JPH01161832A - Projection aligner - Google Patents

Abstract

PURPOSE:To reduce to the minimum both the defocusing in a mark detection optical system and the decrease of alignment accuracy due to a leveling operation by a method wherein an auto-focus or a auto-leveling mechanism is additionally provided to an off-axis type mark detector. CONSTITUTION:A wafer alignment system WGA is arranged at the position separated by maintaining the prescribed interval from the optical axis AX1 of a projection lens PL. Then, the wafer to be subjected to a superposition exposure is shifted to the point located under the alignment system WGA, and a mark detecting operation is conducted. When the mark is detected, the main control system 42 is switched so that the signals Fsg2 and Lsg2 will be selected by a selector circuit 40. Accordingly, the main control system 42 responds the selected signal Fsg2 and servo-controls a motor 14, and the height of a Z-stage ZS is adjusted so that the surface of the local region containing the wafer W mark will be optically coincided with the best image formed plane of an objective lens 28. At the same time, driving sources 10a and 10b are servo-controlled in response to the selected signal Lsg2, and the inclination of a stage LS is adjusted in such a manner that the best image formed plane of the equivalent projection lens PL and the surface of the local region containing the wafer mark are optically paralleled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a step-and-repeat projection exposure apparatus for manufacturing semiconductor IC1 liquid crystal displays, photomasks, and the like.

[Conventional technology]

Conventionally, in this type of apparatus, an autofocus mechanism that detects focus based on position (exposure position) and controls the Z position (vertical position) of the projection optical system in the optical axis direction has been essential for wafer printing. In recent years, the depth of focus has become shallower due to the higher resolution of projection lenses, and problems have arisen in which unevenness and inclination of the wafer surface cause a decrease in resolution and line width uniformity within the exposure area. For this reason, a mechanism (generally referred to as autoleveling) has been proposed that detects and controls the horizontal position of the wafer for each exposure position. For example, as a horizontal position detection device, as disclosed in Japanese Patent Laid-Open No. 58-113706, there is a device that combines an oblique-incidence type collimator-type leveling detection system and an oblique-incidence type focus detection system. Are known.

Incidentally, in recent years, there has been a trend to shorten the wavelength of the exposure light source to achieve high resolution in order to manufacture more highly integrated ICs.For example, as a light source, a KrF excimer laser (wavelength λ=248. 5n,) is considered to be used. In the case of a projection exposure apparatus using this KrF excimer laser, TTL (Through
Since there is no suitable light source close to this wavelength, it is actually difficult to realize an alignment optical system that corrects chromatic aberration. Furthermore, even if alignment is performed using excimer laser light itself, the resist is exposed, and the excimer laser itself is a pulsed light source, which causes problems with accuracy due to large variations in output from pulse to pulse. There are many things that need to be done.

For this reason, in a projection exposure apparatus using a DVV (far ultraviolet) light source, an off-Axis system using a microscope, which is placed at a certain distance from the projection lens and exclusively detects alignment marks on the wafer, is used. Type alignment is valid.

This is because with an off-Axis type wafer mark detection optical system, there are almost no restrictions regarding the exposure wavelength or detection method, and highly reproducible alignment can be expected.

[Problem that the invention seeks to solve]

However, in a projection exposure apparatus equipped with a conventional off-axis type alignment device, autofocus and autoleveling are performed only at the exposure position (the viewing area of the projection lens), so the wafer surface The unevenness may cause the 0ff-Axis type wafer mark detection optical system to go out of focus, and after detecting the position of the alignment mark on the wafer, each exposure area (local shot area) on the wafer is moved to the exposure position. However, since exposure is performed by performing auto-leveling, there is a problem in that positioning accuracy deteriorates due to horizontal positional deviation accompanying the leveling operation.

The present invention has been made in view of these conventional problems, and aims to minimize the defocusing of the mark detection optical system and the decrease in alignment accuracy caused by leveling after detecting the wafer position. .

[Means for solving problems]

In order to solve the above problems, the present invention provides an autofocus or autoleveling mechanism along with an off-Axis type mark detection device, so that autofocus and autoleveling can be performed even at the mark detection position. .

[Function] First, the effect of providing an autofocus mechanism in an off-axis type wafer mark detection device is, needless to say, to prevent the wafer from being out of focus with respect to the detection device due to irregularities on the wafer surface. This eliminates the deterioration in accuracy caused by defocus inherent to the detection device, and also improves the alignment of the wafer caused by defocus when there is a parallel misalignment between the optical axis of the mark detection device and the optical axis of the projection lens (so-called telecentering misalignment). This has the effect of eliminating mark position measurement errors.

