JP4077592B2 - Impurity concentration measuring device for laser equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring the concentration of impurities in a laser chamber.
[0002]
[Prior art]
Ultraviolet laser devices such as excimer laser devices and fluorine laser devices are used as light sources for semiconductor exposure devices. The ultraviolet laser device performs exposure of the IC chip on the semiconductor wafer by alternately repeating exposure and stage movement. During the exposure of the IC chip, the ultraviolet laser device is operated in a burst operation that repeats a continuous pulse oscillation operation that continuously oscillates laser light a predetermined number of times and an oscillation pause that ceases pulse oscillation for a predetermined time. That is, at the time of burst operation, for example, an operation in which the laser beam is continuously oscillated 500 pulses and then the oscillation is stopped for 0.2 seconds is repeated.
[0003]
However, during burst operation, a relatively high energy is obtained at the beginning of continuous pulse oscillation, but a phenomenon in which the pulse energy gradually decreases (hereinafter referred to as “spike phenomenon”) occurs. When this spike phenomenon occurs, the accuracy of exposure decreases.
[0004]
In order to eliminate this spike phenomenon, the applicant of the present invention has already filed a patent application (Japanese Patent Application No. 11-23709) for adding a predetermined concentration (for example, 10 ppm) of xenon Xe to the laser gas in the laser chamber. ing. According to the present invention, the spike phenomenon is eliminated by adding a predetermined concentration of xenon to the laser gas. Furthermore, when xenon is added to the laser gas, the effect of increasing the output energy of the laser beam as a whole can be obtained as compared with the case where xenon is not added.
[0005]
However, even if xenon is added to the laser gas, if impurities (for example, oxygen O2) other than the original laser gas are mixed in the laser chamber, the effects of eliminating the spike phenomenon and increasing the output energy due to the addition of xenon cannot be obtained. 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 mixing, determine the mixing concentration, determine the cause of mixing, and formulate countermeasures.
[0006]
Therefore, conventionally, a method of directly analyzing the gas in the laser chamber has been adopted in order to determine the presence or absence of impurities and determine the concentration.
[0007]
A conventional gas analysis method will be described.
[0008]
FIG. 8A shows the ultraviolet laser device 20. A sampling bottle 21 and a purge unit 22 are connected to the piping of the laser chamber 2 via a valve 23. The analysis procedure in this apparatus is as follows.
[0009]
1) With the laser oscillation operation stopped, the closed valve 23 and the sampling bottle 21 are connected by a pipe capable of purging, and the purge unit 22 is connected to this connection portion.
[0010]
2) The purge unit 22 sufficiently purges the connection portion between the valve 23 and the sampling bottle 21, and then opens the valve 23 to extract the laser gas in the laser chamber 2. That is, laser gas sampling is performed.
[0011]
3) As shown in FIG. 8B, the sampling bottle 21 and the gas analyzer 24 are connected by a pipe that can be purged, and a purge unit 22 is connected to this connecting portion.
[0012]
4) After the purge unit 22 sufficiently purges the connecting portion between the gas analyzer 24 and the sampling bottle 21, the gas analyzer 24 performs gas analysis.
[0013]
FIG. 9 is a diagram for explaining another gas analysis method. The analysis procedure in the apparatus shown in FIG. 9 is as follows.
[0014]
1) The laser chamber 2 is removed from the ultraviolet laser device 20.
[0015]
2) The purge unit 22 and the gas analyzer 24 are attached to the laser chamber 2.
[0016]
3) After purging the piping portion by the purge unit 22, the gas in the laser chamber 2 is introduced into the gas analyzer 24 to analyze the gas. In other words, gas sampling and analysis are performed.
[0017]
[Problems to be solved by the invention]
As described above, in the prior art, it is necessary to prepare the purge unit 22 and the gas analyzer 24 separately from the ultraviolet laser device 20 and perform gas sampling and analysis. For this reason, a device for sampling and analyzing gas is newly required, and the device becomes large. In addition, the gas sampling and analysis work is troublesome, and the work becomes complicated. Further, the work of removing and re-installing the sampling bottle 21 and the laser chamber 2 is not only troublesome, but the original laser operation must be temporarily stopped during this work. This significantly reduces the efficiency of laser operation.
[0018]
The present invention has been made in view of such circumstances, and the concentration of the impurities in the laser gas is measured without complicating the operation of the apparatus and without complicating the operation of the laser. This is a problem to be solved.
[0019]
[Means, functions and effects for solving the problems]
The first invention of the present invention is:
By filling a laser gas in the laser chamber and performing discharge between the discharge electrodes in the laser chamber, a continuous pulse oscillation operation that continuously oscillates laser light a predetermined number of times and an oscillation pause that ceases pulse oscillation for a predetermined time are performed. In the laser device that repeatedly performs and controls the discharge applied voltage so that the discharge applied voltage between the discharge electrodes is constant during the continuous pulse oscillation operation,
When the output energy of the laser beam decreases to a predetermined level with respect to a reference level at the time when pulse oscillation of a predetermined number of pulses has been performed since the continuous pulse oscillation operation was started, the amount of decrease in output energy with respect to the reference level Output energy reduction amount measuring means for obtaining,
A correspondence relationship between the concentration of impurities other than the laser gas and the amount of output energy reduction is prepared in advance,
Impurity concentration measuring means for obtaining an impurity concentration corresponding to the obtained output energy decrease amount from the correspondence relationship;
Having
It is characterized by.
