JPH10173273A - Excimer laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excimer laser device which can obtain a uniform pulsed light output by controlling the power supply voltage from a laser discharge power source and halogen gas supply by giving the highest priority to the suppression of the fluctuation of each output energy. SOLUTION: Laser pulse oscillation is performed in a laser chamber 2 by exciting a laser gas by discharge and the emitted pulsed light is narrowed in band by means of a band narrowing unit 6. The band-narrowed pulsed light returns to the chamber 2 and is outputted as an oscillated laser beam L through a partially transmissive mirror 7 after the pulsed light is amplified in the chamber 2. The laser beam L is sampled through beam splitters 8 and 13 and made incident to a light receiving element 14. A CPU 15 detects the energy Ei of the laser beam L based on the output of the light receiving element 14 and controls a laser power source circuit 16 and gas supplying device 17. Therefore, an excimer laser device which can obtain a uniform pulsed light output by controlling the power supply voltage Vi by means of the laser power source circuit 16 and the laser gas supply to the chamber 2 by means of the gas supplying device 17 can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excimer laser device used as a light source for a stepper type or step & scan type reduction projection exposure apparatus, and more particularly, to a laser chamber in which a laser gas containing a halogen gas is filled. The present invention relates to an excimer laser device that performs pulse oscillation.

[0002]

2. Description of the Related Art
When an excimer laser device is operated using a halogen gas, the halogen gas is consumed due to the evaporation of the electrode material and the chemical reaction with the constituent materials of the laser chamber according to the operation. Therefore, conventionally, the following control has been performed to compensate for a decrease in laser output due to consumption of halogen gas.

[0003] That is, the output of the laser is obtained by applying electric energy stored in a capacitor to excite the laser into a discharge space and performing discharge in a laser medium gas. Increasing the value increases the laser output. Therefore, in the related art, the laser output is detected, and the charging voltage value is controlled in accordance with the detection to stabilize the laser output.
This control is usually called power lock control.

However, even with this control, if the operation is continued for a long time, the oscillation efficiency decreases due to consumption of the halogen gas, and a predetermined output cannot be maintained unless the charging voltage (power lock voltage) is gradually increased. .

To solve such a problem, Japanese Patent Application Laid-Open No. 3-166
In the publication No. 783, attention is paid to the fact that laser gas pressure values that maximize the oscillation efficiency (ratio of output laser energy to input power) exist for each charging voltage value, and charging is performed in accordance with the progress of laser oscillation. As the voltage increases, the charging voltage and the laser gas pressure are controlled so that the oscillation efficiency maintains the maximum value.

That is, this prior art is intended to control the charging voltage and the laser gas pressure such that the oscillation efficiency of the laser is the main focus and the oscillation efficiency always maintains the maximum value.

The technique according to the prior art is an effective method when an excimer laser is used for processing in which it is most important to increase the laser output as much as possible.

However, when an excimer laser is used in a stepper type or step & scan type reduction projection exposure apparatus, the problem is how to increase the laser output of each pulse (to increase the oscillation efficiency). The most important purpose is to obtain a pulse light having a uniform output.

In other words, according to the above-mentioned prior art, the charging voltage control and the laser gas supply control are not performed with a view to obtaining a uniform laser output, so that it is impossible to further improve the exposure accuracy. It is.

The present invention has been made in view of such circumstances, and has as its object to provide an excimer laser device capable of obtaining a uniform pulsed light output.

[0011]

According to the present invention, a laser gas containing a halogen gas is sealed in a laser chamber, and a pulse discharge is performed in the laser chamber to excite the laser gas to generate pulsed laser oscillation. In the excimer laser apparatus to be performed, a gas replenishing unit for replenishing the laser chamber with the laser gas, a variation measuring unit for determining a variation in output energy of each pulsed laser oscillation light, and a power supply voltage of the pulse discharge is maintained substantially constant. Power supply voltage control means and control means for controlling the gas replenishing means so that the calculated variation falls within a predetermined target value range to replenish the halogen gas are provided.

According to the present invention, the supply of the halogen gas is controlled not by giving priority to the output energy of each pulsed light but by giving top priority to suppressing the variation of each output energy. Further, the power supply voltage of the laser discharge power supply is maintained at a substantially constant value. That is, the power supply voltage is kept almost constant without changing the power supply voltage, which causes the output variation to increase, and the halogen gas partial pressure aiming at the halogen gas partial pressure at which the variation of the laser output becomes a minimum value or a value close to the minimum value. The gas supply control is performed.

Therefore, according to the present invention, the variation in the output of each pulsed light can be suppressed to a minimum, and the excimer laser device of the present invention is applied to a light source for a reduced projection exposure apparatus for performing reduced projection exposure of a semiconductor. By doing so, it becomes possible to perform a highly accurate exposure process.

According to the present invention, there is provided an excimer laser apparatus which encloses a laser gas containing a halogen gas in a laser chamber and performs pulse discharge in the laser chamber to excite the laser gas to perform pulsed laser oscillation. Gas replenishing means for replenishing the laser gas to the laser chamber, variation measuring means for determining variation in output energy of each pulsed laser oscillation light,
Power supply voltage control means for adjusting and controlling the power supply voltage of the pulse discharge based on past oscillation history; and halogen gas supply by controlling the gas supply means so that the calculated variation falls within a predetermined target value range. Control means.