Next, the effect of attaching the auto-leveling mechanism to the off-axis type wafer mark detection device will be explained.

Here, the position (sitat coordinates) of each exposure area of the previous layer formed on the wafer to be subjected to overlapping exposure is (
xt '% yt L) (i=1.2...N), the subscript L on the shoulder indicates that leveling was performed for each exposed area in the previous layer exposure as well. .

Similarly, the position of each exposure area when the previous layer is printed without leveling is (Xr, Yr) (i=1
．． 2..., N), the coordinates (x, L, y, L
) and the coordinates (xt, yi) are different due to a positional deviation error caused by the leveling operation. Off-Axis type alignment usually measures the positions of marks attached to several exposure areas on the wafer, interpolates the alignment positions of other exposure areas based on the measured values, and then calculates only those values. The stage is sequentially moved and exposure is performed at the exposure position. The position of the stage is of course precisely monitored by a laser interferometer. Now, let us assume that the position of this measured exposure area is in the state where leveling is applied (XJLSYj) and in the state where leveling is not applied (Xj, Yj). Generally, the exposure process for each layer is performed in a separate exposure device, but since the unevenness on the top surface of the wafer holder is so small that it can be ignored, for i=j, Xt L=
x, L% Y,'=y, L, and Xr ≠Xt L
-, Yr≠y, L. Now, (Xr' % V
t L) is calculated by interpolation, so (X, L, Y
It is better to find (Xt L,)'i') from (JL) than (
This is more accurate than finding (Xi L% Yt L) from (Xj, Yj). Therefore, higher alignment accuracy can be expected if position measurement is performed after leveling is performed.

Of course, each time the position of the wafer mark is measured at each measurement position on the wafer, the measurement mark is moved to the exposure position and leveling is performed, and then the off-A
Although it is possible to measure the position of the measurement mark using a XIS type mark detection device, this method has the disadvantage that it takes a very long time and reduces throughput. In this point, off-
If the Axis-type wafer mark detection device is provided with a leveling mechanism, this problem will not occur.

[Embodiment] FIG. 1 is a diagram showing the overall configuration of a projection exposure apparatus according to an embodiment of the present invention. Exposure illumination light IL with a uniform illuminance distribution illuminates a reticle R having a circuit pattern, etc., and this reticle R is held horizontally by a reticle holder R). In this embodiment, the projection lens PL is:
The principal rays of imaging on the reticle side and wafer side are both on the optical axis AX.
It is designed to be parallel to I. The surface of the wafer W is coated with a resist layer, and the wafer W is arranged so that the surface of the wafer W and the best image formation plane of the pattern image formed by the projection lens PL substantially coincide with each other during exposure.

Now, the wafer W is fixed on the wafer holder WH by vacuum suction, and flattened and corrected so that the desired flatness is maintained. The wafer holder WH is a leveling stage L that can be tilted in any direction under conditions that minimize horizontal deviation.
It is held in S. Leveling stage LS has optical axis A
It is installed on a 2-stage ZS that moves up and down in the + direction,
It can be tilted in any direction by at least two leveling drive units 10a, 10b fixed to the two stages zS and one fixed point. The Z stage ZS is provided via a Z-direction drive mechanism 12 on a stage XYS that moves two-dimensionally in the XY force direction for step-and-repeat or alignment. The vertical movement of the second stage zS with respect to the stage XYS is performed by the motor 14,
Two-dimensional movement of YS is carried out by XY Moke 16 fixed to the base.
This is done by

A movable mirror 18 having reflective surfaces orthogonal to each other in the XY plane is fixed to two sides (only one side in FIG. 1) of the Z stage ZS, and a laser beam from a laser interferometer 20 is directed to the movable mirror 18. Illuminated vertically. The center line of the laser beam of this interferometer 20 is located approximately in the same plane as the surface of the wafer W (
Strictly speaking, it is determined to be located at the best imaging plane of the projection lens PL. Therefore, interferometer 20 sequentially detects the current position (coordinate values) of stage XYS by measuring the distance to the reflecting surface of movable mirror 18 with a resolution of about 0.01 to 0.02 μm. In addition, at one place on the Z stage ZS, there is an effective viewing area (for example, 20 mm) of the projection lens PL.
A reference reflector FP having a certain size is fixed.

Chromium or the like is uniformly deposited on the surface of the reference reflector FP to maintain a constant surface accuracy. Note that a fiducial mark (for example, similar in shape to a mark on a wafer) is formed on the surface of the reflection plate FP, which also serves as a reference for various alignments.

