Laser drawing method and apparatus

A method of laser drawing includes steps of causing laser light from a light source to be incident to an acousto-optical diffraction element, and deflecting the light incident to the element by changing a frequency of a high frequency signal to be inputted to the element to diffract the light, thereby changing a diffraction angle of the diffracted light, and condensing the diffracted light emerging from the element on an object to be processed as an optical spot, thereby scanning the object with the optical spot. A diffracted light intensity control table for controlling a light intensity of the diffracted light so as to be constant independent of the diffraction angle of the diffracted light is prepared in advance, and in the deflecting step, the light intensity of the diffracted light is controlled based on the diffracted light intensity control table.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese Patent Application No. 2007-014002 filed in the Japanese Patent Office on Jan. 24, 2007, the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser drawing method and a laser drawing apparatus suitably adapted to laser annealing and other laser drawings.

2. Description of Related Art

Heretofore, for example in a liquid crystal display apparatus and other flat display apparatuses, a thin film transistor (TFT) has been used for a switching element. In the liquid crystal display apparatus, an active matrix method of forming a thin film transistor in a silicon film formed on a glass substrate has been put into practical use. In micro-fabrication of such a thin film transistor, for crystallizing an amorphous silicon thin film formed on a substrate, a laser annealing method using a laser light is used. By using the laser annealing method, it is possible to make a satisfactory thin silicon film transistor in a low temperature environment at about 500° C.

In the laser annealing method, a laser light emerged from a diffraction optical system using an acousto-optical diffraction element (hereinafter referred to as an AOD) is used. In the diffraction optical system using an AOD, an ultrasonic wave is generated in the AOD with a high frequency signal (hereinafter referred to as an RF signal) inputted to the AOD, and a laser light incident to the AOD is diffracted with the wave surface of the ultrasonic wave.

Generally, by changing the frequency of an RF signal inputted to an AOD while keeping the amplitude of the RF signal constant, the diffraction angle of a laser light incident to the AOD and is diffracted with the wave surface of an ultrasonic wave generated with the inputted RF signal is changed according to the change in the frequency of the RF signal. Further, the light intensity of a diffracted light changes depending on the diffraction angle of the diffracted light, because the diffraction efficiency (the light intensity of a diffracted light/the light intensity of an incident light to the AOD) changes depending on the diffraction angle.

Here, referring toFIG. 1, description is made with respect to an example of a change in the light intensity of a diffracted laser light according to related art.FIG. 1illustrates a change in the light intensity of a diffracted light emerging from an AOD when the frequency of an RF signal inputted to the AOD is changed linearly in a cycle as time progresses and the amplitude of the RF signal is kept constant.

InFIG. 1, the frequency of the FR signal changes periodically in a saw-tooth wave state, and on the other hand, the amplitude of the RF signal is constant regardless of time. If such an RF signal is inputted to the AOD, the light intensity of an emerging diffracted light waves as illustrated inFIG. 1. The light intensity of the diffracted light takes a lower-limit value p1at time t1and an upper-limit value p0at time t0. Similarly, the light intensity of the diffracted light takes an upper limit value p2at time t2. Here, p0≅p2. Thus, even when the frequency of the RF signal increases from f0to f1and from f1to f2with the lapse of time, the light intensity of the diffracted light does not increase correspondingly, and changes between the lower limit value p1and the upper limit value p2as illustrated inFIG. 1.

When forming a thin film transistor using a laser annealing method, if the light intensity of a diffracted laser light is changed while the diffracted laser light is deflected to scan an object to be processed with an optical spot of the diffracted laser light, uneven exposure is caused on the object, resulting in deterioration of quality, which is undesirable.

In addition, the degree of a change in the diffraction angle of a diffracted light relative to a change in the frequency of an RF signal varies depending on the frequency of the RF signal, and even if the frequency of an RF signal is linearly changed, the diffraction angle of a diffracted light does not change linearly, that is, the diffraction angle of a diffracted light does not change at a constant speed.

Here, an example of a change in the diffraction angle of a laser light according to related art is described referring toFIG. 2.FIG. 2illustrates a change in the diffraction angle of a diffracted light emerging from an AOD when the frequency of an RF signal inputted the AOD is changed linearly in a cycle with the lapse of time.

