JPH0820204B2 - Length measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a length measuring apparatus using a laser interferometer, and particularly requires highly accurate position measurement like an exposure apparatus for manufacturing an integrated circuit. The present invention relates to a length measuring device suitable for cases.

[Prior Art] An interferometer using a frequency-stabilized helium-neon (He-Ne) laser as a light source is used for precise length measurement and coordinate measurement. Conventionally, when using this type of interferometer, in order to prevent the wavelength from fluctuating due to the density change (refractive index change) of the air and causing the measurement error, the interferometer can control the temperature and humidity of the air. It is placed in a different chamber and air-conditioned at a temperature of ± 0.1 ° C and a humidity of ± 15%, and the change in atmospheric pressure is monitored by a sensor to correct the wavelength.

[Problems to be Solved by the Invention] However, even when the inside of the chamber in which the interferometer is arranged is air-conditioned as described above, the fluctuation of air due to temperature is reduced to such an extent that the required measurement accuracy is not affected. The reason for this is that it is difficult to make the temperature in a chamber with a considerable volume completely uniform, so there is a lump of air with a locally different temperature, and this lump is caused by an interferometer. It is thought to be due to crossing the measurement beam of.

For example, when such an interferometer is used for positioning a stage of an exposure apparatus for manufacturing an integrated circuit, there are many heat sources such as a stage driving motor and an exposure light source in addition to the laser oscillator of the interferometer itself, It is a cause of fluctuations. In addition, the movement of the stage changes the condition of how the measurement beam is blown from the chamber outlet, so that the temperature around the measurement beam also fluctuates, resulting in air fluctuations.

The present invention has been made in view of the above points,
Reduces air fluctuations in the space where the measurement beam passes,
It is an object of the present invention to provide a length measuring device capable of extremely high precision length measurement.

[Means for Solving the Problem] In the present invention, the space through which the length-measuring beam passes is provided with an air guide means for sending an air flow from a blower opening having a predetermined cross-sectional area. The above object is achieved by arranging a subdividing member that subdivides the air flow in the vicinity in parallel to the flow of the air flow and in a cross-sectional area smaller than the cross-sectional area of the blower port.

[Operation] In the present invention, since the subdivision member for subdividing the air flow is arranged in parallel with the air flow of the air guide means or in the vicinity thereof, the wall surface of the subdivision member and the air Heat is exchanged with the air flow, and while the air flow passes through the subdividing members, air masses having a temperature difference are eliminated, and the temperature of the air flow is made uniform.

Further, since the air flow is subdivided in parallel with the flow, the air flow is laminarized and is sent out to the path of the measurement beam with the temperature kept uniform without involving the air in the peripheral portion. Therefore, the fluctuation of the air in the space through which the measurement beam passes is almost eliminated, and the error in the wavelength of the measurement beam becomes extremely small. That is, in this way, according to the present invention, extremely high precision length measurement is possible.

[Embodiment] FIG. 1 is a perspective view showing the outline of the configuration when the length measuring apparatus according to the present invention is used for coordinate detection of a precision moving stage such as an exposure apparatus for manufacturing integrated circuits. Less than,
The configuration will be described with reference to FIG.

First, the XY stage 1 is provided in the main body of the exposure apparatus so that the wafer 6 can be held and moved in the XY directions by a predetermined amount. On the two sides of this stage 1 which intersect at right angles, X, Y
Directional reflecting mirrors 4 and 5 are attached respectively, and the reflecting mirrors 4 and 5 move together with the XY stage 1.

Further, the laser light source 100 whose frequency is stabilized emits a beam B1 containing two components having different polarization characteristics, which are different in frequency by about 2 MHz due to the Zeeman effect. The beam B1 is split by the beam splitter 7 into a beam B2 directed to the interferometer unit 2 for X-axis coordinate measurement and a beam B3 directed to the interferometer unit 3 for Y-axis coordinate measurement. Then, the interferometer unit 2 in the X-axis direction emits the measuring beam B4 to the reflecting mirror 4 attached to the XY stage 1 and receives the measuring beam B4 reflected by the reflecting mirror 4.
Similarly, for the Y axis, the interferometer unit 3 emits the measuring beam B5 to the reflecting mirror 5 and receives the measuring beam B5 reflected by the reflecting mirror 5.

