JP3276118B2 - Wavelength control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength control device,
In particular, the present invention relates to stabilization of the wavelength of a narrow band excimer laser device used as a light source of a semiconductor exposure apparatus.

[0002]

2. Description of the Related Art The wavelength control of a conventional excimer laser is described in the literature [SPIE Vol. 1088 Optical / La
ser Microlithography 2 (198
As described in 8)], a region dead band in which the wavelength is not controlled and a region limit band which guarantees the stability of a wavelength larger than this band are provided. FIG. 8 shows a flowchart of this wavelength control. First, when the laser emits light, an oscillation wavelength λ is detected by a wavelength detecting device built in the laser. Next, the set wavelength λt and the oscillation wavelength λ
Is calculated (Δλ = λ−λt). Then, it is determined whether or not the absolute value of the difference Δλ is larger than the limit band (LB). If it is larger than the limit band LB, an abnormal wavelength is output to the outside.

[0003] On the other hand, when the wavelength is smaller than the limit band LB, the process returns to the start without controlling the wavelength selection element. When the difference is larger than the dead band or when the wavelength abnormality is output, it is determined whether the difference Δλ is positive or negative. If the difference Δλ is positive, the selected wavelength of the wavelength selection element is shifted in the negative direction by a predetermined amount. on the other hand,
If negative, the selected wavelength of the wavelength selection element is shifted by a predetermined amount in the positive direction. Then, it returns to the starting point.

[0004] The dead band that does not control the wavelength is provided for the following two reasons. (1) Since there is a short-term change in the wavelength due to fluctuations in the discharge of the laser or micro-vibration of the laser resonator, changing the selected wavelength of the wavelength selecting element by the difference Δλ for each pulse causes wavelength control. This is because the gain was too high and diverged. (2) This is because the minimum shift amount of the selection wavelength of the wavelength selection element is large.

[0005]

FIG. 9 shows an example of conventional control, for example. In addition, dead band DB =
The range is set to ± 0.3 pm, the limit band is set to ± 0.5 pm, and the wavelength shift amount is set to 0.2 pm. In this case,
When the difference Δλ is equal to or smaller than the dead band (inside), since the wavelength selection element is not controlled at all as shown in FIG. 9, the wavelength is shifted to one side within the dead band, or
Even if it fluctuates in the same tendency, it is not corrected, so that the dead band cannot be reduced to a predetermined amount or less. Also,
When the wavelength exceeds the dead band, there is a problem that the time until the wavelength is locked becomes extremely long because only a predetermined amount of the wavelength selection element is changed for each pulse.

The present invention has been made in view of the above problems, and relates to a wavelength control apparatus, and more particularly, to an improvement in stabilization of a wavelength of a narrow band excimer laser apparatus used as a light source of a semiconductor exposure apparatus.

[0007]

For that purpose, the first aspect of the present invention is described.
According to the invention, in a narrow-band pulse laser that detects an oscillation wavelength of an output laser beam by a wavelength detection device and controls a wavelength selection element in a laser resonator to have a set wavelength, the oscillation wavelength is within a predetermined range. Comprises means for detecting a predetermined number of sampled wavelengths, controlling the wavelength selection element based on an average value of the sampled wavelengths, and controlling the wavelength selection element immediately after exceeding the predetermined range. I have.

According to a second aspect of the present invention, a wavelength detector detects an oscillation wavelength of an output laser beam and controls a wavelength selection element in a laser resonator so as to have a set wavelength. When the wavelength difference is larger than the predetermined wavelength difference, the emission shutter is immediately closed, and a signal indicating a wavelength abnormality is output to the outside, so that the wavelength selected by the wavelength selection element is returned by substantially the same amount as the wavelength difference. A means for shifting is provided.

In the third aspect, when the set wavelength is changed, when the difference between the wavelength oscillated before the setting and the newly set wavelength is larger than the predetermined wavelength difference, the emission shutter is closed immediately, and Means for outputting a signal indicating a wavelength abnormality to the outside and shifting the selected wavelength of the wavelength selection element so as to be returned by substantially the same amount as the wavelength difference.

[0010]

According to the above arrangement, even if the oscillation wavelength is within the dead band, the oscillation wavelength is averaged to control the wavelength, and if the oscillation wavelength exceeds the dead band, the wavelength is immediately controlled. By doing so, the wavelength stability is improved at high speed. When the set wavelength and the oscillation wavelength are larger than the predetermined wavelength difference, the emission shutter is immediately closed, and a signal indicating a wavelength abnormality is output to the outside, so that the wavelength selected by the wavelength selection element is set to be substantially the same as the wavelength difference. In this case, the wavelength can be locked to the set wavelength at high speed and with a small number of oscillation pulses.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the wavelength control apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of a wavelength control device according to the present invention.
In FIG. 1, windows 2 and 3 for outputting laser light oscillated by a laser medium (not shown) and an exciting means of the laser medium are provided in a laser chamber 1, and a front side (right side in the figure) of the laser chamber 1 is provided at a front side. Mirror 4
A band narrowing unit 10 is provided on the rear side to narrow the band of the output laser light and output the laser light. On the output laser beam side, a beam splitter 5 for detecting the wavelength of the laser beam is provided.
And an exit shutter 6 that closes so that output laser light is not output at an abnormal wavelength.

