JP3788985B2 - Etching solution regeneration method, etching method and etching apparatus - Google Patents

Description

  The present invention relates to an etching solution regeneration method, an etching method, and an etching apparatus composed of an aqueous phosphoric acid solution used for etching a silicon nitride film, and in particular, a silicon compound (silicon nitride and phosphoric acid and silicon oxide) from the etching solution during and / or after the etching process. The reaction product is efficiently removed.

  In an etching process in a mass production line for various substrates and the like, in order to keep the etching solution in the tank clean, the etching solution is filtered and circulated, and the etching is continuously performed while removing foreign matters such as dust in the etching solution. The same applies to the etching of a silicon nitride film with a heated phosphoric acid etching solution. The etching solution is filtered and circulated, and the silicon compound deposited in the etching solution is filtered and purified together with other foreign substances. Etching is performed continuously (see, for example, Patent Document 1).

  However, in the above method, even if a phosphoric acid aqueous solution containing a silicon compound is cooled to room temperature and filtered at a high temperature (for example, filtered with a filter having a pore size of 0.1 μm), most of the silicon compound in the phosphoric acid aqueous solution remains. Not captured. For this reason, in the etching operation of the silicon nitride film, for example, the silicon compound is deposited or fixed in the etching tank and the circulation path of the etching solution, or depending on the silicon compound concentration in the etching solution, the silicon nitride film / silicon oxide film, etc. Since the etching selectivity of the film containing silicon nitride varies, the etching solution must be periodically replaced. Against this background, the present applicant has completed a method (Patent Document 2) in which an etching solution is treated with hydrogen fluoride (HF) as a method for regenerating an etching solution containing a silicon compound. An etching solution regeneration processing apparatus (Patent Document 3) suitable for application to a process is proposed.

Japanese Patent Publication No. 3-20895 Japanese Patent No. 3072876 (page 2-3, FIG. 1) Japanese Patent Laid-Open No. 11-293479 (page 2-5, FIG. 1)

  The above-described method and apparatus for regenerating an etching solution is a method in which a silicon compound in an etching solution is reacted with added HF to remove silicon fluoride as a reaction product together with water vapor. Since it is a substance that affects the etching selectivity of the silicon nitride film in the same manner as described above, the HF concentration remaining in the etching solution is measured with high accuracy, and the end point of the etching solution regeneration process (HF that does not affect etching). Concentration etc. must be confirmed and managed. For example, the end point management is performed by sampling a part of the etching solution. However, the end point management is complicated in maintaining the continuous etching and causes an increase in cost.

  Accordingly, an object of the present invention is directed to an etching solution for a silicon nitride film that uses an aqueous phosphoric acid solution, and it is extremely easy to remove a silicon compound formed in the etching solution, which is more suitable for an industrial process, and a regeneration treatment of the etching solution. An object of the present invention is to provide a method for regenerating an etching solution that can reduce costs. Another object of the present invention is to provide an etching method using the above regeneration method. Still another object of the present invention is to provide an etching apparatus suitable for carrying out the above regeneration method and etching method.

The above object is achieved by the present invention described below. That is, the present invention is, in the etching bath, was used to etch the silicon nitride film, a method of reproducing an etching solution comprising phosphoric acid aqueous solution, taken out etching solution containing a silicon compound caused by the etching from the etching bath, collected Diluting the etched etchant with water to lower the phosphoric acid concentration of the etchant to 80 to 50% by mass (hereinafter, “mass%” is simply indicated by “%”); removing the silicon compound precipitated in the etching solution from the etching solution by lowering the concentration of phosphoric acid etching solution after removal of the silicon compound from the etching solution, close to the concentration suitable for etching up to 80-90% There is provided a method for regenerating an etching solution characterized by comprising the steps of:

  In the regeneration method, it is preferable that the removal of the silicon compound from the etching solution is performed by filtration, and the phosphoric acid concentration of the etching solution is preferably lowered to 75 to 50% by adding water. Thus, the precipitation of the silicon compound in the etching solution can be greatly accelerated, the removal efficiency of the silicon compound can be improved, and the silicon compound deposited in the etching solution can be filtered and separated efficiently.

  In the above regeneration method, when the phosphoric acid concentration of the etching solution is lowered by adding water, the temperature of the etching solution is cooled to 100 ° C. to normal temperature (20 ° C.), preferably 60 ° C. to normal temperature (20 ° C.). Thus, the precipitation of the silicon compound in the etching solution can be further greatly promoted, the removal efficiency of the silicon compound can be improved, and the silicon compound deposited in the etching solution can be filtered and separated more efficiently.

  Moreover, in the said reproduction | regeneration method, it is preferable to heat the etching liquid after the said filtration to 140-180 degreeC, and by heating the etching liquid after the said filtration to this temperature, for example, the temperature of the diluted etching liquid Can be made close to around 160 ° C., which is a temperature suitable for etching, to enable continuous etching.

