JP2002350231A - Light spectrum detector, and spectroscope and laser device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light spectrum detector capable of detecting a spectrum of measured light with relatively high accuracy. SOLUTION: This light spectrum detector is provided with: an optical detector 1 disposed in the vicinity of an image forming position of the measured light having passed a spectroscopic element and having plural channels for outputting a detection signal by converting the incident light into an electric signal according to its intensity; A/D conversion means 4 and 5 for outputting detection data based on the detection signal outputted from the optical detector; and a signal processing means 6 for finding correction data generated by correcting the difference of detection sensitivity among the plural channels of the optical detector based on the detection data outputted from the A/D conversion means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an optical spectrum detecting device, and more particularly, to an excimer laser or F
_2. Related to an optical spectrum detection device used for detecting the spectrum (including wavelength and spectrum width) of output light of a (fluorine molecule) laser. Further, the present invention relates to a spectroscopic device and a laser device using such an optical spectrum detecting device.

[0002]

2. Description of the Related Art With the improvement in the degree of integration of semiconductor devices, excimer lasers and F ₂ (molecular fluorine) lasers, which output short-wavelength laser light, have attracted attention as light sources for exposure apparatuses. These laser devices can output laser light having a narrow spectral width in order to reduce chromatic aberration in the optical system of the exposure device. In order to maintain the wavelength and spectrum width of laser light output from these laser devices at predetermined values, an optical spectrum detection device capable of detecting the spectrum of ultraviolet light is used.

[0003] As such an optical spectrum detecting device,
Japanese Patent No. 2999756 discloses that light to be measured having passed through a spectroscopic element such as an etalon has interference fringes (fringe).
There is disclosed a wavelength detection device which is disposed near a surface forming a plurality of channels and has a plurality of channels for converting incident light into an electric signal corresponding to the intensity thereof. This wavelength detecting device includes, for example, a CCD (charge coupled device).
An image sensor such as ice) is included as a photodetector, and the spectrum of the laser beam is detected based on the output value of each channel of the photodetector.

[0004]

[0005] In recent years, there is a tendency that semiconductor integration is further increased, the need to adjust the wavelength and the spectral width of the output light of the excimer laser and F ₂ laser exposure apparatus more accurately Has occurred. Therefore, there is a demand for an optical spectrum detection device that detects the spectrum of the output light of these lasers to further improve the detection accuracy.

[0005] By the way, since there is a variation in detection sensitivity and linearity (linearity) among a plurality of channels of a photodetector included in an optical spectrum detection apparatus, the output values of each channel for the same light intensity match. Often not. However, in the above-described conventional optical spectrum detection device, the output value of each channel is used as it is to detect the spectrum of the light to be measured. The detection error is a measurement error of the wavelength and the spectrum width of the laser light.

Accordingly, an object of the present invention is to provide an optical spectrum detecting device capable of detecting the spectrum of light to be measured with higher accuracy. Another object of the present invention is to provide a spectroscopic device and a laser device using such an optical spectrum detecting device.

[0007]

In order to solve the above problems, an optical spectrum detecting apparatus according to the present invention is a photodetector arranged near an image forming position of light to be measured passing through a spectral element. A photodetector having a plurality of channels for outputting a detection signal by converting incident light into an electric signal corresponding to the intensity, and an A / D for outputting detection data based on the detection signal output from the photodetector Conversion means and A / D
Signal processing means for obtaining correction data obtained by correcting a difference in detection sensitivity among a plurality of channels of the photodetector based on the detection data output from the conversion means.

Further, the spectroscopic device according to the present invention comprises a spectroscopic element for emitting incident light at an angle corresponding to the wavelength, an image forming means for forming an image of the light emitted from the spectroscopic element, The optical spectrum detection device is provided near the image position and detects the wavelength or the spectrum width of light incident on the spectral element.

Further, a laser device according to the present invention comprises a laser oscillator for generating a laser beam having a predetermined wavelength and a spectrum width, and a spectral device for emitting incident light from the laser oscillator at an angle corresponding to the wavelength. An element, imaging means for forming an image of the light emitted from the light separating element, and the element arranged near the image forming position of the light emitted from the light separating element for detecting the wavelength or the spectrum width of the laser light generated by the laser oscillator. And a light spectrum detecting device.

