JPH05304328A - Dual frequency semiconductor laser source - Google Patents

Abstract

PURPOSE:To make it possible to keep constant emitting directions of two beams emitted from a frequency shifter by constituting a dual frequency semiconductor laser source of a mechanism for varying the relative position of lens or optical system with respect to the light source point of semiconductor laser, and means for detecting the emitting direction of laser beam and performing feedback control. CONSTITUTION:A laser beam emitted from a semiconductor laser 1 is converged through a converging lens 2 to produce a parallel beam, which is then fed through beam splitters 3, 8 and frequency shifters 5, 6 to produce two light beams having slightly different frequencies. Up/down and right/left movement of a mechanism 7 mounting the converging lens 2 is controlled by a signal delivered from a four-split detector 16. Operation of inclination mechanisms 12, 13 mounting the beam splitters 3, 8 is controlled by signals delivered from four-split detectors 9, 17. Since relative position of leans or optical system can be varied with respect to a laser light source point, directions of two laser beams outputted from frequency shifters can be kept constant easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for manufacturing a semiconductor by aligning a mask with a wafer by an optical heterodyne interferometry method using a diffraction grating and then baking a mask pattern on the wafer, and the interferometry method. The present invention relates to a laser light source device having two different frequencies, which is used in an encoder for detecting a position and a size measuring machine.

[0002]

2. Description of the Related Art In optical heterodyne interferometry, two laser beams having different frequencies are interfered with each other to obtain a heterodyne signal, and a phase difference between a reference heterodyne signal (reference signal) and a measured heterodyne signal is obtained. The mask is aligned with the wafer and the position is detected. Normal,
The frequency difference between the two laser beams is from 10 kHz to 10 M
In order to obtain this frequency difference, a transverse Zeeman effect type dual frequency orthogonal polarization He-Ne laser, a semiconductor laser or a He-Ne laser, and a light source combined with a frequency shifter are used. A two-frequency semiconductor laser light source combining the semiconductor laser and the frequency shifter is
Proc. Of the 90th JSPE Spring Conference Academic Lectures (429
7) and a condenser lens 2 for condensing the laser as shown in FIG.
And an optical system (beam splitter 3 and mirror 4) that divides the laser into two, and two frequency shifters 5 and 6 for obtaining two laser beams having different frequencies. FIG. 7A is a plan view and FIG. 7B is a side view.

Laser light emitted from a semiconductor laser 1 whose frequency is stabilized becomes a parallel laser beam by a condenser lens 2 and is divided into two by a beam splitter 3. One of the beams has a light frequency f ₀ of f by a frequency shifter 5. Shift ₁ The other beam is reflected by the mirror 4, and the shifter 6 shifts the frequency f ₀ of the light by f ₂ . Therefore, it is possible to obtain two laser beams A and B whose frequencies differ by Δf = f ₁ −f ₂ . Also,
In some cases, only one of the frequency shifters 5 and 6 is used, in which case one frequency is f ₀ and the other is f _0.
Since it changes by + f, it is possible to obtain two laser beams A and B whose frequencies differ by f.

The condenser lens 2 is used to convert the diverging laser light into a parallel beam, and the light source point P is shown in FIG.
As shown in FIG. 3, the condenser lens 2 is attached so as to match the focus thereof. As shown in FIG. 8 (b), if the condenser lens 2 is mounted so that its center is on the optical axis, the beam will be parallel to the optical axis as shown by the solid line, but as shown by the broken line, When the center of the optical lens 2 is attached so as to be shifted downward from the optical axis by z, the beam is emitted downward from the optical axis by θ, and the two beams whose frequencies are shifted by the frequency shifters 5 and 6. The laser beams A and B are emitted downward by θ with respect to a predetermined direction. This inclination θ increases as the focal length f decreases. Since the two-frequency semiconductor laser light source uses a short focus lens as the condenser lens 2 for downsizing, the mounting error of the condenser lens 2 has a great influence on the emission direction. For example, when the condenser lens 2 with f = 5 mm is used, when the condenser lens 2 is attached with a deviation of 1 μm,
An inclination of 0.2 mrad occurs. This is the condenser lens 2
Are also displaced in the left-right direction, the same occurs, and two laser beams A, B inclined in the left-right direction are emitted from the frequency shifters 5, 6.

Since the beam B is split by the beam splitter 3 and reflected by the mirror 4, two laser beams A and B having slightly different frequencies are provided if they are not attached accurately to the beams. Among them, A is emitted in a predetermined direction, but B is emitted in a different direction with respect to A.

