JP2001244532A - Measuring apparatus of impurities concentration for laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the concentration of impurities in laser gas without requiring a large-scale device and complicated operation, and without deteriorating efficiency of laser operation. SOLUTION: During continuous pulse oscillation operation for making a discharge applied voltage between discharge electrodes fixed, if impurities are mixed inside a laser chamber, an output energy (a) of laser beam lowers to a prescribed level (a2) to a reference level (a1) as of pulse oscillation of a prescribed pulse number (n2) after continuous pulse oscillation operation is started. A lowering amount (a2-a1) of output energy to the reference level (a1) is obtained. Meanwhile, corresponding relation C between a concentration S of impurities exception laser gas and output energy lowering amount (Δa) is prepared in advance. Impurities concentration X1 corresponding to the obtained output energy lowering amount (a2-a1) is obtained from the corresponding relation C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for measuring the concentration of impurities in a laser chamber.

[0002]

2. Description of the Related Art An ultraviolet laser device such as an excimer laser device or a fluorine laser device is used as a light source of a semiconductor exposure apparatus. The ultraviolet laser device performs exposure of an IC chip on a semiconductor wafer by repeating exposure and stage movement alternately. When exposing the IC chip, the ultraviolet laser device is operated in a burst operation in which a continuous pulse oscillation operation for continuously oscillating a laser beam for a predetermined number of times and an oscillation halt for halting the pulse oscillation for a predetermined time are repeated. That is, at the time of the burst operation, for example, an operation of stopping the oscillation for 0.2 seconds after continuously oscillating 500 pulses of the laser light is repeated.

[0003] In the burst operation, however, a relatively high energy is obtained at the beginning of the continuous pulse oscillation, but thereafter, a phenomenon that the pulse energy gradually decreases (hereinafter referred to as "spike phenomenon") occurs. When this spike phenomenon occurs, the accuracy of exposure decreases.

In order to solve this spike phenomenon, the applicant of the present invention has already filed a patent application (Japanese Patent Application No. 11-23709) in which xenon Xe is added to a laser gas in a laser chamber at a predetermined concentration (for example, 10 ppm).
No.) According to the present invention, the spike phenomenon is eliminated by adding a predetermined concentration of xenon to the laser gas. Further, when xenon is added to the laser gas, the effect of increasing the output energy of the laser light as a whole can be obtained as compared with the case where xenon is not added.

However, even if xenon is added to the laser gas, if impurities (for example, oxygen O2) other than the original laser gas are mixed into the laser chamber, the effect of eliminating the spike phenomenon and increasing the output energy by the addition of xenon can be obtained. Disappears. As described above, it is not desirable to mix impurities into the laser chamber. When impurities are mixed into the laser chamber, it is necessary to determine the presence or absence of the impurities, obtain the mixed concentration, determine the cause of the mixing, and take measures against the contamination.

Therefore, conventionally, a method of directly analyzing the gas in the laser chamber has been adopted for determining the presence or absence of impurities and determining the concentration of impurities.

A conventional gas analysis method will be described.

FIG. 8A shows an ultraviolet laser device 20. A sampling bottle 21 and a purge unit 22 are connected to a pipe of the laser chamber 2 via a valve 23. The analysis procedure in this device is as follows.

1) With the laser oscillation operation stopped,
The closed valve 23 and the sampling bottle 21 are connected by a purgeable pipe, and a purge unit 22 is connected to this connection.

2) After the connection between the valve 23 and the sampling bottle 21 is sufficiently purged by the purge unit 22, the valve 23 is opened to extract the laser gas from the laser chamber 2. That is, sampling of the laser gas is performed.

3) As shown in FIG. 8 (b), the sampling bottle 21 and the gas analyzer 24 are connected by a pipe capable of purging.
Connect.

4) The gas analyzer 24 in the purge unit 22
After the connection between the sample and the sampling bottle 21 is sufficiently purged, gas analysis is performed by the gas analyzer 24.

FIG. 9 is a view for explaining another gas analysis method. The procedure of the analysis in the apparatus of FIG. 9 is as follows.

1) The laser chamber 2 is removed from the ultraviolet laser device 20.

2) Purge unit 2 in laser chamber 2
2 and gas analyzer 24.

3) After purging the pipe portion by the purge unit 22, the gas in the laser chamber 2 is purged by the gas analyzer 24.
And analyze the gas. That is, gas sampling and analysis are performed.

[0017]

As described above, in the prior art, it is necessary to prepare a purge unit 22 and a gas analyzer 24 separately from the ultraviolet laser device 20 to perform gas sampling and analysis. . For this reason, a new apparatus for sampling and analyzing gas is required, and the apparatus becomes large. In addition, the work of sampling and analyzing the gas is troublesome, and the work is complicated. In addition, the work of removing and reattaching the sampling bottle 21 and the laser chamber 2 is not only time-consuming but also requires that the original laser operation be temporarily stopped during this work.
Therefore, the efficiency of the laser operation is significantly reduced.

The present invention has been made in view of such circumstances, and does not require a large-scale apparatus, does not require complicated work, does not impair the efficiency of laser operation, and reduces the concentration of impurities in the laser gas. It is an object of the present invention to measure the temperature.

