JP2007059788A - Laser system and laser exposing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser system which can enlarge a dynamic range of a laser output without deteriorating each pulse energy stability, and to provide a laser exposing system. <P>SOLUTION: A main controller 70 of a laser apparatus 1 carries out a charging voltage control and a gas control in order to make a pulse energy Pin before being input to an output attenuating mechanism 50 a value (target pulse energy PL) of little pulse variation. In addition, the main controller 70 controls the transmission factor T of the output attenuating mechanism 50 based on a signal showing a target pulse energy Pt transmitted from an exposing apparatus 200, in order to accord the output energy of the laser apparatus 1 to the target pulse energy Pt (smaller than the target pulse energy PL) required by the exposing apparatus 200. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser system including a gas laser device as a light source of an exposure apparatus and a laser exposure system, and more particularly, to increase or decrease the energy of laser light output from the gas laser apparatus in accordance with the energy value required for exposure in the exposure apparatus. It is.

(Light source for exposure)
As semiconductor integrated circuits are miniaturized and highly integrated, improvement in resolving power is demanded in semiconductor exposure apparatuses. For this reason, the wavelength of light emitted from the exposure light source is being shortened, and a gas laser device is used as the exposure light source instead of the conventional mercury lamp. As the current gas laser apparatus for exposure, a KrF excimer laser apparatus that emits ultraviolet light with a wavelength of 248 nm and an ArF excimer laser apparatus that emits ultraviolet light with a wavelength of 193 nm are used. As a next-generation exposure technique, an immersion technique for shortening the apparent wavelength of the exposure light source by filling the space between the exposure lens and the wafer with a liquid and changing the refractive index is being applied to ArF exposure. ArF immersion results in a wavelength of 134 nm. As a next-generation light source for exposure, an F2 laser device that emits ultraviolet light having a wavelength of 157 nm is promising, and F2 laser immersion exposure may be adopted. The F2 immersion is said to have a wavelength of 115 nm.

(Exposure optics and chromatic aberration)
A projection optical system is adopted as an optical system of many semiconductor exposure apparatuses. In the projection optical system, chromatic aberration correction is performed by combining optical elements such as lenses having different refractive indexes. Currently, the wavelength range of the gas laser apparatus for exposure is 248 nm to 115 nm. In this wavelength range, there are no optical materials other than synthetic quartz and CaF2 suitable for use as the lens material of the projection optical system. As the projection lens for the KrF excimer laser, an all-refractive type monochromatic lens composed only of synthetic quartz is adopted, and as the projection lens for the ArF excimer laser, an all-refractive type partial achromatic lens composed of synthetic quartz and CaF2. Is adopted. However, since the spontaneous amplitude of KrF and ArF excimer lasers is as wide as about 350 pm to 400 pm, when these projection lenses are used, chromatic aberration is generated and the resolving power is lowered. Therefore, before the chromatic aberration can be ignored, it is necessary to narrow the spectral line width of the laser light emitted from the gas laser device. For this reason, the laser device is provided with a narrow-band module having a narrow-band element (such as an etalon or a grating) in the laser resonator, so that the spectral line width is narrowed.

(Higher laser output and two-stage laser system)
In the above-described immersion exposure, the transmittance of the lens decreases due to an increase in NA, so that a high output of a laser as a light source is required to obtain a constant exposure amount. Further, in order to increase the throughput of the exposure apparatus, it is necessary to increase the output of the laser. As a method for obtaining a high output after narrowing the spectral line width, there is a two-stage laser system.

  The two-stage laser system includes an oscillation stage laser (OSC laser) for outputting a narrow-band laser beam and an amplification stage laser for amplifying the narrow-band laser beam (referred to as seed light). (AMP). Two-stage laser systems can be divided into two types, MOPO and MOPA, depending on the means of amplification. MOPO is an abbreviation for Master Oscillator and Power Oscillator, which is also called an injection lock system, and is a laser in which resonators are provided before and after an amplification chamber. On the other hand, MOPA is an abbreviation for Master Oscillator and Power Amplifer, and is a laser in which resonators are not provided before and after the amplification chamber.

FIG. 27 shows a basic configuration of a MOPO type two-stage laser apparatus.
The amplification stage laser 100a is located between a Fabry-Perot type optical resonator composed of an input side mirror (rear side mirror) 20a and an output side mirror (front side mirror) 30a, and encloses a laser gas. A laser chamber 10a is provided. In the laser chamber 10a, there are provided a pair of discharge electrodes 11a, 12a and the like for exciting a laser gas to form a gain region. In FIG. 27, it is assumed that the pair of discharge electrodes 11a and 12a are arranged in a direction perpendicular to the paper surface. Windows 13a and 14a are provided at the laser beam output portion on the optical axis of the laser beam in the laser chamber 10a.

  Further, the oscillation stage laser 100o includes an optical resonator composed of a rear-side mirror and a front mirror 30o that also serve as optical elements in the narrow-band module 20o composed of, for example, a magnifying prism and a grating (diffraction grating). A laser chamber 10o is disposed between the optical resonators and encloses a laser gas. In the laser chamber 10o, there are provided a pair of discharge electrodes 11o, 12o and the like that excite laser gas to form a gain region. In FIG. 27, it is assumed that the pair of discharge electrodes 11o and 12o are arranged in a direction perpendicular to the paper surface. Windows 13o and 14o are provided at the laser beam output portion on the optical axis of the laser beam in the laser chamber 10o.

  A pulse power supply circuit (not shown) for applying a high voltage between the opposing electrodes is connected to the discharge electrodes 11a and 12a and the discharge electrodes 11o and 12o, respectively. When the charging voltage of these pulse power supply circuits is changed, the electric field strength between the opposing electrodes can be changed, so that the laser output can be changed.

  Further, when the gas laser device is an excimer laser, the laser gas is a composition gas constituting the excimer (Kr gas and F2 gas in the case of KrF, Ar gas and F2 gas in the case of ArF) and dilution gas (Ne or He gas). The laser output can be changed by changing the composition ratio and the total pressure of the laser gas.

(Exposure equipment: Stepper method and scanner method)
Since the excimer laser is a pulse discharge excitation gas laser, the laser oscillation is a pulse oscillation as shown in FIG. FIG. 28A shows an oscillation pattern when an excimer laser is used as a light source of a semiconductor exposure apparatus. This operating state is a burst mode oscillation that repeats a continuous pulse oscillation operation in which the laser beam is continuously oscillated a predetermined number of times and an oscillation pause in which the pulse oscillation is stopped for a predetermined time.

First, the stepper method will be described.
FIG. 28B shows a semiconductor wafer W on which a plurality of IC chips TP are arranged. The semiconductor wafer W is placed on the stage and placed at the irradiation position. In exposing one IC chip TP on the semiconductor wafer W, the reticle (mask) is fixed and the movement of the stage is stopped, and a large number (several hundreds) necessary for the resist applied to the semiconductor wafer W to be exposed is exposed. Are applied to the entire surface of the substantially square IC chip TP. When the exposure processing for one IC chip TP is completed, the stage is moved to place the next unirradiated IC chip TP below the reticle, and similarly, continuous pulse light is irradiated. When such exposure and stage movement are alternately performed and exposure of all the IC chips TP on the semiconductor wafer W is completed, the exposed semiconductor wafer W is unloaded from the irradiation position, and the next semiconductor wafer W is set at the irradiation position. Then, the light irradiation described above is repeated.

  This method of alternately repeating exposure and stage movement is called a step-and-repeat (abbreviated stepper) method. In the case of this stepper method, the operation state of the excimer laser serving as the light source is necessarily a burst mode operation. In addition, the following points are raised as features in the case of the stepper method.

  Since it is only necessary to control the energy integrated value of the pulsed light applied to one IC chip TW by constant pulse oscillation, there is an advantage that the exposure amount can be controlled relatively easily. For example, as shown in FIG. 28C, even if the laser pulse intensity changes in the middle of continuous pulse oscillation, the problem arises if the integrated energy value of the laser light applied to the IC chip TW is a required exposure amount. Absent. However, when the IC chip TP to be exposed is large, the field shape (laser irradiation area) of the projection lens becomes the size of the IC chip TP as it is, and a large projection lens is required, which increases the cost.

  The stepper method is the mainstream in conventional exposure apparatus systems, but the step-and-scan (abbreviated scanner) method, which will be described later, is the mainstream in current exposure apparatus systems. On the other hand, in the scanner method, it is necessary to perform the exposure amount control, which is a simple control in the stepper method, with high accuracy.

The scanner method will be described below.
In the scanner method, the field shape (laser irradiation area) of the projection lens is set to a rectangular shape at the time of exposure, and the reticle (mask) and the semiconductor wafer W are simultaneously moved in opposite directions along the short axis direction of the rectangle for exposure. It is a method. Since the reticle (mask) and the semiconductor wafer W are operated in this way, a large area can be exposed even if the projection lens is small. That is, a large IC chip TP can be exposed with a small projection lens, and the cost of the projection lens can be reduced.