Furthermore, the etching solution after filtration was concentrated, when the concentration of phosphoric acid in 80-90%, for example, the phosphate concentration of the diluted etching solution, 87% before and after a concentration suitable etching if it is close to well can be a continuous etching in doing so efficiently.

  Further, the present invention provides an etching method for etching a silicon nitride film using an etching solution made of a phosphoric acid aqueous solution in an etching tank, and a step of taking out an etching liquid containing a silicon compound from the etching tank during or after the etching; There is provided an etching method comprising a step of regenerating an etching solution by the regenerating method of the present invention and a step of returning the regenerated etching solution into the etching tank.

Further, the present invention provides an etching method for etching a silicon nitride film using an etching solution made of a phosphoric acid aqueous solution in an etching tank, and a step of taking out an etching liquid containing a silicon compound from the etching tank during or after the etching; The step of flowing the taken-out etching solution for 2 minutes, the step of filtering the etching solution (A) that has been flowed in 2 minutes and returning it to the etching tank, and the other etching solution (B) that has been flowed in 2 minutes are described above. There is provided an etching method comprising a step of regenerating by the regenerating method and a step of returning the regenerated etching solution (B) to the one etching solution (A) and returning it to the etching tank. .
According to the etching method of the present invention, for example, continuous etching of a silicon nitride film is realized, and it is possible to improve the etching quality of an object to be etched and the operating rate of etching.

Further, the present invention is an etching apparatus for performing any one of the above etching methods, wherein an etching solution containing a silicon compound is taken out from an etching tank, and the taken out etching solution is diluted with water to remove the silicon compound. There is provided an etching apparatus comprising a dilution / precipitation part for precipitation, a filtration part for silicon compound, and a concentration part for etching solution. Furthermore, the apparatus can have a heating section .

  According to the etching apparatus of the present invention, for example, the conventional regeneration HF is added by sequentially arranging the dilution / precipitation part, the filtration part, the concentration part, and the heating part. As a result, the apparatus can be simplified, the equipment cost can be reduced, and the circulation control of the etching solution can be easily performed.

  Furthermore, according to the etching apparatus of the present invention, if the water vapor is evaporated in the concentrating part, the concentrating can be performed simultaneously with the heating, and the concentrating part is arranged in a pre-process or a post-process of the heating part. As a result, the phosphoric acid concentration of the etching solution is concentrated to 80 to 90%, for example, close to about 87%, which is a phosphoric acid concentration suitable for etching, and continuous etching can be made efficient.

  In the present invention, in etching a silicon nitride film with a phosphoric acid aqueous solution, the silicon compound accumulated in the etching solution can be easily removed, and the regeneration of the etching solution can be performed as compared with the above-described method of adding HF. The end point management of the process is not bothered, and the equipment can be simplified or the maintenance cost can be reduced.

  Next, the present invention will be described in more detail with reference to preferred embodiments. Conventionally, a silicon oxide film is formed by oxidizing the wafer as an element isolation film on the surface of a semiconductor silicon wafer or the like. In this silicon oxide film formation step, a silicon nitride film and a silicon oxide film as an oxidation resistant mask exist on the wafer surface, and a concentration of about 85 to 90 is used as an etching solution in order to selectively etch only the silicon nitride film. An etching solution composed of an aqueous solution of phosphoric acid is used. When the silicon nitride film is etched with the etching solution, the silicon component of the silicon nitride film is dissolved in phosphoric acid to form a silicon compound, and the silicon compound is gradually accumulated in the etching solution. In the present invention, the silicon compound is efficiently removed from the phosphoric acid aqueous solution containing the silicon compound, the etching solution is regenerated, and the regenerated etching solution can be recycled and reused.

  The concentration of the silicon compound in the etching solution increases with the number of semiconductor wafers having a silicon nitride film to be processed in the etching tank, but the silicon nitride film is etched at about 160 ° C., which is the boiling point of the etching solution. The saturation concentration of the generated silicon compound in the etching solution is about 85 mg / kg in terms of Si. If the above etching is continued beyond this saturation concentration, the silicon compound is precipitated in the etching solution, and the above-described problems such as pipe blockage occur.

