KR100892017B1 - Injection-locked pulsed laser, interferometer, exposure apparatus, and device manufacturing method - Google Patents

Abstract

According to the present invention, an injection synchronous pulse laser device is disclosed. The injection-synchronous pulsed laser device includes a seed laser, an oscillator in which a part of light output from the seed laser is injected as a seed laser light, a frequency converter for shifting frequencies of other parts of the light output from the seed laser; A photodetector for detecting light synthesized with the light output from the oscillator and the light output from the frequency converter, and a controller for controlling the optical path length of the oscillator based on a bit signal component included in an output signal of the photodetector. .

Description

Injection synchronized pulsed laser device, interferometry, exposure device, and device manufacturing method {INJECTION-LOCKED PULSED LASER, INTERFEROMETER, EXPOSURE APPARATUS, AND DEVICE MANUFACTURING METHOD}

The present invention relates to an injection synchronous pulse laser device, an interferometric device, an exposure device and a device manufacturing method.

7 is a view showing a schematic configuration of a conventional injection synchronous laser device (see J. Rahn, "Feedback stabilization of an injection-seeded Nd: YAG laser", App. Opt., 24, 940 (1985)). In the injection synchronous laser device shown in Fig. 7, a method of minimizing the buildup time is employed as the injection synchronization method.

The pulse oscillator O for generating pulsed light is usually configured in a ring shape in order to avoid the influence of spectral hole burning. The output coupler of the pulse oscillator O is disposed in the PZT mount 4. The PZT mount 4 is driven with high precision by a PZT controller (PZT amplifier) 5. As the gain medium 3 of the laser, for example, Ti: sapphire crystal or the like can be used. An excitation light source 2 such as Nd: YAG can be used for excitation of the crystal, and excitation is performed by irradiating and absorbing a light beam onto the crystal.

The seed laser 1 is an injection light source for the injection motive, and a single longitudinal mode light source having a small enough full width at half maximum is used. The seed laser light output from the seed laser 1 is injected into the pulse oscillator O so as to match the transverse mode of the pulse oscillator O. As the seed laser 1, for example, an external oscillator type semiconductor laser can be used.

The injection synchronous synchronizes the wavelength of the narrow band laser light injected into the oscillator and the optical path length of the oscillator. Since the photons of the injected narrow band laser light are responsible for the induced emission of the initial pulse oscillation, the excitation energy is concentrated in the narrow band. Pulse oscillation is facilitated.

The most efficient injection synchronous is realized when the optical path length of the pulse oscillator O is an integer multiple of the oscillation wavelength of the seed laser 1, and the buildup time is shortest. Under other conditions, build-up time becomes longer because the oscillator loses the seed laser 1.

Here, the buildup time means the time from the excitation laser incident until the pulsed light oscillates. Using the above principle, the buildup time is used to control the oscillator.

In order to detect the build-up time, an excitation light source photodetector 32 and a pulsed light photodetector 33 are inserted in the vicinity of the oscillator. The outputs of both photodetectors 32 and 33 are provided to the control circuit 34. The control circuit 34 calculates a buildup time based on the output signals of both photodetectors 32 and 33, generates an error signal based on the change in the buildup time, and feeds back the error signal. PID filtering is performed.

The filtered signal is provided to the PZT controller 5. The PZT controller 5 drives the PZT mount 4 based on this signal, thereby enabling injection synchronous control.

However, in the conventional control method based on the buildup time, for example, a control error occurs due to a change in the buildup time due to an element other than the oscillator length (for example, intensity jitter, pointing jitter, etc. of the excitation laser). Can be. In addition, noise is easily mixed in the processing circuit for calculating the buildup time from the laser output, and it is difficult to generate an error signal having a high SN. As a result, a synchronous control error occurs and laser characteristic degradation such as intensity or jitter of wavelength occurs.

The present invention can provide an injection synchronous pulse laser device having good wavelength stability, and an interference measuring device and an exposure device using the same.