  The exposure amount control in this method is as follows.

  FIG. 29A shows an enlarged view of the pulse train within one burst period shown in FIG. The energy of each pulsed light is Pi (i = 1, 2,...), And the exposure amount over a certain number of pulses (n) is Si (i = 1, 2,...). The exposure amount Si is an energy integrated value Pi +... + Pi + n of n pulses from the i-th pulse to the (i + n) -th pulse. In the case of a scanner type exposure apparatus, as shown in FIG. 29B, exposure is performed while moving the semiconductor wafer W continuously, so that the exposure amounts S1, S2,. Therefore, it is necessary to control the laser energy of each pulse so that the laser energy of each pulse is constant or the exposure amounts S1, S2,.

Many techniques for making the exposure dose constant over a range of pulse numbers have been disclosed.
For example, Patent Document 1 discloses a method of controlling the charging voltage in order to make the laser energy of each pulse uniform and make the exposure amount constant. Further, Patent Document 2 discloses a method of controlling the composition ratio of halogen gas in order to make the laser energy of each pulse uniform and make the exposure amount constant as in Patent Document 1.

Patent Document 3 will be described with reference to FIG.
FIG. 30 shows a prior art control system. In this system, light output from a pulsed light source 91, that is, a laser device, passes through a variable attenuator 92, energy is measured by an exposure amount monitor 93, and reaches an exposure device 94, that is, an exposure device. The exposure amount monitor transmits the measurement result to the controller 95. The controller 95 calculates the exposure amount based on the received measurement result, obtains the minimum attenuation amount, and sets the variable attenuator 92. Further, the number of shots necessary for the exposure amount is calculated, and the pulsed light source 91 is set.

FIG. 31 shows a prior art variable attenuator. The variable attenuator 92 includes a rotatable disk 92a whose edge on the disk surface is orthogonal to the beam optical path, and a plurality of ND filters 92b having different transmittances fitted to the edge of the disk 92a. The controller 95 controls the rotation of the disk 92a and arranges the ND filter 92b having a desired transmittance on the beam optical path.
JP-A-9-248682 Japanese Patent Laid-Open No. 10-154842 Japanese Patent Laid-Open No. 2-5063

  As described above, in the immersion exposure, the transmittance of the lens is lowered due to the increase in NA, and therefore, it is necessary to increase the output of the laser as a light source in order to obtain a constant exposure amount. Further, in order to increase the throughput of the exposure apparatus, it is necessary to increase the output of the laser.

  While it is necessary to increase the output of the laser, many exposure apparatuses that have been operated at a low output so far have been in operation, so the range of the laser output required for the entire laser apparatus has been expanded. However, when a laser is manufactured in accordance with the laser output required for each exposure apparatus, there is a problem that the versatility of the laser is lost and the cost is enormous. In order to solve such a problem, it is necessary to increase the output range of one laser, that is, the dynamic range so that one laser can cope with many exposure apparatuses.

  As a method of changing the output with one laser, it is conceivable to change the excitation intensity of the laser gas, that is, the charging voltage, or change the gas composition or gas pressure. However, in the gas laser, “charge voltage HV−laser output E” and “charge voltage HV−energy variation σ” have characteristics as shown in FIG. 32. When the laser output E is changed with the charge voltage HV, the oscillation pulse energy is changed. Variation σ becomes large and may exceed the allowable range.

  In the scanner type exposure apparatus, it is necessary to reduce the variation in the energy of each pulse. Therefore, when the charging voltage HV is changed within the allowable range of the energy variation σ required from the exposure apparatus, the variable range of the laser output E becomes small. In general, in a scanner type exposure apparatus, the laser output E can be changed only by about ± 10 W of the center output in order to make the energy variation σ substantially constant. Conversely, if the dynamic range is to be increased, the energy variation σ increases and cannot be used.

  Even if the energy variation σ is ignored, if the charging voltage HV is decreased, the laser oscillation does not occur below a certain value, so that the required dynamic range cannot be obtained. When the charging voltage HV is reduced, the energy variation σ increases because the discharge becomes unstable and a uniform gain region cannot be secured.

  Further, when the gas composition and gas pressure are changed, as in the case of changing the charging voltage, when the dynamic range is increased, the variation σ of oscillation pulse energy increases.

  FIG. 33 shows an example of the required dynamic range of the laser output. In various existing exposure apparatuses, a laser output within a range of about 90 W to 40 W is required. However, the dynamic range when changing the output with the charging voltage is, for example, a range of about 90 ± 10 W for a laser operating at 90 W, a range b of about 60 ± 10 W for a laser operating at 60 W, and a laser operating at 40 W operation. The range c is about 40 ± 10 W, and none of them reach the required dynamic range. For this reason, it is necessary to increase the dynamic range by a method other than the change in charging voltage, gas composition, and gas pressure.

  In the above Patent Documents 1 to 3, it is not assumed that the dynamic range is increased. In particular, the laser devices of Patent Documents 1 and 2 change the charging voltage and the gas composition of the laser gas. Therefore, when the dynamic range is increased, the oscillation pulse energy variation σ increases as described above. Further, the laser device of Patent Document 3 is manufactured in correspondence with each exposure apparatus and only adjusts a slight energy change, and is not versatile.

  In the first place, the problem of increasing the dynamic range of a laser has recently been newly developed. For this reason, there is no clear technique for solving this problem so far, and the above-described problems occur even if the conventional technique is simply used.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a laser system or a laser exposure system that can increase the dynamic range of laser output without deteriorating the stability of each pulse energy. .

The laser system according to the first invention is:
A chamber containing laser gas;
An excitation source for exciting the laser gas in the chamber;
A part of the light output from the chamber with excitation of the laser gas is output to the outside, and the rest is resonated through the chamber;
By controlling at least one of the excitation intensity of the excitation source and the gas composition or gas pressure in the chamber, the pulse variation of the optical energy output from the optical resonator falls within a preset allowable range. A laser controller;
A light transmissive part that allows light output from the optical resonator to pass through, and can increase and attenuate the energy of the transmitted light by changing its own transmittance; and
A transmittance control unit for controlling the transmittance in the light transmitting unit;
Have

  The first invention will be described with reference to FIG.

  When the laser gas in the laser chamber 10 is excited by the power supply circuit 15 and the discharge electrodes 11 and 12 (excitation reduction), the laser beam is output from the laser chamber 10. Part of the laser light resonates at the optical resonators 20 and 30, and part of the laser light is output to the outside of the optical resonators 20 and 30. The laser light output from the optical resonator (front mirror 30) passes through the output attenuation mechanism 50 (light transmission portion) and reaches the exposure apparatus 200.

  The main controller 70 (laser control unit, transmittance control unit) of the laser device 1 performs charge voltage control or gas control, and the pulse energy Pin before being input to the output attenuation mechanism 50 is a value within a preset allowable range. That is, it is set to a value (target pulse energy PL) in which the pulse variation is reduced.

The laser system according to the second invention is:
An oscillation chamber that encloses the laser gas, an oscillation excitation source that excites the laser gas in the oscillation chamber, a part of the light that is output from the oscillation chamber as the laser gas is excited, and the rest An oscillation stage having an optical resonator that resonates through the chamber;
An amplification stage that encloses a laser gas; and an amplification stage that excites a laser gas in the amplification chamber when light output from the oscillation stage is present in the amplification chamber;
Optical energy output from the optical amplification stage by controlling at least one of the oscillation excitation source, the amplification excitation source, the gas composition or the gas pressure in the oscillation chamber and the amplification chamber A laser control unit that keeps the pulse variation within a preset allowable range;
A light transmissive part that allows light output from the amplification stage to be transmitted and can increase and attenuate the energy of light transmitted by changing its own transmittance; and
A transmittance control unit for controlling the transmittance in the light transmitting unit;
A laser system.

  The second invention will be described with reference to FIGS.

  When the laser gas in the laser chamber 10o is excited by the power supply circuit and the discharge electrodes 11o and 12o (not shown in FIG. 27), the laser light is output from the laser chamber 10o. Part of the laser light is resonated by the optical resonators 20o and 30o, and part of the laser light is output outside the optical resonators 20o and 30o. Laser light output from the oscillation stage laser 100o is input to the amplification stage laser 100a. When the laser gas in the laser chamber 10a is excited by the power supply circuit (not shown in FIG. 27) and the discharge electrodes 11a and 12a (hereinafter referred to as amplification reduction for amplification), the laser light is amplified and output. The laser light output from the front mirror 30a passes through the output attenuation mechanism 50 (light transmission portion) and reaches the exposure apparatus 200.

  A main controller 70 '(laser control unit, transmittance control unit) of the laser apparatus 1' shown in FIG. 2 performs charge voltage control and gas control, and presets the pulse energy Pin before being input to the output attenuation mechanism 50. A value within the permissible range, that is, a value (target pulse energy PL) where the pulse variation is reduced.

