JPH0774089A - Projection aligner - Google Patents

Abstract

PURPOSE:To adjust the focus position of a wafer and level it at high speed and accurately even in the case that the discrepancy between the surface of the wafer and the objective plane is large. CONSTITUTION:A projection aligner has an XY-stage 8 on which to place a wafer W. The XY-stage 8 has a leveling stage 9 which can adjust the focus position and the leveling condition. Moreover, the projection aligner has focus sensors 3-7 and 13-17 for detecting the height position of the wafer W, and it is provided with a designation means which designates either open control or monitoring control when controlling the condition (focusing and leveling) of the wafer surface, based on the signal from a focus sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection exposure apparatus having attitude control of a substrate such as a mask substrate for manufacturing semiconductor elements or a semiconductor wafer.

[0002]

2. Description of the Related Art A conventional device of this type is disclosed in, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Unexamined Patent Publication No. 8-103136, height positions of three or more points on the surface of a mask substrate or a wafer are measured in advance, an approximate plane of the substrate surface is obtained based on each measured value, and this approximation is performed. Leveling (tilting) the chuck that holds the substrate so that the plane is parallel to the specified horizontal plane.
And then exposed.

[0003]

As described above, in the conventional technique, the positions of three or more points on the substrate are measured, and the result is used to determine the drive amount of the drive shaft for bringing the substrate into the target posture. Since it is a method of calculating and driving, there is a difficulty in improving the accuracy of the position of the substrate after driving. That is,
Since the measurement system and the drive system are independent of each other, if the drive accuracy is low, the correct positioning accuracy cannot be obtained no matter how good the measurement system accuracy is. This is because good precision cannot be obtained if the precision is lower than the precision of driving.

The present invention has been made in view of such conventional problems, and an object thereof is to improve the precision of the control position of the substrate.

[0005]

In order to solve the above problems, the present invention provides a projection optical system for projecting a mask pattern onto one of a plurality of shot areas on a photosensitive substrate, and the best combination of the projection optical system. A detection point is set at a specific position within the image plane, and a focus sensor that measures the amount of focus shift on the surface of the photosensitive substrate at the detection point and the photosensitive substrate along the best imaging plane
A projection exposure apparatus including an XY stage that moves dimensionally, and an adjustment stage that adjusts the focus position or leveling position of the photosensitive substrate with respect to the best image plane,
Measuring means for detecting the focus shift amount at each of a plurality of points on the photosensitive substrate using a focus sensor and measuring the current planar state of the photosensitive substrate surface; for bringing the measured planar state to a desired target plane. First calculation means for calculating a necessary drive amount of the adjustment stage; first drive means for driving the adjustment stage based on the calculated drive amount and an output of a drive amount detector provided in a drive section of the adjustment stage Calculating the offset amount in the focus direction of an arbitrary point of interest on the photosensitive substrate that occurs when the photosensitive substrate is displaced from the planar state during measurement to a desired state. And a calculation unit for adjusting the position of the point of interest by the calculated offset amount while detecting the focus shift amount of the point of interest on the photosensitive substrate by the focus sensor. Second control means and for driving the over-di; either specify one of the use of the first control means and second control means, and a further comprising a designating means for switching the driving mode of the adjustment stage.

[0006]