[0019]

According to a first aspect of the present invention, a laser chamber is filled with a laser gas.
By performing discharge between the discharge electrodes in the laser chamber, a continuous pulse oscillation operation of continuously oscillating laser light for a predetermined number of times and an oscillation halt of suspending pulse oscillation for a predetermined time are repeatedly performed. In a laser device that controls a discharge applied voltage so that a discharge applied voltage between the discharge electrodes is constant during operation, the laser device is configured to perform a predetermined number of pulse oscillations after the continuous pulse oscillation operation is started. When the output energy of the light is reduced to a predetermined level with respect to a reference level, an output energy reduction amount measuring means for obtaining a reduction amount of the output energy with respect to the reference level; and a concentration of impurities other than the laser gas and the output energy reduction amount Is prepared in advance, and the impurity concentration corresponding to the obtained output energy reduction amount is obtained. , Characterized in that comprises an impurity concentration measuring unit for determining from said relationship.

According to the first aspect of the invention, when impurities are mixed in the laser chamber while the discharge application voltage is controlled to be constant, an energy decrease with respect to a reference level occurs. The amount of the energy decrease corresponds to the impurity concentration. It was made based on the points

The first invention will be described with reference to FIG.

As shown in FIG. 5A, when the continuous pulse oscillation operation is performed so that the applied voltage between the discharge electrodes is constant, when impurities are mixed in the laser chamber,
The predetermined number of pulses n2 since the start of the continuous pulse oscillation operation
When the pulse oscillation is performed, the output energy a of the laser light is reduced to the predetermined level a2 with respect to the reference level a1. Then, a reduction amount a2-a1 of the output energy with respect to the reference level a1 is obtained.

On the other hand, as shown in FIG. 5B, a correspondence C between the concentration X of the impurities other than the laser gas and the output energy reduction amount Δa is prepared in advance.

The output energy reduction amount a2-
The impurity concentration X1 corresponding to a1 is obtained from the above-mentioned correspondence C.

According to the first aspect of the present invention, it is not necessary to newly provide a gas sampling and analysis device as in the prior art, and the impurity concentration can be easily measured only by arithmetic processing. Also, as in the prior art, the sampling bottle 21
There is no need to remove or reattach the laser chamber 2 or reattach it. Therefore, according to the present invention, it is possible to measure the concentration of impurities in the laser gas without reducing the size of the apparatus, requiring a complicated operation, and without impairing the efficiency of the laser operation.

According to a second aspect of the present invention, in the first aspect, the energy reduction amount measuring means is configured to perform the first predetermined number of pulse oscillations after the continuous pulse oscillation operation is started. The output energy of the laser light falls to the second predetermined level when the output energy decreases to the first predetermined level and the pulse oscillation of the second predetermined pulse number is performed after the continuous pulse oscillation operation is started. If the output energy has decreased, the difference between the output energy at the time when the output energy has decreased to the first predetermined level and the output energy at the time when the energy has decreased to the second predetermined level is measured as the amount of decrease in the output energy with respect to the reference level. Characterized in that:

According to the second invention, as shown in FIG. 5 (a), the output energy a of the laser beam is changed at the point of time when the first predetermined pulse number n1 has been pulsed since the start of the continuous pulse oscillation operation. The output energy a of the laser beam decreases to the second predetermined level a2 at the time when the pulse oscillation of the second predetermined pulse number n2 is performed after the continuous pulse oscillation operation is started and the continuous pulse oscillation operation is started. I do. Then, the difference a2-a1 between the output energy a1 at the time when the output energy has dropped to the first predetermined level a1 and the output energy a2 at the time when the output energy a2 has dropped to the second predetermined level a2 is the reduction amount a2-a1 of the output energy with respect to the reference level. It is measured as

According to a third aspect of the present invention, there is provided a continuous pulse oscillation operation for continuously pulsating a laser beam a predetermined number of times by filling a laser chamber with a laser gas and performing discharge between discharge electrodes in the laser chamber. And a laser device for repeatedly performing the oscillation suspension for suspending the pulse oscillation and controlling a discharge application voltage between the discharge electrodes so that the output energy of the laser light becomes constant during the continuous pulse oscillation operation. If the discharge applied voltage to the discharge electrode rises to a predetermined level with respect to a reference level at the time when a predetermined number of pulse oscillations have been performed since the start of the oscillation operation, the amount of increase in the discharge applied voltage with respect to the reference level Means for measuring the applied voltage rise amount, and the concentration of impurities other than the laser gas and the applied voltage rise amount Correspondence prepared in advance, the impurity concentration corresponding to the determined discharge voltage applied increase amount, characterized in that comprises an impurity concentration measuring unit for determining from said relationship.

According to a third aspect of the present invention, when impurities are mixed in the laser chamber while the output energy is controlled to be constant, a discharge applied voltage rises with respect to a reference level, and the amount of the discharge applied voltage rises with respect to the impurity concentration. It is based on the point corresponding to.

The third invention will be described with reference to FIG.

As shown in FIG. 6A, in the case where the continuous pulse oscillation operation is performed so that the output energy of the laser beam becomes constant, when impurities are mixed in the laser chamber, the continuous pulse oscillation operation is started. When the pulse oscillation of the predetermined number of pulses n2 starts, the discharge applied voltage b between the discharge electrodes rises to the predetermined level b2 with respect to the reference level b1. Then, the amount of increase b2-b1 of the discharge applied voltage with respect to the reference level b1 is obtained.

On the other hand, as shown in FIG. 6B, a correspondence D between the concentration Y of the impurity other than the laser gas and the amount of increase in the applied voltage Δb is prepared in advance.

Then, the impurity concentration Y1 corresponding to the discharge applied voltage rise b2-b1 is obtained from the correspondence D.