According to a first aspect of the present invention, a seed laser, an oscillator into which a part of light output from the seed laser is injected as a seed laser light, a frequency converter for shifting frequencies of other parts of light output from the seed laser, A photo detector for detecting light synthesized with the light output from the oscillator and the light output from the frequency converter, and a controller for controlling an optical path length of the oscillator based on a bit signal component included in an output signal of the photo detector. An injection synchronous pulse laser device is provided.

According to the second aspect of the present invention, a seed laser, an oscillator into which a part of the light output from the seed laser is injected as the seed laser light, a frequency converter for shifting the frequency of the light output from the oscillator, and an output from the seed laser And a photodetector for detecting light synthesized with other components of light and the light output from the frequency converter, and a controller for controlling an optical path length of the oscillator based on a bit signal component included in an output signal of the photodetector. An injection synchronous pulse laser device is provided.

Other features of the present invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings.

According to the present invention, it is possible to provide an injection synchronous pulse laser device having excellent wavelength stability, an interferometric device, an exposure device, and a device manufacturing method.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described, referring an accompanying drawing.

[First embodiment]

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the injection synchronous pulse laser apparatus as 1st Embodiment of this invention. The light beam B1 output from the seed laser 1 is divided into two beams B2 and B3 by the semi-transparent mirror M1. The light beam B2 reflected by the translucent mirror M1 is reflected by the mirror M2 and injected into the pulse oscillator O. The pulse oscillator O is preferably ring-shaped in order to avoid the influence of hole burning. The gain medium 3 is disposed in the pulse oscillator O, and the excitation is disposed outside the pulse oscillator O to irradiate the laser light generated by the excitation light source (excitation laser) 2 into the pulse oscillator O. This can be done by. In addition, the output coupling mirror M3 of the pulse oscillator O is disposed in the PZT mount 4. The PZT mount 4 is controlled by a PZT controller 5 including an amplifier, whereby the optical path length of the pulse oscillator O can be controlled with high precision.

On the other hand, the light beam B3 output from the seed laser 1 and transmitted through the semi-transparent mirror M1 enters into the acoustooptical device AOM 6 as the frequency converter via the mirrors M4 and M5. A voltage signal having a frequency f _AOM is applied to the acoustooptical device 6, and a plurality of orders of diffracted light are generated from a light beam passing through the acoustooptical device 6 by the acoustooptic effect. In these plural orders of diffracted light, a frequency shift of n x f _AOM (n is the order) occurs, respectively.

Only the + 1st order light beams are spatially extracted from these plural orders of diffraction light, and are coupled to the first input terminal of the branch fiber 8 by the fiber coupler 7a. The branched fiber 8 is, for example, a polarization plane storage single mode type and includes two input terminals (first and second input terminals) and one output terminal.

Similarly, part of the output of the pulse oscillator O is branched by the translucent mirror M6, and is coupled to the second input terminal of the branch fiber 8 by the fiber coupler 7b.

Here, the branch fiber 8 is very suitable for spatially overlapping the output of the seed laser 1 with the output of the pulse oscillator O. In addition, the polarization-preserving branched fiber is very suitable for maximizing the bit signal amplitude between two luminous fluxes and for preventing the change of polarization due to the stress change to the fiber or the like. Of course, you may superimpose a light beam using a semi-transparent mirror etc., without using a branching fiber.

The output terminal of the branch fiber 8 is connected to the photodetector 9. The photodetector 9 converts the intensity of the light output from the branch fiber 8 into an electric signal. The output light of the photodetector 9 is synthesized by the branch fiber 8 because the output light whose frequency is shifted via the acoustooptic element 6 output from the seed laser 1 and the output light of the pulse oscillator O are synthesized. The signal is given by the following formula (1):

.

.

Where I _seed is the seed laser intensity, I _pulse is the pulse oscillator output, f _seed is the seed laser light frequency, and f _pulse is the pulse laser center light frequency. Hereinafter, the signal I (t) given by the expression (1) is called a bit signal. Fig. 2 is a diagram illustrating the bit signal I (t) obtained by the simulation.

The interpreter 10 extracts an error signal from the bit signal I (t). Hereinafter, the process in the analyzer 10 is demonstrated.

