JP6486879B2 - Etching solution and substrate processing method - Google Patents

Description

  Embodiments according to the present invention relate to an etching solution and a substrate processing method.

  In the manufacturing process of semiconductor devices, the etching process is an important process for pattern formation. Of the silicon nitride film and silicon oxide film formed on the substrate, the silicon nitride film is selectively etched to leave the silicon oxide film. Processing to be removed is requested. As a technique for performing such a selective etching process of a silicon nitride film, a process using a high temperature (140 ° C. to 180 ° C.) phosphoric acid aqueous solution as an etching solution is known.

  In a process that uses a high-temperature phosphoric acid aqueous solution, for example, a silicon nitride film and a silicon oxide film-formed substrate are immersed in a treatment tank that stores a high-temperature phosphoric acid aqueous solution, thereby selectively etching the silicon nitride film. Process.

However, conventionally, there has been a problem that silica concentration is saturated during phosphoric acid treatment, and silica (SiO ₂ ) is precipitated.

JP 2012-33561 A

  An etching solution and a substrate processing method for suppressing silica deposition are provided.

  The etching solution according to the present embodiment contains a phosphoric acid aqueous solution having water and phosphoric acid, and a salt of an organic compound that is soluble in the phosphoric acid aqueous solution.

It is explanatory drawing for demonstrating an example of an effect | action of the nitride film etching liquid by 1st Embodiment. It is a flowchart which shows the substrate processing method by 1st Embodiment. It is sectional drawing which shows the substrate processing method by 1st Embodiment. 4A is a cross-sectional view illustrating the substrate processing method according to the first embodiment following FIG. 3, FIG. 4B is a cross-sectional view illustrating the substrate processing method subsequent to FIG. 4A, and FIG. 4C is continued from FIG. 4B. FIG. 4D is a cross-sectional view illustrating the substrate processing method subsequent to FIG. 4C. It is sectional drawing which shows the substrate processing method by 1st Embodiment following FIG. 4D. FIG. 6 is a cross-sectional view illustrating the substrate processing method according to the first embodiment following FIG. 5. In the 1st experiment example of a 1st embodiment, it is a sectional view showing the amount of silica deposition typically. It is a graph which shows the 1st experiment example of 1st Embodiment. It is a graph which shows the 2nd experiment example of 1st Embodiment. It is a 1st graph which shows the 3rd experiment example of 1st Embodiment. It is a 2nd graph which shows the 3rd experiment example of 1st Embodiment. It is a figure which shows an example of the substrate processing apparatus which can be used for the substrate processing method by 2nd Embodiment. It is a flowchart which shows the substrate processing method by 2nd Embodiment.

  Embodiments according to the present invention will be described below with reference to the drawings. This embodiment does not limit the present invention.

(First embodiment)
(Nitride film etchant)
The nitride film etchant of the first embodiment is used for etching a nitride film, that is, a silicon nitride film (SiN). For example, the nitride film etchant of the first embodiment can be used to selectively remove a nitride film from a substrate provided with a nitride film and a film other than the nitride film. The film other than the nitride film may be a silicon oxide film (SiO ₂ ), but is not limited thereto.

The nitride film etching solution of the first embodiment includes a phosphoric acid aqueous solution containing water (H ₂ O) and phosphoric acid (H ₃ PO ₄ ), a salt of an organic compound soluble in the phosphoric acid aqueous solution, Containing.

  By containing phosphoric acid, the nitride film etchant can reach a high temperature suitable for securing an etching rate with heating. In addition, by containing water, the nitride film etchant dissociates water heated to a high temperature into hydrogen ions and hydroxide ions, and the dissociated hydrogen ions and hydroxide ions serve as an etchant. Can be etched. Further, by containing a salt of an organic compound that is soluble in a phosphoric acid aqueous solution, the nitride film etching liquid can cause the salt of the organic compound to exist in an ionic state in the phosphoric acid aqueous solution. By existing in an ionic state, the salt of the organic compound reacts with orthosilicic acid generated by etching of the nitride film, and can suppress the polymerization reaction of orthosilicic acid. By suppressing the polymerization reaction of orthosilicic acid, silica precipitation can be suppressed.

