric acid concentration equivalent to that of unused etching solution.

[0034] The concentrated etching solution is supplied to the fourth treatment tank 4 by the liquid supply pump 32. At this time, the regeneration device measures the silicon concentration of the etching solution with a silicon concentration meter 33, thereby making it possible to confirm whether the silicon compounds have been normally removed from the etching solution.

[0035] Thereafter, the regeneration device lowers the temperature of the etching solution in the fourth treatment tank 4 by sending the etching solution in the fourth treatment tank 4 to the heat exchanger 41 using the liquid delivery pump 42 to cool the etching solution, thereby preventing the etching solution from being concentrated to a predetermined phosphoric acid concentration or higher. At this time, the regeneration device measures the phosphoric acid concentration of the etching solution in the fourth treatment tank 4 using a phosphoric acid concentration meter 43. When the measured value by the phosphoric acid concentration meter 43 exceeds the predetermined phosphoric acid concentration, the regeneration device adjusts the phosphoric acid concentration of the etching solution in the fourth treatment tank 4 by supplying water from a water supply unit 44 into the fourth treatment tank 4.

[0036] Next, the regeneration device filters the metal or metal ions present in the etching solution through the filter 45 by passing the etching solution (the cooled etching solution) in the fourth treatment tank 4 through the filter 45 using the liquid delivery pump 42. At this time, the regeneration device may circulate the etching solution through a path that passes from the fourth treatment tank 4 through the filter 45 and returns to the fourth treatment tank 4.

[0037] This completes the regeneration process of the etching liquid by the regeneration device, and the etching liquid after the regeneration process is supplied from the drainage section 46 to, for example, an etching treatment device.

[0038] In the above-mentioned regeneration device, the filter 22 becomes clogged when it is repeatedly used to filter silicic acid. Therefore, the regeneration device shown in Fig. 2 is provided with the following means for recovering the filtering performance of the filter 22.

[0039] The regeneration device mixes hydrofluoric acid (for example, 50% by weight) supplied from the liquid supply unit 52 with water supplied from the water supply unit 53 in the cleaning liquid tank 5 to generate a hydrofluoric acid solution of 5% by weight or more and 20% by weight or less. The regeneration device then sends the hydrofluoric acid solution in the cleaning liquid tank 5 using the liquid supply pump 51 and passes it through the filter 22, thereby dissolving the silicic acid filtered by the filter 22, thereby recovering the filtering performance of the filter 22. At this time, the regeneration device may circulate the hydrofluoric acid solution through a path that returns from the cleaning liquid tank 5 through the filter 22 to the cleaning liquid tank 5. The regeneration device then discharges the hydrofluoric acid solution containing the dissolved silicic acid from the drainage unit 54.

[0040] Thereafter, the regeneration device stores only the water supplied from the water supply unit 53 in the cleaning liquid tank 5, and passes the water in the cleaning liquid tank 5 through the filter 22 using the liquid supply pump 51, thereby cleaning the filter 22. At this time, the regeneration device may circulate the water in a path that runs from the cleaning liquid tank 5 through the filter 22 and back to the cleaning liquid tank 5.

[0041] The regenerator may include a plurality of filters 22, which may be switchably connected in parallel. When one of the filters 22 becomes clogged, the regenerator may switch to another filter 22 to filter the silicic acid, and during that time, the clogged filter 22 may be cleaned by the above-mentioned means.

[0042] The above-mentioned playback device is not limited to the one shown in FIG. 2, and may be changed as appropriate to another device capable of executing each step of the above-mentioned playback method (which may be a separate device for each step). EXAMPLES

[0043] <Example 1> As an example, a phosphoric acid solution (H3PO4=85% by weight, H2O=15% by weight) was used as an etching solution in an etching treatment device, and then regenerated in the above-mentioned regeneration device. Specifically, the used phosphoric acid solution containing silicon at a ratio of 40-60 mg / kg was heated to 150-160°C and then supplied to the regeneration device, where it was regenerated under the following treatment conditions.

[0044] (Processing conditions) (1) Pretreatment (dilution and cooling): 20 minutes (2) First temperature control: 20 minutes (3) Second temperature control: 60 minutes.

[0045] The phosphoric acid solution was sampled before and after the regeneration treatment, and the silicon concentration in the phosphoric acid solution was analyzed by ICP-AES. As a result, in Example 1, the silicon concentration, which was 52.1 mg / kg before the treatment, was reduced to 2.2 mg / kg by the regeneration treatment, and the silicon removal rate was 96%. Table 1 shows the results.