The analyzer 10 first performs A / D conversion on the pulse bit signal I (t). As a trigger of A / D conversion, Q switch timing of the excitation light source (excitation laser) 2 is preferable, for example. The sampling number is preferably 2 ⁿ in consideration of subsequent FFT (Fast Fourier Transform) processing.

Next, the analyzer 10 performs frequency analysis on the bit signal I (t). First, the analyzer 10 performs an FFT on the bit signal I (t). The Fourier transform of equation (1) is represented by the following equation (2):

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.

In Fig. 3, the Fourier transform given by Equation (2) is illustrated. As can be seen from equation (2), the spectrum around f _AOM represents the frequency difference between the pulsed light from the pulse oscillator O and the light from the seed laser 1. Therefore, in order to extract frequency information of the pulsed light from the pulse oscillator O, the modulation frequency f _AOM (frequency shift amount) of the _AOM 6 needs to be sufficiently larger than the spectral width of this pulsed light.

The analyzer 10 then calculates the weighted mean of the spectra. Here, using a weighted average instead of the peak position of the spectrum means that in the case of the peak position, the resolution of the error signal is limited to the resolution of the FFT, and in applications such as an interferometer, the wavelength stability is determined by the weighted average of the spectrum. This only affects the fluctuations.

On an actual system, noise data is mixed in a region where spectral components cannot exist due to noise generated by the AD converter in the photodetector 9 or the analyzer 10, which may cause a calculation error of the weighted average. . This can be avoided by defining a significant threshold to the noise level of the system in advance, and applying only the data having a noise level higher than this to the calculation. In addition, since there is a spectral component that does not depend on the frequency of the pulse near the DC level, it is necessary to designate a weighted average calculation region in advance so as not to be affected. From the above, the difference (f _pulse -f _seed ) between the frequency f _seed of the output light of the seed laser 1 and the frequency f _pulse of the output light of the pulse oscillator O is calculated by the following formula (3):

.

.

The result obtained here is only the information of the frequency difference and does not include the sign information. However, since the sign can be determined from the moving direction of the PZT mount 4 and the fluctuation direction of the frequency difference, the feedback system is not a problem. Moreover, although the modulation frequency jitter of the acoustooptical element 6 becomes a measurement error, it can be ignored because it is small enough for general optical frequency stability.

Finally, the analyzer 10 converts the frequency difference f _puls -f _seed into DA and outputs it as an analog error signal. Since the laser device of this embodiment is a pulse laser device, this error signal is held until the next pulse oscillates.

In order to increase the control frequency of the pulse oscillator O, the process in the analyzer 10 is preferably performed for each pulse. When the analyzer 10 is configured using a field programmable gate array (FPGA) or the like, for example, the analyzer 10 can be interpreted at a repetition frequency of about 10 Hz.

The error signal output from the interpreter 10 is provided to the PZT controller 5, which is provided (feedback) to the PZT mount 4 after PID compensation has been made in the PZT controller 5.

In the first embodiment, the control of the pulse oscillator O is performed so that the oscillation wavelength of the pulsed light is the same wavelength as the oscillation wavelength of the seed laser 1. Therefore, the optical path length of the pulse oscillator O is maintained at an integral multiple of the optical path length of the seed laser 1, and stable injection synchronous is realized. According to the first embodiment, since the wavelength difference can be directly extracted in accordance with the pulse bit signal, high precision injection synchronous control is possible because it is not affected by the intensity jitter of the excitation light source.

Second Embodiment

4 is a diagram showing a schematic configuration of an injection synchronous pulse laser device as a second embodiment of the present invention. The light beam B1 output from the seed laser 1 is divided into two beams B2 and B3 by the semi-transparent mirror M1. The light beam B2 reflected by the semi-transparent mirror M1 is injected into the pulse oscillator O via the mirror M2. The pulse oscillator O is preferably ring-shaped in order to avoid the influence of hole burning. In the pulse oscillator O, a Ti: sapphire crystal is disposed as the gain medium 3, and excitation of the gain medium 3 is an excitation light source having a wavelength corresponding to the absorption band of Ti: sapphire from the outside of the oscillator O. (Excitation laser) 2, for example, it can be performed by irradiating a double wave of Nd: YAG. In addition, the output coupling mirror M3 of the oscillator O is disposed in the PZT mount 4. The PZT mount 4 is controlled by a PZT controller 5 including an amplifier, whereby the optical path length of the oscillator O can be controlled with high precision.

