JP2002236094A - Concentration measuring method, oxidizing-force measuring method, oxidizing-force control method and control method for oxidation process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the concentration of peroxosulfuric acid in a solution. SOLUTION: The concentration measuring method includes a step, which finds an absorbance at a wavelength near 190 nm caused by the peroxosulfuric acid in the solution containing the peroxosulfuric acid and a step, in which the concentration of the peroxosulfuric acid in the solution is measured on the basis of the found absorbance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the concentration of peroxosulfuric acid in a solution, a method for measuring the oxidizing power of a mixed solution of ozone and sulfuric acid in which ozone is dissolved in sulfuric acid, and a method of dissolving ozone in sulfuric acid. The present invention relates to a method for controlling the oxidizing power of an ozone / sulfuric acid mixed solution and a method for controlling an oxidizing step using the ozone / sulfuric acid mixed solution.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a mixed solution of sulfuric acid and hydrogen peroxide has been conventionally used in a step of oxidizing a wafer surface, particularly in a step of oxidizing and removing a resist. The liquid property of the mixture of sulfuric acid and hydrogen peroxide is usually controlled by specific gravity. This is because when hydrogen peroxide is added to concentrated sulfuric acid, the concentration of the sulfuric acid is diluted and thinned by the addition of the hydrogen peroxide solution because the concentration of the normal hydrogen peroxide solution is an aqueous solution of 30 to 35%. When,
Further, hydrogen peroxide is decomposed to generate water and reduce the concentration of sulfuric acid, so that the specific gravity of the mixed solution is reduced. When the sulfuric acid concentration decreases, the boiling point of the mixed solution decreases, and the effect of decomposing and removing the resist is lost. For this reason, the mixed solution had to be discarded when the sulfuric acid concentration was 80% or less.

Recently, a mixture of ozone gas dissolved in hot concentrated sulfuric acid instead of hydrogen peroxide has been used as an oxidizing agent.

In the method of dissolving ozone gas in sulfuric acid, since there is almost no increase in water for lowering the sulfuric acid concentration, there is no need to control the sulfuric acid concentration, and the amount of the sulfuric acid solution to be discarded is extremely small.

However, when ozone gas is added to concentrated sulfuric acid, the ozone reacts with sulfuric acid to produce peroxosulfuric acid,
Ozone itself is consumed. Furthermore, the generated peroxosulfate itself is also a strong oxidizing agent, but there is no method for measuring the concentration of peroxosulfate, and the oxidizing power of the solution cannot be detected only by measuring the concentration of ozone. was there.

[0006] Because the oxidizing power of the solution is not known, and therefore, the resist stripping ability cannot be precisely quantified specifically, the conventional resist film removal requires sulfuric acid at an empirical processing temperature and processing time. There was a problem that only ozone gas was mixed.

[0007]

As described above, there has been a problem that the concentration of peroxosulfuric acid in a solution cannot be measured, and a solution containing peroxosulfuric acid cannot be managed. In addition, the concentration of ozone and peroxosulfuric acid in a sulfuric acid solution in which ozone is dissolved (ozone / sulfuric acid mixed solution) cannot be measured, and the oxidizing power of the ozone / sulfuric acid mixed solution cannot be controlled. there were.

In addition, since the oxidizing power of the ozone / sulfuric acid mixed solution is not known, in the conventional oxidation step such as resist stripping,
There was a problem that the oxidation was performed with an empirical processing time.

It is an object of the present invention to provide a method for measuring the concentration of peroxosulfate in a solution.

Another object of the present invention is to provide a method for measuring the concentration of ozone and peroxosulfuric acid in a sulfuric acid solution in which ozone is dissolved.

It is another object of the present invention to provide a method for measuring the oxidizing power of an ozone / sulfuric acid mixed solution, which can measure the oxidizing power of a sulfuric acid solution in which ozone is dissolved.

Another object of the present invention is to provide an oxidizing power control method capable of controlling the oxidizing power of a sulfuric acid solution in which ozone is dissolved.

Another object of the present invention is to provide a method for oxidizing an oxide to be formed on the surface of a substrate to be processed using a sulfuric acid solution in which ozone is dissolved. An object of the present invention is to provide a control method of an oxidation step capable of determining presence or absence.

[0014]

Means for Solving the Problems [Configuration] The present invention is configured as follows to achieve the above object.