Now, within the viewing area of the projection lens PL on the wafer W,
Light transmission system 22 for autofocus and autoleveling
Illumination light (non-exposure wavelength) is emitted obliquely, and the reflected light enters the light receiving system 24. The configurations of the light transmitting system 22 and the light receiving system 24 are disclosed in detail in Japanese Patent Application Laid-open No. 113706/1982, so a detailed explanation will be omitted here. When the surface of the wafer W collides with the best imaging plane of the projection lens PL in an imaging light beam that projects an image, the light receiving system 24 outputs a focus signal Fsgl indicating focus. When the focus signal F Ill is defocused back and forth by a predetermined amount from the above-mentioned in-focus state, the focus signal F Ill becomes an output voltage (so-called S-curve voltage) according to the direction and amount of defocus. Further, the illumination light for auto-leveling from the light transmitting system 22 has a size that includes the exposure area for one shot on the wafer W, and irradiates the wafer W with a parallel light beam obliquely, and the light receiving system 24 illuminates the exposure area of the wafer W. A leveling signal L *** regarding the relative direction and amount of inclination between the average surface and the best imaging plane of the projection lens PL is output.

Further, a wafer alignment system (mark detection optical system) WGA for detecting alignment marks or fiducial marks on the wafer W is arranged at a position separated by a predetermined distance from the optical axis AX of the projection lens PL. Ru. The alignment system WGA has a telecentric system that irradiates illumination light (such as white light) 26 with a non-exposure wavelength toward the wafer W (or reflector FP) and receives reflected light from the wafer W (or reflector FP). An objective lens 28 and a photoelectric receiver 3° for photoelectrically detecting reflected light from marks (or fiducial marks) on the wafer W are provided.

Furthermore, the photoelectric receiver 30 has a built-in index mark 30a that serves as a reference for alignment.In this embodiment, the alignment state between the index mark 3a and the mark on the wafer W is detected. , the illumination light 26 is a spot light (
In the case of a laser beam projecting a slit-shaped sheet beam), the spot light itself serves as an index, so the index mark 30a is not necessary. The photoelectric receiver 30 then outputs an alignment signal A according to the amount of deviation between the index mark 30a and the wafer mark.

Outputs 1. In addition, in the case of the system without the index mark 30a, the photoelectric receiver 30 scans the wafer W in the X or Y direction with respect to the spot light (or sheet beam), and converts the mark profile obtained by scanning the mark into a waveform corresponding to the information. An alignment signal A□ is output, and the position of the mark with respect to the spot light, that is, the position with respect to the optical axis AX of the projection lens PL is measured based on the waveform and the stage position measurement value by the interferometer 20.

Now, when observing the wafer surface using this wafer alignment system WGA, in order to operate the autofocus and autoleveling of the wafer W, the light transmitting system 32 and the light receiving system 3
4 is provided. The light transmitting system 32 and the light receiving system 34 may have exactly the same configuration as the light transmitting system 22 and the light receiving system 24 described above, and the light receiving system 34, like the light receiving system 24, is connected to the best imaging plane of the projection lens PL and the wafer. The focus signals F1 and 2 correspond to the relative deviation of the optical axis A, A leveling signal L□2 regarding the tilt direction and amount is output. Note that the best imaging plane of the objective lens 28 and the best imaging plane of the projection lens PL (the conjugate plane with the reticle R) are made to coincide in polarity.

Each of the above-mentioned focus signals F I**, F*@t, and leveling signals Li**, L**z is input to the main control system 42 via the selector circuit 40. The selector circuit 40 selects which detection system is used to perform autofocus and leveling, and selects one of the selected focus signals Fst.

, leveling signal... Output. The main control system 42 outputs a switching signal SS to the selector circuit 40. This switching is roughly classified according to the sequence of the equipment, and when various marks are detected by the wafer alignment system WGA, the signal F If! s L sl! is the signal Fs. ,
LIl. During the exposure operation on the wafer W, the signals F-I and L□ are selected. The main control system 42 controls the motor 14 based on the selected focus signal F□0.
outputs a signal DS for driving the wafer W (or the reflector FP), adjusts the height position of the surface of the wafer W (or the reflector FP), and further outputs a signal DS for driving the driving sources 10a, 10b based on the selected leveling signal 9°.
It outputs signals DS, , DS, which drive , and adjusts the inclination of the surface of the wafer W. The main control system 42 also includes an interferometer 20
It also inputs measurement values from the XY motor 16, outputs drive signals to the XY motor 16, and inputs alignment signals A and □, thereby controlling the apparatus in an integrated manner.

