JP2012208190A - Optical modulator, control device of optical modulation device, control method of optical modulation device, and drawing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress offset of a diffraction efficiency of a diffraction grating formed inside an electro-optic crystal by eliminating residue of charge to the electro-optic crystal and provide an appropriate optical modulation by the diffraction grating.SOLUTION: An amplitude modulation signal formed by modulating amplitude of a current signal by a data signal is applied to the electro-optic crystal. Thereby, the signal oscillating in both the positive and negative sides is applied to the electro-optic crystal so as to eliminate the residue of the charge to the electro-optic crystal. Consequently, this constitution can suppress the offset of the diffraction efficiency of the diffraction grating formed inside the electro-optic crystal so as to provide the appropriate optical modulation by the diffraction grating.

Description

  The present invention relates to an optical modulation technique for modulating light by a diffraction grating by forming a diffraction grating by a refractive index distribution generated inside an electro-optic crystal and changing the diffraction efficiency of the diffraction grating according to a data signal. It is.

2. Description of the Related Art Conventionally, there has been proposed an optical modulator that performs optical modulation using an optical modulation device formed of a ferroelectric crystal such as lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO ₃ ) that is an electro-optic crystal. Yes. For example, in the optical modulator of Patent Document 1, a ferroelectric crystal having a periodically poled structure is provided, and when an electric signal is applied to the ferroelectric crystal, a refractive index is formed inside the ferroelectric crystal. Distribution occurs. The refractive index distribution functions as a diffraction grating whose diffraction efficiency changes according to the electrical signal. Therefore, the light passing through the diffraction grating can be modulated by changing the diffraction efficiency of the diffraction grating inside the ferroelectric crystal by an electric signal.

JP 2010-152214 A

  By the way, there are cases where electric charges remain in the ferroelectric electro-optic crystal itself due to the influence of the average value of the electric signal applied from the outside being biased to the positive side or the negative side. In such a case, although the value of the electric signal applied to the electro-optic crystal is zero, an electric field due to the residual charge is generated inside the electro-optic crystal, so that the diffraction efficiency of the diffraction grating does not become zero. I have an offset. As a result, there is a possibility that the diffraction efficiency is shifted by the offset and the light modulation by the diffraction grating cannot be executed properly.

  The present invention has been made in view of the above problems, and by eliminating residual charge in the electro-optic crystal, the diffraction efficiency offset of the diffraction grating formed inside the electro-optic crystal is suppressed, and the diffraction grating It is an object of the present invention to provide a technique that makes it possible to realize appropriate light modulation.

  An optical modulator according to the present invention forms a diffraction grating by a refractive index distribution generated inside an electro-optic crystal, and modulates light by the diffraction grating by changing the diffraction efficiency of the diffraction grating according to a data signal. In order to achieve the above object, the optical modulator includes a control unit that applies an amplitude-modulated signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the data signal to the electro-optic crystal, and the amplitude-modulated signal. In the electro-optic crystal, the refractive index distribution having a distribution corresponding to the amplitude of the amplitude modulation signal is changed according to the AC signal.

  The control device of the light modulation device according to the present invention forms a diffraction grating by a refractive index distribution generated inside the electro-optic crystal of the light modulation device, and changes the diffraction efficiency of the diffraction grating according to the data signal. An optical modulation device controller for modulating light by a diffraction grating, in order to achieve the above object, an amplitude-modulated signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the data signal by the data signal, The refractive index distribution having a distribution corresponding to the amplitude of the amplitude modulation signal changes in accordance with the AC signal inside the electro-optic crystal that has received the amplitude modulation signal.

  The method for controlling a light modulation device according to the present invention includes forming a diffraction grating by a refractive index distribution generated in an electro-optic crystal of the light modulation device, and changing a diffraction efficiency of the diffraction grating according to a data signal. A method of controlling an optical modulation device that modulates light with a diffraction grating, and in order to achieve the above object, an amplitude-modulated signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the data signal with the data signal The refractive index distribution having a distribution corresponding to the amplitude of the amplitude modulation signal changes in response to the AC signal inside the electro-optic crystal that has received the amplitude modulation signal in the step. Yes.

  The invention thus configured (light modulator, light modulation device control apparatus, light modulation device control method) changes the diffraction efficiency of the diffraction grating generated in the electro-optic crystal according to the data signal, Modulate. However, the signal applied to the electro-optic crystal is not the data signal itself but an amplitude modulation signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the data signal by the data signal. In the electro-optic crystal to which such an amplitude modulation signal is applied, the refractive index distribution having a distribution corresponding to the amplitude of the amplitude modulation signal changes according to the AC signal. At this time, the refractive index distribution before and after the change has a distribution corresponding to the amplitude of the amplitude modulation signal, and forms a diffraction grating having substantially the same diffraction efficiency. That is, the diffraction efficiency of the diffraction grating is determined by the amplitude of the amplitude modulation signal almost independently of the AC component of the amplitude modulation signal. Since the amplitude modulation signal is an AC signal amplitude-modulated with a data signal, the amplitude of the amplitude modulation signal varies depending on the data signal. Therefore, the diffraction efficiency of the diffraction grating can be appropriately changed by the data signal, and light can be modulated by the diffraction grating.

  In addition, in the present invention, since the amplitude modulation signal applied to the electro-optic crystal is an AC signal amplitude-modulated by a data signal, a signal that vibrates on both the positive and negative sides is applied to the electro-optic crystal. As a result, the residual charge on the electro-optic crystal can be eliminated. As a result, it is possible to realize appropriate light modulation by the diffraction grating while suppressing the offset of the diffraction efficiency of the diffraction grating formed inside the electro-optic crystal.

  At this time, the AC signal may be a rectangular wave. In such a configuration, since the refractive index distribution changes quickly according to the AC signal, the diffraction efficiency of the diffraction grating formed by the refractive index distribution is stabilized, and light modulation is performed more appropriately. Is possible.

  As described above, it is possible to significantly suppress the offset of diffraction efficiency by applying a signal obtained by amplitude-modulating an AC signal to a data signal to an electro-optic crystal. An offset may remain. Therefore, the control unit may configure the optical modulator so as to have an offset adjustment mechanism that adjusts the offset of the diffraction efficiency of the diffraction grating. As a result, the offset of diffraction efficiency can be more reliably suppressed, and light modulation can be performed more appropriately.

  In this case, specifically, the offset adjustment mechanism can adjust the offset by adding a direct current signal to the amplitude modulation signal and applying it to the electro-optic crystal. Alternatively, the offset adjustment mechanism can adjust the offset by changing the duty ratio of the AC signal.

  At this time, the offset adjustment mechanism includes a first detector that detects a value related to the offset, and configures the optical modulator to perform feedback control that adjusts the offset based on the detection value of the first detector. Also good. In such a configuration, for example, since it is possible to effectively cope with offset drift in which the diffraction efficiency offset varies with time, it is possible to more reliably suppress the diffraction efficiency offset and perform optical modulation. It becomes possible to execute more appropriately.

  As the value related to the offset, for example, a direct current component of light that has passed through the optical modulator can be used. Specifically, the first detector has a first sensor that detects a direct current component of the light that has passed through the optical modulator as a value related to the offset, and the offset adjustment mechanism has a detection value of the first sensor. The optical modulator may be configured to adjust the offset based on the above.

  Further, in addition to the diffraction efficiency offset, there may be a case where the diffraction efficiency itself is shifted. Therefore, the control unit may configure the optical modulator so as to have a diffraction efficiency adjustment mechanism for adjusting the diffraction efficiency of the diffraction grating. With this configuration, even when the diffraction efficiency is deviated from a desired value, it is possible to adjust the diffraction efficiency to an appropriate value and appropriately perform light modulation.

