JP2677263B2 - Chemical composition monitoring method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of monitoring the composition of a cleaning chemical solution composed of hydrogen peroxide, ammonia and water used for cleaning Si wafers and the like, and a monitoring device therefor.

[0002]

2. Description of the Related Art A cleaning chemical solution used for cleaning Si wafers and the like, which is a mixed solution of hydrogen peroxide and ammonia, is often heated to about 60 ° C., so that hydrogen peroxide is thermally decomposed and ammonia is evaporated. The composition of the cleaning solution changes with time. Therefore, it is necessary to monitor the composition of the cleaning chemical liquid.

As a method for detecting hydrogen peroxide, there is a method utilizing ultraviolet absorption. Hydrogen peroxide is in the dissociation equilibrium state of H ₂ O ₂ ═HO ₂ ⁻ + H ⁺ (equilibrium constant at 20 ° C. is 1.5 × 10 ⁻¹² ) in solution (1979, “Cotton Wilkinson Fundamental Inorganic Chemistry”). , First edition, Baifukan, p. 305). The absorptivity of ultraviolet light is 4 to 5 for HO ₂ ⁻ compared to H ₂ O _2.
Although it is 0 times larger, from the dissociated state, it is HO at pH 6 or less.
₂ ^- it is possible to ignore the presence of the ultraviolet absorption can be used for the quantitation of hydrogen peroxide. However, in the mixed solution of hydrogen peroxide and ammonia, dissociation of H ₂ O ₂ is promoted, and the contribution of ultraviolet absorption by HO ₂ ⁻ becomes large and cannot be ignored.

As a measure against this, Japanese Patent Laid-Open No. 61-
There is one disclosed in Japanese Patent No. 281532. In this method, an acid is added to the cleaning chemical solution to prepare a reagent having a pH of 4 or less, and this and the cleaning chemical solution itself are irradiated with ultraviolet rays of 300 nm to measure the respective absorbances. Then, the concentration of hydrogen peroxide is detected from the absorbance of the former, and the ammonia concentration is calculated from the absorbance of the latter and the concentration of hydrogen peroxide.

On the other hand, as a method of detecting the ammonia concentration, there is a method of measuring conductivity. Ammonia is in a solution in a dissociation equilibrium state of NH ₃ + H ₂ O = NH ₄ ⁺ + OH ⁻ (equilibrium constant at 25 ° C. is 1.81 × 10 ⁻⁵ ) (1979, “Cotton Wilkinson Basic Inorganic Chemistry”). , First Edition, Baifukan, page 281), and the concentration in the solution can be calculated from the conductivity and equilibrium constant of the solution. However, when an acid or other alkali is added, the dissociated state is greatly affected, and it is impossible to immediately determine the concentration from the conductivity. Further, in a high pH state, a large amount of NH ₃ remains without being dissociated, so that the measurement sensitivity is lowered.

As described above, hydrogen peroxide can be detected by ultraviolet absorption, and ammonia can be detected by conductivity. However, in both cases, the sensitivity depends on pH, and in the case of a cleaning chemical solution consisting of hydrogen peroxide, ammonia and water, ammonia can be detected. Concentration affects UV absorption and hydrogen peroxide concentration affects conductivity. Therefore, JP
In JP 2-8040, the relationship between the ultraviolet absorption and the conductivity and the concentrations of both components is experimentally obtained, and the concentrations of both components are calculated using the obtained formula. A block diagram of a cleaning apparatus using this method is shown in FIG.

Cleaning tank 3 for cleaning Si wafers and the like
A part of the cleaning chemical liquid is taken out as a sample liquid from 4, and the amount of ultraviolet absorption by oxygen in the solution is measured in the first measuring unit 35. The sample solution used in the first measuring unit 35 or the sample solution separately taken out from the cleaning tank 34 is used to
In the measuring section 36, the electric conductivity is measured by the amount of ammonium ions in the solution. Both measured data are led to the arithmetic function block 37 through the interface, and the concentrations of hydrogen peroxide and ammonia are calculated according to a preset calculation formula. Next, this calculated value is compared with the set value in the comparison function block 38, and the command function block 3
A valve or a pump is operated via 9 to supply the liquid in the hydrogen peroxide tank 31, the ammonia tank 32, and the pure water tank 33 to the cleaning tank 34.

