JPH10190103A - Excimer laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always supply a halogen gas to an excimer laser device at appropriate timing by obtaining a uniform pulsed light output by controlling the supply of the halogen gas by not giving a priority to the output energy of each pulsed oscillating light, but to the suppression of the dispersion of each output energy. SOLUTION: The output E of an excimer laser device becomes the maximum when the partial pressure of an F2 gas is a prescribed value Pe and, when the partial pressure is lower than the value Pe, monotonously increases. When the partial pressure is higher than the value Pe, the output E monotonously decrease. On the other hand, the standard deviation σ of the output E becomes the minimum when the partial pressure of the F2 gas is a prescribed value Pf and, when the partial pressure is lower, than the value Pf, monotonously decreases. When the partial pressure is higher than the value Pf, the deviation σ monotonously increases. Therefore, the supply of the F2 gas is controlled by setting the partial pressure value Pf of fluorine which makes the dispersion σ of the output the minimum as the target value having the highest priority even when the output, namely, the oscillating efficiency of the laser device is sacrificed more or less. Therefore, the halogen gas can always be supplied to the laser at appropriate timing by adjusting the supplying timing of the halogen gas.

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 device to be performed, a gas replenishing means for replenishing the laser gas into the laser chamber, a variation measuring means for determining a variation in output energy of each pulsed laser oscillation light, and a target for setting a target upper limit of the variation value A range setting means, a variation monitor storage means for sequentially and continuously monitoring the measurement values of the variation measurement means, and a minimum value derivation for obtaining a minimum value of the variation value based on the monitoring result of the variation monitor storage means Means and the minimum value obtained by the minimum value deriving means. A target range updating means for changing a target upper limit value of the variation value set in the range setting means, and controlling the gas replenishing means so that the calculated variation falls within a target upper limit value set in the target range setting means. And a control means for replenishing the halogen gas.

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. In addition, by changing the target upper limit value of the variation value that determines the supply timing of the halogen gas according to the minimum value of the variation value at each time, the adjustment of the halogen gas supply timing is performed, and the halogen gas supply timing is always adjusted at an appropriate timing. Be able to supply.

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.

[0014]

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 FIGS.

FIG. 3 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, in FIG. 3, the horizontal axis represents the fluorine gas partial pressure PF2 (proportional to the molar concentration of the F2 gas in the laser chamber), and the vertical axis represents the output laser light energy E and the variation (standard deviation) σ of the output laser light energy. On the axis.

According to FIG. 3, 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 when the partial pressure is lower than the partial pressure value Pf, and is higher than the partial pressure value Pf. The partial pressure increases monotonically.

In the characteristic shown in FIG. 3, the phenomenon that the inventor of the present application has noticed is that Pe ≠ Pf. In the present invention, the output variation σ is minimized even though the laser output (oscillation efficiency) is somewhat sacrificed. The F2 gas supply control is performed by setting the fluorine partial pressure value Pf to be the highest priority target value.

In FIG. 3, σmax is an allowable maximum value of the output variation, and the F2 partial pressure corresponding to the allowable maximum value σmax has two values, PMIN and PMAX.
As will be described later, the allowable maximum value σmax is a true allowable limit value in the output variation suppression control. If the variation value σ exceeds the allowable maximum value σmax, an abnormal signal is output.

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. 4 shows that the power supply voltage V is set to three different values.
FIG. 4 shows the relationship between the fluorine partial pressure value Pf and the total gas pressure PGA that minimize 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 power supply voltage values V1, V2, V3, as shown in FIG. Further, according to FIG. 4, 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. 5 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). However, this FIG.
The characteristics shown in (1) vary from laser device to laser device. When the power supply voltage V increases, the fluorine partial pressure value Pf that minimizes the variation σ decreases, and when the power supply voltage V increases, the variation value σ itself increases. In some cases. Further, in the region where the power supply voltage is high, the difference in the Pf value itself corresponding to the same power supply voltage difference may be larger than in the region where the power supply voltage is low.