According to the third aspect of the present invention, it is not necessary to newly provide a gas sampling and analysis device unlike the prior art, and the impurity concentration can be easily measured only by the arithmetic processing. Also, as in the prior art, the sampling bottle 21
There is no need to remove or reattach the laser chamber 2 or reattach it. Therefore, according to the present invention, it is possible to measure the concentration of impurities in the laser gas without reducing the size of the apparatus, requiring a complicated operation, and without impairing the efficiency of the laser operation.

According to a fourth aspect of the present invention, in the third aspect, the discharge applied voltage rise amount measuring means is configured to generate the first predetermined number of pulses after the start of the continuous pulse oscillation operation. The discharge applied voltage between the electrodes is the first
And the voltage applied between the discharge electrodes has increased to the second predetermined level at the time when the pulse oscillation of the second predetermined number of pulses has been performed since the continuous pulse oscillation operation was started. In this case, a difference between the discharge applied voltage at the time of rising to the second predetermined level and the discharge applied voltage at the time of rising to the first predetermined level is measured as an amount of increase of the discharge applied voltage with respect to the reference level. It is characterized by that.

According to the fourth invention, as shown in FIG. 6 (a), the discharge is applied between the discharge electrodes at the time when the first predetermined pulse number n1 has been pulsed since the start of the continuous pulse oscillation operation. When the voltage b rises to the first predetermined level b1, and the pulse oscillation of the second predetermined pulse number n2 is performed after the continuous pulse oscillation operation is started, the discharge applied voltage b between the discharge electrodes becomes the second level. Rises to a predetermined level b2. The difference b2−b1 between the discharge application voltage b2 at the time when the voltage rises to the second predetermined level b2 and the discharge application electrode b1 at the time when the voltage rises to the first predetermined level b1 is the increase amount of the discharge application voltage with respect to the reference level. It is measured as b2-b1.

In a fifth aspect based on the first to fourth aspects, the impurity contains an oxygen element.

In the fifth invention, impurities other than the laser gas are O
2. It is intended for those containing CO2 and other oxygen elements. In addition, impurities including oxygen element include: 1) mixing of oxygen in the atmosphere, 2) chemical reaction between fluorine in the laser gas and water in the laser chamber, 3) insufficient purging in the piping,
4) The cause may be a supply gas cylinder of poor purity.

According to a sixth aspect, in the first to fifth aspects, xenon of a predetermined concentration is added to the laser gas.

According to the sixth aspect, the laser gas has a concentration of 1 for example.
When xenon Xe of 0 ppm is added, the energy reduction amount Δa is 0 when the impurity concentration X is 0 ppm as shown in FIG. 5B, or the impurity concentration Y is 0 ppm as shown in FIG. Discharge applied voltage rise amount Δb
Is 0.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an impurity concentration measuring device for a laser device according to the present invention will be described below with reference to the drawings. In the following embodiment, it is assumed that the present invention is applied to an ArF (argon fluorine) excimer laser device. In the ArF excimer laser device, a spike phenomenon occurs during the burst operation. It is also assumed that, for example, xenon Xe of 10 ppm is added to the laser gas in the laser chamber. When about 10 ppm of xenon Xe is added to the laser gas, the spike phenomenon that occurs during the burst operation of the ArF excimer laser device can be eliminated.

However, the present invention can be applied to a laser device other than the ArF excimer laser device, as long as a spike phenomenon occurs. It is also possible to add additives other than xenon Xe as long as they can eliminate the spike phenomenon that occurs during the burst operation.

FIG. 1 is a block diagram showing the configuration of the ArF excimer laser device of the first embodiment. In the first embodiment, it is assumed that the applied discharge voltage is controlled so that the applied voltage between the discharge electrodes 11 in the laser chamber 2 is constant.

An ArF excimer laser device 1 shown in FIG.
Is roughly divided into a laser chamber 2, a rear mirror 3,
It comprises a front mirror 4, an air supply module 5, an exhaust module 6, a controller 7, a power monitor 8, and a pulse power module 9.

In the laser chamber 2, the discharge electrodes 11, 1
1 are provided to face each other. The laser chamber 2 is filled with a laser gas made of fluorine F2, argon Ar2, and neon Ne. About 10 ppm in laser gas
Of xenon Xe is added.

When pulse discharge is performed between the discharge electrodes 11 and 11, the laser gas is excited, and pulse laser light L1 is oscillated. A fan (not shown) in the laser chamber 2;
A radiator is provided. The laser gas is circulated in the laser chamber 2 at a predetermined cycle by the fan and supplied between the discharge electrodes 11. When the laser gas is circulated by the fan, the heat of the laser gas is exchanged by the radiator.

On the optical axis of the laser beam L1 in the laser chamber 2, windows 2a and 2b are provided to face each other.
The laser light L1 is output to the outside of the laser chamber 2 through the windows 2a and 2b. A rear mirror 3 and a front mirror 4 are provided so as to sandwich the laser chamber 2.
A resonator is constituted by the rear mirror 3 and the front mirror 4. The rear mirror 3 is a mirror that totally reflects light.
The front mirror 4 is a partially transmitting mirror that transmits and outputs only a part of light. As the laser beam L1 reciprocates between the rear mirror 3 and the front mirror 4, the energy is amplified and laser oscillation is performed. A resonator constituted by the rear mirror 3 and the front mirror 4 can be provided with a band narrowing unit. This band narrowing unit includes a beam expander such as a prism, a wavelength selection element such as a grating, and the like.

The gas supply module 5 is a module for supplying a laser gas to which xenon Xe is added into the laser chamber 2. The exhaust module 6 is a module that exhausts the laser gas in the laser chamber 2.

