JPH01144626A - Alignment method - Google Patents

Abstract

PURPOSE:To prevent a decline of through-put and the like and highly precisely allow alignment for a short time by rotating and driving a reticule stage in order that about the same revolution quantity as a wafer stage is detected by a laser interferometer of the reticule stage. CONSTITUTION:A second revolution detector composed of a laser interferometer 13 and a theta counter 27 detecting the revolution quantity of a wafer stage 6 is reset at prescribed value at the time of start of an exposing device, a first revolution detector composed of a laser interferometers 21, 22 and a theta counter 24 detecting the revolution quantity of a reticule stage 2 is reset at prescribed value after relative revolution difference is corrected. Revolution quantities are detected from a reset position of the first revolution quantity detector as a first standard position and another reset position of the second revolution quantity detector as a second standard position. Further, when a circuit pattern of a reticle R is exposed in each shot area on wafers by a step and repeat method a reticle stage 2 is rotated and driven at about the same revolution quantity as the first revolution quantity detector detects and the second revolution quantity detects.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a photo mask for use in a wafer stepper for manufacturing semiconductors, or a proximity single-type or contact I-type batch exposure device. Regarding photorepeater and the like to be manufactured, in particular, the circuit pattern of a mask or reticle is applied by step and process to the circuit pattern of multiple semiconductor elements formed on one photosensitive substrate (semiconductor wafer, hereinafter referred to as wafer). This relates to an alignment method when sequentially overlapping exposure is performed using a repeat method.

[Conventional technology]

Conventionally, in the manufacturing process of semiconductor devices, a reduction projection exposure apparatus, a so-called wafer stepper, is mainly used to process a circuit pattern formed on a mask or reticle (hereinafter referred to as a reticle) and onto a wafer through a projection lens. To accurately overlap and expose an already formed circuit pattern. At this time, it is necessary to accurately align the circuit pattern on the reticle and the circuit pattern on the wafer. Currently, in this type of exposure equipment, the projection exposure field at one time is about 5 mm square to 20 mm square, so a so-called step-and-repeat method is used, in which the wafer is moved forward by a certain pinch and then exposed. We are hiring. In the case of this step-and-repeat type exposure equipment, multiple shot areas to be exposed on the wafer are formed in a matrix, so when stepping the wafer, it is difficult to accurately align the next shot area. It is required that the However, as semiconductor devices become more highly integrated, the exposure area for each shot increases, and the line width of the circuit pattern to be transferred onto the wafer becomes sub-micron. Due to minute rotational deviations that occur and rotational deviations of the wafer stage that occur due to yawing of the wafer stage, the overlay accuracy between the circuit pattern on the reticle and the circuit pattern on the wafer deteriorates. Furthermore, the first
When the circuit pattern of the second layer is transferred, the circuit pattern transferred onto the wafer is slightly rotated with respect to the arrangement coordinates, resulting in insufficient overlapping of the second and subsequent layers. For this reason, it becomes impossible to obtain semiconductor elements satisfying desired characteristics with high productivity. Therefore, for example, an alignment mark (wafer mark) provided along with a shot area corresponding to one projection exposure field on a wafer, and an alignment mark (reticle mark) formed around a circuit pattern on a reticle. simultaneously observed with an alignment optical system installed above the reticle,
The so-called TTR corrects the positional deviation by slightly moving the wafer or reticle for each shot (1=4-) so that the amount of positional deviation between both marks becomes zero.
(through-the-reticle) method step alignment. From this, a slight rotational deviation of the reticle,
This prevents rotational deviation of the wafer stage due to yawing of the wafer stage, deterioration of overlay accuracy due to wafer expansion/contraction (run-out), etc.

[Problem that the invention seeks to solve]

However, in an exposure apparatus using this type of alignment method, the throughput decreases because the reticle mark and wafer mark are detected simultaneously for each shot to correct positional deviations. Therefore, after correcting the relative rotational error between the circuit pattern on the reticle and the circuit pattern already formed on the wafer, the θ table of the wafer stage is rotated by the rotational error. There is a method of overlapping exposure by sequentially stepping the wafer stage by a predetermined amount along the arrangement coordinates of the circuit pattern. However, even in this method, there is a problem in that the overlay accuracy decreases if yawing occurs in the wafer stage.

Also, when exposing the first layer of circuit patterns on a wafer using the step-and-repeat method, irregular rotational deviations occur with respect to the array coordinates for each shot due to rotational deviation of the wafer stage due to yawing. Live. For this reason, there is a problem that the overlay accuracy of the circuit pattern of the reticle and the circuit pattern of the wafer in the second and subsequent layers is reduced, and that alignment takes time and that the throughput is reduced.