FIG. 6 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. 6, 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 is also large (σa>σb> σc). Further, when the total pressure PGA becomes a certain value or less (in this case, PGA <P3), the variation value σ and the fluorine partial pressure value Pf for minimizing the variation σ are almost the same value and do not change. . However, this FIG.
The characteristics shown in the table also vary from laser device to laser device.
As the value increases, the fluorine partial pressure value Pf for minimizing the variation σ may increase, and the variation value σ itself may decrease. Further, as the total pressure increases, the fluorine partial pressure value Pf that minimizes the variation σ decreases,
The variation σ itself may increase. Further, the fluorine partial pressure value P that minimizes the variation σ with the change in the total pressure
Both f and variation σ sometimes fluctuated.

As described above, according to FIGS. 3 to 7, since the variation σ also fluctuates at random with changes in the power supply voltage V and the total gas pressure PGA, it is necessary to make the variation σ as small and constant as possible. The power supply voltage V and the halogen gas partial pressure PF2 in the laser chamber are monitored while monitoring the variation value σ itself.
Need to be adjusted appropriately.

Here, according to the characteristic shown in FIG. 3, in order to control the output variation σ to be always smaller than σmax, control is performed so that the F2 partial pressure value PF2 is between PMIN and PMAX. There is a need.

However, as shown in FIG.
Is not a linear relationship, so even if the variation σ is monitored during the control, from this monitor output only,
It cannot be determined whether to supply F2 gas. That is, when the monitor value of the output variation σ becomes a value close to σmax, it is necessary to supply the F2 gas in order to determine whether the partial pressure of fluorine is closer to PMIN or PMAX. Can't decide what. When the partial pressure of F2 is smaller than PMIN, it is necessary to supply F2 gas. When the partial pressure of F2 is larger than PMAX, F2 gas is supplied.
There is no need to supply two gases.

Therefore, focusing on the fact that the amount of F2 gas decreases with the progress of laser pulse oscillation, the above 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, reaches the minimum value σmin, and then starts increasing, the F2 gas is supplied when σ = σmax thereafter By doing so, the output variation value σ can be controlled to σmax or less.

When laser oscillation is considered in the long term, there is a problem that the minimum value σmin (see FIG. 3) of the variation value σ itself increases due to wear of the laser electrode and the like.

That is, when the laser operation is repeated for a long period of time, the electrode elements and the like deteriorate, and the characteristic of the variation σ of the output energy greatly changes as shown in FIG.

For example, in FIG. 7, assuming that the curve K1 is the σ characteristic in the early stage when the laser device was introduced, after the laser operation has been performed for a long period of time, the σ characteristic becomes the curve K2 or K3. The characteristic changes as shown in FIG.
The local minimum value σmin rises (σmin1 → σmin2 → σm
in3).

Here, in the curve K1, it is desirable that σ itself be as small as possible. Therefore, the target upper limit value σM1 of the variation value for determining the halogen gas supply timing.
Is set to a value smaller than the permissible maximum value σmax (for generating an abnormal signal) of the variation described above, so that halogen gas can be supplied at a more appropriate timing. That is, in the curve K1, the output variation σ
Is controlled to be smaller than the target upper limit value σM1.

However, during such control (that is, during the control on the assumption that the output variation has the characteristic shown by the K1 curve), the σ characteristic becomes the characteristic shown by the curves K2 and K3 in FIG. , The halogen gas control is performed using the target upper limit value σM1 for the curve K1 as it is, and it becomes impossible to supply the halogen gas at an appropriate timing.

That is, in the curve K1, the F2 partial pressure values PF2 that achieve the target upper limit value σM1 are Pmn1 and Pmx1, and the intersection of these partial pressure values Pmn1 and Pmx1 with the curve K2 is u
1, u2, and the partial pressure values Pmn1, Pmx1 and the curve K3.
Intersections with u3 and u4, in particular, in the case of the curve K2, the halogen gas control is performed in a region not including the minimum value σmin2 of the variation.

In the case of the curves K2 and K3 in FIG. 7, the halogen gas control can be performed within the allowable maximum value .sigma.max even though the F2 partial pressure region of the halogen gas control is shifted. It is (intersections u1, u2,
The σ values corresponding to u3 and u4 are smaller than σmax), and depending on the curve, the intersection may exceed the allowable maximum value σmax. In such a case, the variation value is suppressed within the allowable maximum value σmax. Despite being able to do so, an abnormal signal is generated and the device must be stopped.