The etching is intended to selectively etch the silicon nitride film, but the silicon oxide film is slightly etched simultaneously with the etching of the silicon nitride film. The etching rate of the silicon oxide film by the above etching is, for example, about 2 mm (depth) / min. The etching rate decreases as the concentration of the silicon compound in the etching solution increases. When the amount of silicon compound in the etching solution reaches the saturation concentration of silicon compound (about 85 mg / kg in terms of Si), the etching rate of the silicon oxide film is 0 Å / min. It drops to near. Thus, when the etching rate of the silicon oxide film changes depending on the concentration of the silicon compound in the etching solution, the thickness of the silicon oxide film on the wafer surface also changes, which affects the characteristics of the resulting device. According to the method for regenerating an etching solution of the present invention, since the concentration change of the silicon compound in the etching solution is reduced, the thickness fluctuation of the silicon oxide film can be suppressed, and the characteristics of the obtained device can be stabilized. There is.
Therefore, in the etching operation of a semiconductor wafer having a silicon nitride film, in order to stabilize the etching apparatus and to stabilize and uniform the quality of the etched product, the concentration of the silicon compound in the etching solution is set higher than the saturation concentration described above. It must be maintained at a low value, for example, lower than 80 mg / kg in terms of Si.

  The present inventors have found the following phenomenon in the process of pursuing a method of regenerating an etching solution more suitable for an industrial process from the above recognition of the problem. First, when an etching solution containing a silicon compound is diluted with water, the silicon compound is easily precipitated. Moreover, the degree of deposition of such a silicon compound varies greatly depending on the dilution rate of the etching solution with water. As an example, when an etching solution containing a silicon compound is diluted 1.7 times with water, about 80% of the silicon compound contained in the original etching solution is precipitated. As a substitute for the conventional method of adding HF, the method of diluting the etching solution by the above method has been proved to be sufficiently applicable to the regeneration of the etching solution.

  That is, in the etching solution regeneration method according to the first invention of the present invention, in the etching bath, the silicon nitride film is etched using an etching solution made of a phosphoric acid aqueous solution, and the etching solution containing the silicon compound generated by the etching is etched into the etching bath. The step of adding water to the removed etching solution to lower the phosphoric acid concentration of the etching solution to 80 to 50%, and filtering the silicon compound precipitated in the etching solution due to the decrease in the phosphoric acid concentration And a step of removing from the substrate.

  The etching solution to be regenerated in the present invention is an etching solution containing about 80 mg / kg or more of a silicon compound in terms of Si as a result of continuation of etching of the silicon nitride film in the etching tank, and the phosphoric acid concentration is 85 to 90%. is there. The liquid is diluted by adding water (pure water). The form of adding water is not particularly limited, but is preferably mixed and stirred so that the etching solution and water are uniformly mixed (for example, a mode in which both solutions are combined so as to be easily mixed, a mode using a line mixer, a dedicated stirring) A mode of attaching a part).

  When the etching solution and water are mixed and stirred, the silicon compound contained in the etching solution is precipitated. The amount of water added is such that the phosphoric acid concentration of the etching solution is 80 to 50%, preferably 75 to 50%. As shown in Table 1 below, when the phosphoric acid concentration of the diluted etching solution exceeds 80%, the silicon compound is insufficiently precipitated from the etching solution, and the silicon compound is trapped and removed by filtration in a later step. The effect is not demonstrated. If the phosphoric acid concentration of the diluted etching solution is less than 50%, a large amount of water is required for dilution, but the effect of promoting the precipitation of the silicon compound is not improved in proportion to the dilution, and the etching solution This is because it is necessary to evaporate a large amount of water in order to concentrate the etching solution at the time of reuse, and this is not economical.

  As described above, water is added to the etching solution containing a silicon compound to promote precipitation of the silicon compound, and then the deposited silicon compound (and other foreign matters) is removed by filtering the etching solution. There are no particular restrictions on the form of filtration of precipitates, etc., and the precipitates are filtered off with a filter used in this type of etching method, or left in a filtration tank to precipitate the precipitates. The liquid may be allowed to flow out. As a filter configuration used for the filtration of the etching solution, a filter regeneration operation may be reduced by adopting a cross-flow filtration method or a back-washing method capable of removing precipitates accumulated on the filtration surface. Thus, the filtrate from which the silicon compound has been removed (etching solution) is supplied as it is, or heated, and / or concentrated as necessary, and then supplied to the etching tank for reuse.

  The method for regenerating an etching solution according to the first invention of the present invention is a mode in which an etching solution containing a silicon compound is regenerated while taking out a predetermined amount from an etching vessel, and an etching solution containing a silicon compound is once stored in the etching vessel. After moving to, any of the aspects of taking out a predetermined amount from the storage tank and regenerating it may be used. Moreover, as an etching apparatus, the etching solution taken out from the etching tank as in the apparatus form shown in FIG. 1 or FIG. 2 or the etching liquid once taken out from the etching tank to the storage tank may be regenerated. It is preferable to regenerate only a part of the etching solution taken out from the tank as in the apparatus configuration shown in FIG.