According to the invention, the laser power supply voltage is adjusted and controlled for each pulse oscillation based on the past oscillation history. However, even with this control, the power supply voltage does not fluctuate so much and is almost constant. State.

Therefore, according to the present invention, it is also possible to minimize the variation in the output of each pulsed light, and to use the excimer laser device of the present invention as a light source for a reduced projection exposure apparatus for performing reduced projection exposure of a semiconductor. If applied, the exposure processing can be performed with high precision.

[0017]

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

First, the outline of the main part of the present invention will be described with reference to FIG.

FIG. 4 shows a KrF excimer laser.
Laser power supply voltage V and total gas pressure P in laser chamber
The graph shows the output laser beam energy E and the variation (standard deviation) σ of the output laser beam energy corresponding to the fluorine gas partial pressure PF2 when the GA is substantially constant.
That is, the fluorine gas partial pressure PF2 (F in the laser chamber)
The output laser light energy E and the variation (standard deviation) σ of the output laser light energy are plotted on the vertical axis.

According to FIG. 4, the laser output E is F2
When the partial pressure is the predetermined value Pe, the maximum value is obtained (the efficiency is maximum), and when the partial pressure is lower than the partial pressure value Pe, it monotonically increases.
At a partial pressure higher than this partial pressure value Pe, it decreases monotonically.

On the other hand, the standard deviation σ of the laser output takes a minimum value when the F2 partial pressure is a predetermined value Pf, and monotonically decreases at a partial pressure lower than the partial pressure value Pf, and is higher than the partial pressure value Pf. The partial pressure increases monotonically.

In the characteristics shown in FIG. 4, the phenomenon that the inventor of the present application focused on is that Pe ≠ Pf. In the present invention, the laser output (oscillation efficiency) is sacrificed somewhat, but the output variation σ is minimized. The F2 gas supply control is performed by setting the fluorine partial pressure value Pf to be the highest priority target value.

In FIG. 4, σc is an allowable limit value of the output variation (an allowable upper limit value).
The F2 partial pressure corresponding to c has two values, PMIN and PMAX.

Next, the output variation σ of the excimer laser
Are the laser power supply voltage V, the total gas pressure PGA in the laser chamber, and the halogen gas partial pressure PF2 in the laser chamber.
Change in response to a change in such a parameter.

FIG. 5 shows that the power supply voltage V is changed to three different values.
FIG. 5 shows the relationship between the fluorine partial pressure value Pf and the total gas pressure PGA that minimizes the variation σ when 1, V2, and V3 (V1>V2> V3). PGA
Until the pressure reaches a predetermined value PG1, the fluorine partial pressure value Pf that minimizes the variation σ is almost constant even if the total pressure value PGA increases, and when PGA> PG1, the fluorine partial pressure value Pf becomes the total pressure. It shows a decreasing trend in response to an increase in PGA. This property is common across the respective power supply voltage values V1, V2, V3, as shown in FIG. Also, according to FIG. 5, the fluorine partial pressure value P that minimizes the variation σ in response to the increase in the power supply voltage V
f increases.

FIG. 6 shows three types of power supply voltages V
The graph shows output variation characteristics when 1, V2, and V3 (V1>V2> V3). According to FIG.
As the power supply voltage V increases, the fluorine partial pressure value Pf that minimizes the variation σ increases (Pf3 <Pf2 <Pf1), and the variation value σ itself decreases with an increase in the power supply voltage V ( σ1 <σ2 <σ3). It can also be seen that the difference in the Pf value itself corresponding to the same power supply voltage difference is smaller in the region where the power supply voltage is high than in the region where the power supply voltage is low (Pf3−Pf2 <Pf2−Pf1).

FIG. 7 shows that the total gas pressure PGA is set to five different values P1, P2, P3, P4, P5 (P1>P2>P3>P4> P5).
3 shows output variation characteristics in the case of.
According to FIG. 7, as the total pressure PGA increases, the fluorine partial pressure value Pf that minimizes the variation σ decreases as the total pressure PGA increases (Pfa
<Pfb <Pfc) and the variation value σ itself also increases (σa>σb> σc). Further, when the total pressure PGA becomes a value equal to or less than a certain value (in this case, PGA <P3), the variation value σ and the fluorine partial pressure value Pf that minimizes the variation σ become almost the same value and do not change. found.

As described above, according to FIGS. 4 to 8, it is understood that the power supply voltage V is preferably large and the total gas pressure PGA is preferably small in order to keep the variation σ as small and constant as possible. . It is true that the variation σ fluctuates depending on parameters such as the fluorine partial pressure Pf, the gas total pressure PGA, and the power supply voltage V. However, FIGS. 5 to 8 are merely measurement results of a single laser device. In some laser devices, the variation σ decreases as the power supply voltage V decreases or the total gas pressure PGA increases.

FIG. 8 shows a narrow-band excimer laser to which the present invention is applied.

In FIG. 8, a laser chamber 2 of the excimer laser 1 has a discharge electrode and the like (not shown), and a halogen gas such as F 2, a rare gas such as Kr, and a buffer gas such as Ne are sealed in the laser chamber 2. The laser gas is excited by the discharge between the discharge electrodes to perform laser pulse oscillation. The emitted pulse light is applied to the band narrowing unit 6 (in this case, the prism beam expander 3,
4, including the grating 5), is returned to the laser chamber 2, is amplified again, and is output as the oscillation laser light L via the partially transmitting mirror 7.
Part of the output light returns to the laser chamber 2 again, and laser oscillation occurs.