  The diffraction efficiency adjusting mechanism can adjust the diffraction efficiency by changing the amplitude of the amplitude modulation signal. Specifically, the diffraction efficiency adjustment mechanism can change the amplitude of the amplitude modulation signal by changing the data signal. Alternatively, the diffraction efficiency adjustment mechanism can change the amplitude modulation signal by changing the amplitude of the AC signal.

  At this time, the diffraction efficiency adjustment mechanism includes a second detector that detects a value related to the diffraction efficiency, and also performs an feedback control that adjusts the diffraction efficiency based on the detection value of the second detector. It may be configured. In such a configuration, for example, since it is possible to effectively cope with a case where the diffraction efficiency fluctuates with time, it is possible to perform light modulation more appropriately with the diffraction efficiency appropriate. It becomes possible.

  As a value related to the diffraction efficiency of the diffraction grating, a change in the intensity of light that has passed through the optical modulator can be used. Specifically, the second detector has a second sensor that detects a change in the intensity of light that has passed through the optical modulator as a value related to the diffraction efficiency of the diffraction grating. The optical modulator may be configured so as to adjust the diffraction efficiency based on this.

  By the way, the electro-optic crystal has a so-called hysteresis in which the diffraction efficiency of the diffraction grating formed therein varies depending on the application history of the electric signal. Therefore, an offset may occur in the diffraction efficiency due to this hysteresis. However, this hysteresis has a characteristic that it becomes more prominent as the frequency of the applied electrical signal is lower. On the other hand, in the present invention described above, the electric signal applied to the electro-optic crystal is an amplitude modulation signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the data signal by the data signal. That is, a relatively high frequency electric signal is applied to the electro-optic crystal. Accordingly, it is possible to appropriately perform light modulation while suppressing the diffraction efficiency offset due to the hysteresis of the electro-optic crystal.

  In particular, the offset due to hysteresis can be effectively suppressed as the frequency of the electrical signal is higher. Therefore, the frequency of the AC signal may be configured to be twice or more the frequency of the data signal. Moreover, you may comprise so that the frequency of an alternating current signal may be 1 [KHz] or more.

  Various specific configurations of the electro-optic crystal can be employed, and the optical modulator can be configured as follows according to this specific configuration. That is, the electro-optic crystal is a ferroelectric crystal having a periodically poled structure, and the control unit applies an amplitude modulation signal between two electrodes provided across the electro-optic crystal. May be configured. Alternatively, the electro-optic crystal is a ferroelectric crystal having a structure with a uniform polarization direction, and the control unit applies an amplitude modulation signal between two electrodes provided on the same surface of the electro-optic crystal. An optical modulator may be configured.

  By the way, in these configurations, an amplitude modulation signal is applied to the electrode provided in the electro-optic crystal through an insulating layer so that light passing through the crystal does not leak to the electrode (metal). Can be configured. However, in such a configuration, charges remain in the insulating layer, which may cause an offset factor in the diffraction efficiency of the diffraction grating formed inside the electro-optic crystal. In particular, when the insulating layer is silicon dioxide, this problem tends to become remarkable. On the other hand, in the present invention, the amplitude modulation signal applied to the electro-optic crystal is obtained by amplitude-modulating an AC signal using a data signal, and therefore the electro-optic crystal vibrates on both the positive and negative sides. A signal is applied, and residual electric charges in the electro-optic crystal itself and its surroundings (insulating layer) are eliminated. As a result, it is possible to realize appropriate light modulation by the diffraction grating while suppressing the offset of the diffraction efficiency of the diffraction grating formed inside the electro-optic crystal.

  A drawing apparatus according to the present invention is a drawing apparatus that performs drawing by irradiating light on a drawing surface. In order to achieve the above object, the above-described optical modulator and an electro-optic crystal of the optical modulator are provided. And a light source unit that causes light to enter the light source, and an optical system that guides light emitted from the electro-optic crystal after being modulated by the light modulator to the drawing surface. Therefore, it is possible to suppress the offset of the diffraction efficiency of the diffraction grating formed inside the electro-optic crystal and realize appropriate light modulation by the diffraction grating.

  As described above, according to the present invention, it is possible to realize appropriate light modulation by the diffraction grating while suppressing the offset of the diffraction efficiency of the diffraction grating formed inside the electro-optic crystal.

It is a perspective view which shows the pattern drawing apparatus equipped with the optical modulator concerning this invention. It is a side view of the pattern drawing apparatus shown in FIG. It is a block diagram which shows the electrical structure of the pattern drawing apparatus shown in FIG. It is a figure which simplifies and shows the internal structure of an optical head. It is a figure which shows an example of the optical modulator concerning this invention. It is a figure explaining the structure of the modulation exposure signal applied to the electrode which comprises a channel. It is a schematic diagram which shows a mode that the refractive index distribution inside a ferroelectric substrate is reversed. It is a figure which shows the diffraction efficiency of the diffraction grating formed inside a ferroelectric substrate. It is a figure which shows the hysteresis of the diffraction efficiency of the diffraction grating formed in a ferroelectric crystal. It is a figure which shows the offset adjustment operation | movement of the diffraction efficiency which a modulation part performs. It is a figure which simplifies and shows the internal structure of an optical head. It is a figure which shows the other example of the optical modulator concerning this invention. It is a figure which shows the modification of an optical modulator. It is a figure which shows the modification of an optical modulator.

1 is a perspective view showing a pattern drawing apparatus equipped with an optical modulator according to the present invention, FIG. 2 is a side view of the pattern drawing apparatus shown in FIG. 1, and FIG. 3 is shown in FIG. It is a block diagram which shows the electric constitution of a pattern drawing apparatus. The pattern drawing apparatus 100 is an apparatus that draws a pattern by irradiating light onto the surface of a substrate W such as a semiconductor substrate or a glass substrate to which a photosensitive material is applied.

  In this pattern drawing apparatus 100, each part of the apparatus is arranged inside a main body formed by attaching a cover 102 to the main body frame 101 to constitute the main body, and the outside of the main body (in the present embodiment, FIG. As shown in FIG. 2, the substrate storage cassette 110 is disposed on the right hand side of the main body. The substrate storage cassette 110 stores an unprocessed substrate W to be subjected to exposure processing, and is loaded into the main body by a transfer robot 120 disposed inside the main body. Further, after the exposure process (pattern drawing process) is performed on the unprocessed substrate W, the substrate W is unloaded from the main body by the transfer robot 120 and returned to the substrate storage cassette 110.

  In this main body, as shown in FIGS. 1 and 2, the transfer robot 120 is arranged at the right hand end inside the main body surrounded by the cover 102. A base 130 is disposed on the left hand side of the transfer robot 120. One end side region (the right-hand side region in FIGS. 1 and 2) of the base 130 is a substrate delivery region for delivering the substrate W to and from the transfer robot 120, whereas the other end side region (Left-hand side region in FIGS. 1 and 2) is a pattern drawing region for pattern drawing on the substrate W. On the base 130, a head support 140 is provided at the boundary position between the substrate delivery area and the pattern drawing area. In the head support portion 140, two leg members 141 and 142 are erected upward from the base 130, and a beam member 143 is laterally provided so as to bridge the top portions of the leg members 141 and 142. Yes. Then, as shown in FIG. 2, the camera (imaging unit) 150 is fixed to the side of the pattern drawing region side of the beam member 143 and the surface of the substrate W (the drawing surface or the exposed surface) held on the stage 160 is imaged. It is possible.

  The stage 160 is moved on the base 130 by the stage moving mechanism 161 in the X direction, the Y direction, and the θ direction. That is, the stage moving mechanism 161 has an X-axis drive unit 161X (FIG. 3), a Y-axis drive unit 161Y (FIG. 3), and a θ-axis drive unit 161T (FIG. 3) stacked on the upper surface of the base 130 in this order. The stage 160 is moved and positioned two-dimensionally in a horizontal plane. Further, the stage 160 is rotated around the θ axis (vertical axis) to adjust the relative angle with respect to the optical head 3 described later for positioning. As such a stage moving mechanism 161, an XY-θ axis moving mechanism that has been widely used conventionally can be used.