  The temperature of the phosphoric acid aqueous solution in which the salt of the organic compound is soluble is, for example, 150 ° C. or higher, preferably 150 ° C. to 200 ° C., more preferably 150 ° C. to 180 ° C., and still more preferably 150 ° C. to 170 ° C. It is.

  The moisture content of the nitride film etchant is preferably greater than 0% by weight and not greater than 15% by weight. By setting the moisture content of the nitride film etchant to 15% by weight or less, the concentration of phosphoric acid can be increased. By increasing the concentration of phosphoric acid, the temperature of the nitride film etchant can be easily increased to 150 ° C. or higher. The concentration of phosphoric acid is preferably 80% by weight or more.

The organic compound salt contained in the nitride film etchant is preferably at least one compound selected from the compound represented by the following general formula (1) and the compound represented by the following general formula (2). .

In General Formula (1) and General Formula (2), R ^{1 to} R ⁴ are organic groups, a is an integer of 1 to 4, and X ^a− is an f-valent anion. f is an integer of 1 to 4.

Specific examples of the general formula (1) include tetramethylammonium chloride (C ₄ H ₁₂ ClN) (hereinafter also referred to as TMAC), (2-hydroxyethyl) trimethylammonium chloride (C ₅ H ₁₄ ClNO), bis (2 - hydroxyethyl) dimethylammonium chloride _{(C 6 H 16 ClNO 2)} , triethyl ammonium chloride _{(C 7} H 18 ClN), tetraethyl ammonium chloride _{(C 8} H 20 ClN), benzyl dimethylphenyl ammonium chloride _{(C 15} H 18 ClN ), Benzyltrimethylammonium chloride (C ₁₀ H ₁₆ ClN), trimethylphenylammonium chloride (C ₉ H ₁₄ ClN), and the like.

Specific examples of the general formula (2) include tetraethylphosphonium bromide (C ₈ H ₂₀ BrP), tetraphenylphosphonium bromide (C ₂₄ H ₂₀ BrP), tetraphenylphosphonium chloride (C ₂₄ H ₂₀ ClP), benzyltriphenylphosphonium. chloride _{(C 25} H 22 ClP) and the like.

FIG. 1 is an explanatory diagram for explaining an example of the action of the nitride film etchant according to the first embodiment. By etching the silicon nitride film with the nitride film etchant, as shown in FIG. 1, orthosilicate (Si (OH) ₄ ) is generated in the nitride film etchant (step S1).

If the nitride film etchant contains neither the compound represented by the general formula (1) nor the compound represented by the general formula (2), a polymerization reaction between orthosilicic acids via silanol groups, ie, dehydration The condensation is promoted to produce a silica dimer ((HO) ₃ Si—O—Si (OH) ₃ ) (step S2B). And a silica polymer will precipitate because a silica dimer superposes | polymerizes.

On the other hand, according to the nitride film etching solution of the first embodiment containing at least one compound selected from the compound represented by the general formula (1) and the compound represented by the general formula (2). For example, the compound can be present in the nitride film etching solution as a monovalent cation represented by A ⁺ in FIG. The cation A ⁺ can replace hydrogen of the silanol group (step S2A). Thereby, dehydration condensation of orthosilicic acid can be suppressed.

  Therefore, the nitride film etchant contains at least one compound selected from the compound represented by the general formula (1) and the compound represented by the general formula (2), thereby suppressing silica precipitation. Can do.

In high-temperature phosphoric acid, it is assumed that Hofmann decomposition of the salt of the organic compound occurs as shown in Formula (3).

When Hoffman decomposition occurs, the cation (A ⁺ ) in FIG. 1 is reduced, which may reduce the silica precipitation inhibiting function of the nitride film etching solution. For this reason, it is preferable that the salt of an organic compound is hard to decompose | disassemble into the phosphoric acid aqueous solution 150 degreeC or more. For example, the salt of the organic compound is at least one compound selected from compounds in which R ^{1 to} R ⁴ in the general formula (1) and the general formula (2) are methyl groups or phenyl groups, which are examples of organic groups. There may be.

