JP2010261793A - Method and apparatus for measuring dissolved substance content in liquid, and etching solution regeneration system - Google Patents

Abstract

Disclosed is a method and a measuring apparatus that can measure the content of a dissolved substance in a liquid with high accuracy in a short time and can easily perform in-line measurement of a process that uses the liquid.
An optical unit that causes light R1 from a light source 31 to enter a boundary surface 32b of a prism 32 that forms an interface with a liquid 35 and detects the reflectivity of reflected light R2 from the prism boundary surface 32b, and the optical unit A data processing unit 2 that calculates the dissolved substance content of the liquid 35 based on the detection signal of the unit 1. The data processing unit 2 calculates the absorbance (reflection intensity) based on a signal corresponding to the reflected light amount of the reflected light R3 output from the light receiving element 33. Then, the content of the dissolved substance in the sample liquid (liquid) is calculated from the calculated absorbance and the calibration curve.
[Selection] Figure 1

Description

  The present invention relates to a method and an apparatus for measuring dissolved substance content in a liquid. The present invention also relates to an etching solution regeneration system equipped with such an apparatus.

In recent years, in the field of semiconductor device manufacturing, among Si ₃ N ₄ film and SiO ₂ film formed on a semiconductor material such as a silicon wafer, the Si ₃ N ₄ film is selectively etched away leaving the SiO ₂ film, In addition, a precise etching process is required to maintain the selection ratio uniformly.

The etching selectivity of the Si ₃ N ₄ film and the SiO ₂ film is set in a mixed solution of phosphoric acid (H ₃ PO ₄ ) and pure water (H ₂ O) used as an etchant (hereinafter also referred to as “phosphoric acid aqueous solution”). Since the concentration varies depending on the concentration of the produced silicate compound, in order to continue stable etching, it is necessary to maintain and manage the concentration of the Si component in the etching solution at an optimal constant concentration.

For such a problem, for example, Patent Document 1, Si ₃ N ₄ film coming is produced as a byproduct in the etching solution in the etching process, and a part of the Si component to be dissolved is precipitated in the etching solution in the solid An apparatus has been proposed that can be recovered by making the product and the concentration of the Si component in the etching solution can be kept constant. This apparatus extracts a part of the etching solution from the processing tank, deposits and removes a part or all of the Si component generated in the etching process, and then returns to the processing tank again to regenerate the etching solution. The lifetime is long, and the etching selectivity of the Si ₃ N ₄ film and the SiO ₂ film is maintained and managed at a constant level, enabling highly efficient and efficient etching.

  By the way, in the wet etching system as described above, it is desired that the concentration of the Si component in the etching solution is grasped in real time in the process, and the precipitation removal / regeneration is feedback controlled in the shortest possible cycle. . However, the amount (concentration) of the Si component in the etching solution can be measured by atomic absorption analysis, ion chromatography, inductively coupled plasma mass spectrometry (ICP analysis), or the like (Patent Documents 2 and 2). 5), these methods are not suitable for in-line measurement because it is necessary to dilute or burn the etching solution for measurement. Therefore, the present applicant has proposed a concentration measuring method and measuring apparatus using ultraviolet absorption analysis capable of measuring in-line of the process (Patent Document 6). However, in this method, depending on the combination of the etching solution and the dissolved component (for example, phosphoric acid aqueous solution and silicon), a sufficient correlation coefficient cannot be obtained between the ultraviolet absorbance and the dissolved component concentration, and the measurement accuracy is sufficiently high. I found out I couldn't get it. For this reason, the present applicant further proposed a new technique for quantifying the concentration of the Si component dissolved in the etching solution so that in-line measurement can be performed even in a combination of phosphoric acid and silicon (Patent Document 7). In this method, since the transmittance of the etching solution changes due to light scattering by the precipitate when the Si component dissolved in the etching solution exceeds the saturation solubility, the transmittance is first reduced while lowering the temperature of the etching solution. The concentration of the Si component is quantified by finding the temperature that changes to. However, this method also requires additional equipment and operation of sampling and cooling the phosphoric acid solution for measurement, and a simpler measurement method is desired.

  On the other hand, Patent Document 8 proposes an etching apparatus in which the processing time is adjusted according to the degree of deterioration of the etching solution so that an appropriate etching process can be performed even with the deteriorated etching solution. In other words, this device estimates the degree of deterioration of the etching solution from the usage history of the etching solution, and extends the processing time corresponding to the degree of deterioration of the etching solution from the relationship between the degree of deterioration and the processing rate that has been obtained in advance. Although the concentration of the silicate compound (Si component) that affects the degree of deterioration of the etching solution cannot be measured, the correction processing time is based on empirical rules. It has been decided. Therefore, it cannot be said that high-precision processing can be performed because it cannot cope with fluctuations in the actual processing environment. In Patent Document 9, the concentration of a predetermined substance in the etching solution is detected, and when the concentration of the predetermined substance reaches a predetermined concentration, a predetermined amount of the etching solution in the processing tank is discharged, and a new etching solution is prepared. An etching method and apparatus for replenishing a processing tank and adjusting the concentration of a predetermined substance in an etching solution are described. However, the concentration detection means (concentration detection sensor) for detecting the concentration of a predetermined substance in the etching solution is not specifically described, and the concentration control of the etching solution is a novel etching solution (a solute component thereof). However, the etching solution is not regenerated.

