JP2888215B2 - Exposure apparatus and measurement method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus, and more particularly, to measurement of a position of a stage capable of precision movement using a laser interferometer. [0002] A laser interferometer using a helium-neon (He-Ne) laser whose frequency is stabilized as a light source is used for precise length measurement and coordinate measurement. A typical example is a system sold by Hewlett-Packard Company. When this type of conventional device is used for measurement that requires high precision, a special temperature stabilized air conditioning is performed to prevent fluctuation of the refractive index of air, and ± 0.1 ° C.
It stabilizes the air temperature within the range, and monitors the atmospheric pressure to compensate for changes in the atmospheric pressure due to changes in weather, and performs wavelength correction. Further, as an example of a completely different method of correcting the refractive index of air, use of a two-wavelength interferometer as disclosed in JP-A-58-87447 or JP-A-58-169004 has been considered. However, the equipment is complicated and the cost is high, so it has not been commercialized. [0003] Even in a conventional apparatus for stabilizing the temperature of air, variations in measured values due to fluctuations in the refractive index of air cannot be ignored. For example, in the positioning of a stage of a stopper (projection type exposure apparatus) in recent LSI manufacturing, positioning reproducibility is 3σ =
0.08 to 0.15 [mu] m, a considerable part of which is considered to be due to fluctuations in the output of the laser interferometer having a frequency component of 1 Hz to 100 Hz. If the measurement time is sufficiently long and the measured values are averaged, the influence of the fluctuation of the interferometer is reduced, but a problem arises in that it is not possible to cope with high-speed stage positioning or high-speed stage scanning measurement. The present invention solves such a conventional problem,
An object of the present invention is to reduce the fluctuation of the measurement value of the interferometer due to the fluctuation of the refractive index of air by a simple method, and to improve the accuracy of the position measurement of the stage. [0005] In order to solve the above problems, in the present invention, a laser beam (measurement beam and reflected beam) reciprocating to a movable mirror of a laser interferometer is provided at a fixed portion. I decided to blow the wind in the direction. Further, the value of the difference between the measurement values of the beam part on the leeward side and the leeward side of the laser beam is processed to correct the variation of the measurement value due to fluctuation. According to the exposure apparatus of the present invention, the temperature of the laser beam reciprocating with respect to the reflecting mirror is individually controlled, so that the measurement fluctuation of the interferometer can be reduced. Further, in the exposure apparatus of the present invention, since the relationship between the optical system and the wind direction is such that the windward and leeward portions of the laser beam always have the same direction with respect to the wind direction, the fluctuation time of the output of the interferometer Since the change always occurs in the order from the windward side to the leeward side, the time change rate of the measured value is immediately known, and if the wind speed is almost constant, only the fluctuation component of the measured value of the interferometer does not cause a time delay. Can be measured. If the magnitude of the fluctuation component of the measurement value is corrected for the measurement value obtained by the conventional measurement method, the fluctuation can be compensated, and a predetermined pattern can be accurately exposed on a wafer or the like. FIG. 1 is a perspective view of a configuration in which a position detecting device suitable for an exposure apparatus according to an embodiment of the present invention is applied to coordinate measurement of a precision moving stage. A laser light source, about 2 MHz using the Zeeman effect
A light beam 2 containing two components having different polarization characteristics with different frequencies is output. Reference numeral 3 denotes a mirror, and the light beam 2 is divided into an X beam 4X for measuring the x direction of the stage and a Y beam 4Y for measuring the y direction by a beam splitter which cannot be seen in the drawing.
It is led to Y. X interferometer unit 5X measures the amount of movement of X mirror MX in the x direction, and 5Y measures the amount of movement of Y mirror MY in the y direction. ST is an X mirror M orthogonal to each other
A stage on which the X and Y mirrors MY are mounted and moved.
It moves two-dimensionally in parallel with the X and Y directions. A holder WH on which a positioning object such as a wafer is placed on the stage ST.