As described above, the water in the nitride film etchant functions as an etchant for the nitride film by dissociating into hydrogen ions and hydroxide ions at a high temperature. If the salt of the organic compound becomes a cation having a hydration number greater than 3.5 in the phosphoric acid aqueous solution, the cation is likely to undergo coordination with water in the phosphoric acid aqueous solution. When water is coordinated to the cation, water functioning as an etchant decreases, and it becomes difficult to ensure the etching rate of the nitride film. Moreover, as shown in Formula (4), the precipitation of silica is an equilibrium reaction accompanied by the generation of water.

  For this reason, when much water is coordinated to the cation, the equilibrium is inclined so as to promote the precipitation of silica. That is, when the salt of the organic compound becomes a cation having a hydration number greater than 3.5 in the phosphoric acid aqueous solution, a lot of water coordinates to the cation, so that the equilibrium reaction shown in the formula (4) is on the right. It will be inclined and silica will be easily deposited.

  Therefore, from the viewpoint of more effectively achieving both the etching rate of the nitride film and the suppression of silica precipitation, the salt of the organic compound contains an element that becomes a cation having a hydration number of 3.5 or less in the phosphoric acid aqueous solution. Is preferred.

  As described above, according to the nitride film etchant of the first embodiment, silica precipitation can be suppressed.

(Substrate processing method)
Next, the substrate processing method of the first embodiment to which the above-described nitride film etching solution is applied will be described. FIG. 2 is a flowchart showing the substrate processing method according to the first embodiment.

First, as shown in FIG. 2, substrate pretreatment is performed (step S21). The substrate is, for example, a semiconductor substrate, that is, a SiO ₂ substrate. The substrate may be a substrate other than the semiconductor substrate. Pretreatment may include, for example, cleaning and drying of the substrate.

FIG. 3 is a sectional view showing the substrate processing method according to the first embodiment. After pre-processing, as shown in FIG. 3, the 1st film | membrane 2 is formed into a film on the board | substrate 1 (step S22 of FIG. 2). The first film 2 is, for example, a silicon oxide film (SiO ₂ ). The first film 2 may be a film other than the silicon oxide film.

  After the first film 2 is formed, the first film 2 is patterned as shown in FIG. 2 (step S23). FIG. 4A is a cross-sectional view showing the substrate processing method according to the first embodiment following FIG. In patterning the first film 2, first, as shown in FIG. 4A, a resist 3 is applied on the first film 2.

  FIG. 4B is a cross-sectional view illustrating the substrate processing method subsequent to FIG. 4A. After applying the resist 3 on the first film 2, as shown in FIG. 4B, the resist 3 is exposed and developed to form a predetermined pattern on the resist 3.

  FIG. 4C is a cross-sectional view illustrating the substrate processing method subsequent to FIG. 4B. After the exposure and development of the resist 3, as shown in FIG. 4C, the first film 2 is etched using the resist 3 as a mask.

  FIG. 4D is a cross-sectional view illustrating the substrate processing method subsequent to FIG. 4C. After the etching of the first film 2, the resist 3 is peeled from the first film 2 as shown in FIG. 4D. Thereby, the patterning of the first film 2 is completed.

  FIG. 5 is a cross-sectional view showing the substrate processing method according to the first embodiment following FIG. 4D. After patterning the first film 2, as shown in FIG. 5, a silicon nitride film 4 (SiN) is formed on the first film 2 and the substrate 1 (step S24 in FIG. 2).

  FIG. 6 is a sectional view showing the substrate processing method according to the first embodiment following FIG. After the formation of the silicon nitride film 4, as shown in FIG. 6, the silicon nitride film 4 is wet-etched using the nitride film etchant of the first embodiment (step S25 in FIG. 2). In the wet etching process, a nitride film etching liquid heated to 150 ° C. to 160 ° C. is supplied into the processing tank, and the substrate 1 having the silicon nitride film 4 is brought into contact with the nitride film etching liquid supplied into the processing tank, The silicon nitride film 4 is removed from the substrate 1.

  After the wet etching process of the silicon nitride film 4, as shown in FIG. 2, the substrate 1 is rinsed with pure water (step S26).

  After rinsing the substrate 1, the substrate 1 is dried (step S27).