[0046] [Table 1]

[0047] In order to demonstrate the effectiveness of the above-mentioned regeneration technique (Example 1), the results of two examples (Comparative Example 1 and Comparative Example 2) in which the regeneration process was carried out under other conditions are also shown in Table 1. These comparative examples will be described below.

[0048] <Comparative Example 1> In Comparative Example 1, the same used phosphoric acid solution as in Example 1 was regenerated under the following treatment conditions.

[0049] (Processing conditions) (1) Pretreatment (dilution only): 20 minutes (2) Standing: 20 minutes (3) Cooling: 60 minutes.

[0050] In Comparative Example 1, the silicon concentration, which was 49.3 mg / kg before treatment, only decreased to 13.6 mg / kg after regeneration treatment, and the silicon removal rate was low at 72%. By comparing with Comparative Example 1, it can be seen that Example 1 can obtain a high removal rate in a short time, and therefore can remove silicon efficiently.

[0051] <Comparative Example 2> In Comparative Example 2, the same used phosphoric acid solution as in Example 1 was regenerated under the following treatment conditions.

[0052] (Processing conditions) (1) Pretreatment (standing still (slow cooling by heat radiation) and dilution): 20 minutes (2) Standing still (cooling by heat radiation): 20 minutes (3) Slow cooling: 60 minutes.

[0053] In Comparative Example 2, the silicon concentration, which was 50.0 mg / kg before treatment, only decreased to 9.4 mg / kg after regeneration treatment, and the silicon removal rate was low at 81%. By comparing with Comparative Example 2, it can be seen that Example 1 can obtain a high removal rate in a short time, and therefore can remove silicon efficiently.

[0054] The above-mentioned embodiments and examples are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the above-mentioned embodiments and examples. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0055] 1. First treatment tank 2. Second treatment tank 3. Third Treatment Tank 4. Fourth Treatment Tank 5 Cleaning solution tank 11 Heat exchanger 12 Heater 13 Liquid delivery pump 14 Liquid supply section 15 Water supply section 21 Liquid delivery pump 22 Filters 31 Heater 32 Liquid delivery pump 33 Silicon concentration meter 41 Heat exchanger 42 Liquid delivery pump 43 Phosphoric acid concentration meter 44 Water supply section 45 Filters 46 Drain 51 Liquid delivery pump 52 Liquid supply section 53 Water supply section 54 Drain

Claims

1. A method for regenerating an etching solution containing phosphoric acid as a main component after use on an object containing silicon nitride as a main component, comprising the steps of: a first temperature control step of increasing the temperature of the etching solution to break a part of chemical bonds in the silicic acid present in the etching solution, thereby increasing the number of dangling bonds in the silicic acid; a second temperature control step of lowering the temperature of the etching solution after the first temperature control step, thereby growing silicic acid present in the etching solution by bonding between the dangling bonds between other silicic acid; a removing step of removing the silicic acid grown in the second temperature control step from the etching solution; The method for regenerating an etching solution comprises:

2. a pretreatment step of performing at least one of adding water to the etching solution and cooling the etching solution before the first temperature adjustment step; The method for regenerating an etching solution according to claim 1 , further comprising:

3. 3. The method for regenerating an etching solution according to claim 1, wherein in the first temperature adjustment step, the temperature of the etching solution is increased to a predetermined temperature of 50° C. or more and 160° C. or less.

4. 4. The method for regenerating an etching solution according to claim 1, wherein in the second temperature adjustment step, the temperature of the etching solution is lowered at a rate faster than that in the case where the etching solution is allowed to cool naturally.

5. 5. The method for regenerating an etching solution according to claim 1, wherein in the second temperature adjustment step, the temperature of the etching solution is lowered to a predetermined temperature of 45° C. or less.

6. An apparatus for regenerating an etching solution containing phosphoric acid as a main component from a state after use on an object containing silicon nitride as a main component, comprising: a first temperature control unit that increases a temperature of the etching solution to break a part of chemical bonds in the silicic acid present in the etching solution, thereby increasing the number of dangling bonds in the silicic acid; a second temperature control unit that reduces the temperature of the etching solution after the temperature control by the first temperature control unit, thereby growing silicic acid present in the etching solution by bonding between the dangling bonds between other silicic acid; A removal unit that removes the silicic acid grown by temperature control in the second temperature control unit from the etching solution; An etching solution regeneration device comprising:

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