  Further, the optical head 3 is fixedly attached to the box 172 on the pattern drawing region side of the head support portion 140 configured as described above. The optical head 3 is equipped with a light modulator (spatial light modulator) according to the present invention, and exposes the substrate W by irradiating light. The configuration and operation will be described in detail later.

  In addition, two leg members 144 are also erected at the opposite end of the base 130 on the side opposite to the board delivery side (the left-hand side end in FIGS. 1 and 2). A box 172 containing the illumination optical system of the optical head 3 is provided so as to bridge the beam members 143 and the tops of the two leg members 144, and covers the pattern drawing region of the base 130 from above. Yes. Therefore, even if the downflow supplied into the clean room in which the pattern drawing apparatus 100 is installed is drawn into the main body, a space SP in which the downflow is not supplied is formed in the pattern drawing area.

  Therefore, in the pattern drawing apparatus 100 according to the present embodiment, the gas blowout that blows the temperature-controlled gas toward the space SP sandwiched between the stage 160 and the box 172 of the optical head 3 on the side opposite to the robot in the space SP. A part 190 is arranged. In this embodiment, the two gas blowing parts 190 are attached up and down so that the cover 102 which comprises the left-hand side wall of a main-body part may be penetrated. These gas blowing units 190 are connected to an air conditioner 191 and operate according to a command from the exposure control unit 181 to blow out the air temperature-controlled by the air conditioner 191 toward the space SP. Thereby, the temperature-controlled gas blown out from the gas blowing unit 190 flows sideways and passes through the space SP. As a result, the atmosphere of the space SP is changed, and the temperature change in the pattern drawing area is suppressed. In addition, the air that has passed through the space SP flows into the transfer robot 120 in this way, but in this embodiment, an exhaust port 192 is provided in the lower portion of the transfer robot 120 and the exhaust port 192 is air-conditioned via the pipe 193. Connected to the device 191. Therefore, by providing the exhaust port 192, the atmosphere surrounding the transfer robot 120 is exhausted, and a downward airflow, that is, a downflow is formed in the atmosphere. Accordingly, it is possible to effectively prevent the particles from rising and scattering by the transfer robot 120.

  Next, the configuration and operation of the optical head (exposure apparatus) 3 will be described. In this embodiment, the optical head 3 is fixedly attached to the box 172, and is held on the stage 160 by reflecting light onto the substrate W moving at a position immediately below the optical head 3. The substrate W is exposed to draw a pattern. In the present embodiment, the optical head 3 can simultaneously irradiate light in a plurality of channels in the Y direction, and the Y direction corresponds to the “sub-scanning direction”. In addition, by moving the stage 160 in the X direction, a pattern can be drawn two-dimensionally on the substrate W, and the X direction corresponds to the “main scanning direction”.

  FIG. 4 is a diagram showing the internal configuration of the optical head in a simplified manner. FIG. 4A shows the optical head 3 above the optical head 3 along the optical axis OA and the sub-scanning direction Y (that is, in FIG. 1). 1 shows the internal configuration of the optical head 3 when viewed from the (−X) side to the (+ X) side), and FIG. 5B shows the front side of the apparatus in FIG. The internal structure of the optical head 3 when viewed from the optical head 3 side (lower left side) (that is, viewed from the (+ Y) side of the optical head 3) is shown.

  The optical head 3 shown in FIG. 4 includes a light source unit 31 configured by a semiconductor laser or the like that emits a light beam having a predetermined wavelength (for example, 830, 635, 405, or 355 nanometers (nm)). Yes. When a 355 nm laser beam is used, a solid-state laser light source using a third harmonic of a YAG (Yttrium Aluminum Garnet) laser is used. The light source unit 31 has a collimator lens (not shown), and the light beam emitted from the semiconductor laser is converted into parallel light through the collimator lens and enters the illumination optical system 32 through a mirror (not shown). To do.

  The illumination optical system 32 includes three cylindrical lenses 321 to 323, and the light beam emitted from the light source unit 31 passes through the cylindrical lenses 321 to 323 in this order and enters the spatial light modulator 33. Among these, the cylindrical lens 321 has a beam expanding function (negative condensing function) only in the Y direction, and the light passing through the cylindrical lens 321 has a light beam cross section perpendicular to the optical axis OA from the circular shape to the Y direction gradually. It changes to a long oval. On the other hand, with respect to the X direction perpendicular to the optical axis OA and the Y direction, the width of the cross section of the light beam that has passed through the cylindrical lens 321 is (almost) constant. Further, the cylindrical lens 322 has a positive condensing function only in the Y direction, and the light beam that has passed through the cylindrical lens 321 is shaped by the cylindrical lens 322. That is, the light that has passed through the cylindrical lens 322 is made into an elliptical shape having a constant cross-section with a long cross section in the Y direction, and is incident on the cylindrical lens 323. The cylindrical lens 323 has a positive condensing function only in the X direction. When attention is paid only to the X direction, the light LI that has passed through the cylindrical lens 323 is condensed as shown in FIG. However, the light enters the incident surface 331a of the spatial light modulator 33. Regarding the Y direction, as shown in FIG. 4A, the light beam from the cylindrical lens 323 enters the spatial light modulator 33 as a parallel light beam.

  The spatial light modulator 33 generates an electric field in the ferroelectric substrate 11 of the light modulation element 331, the electrode substrate 332, the electric circuit board 336, and the light modulation element 331, and the ferroelectric material of the ferroelectric substrate 11. And a modulator 338 (FIG. 3) for modulating light propagating through the crystal.

FIG. 5 is a view showing the spatial light modulator 33, FIG. 5A is a partial sectional view of the spatial light modulator 33 in the ZX plane, and FIG. 5B is a view of the spatial light modulator 33 in the XY plane. It is a fragmentary sectional view. As described above, the light modulation element 331 included in the spatial light modulator 33 includes the ferroelectric substrate 11 made of a ferroelectric crystal having a periodically poled structure (Periodically Poled), such as SiO ₂ . A ferroelectric substrate 11 is supported by a support substrate 14 via an insulating layer 12 and a junction 13 having a four-layer structure. In this embodiment, by adding a treatment to a single crystal substrate of lithium niobate (LiNbO ₃ : Lithium Niobate) or stoichiometric lithium tantalate (SLT) to which magnesium oxide (MgO) is added, A ferroelectric substrate 11 having a periodically poled structure is formed in a thin film. An insulating layer 12 is uniformly formed on the entire lower surface of the ferroelectric substrate 11. Further, a chromium (Cr) film 13a and a gold (Au) film 13b are formed in this order on the insulating layer 12, and a metal layer having a two-layer structure is formed by the chromium film 13a and the gold film 13b.

  In the spatial light modulator 33, as shown in FIGS. 4 and 5, a wiring region Ra and a placement region Rb for placing the light modulation element 331 are provided on the upper main surface of the electrode substrate 332. It has been. Each of the plurality of electrodes 333 extends in the Z-axis direction from the wiring region Ra to the placement region Rb. More specifically, the (−Z side end) of each electrode 333 extends in the Z direction in the wiring region Ra and reaches the mounting region Rb. In this placement region Rb, the (+ Z side end portion) of each electrode 333 extends substantially parallel to the Z direction. In the present embodiment, a portion of each electrode 333 located on the wiring region Ra, that is, the (−Z side end portion) of each electrode 333 is an inductive coupling to be described later. Part ". Further, a portion located on the mounting region Rb, that is, (+ Z side end portion) of each electrode 333 is opposed to the ferroelectric substrate 11 of the light modulation element 331, and is an electrode for controlling the periodic polarization inversion structure. Since it functions as a part, it is referred to as an “electrode part” below.