The present invention has been made in consideration of the above points, and aims to provide a method that prevents deterioration in overlay accuracy, throughput, etc. due to rotational deviation of the wafer stage, and enables alignment with high precision and in a short time. be.

[Means for solving problems]

In order to solve this problem, in the present invention, a reticle stage on which a reticle is placed and moves two-dimensionally,
In the overlapping exposure of the second and subsequent layers, the relative rotational deviation between each circuit pattern already formed on the wafer and the reticle, or in the exposure of the first layer, step, pull and repeat. The wafer stage is configured to be rotationally driven in order to correct the relative rotational deviation of the reticle with respect to the coordinate system XY, which is the moving coordinate system of the wafer stage on which the wafer is placed and moves two-dimensionally when performing exposure using the method. be done. Further, a second rotation amount detection device consisting of a laser interferometer and a θ counter detects the rotation amount of the wafer stage,
A first rotation amount detection device, which is reset to a predetermined value when the exposure apparatus is started, and is composed of a laser interferometer and a θ counter that detects the rotation amount of the reticle stage, is reset to the predetermined value after the relative rotational deviation is corrected. will be reset to . In this way, the first rotation amount detection device and the second rotation amount detection device are associated with each other, and the first rotation amount detection device is at the center position as the first reference position, and the second rotation amount detection device is at the second reference position.
The rotation amount detection device is configured to detect the rotation amount from the glue set position. Furthermore, when exposing the circuit pattern of the reticle to each film area on the wafer using the step-and-repeat method, the reticle is rotated by an amount of rotation approximately equal to the amount of rotation detected by the first rotation amount detection device. The second rotation amount detection device is configured to detect by rotating the stage.

[Effect]

According to the present invention, the amount of rotation of the wafer stage due to yawing that occurs when stepping the wafer stage is measured using a laser interferometer, and the amount of rotation approximately equal to the amount of rotation of the wafer stage is measured by the laser interferometer of the reticle stage. The reticle stage is rotated so as to be detected by. In this way, since the exposure is performed by correcting the relative rotation error caused by yawing between the circuit pattern of the reticle and the circuit pattern of the wafer for each shot, in the overlapping exposure of the second and subsequent layers, a - It is possible to prevent a decrease in the overlay accuracy between the circuit pattern on the reticle and the circuit pattern on the wafer due to rotational deviation of the wafer stage caused by the wafer stage, and a decrease in throughput due to this decrease in accuracy. The circuit pattern of the first layer can be transferred by the step-and-repeat method to the coordinate system XY as the movement coordinate system of the wafer stage without any rotational deviation, and thus the alignment 1~ can be performed with high precision and in a short time. This is what I did.

〔Example〕

FIG. 1 is a perspective view showing a schematic configuration of a projection exposure apparatus suitable for applying the method according to the first embodiment of the present invention. FIG. 2 is a block diagram of the control system of this projection exposure apparatus.

In FIGS. 1 and 2, exposure light from an illumination optical system (not shown) uniformly illuminates a reticle R placed on a tickle stage 2 that moves two-dimensionally (X direction, Y direction, and rotational direction). do. The optical image of the pattern region Pr of the reticle R is projected onto the wafer W via the projection lens 1 which is telecentric on both sides or on one side. The wafer W is placed on a wafer stage 6 that moves two-dimensionally (X direction, Y direction, and rotational direction) in a step-and-repeat manner. Further, the wafer stage 6 is provided with a reference mark FM having the same pattern shape as an alignment mark (wafer mark) formed on the wafer W. The projection lens 1 used in this embodiment is an optical system in which the reticle R side is non-telecentric and the wafer W side is telecentric. Furthermore, the drive unit 3 slightly moves the reticle stage 2 in the X direction, and the drive unit 4.5 moves the reticle stage 2 in the
This makes it possible to position the reticle R two-dimensionally (including rotationally). The two-dimensional position of the reticle stage 2, that is, the position in the X direction, the
Detected by 20.21.22. The configuration of this laser interferometer 20, 21, 22 is disclosed in, for example, Japanese Patent Laid-Open No. 150721/1983, which was previously filed by the applicant of the present application, so a detailed explanation will be omitted. The laser beam is irradiated onto a right-angle mirror as a movable mirror fixed to the reticle stage 2 and a fixed mirror fixed to the lens barrel of the projection lens. The reflected light flux from the movable mirror and the reflected light flux from the fixed mirror are coaxially combined,
Interference fringes occur on the light receiving surface of the receiver. This receiver photoelectrically detects changes in the interference fringes and generates an amplifier down pulse in response to changes in the position of the moving mirror. These pulses are reversibly counted by counters 23 and 24, and the position of the reticle stage 2 is detected.