Japanese Patent No. 3842657 Japanese Patent Laid-Open No. 7-21973 JP-A-7-280725 JP-A-10-267836 JP 11-326280 A JP 2004-294205 A JP 2009-58306 A JP 2004-288963 A JP 2001-23952 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is, for example, a metal element (silicon (Si)) dissolved in an etching solution (phosphoric acid aqueous solution or the like) in a semiconductor device manufacturing process. Etc.) to provide a method and a measuring apparatus capable of measuring the content of dissolved substances in a liquid in a short time with high accuracy and easily performing in-line measurement of a process using the liquid. It is.

As a result of intensive studies to solve the above problems, the present inventors have found that when the refractive index of the prism that contacts the liquid is close, the reflectance of light at the boundary surface of the prism that forms the interface with the liquid However, it has been found that it changes with high sensitivity to the change in the refractive index of the liquid accompanying the change in the content of dissolved substances in the liquid. That is, by Snell's law, one of the medium (refractive index: n ₁₎ of the two media having different refractive indexes from the other medium (refractive index: n ₂₎ in the case where light is incident, incident at n _1> n ₂ When the angle is smaller than the total reflection angle or when n ₁ <n ₂ , the light is not totally reflected and the light is transmitted and the reflectance is extremely reduced, but the incident angle of the light is kept constant. When the reflectance is measured and n ₁ and n ₂ are in a close range, the reflectance increases as the refractive index difference between n ₁ and n ₂ increases, and the reflectance increases as the refractive index difference decreases. A change that becomes smaller is observed. For example, when a quartz prism is brought into contact with a phosphoric acid aqueous solution that is an etching solution that is circulated and used in a semiconductor device manufacturing process, the refractive index of the phosphoric acid aqueous solution is slightly higher than the refractive index of quartz, and the reflectance does not become zero. This reflectance is observed as a significant change even if the Si component accompanying the etching treatment is dissolved in the phosphoric acid aqueous solution and the refractive index of the phosphoric acid aqueous solution is slightly increased. In other words, when the total reflection condition is not satisfied, the light reflectance (transmittance) changes sensitively to changes in the refractive index of both media, and the change in the content of silicon (Si) in the phosphoric acid aqueous solution is different from that of the phosphoric acid aqueous solution. It was shown as a change in the reflectance of light at the prism interface, and the correlation between the two was found to be very high. Based on such knowledge, the present invention brings a prism having a refractive index close to the refractive index into contact with the liquid to be measured, and makes light incident on the boundary surface of the prism that forms an interface with the liquid at a predetermined incident angle. It has been found out that the content (concentration) of the dissolved substance in the liquid can be measured with high accuracy in a short time by knowing the intensity of the reflected light obtained in this way.

  As a method for measuring the refractive index of the solution, Abbe's refractometer is a method for calculating the refractive index by measuring the total reflection angle of the target solution by changing the incident angle of incident light before and after the total reflection angle. Although the present invention is widely known, the idea is fundamentally different in that it uses a change in reflectance of reflected light at an incident angle that is not in the total reflection condition.

That is, the present invention includes the following contents.
(1) A prism having an absolute value (| N ₁ −N ₂ |) of a difference between its refractive index (N ₁ ) and liquid refractive index (N ₂ ) of 0.30 or less is used as the prism,
Calculating the dissolved substance content of the liquid based on the reflectivity of the reflected light from the prism boundary surface obtained by making light from the light source incident on the boundary surface of the prism that forms an interface with the liquid, A method for measuring the content of dissolved substances in a liquid.
(2) when the refractive index of the prism (N ₁₎ and the refractive index of the liquid (N ₂₎ is in the relation of N _1> N ₂ is the angle of incidence of the light on the boundary surface of the prism (theta) is the total reflection angle The method according to (1) above, which is smaller.
(3) The method according to (1) or (2) above, wherein the dissolved substance is a metal.
(4) The method according to (1) or (2) above, wherein the liquid is an acid solution and the dissolved substance is a metal.
(5) The method according to (1) or (2) above, wherein the liquid is an etching solution for a semiconductor device manufacturing process and the dissolved substance is a metal.
(6) The material of the prism is quartz, and the light from the light source is composed of at least one within a wavelength range of 170 to 190 nm and two or more wavelengths including at least one outside the wavelength range, (1) to (5 ) Any one of the methods.
(7) A prism in which the absolute value (| N ₁ −N ₂ |) of the difference between the refractive index (N ₁ ) and the refractive index (N ₂ ) of the liquid is 0.30 or less is used as the prism. An optical unit that causes light from a light source to enter the boundary surface of the prism that forms the interface of the prism, and detects the reflectivity of reflected light from the prism boundary surface;
A dissolved substance content measuring device in a liquid, comprising: a data processing unit for calculating the dissolved substance content in the liquid based on a detection signal of the optical unit.
(8) when the refractive index of the prism (N ₁₎ and the refractive index of the liquid (N ₂₎ is in the relation of N _1> N ₂ is the angle of incidence of the light on the boundary surface of the prism (theta) is the total reflection angle The apparatus according to (7) above, which is smaller.
(9) The apparatus according to (7) or (8) above, wherein the dissolved substance is a metal.
(10) The apparatus according to (7) or (8) above, wherein the liquid is an acid solution and the dissolved substance is a metal.
(11) The apparatus according to (7) or (8), wherein the liquid is an etching solution for a semiconductor device manufacturing process and the dissolved substance is a metal.
(12) The material of the prism is quartz, and the light from the light source includes at least one within a wavelength range of 170 to 190 nm and two or more wavelengths including at least one outside the wavelength range, (7) to (11 ).