There is. [0008] FN is a fan, and the wind is X duct DCX
To the Y duct DCY through the filter FL for removing dust. The air outlets of the X duct DCX and the Y duct DCY are arranged so as not to spatially interfere with the movement trajectories of the X mirror MX and the Y mirror MY. A temperature-stabilized, nearly constant velocity wind is sent from above. The air temperature of the wind is preferably matched with the temperature of the air conditioning in the surrounding environment of the device. FIG. 2 is a configuration diagram of the X axis of the laser interferometer, and a front view of the interferometer portion is shown. FIG. 3 shows a top view of the interferometer. FIG. 3 shows the optical path of the laser interferometer. A laser beam B1 emitted from the laser light source 1 is split into two by a polarizing beam splitter 10, and one of the polarized beams passing through the polarizing beam splitter 10 passes through a λ / 4 plate 13 to become a beam B2 for length measurement, and X The light is reflected by the mirror MX and returns. The beam that has passed through the λ / 4 plate in reverse has its polarization state inverted, is reflected by the polarizing beam splitter 10, is reflected by the prism 11, is reflected by the polarizing beam splitter 10, becomes a beam B3, and is again formed by the X mirror MX. Is reflected. The returned beam passes through the polarizing beam splitter 10 and goes to the beam splitter 14. The beam splitter 14 has a prism-shaped reflecting surface for splitting an incident beam into two at the center of the beam diameter, and each of the split beams is a photoelectric detector DX.
1, are separately received by DX2. On the other hand, the other polarization component of the laser beam B1 is reflected by the polarization beam splitter 10 as reference light, is reflected by the prism 12, and then returns to the optical path of the length measurement beam in the polarization beam splitter 10. The light is combined and enters the beam splitter 14. In FIG. 2, a temperature-stabilized wind is sent from the X duct DCX to the path of the length measurement beam at a substantially uniform speed as indicated by an arrow 18. The returned laser beam is divided into two parts by a beam splitter 14 in an upper part and a lower part in the cross section, and is reflected.
1, incident on DX2. The detectors DX1 and DX2 output a beat signal because there is a frequency difference between the reference light and the length measuring light,
This beat signal output is output together with the reference difference frequency signal (about 2 MHz) from the laser light source 1 and the signal processing systems CX1 and CX1.
2, and heterodyne detection is performed. Signal processing system C
A coordinate count output (for example, a resolution of 0.01 μm) is obtained from each of X1 and CX2.
5 to obtain a corrected interferometer output (measured value) 16. The beams B2 and B3 generate the wind 18
The optical system is configured so that the direction of the cross section does not reverse. Even if the temperature of the air to be blown is stabilized, there is a certain degree of temperature unevenness, and an air mass slightly different in temperature from the surroundings moves on the wind. Therefore, when the upper and lower portions of the beams B2 and B3 are measured independently while the X mirror MX is stationary, the lower measured value appears later than the upper measured value. If the X mirror MX is moving, the difference between the upper and lower measurement values, that is, the detectors DX1, DX1,
The difference between the measured values according to No. 2 and the time change value due to air fluctuation is shown. The measurement output from the signal processing system CX1 is x1
(T), the measurement output from the signal processing system CX2 is x2 (t)
And It is assumed that these outputs x1 (t) and x2 (t) are reset so as to be simultaneously zero at a predetermined position (for example, the origin of the stage ST). Here the output x1
The difference Δx (t) between (t) and x2 (t) is represented by equation (A). ## EQU1 ## Assuming that the wind speed is constant, ## EQU2 ## X1 (t), x2
The variation xa (t) in (t) due to the fluctuation of the refractive index of air is represented by the following equation, where k is a proportional constant. ## EQU1 ## k1 is xa (t) when there are no fluctuation factors other than the fluctuation due to the refractive index fluctuation of air.
Is determined to be zero. Equation (C) is expressed by using an appropriate time interval T. It can also be expressed as The value of T may be any value as long as the time at which the wind crosses the laser beam. The constant k2 is determined in the same manner as k1 in equation (C). This equation (D) is expressed as x1 (t) and x2 generated within a certain time T.
It is calculated by integrating the difference of (t) and multiplying by the constant k2. Output x0 (t) finally corrected for fluctuation
Is given by: Or (6) Or (7) It is calculated by one of the following equations. Accordingly, the correction circuit 15 determines the interferometer output 16, that is, the output x0 (t) at each time interval T based on the above equation (D) and any of the equations (E), (F) and (G). If there is a temperature fluctuation or pressure fluctuation of the air, the output of the temperature sensor or the pressure sensor may be input to the correction circuit 15 to correct the wavelength of the laser beam. This can be achieved by conventionally known wavelength correction. When the output of the laser interferometer fluctuates due to the pressure wave of a sound wave, wavelength correction by a sound wave may be performed using a high-speed response pressure sensor or an acoustic transducer 17 such as a microphone. In the above embodiments, an example of two-dimensional coordinate measurement has been described, but the same measurement can be performed in one-dimensional or three-dimensional. Further, the laser light source 1 is not limited to the Zeeman stabilized laser, but may be another type of laser light source such as a ram dip stabilized frequency stabilized laser. In that case, the signal processing of the laser interferometer is different, but the present invention is basically applicable. In the above description of the embodiment, an example has been shown in which, when air is blown across one laser beam, interference is detected separately on the leeward and leeward sides of the beam. The leeward side may be two separate laser beams. That is, independent laser interferometers may be provided at predetermined intervals in the direction in which the wind flows to detect the above x1 (t) and x2 (t). In this case, the original laser light sources can be separated. Specifically, as shown in FIG. 4, two measurement beams (reflected beams) B2u and B2d that are vertically parallel to a reflecting plane (parallel to the yz plane) MXr of the reflecting mirror MX.