On the other hand, the light beam B3 emitted from the seed laser 1 and transmitted through the translucent mirror M1 is reflected by the mirror M4 and then enters the translucent mirror M6, thereby providing two beams B4 and B5. Is divided into

The light beam B5 transmitted through the semi-transparent mirror M6 is reflected by the mirror M7, enters the electro-optic modulation element 11, receives a phase modulation of frequency fm, and then passes through the polarization beam splitter 12. Further, the light enters the reference resonator 14 after passing through the λ / 4 wave plate 13. On the opposite side of the polarizing beam splitter 12, a photo detector 15 is provided, and the amount of light provided from the reference resonator 14 is detected by the photo detector 15.

In the second embodiment. The oscillation wavelength of the seed laser 1 is stabilized by the method shown below. In the second embodiment, the Pound-Drever method is used. After being modulated at the frequency fm by the electro-optic modulation element 11, the complex amplitude of the laser beam B6 is represented by the following formula (4):

.

.

Here, νo denotes the center light frequency of the laser light generated by the seed laser 1, Φ (t) is the phase shift from the center light frequency, and Φm represents the modulation depth by the electro-optic modulation element 11.

On the other hand, the transfer function Hr (v) of the reflected light from the reference resonator 14 refers to the amplitude reflectance of the mirror of the reference resonator 14, r ₁ , r ₂ , and the frequency of the light generated by the seed laser 1, ν, as a reference. If the FSR of the resonator 14 is ν _F , it is represented by the following formula (5):

.

.

The intensity signal of the light received by the photodetector 15 is given by multiplication of the equation (4) and the equation (5), and is expressed by the following equation (6) if only a component oscillating at the modulation frequency fm is extracted from this signal. :

.

.

By demodulating this strength signal at frequency fm, a demodulated signal represented by the following formula (7) can be obtained:

.

.

If V (ν) = Nνf + δν, V (ν) exhibits a linear characteristic with respect to the frequency error δν in the vicinity of δν to 0, and thus can be used as an error signal for frequency stabilization. The demodulation of the error signal from the light intensity signal and the filtering process such as the PID for control are performed by the demodulator 16, and the demodulation result is fed back to the wavelength modulation terminal of the seed laser 1.

As described above, the oscillation wavelength of the seed laser 1 is stabilized by using the oscillation wavelength of the reference resonator 14 as a reference by the stabilization unit including the reference resonator 14. Here, since the frequency variation of the reference resonator 14 is an error factor, it is necessary to pay sufficient attention to the optical path length change caused by disturbance such as vibration, temperature or noise. Specifically, it is important that a high rigidity mechanical structure and a low vibration installation environment are provided, while an injection synchronous pulse laser device is disposed in the sound insulation air conditioning chamber.

In addition, as a characteristic of the Pound-Drever method, since the SN of the error signal depends on the finesse of the reference resonator 14, the mirror constituting the reference resonator 14 is selected to have a sufficiently high reflectance while the reference resonator is selected. It is necessary to sufficiently adjust (14).

Further, the light beam B4 of the seed laser 1 reflected by the translucent mirror M6 is incident on the AOM 6. A voltage signal having a frequency f _AOM is applied to the AOM 6 to generate a plurality of orders of diffraction light flux from the light flux that passes through the AOM 6 by the acoustooptic effect. The frequency shift of _{nxf AOM} occurs with respect to these multiple orders of diffraction light flux, respectively.

Only the + 1st order light is spatially extracted from these plural orders of diffraction light flux, and is coupled to the first input terminal of the branch fiber 8 by the fiber coupler 7a. The branched fiber 8 is, for example, a polarization plane storage single mode type and includes two input terminals (first and second input terminals) and one output terminal.