Therefore, in the present apparatus, when the variation characteristics change, the control range of σ, specifically, the target upper limit σMj (j = 1, 2,...) Is changed and set in accordance with the changed characteristics. I am trying to do it. That is, in the case of the curve K2,
ΣM2 is set as the target upper limit value, and the supply control of the halogen gas is performed so that σ becomes smaller than σM2 (Pmn2 ≦ PF2
≦ Pmx2), and in the case of the curve K3, σM
3, the supply control of the halogen gas is performed so that σ becomes smaller than σM3 (Pmn3 ≦ PF2 ≦ Pm
x3).

That is, in the present apparatus, the change of σ itself with time is continuously monitored in order to measure the fluctuation of σ itself and the minimum value σmin of σ. , Σ, the target upper limit value σMj is changed.

Specifically, when the minimum value of σ obtained from the monitoring result of σ changes from the minimum value of σ obtained immediately before, the predetermined value Σmin + Δ obtained by adding the set value Δσ (see FIG. 7) of
σ is reset as a new target upper limit value σMj.

That is, referring to FIG. 7, the following relationship is established: σM1−σmin1 = σM2−σmin2 = σM3−σmin3 = Δσ.

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

In FIG. 8, the laser chamber 2 of the excimer laser 1 has a discharge electrode and the like (not shown). The laser chamber 2 is filled with a halogen gas such as F 2, a rare gas such as Kr, and a buffer gas such as Ne. 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 enters the etalon spectroscope 9 through the light diffusion plate 18, where the lens 19
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. Note that the CPU 15 continuously monitors the output variation σ by using the detected light energy Ei of each pulse oscillation by a method described later.

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

In FIGS. 9A to 9D, two gas cylinders 20 and 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 target range), 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.

When 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, and 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 out of the laser chamber is made as far as possible, the supply can be performed. It is possible to reduce the amount of exhausting the new gas as it is. In FIGS. 9A, 9B, and 9C, reference numeral 40 denotes a total gas pressure detection sensor.

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.

That is, 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 in 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, the standardized value ε is obtained by dividing the standard deviation σ as the variation data by the average value EA of the pulse output.
(= 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).

[0064] 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, the 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 system, exposure is performed while the stage is stopped, whereas in the step & scan system, 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, a single pulse laser (an elongated sheet called a sheet beam) is applied so that a predetermined number N 0 of pulse lasers are respectively set 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 exposed to four pulsed laser beams E2, 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 in one set when the standard deviation σ is obtained, and the standard deviation σ is obtained by using the above equation (1). Should be obtained.
Further, the variation may be obtained by regarding 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, by continuously monitoring the variation σ of the laser output,
The minimum value σm is detected, the change of the minimum value σmin is grasped, and when the change of the minimum value σmin is detected, the minimum value σm
In accordance with the value of in, the target upper limit value σMj of the variation is varied according to the following equation.

ΣMj = σmin + Δσ In the first embodiment, the power supply voltage V is calculated by using the past (in this case, the immediately preceding) oscillation history in order to make each pulsed light energy as constant as possible. To control the power supply voltage.

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 voltage is controlled by the above-described control, the variation is actually very small, and becomes a substantially constant voltage value.

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

First, the operator selects an ideal σ characteristic adopted at the beginning of the laser operation. That is, the minimum value σmi of the variation as shown by the curve K1 in FIG. 3 or FIG.
Select the smallest possible characteristic pattern of n. Then, the power supply voltage V and the total gas pressure PGA for achieving the selected σ characteristic are set, and the laser operation is performed near these set values. That is, if the power supply voltage V and the total gas pressure in the laser chamber are kept within predetermined ranges, the σ characteristic does not fluctuate much in the short term. Therefore, when initially filling the laser chamber with a laser gas (filling the vacuum laser chamber with a new gas in the passivated vacuum laser chamber), the halogen gas is replaced with a partial pressure value (min) corresponding to the minimum value σmin of the selected σ characteristic. (Molar concentration) Pf, and other buffer gases are also filled by a preset predetermined partial pressure value to adjust the total gas pressure in the laser chamber to match the set value. If the set power supply voltage value V is used, a minimum value σmin of variation in the halogen gas partial pressure Pf is obtained.