The band narrowing unit 10 is a wavelength selecting element 1 such as an etalon, a grating or a beam expander.
1 is comprised. The wavelength selection element 11 of the band-narrowing unit 10 is connected to a driver 30 driven by a command from a wavelength controller 20 for controlling the wavelength, and changes the wavelength of the output laser light.

The wavelength controller 20 includes a driver 30
And a wavelength detecting device 40 connected to the beam splitter 5
, The exit shutter 6 and the stepper controller 50. The wavelength controller 20 calculates the wavelength of the sample light, and the driver 30
When the difference between the oscillation wavelength and the set wavelength is larger than a predetermined range, a signal that changes the wavelength of the laser light to be driven and output is output to the exit shutter 6 as an abnormal wavelength so that the output laser light is not output or when the wavelength is normal. An open signal is output, and a signal having an abnormal wavelength is output to the stepper 40. The wavelength controller 20 receives a signal of the sampled and detected wavelength from the wavelength detecting device 40 and a set wavelength changing command signal from the stepper control device 50.

The operation of the above configuration will be described.
FIG. 2 shows a flowchart example of the present invention. First, regarding the number of sampling times N and the average value Δλa (the average value of the difference Δλ between the set wavelength λt and the oscillation wavelength λ), step 101
Initial setting, N = 0, Δλa = 0. Step 10
In 2, it is determined whether or not the laser oscillates, and when light is emitted, N = N + 1 is executed (step 103). In the next step 104, the oscillation wavelength λ is
Is detected, and in step 105, the oscillation wavelength λ and the set wavelength λt
Is calculated.

Next, the absolute value of the difference Δλ is equal to the limit band L
It is determined whether it is smaller than B (step 10).
6). If not (NO), the process proceeds to step 107 to output a wavelength abnormal signal, and at the same time, closes the exit shutter 6. Then, in step 108, the driver 30 of the wavelength selection element 11 is driven to shift the selected wavelength by the difference Δλ. After shifting by the difference Δλ, the process returns to step 101. In the case of YES in step 106, the normal wavelength is output, and the exit shutter 6 is opened (step 1).
09).

Next, at step 110, it is determined whether or not the absolute value of the difference Δλ is smaller than the dead band DB.
If no (NO), the process proceeds to step 108, in which the driver 30 of the wavelength selection element 11 is driven to shift the selected wavelength by the difference Δλ. After shifting by the difference Δλ, the process returns to step 101. If YES in step 110, the average value Δλa = difference Δλ is set in step 111, and Δλas = Δλas + Δλa is performed in step 112.

Subsequently, it is determined whether or not the number of samplings N is smaller than the average number of samplings Nsum (step 113). If not (NO), the process returns to step 102. In the case of YES, in step 114, the average value Δλa of the difference Δλ between the oscillation wavelength λ and the set wavelength λt is calculated [Δλa = (Δλas / Nsum)]. Then, the process proceeds to step 108, in which the driver 30 of the wavelength selection element 11 is driven to shift the selected wavelength by the difference Δλa.
After shifting by the difference Δλa, the process returns to step 101.

FIG. 3 shows a change in the oscillation wavelength when the wavelength control of the present invention is performed. Here, it is assumed that the average number of samplings Nsum = 10. In FIG. 3, the initial 10 pulses (indicated by ● in the figure) are within the dead band DB, and the oscillation wavelength λ of these 10 pulses is averaged to obtain 1 pulse.
The selected wavelength of the wavelength selection element 11 is controlled so as to have a set wavelength (the symbol ◎ in the figure, hereinafter the symbol 〇 in the normal case) at the first pulse. Since the oscillation wavelength exceeds the dead band DB at the 17th pulse (symbol in the figure), the selection wavelength of the wavelength selection element 11 is controlled so as to immediately reach the set wavelength.

Since the oscillation wavelength exceeds the limit band LB at the 26th pulse (the symbol x in the figure), a wavelength abnormal signal is output, the exit shutter 6 is closed, and the wavelength selected by the wavelength selection element 11 is set to the set wavelength. Shift so that
At the next pulse, the oscillation wavelength becomes the set wavelength, a normal wavelength signal is output, and at the same time, the exit shutter 6 is opened. In this way, by averaging even within the dead band range, control can be performed with high accuracy without diverging the wavelength control. Further, when the wavelength exceeds the dead band, the wavelength is controlled immediately, so that high-speed control is possible.

