JP3779010B2 - Gas supply control device and gas supply control method for excimer laser device - Google Patents

Description

[0001]
BACKGROUND 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 reduced projection exposure apparatus, and more particularly, an excimer laser device that performs laser pulse oscillation by filling a laser gas containing a halogen gas into its laser chamber. The present invention relates to a gas supply control apparatus and method.
[0002]
[Prior art and problems to be solved by the invention]
Conventionally, when an excimer laser device is operated using a halogen gas, the halogen gas is consumed by evaporation of the electrode material and chemical reaction with the laser chamber constituent material according to the operation. Therefore, conventionally, the following control is performed in order to compensate for a decrease in laser output due to consumption of the halogen gas.
[0003]
That is, the laser output is obtained by charging the electric energy stored in the capacitor to excite the laser into the discharge space and discharging it in the laser medium gas. Will increase. Therefore, conventionally, the laser output is detected, and the laser output is stabilized by controlling the charging voltage value according to this detection. This control is usually called power lock control.
[0004]
However, even if this control is continued for a long time, the oscillation efficiency is lowered due to the exhaustion of the halogen gas, and the predetermined output cannot be maintained unless the charging voltage (power lock voltage) is gradually increased.
[0005]
In order to solve such a problem, Japanese Patent Laid-Open No. 3-166783 discloses that there is a laser gas pressure value for maximizing oscillation efficiency (ratio of output laser energy to input power) for each charging voltage value. The charging voltage and the laser gas pressure are controlled so that the oscillation efficiency is maintained at the maximum value as the charging voltage increases corresponding to the progress of laser oscillation.
[0006]
In other words, this prior art focuses on the oscillation efficiency of the laser and attempts to control the charging voltage and the laser gas pressure so that the oscillation efficiency always maintains the maximum value.
[0007]
This 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.
[0008]
However, when an excimer laser is used in a stepper type or step & scan type reduction projection exposure apparatus, it does not matter how to increase the laser output of each pulse (to increase the oscillation efficiency). The most important purpose is to obtain pulsed light with uniform output.
[0009]
That is, according to the above-described prior art, since the charging voltage control and the laser gas supply control are not performed mainly for obtaining a uniform laser output, it is impossible to further improve the exposure accuracy.
[0010]
The present invention has been made in view of such circumstances, and an object thereof is to provide a gas supply control device and method for an excimer laser device that can obtain uniform pulsed light output.
[0011]
[Means for solving the problems and effects]
According to the present invention, in an excimer laser apparatus that excites the laser gas by enclosing a laser gas containing a halogen gas in a laser chamber and performing pulse discharge in the laser chamber, the laser gas is contained in the laser chamber. Gas replenishing means for replenishing, halogen gas partial pressure setting means for presetting a halogen gas partial pressure value at which variation in output energy of each pulsed laser oscillation light is substantially minimized, and halogen gas partial pressure in the laser chamber The halogen gas partial pressure detecting means for detecting the gas and the gas replenishing means are controlled so that the detected value of the halogen gas partial pressure detecting means becomes the set value of the halogen gas partial pressure setting means to control the replenishment of the halogen gas Control means.
[0012]
According to such an invention, the halogen gas supply control is performed with the highest priority given to the suppression of variations in the output energy, rather than giving priority to the output energy of each pulse oscillation light. That is, the halogen gas supply control is performed aiming at a halogen gas partial pressure at which the variation in laser output is substantially minimized.
[0013]
Therefore, in the present invention, the output variation of each pulse oscillation light can be suppressed to the minimum, and the excimer laser device of the present invention can be applied to a light source such as a reduction projection exposure device that performs reduction projection exposure of a semiconductor. Thus, it is possible to perform highly accurate exposure processing.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
First, the outline of the main part of the present invention will be described with reference to FIG.
