JP2004356290A - Exposure apparatus and exposure method - Google Patents

Abstract

An exposure apparatus and an exposure method capable of controlling the flatness of a pattern forming surface of an original (reticle) with high accuracy.
A reticle stage (3) includes a chuck (33) for holding a reticle (original plate) and a reference plane member (43). The flatness of the surface of the reference plane member 33 is prepared in advance. First, using a plurality of sensors for detecting the height of the original plate surface, the flatness of the surface of the reference plane member 33 is measured, and the measurement result is corrected according to the flatness of the reference plane member 33. Calibrate multiple sensors. The exposure is performed while controlling the height of the original surface in accordance with the flatness of the original surface measured by the plurality of calibrated sensors.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure apparatus and an exposure method that use energy rays such as EUV light (Extreme Ultra Violet light, extreme ultraviolet light), ultraviolet laser, and charged particle beam. In particular, the present invention relates to an exposure apparatus and an exposure method capable of controlling the flatness of a pattern-formed original plate with high accuracy.
[0002]
[Prior art]
Description will be made by taking an EUV exposure apparatus as an example.
An EUV exposure apparatus is provided with a reflection reduction projection optical system which usually includes four to eight reflection mirrors. Also, a reflection type is used as an original (reticle) on which a pattern is formed. The illumination light formed in an arc shape is applied obliquely to the reticle. This is because, at the wavelength of EUV light (about 13 nm), there is no effective beam splitter or half mirror, and the only way to change the optical path of illumination light and reflected light is to make the optical axis oblique.
[0003]
When a reflective reticle is used, if the reticle surface is displaced (up, down, tilted) in the optical axis direction (height direction), the pattern projected on the wafer is laterally shifted, and as a result, the magnification of the pattern image is increased. Or the position changes. For this reason, it is necessary to keep the pattern forming surface of the reflective reticle as flat as possible, and it is necessary to control the displacement in the optical axis direction with high accuracy within, for example, several tens of nm.
[0004]
For that purpose, it is necessary to measure the height of the pattern forming surface of the reticle at at least two points. This is because the inclination of the pattern formation surface can be obtained by measuring at two points. Since the length of the exposure area on the reticle is at least 100 mm or more in the longitudinal direction, the height of the pattern formation surface of the reticle is measured using the same sensor (AF sensor) used for measuring the height of the wafer. When measuring the height, a plurality of sensors are required.
[0005]
[Problems to be solved by the invention]
However, when a plurality of sensors are used, a measurement error due to a zero point drift between the sensors becomes a problem.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an exposure apparatus and an exposure method that can control the flatness of a pattern forming surface of an original (reticle) with high accuracy.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, an exposure apparatus of the present invention is an exposure apparatus that transfers a pattern formed on an original onto a sensitive substrate, and a plurality of sensors for detecting the height of the original surface, A reference plane member whose height can be simultaneously detected by the plurality of sensors whose flatness is known in advance.
The height of the reference plane member whose flatness is known in advance is detected by a plurality of sensors, and calibration between the sensors is performed. This makes it possible to calibrate the drift between the sensors that occurs when a plurality of sensors are used. Since the flatness of the original (reticle) is measured by the calibrated sensor, the accuracy of the measurement result is improved.
[0007]
In the present invention, if the reference flat member is integrated with the chuck for holding the original plate, a mechanism for holding the chuck and the reference flat member on the reticle stage can be shared, so that the reticle stage can be reduced in size. And the stroke of the reticle stage can be shortened.
[0008]
In the present invention, a reference mark for detecting a plane position of the pattern image is formed on the reference plane member, and a spatial image of the reference mark is detected at a position where the pattern is projected. If a sensor is provided, the magnification and distortion of the projection optical system can be monitored simultaneously.
[0009]
The exposure method of the present invention is an exposure method for transferring a pattern formed on an original onto a sensitive substrate, wherein the flatness is known in advance using a plurality of sensors for detecting the height of the original surface. The flatness of the reference plane portion is measured, and the measurement result is corrected according to the flatness of the reference plane portion to calibrate the plurality of sensors, and the measurement is performed by the plurality of calibrated sensors. The exposure is performed while controlling the height of the original plate surface in accordance with the flatness of the original plate surface.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, description will be made with reference to the drawings.
First, an example of an EUV exposure apparatus will be described.
FIG. 3 is a view schematically showing a configuration of an EUV exposure apparatus (four-projection system) according to the embodiment of the present invention.
The EUV exposure apparatus includes an illumination system IL including a light source. EUV light (generally, light having a wavelength of 5 to 20 nm, specifically, light having a wavelength of 13.5 nm is used) emitted from the illumination system IL is reflected by the folding mirror 1 and reticle 2 Irradiated.