[0020]
According to the first aspect of the present invention, when impurities are mixed in the laser chamber when the discharge applied voltage is controlled to be constant, energy is reduced with respect to the reference level, and this energy reduction corresponds to the impurity concentration. It was made based on.
[0021]
The first invention will be described with reference to FIG.
[0022]
As shown in FIG. 5A, when the continuous pulse oscillation operation is performed so that the discharge applied voltage between the discharge electrodes is constant, the continuous pulse oscillation operation is started when impurities are mixed in the laser chamber. When the pulse oscillation of the predetermined number of pulses n2 is performed, the output energy a of the laser beam is lowered 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.
[0023]
On the other hand, as shown in FIG. 5B, a correspondence C between the concentration X of impurities other than the laser gas and the output energy reduction amount Δa is prepared in advance.
[0024]
The impurity concentration X1 corresponding to the output energy reduction amount a2-a1 obtained there is obtained from the correspondence C.
[0025]
According to the first 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 the arithmetic processing. Further, it is not necessary to remove or reattach the sampling bottle 21 or the laser chamber 2 as in the prior art. Therefore, according to the present invention, the concentration of the impurities in the laser gas can be measured without making the apparatus large-scale, without requiring complicated work, and without impairing the efficiency of laser operation.
[0026]
The second invention is the first invention,
The energy reduction amount measuring means reduces the output energy of the laser beam to a first predetermined level at the time when the first predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started. When the output energy of the laser beam has decreased to a second predetermined level at the time when pulse oscillation of the second predetermined number of pulses has been made since the start of continuous pulse oscillation operation, the level has decreased to the first predetermined level. The difference between the output energy at the time point and the output energy at the time point when the output energy is reduced to the second predetermined level is measured as a reduction amount of the output energy with respect to the reference level.
It is characterized by.
[0027]
According to the second invention, as shown in FIG. 5 (a), the output energy a of the laser beam is the first when the pulse oscillation of the first predetermined number of pulses n1 is performed after the continuous pulse oscillation operation is started. The output energy a of the laser beam decreases to the second predetermined level a2 when the pulse oscillation of the second predetermined number of pulses n2 is performed after the continuous pulse oscillation operation is started. The difference a2-a1 between the output energy a1 at the time when the output energy a1 is reduced to the first predetermined level a1 and the output energy a2 at the time when the output energy a2 is reduced to the second predetermined level a2 is the reduction amount a2-a1 of the output energy relative to the reference level As measured.
[0028]
Also, the third invention is
By filling a laser gas in the laser chamber and performing discharge between the discharge electrodes in the laser chamber, a continuous pulse oscillation operation that continuously oscillates laser light a predetermined number of times and an oscillation pause that ceases pulse oscillation for a predetermined time are performed. In the laser device that repeatedly performs, and controls the discharge applied voltage between the discharge electrodes so that the output energy of the laser light is constant during the continuous pulse oscillation operation,
The discharge applied voltage with respect to the reference level when the discharge applied voltage to the discharge electrode rises to a predetermined level with respect to the reference level at the time when the pulse oscillation of a predetermined number of pulses has been made since the continuous pulse oscillation operation was started. Discharge applied voltage rise measuring means for obtaining the rise amount of
A correspondence relationship between the concentration of impurities other than the laser gas and the discharge applied voltage increase amount is prepared in advance,
Impurity concentration measuring means for obtaining an impurity concentration corresponding to the obtained increase in discharge applied voltage from the correspondence relationship;
Having
It is characterized by.
[0029]
According to the 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 the reference level, and the discharge applied voltage rise corresponds to the impurity concentration. It was made based on the points.
[0030]
The third invention will be described with reference to FIG.
[0031]
As shown in FIG. 6A, when the continuous pulse oscillation operation is performed so that the output energy of the laser light is constant, if impurities are mixed in the laser chamber, the predetermined pulse is generated after the continuous pulse oscillation operation is started. When a pulse oscillation of several n2 is made, the discharge applied voltage b between the discharge electrodes rises to a predetermined level b2 with respect to the reference level b1. Then, an increase b2-b1 of the discharge applied voltage with respect to the reference level b1 is obtained.
[0032]
On the other hand, as shown in FIG. 6B, a correspondence D between the concentration Y of impurities other than the laser gas and the discharge applied voltage increase Δb is prepared in advance.
[0033]
Therefore, the impurity concentration Y1 corresponding to the discharge applied voltage rise b2-b1 obtained from the correspondence relationship D is obtained.