The controller 7 receives the data output from the power monitor 8 and controls the supply of the laser gas into the laser chamber 2 by the air supply module 5 and the exhaust of the laser gas from the laser chamber 2 by the exhaust module 6. I do. The controller 7 controls power supply to the pulse power module 9. Further, the controller 7 inputs data output from the power monitor 8 and
The presence or absence of impurities other than the laser gas in the laser chamber 2, such as O2, is determined, and the impurity concentration is measured.

The power monitor 8 is a device for detecting the output energy a of the laser beam L 1, that is, the pulse energy a per pulse, and includes a beam splitter 8 a and a sensor 8.
b. The beam splitter 8a transmits part of incident light and reflects part of the light. The sensor 8b detects the pulse energy a of the laser light L1.

That is, the laser beam L 1 emitted from the front mirror 4 is transmitted to the beam splitter 8 of the power monitor 8.
a. Part of the laser light L1 incident on the beam splitter 8a passes through the beam splitter 8a and is output to an exposure device external to the excimer laser device 1. Another part of the laser light L1 incident on the beam splitter 8a is incident on the sensor 8b. The sensor 8b detects the pulse energy a of the laser beam L1 and outputs it to the controller 7.

The pulse power module 9 includes the discharge electrode 1
A discharge application voltage b, that is, a pulse discharge application voltage b per pulse is applied to 1 and 11. The pulse discharge application voltage b is controlled by the controller 7.

The above is the configuration of the ArF excimer laser device 1 of the embodiment.

Next, the change of the pulse energy a when various impurities are mixed in the laser chamber 2 will be described.

FIG. 2 is a graph showing a change in pulse energy a during the continuous pulse oscillation operation. FIG. 2A shows a case where O2 is not mixed as an impurity (0 ppm), and FIG.
It shows the case of mixing at a concentration of ppm and the case of mixing at a concentration of 30 ppm, respectively.

FIG. 2B shows a case where CO2 is not mixed as an impurity (0 ppm), a case where CO2 is mixed at a concentration of 10 ppm, and a case where CO2 is mixed at a concentration of 20 ppm.

FIG. 2C shows a case where SiF4 is not mixed as an impurity (0 ppm), a case where SiF4 is mixed at a concentration of 20 ppm, and a case where SiF4 is mixed at a concentration of 50 ppm.

FIG. 2D shows a case where HF is not mixed as an impurity (0 ppm), a case where HF is mixed at a concentration of 10 ppm, and a case where HF is mixed at a concentration of 30 ppm, respectively.

FIG. 2E shows a case where N2 is not mixed as an impurity (0 ppm), a case where N2 is mixed at a concentration of 20 ppm, and a case where N2 is mixed at a concentration of 100 ppm, respectively.

FIG. 2F shows a case where CF4 is not mixed as an impurity (0 ppm), a case where CF4 is mixed at a concentration of 50 ppm, and a case where CF4 is mixed at a concentration of 100 ppm, respectively.

The vertical axis in FIGS. 2A to 2F shows the pulse energy a, and the pulse energy a when no impurity is mixed (0 ppm) is normalized to “1”. The horizontal axis indicates the number n of oscillation pulses since the start of the continuous pulse oscillation operation.

Here, referring to FIG.
Is described.

As shown in FIG. 2A, when O 2 is not mixed in the laser chamber 2 (0 ppm), the pulse energy a is almost stabilized at about 1.0 immediately after the start of the continuous pulse oscillation operation. .

In the laser chamber 2, O 2 is 10 pp.
m, the pulse energy a
Drops to a level a1 of about less than 1.0 with the number of pulses n'1 within 10 pulses immediately after the start of the continuous pulse oscillation operation, and is once stabilized at this level a1. Let n1 be the number of pulses when stable
Indicated by Subsequently, the pulse energy a starts to decrease when the pulse number n'2 of about 40 to 60 pulses has elapsed since the start of the continuous pulse oscillation operation, and the pulse energy a becomes 2 after the start of the continuous pulse oscillation operation.
About a level of about 0.8 after about 300 to 300 pulses elapses
Stabilizes at 2. The number of pulses when stabilized is indicated by n2. Further, when O2 is mixed at a concentration of 10 ppm, the pulse energy a is reduced as a whole as compared with the case where O2 is not mixed (0 ppm).

The case where O2 is mixed in the laser chamber 2 at a concentration of 30 ppm shows the same tendency as the case where O2 is mixed at a concentration of 10 ppm. O2 is 30 ppm
In this case, the pulse energy a is further reduced as a whole as compared with the case where the impurity is mixed at a concentration of 10 ppm. That is, the amount of energy reduction at the level of a2 with respect to the level of a1 increases as the O2 concentration increases.

The level a from the start of the continuous pulse oscillation operation
The pulse number n'1 at the time when the pulse number decreases to 1 changes depending on the laser repetition frequency, the circulation flow rate of the fan in the laser chamber 2, and the like.

As shown in FIG. 2B, when the impurity is CO2, the same tendency as in the case where the impurity is O2 (FIG. 2A) is shown, and the impurity CO2 is mixed at a concentration of 10 ppm to 20 ppm. If you have two levels, a1 level and a2 level
The energy decreases in stages, and the amount of energy reduction at the level of a2 relative to the level of a1 increases as the concentration of CO2 increases.

That is, in the case where the impurity contains oxygen element, the phenomenon that the energy is reduced in two stages of the level of a1 and the level of a2 is observed.

