JP2006352097A - Apparatus and method for measuring silicon concentration in phosphoric acid solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and method for continuously and simply measuring a silicon concentration in a phosphoric acid solution of high temperature and high concentration used by circulating in an etching process at a low cost without pretreating, to manage an etching device under a condition where excellent process is always performed. <P>SOLUTION: The apparatus is used for measuring the silicon concentration in the phosphoric acid solution under use as an etching solution during operation of a semiconductor substrate processing system. The equipment is provided with at least a reaction tank and a concentration-measuring tank. The reaction tank includes a reaction unit for adding hydrofluoric acid to a fixed amount of the phosphoric acid solution drawn out of the semiconductor substrate processing system to form a silicon fluoride compound and then causing the silicon fluoride compound to evaporate. The concentration-measuring tank comprises a hydrolysis unit for aerating the silicon fluoride compound, which has evaporated from the reaction tank, to deionized water to hydrolyze the silicon fluoride compound and a measurement unit for determining a change rate of silicon concentration in the deionized water subsequent to the aerating. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a measuring apparatus and a measuring method for measuring a silicon concentration in a phosphoric acid solution that is circulated and used as an etching solution during operation of a semiconductor substrate processing apparatus (hereinafter referred to as an etching apparatus). The present invention is useful for a method of etching a silicon compound film formed on a semiconductor silicon substrate with a phosphoric acid solution in which silicon is dissolved from the beginning, in order to measure the silicon concentration in a circulating phosphoric acid solution. The present invention relates to a measuring apparatus and a measuring method.

  When the silicon compound film on the semiconductor silicon substrate is removed by an etching apparatus, the silicon compound film is usually etched with a high-temperature and high-concentration phosphoric acid solution. The etching chemical solution (phosphoric acid solution) used at this time is circulated many times, and the silicon component after each etching treatment remains in the phosphoric acid solution as a non-volatile silicon compound. Etching is performed. For this reason, the silicon concentration contained as a silicon compound in the phosphoric acid solution varies for each etching process. On the other hand, as described below, the etching characteristics of the silicon compound film to be etched vary with the variation of the silicon concentration in the etching chemical.

  First, when the silicon concentration in the phosphoric acid solution increases, the etching rate of the silicon compound film decreases. On the other hand, in order to suppress the decrease in the etching rate, the dissolved matter (silicon component) in the phosphoric acid solution used in the etching process is concentrated and removed to extend the liquid life of the phosphoric acid solution. Has been proposed (for example, Patent Document 1 and Patent Document 2).

  Furthermore, according to the study by the present inventors, the decrease rate of the etching rate described above may vary greatly depending on the type of silicon compound film to be etched. For example, when a silicon nitride film and a silicon oxide film are compared, there are the following differences. That is, when the silicon concentration in the phosphoric acid solution is increased from 0 ppm to 50 ppm under certain etching conditions, the etching rate of the silicon nitride film is reduced by about 10 to 20%, whereas the etching rate of the silicon oxide film is reduced. In this case, it is greatly reduced to 75 to 85%. Therefore, accurately grasping the silicon concentration in the phosphoric acid solution used as an etching chemical solution in the etching apparatus and managing (controlling) the silicon concentration is very important in performing a uniform etching process.

  The management method for the phosphoric acid solution used in the etching apparatus in operation that has been conventionally performed is to periodically replace the phosphoric acid solution that is being used for each lot. That is, by periodically replacing the phosphoric acid solution, the silicon concentration in the phosphoric acid solution used for the etching process is prevented from exceeding an allowable range. However, the chemical life that is the basis of the above management method is derived from an empirical rule, and is managed in the original sense, that is, the silicon concentration in the phosphoric acid solution used in the etching process is managed. I'm not.

  The etching method described above is a method of performing etching using a phosphoric acid solution that does not contain much silicon. In contrast to this method, an etching chemical solution is used for the purpose of improving the etching selectivity in the multilayer film processing. There is also an etching method in which silicon is intentionally melted using a wafer having a silicon compound film and etched using a phosphoric acid solution containing silicon from the beginning. In the case of this etching method, as in the case of the management method described above, the management of the life of the etching chemical used is based on empirical rules. Furthermore, the silicon concentration initially dissolved in the phosphoric acid solution in the case of this etching method is also such that silicon is dissolved in the phosphoric acid solution under the conditions derived from experience by the above-described method. That is, even in this etching method, the etching process is not performed while managing whether or not a desired amount of silicon is actually dissolved in the phosphoric acid solution in use.