A part of the oscillated laser light L is sampled by the beam splitter 8, and then is incident on the etalon spectroscope 9 through the light diffusion plate 18, where
To form a concentric fringe pattern. The etalon spectroscope 9 also receives reference light of a known wavelength in advance, and the CPU 11 compares the reference light formed on the light receiving element 10 with the fringe pattern of the laser light L to determine the wavelength of the output laser light L. And the spectrum width. The CPU 11 outputs the measured wavelength and spectrum width data to the wavelength controller 12. The wavelength controller 12 adjusts and controls the laser oscillation wavelength by changing the angle of the grating 5 based on the input wavelength and spectrum width data, thereby changing the light incident angle on the grating 5 which is a wavelength selection element.

On the other hand, a part of the laser light transmitted through the beam splitter 8 is further sampled by the beam splitter 13 and incident on the light receiving element 14. CPU
At 15, the light energy Ei of each pulse oscillation is detected based on the light receiving output of the light receiving element 14, and the laser power supply circuit 16 and the gas replenishing device 17 are controlled based on the output Ei. In the laser power supply circuit 16, the power supply voltage Vi is controlled,
In the gas supply device 17, the supply of the laser gas to the laser chamber 2 is controlled.

FIG. 9 shows various specific examples of the gas supply device 17.

9 (a) to 9 (d), two gas cylinders 20, 21 are used.
F2, Kr, and Ne are α: b: c (α = n · a, n>
The other gas cylinder 21 is filled at a molar ratio of 1).
Is filled with Kr and Ne in a molar ratio of b: c.

That is, when injecting a laser gas into the laser chamber 2 (when initially filling the laser chamber in a vacuum state with gas, or when replenishing the gas halfway when the output variation σ is outside the allowable range), 2 By injecting a predetermined amount of gas from one of the gas cylinders 20 and 21 into the laser chamber 2, the F 2 gas injected from the gas cylinder 20 is diluted by the gas injected from the other cylinder 21, and as a result, Is an ideal mixture ratio a: b: c. It should be noted that the same effect can be obtained by replenishing gas only from the gas cylinder 20 when replenishing gas in the middle.

If the total pressure of the gas in the laser chamber rises excessively during gas replenishment, the exhaust valve 22 is opened to exhaust a part of the gas so that the total pressure in the laser chamber becomes a predetermined pressure. They are adjusted so that they can be maintained. Also,
The total gas pressure measuring device 40 measures the total gas pressure in the laser chamber 2 and is used for controlling to maintain the total pressure at a predetermined pressure.

In FIG. 9A, the on-off valve 2
The supply of gas is controlled by 3 and 24, and the gas flow rate is adjusted by adjusting the opening and closing time of the on / off valves 23 and 24.

In FIG. 9B, sub-tanks 25 and 26 are provided in the gas supply path,
On / off valves 27 and 28 are provided on the downstream side of 26.

In FIG. 9C, mass flow controllers (mass flow controllers) 29 and 30 are provided in the gas supply path. This mass flow controller 2
Numerals 9 and 30 control the amount of gas passing so that the mass flow rate becomes a desired constant value. In the case of the configuration of FIG. 9 (c), the gas flow rate can be controlled with high accuracy by setting the flow rates of the mass flow controllers 29, 30 to be constant and adjusting the opening / closing time of the on / off valves 23, 24. become. The gas flow rate may be controlled only by the mass flow controllers 29 and 30 without the on / off valves 23 and 24.

In the configuration of the gas replenishing device 17, if the distance between the injection port for injecting the laser gas into the laser chamber and the exhaust port for exhausting the laser gas to the outside of the laser chamber is made as far as possible, the supply is made possible. It is possible to reduce the amount of exhausting the new gas as it is.

Next, a method of obtaining the output variation (standard deviation) σ will be described with reference to FIGS.

As described above, since the excimer laser is a so-called pulse discharge excitation gas laser, the laser oscillation has a pulse oscillation as shown in FIG. Note that FIG.
In the time chart, pulse oscillation is shown when an excimer laser is used as a light source of a semiconductor exposure apparatus. Therefore, the operation state includes a continuous pulse oscillation operation in which laser light is continuously pulsed a predetermined number of times, and a predetermined pulse oscillation operation. This is a burst mode in which a pulse oscillation is suspended for a period of time and an oscillation suspension time t is repeated.

FIG. 11 shows a plurality of IC chips TP
Shows a semiconductor wafer W on which a plurality of (several hundred or more) pulse lights are irradiated to one IC chip TP on the semiconductor wafer W in the stepper type exposure. Upon completion, the wafer W or the optical system is moved so that the next unirradiated IC chip TP is irradiated with the continuous pulse light, and the same light irradiation as described above is performed after this stage movement. While performing such exposure and stage movement alternately, all the IC chips TP on the semiconductor wafer W
When the exposure of the wafer W is completed, the exposed wafer W is carried out, the next wafer W is set at the irradiation position, and the same light irradiation as described above is repeated.

As described above, in the stepper type semiconductor exposure apparatus, the exposure and the stage movement are alternately repeated, so that the operating state of the excimer laser which is the light source of the exposure apparatus is necessarily as shown in FIG. Burst mode.

FIG. 12 is an enlarged view of the pulse train within one burst period shown in FIG. The energy of each pulse light is Ei (i = 1, 2,...), And the number of pulses in one set for obtaining the variation σ is Ns.