InFIG. 2also, the frequency of the RF signal changes periodically in a saw-tooth wave state. It is understood fromFIG. 2that if such an RF signal is inputted to the AOD, as the frequency of the RF signal increases, the diffraction angle of a diffracted light also increases. Here, at time t1′, the frequency of the RF signal is f1′ and the diffraction angle takes a lower limit value θ1′. At time t2′, the frequency of the RF signal is f2′ and the diffraction angle takes an upper limit value θ2′. Thus, as the frequency of the RF signal linearly increases from f1′ to f2′ with the lapse of time, the diffraction angle of the diffracted light changes non-linearly between the lower limit value θ1′ and the upper limit value θ2′. That is, even when the frequency of an RF signal inputted to an AOD is changed linearly to diffract and thereby deflect a laser light incident to the AOD at a constant angular speed, the diffraction angle of a diffracted light is not changed at a constant speed (the angular speed of a diffracted light is not constant).

This can be explained as follows. When the propagation velocity of an RF signal in an AOD is “v” and the frequency of the RF signal is “f”, a distance “d” of a compressional wave formed in the AOD is expressed as d=v/f. A laser light incident to the wave surface of the compressional wave at an angle of θ1is diffracted as a first order diffracted light in the direction of an angle of θ2satisfying “d×sin θ1+d×sin θ2=λ”, wherein λ is the wave length of the laser light. Here, when θ1=θ2, that is, when 2d×sin θ1=λ, the diffraction efficiency (the light intensity of a diffracted light/the light intensity of an incident light to the AOD) becomes the maximum, and generally an AOD element is arranged such that the laser light is incident to the AOD element at an angle where the diffraction efficiency becomes the maximum. When the above-described formulas are modified and θ2is expressed as a function of “f”, θ2=Sin−1(λf/v−sin θ1). That is, the diffraction angle θ2of a diffracted light changes non-linearly relative to linear changing of the frequency of the RF signal. That is, the angular velocity of a diffracted light when the diffracted light is deflected is not constant.

If the diffraction angle of a diffracted laser light does not change at a constant speed, that is, if the angular velocity of a diffracted light when the diffracted light is deflected is not constant, the position of an optical spot of the diffracted light on an object to be processed is not moved at a constant speed and results in exposure unevenness on the object to be processed, which is undesirable.

A laser annealing apparatus irradiating a laser light to a substrate in a low oxygen density environment is disclosed in Japanese Unexamined Patent Application Publication No. 2004-87962.

SUMMARY OF THE INVENTION

When forming a thin film transistor using a laser annealing method, if the light intensity of a diffracted laser light changes while the diffracted laser light is deflected and irradiated on an object to be processed, exposure unevenness is caused on the object. Further, if the position of an optical spot of the diffracted laser light on the object is not moved at a constant speed, exposure unevenness is also caused on the object. Because exposure unevenness causes quality deterioration, it is desirable to avoid exposure unevenness.

The present invention has been made in view of the above-described and other problems and provides a laser drawing method and a laser drawing apparatus that change the position of an optical spot of a diffracted laser light on a processing target at a constant speed and/or keep constant the light intensity of a diffracted laser light independent of the diffraction angle of the laser light.

According to an embodiment of the present invention, a method of laser drawing includes the steps of: causing a laser light from a light source to be incident to an acousto-optical diffraction element; and deflecting the light incident to the acousto-optical diffraction element by changing a frequency of a high frequency signal to be inputted to the acousto-optical diffraction element to diffract the light, thereby changing a diffraction angle of the diffracted light, and condensing the diffracted light emerging from the acousto-optical diffraction element through an intermediate optical lens system and a condensing lens on an object to be processed as an optical spot, thereby scanning the object with the optical spot of the diffracted light. A diffracted light intensity control table for controlling an amplitude of the high frequency signal to be inputted to the acousto-optical diffraction element so as to keep a light intensity of the diffracted light emerging from the acousto-optical diffraction element constant independent of the diffraction angle of the diffracted light is prepared in advance. In the deflecting step, the amplitude of the high frequency signal to be inputted to the acousto-optical diffraction element is controlled based on the diffracted light intensity control table, thereby the light intensity of the diffracted light emerging from the acousto-optical diffraction element is kept constant independent of the diffraction angle of the diffracted light.

According to another embodiment of the present invention, a method of laser drawing includes the steps of: causing a laser light from a light source to be incident to an acousto-optical diffraction element; and deflecting the light incident to the acousto-optical diffraction element by changing a frequency of a high frequency signal to be inputted to the acousto-optical diffraction element to diffract the light, thereby changing a diffraction angle of the diffracted light, and condensing the diffracted light emerging from the acousto-optical diffraction element through an intermediate optical lens system and a condensing lens on an object to be processed as an optical spot, thereby scanning the object with the optical spot of the diffracted light. A diffraction angle control table for controlling the frequency of the high frequency signal to be inputted to the acousto-optical diffraction element so as to change the diffraction angle of the diffracted light emerging from the acousto-optical diffraction element at a constant speed is prepared in advance. In the deflecting step, the frequency of the high frequency signal to be inputted to the acousto-optical diffraction element is controlled based on the diffraction angle control table, thereby the diffraction angle of the diffracted light emerging from the acousto-optical diffraction element is changed at a constant speed, so that the position of the optical spot of the diffracted light on the object is changed at a constant speed.