  On the other hand, if the silicon concentration in the phosphoric acid solution that is circulated and used in the etching process of the silicon compound film with the phosphoric acid solution is sequentially measured, the silicon concentration in the phosphoric acid solution can be managed (controlled) in the original sense. It becomes. And, as described above, managing the silicon concentration actually contained in the phosphoric acid solution used as the etching chemical solution directly leads to the management of the etching rate and the etching selectivity.

JP 2002-299313 A Japanese Patent Laid-Open No. 11-293479

  However, as described above, at present, the management of the life of the phosphoric acid solution (the management of the silicon concentration in the phosphoric acid solution) is performed exclusively by empirical rules. This can be used on-line (that can be used for automatic management) for an etching apparatus that etches a silicon compound film formed on a semiconductor silicon substrate with a high-temperature phosphoric acid solution. This is due to the fact that there is no known method or apparatus for measuring the silicon concentration present in the phosphoric acid solution. The current situation is described below.

  Spectral analysis methods such as ICP-AES (inductively coupled plasma atomic emission spectrometry) conforming to JIS-K0116 and atomic absorption spectrometry conforming to JIS-K0121 are common methods for analyzing the silicon concentration in a phosphoric acid solution. Is mentioned. If these analysis methods are used, an extremely accurate and accurate analysis is possible.

  However, when these methods are adopted, a light emitting device for emitting an analysis object, a spectroscope that divides the light, a detector that detects the dispersed light, and the like are necessary, and are complicated. A large device is required. In addition, since the phosphoric acid solution used as the etching solution in the etching apparatus to be measured has a high concentration and a high temperature, when using the analysis method as described above, the phosphoric acid solution is brought to a temperature near room temperature before the measurement. It is necessary to perform a pretreatment on the measurement sample such as cooling and then diluting. For this reason, it is very difficult to perform continuous (temporal) measurement by incorporating the analyzer as described above into the etching processing apparatus. Furthermore, in terms of price, these devices are expensive both in terms of the price and maintenance cost of the devices themselves, which is problematic in this respect.

  Accordingly, an object of the present invention is to perform any pretreatment of the silicon concentration in a high-temperature and high-concentration phosphoric acid solution that can be effectively used in an etching apparatus that uses a phosphoric acid solution as an etching solution and is circulated in a normal etching process. An object of the present invention is to provide a measuring apparatus and a measuring method that can be measured continuously (over time), easily, and inexpensively without performing the above. Furthermore, an object of the present invention is to make it possible to manage (control) the silicon concentration in the phosphoric acid solution used in the etching apparatus so that a good etching process can be performed at all times. This is to contribute to stable and efficient production.

  The above object is achieved by the present invention described below. That is, an apparatus for measuring a silicon concentration in a phosphoric acid solution used as an etching solution during operation of a semiconductor substrate processing apparatus, comprising at least a reaction vessel and a concentration measurement vessel, the reaction vessel Has a reaction unit for generating a silicon fluoride compound by adding hydrofluoric acid to a certain amount of phosphoric acid solution extracted from the semiconductor substrate processing apparatus, and further evaporating the silicon fluoride compound, and The concentration measuring tank is a hydrolytic unit that hydrolyzes the evaporated silicon fluoride compound from the reaction tank by passing it through deionized water, and a measurement that measures the change rate of the silicon concentration in the deionized water after the aeration. And a unit for measuring a silicon concentration in a phosphoric acid solution.

  Another embodiment of the present invention is a method for measuring a silicon concentration in a phosphoric acid solution that is circulated and used as an etching solution in an operating semiconductor substrate processing apparatus, wherein a certain amount of phosphoric acid is supplied from the semiconductor substrate processing apparatus. Extracting the solution, adding hydrofluoric acid to the predetermined amount of phosphoric acid solution to generate a silicon fluoride compound by reaction between the two, and evaporating the silicon fluoride compound from the predetermined amount of phosphoric acid solution And a step of hydrolyzing the evaporated silicon fluoride compound by passing it through deionized water, and measuring the change rate of the silicon concentration in the deionized water. This is a method for measuring concentration.