(1) The method for measuring the concentration of peroxosulfuric acid according to the present invention comprises the steps of determining the absorbance of a solution containing peroxosulfuric acid at a wavelength around 190 nm caused by peroxosulfuric acid, Measuring the concentration of sulfuric acid.

(2) The method for measuring the concentration of ozone and peroxosulfuric acid according to the present invention comprises dissolving ozone in a sulfuric acid solution, and reacting the sulfuric acid solution with ozone to generate peroxosulfuric acid. Producing a mixed solution, measuring the absorbance of the ozone / sulfuric acid mixed solution near 254 nm wavelength due to ozone, and measuring the absorbance near 190 nm wavelength due to peroxosulfuric acid; Determining the concentration of ozone gas in the ozone / sulfuric acid mixture from the absorbance, and measuring the concentration of peroxosulfuric acid in the ozone / sulfuric acid mixture from the absorbance caused by the measured peroxosulfuric acid. And

(3) The method for measuring the oxidizing power of an ozone / sulfuric acid mixed solution according to the present invention comprises dissolving ozone in a sulfuric acid solution and reacting the sulfuric acid solution with ozone to generate peroxosulfuric acid. Producing a sulfuric acid mixed solution, measuring the absorbance of the ozone / sulfuric acid mixed solution near 254 nm wavelength due to ozone, and measuring the absorbance near 190 nm wavelength caused by peroxosulfuric acid in the solution. Obtaining the oxidizing power of ozone in the ozone / sulfuric acid mixed solution from the absorbance caused by ozone, and obtaining the oxidizing power of peroxosulfuric acid in the ozone / sulfuric acid mixed solution from the measured absorbance caused by peroxosulfuric acid. Obtaining the oxidizing power of the ozone / sulfuric acid mixed solution by integrating the obtained two oxidizing powers. .

(4) In the method for controlling the oxidizing power of an ozone / sulfuric acid mixed solution according to the present invention, ozone is continuously introduced into a sulfuric acid solution to dissolve ozone in the sulfuric acid solution, and the sulfuric acid solution and the ozone are mixed with each other. To produce peroxosulfuric acid to produce an ozone / sulfuric acid mixed solution, and a wavelength 254n caused by ozone in the ozone / sulfuric acid mixed solution.
measuring the absorbance at around m and the absorbance at a wavelength of about 190 nm caused by peroxosulfuric acid in the mixed solution; and determining the oxidizing power of ozone in the ozone / sulfuric acid mixed solution from the measured absorbance attributable to ozone. Obtaining the oxidizing power of peroxosulfuric acid in the ozone / sulfuric acid mixed solution from the measured absorbance caused by peroxosulfuric acid, and integrating the obtained two oxidizing powers to obtain the ozone.
The method includes a step of determining the oxidizing power of the sulfuric acid mixed solution and a step of controlling the amount of ozone dissolved in the solution according to the obtained oxidizing power of the ozone / sulfuric acid mixed solution.

(5) The method for controlling an oxidation step using an ozone / sulfuric acid mixed solution according to the present invention is a method for continuously introducing ozone into a sulfuric acid solution to dissolve ozone in the sulfuric acid solution, Producing peroxosulfuric acid by reacting the mixture with ozone to produce an ozone / sulfuric acid mixed solution, and charging the substrate to be processed having an oxide to be formed in the ozone / sulfuric acid mixed solution, Oxidizing the material, the absorbance of the ozone / sulfuric acid mixed solution into which the wafer is introduced near 254 nm, and 190 n of the mixed solution.
measuring at least one of the absorbances in the vicinity of m, and extracting the wafer from the ozone concentration in the ozone / sulfuric acid mixed solution when the measured absorbance reaches a predetermined state.

Preferred embodiments of the present invention (a method for controlling an oxidation step using a mixed solution of ozone and sulfuric acid) are described below.
The predetermined state is a state in which a value corresponding to the measured absorbance is equal to a value corresponding to the absorbance measured before the wafer is loaded. The predetermined state is a state in which a value corresponding to the measured absorbance shows an increasing tendency.

[Function] The present invention has the following functions and effects by the above configuration.

The concentration and oxidizing power of peroxosulfuric acid can be measured by measuring the absorbance near 190 nm.

