JPH05129184A - Projection aligner - Google Patents

Abstract

PURPOSE:To eliminate influence of fluctuation, temperature uneven distribution of the air around a wafer stage by employing a lattice interference distance measuring instrument for measuring the position of the stage. CONSTITUTION:A linear motor is used as a driving mechanism, and a static pressure air bearing is used as a guiding mechanism to constitute an X-Y stage. Heads 24a-24d of a lattice interference distance measuring instrument are provided at both ends of X and Y guides 22, 23, and diffraction gratings 30a-30d of the instrument are mounted at a member (barrel base) 31 integral with a barrel 32. Coordinates of the position of a wafer stage 25 are measured. Thus, the position of the stage can be accurately measured without influences of environmental conditions such as fluctuation, temperature uneven distribution of the air around the stage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus used in semiconductor manufacturing, and more particularly to a projection exposure apparatus using a grating interferometer for measuring the position of a stage used in the apparatus.

[0002]

2. Description of the Related Art With the recent increase in the degree of integration of semiconductor integrated circuits (LSIs), reduction projection type exposure apparatuses used in the manufacture of LSIs, so-called steppers, have increasingly higher resolution, higher precision alignment, and higher throughput. Performances such as are required. Among the demands for higher performance of such steppers, the stage part is required for alignment accuracy and
It is an important component related to puts.

As a configuration of the stage portion, for example, one described in "Mechanical Design" August 1990, "Recent Positioning Technology and Sensors" and the like is known. The stage has an XY stage and a Z stage formed on a base, and a movable mirror for a laser interferometer is arranged on the Z stage. Further, an inclination correction mechanism and a θ stage used for rotation correction for position adjustment are arranged, and a wafer holder is mounted on the θ stage to vacuum suction the wafer.

In the case of a stepper, since alignment between the reticle and the wafer is important, a laser interferometer is usually used. The reference position of the interferometer is formed by supporting and fixing a fixed mirror with a member lowered from the lens barrel of the projection lens. The position of the stage is measured as a position coordinate by a known laser interferometer by the interference of the laser light reflected from the fixed mirror and the moving mirror on the Z stage.

For the XY stage, a system is known in which a ball screw drive by a DC motor is used as a drive mechanism, and a VF guide is used as a guide mechanism and a needle bearing is used as a sliding surface. In addition, “OMRON TECHNICS” No. 76
(1985), a linear motor is used for a drive mechanism and a static pressure air bearing is used for a guide mechanism, and an XY stage has recently become conspicuous.

FIG. 7 shows an example of the structure of a static pressure type XY stage. Reference numerals 71a to 71d are linear motor coils and a yaw guide, and a static pressure air bearing is used for this guide. 7
0a to 70d are linear motor yokes, each of which
The square is connected to a guide for moving the central wafer stage 74 in the XY directions. The 70a and 70c linear motor yokes are connected to the guide 72 for moving in the Y direction, and
The yokes 70b and 70d are connected to a guide 73 which moves in the X direction. Hydrostatic air bearings are also used for the 72 and 73 guides.

Reference numeral 74 is a wafer stage, and 75 is a wafer holder for holding a wafer. On the wafer stage 74, mirrors 76 and 77 for measuring the XY coordinates of the position of the wafer stage 74 using the above-mentioned laser interferometer are attached. Reference numerals 78 and 79 denote fixed mirrors which are supported by a member lowered from the above-mentioned projection lens. The X coordinate of the position of the wafer stage 74 is measured by a method such as heterodyne by two laser beams reflected from the moving mirror 76 and the fixed mirror 79, and the Y coordinate is also measured from the mirror 77 and the fixed mirror 78. Similar measurements are performed using laser light.

[0008]

However, since the laser interferometer is used to measure the position of the stage in the above-mentioned conventional example, a server that stores the entire device including the stage is stored.
Measurement errors occur due to environmental changes in the round chamber.

In general, environmental fluctuations such as temperature, humidity, atmospheric pressure and carbon dioxide gas concentration cause the refractive index of air to change the wavelength in the air of the laser. Therefore, temperature unevenness and air fluctuations generated in the optical path of the interferometer in the chamber change the refractive index of the air, but it is difficult to monitor because it is not a uniform change, which adversely affects the measurement results of the laser interferometer. ..

Particularly around the stage, since the stage itself moves to the next position each time the exposure is completed and the air is stirred, fluctuations are likely to occur. Further, the heat generated by the driving mechanism used for driving the stage is also under severe conditions such that the temperature distribution may be uneven.