On the other hand, the impurity S containing no oxygen element
In the case of iF4, HF, N2, CF4 (Fig. 2 (c) ~
(F)) does not show a phenomenon in which the energy is reduced in two stages of the level of a1 and the level of a2.

However, when the impurity is mixed at a predetermined concentration, the pulse energy a is reduced as a whole as compared with the case where the impurity is not mixed (0 ppm). Becomes larger as becomes larger.

For example, taking SiF4 of FIG. 2C as an example, if SiF4 is mixed at a concentration of 20 ppm,
The pulse energy a is reduced from the level of a0 to the level of a2 as compared with the case where it is not mixed (0 ppm). The energy reduction amount a2-a0 with respect to the level a0 at the time of 0 ppm is as follows.
It increases as it increases to 0 ppm.

FIG. 3 shows the relationship between the impurity concentration X and the pulse energy a for each impurity. The vertical axis in FIG. 3 shows the pulse energy a, and the pulse energy when no impurity is mixed is normalized to “1”. The horizontal axis indicates the impurity concentration X. As can be seen from FIG. 3, the impurities most contributing to the reduction of the pulse energy a are CO2 and O2. HF,
In the order of SiF4, HF, N2, and CF4, the contribution to the reduction of the pulse energy a decreases.

FIG. 4 shows the impurity concentration required to reduce the pulse energy a by 10% for each impurity. FIG. 4 shows an ArF excimer laser and a KrF excimer laser in comparison.

As shown in FIG. 4, the numerical value of the impurity concentration required to reduce the pulse energy a by 10% is generally lower in the ArF excimer laser than in the KrF excimer laser. From this, it can be seen that the influence of the impurity mixing on the energy reduction is greater in the ArF excimer laser than in the KrF excimer laser.

As for the ArF excimer laser, impurities containing oxygen elements such as O 2 and CO 2 are only 5%.
Although the pulse energy a is reduced by 10% only by mixing in ppm, the impurity containing no oxygen element is 1%.
Pulse energy a is 10% if not more than 0ppm
Does not drop. From this, it can be seen that the effect of impurity contamination on energy reduction is greater for impurities containing oxygen element than for impurities not containing oxygen element.

As described above, when the impurity O2 or CO2 containing the oxygen element is mixed, the energy is reduced in two stages, that is, the level of a1 and the level of a2.
The level of energy decrease at the level of increases as the impurity concentration increases. In addition, impurity O2 containing oxygen element
Or the effect of CO2 on energy reduction
It is larger than when other impurities containing no oxygen element are mixed. In addition, the influence becomes larger in the ArF excimer laser device.

Referring now to FIG. 5, a description will be given, with reference to FIG. 5, of a process of determining whether oxygen O2 has entered the laser chamber 2 of the ArF excimer laser apparatus 1 of FIG. 1 and measuring the concentration of the impurity O2. . The contamination of the impurity O2 is caused by 1) contamination of oxygen in the atmosphere, 2) chemical reaction between fluorine in the laser gas and moisture in the laser chamber 2, 3) insufficient purge in the piping, 4) supply gas cylinder of poor purity, etc. Caused by the cause.

FIG. 5 (a) is a graph corresponding to FIG. 2 (a), which is a simplified version of the graph of FIG. 2 (a). A line E2 shown in FIG. 5A shows a change in the pulse energy a with an increase in the pulse number n when the impurity O2 is not mixed in the laser chamber 2, and a line E1 shows the impurity O2 mixed in the laser chamber 2. This shows the change in the pulse energy a with the increase in the pulse number n when the pulse energy a is increased.

FIG. 5B is a graph showing the correspondence C between the concentration X of O2 mixed in the laser chamber 2 and the amount of change in pulse energy, that is, the amount of decrease in pulse energy Δa. This correspondence C corresponds to the above-described tendency that the concentration X of O2 increases as the pulse energy reduction amount Δa increases. The correspondence C is stored in advance in the memory of the controller 7 in the form of a data table of the correspondence between Δa and X, or in the form of an arithmetic expression for obtaining X from Δa. Concentration 10 in laser gas
When xenon Xe of about ppm is added, as shown in FIG. 5B, when the impurity concentration X is 0 ppm, the energy reduction amount Δa becomes zero.

The following arithmetic processing is executed in the controller 7.

The controller 7 inputs the pulse energy a per pulse detected by the sensor 8b and instructs the pulse module 9 on the pulse discharge applied voltage b to be given for each pulse. This makes it possible to measure the relationship between the number of oscillation pulses n from the start of the continuous pulse oscillation operation and the pulse energy a.

When O2 is mixed in the laser chamber 2 at a predetermined concentration, it changes as shown by the line E1 in FIG. That is, the pulse energy a drops to the level a1 within the pulse number n'1 within 10 pulses immediately after the start of the continuous pulse oscillation operation, and is once stabilized at this level a1. The number of pulses at the time of stabilization is indicated by n1. Subsequently, the pulse energy a starts decreasing when the number of pulses n'2 of about 40 to 60 pulses has elapsed since the start of the continuous pulse oscillation operation, and stabilizes at the level a2 when about 200 to 300 pulses have elapsed since the start of the continuous pulse oscillation operation. The number of pulses when stabilized is indicated by n2.

On the other hand, when O2 is not mixed in the laser chamber 2, the state changes as indicated by a line E2 in FIG. FIG. 5B shows a case where the impurity O2 is not mixed.
There is no tendency for the pulse energy a to decrease in two stages of the level of a1 and the level of a2 as shown in the line E1 of FIG.