A laser exposure system according to a third invention is:
A chamber containing laser gas;
An excitation source for exciting the laser gas in the chamber;
A part of the light output from the chamber with excitation of the laser gas is output to the outside, and the rest is resonated through the chamber;
By controlling at least one of the excitation intensity of the excitation source and the gas composition or gas pressure in the chamber, the pulse variation of the optical energy output from the optical resonator falls within a preset allowable range. A laser controller;
A light transmissive part that allows light output from the optical resonator to pass through, and can increase and attenuate the energy of the transmitted light by changing its own transmittance; and
An exposure apparatus that has an energy value of light required for exposure equal to or lower than an energy value of light before being input to the light transmission unit, and further converts the energy value of light required for exposure into a signal and transmits the signal to the outside;
The transmittance of the light transmission unit is controlled according to the signal transmitted from the exposure apparatus, and the energy value of the light output from the light transmission unit is changed to the energy value indicated by the signal transmitted from the exposure apparatus. A matching transmittance control unit;
Have

  The third invention will be described with reference to FIG.

  When the laser gas in the laser chamber 10 is excited by the power supply circuit 15 and the discharge electrodes 11 and 12 (excitation reduction), the laser beam is output from the laser chamber 10. Part of the laser light resonates at the optical resonators 20 and 30, and part of the laser light is output to the outside of the optical resonators 20 and 30. The laser light output from the optical resonator (front mirror 30) passes through the output attenuation mechanism 50 (light transmission portion) and reaches the exposure apparatus 200.

  The main controller 70 (laser control unit, transmittance control unit) of the laser device 1 performs charge voltage control or gas control, and the pulse energy Pin before being input to the output attenuation mechanism 50 is a value within a preset allowable range. That is, it is set to a value (target pulse energy PL) in which the pulse variation is reduced. Further, based on the signal indicating the target pulse energy Pt transmitted from the exposure apparatus 200, the transmittance T of the output attenuation mechanism 50 is controlled, and the output energy of the laser apparatus 1 is changed to the target pulse energy required by the exposure apparatus 200. It is made to coincide with Pt (<target pulse energy PL).

A laser exposure system according to a fourth invention is:
An oscillation chamber that encloses the laser gas, an oscillation excitation source that excites the laser gas in the oscillation chamber, a part of the light that is output from the oscillation chamber as the laser gas is excited, and the rest An oscillation stage having an optical resonator that resonates through the chamber;
An amplification stage that encloses a laser gas; and an amplification stage that excites a laser gas in the amplification chamber when light output from the oscillation stage is present in the amplification chamber;
Optical energy output from the optical amplification stage by controlling at least one of the oscillation excitation source, the amplification excitation source, the gas composition or the gas pressure in the oscillation chamber and the amplification chamber A laser control unit that keeps the pulse variation within a preset allowable range;
A light transmissive part that allows light output from the amplification stage to be transmitted and can increase and attenuate the energy of light transmitted by changing its own transmittance; and
An exposure apparatus that has an energy value of light required for exposure equal to or lower than an energy value of light before being input to the light transmission unit, and further converts the energy value of light required for exposure into a signal and transmits the signal to the outside;
The transmittance of the light transmission unit is controlled according to the signal transmitted from the exposure apparatus, and the energy value of the light output from the light transmission unit is changed to the energy value indicated by the signal transmitted from the exposure apparatus. A matching transmittance control unit;
Have

  The fourth invention will be described with reference to FIGS.

  When the laser gas in the laser chamber 10o is excited by the power supply circuit and the discharge electrodes 11o and 12o (not shown in FIG. 27), the laser light is output from the laser chamber 10o. Part of the laser light is resonated by the optical resonators 20o and 30o, and part of the laser light is output outside the optical resonators 20o and 30o. Laser light output from the oscillation stage laser 100o is input to the amplification stage laser 100a. When the laser gas in the laser chamber 10a is excited by the power supply circuit (not shown in FIG. 27) and the discharge electrodes 11a and 12a (hereinafter referred to as amplification reduction for amplification), the laser light is amplified and output. The laser light output from the front mirror 30a passes through the output attenuation mechanism 50 (light transmission portion) and reaches the exposure apparatus 200.

  A main controller 70 '(laser control unit, transmittance control unit) of the laser apparatus 1' shown in FIG. 2 performs charge voltage control and gas control, and presets the pulse energy Pin before being input to the output attenuation mechanism 50. A value within the permissible range, that is, a value (target pulse energy PL) where the pulse variation is reduced. Further, based on the signal indicating the target pulse energy Pt transmitted from the exposure apparatus 200, the transmittance T of the output attenuation mechanism 50 is controlled so that the output energy of the laser apparatus 1 'is the target pulse required by the exposure apparatus 200. It is made to coincide with the energy Pt (<target pulse energy PL).

A laser system according to a fifth invention is the third invention to the fourth invention,
The transmittance control unit controls the transmittance of the light transmission unit to (energy value of light required for exposure) / (energy value of light before being input to the light transmission unit).

  The transmittance T of the output attenuation mechanism 50 is obtained by using the energy of light required for exposure by the exposure apparatus 200, that is, the target pulse energy Pt, and the energy of light before being input to the output attenuation mechanism 50, that is, the target pulse energy PL value. T = Pt / PL.

  According to the present invention, the laser device is set so as to be able to stably output energy larger than the energy required by the exposure device, and the energy is attenuated by the output attenuation mechanism and output. That is, it is not necessary to largely control the discharge parameter such as the charging voltage in order to control the energy, in other words, the energy can be controlled without deteriorating the energy variation. Therefore, it is possible to realize an expansion of the dynamic range that could not be realized conventionally for suppressing energy variation.

The laser exposure system of the present invention will be described below with reference to the drawings.
(1. Configuration and basic operation of laser exposure system)
[1-1. (Single laser)
FIG. 1 shows a control system diagram when a single laser is used.
The laser exposure system according to the present embodiment includes a laser device 1 and an exposure device 200. The exposure apparatus 200 requests light energy required for exposure of the IC chip to the laser apparatus 1, and the laser apparatus 1 outputs light according to the request of the exposure apparatus 200. The upper limit of the dynamic range of the laser apparatus 1 is set to be equal to or higher than the light energy value required by the exposure apparatus 200.

  In the exposure apparatus 200, an energy value necessary for exposure of the IC chip is set. The exposure apparatus 200 converts information of light required for exposure including the energy value into a signal and transmits the signal to the laser apparatus 1. The exposure apparatus 200 of the present embodiment is a scanner type, but may be a stepper type.

Next, the configuration of the laser device 1 will be described.
Inside the laser chamber 10, a pair of discharge electrodes 11 and 12 are provided that are separated by a predetermined distance, are parallel to each other in the longitudinal direction, and face the discharge surfaces. In FIG. 1, the discharge electrodes 11 and 12 are arranged in a direction perpendicular to the paper surface. Further, windows 13 and 14 are provided on the laser beam output portion on the optical axis of the laser beam in the laser chamber 10. The windows 13 and 14 are made of a material having transparency to laser light, such as CaF2. Both windows 13 and 14 are arranged with their outer surfaces arranged parallel to each other and at a Brewster angle to reduce reflection loss with respect to the laser beam.

  A laser gas is sealed in the laser chamber 10 as a laser medium. In the case of the F2 laser, the laser gas is a mixed gas of F2 gas and a buffer gas made of He, Ne or the like. In the case of a KrF excimer laser, the laser gas is a mixed gas of Kr gas and F2 gas and a buffer gas made of He, Ne or the like. In the case of an ArF excimer laser, the laser gas is a mixed gas of Ar gas and F2 gas and a buffer gas made of He, Ne, or the like. Supply and discharge of each gas is controlled by the gas supply / discharge mechanism 16.

  A high voltage is applied to the discharge electrodes 11 and 12 provided in the laser chamber 10 by the power supply circuit 15. When the voltage between the discharge electrodes 11 and 12 exceeds a predetermined voltage, discharge occurs. Then, after the laser gas is excited and shifted to a high energy level, the laser gas shifts to a low energy level. At this time, light is emitted.

  A band-narrowing module 20 is disposed on the rear side of the laser chamber 10. The band narrowing module 20 is provided with optical elements such as a prism beam expander and a grating, for example. The band narrowing module 20 may be provided with optical elements such as an etalon and a total reflection mirror.

  A front mirror 30 is disposed on the front side of the laser chamber 10. The front mirror 30 and the grating in the band narrowing module 20 constitute an optical resonator. Part of the light output from the laser chamber 10 passes through the front mirror 30 and is output to the outside, and the rest of the light output from the laser chamber 10 passes through the laser chamber 10 to the optical resonators 20, 30. Amplified by reciprocating between them.

  A first pulse energy monitor 40 is disposed on the output side of the front mirror 30. The first pulse energy monitor 40 includes a light receiving sensor and the like, samples a part of the pulsed light output from the front mirror 30, and measures the energy of the pulsed light and the like.