  The etching method and the etching apparatus according to the second to fourth inventions of the present invention utilize the etching solution regeneration method according to the first invention of the present invention. More specific description will be given with reference to the illustrated embodiment. 1 and 3 show an etching method and apparatus of two embodiments of the present invention, and FIG. 2 shows a modification of the embodiment of FIG. Each drawing schematically shows the etching method and the etching apparatus of the present invention, mainly based on the method of regenerating the etching solution of the present invention. In the following description, the same reference numerals are given to the same members in terms of operation, and redundant description is omitted. Of course, the present invention is not limited to these forms.

<First form>
In the etching method and apparatus of the present invention shown in FIG. 1, after the etching tank 1 takes out a part of an etching solution containing a silicon compound (hereinafter referred to as “target etching solution”) from the tank 1 and regenerates it. A dilution / precipitation regeneration unit 2 is provided for returning the target etching solution that has been regenerated to the tank 1 again. The dilution / precipitation regeneration unit 2 is in the piping path for circulation of the target etching solution, and from the side from which the target etching solution is taken out from the etching tank 1, the water supply unit 3, the dilution / precipitation unit 4, the pump 5, The filtration part 6, the concentration part 7, and the pump 8 are arrange | positioned in order. Here, the etching tank 1 is a tank in which a semiconductor wafer having at least a silicon nitride film or the like is taken in and out of the tank, and may be a storage tank in which a target etching solution after use is transferred from the etching tank.

  Although not shown in the drawing, the etching tank 1 is provided with a heating means and a temperature controller, a supply means for introducing a new etching liquid, a temperature sensor for detecting the liquid temperature, and the like. The dilution / precipitation unit 4 is provided in front of the filtering unit 6 in the piping path of the target etching solution, and the target etching solution is supplied from the tank 1 to the dilution / precipitation unit 4 at a predetermined flow rate via the flow rate control valve 10a. At the same time, pure water is introduced from the water supply unit 3 into the dilution / precipitation unit 4 at a predetermined flow rate through the flow rate control valve 10b, etc., so that the target etching solution is diluted with pure water, A part of the silicon compound is deposited. Further, the diluting / depositing portion 4 is provided with a cooler (not shown) in order to efficiently deposit the deposited silicon compound, and the target etching solution is set to 100 ° C. to room temperature (20 ° C.), preferably 60 ° C. to It is preferable to cool to room temperature (20 ° C.).

  The mixing / stirring means in the dilution / precipitation section 4 may be constituted by, for example, a line mixer such as a static mixer, or the inlet side of the dilution / precipitation section 4 where the liquids join together to devise the target etching solution and pure water. May be mixed uniformly, or the dilution / precipitation unit 4 may be provided with a stirrer.

  The filtration unit 6 subsequent to the dilution / precipitation unit 4 is, for example, a filter having the same pore diameter of 0.1 μm as the conventional one. And in the filtration part 6, in the process of passing the object etching liquid diluted with water supplied from the dilution / precipitation part 4 through the pump 5, the precipitate (silicon | silicone) contained in the said object etching liquid The compound and other foreign substances) are filtered (captured and removed), and only the filtrate (target etching solution from which at least a part of the silicon compound has been removed) is supplied to the concentration unit 7.

  The concentrating unit 7 heats and concentrates the filtrate supplied from the filtering unit 6 so that the phosphoric acid concentration of the filtrate approaches the phosphoric acid concentration suitable for etching. In the etching tank 1, the target etching solution always boils, the water evaporates, and the phosphoric acid concentration of the target etching solution increases. For this reason, in the concentration unit 7, for example, the concentration of the filtrate is controlled so that the concentration of the filtrate is 13 minutes of water vapor evaporating from the tank 1, and the phosphoric acid concentration is slightly less than the phosphoric acid concentration suitable for etching. Thus, the target etchant concentrated to a predetermined concentration is supplied into the etching tank 1 via the pump 8. In addition, in the apparatus shown in FIG. 1, for example, the present invention further uses a storage tank in combination with an etching tank, recycles all of the etching liquid taken out from the etching tank into a batch type, and transfers it to the storage tank. You may make it send from this storage tank to an etching tank.

<Modification of the first embodiment>
The etching method and apparatus shown in FIG. 2 are changed from the example shown in FIG. 1 in the following points. That is, the etching tank 1 is a tank for performing an etching process by taking a semiconductor wafer having at least a silicon nitride film into and out of the tank, and has an overflow weir 1a provided on the upper part of the tank wall, A part flows into the overflow weir 1a, the target etching solution is taken out from the bottom of the overflow weir 1a, the target etching solution is regenerated in the dilution / precipitation regenerating unit 2, and then regenerated. Is introduced again from the lower part of the etching tank 1.

  The dilution / precipitation regeneration unit 2 has a configuration in which a heating unit 9 is provided in place of the concentration unit 7. In this configuration, the target etching solution is preferably 100 ° C. to normal temperature (20 ° C.), preferably 60 ° C. by a cooler (not shown) in order to efficiently deposit the precipitated silicon compound in the dilution / precipitation unit 4. Since it is cooled to room temperature (20 ° C.), in the heating unit 9, the temperature of the diluted and cooled target etching solution is around 160 ° C. (140 to 180 ° C.), which is a temperature suitable for etching. The continuous etching can be made close.