Therefore, when it is measured that the pulse energy a has decreased in two stages of the level of a1 and the level of a2 as shown by the line E1 in FIG. 5A, it is determined that the impurity O2 has entered, and the line As shown in E2, the level of a1 and a
If it is not measured that the pulse energy a has decreased in two stages of the level 2, it is determined that the impurity O2 is not mixed.

Next, a process for measuring the impurity concentration X assuming that the impurity O2 has been mixed will be described.

As shown in FIG. 5A, the pulse energy a1 when the number of pulses is n1 and the pulse energy a2 when the number of pulses is n2 are measured. Then, a difference a2-a1 between the pulse energy a1 and the pulse energy a2 is calculated as an energy reduction amount a2-a1.

Next, as shown in FIG. 5B, the impurity concentration X1 corresponding to the calculated pulse energy reduction amount a2-a1 is obtained from the correspondence C.

As described above, the presence / absence of oxygen O2 in the laser chamber 2 is determined only by the arithmetic processing in the controller 7, and the concentration X1 of the impurity O2 is measured.

In this embodiment, the presence / absence of impurities is determined by the arithmetic processing of the controller 7 and the impurity concentration is measured. However, the same measurement is carried out by manually determining the result of FIG. May be performed.

As described above, according to the present embodiment, the presence or absence of impurities can be determined only by the arithmetic processing of the controller 7, and the impurity concentration can be measured. Therefore, a gas sampling and analysis apparatus as in the prior art is newly provided. And the impurity concentration can be easily measured only by the arithmetic processing. Further, there is no need to remove or reattach the sampling bottle 21 and the laser chamber 2 as in the conventional technique. For this reason, according to the present embodiment, the concentration of impurities in the laser gas can be measured without a large-scale apparatus, without requiring complicated work, and without impairing the efficiency of laser operation.

In the first embodiment, the impurity is C
The same applies to the case of O2.

In the first embodiment, the case where the pulse discharge applied voltage b is controlled so that the pulse discharge applied voltage value b is constant has been described.

Next, a second embodiment in which the pulse discharge applied voltage b is controlled so that the pulse energy a becomes constant will be described. In the second embodiment, similarly to the first embodiment, when oxygen O2 is mixed in the laser chamber 2 of the ArF excimer laser apparatus 1 of FIG. 1, it is determined whether or not oxygen O2 is mixed and the concentration of the impurity O2 is measured. Will be described.

FIG. 6A is a graph corresponding to FIG. 5A. A line V2 shown in FIG. 6A shows a change with an increase in the pulse number n of the pulse discharge application voltage b when the impurity O2 is not mixed into the laser chamber 2, and the line V2
Numeral 1 indicates a change in the pulse discharge applied voltage b with an increase in the pulse number n when the impurity O2 is mixed in the laser chamber 2.

FIG. 6B is a graph corresponding to FIG. 5B. FIG. 6B is a graph showing the correspondence D between the concentration Y of O2 mixed in the laser chamber 2 and the amount of change in the pulse discharge applied voltage, that is, the amount of increase in the pulse discharge applied voltage Δb. This correspondence D corresponds to the tendency that the concentration X of O2 increases as the pulse energy decrease amount Δa shown in FIG. 5B increases, and the O2 concentration increases as the pulse discharge applied voltage increase amount Δb increases.
Shows a tendency that the density Y of. This correspondence D is stored in advance in the memory of the controller 7 in the form of a data table of the correspondence between Δb and Y, or in the form of an arithmetic expression for obtaining Y from Δb. Concentration 10 in laser gas
When xenon Xe of about ppm is added, as shown in FIG. 6B, when the impurity concentration Y is 0 ppm, the discharge applied voltage rise Δb becomes zero.

The controller 7 executes the following arithmetic processing.

The controller 7 inputs the pulse energy a per pulse detected by the sensor 8b, and instructs the pulse module 9 to apply a pulse discharge applied voltage b applied to each pulse so that the pulse energy a is constant. ing. This makes it possible to measure the relationship between the number n of oscillation pulses from the start of the continuous pulse oscillation operation and the pulse discharge applied voltage b.

When O2 is mixed in the laser chamber 2 at a predetermined concentration, it changes as shown by the line V1 in FIG. That is, the pulse discharge applied voltage b rises to the level b1 with the pulse number n'1 within 10 pulses immediately after the start of the continuous pulse oscillation operation, and is once stabilized at this level b1.
The number of pulses at the time of stabilization is indicated by n1. Subsequently, the pulse discharge applied voltage b is 40 to 6 from the start of the continuous pulse oscillation operation.
When the number of pulses n'2 of about 0 has elapsed, it starts rising, and when about 200 to 300 pulses have elapsed since the start of the continuous pulse oscillation operation, the level stabilizes at level b2. The number of pulses when stabilized is indicated by n2.

On the other hand, when O2 is not mixed in the laser chamber 2, the voltage changes as indicated by the line V2 in FIG. FIG. 6B shows the case where the impurity O2 is not mixed.
There is no tendency that the pulse discharge applied voltage b increases in two stages of the level of b1 and the level of b2 as shown in the line V1 of FIG.

Therefore, when it is measured that the pulse discharge application voltage b has increased in two stages of the level of b1 and the level of b2 as shown by the line V1 in FIG. 6A, it is determined that the impurity O2 has been mixed. If it is not measured that the pulse discharge applied voltage b has increased in two steps of the level of b1 and the level of b2 as shown in the line V2, it is determined that the impurity O2 is not mixed.