Also, the absorbance near 190 nm and 254 nm
By measuring the absorbance in the vicinity, the concentrations of ozone and peroxosulfuric acid in the ozone / sulfuric acid mixed solution and the oxidizing power can be obtained. Furthermore, by adjusting the amount of ozone to be introduced according to the oxidizing power determined,
The oxidizing power of the ozone / sulfuric acid mixed solution can be adjusted.

In the oxidation step using an ozone / sulfuric acid mixed solution, the absorbance at around 190 nm and the 254n
By measuring at least one of the absorbances near m, the end of the oxidation step can be determined, and the process time can be reduced.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment (First Experiment) First, an ultraviolet (UV) continuous spectrum of the absorbance of a sulfuric acid solution in which ozone was introduced into concentrated sulfuric acid was measured.

[0027] Oxygen (O ₂₎ by performing a discharge in the gas generating ozone (O _3), O ₃ / O ₂ containing the O ₃ and O ₂
The mixed gas was bubbled with sulfuric acid to dissolve ozone in the sulfuric acid. The amount and temperature of the sulfuric acid solution and the flow rate and concentration of the O ₃ / O ₂ mixed gas were set to 200 ml and 130 ml, respectively.
C, 3.0 SLM, while keeping it constant at 150 mg / Nl,
The continuous spectrum of the absorbance was measured while changing the ozone introduction time to 60 minutes, 120 minutes, and 180 minutes.

FIG. 1 shows the measurement results. As shown in FIG. 1, a peak is observed at around 254 nm, and this peak is a peak due to a known ozone. This peak hardly depends on the ozone gas introduction time.

Further, a peak is observed at around 190 nm. As for this peak, the intensity peak increases as the introduction time of the ozone gas increases. In addition, no peak is observed in the absorbance of sulfuric acid near 190 nm in a state where the ozone gas is not introduced. Therefore, it is considered that the absorbance near 190 nm is caused by peroxosulfuric acid.

(Second Experiment) Next, an experiment was conducted to determine whether the absorption peak near 190 nm was actually caused by peroxosulfuric acid. Here, a continuous spectrum of absorbance of a solution in which potassium peroxosulfate was dissolved in sulfuric acid was measured. By dissolving potassium peroxosulfate in sulfuric acid, potassium peroxosulfate undergoes ionic decomposition to form peroxosulfate ions. Therefore,
By measuring the continuous spectrum of the absorbance of a solution of potassium peroxosulfate dissolved in sulfuric acid, 190 n
It can be checked whether the absorption near m is due to peroxosulfuric acid.

Here, the concentration of potassium peroxosulfate in sulfuric acid at room temperature was adjusted to 0.01%, 0.05%, 0.10
%, 0.20%, 0.35%, 0.50%, 1.00%
Prepare a solution that has been changed to
Examined by continuous spectrum.

FIG. 2 shows a continuous spectrum of absorbance. As shown in FIG. 2, an absorption peak is observed at around 190 nm in the sulfuric acid solution. Furthermore, it was also found that the peak position shifted to a higher wavelength side as the concentration of potassium peroxosulfate increased.

From this experimental result, it was confirmed that the absorption due to peroxosulfuric acid appeared at around 190 nm.

(Third Experiment) Next, since an absorption band caused by peroxosulfuric acid was found, ozone gas was actually introduced into sulfuric acid to monitor a change in UV absorption. First, potassium peroxodisulfate was added to the solution to a concentration of 0.1%. Thereafter, ozone gas was introduced into each solution for 60, 120, and 180 minutes, and a continuous spectrum of absorbance was measured each time. Ozone gas was generated by the discharge of oxygen, and the ozone gas concentration was about 10% with respect to 1 liter of sulfuric acid solution. O ₃ / O ₂ mixed gas was introduced by bubbling to form an ozone / sulfuric acid mixed solution. .

FIG. 3 shows the experimental results in a mixed solution of potassium peroxosulfate / ozone / sulfuric acid at room temperature. As shown in FIG. 3, in the continuous spectrum of the absorbance of the sulfuric acid solution into which the O ₃ / O ₂ mixed gas was not introduced, no ultraviolet light absorption due to ozone gas was observed, and the absorption due to peroxosulfuric acid was not observed.
Only a peak near 90 nm is observed.

When ozone gas is introduced into the sulfuric acid solution, 2
It can be seen that the absorption peak due to the ozone gas appears near 54 nm and the absorption peak near 190 nm increases. This peak value near 190 nm is
This suggests the amount of peroxosulfuric acid formed when ozone gas is introduced into sulfuric acid.