[0034]
According to the third 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 the arithmetic processing. Further, it is not necessary to remove or reattach the sampling bottle 21 or the laser chamber 2 as in the prior art. Therefore, according to the present invention, the concentration of the impurities in the laser gas can be measured without making the apparatus large-scale, without requiring complicated work, and without impairing the efficiency of laser operation.
[0035]
The fourth invention is the third invention, wherein
The discharge applied voltage increase amount measuring means sets the discharge applied voltage between the discharge electrodes to the first predetermined level at the time when the first predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started. When the discharge applied voltage between the discharge electrodes rises to a second predetermined level at the time when the second predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started, 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 measured as an increase amount of the discharge applied voltage with respect to the reference level. thing
It is characterized by.
[0036]
According to the fourth aspect of the invention, as shown in FIG. 6 (a), the discharge applied voltage b between the discharge electrodes at the time when the pulse oscillation of the first predetermined number of pulses n1 is performed after the continuous pulse oscillation operation is started. The discharge applied voltage b between the discharge electrodes is increased to the second predetermined level at the point of time when the pulse oscillation of the second predetermined number of pulses n2 is performed after the continuous pulse oscillation operation is started after rising to the first predetermined level b1. It rises to b2. The difference b2-b1 between the discharge applied voltage b2 at the time of rising to the second predetermined level b2 and the discharge applied electrode b1 at the time of rising to the first predetermined level b1 is the amount of increase in the discharge applied voltage with respect to the reference level. It is measured as b2-b1.
[0037]
The fifth invention is the first invention to the fourth invention,
The impurity includes an oxygen element.
It is characterized by.
[0038]
In the fifth aspect of the invention, the impurity other than the laser gas is O2, CO2, etc. and contains oxygen element. Impurities including oxygen elements are mixed in 1) oxygen in the atmosphere, 2) chemical reaction between fluorine in the laser gas and moisture in the laser chamber, 3) insufficient purge in the piping, and 4) supply of poor purity. Possible causes such as gas cylinders.
[0039]
The sixth invention is the first invention to the fifth invention,
Adding xenon at the specified concentration to the laser gas
It is characterized by.
[0040]
In the sixth invention, for example, xenon Xe having a concentration of 10 ppm is added to the laser gas, and the amount of energy decrease Δa when the impurity concentration X is 0 ppm as shown in FIG. 5B is 0 or as shown in FIG. As described above, the case where the discharge applied voltage increase Δb when the impurity concentration Y is 0 ppm is 0.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an impurity concentration measuring apparatus for a laser apparatus according to the present invention will be described below with reference to the drawings. In the embodiment described below, 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 burst operation. Further, for example, 10 ppm of xenon Xe 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.
[0042]
However, the present invention can be applied to any laser apparatus other than the ArF excimer laser apparatus as long as the spike phenomenon occurs. Moreover, even if it is an additive other than xenon Xe, if it is an additive which can eliminate the spike phenomenon which generate | occur | produces at the time of burst operation, implementation which adds this is also possible.
[0043]
FIG. 1 is a block diagram showing the configuration of the ArF excimer laser device according to the first embodiment. In the first embodiment, it is assumed that the discharge application voltage is controlled so that the discharge application voltage value between the discharge electrodes 11 and 11 in the laser chamber 2 is constant.
[0044]
The ArF excimer laser device 1 shown in FIG. 1 mainly includes a laser chamber 2, a rear mirror 3, a front mirror 4, an air supply module 5, an exhaust module 6, a controller 7, a power monitor 8, and a pulse. The power module 9 is configured.
[0045]
Discharge electrodes 11 are provided in the laser chamber 2 so as to face each other. In the laser chamber 2, a laser gas made of fluorine F2, argon Ar2, and neon Ne is sealed. Further, xenon Xe having a concentration of about 10 ppm is added to the laser gas.
[0046]
When pulse discharge is performed between the discharge electrodes 11, 11, the laser gas is excited and the pulse laser beam L1 is oscillated. A fan and a radiator (not shown) are provided in the laser chamber 2. Laser gas is circulated in the laser chamber 2 at a predetermined cycle by the fan and supplied between the discharge electrodes 11 and 11. When the laser gas is circulated by the fan, the heat of the laser gas is exchanged by the radiator.
[0047]
On the optical axis of the laser beam L1 in the laser chamber 2, windows 2a and 2b are provided facing each other. 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. The rear mirror 3 and the front mirror 4 constitute a resonator. The rear mirror 3 is a mirror that totally reflects light. The front mirror 4 is a partial transmission mirror that transmits only a part of the light. The laser beam L1 reciprocates between the rear mirror 3 and the front mirror 4, whereby the energy is amplified and laser oscillation is performed. A resonator composed of the rear mirror 3 and the front mirror 4 can be provided with a band narrowing unit. This narrow band unit is composed of a beam expander such as a prism and a wavelength selection element such as a grating.
[0048]
The air supply module 5 is a module for supplying a laser gas in 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.