Next, the process of measuring the impurity concentration X assuming that the impurity O2 has been mixed will be described.

As shown in FIG. 6A, the pulse discharge applied voltage b1 when the number of pulses is n1 and the pulse discharge applied voltage b2 when the number of pulses is n2 are measured. Then, a difference b2-b1 between the pulse discharge applied voltage b2 and the pulse discharge applied voltage b1 is calculated as a discharge applied voltage rise amount b2-b1.

Next, as shown in FIG. 6B, an impurity concentration Y1 corresponding to the calculated pulse discharge applied voltage rise amount b2-b1 is obtained from the correspondence D.

As described above, the presence or absence of oxygen O2 in the laser chamber 2 is determined only by the arithmetic processing in the controller 7, and the concentration Y1 of the impurity O2 is measured.

In this embodiment, the presence / absence of impurities is determined by the arithmetic processing of the controller 7 to measure the impurity concentration. However, the same measurement is performed by the result of FIG. May be performed.

In the second embodiment, the impurity is C.
The same applies to the case of O2.

As described above, in the second embodiment, as in the first embodiment, the apparatus does not become large-scale, does not require complicated work, and does not impair the efficiency of laser operation. The effect of being able to measure the concentration of impurities in the laser gas is obtained.

In the first embodiment, as shown in FIG. 5 (a), the energy reduction amount a2-a1 is calculated using the energy level a1 which is first reduced during the continuous pulse oscillation operation as a reference level.

However, the reference level serving as a reference for the energy reduction is not limited to the energy level a1 which was first reduced during the continuous pulse oscillation operation. In the present invention, the energy level at the time of shipment of the laser device may be set as the reference level, or the energy level at the time when the gas in the laser chamber 2 is replaced may be set as the reference level.

For example, as shown by a line E2 in FIG. 5A, an energy level a0 when the impurity O2 is not mixed (for example, a level at the time of the pulse number n2) is obtained in advance, and this level a0 is set as a reference level. May be used to calculate the energy reduction amount a2-a0.

When this is applied to FIG. 2A, the impurity O
This corresponds to calculating an energy level a0 (for example, the level at the time of the pulse number n2) in advance when 2 is not mixed (0 ppm), and calculating the energy reduction amount a2-a0 using this level a0 as a reference level.

Therefore, the present invention relates to SiF containing no oxygen element.
4. It can also be applied to the case of measuring the concentration of impurities of HF, N2 and CF4.

For example, taking SiF4 in FIG. 2C as an example, the energy level a0 (for example, the level at the time of the pulse number n2) when the impurity O2 is not mixed (0 ppm) is obtained in advance. Is used as a reference level to calculate the energy reduction amount a2-a0. And FIG.
As in (a), the concentration Z of SiF4 and the amount of energy decrease Δa
Is prepared in advance, and the concentration Z1 of SiF4 corresponding to the calculated energy reduction amount a2-a0 is prepared.
May be obtained from the correspondence C ′.

The same applies to the case of obtaining the discharge applied voltage rise amount in the second embodiment. The discharge applied voltage level at the time of shipment of the laser device may be set as the reference level, or the discharge applied voltage level when the gas in the laser chamber 2 is replaced may be set as the reference level. In addition, the concentrations of impurities SiF4, HF, N2, and CF4 containing no oxygen element can be measured in the same manner.

Next, a third embodiment will be described.

In the burst operation of the ArF excimer laser device 1, a small amount of laser gas is supplied and exhausted. Thus, the deteriorated laser gas in the laser chamber 2 is exhausted, and a new laser gas is supplied. However, the laser gas in the laser chamber 2 gradually but gradually deteriorates. Therefore, it is necessary to periodically exchange the laser gas in the laser chamber 2.

It is conceivable that oxygen O2 may accidentally enter the laser chamber 2 during the laser gas exchange operation. Therefore, a third embodiment in which an oxygen contamination check is performed at the time of laser gas exchange will be described.

FIG. 7 is a flowchart showing the procedure of the oxygen mixing check process.

That is, when the laser gas in the laser chamber 2 is exchanged (step 501), after the laser gas exchange operation, the ArF excimer laser device 1 performs the burst operation while controlling the discharge applied voltage b so that the pulse energy a becomes constant. Be started. Here, when O2 is mixed in the laser chamber 2, a change as shown by a line V1 in FIG.

Therefore, the pulse discharge applied voltage value of pulse number n1 several tens of pulses after the start of the continuous pulse oscillation operation is b1
Is obtained, and the pulse discharge applied voltage value b2 is obtained with the number of pulses n2 several hundred pulses after the start of the continuous pulse oscillation operation. Then, the amount of change b2−
b1 is determined (step 502).

Next, the variation b2-b1 of the pulse discharge applied voltage value obtained above is compared with a predetermined specified value Δbc, and the variation b2-b1 of the pulse discharge applied voltage value is determined to be the specified value Δ
It is determined whether it is within bc (step 50).
3). If the change amount b2-b1 of the pulse discharge applied voltage value is within the specified value Δbc, it is determined that oxygen is not mixed,
The ArF excimer laser device 1 continues the normal burst operation as it is (Yes in step 503, step 504).

On the other hand, the amount of change b2-
If b1 exceeds the specified value Δbc, it is determined that oxygen has been mixed, and an error message of “oxygen mixed error” is displayed (No in step 503, step 505). When the operator sees the error message, appropriate abnormal treatment is performed on the ArF excimer laser device 1. The burst operation may be automatically stopped in addition to displaying the error message.