The X counter 23 reversibly counts the amplifier down pulses output from the X-axis interference needle (receiver) 20 to detect the position of the reticle stage 2 in the X direction.

The Y-axis interference needle 21, the θ-axis interferometer 22, and the θ counter 24 serve as the first rotation amount detection device.
The amount of rotation of the reticle stage 2 is detected by reversibly counting the difference between the amplifier down pulses outputted from the reticle stage 2. At this time, the position in the X direction is also detected at the same time.

On the other hand, the wafer stage 6 is moved in the X direction and the ia It is configured to rotate a small amount. In order to detect the two-dimensional position of the wafer stage 6, a light wave interference length measuring device (hereinafter referred to as a laser interferometer) 11, 12, 13 such as a laser interferometer and a laser beam as shown in FIG. an X counter 25 that reversibly counts the amplifier down pulses output from the interferometers 11, 12, and 13;
A Y counter 26 and a θ counter 27 are provided.

The mirror 14 serving as a movable mirror has its reflection plane extended in the X direction, and the mirror 15 has its reflection plane extended in the X direction, and both are provided on the wafer stage 6. Therefore, the laser interferometer 11 irradiates the mirror 14 with a laser beam Bx having an optical axis parallel to the coordinate axis It also irradiates a laser beam. The laser interferometer 11 photoelectrically converts changes in interference fringes caused by interference between the reflected light beam from the mirror 14 and the fixed mirror, and outputs an amplifier down pulse. The X counter 25 reversibly counts these up and down pulses to detect the position of the wafer stage 6 in the X direction.

Similarly, the laser interferometer 12 and the Y counter 26
5 is irradiated with a laser beam By having an optical axis parallel to the coordinate axis Y, and the position of the wafer stage 6 in the X direction is detected by interference between the reflected light beam from the fixed mirror and the reflected light beam from the mirror 15. Furthermore, a projection lens 1 and a laser interferometer 11.
Reference numeral 12 indicates that the laser beam Bx and the laser beam By are perpendicular to each other in the same plane, and the optical axis AX of the projection lens 1 passes through the intersection, and the plane that includes these two measurement axes (for example, the center line of the laser beam) is projected. It is arranged so as to substantially coincide with the projection image plane of the lens 1.

On the other hand, the parallel laser beam from the laser interferometer 13 is split into two by a beam splitter (not shown).

The laser beam Bθ1 and the laser beam Bθ2 transmitted through the beam splinter and reflected by a reflecting mirror (not shown) enter the mirror 15 perpendicularly. This laser beam flux Bθ1, Bθ
Second, the laser beam By is irradiated onto the mirror 15 so as to be symmetrical with respect to the Y axis of the coordinate system XY. By the interference of the two reflected beams from the mirror 15, a laser interferometer 13 as a second rotation amount detection device and a θ counter 27 are detected.
detects the amount of rotation of the wafer stage 6 due to yawing or the like. Since the amount of rotation of the wafer stage 6 is minute, the laser interferometer 13 can simultaneously receive the reflected beams from the mirrors 15 of each of the laser beams Bθ1 and Bθ2, and the amount of rotation can be detected by the interference of the reflected beams. It becomes possible.

Now, the TTR type die-pi-dia-alignment I system (hereinafter referred to as the DDA system) 16a shown in FIG.
The mark Rsa on the reticle R''2 and the mark on the wafer W or the mark on the fiducial mark FM are superimposed and observed simultaneously through the projection lens 1, and both mark images are photoelectrically detected. Then, a positional deviation in the X direction between the mark image of the reticle R and the wafer W or the fiducial mark FM is detected. Further, laser step primer 1-systems (hereinafter referred to as LSA systems) 17a and 17b are provided at intervals of 90 degrees with respect to the optical axis AX, as shown in the figure. This L S
The A systems 17a and 17b each use a TTL (through-the-lens) method to detect a predetermined mark (wafer mark) on the wafer W or a reference mark FM with a laser beam,
The positional deviation of the wafer W or the fiducial mark FM in the X direction and the X direction is detected.