[0049]
The controller 7 receives data output from the power monitor 8 and controls supply of laser gas into the laser chamber 2 by the air supply module 5 and exhaust of laser gas from the laser chamber 2 by the exhaust module 6. The controller 7 controls power supply to the pulse power module 9. Further, the controller 7 receives data output from the power monitor 8, determines whether impurities other than the laser gas in the laser chamber 2, such as O 2, are mixed, and measures the impurity concentration.
[0050]
The power monitor 8 is a device that detects the output energy a of the laser beam L1, that is, the pulse energy a per pulse, and is composed of a beam splitter 8a and a sensor 8b. The beam splitter 8a transmits a part of incident light and reflects a part thereof. The sensor 8b detects the pulse energy a of the laser beam L1.
[0051]
That is, the laser beam L 1 emitted from the front mirror 4 is incident on the beam splitter 8 a of the power monitor 8. 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 outside the excimer laser device 1. Another part of the laser beam L1 incident on the beam splitter 8a is incident on the sensor 8b. The sensor 8b detects the pulse energy a of the laser light L1 and outputs it to the controller 7.
[0052]
The pulse power module 9 applies a discharge applied voltage b, that is, a pulse discharge applied voltage b per pulse, to the discharge electrodes 11 and 11. The pulse discharge application voltage b is controlled by the controller 7.
[0053]
The above is the configuration of the ArF excimer laser device 1 according to the embodiment.
[0054]
Next, changes in pulse energy a when various impurities are mixed in the laser chamber 2 will be described.
[0055]
FIG. 2 is a graph showing changes in pulse energy a during continuous pulse oscillation operation. FIG. 2A shows a case where O2 is not mixed as an impurity (0 ppm), a case where it is mixed at a concentration of 10 ppm, and a case where it is mixed at a concentration of 30 ppm.
[0056]
FIG. 2B shows a case where CO2 is not mixed as an impurity (0 ppm), a case where it is mixed at a concentration of 10 ppm, and a case where it is mixed at a concentration of 20 ppm.
[0057]
FIG. 2C shows a case where SiF4 is not mixed as an impurity (0 ppm), a case where it is mixed at a concentration of 20 ppm, and a case where it is mixed at a concentration of 50 ppm.
[0058]
FIG. 2D shows a case where HF is not mixed as an impurity (0 ppm), a case where it is mixed at a concentration of 10 ppm, and a case where it is mixed at a concentration of 30 ppm.
[0059]
FIG. 2E shows the case where N2 is not mixed as an impurity (0 ppm), the case where it is mixed at a concentration of 20 ppm, and the case where it is mixed at a concentration of 100 ppm.
[0060]
FIG. 2F shows the case where CF4 is not mixed as an impurity (0 ppm), the case where it is mixed at a concentration of 50 ppm, and the case where it is mixed at a concentration of 100 ppm.
[0061]
2A to 2F show the pulse energy a, and the pulse energy a when no impurities are mixed (0 ppm) is normalized to “1”. The horizontal axis indicates the number of oscillation pulses n after the continuous pulse oscillation operation is started.
[0062]
Here, the case where the impurity is O2 will be described with reference to FIG.
[0063]
As shown in FIG. 2A, when O2 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.
[0064]
Further, when O2 is mixed in the laser chamber 2 at a concentration of 10 ppm, the pulse energy a is a level a1 of about 1.0 or less at the pulse number n'1 within 10 pulses immediately after the start of the continuous pulse oscillation operation. It decreases and once stabilizes at this level a1. The number of pulses when stabilized is indicated by n1. Subsequently, the pulse energy a starts to decrease when a pulse number n'2 of about 40 to 60 pulses elapses from the start of continuous pulse oscillation operation, and reaches a level a2 of about 0.8 after about 200 to 300 pulses elapses from the start of continuous pulse oscillation operation. To stabilize. The number of pulses when stabilized is indicated by n2. 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).
[0065]
When O2 is mixed in the laser chamber 2 at a concentration of 30 ppm, the same tendency as in the case where O2 is mixed at a concentration of 10 ppm is shown. Further, when O2 is mixed at a concentration of 30 ppm, the pulse energy a is further reduced as a whole as compared with the case where O2 is mixed at a concentration of 10 ppm. That is, the amount of energy reduction at the level a2 with respect to the level a1 increases as the O2 concentration increases.
[0066]
Note that the pulse number n'1 at the time point when the continuous pulse oscillation operation starts to decrease to the level a1 varies depending on the laser repetition frequency, the circulation flow rate by the fan in the laser chamber 2, and the like.
[0067]
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 if the impurity CO2 is mixed at a concentration of 10 ppm to 20 ppm, a1 The energy decreases in two stages, i.e., a2 and a2, and the amount of energy decrease at the a2 level with respect to the a1 level increases as the CO2 concentration increases.
[0068]
That is, when the oxygen element is contained in the impurity, such a phenomenon that the energy is reduced in two stages of the a1 level and the a2 level is observed.
[0069]
On the other hand, in the case of impurities SiF4, HF, N2 and CF4 that do not contain oxygen elements (FIGS. 2 (c) to (f)), the phenomenon that energy is reduced in two steps, the level of a1 and the level of a2. Is not seen.