According to still another embodiment of the present invention, a laser drawing apparatus includes: a laser light source emitting a laser light; an acousto-optical diffraction element diffracting the light incident from the light source with inputting of a high frequency signal; an intermediate optical lens system and a condensing lens condensing the diffracted light emerging from the acousto-optical diffraction element on an object to be processed as an optical spot; and a high frequency signal output device outputting the high frequency signal to be inputted to the acousto-optical diffraction element. The high frequency signal output device changes a frequency of the high frequency signal to be inputted to the acousto-optical diffraction element to change a diffraction angle of the diffracted light to thereby deflect the diffracted light to scan an object to be processed with the optical spot of the diffracted light. The apparatus further includes a diffracted light intensity detection device detecting a light intensity of the diffracted light for each diffraction angle of the diffracted light; and a diffracted light intensity control table for controlling an amplitude of the high frequency signal to be inputted to the acousto-optical diffraction element so as to keep a light intensity of the diffracted light emerging from the acousto-optical element constant independent of the diffraction angle of the diffracted light. The table being prepared in advance using the diffracted light intensity detection device. The high frequency signal output device controls amplitude of the high frequency signal to be inputted to the acousto-optical diffraction element based on the diffracted light intensity control table, thereby a light intensity of the diffracted light emerging from the acousto-optical diffraction element is kept constant independent of the diffraction angle of the diffracted light.

According to still another embodiment of the present invention, a laser drawing apparatus includes: a laser light source emitting a laser light; an acousto-optical diffraction element diffracting the light incident from the light source with inputting of a high frequency signal; an intermediate optical lens system and a condensing lens condensing the diffracted light emerging from the acousto-optical diffraction element on an object to be processed as an optical spot; and a high frequency signal output device outputting the high frequency signal to be inputted to the acousto-optical diffraction element. The high frequency signal output device changes a frequency of the high frequency signal to be inputted to the acousto-optical diffraction element to change a diffraction angle of the diffracted light to thereby deflect the diffracted light to scan an object to be processed with the optical spot of the diffracted light. The apparatus further includes a position detection device detecting a position on the object of the optical spot of the diffracted light for each frequency of the high frequency signal; and a diffraction angle control table for controlling the frequency of the high frequency signal to be inputted to the acousto-optical diffraction element so as to change the diffraction angle of the diffracted light emerging from the acousto-optical diffraction element at a constant speed. The table is prepared in advance using the position detection device. The high frequency signal output device controls the frequency of the high frequency signal to be inputted to the acousto-optical diffraction element based on the diffraction angle control table, thereby the diffraction angle of the diffracted light emerging from the acousto-optical diffraction element is changed at a constant speed, so that a position of the optical spot of the diffracted light on the object is changed at a constant speed.

According to the present invention, the light intensity of a diffracted light emerging from an acousto-optical diffraction element can be made constant independent of the diffraction angle of the diffracted light by preparing a diffracted light intensity control table for controlling an amplitude of the high frequency signal to be inputted to the acousto-optical diffraction element so as to keep the light intensity of the diffracted light emerging from the acousto-optical diffraction element constant independent of the diffraction angle of the diffracted light and by controlling the amplitude of the high frequency signal to be inputted to the acousto-optical diffraction element based on the diffracted light intensity control table.

Further, according to the present invention, the diffraction angle of a laser light incident to an acousto-optical diffraction element and diffracted with inputting of an RF signal to the acousto-optical diffraction element can be changed at a constant speed by preparing a diffraction angle control table for controlling the frequency of the high frequency signal to be inputted to the acousto-optical diffraction element so as to change the diffraction angle of the diffracted light emerging from the acousto-optical diffraction element at a constant speed and by controlling the frequency of the RF signal to be inputted to the acousto-optical diffraction element based on the diffraction angle control table.

According to a laser drawing method and a laser drawing apparatus of the present invention, in laser drawing such as laser annealing, it is possible to keep constant the light intensity of a diffracted light emerging from an acousto-optical diffraction element independent of the diffraction angle of the diffracted light and/or to change the diffraction angle of the diffracted light at a constant speed to thereby move the position of an optical spot of the diffracted light on an object to be processed at a constant speed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, referring to drawings, embodiments of the present invention are described.