A protective film 334 made of an insulating material such as SiO ₂ is formed on the entire upper main surface of the electrode substrate 332 so as to cover these electrodes 333 to protect the electrode 333 and the surface of the protective film 334 (upper main surface). ) Is flattened. In the placement region Rb, the light modulation element 331 is placed on a position corresponding to the placement region Rb. In this way, as shown in FIG. 5, the electrode portion of each electrode 333 is arranged to face the other main surface S2A of the ferroelectric substrate 11 with the protective film 334 interposed therebetween.

  In the light modulation element 331 arranged in this way, the joint portion 13 is formed via the insulating layer 12 so as to cover the entire one main surface S1A of the ferroelectric substrate 11. Then, a ground voltage is applied to the junction 13. On the other hand, for each of the plurality of electrodes 333 described above, a voltage corresponding to light modulation is modulated by inductive coupling via a wiring (not shown) provided on the upper main surface of the electric circuit board 336. It is given from.

  On the upper main surface of the electric circuit board 336, a wiring made of a conductive material having the same shape as the induced pattern portion is a guided pattern portion (a portion of the electrode 333 located on the wiring region Ra). They are formed in a one-to-one correspondence. For this reason, the electrodes facing one another are electrically connected by inductive coupling. In addition, a plurality of electronic components 3381 constituting the modulation unit 338 are mounted on the lower main surface of the electric circuit board 336, and are electrically connected to the electrodes 333 via the electric circuit board 336. As described above, a voltage is applied to the electrode 333 independently according to various signals and data from the exposure control unit 181.

  As shown in FIG. 3, the exposure timing signal, the exposure position signal, and the exposure data are given to the modulation unit 338 from the exposure control unit 181. The modulation unit 338 has an analog circuit (not shown) for each electrode 333, that is, for each channel, and applies a voltage based on the exposure data supplied from the exposure control unit 181 to the electrode 333. The exposure control unit 181 controls a plurality of electrodes 333 (for example, two or more adjacent electrodes 333) as one channel so as to be longer than the period of the periodically poled structure.

  In the spatial light modulator 33, the junction 13 is grounded, whereas the electrodes 333 constituting each channel are independently modulated according to the exposure data from the exposure controller 181 as described above. Receives voltage signal from. Therefore, in the periodic polarization reversal structure of the light modulation element 331, the electrode 333 and the junction 13 are only in a region corresponding to the electrode 333 to which the finite voltage V1 (voltage other than 0 [V]) is applied from the modulation unit 338. A refractive index change according to the polarization direction is generated by the electric field generated between the two, and a diffraction grating is formed. More specifically, in the channel to which the voltage V1 is applied, a diffraction grating having a diffraction efficiency I corresponding to the magnitude of the voltage V1 is formed. As a result, in the channel, diffracted light DL having a magnitude corresponding to the diffraction efficiency I is generated, and the remaining light passes through the light modulation element 331 as 0th-order light L0. On the other hand, in other channels, incident light passes through the light modulation element 331 as it is as 0th-order light L0.

Returning to FIG. 4, the description of the configuration of the optical head 3 will be continued. An aperture plate 352 having a cylindrical lens 34 having a positive condensing function only in the X direction, a lens 351, and an aperture 3521 on the emission side (right hand side in FIG. 4) of the spatial light modulator 33 configured as described above. The lenses 353 are arranged in this order. The cylindrical lens 34 has a positive condensing function only in the X direction, and the zero-order light L0 from the spatial light modulator 33 is, as shown in FIG.
The cylindrical lens 34 makes the light substantially parallel to the X direction and enters the lens 351 having a positive light collecting function.

  Here, the front focal point of the lens 351 is a position in the light modulation element 331 in the vicinity of the end of the electrode 333 on the (+ Z) side, and the aperture plate 352 is disposed so that the aperture 3521 is positioned at the rear focal point of the lens 351. Is done. Therefore, the zero-order light L0 that is not diffracted in the light modulation element 331, passes through the lens 34, and is substantially parallel to both the Y direction and the X direction is indicated by a thin solid line in FIG. As described above, the light is condensed on the aperture 3521 through the lens 351, passes through the aperture 3521, and enters the lens 353. The lens 353 is arranged so that the front focal point is located in the vicinity of the aperture 3521 and the rear focal point is on the surface of the substrate W held by the stage 160, and the 0th-order light L 0 passes through the lens 353. The surface of the substrate W is irradiated and exposed. On the other hand, as shown by a broken line in FIG. 4A, the diffracted light DL is emitted from the light modulation element 331 with a predetermined angle with respect to the optical axis OA. It is shielded by the surface of the aperture plate 352.

  Thus, in the present embodiment, the so-called Schlieren optical system 35 is configured by the lens 351, the aperture plate 352, and the lens 353. The schlieren optical system 35 has the same arrangement as the double-sided telecentric optical system. As shown in FIG. 4, even when the substrate W is exposed with the optical head 3 having a plurality of channels, the exposure surface (surface of the substrate W). ) Of the 0th-order light L0 of each channel is vertical (two-dot chain line in FIG. 4), and is not affected by a change in magnification with respect to a change in the focus direction Z of the exposure surface. As a result, highly accurate exposure is possible. Thus, in this embodiment, pattern drawing on the substrate W is performed using zeroth-order light. Further, the lens 34 and the schlieren optical system 35 arranged as described above guide light from the spatial light modulator 33 to the surface (exposed surface, drawn surface) of the substrate W.

  The pattern drawing apparatus 100 configured as described above has a computer 200 for controlling the entire apparatus. The computer 200 includes a CPU, a storage unit 201, and the like, and is disposed in an electrical rack (not shown) together with the exposure control unit 181. In addition, the rasterization unit 202, the expansion / contraction rate calculation unit 203, the data correction unit 204, and the data generation unit 205 are realized by the CPU in the computer 200 performing arithmetic processing according to a predetermined program. For example, pattern data corresponding to one LSI is data generated by an external CAD or the like, and is prepared in advance in the storage unit 201 as LSI data 211. Based on the LSI data 211, the LSI data is as follows. A pattern is drawn on the substrate W.

  The rasterizing unit 202 divides and rasterizes the unit area indicated by the LSI data 211, generates raster data 212, and stores it in the storage unit 201. Thus, after preparing the raster data 212 or in parallel with the preparation of the raster data 212, the unprocessed substrate W stored in the cassette 110 as described above is unloaded by the transfer robot 120, and the stage is set by the transfer robot 120. 160.

  Thereafter, the stage 160 is moved to a position immediately below the camera 150 by the stage moving mechanism 161, and the alignment marks (reference marks) on the substrate W are sequentially positioned at the imageable positions of the camera 150, and mark imaging by the camera 150 is executed. Is done. The image signal output from the camera 150 is processed by an image processing circuit (not shown in FIG. 3) in the electrical rack, and the position of the alignment mark on the stage 160 is accurately determined. Then, the θ-axis drive unit 161T operates based on these pieces of position information, and the stage 160 is slightly rotated about the vertical axis to be aligned (positioned) in a direction suitable for pattern drawing on the substrate W. Here, the alignment may be performed after the stage 160 is moved to a position directly below the optical head 3.

  The stretch rate calculation unit 203 illustrated in FIG. 3 acquires the position of the alignment mark on the substrate W obtained by the image processing circuit and the correction amount of the orientation of the substrate W, the position of the alignment mark after alignment, and The expansion / contraction ratio of the substrate W with respect to the main scanning direction X and the sub-scanning direction Y (that is, the expansion ratio of the main surface) is obtained.

  On the other hand, the data correction unit 204 acquires the raster data 212 and corrects the data based on the expansion / contraction rate that is the detection result of expansion / contraction. For this data correction, for example, the method described in Japanese Patent No. 40020248 can be adopted. When the data correction of one divided area is completed, the corrected raster data 212 is sent to the data generation unit 205. . The data generation unit 205 generates drawing data corresponding to the changed divided area, that is, data corresponding to one stripe.