[0070]
However, when impurities are mixed at a predetermined concentration, the pulse energy a is reduced as a whole compared to the case where impurities are not mixed (0 ppm), and the amount of reduced energy with respect to the level at 0 ppm increases the concentration of impurities. As it grows.
[0071]
For example, in the case of SiF4 in FIG. 2 (c), when SiF4 is mixed at a concentration of 20 ppm, the pulse energy a is changed from the level of a0 to the level of a2 as compared with the case where SiF4 is not mixed (0 ppm). To drop. The energy reduction amount a2-a0 with respect to the level a0 at 0 ppm increases as the SiF4 concentration increases from 20 ppm to 50 ppm.
[0072]
FIG. 3 shows the relationship between the impurity concentration X and the pulse energy a for each impurity. The vertical axis in FIG. 3 indicates the pulse energy a, and the pulse energy when no impurities are mixed is normalized to “1”. The horizontal axis represents the impurity concentration X. As is apparent from FIG. 3, the impurities that contribute most to the decrease in the pulse energy a are CO2 and O2. Hereinafter, the contribution to the decrease of the pulse energy a becomes smaller in the order of HF, SiF4, HF, N2, and CF4.
[0073]
FIG. 4 shows the concentration of impurities necessary for reducing the pulse energy a by 10% for each impurity. FIG. 4 shows an ArF excimer laser and a KrF excimer laser in comparison.
[0074]
As shown in FIG. 4, the ArF excimer laser generally has a lower numerical value of the impurity concentration required to reduce the pulse energy a by 10% than the KrF excimer laser. From this, it can be seen that the influence of mixing impurities on the energy reduction is larger in the ArF excimer laser than in the KrF excimer laser.
[0075]
In addition, regarding ArF excimer laser, the pulse energy a is reduced by 10% when impurities containing oxygen elements such as O2 and CO2 are mixed by only 5 ppm, whereas impurities not containing oxygen elements are not mixed by 10 ppm or more. And the pulse energy a does not decrease by 10%. From this, it can be seen that the influence of impurity mixing on the energy reduction is greater for impurities containing an oxygen element than for impurities not containing an oxygen element.
[0076]
As described above, when the impurity O2 or CO2 containing oxygen element is mixed, the energy is reduced in two stages of the a1 level and the a2 level, and the amount of energy reduction at the a2 level with respect to the a1 level increases the impurity concentration. As it grows. Further, the influence of the mixing of impurities O2 or CO2 containing oxygen elements on the energy reduction is greater than when impurities not containing other oxygen elements are mixed. In addition, the influence becomes larger in the ArF excimer laser apparatus.
[0077]
A process for determining whether or not oxygen O2 is mixed in the laser chamber 2 of the ArF excimer laser apparatus 1 shown in FIG. 1 and measuring the concentration of the impurity O2 will be described with reference to FIG. The impurities O2 are mixed in 1) 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 pipe, 4) supply gas cylinder with poor purity, etc. Caused by the cause of
[0078]
FIG. 5A is a graph corresponding to FIG. 2A and is a simplified graph of FIG. A line E2 shown in FIG. 5A shows a change in the pulse energy a when the number of pulses n increases when no impurity O2 is mixed in the laser chamber 2, and a line E1 is mixed with the impurity O2 in the laser chamber 2. The change with the increase of the pulse number n of the pulse energy a at the time is shown.
[0079]
On the other hand, FIG. 5B is a graph showing the correspondence C between the concentration X2 of O2 mixed in the laser chamber 2 and the pulse energy change amount, that is, the pulse energy decrease amount Δa. This correspondence C corresponds to the above-described tendency that the O 2 concentration X increases as the pulse energy decrease amount Δa increases. This 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. When xenon Xe having a concentration of about 10 ppm is added to the laser gas, as shown in FIG. 5B, the amount of energy decrease Δa when the impurity concentration X is 0 ppm is zero.
[0080]
The controller 7 executes the following arithmetic processing.
[0081]
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 to be given for each pulse. Thus, the relationship between the number of oscillation pulses n and the pulse energy a from the start of the continuous pulse oscillation operation can be measured.
[0082]
When O2 is mixed in the laser chamber 2 at a predetermined concentration, it changes as shown by a line E1 in FIG. That is, the pulse energy a is lowered to the level a1 at the pulse number n'1 within 10 pulses immediately after the start of the continuous pulse oscillation operation, and is temporarily stabilized at this level a1. The number of pulses when stabilized is indicated by n1. Subsequently, the pulse energy a starts to decrease when the pulse number n'2 of about 40 to 60 pulses elapses from the start of the continuous pulse oscillation operation, and stabilizes at the level a2 when about 200 to 300 pulses elapse from the start of the continuous pulse oscillation operation. The number of pulses when stabilized is indicated by n2.
[0083]
On the other hand, when O2 is not mixed in the laser chamber 2, it changes as shown by a line E2 in FIG. When the impurity O2 is not mixed, there is no tendency for the pulse energy a to decrease in two stages of the level a1 and the level a2 as shown by the line E1 in FIG.
