JP5846821B2 - Discharge lamp lighting device and lighting method - Google Patents

Description

  The present invention relates to a discharge lamp lighting device used for an exposure apparatus or the like, and more particularly to a low-frequency rectangular wave lighting method used for a high-pressure discharge lamp.

  As a lighting system for a high-pressure discharge lamp, a low-frequency rectangular wave lighting system in which an AC lamp current of a low frequency (several tens to hundreds of Hz) is supplied and an AC operation is performed by switching the lighting polarity is known. In this lighting method, if the starting point (arc spot) of the arc discharge is not determined every time the polarity is switched to the cathode, fluctuation occurs. In order to suppress this, a current pulse is superimposed immediately before the lamp current polarity is switched (see Patent Document 1).

  By superimposing the current pulse, the amount of current increases immediately before the polarity is switched, and the electrode temperature rises significantly at that moment. As a result, in the cathode phase, the starting point of arc discharge always occurs at the same location on the tip of the electrode, preventing the occurrence of fluctuations.

  On the other hand, a lighting method is known in which a high-frequency rectangular wave current is applied to a low-frequency rectangular current instead of superimposing a current pulse (see Patent Document 2). Here, immediately after the polarity change of the low-frequency rectangular wave current, a high-frequency rectangular wave current starting from a different polarity is applied for one period (cycle). This prevents fluctuations from occurring.

  In a projection device such as a projector, a sudden change in light output due to an increase in current pulses causes flickering in an image. In order to suppress this brightness change, a lighting method is known that supplies a low-frequency rectangular wave current having a maximum value immediately after polarity inversion without increasing the amount of current before the end of polarity inversion (see Patent Document 3).

Japanese Patent No. 3714727 Japanese Patent No. 3844046 Japanese Patent No. 4426132

  In an apparatus using a high-pressure discharge lamp such as a projector, since constant power lighting is generally performed, the power supplied to the discharge lamp is constant. However, in an exposure apparatus or the like, the illuminance is periodically measured, and the constant illuminance lighting is performed by adjusting the input power.

  In the case of the lighting method described above, the electrode temperature during lighting cannot always be maintained in an appropriate range. For this reason, in a situation where the electrode temperature is not within the proper range, the illuminance fluctuation in which noise is dominant is likely to occur. For example, in the case of a discharge lamp that emits spectrum light including emission lines of g-line (436 nm), h-line (405 nm), and i-line (365 nm), only the emission spectrum near the emission line varies.

  Due to the influence of the illuminance fluctuation that is dominant due to such noise, a situation occurs in the exposure apparatus or the like in which the input power is adjusted based on erroneous illuminance measurement. As a result, unnecessary power fluctuations occur frequently, reducing productivity and affecting lamp life.

  On the other hand, if the fluctuation amount of input power per unit time is reduced in order to prevent the electrode temperature from deviating from the appropriate range, it takes time to adjust the power and decreases productivity.

  Therefore, there is a need for a lighting system that can maintain the electrode temperature in an appropriate range against power fluctuations while performing constant illumination on a discharge lamp such as a high-pressure discharge lamp.

  The discharge lamp lighting method of the present invention is a discharge lamp lighting method for supplying an AC lamp current to a discharge lamp, and can be applied to a discharge lamp lighting device for lighting a discharge lamp, an exposure device equipped with a high-pressure discharge lamp, and the like. .

  According to the discharge lamp lighting method of the present invention, an AC lamp current waveform based on a low-frequency rectangular wave current is converted into an inversion type correction signal having a shorter cycle than the AC lamp current without generating and superimposing current pulses. Correct based on. In this waveform correction, the waveform portion having the maximum current value immediately before the end of the half cycle of the AC lamp current, the waveform portion having the minimum current value immediately before reaching the maximum current value, and the maximum current immediately after the half cycle starts. A waveform portion having a maximum current value smaller than the value is formed in the AC lamp current. For example, a rectangular wave signal can be applied as the correction signal.

  By generating a waveform current with maximum current value, minimum current value, and maximum current value as an AC lamp current, it is easy to re-ignite, correct the starting point of the arc discharge position, and arc starting from the same electrode Discharge generation is realized. This leads to maintenance of the proper electrode temperature at the arc discharge starting point.

  In consideration of effectively generating the waveform portion of the maximum current value and the waveform portion of the maximum current value, the waveform portion having the maximum current value and the maximum current value by the signal in the latter half of one cycle of the correction signal. Can be formed into the alternating lamp current. Further, it is possible to form a waveform portion having the minimum current value in the AC lamp current by a signal in the first half of one cycle of the correction signal.