[0022]
FIG. 2 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 in a state where the laser power supply voltage is constant in the KrF excimer laser. . That is, the horizontal axis represents fluorine gas partial pressure PF2 (proportional to the molar concentration of F2 gas in the laser chamber), and the vertical axis represents output laser light energy E and output laser light energy variation (standard deviation) σ. .
[0023]
According to FIG. 2, the laser output E takes a maximum value (maximum efficiency) when the F2 partial pressure is P1, and monotonically increases at a partial pressure lower than the partial pressure value P1, and this partial pressure value P1. Higher partial pressures are monotonically decreasing.
[0024]
On the other hand, the variation σ of the laser output takes a minimum value when the F2 partial pressure is P2, monotonically decreasing at a partial pressure lower than the partial pressure value P2, and monotonically increasing at a partial pressure higher than the partial pressure value P2. Become.
[0025]
In FIG. 2, the phenomenon that the present inventor has focused on is that P1 ≠ P2, and in the present invention, even if the laser output (oscillation efficiency) is somewhat sacrificed, the fluorine partial pressure value that minimizes the output variation σ. F2 gas supply control is performed with P2 as the highest priority target value.
[0026]
In FIG. 2, σc is an allowable limit value (allowable upper limit value) of output variation, and the F2 partial pressure corresponding to the allowable limit value σc has two values, PMIN and PMAX. Therefore, in order to control the output variation σ to be always smaller than σc, it is necessary to control the F2 partial pressure value PF2 to be a value between PMIN and PMAX.
[0027]
However, since the output variation σ shown in FIG. 2 is not a linear relationship, when the output variation value σ becomes a value close to σc during the control, this state is either fluorine partial pressure PMIN or PMAX. It is impossible to determine whether or not to supply F2 gas without judging whether or not the state is close. That is, it is necessary to supply F2 gas when the F2 partial pressure is smaller than PMIN, and it is not necessary to supply F2 gas when the F2 partial pressure is larger than PMAX.
[0028]
As described above, since the output variation σ is monitored, the current F2 partial pressure state cannot be grasped. Therefore, in this apparatus, the F2 gas partial pressure is monitored. Since the F2 gas partial pressure cannot actually be monitored, in this embodiment, the spectral width Δλ of the oscillation laser having a positive correlation with the F2 partial pressure is adopted as an alternative monitor parameter.
[0029]
That is, FIG. 3 shows the relationship between the fluorine partial pressure PF2 and the spectral width Δλ, and the spectral width Δλ is substantially proportional to the fluorine partial pressure PF2. Therefore, the spectral widths Δλ1 and Δλ2 corresponding to the PMIN value and the PMAX value in FIG. 2 are preliminarily examined through experiments or the like and registered, and the detected value Δλ of the spectral width is between the lower limit value Δλ1 and the upper limit value Δλ2. The supply variation of the halogen gas is controlled so as to enter, and the output variation σ is maintained within the allowable range.
[0030]
FIG. 4 shows a narrow-band excimer laser to which the present invention is applied.
[0031]
In FIG. 4, a laser chamber 2 of the excimer laser 1 has a discharge electrode (not shown) and the like, 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. These laser gases are excited by the discharge between the discharge electrodes to perform laser pulse oscillation. The emitted pulsed light is narrowed by the band narrowing unit 6 (in this case, including the prism beam expanders 3 and 4 and the grating 5), is returned to the laser chamber 2 again, and is amplified. And output as oscillation laser light L. A part of the output light is returned to the laser chamber 2 to cause laser oscillation.
[0033]
A part of the oscillated laser beam L is sampled by the beam splitter 8 and then incident on the etalon spectroscope 9 and incident on the light receiving element 10 composed of a line sensor or the like to form a concentric fringe pattern. To do. Reference light having a known wavelength is also incident on the etalon spectrograph 9 in advance, and the CPU 11 compares the fringe pattern of the reference light and the laser light L formed on the light receiving element 10 to thereby determine the wavelength of the output laser light L. And the spectral width Δλ and the like are measured. 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 that is a wavelength selection element by changing the angle of the grating 5 based on the input wavelength and spectrum width data. Further, the CPU 11 compares the measured spectral width Δλ with the two threshold values Δλ1 and Δλ2 described above, and executes halogen gas supply control by the gas supply device 17 based on the comparison result.