The main control system 60 shown in FIG. 1 includes a processor (hereinafter referred to as a CPU) 30 such as a microcomputer or minicomputer, an interface circuit (hereinafter referred to as an IFC) 31, etc., as shown in FIG. , the two alignment systems mentioned above (DDA system, LSA system) through these
Overall control of the operation of the entire device including Laser step alignment processing circuit (hereinafter referred to as LSAC)
Reference numeral 32 uses the LSA systems 17a and 17b to detect the position of the alignment mark on the wafer W with respect to the spot light (sheet beam) from the LSA systems 17a and 17b. Also, die-pie-die alignment processing circuit (
(hereinafter referred to as DDAC) 33 works together with the DDA system 16a to detect the relative positional deviation amount of the mark Rsa on the reticle R and the alignment mark on the wafer W or the mark My of the reference mark FM in the X direction. It is. C.P.
U30 drives the wafer stage 6 in the X direction via the IFC 31 according to the calculated value of the CPU 30 and the amount of positional deviation detected by various alignment systems.
8), an X-direction drive unit 9 (hereinafter referred to as Y-ACT9
) and a drive unit 10 for rotating the wafer boulder 7 (
(Hereinafter, referred to as θ-ACTIO), predetermined drive commands are outputted to each of them. Similarly, in the reticle stage 2, depending on the amount of rotation of the wafer stage 6, the amount of positional deviation detected by the alignment system, etc., the drive unit 3 (hereinafter referred to as
3), an X-direction drive unit 4 (hereinafter referred to as Y-ACT4), and a rotational direction drive unit 5 (hereinafter referred to as θ-ACT5).
A predetermined drive command is output to the

= 16- Next, the operation of this embodiment will be explained based on the schematic flowchart 1 shown in FIG. FIG. 3 shows the second wave that occurs when the circuit patterns of the second and subsequent layers are superimposed and exposed on the wafer W on which the circuit patterns of the first layer are arranged.
The projected image Pr' of the circuit pattern of the reticle R after the layer and the circuit pattern arranged on the wafer W (hereinafter referred to as chip C)
This figure shows the basic operation for correcting relative rotational errors due to yawing. Here, the operations from alignment of the reticle R and wafer W to exposure, that is, step 201, are disclosed in, for example, Japanese Unexamined Patent Publication No. 86845, filed earlier by the applicant of the present application, and will therefore be briefly explained. do. The case where the second layer circuit pattern is superimposed on each chip C on the wafer W and exposed to light will be described below.

In step 200, when the exposure apparatus is started up, the CPU 3
0 resets the count value of the θ counter 27, which reversibly counts amplifier down pulses according to the amount of rotation of the wafer stage 6, to a constant value, for example, zero.

By this reset operation, the amount of rotation of the wafer stage 6 due to yawing or the like is always detected with the zero reset position as a reference, that is, the origin of the rotation direction of the wafer stage 6 (hereinafter referred to as the θ axis) is determined. Here, the position of the θ-axis with respect to the coordinate system xy determined by the laser interferometer 11.12 is determined by the X-axis and the reflective surface of the mirror 15 that reflects the laser beams Bθ1 and BO2 emitted from the laser interferometer 13. Determined by minute inclination. This is because the mirror 15 may be set slightly rotated with respect to the coordinate system XY due to mounting errors during manufacture. Therefore, in this embodiment, as shown in FIG. 4, it is assumed that the θ counter 27 is reset to zero when the θ axis (the reflective surface of the mirror 15) is rotationally displaced by θm with respect to the coordinate system XY.

In FIG. 4, each rotational deviation is exaggerated.

Next, in step 201, a reticle alignment microscope (not shown) used for reticle alignment is first adjusted (checked). Using this reticle alignment microscope, reticle alignment is performed so as to eliminate the rotational deviation of the reticle R with respect to the coordinate system XY, but the rotational deviation remains, albeit at a small angle. Therefore, the residual rotation error of the reticle R, that is, the reticle rotation RR is measured. Therefore, the operation of reticle low-chie silane measurement will be explained using FIGS. 4 and 5. Here, when measuring the reticle rotation, it is assumed that the wafer stage 6 moves parallel to the θ axis without rotating (yawing) as shown in FIG. In FIG. 5, the DDA system 16a irradiates the mark R3a of the reticle R with the illumination light beam Ba through the reflecting mirror 15ma, and directs the mark R3a through the projection lens 1 onto the fiducial mark FM as shown in FIG. 4(A). image is formed. The CPU 30 determines whether the linear mark My of the fiducial mark FM is the mark R3a of the reticle R.
The wafer stage 6 is moved so that it is placed exactly in the center of the projected image R3a' (rectangular transparent window). This state is observed by the DDA system 16a as shown in FIG. At this time, the DDAC 33 is connected to Y of the wafer stage 6.
The position in the direction is detected by the laser interferometer 12, and the CPU 3
0 stores this Y coordinate value Y1'. Next CPU30
As shown in FIG. 4(B), the wafer stage 6 is moved along the X axis of the coordinate system Positioning is performed so that R3b' and mark My are detected simultaneously. At this time, the reticle R is in the coordinate system
If the mark My is placed on the reticle stage 2 without rotational deviation relative to the projection image R3b, as shown in FIG.
′, and the amount of reticle rotation is zero. However, since there is generally a rotation error, albeit a small angle, the projected image R3b'
and mark My are observed while being relatively displaced in the Y direction.