<Second form>
The etching method and apparatus shown in FIG. 3 schematically illustrates the structure of an etching apparatus used in Example 3 to be described later, and in combination with the target etchant dilution / deposition regenerator 2 for the above two examples, filtration is performed. This is an example provided with a circulation path section 12.

  Although the filtration circulation path part 12 itself is basically the same as that of the prior art, the pure water supply part that supplements the 13 minutes of water vapor evaporated from the tank 1 is omitted. That is, the filtration circulation path section 12 is in the circulation piping path, and has a pump 11, a filtration section 6, and a heating section 9 from the side from which the target etching solution is taken out from the overflow weir 1 a of the etching tank 1. The target etchant to be diverted here is a portion that is heated and circulated to the etching tank 1 after removing insoluble matters such as foreign matters by the filtration unit 6.

  On the other hand, the dilution / precipitation regenerating unit 2 is in the pipe path of the target etching solution, and the water supply unit 3 and the dilution / precipitation unit 4 from the side branched from the pipe leading to the filtration circulation path unit 12. And the pump 5, the filtration part 6, the concentration part 7, and the pump 8 are arrange | positioned in order. Then, a part of the target etchant diverted from the filtration circulation path portion 12 side out of the etching solution taken out from the etching tank 1 is regenerated as shown in FIG. 1 and FIG. It is configured to be returned to the etching tank 1 together with the target etching liquid that is introduced into the section 12 and flows through the filtration circulation path section 12.

  The target etchant diversion method in the above is a configuration in which the piping portion on the filtration circulation path portion 12 side is connected to the piping connecting the overflow weir 1a and the dilution / precipitation portion 4 in the middle of the piping. The flow valve 10a attached to the pipe connecting the overflow weir 1a and the dilution / precipitation section 4 and the flow valve 10c attached to the branched filtration circulation path section 12 side pipe The etching solution is divided into a predetermined distribution rate. However, other methods may be used for diverting the target etchant to the dilution / precipitation regeneration unit 2 and the filtration circulation path unit 12.

  In the above example, the target etchant concentrated to a predetermined concentration by the concentration unit 7 is introduced into the filtration circulation path unit 12 upstream of the pump 11 via the pump 8. If it is in the piping route, it may be upstream of the heating unit 9 or the filtering unit 6. Further, for example, in the present invention, the apparatus shown in FIG. 3 is changed, and a storage tank is further used in combination with the etching tank 1, and all the etching liquid taken out from the etching tank is regenerated in a batch manner and transferred to the storage tank. In addition, it may be sent to the etching tank 1 directly from the storage tank or through the filtration circulation path 12 when necessary.

<Operation>
In each of the above methods and apparatuses, the target etching solution taken out from the etching tank 1 is diluted and precipitated in the regeneration unit 2 with water (pure water), and the phosphoric acid concentration of the diluted etching solution is 80 to 50% (preferably 75 to 50%), and after mixing, the mixed solution is filtered, and the filtrate is concentrated as necessary and returned to the tank 1 in common. In the example shown in FIGS. 1 and 2, all of the target etching solution taken out from the tank 1 is diluted by adding and mixing a required amount of water (pure water) in the dilution / precipitation unit 4. The precipitation of the silicon compound therein is promoted, and then the silicon compound (and other foreign matters) deposited through the filtration unit 6 is captured and removed. Therefore, the dilution / precipitation regenerating unit 2 replaces the conventional filtration circulation path unit.

  On the other hand, the example shown in FIG. 3 is also a system in which the target etching solution is continuously circulated by continuously filtering the target etching solution in the filtration circulation path portion 12, and for example, the etching amount (etching volume) per unit time is It is suitable for an etching process that increases. As an example, assuming the etching of a semiconductor wafer having at least a silicon nitride film having a diameter of 300 mm, the target etchant overflowing from the etching tank 1 is 1.5 kg / min. Is led out to the dilution / precipitation section 4 at a flow rate of 12.05 kg / min. To the filtration circulation path section 12 at a flow rate of

  Pure water is supplied from the water supply unit 3 to 250 ml / min. When the dilute / precipitation unit 4 adds and mixes with the target etching solution, the saturation concentration of the silicon compound in the target etching solution decreases and the silicon compound precipitates in the target etching solution. Preferably, a cooling unit (not shown) is provided in the dilution / precipitation unit 4, and the target etching solution is cooled to 100 ° C. to normal temperature (20 ° C.), preferably 60 ° C. to normal temperature (20 ° C.). Efficiency can be further improved. The said target etching liquid is sent to the filtration part 6 with the deposit, and the filter of the filtration part 6 captures the said deposit.