For example, the inside of the chamber is ± 0.1. Even if the temperature is controlled to C and the temperature fluctuation and the air fluctuation are considerably suppressed, an error of about 0.01 to 0.04 μm occurs in the measurement. The detrimental factors are, on the one hand, essential to the operation of the machine and cannot be completely eliminated.

For these error factors, improvement methods such as making the optical path of the interferometer a vacuum or setting an atmosphere of He gas whose refractive index fluctuation is smaller than that of air can be considered. Is difficult to hire. Although an interferometer that is not easily affected by the local refractive index fluctuation as described above has been developed, there is a problem that the device becomes complicated.

On the other hand, in the conventional apparatus using the laser interferometer, the absolute reference of the stage position is the fixed mirror fixed to the member lowered from the lens barrel of the projection lens. Therefore, the relationship between the lens barrel and the stage is indirect, and vibration,
The position of the fixed mirror, which should have been fixed against external factors such as heat, may fluctuate slightly. As a result, there is a problem that the positions of the lens barrel and the stage cannot be matched.

[0014]

SUMMARY OF THE INVENTION The present invention uses a linear motor as a driving mechanism as in the above-mentioned conventional example and a grid for measuring the position of a wafer stage in an XY stage using a static pressure air bearing as a guide mechanism. By using an interferometer, it is possible to prevent the fluctuation of air around the stage and temperature unevenness from being affected at all. Therefore, in the present invention, the heads of one or a plurality of grating interferometers are provided at both ends of each of the XY guides, and the diffraction grating of the grating interferometers is formed in a structure integrated with the lens barrel at a position facing each other. It is characterized by being attached to a member and measuring the position coordinates of the wafer stage. The position coordinates are converted into corresponding one-dimensional coordinates by the grating interference length measuring device attached in the X and Y directions. Further, the head and the diffraction grating of this grating interferometer may be mounted on the member integrally formed with the lens barrel and the movable part of the linear motor in reverse relationship. In this way, the position with respect to the lens barrel can always be strictly monitored even with respect to factors such as the lens barrel and vibrations around the lens barrel, temperature distribution fluctuations, and the like, so that more precise measurement can be performed.

[0015]

1 and 2 show Embodiment 1 of the present invention. FIG. 1 is an observation of the stage of a stepper from the direction of the projection lens, and shows a stage of a known structure using a movable yoke type linear motor as a drive mechanism and a static pressure air bearing as a guide mechanism. ing. Reference numeral 20 in the drawing denotes a base, ie, a stage base, which serves as a reference surface when the central wafer stage 25 moves via the static pressure air bearing. 21a-2
1d is a linear motor coil and a yaw guide, and 21a and 2
1c corresponds to the X direction, and 21b and 21d correspond to the Y direction. Reference numerals 27a to 27d denote linear motor yokes, which serve to move the wafer stage 25 by obtaining thrust with the linear motor coil. 27a and 27c are in the X direction, 27
Reference numerals b and 27d denote linear motor yokes in the Y direction, which are connected to guides 22 and 23 for moving the central wafer stage 25 in the X and Y directions. As shown in the figure, the X guide 23 is a linear motor yoke of 27b and 27d, and the Y guide 22 is a linear motor yoke of 27a and 27c.
It is connected to the network. A wafer holder 26 is mounted on the wafer stage 25.

Reference numerals 24a to 24d are the heads of the grating interferometers mounted on the respective linear motor yokes, which form the basis of the present invention. The position coordinates of the wafer stage 25 are replaced with the one-dimensional coordinates of the linear motor yokes 27a to 27d, and the values measured by the respective grating interference length measuring devices correspond to the X and Y coordinates. Heads 24a and 24c are X
Directional position coordinate measurement, and the heads 24b and 24d perform Y-direction position coordinate measurement.

FIG. 2 is a view of the configuration of the projection lens unit facing the wafer stage of FIG. 1 as observed from the stage direction. In the figure, 33 is the final surface of the projection lens, and 32 is the lens barrel in which the projection lens is housed. Reference numeral 31 is a member formed integrally with the lens barrel 32, which serves as a reference on the lens barrel side, and will be referred to as a lens barrel base here. Reference numerals 30a to 30d denote diffraction gratings of the grating interferometer, which are attached to the lens barrel base 31. Diffraction gratings are formed in the Y direction on 30a and 30c. Reference numeral 30a indicates the head 2 of the above-mentioned grating interferometer.
4a and the diffraction grating 30c face the head 24c, and the coordinates of the wafer stage 25 in the X direction are measured from the measured values of both. Similarly, diffraction gratings are formed in the X direction on 30b and 30d. The diffraction grating 30b faces the head 24b and the diffraction grating 30d faces the head 24d, and the Y coordinate of the wafer stage 25 is measured from the measured values of both. To be done.