FIG. 3illustrates a laser drawing apparatus according to an embodiment of the present invention. A laser drawing apparatus1according to this embodiment includes a laser light source2emitting a laser light and an AOD4diffracting and thereby deflecting the laser light incident from the light source2to be emerged as a diffracted light. The laser drawing apparatus1further includes a first fθ lens group6aand a second fθ lens group6bconstituting an afocal-relay optical system serving as an intermediate optical lens system, and an object lens7opposing a sample15as an object to be processed. The object lens7is a condensing lens. The diffracted laser light emerged from the AOD4is condensed as an optical spot of the diffracted laser light on the sample15by the first fθ lens group6a, the second fθ lens group6b, and the object lens7. A collimator lens3is arranged between the laser light source2and the AOD4to make the laser light to a parallel light. For the laser light source2, for example, a semiconductor laser may be used.

A first beam splitter5aand a second beam splitter5bare arranged on a light path between the AOD4and the first θ lens group6a. A portion of a diffracted light emerged from the AOD4is reflected by the first beam splitter5aand is received through a first condensing lens8aon a photodiode9serving as a diffracted light intensity detection device detecting the light intensity of a diffracted light. Thereby, the light intensity of the diffracted light is detected with the photodiode9. A return light of the diffracted light emerged from the AOD4, passed through respective lenses (the first fθ lens group6a, the second fθ lens group6b, and the object lens7), and reflected by the object to the processed (the sample15) is reflected by the second beam splitter5band is received, through a second condensing lens8b, by a position detection device10serving as a position detection device detecting the position of an optical spot of the diffracted light on the sample15. Thereby, a position of the optical spot of the diffracted light on the object is detected.

The laser drawing apparatus1further includes an RF signal output device13outputting an RF signal to be inputted to the AOD4to diffract a laser light incident to the AOD4. As described later, the RF signal output device13supplies the RF signal to the AOD4while controlling the amplitude and/or frequency of the RF signal so as to make the light intensity of a diffracted light emerging from the AOD4constant independent of the diffraction angle of the diffracted light and/or to change the diffraction angle of the diffracted light at a constant speed to thereby move the position of an optical spot of the diffracted light on the sample15at a constant speed. The RF signal output device13controls the frequency and/or amplitude of an outputting RF signal by referring to a diffracted light intensity control table11for controlling the light intensity of a diffracted light emerging from the AOD4so as to be constant independent of the diffraction angle of the diffracted light and/or a diffraction angle control table12for controlling the diffraction angle of the diffracted light so as to be changed at a constant speed. The diffracted light intensity control table11to be referred to for controlling the light intensity of a diffracted light emerging from the AOD4and the diffraction angle control table12to be referred to for controlling the diffraction angle of the diffracted light are stored in a storage unit not shown.

In the diffracted light intensity control table11, control values for controlling the light intensity of a diffracted light emerging from the AOD4so as to be constant independent of the diffraction angle of the diffracted light are stored. The values to be stored in the diffracted light intensity control table11are prepared in advance as described later using the photodiode9. Further, in the diffraction angle control table12, control values for controlling the diffraction angle of a diffracted light emerging from the AOD4so as to be changed at a constant speed are stored. The values to be stored in the diffraction angle control table12are prepared in advance using the position detection device10.

The first fθ lens group6amay be constituted for example by two pieces of lenses in one group, and the second fθ lens group6bmay be constituted for example by four pieces of lenses in three groups. The first fθ lens group6aand the second fθ lens group6bare arranged to oppose to each other so that respective rear-side focal points agree with each other and a front-side focal point of the first fθ lens group6ais caused to agree with a diffraction position of the AOD4and a front-side focal point of the second fθ lens group6bis caused to agree with the position of an incident pupil of the object lens7. Thereby, the first fθ lens group6aand the second fθ lens group6bfunctions as an afocal-relay optical system having little aberration.

Now, using the above-described laser drawing apparatus1, a laser drawing method according to an embodiment of the present invention is described.

As illustrated inFIG. 3, the light source2emits a laser light. For the laser light, for example a blue color laser light having the wavelength of 405 nm may be used. The laser light emitted from the light source2is made a parallel light by the collimator lens3converting a divergent light into a parallel light. The laser light converted to a parallel light enters the AOD4, which ejects a first order diffracted light of the laser light (hereinafter, referred to as a diffracted light). The diffracted light emerging from the AOD4is used as a drawing laser beam, for example as a beam for exposure, and is caused to scan on the sample15as the diffracted light is diffracted and thereby deflected within a predetermined angle range by an RF signal inputted to the AOD4. The deflecting direction of the diffracted light can be controlled by changing of the frequency of the RF signal to be inputted to the AOD4.