  In addition, due to the undershoot effect, the AC lamp current can have a minimum current value larger than the minimum current value immediately after the maximum current value.

  Considering that the temperature rise at the arc discharge starting point and the cooling around the starting point are surely performed, the period (width) of the signal portion of the first half of one cycle of the correction signal, that is, the waveform portion having the minimum current value Is preferably shorter than the period of the waveform portion having the maximum current value in the latter half of one cycle of the correction signal.

  A discharge lamp lighting device according to another aspect of the present invention converts a direct current of a direct current voltage into an alternating current lamp current based on a direct current voltage conversion means for converting a direct current voltage into a predetermined voltage value and a low-frequency rectangular wave current. DC / AC converting means, and DC voltage converting means, comprising: AC lamp current correcting means for adjusting the direct current of the DC voltage sent to the DC / AC converting means by PWM control and correcting the waveform of the AC lamp current. The AC lamp current correcting means has a maximum current value immediately before the end of the half cycle of the AC lamp current based on an inversion type correction signal having one cycle shorter than the AC lamp current, and immediately before the maximum current value. The duty ratio is determined so as to have a minimum current value and to have a maximum current value smaller than the maximum current value immediately after the start of the half cycle.

  ADVANTAGE OF THE INVENTION According to this invention, stable constant illumination lighting can be implement | achieved based on appropriate illumination intensity measurement with respect to a discharge lamp.

It is a schematic block diagram of the exposure apparatus which is this embodiment. It is a schematic block diagram of a lamp lighting part. It is the figure which showed the signal waveform in each circuit of a lamp lighting part. It is the schematic waveform diagram which showed the alternating lamp current supplied to a discharge lamp.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram of an exposure apparatus according to this embodiment.

  The exposure apparatus 10 is a maskless exposure apparatus that directly forms a pattern on a substrate SW having a photosensitive member such as a photoresist formed thereon, and includes a discharge lamp 20 and a DMD (Digital Micro-mirror Device) 22. The substrate SW is irradiated with illumination light from the discharge lamp 20 as pattern light.

 Here, the discharge lamp 20 is constituted by a high-pressure discharge lamp such as a high-pressure / ultra-high-pressure mercury lamp, and is lit by a lamp lighting unit 21. The light emitted from the discharge lamp 20 is corrected to parallel light by an illumination optical system (not shown) and then guided to the DMD 22. The DMD 22 is a light modulation element array (for example, 1024 × 1280) in which micro rectangular micromirrors of several μm to several tens μm are two-dimensionally arranged in a matrix, and is driven by the DMD driving circuit 24.

  Vector data such as CAD / CAM data transmitted from a workstation (not shown) is converted into raster data of a two-dimensional dot pattern by the raster conversion circuit 26. Then, the DMD drive circuit 24 transmits exposure data to the DMD 22 according to the raster data.

  In the DMD 22, each micromirror is selectively ON / OFF controlled based on the exposure data sent from the DMD drive circuit 24. The light reflected by the micromirror in the ON state passes through a projection optical system (not shown) and is irradiated onto the substrate SW as light of a pattern image.

  The substrate SW mounted on the table 12 is moved in the scanning direction by the stage driving mechanism 14. While the exposure target area relatively moves with the movement of the substrate SW, the exposure operation is executed at a predetermined exposure pitch. A pattern is formed on the entire substrate by moving the exposure target area over the entire substrate SW. The position of the substrate SW is detected by the position detection sensor 15.

  The controller 30 outputs a control signal to the lamp lighting unit 21 and the like to control the entire exposure operation. A control program for the exposure operation is stored in a ROM (not shown) in the controller 30.

  The exposure apparatus 10 includes a photometric device 34 that measures the illuminance of the discharge lamp 20 in order to periodically measure the illuminance. The position of the photometric device 34 is controlled by a photometric drive unit 35. During the illuminance measurement, the photometric drive unit 35 places the photometric device 34 on the optical path, and moves the photometric device 34 to the retracted position when the measurement is completed.

  The controller 30 adjusts the amount of light irradiated to the substrate SW based on the measured illuminance. Specifically, constant illuminance lighting control is performed by adjusting the input power to the discharge lamp 20.

  FIG. 2 is a schematic block diagram of the lamp lighting unit.