  An output attenuation mechanism 50 is arranged on the output side of the first pulse energy monitor 40. The output attenuation mechanism 50 basically attenuates the energy of light output from the optical resonator (front mirror 30) by changing its own transmittance T (T ≦ 1). The output attenuating mechanism 50 can increase and attenuate the energy by setting the energy of the light output from the optical resonator (front mirror 30) as a maximum value. A specific configuration of the output attenuation mechanism 50 will be described later.

  A second pulse energy monitor 60 is disposed on the output side of the output attenuation mechanism 50. Similar to the first pulse energy monitor 40, the second pulse energy monitor 60 includes a light receiving sensor and the like, samples a part of the pulsed light output from the output attenuation mechanism 50, and measures the energy of the pulsed light and the like.

  The main controller 70 transmits and receives signals to and from other components in the laser exposure system, and controls various operations of the laser apparatus 1. Here, transmission and reception of signals centered on the main controller 70 will be described below.

  The target pulse energy of light required for exposure in the exposure apparatus 200 is Pt, and the target pulse energy of light output from the optical resonator (front mirror 30) and input to the output attenuation mechanism 50 is PL.

  Before the exposure process, the exposure apparatus 200 transmits a signal indicating the target pulse energy Pt to the main controller 70 of the laser apparatus 1.

  The main controller 70 that has received this signal determines the target pulse energy PL to make the energy variation of the light input to the output attenuation mechanism 50 near the minimum, based on the characteristics shown in FIG. The minimum neighborhood means within the allowable range σ shown in FIG. This allowable range σ is set in advance. Next, the main controller 70 obtains the transmittance T (= Pt / PL) of the output attenuation mechanism 50 and transmits a signal for controlling the transmittance to the output attenuation mechanism 50 in order to obtain the transmittance T.

  The first pulse energy monitor 40 detects the pulse energy of the light input to the output attenuation mechanism 50, that is, the pulse energy Pin before the attenuation, and transmits the result to the laser controller 70.

  The main controller 70 that has received this signal transmits a signal for controlling the charging voltage to the power supply circuit 15 via the charger controller 71 for each pulse so that the pulse energy Pin before attenuation becomes the target pulse energy PL. Further, when the pulse energy Pin decreases due to the deterioration of the laser gas, a signal for controlling the supply amount and discharge amount of various gases is transmitted to the gas supply / discharge mechanism 16 via the gas controller 72.

  The second pulse energy monitor 60 detects the pulse energy of the light output from the output attenuation mechanism 50, that is, the pulse energy Pout after attenuation, and transmits the result to the laser controller 70.

The main controller 70 that has received this signal confirms (a) and (b) below.
(A) Whether the target pulse energy Pt transmitted from the exposure apparatus 200 and the detected pulse energy Pout are controlled within a predetermined range, and variations in pulse energy are within an allowable range. (B) Whether the ratio of the pulse energy Pin and Pout before and after attenuation is a predetermined transmittance T (= Pout / Pin).

Here, a dynamic range control method will be described.
The laser device 1 is designed to operate at the maximum output of the required dynamic range. That is, the laser beam output from the optical resonator (front mirror 30) is stably output at a value close to the maximum value of the dynamic range.

  The laser light output from the optical resonator (front mirror 30) passes through the output attenuation mechanism 50. The laser light that has passed through the output attenuation mechanism 50 is measured for pulse energy Pout by the second pulse energy monitor 60. When the main controller 70 of the laser apparatus 1 receives exposure apparatus type information (light energy information required by the exposure apparatus 200) from the scanner type exposure apparatus 200, a target pulse energy Pt is set, and this value is set to this value. Based on this, the transmittance of the output attenuation mechanism 50 is set.

  Thus, by placing the output attenuation mechanism 50 outside the laser resonator, it is possible to arbitrarily control the laser light output input to the exposure apparatus 200 without affecting the laser oscillation conditions. That is, since the discharge parameters such as the charging voltage are not largely controlled, the dynamic range can be expanded without deteriorating the energy variation σ.

  Next, charging voltage control and gas control will be described.

  The control of the pulse energy (exposure amount) can use, for example, the charge voltage control disclosed in Patent Document 1 above. In Patent Document 1, the main controller calculates the charging voltage of the next pulse based on the energy measured by the pulse energy monitor so as to obtain the target pulse energy, and transmits the calculated value to the charger controller. The charger controller controls the charging voltage to be that value.

  More specifically, for the first predetermined number of pulses, the oscillation stop time and the order of pulses within one burst cycle are the same among the past pulse oscillation data, and the current pulse oscillation target is set. Read at least one set of output pulse energy monitor value close to the pulse energy PL and the excitation intensity of the pulse at that time, calculate the excitation intensity at the time of the current pulse oscillation based on the read value, and calculate the calculated excitation intensity The charging voltage is controlled based on the value, and for each pulse generated after the first predetermined number of pulses, the pulse energy monitor value of the previous pulse already output within the current burst cycle and the charging at that time Read the voltage value, calculate the charging voltage value at the time of this pulse oscillation based on these values, and control based on this charging voltage Do.

  If the laser operation is repeated and impurity gas or the like is generated inside the chamber and the charging voltage is maximized, the gas composition or gas pressure may be controlled if the target pulse energy PL is not reached. In general, the laser output can be increased by increasing the halogen gas partial pressure or increasing the total gas pressure. By controlling the gas, the charging voltage may be controlled so that the pulse energy becomes constant while the gain is increased.

[In case of 1-2.2 stage laser]
Since the output of the two-stage laser is larger than the output of the single laser, the dynamic range can be further increased according to the present invention.

  FIG. 2 shows a control system diagram when a two-stage laser is used. FIG. 2 shows a MOPO type of a two-stage laser, but the present invention can also be applied to a MOPA type. The configuration shown in FIG. 2 is similar to the configuration shown in FIG. 1, and the configuration excluding the components given the same reference numerals will be described here.

  The laser exposure system according to the present embodiment includes a laser device 1 ′ and an exposure device 200. The exposure apparatus 200 requests light energy required for exposure of the IC chip from the laser apparatus 1 ′, and the laser apparatus 1 ′ outputs light according to the request of the exposure apparatus 200. The upper limit of the dynamic range of the laser apparatus 1 ′ is set to be equal to or higher than the light energy value required by the exposure apparatus 200.

  The oscillation stage laser 100o and the amplification stage laser 100a are the same as those shown in FIG.

  A first pulse energy monitor 40 'is disposed on the output side of the oscillation stage laser 100o, an amplification stage laser 100a is disposed on the output side of the first pulse energy monitor 40', and an output is provided on the output side of the amplification stage laser 100o. An attenuation mechanism 50 is disposed, and a second pulse energy monitor 60 ′ is disposed on the output side of the output attenuation mechanism 50.

  The first pulse energy monitor 40 'is the same as the first pulse energy monitor 40 shown in FIG. 1, and the second pulse energy monitor 60' is the same as the second pulse energy monitor 60 shown in FIG.

  The main controller 70 'transmits and receives signals to and from other components in the laser exposure system, and controls various operations of the laser apparatus 1'. The charger controller 71 'controls the charging voltage of the oscillation stage laser 100o and the amplification stage laser 100a in accordance with a control signal from the main controller 70'. The gas controller 72 'performs gas control of the oscillation stage laser 100o and the amplification stage laser 100a in accordance with a control signal from the main controller 70'.

Here, a dynamic range control method will be described.
The amplification stage laser 100a is designed to operate at the maximum output of the required dynamic range. For example, if the required dynamic range of pulse energy is 5 mJ to 15 mJ, it is assumed that the laser apparatus 1 ′ can output energy of 5 mJ to 15 mJ while maintaining energy stability. That is, the laser beam output from the amplification stage laser 100a is stably output at a value close to the maximum value of the dynamic range.

  The laser light output from the amplification stage laser 100a passes through the output attenuation mechanism 50. The laser light that has passed through the output attenuation mechanism 50 is measured for pulse energy Pout by the second pulse energy monitor 60 '. When the main controller 70 'of the laser apparatus 1' receives information on the exposure apparatus type (light energy information required by the exposure apparatus 200) from the scanner type exposure apparatus 200, the target pulse energy Pt is set. Based on the value, the transmittance of the output attenuation mechanism 50 is set.

  For example, as shown in FIG. 3, when the maximum output of the laser apparatus 1 'is 15 mJ and the energy required by the exposure apparatus 200 is 15 mJ, the transmittance T of the output attenuation mechanism 50 is set to 15 mJ / 15 mJ. = Set to 1. If the energy required by the exposure apparatus is 10 mJ, the transmittance T of the output attenuation mechanism 50 is set to 10 mJ / 15 mJ = 0.67. If the energy required by the exposure apparatus is 6.7 mJ, the transmittance T of the output attenuation mechanism 50 is set to 6.7 mJ / 15 mJ = 0.44.