In this case, a standardized value ε obtained by dividing the standard deviation σ as the variation data by the average value EA of the pulse output is used.
(= 3 · σ / EA) is used. That is, the standard deviation σ and the output average value EA are set for each set including the Ns pulses.
Is calculated, and the calculated standard deviation σ and output average value EA are calculated.
Is used to calculate the variation data ε.

The standard deviation σ is obtained as follows.

First, the integrated value ET of the light energy of Ns pulses is obtained according to the following equation. Note that Σ (i = 1, Ns)
Is a symbol meaning that integration is performed from i = 1 to i = Ns.

ET = Σ (i = 1, Ns) Ei = E1 + E2 + E3 +... + ENs Next, the average value EA of these Ns pulsed light outputs is determined according to the following equation.

EA = ET / Ns Next, using the average value EA obtained above, the standard deviation σ of these Ns pulses is obtained according to the following equation (1).

[0051] Thus, in the case of the stepper method, 1 to Ns, Ns + 1
Σ is determined for each set of ２2Ns, 2Ns + 1、２3Ns.

Next, using the standard deviation σ and the output average value EA obtained above, an output variation ε is obtained according to the following equation.

Ε = 3 · σ / EA (2) Next, a method of obtaining the standard deviation σ by the step & scan method will be described.

That is, in the stepper method, exposure is performed while the stage is stopped, whereas in the step & scan method, exposure is performed while moving the stage, which has the advantage that a large area can be exposed. .

That is, in this step & scan method, one pulse laser (an elongated sheet called a sheet beam) is applied so that a predetermined number N 0 of pulse lasers are set in advance at all points on the IC chip TP. Processing is performed while shifting the irradiation area of the pulse laser beam on the workpiece by a predetermined pitch every time a beam having a rectangular cross-sectional shape is incident. That is, as shown in FIG. 13, the irradiation area of each sheet beam (the area indicated by E1, E2, E3,...) Is smaller than the area of the IC chip 31, and these pulsed laser beams are sequentially arranged at a predetermined pitch ΔP Are scanned while being superimposed, and a predetermined number N0 of sheet beams are incident on each point, and the entire surface of the IC chip TP is exposed.

For example, in FIG. 13, N0 = 4, point A is exposed by the integrated energy of four pulsed laser beams E1, E2, E3 and E4, and point B is four pulsed laser beams E2, The exposure is performed by the integrated energy of E3, E4 and E5. The following points C are similarly exposed by the integrated energy of the four pulsed laser beams.

Therefore, when the standard deviation σ is obtained by such a step-and-scan method, the number of pulses Ns = No of one set for obtaining the standard deviation σ is obtained by the above (1).
The standard deviation may be obtained using an equation. Also,
Variations may be obtained by using the total number of sheet beams irradiated to one IC chip as one set.

Hereinafter, a first embodiment of the supply control of the halogen gas will be described with reference to the flowcharts of FIGS.

In the first embodiment, the power supply voltage V is maintained at a substantially constant value, and the variation σ of the laser output is reduced to the minimum value σ.
The supply control of the halogen gas is controlled so as to have a value near min.

Here, in order to control the output variation σ to be always smaller than σc, the F2 partial pressure value PF2 must be equal to PM.
It is necessary to control so as to be between IN and PMAX.

However, as shown in FIG.
Is not a linear relationship, therefore, if the output variation value σ becomes close to σc during the control, it is not necessary to determine whether this state is closer to the fluorine partial pressure PMIN or PMAX. Cannot determine whether to supply the F2 gas. That is, when the partial pressure of F2 is smaller than PMIN, it is necessary to supply the F2 gas. When the partial pressure of F2 is larger than PMAX, there is no need to supply the F2 gas.

Therefore, if attention is paid to the fact that the amount of F2 gas decreases with the progress of laser pulse oscillation, the above-mentioned problem can be solved by performing the following control.

That is, after the laser gas is replenished in the laser chamber, or after all the laser gas in the laser chamber is replaced with a new laser gas, the F2 gas is decreasing as the laser pulse oscillation progresses. If the output variation .sigma. Is monitored after the gas replenishment or gas replacement, it is possible to determine which position on the .sigma. Curve in FIG.

For example, at the time of gas replenishment or gas exchange,
If the partial pressure of F2 in the laser chamber is set to a value between PMAX and Pf (for example, a partial pressure slightly lower than PMAX), the halogen gas decreases as the number of laser oscillations increases. Correspondingly, the variation value σ moves along the arrow F on the σ curve in FIG.
That is, since σ continues to decrease from the value corresponding to the partial pressure value slightly lower than PMAX and reaches the minimum value σMIN and then starts increasing, the F2 gas is supplied when σ = σc is reached thereafter. By doing so, the output variation value σ can be controlled to σc or less.

Hereinafter, the above control will be described in detail with reference to FIG.

First, the operator sets the number of data Ns and the permissible limit value St of the variation value for obtaining the variation to appropriate values (step 100). Note that the allowable limit value St of the variation value is a threshold value for comparison with the output variation ε and is a value corresponding to σc in FIG. St is, for example, 7%
It is set to a predetermined numerical value such as.

Next, the operator sets the power supply voltage Vc, the total gas pressure PGA, and the halogen gas partial pressure Pf that can keep the output variation ε as small as possible from the relationships shown in FIGS. 4 to 8 (step 110). . That is, as can be seen from FIG. 6, the power supply voltage Vc is set to be as small as possible in view of the output energy E (the output energy increases as the power supply voltage increases) in order to reduce the output variation σ. Is desirable.