[0008] By the way, the sample solution, the reagent,
After continuously feeding the carrier liquid and switching the flow path switching valve provided in the middle to mix and react these liquids, the absorbance etc. are detected on the downstream side by a detector with a flow cell, A method for quantifying the concentration of an analytical component has been put into practical use. This analysis method, which is called flow injection analysis method (hereinafter referred to as FIA method) (1987, "Analysis Chemistry Handbook", Maruzen, pp. 629-634), includes pump flow rate, pipe length, valve switching time, etc. By controlling the, it is easy to control the reaction accurately, and even a small amount of sample can be quantitatively analyzed accurately. Also, automation is easy.

[0009]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-open No.
In the methods described in Japanese Patent No. 281532 and Japanese Patent Application Laid-Open No. 62-8040, the chemical solution itself (or an acid solution added to the chemical solution) is used as a measurement target, and therefore the following inconvenience occurs. Since the cleaning chemical liquid generally contains a high concentration of chemicals, it is easy to foam, and if foaming occurs in the flow cell (detection cell) in the ultraviolet absorption measuring section, for example, erroneous data will be detected. Further, since the sample liquid has a high concentration, the detection cell deteriorates quickly and cannot be used for a long period of time. Furthermore, it is difficult to measure with high accuracy in the measurement of a high-concentration sample liquid.

Further, these conventional examples require two measuring units (two ultraviolet absorption measuring units or two ultraviolet absorption measuring units and conductivity measuring unit), and an interface for inputting data to a computer. You also need two. For this reason, the size of the apparatus is increased and the cost is increased. Further, in the method of determining the concentration by using two mutually dependent measured values, as in the method of Japanese Patent Laid-Open No. 62-8040, measurement errors are likely to be accumulated, so that highly accurate data can be obtained. Have difficulty.

Therefore, an object of the present invention is to make it possible to detect the concentration in a chemical liquid with high accuracy without increasing the size of the device. In addition, it is also possible to prevent deterioration and damage of the detection element.

[0012]

[Means for Solving the Problems] A method for monitoring a chemical solution composition of the present invention for achieving the above object is as follows: (1) A chemical solution comprising hydrogen peroxide, ammonia and water is diluted with pure water, and the diluted solution is diluted. And the process of measuring the conductivity of the chemical solution,
(2) a step of preparing a liquid diluted with an acid solution of the chemical liquid and pure water, and measuring the conductivity of this liquid; and (3) the conductivity obtained from the conductivity obtained in the second process. And a step of determining the concentration of ammonia in the chemical solution and the concentration of hydrogen peroxide in the chemical solution based on the ammonia concentration and the conductivity obtained in the first step (1).

Further, the chemical composition monitoring device according to the present invention comprises a chemical solution supply section for supplying a chemical solution consisting of ammonia, hydrogen peroxide and water, an acid solution supply section for supplying an acid solution, and pure water for supplying pure water. Supply unit, a plurality of flow path switching valves installed on the downstream side of each supply unit, a mixer installed downstream of any of the flow path switching valves, and a conductivity installed downstream of the mixer. A mixing section and the conductivity measuring section, by sequentially switching the flow path switching valve, pure water only, pure water and chemical solution, chemical solution, pure water and acid solution, sequentially. The flow path to be introduced can be set.

[0014]

[Function] Ammonia is in the dissociation equilibrium state of NH ₃ + H ₂ O = NH ₄ ⁺ + OH ⁻ (equilibrium constant at 25 ° C. is 1.81 × 10 ⁻⁵ ) in the solution, and NH ₄ ⁺ is the conductivity of the solution. To decide. However, as mentioned above, the conductivity of the ammonia solution is affected by hydrogen peroxide. Therefore, in the present invention, the chemical solution is diluted and an acid solution is added to the chemical solution to promote the dissociation of ammonia so that the conductivity does not depend on the concentration of hydrogen peroxide. That is, at pH 6 and below, NH ₃
The presence of γ can be neglected, but by creating this state, the conductivity of the solution depends only on the concentration of ammonia.