According to the above configuration, in the measurement of the optical spectrum, the detection signals output from the plurality of channels of the photodetector are corrected based on the variations in the detection sensitivity and linearity between the plurality of channels, and the measured light is measured. Performs spectrum detection, reducing detection errors due to variations in detection sensitivity and linearity between multiple channels of the photodetector,
The wavelength and spectrum width of the light to be measured can be obtained with high accuracy.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same components are denoted by the same reference numerals, and description thereof will be omitted. The following numerical values are used for simplifying the description of the embodiment of the present invention, and may be changed to other numerical values.

FIG. 1 shows a configuration of an optical spectrum detecting apparatus according to an embodiment of the present invention. This optical spectrum detection device uses excimer laser light or F ₂ (molecular fluorine: molecular).
fluorine) Suitable for detecting the spectrum of ultraviolet light such as laser light. Optical spectrum detection device 100
Includes an image sensor (photodetector) 1 arranged near a surface on which light to be measured that has passed through a spectral element such as an etalon forms interference fringes (fringes). As the image sensor 1, for example, a CCD (charge coupled device: charge
An imaging device such as a coupled device is used. The image sensor 1 converts a plurality of (in this embodiment, 256) channels CH0 to CH2 that output a detection signal by converting incident light into an electric signal corresponding to the intensity.
55. These channels are provided so as to be arranged in one line along one direction parallel to the plane on which the interference fringes of the measured light are formed. When the power is supplied from the power supply circuit 2 and driven by the drive circuit 3, the image sensor 1 sequentially outputs a plurality of detection signals respectively generated in the plurality of channels CH0 to CH255.

The detection signal output from the image sensor 1 is amplified by the amplifier circuit 4 at a predetermined amplification factor,
It is input to the D converter 5. The A / D converter 5 converts the detection signal input from the amplifier circuit 4 into a digital signal having, for example, a 12-bit resolution (0 to 4095), and sequentially outputs the digital data to the signal processing unit 6 as detection data.

When measuring the reference light, the signal processing unit 6
The detection data output from the / D converter 5 is supplied to the output circuit 10 as initial data. The signal processing unit 6
Converts the detection data output from the A / D converter 5 when measuring the light to be measured into correction data in which variations in detection sensitivity and linearity between a plurality of channels of the image sensor 1 are corrected, and an output circuit Supply 10 The output circuit 10 outputs initial data and correction data to the outside.

First, a CPU (central processing unit) 20 is connected to the output circuit 10 when obtaining correction data used in the signal processing section 6. The CPU 20 creates correction data based on the initial data output from the output circuit 10 when the reference light is measured, using a method described later in detail, and supplies the correction data to the signal processing unit 6. After that, the signal processing unit 6 converts the detection data obtained by measuring the light to be measured into the correction data, thereby correcting the variation in the detection sensitivity and the linearity among the plurality of channels of the image sensor 1. .

FIG. 2 shows a specific configuration example of the signal processing unit 6. The signal processing unit 6 uses a flash memory 7 for storing the correction data, a correction data writing circuit 8 for writing the correction data to the flash memory 7, and detection data output from the A / D converter 5 as an address. And an address circuit 9 for accessing the flash memory 7 to read out the correction data.

When writing correction data to the flash memory 7, the CPU 20 is connected to the correction data writing circuit 8, and correction data for each channel of the image sensor is supplied. The correction data writing circuit 8 writes these correction data to a predetermined address of the flash memory 7 determined for each channel of the image sensor.

In this embodiment, part of the address of the flash memory corresponds to the channel number of the image sensor, and another part of the address of the flash memory corresponds to
This corresponds to detection data corresponding to correction data to be stored. Therefore, when the address of the flash memory is determined by the channel number of the image sensor and the detection data obtained from the channel, the correction data is immediately obtained by reading the correction data stored at the address.

Here, an example of the operation of writing and reading correction data to and from the flash memory will be described in detail. FIG. 3 shows an example of address setting in the flash memory. For example, channel C of the image sensor
For H0, addresses (00000000-0004) corresponding to the detection data (0000-4095), respectively.
095) is set. Similarly, for the channel CH255 of the image sensor, the detection data (000
0 to 4095) (2550)
000 to 2554095) are set. here,
In the seven-digit numerical value of the address, the numerical value of the upper three digits represents the number of the channel from which the detection data was obtained, and the numerical value of the lower four digits represents the detection data itself.

When the reference light is measured, correction data obtained by calculation is written to each address of the flash memory. FIG. 4 shows an example of setting correction data for each channel of the image sensor. Here, the detection data of channel CH0 (000
0 to 4095) is uniformly corrected by +5, and correction data (0005 to 4095) is written to the address (00000000 to 0004095). Hereinafter, +10 is uniformly corrected for channel CH1, and
255 is uniformly corrected by +100, and correction data is written to each address. Here, the maximum value of the correction data is set to 4095.