  Thus, by placing the output attenuation mechanism 50 outside the laser resonator, it is possible to arbitrarily control the laser light output input to the exposure apparatus 200 without affecting the laser oscillation conditions. That is, since the discharge parameters such as the charging voltage are not largely controlled, the dynamic range can be expanded without deteriorating the energy variation σ.

  Next, charging voltage control and gas control will be described.

  The control of the pulse energy (exposure amount) can use, for example, the charge voltage control disclosed in Patent Document 1 above. In Patent Document 1, the main controller calculates the charging voltage of the next pulse based on the energy measured by the pulse energy monitor so as to obtain the target pulse energy, and transmits the calculated value to the charger controller. The charger controller controls the charging voltage of the amplification stage laser to be the value.

  More specifically, for the first predetermined number of pulses, the oscillation stop time and the order of pulses within one burst cycle are the same among the past pulse oscillation data, and the current pulse oscillation target is set. Read at least one set of output pulse energy monitor value close to the pulse energy PL and the excitation intensity of the pulse at that time, calculate the excitation intensity at the time of the current pulse oscillation based on the read value, and calculate the calculated excitation intensity The charging voltage is controlled based on the value, and for each pulse generated after the first predetermined number of pulses, the pulse energy monitor value of the previous pulse already output within the current burst cycle and the charging at that time Read the voltage value, calculate the charging voltage value at the time of this pulse oscillation based on these values, and control based on this charging voltage Do.

  In the configuration shown in FIG. 2, the second energy monitor 60 'is arranged on the output side of the output attenuation mechanism 50, but the energy monitor is not arranged on the output side of the amplification stage laser 100a. In such a case, the laser output value Pin before attenuation is obtained by dividing the energy value Pout measured by the second energy monitor 60 'by the transmittance T of the output attenuation mechanism 50 (Pin = Pout / T). use. Alternatively, when it is desired to monitor the laser output excluding the influence of the output attenuation mechanism 50, a pulse energy monitor is arranged on the input side of the output attenuation mechanism 50, that is, on the output side of the amplification stage laser 100a as shown in FIG. Then, charging voltage control may be performed based on the monitor value.

  If the laser operation is repeated and impurity gas or the like is generated inside the chamber and the charging voltage is maximized, the gas composition or gas pressure may be controlled if the target pulse energy PL is not reached. In general, the laser output can be increased by increasing the halogen gas partial pressure or increasing the total gas pressure. By controlling the gas, the charging voltage may be controlled so that the pulse energy becomes constant while the gain is increased.

(2. Processing flow of laser exposure system)
Hereinafter, the processing flow of the laser exposure system including the single laser shown in FIG. 1 will be described as a representative, but the processing flow of the laser exposure system including the two-stage laser shown in FIG. 2 is basically the same. .

FIG. 4 shows a flowchart of the main routine.
The processing flow of the main routine can be broadly divided into a processing flow for adjustment oscillation (steps S11 to S14) and a processing flow during exposure (steps S15 to S17).

First, the processing flow of adjusted oscillation will be described.
The exposure apparatus 200 transmits a signal indicating the target pulse energy Pt to the main controller 70 of the laser apparatus 1. The main controller 70 receives this signal and closes the shutter provided at the exit of the laser device 1 for the adjustment oscillation (step S11).

  Next, the target pulse energy PL and the transmittance T are determined, and the target pulse energy PL and the transmittance T are determined (step S12). Further, the transmittance control subroutine is processed, and the output attenuation mechanism 50 is controlled to obtain the determined transmittance T (step S13). Details of each subroutine will be described later.

  If the difference between the attenuated pulse energy Pout and the target pulse energy Pt is within an allowable range, the main controller 70 transmits a signal indicating preparation OK to the exposure apparatus 200 and is provided at the exit of the laser apparatus 1. The opened shutter is opened (step S14). Thus, the adjustment oscillation ends, and the process proceeds to exposure processing.

Next, a processing flow during exposure will be described.
The exposure apparatus 200 transmits an oscillation command signal to the main controller 70 of the laser apparatus 1, and the main controller 70 starts laser oscillation in response to reception of this command signal. The main controller 70 supplies power so that the energy variation of the laser light becomes small at the transmittance T of the output attenuation mechanism 50 determined by the adjustment oscillation, that is, the pulse energy Pin before attenuation becomes the target pulse energy PL. The charging voltage of the circuit 15 is controlled, and the gas supply amount and discharge amount of the gas supply / discharge mechanism 16 are controlled (step S15).

  In each pulse, the difference between the pulse energy Pout after attenuation and the target pulse energy Pt is within the allowable range, and the energy variation of the pulse energy Pin before attenuation or the pulse energy Pout after attenuation is within the allowable range. The exposure is continued (Yes in step S16, Yes in step S17).

  If the difference between the pulse energy Pout after attenuation and the target pulse energy Pt is outside the allowable range, or if the energy variation of the pulse energy Pin before attenuation or the pulse energy Pout after attenuation is outside the allowable range, the exposure is interrupted. Then, the adjustment oscillation is performed again (No in Step S16, No in Step S17).

  At the time of laser oscillation, the main controller 70 performs a pulse control of the output energy in order to suppress the variation in the pulse energy to an allowable value so that the exposure amount becomes constant. This control is performed by charge voltage control, gas composition, gas pressure control, or the like. This control method uses a method disclosed in the prior art, for example, Patent Document 1 described above. However, the charging voltage control, gas composition, and gas pressure control performed here are not controls that cause the energy variation to exceed the allowable range.

  Next, among the subroutines shown in FIG. 4, a subroutine for determining the target pulse energy PL and the transmittance T will be described.

FIG. 5 shows a flowchart of a subroutine for determining the target pulse energy PL and the transmittance T.
First, the target pulse energy PL determination subroutine is processed (step S21). Next, the main controller 70 calculates the transmittance T = Pt / PL in the output attenuation mechanism 50 (step S22). After the above processing ends, the process returns to the main routine shown in FIG.

FIGS. 6A and 6B show a flowchart of a subroutine for determining the target pulse energy PL.
In the subroutine of FIG. 6A, the maximum rated output Pmax of light input to the output attenuation mechanism 50 is determined as the target pulse energy PL, and the process returns to the main routine shown in FIG.

  In the subroutine of FIG. 6B, the pulse energy Pin before attenuation that minimizes the energy variation is detected by the adjustment oscillation in advance, this value is determined as the target pulse energy PL, and the process returns to the main routine shown in FIG.

  An example of the process of FIG. 6B will be specifically described. In order to measure the relationship between the target pulse energy PL and the energy variation, the main controller 70 changes the target pulse energy PL at several levels (1 to n), and each target pulse energy PLx (x = 1 to n). Measure the energy variation over time. Among these, the target pulse energy PLx having the smallest energy variation is set as the optimum target pulse energy PL.

  Next, the transmittance control subroutine among the subroutines shown in FIG. 4 will be described. Hereinafter, a specific example of the configuration of the output attenuation mechanism 50 will be shown as [specific examples 1 to 5], and the transmittance control process for each output attenuation mechanism 50 will be described.

[Specific Examples of Energy Attenuator 1. Transmittance control by transflective element)
The transmittance can be controlled by controlling the incident angle of the laser beam with respect to the transmission / reflection element.

  As shown in FIGS. 7A and 7B, the output attenuation mechanism 50 is a signal for controlling the transmittance T transmitted from the two substrates 51a of CaF2 arranged on the laser optical axis and the main controller 70. And a rotation stage 51b that rotationally drives the two substrates 51a. The rotation center axis of the rotary stage 51b is parallel to the direction perpendicular to the paper surface of FIG. 7, and the rotary stage 51b is rotatable in the direction of the arrow shown in FIG. When the laser light is incident on the substrate 51a, a part of the light is transmitted through the substrate 51a, but the remaining light is reflected on the surface of the substrate 51a. The laser beam is attenuated by this reflected amount. The rate of light attenuation is determined according to the incident angle of the laser light with respect to the substrate 51a (the angle formed between the normal line of the substrate 51a and the laser optical axis). The principle will be described with reference to FIGS.

When laser light is incident on a substrate 51a having a refractive index n2 from a medium having a refractive index n1 at an incident angle θi, the transmission angle θt of the light transmitted through the substrate 51a is determined by Snell's law (the following equation (1)). Desired.
sin θt / sin θi = n1 / n2 (1)
Further, when the substrate 51a is uncoated, the reflectance is determined by the Fresnel reflection formula (the following formulas (2) and (3)).
rs = [sin (θi−θt) / sin (θi + θt)] ² (2)
rp = [tan (θi−θt) / tan (θi + θt)] ² (3)
The subscripts s and p mean s-polarized light and p-polarized light, respectively. The p-polarized light is a polarized light component whose electric field vector is parallel to the incident surface (direction parallel to the paper surface in FIG. 8), and the s-polarized light is a polarized light component whose electric field vector is perpendicular to the incident surface (direction perpendicular to the paper surface in FIG. 8). is there.

  Thus, the reflectance of light on the substrate surface varies depending on the polarization component. Usually, since a laser beam is linearly polarized light, the reflectance according to the Fresnel reflection formula can be obtained by making the linearly polarized light incident on p-polarized light or s-polarized light.