[0034]
On the other hand, a part of the laser light transmitted through the beam splitter 8 is sampled by the beam splitter 13 and incident on the light receiving element 14. The CPU 15 detects the light energy Pi of each pulse oscillation based on the light reception output of the light receiving element 14 and controls the laser power supply circuit 16 based on the output Pi. The laser power supply circuit 16 controls the power supply voltage Vi.
[0035]
FIG. 5 shows various specific examples of the gas supply device 17.
[0036]
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0037]
5A to 5D, two gas cylinders 20 and 21 are used. In one gas cylinder 20, F2, Kr, and Ne are α: b: c (α = n · a, n>). 1) and the other gas cylinder 21 is filled with Kr and Ne at a molar ratio of b: c.
[0038]
That is, when the laser gas is injected into the laser chamber 2 (when the gas is initially filled into the laser chamber in a vacuum state, or when the output variation σ is out of the allowable range and the gas is replenished halfway), the two gas cylinders 20 , 21 injects a predetermined amount of gas into the laser chamber 2 so that the F 2 gas injected from the gas cylinder 20 is diluted by the gas injected from the other cylinder 21, resulting in a mixed gas in the laser chamber 2. Is an ideal mixing ratio a: b: c. It should be noted that the same effect can be obtained by supplying gas only from the gas cylinder 20 when supplying gas halfway.
[0039]
Further, when the total pressure of the gas in the laser chamber rises excessively during gas supply, the exhaust valve 22 is opened to exhaust a part of the gas so that the total pressure in the laser chamber can be maintained at a predetermined pressure. I try to adjust it.
[0040]
In FIG. 5A, the gas supply control is performed by the on / off valves 23 and 24, and the gas flow rate is adjusted by adjusting the opening and closing time of the on / off valves 23 and 24.
[0041]
In FIG. 5B, the sub tanks 25 and 26 are provided in the gas supply path, and the on / off valves 27 and 28 are provided on the downstream side of the sub tanks 25 and 26.
[0042]
In FIG. 5C, mass flow controllers (mass flow rate control devices) 29 and 30 are provided in the gas supply path. The mass flow controllers 29 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 shown in FIG. 5 (c), the gas flow rate can be controlled with high accuracy by adjusting the opening / closing time of the on / off valves 23 and 24 while setting the flow rates of the mass flow controllers 29 and 30 constant. become. The on / off valves 23 and 24 may be omitted, and the gas flow rate may be controlled only by the mass flow controllers 29 and 30.
[0043]
When the gas replenishment, if the halogen gas partial pressure value in the gas cylinder 21 is as small as about 1%, the laser gas containing the halogen gas may be supplied to the laser chamber 2 only from the gas cylinder 21. In this case, since the halogen gas concentration is low, it is necessary to supply a relatively large amount of gas. Therefore, the increase in the total pressure in the laser chamber 2 becomes large. Therefore, the total pressure is adjusted by exhausting. .
[0044]
Hereinafter, replenishment control of the halogen gas will be described with reference to the flowchart of FIG.
[0045]
First, the lower limit values Δλ1 and Δλ2 of the spectrum width Δλ corresponding to the allowable maximum value σc of the variation σ are set to appropriate values and stored.
[0046]
When the pulse oscillation is started, the CPU 11 measures the spectrum width Δλ every time the pulse oscillation is performed, and determines whether or not the measured value Δλ is within the set upper and lower limit values Δλ1, Δλ2 (step 130). ). If Δλ1 <Δλ <Δλ2 is established as a result of this determination, halogen gas replenishment is not necessary, so the procedure proceeds to step 120 and the spectrum width Δλ of the next pulse oscillation is measured.