  According to the present invention, it is continuously and inexpensively used by a method that is much simpler than the conventional method for measuring the silicon concentration in a phosphoric acid solution, and it is circulated and used during the operation of the etching apparatus. It is possible to measure the silicon concentration in a high temperature and high concentration phosphoric acid solution without any pretreatment. In addition, according to the present invention, the process performance can be improved in the etching process of the silicon compound film using the high-temperature phosphoric acid solution by a simple method, and the phosphoric acid solution as the etching solution can be used efficiently. become. For this reason, it leads also to the reduction of the waste liquid amount of phosphoric acid, and also from this point, economically favorable etching can be performed, and the high efficiency of etching is achieved.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments. The outline of the measurement principle in the method for measuring the silicon concentration in the phosphoric acid solution according to the present invention is as follows. First, a certain amount of phosphoric acid solution is extracted from a semiconductor substrate processing apparatus in which the phosphoric acid solution is used as an etching solution, and hydrofluoric acid is added to the phosphoric acid solution and reacted to form a silicon fluoride compound. Next, the silicon fluoride compound is evaporated, and the evaporated gaseous silicon fluoride compound is passed through deionized water for hydrolysis. Finally, the change rate of the silicon concentration in the deionized water after aeration is measured, and thereby the silicon concentration in the phosphoric acid solution used as the etching solution is managed. Inexpensive devices useful for measuring the rate of change of silicon concentration in deionized water include a conductivity meter, an ultrasonic concentration meter, an ion meter, and the like. Measuring with a rate meter gives favorable results. Hereinafter, although the case where a conductivity meter is used is demonstrated as a representative example, this invention is not limited to this.

  The measuring apparatus according to the present invention capable of realizing the above measurement principle can easily and economically measure the silicon concentration in a phosphoric acid solution that is circulated and used as an etching solution during operation of the etching apparatus. . The measuring apparatus according to the present invention basically includes a reaction tank, a concentration measuring tank, and a piping system provided in these. A part of the phosphoric acid solution that is circulated in the etching apparatus in operation is taken out and supplied to the reaction tank. Then, the phosphoric acid solution supplied to the reaction tank is reacted with hydrofluoric acid in the reaction tank. As a result, a silicon fluoride compound is generated from the silicon component in the phosphoric acid solution in the reaction vessel.

  In the measuring apparatus according to the present invention, the silicon fluoride compound generated by this reaction is further evaporated and introduced into the concentration measuring tank adjacent to the gas sent from the reaction tank. In the concentration measuring tank, the gas containing the evaporated silicon fluoride compound sent from the reaction tank is passed through deionized water, thereby hydrolyzing the silicon fluoride compound. Further, the change rate of the silicon concentration in the deionized water in the concentration measuring tank after the gas sent from the reaction tank is vented is measured. The time for venting the gas in the deionized water at this time is not particularly limited because it depends on the method of extracting, that is, measuring the amount of the phosphoric acid solution to be sampled and the change rate of the silicon concentration. Therefore, the ventilation time may be appropriately determined according to sampling conditions, reaction conditions, and the like. For example, when the amount of phosphoric acid solution to be sampled is 300 to 500 mL and the change rate of silicon concentration is measured using a conductivity meter, the time for venting the gas into deionized water should be about 3 to 10 minutes. It is enough. Through this series of operations, it is possible to know the silicon concentration in the phosphoric acid solution that is circulated during the operation of the etching apparatus.

  The method for analyzing the silicon concentration in the phosphoric acid solution that is preferably performed in the measuring apparatus according to the present invention having the above-described configuration will be described in more detail later on. First, a fixed amount of phosphoric acid solution is extracted from the phosphoric acid solution circulation line of the etching apparatus and supplied to the reaction vessel, and hydrofluoric acid is added to the phosphoric acid solution to cause a reaction. In the present invention, it is preferable to add hydrofluoric acid in a state where the phosphoric acid solution is controlled within a temperature range of 70 to 180 ° C. In a normal etching process, a phosphoric acid solution having a concentration of about 85% is circulated at a liquid temperature of 150 to 160 ° C. The temperature of the phosphoric acid solution supplied from the phosphoric acid solution circulation line to the reaction vessel is lowered in the process. According to the study by the present inventors, it is most preferable to raise the temperature of the phosphoric acid solution by a heating means provided in the reaction vessel until the liquid temperature of the phosphoric acid solution becomes about 130 ° C. However, according to further studies, it is possible to measure the silicon concentration in the phosphoric acid solution if the temperature of the phosphoric acid solution supplied to the reaction vessel from the etching apparatus is 70 ° C. or higher. Accordingly, in this case, since it is not necessary to provide a heating means in the reaction vessel, the apparatus can be made simpler. However, since the measurement accuracy tends to decrease with a decrease in the temperature of the phosphoric acid solution, it is preferable to add hydrofluoric acid in a state where the temperature of the phosphoric acid solution is controlled at 70 ° C. or higher.

