JPH09223650A - Aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the influence of a sign error to the actually measured value by obtaining the sign error at the measured vale obtained by a laser interferometer when a moving mirror on a leveling stage is inclined. SOLUTION: The aligner exposes a wafer W mounted on a focus leveling stage 15 with a pattern drawn on a reticle R via a projection lens PL. The aligner comprises an actuator 21 for inclining the stage 15 at a predetermined angle with respect to the optical axis of the lens PL, a moving mirror for mounting the stage 15, a laser interferometer 34 for emitting a laser beam to the mirror to obtain a coordinate value, an alignment sensor 20 for detecting an alignment mark, a main controller 50 for reading the coordinate value of the interferometer 34 in the state that the wafer W is inclined by the actuator while confirming the mark by the sensor 20 to calculate the sign error generated in response to the inclined angle of the wafer W, and a having 35 for regulating the interferometer 34 so as not to generate the sign error.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an apparatus for projecting and exposing a semiconductor circuit pattern, a liquid crystal display element pattern, or the like drawn on a reticle onto a photosensitive substrate (semiconductor wafer or glass plate coated with a resist layer). . In particular, it improves the detection accuracy of a laser interferometer that detects the stage position on which the photosensitive substrate is placed.

[0002]

2. Description of the Related Art A semiconductor integrated circuit or a liquid crystal (hereinafter described as a semiconductor integrated circuit) is manufactured by repeating exposure of a circuit pattern several times to ten or more times. Therefore, the projection exposure apparatus detects the position and rotation in the X and Y directions of the photosensitive substrate (hereinafter described as wafer) or reticle (or circuit pattern) using various alignment sensors during pattern exposure.

Further, when the circuit pattern drawn on the reticle is exposed, the wafer cannot be exposed unless the wafer is moved within the depth of focus of the projection lens. Therefore, the projection exposure apparatus moves the wafer in the optical axis direction of the projection lens and tilts the wafer by a predetermined amount.
Equipped with a leveling stage. Such focus
In addition to the wafer, the leveling stage is provided with a moving mirror that reflects the laser light emitted from the laser interferometer.

Therefore, when bringing the wafer into the depth of focus in accordance with the pattern projection image of the reticle, the focus / leveling stage needs to move the wafer in the optical axis direction of the projection lens and tilt the wafer. Then
The movable mirror on the focus / leveling stage also moves and tilts in the optical axis direction. Therefore, when a laser interferometer mounted on the base measures the XY coordinates in a plane orthogonal to the optical axis of the projection lens, a so-called sine error E occurs in the measured value of the laser interferometer.

When exposing a so-called contact hole in a scanning type projection exposure apparatus, the focus / leveling stage is intentionally tilted to increase the depth of focus, and the reticle and focus / leveling stage are synchronously scanned. In some cases. Also in this case, a so-called sine error E occurs in the measurement value of the laser interferometer.

Further, when the running guide surface of the XY stage has an undulation with respect to the laser interferometer and the XY stage is driven, the movable mirror on the focus / leveling stage may be tilted as so-called rolling or pitching. In such a case as well, a so-called sine error E occurs in the measurement value of the laser interferometer.

[0007]

However, the sine error E
If the exposure of the circuit pattern is repeated with the occurrence of the error, the exposure is repeated without the positioning accuracy being obtained, and it becomes impossible to manufacture a semiconductor integrated circuit with high integration.

[0008]

Therefore, the exposure apparatus of the present invention includes an actuator 21 for inclining the leveling stage 15 at a predetermined angle with respect to the optical axis of the projection lens PL, and a movable mirror 32 mounted on the leveling stage 15. , A laser interferometer 34 for irradiating the movable mirror 32 with laser light to obtain coordinate values, an alignment sensor 20 for detecting an alignment mark, and an actuator while checking the alignment mark with the alignment sensor 20.
The coordinate value is read by the laser interferometer in a tilted state, and the measurement position of the laser interferometer 34 and the main control unit 50 that calculates the sine error E generated according to the tilt angle of the wafer W are set to the optical axis of the projection lens PL. And a herbing glass 35 for adjusting the direction.