Next, the internal configuration of the interferometer unit 2 (same for the interference unit 3) will be described with reference to FIG. First, the beam B2 is divided by the polarization beam splitter 21 into a reference beam B13 and a measurement beam B4 having different polarization directions. The measurement beam B4 transmitted through the polarization beam splitter 21 is a λ / 4 plate 24
Then, the light enters the reflecting mirror 4 that can move at a predetermined speed together with the XY stage, is reflected here, and again enters the polarizing beam splitter 21 via the λ / 4 plate 24. Here, since the measuring beam B4 has passed through the λ / 4 plate 24 twice, the polarization direction is
It has changed by 90 °, and this time it is reflected by the polarization beam splitter 21 and enters the rectangular prism 23. Here, the measuring beam B4 is reflected twice, returns in the incident direction, is reflected by the polarization beam splitter 21, and is incident again on the reflecting mirror 4 and is reflected. Here again, the measuring beam B4 has its polarization direction changed by 90 ° by passing through the λ / 4 plate 24 twice as before, so the measuring beam B4 reflected by the reflecting mirror 4 is now the polarizing beam splitter. Continue straight through 21.

On the other hand, the other beam split by the polarization beam splitter 21, that is, the reference beam B13, is incident on the rectangular prism 22 as a reference mirror fixed at a predetermined position,
Here, it is reflected twice and enters the polarization beam splitter 21 again and is deflected by 90 degrees. In this way, the reference beam B1
3 and the measuring beam B4 again overlap and become an interference beam B6, which is incident on the photoelectric sensor 25.

Here, since the beam B2 has two components having different frequencies as described above, it originally causes a beat, but is reflected by the reflecting mirror 4 when the reflecting mirror 4 moves. The frequency of the measurement beam B4 changes due to the Doppler effect, and the beat cycle of the interference beam B6 changes. That is, the interference fringes generated by causing the measurement beam B4 and the reference beam B13 to interfere with each other change. Therefore, the movement amount of the reflecting mirror 4 (that is, the movement amount of the XY stage) can be detected by detecting the change in the interference fringes with the photoelectric sensor 25.

As a configuration of the interferometer unit 2 other than the above, one in which the paths of the reference beam and the measurement beam are parallel to each other can be considered. This structure will be described with reference to FIG. The beam B2 emitted from the light source is divided by the polarization beam splitter 31 into a measurement beam B4 and a reference beam B13 having different polarization directions, and the measurement beam B4 is reflected by the reflecting mirror 4 which moves together with the XY stage. It is similar to the case shown in the figure.

On the other hand, the reference beam B13 is the polarization beam splitter 31.
After being separated from the measuring beam B4 by, is reflected by the reflecting mirror 32 and is incident on the reflecting mirror 36 attached to an object fixed at a predetermined position such as an exposure lens through the λ / 4 plate 37, for example. To do. Then, after being reflected by the reflecting mirror 36, it again enters the reflecting mirror 32 through the λ / 4 plate 37, is bent 90 ° and enters the polarizing beam splitter 31.

Here, the reference beam B21 has its polarization direction changed by 90 ° by passing through the λ / 4 plate 37 similarly to the measuring beam B4 described in FIG. 3, and this time it passes through the polarization beam splitter 31. , Enters the right-angle prism 33. Then, the reference beam B1 reflected by the two sides of the rectangular prism 33
3 again passes through the polarizing beam splitter 31, and the reflecting mirror 32
It is bent by and is incident on the reflecting mirror 36 again via the λ / 4 plate 37. The reference beam B13 reflected here passes through the λ / 4 plate 37 and reaches the reflecting mirror 32, where it is bent 90 ° and enters the polarizing beam splitter 31. Also in this case λ / 4 plate
Since the reference beam B13 has passed through 37 twice, the polarization direction of the reference beam B13 has changed by 90 °.
The light beam is deflected by 90 ° and is emitted without passing through it, where it is overlapped with the measurement beam B4 and enters the photoelectric sensor 35 as an interference beam B6.

Here, when the interferometer unit has the configuration shown in FIG. 4, since the optical paths of the reference beam B13 and the measurement beam B4 are parallel, the situation of air fluctuations is the same, and Therefore, when the optical path lengths are equal, they are not affected by the change in air density (dead
Path error = 0), which is considered to be more advantageous than the case of FIG. However, in reality, there is a difference in air density between the reference beam B13 and the measurement beam B4 shown in FIG. 4, and the vibration of the reflecting mirror 36 also affects the structure. It is not possible to say which is advantageous.