  As the “liquid” in the present invention, for example, an etching solution (for example, an acid solution such as an aqueous solution of phosphoric acid, hydrofluoric acid, hydrochloric acid, acetic acid, nitric acid, sulfuric acid, etc.) used in a wet etching process in a semiconductor device manufacturing process; Aqueous ammonia solution; aqueous hydrogen peroxide solution and their mixtures), ozone water used in washing machines that clean (sterilize) food and clothing, etc., photographs that develop a large amount of film and photographic paper Examples thereof include a liquid having a predetermined function that is repeatedly used in various apparatuses and systems such as a developer (chemical solution) used in a developing machine.

  The “dissolved substance” to be measured is determined according to the type of liquid, the use (process to which the liquid is applied, etc.), etc., and may be either an inorganic substance or an organic substance. However, typically, it is a metal (ion). For example, in the case where the “liquid” is an etching solution that is circulated and used in the wet etching process of the semiconductor device manufacturing process, the dissolved substance is included in the liquid along with the etching process. These are aluminum (Al), magnesium (Mg), manganese (Mn), nickel (Ni), copper (Cu), silicon (Si), phosphorus (P), tungsten (W), and the like. The term “metal” used in the present specification is a concept that includes not only a metal element but also a metal-like element that exhibits metallic properties such as silicon (Si) and phosphorus (P). Further, when the “liquid” is, for example, ozone water used as a cleaning liquid, ozone whose dissolved amount increases or decreases depending on the cleaning process or time is the “dissolved substance” to be measured.

  The “liquid” in the present invention may be a liquid in which only the “dissolved substance” to be measured is dissolved or a solution in which a substance other than the “dissolved substance” to be measured is dissolved.

  In the liquid dissolved substance concentration measuring method and apparatus of the present invention, the change in the content (concentration) of the liquid dissolved substance can be detected with high sensitivity, and therefore the content can be measured with high accuracy. In addition, since the means necessary for the measurement may be substantially a light source, a prism, and a light receiving element, it can be easily incorporated into a process (system) in which a liquid is used (that is, in-line measurement of a process is possible). It is possible to measure the dissolved substance content (concentration) in the liquid in various processes in real time.

It is a system configuration figure of the dissolved substance concentration measuring device of a 1st embodiment of the present invention. It is a principal part enlarged view of the dissolved substance concentration measuring apparatus of 2nd Embodiment of this invention. It is the schematic of the etching liquid reproduction | regeneration system using the dissolved substance concentration measuring apparatus of this invention. It is an enlarged view of the bottom wall part to which the dissolved substance content measuring apparatus of the overflow tank in FIG. 3 was attached. FIGS. 1A to 1D are schematic views of first to fourth examples of an etching solution regenerating apparatus.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.
FIG. 1 is a system configuration diagram of a dissolved substance content measuring apparatus according to a first embodiment of the present invention. The measurement device 3 is substantially composed of an optical unit 1 and a data processing unit 2.

  First, a specific configuration of the optical unit 1 will be described. The optical unit 1 includes a light source 31, a prism 32, a light receiving element 33, and a flow cell 34. As the light source 31, for example, an LED that emits single wavelength light having a predetermined wavelength, a deuterium lamp that emits continuous wavelength light, a halogen lamp, a xenon lamp, or the like is used. When a light source that emits continuous wavelength light such as a deuterium lamp, a halogen lamp, or a xenon lamp is used, an ultraviolet spectrometer (grating) or an interference filter for extracting light of a predetermined wavelength is usually used.

  The flow cell 34 includes a light shielding wall 34a and a window 34b formed by a part of the prism 32 on the lower surface, and a sample solution 35 is introduced therein. The light beam R1 incident on the prism 32 from the light source 31 disposed on the surface 32a on one side of the prism 32 is reflected by the transmitted light R2 transmitted through the boundary surface 32b of the prism 32 that forms the interface with the sample liquid 35 and the boundary surface 32b. The light receiving element 33 arranged on the other surface 32c of the prism 32 receives the reflected light R3 and converts the reflected light R3 into a photocurrent corresponding to the intensity of the reflected light R3. , Output an electrical signal. When the measurement wavelength is ultraviolet light of 200 nm or less, the measurement light is attenuated by oxygen in the air. Therefore, it is preferable to replace the air in the measurement environment with an inert gas such as nitrogen.