Next, the operation of this embodiment will be explained with reference to FIG. Second
The figure shows the planar arrangement relationship between the projection lens PL and the objective lens 28 of the wafer alignment system WGA, and also shows the positional relationship with the wafer W during alignment and exposure. Furthermore, the wafer W in FIG. 2 shows four representative SIT areas SA. In addition, a scribe line area (width 50 to 11
001I) have alignment marks WM, , WM
! is provided. Now, wafer alignment WG
Assuming that the optical axis A X z of A, that is, the distance between the index mark 30a and the center of the pattern projection image of the reticle R, has been accurately determined in advance, the main control system 42 first controls the reflection as shown in FIG. Move the plate FP below the alignment system WGA. Here, the main control system 42 transmits the direction and amount of inclination of the surface of the reflection plate FP detected by the light receiving system 34 to the signal L11. The main control system 42 similarly moves the stored 0-order reflector FP under the projection lens PL based on , and here, the main control system 42 similarly sends the tilt direction and amount of the reflector FP detected by the light receiving system 24 to the signal Ls1. Remember based on. This action causes
The relative detection offsets of the two leveling sensors are determined and calibrated.

Specifically, it is desired that the common reflector FP detected by the two leveling sensors (light receiving system 24 and light receiving system 34) be detected as the same reference plane. Therefore, a parallel plate glass or the like is provided in the optical path of at least one of the two leveling sensors, for example, a part of the light receiving system 34 and light transmitting system 32 set, and by changing the angle of this parallel plate glass with respect to the optical path, the light can be received. The virtual plane, which is detected by the system 34 as having zero inclination, is tilted to the same polarity. Then, the angle of the parallel flat glass is adjusted so that the previously detected relative detection offset becomes zero. This operation performs calibration between the two leveling sensors. This method of adjusting the inclination of the virtual reference plane by inserting parallel flat glass into the optical path of the belling sensor was developed, for example, in Japanese Patent Laid-Open No. 62
-58624 can be used as is.

In addition, leveling off-cellar l-m using parallel flat glass
The adjustment mechanism may be provided in the combination of the light receiving system 24 and the light transmitting system 22. Furthermore, if the reflector FP shown in Fig. 1 is provided in a part of the leveling stage LS,
First, using the signal L s4+ from the light receiving system 24,
The inclination of the leveling stage LS is adjusted so that the reflector FP is parallel to the virtual reference plane, and the leveling stage LS is fixed at that inclination. Next, the reflection plate FP is detected by the light receiving system 34,
Based on the signal L1.2, the angle of the parallel flat glass is servo-controlled by motor drive. That is, the angle of the parallel flat glass is corrected so that the light receiving system 34 detects the reflecting plate FP whose inclination is fixed as having zero inclination. This calibrates the relative detection offset between the two leveling sensors to zero.

Next, the wafer W to be overlappingly exposed is moved under the wafer alignment system WGA, and a mark detection operation is performed as shown on the left side of FIG. 2. In FIG. This figure shows the mark WM being detected by the index mark 30a of the alignment system WGA. The main control system 42 controls the index mark 30a based on the alignment signal A, □ and the measured value from the interferometer 20.
Mark position (
coordinate values) and store them. The positions of other marks WM on the wafer W are similarly detected and stored. The above mark detection operation is similarly executed by moving stage XYS for each of a plurality of shot areas on wafer W to obtain a plurality of mark position information. Now, when detecting marks WM1 and WMt on wafer W in this way, main control system 42 switches so that selector circuit 40 selects signals F3□ and L□2. Therefore, the main control system 42 servo-controls the motor 14 in response to the selected signals F, , 2, so that the surface of the local area including the mark on the wafer W is the best imaging plane of the objective lens 2 (or the index mark 30a). ) The height of the Z stage zS is sequentially adjusted so that it optically matches the height.

At the same time, the main control system 42 servo-controls the drive sources 10a and 10b in response to the selected signal L3□, so that the best imaging plane of the projection lens PL with equal deflection and the surface of the local area including the mark on the wafer are The inclination of the leveling stage LS is successively adjusted so that it becomes optically parallel.

Note that the main control system 42 receives the focus signal Fs.

□, leveling signal, 1. After confirming that autofocus and leveling are correctly servo-locked in response to , mark position detection is performed based on the alignment signal A□1.

Next, the main control system 42 determines the regularity of the arrangement of the center points of each shot area SA on the wafer W based on the measured mark position information using a statistical calculation method, and determines the regularity of the arrangement of the center points of each shot area SA on the wafer W, and determines the regularity of the arrangement of the center points of each shot area SA on the wafer W. Find the coordinate values (shot address).