[0011]
The reticle 2 is held by suction on the reticle stage 3 with the pattern forming surface facing downward in the direction of gravity. The configuration of reticle stage 3 will be described later. The reticle stage 3 has a stroke of 100 mm or more in the scanning direction (Y direction), has a minute stroke in a direction orthogonal to the scanning direction (X direction), and has a minute stroke in the optical axis direction (Z direction). . The position in the XY directions is monitored with high precision by a laser interferometer (not shown), and the position in the Z direction is monitored by a reticle focus sensor including a reticle focus light transmitting system 4 and a reticle focus light receiving system 5.
[0012]
Although only one reticle focus sensor is illustrated in FIG. 3, a plurality (five in this example) of reticle focus sensors are actually arranged. These sensors are arranged such that the spot hits as wide an area as possible within the arc-shaped exposure area.
[0013]
The EUV light reflected by the reticle 2 enters the lower optical barrel 14 in the figure. The EUV light includes information on a circuit pattern drawn on the reticle 2. On the reticle 2, a multilayer film (for example, Mo / Si or Mo / Be) that reflects EUV light is formed, and is patterned with or without an adsorption layer (for example, Ni or Al) on the multilayer film. .
[0014]
The EUV light that has entered the optical lens barrel 14 is reflected by the first mirror 6, then sequentially reflected by the second mirror 7, the third mirror 8, and the fourth mirror 9, and finally becomes perpendicular to the wafer 10. Incident on. The reduction magnification of the projection optical system including these mirrors is, for example, 1/4 or 1/5. In this figure, there are four mirrors. A. It is effective to increase the number of mirrors to six or eight in order to further increase. An off-axis microscope 15 for alignment is arranged near the lens barrel 14.
[0015]
The wafer 10 is mounted on a wafer stage 11. The wafer stage 11 can move in a plane (XY plane) perpendicular to the optical axis, and has a movement stroke of, for example, 300 to 400 mm. The wafer stage 11 can be moved up and down with a small stroke also in the optical axis direction, and the position in the optical axis direction (Z direction position) is monitored by a wafer autofocus sensor composed of a wafer autofocus light transmitting system 12 and a wafer autofocus light receiving system 13. Have been. The position of the wafer stage 11 in the XY directions is monitored with high accuracy by a laser interferometer (not shown). In the exposure operation, the reticle stage 3 and the wafer stage 11 perform synchronous scanning at the same speed ratio as the reduction magnification of the projection optical system, that is, at 4: 1 or 5: 1.
[0016]
Next, the configuration of the reticle stage 3 will be described.
FIG. 1 is a plan view of a reticle stage of the exposure apparatus according to the embodiment of the present invention.
The reticle stage 3 has a holding portion 31 for holding a chuck and a holding portion 41 for holding a reference flat plate. The reference flat plate holder 41 and the chuck holder 31 are arranged side by side in the scanning direction (Y direction).
[0017]
The chuck 33 is supported by the chuck holding unit 31 at three locations by a fixing member 35 such as a leaf spring. The reference plane plate 43 is supported by the fixing member 45 at three positions on the reference plane plate holding portion 41. By holding the chuck 33 and the reference flat plate 43 at three locations, the holding deformation of the chuck 33 and the reference flat plate 43 can be reduced, and reproducibility can be given to the holding deformation.
[0018]
The reference plane plate 43 is made of low-expansion glass or low-expansion ceramic having a small coefficient of linear expansion due to heat. The surface of the reference flat plate 43 has a flatness similar to that of the chuck 33, and a flatness map is prepared in advance. The surface of the plate 43 is coated with a substance that reflects the AF light of the reticle focus sensor. When the reticle focus sensor is of a capacitance type, this coating is not necessary.
[0019]
Next, a method of measuring the pattern surface of the reticle using the reference flat plate 43 will be described.
First, the reticle stage 3 is moved in the Y direction to move the surface of the reference flat plate 43 to the exposure position. In FIG. 1, the hatched hatching on the reference plane plate 43 is the arc-shaped illumination light flux IB. The illumination light beam IB is fixed with respect to the optical axis of the projection optical system of the exposure apparatus, but is scanned in the Y direction on the reticle stage 3 in accordance with the movement of the reticle stage 3 in the Y direction. Five points P shown in the area where the illumination light beam IB is applied indicate the sensing spots of the five reticle focus sensors. As can be seen from FIG. 1, one spot P hits the center in the same area, one spot near both ends, and one spot between the center and both ends.
[0020]
In such a state, the surface of the reference flat plate 43 is measured by each reticle autofocus sensor. The relative position calibration between the sensors is performed with reference to the measurement result and the flatness map of the reference flat plate 43 described above.