[0084]
Therefore, when it is measured that the pulse energy a has decreased in two steps of the level a1 and the level a2 as indicated by the line E1 in FIG. 5A, it is determined that the impurity O2 is mixed, and the line E2 is indicated. As described above, if it is not measured that the pulse energy a has decreased in two steps of the a1 level and the a2 level, it is determined that the impurity O2 is not mixed.
[0085]
Next, a process of measuring the impurity concentration X assuming that the impurity O2 is mixed will be described.
[0086]
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. The difference a2−a1 between the pulse energy a1 and the pulse energy a2 is calculated as the energy decrease amount a2−a1.
[0087]
Next, as shown in FIG. 5B, the impurity concentration X1 corresponding to the calculated pulse energy decrease amount a2-a1 is obtained from the correspondence C.
[0088]
As described above, only the calculation process in the controller 7 determines whether or not oxygen O2 is mixed in the laser chamber 2, and the concentration X1 of the impurity O2 is measured.
[0089]
In this embodiment, the presence or absence of impurities is determined by the calculation process of the controller 7 and the impurity concentration is measured. However, the same measurement is performed by manually determining and manually calculating the result of FIG. It may be.
[0090]
As described above, according to the present embodiment, since 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, it is necessary to newly provide a gas sampling and analysis device as in the prior art The impurity concentration can be easily measured by only the arithmetic processing. Further, it is not necessary to remove or reattach the sampling bottle 21 or the laser chamber 2 as in the prior art. For this reason, according to this embodiment, the apparatus does not become large-scale, and it is possible to measure the concentration of impurities in the laser gas without complicating work and without impairing the efficiency of laser operation.
[0091]
Further, the first embodiment described above can be similarly applied when the impurity is CO2.
[0092]
The first embodiment has described the case where the pulse discharge application voltage b is controlled so that the pulse discharge application voltage value b is constant.
[0093]
Next, a second embodiment in which the pulse discharge applied voltage b is controlled so that the pulse energy a is constant will be described. Also in the second embodiment, when oxygen O2 is mixed in the laser chamber 2 of the ArF excimer laser apparatus 1 in FIG. 1 as in the first embodiment, the presence or absence of the mixing is determined and the concentration of the impurity O2 is measured. Processing to be performed will be described.
[0094]
FIG. 6A is a graph corresponding to FIG. A line V2 shown in FIG. 6A shows a change accompanying an increase in the number of pulses n of the pulse discharge applied voltage b when the impurity O2 is not mixed in the laser chamber 2, and a line V1 shows the impurity O2 in the laser chamber 2. The change with the increase in the pulse number n of the pulse discharge applied voltage b when the is mixed is shown.
[0095]
On the other hand, FIG. 6B is a graph corresponding to FIG. 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 pulse discharge applied voltage, that is, the amount of increase in 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 as the pulse discharge applied voltage increase amount Δb increases, O2 increases. This shows a tendency that the density Y of the toner increases. 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. When xenon Xe having a concentration of about 10 ppm is added to the laser gas, as shown in FIG. 6B, the discharge applied voltage increase Δb when the impurity concentration Y is 0 ppm is zero.
[0096]
The controller 7 executes the following arithmetic processing.
[0097]
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 to be given to each pulse so that the pulse energy a becomes constant. Thus, the relationship between the number of oscillation pulses n from the start of the continuous pulse oscillation operation and the pulse discharge applied voltage b can be measured.
[0098]
When O2 is mixed in the laser chamber 2 at a predetermined concentration, it changes as shown by a line V1 in FIG. That is, the pulse discharge applied voltage b rises to the level b1 at the pulse number n'1 within 10 pulses immediately after the start of the continuous pulse oscillation operation, and once stabilizes at this level b1. The number of pulses when stabilized is indicated by n1. Subsequently, the pulse discharge applied voltage b starts to rise when the pulse number n'2 of about 40 to 60 pulses elapses from the start of the continuous pulse oscillation operation, and stabilizes at the level b2 after about 200 to 300 pulses elapses from the start of the continuous pulse oscillation operation. . The number of pulses when stabilized is indicated by n2.
[0099]
On the other hand, when O2 is not mixed in the laser chamber 2, it changes as shown by a line V2 in FIG. When the impurity O2 is not mixed, there is no tendency for the pulse discharge applied voltage b to rise in two stages, the level of b1 and the level of b2, as indicated by the line V1 in FIG. 6B.
[0100]
Therefore, if it is measured that the pulse discharge applied voltage b has risen in two steps, b1 level and b2 level, as indicated by the line V1 in FIG. 6A, it is determined that the impurity O2 is mixed, and the line V2 If it is not measured that the pulse discharge applied voltage b has risen in two stages, b1 level and b2 level, it is determined that the impurity O2 is not mixed.
[0101]
Next, a process of measuring the impurity concentration X assuming that the impurity O2 is mixed will be described.
[0102]
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. 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 increase amount b2-b1.