The prism 32 has a refractive index (N ₁ ) of N ₁ <N ₂ or a refractive index (N ₂ ) of the sample liquid 35 or N ₁ > N _2. (N ₁ and N ₂ here are the refractive index at the temperature and the light source wavelength (the wavelength of the incident light R 1) of the measurement system to be implemented.)

When N ₁ <N ₂ , the reflected light R3 is obtained regardless of the incident angle (θ) of the incident light R1, but in this case, when the incident angle (θ) decreases, the reflectance itself decreases. Since it becomes difficult to measure, it is general to select an incident angle at which the reflectance is 1% or more. On the other hand, when N ₁ > N ₂ , the incident angle (θ) of the incident light R1 needs to be smaller than the total reflection angle. In this case, when the incident angle (θ) of the incident light R1 reaches the total reflection angle, the change in reflectance cannot be observed. Therefore, the reflectance that does not reach the total reflection condition is an incident angle that is 10% or less. Is desirable.

In the present invention, the absolute value (| N ₁ −N ₂ |) of the difference between the refractive index (N ₁ ) of the prism 32 and the refractive index (N ₂ ) of the sample liquid 35 is 0.30 or less (preferably 0). .15 or less, and more preferably 0.05 or less). This is because when the absolute value (| N ₁ −N ₂ |) of the refractive index difference exceeds 0.30, a slight change in the refractive index of the sample liquid 35 is not likely to appear as an intensity change of the reflected light R3. .

  As a specific example of the combination of the sample solution 35 and the prism 32, for example, a combination of an aqueous phosphoric acid solution that is an etching solution in a semiconductor device manufacturing process and a quartz prism can be given.

  When the wavelength of the incident light R1 is 250 nm, the refractive index (25 ° C.) of the phosphoric acid aqueous solution (phosphoric acid concentration: 86 ± 0.5 wt%) is 1.469, and the refractive index (25 ° C.) of the quartz prism is 1.508. The total reflection angle of light is 77 degrees. In this case, when the incident angle (θ) of the incident light R1 is 75 degrees, the reflectance is 10%, and the amount of change in absorbance calculated from the change in reflectance when the refractive index of phosphoric acid changes by 0.001 is 0.046.

  When the material of the prism is quartz, when the wavelength of the incident light R1 is 190 nm or less, the difference in refractive index between quartz and the phosphoric acid aqueous solution becomes small, and the change in reflectance can be observed with higher sensitivity. For example, when the wavelength of the incident light R1 is 187 nm, the refractive index (25 ° C.) of the phosphoric acid aqueous solution (phosphoric acid concentration: 86 ± 0.5 wt%) is 1.548, and the refractive index (25 ° C.) of the quartz prism is At 1.571, the total reflection angle is 80 degrees. In this case, when the incident angle of the incident light R1 is 75 degrees, the reflectivity is 1.6%, and the change in absorbance calculated from the change in reflectivity when the refractive index of phosphoric acid is changed by 0.001 is 0. .057.

  Further, when the wavelength of the incident light R1 is 190 nm or less, the refractive index of water contained in the phosphoric acid aqueous solution increases, and the change in the moisture content and the change in the water temperature are reflected according to the measurement result. Therefore, select a plurality of incident light R with a wavelength of 190 nm as a boundary (preferably, select at least two wavelengths including at least one within a wavelength range of 170 to 190 nm and at least one outside the wavelength range (over 190 nm). However, measurement errors due to changes in moisture content or changes in the temperature of the sample can be corrected using the spectral changes observed in these lights.

  When the material of the prism is sapphire, the total reflection angle when the wavelength of the incident light R1 is 250 nm is 53 degrees. In this case, when the incident angle (θ) of the incident light R1 is 45 degrees, Similar to the embodiment using the quartz prism, the reflectance is 10% or less. However, since the difference between the refractive index of sapphire and the refractive index of the sample is as large as 0.377, the refractive index of phosphoric acid changed by 0.001. The amount of change in absorbance calculated from the change in reflectance in this case is as small as 0.004, and a slight change in refractive index of the sample tends not to appear as a significant change in absorbance.

Next, a specific configuration of the data processing unit 2 will be described in detail.
The data processing unit 2 includes an amplifier 14 that amplifies a light intensity signal output from the light receiving element 33 and corresponding to the intensity of the reflected light R3. Further, the data processing unit 2 includes an A / D converter 15 that converts the analog signal output from the amplifier 14 into a digital signal, and a data processing device 16 that receives the digital signal from the A / D converter 15. Yes.