It is convenient to use boric acid as the acid added for the purposes mentioned above. This is because the conductivity of the boric acid solution itself is very low, and therefore by using the boric acid solution as the carrier liquid, it is possible to detect the conductivity with a good S (signal) / B (background) ratio. is there. FIG.
In (a), the measurement result of the relationship between the ammonia concentration and the electrical conductivity is shown, with the hydrogen peroxide concentration as a parameter, when a 20 mmol / l boric acid solution is added. As shown in the figure, when boric acid having the above concentration is added, the ammonia concentration is uniquely determined from the measured conductivity.

In the present invention, the conductivity of the chemical solution diluted with pure water is measured before the conductivity of the chemical solution diluted with the acid solution and pure water is measured. This conductivity depends on the concentration of both ammonia and hydrogen peroxide.
However, when the concentration of one (ammonia in this case) is determined, the conductivity depending on the two and the concentration of the other uniquely determine the concentration of the other (hydrogen peroxide in this case). You can ask. FIG. 9 (b) shows the measurement results of the relationship between the ammonia concentration and the electrical conductivity with the hydrogen peroxide concentration as a parameter (contrary to the case shown, the hydrogen peroxide concentration and the electrical conductivity with the ammonia concentration as a parameter. You can also ask for a relationship with). This measurement data is stored in the memory of the computer, and the concentration of hydrogen peroxide can be calculated by referring to this data when measuring the conductivity.

In the present invention, the FIA method is applied, the flow passage switching valve is operated to prepare a diluted solution of the chemical liquid, and the conductivity thereof is measured, and then the flow passage switching valve is further operated to adjust the dilution liquid. The conductivity is measured by adding an acid solution such as an acid solution. Therefore, only one detector and its associated interface can be used. Here, the amount of cleaning chemical solution or acid solution introduced can be fixed to a predetermined value by the capacity of the thin tube attached to the flow path switching valve, and by connecting to a computer, measurement conditions such as valve switching time and pump flow rate are also easy. Since the cleaning chemicals can be accurately controlled, the cleaning chemicals can be accurately diluted by an automatic operation, and the diluted cleaning chemicals can also be measured with high accuracy. Therefore, highly accurate and reproducible automatic chemicals monitoring is possible. Moreover, since the volume of the chemical solution that is normally introduced is about several tens of μl, the amount of the chemical solution that is sampled for monitoring can be suppressed to a range that does not affect the actual cleaning operation. Further, since the concentrated chemical solution is not constantly introduced into the detector, deterioration and damage of the detection cell can be suppressed, and reliable measurement can be performed for a long period of time. Further, it is possible to suppress foaming in the detection cell.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a chemical composition monitoring device of the present invention. As shown in the figure, the cleaning liquid taken out from the cleaning tank (not shown) is sent to the flow path switching valve 5 having a hexagonal valve structure via the cooler 15 and the defoamer 16. The unnecessary cleaning liquid is discarded from the defoamer 16 via the check valve 17. Pure water is sent through the liquid feed pump 1, and boric acid solution is sent through the liquid feed pump 4 to the flow path switching valve 8 having a hexagonal valve structure. Pure water is also sent to the flow path switching valve 7 having a hexagonal valve configuration via the flow path switching valve 6 having a four-way valve configuration and the liquid feed pump 3.

Loops 12, 13 are provided between the flow path switching valves.
23 and 24 are provided. Also, the flow path switching valve 5
Is provided with a loop 11 for holding a predetermined amount of cleaning liquid, and the flow path switching valve 7 is provided with a loop 14 for holding a predetermined amount of diluted cleaning liquid. Here, the capacities of the loop 12 and the loop 13 are the loop 11,
It is made dozens of times the capacity of 14. Each flow path switching valve is switched between a solid line state and a broken line state. The diluted chemical liquid sent from the flow path switching valve 8 is mixed in the mixer 20.
It is sent to the conductivity detection unit 21 via.

Next, the operation of the chemical composition monitor of FIG. 1 will be described. In the first step, as shown in FIG. 2, the flow path switching valves 5, 6, 7 are operated in a broken line state,
The flow path switching valve 8 is operated in the solid line state. In this state, the cleaning liquid and the boric acid solution are discarded via the flow path switching valves 5 and 8, respectively, and all the loops are filled with pure water. In the second step, as shown in FIG. 3, the flow path switching valve 5 is switched to the solid line state. In this state, the cleaning liquid cooled by the cooler 15 and defoamed by the defoamer 16 passes through the flow path switching valve 5 to form the loop 1
1 and the loop 11 is filled with this liquid. The other loops remain filled with pure water.