  When hydrofluoric acid is added to the phosphoric acid solution in the reaction vessel as described above, the silicon compound in the phosphoric acid solution reacts with hydrofluoric acid, and the silicon compound in the phosphoric acid solution is converted into silicon tetrafluoride gas and Become. In the present invention, this silicon tetrafluoride gas is evaporated from the phosphoric acid solution using an inert gas such as nitrogen gas as a medium, and sent to the concentration measuring tank, and these gases are sent to deionized water in the concentration measuring tank. The silicon tetrafluoride in the gas is hydrolyzed to hexafluorosilicic acid. During the operation of sending the silicon tetrafluoride gas from the phosphoric acid solution to the deionized water and venting it as described above, it is preferable to keep the temperature of the phosphoric acid solution in the reaction vessel constant. For example, it is preferable to keep the temperature constant by the heating means provided in the reaction vessel. On the other hand, when no heating means is provided in the reaction tank, it is preferable to keep the temperature reduction rate of the phosphoric acid solution constant by keeping the measurement environment temperature constant. In the present invention, finally, the conductivity of the hexafluorosilicic acid solution (deionized water after aeration) obtained as described above is measured using a conductivity meter. As a result, it is possible to indirectly measure the silicon concentration contained in the phosphoric acid solution that is circulated in the etching apparatus.

  The series of operations described above can be performed automatically. Therefore, when the phosphoric acid solution circulation line of the etching apparatus is set in a state in which the phosphoric acid solution can be sampled at regular intervals and the measuring apparatus according to the present invention is incorporated in the etching processing system, it is used in an operating etching apparatus. It becomes possible to continuously monitor and control the silicon concentration contained in the phosphoric acid solution.

  In the measurement of the conductivity in the concentration measuring tank, the conductivity of the liquid also varies depending on the temperature, but this variation can be corrected with a simple calculation formula. Can compensate.

  The gaseous substance transferred from the reaction vessel to the concentration measurement vessel using an inert gas as a medium contains not only silicon tetrafluoride but also water and hydrogen fluoride. However, as described below, these effects can be ignored in the present invention. First, water is a substance having no electrical conductivity, and the amount transferred to the concentration measuring tank is very small compared to the amount of deionized water supplied in the tank, and can be ignored. Hydrofluoric acid has electrical conductivity, but its conductivity is small compared with hexafluorosilicic acid, which is strongly dibasic. Further, according to the study by the present inventors, when the amount of hydrofluoric acid added to the phosphoric acid solution in the reaction tank is made constant and the reaction conditions such as temperature are made constant, the concentration measurement tank The amount of substance transferred varies depending on the amount of silicon tetrafluoride produced in the reaction vessel. This is because, under certain reaction conditions, the change in the conductivity of deionized water in the concentration measurement tank is dominated by the hexafluorosilicic acid concentration, that is, the silicon concentration in the phosphoric acid solution. Means negligible.

  Hereinafter, an example of a measuring apparatus according to the present invention capable of realizing the method of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic view of the apparatus. As shown in FIG. 1, the measuring apparatus according to the present invention is provided with a reaction tank 1 and a concentration measuring tank 7 as main components. Both the reaction tank 1 and the concentration measurement tank 7 have a structure that can be hermetically sealed during the measurement operation by the measurement apparatus according to the present invention. The reaction tank 1 is supplied with a certain amount of phosphoric acid solution extracted from a phosphoric acid solution that is circulated and used as an etching chemical during the operation of the etching apparatus, and the silicon component contained in the phosphoric acid solution is used as a silicon fluoride compound. Any structure having a reaction unit to be evaporated may be used. One concentration measuring tank 7 is supplied with a gas containing a silicon fluoride compound evaporated in the reaction tank 1 and passes the gas through deionized water to hydrolyze, and the silicon concentration of the deionized water. Any structure may be used as long as it has a measurement unit for measuring the change rate. Hereinafter, these units will be described.

  A phosphoric acid solution used as an etching chemical during the operation of the etching apparatus is circulated through a phosphoric acid solution circulation line L in the etching apparatus. In the apparatus illustrated in FIG. 1, a supply line 2 that connects the phosphoric acid solution circulation line L in the etching apparatus and the reaction tank 1 is provided, and a part of the phosphoric acid solution is drawn from the circulation line L to react. A certain amount of phosphoric acid solution is supplied to the tank 1.

  Further, the reaction tank 1 has a structure in which a hydrofluoric acid solution can be added to the phosphoric acid solution in the reaction tank 1 while being connected to an inert gas supply line 3 for supplying an inert gas to the reaction tank 1. A hydrofluoric acid solution supply line 4 is provided. Furthermore, in the illustrated reaction tank 1, a liquid level sensor 15A for enabling supply of a certain amount of liquid into the reaction tank 1, and a heater 11 for heating the supplied phosphoric acid solution as necessary. A thermocouple 12A for measuring the liquid temperature for measuring the liquid temperature in the reaction tank 1 is installed.