When the measured light is measured, the correction data stored at each address of the flash memory is read based on the detection data obtained by the measurement. Referring to FIG. 2 again, the address circuit 9 accesses the flash memory 7 using the combination of the channel number of the image sensor and the detection data output from the A / D converter 5 as address information. As a result, the correction data stored at the address in the flash memory 7 is supplied to the output circuit 10. The address information may be obtained by decoding the detection data output from the A / D converter 5 in the address circuit 9.

Next, a specific method for obtaining correction data to be stored in the flash memory will be described with reference to FIGS. First, using a light source having a uniform intensity profile, all channels C of the image sensor are used.
H0 to CH255 are exposed. The light source may generate ultraviolet light, or may generate visible light.

The output value of an image sensor such as a CCD is proportional to the amount of incident light, that is, the product of the intensity of the incident light and the exposure time. For this reason, the output values of the multiple channels of the image sensor are corrected for the incident light of various intensities by correcting the output values of the multiple channels of the image sensor for the multiple exposure times using light of uniform intensity. It is possible to make it uniform.

[0024] Therefore, in the present embodiment, a plurality of exposure times, such as the output values of the image sensor is not saturated _{T 1, T 2, ···,} T k (T 1 <T 2 <··· <T k : K represents an integer of 2 or more), the output levels of the channels CH0 to CH255 of the image sensor are measured, and the detection data obtained based on these is stored. Thereby, as shown in FIG.
, The correspondence between the exposure time and the detection level is grasped. Note that such measurement may be repeatedly performed, and an average value of the measured detection levels may be _obtained for each of the exposure times T ₁ , T ₂ ,..., T _k . By doing so, it is possible to reduce variations in the measurement of the detection level.

Next, for each of the channels CH0 to CH255, the relationship between the exposure time and the detection level is approximated by a single curve. Here, as an example, a case of approximation by a straight line is described. This approximate straight line is represented by the following equation (1). Yi = Ai · Tj + Bi (1) (i = 0, 1,... 255, j = 1, 2,...)
·, K) Here, each symbol represents the following value. Tj: Exposure time of each Yi: Approximate value of detection level of channel of number i Ai: Slope of approximate line of channel of number i Bi: Intercept of approximate line of channel of number i To find the value,
For example, the least square method may be used.

Next, a method of correcting the detection level of another channel based on the detection level of one channel will be described. Here, as an example, channel C
The detection level of H128 is used as a reference. The detection level is indicated by 12 bits. In the following, a value Ti for each channel is considered as the exposure time. Yi = Ai · Ti + Bi (2) By transforming equation (2), the following equation (3) is obtained. Ti = (Yi−Bi) / Ai (3) Here, for each of the channels CH0 to CH255, a plurality of numerical values Y = 0, 1,.
.., 4095 are sequentially substituted into Expression (3). Thereby, a plurality of exposure times Ti (Y) respectively corresponding to a plurality of detection levels, that is, Ti (0), Ti (1),.
・, Ti (4095) is required.

For example, for the detection level Y1 obtained in the channel CH1, the corresponding exposure time T1 (Y
The value of 1) is obtained. In order to correct the detection level of the channel CH1 so as to be the same as the detection level of the channel CH128, the detection level of the channel CH128 corresponding to the exposure time T1 (Y1) may be obtained based on Expression (2). That is, assuming that the corrected detection level in the channel CH1 is Yc1, the following equation is established. Yc1 = A128 · T1 (Y1) + B128 In general, to make the detection level of the channel of the number i equal to the detection level of the channel CH128,
The detection level Yi of the channel with the number i may be corrected as in the following equation, and the corrected detection level Yci may be obtained. Yci = A128 · Ti (Yi) + B128 (4)

The detection level thus corrected is:
This is equivalent to unifying the detection sensitivity and linearity approximated by a straight line different for each channel to the detection sensitivity and linearity expressed by an approximate straight line of the reference channel CH128. Instead of using the channel CH128 as a reference, a curve representing ideal input / output characteristics (for example, a straight line passing through the origin) may be used as a reference.

As shown in FIG. 6, a plurality of correction data respectively corresponding to a plurality of detection data (0 to 4095) for each channel correspond to an address determined by a combination of a channel number and detection data in a flash memory. And constitutes a correction table.