  The drawing data generated in this way is sent from the data generation unit 205 to the exposure control unit 181, and the exposure control unit 181 controls each unit of the modulation unit 338 and the stage moving mechanism 161 to perform drawing for one stripe. . Note that the exposure operation is performed by the electric field generation control by the modulation unit 338 as described above. When the exposure recording for one stripe is completed, the same processing is performed for the next divided region, and drawing for each stripe is repeated. Thus, when drawing of all the stripes on the substrate W is completed and drawing of a desired pattern on the surface of the substrate W is completed, the stage 160 keeps the drawn substrate W on the substrate delivery position (see FIGS. 1 and 2). After moving to the right region), the substrate transport robot 120 returns the substrate W to the cassette 110, the next substrate W is taken out, and the same series of processing as described above is repeated. Further, when the pattern drawing on all the substrates W stored in the cassette 110 is completed, the cassette 110 is unloaded from the pattern drawing apparatus 100.

  The above is the outline of the configuration and operation of the spatial light modulator 33 and the pattern drawing apparatus 100 equipped with the spatial light modulator 33. As described above, a voltage corresponding to the exposure data is applied from the modulator 338 to the electrodes 333 constituting each channel in the spatial light modulator 33. Incidentally, in this embodiment, the signal applied to each electrode 333 is not the exposure data itself but a modulated exposure signal (voltage signal) obtained by amplitude-modulating an AC signal (voltage signal) with the exposure data (FIG. 6). .

  FIG. 6 is a diagram for explaining the configuration of the modulated exposure signal applied to the electrodes constituting the channel. More specifically, in the columns of “exposure data”, “AC signal”, and “modulated exposure signal” in FIG. 6, respective waveforms are shown in a graph with the voltage V as the vertical axis and the time t as the horizontal axis. ing. As shown in the column “Exposure Data” in FIG. 6, the exposure data is a signal in which a positive voltage changes with a relatively long period. In the example of FIG. 6, exposure data having a rectangular waveform that changes between a voltage value Ea (0 [V] <Ea) and a voltage value Eb (0 [V] <Eb <Ea) is shown. Specifically, when a precise pattern is drawn on a semiconductor, FPD (flat panel display) or printed circuit board, the frequency of the exposure data is 1 [MHz]. The modulation unit 338 amplitude-modulates the AC signal based on the exposure data received from the exposure control unit 181. This AC signal is a rectangular wave that vibrates around 0 [V] with a cycle Tc shorter than the exposure data and a higher frequency fc. Specifically, the frequency of the AC signal is preferably 2 [MHz] or higher. The modulation unit 338 generates a modulated exposure signal by amplitude-modulating such an AC signal with exposure data. Here, the AC signal may be generated inside the modulation unit 338, or may be generated by the exposure control unit 181 and output to the modulation unit 338.

  The modulated exposure signal thus generated oscillates around 0 [V] at the same cycle Tc as the AC signal and changes its amplitude according to the exposure data. In the example of FIG. 6, the modulated exposure signal has a period in which it changes between (−Ma) [V] and (+ Ma) [V] corresponding to the voltage value Ea of the exposure data, and the voltage value Eb of the exposure data. Corresponding to (−Mb) [V] and (+ Mb) [V] (0 <Mb <Ma). The modulation unit 338 generates this modulated exposure signal for each channel of the spatial light modulator 33 and applies it to the electrode 333 of the channel. Accordingly, in the region corresponding to each electrode 333 in the ferroelectric substrate 11 having the periodic polarization reversal structure, the refractive index changes according to the light modulation signal, and as a result, the refractive index is refracted into the ferroelectric substrate 11. A rate distribution is formed. In particular, in this embodiment, since the modulated exposure signal applied to each electrode 333 is a signal that vibrates around 0 [V], the refractive index distribution is inverted according to the AC signal (FIG. 7).

  FIG. 7 is a schematic diagram showing a state in which the refractive index distribution inside the ferroelectric substrate 11 is reversed, as a graph in which the horizontal axis is the Y direction and the vertical axis is the refractive index n. Before and after inversion. Further, in the same figure, in order to facilitate understanding of the reversal phenomenon of the refractive index distribution, a refractive index distribution formed when a modulated image signal is applied to adjacent electrodes is illustrated. When the modulated image signal is applied to the ferroelectric substrate 11 having the periodically poled structure as described above, roughly, there are a region having a refractive index n (+) and a region having a refractive index n (−). They are arranged alternately in the Y direction (n (−) <n (+)).

  Such a refractive index distribution is inverted about the refractive index n0 in the half cycle (= Tc / 2) of the modulated image signal, and the upper and lower states in the figure are alternately repeated. As described above, the refractive index distribution is inverted in accordance with the AC signal of the modulated image signal, but the diffraction efficiency I of the diffraction grating formed by the refractive index distribution has the property that it is equal before and after the inversion. This will be described with reference to FIG.

FIG. 8 is a diagram showing the diffraction efficiency of the diffraction grating formed inside the ferroelectric substrate 11. In the figure, the horizontal axis represents the voltage V, and the time change of the modulated image signal (lower side in the figure) and the change in diffraction efficiency (upper side in the figure) are also shown. That is, on the lower side of the figure, time t is taken on the vertical axis, and the time change of the modulated image signal is shown. On the other hand, in the upper side of the figure, the vertical axis indicates the diffraction efficiency I, and the change of the diffraction efficiency I with respect to the voltage V is shown. More specifically, when the diffraction grating is a Bragg diffraction type, the diffraction efficiency I is proportional to (sin (αV)) ² , and when the diffraction grating is a Ramanus type, the diffraction efficiency I is (Jq ( βV)) proportional to ² . Here, the function Jq is a q-order Bessel function.

  As can be seen from the voltage characteristic of the diffraction efficiency I shown on the upper side of the figure, when the voltage is in the vicinity of 0 [V], the diffraction efficiency I has a characteristic that increases as the absolute value of the voltage V increases. It is substantially inversion symmetric about a vertical axis passing through a point where the voltage is 0 [V]. Accordingly, the diffraction gratings formed by applying the respective voltages (−Ma) [V] and (+ Ma) [V] having the same absolute value have the same diffraction efficiency Ia. Similarly, diffraction gratings formed by applying voltages of (−Mb) [V] and (+ Mb) [V] having the same absolute value have the same diffraction efficiency Ib (<Ia).

  Since the diffraction grating formed by the refractive index distribution has such a property, a signal changing between (−Ma) [V] and (+ Ma) [V] is applied as a modulated exposure signal. The diffraction grating having the diffraction efficiency Ia is formed while the diffraction grating having the diffraction efficiency Ia is formed and a signal varying between (−Mb) [V] and (+ Mb) [V] is applied as the modulated exposure signal. A lattice is formed. In other words, the diffraction efficiency of the diffraction grating is determined by the amplitude of the modulated exposure signal almost independently of the AC component of the modulated exposure signal. Since the modulated exposure signal is an AC signal amplitude-modulated with exposure data, the amplitude of the amplitude-modulated signal varies depending on the exposure data. Therefore, the modulation unit 338 of this embodiment modulates light by the diffraction grating by controlling the diffraction efficiency of the diffraction grating formed by the refractive index distribution by the exposure data.

  As described above, in this embodiment, light is modulated by changing the diffraction efficiency I of the diffraction grating generated in the ferroelectric substrate 11 in accordance with the exposure data. However, the signal applied to the ferroelectric substrate 11 is not the exposure data itself but a modulated exposure signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the exposure data with the exposure data. In the ferroelectric substrate 11 to which such a modulated exposure signal is applied, the refractive index distribution having a distribution corresponding to the amplitude of the modulated exposure signal is inverted according to the AC signal. At this time, since the refractive index distribution before and after inversion has a distribution corresponding to the amplitude of the modulated exposure signal and is in an inverted relationship with each other, a diffraction grating having substantially the same diffraction efficiency I is formed. In other words, the diffraction efficiency I of the diffraction grating is determined by the amplitude of the modulated exposure signal almost independently of the AC component of the modulated exposure signal. Since the modulated exposure signal is obtained by amplitude-modulating an AC signal with exposure data, the amplitude of the modulated exposure signal changes depending on the exposure data. Accordingly, the diffraction efficiency I of the diffraction grating can be appropriately changed according to the exposure data, and the light can be modulated by the diffraction grating.