  According to the substrate processing method of the first embodiment, when the silicon nitride film 4 is selectively removed from the first film 2 by using the nitride film etching solution of the first embodiment, silica is precipitated. Can be suppressed. By suppressing the precipitation of silica, the yield of products (for example, semiconductor devices) including the wet etching process of the silicon nitride film 4 in the manufacturing process can be improved.

(First Experiment Example)
Next, a first experimental example of the first embodiment will be described. FIG. 7 is a cross-sectional view schematically showing the amount of precipitated silica in the first experimental example of the first embodiment.

  In the first experimental example, TMAC was added as an example of an organic compound salt to a phosphoric acid aqueous solution containing 85% by weight of phosphoric acid to obtain a nitride film etching solution. Then, the semiconductor substrate on which the silicon nitride film and the silicon oxide film were formed was immersed in the heated nitride film etchant for a predetermined time. After immersion, the semiconductor substrate was rinsed with pure water and dried, and then the semiconductor substrate was observed with an SEM. Then, as shown in FIG. 7, the amount of silica deposited on the silica 6 deposited on the inner wall of the recess 201 of the silicon oxide film 20 formed by removing the silicon nitride film was calculated. Further, as a comparative example, the amount of deposited silica was calculated after treating a semiconductor substrate under the same conditions as in the case of a nitride film etchant containing TMAC using a nitride film etchant not containing an organic compound salt. . FIG. 8 shows the calculation results of the amount of silica deposited on these two semiconductor substrates.

  FIG. 8 is a graph showing a first experimental example of the first embodiment. FIG. 8 shows a graph of silica deposition when the nitride film etchant of the first embodiment to which TMAC is added (“with addition”) and a nitride film etchant of a comparative example without addition of TMAC (“ A graph of the amount of silica deposited when "no addition") is used is shown.

  As shown in FIG. 8, according to the first experimental example, by using the nitride film etchant of the first embodiment to which TMAC is added, and using the nitride film etchant of the comparative example to which TMAC is not added, In comparison, it was found that the amount of silica deposited can be suppressed. This is presumably because the TMAC cation present in the phosphoric acid aqueous solution suppressed the polymerization reaction of silanol as shown in FIG. Even when a salt of an organic compound other than TMAC is added, it is presumed that the same effect as TMAC can be obtained by the presence of a salt in a phosphoric acid aqueous solution in a cation state.

(Second experiment example)
Next, a second experimental example of the first embodiment will be described. In the second experimental example, the sample No. 1 was used as the salt of the organic compound. 1-No. Eleven types of 11 samples were prepared. Each sample is as follows.

No. 1: TMAC
No. 2: Benzyltrimethylammonium chloride 3: Trimethylphenylammonium chloride No. 3 4: Tetraphenylphosphonium bromide 5: Tetraphenylphosphonium chloride No. 5 6: Benzyltriphenylphosphonium chloride 7: (2-Hydroxyethyl) trimethylammonium chloride 8: Bis (2-hydroxyethyl) dimethylammonium chloride 9: Triethylmethylammonium chloride 10: Benzyldimethylphenylammonium chloride 11: Tetraethylphosphonium bromide In the second experimental example, a sample No. 1 was prepared with respect to a phosphoric acid aqueous solution having a phosphoric acid concentration of 85% by weight. 1-No. Each of the 11 samples was added with 0.1 M to obtain 11 types of nitride film etchants. And each nitride film etching liquid was heated at 160 degreeC for 15 minute (s), and the density | concentration of the sample before a heating and the density | concentration of the sample after a heating were compared.

  In the second experimental example, an analyzer capable of analyzing the sample according to the structure of the sample was used for measuring the concentration of the sample. Specifically, Sample No. For the nitride film etchant to which 1 was added, the concentration of the sample was measured using an ion chromatography mass spectrometer (IC-MS). Sample No. 9 and sample no. For the nitride film etching solution to which 11 was added, the concentration of the sample was measured using a liquid chromatography mass spectrometer (LC-MS). Sample No. 2-Sample No. 2 8 and sample no. For the nitride film etching solution to which 10 was added, the concentration of the sample was measured using an ultraviolet-visible spectrophotometer. The measurement results of the sample concentration are shown in FIG.