As can be seen from FIG. 7, the total gas pressure PGA
However, in order to reduce the output variation σ, it is desirable to make it as small as possible.

The target fluorine partial pressure Pf is determined by the output variation σ according to the set charging voltage Vc and the total gas pressure PGA.
Is set to the fluorine partial pressure value Pf that minimizes the pressure.

Then, the laser gas is initially charged into the laser chamber so that the total gas pressure PGA and the halogen gas partial pressure Pf are set as described above (the vacuum laser chamber which has been passivated is filled with new gas). .

Next, the CPU 15 determines whether or not to execute the gas supply subroutine by referring to the flag FL.
AG, the counter value i of the counter that counts the current pulse oscillation number in the burst cycle, and the count value ET of the integration counter that sequentially integrates the output energy Ei of each oscillation pulse are initialized to 0 (steps 120 and 13).
0).

Next, after incrementing the pulse counter value i by 1 (step 140), the CPU 15 starts pulse oscillation. The power supply voltage value V at this time is the set voltage value Vc.
The power supply voltage Vc is maintained during the subsequent pulse oscillation (step 150). And CP
U15 measures and stores the output energy Ei of the first oscillation pulse (step 150). Further, the measured output energy Ei is added to the previous pulse energy integrated value ET (= 0 in this case), and the addition result ET +
The integrated counter value ET is updated with Ei (step 16).
0). Next, it is determined whether or not the pulse count value i matches the set value Ns (step 170).
Repeat step 0.

Thereafter, when the pulse oscillating operation proceeds and the pulse count value i matches Ns, the CPU 15 calculates the standard deviation σ of these Ns oscillating pulses according to the above equation (1), The average output value EA (= ET / Ns) of the output of the oscillation pulse is calculated, and the standard deviation σ is divided by the output average value EA to standardize the output variation ε (= 3 · σ / EA). (Step 18)
0).

Then, the CPU 15 compares the calculated output variation ε with the set allowable limit value St. As a result of this comparison, if the output variation ε is within the range of the set value St (ε ≦ St), the halogen gas supply is not necessary, so the procedure shifts to step 120 and the flag FL
After setting AG to 0, the procedure of steps 130 to 170 is repeated to calculate the output variation ε of the next Ns pulse oscillations.

However, in the determination at step 190,
If ε> St holds, it is determined whether or not the flag FLAG = −1. If the flag FLAG is -1, it is determined that the F2 partial pressure is equal to or higher than PMAX, and the procedure shifts to step 130 without refilling the halogen gas. Is calculated. That is, when the flag FLAG = -1, the pulse oscillation is continued without replenishing the F2 gas, whereby the F2 gas is naturally reduced along the arrow Q in FIG. The F2 gas itself is reduced by reacting with a material such as an electrode to form a fluoride), and the output variation ε is made smaller than the set value St by natural decrease of the F2 gas.

In step 200, the flag FLAG = -1
If halogen gas replenishment is performed when
Since the F2 partial pressure increases, the output variation ε increases further along the arrow R in FIG.

Next, the flag FLAG
If not, the flag FLAG is set in the next step 210.
= 1 is set, and if the flag FLAG is not 1, the flag FLAG is set to 1 (step 240).
The gas supply subroutine shown in FIG. 2 is executed (step 250). This gas supply subroutine will be described later.

On the other hand, if the flag FLAG = 1 in step 210, the variance εk-1 of the previous set calculated before is compared with the variance εk of the current set calculated this time, and εk-1> ε
If it is k, it is determined that the variation ε along the arrow S in FIG. 4 has been reduced by the previous gas replenishment, and the procedure shifts to step 250 to execute the gas replenishment subroutine to further replenish the gas. Execute

However, at step 220, εk-1
If ≤εk is satisfied, it is determined that the variation ε along the arrow R in FIG. 4 has increased, the flag FLAG is set to −1 (Step 230), and the procedure is shifted to Step 130. , Without refilling halogen gas
Thereafter, the variation ε of the next set is calculated. That is,
In this case, the pulse oscillation is continued without replenishing the F2 gas, whereby the F2 gas is naturally reduced along the arrow Q in FIG. 4, and the variation ε is made smaller than the set value St by the natural reduction of the F2 gas. It is.

According to the control procedure shown in FIG. 1, ε ≦ S
If it is t (NO in step 190), the F2 gas is not supplied.

When it is determined that ε> St and PF2 ≧ PMAX (the determination in step 200 is YE
At the time of S or when the determination at step 220 is NO),
Wait for the natural decrease of F2 gas without supplying F2 gas.

However, ε ≧ St and PF2 <PMIN
Is determined to be (the determination in step 210 is N
At the time of O or when the determination at step 220 is YES), the supply control of the F2 gas is executed until ε <St.

In the control procedure shown in FIG. 1, when ε exceeds the maximum allowable value St, an abnormal signal is output, and this abnormal signal is transmitted to the semiconductor exposure apparatus, and the excimer laser emission side is output. May be closed to interrupt the exposure process. In this case, after that, when ε <St, the shutter may be opened to restart the exposure processing.

Further, a region where the laser oscillation efficiency is high, that is, F
If the two-part pressure value is controlled so as to be between Pf and PMAX in FIG. 4, the laser output variation σ can be reduced and the laser oscillation efficiency can be kept in a high range.