  On the other hand, the concentration measurement tank 7 needs to have a hydrolysis unit and a measurement unit as described above. For this reason, between the reaction tank 1 and the concentration measurement tank 7, as shown in FIG. 1, the gas containing the silicon fluoride compound from the reaction tank 1 is supplied into the concentration measurement tank 7. A gas supply line 6 is provided. Further, a deionized water supply line 8, an exhaust line 9 and a waste liquid line 10 are connected to the concentration measuring tank 7. The concentration measuring tank 7 includes a liquid level sensor 15B for enabling a certain amount of deionized water to be supplied into the tank, and a thermocouple 12B for measuring the temperature of the deionized water in the concentration measuring tank 7. A conductivity sensor 13 of deionized water in the concentration measuring tank 7 is installed. The conductivity sensor 13 is connected to a conductivity monitor 14 as shown in FIG.

  Reference numeral 16 shown in FIG. 1 denotes a deionized water supply line for washing the phosphoric acid solution supply line 2 and the reaction tank 1, and further the gas supply line 6. Reference numeral 17 denotes an inert gas supply line for purging after washing with water.

  Next, an example of operation of the measuring apparatus having the above configuration will be outlined, but this is only an example, and the present invention is not limited to the example of operation. First, 350 mL of an 85% phosphoric acid solution that is circulated and used at a liquid temperature of 150 to 160 ° C. is supplied from an operating etching apparatus to the reaction tank 1 via a supply line 2. At the same time, 400 mL of deionized water is supplied to the concentration measuring tank 7 via the deionized water supply line 8. The amount of these liquids supplied into the reaction tank 1 and the concentration measurement tank 7 can be controlled by liquid level sensors 15A and 15B.

  Since the temperature of the phosphoric acid solution supplied into the reaction tank 1 is 110 to 130 ° C. due to the loss of heat during the above-described supply operation, the liquid temperature in the reaction tank 1 is measured by the thermocouple 12A for liquid temperature measurement. The heater 11 is heated while measuring. Then, when the phosphoric acid solution in the reaction vessel 1 reaches 130 ° C., a 50% hydrofluoric acid solution is prepared using nitrogen gas as a carrier via an inert gas supply line 3 and a hydrofluoric acid solution supply line 4. Add into 2 mL phosphoric acid solution. Next, the phosphoric acid solution is bubbled from the inert gas supply line 3 with 5 L / min of nitrogen gas for 5 minutes. Here, even during bubbling with nitrogen gas, the temperature of the phosphoric acid solution is maintained at 130 ° C. by heating with the heater 11.

  Almost simultaneously with the start of the addition of the hydrofluoric acid solution and the supply of nitrogen gas, the transfer of the gas containing the silicon fluoride compound gas as the reaction product from the reaction tank 1 to the concentration measurement tank 7 is performed. Start via the gas supply line 6. The gaseous silicon fluoride compound present in the gas is hydrolyzed when the transferred gas is passed through the deionized water in the concentration measuring tank 7, and is taken into the deionized water as silicic acid. In the present invention, during the supply of the gaseous silicon fluoride compound to the concentration measuring tank 7 via the gas supply line 6, the solution (deionized water) temperature and conductivity in the concentration measuring tank 7 are set to the liquid temperature. It is preferable that the measurement is performed by the conductivity monitor 14 connected to the thermocouple 12 </ b> B for measurement and the conductivity sensor 13.

  Below, the reaction considered to occur in the reaction tank 1 or the concentration measurement tank 7 is shown by an equation. In addition, the chemical formula shown here is an assumption to the last, and does not restrict | limit this invention at all. In addition, since there are various types of silicon compounds in the phosphoric acid solution, in the following chemical formula, they are collectively referred to as X-Si.

  The above formulas (1-1) and (1-2a) indicate the reaction between a silicon compound and hydrofluoric acid in a phosphoric acid solution. The silicon compound in the phosphoric acid solution reacts with the added hydrofluoric acid to form silicon tetrafluoride gas. This is shown in equation (1-1). At the same time, hexafluorosilicic acid is also produced. This is shown in equation (1-2a). The hexafluorosilicic acid produced here is then decomposed into gaseous silicon tetrafluoride gas and hydrofluoric acid gas because the dissolved phosphoric acid solution is hot. This is shown in equation (1-2b). The silicon tetrafluoride gas generated in the reaction tank 1 is transferred to a concentration measurement tank 7 containing deionized water using an inert gas as a medium, and is hydrolyzed as shown in the formula (2-1). To hexafluorosilicic acid and orthosilicic acid. The orthosilicic acid produced at this time is converted to hexafluorosilicic acid by hydrogen fluoride transferred together with silicon tetrafluoride from the reaction vessel 1 as shown in the formula (2-2). In the present invention, as described above, the concentration of silicon contained in the phosphoric acid solution is indirectly measured by measuring the conductivity of the solution containing hexafluorosilicic acid.