Next, the temperature of each sulfuric acid solution was raised to 70 to 7
The temperature was raised to about 5 ° C., and ozone gas was introduced. FIG. 4 shows the results of the sulfuric acid solution. Similar to the ultraviolet continuous spectrum of the absorbance shown in FIG. 3, absorption due to ozone appears near 254 nm, and absorption due to peroxodisulfuric acid appears near 190 nm.

From the results of these experiments, it was clarified that absorption caused by peroxosulfuric acid caused by introducing ozone gas in sulfuric acid appears at around 190 nm. Therefore, in order to simultaneously monitor ozone and peroxosulfuric acid in sulfuric acid, it was found that it was necessary to simultaneously monitor absorption at 190 nm to 260 nm.

In addition to the method of using a continuous spectrum of absorbance for measurement, a method of monitoring peroxosulfuric acid in sulfuric acid using light absorption near 190 nm and a method of measuring light absorption due to ozone near 254 nm are described. The concentration of both oxidants can also be monitored by combining them.

Next, a method for obtaining the concentrations (oxidizing power) of ozone and peroxosulfuric acid from the measured absorbance will be described. First, the oxidizing power of the ozone / sulfuric acid mixed solution is determined in advance. The iodine titration method was used to determine the oxidizing power of the ozone / sulfuric acid mixed solution.

First, 254 when ozone was introduced into pure water.
From the relationship between the absorbance at nm and the ozone oxidizing power in pure water determined using iodine titration, a calibration curve of the oxidizing power of ozone with respect to the absorbance caused by ozone is created. Further, since the concentration can be obtained from the oxidizing power of ozone, a calibration curve of the concentration of ozone with respect to the absorbance caused by ozone can be immediately created. Then, the oxidizing power or concentration of ozone can be determined from the measured absorbance due to ozone and the calibration curve.

With respect to the oxidizing power of ozone and peroxosulfuric acid in the sulfuric acid this time, the concentration of ozone was corrected by using a calibration curve prepared using pure water to obtain a value of 2%.
The oxidizing power (concentration) can be easily obtained from the absorbance at 54 nm.

The oxidizing power of peroxosulfuric acid is calculated from the oxidizing power of the ozone / sulfuric acid mixed solution determined by iodine titration and the oxidizing power of ozone in the mixed solution obtained from the absorbance near 254 nm of the ozone / sulfuric acid mixed solution. After subtracting,
Determined as the oxidizing power of peroxosulfuric acid. Then, the relationship between the obtained oxidizing power of peroxosulfuric acid and the absorbance near 190 nm is examined, and a calibration curve of the oxidizing power of peroxosulfuric acid with respect to the absorbance near 190 nm is created. Then, the oxidizing power of peroxosulfuric acid can be determined from the measured absorbance due to peroxosulfuric acid and the calibration curve. Further, since the concentration can be immediately obtained from the oxidizing power of peroxosulfate, a calibration curve of the concentration of peroxosulfate with respect to the absorbance caused by peroxosulfate can be created. Therefore, the concentration of peroxosulfuric acid in the ozone / sulfuric acid mixed solution can be determined by measuring the absorbance near 190 nm and referring to the calibration curve of the concentration.

Then, the measured values around 254 nm and 1
The concentration of ozone and peroxosulfuric acid in the ozone / sulfuric acid mixed solution is determined by referring to the ultraviolet light absorption near 90 nm and two previously determined quantitative lines (third experiment). Of dissolved amounts of peroxosulfuric acid (190 nm) and ozone (254 nm) with respect to time when the amount of ozone gas (mixed gas of ozone and oxygen gas: ozone concentration 160 mg / NL) introduced into sulfuric acid was changed. State.

FIGS. 5 and 6 show the change with time of the ozone gas bubbling at 190 nm and 254 nm absorbance, respectively. Peroxosulfuric acid increases its rate of increase as the amount of ozone gas to be introduced is increased, and increases in the amount of peroxosulfuric acid as the introduction time is increased.

On the other hand, although the amount of ozone dissolved in sulfuric acid has some time lag, even if the amount of gas introduced into sulfuric acid is increased,
The introduction time is further extended to saturate at a constant concentration. Thus, the dissolved ozone does not change when it reaches a temperature-dependent saturated concentration of the sulfuric acid solution. On the other hand, since peroxosulfuric acid does not reach the saturation concentration at the same time as the introduction of ozone, it can be seen that it is generated by the reaction between ozone gas and sulfuric acid.