Therefore, the DDAC 33 detects the positional deviation in the Y direction using the DDA system 16b, and moves the wafer stage 6 slightly in the Y direction so that this positional deviation is eliminated. and CPU3
0 is Y when the positional deviation is corrected as shown in Figure 4 (C)
Coordinate value Y2' is stored. Also, the moving distance of the wafer stage 6 in the X direction at this time is the design value (mark R of the reticle R).
3a and R3b), but
Here, the moving distance Lx of the wafer stage 6 in the X direction detected by the laser interferometer 11 is used.

When measuring the reticle rotation here, it was assumed that the wafer stage 6 was not rotating about the θ axis as shown in FIG. However, in reality, since the wafer stage 6 is moved so that the mark My and the marks R5a and Rsb of the reticle R are detected simultaneously, yawing may occur in the wafer stage 6. For this reason, C
The PU 30 detects Y coordinate values Y,', Y2' that include the rotational deviation of the wafer stage 6 due to yawing as an error. Therefore, in order to prevent the measurement accuracy from decreasing due to the occurrence of yawing, the CPU 30 uses the laser interferometer 13 and the θ counter 2 to calculate the amount of rotation of the wafer stage 6 when the mark My, marks Rsa, and Rsb are detected simultaneously.
Find it from 7. Next, the CPU 30 calculates the detected Y coordinate values Y, ', Y2 based on the detected rotation amounts as described above.
' respectively, and the corrected Y coordinate values are respectively Yl,
Store as Y2.

Also, as shown in FIG. 4, the θ-axis of the wafer stage 6 is in the coordinate system
It is determined to be shifted from Y by θm. Therefore, the moving distance L x and the moving distance Δ of the wafer stage 6 in the X direction and the Y direction, respectively, detected by the laser interferometers 11 and 12.
Y-(Y2-Y, ) is detected shifted by x' and y' from the actual moving distance, respectively. Therefore, the amount of reticle rotation is calculated as the amount of rotation θr of the reticle R, not with respect to the coordinate system
Calculated by J30.

From this, the CPU 30 calculates the amount of rotation θr of the reticle R with respect to the θ axis from equation (1).

-x However, since the rotation amount θr is extremely small, an approximation calculation is performed using equation (2).

Lx Lx To measure this reticle rotation, similar measurements are performed multiple times in order to improve accuracy, and the CPU 30 stores an average value of the rotation amount θr determined for each measurement.

Now, on the wafer W, the circuit pattern of the first layer reticle R is in the coordinate system X as the moving coordinate system of the wafer stage 6.
It is assumed that the image is transferred to Y without rotational deviation. However, in reality, rotational deviations of each chip C may remain due to factors such as a decrease in alignment accuracy. Therefore, when exposing the patterns of the second and subsequent layers in a superimposed manner, it is necessary to take into account the residual rotational error of the chip C, that is, the chip rotation.

FIG. 7 shows the arrangement of specific chips C transferred on the X-axis, and each rotational shift is exaggerated. In Figure 7, if counterclockwise is the positive direction, the center of each chip C is located exactly on the X axis of the coordinate system XY, but each chip C is in the positive direction with respect to the θ axis due to chip rotation. Assume that it is rotated by θC. The projected image Pr' of the circuit pattern of the second layer reticle R is rotated by θr in the negative direction with respect to the θ axis due to reticle rotation. Therefore, the projected image Pr' and the chip C are Δ
This results in a relative rotation of θ-(θC-θr). Also, on both sides of each chip C on the wafer W, mark images Sy and sy' of marks formed in association with the pattern region Pr of the first layer reticle R are formed. Both marks sy and sy' are known diffraction grating patterns extending on the X axis.

Next, CPU 30 measures chip rotation.

For chip rotation measurement, spot light from the LSA system 17a is used, and the rotation amount θC of the chip C is determined by detecting the positional deviation of the marks Sy and Sy' in the Y direction. Here, in this chip rotation measurement, as well as reticle rotation measurement, in order to prevent a decrease in measurement accuracy due to yawing during measurement, the wafer stage 6 at the time of measurement detected by the laser interferometer 13, etc.
The detected Y coordinate value is corrected based on the amount of rotation.