[0021]
Next, the reticle stage 3 is moved in the Y direction, and the pattern surface of the reticle 2 is moved to the exposure position. Thereafter, the reticle stage 3 is moved to scan and expose the pattern surface of the reticle 2. During the exposure, the height of the pattern surface of the reticle 2 is measured by the reticle autofocus sensor. The detected value is sent to the control unit, and if necessary, the reticle stage 3 is moved in the Z direction to control the height of the reticle in the Z direction. At this time, as described above, since each sensor has been calibrated and the point drift between the sensors has been calibrated, the position of the reticle in the Z direction can be measured with high accuracy.
[0022]
FIG. 2 is a view for explaining another example of the reference plane plate. FIG. 2 (A) is a plan view, and FIG. 2 (B) is a side view.
The reference plane plate of this example is integrated with the reticle chuck 50. As shown in FIG. 2B, a reticle suction area 51 and a reference plane area 53 are formed in the chuck 50. The chuck 50 is supported by the fixing member 35 at three locations on the chuck holding portion 31 'of the reticle stage 3'.
[0023]
The reticle suction area 51 and the reference plane area 53 are separated by a groove 55. The reticle suction area 51 is provided with, for example, an electrostatic reticle suction mechanism, like a general chuck. The reference plane area 53 has the same degree of flatness as the chuck similarly to the above-described example, and a flatness map is prepared in advance.
The reticle suction area 51 and the reference plane area 53 can be manufactured by processing one member. Further, those separately processed may be integrated by bonding or the like. In this case, it is desirable that both are made of the same material.
[0024]
The reticle chuck and the reference plane plate (reference plane region) need to be supported on the reticle stage while paying attention to holding deformation. For this purpose, the mechanism for holding the chuck and the reference flat plate on the stage becomes complicated, and when the reticle chuck and the reference flat plate are separately arranged on the reticle stage, the distance between the two is determined by the size of such a holding mechanism. Is expected to be wider. However, in this example, since the chuck 51 and the reference plane plate (reference plane area) 53 are supported on the reticle stage 3 ′ by the common holding mechanism (fixing member) 35, the distance between the chuck and the reference plane plate is increased. Can be narrowed. Therefore, the stroke of the reticle stage 3 'can be shortened when measuring the height in the Z direction with the autofocus sensor. For this reason, the space efficiency in the exposure apparatus can be improved.
[0025]
Next, a configuration near a reticle stage of an exposure apparatus according to another embodiment of the present invention will be described. This example shows a case where a plurality of reticle autofocus sensors cannot be arranged in the space below the reticle stage.
FIG. 4 is a diagram showing a configuration near a reticle stage of an exposure apparatus according to another embodiment of the present invention. As reticle stage 3, the reticle stage shown in FIGS. 1 and 2 is used. In the figure, the reticle stage 3 is shown at two places on the left and right, and the position shown by the two-dot chain line on the left is the exposure position, and the position shown by the solid line on the right is the calibration position. If a plurality of reticle autofocus sensors cannot be arranged below the reticle 2 at the left exposure position, the reticle stage 3 is moved from the exposure position in the Y direction (right direction in the drawing) to the calibration position in which the reticle stage 3 is moved in the Z direction. The sensor 61 is arranged. As the sensor 61, an interferometer can be used. Alternatively, an autofocus sensor or a capacitance sensor can be used as the sensor.
[0026]
In this example, first, the reticle stage 3 is moved in the Y direction and positioned at the Z direction measurement position, and the Z direction position of the reference plane area 43 is measured using the sensor 61 as in the above-described example. Calibration is performed. Thereafter, the Z direction position of the pattern forming surface of the reticle 2 is measured using the calibrated sensor 61. Then, at the time of exposure, the displacement of the reticle 2 in the Z direction is controlled using the flatness (flatness profile) of the pattern forming surface of the reticle 2 measured in advance.
[0027]
In this method, it is not necessary to arrange a plurality of Z-direction sensors in a narrow space below the reticle stage 3. Also, when the field slit is arranged close to the lower surface (pattern forming surface) of the reticle 2, it is effective because it is difficult to arrange the oblique incidence autofocus sensor.
[0028]
In the above-described example, the height in the Z direction is measured using the reference plane plate, but the XY position can be measured using the plate to evaluate the magnification and the distortion.
5 and 6 are plan views showing a configuration of a reticle stage of an exposure apparatus according to another embodiment of the present invention.
The reticle stage 3 in FIG. 5 has the same configuration as the reticle stage in FIG. 1, but has a large number of reference marks M on the surface of a reference plane plate 73.
The reticle stage 3 ′ in FIG. 6 has the same configuration as the reticle stage in FIG. 2, but a reticle chuck area 51 and a reference plane area 83 provided with a number of reference marks M are formed on a chuck 80. .