Independent laser interferometer 1FM so that light is irradiated
u, 1FMd. The interferometers 1FMu and 1FMd
Independently measure the position and distance of the reflecting mirror MX in the x direction and output the measured values CPu and CPd. Measured value CP
u and CPd are set in advance so as to have the same value when the reflecting mirror MX (stage ST) is at the reference position.
Then, the correction circuit 15 calculates the measured value CP similarly to the previous embodiment.
Interferometer measurement value 1 in which the amount of fluctuation due to the fluctuation of the refractive index of air is corrected (or reduced) based on the input of u and CPd.
6 is output. Also in such a configuration, the temperature-stabilized and substantially constant velocity wind 18 flows from top to bottom, that is, from the measurement beams B2u to B2d, as in the previous embodiment. The measuring beams B2u and B2d
In FIG. 4, a single beam type interferometer having only one interferometer has been described. However, as shown in FIG. 3 of the previous embodiment, one interferometer has two (or more) interferometers. A double beam type having a measuring beam (reflected beam) can also be used. The calculation of the correction circuit 15 is performed at fixed time intervals T, but may be performed each time the stage ST moves by a certain distance. Further, it may be switched so that the correction calculation is performed at regular intervals while the stage ST is moving, and the correction calculation is performed at regular intervals while the stage ST is stopped. In the equation (D) of the operation of the correction circuit 15, the value of the constant k2 may be changed successively according to the position (or moving speed) of the stage ST. This is because the wind speed from the duct changes according to the stage position (speed) and the like. The correction circuit 15 is configured to always correct the fluctuation of the measured value due to the fluctuation of the refractive index of air. However, depending on how the stage ST is moved (in the case of a stepper, a step and repeat method). The correction need not always be made. For example, in an exposure apparatus of the step-and-repeat method, the fluctuation of the output value of the interferometer due to the fluctuation during the exposure of one shot area on the wafer (for 0.2 to 0.5 seconds) is caused by the position of the stage ST. Since the servo system responds, the stage ST may slightly move.
This causes blurring of the exposed pattern and poor resolution. When the exposure is performed by the step-and-repeat method only to prevent the resolution failure, during the stepping movement to the next shot area of the stage ST, the above equation (E),
The correction by (F), (G), etc. is not particularly performed, and a time interval T is between the time when the stepping is completed and the time when the exposure is completed.
It is preferable to perform the correction by the following. Also, when photoelectrically detecting an alignment mark on a wafer with reference to a measurement value (or a time-series count pulse) of a laser interferometer, fluctuations occur in the signal waveform and position of the detected mark. It is preferable that the correction circuit 15 performs the correction operation also at the time of detection. In each of the embodiments of the present invention, only the temperature-stabilized wind is sent from one direction.
As shown in FIG. 9, the wind may flow without stagnation in combination with an exhaust system (exhaust duct) not shown. As described above, according to the present invention, the effect that the refractive index fluctuation of the air in the exposure apparatus can be reduced is obtained, and only the fluctuation component of the laser interferometer can be monitored. The measurement value is corrected using the amount, and a more accurate measurement value that is not affected by the refractive index fluctuation can be obtained. Therefore, it is effective for measuring the position and distance of a precisely movable stage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a configuration of a measuring device according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of an X interferometer of the present embodiment. FIG. 3 is a plan view showing the configuration of the X interferometer of the present embodiment. FIG. 4 is a perspective view showing a configuration of a measuring device according to another embodiment of the present invention. [Description of Signs of Main Parts] 1 ... Laser light source, 15 ... Correction circuit, 18 ...