Therefore, first, the CPU 30 moves the wafer stage 6 so that the spot light scans the mark sy of an arbitrary chip C on the wafer W in the Y direction. Then, the Y coordinate value when the spot light and the mark Sy match is determined by the laser interferometer 12.
A value corrected based on the amount of rotation of the wafer stage 6 at the time of measurement (amount of change from zero reset) is stored as the Y coordinate value Y3. Next, the spot light marks Sy'
The wafer stage 6 is moved in the X direction so that the wafer stage 6 is aligned parallel to the wafer stage 6. The amount of movement is the distance between the marks sy and Sy', but it is assumed that it is accurately read from the laser interferometer 11, and this value is stored as Px.

Similarly, the CPU 30 scans the mark Sy' in the Y direction with the spot light, reads the Y coordinate value when the spot light and the mark Sy' match from the laser interferometer 12, and calculates the amount of rotation of the wafer stage 6 at the time of measurement ( The value corrected based on the amount of change from zero reset) is stored as the Y coordinate (liY4. Also, like the RR measurement, these measurement values include the rotational deviation θm of the θ axis with respect to the coordinate system XY as an error. Therefore, the chip rotation is calculated by the CPU 30 as the apparent rotation amount θC of the chip C with respect to the θ axis.

From this, the CPU 30 calculates the chip C by the following equation (3).
The rotation amount θC is calculated. However, since θC is extremely small, this is an approximation.

Px Px --------------- (3) This chip rotation measurement is performed using multiple chips located near the center of the wafer W or at the vertices of a regular polygon around the wafer W, for the purpose of improving accuracy. The same process is performed for the chips C, and the average value of θC obtained for each chip C is used.

Next, the CPU 30 corrects the relative rotation error between the projected image Pr' of the reticle R and the chip C based on the measured chip rotation and reticle rotation. Therefore, first, the relative rotation amount Δθ-(θc-θr) between the chip C and the projected image Pr' is determined. Then, the reticle stage 2 is rotated by Δθ in the positive direction with respect to the coordinate system XY via the drive unit 4. Reticle stage 2
The rotation of the reticle stage 2 is monitored by laser interferometers 20, 21, and 22, and the reticle stage 2 is rotationally driven without being displaced in the X, Y directions. Therefore, the relative rotation error between each chip C on the wafer W and the projected image Pr' of the second layer pattern is corrected, and the chips are accurately superimposed.

Next, in step 202, the CPU 30 starts the θ counter 2 for detecting the amount of rotation of the reticle stage 2 when the relative rotational error between the chip C and the projection image Pr' is corrected.
Reset the count value of 4 to zero. By this reset operation, when the chip C and the projected image Pr' are accurately superimposed, each count value from the θ counter 27 and the θ counter 24 becomes zero, and the θ counter 24 and the θ counter 2
7, that is, the rotation reference of the reticle stage 2 and the rotation reference of the wafer stage 6 are associated with each other. Then, the CPU 30 performs the second
In order to superimpose and expose each chip C on the wafer W, the wafer stage 6 is moved via the drive unit 8.9, and the wafer W is centered at a predetermined exposure start position.

Next, in step 203, the CPU 30 superimposes each chip C on the wafer W and the projected image Pr' of the second layer pattern and exposes them. Here, first, the first chip C on the wafer W is subjected to overlay exposure. At this time, it is assumed that the first chip C and the projected image Pr' have no relative rotational error (change in the count value of the θ counter 2) and are accurately overlapped and exposed.

Next, in step 204, the CPtJ30
It is determined whether the second layer circuit pattern has been overlaid and exposed on the entire surface. Here, only the overlay exposure was performed on the first chip C on the wafer W, so
The next step 205 is executed -28=.

In step 205, the CPU 30 moves the wafer stage 6 by a step-and-repeat method along the X-axis or Y-axis of the coordinate system The driving section 9 (or the driving section 8) causes stepping.

When yawing occurs in the wafer stage 6 due to this stepping and the wafer stage 6 rotates, CP t
In step 206, the wafer stage 6
The rotation amount Wθ is detected. The rotation amount Wθ is determined by the θ counter 27.
However, since the θ counter 27 has been reset to zero in advance as described above, this counted value corresponds to the rotation amount Wθ of the wafer stage 6 from the reference value. Through the above steps, the measurement of the rotation amount Wθ of the wafer stage 6 is completed, and the next step 20 is performed to correct this rotational deviation.
Execute step 7.