Next, the gas supply subroutine will be described with reference to FIG.

The gas replenishment subroutine includes two methods, a method of not exhausting gas and a method of exhausting gas to maintain the total pressure within a predetermined range.

That is, when the partial pressure of F2 of one gas cylinder 20 of the gas replenishing device 17 shown in FIG. 5 is increased to about 5%, as described above, both gas cylinders 20,
The gas supply is performed by using the gas supply 21. In this case, since the gas supply amount is small, the exhaust step can be omitted. On the other hand, when the F2 partial pressure of the gas cylinder 20 is set to be as low as about 1%, a large amount of gas is supplied using only the gas cylinder 20, and the increase in the total pressure is reduced by exhaust.

The gas replenishment subroutine shown in FIG. 2A is a case in which gas exhaust is not performed. When the gas replenishment subroutine is started, the halogen gas is supplied using the two gas cylinders 20 and 21. That is, the halogen gas partial pressure in the laser chamber is a low value of 0.3% or less, and the gas supply amount in this case is small. Therefore, the gas supply amount is offset by the halogen gas consumption amount, and the total gas pressure is reduced. The gas exhaust process is omitted because it is considered to be substantially constant. However, even in such a case, when the number of times of gas supply increases, the total gas pressure exceeds the pressure P3 in FIG.
, And when this occurs, the minimum value of the variation value is also increased by the increase in the total pressure, so that (σc → σ
b), even if the halogen gas is supplied, the variation σ does not decrease but increases. That is, the range of the value of σ is not affected by the total pressure PGA (PF2 ≦
If the halogen gas replenishment control is performed in P3), the value of σ can be reduced by replenishing the halogen gas, but if the halogen gas replenishment is repeated,
The total pressure rises and finally reaches the characteristic of pressure P2 in FIG.

In this embodiment, since the variation σ (or ε) is monitored, if the phenomenon that σ (or ε) increases when the halogen gas is supplied is determined, the above total pressure can be determined. Can be grasped. Therefore, when such a total pressure increase phenomenon occurs, if the laser oscillation is continued and the halogen gas partial pressure inside the laser chamber is continuously reduced, the value of σ becomes the value indicated by the arrow U in FIG.
And eventually enters a range smaller than σc. At that time, the above-described control for replenishing the halogen gas according to the value of σ may be started again.

Next, the gas replenishment subroutine shown in FIG. 2 (b) is a case where a gas exhaust step is performed. When the gas replenishment subroutine is started, first, a part of the gas in the laser chamber is partially exhausted (step 300). That is, by performing gas exhaustion before gas replenishment, a gas containing laser-oscillated impurities is exhausted. Next, F2, Kr and Ne are supplied by the gas replenishing device 17 shown in FIG.
By supplying a predetermined amount of the mixed gas into the laser chamber 2, the halogen gas F2 is supplied into the laser chamber (step 310). After the replenishment, the total pressure PGA in the laser chamber is measured by the total pressure measurement sensor 40 (step 320), and when the measured value becomes larger than the predetermined set pressure Pga1 (step 33).
0), and the gas in the laser chamber 2 is exhausted (step 340).

When the total pressure PGA in the laser chamber rises, the power supply voltage value for keeping the output light energy constant decreases, and if the voltage value is monitored, the total voltage in the laser chamber can be reduced. The pressure PGA will be measured indirectly. In this case, the total pressure sensor 40 is not always necessary.

That is, if the total gas pressure in the laser chamber rises too much, as can be seen from FIG. 7, the variation value σ itself also rises, and there is a possibility that σ exceeds the allowable upper limit σc. Further, if the total gas pressure in the laser chamber rises too much, the fluorine partial pressure PF2 decreases, and the laser oscillation efficiency (output laser light energy E) drops extremely (see FIG. 4). Therefore, according to the gas replenishment routine of FIG. 2B, in order to eliminate the above-mentioned phenomenon, a part of the gas is exhausted from the laser chamber, and the total gas pressure is always kept within a predetermined pressure Pga1. (For example, about P3 in FIG. 7).

Next, a second embodiment of the halogen gas supply control will be described with reference to FIG.

In the second embodiment, in order to make each pulsed light energy as constant as possible, the power supply voltage is controlled by the following equation using the past (in this case, the immediately preceding) oscillation history. I have.

Vi = Vi-1 + G * (Er-Ei-1) Vi: power supply voltage of the current pulse Vi-1: power supply voltage of the immediately preceding pulse G: gain Er: target value of pulse light energy Ei-1: immediately before Even though the power supply pressure reduction is controlled by the above-described control, the variation is actually very small, and the voltage is almost constant.

That is, in the flowchart of FIG. 3, step 100 of the flowchart of FIG. 1 is replaced with step 105, and step 165 is added between step 160 and step 170 of FIG. Is exactly the same as the procedure in FIG.

In step 105 in FIG. 3, a target value Er of the pulse light energy is set in addition to the number of data Ns and the allowable limit value St of the variation value when obtaining the variation. The Er value may be set by an operator, or may be automatically given from the semiconductor exposure apparatus.

In step 165 of FIG.
After the pulse oscillation of the pulse, the power supply voltage value VI + 1 at the time of the next pulse oscillation is calculated from the monitored oscillation energy value Ei of the pulse and the power supply voltage value Vi at that time according to the following equation. I have. The next pulse oscillation is performed by the calculated power supply voltage value Vi + 1.