Wind, DX1, DX2 ... detector, FN ... fan,
FL: filter, ST: stage, DCX,
DCY: Duct, MX, MY: Reflecting mirror

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01B 11/00-11/30 G01B 9/00-9/10 H01L 21/68 H01L 21/30

Claims (1)

(57) [Claims] A movable stage, and measuring means for measuring a position of the movable stage with a light beam irradiated between the movable stage and the fixed portion, and a predetermined pattern is formed on a sensitive substrate mounted on the movable stage. An exposure apparatus that performs exposure, comprising: a gas supply source that generates a gas flow; and a wind guiding unit that guides a gas flow from the gas supply source to a space through which the light beam passes. Equipped with an air outlet to discharge the flow,
The blower port is arranged in a space surrounding the light beam passage space, which does not interfere with the movement trajectory of the movable stage,
An exposure apparatus, wherein the gas flow is directly blown to the light beam from the blowing port. 2. The exposure apparatus according to claim 1, wherein the movable stage moves in parallel with the sensitive substrate. 3. The exposure apparatus according to claim 1, wherein the light beam is a laser beam. 4. The movable stage is provided with a reflection surface on which the light beam is irradiated, and the air outlet is arranged so as not to interfere with a movement locus of the movable stage and the reflection surface. 2. The exposure apparatus according to 1. 5. The measurement means includes a laser interferometer, the laser interferometer includes a laser light source that emits a laser beam as the light beam, and the laser beam is irradiated toward the reflecting mirror, and the laser beam The exposure apparatus according to claim 1, wherein the gas flow is blown from the blowing port. 6. The exposure apparatus according to claim 1, further comprising a dividing unit that divides the light beam into a plurality of parts corresponding to each of a windward part and a leeward part with respect to a gas flow crossing the light beam, A photoelectric detector that separately photoelectrically detects the plurality of light beams divided by the dividing unit,
An exposure apparatus, wherein the position of the stage is measured using the output of the photoelectric detector. 7. 7. The exposure apparatus according to claim 1, wherein the gas supply source generates a gas flow at a constant speed. 8. 2. The gas supply source according to claim 1, wherein the temperature of the gas flow is set substantially equal to an air conditioning temperature in the apparatus.
An exposure apparatus according to any one of claims 1 to 5. 9. The reflecting mirror has two reflecting surfaces orthogonal to each other, and the baffle guides the gas flows to spaces through which the beams respectively applied to the two reflecting surfaces pass. An exposure apparatus according to claim 5. 10. 7. The exposure apparatus according to claim 6, wherein the measurement unit includes a correction unit that corrects an error amount caused by fluctuation of a refractive index in a space through which the light beam passes, using an output of the photoelectric detection unit. apparatus. 11. 11. The exposure apparatus according to claim 10, wherein the correction unit performs the correction every fixed time or every time the stage moves a predetermined distance. 12. 11. The exposure apparatus according to claim 10, wherein the correction unit performs correction each time the stage moves by a predetermined distance during the movement of the stage, and at predetermined time intervals when the stage is stationary. . 13. An exposure apparatus for exposing a predetermined pattern on a sensitive substrate mounted on a stage, comprising: irradiating a reflecting mirror provided on the stage with a measuring beam from a laser light source; Measuring means for measuring the position and distance of the stage by photoelectrically detecting the interference beam, and a space through which at least one of the measurement beam and the reflected beam passes Gas supply means for supplying a gas flow so as to cross the beam, and splitting means for splitting the interference beam into a plurality of parts corresponding to each of the windward and leeward parts of the beam with respect to the gas flow. Wherein the measuring means comprises: a photoelectric detector for separately photoelectrically detecting a plurality of interference beams split by the splitting means; An exposure apparatus for measuring the position and the distance of the stage using the output of the stage. 14． An exposure apparatus for exposing a predetermined pattern on a sensitive substrate mounted on a stage, comprising irradiating a reflecting mirror provided on the stage with a first measurement beam, and using the reflected beam to position the stage. Measuring means for measuring the position and the distance of the stage, irradiating the reflecting mirror with a second measuring beam in parallel with the first measuring beam, and using the reflected beam. (2) a gas for supplying gas so as to cross the beam in a space where the beam passes so that the first measurement beam is located on the leeward side and the second measurement beam is located on the leeward side; An exposure apparatus, comprising: a supply unit. 15. In a measuring method for irradiating a measuring beam to a reflecting mirror provided on an object to be measured and using the reflected beam to measure a position and a distance of the object to be measured, at least the measuring beam and the reflected beam Providing a gas flow across the beam into the space through which one of the beams passes; and corresponding to the windward and leeward portions of the gas flow traversing the beam, respectively, from the reflected beam to a first reflected beam. Forming a second reflected beam; and separately detecting photoelectrically the first reflected beam and the second reflected beam, and measuring a position and a distance of the device under test using an output obtained by the photoelectrically detected light. And a measuring method characterized by including.