The diffracted light emerged from the AOD4passes through the first fθ lens group6aand the second fθ lens group6band is condensed by the object lens7to be irradiated on the sample5and at the same time, is caused to scan on the sample15based on deflection of the diffracted light at the AOD4, and thereby laser drawing is conducted. In this embodiment, the range of a diffraction angle of a diffracted light emerging from the AOD4, i.e., the deflection angle of the diffracted light, is set to a predetermined range. In this embodiment, the diffraction angle is set at about 35 mrad. In this case, the optical axis is deviated about ±3.5 mm on the incident surface of the object lens7, which is 200 mm from the diffraction position of the AOD4.

If the incident pupil diameter of the object lens7which stops down the diffracted light irradiating the sample15is Φ3.8 mm, the diffracted light hardly enters the incident pupil of the object lens7. Therefore, in this embodiment, the diffracted light is caused by the afocal-relay optical system constituted by the first fθ lens group6aand the second fθ lens group6bto be incident to the incident pupil of the object lens7at a position corresponding to the diffraction position of the AOD4. Then, the whole portion of the diffracted light is caused to be incident to the incident pupil of the object lens7and is condensed onto the sample15.

The RF signal output device13reads out the diffracted light intensity control table11and/or the diffraction angle control table12and controls an RF signal to be inputted to the AOD4so as to keep the light intensity of a diffracted light emerging from the AOD4constant independent of the diffraction angle of the diffracted light and/or to change the diffraction angle of the diffracted light at a constant speed based on the diffracted light intensity control table11and/or the diffraction angle control table12. The relation between the diffracted light intensity control table11and the diffraction angle control table12and changes in the intensity and the diffraction angle of a diffracted light emerging from the AOD4will be described later.

Next, methods of preparing the diffracted light intensity control table11and the diffraction angle control table12are described. The diffracted light intensity control table11and the diffraction angle control table12are prepared using the laser drawing apparatus1.

First, a method of preparing the diffracted light intensity control table11using the laser drawing apparatus1is described. A portion of a diffracted laser light emerged from the AOD4is reflected by the first beam splitter5asplitting a light flux and is converged to the first condensing lens8a. The laser light converged to the first condensing lens8ais condensed to the photodiode9converting a detected light into an electric signal. Thereby, the light intensity of the diffracted light is detected. At this time, alignment of the first beam splitter5a, the first condensing lens8a, and the photodiode9is adjusted so that a diffracted light at each of arbitrary diffraction angles (described later) is detected by the photodiode9. Then, based on a detection result of the diffracted light intensity detection device, i.e., the light intensity of a diffracted light for each diffraction angle, the diffracted light intensity control table11is prepared (described in detail later).

Next, an exemplary method of preparing the diffraction angle control table12using the laser drawing apparatus1is described. A diffracted light emerged from the AOD4and passed through the object lens7is converged on a surface of the sample15. A return light of the diffracted light reflected by the sample15passes the object lens7, the second fθ lens group6b, and the first fθ lens group6ain that order, and a portion of the return light passed the first fθ lens group6ais reflected by the second beam splitter5band is converged to the second condensing lens8b. The return light converged by the second condensing lens8bis received by the position detection device10detecting the position of a condensed optical spot of the diffracted light on the sample15and thereby a position of the optical spot of the diffracted light on the sample15is detected. Then, based on a detection result with the position detection device10, a relation of the frequency of an RF signal inputted to the AOD4to diffract an incident laser light and the position on the sample15of the optical spot of the diffracted light is obtained. At this time, alignment of the second beam splitter5b, the second condensing lens8b, and the position detection device10is adjusted so that a diffracted light at each of arbitrary diffraction angles (frequencies of the RF signal) is detected by the position detection device10. Then, based on the relation of the frequency of the RF signal and the position on the sample15of the optical spot of the diffracted light, the diffraction angle control table12is prepared (described in detail later).

Here, the RF signal output device13outputting an RF signal to the AOD4controls the amplitude and/or the frequency of the RF signal using the diffracted light intensity control table11and/or the diffraction angle control table12, and thereby the intensity and/or the diffraction angle of a diffracted light emerging from the AOD4are controlled.

Next an example of the diffracted light intensity control table11used in the laser drawing apparatus1according to this embodiment of the present invention is described in detail referring toFIG. 4.