The reference mark M is disposed within a range R as large as possible within a region R corresponding to the shape of the arc-shaped illumination light beam IB of the reference plane plate 73 and the reference plane region 83. In this example, the area R is arranged in two vertical stages from the end in the X direction to the end.
[0029]
These reference marks M are detected by exposure light from an exposure device. For this reason, the surface of the reference plane plate 73 and the reference plane area 83 have the same flatness as the chuck surface and reflect the reference mark M as in the above-described example. In order to reflect the reference mark M, a multilayer film similar to the reticle is formed on the surface of the reference plane plate 73 and the reference plane area 83. Then, an absorbing film is formed on a portion other than the + -shaped portion serving as the reference mark M, and the multilayer film is exposed on the + -shaped reference mark portion. When the exposure light is applied to the reference mark, the exposure light is reflected at the mark.
In this manner, even if a portion having a different film thickness is formed on the reference plane plate or the reference plane region as the reference mark, the spatial resolution of the autofocus sensor used for measuring the height in the Z direction is the line width of the reference mark. The difference in film thickness does not affect the height measurement result in the Z direction.
[0030]
The image of the reference mark M irradiated with the exposure light is detected by the aerial image sensor 17 on the wafer stage 11 (see FIG. 3). The aerial image sensor 17 includes, for example, a slit formed on the wafer stage 11 and a photodetector arranged downstream of the slit 11.
Such a method of evaluating the magnification and distortion of the projection optical system using the reference marks on the reticle is described in, for example, JP-A-8-78313 and JP-A-11-219900. .
[0031]
In this example, by providing the reference marks on the reference plane plate 73 and the reference plane region 83, not only the flatness of the reticle surface but also the change over time of the magnification and distortion of the projection optical system can be monitored.
[0032]
Although a plurality of autofocus sensors are used in the above-described example, an interferometer (for example, a product manufactured by Zygo or the like) that measures a surface shape may be used instead of such a sensor. .
[0033]
【The invention's effect】
As is clear from the above description, according to the present invention, after performing calibration of a plurality of height sensors using the reference plane member, the height of the pattern forming surface of the reticle is measured, so that the accuracy is high. Measurement results can be obtained. Therefore, the height control of the reticle surface at the time of exposure can be performed with high accuracy.
[Brief description of the drawings]
FIG. 1 is a plan view of a reticle stage of an exposure apparatus according to an embodiment of the present invention.
FIGS. 2A and 2B are diagrams illustrating another example of a reference plane plate. FIG. 2A is a plan view and FIG. 2B is a side view.
FIG. 3 is a diagram schematically showing a configuration of an EUV exposure apparatus (four-projection system) according to an embodiment of the present invention.
FIG. 4 is a diagram showing a configuration near a reticle stage of an exposure apparatus according to another embodiment of the present invention.
FIG. 5 is a plan view showing a configuration of a reticle stage of an exposure apparatus according to another embodiment of the present invention.
FIG. 6 is a plan view showing a configuration of a reticle stage of an exposure apparatus according to another embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 1 folding mirror 2 reticle 3 reticle stage 4 reticle focus light transmitting system 5 reticle focus light receiving system 6 first mirror 7 second mirror 8 third mirror 9 fourth mirror 10 wafer 11 wafer stage 12 wafer auto focus light transmission system 13 wafer auto Focus light receiving system 14 Optical barrel 15 Off-axis microscope 17 Spatial image sensor 31 Chuck holding unit 33 Chuck 35 Fixing member 41 Reference plane plate holding unit 43 Reference plane plate 45 Fixing member 50 Chuck 51 Reticle suction area 53 Reference plane area 55 Groove 61 Sensor 73 Reference plane plate 80 Chuck 83 Reference plane area

Claims (4)

An exposure apparatus that transfers a pattern formed on an original onto a sensitive substrate,
A plurality of sensors for detecting the height of the original plate surface,
A reference plane member capable of simultaneously detecting the height with the plurality of sensors whose flatness is known in advance,
An exposure apparatus comprising: 2. The exposure apparatus according to claim 1, wherein the reference flat member is integrated with a chuck for holding the original. Furthermore, a reference mark for detecting a plane position of the pattern image is formed on the reference plane member,
2. The exposure apparatus according to claim 1, wherein a sensor for detecting an aerial image of the reference mark is provided at a position where the pattern is projected. An exposure method for transferring a pattern formed on an original onto a sensitive substrate,
Using a plurality of sensors to detect the height of the original plate surface, measure the flatness of the reference plane portion where the flatness is known in advance,
To the measurement result, perform calibration of the plurality of sensors by adding a correction according to the flatness of the reference plane portion,
An exposure method, wherein exposure is performed while controlling the height of the original plate surface in accordance with the flatness of the original plate surface measured by the plurality of calibrated sensors.

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