FIG. 9 is a graph showing a second experimental example of the first embodiment. As shown in FIG. 9, according to the second experimental example, the sample No. 1-No. 6 was confirmed to be difficult to decompose for at least 15 minutes in a heated phosphoric acid aqueous solution, that is, to have a heat phosphate resistance of 15 minutes. Sample No. 1-No. 6 is a compound in which R ^{1 to} R ⁴ in the general formula (1) or the general formula (2) are methyl groups or phenyl groups.

(Third experimental example)
Next, a third experimental example of the first embodiment will be described. In the third experimental example, sample No. 1 was selected from the samples confirmed to be difficult to decompose by heating for 15 minutes in experimental example 2. 1-No. 3 and sample no. 5 was selected. And about the nitride film etching liquid which added each of each selected sample, the heating time was extended to 180 minutes or more, and the density | concentration change of the sample according to time passage was measured in the process of heating. Sample No. 1 shows the measurement result of the concentration change of Sample No. 1. 2, Sample No. 3 and sample no. The measurement result of the density change of 5 is shown in FIG. Sample No. 2, Sample No. 3 and sample no. In the measurement of the change in the concentration of the nitride film etching solution to which 5 was added, the same sample was measured several times depending on the heating processing time. For this reason, in FIG. 11, a plurality of measurement results for the same sample are plotted for the processing time in which a plurality of measurements were performed.

  As shown in FIGS. 10 and 11, according to the third experimental example, the sample No. 1-No. 3 and sample no. In any of the nitride film etching solutions to which any of 5 was added, the concentration did not change from around 0.1 M within the heating time of 180 minutes. For this reason, sample no. 1-No. 3 and sample no. It was confirmed that the nitride film etching solution to which 5 was added had a resistance to hot phosphoric acid for 180 minutes.

(Second Embodiment)
(Substrate processing apparatus 10)
Next, a second embodiment will be described. FIG. 12 is a diagram illustrating an example of the substrate processing apparatus 10 that can be used in the substrate processing method according to the second embodiment. The substrate processing apparatus 10 is a wet etching processing apparatus for selectively removing the silicon nitride film 4 by immersing the substrate 1 on which the first film 2 and the silicon nitride film 4 shown in FIG. 5 of the first embodiment are formed. Can be used as

  As shown in FIG. 12, the substrate processing apparatus 10 includes a processing tank 11, a circulation path 12, a heating unit 13, and a charging unit 14. Further, the substrate processing apparatus 10 includes a pump 15, a filter 16, and an intermediate tank 17.

  The processing tank 11 includes an inner tank 111 and an outer tank 112. The inner tank 111 is formed in a box shape having an upper end opening 111a. The inner tank 111 is supplied with the nitride film etching solution 7 therein. The inner tank 111 stores the supplied nitride film etching solution 7. Further, the inner tank 111 immerses, that is, contacts the substrate 1 in the stored nitride film etching solution 7. By being immersed in the nitride film etching solution 7, the silicon nitride film 4 on the substrate 1 is dissolved and removed in the nitride film etching solution 7. The substrate 1 may be immersed in the nitride film etching solution 7 using a substrate holding mechanism or a substrate lifting mechanism (not shown). The outer tub 112 surrounds the upper end portion of the inner tub 111 over the entire circumference. The outer tub 112 has an upper end opening 112 a that surrounds the upper end opening 111 a of the inner tub 111. The outer tank 112 collects the nitride film etching solution 7 overflowed from the upper end opening 111 a of the inner tank 111. The processing tank 11 may be a batch type processing tank that simultaneously processes a plurality of substrates 1.

  The circulation path 12 fluidly communicates the bottom of the outer tank 112 and the bottom of the inner tank 111 to circulate the nitride film etching solution 7 through the processing tank 11. The circulation path 12 returns the nitride film etching solution 7 overflowed from the inner tank 111 and stored in the outer tank 112 after the removal of the silicon nitride film 4 to the inner tank 111. During the reflux process, the nitride film etching solution 7 is processed by the heating unit 13, the charging unit 14, and the filter 16 so that the silicon nitride film 4 can be removed again.

  The pump 15 is provided in the circulation path 12. The pump 15 sucks the nitride film etching solution 7 stored in the outer tank 112 to introduce the nitride film etching solution 7 from the processing tank 11 into the circulation path 12. Then, the pump 15 causes the nitride film etching solution 7 introduced from the processing tank 11 to flow back to the inner tank 111 through the circulation path 12.