As described above, when the light source is assembled so as to be displaced from the optical axis of the laser, the emitted light is emitted while being inclined from the optical axis by a certain angle, and the two laser beams emitted from the frequency shifter. Is emitted in a direction deviated from a predetermined direction. In order to put this inclination within 1 mrad,
High precision assembly accuracy (± 2.5 μm or less) is required. Even if the condenser lens 2 is accurately attached on the optical axis during assembly, heat generated by the semiconductor laser or the frequency shifter causes the fixing brackets of the semiconductor laser and the lens to be thermally deformed, so that the light source point P and The relative position of the optical lens changes. Even when the outside air temperature changes, the temperature of the fixture is affected, the relative position changes, and the two laser beams emitted from the frequency shifter are not emitted in a predetermined direction. These things similarly occur in the beam splitter 3 and the mirror 4, and the two laser beams are emitted in mutually different directions. Therefore, there is a drawback that a beam emitted in a predetermined direction cannot be obtained when the assembling accuracy is poor, or when the temperature around the light source changes even though the assembling accuracy is good.

On the other hand, 2 emitted from the frequency shifters 5 and 6
The two beams are finally superimposed on one beam to form a heterodyne beat signal. For this reason, when the two beams are not emitted in parallel to each other, a complicated optical system is required to overlap the beams, and at the same time, the overlapping work takes a long time. further,
If the output direction of the beam changes due to temperature change,
After turning on the power, it takes a long time for the temperature to stabilize and the device can be used, and the change in the outside temperature makes the overlapping of the two beams worse, which reduces the strength of the heterodyne beat signal. It was

[0008]

SUMMARY OF THE INVENTION According to the present invention, the relative position of a lens or an optical system can be changed with respect to a laser light source point, and there is a change in heat generated by a semiconductor laser or a frequency shifter or outside temperature. Another object of the present invention is to provide a two-frequency semiconductor laser light source device capable of keeping the directions of two laser beams generated from the frequency shifter constant.

[0009]

A frequency semiconductor laser light source device of the present invention comprises a semiconductor laser, a lens for condensing the laser, and two parallel laser beams emitted from the lens.
In a two-frequency semiconductor laser light source device in which an optical system that is divided and is incident on a frequency shifter and a frequency shifter that makes the frequencies of these two parallel laser beams different from each other are integrated, the lens is provided with respect to the light source point of the semiconductor laser. And one or more mechanisms that can change the relative position of the optical system, one or more detectors that detect the position in the emitting direction of the laser beam, and feed back the detected position,
It comprises means for controlling the emission directions of the two beams emitted from the frequency shifter to a predetermined direction.

[0010]

When the light source point of the semiconductor laser is assembled with a slight deviation from the optical axis of the lens for converting the light into a parallel laser beam, the two laser beams emitted from the frequency shifter are directed in different directions from a predetermined direction. Emit. At this time, by feeding back the signal from the detector that detects the laser beam position to the mechanism that displaces the lens,
Since the position of the lens can be easily aligned with the light source point, highly accurate assembly accuracy (± 2.5 μm or less) is not required. Similarly, the beam emitted from the lens
Even if the splitting beam splitter or the mirror that reflects the beam is not assembled correctly, it is possible to easily correct the angle by controlling these optical systems with the signal from the detector, so it is highly assembled. Does not require precision. In addition, even if the light source is turned on or the emitting directions of the two beams change due to the temperature change around the light source, the position error of the emitting directions of the two beams is detected and the lens or By moving the beam splitter or the mirror, the beam can be constantly emitted in a predetermined direction.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.
(b) is a plan view and a side view of a dual-frequency semiconductor laser light source section, respectively, and (c) is an overall device configuration diagram including control means.

In FIGS. 1 (a) and 1 (b), the laser light emitted from the frequency-stabilized semiconductor laser 1 is
It diverges greatly in the vertical direction, especially in the horizontal direction. This light is condensed by the condenser lens 2 to form a parallel laser beam.
In this embodiment, an aspherical lens is used as the condenser lens 2. The laser beam is split by a beam splitter 3 into a transmitted beam and a reflected beam. The transmitted beam is incident on the frequency shifter 5, and the frequency f _{0 of} the light is shifted by f ₁ . On the other hand, most of the reflected beam is reflected by the beam splitter 8, and after entering the frequency shifter 6, the frequency shifts by f ₂ . Therefore, it is possible to obtain two lights whose frequencies differ by Δf = f ₁ −f ₂ . Further, when only one of the frequency shifters 5 and 6 is used, one of the frequencies changes by f ₀ and the other changes by f ₀ + f, so that two lights having different frequencies by f can be obtained. The beam transmitted through the beam splitter 8 is incident on the four-division detector 9. The two laser beams that have passed through the frequency shifters 5 and 6 are split into two beams by the beam splitters 14 and 15, respectively. Part of the beams that have been split and reflected enter the four-split detectors 16 and 17 that detect the positions of the beams in the emission direction. And most of the other beams are transmitted as they are, and become two laser beams having slightly different frequencies.