As described above, because the diffraction efficiency (the light intensity of a diffracted light/the light intensity of an incident light to the AOD4) changes depending on the diffraction angle, the light intensity of a diffracted light changes depending on the diffraction angle of the diffracted light, and as a result, exposure unevenness is caused on the sample15. And, as described above, as the frequency of an RF signal supplied to the AOD4increases, the diffracted light intensity changes (seeFIG. 1). In the laser drawing apparatus1in this embodiment, the amplitude of the RF signal supplied to the AOD4is controlled such that the light intensity of a diffracted light emerging from the AOD4is kept constant independent of the diffraction angle of the diffracted light.

In the diffracted light intensity control table11, first frequency instructing values specifying a range of frequencies of an RF signal to be inputted to the AOD4to change the diffraction angle of an incident light are recorded in advance. Further, in this embodiment, 9 dividing points F1-F9that divides the range of frequencies of the RF signal in 8 equal parts are provided. A range of diffraction angles of the laser light incident to the AOD4is determined (for example, to 35 mrad) based on the first frequency instructing values.

When preparing the diffracted light intensity table11using the laser drawing apparatus1, the RF signal output device13controls the frequency of the RF signal to be inputted to the AOD4based on the first frequency instructing values of the diffracted light intensity table11. In a state that the amplitude of the RF signal is set to a possible maximum value, the light intensity of a diffracted light emerging from the AOD4is detected with the photodiode9for each diffraction angle (for each frequency of 9 dividing points), and based on a detection result, values of the diffraction efficiency (the light intensity of a diffracted light/the light intensity of an incident light to the AOD4) are obtained for respective diffraction angles (frequencies), and inverse numbers of the obtained diffraction efficiency values are determined for respective diffraction angles (frequencies). Inverse numbers of diffraction efficiency values with respect to diffraction angles (frequencies) deviated from the dividing points F1-F9are supplemented by a spline curve. Then, a diffraction angle (frequency) at which the detected diffracted light intensity is the lowest is taken as a criterion, and values proportional to respective inverse numbers of the obtained diffraction efficiency values are determined such that the light intensity of the diffracted light at each diffraction angle (frequency) becomes the same as the lowest. The values proportional to the inverse numbers of the diffraction efficiency values for respective diffraction angles (frequencies) of the diffracted light are stored in the diffracted light intensity control table11as amplitude control values for respective frequencies of the RF signal.

The RF signal output device13reads out the amplitude control values from the diffracted light intensity control table11and controls the amplitude of the RF signal to be outputted according to the amplitude control values, and thereby it becomes possible to control the light intensity of the diffracted light emerging from the AOD4. Because the inverse numbers of diffraction efficiency values with respect to diffraction angles (frequencies) deviated from the dividing points F1-F9are supplemented by a spline curve, even when the laser light is diffracted at a diffraction angle where the light intensity of the diffracted light has not been not actually detected with the photodiode9, it is possible to keep the diffracted light intensity substantially constant.

FIG. 5illustrates a relation between the frequency of an RF signal inputted to the AOD4and the light intensity of a diffracted light emerging from the AOD4when the amplitude of the RF signal has been controlled based on the diffracted light intensity control table11.

The RF signal output device13reads out the first frequency instructing values from the diffracted light intensity control table11. Then, in response to the change in the frequency, the amplitudes of the RF signal at 9 dividing points F1-F9of the frequency range are controlled based on the amplitude control values of the diffracted light intensity control table11. The frequency of the RF signal outputted by the RF signal output device13changes from the lower limit value F1to the upper limit value F9between time T1and time T9and at this time, the amplitude of the RF signal changes between the lower limit value A1and the upper limit value A2as illustrated inFIG. 5. Thus, the amplitude of the RF signal is controlled in response to the frequency of the RF signal, and thereby the light intensity of a diffracted light emerging from the AOD4is controlled to be at a fixed value P.

Next, an example of the diffraction angle control table12used in the laser drawing apparatus1according to this embodiment of the present invention is described more in detail referring toFIG. 6.

As described above, as the diffraction angle of a diffracted light emerging from the AOD4changes with changing of the frequency of an RF signal to be inputted to the AOD4, the position on the sample15of a condensed optical spot of a diffracted light emerging from the AOD4is moved. Meanwhile, even if the frequency of an RF signal is linearly changed, the diffraction angle does not change at a constant speed (seeFIG. 2), and there is a possibility that exposure unevenness is caused on the sample15. Therefore, in the laser drawing apparatus1in this embodiment, for changing the diffraction angle of a diffracted light emerging from the AOD4at a constant speed, the frequency of an RF signal to be inputted to the AOD4is controlled based on the diffraction angle control table12.