In the embodiments described below,
It is assumed that the σ characteristic corresponding to the K1 curve in FIG. 7 is selected.

When the above pre-process is completed, the operator adds the number of data Ns to obtain the variation, the target value Er of the pulse light energy, the maximum allowable value σmax of the variation, and the additional amount Δσ for calculating the target upper limit value σMj of the variation. Is set to an appropriate value (step 100). The Er value is
The information may be automatically provided from the semiconductor exposure apparatus side.

Next, the operator adds the set value Δσ to the selected minimum value σmin1 of the variation of the σ characteristic, sets and stores the addition result σmin1 + Δσ as the target upper limit value σM1 (step 110).

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 increasing the pulse counter value i by 1 (step 140), the CPU 15 starts the first pulse oscillation. As the power supply voltage for the first pulse oscillation, a power supply voltage value V set to achieve the selected σ characteristic is adopted. Then, the CPU 15 measures and stores the output energy Ei of the first oscillation pulse (step 15).
0).

Further, the measured output energy Ei is compared with the previous pulse energy integrated value ET (in this case, =
0), and the addition result ET + Ei is used to calculate the integrated counter value E.
T is updated (step 160).

In the next step 170, a power supply voltage value Vi + 1 at the time of the next pulse oscillation is calculated from the monitored oscillation energy value Ei and the power supply voltage value Vi at that time according to the following equation. I do. The next pulse oscillation is performed by the calculated power supply voltage value Vi + 1 (step 170).

Vi + 1 = Vi + G × (Er−Ei) In this case, the power supply voltage value of the current pulse oscillation is determined as the past oscillation history with reference to the immediately preceding pulse oscillation. 1)) The pulse energy value Pi-N of the pulse N (for example, N = 2, N = 3, etc.) before the pulse and the charging voltage Vi-N at that time, (2) Younger than the pulse number of the pulse The average value of the pulse energies Pi to Pi + n of the n pulses having the pulse numbers and the average value of the corresponding charging voltages Vi to Vi + n (3) In the same pulse order one burst cycle before the pulse. The pulse energy value Pi of the pulse and the charging voltage Vi at that time may be adopted.

Next, the CPU 15 sets the pulse count value i
Is determined to be equal to the set value Ns (step 170). If they do not match, the procedure of steps 140 to 170 is repeated until they match.

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 equation (1), and calculates the standard deviation σ of the Ns oscillating pulses. 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 19)
0).

Then, the CPU 15 compares the calculated output variation ε with the set target upper limit σMj (step 200). As a result of this comparison, if the output variation ε is within the range of the target upper limit σMj (ε ≦ σMj),
Since halogen gas replenishment is not required,
After moving to 0 and setting the flag FLAG to 0, step 1
By repeating steps 30 to 190, the output variation ε of the next Ns pulse oscillations is calculated.

However, in the determination of step 200,
If ε> σMj holds, it is determined whether or not the flag FLAG = −1 (step 210). And the flag
If FLAG = -1, it is determined that the F2 partial pressure is equal to or higher than Pmx1, and the procedure shifts to step 130 without refilling the halogen gas, and thereafter, the output variation ε of the next set is calculated. . That is, when the flag FLAG is -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 fluoride, and the natural variation of the F2 gas causes the output variation ε to be smaller than the target upper limit σM1.

In step 210, the flag FLAG = -1
If halogen gas replenishment is performed when
Since the F2 partial pressure increases, the output variation .epsilon. Further increases along the arrow R in FIG.

Next, the flag FLAG
If not, the flag FLAG is set in the next step 220.
= 1, and if the flag FLAG is not 1, the flag FLAG is set to 1 (step 280).
The gas supply subroutine shown in FIG. 2 is executed (step 290). This gas supply subroutine will be described later.

On the other hand, if the flag FLAG = 1 in step 220, 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
In the case of k, it is determined that the variation ε along the arrow S in FIG. 7 has been reduced by the previous gas replenishment, and the procedure shifts to step 290 to execute the gas replenishment subroutine to further replenish the gas. In order to further reduce the variation ε.