Next, the air guide means, which is a main component of the present invention, and the subdivided member for achieving uniform temperature and laminar flow of the air flow will be described. In the embodiment shown in FIG. 1, the air outlets of the air guide means 8 and 9 are installed parallel to the passages of the measurement beams B4 and B5, respectively. That is, the wind guide means 8 for the X axis is the measurement beam.
The air flow is sent vertically across B4, and similarly the air guide means 9 for the Y axis is arranged to send the air flow vertically across the measurement beam B5. And such a wind guide means 8,
Subdividing members 10 and 11 described later are arranged inside the vicinity of the blower port of 9 to make the temperature of the air flow passing through the inside uniform and laminar.

Further, since it is desirable to supply the air guiding means 8 and 9 with air having a stable temperature which is almost equal to the air temperature near the measuring beams B4 and B5, respectively, the chamber of the chamber in which the length measuring apparatus according to the present invention is installed. It is desirable to take the air directly into the air guide means 8 and 9 from the air outlet of the air conditioner. Further, since the air flow requires a certain speed, a fan is provided at the air intake of the air guide means 8 or 9, or the cross section of the intake is enlarged and the cross section is gradually narrowed. There is a need.

It is necessary to install the blower openings of the air guide means 8 and 9 above or below the stage 1 so that they do not come into contact with each other even if the stage 1 moves in the XY plane.
Since it is difficult to install because there is a surface plate or the like on which the vehicle rides, it is appropriate to arrange so that the air is blown obliquely from above or directly above, as shown in FIG.

Also, in FIG. 1, the configuration of the interferometer units 2 and 3 is shown in FIG.
Although shown in the figure, the configuration shown in FIG. 4 can be applied in the same manner. In this case, the measurement beam B4 and the reference beam are used.
It is advisable to determine the duct shape of the blower ports of the air guide means 8 and 9 so that the air flow is equally sent to B13.

Next, the shape of the subdivided members 10 and 11 according to the present invention is changed to the second
This will be described with reference to the drawings. The subdivision member is configured to subdivide the airflow in parallel with the flow of the airflow in order to make the airflow laminar. That is, as the shape of the subdivided member, for example, the shapes shown in FIGS. 2A and 2B can be considered. (A) is obtained by alternately bending thin metal plates and the like, and (b) is an array of pipes having a square cross section, both of which are installed in the vicinity of the blower port in parallel with the outer tube of the air guide means. The shape of the subdividing member is not limited to that shown in FIG. 2, but in order to make the airflow a laminar flow, the subdividing member has a certain size or more in the flow direction of the airflow. It is desirable to have a length.

Further, the subdividing members 10 and 11 are preferably made of a material having a high thermal conductivity and a large heat capacity, such as a metal, in order to promote the uniformization of the temperature of the air flow, and contact with the air flow. In order to increase the area, it is desirable to subdivide the cross section of the air flow as much as possible within a range in which the resistance to the flow of the air flow does not become too large. Further, when the present invention is applied to an exposure apparatus for manufacturing integrated circuits as in this embodiment, dust generation is an important problem. It is also possible to attach the filter to the air outlet of the air guide means.

Next, the angle of the air flow with respect to the beam will be described.
In the example shown in FIG. 1, the air blowing means 8 and 9 are provided with the measurement beam B.
Although an example of parallel installation along B4 and B5 is shown, the ventilation port is installed near the interferometer units 2 and 3 or near the reflecting mirrors 4 and 5 and is parallel or parallel to the measurement beams B4 and B5. A method of flowing an air flow at an angle close to is also conceivable.

Here, the advantage of the arrangement as shown in FIG. 1 is that the air outlet of the air guide means and the beam are close to each other, a uniform air flow is sent over the entire length of the beam, and a very high wind speed is obtained. There are some points that you do not need. On the other hand, the advantage of flowing the air flow parallel to the beam is that the temperature of the air flow is not completely uniform, and even if there are lumps with different air temperatures, the lumps of air will be in the beam passage for a long time. It is conceivable that the fluctuation cycle becomes sufficiently long to pass over the air, and the influences of the air masses are averaged by overlapping in time, and the influence on the measurement is reduced. But,
In this case, the air flow does not reach the beam far from the air outlet, and air having a different temperature may be mixed from the surroundings. For this reason, it is generally difficult to provide superiority or inferiority in the direction of air flow, and air may be blown at an angle intermediate between the two. Next, a method of adjusting the flow velocity of the air flow sent from the air guide means will be described. If the air flow is too slow, the air will not be sufficiently sent to the beam, and if it is too fast, the air flow will be turbulent due to the reflection of the air flow and the measured object will vibrate, so the air flow speed is adjusted to an appropriate value. It is desirable to do. For this reason, if the optimum flow velocity is not known in advance, the air guide means may be provided with an escape hole with a variable area to adjust the velocity of the air flow, or the speed and area of the fan at the air intake may be varied. It is desirable that a means for doing so be provided. To optimally adjust the flow velocity of the air flow, for example, fix the XY stage 1, monitor the coordinate reading value in the interferometer unit, and adjust the flow velocity so that the fluctuation becomes the smallest, or the actual device. It is conceivable to adjust the flow velocity so as to obtain the most accuracy by operating the. Further, since the state of the air flow around the beam is different between when the XY stage 1 is stopped and when it is moving, it is more desirable to control the flow velocity of the air flow to the optimum flow velocity in each case.