  Next, an Example is given and this invention is demonstrated further in detail. However, the examples are merely examples, and the present invention is not limited to these examples.

<Example 1>
Standard samples of four types of 85% phosphoric acid solutions with known silicon concentrations of 0, 23, 46, and 69 ppm using the experimental apparatus configured as shown in FIG. Conductivity measurement was performed on. This conductivity value is temperature compensated.

  After 350 mL of each phosphoric acid solution sample having the above concentration was supplied to the reaction vessel 1, the solution was heated by the heater 11 to adjust the liquid temperature to 130 ° C. Next, as described above, 2 mL of 50% hydrofluoric acid solution was added to the phosphoric acid solution in the reaction vessel 1 using the nitrogen gas from the line 3 shown in FIG. 1 as a carrier. Thereafter, nitrogen gas of 5 L / min is sent from the inert gas supply line 3 and bubbled for 5 minutes, and from the reaction tank 1 into 400 mL of deionized water in the concentration measuring tank 7 through the gas supply line 6. The gas in the reaction tank 1 was transferred. In this way, the conductivity value of the deionized water in the concentration measuring tank 7 after aeration for 5 minutes from the addition of the hydrofluoric acid solution to the phosphoric acid solution is measured with the conductivity sensor (875EC-JIF (trade name), FOXBORO). During the above operation, the temperature of the phosphoric acid solution in the reaction vessel 1 was maintained at 130 ° C. by heating with the heater 11. Table 1 shows the known silicon concentration [ppm] in each phosphoric acid solution sample and the conductivity value of the aerated deionized water (solution) in the concentration measuring tank 7.

FIG. 2 is a graph showing the relationship between the obtained conductivity value G and the corresponding silicon concentration C ₁ in the phosphoric acid solution. From these results, at least within the range of the silicon concentration in the phosphoric acid solution used in the above test, the conductivity value G tends to increase with an increase in the silicon concentration C ₁ in the phosphoric acid solution. It was confirmed that the relationship can be expressed by a linear function equation.

Furthermore, the relationship between the silicon concentration C ₁ in each phosphoric acid solution used in the above test and the conductivity value G of the corresponding solution in the concentration measuring tank 7 is the silicon concentration in each phosphoric acid solution used as the standard sample. It was verified by the following method whether it was inevitable due to the difference. Using ICP-AES analysis (Inductively Coupler Plasma Atomic Emission Spectroscopy) for each solution in the concentration measuring tank 5 minutes after the addition of the hydrofluoric acid solution performed in the above test. The silicon concentration was analyzed. The obtained results are shown in Table 2. In Table 2, the conductivity value G of each solution in the concentration measuring tank 7 is also shown.

FIG. 3 shows the ICP for the known silicon concentration C ₁ of each standard sample used in the test and the solution in the concentration measuring tank 7 after the gas transferred from the reaction tank 1 was aerated for 5 minutes in deionized water. -AES shown graphed the relationship between the silicon concentration C ₂ obtained by measurement by analysis. Further, in FIG. 3, the silicon concentration C ₂ and the conductivity value G of the solution in the concentration measuring tank 7 after the gas measured from the reaction tank 1 previously measured and passed through the deionized water for 5 minutes. The relationship is shown in a graph.

From these results, the silicon concentration C ₁ in the phosphoric acid solution when supplied to the reaction vessel 1 or the concentration after a certain time (after 5 minutes) from the addition of hydrofluoric acid to the phosphoric acid solution in the reaction vessel 1 It was confirmed that the relationship between the silicon concentration (C ₂ ) and the conductivity value in the solution in the measuring tank 7 can be expressed by a linear function equation. Further, the above study, the silicon concentration C ₂ of the concentration measuring tank 7, the silicon concentration C ₁ of the phosphoric acid solution in when fed to the reaction vessel 1 was confirmed that a proportional relationship.

From the relationship confirmed as described above, the silicon concentration C ₁ in the phosphoric acid solution when supplied to the reaction vessel 1 and the solution in the concentration measurement vessel 7 after a certain time from the addition of hydrofluoric acid to the reaction vessel 1 It was found that the following formulas (A-1) and (A-2) are established between the silicon concentration C ₂ and the conductivity G of the solution in the concentration measuring tank 7 at that time. In these formulas, a, b and c are constants derived from experimental values. Also, equation (B) is derived from these two equations. The formula (B) shows that the silicon concentration C ₁ in the phosphoric acid solution when supplied to the reaction tank 1 can be obtained by measuring the conductivity G of the corresponding solution in the concentration measuring tank 7. I mean.