  The lamp lighting unit 21 includes a DC / DC converter 54 and a full bridge circuit 56, and supplies a lamp input voltage based on an AC lamp current to the discharge lamp 20. The DC / DC converter 54 is a DC voltage conversion circuit including a switching element, a capacitor, a diode, a choke coil, a drive circuit, and the like, and a voltage for supplying a DC voltage value input by the DC power supply voltage 52 to the discharge lamp 20. Convert to value. Note that a chopper circuit may be provided instead of the DC / DC converter.

  The full bridge circuit 56 is a DC-AC conversion circuit that converts a DC current supplied from the DC / DC converter 54 into an AC current, and includes a starting igniter circuit and two transistor pairs. Under stable lighting, based on the low-frequency rectangular wave signal sent from the low-frequency rectangular wave generation circuit 60, the two transistor pairs are alternately turned on to alternately invert the polarity of the direct current. Thus, a rectangular wave AC lamp current whose polarity is inverted every half cycle is generated.

  Further, the lamp lighting unit 21 includes a current setting DC signal output circuit 62, a waveform synthesis circuit 64, a waveform correction signal output circuit 66, and a PWM control circuit 58. The PWM control circuit 58 can adjust the amount of direct current sent from the DC / DC converter 54 to the full bridge circuit 56, adjust the voltage level supplied to the discharge lamp 20, and change the amount of current to change the AC lamp current. Correct or change the waveform. Hereinafter, correction of the AC lamp current waveform will be described.

  FIG. 3 is a diagram showing signal waveforms in each circuit of the lamp lighting unit. FIG. 4 is a schematic waveform diagram showing an AC lamp current supplied to the discharge lamp.

  The low-frequency rectangular wave signal L1 is a rectangular wave signal having the same frequency as the AC lamp current, and is output from the low-frequency rectangular wave generation circuit 60 according to a low frequency of several tens to several hundreds of Hz. Based on this rectangular wave signal, the full bridge circuit 56 outputs an AC lamp current whose polarity is alternately switched every half cycle.

  On the other hand, the waveform correction signal C1 is a signal obtained by intermittently extracting one period of a high-frequency rectangular wave signal having a frequency several times to several tens of times that of the low-frequency rectangular wave signal. The generation interval of the waveform correction signal C1 corresponds to the frequency of the low-frequency rectangular wave signal L1, that is, the frequency of the AC lamp current.

  In the waveform correction signal C1, the polarity switching in one cycle is inverted, the first half of the first half cycle is a waveform that starts at the falling edge, and the second half of the next half cycle is the rising edge. (Here, such a waveform is called an inverted type). Further, the waveform correction signal C1 has a shorter period (width) in the first half of the waveform than in a period of the second half of the waveform.

  Then, by adding the constant value DC signal B1 output from the current setting DC signal output circuit 62 to the waveform correction signal C1, an inverted composite waveform signal D1 (correction signal) similar to the waveform correction signal C1 is obtained. Signal). The generated combined waveform signal D1 is sent to the PWM control circuit 58.

  The PWM pulse signal E1 is a pulse signal for controlling the direct current amount of the DC / DC converter 54, and adjusts the ON / OFF time of the switching element of the DC / DC converter 54 based on the duty ratio. In FIG. 3, the PWM pulse signal is represented as a pulse signal having the same pulse width. However, as shown in the enlarged partial waveform of the PWM pulse signal E1, the pulse width is actually in accordance with the composite waveform signal D1. Is modulated.

  More specifically, the waveform has a constant pulse width except for the output period of the composite waveform signal D1, and the pulse width EN is shorter than the constant pulse width according to the first half portion DN that is the first half cycle of the composite waveform signal D1. Thus, the pulse width EM becomes larger than the constant pulse width in accordance with the latter half portion DM which is the next half cycle. That is, the duty ratio decreases in accordance with the first half portion DN, and the duty ratio increases in accordance with the second half portion DM.

  As a result, the amount of direct current supplied from the DC / DC converter 54 to the full bridge circuit 56 decreases during a period when the duty ratio is small, and the amount of current increases when the duty ratio is large. As a result, an alternating lamp current that forms a waveform portion corresponding to the combined waveform signal D1 (waveform correction signal C1) is generated.

  The AC lamp current P shown in FIG. 4 has a maximum value KM and a minimum value KN in the latter half of the half cycle. The synthesized waveform signal D1 has one cycle end timing corresponding to the falling edge of the low-frequency rectangular wave signal L1.

  Therefore, a waveform portion corresponding to the waveform of the composite waveform signal D1 is formed, and the current value KM that is the maximum as an absolute value is obtained immediately before the end of the half cycle of the AC lamp current P, and the maximum current value Immediately before KM, a current value KN that is the minimum in absolute value is obtained. The period during which the minimum current value KN is obtained is shorter than the period during which the maximum current value KM is obtained.