Further, in an ordinary interferometer system, the atmospheric pressure and temperature around the measurement beam are monitored and the wavelength is corrected, but in the length measuring device according to the present invention, the atmospheric pressure and temperature of the air around the beam are sent out from the air guide means. Since these are the same as the atmospheric pressure and temperature of the air, these sensors may be provided inside or near the air blowing means.

Further, the subdivided member according to the present invention not only makes the temperature of the airflow uniform, but also controls the temperature of the subdivided member itself so as to send the airflow homogenized to a desired temperature. It is also possible. As a method for controlling the temperature of the subdivided member, for example, a method of flowing a liquid or the like into the subdivided member (inner wall) and controlling the temperature is conceivable, and a signal from the temperature sensor provided near the blower opening is used. Therefore, it is desirable to perform feedback control so that the air flow is maintained at a desired temperature. By doing so, even if the temperature of the air taken into the air guide means is unstable to some extent, the temperature of the air flow sent out from the air outlet becomes substantially constant, and stable high measurement accuracy can be secured. Since the air guide means is a hollow cylinder except for the portion where the subdivision member is installed, it is highly likely to resonate even with minute vibrations, especially when a fan is used for the air intake port, It is considered that such an air guide means is constantly vibrating. If this vibration is transmitted to the interferometer unit, a measurement error corresponding to the amplitude will occur, so it is desirable to isolate the vibration between the air guide means, the interferometer unit, and the object to be measured. As this method, a method of insulating with a vibration-proof rubber or the like, a method of arranging the duct and the interferometer unit, and a method of arranging the object to be measured so as not to come into direct contact with each other can be considered. In addition to this, vibration and air turbulence due to movement and stop of the XY stage 1 may occur, but these are difficult to prevent, so wait a few seconds after stopping the stage if necessary. It is advisable to start exposure. Further, when there are heat sources such as a motor and a laser oscillator such as an exposure apparatus, it is desirable to thermally insulate these heat sources from the length measuring device as well as against vibration. Needless to say.

[Advantages of the Invention] As described above, in the present invention, since the air in the vicinity of the passage of the measuring beam is always kept at a substantially uniform temperature, the air density hardly changes due to the temperature difference. Therefore, the wavelength of the measurement beam is kept substantially constant, and stable and extremely high measurement accuracy can be secured.

If such a length measuring device is used for detecting the coordinates of the XY stage of the exposure apparatus for manufacturing an integrated circuit, the alignment can be performed very accurately, which is extremely useful in achieving high integration of the integrated circuit.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a perspective view showing a configuration example of a subdivided member, and FIGS. 3 and 4 are schematic diagrams showing a configuration of an interferometer unit. [Explanation of symbols for main parts] 1 ... XY stage 2,3 ... Interferometer unit 4,5 ... Reflecting mirror 8,9 ... Bending means 10,11 ... Subdividing member B13 .... Reference beam B4, B5 ... Measuring beam

Claims (2)

[Claims] 1. A reference beam reflected by the reference mirror, which is obtained by dividing a beam emitted from a light source into a reference mirror provided at a predetermined position and a movable mirror that can move at a predetermined speed and dividing the beam. In the length measuring device for measuring the moving distance of the movable reflecting mirror by interfering the beam and the measuring beam reflected by the movable mirror with each other, and photoelectrically detecting a change in interference fringes caused by the interference, The air passage has a predetermined cross-sectional area in the space through which the beam passes, and has an air guide means for sending an air flow, and the air blow opening of the air guide means or in the vicinity thereof is parallel to the air flow and A length measuring device comprising a subdivision member for subdividing the air flow into a cross-sectional area smaller than the cross-sectional area of the blower opening. 2. The length measuring apparatus according to claim 1, wherein the air blowing port of the air guiding means is arranged so that the air flow crosses the passage of the measuring beam vertically.