[0047]
However, if Δλ ≧ Δλ2 or Δλ ≦ Δλ1 is satisfied in the determination of step 130, it is next determined whether Δλ ≦ Δλ1 is satisfied (step 140). If not, (Δλ ≧ Δλ2). In this case, the procedure is shifted to step 120 without replenishing the halogen gas, and the spectral width Δλ of the next pulse oscillation is measured thereafter.
[0048]
That is, when Δλ ≧ Δλ2, the F2 partial pressure is PMAX or more. Therefore, by continuously pulsing without supplying the F2 gas, the F2 gas is naturally reduced along the arrow F in FIG. (F2 gas reacts with a material such as a laser electrode by laser oscillation to become fluoride and F2 gas itself is reduced), and the output variation σ is made smaller than the set value σc by the natural decrease of the F2 gas.
[0049]
Note that if the halogen gas is replenished in the case of Δλ ≧ Δλ2, the F2 partial pressure increases, so that the output variation σ further increases along the arrow R in FIG.
[0050]
Next, when Δλ ≦ Δλ1 is satisfied, the gas replenishment control is performed by controlling the gas replenishing device 17 to replenish the halogen gas, thereby reducing the output variation σ along the arrow S in FIG. Let In the gas supply control, a predetermined amount of mixed gas of F2, Kr, Ne is supplied into the laser chamber 2 by the gas supply device 17 shown in FIG. 5 (step 150). After the replenishment, when the total pressure PT in the laser chamber becomes larger than a predetermined set pressure Pth (step 160), the gas in the laser chamber 2 is exhausted (step 170).
[0051]
When the supply of F2 gas is completed in this way, the procedure is shifted to step 120 and the spectrum width Δλ of the next pulse oscillation is again measured.
[0052]
Thus, in this embodiment, when Δλ1 <Δλ <Δλ2 holds, F2 gas is not supplied. Even when Δλ ≧ Δλ2 is satisfied, the F2 gas is not supplied and the natural decrease of the F2 gas is awaited. However, when Δλ <Δλ1 is satisfied, supply control of F2 gas is executed.
[0053]
In the above embodiment, the spectral width Δλ is adopted as a parameter for detecting the halogen gas partial pressure. However, if the parameter has a correlation with the halogen gas partial pressure, other parameters are used. Also good.
[0054]
Further, since the amount of F2 gas decreases with the progress of laser pulse oscillation, the number of pulse oscillations or pulse oscillation time may be monitored, and supply of halogen gas may be controlled based on the monitoring result.
[0055]
That is, the number of pulse oscillations N from the time of gas replenishment is counted, and when the counted value N reaches a preset predetermined value Nc, the halogen gas partial pressure is replenished by replenishing the reduced halogen gas. Maintain PF2 within the range of PMAX and PMIN. The replenishment amount of the halogen gas is set to an appropriate value according to the set value Nc.
[0056]
In addition, when the halogen gas supply control is performed based on the pulse oscillation time T, the halogen gas supply is performed at a predetermined time interval T after the pulse oscillation starts. That is, the CPU 11 outputs a gas supply signal to the gas supply device 17 at a predetermined time interval T set in advance after the start of pulse oscillation, and the gas supply device 17 outputs a gas supply signal from the CPU 11 each time. Refill with halogen gas. Also, during this control, the number of oscillations N of the laser pulse from the previous replenishment of the halogen gas to the current replenishment of the halogen gas is counted, and the replenishment amount of the halogen gas is determined according to the magnitude of the counted value N. If the adjustment is made, more accurate halogen gas supply control can be performed.
[0057]
The present invention can be applied to both a stepper type reduction projection exposure apparatus and a step-and-scan reduction projection exposure apparatus.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an embodiment of the present invention.
FIG. 2 is a graph for explaining the idea of the present invention.