  On the other hand, the cycle of the composite waveform signal D1 is the same as the cycle of the low-frequency rectangular wave signal L1, but the phase is slightly delayed with respect to the low-frequency rectangular wave signal L1. As a result, the end timing of one cycle of the synthesized waveform signal D1 is shifted from the falling timing of the low-frequency rectangular wave signal L1.

  Part of the latter half DM of the combined waveform signal D1 affects the waveform of the AC lamp current after polarity inversion due to the pulse width EM having a large duty ratio. Thereby, the amount of current immediately after inversion increases. The current value PM as an absolute value at this time is smaller than the maximum current value KM (here, referred to as a maximum current value).

  On the other hand, if the AC lamp current P has a maximum current value PM immediately after polarity inversion, the current value immediately after that decreases. This is due to the undershoot effect. The current value PN as an absolute value is larger than the minimum current value KN (here, referred to as a minimum current value).

  When the lamp is lit by such an AC lamp current waveform P, the electrode temperature is always maintained in an appropriate range. First, when the starting point of arc discharge is provided by switching to the cathode phase, the electrode is instantaneously heated when the maximum current value PM flows, thereby facilitating re-ignition.

  Then, by generating a minimal current value PN immediately after the instantaneous heating of the electrode, the part other than the electrode tip that is the starting point of the arc discharge is cooled, the position of the starting point of the arc discharge is corrected to an appropriate position, It stabilizes during the cathode phase.

  Further, before the end of the half cycle of the AC lamp current P switching from the cathode phase to the anode phase, the minimum current value KN and the maximum current value KM are continuously obtained. Immediately after the maximum current value KM is obtained, the AC lamp current The polarity of P is reversed.

  By once cooling the portions other than the electrode tip that is the starting point of the arc discharge, after the position of the starting point of the arc discharge is corrected to an appropriate position, only the electrode tip is instantaneously heated. As a result, in the next cathode phase, the starting point of arc discharge occurs at the same location on the tip of the electrode. In particular, since the period of the maximum current value KM is longer than the period of the minimum current value KN, the cooling around the arc discharge starting point and the temperature rise at the starting point part are reliably realized.

  As a result, even when the power is changed for lighting at a constant illuminance, the temperature of the entire electrode falls within an appropriate range for stabilizing the arc discharge, and the discharge is stabilized by quickly shifting to the stable lighting state in a short time. In particular, in a discharge lamp that emits spectrum light including emission lines of g-line (436 nm), h-line (405 nm), and i-line (365 nm), the effect is remarkable when only the emission spectrum near the emission line varies.

  Such an electrode temperature is maintained over the entire period of the AC lamp current P. Therefore, when performing constant illuminance lighting control, fluctuations in illuminance dominated by noise are suppressed, and irradiance is accurately detected according to adjustment of input power. As a result, stable constant illuminance lighting can be realized without wasteful power adjustment.

  In addition, the waveform portion having the maximum current value KM and the maximum current value PM is formed by the composite waveform signal D1, thereby effectively correcting and changing the waveform portion at the start and end of the half cycle of the AC lamp current P at the same time. ing.

  In addition, when increasing electric power in constant illumination lighting, you may make the minimum electric current value KN smaller than the time of constant electric power, or may set the period long. On the contrary, when the power is decreased, it is preferable to set the minimum current value KN to be larger than that at the constant power or to set the period shorter.

Actually, when constant illumination illumination control was performed using a high pressure discharge lamp in which 0.2 mg / mm ³ or more of mercury was sealed in a discharge tube, the power adjustment frequency when the AC lamp current was supplied, and the adjustment at that time The power amplitude is significantly smaller than the power adjustment frequency and the adjusted power amplitude when a conventional pulse discharge lamp current is supplied, and the time required for power adjustment can be shortened.

  As described above, according to the present embodiment, the lamp lighting unit 21 supplies the AC lamp current to the discharge lamp 20 in accordance with the low-frequency rectangular wave lighting method, and causes the discharge lamp 20 to be AC-operated. The amount of direct current sent from the DC / DC converter 54 to the full bridge circuit 56 is adjusted by PWM control based on the inverted composite waveform signal D1 (waveform correction signal C1). As a result, an AC lamp current P having a maximum current value PM immediately after the start of the half cycle, a minimum current value PN immediately after that, and a minimum current value KN and a maximum current value KM immediately before the end of the half cycle is generated.