  The data processing device 16 is substantially composed of a microprocessor 17, a RAM 18, a ROM 19, an input device 20, and an output device 21. Here, the microprocessor 17 performs a calculation for deriving the content of the dissolved substance in the sample solution. The RAM 18 stores a calibration curve type and various data. The ROM 19 stores a program for operating the microprocessor 17 and the like. The input device 20 includes a keyboard for inputting data and various commands. The output device 21 includes a printer, a display, and the like that output data processing results.

Hereinafter, specific contents of data processing in the data processing device 16 will be described.
When the light source 31 emits ultraviolet light having a predetermined wavelength, the light receiving element 33 generates a signal proportional to the intensity of the reflected light R3 reflected by the boundary surface 32b of the prism 32 that forms an interface with the sample liquid 35 in the flow cell 34. This signal is amplified by the amplifier 14, converted to a digital signal by the A / D converter 15, and input to the microprocessor 17 of the data processing device 16.

  The microprocessor 17 performs a calculation process according to the following expression 1 on the digital signal input from the A / D converter 15 to calculate the absorbance S (the intensity of the reflected light R3).

[Equation 1]
S = -log ₁₀ A / B ..................... Formula 1

  In Equation 1, A is a reflection intensity value (actual measurement value) obtained from the sample liquid, and B is a reflection intensity value obtained from a reference liquid that does not contain dissolved substances introduced into the flow cell 34. B is data measured in advance, and is stored in the RAM 18 of the data processing device 16. For example, when the sample solution is a phosphoric acid aqueous solution (silicon (Si) dissolved) circulated and used in the wet etching process in the semiconductor device manufacturing process, the reference solution is an unused phosphoric acid aqueous solution that has not been subjected to the wet etching process. is there.

  Next, based on the absorbance (reflection intensity) S obtained by Equation 1, the following Equation 2 is calculated to calculate the content (concentration) C of the dissolved substance to be measured.

[Equation 2]
C = F (S) …………………… Formula 2

  In Equation 2, F (S) is a calibration curve equation for dissolved substances, and includes a first-order term and a higher-order term for S, and is represented by the following Equation 3, for example.

[Equation 3]
C = ΣαS + ΣβS ² + ΣγS ³ + …… + Z ₀ ……………………

In Equation 3, S is data obtained by Equation 1. α, β and γ are coefficients of the calibration curve equation. Z ₀ is a constant term. Each data included in Equation 3 is obtained in advance by the measurement device 3 using a standard sample of a sample solution having a known dissolved substance content (dissolved substance concentration), and is stored in the RAM 18 of the data processing device 16. Has been.

  The microprocessor 17 of the data processing device 16 outputs the dissolved substance content C obtained by the calculation of Equation 3 to the output device 21 such as a CRT or a printer and displays it on the CRT screen or hard copy it on the printing paper. Or send to the outside. Further, the microprocessor 17 of the data processing device 16 manages the predetermined process (for example, semiconductor device manufacturing process) in which the dissolved substance concentration measuring apparatus is incorporated based on the dissolved substance content (concentration) C data. Necessary parameter values (for example, a stock solution addition amount, a stock solution addition time, a waste solution amount, a waste solution time, etc. in a semiconductor device manufacturing process) are calculated, and the results are output to the output device 21.

  In other words, in the measuring device or measuring method for the dissolved substance content of such a liquid, the amount of reflected light (reflected light) reflected at the boundary surface that forms the interface with the sample liquid of the prism in contact with the liquid (sample liquid) to be measured. Since the dissolved substance content is calculated based on (strength), the dissolved substance content can be accurately measured in a short time, and in-line measurement can be performed.

  FIG. 2 is a view showing a main part of the dissolved substance content measuring apparatus according to the second embodiment of the present invention. The measuring apparatus shows the optical unit 1 in the apparatus 3 (FIG. 1) of the first embodiment in FIG. The optical unit 1 ′ shown is changed. In FIG. 2, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  In the dissolved substance content measuring apparatus of the second embodiment, in the optical unit 1 ′, the light incident on the prism 32 is opposed to the boundary surface 32b that forms the interface with the sample liquid 35 of the prism 32 and the boundary surface 32b. Multiple reflections are made between the opposing surface 32d. With such a configuration, the intensity change of the reflected light R3 'with respect to the change in the refractive index of the sample liquid 35 can be increased, and the measurement accuracy can be increased.

  The liquid dissolved substance content measuring device of the present invention (FIGS. 1 and 2) is substantially composed of a small number of space-saving members, ie, a flow cell 34, a light source 31, a prism 32, and a light receiving element 33. In addition to the semiconductor device manufacturing process, it can be easily incorporated into various processes and systems using liquids.

  By incorporating the liquid dissolved substance content measuring apparatus of the present invention into, for example, a wet etching apparatus of a semiconductor device manufacturing process, an etching solution regeneration system can be configured.

As an example, illustrating the etching solution regeneration system of the wet etching apparatus for etching process of a semiconductor material using aqueous phosphoric acid _{(H 3 PO 4 + H 2} O) as an etchant in semiconductor device fabrication processes.