Similarly, part of the output of the pulse oscillator O is branched by the translucent mirror M6, and is coupled to the second input terminal of the branch fiber 8 by the fiber coupler 7b. The photodetector 9 converts the intensity of the light output from the branch fiber 8 into an electrical signal and provides it to the analyzer 10.

The analyzer 10 generates a feedback signal for the pulse oscillator O by the same processing as in the first embodiment. This feedback signal is fed back to the PZT mount 4 of the pulse oscillator O via a PZT controller (PZT amplifier) 5.

As described above, the pulse oscillator O is controlled so that the oscillation frequency of the pulse oscillator O coincides with the oscillation frequency of the seed laser 1.

Since the seed laser 1 stabilizes the wavelength using the oscillation wavelength of the reference resonator 14 as a reference as described above, the oscillation wavelength of the seed laser 1 and the oscillation wavelength of the pulse oscillator O are used. As a result, high-precision wavelength stabilization of the pulsed laser light is realized as a result.

[Third Embodiment]

Fig. 5 is a diagram showing a schematic configuration of an interference measuring device as a third embodiment of the present invention. The injection synchronous pulse laser device of the second embodiment is incorporated in the interference measuring device of the third embodiment of the present invention.

The interference measuring device of the third embodiment of the present invention is very suitable for inspecting the imaging performance of a projection optical system built in an exposure device such as a semiconductor exposure device. Since the exposure apparatus uses an excimer laser such as KrF or ArF as the illumination light source, the projection optical system is designed to optimize the imaging performance at the wavelength of the illumination light. Therefore, the inspection apparatus for inspecting the imaging performance of the projection optical system also performs inspection using a wavelength that approximately matches the wavelength of the illumination light. In the third embodiment, an inspection apparatus for the projection optical system optimized to the wavelength of 193 nm is illustrated.

First, a method of adjusting the oscillation wavelength will be described. The interferometer measurement as the inspection apparatus includes a wavelength conversion unit 17 at the output of the injection synchronous pulse laser device shown in the second embodiment. The wavelength conversion unit 17 converts the wavelength of incident light into a wavelength of its quarter using the nonlinear optical effect and outputs it. In order to set the wavelength of the light output from the wavelength conversion unit 17 to 193 nm, the wavelength of the light incident on the wavelength conversion unit 17, that is, the wavelength of the light output from the injection synchronous pulse laser device needs to be stabilized at 772 nm. There is.

The mirror M7 of 2nd Embodiment is substituted by the semi-transparent mirror M8. A part of the output from the seed laser 1 passes through the translucent mirror M8, is reflected by the mirror M9, and guided to the wavelength meter 30. The light beam output from the seed laser 1 is also branched to the pulse oscillator O (injection motor), AOM 6 (bit detection), and external resonator 14 (wavelength stabilization) similarly to the second embodiment. You are guided.

The wavemeter 30 has a built-in etalon calibrated with high precision, and the absolute value of the wavelength can be measured with a precision of sub pm or less. The wavelength meter 30 is connected to the computer 29, and the computer 29 calculates the wavelength shift amount from the set wavelength of the seed laser 1, and transmits the result to the adder 31.

The adder 31 performs a PID operation on the wavelength shift amount provided from the computer 29 to generate a feedback signal for use with the wavelength meter 30 as a reference. The adder 31 also adds a feedback signal from the computer 29 and a feedback signal (wavelength feedback signal) used as the reference resonator 14 as a reference, and adds the addition result to the wavelength modulation terminal of the seed laser 1. Feedback to.

Although the wavelength feedback signal and the frequency feedback signal are provided to the seed laser 1, if the control frequency of the wavelength feedback signal is set sufficiently low compared to the control frequency of the frequency feedback signal, the influence of the interference between the wavelength feedback signal and the frequency feedback signal is affected. It can be minimized.

As described above, according to the third embodiment, the absolute value guarantee and the frequency stabilization of the center wavelength of the seed laser 1 are realized by the wavelength stabilization unit including the reference resonator 14 and the wavelength meter 30. Therefore, according to the third embodiment, as in the second embodiment, by controlling the optical path length (oscillator length) of the pulse oscillator O, the guarantee and the frequency stabilization of the center wavelength of the pulsed light source are realized.