The condenser lens 2 is several tens of μm vertically and horizontally.
It is installed on the vertically moving and laterally moving mechanism 7 which is displaced. An example of the vertical and horizontal movement mechanism is shown in FIG. In FIG.
The condenser lens 2 is a bimorph-type piezoelectric actuator (PZT) T1 that moves the condenser lens 2 in the vertical (Y) direction.
Is attached to one end of. The other end of the actuator T1 is coupled to an L-shaped plate 10 that connects to the tip of an actuator T2 that moves the condenser lens 2 in the left-right (X) direction. The actuator T2 is fixed on the substrate 11 on which the frequency-stabilized semiconductor laser 1 and the frequency shifters 5 and 6 are mounted. The operation of the vertical / horizontal moving mechanism 7 is performed by a signal from the four-divided detector 16.

FIG. 3 shows a state in which the beam reflected by the beam splitter 14 is irradiated onto the four-division detector 16 as a spot BS1. The beam spot BS1 is on the center of the four-divided detector 16, and the first, second, third and fourth divided surfaces D1, D2, D3 of the four-divided detector.
The voltages generated at D4 are equal, and the signal voltage for operating the vertical / horizontal moving mechanism 7 is zero. On the other hand, when the beam spot is displaced in the X direction like BS2 shown by the broken line, D
Since the voltage generated at D3 and D4 is higher than the voltage generated at 1 and D2, a signal voltage for operating the actuator T2 is generated. When the beam spot is displaced in the Y direction, D is compared with the voltage generated in D2 and D3.
Since the voltage generated at 1 and D4 becomes high, a signal voltage for operating the actuator T1 is generated. In this way, the up / down and left / right moving mechanism 7 always has a beam spot of 4
Feedback control is performed so that the split detector 16 is located at the center. Therefore, the relative positional relationship between the light source point P of the laser and the condenser lens 2 shown in FIG.
The light source point P is kept on the optical axis of, and the emission directions of the laser beams emitted from the frequency shifter 5 having slightly different frequencies are always constant.

On the other hand, the beam splitter 3 and the beam splitter 8 shown in FIG. 1 are installed on tilting mechanisms 12 and 13 which can be tilted independently of each other. The operations of the tilting mechanisms 12 and 13 are performed by signals from the four-divided detectors 9 and 17, respectively, and feedback control is performed so that the beam spot comes to the center of the four-divided detectors 9 and 17 as in the above-described control method. ..

In FIG. 1 (c), 20 is a power supply unit,
Reference numeral 21 denotes a control circuit section, which is an optical frequency shifter driver section 22.
And semiconductor laser drive unit and feedback control circuit unit
It is composed of 23, 24 is a two-frequency semiconductor laser light source unit, and 25 is a cable.

The vertical and horizontal moving mechanism 7 is a laminated type PZ.
A combination of T and the displacement magnifying mechanism may be used, or an elastic spring and a DC servo motor may be used. Also, instead of a 4-division detector, a 2-dimensional PSD (Position Sensi
tive Detector) may be used.

FIG. 4 shows a second embodiment of the present invention. In order to make the size of the apparatus as small as possible, instead of the beam splitters 14, 15 and the four-divided detectors 16, 17 of the first embodiment, beam position detectors 18, 19 having a hole in the center are installed. When the beam passes through the center of the hole, there is no output from the detector, and when the beam passes out of the center of the detector, an output corresponding to the deviation is generated. These outputs are output to the up / down and left / right moving mechanism 7 and the tilting mechanism, respectively.
It is fed back to 13, and the emission directions of the two beams emitted from the frequency shifter are controlled to be constant.

FIG. 5 shows a third embodiment of the present invention, in which the beam position is detected from the second embodiment when the displacement of the beam splitter 8 due to the heat generated by the laser and the frequency shifter and the fluctuation of the outside air temperature is small. The device 19 and the tilting mechanism 13 are removed. The emission direction of the beam A is controlled by the signal from the beam position detector 18 being fed back to the vertical / horizontal moving mechanism 7, and the emission direction of the beam B is the signal from the four-division detector 9 to the tilting mechanism 12. It is controlled by being fed back.

FIG. 6 shows a fourth embodiment of the present invention, in which the displacement of the beam splitter 8 is small and the displacement of the beam splitter 3 is also small due to the fluctuations of heat generated by the laser and the frequency shifter and the ambient temperature. The beam position detector 18 and the tilt mechanism 12 are removed from the third embodiment. Four
Signals from the split detector 9 are sent to the vertical and horizontal movement mechanism 7
And the two laser beams A and B are always emitted in a fixed direction.