However, at step 230, εk−1
If ≤εk is satisfied, the variation ε has increased despite the replenishment of the halogen gas. Therefore, it is determined that the initial σ characteristic has changed, and the σ characteristic is reset. (Step 240).

That is, since the variation value σ is continuously monitored, the minimum value σmin of the variation is obtained based on the monitor output, and the addition set value Δσ is added to the obtained minimum value σmin. The result σmin + Δσ is set and stored as a new target upper limit value σMj.

Next, after setting the flag FLAG to −1 (step 280), the CPU 15 compares the reset target upper limit value σMj with the allowable maximum value σmax (step 26).
0). Then, as a result of this comparison, when σMj <σmax, the procedure shifts to step 139, and the above procedure is repeatedly executed. However, if σMj <σmax, then
Assuming that the required variation specification cannot be achieved, an abnormal signal is generated (step 270). With this abnormal signal, the operator causes the laser oscillation to stop urgently. Alternatively, the shutter provided on the laser emission side is closed by the occurrence of the abnormal signal to prevent laser light from being incident on the semiconductor exposure apparatus. In this case, after that, when σMj <σmax, the shutter may be opened to restart the exposure processing. In addition,
In the above embodiment, at any stage of the control procedure, when the variation value σ itself becomes larger than the allowable maximum value σmax, an abnormal signal is output.

In the above-described halogen gas supply control, the region where the laser oscillation efficiency is high, that is, the partial pressure value of F2 is
, The laser output variation σ can be reduced and the laser oscillation efficiency can be maintained in a high range.

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

This 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 F2 partial pressure of one of the gas cylinders 20 of the gas replenishing device 17 shown in FIG. 8 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 where no gas is exhausted. 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 of the total pressure, so (σmax →
σb), 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 (in FIG. 6, 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 phenomenon that the total pressure rises 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 of the arrow U in FIG.
And eventually enters a range smaller than σmax. 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 supply subroutine shown in FIG. 2 (b) is a case where a gas exhaust step is performed. When the gas supply subroutine is started, first, a part of the gas in the laser chamber is exhausted (step S1). 300). That is, by performing gas exhaustion before gas replenishment, a gas containing laser-oscillated impurities is exhausted. Next, F2, Kr, 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. 6, the variation value σ itself also rises, and σ may exceed the target upper limit σmax. Also, if the total gas pressure in the laser chamber rises too much, the fluorine partial pressure PF2 will decrease, and the laser oscillation efficiency (output laser light energy E) will drop extremely (see FIG. 3). 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. 6).

FIGS. 14 (a), 14 (b) and 14 (c) show the variation σ and the power supply voltage V when the target upper limit variable control is performed as described above.
And the change over time of the average output EA of the laser.

In FIG. 14A, the minimum value of the variation increases with the progress of the laser oscillation (σmin1 →
σmin2 → σmin3 → σmin4 →), and the target upper limit increases accordingly (σM1 → σM2 → σM3 → σM4
→). Further, when the variation σ exceeds the allowable maximum value σmax, an abnormal signal is output.

In the voltage change shown in FIG. 14B, during the period in which the variation σ is increasing, as can be seen from FIG. 3, the output energy E decreases. Is to rise. This allows
The average output EA of the laser takes a substantially constant value as shown in FIG.

FIG. 15 shows a second embodiment of the present invention. In this case, the halogen gas supply control and the target upper limit σ
Only the variable control part of Mj is extracted and shown.

First, the variation σ calculated at a certain time is read, and this variation value σ is compared with the target upper limit σMj (= σmin + Δσ) set at that time (steps 400 and 410). As a result of this comparison, σ> σ
If it is Mj, the current variation minimum value σmin is rewritten to the current variation value σ in order to detect the current variation minimum value of the σ characteristic (step 420). Next, in order to increase the fluorine partial pressure PF2, a predetermined amount of F2 gas is injected into the laser chamber (step 430).

Next, after waiting for a predetermined time until the influence of the F2 gas injection is reflected on the variation σ, the variation value σ after the F2 gas injection is read (steps 440, 440).
50).