Here, the light output from the pulse oscillator O is converted into 193 nm by performing 1/4 wavelength conversion by the wavelength conversion unit 17. The coefficient 1/4 at the time of wavelength conversion is physically fixed, and since the wavelength of the light output from the wavelength conversion unit 17 is determined only by the wavelength of the light incident on the wavelength conversion unit 17, the guarantee of the center wavelength for 193 nm pulses is guaranteed. And frequency stabilization is performed.

Next, the interferometer will be described. The light beam emitted from the wavelength conversion unit 17 passes through the condensing lens 18, and thereafter, the wavefront shape is shaped by passing through the pinhole 19 having the diffraction limit or less. The light beam transmitted through the pinhole 19 passes through the translucent mirror 20 while being diffused, is converted into a parallel light beam by the collimator lens 21, and enters the TS lens 23. Here, the TS lens 23 is a lens designed such that the radius of curvature of the final surface and the distance from the final surface to the focal position are the same, and the anti-reflection film is coated except for the final surface. On the final surface of the TS lens 23, a reflected light flux of about 5% is generated due to the difference in refractive index between air and glass, and returns along the incident light path. Hereinafter, the luminous flux reflected by the TS surface and the TS surface of the final surface of the TS lens is referred to as a reference luminous flux. The TS lens 23 is fixed on the phase shift unit 22, and can be driven in the optical axis direction by the PZT element in the phase shift unit 22.

On the other hand, the light beam passing through the TS plane is condensed once on the object surface of the projection optical system 24 of the exposure apparatus, and then enters the projection optical system 24 while being diffused and exits from the projection optical system 24, and then the projection optical system Condensed in the shop of 24. On the image side, a spherical RS mirror 25 having a center of curvature at the shop position of the projection optical system 24 is inserted. The reflecting surface of the RS mirror 25 is glass without coating, and has a reflectance of about 5% as the TS surface. The light beam focused on the shop is reflected by the RS plane and returns to the same light path. Hereinafter, the light beam reflected by the RS surface and the RS surface of the reflecting surface of the RS mirror is called a light beam to be examined.

Both the reference light beam and the light beam to be transmitted pass through the TS lens 23 again, become parallel light beams, and then enter the collimator lens 21 again, are focused and reflected by the semi-transparent mirror 20. The spatial filter 26 is inserted in the focal position opposite to the translucent mirror 20. The inspected light beam and the reference light beam whose unnecessary high frequency region is cut by the spatial filter 26 enter the imaging lens 27 and become incident on the imaging element (for example, CCD) 28 after the parallel light beam. In the imaging device 28, interference fringes of the light beam to be examined and the reference light beam are picked up, and the captured image information is transmitted to the computer 29.

For the interference fringe, the intensity of the reference light beam is I _ref , the intensity of the light beam under _test is I _test , the wavefront of the projection optical system 24 is W (r), the optical path length between the TS plane and the RS plane is L, and the wavelength of the laser light is λ. Is expressed by the following formula (8):

.

.

The phase shift method can be used to perform highly accurate wavefront measurement from interference fringes. The phase shift method is a method of calculating a wavefront from images of a plurality of interference fringes given a known phase shift.

The computer 29 applies the voltage to the phase shift unit 22 in synchronization with the imaging timing in the image pickup device 28 to drive the TS lens 23 along the optical axis, thereby achieving a desired phase shift.

If the cosine component and the sinusoidal component of the interference fringe change are extracted from the plurality of interference fringe images at the time of phase shift, and each is Ic and Is, the wavefront W (r) of the inspected lens is expressed as 9) is indicated:

.

.

The main cause of the error occurring in the wavefront measurement is the variation of the interference fringe at the time of phase shift. As is apparent from Equation (8), the variation of the interference fringe also occurs due to a change in the optical path length L between the TS surface and the RS surface due to stage vibration or the like, or a variation in the wavelength? Of the laser light.