In step 207, the CPU 30 performs step 2
The reticle stage 2 is moved by the drive unit 4.5 in accordance with the rotation amount Wθ of the wafer steering wheel detected by the θ counter 27 at
The wafer stage 6 is rotated by Wθ in the same direction as the rotation direction of the wafer stage 6. That is, the θ counter 24 of the reticle stage 2 is reset to zero in step 202, and θ
Since it is associated with counter 27, θ counter 2
The reticle stage 2 is rotated so that the rotation amount R.theta. of the reticle stage 2 detected by 4 is equal to the value of the .theta. counter 27, that is, the rotation amount R.theta. changes from R.theta.-0 to R.theta.-W.theta. The rotation of the reticle stage 2 is also monitored by the laser interferometers 20, 21, and 22, and the reticle stage 2 is rotationally driven without being displaced in the X, Y directions. From this, the second chip C on the wafer W and the projected image Pr' are accurately superimposed,
Next, the CPU 30 executes step 203 again to perform overlapping exposure.

As described above, the overlapping exposure of the second layer is performed by the CPU 30.
repeats the operations from step 203 to step 207, corrects the rotational deviation of the wafer stage 6 by the rotation of the reticle stage 2, overlaps the circuit pattern of the second layer with each chip C of the wafer w, and performs the steps. Expose using the and-repeat method. Therefore, each chip C on the wafer W and the projected image Pr' are accurately superimposed, and the second layer circuit pattern is exposed without reducing the superposition accuracy due to yawing.

Furthermore, for the exposure of the third and subsequent layers, the same operations as those for the second layer, ie, operations from step 200 to step 207, are performed. As a result, rotational errors between the overlapping patterns due to yawing of the wafer stage 6 are corrected,
Accurate overlapping exposure is performed.

(Thus, according to the present embodiment, errors in the vertical direction due to yawing during measurement of RR (reticle rotation) and CR (chip rotation) are both based on the amount of rotation of the wafer stage 6 detected from the θ counter 27. Then, based on these measured values, the reticle stage 2 is rotated by Δθ, which prevents the influence of yawing accompanying all movements of the webber stage 6, and accurately calculates θ. The counters 24 and 27 are correlated.For this reason, the relative rotational error between the projected image Pr' of the circuit pattern of the reticle R and each chip C arranged on the wafer W due to the yawing of the wafer stage 6 is determined by the wafer stage 6. Correction can be made by rotating the reticle stage 2 by Wθ in the same direction as the rotation direction of the stage 6.

Also, based only on the data of the yawing measurement of the wafer stage 6 by the laser interferometer 13, the reticle stage 2
Since the reticle stage 2 is simply rotated so that the θ counter 24 measures the same amount of rotation, even if alignment (mark detection operation) is performed for each shot, the projected image Pr' of the pattern of the reticle R and the wafer W A relative rotational error with each chip C arranged above is corrected.

As described above, in one embodiment of the present invention, a case has been described in which the circuit patterns of the second and subsequent layers are overlapped with each chip C on the wafer W and exposed. However, even if the method of the present invention is applied to the case where the first layer circuit pattern is exposed on the wafer W using a step-and-repeat method, the first layer circuit pattern may be exposed in steps due to the yawing of the wafer stage 6. - It is clear that exposure on the wafer W by rotating with respect to the coordinate system XY as a moving coordinate system by the AND repeat method is prevented.

That is, the relative rotational deviation of the reticle due to reticle rotation with respect to the coordinate system XY in the first layer exposure is corrected by rotating the reticle stage 2 in the positive direction by Δθ in the same manner as described above.

At this time, the rotation amount Δθ of the reticle stage 2 is 80 −θr because the chip rotation is zero (no chips are formed on the wafer W). Then, the wafer stage 6 is stepped by a predetermined amount to sequentially perform exposure. Rotation amount Wθ of wafer stage 6 due to yawing
is detected using a laser interferometer 13 and a θ counter 27,
The rotational deviation of the circuit pattern is corrected by rotating the reticle stage 2 by Wθ in the same direction as the rotational direction of the wafer stage 6 in accordance with the rotation amount Wθ.