As described above, it can be seen that ozone gas introduced into sulfuric acid not only dissolves in sulfuric acid to a certain saturation concentration but also reacts with sulfuric acid to form peroxosulfuric acid.

The production state of this peroxosulfuric acid is 190 n.
By monitoring the UV absorption near m, the generation state can be monitored. In other words, by controlling at least one of the concentration of ozone gas and the amount of ozone gas to be introduced, the amount of peroxosulfuric acid produced can be controlled by controlling the concentration of peroxosulfuric acid at a certain concentration or higher in sulfuric acid.

(Fourth experiment) In a state where the ozone gas is constantly supplied to the sulfuric acid solution, it is caused by ozone when the wafer coated with the resist film is inserted into the sulfuric acid solution saturated with ozone to a certain concentration. The time change of the absorbance was measured. FIG. 7 shows the measurement results. Since the absorbance depends on the concentration, the absorbance also rises and falls according to the rise and fall of the concentration.

As shown in FIG. 7, since the introduction of the wafer dissolves the resist film in the ozone sulfuric acid solution, it can be seen that the absorbance (ozone concentration) decreases. This is because the concentration of ozone decreases because the resist film is oxidized and stripped by ozone.

Further, when the dissolution reaction of the resist film is completed, the ozone concentration is restored to the saturation concentration because the oxide is not consumed and the ozone is not consumed. Return to Therefore, by monitoring the absorbance due to ozone as the oxidizing agent in the sulfuric acid solution, the state of peeling of the resist film can be monitored in-line, and the end point of resist film peeling can be detected.

In this embodiment, 254n due to ozone
Although the resist stripping state was explained based on the change in absorbance near m, it goes without saying that the evaluation can be similarly performed using peroxosulfuric acid near 195 nm. Further, even if the absorbance caused by ozone and the absorbance caused by peroxosulfuric acid are simultaneously measured, the end point of the resist film peeling can be detected. Alternatively, the concentration may be obtained from the absorbance, and the end point of the resist film peeling may be detected from the change in the concentration.

The present invention can be used in an oxidation step using a mixed solution of ozone and sulfuric acid other than stripping of the resist film.

(First Embodiment) From the above experimental results,
It was found that the oxidizing ability of the ozone / sulfuric acid mixed solution can be determined by measuring the absorbance near 254 nm caused by ozone and the absorbance near 190 nm caused by peroxosulfuric acid. Further, in the resist film stripping step, the end point of the resist stripping can be detected by measuring at least one of the time change of absorption caused by ozone and the absorption caused by peroxosulfuric acid. Absorbance of 190nm
A method for forming an ozone / sulfuric acid mixed solution in which the oxidizing ability of the ozone / sulfuric acid mixed solution is determined from the absorbance in the vicinity and the oxidizing ability is adjusted according to the determined oxidizing ability will be described. Further, FIG. 8 shows an ozone gas according to the first embodiment of the present invention.
It is a block diagram showing a schematic structure of a resist film removal system using a sulfuric acid mixed solution. FIG. 9 is a flowchart for explaining the resist film removing method of the system shown in FIG.

Referring to the flowchart of FIG.
The configuration of the system shown in FIG. 8 will be described while explaining the method for forming the sulfuric acid mixed solution and the resist film removing step.

(Step S101) The oxygen gas in the oxygen (O ₂ ) cylinder 101 is introduced into the ozone generator 103 via the mass flow controller 102 for adjusting the gas flow rate. The ozone generator 103 generates ozone by discharging in an oxygen atmosphere. Since the ozone generation rate is low, the gas discharged from the ozone generator 103 is O
It is a mixed gas of ₃ and O ₂ .

O ₃ / emitted from the ozone generator 103
The O ₂ mixed gas is released into the sulfuric acid solution from the bubbler 105 provided in the solution tank 104 filled with the sulfuric acid solution. The released O ₃ / O ₂ mixed gas bubbling in the sulfuric acid solution dissolves ozone in the sulfuric acid solution to form an ozone / sulfuric acid mixed solution. Further, a part of O ₃ reacts with sulfuric acid to generate peroxosulfuric acid. Then, the ozone / sulfuric acid mixed solution circulates between the solution tank 104 and the cell 106.