In the diffraction angle control table12, for changing the diffraction angle of an incident laser light, second frequency instructing values specifying frequencies of an RF signal to be inputted to the AOD4are recorded in advance. Based on the second frequency instructing values, a range of frequencies of an RF signal to be inputted to the AOD4is determined. Further, in this embodiment, 9 dividing points that divide the range of frequencies of the RF signal based on the second frequency instructing values in 8 equal parts are provided.

When preparing the diffraction angle control table12using the laser drawing apparatus1, the RF signal output device13supplies an RF signal based on the second frequency instructing values of the diffraction angle control table12to the AOD4. Then, the position information of an optical spot of a diffracted light emerging from the AOD4for each of 9 dividing points of the range of frequencies of the RF signal is obtained with the position detection device10, and based on the obtained position information, frequencies of the RF signal to be inputted to the AOD4to obtain desired diffraction angles of the diffracted light (desired positions of the optical spot of the diffracted light on the object) are sequentially determined. The frequencies of the RF signal between respective dividing points are supplemented by a spline curve.FIG. 6illustrates a relation between frequencies F′1-F′9thus determined and corresponding diffraction angles θ1-θ9. In the diffraction angle control table12, values specifying the frequencies of the RF signal thus determined are stored as frequency control values.

The RF signal output device13reads out the frequency control values of the diffraction angle control table12and controls the frequency of the RF signal to be inputted to the ADO4according to the frequency control values. The frequency control values of the diffraction angle control table12may be read out in a constant time sequentially from the one for the smaller or larger diffraction angle. Because the frequencies of the RF signal between respective dividing points are supplemented by a spline curve, even when the laser light is diffracted at a diffraction angle where the position of an optical spot of the diffracted light on the object15has not been not actually detected with the position detection device10, the diffraction angle of a diffracted light emerging from the AOD4is changed at a constant speed and thereby the optical spot of the diffracted laser light on the sample15is moved at a constant speed.

FIG. 7illustrates a relation between the frequency of an RF signal inputted to the AOD4and the diffraction angle of a diffracted light emerging from the AOD4when the frequency of the RF signal has been controlled based on the frequency control values of the diffraction angle control table12.

The RF signal output device13reads out the frequency control values from the diffraction angle control table12and controls the frequency of the RF signal to be inputted to the AOD4according to the frequency control values. The frequency of the RF signal outputted by the RF signal output device13is changed between time T1and time T9from the lower limit value F1′ to the upper limit value F2′ and at this time the diffraction angle of a diffracted light changes between the lower limit value θ1and the upper limit value θ2as illustrated inFIG. 7. Thus, the diffraction angle of a diffracted light emerging from the AOD4is changed at a constant speed in response to the change in the frequency of the RF signal based on the diffraction angle control table12, and thereby the position of an optical spot of the diffracted light on the object is changed at a constant speed.

Generally, in a diffraction optical system using an AOD, an ultrasonic wave is generated in the AOD with an RF signal inputted to the AOD and a laser light incident to the AOD is diffracted by a wave surface of the ultrasonic wave, so that it is difficult to feed back a result of detecting the light intensity of a diffracted light with a diffracted light intensity detection device to control the RF signal. Therefore, in this embodiment, the diffracted light intensity control table11and/or the diffraction angle control table12are prepared in advance and are stored in the laser drawing apparatus1. Then, without feeding back a result of detecting the light intensity of a diffracted light with the photodiode9and/or the position of an optical spot of the diffracted light on the sample15with the position detection device10, the amplitude and/or the frequency of an RF signal to be inputted to the AOD4can be properly controlled. As a result of this, it becomes possible to keep the light intensity of a diffracted light emerging from the AOD4constant and to change the diffraction angle of the diffracted light at a constant speed.

Here, actual results of detecting the light intensity of a diffracted light emerging from the AOD4and the position of an optical spot of the diffracted light on the sample15using the photodiode9and the position detection device10are described referring toFIG. 8. The cycle of the RF signal outputted by the RF signal output device13is set to 100 μsec.FIG. 8illustrates waveforms displayed on an oscilloscope.

A waveform21illustrates the light intensity of a diffracted light emerging from the AOD4when the amplitude of an RF signal to be inputted to the AOD4is not controlled based on the diffracted light intensity control table11. The waveform21is slightly asymmetrical due to deviation in optical adjustment. A waveform22illustrate the light intensity of a diffracted light emerging from the AOD4when the amplitude of the RF signal to be inputted to the AOD4has been controlled based the diffracted light intensity control table11. From the waveform22, it is understood that the light intensity of the diffracted light is kept at a substantially fixed value.