In the third embodiment, it is assumed that the pulse energy a is controlled to be constant.
The present invention can also be applied to a case where the pulse discharge application voltage b is controlled to be constant. In this case, step 50
In step 3, it may be determined whether or not the actual pulse energy reduction amount is within the specified value.

As described above, according to the third embodiment, even if O2 is mixed in the laser chamber 2 when the laser gas is exchanged, it is possible to easily check the mixing. The third embodiment can be applied to a case where the impurity is CO2.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an excimer laser device according to a first embodiment.

FIG. 2 is a graph showing a change in pulse energy with an increase in the number of pulses. FIG. 2 (a) is O2, FIG. 2 (b) is CO2, FIG. 2 (c) is SiF4, FIG. 2D is a graph when HF is an impurity, FIG. 2E is a graph when N2 is an impurity, and FIG. 2F is a graph when CF4 is an impurity.

FIG. 3 is a graph showing a relationship between a mixed concentration for each impurity and a pulse energy with respect to the concentration.

FIG. 4 shows a pulse energy of a laser device of 10%.
4 is a table showing the concentration of impurities necessary for reducing the concentration.

FIG. 5A is a graph showing a change in pulse energy with an increase in the number of pulses, and FIG.
7 is a graph showing the correspondence between the density of No. 2 and the amount of change in pulse energy.

6 (a) is a graph showing a change in pulse discharge applied voltage with an increase in the number of pulses, and FIG. 6 (b) is a graph showing a correspondence relationship between O2 concentration and pulse voltage change amount. is there.

FIG. 7 is a flowchart illustrating a procedure of an oxygen mixing check process according to the third embodiment;

8 (a) and 8 (b) are diagrams for explaining the prior art, and for explaining the operation of measuring the concentration of impurities using a gas analyzer.

FIG. 9 is a diagram illustrating a conventional technique, and is a diagram illustrating an operation of measuring the concentration of an impurity using a gas analyzer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... ArF excimer laser apparatus 2 ... Laser chamber 7 ... Controller 8 ... Power monitor 8b ... Sensor 9 ... Pulse power module 11 ... Discharge electrode

Claims (6)

[Claims] 1. A continuous pulse oscillation operation for continuously pulsating a laser beam a predetermined number of times and a pulse oscillation for a predetermined time are suspended by filling a laser chamber with a laser gas and performing discharge between discharge electrodes in the laser chamber. And a laser device that controls a discharge applied voltage so that a discharge applied voltage between the discharge electrodes is constant during the continuous pulse oscillation operation, after the continuous pulse oscillation operation is started. When the output energy of the laser light decreases to a predetermined level with respect to a reference level at the time when the pulse oscillation of a predetermined number of pulses is performed, an output energy reduction amount measuring unit that obtains a reduction amount of the output energy with respect to the reference level, A correspondence relationship between the concentration of impurities other than the laser gas and the output energy reduction amount is prepared in advance. An impurity concentration corresponding to the output energy reducing amount calculated above, the impurity concentration measuring apparatus of a laser device, characterized in that it comprises an impurity concentration measuring unit for determining from said relationship. 2. The method according to claim 1, wherein the output energy of the laser beam is set to a first predetermined level at a point in time when a first predetermined number of pulses have been oscillated after the continuous pulse oscillation operation was started. The output energy of the laser light decreases to a second predetermined level at the time when the pulse oscillation of the second predetermined number of pulses has been performed since the continuous pulse oscillation operation was started, The method according to claim 1, wherein a difference between the output energy at the time when the output level is reduced to the predetermined level and the output energy at the time when the output energy is lowered to the second predetermined level is measured as a reduction amount of the output energy with respect to the reference level. Item 2. An impurity concentration measuring device for a laser device according to Item 1. 3. A continuous pulse oscillation operation for continuously pulsating a laser beam a predetermined number of times and a pulse oscillation for a predetermined time are suspended by filling a laser chamber with a laser gas and performing discharge between discharge electrodes in the laser chamber. And a laser device that controls a discharge application voltage between the discharge electrodes so that the output energy of the laser light becomes constant during the continuous pulse oscillation operation, wherein the continuous pulse oscillation operation is started. When the discharge application voltage to the discharge electrode rises to a predetermined level with respect to a reference level at a point in time when a predetermined number of pulse oscillations have been performed, the discharge application for determining the amount of increase in the discharge application voltage with respect to the reference level Voltage rise amount measuring means, and a correspondence relationship between the concentration of impurities other than the laser gas and the discharge applied voltage rise amount. And because prepared, an impurity concentration corresponding to the determined discharge voltage applied increase amount, the impurity concentration measuring apparatus of a laser device, characterized in that it comprises an impurity concentration measuring unit for determining from said relationship. 4. The apparatus according to claim 1, wherein said discharge applied voltage rise amount measuring means is configured to reduce a discharge applied voltage between said discharge electrodes when a first predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started. 1 and the voltage applied to the discharge electrodes between the discharge electrodes rises to a second predetermined level when a second predetermined number of pulses are generated after the continuous pulse oscillation operation is started. In this case, the difference between the discharge applied voltage at the time of rising to the second predetermined level and the discharge applied voltage at the time of rising to the first predetermined level is defined as the amount of increase of the discharge applied voltage with respect to the reference level. The impurity concentration measuring device for a laser device according to claim 3, wherein the impurity concentration is measured. 5. The apparatus according to claim 1, wherein the impurity includes an oxygen element. 6. The apparatus according to claim 1, wherein a predetermined concentration of xenon is added to said laser gas.