In the huge projection optical system for the semiconductor exposure apparatus, the optical path length L needs to be several m long. This makes it impossible to ignore the influence of the wavelength variation. In this embodiment, since high-precision wavelength stabilization is implement | achieved, the high-precision wavefront measurement is attained compared with the former.

Moreover, by connecting the wavelength meter 30, the demodulator 16, and the analyzer 10 to the computer 29, it becomes possible to monitor the laser wavelength change at the time of phase shift measurement. Therefore, when the wavelength variation is large, a warning is issued and the wavelength change is fed back to the measured value, whereby the measurement can be performed with higher accuracy.

Fourth Embodiment

6 is a diagram showing a schematic configuration of an exposure apparatus as a fourth embodiment of the present invention. In the exposure apparatus of the fourth embodiment of the present invention, the interference measuring device of the third embodiment is incorporated.

In Fig. 6, the phase shift unit 22 and the TS lens 23 are inserted in the optical path of the exposure light, but in actual exposure, they are retracted out of the optical path. At the time of exposure, on the upper side of the projection optical system 24. The wafer stage 40 is driven so that a wafer (also referred to as a substrate) to be exposed is disposed instead of the RS mirror 25.

The light beam emitted from the excimer laser 36 enters the incoherent unit 37 through the transmission system. In the incoherent unit 37, shaping of the incident light beam and reduction of spatial coherence are performed simultaneously. The light beam emitted from the incoherent unit 37 enters the illumination optical system 38, and after uniformization of illuminance and generation of a desired effective light source, is formed on the reticle stage 39 (also called a disc or mask) Lighting). The incident light beam diffracted by the pattern of the reticle is reduced and projected onto the wafer disposed on the wafer stage 40 by the projection optical system 24, so that the pattern of the reticle is transferred onto the wafer surface. After pattern transfer, the wafer stage 40 is moved stepwise from the exposure area to the next exposure area to expose the next exposure area.

Next, a method of measuring the wave front aberration of the projection optical system 24 will be described. The interferometer described in the second embodiment is used for the measurement of the wave front aberration. The light source for an interferometer has wavelength stabilization, and the wavelength is set to the same stable wavelength as the excimer laser 36. The phase shift unit 22 and the TS lens 23 are driven from the retracted position at the time of semiconductor exposure, and inserted in the desired object point position of the projection optical system 24. In addition, by driving the reticle stage 39, the reticle arranged at the object point is evacuated. On the other hand, the RS mirror 25 is disposed around the wafer holding portion of the wafer stage 40. When the wafer stage 40 is driven, the center of curvature of the RS mirror 25 is disposed at a position that is conjugate with the object point position of the projection optical system 24. By the above procedure, the interference fringes of the test light and the reference light can be picked up by the imaging element (CCD camera) 28. The wavefront is measured in accordance with the phase shift method using the phase shift unit 22 as in the third embodiment.

In the fourth embodiment, since the laser whose wavelength is stabilized with high accuracy can be used as the light source, high-precision wavefront measurement on the semiconductor exposure apparatus can be performed. By optimizing the wavefront aberration of the projection optical system using the measurement result, the imaging performance of the projection optical system can be optimized, thereby enabling high-precision pattern transfer.

In the above embodiment, a bit signal is obtained by shifting the frequency of the light emitted from the seed laser 1 by the acoustooptic element 6 and combining the frequency shifted light and the light emitted from the pulse oscillator O. FIG. . However, the present invention is not limited to such a configuration. For example, the bit signal may be obtained by shifting the frequency of the light emitted from the pulse oscillator O by the acoustooptic element 6 and combining the frequency shifted light and the light emitted from the seed laser 1.