  In addition, in this embodiment, the modulated exposure signal applied to the ferroelectric substrate 11 is obtained by amplitude-modulating an AC signal with exposure data, so that the ferroelectric substrate 11 has both positive and negative sides. An oscillating signal is applied, and the residual charge on the ferroelectric substrate 11 can be eliminated. As a result, the offset of the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11 can be suppressed, and appropriate light modulation by the diffraction grating can be realized.

  At this time, as shown in this embodiment, the AC signal may be a rectangular wave. In such a configuration, since the reversal of the refractive index distribution according to the AC signal is performed quickly, the diffraction efficiency I of the diffraction grating formed by the refractive index distribution is stabilized, and light modulation is executed more appropriately. It becomes possible.

  By the way, the ferroelectric substrate 11 has a so-called hysteresis in which the diffraction efficiency I of the diffraction grating formed therein changes depending on the application history of the electric signal. Therefore, an offset may occur in the diffraction efficiency I due to this hysteresis.

  However, this hysteresis has a characteristic that it becomes more prominent as the frequency of the applied electrical signal is lower (FIG. 9). Here, FIG. 9 is a diagram showing the hysteresis of the diffraction efficiency of the diffraction grating formed inside the ferroelectric crystal. In the figure, a curve indicated by a broken line indicates a change in the diffraction efficiency I when the voltage V applied to the ferroelectric substrate 11 is vibrated at a low frequency, and a curve indicated by a solid line indicates the ferroelectric substrate 11. 6 shows a change in diffraction efficiency I when the applied voltage V is vibrated at a high frequency. Thus, when the applied voltage V is changed quickly, no hysteresis is observed in the diffraction efficiency I, whereas when the applied voltage V is changed slowly, the diffraction efficiency I forms a hysteresis loop. To do.

  On the other hand, in this embodiment, the electrical signal applied to the ferroelectric substrate 11 is a modulated exposure signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the exposure data with the exposure data. That is, a relatively high frequency electric signal is applied to the ferroelectric substrate 11. Therefore, it is possible to suppress the offset of the diffraction efficiency I caused by the hysteresis of the ferroelectric substrate 11 and appropriately execute light modulation.

  In particular, the offset due to hysteresis can be effectively suppressed as the frequency of the electrical signal is higher. Therefore, in the above embodiment, the frequency of the AC signal may be set to be twice or more the frequency of the exposure data. Further, the frequency of the AC signal may be set to 1 [KHz] or higher.

By the way, in this embodiment, an insulating layer is provided on the electrode 333 provided on the ferroelectric substrate 11 of the light modulation element 331 in order to prevent light passing through the crystal from leaking to the electrode 333 (metal). A modulated exposure signal is applied via 12. However, in such a configuration, charges remain in the insulating layer 12, which may cause an offset factor of the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11. In particular, when the insulating layer 12 is SiO ₂ (silicon dioxide), this problem tends to become remarkable. On the other hand, in this embodiment, the modulated exposure signal applied to the ferroelectric substrate 11 is an AC signal whose amplitude is modulated by the exposure data. Thus, a signal that oscillates is applied to both sides of the semiconductor substrate, and the residual charge on the ferroelectric substrate 11 itself and its surroundings (insulating layer 12) is eliminated. As a result, the offset of the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11 can be suppressed, and appropriate light modulation by the diffraction grating can be realized.

  In addition, the pattern drawing apparatus 100 described in this embodiment performs drawing by irradiating the substrate W with light modulated using the spatial light modulator 33 described above. Therefore, it is possible to suppress the offset of the diffraction efficiency of the diffraction grating formed inside the ferroelectric substrate 11 and realize appropriate light modulation by the diffraction grating.

Second Embodiment By the way, as described in the first embodiment, the offset of the diffraction efficiency I can be significantly suppressed by applying to the ferroelectric substrate 11 a signal obtained by amplitude-modulating an AC signal with exposure data. However, some offset may remain depending on the situation. Alternatively, an offset may occur in the diffraction efficiency I due to factors other than the residual charge. Therefore, the modulation unit 338 of the second embodiment executes an offset adjustment operation for adjusting the offset of the diffraction efficiency of the diffraction grating. Since the difference between the first embodiment and the second embodiment is mainly in the offset adjustment operation, the difference will be mainly described below, while the common parts are denoted by the same reference numerals and the description thereof is omitted. Incidentally, it goes without saying that the same effects can be obtained in the second embodiment by providing the same configuration as that of the first embodiment.

  FIG. 10 is a diagram illustrating an offset adjustment operation of the diffraction efficiency I performed by the modulation unit. The method of taking the coordinates in the graph shown in FIG. 10 is the same as that in FIG. On the upper side of the figure, the curve indicated by the broken line indicates the voltage characteristic of the diffraction efficiency I without offset, and the curve indicated by the solid line indicates the voltage characteristic of the diffraction efficiency I having offset. That is, the voltage characteristic of the diffraction efficiency I indicated by the solid line curve is a finite value Io (> 0 [V]) in a state where the modulation image signal is not applied (in other words, in a state where the applied voltage V is 0 [V]). have. Therefore, the modulation unit 338 has a built-in offset adjustment mechanism, and applies a DC voltage Vdc to each electrode 333 of the ferroelectric substrate 11 so that the offset becomes 0 [V]. As a result, the offset of the diffraction efficiency is adjusted, and the offset of the diffraction efficiency I becomes zero in a state where the modulated image signal is not applied.

  In the second embodiment, the modulation unit 338 applies the same modulated image signal as that in the first embodiment to each electrode 333 of the ferroelectric substrate 11 after performing the offset adjustment. As a result, a modulated image signal that vibrates around the DC voltage Vdc at which the diffraction efficiency I is zero is applied to the electrode 333. Therefore, while a signal that changes between (−Ma + Vdc) [V] and (Ma + Vdc) [V] is applied as a modulated exposure signal, a diffraction grating having a diffraction efficiency Ia is formed, and a modulated exposure signal ( While a signal changing between −Mb + Vdv) [V] and (+ Mb + Vdv) [V] is applied, a diffraction grating having a diffraction efficiency Ib is formed. That is, as in the first embodiment, the diffraction efficiency I of the diffraction grating is determined by the amplitude of the modulated exposure signal, regardless of the AC component of the modulated exposure signal. Since the modulated exposure signal is an AC signal amplitude-modulated with exposure data, the amplitude of the amplitude-modulated signal varies depending on the exposure data. Therefore, the modulation unit 338 can modulate the light by the diffraction grating by controlling the diffraction efficiency of the diffraction grating formed by the refractive index distribution by the exposure data.

  As described above, also in the second embodiment, the modulated exposure signal applied to the ferroelectric substrate 11 is an AC signal whose amplitude is modulated by the exposure data. A signal that oscillates is applied to both sides of the negative side, and the residual charge on the ferroelectric substrate 11 can be eliminated. As a result, the offset of the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11 can be suppressed, and appropriate light modulation by the diffraction grating can be realized.

  In the second embodiment, the modulation unit 338 has a built-in offset adjustment mechanism that adjusts the offset of the diffraction efficiency of the diffraction grating. As a result, the offset of the diffraction efficiency I can be more reliably suppressed, and light modulation can be performed more appropriately.