  The intermediate tank 17 is provided in the circulation path 12 upstream of the pump 15. The intermediate tank 17 temporarily stores the refluxed nitride film etchant 7.

  The charging unit 14 is provided so as to face the intermediate tank 17. The charging unit 14 charges, that is, adds, the salt 71 of the organic compound described in the first embodiment to the nitride film etching solution 7 stored in the intermediate tank 17. The specific aspect of the charging unit 14 is not particularly limited, and may include, for example, a weighing tank for weighing the amount of the organic compound salt 71 and a charging valve for charging the weighed organic compound salt 71. . Further, the intermediate tank 17 may be provided downstream of the pump 15. Further, the charging unit 14 may be provided at a position facing the upper opening 112 a of the outer tank 112 so that the organic compound salt 71 can be charged into the nitride film etching solution 7 stored in the outer tank 112. . In this case, the intermediate tank 17 may be omitted.

  The aqueous phosphoric acid solution 70 before the organic compound salt 71 is introduced is supplied from the supply valve 19 to the inner tank 111. The aqueous phosphoric acid solution 70 supplied to the inner tank 111 overflows from the inner tank 111 and is collected in the outer tank 112, and then stored in the intermediate tank 17 through the circulation path 12 communicating with the outer tank 112. Then, the phosphoric acid aqueous solution 70 stored in the intermediate tank 17 is mixed with the organic compound salt 71 introduced from the introduction unit 14 to become the nitride film etching solution 7. Alternatively, the phosphoric acid aqueous solution 70 is mixed with the nitride film etching solution 7 already stored in the inner tank 111. The supply valve 19 may be installed so as to supply the phosphoric acid aqueous solution 70 to the outer tub 112, or may be installed in the circulation path 12 or so as to supply the phosphoric acid aqueous solution 70 to the intermediate tank 17. Also good.

  The filter 16 is provided in the circulation path 12 downstream of the intermediate tank 17 and the pump 15. The filter 16 removes foreign matters (insoluble substances) in the phosphoric acid solution 3 by filtering the phosphoric acid solution 3. The filter 16 may be installed upstream of the intermediate tank 17 or the pump 15.

  The heating unit 13 is provided in the circulation path 12 downstream of the filter 16 and in the vicinity of the processing tank 11. The heating unit 13 heats the nitride film etchant 7 to a predetermined temperature. The nitride film etching solution 7 heated by the heating unit 13 is discharged into the inner tank 111 by the discharge unit 113 provided in the inner tank 111. The heating unit 13 may be provided in the circulation path 12 upstream of the filter 16.

(Substrate processing method)
Next, the substrate processing method of the second embodiment will be described. FIG. 13 is a flowchart showing a substrate processing method according to the second embodiment. In the following substrate processing method, an example of the wet etching process (step S25) in FIG. 2 will be described. In the initial state of FIG. 2, it is assumed that the processing tank 11 does not store the nitride film etchant 7.

  From the initial state, first, the supply valve 19 of the substrate processing apparatus 10 supplies the phosphoric acid aqueous solution 70 into the inner tank 111 of the processing tank 11 (step S251). The aqueous phosphoric acid solution 70 supplied into the inner tank 111 overflows from the inner tank 111 and is stored in the outer tank 112. The phosphoric acid aqueous solution 70 stored in the outer tank 112 is introduced into the intermediate tank 17 on the circulation path 12 by the suction force of the pump 15. The aqueous phosphoric acid solution 70 introduced into the intermediate tank 17 is temporarily stored in the intermediate tank 17. The supply valve 19 may be installed so as to supply the phosphoric acid aqueous solution 70 to the outer tub 112, or may be installed so as to supply the phosphoric acid aqueous solution 70 in the circulation path 12 or to the intermediate tank 17. .

    Next, the charging unit 14 adds an organic compound salt 71 to the phosphoric acid aqueous solution 70 stored in the intermediate tank 17 (step S252). Thereby, the nitride film etching solution 7 is generated. At this time, based on the detection result of the densitometer 171 installed in the intermediate tank 17, the input unit 14 has a predetermined concentration (mol / L) of the salt 71 of the organic compound in the nitride film etching solution 7. As such, an organic compound salt 71 may be added.