  Since the filtrate that has passed through the filter is diluted with a large amount of pure water, if it is supplied to the filtration circulation path 12 or the etching tank 1 as it is, the temperature / concentration control in the tank 1 will be adversely affected. In the second embodiment, in order to prevent such a problem, the filtrate (target etching solution) that has passed through the filter is concentrated to the vicinity of the phosphoric acid concentration when the tank 1 is taken out. In this case, depending on the concentration ratio, pure water is injected into the target etching solution after concentration to control the temperature / concentration of the target etching solution, or the filtrate is left to a concentration that leaves moisture necessary for the temperature / concentration control. Concentrate to eliminate the injection of pure water. As a method for concentrating the target etching solution, since the concentration of the target etching solution is determined by the boiling point or specific gravity of the target etching solution, a method of concentrating the target etching solution to an appropriate concentration by managing the boiling point or specific gravity can be mentioned. For example, the target etchant is kept boiling at a constant temperature to concentrate the etchant, or heated to evaporate moisture until the back pressure of the nitrogen purge reaches the target value, This is a method of controlling the phosphoric acid concentration of the target etching solution to a desired concentration. These also apply to the concentration unit 7 of the apparatus shown in FIG.

  In the above continuous etching operation and the continuous regeneration operation of the etching solution, the trapped precipitates gradually increase in each filtration unit 6. For this reason, in order to continuously regenerate the target etching solution, for example, a plurality of filtration units are provided in parallel between the pump 5 and the concentration unit 7 or between the pump 5 and the heating unit 9, and the filtration reaches the limit. It is preferable to switch from one section to the next filtration section so that the filtration can be operated continuously.

  Further, since the target etching solution decreases as the number of wafers processed increases, for example, by adhering to a wafer that is taken in and out of the tank 1, it is necessary to replenish fresh etching solution. The supply point of the fresh etching solution may be any of the etching tank 1, the overflow weir 1 a, the dilution / precipitation regenerating unit 2, and the filtration circulation path unit 12. Preferably, the tank 1 or the enrichment unit 7 is suitable in the example of FIG. 1, the tank 1 or the overflow weir 1a is suitable in the example of FIG. 2, and the tank 1 or the overflow weir 1a or the enrichment unit 7 is suitable in the example of FIG. Is suitable. Since these are all supplied under atmospheric pressure, there is no fear of backflow of fresh etching solution to the supply part side. In addition to this, when supplying to the concentration unit 7, it is possible to prevent a rapid temperature drop in the tank 1. Further, in the mass production line, as a detailed configuration, for example, the target etching solution is cooled and then sent to the dilution / deposition unit 4, or the etching solution is put into the stationary storage tank from the dilution / precipitation unit 4, and then the storage tank It is also conceivable to send the filter to the filtration unit 6. The present invention may add such details.

  Hereinafter, a test when the saturation concentration of the silicon compound with respect to the phosphoric acid concentration (70 to 85%) of the etching solution (phosphoric acid aqueous solution) was examined (Example 1), a test of the removal efficiency of the silicon compound depending on the cooling temperature of the phosphoric acid aqueous solution (implementation) Example 2) is given. In addition, a test (Example 3) when all the etching liquid in the etching tank was regenerated at once, and a test (Example) when the etching liquid was regenerated using an apparatus similar to the apparatus shown in FIG. 4) will be described. The silicon compound concentration is expressed in terms of Si. The concentration of the silicon compound was measured with an atomic absorption flame spectrophotometer (atomic absorption).

Example 1
This test is an example when the phosphoric acid aqueous solution is diluted with water to each predetermined concentration, and the change in the concentration of the silicon compound in the diluted phosphoric acid aqueous solution before and after filtration is examined. The prepared phosphoric acid aqueous solution is used for etching a silicon nitride film and has a phosphoric acid concentration of 89% in which a silicon compound is dissolved at 63 mg / kg (hereinafter referred to as “phosphoric acid stock solution”). The required amount of the phosphoric acid stock solution was put into each flask, diluted with distilled water so that the phosphoric acid concentration was 85% (comparative example), 80%, 75%, and 70%, and cooled to 20 ° C. (each The concentration of the phosphoric acid aqueous solution is set to 100 g or more). The phosphoric acid aqueous solution of each concentration was stirred in the flask under the same conditions, and then 50 g of each was filtered through a filter having a pore size of 0.1 μm, and the filtrate was used as a filtered phosphoric acid aqueous solution. Moreover, the phosphoric acid aqueous solution which remained without filtering was made into the phosphoric acid aqueous solution before filtration. And about each said phosphoric acid aqueous solution before filtration and the phosphoric acid aqueous solution after filtration, the density | concentration of the silicon compound in phosphoric acid aqueous solution was measured by atomic absorption. Table 1 lists the measured values of the silicon compound concentration before and after filtration.