  Note that when the current is small, the undershoot effect does not work, so the waveform portion of the minimum current value does not occur, or even if the AC lamp current is not intentionally given to the AC lamp current, the arc discharge can be re-ignited. Since it occurs at the same location of the electrode, the electrode temperature is maintained in a sufficiently appropriate range. In addition, the waveform portion having the maximum current value can be formed by a signal other than the synthesized waveform signal.

  Further, a signal having a waveform other than a rectangular wave can be applied as the correction signal.

20 discharge lamp 21 lamp lighting unit 54 DC / DC converter (DC voltage conversion means)
56 Full bridge circuit (DC / AC conversion means)
58 PWM control circuit 60 Low frequency rectangular wave generation circuit 62 DC signal output circuit for current setting 64 Waveform synthesis circuit 66 Waveform correction signal output circuit C1 Waveform correction signal D1 Composite waveform signal E1 PWM pulse signal L1 Low frequency rectangular wave signal P AC lamp Current

Claims (9)

A discharge lamp lighting method for supplying an AC lamp current to a discharge lamp,
Without generating or superimposing current pulses, the waveform of the AC lamp current based on the low-frequency rectangular wave current is corrected based on an inversion type correction signal having a shorter period than the AC lamp current,
A waveform portion having a maximum current value immediately before the end of the half cycle of the AC lamp current, a waveform portion having a minimum current value immediately before reaching the maximum current value, and a maximum smaller than the maximum current value immediately after the start of the half cycle A discharge lamp lighting method for forming a waveform portion having a current value into an alternating lamp current,
Correct the waveform of the AC lamp current to have the minimum current value and the maximum current value in the latter half of the half cycle ;
The discharge lamp lighting method characterized in that the AC lamp current has a minimum current value larger than the minimum current value immediately after the maximum current value .   2. The discharge lamp lighting method according to claim 1, wherein a waveform portion having the maximum current value and the maximum current value is formed in the AC lamp current by a signal in the latter half of one period of the correction signal.   3. The discharge lamp lighting method according to claim 1, wherein a waveform portion having the minimum current value is formed in the AC lamp current by a signal in the first half of one cycle of the correction signal. A discharge lamp lighting method for supplying an AC lamp current to a discharge lamp,
Without generating or superimposing current pulses, the waveform of the AC lamp current based on the low-frequency rectangular wave current is corrected based on an inversion type correction signal having a shorter period than the AC lamp current,
A waveform portion having a maximum current value immediately before the end of the half cycle of the AC lamp current, a waveform portion having a minimum current value immediately before reaching the maximum current value, and a maximum smaller than the maximum current value immediately after the start of the half cycle A waveform portion having a current value is formed into an AC lamp current,
The discharge lamp lighting method characterized in that the AC lamp current has a minimum current value larger than the minimum current value immediately after the maximum current value.   The period of the waveform portion having the minimum current value formed by the signal in the first half of one cycle of the correction signal is the waveform portion having the maximum current value formed by the signal in the second half of the correction signal. The discharge lamp lighting method according to any one of claims 2 to 4, wherein the discharge lamp lighting method is shorter than the period.   A discharge lamp lighting device for lighting a discharge lamp by the lighting method according to any one of claims 1 to 5. A high pressure discharge lamp,
An exposure apparatus comprising: a discharge lamp lighting device that lights the high-pressure discharge lamp by the lighting method according to any one of claims 1 to 5. DC voltage conversion means for converting a DC voltage into a predetermined voltage value;
DC / AC conversion means for converting a DC current of a DC voltage into an AC lamp current based on the low-frequency rectangular wave current;
The DC voltage conversion means includes an AC lamp current correction means that adjusts the direct current of the DC voltage sent to the DC / AC conversion means by PWM control and corrects the waveform of the AC lamp current,
The AC lamp current correcting means has a maximum current value immediately before the end of a half cycle of the AC lamp current based on an inversion type correction signal having a cycle shorter than the AC lamp current, and immediately before the maximum current value. has a minimum current value, and, together with the smaller maximum current than said maximum current value immediately after the semi cycle starts, Chi also said minimum current value and said maximum current value in the half period the latter part, further, the A discharge lamp lighting device, wherein a duty ratio is determined so that a minimum current value larger than the minimum current value is immediately after a maximum current value . A high pressure discharge lamp,
An exposure apparatus comprising: a discharge lamp lighting device for lighting the high-pressure discharge lamp according to claim 8.

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