FIG. 3 shows a specific example of a wet etching apparatus. An etching tank 41 contains an etching solution M, and a material to be etched (not shown) such as a semiconductor material is immersed in the etching solution M to perform an etching process. And an overflow tank 41-2 for receiving the etching solution M overflowing from the processing tank 41-1. Specifically, for example, the inside of the treatment tank 41-1 is filled with an etching solution (phosphoric acid aqueous solution (H ₃ PO ₄ + H ₂ O)) M that is heated and controlled at 150 to 175 ° C., and Si ₃ N ₄ is filled there. By immersing the semiconductor material (not shown) on which the film and the SiO ₂ film are formed, the Si ₃ N ₄ film is selectively etched away from the semiconductor material, and an etching process is performed to leave the SiO ₂ film. . By this etching process, SiO ₂ (etching residue) is generated as a by-product and gradually increases in accumulation, so that the Si ion concentration in the etching solution (phosphoric acid aqueous solution) M increases.

The etching solution M overflows from the treatment tank 41-1 to the overflow tank 41-2, and the overflowed etching solution M is circulated by the pump 43 and returned to the overflow tank 41-2. A filter 44 to be removed and a line heater 45 for heating to 150 to 175 ° C. and maintaining the circulation path 42 at a constant temperature are attached. Further, a branch path 46 is formed from the circulation path 42 by a branch pipe, and a regenerator 47 for removing a part of the etching solution M and forcibly depositing and collecting SiO ₂ (etching residue) is attached along the path. ing.

  The overflow tank 41-2 is equipped with the dissolved substance content measuring device 3 of the present invention, and dissolved in the etching solution M (phosphoric acid aqueous solution) in the overflow tank 41-2 by the dissolved substance content measuring device 3. The content of Si ions to be measured is measured. FIG. 4 is an enlarged view of the device part of the dissolved substance content measuring device 3. In FIG. 1 described above, the flow cell is provided. Here, as shown in FIG. 4, a part of the bottom wall 48 of the overflow tank 41-2 is cut out, and the prism 32 is embedded therein, The prism 32 is brought into contact with the etching solution M (phosphoric acid aqueous solution) in the overflow tank 41-2.

In the dissolved substance content measuring apparatus 3, the content (Si ion concentration) of the Si ions in the etching solution (phosphoric acid aqueous solution) M, which is the sample liquid to be measured, is constantly calculated by the operation described above. , the content of the measured Si ions in the measuring device 3 is fed back, based on the content of the Si ions (concentration), SiO 2 _(etch residue) some or all of the dissolved is at reproducing apparatus 47 The amount of the etching solution (regenerated etching solution) forcibly deposited and recovered is returned to the etching tank 41. That is, an electronic control valve 70 is attached to the outlet connection pipe of the regeneration device 47 provided in the branch path 46, and the content (concentration) of Si ions measured by the dissolved substance content measuring device 3 is the CPU 61. In order to keep the content (concentration) of Si ions in the etching solution M in the processing tank 41-1 constant from the content (concentration) of the Si ions and the information stored in advance, the CPU 61 Then, the amount of the regenerated etching solution to be returned from the regenerating device 47 to the etching tank 41 is determined, a control signal is sent to the electronic control valve 70, and a valve opening / closing command is issued. As a result, the determined amount of the regenerated etching solution is returned from the regenerator 47 to the overflow tank 41-2. By repeating this operation in a short time, the Si ion concentration of the etching solution M in the processing tank 41-1 is controlled precisely and constantly, the etching rate is maintained and maintained, and the lifetime of the etching solution is also long. Become. Specifically, it is possible to perform efficient etching with the Si ₃ N ₄ film and the Si ₃ N ₄ film precision while managing kept constant etching selectivity with respect to the SiO ₂ film.

The processing tank 41-1 is made of a desired material such as quartz, and is formed in a bottomed box shape having a substantially rectangular shape in a plan view with a size capable of accommodating a plurality of semiconductor materials in a vertically parallel shape. Tank. A rectifying plate (not shown) is provided on the bottom side in the processing tank 41-1, and the etching solution fed and circulated from the bottom center is supported by all semiconductor materials supported and accommodated in a vertical parallel configuration. The Si ₃ N ₄ film flows (increases) while contacting at an optimum flow rate (m / s) for effectively etching the Si ₃ N ₄ film.

  The branch path (branch pipe) 46 normally has a pipe diameter smaller than the pipe diameter of the circulation path 42, and exhausts the air that enters the circulation path 42 together with the overflowed etchant to the outside, thereby It serves to maintain the flow rate and flow rate of the etching solution smoothly and at a constant flow rate. One end of a part of the circulation path 42 that connects between the filtration filter 44 and the treatment tank 41-1 is provided. Connect and branch piping from the circulation path 42 in an open state with the other end facing the upper opening of the treatment tank 41-1.