FIG. 3 is a diagram showing a relationship between a laser spectrum width and a halogen gas partial pressure value.
FIG. 4 is a block diagram illustrating a configuration example of an excimer laser device.
FIG. 5 is a block diagram showing various configuration examples of the gas supply device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Excimer laser apparatus 2 ... Laser chamber 3, 4 ... Prism beam expander 5 ... Grating 6 ... Narrow-band unit 7 ... Partial transmission mirror 8, 13 ... Beam splitter 9 ... Etalon spectrometer 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 (10)

In an excimer laser device that encloses a laser gas containing a halogen gas in a laser chamber and performs pulsed laser oscillation by exciting the laser gas by performing pulse discharge in the laser chamber.
Gas supply means for supplying the laser gas into the laser chamber;
A halogen gas partial pressure setting means for presetting a halogen gas partial pressure value at which variation in output energy of each pulse laser oscillation light is substantially minimized;
A halogen gas partial pressure detecting means for detecting a halogen gas partial pressure in the laser chamber;
Control means for controlling supply of the halogen gas by controlling the gas supply means so that a detection value of the halogen gas partial pressure detection means becomes a set value of the halogen gas partial pressure setting means;
A gas supply control device for an excimer laser device. Halogen gas partial pressure detecting means detects the spectral width of the pulsed laser oscillation light,
The gas supply control device for an excimer laser device according to claim 1, wherein the halogen gas partial pressure setting means sets in advance a spectrum width at which variation in output energy of each pulsed laser oscillation light is substantially minimized.   The gas replenishing means has a gas supply source including a halogen gas, a rare gas, and a buffer gas, and the partial pressure of the halogen gas in the gas supply source is set to a value larger than the halogen gas partial pressure in the laser chamber. 2. The gas supply control device for an 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 be substantially the same as a partial pressure ratio between the rare gas and the buffer gas in the laser chamber.   The gas replenishing means includes a first gas supply source including a halogen gas, a rare gas, and a buffer gas, and a second gas supply source including the rare gas and the buffer gas, and the halogen in the first gas supply source. The partial pressure of the gas 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 the rare gas and the buffer in the laser chamber, respectively. 2. The gas supply control device for an excimer laser device according to claim 1, wherein the gas supply control device is set to a value substantially equal to a gas partial pressure ratio.   The excimer laser according to claim 3 or 4, wherein the gas replenishing means has a mass flow controller in a gas supply path from a gas supply source to the laser chamber, and the control means replenishes halogen gas by controlling the mass flow controller. Equipment gas supply control device.   The excimer laser according to claim 3 or 4, wherein the gas supply means has an on / off valve in a gas supply path from a gas supply source to the laser chamber, and the control means controls the on / off valve to supply halogen gas. Equipment gas supply control device.   The gas supply means has a mass flow controller and an on / off valve in a gas supply path from a gas supply source to the laser chamber, and the control means supplies the halogen gas by controlling the mass flow controller and the on / off valve. Or the gas supply control apparatus of the excimer laser apparatus of 4.   5. The gas supply control device for an excimer laser device according to claim 3, wherein the gas replenishing means includes a sub tank in a gas supply path from a gas supply source to the laser chamber, and supplies laser gas from the sub tank to the laser chamber.   8. The excimer laser device according to claim 5, wherein the gas replenishing means includes a sub tank in a gas supply path from a gas supply source to the laser chamber, and supplies laser gas from the sub tank to the laser chamber. Gas supply control device. In a gas supply control method of an excimer laser device that encloses a laser gas containing a halogen gas in a laser chamber and excites the laser gas by performing pulse discharge in the laser chamber to perform pulsed laser oscillation.
A halogen gas partial pressure value at which variation in output energy of each pulsed laser oscillation light is substantially minimized is set in advance, and the detected halogen gas partial pressure value is set to the set halogen gas partial pressure value. A gas supply control method for an excimer laser device, characterized in that supply is performed.

Images