A waveform23illustrates the position on the sample15of an optical spot of a diffracted light emerging from the AOD4when the frequency of an RF signal to be inputted to the AOD4is not controlled based on the diffraction angle control table12. The waveform23is in a gentle curve in substantially a linear shape. A waveform24illustrates the position on the sample15of a diffracted light emerging from the AOD4when the frequency of the RF signal has been controlled based on the diffraction angle control table12. It is understood from the waveform24that the position of the optical spot of the diffracted light on the sample15changes substantially at a constant speed.

According to the above-described embodiment, the RF signal output device13controls the amplitude of an RF signal to be inputted to the AOD4based on the diffracted light intensity control table11, and thereby the light intensity of a diffracted light emerging from the AOD4is kept constant independent of the diffraction angle of the diffracted light. Also, the RF signal output device13controls the frequency of an RF signal to be inputted to the AOD4based on the diffraction angle control table12, and thereby the diffraction angle of a diffracted light emerging from the AOD4is changed at a constant speed, that is, the angular speed of the diffracted light is kept constant, and thereby the position of an optical spot of the diffracted light on the sample15is moved at a constant speed. Thus, for example, in anneal processing a sample, exposure unevenness is avoided in the micro-fabricated sample.

When the diffraction angles vary depending on AODs or the coupling efficiencies varies depending on optical systems, respective instructing values and control values of the diffracted light intensity control table11and the diffraction angle control table12may be appropriately adjusted.

Furthermore, in related art laser drawing apparatuses in which an irradiated laser light is made directly incident on an object lens, it occurs that an optical axis of an optical system is deviated. Then, when an AOD that can obtain a relatively large diffraction angle is used, the whole portion of a diffracted light emerging from the AOD does not enter the incident pupil of the object lens, and thereby the light intensity of the diffracted light greatly decreases. On the other hand, in the laser drawing apparatus1of this embodiment, with the provision of the intermediate optical lens system as an afocal-relay optical system, the optical axis of a diffracted light emerging from the AOD4and incident on the object lens7can be caused to agree with the center of the incident pupil of the object lens7independent of the diffraction angle of the diffracted light. Thereby, the above-described problem occurring in the related art laser drawing apparatuses is avoided.

According to the above-described embodiment of the present invention, the RF signal to be inputted to the AOD4may be controlled based on either of or both of the diffracted light intensity control table11and the diffraction angle control table12. When preparing the diffracted light intensity control table11for controlling the RF signal based on both of the diffracted light intensity control table11and the diffraction angle control table12, the frequencies of the RF signal determined based on the frequency control values of the diffraction angle control table12are used for the first frequency instructing values of the diffracted light intensity control table11. Then, the RF signal output device13controls the frequency of the RF signal to be inputted to the AOD4based on the frequency control values of the diffraction angle control table12serving as the first frequency instructing values of the diffracted light intensity control table11, and thereby amplitude control values for respective frequencies of the RF signal are obtained in a similar manner as described above.

In the above-described embodiment, when preparing the diffracted light intensity control table11, the values proportional to respective inverse numbers of the obtained diffraction efficiency values as the amplitude control values are determined such that the light intensity of the diffracted light at each diffraction angle (frequency) other than the criterion diffraction angle (frequency) becomes the same as the lowest. However, the values proportional to respective inverse numbers of the obtained diffraction efficiency values as the amplitude control values may be determined otherwise appropriately, for example depending upon the kind of the sample15.

Further, in the diffracted light intensity control table11and the diffraction angle control table12, 9 dividing points dividing the frequency of an RF signal are provided, respectively, however, the number of diving points for one cycle of the RF signal is not limited to 9 points (8 divided parts). For example, the number of dividing points may be 5 points (4 divided parts) or 41 points (40 divided parts).

Furthermore, the lens group constituting the intermediate optical lens system of the laser drawing apparatus1is constituted by an fθ lens group, however, it may be constituted by a lens group other than the fθ lens group as long as the positional relationship between the AOD4and the incident pupil surface of a final condensing lens in the previous stage of the sample15(in this embodiment, the object lens7) is similar to that of an afocal-relay optical system.

Further, the laser drawing apparatus1has been described as an example for a case that it is used in laser annealing for making a thin film transistor, which is used, for example, in a liquid crystal display apparatus, however, the laser drawing apparatus1may be configured to produce a wire-grid polarizer by inscribing thin parallel grooves at equal intervals on the surface of a glass and by arranging wirings in the grooves to deflect specific light rays. The laser drawing1may be used for other micro-fabrication.

The present invention is not limited to the above-described respective embodiments and may have various other arrangements without departing from the gist of the present invention.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending upon design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.