Thus, a part (a small amount) of the etchant overflowing the overflow tank 41-2 and taken out of the tank by the circulation pump 43 through the circulation path 42 and pumped and circulated flows into the branch path 46. The etching solution M that has flowed into 46 is returned to the processing tank 41-1 from the open discharge port facing the upper opening of the processing tank 41-1. At this time, the air mixed in the etching solution is separated from the etching solution by the flow in which the etching solution M is discharged back into the processing tank 41-1. Then, a regenerator 47 is connected and installed in the middle of the branch path 46, and the regenerator 47 forcibly deposits and removes SiO ₂ (etching residue) dissolved in the etching solution M.

  Reference numeral 50 in the drawing is an open / close valve connected by piping to the connection side of the branch path 46 with respect to the circulation path 42, and temporarily closes the path 46 when performing maintenance, inspection, replacement, etc. of the regeneration device 47. I can do it.

The regenerator 47 is manufactured from a desired material such as quartz or Teflon (registered trademark), and forcibly precipitates SiO ₂ in the etching solution M introduced through the branch path 46 by cold water or air cooling and oxidation. To recover and remove. The specific structure of the playback device 47 is not particularly limited. The point is that the SiO ₂ (etching residue) dissolved in the etching solution M is forcibly deposited to recover and remove it efficiently and reliably, and the recovered SiO ₂ accumulates in the apparatus 47 and deposits. Any structure can be used as long as it can be easily removed from the path 46 when (recovery capacity) is lowered and washed with a chemical solution such as hydrofluoric acid (HF) for reuse or easy replacement with a new one. . The structure of the embodiment is shown in FIGS. 5 (a) to 5 (d), respectively.

FIG. 5A shows a first example of the regenerator 47, in which a cooling pipe 52 that circulates a cooling medium such as cold water is spirally wound around a precipitation vessel 51 formed in a box shape of an appropriate size. In addition, the access port pipes 53 and 54 for detachably connecting to the branch path (branch pipe) 46 are respectively inserted into the container 51, and the container 51 contains an etching solution. A precipitation nucleus mesh 55 for actively and efficiently precipitating and recovering SiO ₂ is contained. Although not shown in the drawings, it is preferable to use a joint means such as a coupling that can be easily performed as a structure for attaching and detaching the connection port pipes 53 and 54 to the branch path 46.

Thus, according to such a regenerating apparatus 47, the etching solution M introduced into the deposition vessel 51 from the branch path 46 through the inlet connection port pipe 53 is cooled. Then, SiO ₂ in the etchant M is attached to precipitation nuclei for mesh 55 is forced precipitation. As a result, SiO ₂ is efficiently and reliably recovered and removed from the etching solution M. The etching solution M from which SiO ₂ has been recovered and removed is returned from the outlet connection pipe 54 to the branch path 46, and then returned to the processing tank 41-1 through the path 46.

FIG. 5B shows a second example of the regenerator 47, and countless small holes (in the outlet 51 in the inlet 51 of the inlet connection pipe 53 inserted and connected to the precipitation container 51 described in detail in the first example) ( While attaching a substantially trumpet-shaped discharge port 56 having an unshown), a small discharge pump 57 is connected to the pipe portion of the inlet connection port tube 53 located outside the container 51, so that the discharge pump 57 The etching liquid M is configured to be diffused and discharged into the container 51. That is, the etching liquid M is expanded and cooled by diffusing and discharging the etching liquid M from the discharge port 56 into the container 51 by the discharge pump 57, and the precipitation nucleus mesh while forcibly depositing SiO ₂ in the etching liquid M. By adhering to 55, SiO ₂ can be efficiently and reliably recovered and removed from the etching solution M. Note that the same reference numerals are used for the same components as those in the detailed description of the above-described embodiment, and redundant description is omitted.

FIG. 5C shows a third example of the regenerating apparatus 47. The inlet connection port pipe 53 described in detail in the first example is inserted and connected, and the etching solution is introduced from the connection port pipe 53 and stored. The outlet connection port tube 54 described in the first embodiment is inserted and connected to the dilution container 58 for adding a diluent such as pure water to the M via the introduction tube 59, and the precipitation nucleus mesh 55 is contained. The container 60 is connected and equipped, and the etching solution M is cooled by air cooling (atmosphere temperature) in the precipitation vessel 60 as described above, so that SiO ₂ in the solution M is forcibly precipitated to precipitate nuclei. It is configured to be collected and removed by adhering to the mesh 55 for use. In the figure, reference numeral 61 is a dilution replenishment pipe inserted into and connected to the dilution container 58, and 62 is a replenishment valve equipped to the replenishment pipe 61. By this replenishment valve 62, pure water or the like to the dilution container 58 is provided. The replenishment amount of the diluent can be arbitrarily changed and set.