In the third step, as shown in FIG.
The flow path switching valve 5 is in a broken line state, and the flow path switching valve 6 is
Is switched to the solid line state. This makes loop 1
A circulation flow path including the loop 1, the loop 13, the pump 3, the loop 14, and the loop 12 is formed, and the cleaning chemical liquid filled in the loop 11 is taken into the circulation flow path. Pump 3
By operating for a predetermined time, the liquid in the circulation flow channel is mixed by the flow in the thin tube, and the cleaning chemical liquid is diluted. Therefore, the loop 14 is filled with the diluent of the cleaning chemical liquid.

In the fourth step, as shown in FIG.
The flow path switching valve 7 is switched to the solid line state. As a result, the pure water flowing out from the liquid feed pump 1 is supplied with the diluted cleaning chemical liquid filled in the loop 14 from the loop 23 and the loop 24.
It is extruded into the mixer 20 while being sandwiched by the pure water of. The diluted cleaning chemical liquid is mixed with the pure water in the loop 23 and the loop 24 in the mixer 20 by the flow inside the thin tube, and then passes through the conductivity measuring flow cell 22 in the conductivity measuring unit 21. The conductivity at this time is a value obtained by simply diluting the chemical liquid with pure water, and is a value depending on the hydrogen peroxide concentration and the ammonia concentration. 8A or 8C is an example of the signal at this time. In the fourth step, the diluted cleaning chemical liquid is circulated in the circulation flow path including the loop 11, the loop 13, the pump 3, and the loop 12 except for the one filled in the inner loop 14.

In the fifth step, as shown in FIG.
The flow path switching valves 7 and 8 are switched to the broken line state. As a result, the loops 23 and 24 are filled with the boric acid solution. Further, the circulation flow path including the loop 11, the loop 13, the pump 3, the loop 14, and the loop 12 is formed again,
The diluted cleaning chemical solution circulates in this. Since the volume of the loop 14 is smaller than that of the loops 12 and 13, the concentration of the chemical liquid at this time is almost the same as the concentration of the diluted chemical liquid previously taken into the loop 14.

In the sixth step, as shown in FIG.
The flow path switching valves 7 and 8 are switched to the solid line state. As a result, the pure water flowing out of the liquid delivery pump 1 is
The diluted cleaning chemical liquid filled in 4 is sandwiched by the boric acid solutions in loops 23 and 24, and is extruded to mixer 20. Due to the flow inside the thin tube, the above-mentioned diluted cleaning chemical liquid is fed into the mixer 20 through the loop 23 and the loop 24.
After being mixed with the boric acid solution inside, it passes through the conductivity measuring flow cell 22 inside the conductivity measuring section 21. The conductivity at this time depends only on the ammonia concentration. FIG.
B or D is an example of the signal at this time. The conductivity of the obtained signal B is stored in the computer in advance,
Data processing is performed to determine the ammonia concentration in the chemical solution, in contrast with the calibration curve data [shown in FIG. 9 (a)] showing the relationship between the ammonia concentration and the electrical conductivity. Subsequently, the calibration curve data previously stored in a computer prepared by measuring the conductivity of several kinds of chemical liquids having known compositions and different compositions is used for the conductivity of the signal A previously obtained [for example, FIG. 9].
In contrast to the one shown in (b)], data processing is performed to determine the hydrogen peroxide concentration in the chemical solution. After that, all the valves are returned to the state of the first step again. And the first
~ Continuous monitoring of the chemical liquid composition is performed by repeating the sixth step.

[0025]

As described above, according to the present invention,
The composition of a cleaning chemical solution composed of hydrogen peroxide, ammonia and water can be monitored with high accuracy and reproducibility by collecting a small amount of the chemical solution with a relatively simple and small-scale device. Further, since the concentrated chemical solution is not constantly introduced into the detector, deterioration and damage of the detection cell can be suppressed, and reliable measurement can be performed in the long term. Therefore, according to the present invention, stable cleaning can be performed and the reliability of the product can be improved by combining this device and the chemical liquid supply device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a chemical composition monitoring device of the present invention.