(Step S 102) Light emitted from the ozone measurement light source 111 having a strong radiation intensity of 250 nm or more is incident on the first half mirror 112. The light transmitted through the first half mirror 112 enters the ozone / sulfuric acid mixed solution in the cell 106. Ozone in the cell 106
The transmitted light that has passed through the sulfuric acid mixed solution is incident on the first measurement-side light receiving element 113 having an absorption sensitivity characteristic near 254 nm, and the light intensity is measured. Also, the first half mirror 11
The light reflected by 2 enters the first comparison-side light receiving element 114 having an absorption sensitivity characteristic near 254 nm, and the light intensity is measured. The respective measured intensities measured by the first measurement side light receiving element 113 and the first comparison side light receiving element 114 are as follows:
Input to the ozone absorbance measurement unit. The ozone absorbance measurement unit measures the absorbance near 254 nm due to ozone from the two input light intensities.

The light emitted from the peroxosulfate side light source 121 having a strong radiation intensity of 250 nm or less is the second light.
Is incident on the half mirror 122. The light transmitted through the second half mirror 122 enters the ozone / sulfuric acid mixed solution in the cell 106. The transmitted light that has passed through the ozone / sulfuric acid mixed solution in the cell 106 is incident on the second measurement-side light receiving element 123 having an absorption sensitivity characteristic at 150 to 220 nm, and the light intensity is measured. The light reflected by the second half mirror 122 is incident on a second comparison side light receiving element having an absorption sensitivity characteristic at 150 to 220 nm, and the light intensity is measured.
The respective measured intensities measured by the second measuring-side light receiving element 123 and the second comparing-side light receiving element 124 are input to the absorbance measuring unit 125 for peroxosulfuric acid. The absorbance measuring unit 125 for peroxosulfuric acid measures the absorbance due to peroxosulfuric acid from the two input light intensities.

(Step S103) The respective absorbances obtained by the ozone absorbance measurement section 115 and the peroxosulfuric acid absorbance measurement section 125 are input to the oxidizing power calculation section 131. The oxidizing power calculating unit 131 obtains the oxidizing power due to ozone from the absorbance due to ozone measured by the absorbance measuring unit 115 for ozone and a previously determined quantitative line. Here, the concentration of ozone in the ozone / sulfuric acid mixed solution may be determined. Further, the oxidizing power due to peroxosulfuric acid is determined from the absorbance due to peroxosulfuric acid determined by the absorbance measuring unit 125 for peroxosulfuric acid and the previously determined quantitative line. Here, the concentration of peroxosulfuric acid in the ozone / sulfuric acid mixed solution may be determined. Then, the oxidizing power calculating unit 131 calculates the oxidizing power of the ozone / sulfuric acid mixed solution by adding the two obtained oxidizing powers.

(Step S104) Oxidizing power calculator 131
The oxidizing power of the ozone / sulfuric acid mixed solution obtained in step (1) is input to the ozone amount control unit 132. The ozone amount control unit 132 compares the input oxidizing power with a predetermined value, and determines whether the oxidizing power is equal to or more than the predetermined value. This predetermined value is determined from the oxidizing power required to oxidize and peel off the resist film.

(Step S105) If the result of determination in step S104 is that the oxidizing power has not reached the predetermined value, the ozone amount control unit 132 sets the ozone concentration in the O ₃ / O ₂ mixed gas and O ₃ / O ₂ By adjusting at least one of the flow rates of the mixed gas, the amount of ozone dissolved in the ozone / sulfuric acid mixed solution is adjusted. The flow rate control of the O ₃ / O ₂ mixed gas is performed by controlling the mass flow controller 102. The ozone concentration in the O ₃ / O ₂ mixed gas is controlled by controlling the discharge voltage of the ozone generator 103.

(Step S106) If the oxidizing power of the ozone / sulfuric acid mixed solution has reached a predetermined value as a result of the determination in step S104, the ozone amount control unit 132 causes the stripping control unit 141 to oxidize the ozone / sulfuric acid mixed solution. Signals that the force has reached a predetermined value.

The peeling control unit 141 includes a wafer elevating unit 142
Is lowered, and the semiconductor wafer 151 having the resist film 152 formed on the surface thereof is loaded into the ozone / sulfuric acid mixed solution in the ozone / sulfuric acid mixed solution tank.

Using the above-described method, the absorbance due to ozone is obtained by the ozone absorbance measurement unit 115.