  FIG. 5 (d) shows a fourth example of the regenerator 47, which is provided with a precipitation vessel having both the inlet and outlet connection pipes 53 and 54 described in detail in the first example and having a precipitation nucleus mesh 55 therein. 63 is equipped with an air supply pipe 64 that blows clean air toward the discharge port in the container 63 of the inlet connection pipe 53 and an air cooling nozzle 65 in a state of being connected in communication with the supply pipe 64. In order to maintain the internal pressure and the like of the deposition container 63 in a constant atmosphere, an air exhaust pipe 66 that exhausts excess air from the inside of the container 63 is connected with the blowing of air from the air supply pipe 64. In the figure, reference numeral 67 denotes an air valve installed in the air supply pipe 64 so that the amount of air blown out can be arbitrarily changed and set by the valve 67. Reference numeral 68 denotes a gas-liquid separation filter that is present in the air exhaust pipe 66. The filter 68 does not drain the etching solution M to the outside, and only excess air is exhausted to the outside.

Thus, according to the reproducing apparatus 47 having such a configuration, clean air is supplied to the etching solution M discharged and introduced into the deposition vessel 63 from the branch path (branch pipe) 46 through the inlet connection pipe 53. Be sprayed. Then, SiO ₂ in the etching solution M is forcibly precipitated by oxidation, adheres to the precipitation nucleus mesh 55, and is recovered and removed from the etching solution M. The etching solution M from which SiO ₂ has been recovered and removed is returned to the branch path 46 from the outlet connection pipe 54 inserted and connected near the bottom in the recovery container 63, and passes through the path 46 to the treatment tank 41-1. Returned to

  As described above, in the etching solution regeneration system, the etching process is performed in the circulating use of the etching solution in which the regenerated etching solution is used again for the etching process by removing or reducing the dissolved substances in the etching solution used for the etching process. Since the dissolved inorganic substance in the etching solution in the processing tank can be controlled precisely and constantly, the etching rate is maintained and controlled, and highly accurate and efficient etching can be performed.

  In the wet etching apparatus of FIG. 3, the dissolved substance content in the etching solution in the processing tank 41-1 is incorporated by incorporating the dissolved substance content measuring device 3 of the present invention into the bottom wall portion of the overflow tank 41-2 of the etching tank 41. However, the dissolved substance content measuring device 3 of the present invention is incorporated in a part of the circulation path 42 and the dissolved substance content (concentration) of the etching solution flowing through the circulation path 42 is measured. ) May be measured.

DESCRIPTION OF SYMBOLS 1 Optical part 2 Data processing part 3 Dissolved substance content measuring apparatus 14 Amplifier 16 Data processing apparatus 17 Microprocessor 31 Light source 32 Prism 33 Light receiving element 34 Flow cell 35 Sample liquid 41-1 Processing tank 41-2 Overflow tank 42 Circulation path 46 Branch Route 47 Playback device 48 Bottom wall 61 CPU
70 Electronic control valve

Claims (12)

A prism having an absolute value (| N ₁ −N ₂ |) of a difference between the refractive index (N ₁ ) and the liquid refractive index (N ₂ ) of 0.30 or less is used as the prism.
Calculating the dissolved substance content of the liquid based on the reflectivity of the reflected light from the prism boundary surface obtained by making light from the light source incident on the boundary surface of the prism that forms an interface with the liquid, A method for measuring the content of dissolved substances in a liquid. If the refractive index of the prism (N ₁₎ and the refractive index of the liquid (N ₂₎ is in the relation of N _1> N _2, it incident angle of light on the boundary surface of the prism (theta) is less than the total reflection angle The method of claim 1, wherein:   The method according to claim 1 or 2, wherein the dissolved substance is a metal.   The method according to claim 1 or 2, wherein the liquid is an acid solution and the dissolved substance is a metal.   The method according to claim 1, wherein the liquid is an etching solution for a semiconductor device manufacturing process and the dissolved substance is a metal.   The material of the prism is quartz, and the light from the light source includes at least one within a wavelength range of 170 to 190 nm and two or more wavelengths including at least one outside the wavelength range. The method described in 1. A prism having an absolute value (| N ₁ −N ₂ |) of a difference between the refractive index (N ₁ ) and the refractive index (N ₂ ) of the liquid of 0.30 or less is used as the prism. An optical unit that makes light from a light source incident on a boundary surface of the prism to be formed, and detects the reflectivity of reflected light from the prism boundary surface;
A dissolved substance content measuring device in a liquid, comprising: a data processing unit for calculating the dissolved substance content in the liquid based on a detection signal of the optical unit. If the refractive index of the prism (N ₁₎ and the refractive index of the liquid (N ₂₎ is in the relation of N _1> N _2, it incident angle of light on the boundary surface of the prism (theta) is less than the total reflection angle The device according to claim 7, characterized in that:   The device according to claim 7 or 8, wherein the dissolved substance is a metal.   The apparatus according to claim 7 or 8, wherein the liquid is an acid solution and the dissolved substance is a metal.   The apparatus according to claim 7 or 8, wherein the liquid is an etching solution for a semiconductor device manufacturing process and the dissolved substance is a metal.   The material of the prism is quartz, and the light from the light source includes at least one within a wavelength range of 170 to 190 nm and two or more wavelengths including at least one outside the wavelength range. The device described in 1.

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