[0103]
Next, as shown in FIG. 6B, the impurity concentration Y1 corresponding to the calculated pulse discharge applied voltage increase b2-b1 is obtained from the correspondence D.
[0104]
As described above, only the calculation process in the controller 7 determines whether or not oxygen O2 is mixed in the laser chamber 2, and the concentration Y1 of the impurity O2 is measured.
[0105]
In this embodiment, the presence / absence of impurities is determined by the calculation process of the controller 7 and the impurity concentration is measured. However, the same measurement is performed by manually determining and manually calculating the result of FIG. It may be.
[0106]
Further, the second embodiment described above can be similarly applied when the impurity is CO2.
[0107]
As described above, also in the second embodiment, as in the first embodiment, the apparatus is not large-scale, does not require complicated work, and does not impair the efficiency of laser operation. The effect of measuring the impurity concentration is obtained.
[0108]
In the first embodiment, as shown in FIG. 5A, the energy reduction amount a2-a1 is calculated using the energy level a1 first reduced during the continuous pulse oscillation operation as the reference level.
[0109]
However, the reference level that serves as a reference for energy reduction is not limited to the energy level a1 that first decreases during continuous pulse oscillation operation. In the present invention, the energy level at the time of shipment of the laser apparatus 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.
[0110]
For example, as shown by a line E2 in FIG. 5A, an energy level a0 (for example, a level at the time of the number of pulses n2) when no impurity O2 is mixed is obtained in advance, and this level a0 is used as a reference level to reduce energy. The quantity a2-a0 may be calculated.
[0111]
When this is applied to FIG. 2 (a), 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, and this level a0 is used as a reference level to reduce the energy. This corresponds to calculating the quantity a2-a0.
[0112]
Therefore, the present invention can also be applied to the case of measuring the concentration of impurities of SiF4, HF, N2, and CF4 that do not contain an oxygen element.
[0113]
For example, in the case of SiF4 in FIG. 2C, an energy level a0 (for example, a level at the time of the number of pulses n2) when no impurity O2 is mixed (0 ppm) is obtained in advance, and this level a0 is set as a reference level. As a result, an energy reduction amount a2-a0 is calculated. Similarly to FIG. 5A, a correspondence C ′ between the SiF4 concentration Z and the energy decrease amount Δa is prepared in advance, and the SiF4 concentration Z1 corresponding to the calculated energy decrease amount a2−a0 is obtained as follows. What is necessary is just to obtain | require from correspondence C '.
[0114]
The same applies to the case where the discharge applied voltage increase amount is obtained in the second embodiment. The discharge applied voltage level at the time of shipment of the laser apparatus may be set as the reference level, or the discharge applied voltage level at the time when the gas in the laser chamber 2 is replaced may be set as the reference level. The concentrations of impurities SiF4, HF, N2, and CF4 that do not contain oxygen elements can be measured in the same manner.
[0115]
Next, a third embodiment will be described.
[0116]
Now, during the burst operation of the ArF excimer laser apparatus 1, a small amount of laser gas is supplied and exhausted. In this way, the deteriorated laser gas in the laser chamber 2 is exhausted, and new laser gas is supplied. However, the laser gas in the laser chamber 2 gradually deteriorates with time. For this reason, it is necessary to periodically replace the laser gas in the laser chamber 2.
[0117]
It is conceivable that oxygen O2 is erroneously mixed into the laser chamber 2 during this laser gas exchange operation. Therefore, a third embodiment in which an oxygen mixing check is performed during laser gas exchange will be described.
[0118]
FIG. 7 is a flowchart showing the procedure of the oxygen contamination check process.
[0119]
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 apparatus 1 starts burst operation while controlling the discharge applied voltage b so that the pulse energy a becomes constant. . Here, when O2 is mixed in the laser chamber 2, a change as shown by a line V1 in FIG.
[0120]
Therefore, the pulse discharge applied voltage value of pulse number n1 after several tens of pulses from the start of continuous pulse oscillation operation is obtained as b1, and the pulse discharge applied voltage value b2 at pulse number n2 after several hundred pulses from the start of continuous pulse oscillation operation. Desired. Then, a change amount b2-b1 of these pulse discharge applied voltage values is obtained (step 502).
[0121]
Next, the amount of change b2-b1 of the pulse discharge applied voltage value obtained above is compared with a preset specified value Δbc to determine whether or not the amount of change b2-b1 of the pulse discharge applied voltage value is within the specified value Δbc. Determination is made (step 503). 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, and the ArF excimer laser device 1 continues the normal burst operation as it is (determination Yes in step 503). Step 504).
[0122]
On the other hand, when the change amount b2-b1 of the pulse discharge applied voltage value exceeds the specified value Δbc, it is determined that oxygen has been mixed, and an error message “oxygen mixing error” is displayed (step 503). No, step 505). When the operator sees the error message, the ArF excimer laser device 1 is appropriately treated. In addition to displaying an error message, burst operation may be automatically stopped.