(Step S 107) Next, the absorbance caused by ozone obtained by the ozone absorbance measuring section 115 is input to the peeling control section 141. The peeling controller calculates the ozone concentration in the ozone / sulfuric acid mixed solution from the input absorbance.

(Step S108) Peeling control section 141
Determines whether the calculated ozone concentration has reached the saturation concentration. This saturation concentration is determined in advance by an experiment.

(Step S109) If the result of determination in step S108 is that the ozone concentration has not returned to the saturated concentration, it is determined that the resist film 152 on the surface of the semiconductor wafer 151 has not been peeled off, and the semiconductor The wafer 151 is kept in the solution tank 104.

(Step S110) If it is determined in step S108 that the ozone concentration has returned to the saturated concentration, it is determined that the resist film 152 has been stripped from the surface of the semiconductor wafer 151, and the stripping control unit 141 controls the wafer elevating unit 142 to elevate the stage and lift the semiconductor wafer 151 from the solution tank 104.
Thus, the step of removing the resist film on the surface of the semiconductor wafer is completed.

Even if the saturation concentration of ozone is not known, the ozone concentration before the introduction of the wafer is stored, and when the ozone concentration exceeds the value before the introduction of the wafer, it is assumed that the resist film is peeled off. It may be determined. Further, the change with time of the ozone concentration is measured, and when the ozone concentration shows a tendency to increase, it can be determined that the resist film has been stripped.

It should be noted that the end of the resist film peeling may be determined by comparing the measured ultraviolet light absorption values without obtaining the concentration.

The present invention is not limited to the above embodiment. For example, the present invention can be variously modified and implemented without departing from the gist thereof.

[0073]

As described above, according to the present invention, 1
By measuring the absorbance near 90 nm, the concentration and oxidizing power of peroxosulfuric acid can be measured.

Further, the absorbance near 190 nm and 254 nm
By measuring the absorbance in the vicinity, the concentrations of ozone and peroxosulfuric acid in the ozone / sulfuric acid mixed solution and the oxidizing power can be obtained. Furthermore, by adjusting the amount of ozone to be introduced according to the oxidizing power determined,
The oxidizing power of the ozone / sulfuric acid mixed solution can be adjusted.

In the oxidation step using an ozone / sulfuric acid mixed solution, the absorbance at around 190 nm and the 254 n
By measuring at least one of the absorbances near m, the end of the oxidation step can be determined, and the process time can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a continuous spectrum of absorbance of an ozone / sulfuric acid mixed solution in which ozone is dissolved in sulfuric acid.

FIG. 2 is a diagram showing a continuous spectrum of the absorbance of a mixed solution of sulfuric acid with potassium peroxosulfate and sulfuric acid to which potassium peroxosulfate is added.

FIG. 3 is a diagram showing a continuous spectrum of absorbance of a mixed solution of potassium peroxosulfate / ozone / sulfuric acid in which ozone is dissolved in sulfuric acid (room temperature) to which potassium peroxosulfate is added.

FIG. 4: Sulfuric acid (75
The figure which shows the continuous spectrum of the light absorbency of the potassium peroxosulfate / ozone / sulfuric acid mixed solution which melt | dissolved ozone in (C).

FIG. 5 is a characteristic diagram showing a temporal change in absorbance at 195 nm when the amount of ozone gas introduced into a sulfuric acid solution (130 ° C.) is changed.

FIG. 6 is a characteristic diagram showing a temporal change in absorbance at 254 nm when the amount of ozone gas introduced into a sulfuric acid solution (130 ° C.) is changed.

FIG. 7 is a characteristic diagram showing a temporal change in absorbance caused by ozone when a wafer coated with a resist film is inserted into a sulfuric acid solution saturated with ozone to a certain concentration.

FIG. 8 is a block diagram showing a schematic configuration of a resist film removing system using an ozone / sulfuric acid mixed solution according to the first embodiment.