According to the present embodiment, since the detection sensitivity and linearity of a plurality of channels of the image sensor are unified by correction, when light with uniform intensity is incident on all channels, the output data has the same value. Becomes
Thereby, the wavelength and the spectrum width of the light to be measured can be detected with high accuracy.

Next, a spectroscopic device according to an embodiment of the present invention will be described with reference to FIG. Note that the spectrometer is vacuum ultraviolet light (e.g., ArF (argon-fluorine: argon would be fluoride) excimer laser, F ₂ laser) in the case is for, either evacuated inside before the operation, or, Purge with dry nitrogen gas is desirable.

The spectrometer shown in FIG. 7 has a polishing glass 40 for scattering incident light. The light that has passed through the polishing glass 40 enters an etalon 41 used to extract light having a target wavelength from the incident light.

The etalon 41 has etalon plates 42 and 43 arranged so as to face each other. Etalon board 4
Spacers 44, 45 for forming a gap between them are provided between 2, 43. When this spectroscopic device is for vacuum ultraviolet light, fluorite (CaF ₂ ) or synthetic quartz doped with fluorine is used as the material of the etalon plate, and fluorine is doped as the material of the spacer. Synthesized quartz, ceramic glass having a small coefficient of thermal expansion, or the like is used.

An optical spectrum detecting device 47 having the above-described configuration is disposed near a surface on which light sequentially passing through the etalon 41 and the condenser lens 46 forms an interference fringe (fringe) IF. . Optical spectrum detector 47
Converts the data related to the detected light spectrum into CPU data.
The data is output to the data processing device 50 configured as described above. The data processing device 50 calculates and displays the wavelength and the spectrum width of the incident light based on the input data.

Next, a laser device according to an embodiment of the present invention will be described with reference to FIG. Note that when the laser device is a ArF excimer laser device or F ₂ laser device, inside or vacuuming before operation, or, it is desirable to purge with dry nitrogen gas.

The laser device shown in FIG. 8 has a laser chamber 60 for accommodating a laser medium which is excited by discharge to generate vacuum ultraviolet light. When the laser device is an ArF excimer laser device or an F ₂ laser device, a mixed gas containing fluorine molecules is used as a laser medium. Light generated within the laser chamber 60 exits the laser chamber 60 through the window 61 or 62. The windows 61 and 62 are provided in the laser chamber 60 so as to form a predetermined Brewster angle with an optical axis passing through the laser chamber 60. In this manner, loss caused by the light generated in the laser chamber 60 being reflected from the window 61 or 62 is prevented.

Light emitted from the laser chamber 60 through the window 61 enters a narrow-band module 63 for narrowing the spectrum width of incident light having a wavelength set from the controller 70 via a driver 71 to a target value. Light that has passed through the window 61 and the narrow band module 63 in order is reflected by the total reflection mirror 64 toward the narrow band module 63. On the other hand, part of the light emitted from the laser chamber 60 through the window 62 is reflected by the partial reflecting mirror 65 toward the laser chamber 60, and the rest is reflected by the partial reflecting mirror 6
Pass 5

The total reflection mirror 64 and the partial reflection mirror 65 are arranged such that a structure for resonating light having a target wavelength is formed therebetween. Laser chamber 6
A part of the light generated within 0 is amplified each time it passes through the laser chamber 60 while reciprocating between the total reflection mirror 64 and the partial reflection mirror 65, and the narrow band module 63 sets the spectrum width to the target value. Narrowed down to

The light that has passed through the partial reflecting mirror 65 is converted into a laser beam L ₁ having the same wavelength and phase as the beam splitter 66.
Incident on. Some of the laser light L ₁ incident on the beam splitter 66 is output through the beam splitter 66, the rest is reflected by the beam splitter 66,
Further, the light is incident on the beam splitter 67. Beam splitter 67, the reference light L ₂ incident from the reference light source 68 which is controlled by the controller 70, is reflected in the direction parallel to the traveling direction of the laser light L ₁ reflected by the beam splitter 66. Reference light L ₂ output from the reference light source 68 has a known spectral distribution, as a reference for obtaining the wavelength of the laser light L _1.

The laser light L ₁ passing through the beam splitter 67 and the reference light L ₂ reflected from the beam splitter 67
Is input to the spectroscopic device 69 having the configuration as described above. Output data of the optical spectrum detection device included in the spectrometer 69 is input to the controller 70. The controller 70, by comparing the output data when measuring the reference light L ₂ with the output data when measuring laser beam L _1, determine the wavelength and the spectral width of the laser beam L _1, on the basis of this The narrow-band module 63 is controlled via the driver 71.