Then, the main control system 42 moves the wafer W under the projection lens PL as shown on the right side of FIG.
Overlapping exposure of the patterns of the reticle R is performed for each area SA. At this time, the main control system 42 switches the selector circuit 40 to select the focus signal Fal+ and the leveling signal Ls.
Select g+. As a result, the height position of the second stage zS is servo-controlled by the motor 14 in response to the signal F1,1 via the main control system 42, and the inclination of the leveling stage LS is controlled by the drive 1111X in response to the signal F1,1.
Servo-controlled by 10a and 10b. As a result, the best imaging plane of the projection lens PL and the wafer surface are aligned and matched for each shot area, and optimal image quality and alignment accuracy are obtained. In this way, off
When performing mark detection using the axis method, by keeping the wafer surface parallel to the best imaging plane of the projection lens PL,
Extremely high precision alignment can be achieved.

As described above, in this embodiment, each focus sensor and leveling sensor is the projection lens PL or the objective lens 28.
A similar effect can be obtained by using a so-called TTL (through-the-lens) method, in which the positional relationship between the best imaging plane of each lens PL, 28 and the wafer surface is directly detected through the wafer surface. Focus sensors and leveling sensors also use a so-called air micrometer method, which injects gas at a constant pressure onto the wafer surface from a minute nozzle and detects the back pressure to detect the distance between the nozzle and the wafer surface. A similar effect can be obtained. However, for leveling, at least 3
It is necessary to provide minute nozzles at several locations and to average the spacing at each nozzle position to form the wafer surface.

In addition, in the autofocus and leveling sensor of this embodiment, the illumination light was irradiated obliquely from one direction onto the wafer surface, but the illumination light was incident from each of two orthogonal axial directions, and the inclination angle of the wafer surface was Or use a separate light receiving system (two-split sensor, PSD, etc.) with the focus plane in both wheel directions separately.
It may be detected by.

Furthermore, in this embodiment, the attitude of the wafer surface is controlled using both the leveling signal Ls0 and the focus signal F□2 from the light receiving system 34 provided in the off-Axis type wafer alignment optical system WGA, and the mark is Although the detection has been performed, it may be sufficient to perform the attitude side m (one of the Z direction or leveling) using at least one of the signals.

〔Effect of the invention〕

As described above, according to the present invention, in a projection fogging apparatus that performs off-Axis alignment and leveling of a photoreceptor (wafer, etc.), the off-Axis alignment can be performed without reducing throughput. It is possible to prevent the detection optical system from being out of focus due to unevenness on the surface of the photoreceptor. Furthermore, it is possible to minimize the deterioration in positioning accuracy caused by the leveling operation.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a projection exposure apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view showing the planar arrangement of a projection lens and a wafer alignment optical system and the positional relationship of a wafer. [Explanation of symbols of main parts] R...Reticle, PL...Projection lens, W...Wafer, LS...Leveling stage, ZS...Z stage, WGA...Wafer alignment system, 22 .32... Light transmitting system, 24.34... Light receiving system, 40... Selector circuit, 42... Main control system. Applicant Nippon Kogaku Kogyo Co., Ltd.

Claims (3)

[Claims] (1) The pattern of the mask is exposed to each local area of the photoreceptor through a projection optical system in a step-and-repeat manner, and the mark detection optical system disposed at a predetermined distance from the projection optical system In a projection exposure apparatus that detects alignment marks formed on a photoreceptor and relatively aligns the mask and the photoreceptor, the photoreceptor is held and the surface of the photoreceptor is moved in an arbitrary direction. an attitude adjustment means for tilting the projection optical system or the mark detection optical system in parallel in the optical axis direction; a first detection means for detecting first information regarding at least one of a relative inclination and a relative distance to a surface; and a first detection means for detecting the mark and the photoreceptor surface located within a viewing area of the mark detection optical system; a second related to at least one of the relative inclination and relative spacing with respect to the imaging plane of the optical system;
A second detection means for detecting information; and a control means for selecting either the first information or the second information and controlling the attitude adjustment means based on the selected information. Projection exposure equipment. (2) the control means selects the second information when the mark detection optical system detects a mark on the photoreceptor;
2. The apparatus according to claim 1, further comprising an information switching unit that selects the first information when performing exposure using the step-and-repeat method. (3) The attitude adjustment means includes a leveling stage section on which the photoconductor is placed and tilted in an arbitrary direction, and a leveling stage section that moves the photoconductor in parallel in the optical axis direction while maintaining the tilted state. and a Z-stage section to control the selected first information or second information.
Claim 1, wherein the leveling stage section is controlled based on information regarding the relative inclination among the information, and the Z stage section is controlled based on information regarding the relative spacing. The device according to paragraph 2 or paragraph 2.