FIG. 4 shows an example of a control flowchart when the set wavelength is changed. First, a newly set wavelength λa is read (step 201). Next, in step 202, the wavelength λ oscillated before the new setting is performed.
The difference Δλ from b is calculated. It is determined whether the absolute value of the difference Δλ is smaller than the limit band LB (step 2).
03). If not (NO), the process proceeds to step 204, where a wavelength abnormality signal is output, and at the same time, the exit shutter 6 is closed.

Then, in step 6, the steady control shown in FIG. 2 is performed. On the other hand, in the case of YES in step 203, the process proceeds to step 6. In this way, when the set wavelength is changed, it is determined whether or not there is an abnormality in the wavelength before laser oscillation, so that the laser light does not go out of the set range.

FIG. 5 shows the change of the oscillation wavelength in the case of the conventional case and the case of the present invention when the set wavelength is changed. In the conventional method, the oscillation wavelength shifts by a predetermined amount for each pulse from the wavelength λb oscillated before newly setting, enters the limit band at the tenth pulse (symbol “△” in the figure), and the wavelength becomes normal. The inside of the dead band is indicated by the middle symbol (symbol), and the control of the selected wavelength of the wavelength selection element is stopped in the following.

On the other hand, in the case of the present invention, when the set wavelength is changed, a wavelength abnormal signal is output, the exit shutter 6 is closed, and the selected wavelength of the wavelength selection element is set to the newly set wavelength λa. After that, the laser is oscillated, and within the dead band at the second pulse (symbol in the figure), a normal wavelength signal is output, and the emission port shutter 6 is opened. Thus, in the present invention, with a small number of pulses,
Moreover, it is possible to lock the set wavelength at high speed with high accuracy.

Next, FIG. 6 shows an example of a flowchart in which the average value dead band DBav is set to further improve the wavelength stability. First, the number of samplings N and the average value Δλa (the average value of the difference Δλ between the set wavelength λt and the oscillation wavelength λ) are initialized in step 301, N = 0, Δ
λa = 0 is performed. In step 302, it is determined whether or not the laser oscillates, and when light is emitted, N = N + 1 is executed (step 303).

In the next step 304, the wavelength detector 4
At step 305, a difference Δλ between the oscillation wavelength λ and the set wavelength λt is calculated. Next, the difference Δ
It is determined whether or not the absolute value of λ is smaller than the limit band LB (step 306). If not (in the case of NO), the flow shifts to step 307 to output a wavelength abnormal signal,
At the same time, the exit shutter 6 is closed. Then, in step 308, the driver 30 of the wavelength selecting element 11 is driven to shift the selected wavelength to the set wavelength side by a predetermined amount. After shifting by a predetermined amount, the process returns to step 301. Step 306
In the case of YES, the normal wavelength is output and the exit shutter 6 is opened (step 309).

Next, at step 310, it is determined whether or not the absolute value of the difference Δλ is smaller than the dead band DB.
If not (NO), the process proceeds to step 308, in which the driver 30 of the wavelength selection element 11 is driven to shift the selected wavelength to the set wavelength side by a predetermined amount. After shifting by a predetermined amount, the process returns to step 301. If YES in step 310, the average value Δλa = difference Δλ is set in step 311, and Δλas = Δλas + Δλa is performed in step 312.

Subsequently, it is determined whether or not the number of times of sampling N is smaller than the average number of times of sampling Nsum (step 313). If not (NO), the process returns to step 302. In the case of YES, it is determined in step 314 whether or not the absolute value of the average value of the difference Δλ [Δλas / Nsum] is smaller than the dead band DBav. N
In the case of O, the process proceeds to step 308, in which the driver 30 of the wavelength selection element 11 is driven to shift the selected wavelength to the set wavelength side by a predetermined amount. After shifting by a predetermined amount, the process returns to step 301. If YES, the process immediately returns to step 301.

FIG. 7 shows a change in the oscillation wavelength when the wavelength control of the present invention is performed. Here, it is assumed that the average number of samplings Nsum = 10. In FIG. 7, the initial 10 pulses (indicated by ● in the figure) are in the dead band DB, and the oscillation wavelength λ of these 10 pulses is averaged to obtain 1 pulse.
The selected wavelength of the wavelength selection element 11 is controlled so as to have a set wavelength (the symbol ◎ in the figure, hereinafter the symbol 〇 in the normal case) at the first pulse.

Since the oscillation wavelength exceeds the dead band DB at the 22nd pulse (symbol in the figure), the wavelength selected by the wavelength selection element 11 is immediately shifted by a predetermined amount to the setting side.
Although the 23rd pulse is in the DB, the shift is continued by a predetermined amount until the average of the 10 pulses enters the DBav (the 33rd pulse and the 43rd pulse).