FIG. 2 is a configuration diagram for explaining the operation of the chemical composition monitoring device shown in FIG.

FIG. 3 is a configuration diagram for explaining the operation of the chemical composition monitoring device shown in FIG.

FIG. 4 is a configuration diagram for explaining the operation of the chemical composition monitoring device shown in FIG.

5 is a configuration diagram for explaining the operation of the chemical composition monitoring device shown in FIG.

6 is a configuration diagram for explaining the operation of the chemical liquid composition monitoring device shown in FIG.

FIG. 7 is a configuration diagram for explaining the operation of the chemical composition monitoring device shown in FIG. 1.

FIG. 8 is a diagram showing an example of measurement data by the chemical composition monitoring device of the present invention.

FIG. 9 is a characteristic diagram showing the relationship between ammonia concentration and conductivity for explaining the action of the chemical liquid composition monitoring device of the present invention.

FIG. 10 is a schematic configuration diagram for explaining a conventional chemical liquid composition monitoring device.

[Explanation of symbols]

 1, 2, 3, 4 Liquid-sending pump 5, 6, 7, 8 Flow path switching valve 11, 12, 13, 14, 23, 24 Loop 15 Cooler 16 Defoamer 17 Check valve 20 Mixer 21 Conductivity Detection unit 22 Conductivity measurement flow cell 31 Hydrogen peroxide tank 32 Ammonia tank 33 Pure water tank 34 Cleaning tank 35 First measurement unit 36 Second measurement unit 37 Calculation function block 38 Comparison function block 39 Command function block

Claims (7)

(57) [Claims] 1. A process of (1) diluting a chemical solution comprising hydrogen peroxide, ammonia and water with pure water and measuring the conductivity of the diluted chemical solution, and (2) an acid solution and a pure solution of the chemical solution. A process of preparing a liquid diluted with water and measuring the conductivity of this liquid, and (3) determining the ammonia concentration in the chemical liquid from the conductivity obtained in the process of (2) above, And a step of determining the concentration of hydrogen peroxide in the chemical solution based on the ammonia concentration and the conductivity obtained in the first step (1). 2. In the third step (3), the calibration curve data of the conductivity with respect to the ammonia concentration using the hydrogen peroxide concentration obtained in advance as a parameter, or the ammonia concentration obtained in advance as a parameter is used. The chemical solution composition monitoring method according to claim 1, wherein the hydrogen peroxide concentration is determined by referring to the calibration curve data of the conductivity with respect to the hydrogen peroxide concentration. 3. The chemical solution composition monitoring method according to claim 1, wherein the acid solution used in the second step (2) is a boric acid solution. 4. The pH of the liquid prepared in the second step (2) is 6 or less.
Alternatively, the chemical liquid composition monitoring method described in 3 above. 5. A chemical solution supply section for supplying a chemical solution consisting of ammonia, hydrogen peroxide and water, an acid solution supply section for supplying an acid solution, a pure water supply section for supplying pure water, and downstream of each supply section. A plurality of flow path switching valves installed on the side, a mixer installed downstream of any of the flow path switching valves, and a conductivity measuring unit installed downstream of the mixer, By switching the switching valve, it is possible to set a flow path for introducing only pure water, pure water and chemical solution, and chemical solution, pure water and acid solution into the mixing section and the conductivity measuring section. Liquid chemical composition monitoring device. 6. The plurality of flow path switching valves are connected to a chemical liquid supply section, a waste water path, and a first bypass path,
A first valve consisting of a hexagonal valve or a valve having the same function as the hexagonal valve, and a hexagonal valve or a function equivalent to the hexagonal valve connected to the pure water supply unit, the acid solution supply unit, the mixing unit, and the waste water channel. A second valve including a valve having the same, a third valve including a pure water supply unit, the first valve, and a four-way valve connected to the waste water channel, or a valve having a function equivalent to that of the four-way valve; , A second valve, a third valve, and a fourth valve, which is connected to the second bypass passage and includes a hexagonal valve or a valve having a function equivalent to that of the hexagonal valve. Item 5. A chemical composition monitoring device according to item 5. 7. The chemical liquid supply unit is provided with a cooling device and a defoaming device, and unnecessary liquid from the defoaming device is discharged through a check valve. Alternatively, the chemical liquid composition monitoring device according to claim 6.