Therefore, the sine error is obtained by using the tilt angle θ of this stage and the coordinate value obtained by the laser interferometer, and the measurement position of the laser interferometer is adjusted so that the sine error does not occur due to the herring glass. Therefore, it is possible to obtain coordinates with high positioning accuracy.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION This embodiment will be described below. FIG.
4 shows a step-and-scan (hereinafter referred to as scanning) projection exposure apparatus of the present embodiment. Here, the Z axis is taken parallel to the optical axis of the projection lens PL, the X axis is taken parallel to the paper surface of FIG. 1 in the two-dimensional plane perpendicular to the optical axis, and the Y axis is taken on the paper surface of FIG.

In FIG. 1, the illumination light for exposure from the light source 11 illuminates the slit-shaped illumination area on the pattern forming surface of the reticle R with a uniform illuminance distribution via the condenser lens 12. The pattern in the illumination area on the reticle R is projected and exposed as a slit-shaped image on the wafer W coated with the photoresist via the projection lens PL. The reticle R is held on the reticle stage 13,
The reticle stage 13 is placed on the reticle base 14. The reticle stage 13 is driven on the reticle base 14 in the scanning direction (X direction) by, for example, a linear motor. The X coordinate of the reticle R is measured by the movable mirror 31 and the laser interferometer 33 on the reticle stage 13, and the X coordinate coordinates the main control system 50 for controlling the operation of the entire apparatus.
Is supplied to. Although not shown in the figure, the Y coordinate is also X.
A moving mirror and an interferometer are provided as well as the coordinates. The main control system 50 controls the position and movement speed of the reticle R via the reticle stage drive circuit 41 and the reticle stage 13.

On the other hand, the wafer W is held on the focus / leveling stage 15 via a wafer holder (not shown). Focus / leveling stage 15 is 3
It is mounted on the Y stage 16 via the actuators 21 (two are shown in FIG. 1) that are movable in the Z direction. The displacement of each actuator is measured by the encoder 22 attached to each. Y stage 16 is X
It is placed on the stage 17. The Y stage 16 and the X stage 17 are held by air bearings and placed on the base 18 so as to be moved in the XY directions by, for example, a linear motor.

The focus / leveling stage 1
A movable mirror 32 (32X, 32) for the X and Y axes is provided at the upper end of 5.
Y) is fixed. Laser light from the laser interferometer 34 (34X, 34Y) mounted on the base 18 is irradiated on the moving mirror 32, and the XY coordinates of the wafer W (projection lens PL
(In the plane orthogonal to the optical axis of) is constantly monitored. Moving mirror 32
Between the laser interferometer 34 and the laser interferometer 34, a herbing (transparent parallel plate) 35 is provided. Details of these will be described later.

The main control system 50 controls the operations of the X and Y stages 16 and 17 and the focus / leveling stage 15 via the wafer stage drive circuit 42 based on the supplied coordinates. For example, if the projection lens PL has a projection magnification β
Assuming that the inverted image is projected at (β is, for example, 1/4), the reticle R is scanned through the reticle stage 13 in the + X direction (or −X direction) at the speed VR in synchronization with the illumination area. Thus, the wafer W is scanned in the −X direction (or + X direction) at the speed VW (= β · VR) via the X stage 17.

In the projection exposure apparatus, it is necessary to align the reticle R and the wafer W with high accuracy prior to the exposure of the pattern area. There are roughly three methods for detecting the position of a mark on a wafer. The first method is to take an image of the mark and detect its position by image processing. The second method is to relatively scan a lattice-shaped alignment mark having a periodicity in a direction orthogonal to the measurement direction and a sheet beam of a He-Ne laser, and intensify scattered light or diffracted light generated from the mark. This is a laser beam scanning method that detects the mark position based on the change. The third method is a method called "lattice alignment" which uses a lattice-shaped alignment mark having periodicity in the measurement direction. This method is further subdivided into a homodyne method and a heterodyne method depending on the configuration of the optical system. Also, as the position detection optical system,
There are an off-axis method that uses a dedicated microscope provided separately from the projection lens, and a TTL (Through The Lens) method that uses the projection lens as a position detection optical system. In this embodiment, a TTL position detection optical system (alignment sensor) 20 is shown in FIG. The alignment signal obtained by the alignment 20 is supplied to the main control system 50.