From the graph shown in FIG. 3, the constants a, b, and c in the formula are derived as a = 0.993, b = 64.5, and c = -65.9, respectively. When these are applied to the above equation (B), it can be seen that C ₁ = f (G) = 62.8G−64.1. This equation is almost coincident with C ₁ = 62.7G-63.8 which is a linear function equation in the graph shown in FIG. From this, it can be said that the relationship between the silicon concentration in the phosphoric acid solution supplied to the reaction vessel 1 and the conductivity of the solution in the concentration measurement vessel 7 is inevitable. Then, the silicon concentration in the phosphoric acid solution supplied to the reaction tank 1, that is, the phosphoric acid solution used in the etching apparatus, can be derived by measuring the conductivity of the solution in the concentration measuring tank 7. I understand that.

<Example 2>
Example 1 is an example in the case where a heating means (for example, a heater) is provided for the phosphoric acid solution in the reaction vessel of the measuring apparatus, but in this example, no heating means is provided or heating This is an embodiment in which no means is used. Experiments were performed under substantially the same conditions and procedures as in Example 1 using the same experimental apparatus as the configuration shown in FIG. In the present embodiment, without using the heater 11 which is a heating means for the phosphoric acid solution in the reaction tank 1, the temperature of the phosphoric acid solution supplied to the reaction tank 1 is lowered to an arbitrary temperature described later and fluorinated at the same time. The hydrogen acid solution was added, and bubbling with nitrogen gas from the inert gas supply line 3 was started and ended after 5 minutes. By performing the above-described series of measurements in a normal temperature atmosphere of 24 to 26 ° C., the temperature decrease rate of the phosphoric acid solution during bubbling was made constant. In this example, the volume of the phosphoric acid solution supplied into the reaction tank 1 was 150 mL, and the volume of deionized water in the concentration measurement tank 7 was 80 mL. Other experimental procedures and conditions were the same as in Example 1.

  In the test conditions described above, Example 1 was prepared by using two known 85% phosphoric acid solution standard samples having silicon concentrations of 0 ppm and 69 ppm and changing the liquid temperature of the phosphoric acid solution when hydrofluoric acid was added. The possibility of measurement at a liquid temperature lower than the liquid temperature used in the above was investigated. Specifically, when the liquid temperature of the phosphoric acid solution at the time of addition of hydrofluoric acid is changed to four types of 70, 80, 90 and 100 ° C., the conductivity of the solution in the concentration measuring tank 7 is measured. Went. This conductivity is temperature compensated. The obtained results are shown in Table 3.

  FIG. 4 is a graph showing the change in conductivity value accompanying the change in the addition temperature of hydrofluoric acid at each silicon concentration. From this result, when the addition temperature of hydrofluoric acid is in the range of 70 to 100 ° C., even when the phosphoric acid solution in the reaction vessel during bubbling is not heated, the silicon concentration in the phosphoric acid solution It was found that the conductivity value changes due to the difference. From this, it can be said that even under these conditions, silicon tetrafluoride gas was generated by the reaction of the silicon compound and hydrofluoric acid in the phosphoric acid solution. This also means that the silicon concentration in the phosphoric acid solution can be measured by a measurement technique in which the phosphoric acid solution in the reaction vessel in the present invention is not heated.

  The above results show that if the measuring apparatus or method according to the present invention is used, the silicon concentration in a high-temperature and high-concentration phosphoric acid solution that is circulated and used during the operation of the etching apparatus is measured without any pretreatment. It shows what you can do. Further, for example, a part of the phosphoric acid solution that is circulated in the etching apparatus in operation is extracted and sampled every 10 to 20 minutes, supplied to the reaction tank 1, and the solution in the concentration measurement tank 7 If the measuring device or method according to the present invention is configured to monitor the electrical conductivity of the phosphoric acid solution at regular intervals, the state of the silicon concentration in the phosphoric acid solution can be easily known. In addition, depending on the conductivity value of the solution in the concentration measuring tank 7 being monitored, the replacement time of the used phosphoric acid solution is set, or the amount of silicon dissolved in the phosphoric acid solution is increased. be able to.

  As a result, the silicon concentration in the phosphoric acid solution used in the etching process is the same as when the phosphoric acid solution having a low silicon concentration is used as the phosphoric acid solution, or when the phosphoric acid solution in which silicon is first dissolved is used as the phosphoric acid solution. However, since it can be managed (controlled) so that a good etching process can always be performed, the measuring apparatus and method according to the present invention can contribute to stable and efficient production of a high-performance semiconductor substrate.