The p-polarized light has an incident angle at which the reflectance becomes 0, and this angle is referred to as the Brewster angle θb. Brewster angle θb is
θb = arctan (n2 / n1) (4)
Indicated by

  FIG. 9 shows the relationship between the incident angle of p-polarized light and s-polarized light and the reflectance. In FIG. 9, the vertical axis represents the reflectance, and the horizontal axis represents the incident angle θi with the Brewster angle θb as a reference (angle 0). When the laser beam is incident on the substrate, if the polarization is in the direction of p-polarized light and the incident angle is the Brewster angle θb, the reflectance will be 0, so that absorption inside the substrate or scattering on the substrate surface will occur. If neglected, the laser beam is 100% transmitted through the substrate. As can be seen from FIG. 9, when the incident angle θi is increased from the Brewster angle θb, the reflectance increases rapidly. Therefore, in order to increase the attenuation factor (= 1−transmittance), the incident angle θi of the laser beam with respect to the substrate 51a may be increased from the Brewster angle θb as shown in FIG. 7B.

  If there is only one substrate 51a, the optical axis after transmitting through the substrate deviates from the optical axis before transmitting through the substrate. Also, when the incident angle θi is changed by rotating the substrate 51a, the amount of deviation of the optical axis changes according to the incident angle θi. In order to correct such an optical axis shift, the two mirror-targeted substrates 51a are arranged with the same incident angle θi of the laser beam before and after the laser optical axis. The two substrates 51a are rotationally driven at the same time, and the incident angles θi are controlled simultaneously.

When two substrates 51a are provided, there are four reflecting surfaces. When the transmittance at one surface and t, the total transmittance T after fourth surface transmittance becomes T = t ^4. Assuming that the Fresnel reflectivity on one surface is r, t = (1−r), so that T = (1−r) ⁴ .

FIG. 10 shows a flowchart of a transmittance control subroutine when two substrates are used. First, the main controller 70 calculates the incident angle θi of the laser beam with respect to the substrate 51a so that the transmittance of the output attenuation mechanism 50 is T. Here, it is assumed that the laser light is incident on the substrate 51a as p-polarized light. As described above, the reflective surface when the substrate 51a is two becomes T = ^{(1-rp) 4} to become four sides. Since the transmittance T has been determined in the previous processing (target pulse energy PL and transmittance T determination subroutine), the reflectance rp of the p-polarized component is obtained. Further, the incident angle θi is obtained from the Snell's law (the above formula (1)), the Fresnel reflection formula (the above formula (3)), and the reflectance rp (step S31).

  After calculating the incident angle θi necessary for attenuation, the main controller 70 transmits a control signal to the output attenuation mechanism 50. When the output attenuation mechanism 50 receives this signal, the rotary stage 50b rotationally drives the substrate 51a to set the incident angle of the laser beam to the substrate 51a to θi calculated (step S32).

  Next, in order to confirm the control of the substrate 51a, the processing of the output confirmation subroutine 1 is performed, and then the process returns to the main routine shown in FIG. 4 (step 33).

FIG. 11 shows a flowchart of the output confirmation subroutine 1.
First, the laser is oscillated at rated power (oscillated at the target pulse energy PL) (step S41). At this time, the second pulse energy monitor 60 measures the attenuated pulse energy Pout (step S42). The main controller 70 determines whether or not the pulse energy Pout measured by the second pulse energy monitor 60 is the target pulse energy Pt required by the exposure apparatus 200. Specifically, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated. If the error (| Pout−Pt |) is within the allowable error dP, the control in the dynamic range is terminated and the process returns to the main routine shown in FIG. 4 (Yes in step 43).

  On the other hand, if the error (| Pout−Pt |) is larger than the allowable error dP, the incident angle θi is finely adjusted (No in Step S43). The main controller 70 determines whether the pulse energy Pout is larger or smaller than the target pulse energy Pt (step S44). When Pout> Pt, the attenuation amount in the output attenuation mechanism 50 must be increased, so the main controller 70 performs control to slightly increase the incident angle θi. If the slight increase is dθ, the incident angle is changed from θi to θi + dθ (step S45). In the case of Pout <Pt, the attenuation amount in the output attenuation mechanism 50 must be reduced, so the main controller 70 performs control to slightly reduce the incident angle θi. When the slight reduction amount is dθ, the incident angle is changed from θi to θi−dθ (step S46). The above processing is repeated until the error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt becomes equal to or less than the allowable error dP.

  As another fine adjustment control method, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated, and a change amount of the incident angle corresponding to the difference is calculated. The incident angle may be changed by that amount.

[Specific Example of Energy Attenuator 2. (Transmittance control by polarizer)
As described above, the laser beam is linearly polarized light. The transmittance can be controlled by controlling the polarization.

  As shown in FIGS. 12B and 12D, the output attenuation mechanism 50 includes a λ / 2 plate 52a disposed perpendicular to the laser optical axis, and laser light on the output side of the λ / 2 plate 52a. A CaF2 substrate 52c having a ps separation film 52b formed on the surface and a λ / 2 plate 52a centered on the optical axis according to a signal for controlling the transmittance T transmitted from the main controller 70. And a rotation mechanism 52d for rotationally driving.

  The λ / 2 plate 52a can shift the phase difference of the slow axis component by 180 ° with respect to the fast axis. For example, as shown in FIGS. 12A and 12B, when linearly polarized light whose polarization direction is parallel to the horizontal plane is incident on the λ / 2 plate 52a at an angle of 45 ° to the fast axis, the λ / 2 plate 52a The polarization direction of the laser light transmitted through the laser beam changes in a direction orthogonal to the horizontal plane.

  The substrate 52c is arranged so that the laser beam is obliquely incident, and the ps separation film 52b is formed on the incident surface so that the p-polarized component of the laser beam is transmitted 100% and the s-polarized component is highly reflected.

As shown in FIG. 12B, when laser light in the p-polarized direction is incident on the ps separation film 52b, 100% of the laser light component is transmitted.

  In the state shown in FIGS. 12A and 12B, the laser light having the s polarization direction with respect to the ps separation film 52b is in the p polarization direction with respect to the ps separation film 52b by the λ / 2 plate 52a. Laser light. Therefore, almost 100% of the laser beam is transmitted through the ps separation film 52b.

  Here, the angle of the fast axis of the λ / 2 plate 52a is θ, and the angle formed by the polarization direction of the laser beam incident on the λ / 2 plate 52a and the fast axis is 45 °, that is, FIG. The state shown in a) and (b) is defined as θ = 0. 12C and 12D show a state where the λ / 2 plate 52a is rotated about the optical axis so that the angle of the fast axis is θ ≠ 0. As shown in FIGS. 12C and 12D, when θ ≠ 0, the light transmitted through the λ / 2 plate 52a becomes elliptically polarized light. That is, both p-polarized light and s-polarized light exist. The s-polarized component is not transmitted because it is reflected by the ps separation film 52b. For this reason, the entire transmittance is reduced by the intensity of the s-polarized component.

  In the λ / 2 plate 52a, when the angle θ is 45 °, that is, when the phase direction of the laser beam is the same as that of the laser beam, the phase of the laser beam does not change in the λ / 2 plate 52a. Are emitted from the λ / 2 plate 52a. Then, since the laser light is reflected by the ps separation film 52b, the entire transmittance becomes almost zero. Actually, it is difficult to manufacture a film that reflects 100%, so that a few percent is transmitted.

  FIG. 13 shows the relationship between the transmittance of the ps separation membrane 52b and the angle θ of the fast axis of the λ / 2 plate 52a. In order to control the transmittance, the λ / 2 plate 52a may be arranged so that θ = 0, and the rotation angle of the λ / 2 plate 52a may be controlled in the range of θ = 0 to 45 °. That is, θ can be reduced to increase the transmittance, and θ can be increased to decrease the transmittance.

  FIG. 14 shows a flowchart of a transmittance control subroutine when a λ / 2 plate is used. First, the main controller 70 obtains the angle θ of the λ / 2 plate 52a corresponding to the transmittance T from the relationship shown in FIG. 13 so that the transmittance of the output attenuation mechanism 50 is T. (Step S51).

  When the main controller 70 obtains the angle θ necessary for attenuation, the main controller 70 transmits a control signal to the output attenuation mechanism 50. When the output attenuating mechanism 50 receives this signal, the rotating mechanism 52d rotationally drives the λ / 2 plate 52a to set the angle of the fast axis of the λ / 2 plate 52a to θ obtained (step S52).

  Next, in order to confirm the control of the λ / 2 plate 52a, the process of the output confirmation subroutine 2 is performed, and then the process returns to the main routine shown in FIG. 4 (step 53).

  FIG. 15 shows a flowchart of the output confirmation subroutine 2. The subroutine shown in FIG. 15 has many processes in common with the subroutine shown in FIG. 11, but all processes will be described here again.