A multipoint focal position detection system (hereinafter, referred to as a focal position) for detecting the position (focal position) of the surface of the wafer W in the Z direction.
The configuration of 19 (19S, 19R) referred to as "AF sensor" will be described. In the multipoint AF sensor 19, the photoresist is irradiated with non-photosensitive detection light from the light source 19S. The detection light is projected onto the field on the wafer W obliquely with respect to the optical axis of the projection lens PL. Reflected light from these measurement points is condensed by the light receiving portion 19R to form an image. The reflected light that has formed an image is photoelectrically converted by a large number of photoelectric conversion elements, and then these photoelectric conversion signals are subjected to signal processing. The AF sensor thereby obtains the focus position of the wafer W and the tilt of the wafer W, and the focus position of the wafer W and the tilt of the wafer W are supplied to the main controller 50.

FIG. 2 is a perspective view showing the control around the focus / leveling stage 15 of this embodiment. In FIG. 2, movable mirrors 32X and 32Y for X and Y axes are fixed to the upper surface of the focus / leveling stage 15. The moving mirror 32X is irradiated with the laser light from the laser interferometer 34X, and the X coordinate of the wafer W is constantly monitored. A harbing 35X is attached between the movable mirror 32X and the laser interferometer 34X to bend the optical path of the laser light. Further, the Y coordinate of the wafer W is constantly monitored by the movable mirror 32Y for Y axis and the laser interferometer 34Y. Similar to the X-axis, the moving mirror 32Y and the laser interferometer 34
Harbing 35Y is attached between Y and Y.
The X and Y coordinates detected by these are the main control system 5
0 is supplied.

In FIG. 2, one X-axis laser interferometer 34X and one Y-axis laser interferometer 34Y are shown, but a laser interferometer is further used to measure yawing. One for each (not shown). The actuator 21 is configured using a method using a rotary motor and a cam, or a laminated piezoelectric element (piezo element) or the like. When a linearly displacing drive element is used as the actuator 21, a linear encoder 22 of an optical type or a capacitance type is arranged near the actuator 21 as an encoder for detecting the position in the Z direction. . The values in the Z direction obtained from the linear encoders 22 having three fulcrums are supplied to the main control system 50. In the main control system 50, the Z-direction position of the wafer W, the tilt angle around the X-axis, and the Y-direction are calculated from the Z-direction values of the three fulcrums.
Find the tilt angle around the axis. Then, the main control system 50 sends a control signal to the wafer stage drive circuit 42 based on the information on the focus position of the AF sensor, the position of the wafer W in the Z direction, and the tilt angle. Wafer stage drive circuit 42
Then, the Z-direction position (focus position) of the focus / leveling stage 15 is adjusted by uniformly expanding and contracting the three actuators 21, and the expansion and contraction amounts of the three actuators 21 are individually adjusted. The tilt angle of the focus / leveling stage 15 around the X and Y axes is adjusted.

Next, the difference H between the image plane A of the projection lens PL and the measurement position B of the laser interferometer in the above-mentioned scanning projection exposure apparatus will be described with reference to FIG. In FIG. 3A, only the scanning direction (X direction) will be described. Focus / leveling stage 1 so that the wafer W comes to the imaging position A obtained by the AF sensor 19.
3 actuators 5 are provided on the Y-axis stage
Moved by 1. At this time, the focus / leveling stage 15 is tilted at an angle θ (around the Y axis), and the movable mirror 32X is also tilted at an angle (90 ° −θ). On the other hand, the laser light of the laser interferometer 34X is applied to the measurement position B of the movable mirror 32X. Therefore, the imaging position A and the measurement position B
And the difference in the Z direction is H. In such a case, the sine error E will appear on the X coordinate obtained by the laser interferometer 34X. The sign error E is E = H * sin θ≈H * θ (1).