[0041]

As described above, according to the present invention,
In the measurement of an optical spectrum, a detection error due to a variation in detection sensitivity and linearity among a plurality of channels of a photodetector can be reduced, and the wavelength and spectrum width of light to be measured can be obtained with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical spectrum detection device according to one embodiment of the present invention.

FIG. 2 is a block diagram illustrating a specific configuration example of a signal processing unit in FIG. 1;

FIG. 3 is a diagram showing an example of address setting in the flash memory of FIG. 2;

FIG. 4 is a diagram showing an example of setting correction data in the flash memory of FIG. 2;

FIG. 5 is a diagram illustrating a relationship between an exposure time and a detection level in each channel of the optical spectrum detection device.

FIG. 6 is a diagram showing a configuration example of a correction table stored in a flash memory of FIG. 2;

FIG. 7 is a diagram illustrating a configuration of a spectroscopic device according to an embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a laser device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 2 Power supply circuit 3 Drive circuit 4 Amplification circuit 5 A / D converter 6 Signal processing unit 7 Flash memory 8 Correction data writing circuit 9 Address circuit 10 Output circuit 20 CPU 40 Polishing glass 41 Etalon 42, 43 Etalon plate 44, 45 Spacer 46 Condenser Lens 47 Optical Spectrum Detector 50 Data Processor 60 Laser Chamber 61, 62 Window 63 Narrow Band Module 64 Total Reflector 65 Partial Reflector 66, 67 Beam Splitter 68 Reference Light Source 69 Spectrometer 70 Controller 71 Driver 100 Optical spectrum detector

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takeo Omori 400 Yokokura Nitta, Oyama City, Tochigi Prefecture Gigaphoton F Term (reference) 2G020 AA05 CB23 CB43 CB44 CC23 CD16 CD24 CD34 CD38 CD39 5F071 AA06 HH05 JJ10 5F072 AA04 AA06 HH05 JJ13 KK01 KK08 KK15 RR05 YY11

Claims (9)

[Claims] 1. A photodetector arranged near an image forming position of light to be measured having passed through a spectral element, and outputs a detection signal by converting incident light into an electric signal corresponding to the intensity of the light. The photodetector having a plurality of channels, A / D conversion means for outputting detection data based on a detection signal output from the photodetector, and based on the detection data output from the A / D conversion means A signal processing unit for obtaining correction data obtained by correcting a difference in detection sensitivity between a plurality of channels of the photodetector;
An optical spectrum detection device comprising: 2. The apparatus according to claim 1, wherein said signal processing means obtains, for each of a plurality of channels of said photodetector, a plurality of correction data corresponding to a plurality of levels of a detection signal of said photodetector. An optical spectrum detection apparatus according to claim 1. 3. A memory for storing correction data, a writing circuit for writing correction data to the memory, and a detection data output from the A / D conversion means, wherein the signal processing means is a part of an address. 3. The optical spectrum detection device according to claim 1, further comprising: an address circuit that accesses the memory to read out correction data corresponding to the detection data output from the A / D conversion means. 4. A signal processing device comprising: a memory for storing correction data; a writing circuit for writing correction data to the memory; and a channel number included in the photodetector as a part of an address. And an address circuit that accesses the memory to sequentially read a plurality of correction data respectively corresponding to a plurality of channels of the photodetector,
The optical spectrum detection device according to claim 1. 5. A light-splitting element that emits incident light at an angle corresponding to the wavelength thereof; an imaging unit that forms an image of the light emitted from the light-splitting element; A spectrometer comprising: the light spectrum detector according to any one of claims 1 to 4 for detecting a wavelength or a spectrum width of light incident on the spectroscopic element. 6. The spectroscopic device according to claim 5, wherein the spectroscopic element includes an etalon. 7. A laser oscillator that generates a laser beam having a predetermined wavelength and a spectrum width; a spectroscopic element that emits incident light from the laser oscillator at an angle corresponding to the wavelength; 5. An image forming means for forming an image of the outgoing light, and arranged near an image forming position of the outgoing light from the spectroscopic element, for detecting a wavelength or a spectrum width of the laser light generated by the laser oscillator. A laser device comprising: the optical spectrum detection device according to any one of the above. 8. The laser device according to claim 7, further comprising a reference light source that outputs light having a wavelength that is used as a reference when determining the wavelength of the laser light. 9. The laser device according to claim 7, wherein the laser oscillator includes an excimer laser oscillator or an F ₂ (fluorine molecule) laser oscillator.