The operation of measuring the position of the wafer stage 25 in this embodiment will be described with reference to FIG. FIG. 3 shows a coordinate system showing the movable range of the wafer stage, and the circled portion in the drawing is the center position of the wafer stage.
Here, the wafer stage changes from coordinates (X1, Y1) to (X
2, Y2). First (X1, Y
When there is a stage in 1), the coordinate values produced from each grating interferometer are (X1,0), (X1, L),
(0, Y1) and (L, Y1). Here, the coordinate origin is at the lower left as shown, and L is the wafer stage 25.
Is the value of the maximum movable position of. In the movement from the coordinates (X1, Y1) to (X2, Y2), the movement to (X2, Y1) is first performed. At this time, the wafer stage is not always located at the center of the Y guide. Therefore, from X1 to X
X-direction linear motors 21a, 27 for moving to 2
The thrusts of a and the linear motors 21c and 27c are proportionally distributed in consideration of the moment from the readings by the grating interferometers 24b, 30b and 24d, 30d. The wafer stage 25 starts to move without receiving the force of an extra rotational component due to the proportionally distributed thrust, and the head 24a, the diffraction grating 30a and the head 2 which are a pair of grating interferometers for measuring the position in the X direction.
4c, the movement is performed until the coordinate value calculated from the diffraction grating 30c reaches a predetermined value X2. The two linear motors 21a, 27a and 21c, 27c are separate filters.
Independent control is performed by the buckle loop.

Next, the wafer stage 25 is set to (X2, Y
The operation moves from 1) to (X2, Y2). Also in this case, the thrusts of the linear motors 21b and 27b and the linear motors 21d and 27d in the Y direction are determined by the grating interferometers 24a and 30.
From the readings of a, 24c, and 30c, proportional distribution is performed considering the moment. The wafer stage 25 starts to move by the proportionally distributed thrust without receiving the force of an excessive rotation component, and is a pair of grating interferometers for measuring the position in the Y direction. The head 24b, the diffraction grating 30b and the head 24d. , Until the coordinate value calculated from the diffraction grating 30d reaches a predetermined value Y2. Two linear motors 21b and 27
b and 21d and 27d are independently controlled by separate feedback loops. By independently controlling XY in this way, the wafer stage can be moved from coordinates (X1, Y1) to (X2, Y2) with easy control.

In this embodiment, since the grating interferometer is closely placed, it is not affected by the fluctuation of the air and the change of the refractive index of the air due to the temperature unevenness as in the prior art, and the reference position is the mirror. Since it is attached directly to the cylinder base, the error factor can be made extremely small. Also, if the wafer stage is moved independently of XY, stable control can be performed without being affected by an extra rotation component by a simple calculation.

FIG. 4 and FIG. 5 show the second embodiment of the present invention.
2 is an example in which the grating interferometer length measuring device according to the first embodiment is downsized. In the figure, the same members as those in the previous embodiment are designated by the same reference numerals. In the case of the first embodiment, one problem is that the diffraction grating becomes long when the length measuring range is large, but in the present embodiment, a plurality of heads are provided to achieve compactness.

FIG. 4 shows an XY stage configuration, and FIG. 5 shows FIG.
3 is a view of the projection lens facing the stage of FIG. 1 viewed from the stage side. The difference from the first embodiment on the stage side is that the heads 40a to 40h of the grating interferometers attached to the linear motor yokes 27a to 27d have a pair configuration. Further, 30a 'to 30d' on the side of the projection lens represent diffraction gratings of the grating interferometer.

When the wafer stage 25 moves, 40
The heads of a, 40b, 40e, and 40f cooperate with the opposing diffraction gratings 30a 'and 30c' to measure the coordinates in the X direction, and similarly, the heads 40c, 40d, and heads 40g, 4g.
0h measures the coordinate in the Y direction. The correspondence between the diffraction grating and the head is 40a and 40b for 30a 'and 40c for 30b'.
And 40d, 30c 'is 40e and 40f, 30d' is 40
g and 40h. Here, the diffraction gratings 30a'-3
The feature of this embodiment is that 0d 'is shorter than the diffraction gratings 30a to 30d in FIG. 2, which is a result of the heads facing the diffraction gratings being provided at two places.