  First, the laser is oscillated at rated power (oscillated at the target pulse energy PL) (step S61). At this time, the second pulse energy monitor 60 measures the attenuated pulse energy Pout (step S62). The main controller 70 determines whether or not the pulse energy Pout measured by the second pulse energy monitor 60 is the target pulse energy Pt required by the exposure apparatus 200. Specifically, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated. If the error (| Pout−Pt |) is within the allowable error dP, the control in the dynamic range is terminated, and the process returns to the main routine shown in FIG. 4 (Yes in step 63).

  On the other hand, if the error (| Pout−Pt |) is larger than the allowable error dP, the angle θ is finely adjusted (No in Step S63). The main controller 70 determines whether the pulse energy Pout is larger or smaller than the target pulse energy Pt (step S64). In the case of Pout> Pt, the attenuation amount in the output attenuation mechanism 50 must be increased, so the main controller 70 performs control to slightly increase the angle θ. If the slight increase is dθ, the angle is changed from θ to θ + dθ (step S65). In the case of Pout <Pt, the amount of attenuation in the output attenuation mechanism 50 must be reduced, so the main controller 70 performs control to slightly reduce the angle θ. When the slight reduction amount is dθ, the angle is changed from θ to θ−dθ (step S66). The above processing is repeated until the error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt becomes equal to or less than the allowable error dP.

  As another fine adjustment control method, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated, and an amount of change in angle corresponding to the difference is calculated. Only the angle may be changed.

[Specific Example of Energy Attenuator 3. Transmission control by slit 1]
The transmittance can be controlled simply by controlling the optical path area of the laser beam by means of a slit or the like.

  As shown in FIGS. 16A and 16B, the output attenuation mechanism 50 includes a slit 53a that is movable toward and away from each other via the optical path of the laser beam, and a transmittance that is transmitted from the main controller 70. And a drive mechanism 53b for driving the slit 53a in accordance with a signal for controlling T. As shown in FIG. 16A, the transmittance T is 1 when the slit 53a does not block the laser beam. As shown in FIG. 16B, when the slit 53a blocks the laser beam, the transmittance T decreases to less than 1.

  In FIG. 16, two slits 53a are arranged in the vertical direction of the laser beam. However, two slits may be arranged in the horizontal direction of the laser beam, and one slit is inserted from one direction. But it ’s okay.

  FIG. 17 shows the relationship between the amount of movement x of the slit and the transmittance. If this relationship is represented by the relationship y = f (x), the transmittance T can be adjusted by T = f (x).

FIG. 18 shows a flowchart of a transmittance control subroutine when a slit is used. First, the main controller 70 obtains the slit movement amount x with respect to the transmittance T so that the transmittance of the output attenuation mechanism 50 is T. The slit movement amount x is calculated using the relationship f (x) shown in FIG. 17 measured in advance (x = f ⁻¹ (T)). When the relational expression T = f (x) between the slit movement amount x and the transmittance T cannot be expressed, a database (x, T) of the slit movement amount x and the transmittance T is created, and the main controller 70 The value of the slit movement amount x with respect to the transmittance T may be read from the database (step S71).

  After obtaining the slit movement amount x necessary for attenuation, the main controller 70 transmits a control signal to the output attenuation mechanism 50. When the output attenuation mechanism 50 receives this signal, the drive mechanism 53b drives the slit 53a by the movement amount x (step S72).

  Next, in order to confirm the control of the slit 53a, the process of the output confirmation subroutine 3 is performed, and then the process returns to the main routine shown in FIG. 4 (step 73).

  FIG. 18 shows a flowchart of the output confirmation subroutine 3. The subroutine shown in FIG. 18 has many processes in common with the subroutines shown in FIGS. 11 and 15, but here, all the processes will be described again.

  First, the laser is oscillated at rated power (oscillated at the target pulse energy PL) (step S81). At this time, the second pulse energy monitor 60 measures the attenuated pulse energy Pout (step S82). The main controller 70 determines whether or not the pulse energy Pout measured by the second pulse energy monitor 60 is the target pulse energy Pt required by the exposure apparatus 200. Specifically, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated. If the error (| Pout−Pt |) is within the allowable error dP, the control in the dynamic range is terminated, and the process returns to the main routine shown in FIG. 4 (Yes in step 83).

  On the other hand, if the error (| Pout−Pt |) is larger than the allowable error dP, the movement amount x is finely adjusted (No in Step S83). The main controller 70 determines whether the pulse energy Pout is larger or smaller than the target pulse energy Pt (step S84). When Pout> Pt, the attenuation amount in the output attenuation mechanism 50 has to be increased, so the main controller 70 performs control to slightly increase the movement amount x. When the slight increase amount is dx, the movement amount is changed from x to x + dx (step S85). In the case of Pout <Pt, the attenuation amount in the output attenuation mechanism 50 must be reduced, so the main controller 70 performs control to slightly reduce the movement amount x. If the slight reduction amount is dx, the movement amount is changed from x to x-dx (step S86). The above processing is repeated until the error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt becomes equal to or less than the allowable error dP.

  As another fine adjustment control method, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated, a change amount of the movement amount corresponding to the difference is calculated, and the change amount is calculated. The amount of movement may be changed by that amount.

[Specific Example of Energy Attenuator 4. Transmittance control by slit 2]
As shown in FIGS. 20A and 20B, the output attenuation mechanism 50 controls the aperture slit 54a in which the aperture amount of the hole through which the laser light passes is variable, and the transmittance T transmitted from the main controller 70. And a drive mechanism 54b for controlling the aperture amount of the aperture slit 54a according to the signal to be transmitted. As shown in FIG. 20A, the transmittance T is 1 when the diaphragm slit 54a does not block the laser beam. As shown in FIG. 20B, when the diaphragm slit 54a blocks the laser beam, the transmittance T decreases to less than 1.

  FIG. 21 shows the relationship between the aperture amount z of the aperture slit and the transmittance. If this relationship is represented by the relationship y = g (z), the transmittance T can be adjusted by T = g (z).

FIG. 22 shows a flowchart of a transmittance control subroutine when a diaphragm slit is used.
First, the main controller 70 obtains the slit aperture amount z with respect to the transmittance T so that the transmittance of the output attenuation mechanism 50 is T. The slit aperture amount z is calculated using the relationship g (z) shown in FIG. 21 measured in advance (z = g ⁻¹ (T)). When the relational expression T = g (z) between the slit aperture amount z and the transmittance T cannot be expressed, a database (z, T) of the slit aperture amount z and the transmittance T is created, and the main controller 70 The value of the slit aperture amount z with respect to the transmittance T may be read from the database (step S91).

  When the main controller 70 obtains the slit aperture amount z necessary for attenuation, the main controller 70 transmits a control signal to the output attenuation mechanism 50. When the output attenuation mechanism 50 receives this signal, the drive mechanism 54b controls the aperture amount z of the aperture slit 54a (step S92).

  Next, in order to confirm the control of the aperture slit 54a, the process of the output confirmation subroutine 4 is performed, and then the process returns to the main routine shown in FIG. 4 (step 93).

  FIG. 23 shows a flowchart of the output confirmation subroutine 4. The subroutine shown in FIG. 23 has many processes in common with the subroutine shown in FIG. 18, but all processes will be described here again.

  First, the laser is oscillated at rated power (oscillated at the target pulse energy PL) (step S101). At this time, the second pulse energy monitor 60 measures the attenuated pulse energy Pout (step S102). The main controller 70 determines whether or not the pulse energy Pout measured by the second pulse energy monitor 60 is the target pulse energy Pt required by the exposure apparatus 200. Specifically, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated. If the error (| Pout−Pt |) is within the allowable error dP, the control in the dynamic range is terminated, and the process returns to the main routine shown in FIG. 4 (Yes in Step 103).

  On the other hand, if the error (| Pout−Pt |) is larger than the allowable error dP, the aperture amount z is finely adjusted (No in Step S93). The main controller 70 determines whether the pulse energy Pout is larger or smaller than the target pulse energy Pt (step S104). When Pout> Pt, the attenuation amount in the output attenuation mechanism 50 must be increased, so the main controller 70 performs control to slightly increase the aperture amount z. When the slight increase amount is dz, the aperture amount is changed from z to z + dz (step S105). In the case of Pout <Pt, the attenuation amount in the output attenuation mechanism 50 must be reduced, so the main controller 70 performs control to slightly reduce the aperture amount z. If the slight reduction amount is dz, the aperture amount is changed from z to z-dz (step S106). The above processing is repeated until the error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt becomes equal to or less than the allowable error dP.

  As another fine adjustment control method, an error (| Pout−Pt |) of the pulse energy Pout with respect to the target pulse energy Pt is calculated, a change amount of the aperture amount corresponding to the difference is calculated, and the change amount is calculated. The aperture amount may be changed by the amount.

[Specific Example of Energy Attenuator 5. (Transmittance control by partially reflective film)
The transmittance can be controlled by controlling the reflectance of the partially reflective film through which the laser light is transmitted.