In the second to fourth embodiments as well,
Except for the configuration of the two-frequency semiconductor laser light source unit 24, the control means including the power supply unit 20 and the control circuit unit 21 is common to the first embodiment.

Although the four embodiments have been described above, the beam position detectors 18 and 19 used in the second and third embodiments may be mounted at positions between the beam splitters 3 and 8 and the frequency shifters 5 and 6. It may be outside the dual frequency semiconductor laser light source. Also, the beam splitter 1 used in the first embodiment
The same applies to the mounting positions of 4, 15 and the four-divided detectors 16, 17.

Although the case where the condenser lens 2 is displaced has been described above, the frequency-stabilized semiconductor laser 1 may be displaced.

[0024]

As described above, in the two-frequency semiconductor laser light source device of the present invention, the relative position of the lens and the optical system can be changed with respect to the laser light source point, so that high precision is required during assembly. Even if the relative position of the beam and the lens or the optical system changes due to the ease of assembly, the heat generated by the semiconductor laser or the frequency shifter, or the change in the outside air temperature, the two beams generated by the frequency shifter A remarkable effect is obtained such that it is easy to keep the direction of the laser beam constant.

Further, by vibrating the vertical / horizontal moving mechanism 7 up / down or left / right with a slight amplitude, the angle of the emitted beam is changed, and on the object irradiated with the laser
The laser can be easily scanned in the two-dimensional direction.

[Brief description of drawings]

FIG. 1A is a plan view of a dual-frequency semiconductor laser light source section according to a first embodiment of the present invention. FIG. 3B is a side view of the dual frequency semiconductor laser light source unit according to the first embodiment of the present invention.
(c) is a block diagram of the entire apparatus including a control means in addition to the two-frequency semiconductor laser light source section of the first embodiment of the present invention.

FIG. 2 is an explanatory view of an up / down and left / right moving mechanism configured by a bimorph type actuator.

FIG. 3 is an explanatory diagram of a 4-division detector.

FIG. 4 is a plan view of a dual frequency semiconductor laser light source section according to a second embodiment of the present invention.

FIG. 5 is a plan view of a dual frequency semiconductor laser light source section according to a third embodiment of the present invention.

FIG. 6 is a plan view of a dual frequency semiconductor laser light source section according to a fourth embodiment of the present invention.

FIG. 7A is a plan view of a conventional dual frequency semiconductor laser light source unit. (B) is a side view of a conventional dual-frequency semiconductor laser light source unit.

FIG. 8A is a diagram showing a relative positional relationship between the laser light source point and the condenser lens when the center of the condenser lens is on the optical axis. In (b), the center of the condenser lens is z below the optical axis.
It is a figure which shows the relative positional relationship of a laser light source point and a condensing lens when only it shifts.

[Explanation of symbols]

1 frequency-stabilized semiconductor laser 2 condenser lens 3 beam splitter 4 mirror 5,6 frequency shifter 7 up / down and left / right moving mechanism 8,14, 15 beam splitter 9, 16, 17 4 split detector 10 L-shaped plate 11 substrate 12, 13 Tilt mechanism 18, 19 Beam position detector 20 Power supply section 21 Control circuit section 22 Optical frequency shifter driver section 23 Semiconductor laser drive section and feedback control circuit section 24 Dual frequency semiconductor laser light source section 25 Cables A, B Frequency slightly different from each other Laser beam P Laser light source point T1, T2 Bimorph actuator BS1, BS2 Beam spot D1, D2, D3, D4 4th, 1st, 2nd, 3rd and 4th division planes of the detector

Front page continuation (72) Inventor Masanori Suzuki 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Hitoshi Yamaura 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Hoya Incorporated (72) Inventor Nobuo Hori 75-1 Hasunumacho, Itabashi-ku, Tokyo Topcon Co., Ltd.

Claims (1)

[Claims] 1. A semiconductor laser, a lens that condenses the laser, an optical system that splits a parallel laser beam emitted from the lens into two, and enters the frequency shifter, and the frequencies of these two parallel laser beams are mutually different. In a two-frequency semiconductor laser light source device integrated with different frequency shifters, one or a plurality of mechanisms capable of changing the relative positions of the lens and the optical system with respect to the light source point of the semiconductor laser, and the emission direction of the laser beam Feed back one or more detectors that detect the position and the detected position,
A two-frequency semiconductor laser light source device comprising means for controlling the emission directions of the two beams emitted from the frequency shifter to a predetermined direction.