Next, the measurement of the sine error E caused by the difference H between the image plane A of the projection lens PL and the measurement position B of the laser interferometer will be described (see FIG. 5). First, AF
The image forming position is obtained by the sensor 19, and the leveling stage 15
Is horizontally moved to a plane orthogonal to the optical axis of the projection lens PL, and the wafer W is aligned with the image forming position. Then, the X stage 17 and the Y stage 16 are moved to hold the wafer W so that the alignment mark formed on the wafer W can be measured by the TTL alignment sensor 20. In this state, while keeping the alignment mark at the image forming position A of the projection lens PL, the focus / leveling stage 15
Is rotated stepwise from the tilt (−θ0) to the tilt (+ θ0) by the actuator 21. The deviation of the X coordinate obtained by the laser interferometer 34 when rotated is Xif.
Further, the deviation obtained by the TTL alignment sensor 20 when the focus / leveling stage 15 is tilted is Xalg. The focus / leveling stage 15 is rotated within a range in which the focus / leveling stage 15 is tilted (predetermined rotation angle Θ), and deviations Xif and Xalg at various tilt angles θ are obtained. Therefore, the main control unit 50 can obtain the measured sine error E of the laser interferometer that occurs according to the tilt angle of the focus / leveling stage 15 using Equation 2.

E = Xalg-Xif (2) Then, the main control unit 5 calculates the sine error E at each inclination angle θ.
Stored in memory within 0. Although the alignment mark on the wafer W is detected by the TTL alignment sensor 20, the fiducial mark FM on the focus / leveling stage 15 may be detected by the TTL alignment sensor 20. Further, the deviation Xalg may always be 0.

Although the TTL alignment sensor 20 is used to obtain the actually measured sign error E of the laser interferometer 34X, an off-axis type alignment sensor may be used. Further, the position detecting method includes the above-described first method (capturing an image of a mark and performing image processing), the second method.
Method (a laser beam scanning method in which a lattice-shaped alignment mark and a laser sheet beam are relatively scanned), and a third method (lattice alignment). Here, the relationship between the tilt amount θ of the focus / leveling stage 15 and the measured sine error E is shown in FIG.
Shown in As shown in FIG. 4, the inclination amount θ and the sine error E have a proportional relationship. However, when the running guide surface of the XY stage has a waviness ψ with respect to the laser interferometer, the sine error E is E = H (θ + ψ) (3). Since the waviness ψ of the stage guide surface changes depending on the positions of the XY stages 16 and 17, even if the inclination θ of the leveling stage 15 with respect to the XY stage is 0, the moving mirror 32 for the laser beam of the laser interferometer 34 is used. The slope of changes. That is, the projection lens P
The difference H between the image plane A of L and the measurement position B of the laser interferometer 34
Is not 0, it becomes a factor of deteriorating the lattice property of the array of exposure shots. Here, since the undulation ψ is constant in a state where the XY stages 16 and 17 are stopped at specific positions (both the XY axes), the difference H between the image plane A and the measurement position B is as shown in FIG. As shown in 3), it is obtained as a proportional coefficient between the tilt amount θ of the focus / leveling stage 15 and the sine error E. Therefore, the harving 35 may be rotationally adjusted so that the difference H becomes zero. This state is shown in FIG.

Actually, not only does the movable mirror 32 tilt due to the driving of the focus / leveling stage 15 to cause a sine error E, but also the optical path of the laser interferometer 34 tilts as the movable mirror 32 tilts. Will end up.
Therefore, the relationship between the tilt angle θ of the focus / leveling stage 15 and the sine error E shown in FIG. 4 is not a perfect straight line, but is almost parabolic as shown in a plural-point plot. Since this error component is proportional to the square of the angle θ, it cannot be removed by adjusting the position of the laser interferometer 34. Including this component, the error E ′ of the laser interferometer 34 can be expressed as follows. E ′ = A * θ * θ + B * θ + E ………… (4) Here, these are variables given by the optical path length of the laser interferometer 34 and the mounting error of the movable mirror 32, and these can be separately measured in advance, so this error can be corrected at the stage position during exposure.