It is a block diagram which shows typically the example of a measuring device to which this invention is applied. A silicon concentration C ₁ of the phosphoric acid solution was fed to the reaction vessel, is a graph showing the relationship between the conductivity G of a solution of a concentration measuring tank after venting predetermined time gas. The silicon concentration C ₂ in the solution concentration measuring vessel is a graph showing the relationship between the conductivity values G of the solutions in a concentration measuring tank. It is a graph which shows the electrical conductivity value change accompanying the change of the silicon concentration in a phosphoric acid solution, and the addition temperature of hydrofluoric acid.

Explanation of symbols

1: Reaction tank 2: Supply line of phosphoric acid solution (etching solution) to reaction tank 3: Inert gas supply line 4: Hydrofluoric acid supply line 5: Waste liquid line 6: Gas supply line 7: Concentration measuring tank 8: Deionized water supply line 9: Measurement tank exhaust line 10: Measurement tank waste liquid line 11: Heating heaters 12A, 12B: Thermocouple 13: Conductivity sensor 14: Conductivity monitor 15A, 15B: Liquid level sensor 16: In the apparatus Deionized water supply line for cleaning 17: Inert gas supply line for purging in the apparatus L: Phosphoric acid solution circulation line in the etching apparatus

Claims (8)

  An apparatus for measuring a silicon concentration in a phosphoric acid solution used as an etchant during operation of a semiconductor substrate processing apparatus, comprising at least a reaction vessel and a concentration measurement vessel, wherein the reaction vessel comprises: A reaction unit for generating a silicon fluoride compound by adding hydrofluoric acid to a certain amount of phosphoric acid solution extracted from the semiconductor substrate processing apparatus, and further evaporating the silicon fluoride compound; and The concentration measuring tank includes a hydrolysis unit for hydrolyzing the evaporated silicon fluoride compound from the reaction tank through deionized water, a measurement unit for measuring a change rate of the silicon concentration in the deionized water after the aeration. An apparatus for measuring a silicon concentration in a phosphoric acid solution, comprising:   Means for adding hydrofluoric acid in a state where the phosphoric acid solution in the reaction vessel is controlled within a temperature range of 70 to 180 ° C., and the silicon compound in the phosphoric acid solution is a gaseous silicon fluoride compound. The apparatus for measuring a silicon concentration in a phosphoric acid solution according to claim 1, further comprising: means for evaporating from the phosphoric acid solution.   The reaction tank supplies an inert gas from the lower part of the reaction tank to the phosphoric acid solution in which the hydrofluoric acid is added to form a silicon fluoride compound, and only the gas in the reaction tank is supplied from the upper part of the reaction tank. The apparatus for measuring the concentration of silicon in a phosphoric acid solution according to claim 1 or 2, further comprising means for discharging gas.   The silicon concentration measuring device in a phosphoric acid solution according to any one of claims 1 to 3, wherein the concentration measuring tank has means for measuring a change rate of silicon concentration in deionized water using a conductivity meter.   The phosphoric acid solution according to any one of claims 1 to 4, wherein the reaction tank is further provided with heating means for controlling the phosphoric acid solution in the reaction tank within a temperature range of 70 to 180 ° C. Inside silicon concentration measuring device.   A method for measuring a silicon concentration in a phosphoric acid solution that is circulated and used as an etching solution in an operating semiconductor substrate processing apparatus, wherein a predetermined amount of phosphoric acid solution is extracted from the semiconductor substrate processing apparatus, A step of adding hydrofluoric acid to produce a silicon fluoride compound by a reaction between the two, further evaporating the silicon fluoride compound from the fixed amount of phosphoric acid solution, and deionizing the evaporated silicon fluoride compound A method for measuring the silicon concentration in a phosphoric acid solution, comprising the steps of hydrolyzing by aeration in water and further measuring a change rate of the silicon concentration in the deionized water.   The reaction between the phosphoric acid solution and hydrofluoric acid is carried out by adding hydrofluoric acid to the certain amount of phosphoric acid solution whose liquid temperature is controlled at 70 to 180 ° C. The method for measuring the silicon concentration in a phosphoric acid solution according to claim 6, wherein the silicon compound in the solution is evaporated as a gaseous silicon fluoride compound from the predetermined amount of phosphoric acid solution. The method for measuring a silicon concentration in a phosphoric acid solution according to claim 6 or 7, wherein the change rate of the silicon concentration in the deionized water is measured by measuring the conductivity of the deionized water.

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