Vi + 1 = Vi + G × (Er−Ei) In the second embodiment, (1)) N (for example, N = 2, N = 3, etc.) The pulse energy value Pi-N of the previous pulse and the charging voltage Vi-N at that time, (2) the average value of the pulse energies Pi to Pi + n of n pulses having pulse numbers smaller than the pulse number of the pulse (3) The pulse energy value Pi of the pulse in the same pulse sequence one burst cycle before the pulse and the charging voltage Vi at that time are used. You may do so.

The following control is also possible as the halogen gas supply control.

That is, while monitoring the output variation ε, the halogen gas is continuously and continuously (smallly) supplied little by little into the laser chamber so that the value of ε does not greatly deviate from the minimum value. Also in this control, the total pressure continues to increase, and eventually exceeds the value P3 in FIG. 7, and the supply of the halogen gas causes only the increase in ε. Therefore, in this case, when the above state is detected, a part of the gas is exhausted from the inside of the laser chamber to reduce the total pressure, and desirably, the total pressure is reduced to the value P3 or less in FIG. What should I do?

In addition, when the halogen gas is supplied, the gas is exhausted at the same time, so that the total gas pressure in the laser chamber can hardly be changed.

In the above embodiment, the value ε obtained by dividing the standard deviation σ of the Ns oscillation pulses by the average value EA (= ET / Ns) of the Ns oscillation pulses is used as the output variation value. However, the standard deviation σ may be used as the output variation.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a gas supply subroutine.

FIG. 3 is a flowchart showing a second embodiment of the present invention.

FIG. 4 is a graph showing the relationship between output variation and output energy with respect to fluorine partial pressure.

FIG. 5 is a graph showing the relationship between the total gas pressure and a fluorine partial pressure value that minimizes output variations.

FIG. 6 is a graph showing a relationship between a partial pressure of fluorine and output variation using a power supply voltage as a parameter.

FIG. 7 is a graph showing the relationship between the partial pressure of fluorine and output variation using the total gas pressure as a parameter.

FIG. 8 is a block diagram illustrating a configuration example of an excimer laser device.

FIG. 9 is a block diagram showing various configuration examples of a gas supply device.

FIG. 10 is a time chart showing a state of pulse oscillation in a burst operation.

FIG. 11 is a diagram showing a state of exposure processing on a wafer.

FIG. 12 is a view for explaining a method of obtaining a variation value within one burst period.

FIG. 13 is a view for explaining a step-and-scan method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Excimer laser apparatus 2 ... Laser chamber 3, 4 ... Prism beam expander 5 ... Grating 6 ... Narrowing unit 7 ... Partial transmission mirror 8, 13 ... Beam splitter 9 ... Etalon spectroscope 10, 14 ... Light receiving element 11, 15 CPU 12 Wavelength controller 17 Gas replenishing device 20, 21 Gas cylinder 23, 24 On-off valve 25, 26 Sub-tank 29, 30 Mass flow controller

Claims (23)