Since the oscillation wavelength exceeds the limit band LB at the 53rd pulse (x symbol in the figure), a wavelength abnormal signal is output, the exit shutter 6 is closed, and the wavelength selected by the wavelength selection element 11 is set to the set wavelength. To the side until it enters the DB. When one pulse oscillation enters the DB, a normal wavelength signal is output, and at the same time, the exit shutter 6 is opened. Thereafter, the shift is continued by a predetermined amount until the average value of 10 pulses falls within DBav (66th pulse and 76th pulse). In this way, by averaging even within the dead band range, control can be performed with high accuracy without diverging the wavelength control. Further, when the wavelength exceeds the dead band, the wavelength is controlled immediately, so that high-speed control is possible.

In the embodiments of FIGS. 6 and 7, when the shift of the oscillation wavelength is controlled by a pulse motor or the like, the average value of the dead band DBav is set, so that the wavelength can be stabilized with very high accuracy. Can be.

[0032]

As described above, according to the present invention, as one reason, even if the oscillation wavelength is within the dead band, the oscillation wavelength is averaged to control the wavelength, and the oscillation wavelength is reduced to the dead band. If it exceeds, by controlling the wavelength immediately, the wavelength stability is improved at high speed. In addition, when the set wavelength and the oscillation wavelength are larger than the predetermined wavelength difference, the emission shutter is closed immediately, and a signal indicating a wavelength abnormality is output to the outside, and the selected wavelength of the wavelength selection element is changed to the wavelength difference. An excellent effect of being able to lock to a set wavelength at high speed and with a small number of oscillation pulses is obtained by shifting so as to return by almost the same amount as.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a wavelength control device according to the present invention.

FIG. 2 shows an example of a flowchart of the present invention.

FIG. 3 is a diagram showing a change in oscillation wavelength when the wavelength control of the present invention is performed.

FIG. 4 is a flowchart of control when a set wavelength is changed.

FIG. 5 is a diagram illustrating a change in the oscillation wavelength in the case of the related art and the case of the present invention when the set wavelength is changed.

FIG. 6 is a flowchart illustrating another example of control when the set wavelength is changed.

FIG. 7 is a diagram illustrating a change in the oscillation wavelength in the case of FIG. 6 in which the set wavelength is changed.

FIG. 8 is a flowchart of conventional wavelength control.

FIG. 9 is a diagram showing a change in the oscillation wavelength without performing the conventional control.

[Explanation of symbols]

 Reference Signs List 1 laser chamber, 2, 3 window, 4 front mirror, 5 beam splitter, 6 emission port shutter, 10 band narrowing unit, 11 wavelength selection element, 20 wavelength controller, 30 driver, 40 wavelength detection device, 50 stepper control device,

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01S 3/00-3/30 G03F 7/20 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. An oscillation wavelength (λ) for each pulse of an output laser beam whose wavelength is narrowed is detected, and a deviation (Δt) of the detected oscillation wavelength (λ) from a set wavelength (λt) is detected.
λ) is a predetermined limit band (LB) In a wavelength control device of a narrow band pulse laser device that controls the wavelength of the output laser light so as to be equal to or less than a dead band (DB) smaller than the limit band (LB)
If the deviation (Δλ) is less than the dead band (DB), the oscillation wavelength (λ) of the output laser light is sampled by a predetermined number of pulses, and the set wavelength of the sampled oscillation wavelength (λ) is set. Based on the average value (Δλa) of the deviation (Δλ) from (λt), the wavelength of the output laser light is controlled to be the set wavelength (λt), and the deviation (Δλ) is equal to or greater than the dead band (DB). A wavelength control device that controls the wavelength of the output laser light to become a set wavelength (λt) based on the detected oscillation wavelength (λ) when the wavelength is less than the limit band (LB). 2. The wavelength control apparatus according to claim 1, wherein a deviation (Δ) of the detected oscillation wavelength (λ) from a set wavelength (λt).
λ) is equal to or greater than the limit band (LB), a signal indicating an abnormal wavelength is output, the output laser light is shielded from being emitted to the outside of the narrow band pulse laser device, and the wavelength of the output laser light is adjusted. A wavelength control device for controlling the wavelength to be a set wavelength (λt). 3. The wavelength control device according to claim 1, wherein when the set wavelength (λt) is changed, a deviation of the detected oscillation wavelength (λ) from the set wavelength (λt). Δλ) is calculated, and if the deviation (Δλ) is equal to or larger than the limit band (LB), a signal having an abnormal wavelength is output, and the output laser light is shielded from being emitted to the outside of the narrow band pulse laser device. A wavelength controller that controls a wavelength of an output laser beam so as to be a set wavelength (λt).