Third Embodiment As shown in the above embodiment, the modulation unit 338 controls the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11 by applying a voltage to the electrode of the ferroelectric substrate 11. Or the offset of the diffraction efficiency I is adjusted. As will be described below, in the third embodiment, the modulation unit 338 is controlled by feedback control. Since the difference between the third embodiment and the above embodiment is mainly in this feedback control, the difference will be mainly described below, while the common parts are denoted by the same reference numerals and the description thereof is omitted. Incidentally, it goes without saying that the third embodiment has the same effect as that of the above-described embodiment by providing the same configuration.

  FIG. 11 is a diagram showing the internal configuration of the optical head in a simplified manner. FIG. 11A shows the optical head 3 upward (that is, in FIG. 1) along the optical axis OA and the sub-scanning direction Y of the optical head 3. 1 shows the internal configuration of the optical head 3 when viewed from the (−X) side to the (+ X) side), and FIG. 5B shows the front side of the apparatus in FIG. The internal structure of the optical head 3 when viewed from the optical head 3 side (lower left side) (that is, viewed from the (+ Y) side of the optical head 3) is shown.

  As shown in FIG. 11, the optical head 3 has a beam splitter 36 between the aperture plate 352 and the lens 353. The beam splitter 36 divides a part of the zero-order light L0 that has passed through the aperture plate 352 into light that travels in the Z direction and enters the lens 353 and light that travels in the Y direction. Then, the light split in the Y direction by the beam splitter 36 enters the modulation unit 338.

  That is, the modulation unit 338 according to the third embodiment includes a beam splitter 338b, a high-speed response sensor 338c, and a power meter that divides light incident from the Y direction, in addition to a control circuit 338a configured by a plurality of electronic components 3381. 338d. The beam splitter 338b divides incident light into a high-speed response sensor 338c and a power meter 338d.

  The high-speed response sensor 338c detects the light split by the beam splitter 338b and outputs the result to the control circuit 338a. That is, the high-speed response sensor 338c detects the intensity change of the 0th-order light L0 that has passed through the spatial light modulator 33 and outputs the detected change to the control circuit 338a. On the other hand, the control circuit 338a adjusts the amplitude of the modulated exposure signal applied to the electrode 333 based on the value received from the high-speed response sensor 338c, and sets the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11. Move closer to the target value. Specifically, the amplitude of the modulated exposure signal can be changed by changing the exposure data. Alternatively, the amplitude of the modulated exposure signal can be changed by changing the amplitude of the AC signal. Thus, the diffraction efficiency I of the diffraction grating is feedback controlled.

  The power meter 338d detects the light split by the beam splitter 338b and outputs the result to the control circuit 338a. The power meter 338d captures a gradual light change, and substantially detects a direct current component of incident light and outputs it to the control circuit 338a. That is, the power meter 338d detects the direct current component of the 0th-order light L0 that has passed through the spatial light modulator 33 and outputs the detected direct current component to the control circuit 338a. On the other hand, the control circuit 338a adjusts the DC voltage Vdc applied to the electrode 333 based on the value received from the power meter 338d to reduce the offset of the diffraction efficiency I of the diffraction grating formed inside the ferroelectric substrate 11. Let In this way, the offset of the diffraction efficiency I of the diffraction grating is feedback controlled.

  As described above, in the third embodiment, the DC component of the zero-order light L0 is detected by the power meter 338d as a value related to the offset of the diffraction efficiency I, and the offset of the diffraction efficiency I is adjusted based on this detected value. Feedback control is performed. In such a configuration, for example, an offset drift in which the offset of the diffraction efficiency I fluctuates with time can be effectively dealt with. Modulation can be performed more appropriately.

  In addition to the diffraction efficiency I offset, the diffraction efficiency I itself may be deviated. On the other hand, the modulation unit 338 of the third embodiment has a control circuit 338a that adjusts the diffraction efficiency I of the diffraction grating. Therefore, even if the diffraction efficiency I deviates from a desired value, it is possible to adjust the diffraction efficiency I to an appropriate value and appropriately perform light modulation.

  In particular, in the third embodiment, as a value related to the diffraction efficiency I, an intensity change of the 0th-order light L0 that has passed through the spatial light modulator 33 is detected by the high-speed response sensor 338c, and the diffraction efficiency I is based on the detected value. Feedback control is performed to adjust. In such a configuration, for example, since it is possible to effectively cope with a case where the diffraction efficiency I varies with time, the light modulation is performed more appropriately with the diffraction efficiency I being appropriate. It becomes possible.

Others As described above, in the above embodiment, the pattern drawing device 100 corresponds to the “drawing device” of the present invention, the spatial light modulator 33 corresponds to the “modulator” of the present invention, and the light modulation element 331 is the main device. It corresponds to the “light modulation device” of the invention, and the modulation unit 338 and the exposure control unit 181 work together to function as the “light modulation device control device” of the present invention. The exposure control unit 181 and the modulation unit 338 cooperate to function as the “control unit” of the present invention. The exposure data (FIG. 6) corresponds to the “data signal” of the present invention, the AC signal (FIG. 6) corresponds to the “AC signal” of the present invention, and the modulated exposure signal corresponds to the “amplitude modulated signal” of the present invention. It corresponds to. The modulation unit 338 corresponds to the “offset adjustment mechanism” or the “diffraction efficiency adjustment mechanism” of the present invention. The power meter 338d corresponds to the “first detector” or “first sensor” of the present invention, and the high-speed response sensor 338c corresponds to the “second detector” or “second sensor” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the second and third embodiments, the offset of the diffraction efficiency I is adjusted by applying the DC voltage Vdc. However, the offset of the diffraction efficiency I can be adjusted by a method other than the method of applying the DC voltage Vc.

  As a specific example, the offset of the diffraction efficiency I can also be adjusted by changing the duty ratio of the modulated exposure signal. At this time, a change in the offset of the diffraction efficiency I with respect to the duty ratio of the modulation exposure signal is measured in advance and stored in a memory in a table format or the like, and the modulation unit 338 calculates the duty ratio of the modulation exposure signal from the result of reading this. It is sufficient to adjust the offset of the diffraction efficiency I by adjusting. As a result, the offset of the diffraction efficiency I can be more reliably suppressed, and light modulation can be performed more appropriately.

  When feedback control is performed as shown in the third embodiment, the offset of the diffraction efficiency I may be adjusted by changing the duty ratio of the modulated exposure signal based on the detection value of the power meter 338d. In such a configuration, for example, an offset drift in which the offset of the diffraction efficiency I fluctuates with time can be effectively dealt with. Modulation can be performed more appropriately.

  Alternatively, in the third embodiment, the offset can be adjusted based on the detection result of the high-speed response sensor 338c. That is, since the high-speed response sensor 338c detects a change in the intensity of the 0th-order light L0 that has passed through the spatial light modulator 33, the duty ratio of the 0th-order light L0 can be obtained from the detection result. Therefore, the offset of the diffraction efficiency I may be adjusted by changing the duty ratio of the modulated exposure signal based on the duty ratio of the 0th-order light L0.

  Various specific configurations of the electro-optic crystal can be adopted, and the configuration of the optical modulator can be modified according to the specific configuration. That is, in the optical head 3, the optical modulator 33 is configured by arranging the ferroelectric substrate 11 so as to face the electrode substrate 332 on which the plurality of electrodes 333 are formed. However, for example, as shown in FIG. 12, a plurality of electrodes may be arranged on the other main surface of the ferroelectric substrate 11, and a drive voltage may be applied to each electrode from the modulation section.

  Alternatively, the optical modulator can be modified so as to use an electro-optic crystal as described in, for example, JP-A-2009-020306. FIGS. 13 and 14 are views showing modifications of the optical modulator, in particular, FIG. 13A shows a ZX section, and FIG. 13B shows an XY section. The light modulation element 331 provided in this light modulator has a configuration in which signal electrodes 333a and ground electrodes 333b are alternately arranged on the surface of the ferroelectric substrate 11 having a structure with a uniform polarization direction. When the modulation unit 338 applies a finite voltage V1 to the signal electrode 333a, an electric field as shown by a broken line in FIG. 14 is generated between the signal electrode 333a and the ground electrode 333b, and the ferroelectric substrate 11 is periodically formed. Refractive index distribution occurs in That is, regions having a refractive index n (+) and regions having a refractive index n (−) are alternately arranged.