FIG. 6 is an explanatory view showing the relative relationship between the diffraction grating and the head in the present embodiment. As a representative, the diffraction grating 30 is shown.
a ', heads 40a, 40b, linear motor yoke 27
The state which observed a from the -Y direction is shown. The wafer stage 25 is now at the position where the linear mode at that time is.
The positions of the yoke 27a and the diffraction grating 30a 'are shown in FIG. 6 (A).
It looks like this. It is the head 40a that measures the position of the wafer stage 25 in this state.

From the state of FIG. 6A, the wafer stage 25
6 shows the state of moving in the −X direction.
(B). As the wafer stage 25 moves, the linear motor yoke 27a moves, and both the heads 40a and 40b are covered with the diffraction grating 30a '. The coordinate measurement in this state is performed by the head 40a. Further, the wafer stage 25 moves in the -X direction, and the linear motor yoke 2
FIG. 6C shows a state in which 7a has moved. It is the head 40b, which in turn faces the diffraction grating 30a 'for measurement.

The measurement head is switched from the head 40a to the head 40b automatically. The switching is such that when the signal pulse from the head 40a reaches a predetermined count number, the inactive head 40b, which previously measured the signal pulse for a short period of time, is automatically activated to become a coordinate measuring head. Can be easily achieved with.

When two heads are provided in the structure of the grating interferometer as in the second embodiment, the length of the diffraction grating can be reduced to about 1/2 of that in the first embodiment, and a compact length measuring system is provided. Is realized.

Contrary to this embodiment, when the head is fixed and the diffraction grating is movable, that is, the linear motor yoke 27a.
The same applies to the case where a diffraction grating is attached to d and a head is attached to the lens barrel base 31. Since the diffraction grating must always be present facing the head position, when there is only one head, the movable range at both ends is large and a long diffraction grating is required.
If a plurality of heads are used as in the second embodiment, the effect of downsizing is great. Further, although two heads are provided for one diffraction grating in this embodiment, a larger number of heads are provided,
You may interlock them.

Also in the case of this embodiment, since the grating interferometer is closely placed, it is not affected by the fluctuation of the air and the change of the refractive index of the air caused by the temperature unevenness as in the conventional example.
Further, since the reference position is directly attached to the lens barrel base, the error factor can be reduced.

[0030]

As described above, in the projection exposure apparatus of the present invention, a pair of diffraction gratings constituting a grating interferometer and one or a plurality of heads are driven by a stage like a linear motor. By attaching the movable part of the mechanism and the member integrally formed with the lens barrel, which is the reference position of the apparatus main body, corresponding to each other, the position of the stage can be adjusted to prevent fluctuations of air around the stage. This enables accurate measurement without being affected by environmental conditions such as temperature unevenness.
In addition, with respect to factors such as the temperature distribution of the lens barrel and the vicinity of the lens barrel, the reference of the length measuring device is integrated with the lens barrel, so the positional relationship is clear, and more accurate measurement than the conventional example is possible. It became possible to do it.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an XY stage according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a lens barrel portion according to the first embodiment of the present invention.

FIG. 3 is an explanatory view of position coordinates of a wafer stage according to the present invention.

FIG. 4 is a diagram showing a configuration of an XY stage according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a lens barrel portion according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the operation principle of a plurality of grating interferometer length measuring heads.

FIG. 7 is a diagram showing a configuration of an XY stage of a conventional example.

[Explanation of symbols]

 21,71 Linear motor coil and yaw guide 22,72 Y guide 23,73 X guide 24,40 Lattice interferometer length head 25,74 Wafer stage 26,75 Wafer holder 27,70 Linear motor yoke 30 Lattice Diffraction grating of interferometer length 31 lens barrel base 32 final surface of projection lens 33 lens barrel of projection lens 76,77 laser interferometer mirror 78,79 fixed mirror

Claims (1)

[Claims] 1. A projection exposure apparatus equipped with a stage movable in the XY directions, wherein a drive mechanism section for the stage and a fixed section integrally formed with a reference member of the main body of the projection exposure apparatus. The diffraction grating constituting the grating interferometer is attached to one of the two, and one or a plurality of heads of the grating interferometer are attached to the opposing portions of the other, and
A projection exposure apparatus characterized by measuring the position of the edge.