In addition, the θ counter 24 and the θ counter 27 are each reset to zero, and the relative rotational error between the reticle R and the wafer W due to coing is corrected by using the rotation 1wθ of the wafer stage 6 as a secondary side. was. However, instead of resetting the θ counters 24 and 27 to zero, the θ counter 2 after rotating the reticle stage 2 by 80 degrees
4 count value θ1 and the θ counter 27 at the time of startup of the exposure device
and the count value θ2 are stored in the CPU 30 as initial values. Then, based on these initial values θ1 and θ2, the amount of rotation of the reticle stage 2 and wafer stage 6 is determined,
It is clear that the same effect can be obtained even if the relative rotational error between the reticle R and the wafer W is corrected. Further, resetting the θ counter 27 to zero or storing the count value θ2 is not limited to the time when the exposure apparatus is started, but may be performed from the time the exposure apparatus is started until just before the RR and CR measurements are performed. Similarly, resetting the .theta. counter 24 to zero or storing the count value .theta.1 may be carried out between after the completion of RR and CR correction and before the overlapping exposure of the first shot position is executed.

Also, in this embodiment, as in step 201, the LSA system 1
7a, perform the CR measurement with correction of Atsube's error, average the CR of multiple chips C located near the center of the wafer W, and find the rotation amount θC of the chip C on the wafer W with respect to the θ axis. was. However, the method for measuring the rotation amount θC used in this embodiment is not limited to the above method. For example, the CR of a plurality of arbitrary chips C located near the center and the outer periphery of the wafer W is detected by the LSA system 17a, Atsube's error is corrected, and the optimal one is determined using a statistical method such as the least squares method. It is clear that the same effect can be obtained by determining the rotation amount θC.

〔Effect of the invention〕

As described above, according to the present invention, even if rotational deviation of the wafer stage occurs due to stepping of the wafer stage, the circuit pattern on the wafer and the circuit of the reticle in the overlapping exposure of the second and subsequent layers due to this influence. Coordinate system XY as a movement coordinate system of the wafer stage 6 due to the rotation error relative to the pattern and the step-and-repeat method of the first layer circuit pattern arranged on the wafer.
It has the advantage that rotational deviation can be prevented from occurring, exposure can be performed with high precision and in a short time according to the movement of the wafer stage, and a decrease in throughput can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of a system suitable for implementing an alignment method according to an embodiment of the present invention, and FIG. 2 is a control of an apparatus that applies an alignment method according to an embodiment of the present invention. 3 is a flowchart for explaining the operation of this embodiment, FIGS. 4, 5, and 6 are diagrams for explaining the reticle rotation measurement operation, and FIG. 7 is a block diagram of the system. Chip C and reticle R by chip rotation and reticle rotation
FIG. 4 is a diagram for explaining correction of a rotational error relative to that of FIG. 1... Projection lens, 2... Reticle stage, 3.
4.5... Reticle stage drive unit, 6... Wafer stage, 10.11.12.20.21.22...
・Laser interferometer, 16a, 16b...Gui high dial alignment system, 1.7a, 17b...Laser...
Step alignment system, 24.27...θ counter, 30...processor (CPU), R...reticle, W...wafer.

Claims (3)

[Claims] (1) A device is used that sequentially positions and exposes a pattern formed on a mask via a projection optical system onto each of a plurality of shot areas arranged in a matrix on a photosensitive substrate using a step-and-repeat method. a first step of setting the mask so that a relative rotational deviation of the mask with respect to the photosensitive substrate is within a predetermined tolerance; from a predetermined first reference position of the mask; a first rotation amount detection means for detecting the rotation amount of the photosensitive substrate;
A second sensor for detecting the amount of rotation of the photosensitive substrate from a predetermined second reference position that occurs when the photosensitive substrate is moved in an and-repeat manner.
a second step of associating the detection results with the rotation amount detection means after the first step; when exposing the pattern to each of the shot areas in the step-and-repeat method, a third step of rotationally driving the mask so that the amount detection means detects the amount of rotation that is approximately equal to the amount of rotation based on the detection result of the second amount of rotation detection means associated with the second step; An alignment method comprising: (2) The first rotation amount detection means includes a first counting circuit that measures the rotation amount of the mask from the predetermined first reference position in an incremental manner, and the second rotation amount detection means includes: a second counting circuit that incrementally measures the amount of rotation of the photosensitive substrate from the predetermined second reference position; the second counting circuit is reset to a second predetermined value before the first step; The first counting circuit is reset to a first predetermined value after the first step, and in the third step, the count value change by the second counting circuit of the second rotation amount detection means and the first rotation Claim 1, characterized in that the mask is rotationally driven so that the change in the count value by the first counting circuit of the amount detection means is approximately equal.
Alignment method described in section. (3) In the first step, detect the relative rotational deviation amount between the shot area previously formed on the photosensitive substrate and the mask, and rotate the mask until the rotational deviation amount becomes approximately zero. 3. The alignment method according to claim 2, further comprising resetting the first counting circuit to the first predetermined value in the second step.