  From the above test, it can be seen that the silicon compound contained in the phosphoric acid aqueous solution is more precipitated by the lowering of the phosphoric acid concentration with water, and the concentration of the silicon compound varies greatly before and after filtration. . In particular, when the aqueous phosphoric acid solution is diluted to 75% or less, the precipitation of the silicon compound is greatly promoted, and the concentration of the silicon compound is reduced from 53.0 ppm to 12.4 ppm at the 75% dilution by filtration, and the 70% dilution. At 49.5 ppm to 2.9 ppm, the silicon compound can be effectively removed from the phosphoric acid aqueous solution. The present invention has been completed by paying attention to the change in the saturation concentration of the silicon compound due to such a difference in phosphoric acid concentration.

Example 2
Next, the removal efficiency of the silicon compound by changing the cooling temperature of the phosphoric acid stock solution was tested. After 4 samples of 676.3 g of phosphoric acid stock solution were cooled to the temperature described in Table 2, 164.38 g of pure water was added to each to make the total amount of 840.68 g, and the phosphoric acid concentration of each phosphoric acid stock solution was 70% Each was stirred and immediately filtered. As a result, as shown in Table 2, the silicon compound removal efficiency was improved as the cooling temperature of the phosphoric acid stock solution was lowered. In addition, the value of the concentration of the silicon compound after filtration of the phosphoric acid stock solution sample diluted in water shown in Table 2 is obtained by filtering the diluted phosphoric acid stock solution sample after standing for a predetermined time after dilution with water. The value was reduced to the same level as (phosphoric acid concentration 70%).

Example 3
This test is an example when, for example, an etching process is performed assuming that a phosphoric acid aqueous solution containing a silicon compound is collectively regenerated, that is, regenerated in a batch manner, in an etching tank for a mass production line. In the test, 30 kg of 87% phosphoric acid aqueous solution containing 71 mg / kg of silicon compound was placed in the first test tank, 21 kg of pure water was added to the first test tank, and the mixture was stirred uniformly and up to 25 ° C. It cooled and adjusted so that phosphoric acid concentration might be 51%. The adjusted phosphoric acid aqueous solution was replaced from the first test tank to the second test tank through a pipe and a pump provided with a filter, and at the time of the replacement, the silicon compound precipitate was filtered off with the filter. The filtrate in the second test tank was concentrated with a concentrator to an initial phosphoric acid concentration of 87%. And as a result of measuring the silicon compound content contained in the concentrated phosphoric acid aqueous solution, it was 14 mg / kg. This value corresponds to about 80% as a silicon removal rate, and indicates that the regeneration method of the present invention is sufficiently effective in practice as a regeneration method for removing a silicon compound.

Example 4
This test is an example when the etching solution is regenerated by an apparatus similar to that shown in FIG. 3, and when the filtration circulation path section 12 and the dilution / precipitation regeneration section 2 of FIG. 3 are operated (invention embodiment). A comparison was made with the case where only the circulation path 12 was operated (comparative example). In the test, the etching solution (phosphoric acid concentration 87%, silicon compound concentration 85 mg / kg) in the etching tank 1 was used at 13.55 kg / min. From the inside of tank 1. In the embodiment of the invention, the filtration circulation path portion 12 is set to 12.05 kg / min. Flow rate of 1.5 kg / min. The flow was diverted at a flow rate of. The etching solution introduced into the dilution / precipitation regeneration section 2 is sent to the dilution / precipitation section 4 and pure water is supplied at 0.25 kg / min. The mixture was added so as to be uniformly mixed at the same flow rate, and simultaneously cooled to 60 ° C. to precipitate a silicon compound.

  Subsequently, the precipitate of the silicon compound was removed by the filter of the filtration unit 6, and the filtrate (phosphoric acid concentration 74.6%, silicon compound concentration 38 mg / kg) was sent to the tank of the concentration unit 7. In the concentrating part 7, the boiling point is controlled and water is supplied at 0.2 kg / min. Distilled to a phosphoric acid concentration of 84%. Then, it sends to the filtration circulation path part 12, joins the phosphoric acid aqueous solution flowing through the filtration circulation path part 12 and heats it to 160 ° C. through the filter of the filtration part 6 and the heating part 9 of the path part 12, and then the etching tank 1 Circulated to

  On the other hand, in the comparative example, all of the etching solution that has flowed out of the etching tank 1 is sent to the filtration circulation path portion 12, and the insoluble matter is removed by the filter of the filtration portion 6 of the passage portion 12. It was heated and circulated and supplied to the etching tank 1. In this test, the etching solution in the etching tank 1 after a predetermined time was sampled to measure the silicon compound concentration. As a result, the inventive example was about 70 mg / kg, and the comparative example was 85 mg / kg, which is the same as the initial value. From the comparison of the both, the regeneration and etching method and the etching apparatus of the present invention can extend the life of the etching solution as compared with the conventional regeneration and etching method and the etching apparatus provided with the filtration circulation path portion 12. It can be seen that the concentration of the silicon compound contained in the etching solution used can be kept at a sufficiently low value despite the simple and easy management.