Next, the variation value σ after the F2 gas injection is compared with the previous σ (= σmin) (step 46).
0), if σ <σmin is satisfied (ie, if σ is reduced by injecting F2), the procedure proceeds to step 420
Then, the supply control of the F2 gas is executed. As described above, when the variation value becomes smaller than the previous variation value by injecting the F2 gas, the supply of the F2 gas is continued until σ ≧ σmin.

Finally, when σ ≧ σmin, the supply of the F 2 gas is stopped, and the σmin value in step 420 in the immediately preceding loop is adopted as the minimum value of the σ characteristic. In step 410, the target upper limit value σMj is recalculated using the minimum value of the σ characteristic adopted. That is, in this embodiment, the F2 gas is intermittently injected at a constant rate, and the σ value at the time when the variation value σ changes from the decreasing direction to the increasing direction in the F2 gas injection process is the minimum value of the σ characteristic. It is adopted as σmin. That is, in FIG. 16, as the injection of the F2 gas advances, the variation value σ decreases as shown by the arrow D in the drawing, and thereafter, the variation value σmin when the variation value changes from decreasing to increasing is represented by the σ characteristic. It is adopted as the minimum value.

FIG. 17 shows a third embodiment of the present invention. In this case, when supplying the F2 gas, the mass flow controller MFC shown in FIG. 9C is used to reduce the F2 gas until a minimum value is found. During the period, the continuous supply is performed. That is, first, the variation σ calculated at a certain point in time
Is read, and this variation value σ is compared with the target upper limit value σMj (= σmin + Δσ) set at that time (steps 500 and 510). As a result of this comparison, σ> σ
If Mj, the valve of the mass flow controller MFC is opened to start supplying F2 gas to the laser chamber (step 520).

Next, in order to detect the current minimum variation value of the σ characteristic, the current minimum variation value σmin is rewritten to the current variation value σ (step 530).

Next, after waiting for a predetermined time until the influence of the F2 gas injection is reflected on the variation σ, the variation value σ after the F2 gas injection is read (steps 540, 540).
50).

Next, the variation value σ after the F2 gas injection is compared with the previous σ (= σmin) (step 56).
0), if σ <σmin is satisfied (ie, if σ is reduced by injecting F2), the procedure proceeds to step 530.
And the supply control of the F2 gas is further continued. That is, when the variation value becomes smaller than the previous variation value after the injection of the F2 gas, the supply of the F2 gas is continued until σ ≧ σmin.

Finally, when σ ≧ σmin, the supply of the F 2 gas is stopped by closing the valve of the mass flow controller MFC (step 570).
The σ min value of step 530 in the immediately preceding loop is adopted as the minimum value of the σ characteristic, and the subsequent step 510
, The target upper limit value σMj is recalculated using the minimum value of the σ characteristic adopted above.

Note that in the embodiment shown in FIG.
Although the power supply voltage V is varied with reference to the past oscillation history, the power supply voltage V may be maintained at a substantially constant value Vc.

The power supply voltage value that minimizes the variation value σ is stored in advance as table data using the oscillation stop time t (see FIG. 10) and the pulse number i of each pulse oscillation as parameters, and the table data is used. Power supply voltage V
There is a voltage control called a so-called spike killer control for controlling the voltage, but the present invention may be applied to the voltage control using the spike killer.

That is, in the excimer laser, a relatively high pulse energy is initially obtained in the spike region including the first few pulses after the elapse of the oscillation pause period t, and thereafter the pulse energy gradually decreases. A so-called loose spiking phenomenon appears. At the end of this spike region, the pulse energy goes through a plateau region followed by a relatively high level of stable values before entering the steady region. This spike-king phenomenon is greatly affected by the oscillation stop time.

Therefore, in certain spike killer control, discharge voltage data for setting the energy of each pulse of the continuous pulse oscillation to a desired target value Er in consideration of various parameters such as the oscillation pause time t and the pulse number i is expressed as follows. While storing in a table in advance for each pulse of continuous pulse oscillation,
The actual pulse energy Ei (i = 1,
2,...) Are detected, the detected value Ei is compared with the pulse energy target value Er, and the prestored discharge voltage data for each pulse is corrected and updated based on the comparison result. The voltage control of the next burst cycle is performed according to the correction voltage data, and the target upper limit variable control of the present invention may be applied to the spike killer control.