FIG. 9 is a flowchart for explaining a resist film removing method of the system shown in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Oxygen cylinder 102 ... Mass flow controller 103 ... Ozone generator 104 ... Solution tank 105 ... Bubbler 106 ... Cell 111 ... Ozone measurement light source 112 ... 1st half mirror 113 ... 1st measurement side light receiving element 114 ... 1st Comparison side light receiving element 115 ... Ozone absorbance measurement unit 121 ... Peroxosulfuric acid side light source 122 ... Second half mirror 123 ... Second measurement side light receiving element 124 ... Second comparison side light receiving element 125 ... Peroxosulfuric acid absorbance measurement unit 131: Oxidizing power calculation unit 132: Ozone amount control unit 141: Peeling control unit 142: Wafer elevating unit 151: Semiconductor wafer 152: Resist film

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Soichi Nadahara 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term in Toshiba Yokohama Office (reference) 2G042 AA01 BB10 BB13 BB20 BE03 CA02 CB03 DA03 2G054 AA02 CA08 EA04 EB02 FA33 GA02 2G059 AA01 BB01 BB16 DD13 DD15 EE12 GG03 GG10 HH03 HH06 JJ01 JJ13 KK03 MM05 MM10 2H096 AA25 LA03

Claims (7)

[Claims] 1. A method comprising: determining the absorbance of a solution containing peroxosulfuric acid at a wavelength near 190 nm caused by peroxosulfuric acid; and measuring the concentration of peroxosulfuric acid in the solution from the determined absorbance. Concentration measurement method. 2. Dissolving ozone in a sulfuric acid solution,
Reacting the sulfuric acid solution with ozone to generate peroxosulfuric acid to produce an ozone / sulfuric acid mixed solution;
Measuring the absorbance around 4 nm and the absorbance around 190 nm wavelength caused by peroxosulfuric acid; obtaining the concentration of ozone gas in the ozone / sulfuric acid mixed solution from the measured absorbance caused by ozone; Measuring the concentration of peroxosulfuric acid in said ozone / sulfuric acid mixed solution from the absorbance caused by said peroxosulfuric acid. 3. Dissolving ozone in a sulfuric acid solution,
Reacting the sulfuric acid solution with ozone to generate peroxosulfuric acid to produce an ozone / sulfuric acid mixed solution;
Measuring the absorbance around 4 nm and the absorbance around 190 nm wavelength caused by peroxosulfuric acid in the solution; obtaining the oxidizing power of ozone in the ozone / sulfuric acid mixed solution from the measured absorbance due to ozone; Obtaining the oxidizing power of peroxosulfuric acid in the ozone / sulfuric acid mixed solution from the measured absorbance caused by peroxosulfuric acid; and integrating the obtained two oxidizing powers to obtain the oxidizing power of the ozone / sulfuric acid mixed solution. Determining the oxidizing power. 4. Ozone is continuously introduced into a sulfuric acid solution,
Dissolving ozone in the sulfuric acid solution and reacting the sulfuric acid solution with ozone to produce peroxosulfuric acid to produce an ozone / sulfuric acid mixed solution; and a wavelength 25 due to ozone of the ozone / sulfuric acid mixed solution.
Measuring the absorbance around 4 nm and the absorbance around 190 nm caused by peroxosulfuric acid in the mixed solution; and determining the oxidizing power of ozone in the ozone / sulfuric acid mixed solution from the measured absorbance caused by ozone. Obtaining the oxidizing power of peroxosulfuric acid in the ozone / sulfuric acid mixed solution from the measured absorbance caused by peroxosulfuric acid; and integrating the obtained two oxidizing powers to obtain the oxidizing power of the ozone / sulfuric acid mixed solution. And controlling the amount of ozone dissolved in the ozone / sulfuric acid mixed solution according to the determined oxidizing power of the mixed solution. 5. A method for continuously introducing ozone into a sulfuric acid solution,
Dissolving ozone in the sulfuric acid solution, and reacting the sulfuric acid solution with ozone to produce peroxosulfuric acid, thereby producing an ozone / sulfuric acid mixed solution; and forming an oxide in the ozone / sulfuric acid mixed solution. Charging the substrate to be processed and oxidizing the oxide; and 254 of the ozone / sulfuric acid mixed solution into which the wafer has been introduced.
measuring at least one of the absorbance near nm and the absorbance near 190 nm of the mixed solution, and when the measured absorbance is in a predetermined state, extracting the wafer from the ozone concentration in the ozone / sulfuric acid mixed solution. And a method for controlling an oxidation process. 6. The predetermined state is a state in which a value corresponding to the measured absorbance is equal to a value corresponding to the absorbance measured before loading the wafer. 6. The method for controlling an oxidation step using the ozone / sulfuric acid mixed solution according to 5. 7. The method according to claim 5, wherein the predetermined state is a state in which a value corresponding to the measured absorbance shows an increasing tendency.