  Examples of an object to be etched that can be manufactured by applying the etching method and the etching apparatus of the present invention include the following aspects, and all of them are inexpensive and uniform by the etching method and the etching apparatus of the present invention. Etching can be performed with excellent efficiency. In the etching, the same etching solution can be used repeatedly over a long period of time by using the method for regenerating an etching solution of the present invention.

  That is, for wafer processing in the manufacture of semiconductor devices and the like, a silicon nitride film pattern is formed on the wafer, and the silicon wafer is selectively oxidized using the silicon nitride film as an oxidation-resistant mask to form a silicon oxide film, so-called LOCOS (Local Oxidation). of Silicon) is widely used. In this LOCOS process, the mask made of the silicon nitride film that is no longer needed is etched using a phosphoric acid aqueous solution having a high etching selectivity between the silicon nitride film and the silicon oxide film. Recently, trench isolation has emerged as an element isolation technique that breaks the limits of miniaturization of LOCOS isolation, and has become the mainstream element isolation technique. In general, an LSI manufactured with a design rule of 0.2 μm or less is said to be shallow trench isolation (STI) because the groove has a relatively shallow depth of 200 to 400 nm. Also in this technique, an aqueous phosphoric acid solution is used as an etchant to remove the silicon nitride film that is no longer needed.

The schematic diagram of the etching apparatus by the 1st embodiment of this invention which enforces the etching method of this invention. The schematic diagram which deform | transformed the apparatus of FIG. The schematic diagram of the etching apparatus by the 2nd embodiment of this invention which enforces the etching method of this invention.

Explanation of symbols

1: Etching tank 2: Dilution / precipitation regeneration unit 3: Water supply unit 4: Dilution / precipitation unit 5, 8, 11: Pump 6: Filtration unit 7: Concentration unit 9: Heating unit 12: Filtration circulation path unit 13: Water vapor

Claims (9)

In the etching bath was used to etch the silicon nitride film, a method of reproducing an etching solution comprising phosphoric acid aqueous solution, taken out etching solution containing a silicon compound caused by the etching from the etching bath, the Eject etchant Diluting by adding water to lower the phosphoric acid concentration of the etching solution to 80 to 50% by mass, removing the silicon compound precipitated in the etching solution from the lowering of the phosphoric acid concentration, and silicon compound; the method of reproducing the etching solution, characterized in that it comprises a a phosphoric acid concentration of the etching solution after removal from the etching solution, that close to a concentration suitable for etching raised to 80-90 wt% steps.   The method for regenerating an etching solution according to claim 1, wherein the silicon compound is removed from the etching solution by filtration. In the step of reducing the phosphoric acid concentration of the etching solution, a method of reproducing the etching solution according to claim 1 to lower the phosphoric acid concentration of the etching solution to 7 5 to 50 mass%.   The method for regenerating an etching solution according to claim 1, wherein when the etching solution is diluted, the etching solution is cooled to 100 ° C. to room temperature.   The method for regenerating an etching solution according to claim 1, wherein the etching solution after removing the silicon compound from the etching solution is heated to 140 to 180 ° C. In an etching method for etching a silicon nitride film using an etching solution made of a phosphoric acid aqueous solution in an etching tank,
A step of removing an etching solution containing a silicon compound from the etching tank during or after the etching, a step of regenerating the etching solution by the method according to any one of claims 1 to 5, and the regenerated etching solution And a step of returning to the etching tank. In an etching method for etching a silicon nitride film using an etching solution made of a phosphoric acid aqueous solution in an etching tank,
During or after the etching, a step of removing an etching solution containing a silicon compound from the etching tank, a step of flowing the extracted etching solution for two minutes, and a step of filtering the one etching solution (A) that has been flowed for two minutes, The step of regenerating the other etching solution (B) divided into two by the method according to any one of claims 1 to 5, and regenerating the regenerated etching solution (B) into the one etching solution (A). And a step of returning the combined etching solution to the etching tank. An etching apparatus for performing the etching method according to claim 6 or 7,
An etching solution containing a silicon compound is taken out from the etching tank, and the diluted etching solution for diluting the taken-out etching solution with water to precipitate the silicon compound, a filtration portion for the silicon compound, and a concentration portion for the etching solution are sequentially arranged. An etching apparatus characterized by being arranged.   Furthermore, the etching apparatus of Claim 8 with which the heating part is arrange | positioned.

Images