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

That is, while monitoring the output variation ε, the halogen gas is continuously (continuously) supplied little by little into the laser chamber without interruption, 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. 6, 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, a value ε obtained by dividing the standard deviation σ of Ns oscillation pulses by the average value EA (= ET / Ns) of 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 graph showing a relationship between output energy and output energy with respect to fluorine partial pressure.

FIG. 4 is a graph showing a relationship between a total gas pressure and a fluorine partial pressure value that minimizes output variation.

FIG. 5 is a graph showing the relationship between fluorine partial pressure and output variation using a power supply voltage as a parameter.

FIG. 6 is a graph showing the relationship between the partial pressure of fluorine and output variation using the total gas pressure as a parameter.

FIG. 7 is a graph showing a long-term variation in output variation characteristics.

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.

FIG. 14 is a time chart for explaining the operation of the present invention.

FIG. 15 is a flowchart showing a second embodiment of the present invention.

FIG. 16 is a variation characteristic diagram for explaining the operation of the second embodiment.

FIG. 17 is a flowchart showing a third embodiment of the present invention.

[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 (9)

[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. Gas replenishing means for replenishing the laser gas, variation measuring means for determining variation in output energy of each pulsed laser oscillation light, target range setting means for setting a target upper limit of the variation value, and measurement of the variation measuring means A variation monitor storage means for successively monitoring values and storing the same; a minimum value derivation means for obtaining a minimum value of the variation value based on a monitoring result of the variation monitor storage means; and a minimum value derivation means. Of the variation value set in the target range setting means according to the minimum value Target range updating means for changing the target upper limit value, and control means for controlling the gas supply means so as to supply the halogen gas so that the calculated variation falls within the target upper limit value set in the target range setting means. An excimer laser device comprising: 2. The method according to claim 1, wherein the target range updating unit is configured to output the target range setting unit when the variation value measured by the variation measuring unit exceeds a current target upper limit value set in the target range setting unit. 2. The excimer laser device according to claim 1, wherein the target upper limit value of the set variation value is changed. 3. The excimer laser device according to claim 2, wherein said target range updating means sets a value obtained by adding a predetermined set value to a minimum value of the variation value as a target upper limit value. 4. When the variation value measured by the variation measuring means exceeds a current target upper limit value set in the target range setting means, the control means controls the gas replenishing means to control the halogen supply. In addition to replenishing the gas, the minimum value deriving unit is configured to perform the transition when the transition from the decrease to the increase in the variation value is detected by the output of the monitor storage unit due to the replenishment of the halogen gas by the gas replenishing unit. 3. The excimer laser device according to claim 2, wherein the variation value at the start is a minimum value of the variation value. 5. When the variation value measured by the variation measuring means exceeds a current target upper limit value set in the target range setting means, the control means controls the gas replenishing means to control the halogen supply. In addition to replenishing the gas, the minimum value deriving unit is configured to detect the transition from a decrease to an increase in the variation value by an output of the monitor storage unit in accordance with the replenishment of the halogen gas by the gas replenishment unit. 3. The excimer laser device according to claim 2, wherein the minimum value of the monitor value of the variation value up to the time point is set as the minimum value of the variation value. 6. An output energy detecting means for detecting an output energy of the pulsed laser oscillation light in pulse units, and calculating 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. 7. The excimer laser device according to claim 1, wherein said variation calculating means obtains a standard deviation of output energy of a predetermined number of pulsed oscillation lights, and sets the standard deviation as an output variation value. 8. The variation calculation means calculates a standard deviation and an average value of output energies of a predetermined number of pulsed oscillation lights, and sets a value obtained by dividing the standard deviation by an average value as an output variation value. 2. The excimer laser device according to 1. 9. An apparatus according to claim 1, further comprising an allowable maximum value setting means for setting an allowable maximum value that is larger than said target upper limit value, wherein said control means determines whether said measured variation value exceeds said allowable maximum value. The excimer laser device according to claim 1, which outputs an abnormal signal.