When the waviness ψ of the stage is added,
Although the above correction includes an error, its influence is minor compared with the dominant sign error E in the error E ′. In the embodiment described above, the sign error E in the leveling stage 15 for the wafer W has been described, but it goes without saying that it may be applied to the reticle stage 13. Further, the scanning type projection exposure apparatus has been described, but the same can be applied to any apparatus as long as the movable mirror is mounted on the leveling stage and the movable mirror is also inclined according to the inclination of the leveling stage.

[0025]

As described above, according to the present invention, the sign error E caused by the difference H between the measurement position of the laser interferometer and the image plane position of the projection optical system is used by using the position detection optical system. Can be obtained by inclining. Further, since a parallel plate can be inserted between the laser interferometer and the movable mirror to adjust the measurement position of the interferometer to the image plane of the projection lens, the coordinate value obtained by the laser interferometer does not include the sign error E. You can

This is because the scanning projection exposure apparatus tilts the projected area (illumination slit area; narrower than the shot area) of the reticle R in the scanning direction (X-axis direction) and scans the shot area to obtain the depth of focus. In the case of obtaining a contact hole that is 2 or 3 times larger, the coordinates obtained by the laser interferometer will be highly accurate even if the guide surfaces of the X and Y stages have undulations.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a scanning projection exposure apparatus of this embodiment.

FIG. 2 is a diagram showing a configuration around a focus / leveling stage for a wafer W.

FIG. 3A shows that a difference H (Z direction) occurs between the measurement position B of the laser interferometer and the image formation position A of the projection lens due to the tilt of the focus / leveling stage. It is a figure. FIG. 3B shows the difference H (Z direction).
It is the figure which correct | amended by the parallel plate (harving).

FIG. 4 is a graph showing a relationship between a tilt angle θ of a focus / leveling stage and a sine error E.

FIG. 5 is a graph showing a relationship between a tilt angle θ of a focus / leveling stage and a sine error E.

[Explanation of symbols]

Reticle …… R wafer
…… W Reticle stage …… 13 Projection lens …… PL Leveling stage …… 15 Y stage …… 16 Actuator …… 21 Encoder …… 22 Reticle interferometer mirror …… 31 Reticle interferometer …… 33 Wafer interferometer Mirror ・ ・ ・ 32 Wafer interferometer ・ ・ ・ 34 Harbing (parallel plate) ・ ・ ・ 35 Servo motor ・ ・ ・ 36

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 21/30 526B

Claims (4)

[Claims] 1. A projection exposure apparatus that exposes a pattern drawn on a mask onto a photosensitive substrate mounted on a substrate table via a projection optical system, wherein the substrate table is predetermined with respect to an optical axis of the projection optical system. An actuator that tilts at an angle, a movable mirror mounted on the substrate table, an interferometer that obtains coordinate values by irradiating the movable mirror with laser light, a position detection optical system that detects the position of the photosensitive substrate, and While confirming the position of the photosensitive substrate with the position detection optical system,
The coordinate value is read by the interferometer in a state where the photosensitive substrate is tilted by the actuator, and calculation means for calculating a sine error generated according to the tilt angle of the photosensitive substrate; An exposure apparatus comprising: an adjusting unit that adjusts in an axial direction. 2. The exposure apparatus according to claim 1, further comprising a focus detection optical system that obtains an image formation position where the pattern is formed by the projection optical system, and the actuator fixes the photosensitive substrate. The position detection optical system detects the position of the photosensitive substrate in a state of being moved to the image position. 3. A method of calculating a sine error that occurs according to an inclination angle of a photosensitive substrate mounted on a substrate stage includes the following steps. The substrate stage equipped with a movable mirror is moved to the image forming position of the projection optical system, and the substrate stage is tilted at a predetermined angle while detecting the position of the photosensitive substrate, and the movable mirror is irradiated with laser light each time. Then, the coordinate value in the plane orthogonal to the optical axis of the projection optical system is obtained, and the sine error for each of the predetermined angles is detected. 4. The method of calculating the sine error according to claim 1 includes the step of first detecting an imaging position of the projection optical system.