[Etc]

Next, a device manufacturing method using the above exposure apparatus will be described. 8 is a flowchart showing a sequence of an overall manufacturing process of a semiconductor device. In step 1 (circuit design), the circuit design of the semiconductor device is performed. In step 2 (reticle fabrication), a reticle is fabricated based on the designed circuit pattern. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a preprocess, and the actual circuit is formed on the wafer by lithography using the above-described reticle and wafer. The following step 5 (assembly) is called a post process, and is a step of semiconductor chip formation using the wafer produced in step 4, and includes a step such as an assembly step (dicing and bonding), a packaging step (chip sealing), and the like. . In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device fabricated in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

9 is a flowchart showing the detailed procedure of the wafer process. In step 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (CMP), the insulating film is planarized by the CMP process. In step 16 (resist process), a photosensitive agent is applied to the wafer. In step 17 (exposure), the photosensitive agent is exposed to the wafer on which the photosensitive agent is applied through the mask on which the circuit pattern is formed, to form a latent image pattern in the resist. In step 18 (development), a latent image pattern formed in the resist on the wafer is developed to form a resist pattern. In step 19 (etching), the layer or substrate under the resist pattern is etched through the portion where the resist pattern is opened. In step 20 (resist stripping), the unnecessary resist is removed by etching. By repeating these steps, a circuit pattern is formed multiplely on a wafer.

While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to this disclosed exemplary embodiment. The following claims are to be accorded the broadest interpretation so as to encompass all such modifications and equivalent constructions and functions.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows schematic structure of the injection synchronous pulse laser apparatus as 1st Embodiment of this invention.

Fig. 2 illustrates the bit signal I (t) obtained by the simulation;

3 illustrates a Fourier transform of a bit signal;

4 is a diagram showing a schematic configuration of an injection synchronous pulse laser device according to a second embodiment of the present invention;

5 is a diagram showing a schematic configuration of an injection synchronous pulse laser device according to a third embodiment of the present invention;

6 shows a schematic configuration of an exposure apparatus as a fourth embodiment of the present invention;

7 is a view showing a schematic configuration of a conventional injection synchronous laser device;

8 is a flowchart showing a sequence of an overall manufacturing process of a semiconductor device;

9 is a flow chart showing the detailed procedure of the wafer process.

Claims (10)

Seed laser; An oscillator into which a part of the light output from the seed laser is injected as a seed laser light; A frequency converter for shifting the frequency of other components of the light output from the seed laser; A photo detector for detecting light synthesized from the light output from the oscillator and the light output from the frequency converter; And A controller for controlling an optical path length of the oscillator based on a bit signal component included in an output signal of the photo detector; Injection synchronous pulse laser device comprising: a. The method of claim 1, And the frequency shift amount used in the frequency converter is greater than the spectral width of the light output from the oscillator. The method of claim 1, And said frequency converter comprises an acoustooptical device. The method of claim 1, And a stabilization unit for stabilizing the wavelength of light output from the seed laser. The method of claim 4, wherein And said stabilizing unit includes a reference resonator and stabilizes the wavelength of light output from said seed laser by using the wavelength of light output from said reference resonator as a reference. The method of claim 4, wherein And said stabilizing unit includes a wavelength meter for measuring the wavelength of light output from said seed laser, and stabilizes the wavelength of light output from said seed laser based on the output of said wavelength meter. Seed laser; An oscillator into which a part of the light output from the seed laser is injected as a seed laser light; A frequency converter for shifting the frequency of light output from the oscillator; A photo detector for detecting light in which the other component of the light output from the seed laser and the light output from the frequency converter are synthesized; And A controller for controlling an optical path length of the oscillator based on a bit signal component included in an output signal of the photo detector; Injection synchronous pulse laser device comprising: a. An injection synchronous pulse laser device according to any one of claims 1 to 7; And An interferometer for generating a reference light beam and a light beam to be inspected using the light output from the injection synchronous pulse laser device, and interfering with the reference light beam and the light beam to be inspected; Interferometry device comprising a. An injection synchronous pulse laser device according to any one of claims 1 to 7; An interferometer for generating a reference light beam and a light beam to be inspected by using the light output from the injection synchronous pulse laser device, and interfering with the reference light beam and the light beam to be inspected; And A projection optical system for projecting a pattern of the original onto a substrate, And the interferometer measures aberrations of the projection optical system. As a device manufacturing method, A process of forming a latent image pattern in the photosensitive agent apply | coated to the board | substrate using the exposure apparatus of Claim 9; And Developing the latent image pattern; Device manufacturing method comprising a,

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