  Next, the filter 16 removes foreign matters from the nitride film etching solution 7 (step S253).

  Next, the heating unit 13 heats the nitride film etchant 7 from which the foreign matter has been removed (step S254).

  Next, the pump 15 supplies the heated nitride film etching solution 7 into the processing bath 11 (step S255).

  Next, the silicon nitride film 4 is wet-etched by immersing the substrate 1 in the heated nitride film etchant 7 in the treatment tank 11 (step S256). At this time, the nitride film etchant 7 contacts the silicon nitride film 4 formed on the substrate 2 and selectively removes the silicon nitride film 4. The nitride film etchant 7 used for the wet etching process overflows from the inner tank 111 and is stored in the outer tank 112.

  Next, the pump 15 sucks the nitride film etching solution 7 stored in the outer tank 112 and recirculates it through the circulation path 12 (step S257). In the course of reflux, the addition of the organic compound salt 71 to the nitride film etchant 7 (step S252), the removal of foreign matter (step S253), heating (step S254), and the supply into the processing bath 11 (Step S255) is performed again. Such various treatments for the nitride film etching solution 7 accompanying the circulation of the phosphoric acid aqueous solution 70 or the nitride film etching solution 7 may be repeated for the time required for the wet etching treatment.

  As described above, according to the second embodiment, etching is performed by etching the silicon nitride film 4 formed on the substrate 1 using the nitride film etchant 7 containing the salt 71 of the organic compound. Silica precipitation can be suppressed.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

1 Substrate 11 Treatment tank 4 Silicon nitride film

Claims (7)

A phosphoric acid aqueous solution having water and phosphoric acid, and a salt of an organic compound soluble in the phosphoric acid aqueous solution,
The salt of the organic compound is
Tetramethylammonium chloride, (2-hydroxyethyl) trimethylammonium chloride, bis (2-hydroxyethyl) dimethylammonium chloride, triethylmethylammonium chloride, tetraethylammonium chloride, benzyldimethylphenylammonium chloride, benzyltrimethylammonium chloride and trimethylphenylammonium chloride An etching solution for a silicon nitride film containing at least one compound selected from the group consisting of: A phosphoric acid aqueous solution having water and phosphoric acid, and a salt of an organic compound soluble in the phosphoric acid aqueous solution,
The salt of the organic compound is an etching solution for a silicon nitride film containing at least one compound selected from compounds represented by the following general formula (2).

(In General formula (2), R < ¹ > -R < ⁴ > is an organic group, a is an integer of 1-4, X ^<a-> is a ^fvalent anion.) 3. The silicon nitride film etching solution according to claim 1, wherein the salt of the organic compound is soluble in the phosphoric acid aqueous solution having a liquid temperature of 150 ° C. or higher. In the general formula (2), R ¹ ~R ⁴ is as defined in claim 2 is a methyl group or a phenyl group, an etching solution of the silicon nitride film. The silicon nitride film etching solution according to claim 1, wherein a moisture content of the phosphoric acid is 15 wt% or less. 3. The silicon nitride film etching solution according to claim 1, wherein the salt of the organic compound includes an element that becomes a cation having a hydration number of 3.5 or less in an aqueous phosphoric acid solution. 4. An etching solution containing a phosphoric acid aqueous solution having water and phosphoric acid and a salt of an organic compound soluble in the phosphoric acid aqueous solution is heated to 150 ° C. or higher,
A substrate having a silicon nitride film is brought into contact with the etching solution, and the silicon nitride film is removed from the substrate.
The salt of the organic compound is
Tetramethylammonium chloride, (2-hydroxyethyl) trimethylammonium chloride, bis (2-hydroxyethyl) dimethylammonium chloride, triethylmethylammonium chloride, tetraethylammonium chloride, benzyldimethylphenylammonium chloride, benzyltrimethylammonium chloride, trimethylphenylammonium chloride And a substrate processing method comprising at least one compound selected from compounds represented by the following general formula (2).

(In General formula (2), R < ¹ > -R < ⁴ > is an organic group, a is an integer of 1-4, X ^<a-> is a ^fvalent anion.)

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