  As shown in FIG. 24, the output attenuation mechanism 50 includes a substrate 55b made of CaF2 on which a plurality of different partial reflection films 55a are formed, and a substrate 55b according to a signal for controlling the transmittance T transmitted from the main controller 70. And a drive mechanism 55c for driving the motor. In FIG. 24, three types of partial reflection films 55a1 to 55a3 are linearly formed on the substrate 55b, and the drive mechanism 55c drives the substrate 55b in the vertical direction on the paper surface, so that any of the partial reflection films 55a1 to 55a3 is formed. Is arranged in the laser beam path. Actually, it is only necessary to form a partial reflection film necessary for exposure.

  The partial reflection film does not need to be arranged linearly as shown in FIG. For example, they may be arranged on concentric circles.

  FIG. 25 shows the transmittance of the partial reflection films 55a1 to 55a3. As shown in FIG. 25, since the output attenuation mechanism 50 using the partial reflection film 55a only switches the reflectance to a plurality of stages, the transmittance changes stepwise.

  FIG. 26 shows a flowchart of a transmittance control subroutine when a partially reflective film is used. First, the main controller 70 selects the partial reflection film 55a from the relationship shown in FIG. 25 so that the transmittance of the output attenuation mechanism 50 is close to T. (Step S111).

  When the main controller 70 selects the partial reflection film 55 a, it transmits a control signal to the output attenuation mechanism 50. When the output attenuation mechanism 50 receives this signal, the drive mechanism 55c drives the substrate 55a, places the selected partial reflection film 55a in the laser beam path, and returns to the main routine shown in FIG. 4 (step S112).

  According to the present invention described above, the laser apparatus is set so as to be able to stably output energy larger than the energy required by the exposure apparatus, and the energy is attenuated by the output attenuation mechanism and output. That is, it is not necessary to largely control the discharge parameters such as the charging voltage in order to control the energy, in other words, the energy can be controlled without deteriorating the energy variation. Therefore, it is possible to realize an expansion of the dynamic range that could not be realized conventionally for suppressing energy variation.

FIG. 1 is a control system diagram when a single laser is used. FIG. 2 is a control system diagram when a two-stage laser is used. FIG. 3 is a diagram showing the relationship between the laser output and the transmittance of the output attenuation mechanism. FIG. 4 is a flowchart of the main routine. FIG. 5 is a flowchart of a subroutine for determining the target pulse energy PL and the transmittance T. FIGS. 6A and 6B are flowcharts of a subroutine for determining the target pulse energy PL. FIGS. 7A and 7B are configuration diagrams of specific example 1 of the output attenuation mechanism. FIG. 8 is a diagram showing light incidence, reflection, and transmission. FIG. 9 shows the relationship between the incident angle of p-polarized light and s-polarized light and the reflectance. FIG. 10 is a flowchart of a transmittance control subroutine when two substrates are used. FIG. 11 is a flowchart of the output confirmation subroutine 1. 12A, 12B, 12C, and 12D are configuration diagrams of a specific example 2 of the output attenuation mechanism. FIG. 13 is a graph showing the relationship between the transmittance of the ps separation membrane and the angle θ of the fast axis of the λ / 2 plate. FIG. 14 is a flowchart of a transmittance control subroutine when a λ / 2 plate is used. FIG. 15 is a flowchart of the output confirmation subroutine 2. FIGS. 16A and 16B are configuration diagrams of specific example 3 of the output attenuation mechanism. FIG. 17 is a diagram showing the relationship between the amount of movement x of the slit and the transmittance. FIG. 18 is a flowchart of a transmittance control subroutine when a slit is used. FIG. 19 shows a flowchart of the output confirmation subroutine 3. 20A and 20B are configuration diagrams of a specific example 4 of the output attenuation mechanism. FIG. 21 is a diagram showing the relationship between the aperture amount z of the aperture slit and the transmittance. FIG. 22 is a flowchart of a transmittance control subroutine when a diaphragm slit is used. FIG. 23 shows a flowchart of the output confirmation subroutine 4. FIG. 24 is a configuration diagram of a specific example 5 of the output attenuation mechanism. FIG. 25 is a diagram showing the transmittance of the partial reflection film. FIG. 26 is a flowchart of a transmittance control subroutine when a partially reflective film is used. FIG. 27 is a diagram showing a basic configuration of a MOPO type two-stage laser apparatus. FIGS. 28A, 28B, and 28C are diagrams for explaining the oscillation operation of the stepper type exposure apparatus. FIGS. 29A and 29B are diagrams for explaining the oscillation operation of the scanner type exposure apparatus. FIG. 30 is a conventional control system diagram. FIG. 31 is a diagram showing a conventional variable attenuator. FIG. 32 is a diagram showing the relationship between “charging voltage HV−laser output E” and “charging voltage HV−energy variation σ”. FIG. 33 is a diagram illustrating an example of a dynamic range.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser apparatus 10 ... Laser chamber 11, 12 ... Discharge electrode 15 ... Power supply voltage 16 ... Gas supply / discharge mechanism 50 ... Output attenuation mechanism 70 ... Main controller 200 ... Exposure apparatus

Claims (5)

A chamber containing laser gas;
An excitation source for exciting the laser gas in the chamber;
A part of the light output from the chamber with excitation of the laser gas is output to the outside, and the rest is resonated through the chamber;
By controlling at least one of the excitation intensity of the excitation source and the gas composition or gas pressure in the chamber, the pulse variation of the optical energy output from the optical resonator falls within a preset allowable range. A laser controller;
A light transmissive part that allows light output from the optical resonator to pass through, and can increase and attenuate the energy of the transmitted light by changing its own transmittance; and
A transmittance control unit for controlling the transmittance in the light transmitting unit;
A laser system. An oscillation chamber that encloses the laser gas, an oscillation excitation source that excites the laser gas in the oscillation chamber, a part of the light that is output from the oscillation chamber as the laser gas is excited, and the rest An oscillation stage having an optical resonator that resonates through the chamber;
An amplification stage that encloses a laser gas; and an amplification stage that excites a laser gas in the amplification chamber when light output from the oscillation stage is present in the amplification chamber;
Optical energy output from the optical amplification stage by controlling at least one of the oscillation excitation source, the amplification excitation source, the gas composition or the gas pressure in the oscillation chamber and the amplification chamber A laser control unit that keeps the pulse variation within a preset allowable range;
A light transmissive part that allows light output from the amplification stage to be transmitted and can increase and attenuate the energy of light transmitted by changing its own transmittance; and
A transmittance control unit for controlling the transmittance in the light transmitting unit;
A laser system. A chamber containing laser gas;
An excitation source for exciting the laser gas in the chamber;
A part of the light output from the chamber with excitation of the laser gas is output to the outside, and the rest is resonated through the chamber;
By controlling at least one of the excitation intensity of the excitation source and the gas composition or gas pressure in the chamber, the pulse variation of the optical energy output from the optical resonator falls within a preset allowable range. A laser controller;
A light transmissive part that allows light output from the optical resonator to pass through, and can increase and attenuate the energy of the transmitted light by changing its own transmittance; and
An exposure apparatus that has an energy value of light required for exposure equal to or lower than an energy value of light before being input to the light transmission unit, and further converts the energy value of light required for exposure into a signal and transmits the signal to the outside;
The transmittance of the light transmission unit is controlled according to the signal transmitted from the exposure apparatus, and the energy value of the light output from the light transmission unit is changed to the energy value indicated by the signal transmitted from the exposure apparatus. A matching transmittance control unit;
A laser exposure system. An oscillation chamber that encloses the laser gas, an oscillation excitation source that excites the laser gas in the oscillation chamber, a part of the light that is output from the oscillation chamber as the laser gas is excited, and the rest An oscillation stage having an optical resonator that resonates through the chamber;
An amplification stage that encloses a laser gas; and an amplification stage that excites a laser gas in the amplification chamber when light output from the oscillation stage is present in the amplification chamber;
Optical energy output from the optical amplification stage by controlling at least one of the oscillation excitation source, the amplification excitation source, the gas composition or the gas pressure in the oscillation chamber and the amplification chamber A laser control unit that keeps the pulse variation within a preset allowable range;
A light transmissive part that allows light output from the amplification stage to be transmitted and can increase and attenuate the energy of light transmitted by changing its own transmittance; and
An exposure apparatus that has an energy value of light required for exposure equal to or lower than an energy value of light before being input to the light transmission unit, and further converts the energy value of light required for exposure into a signal and transmits the signal to the outside;
The transmittance of the light transmission unit is controlled according to the signal transmitted from the exposure apparatus, and the energy value of the light output from the light transmission unit is changed to the energy value indicated by the signal transmitted from the exposure apparatus. A matching transmittance control unit;
A laser exposure system. The transmittance control unit controls the transmittance of the light transmission unit to (energy value of light required for exposure) / (energy value of light before being input to the light transmission unit). The laser exposure system described.

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