[0123]
In the third embodiment, it is assumed that the pulse energy a is controlled to be constant, but the present invention can also be applied to the case where the pulse discharge applied voltage b is controlled to be constant. In this case, it may be determined in step 503 whether or not the actual pulse energy reduction amount is within a specified value.
[0124]
As described above, according to the third embodiment, even when O2 is mixed into the laser chamber 2 when the laser gas is exchanged, the mixing can be easily checked. The third embodiment can also be applied when the impurity is CO2.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an excimer laser device according to a first embodiment.
FIG. 2 is a graph showing changes in pulse energy as the number of pulses increases. FIG. 2 (a) is O2, FIG. 2 (b) is CO2, FIG. 2 (c) is SiF4, FIG. d) is a graph when HF, FIG. 2 (e) is N2, and FIG. 2 (f) is a graph when CF4 is an impurity.
FIG. 3 is a graph showing the relationship between the concentration of each impurity and the pulse energy with respect to that concentration.
FIG. 4 is a table showing impurity concentrations necessary to reduce the pulse energy of the laser device by 10%.
FIG. 5 (a) is a graph showing changes in pulse energy as the number of pulses increases, and FIG. 5 (b) is a graph showing a correspondence relationship between O2 concentration and pulse energy change amount.
FIG. 6 (a) is a graph showing a change in pulse discharge applied voltage as the number of pulses increases, 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 contamination check process according to the third embodiment.
FIGS. 8A and 8B are diagrams for explaining the prior art, and for explaining the work of measuring the concentration of impurities using a gas analyzer.
FIG. 9 is a diagram for explaining the prior art, and is a diagram for explaining an operation of measuring the concentration of impurities using a gas analyzer.
[Explanation of symbols]
1 ... ArF excimer laser device
2 ... Laser chamber
7 ... Controller
8 ... Power monitor
8b ... Sensor
9 ... Pulse power module
11 ... discharge electrode

Claims (6)

By filling a laser gas in the laser chamber and performing discharge between the discharge electrodes in the laser chamber, a continuous pulse oscillation operation that continuously oscillates laser light a predetermined number of times and an oscillation pause that ceases pulse oscillation for a predetermined time are performed. In the laser device that repeatedly performs and controls the discharge applied voltage so that the discharge applied voltage between the discharge electrodes is constant during the continuous pulse oscillation operation,
When the output energy of the laser beam decreases to a predetermined level with respect to a reference level at the time when pulse oscillation of a predetermined number of pulses has been performed since the continuous pulse oscillation operation was started, the amount of decrease in output energy with respect to the reference level Output energy reduction amount measuring means for obtaining,
A correspondence relationship between the concentration of impurities other than the laser gas and the amount of output energy reduction is prepared in advance,
An impurity concentration measuring device for a laser device, comprising: an impurity concentration measuring means for obtaining an impurity concentration corresponding to the obtained output energy reduction amount from the correspondence relationship. The energy reduction amount measuring means reduces the output energy of the laser beam to a first predetermined level at the time when the first predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started. When the output energy of the laser beam has decreased to a second predetermined level at the time when pulse oscillation of the second predetermined number of pulses has been made since the start of continuous pulse oscillation operation, the level has decreased to the first predetermined level. 2. The laser according to claim 1, wherein a difference between the output energy at the time point and the output energy at the time point 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. Equipment impurity concentration measuring device. By filling a laser gas in the laser chamber and performing discharge between the discharge electrodes in the laser chamber, a continuous pulse oscillation operation that continuously oscillates laser light a predetermined number of times and an oscillation pause that ceases pulse oscillation for a predetermined time are performed. In the laser device that repeatedly performs, and controls the discharge applied voltage between the discharge electrodes so that the output energy of the laser light is constant during the continuous pulse oscillation operation,
The discharge applied voltage with respect to the reference level when the discharge applied voltage to the discharge electrode rises to a predetermined level with respect to the reference level at the time when the pulse oscillation of a predetermined number of pulses has been made since the continuous pulse oscillation operation was started. Discharge applied voltage rise measuring means for obtaining the rise amount of
A correspondence relationship between the concentration of impurities other than the laser gas and the discharge applied voltage increase amount is prepared in advance,
An impurity concentration measuring device for a laser device, comprising: an impurity concentration measuring means for obtaining an impurity concentration corresponding to the obtained increase in discharge applied voltage from the correspondence. The discharge applied voltage increase amount measuring means sets the discharge applied voltage between the discharge electrodes to the first predetermined level at the time when the first predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started. When the discharge applied voltage between the discharge electrodes rises to a second predetermined level at the time when the second predetermined number of pulses are oscillated after the continuous pulse oscillation operation is started, 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 measured as an increase amount of the discharge applied voltage with respect to the reference level. 4. The impurity concentration measuring apparatus for a laser device according to claim 3, wherein 5. The impurity concentration measuring apparatus for a laser device according to claim 1, wherein the impurity contains an oxygen element. 6. The impurity concentration measuring apparatus for a laser device according to claim 1, wherein xenon having a predetermined concentration is added to the laser gas.

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