[Claims] An excimer laser device for sealing a laser gas containing a halogen gas in a laser chamber and performing pulse discharge in the laser chamber to excite the laser gas to perform pulsed laser oscillation. A gas replenishing unit for replenishing the laser gas; a variation measuring unit for determining a variation in output energy of each pulsed laser oscillation light; a power supply voltage control unit for maintaining a power supply voltage of the pulse discharge substantially constant; An excimer laser device comprising: a control unit that controls the gas replenishing unit so that the variation falls within a predetermined target value range to replenish the halogen gas. 2. The variation measuring means: an output energy detecting means for detecting output energy of the pulsed laser oscillation light in pulse units; and an output variation of each pulsed oscillation light based on a detection output of the output energy detecting means. The excimer laser device according to claim 1, further comprising: a variation calculating means. 3. The excimer laser device according to claim 2, wherein said variation calculating means obtains a standard deviation of the output energy of a predetermined number of pulsed oscillation lights, and sets the standard deviation as an output variation value. 4. The variation calculation means calculates a standard deviation and an average value of output energies of a predetermined number of pulsed light beams, and sets a value obtained by dividing the standard deviation by an average value as an output variation value. 3. The excimer laser device according to 2. 5. The variation in the output energy of each pulsed laser oscillation light takes a predetermined minimum value corresponding to the partial pressure of the halogen gas in the laser chamber, and the limit value of the target value range is: A first value smaller than the halogen gas partial pressure value corresponding to the minimum value; and a second value larger than the halogen gas partial pressure value corresponding to the minimum value. When the calculated output variation is out of the target value range, the state at that time is a state where the current halogen gas partial pressure is smaller than the first value or the current halogen gas partial pressure value. 2. The excimer laser device according to claim 1, wherein it is determined whether or not is larger than the second value, and only in the former case, the gas control means is controlled to supply the halogen gas. 6. An exhaust unit for exhausting a laser gas in the laser chamber, wherein the control unit causes the exhaust unit to perform an exhaust operation before the halogen gas is supplied by the gas supply unit. The excimer laser device as described in the above. 7. An exhaust unit for exhausting a laser gas in the laser chamber, wherein the control unit causes the exhaust unit to perform an exhaust operation while the gas supply unit supplies the halogen gas. The excimer laser device as described in the above. 8. A gas total pressure measuring means for measuring a total pressure of a laser gas in the laser chamber, wherein the control means comprises a gas total pressure in the laser chamber based on a measured value of the gas total pressure measuring means. 8. The excimer laser device according to claim 6, wherein gas supply by said gas supply means and gas exhaustion by said exhaust means are controlled such that does not exceed a predetermined upper limit. 9. The excimer laser device according to claim 1, wherein said control means outputs an abnormal signal when said calculated variation falls outside a predetermined target value range. 10. The gas supply means has a gas supply source containing a halogen gas, a rare gas and a buffer gas, and the partial pressure of the halogen gas in the gas supply source is larger than the partial pressure of the halogen gas in the laser chamber. Is set to
2. The excimer laser device according to claim 1, wherein a partial pressure ratio between the rare gas and the buffer gas in the gas supply source is set to substantially the same value as a partial pressure ratio between the rare gas and the buffer gas in the laser chamber. 11. The gas supply means has a first gas supply source containing a halogen gas, a rare gas and a buffer gas, and a second gas supply source containing a rare gas and a buffer gas.
The partial pressure of the halogen gas in the first gas supply source is set to a value larger than the partial pressure of the halogen gas in the laser chamber, and the partial pressure ratio between the rare gas and the buffer gas in the first and second gas supply sources is respectively set. 2. The excimer laser device according to claim 1, wherein the partial pressure ratio between the rare gas and the buffer gas in the laser chamber is set to substantially the same value. 12. An excimer laser device which encloses a laser gas containing a halogen gas in a laser chamber and performs pulse discharge in the laser chamber to excite the laser gas to perform pulsed laser oscillation. Gas replenishing means for replenishing the laser gas, variation measuring means for determining variation in output energy of each pulsed laser oscillation light, and power supply voltage control means for adjusting and controlling the power supply voltage of the pulse discharge based on past oscillation history. An excimer laser device comprising: a control unit that controls the gas replenishing unit to replenish the halogen gas so that the calculated variation falls within a predetermined target value range. 13. The variation measuring means: an output energy detecting means for detecting the output energy of the pulsed laser oscillation light in pulse units; and an output variation of each pulsed oscillation light based on a detection output of the output energy detection means. 13. The excimer laser device according to claim 12, comprising: a variation calculating means. 14. The excimer laser device according to claim 13, wherein said variation calculating means obtains a standard deviation of output energies of a predetermined number of pulse oscillation lights set in advance, and uses the standard deviation as an output variation value. 15. The variation calculation means calculates a standard deviation and an average value of output energies of a predetermined number of pulsed light beams, and sets a value obtained by dividing the standard deviation by an average value as an output variation value. 14. The excimer laser device according to item 13. 16. The variation of the output energy of each pulsed laser oscillation light takes a predetermined minimum value corresponding to the partial pressure of the halogen gas in the laser chamber, and the limit value of the target value range is: A first value smaller than the halogen gas partial pressure value corresponding to the minimum value, and a second value larger than the halogen gas partial pressure value corresponding to the minimum value.
When the calculated output variation is out of the target value range, the state at that time is a state where the current halogen gas partial pressure is smaller than the first value. 13. The method according to claim 12, wherein it is determined whether or not the current halogen gas partial pressure value is greater than the second value, and only when the former is the former, the gas control means is controlled to supply the halogen gas. Excimer laser device. 17. The power supply voltage control means calculates a value obtained by adding a power supply voltage value at the time of the immediately preceding pulse oscillation to a deviation between a target value of the pulse energy and the pulse energy of the immediately preceding pulse oscillation as a current power supply voltage value. The excimer laser device according to claim 12, wherein 18. An exhaust unit for exhausting a laser gas in the laser chamber, wherein the control unit causes the exhaust unit to perform an exhaust operation before the halogen gas is supplied by the gas supply unit. Excimer laser device. 19. The apparatus according to claim 12, further comprising an exhaust unit for exhausting a laser gas in the laser chamber, wherein the control unit causes the exhaust unit to perform an exhaust operation while the halogen gas is supplied by the gas supply unit. The excimer laser device as described in the above. 20. A gas total pressure measuring means for measuring a total pressure of a laser gas in the laser chamber, wherein the control means controls a gas total pressure in the laser chamber based on a measurement value of the gas total pressure measuring means. 20. The excimer laser device according to claim 18, wherein gas supply by said gas supply means and gas exhaustion by said exhaust means are controlled such that does not exceed a predetermined upper limit. 21. The excimer laser device according to claim 12, wherein said control means outputs an abnormal signal when said calculated variation falls outside a predetermined target value range. 22. The gas replenishing means has a gas supply source containing a halogen gas, a rare gas and a buffer gas, and a partial pressure of the halogen gas in the gas supply source is larger than a partial pressure of the halogen gas in the laser chamber. Is set to
13. The excimer laser device according to claim 12, wherein a partial pressure ratio between the rare gas and the buffer gas in the gas supply source is set to substantially the same value as a partial pressure ratio between the rare gas and the buffer gas in the laser chamber. 23. The gas supply means has a first gas supply source containing a halogen gas, a rare gas and a buffer gas, and a second gas supply source containing a rare gas and a buffer gas.
The partial pressure of the halogen gas in the first gas supply source is set to a value larger than the partial pressure of the halogen gas in the laser chamber, and the partial pressure ratio between the rare gas and the buffer gas in the first and second gas supply sources is respectively set. 13. The excimer laser device according to claim 12, wherein the partial pressure ratio between the rare gas and the buffer gas in the laser chamber is set to substantially the same value.