  Therefore, as shown in the above embodiment, the refractive index distribution inside the ferroelectric substrate 11 is repeatedly inverted by applying a modulation exposure signal obtained by amplitude-modulating an AC signal with exposure data to the signal electrode 333a. Become. In such a configuration, the diffraction efficiency I of the diffraction grating composed of the refractive index distribution can be controlled by changing the amplitude of the modulated exposure signal in accordance with the exposure data, and the charge to the ferroelectric substrate 11 can be controlled. Similar to the above-described embodiment, it is possible to eliminate the residual and suppress the offset of the diffraction efficiency I to realize appropriate light modulation.

Further, in the above embodiment, the SiO ₂ as the insulating layer may be a transparent dielectric film such as nitrogen oxide film _(SiO x _{N y)} or aluminum oxide _(Al 2 _{O 3).}

  In the above embodiment, the case where the present invention is applied to the pattern drawing apparatus that draws the pattern by irradiating the substrate W with the 0th-order light L0 has been described. However, the present invention is also applicable to a pattern drawing apparatus that draws a pattern by irradiating the substrate W with first-order or higher-order diffracted light.

  In the above embodiment, a rectangular wave-shaped modulated exposure signal obtained by amplitude-modulating a rectangular wave is applied to the ferroelectric substrate 11. However, for example, a sine wave-shaped modulated exposure signal obtained by amplitude-modulating a sine wave other than the rectangular wave may be applied to the ferroelectric substrate 11.

  Further, the frequency of the modulated exposure signal is not limited to that described above, and can be changed as appropriate.

  Further, in FIG. 7, in order to facilitate understanding of the reversal phenomenon of the refractive index distribution, the control in which the anti-phase modulated image signal is applied to the adjacent channel is illustrated. However, the relationship of the modulated image signal applied to each channel is not limited to this, and it is needless to say that it can be appropriately modified according to the image pattern to be drawn.

  The present invention relates to a light modulator using an electro-optic crystal, a drawing apparatus using the light modulator, a control device for a light modulation device composed of an electro-optic crystal, or a control of a light modulation device composed of an electro-optic crystal. Can be applied to the method.

DESCRIPTION OF SYMBOLS 100 ... Pattern drawing apparatus 11 ... Ferroelectric substrate 12 ... Insulating layer 181 ... Exposure control part 3 ... Optical head 33 ... Spatial light modulator 331 ... Light modulation element 333a ... Signal electrode 333b ... Ground electrode 333 ... Electrode 338a ... Control circuit 338b ... Beam splitter 338c ... High-speed response sensor 338d ... Power meter 338 ... Modulator 36 ... Beam splitter

Claims (22)

An optical modulator that modulates light by the diffraction grating by forming a diffraction grating by a refractive index distribution generated inside the electro-optic crystal and changing a diffraction efficiency of the diffraction grating according to a data signal,
A control unit that applies an amplitude-modulated signal obtained by amplitude-modulating an alternating-current signal having a frequency higher than that of the data signal to the electro-optic crystal,
In the electro-optic crystal that has received the amplitude modulation signal, a refractive index distribution having a distribution corresponding to the amplitude of the amplitude modulation signal changes according to the AC signal.   The optical modulator according to claim 1, wherein the AC signal is a rectangular wave.   The optical modulator according to claim 1, wherein the control unit includes an offset adjustment mechanism that adjusts an offset of diffraction efficiency of the diffraction grating.   The optical modulator according to claim 3, wherein the offset adjusting mechanism adjusts the offset by adding a direct current signal to the amplitude modulation signal and applying the DC signal to the electro-optic crystal.   The optical modulator according to claim 3, wherein the offset adjustment mechanism adjusts the offset by changing a duty ratio of the AC signal.   The offset adjustment mechanism includes a first detector that detects a value related to the offset, and performs feedback control that adjusts the offset based on a detection value of the first detector. The optical modulator according to item. The first detector has a first sensor that detects a direct current component of light that has passed through the optical modulator as a value related to the offset,
The optical modulator according to claim 6, wherein the offset adjustment mechanism adjusts the offset based on a detection value of the first sensor.   The optical modulator according to claim 1, wherein the control unit includes a diffraction efficiency adjustment mechanism that adjusts a diffraction efficiency of the diffraction grating.   The optical modulator according to claim 8, wherein the diffraction efficiency adjustment mechanism adjusts the diffraction efficiency by changing an amplitude of the amplitude modulation signal.   The optical modulator according to claim 9, wherein the diffraction efficiency adjustment mechanism changes the amplitude of the amplitude modulation signal by changing the data signal.   The optical modulator according to claim 9, wherein the diffraction efficiency adjusting mechanism changes the amplitude modulation signal by changing an amplitude of the AC signal.   The diffraction efficiency adjusting mechanism includes a second detector for detecting a value related to the diffraction efficiency, and performs feedback control for adjusting the diffraction efficiency based on a detection value of the second detector. The optical modulator according to any one of the above.   The second detector includes a second sensor that detects a change in the intensity of light that has passed through the optical modulator as a value related to the diffraction efficiency of the diffraction grating, and is based on a detection value of the second sensor. The optical modulator according to claim 12, wherein the diffraction efficiency is adjusted.   The optical modulator according to claim 1, wherein the frequency of the AC signal is twice or more the frequency of the data signal.   The optical modulator according to claim 1, wherein the frequency of the AC signal is 1 [KHz] or more. The electro-optic crystal is a ferroelectric crystal having a periodically poled structure,
The optical modulator according to claim 1, wherein the control unit applies the amplitude modulation signal between two electrodes provided with the electro-optic crystal interposed therebetween. The electro-optic crystal is a ferroelectric crystal having a structure with a uniform polarization direction,
The optical modulator according to claim 1, wherein the control unit applies the amplitude modulation signal between two electrodes provided on the same surface of the electro-optic crystal.   The optical modulator according to claim 16 or 17, wherein the amplitude modulation signal is applied to the electrode provided in the electro-optic crystal via an insulating layer.   The optical modulator according to claim 18, wherein the insulating layer is silicon dioxide. A drawing apparatus that performs drawing by irradiating light on a drawing surface,
An optical modulator according to any one of claims 1 to 19,
A light source unit for making light incident on the electro-optic crystal of the light modulator;
A drawing apparatus comprising: an optical system that guides light emitted from the electro-optic crystal modulated by the light modulator to the drawing surface. Light modulation that modulates light by the diffraction grating by forming the diffraction grating by the refractive index distribution generated inside the electro-optic crystal of the light modulation device and changing the diffraction efficiency of the diffraction grating according to the data signal A device controller,
A control unit that applies an amplitude-modulated signal obtained by amplitude-modulating an alternating-current signal having a frequency higher than that of the data signal to the electro-optic crystal,
In the electro-optic crystal that has received the amplitude modulation signal, a refractive index distribution having a distribution according to the amplitude of the amplitude modulation signal changes according to the AC signal. apparatus. Light modulation that modulates light by the diffraction grating by forming the diffraction grating by the refractive index distribution generated inside the electro-optic crystal of the light modulation device and changing the diffraction efficiency of the diffraction grating according to the data signal A device control method,
Applying an amplitude-modulated signal obtained by amplitude-modulating an AC signal having a frequency higher than that of the data signal to the electro-optic crystal,
In the electro-optic crystal that has received the amplitude modulation signal in the step, a refractive index distribution having a distribution corresponding to the amplitude of the amplitude modulation signal changes according to the AC signal. How to control the device.

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