In the present invention, the first control means for driving the adjustment stage and the photosensitive substrate are measured based on the drive amount of the adjustment stage required to bring the plane state of the substrate to the desired target plane. The offset amount of the point of interest on the photosensitive substrate that occurs when the plane state is shifted to the desired state,
A second control means for driving the adjustment stage so that the position of the point of interest is corrected, and the use of either the first control means or the second control means is designated, and the adjustment stage drive mode Since it was decided to switch, even if the amount of deviation between the desired target plane and the current plane state of the substrate is large,
The posture of the substrate can be controlled at high speed and with high accuracy.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of a step-and-repeat type projection exposure apparatus to which an attitude control apparatus according to an embodiment of the present invention is applied. Reticle R with circuit pattern
Are held by the reticle holder 2 and are illuminated by the illumination light IL having a uniform illuminance. The pattern of the reticle R is image-projected by the projection lens PL onto the wafer W for semiconductor device fabrication. The wafer W is placed on the leveling stage 9 and tilted in arbitrary directions by the drive systems 10, 11 and 12 at three places. In FIG. 1, the wafer W has a taper, and in order to correct this taper so that the surface of the wafer W and the best image plane of the projection lens PL (the conjugate plane with the reticle R) coincide (parallel), the leveling stage The state in which 9 is tilted is exaggerated. The leveling stage 9 and the drive systems 10, 11 and 12 are provided on the xy stage 8 that two-dimensionally translates in a horizontal plane.
The xy stage 8 is driven by a stage drive unit 30 including a motor and the like, and its coordinate position is sequentially measured by a stage interferometer 32. Also, the above leveling stage 9
In the present embodiment, for example, the drive system 10 is fixed, and the two drive systems 11 and 12 are independently moved up and down (movement in the optical axis direction of the projection lens PL).
Shall be allowed. The drive systems 11 and 12 move up and down in response to a drive amount command from the leveling drive unit 34.

The control unit 36 outputs a predetermined drive command to the stage drive unit 30 based on the measured coordinate value from the stage interferometer 32, and x at an arbitrary position in the xy coordinate system.
The y stage 8 (that is, the wafer W) is positioned. Now, in order to match the best image plane of the projection lens PL with the local shot area surface on the wafer W, an oblique incident light type focus sensor is provided. This sensor enters a light source 3 such as a multicolor LED or a halogen lamp having a broad wavelength distribution, a condenser lens 4, a slit 5, a slit image projection objective lens 7, and a slit image reflected light from the surface of the wafer W. Receiving objective lens 13, vibrating mirror 1
4, a herbing glass (parallel plate glass) 6, a light receiving slit 15, a photoelectric element 16 and the like, and the details are the same as those disclosed in JP-A-60-168112. Therefore, when the reflection image of the slit image on the wafer W vibrates across the slit 15 due to the action of the vibrating mirror 14, and when the vibration center of this reflection image and the center of the slit 15 coincide with each other, the surface of the wafer W is best bonded. The image plane is set to match (focus). Although not shown in FIG. 1, the photoelectric signal (AC) from the photoelectric element 16 is synchronously detected based on the vibration frequency of the vibrating mirror 14 and becomes OV at the time of focusing, depending on the front focus and rear focus of the focus shift. As a focus signal, an analog signal (so-called S-curve signal) whose voltage changes positively and negatively is obtained. A Z stage (not shown) (which is included in the xy stage 8) is vertically moved by servo control so that the focus signal is always OV, so that the pattern image of the reticle R is focused for each shot area. Exposed. Further, the harving glass 6 relatively displaces the light receiving slit 15 and the vibration center of the slit reflection image, and by tilting the harbing glass 6, the surface height of the wafer W detected as the focal point can be adjusted. The projection lens PL can be shifted (focused offset) in the optical axis direction. The inclination of the harving glass 6 depends on the harving drive unit 38.
The tilt amount (focus offset) is detected by using the rotary encoder 17.

Here, the control unit 36 controls the harving drive unit 3
8 to execute either one of the two modes. One mode is a height measurement mode in which the inclination of the harving glass 6 is fixed at a predetermined origin (or a preset point) in order to measure heights at multiple points on the surface of the wafer W, and the other modes are , The best imaging plane of the projection lens PL itself is changed in the optical axis direction due to changes in environmental temperature, humidity, atmospheric pressure, or accumulation of exposure energy, and the inclination of the harving glass 6 is sequentially changed. It is a follow-up mode.

A detailed operation of inclining the harving glass 6 in this follow-up mode is described in, for example, Japanese Patent Laid-Open No.
It is disclosed in Japanese Patent Publication No. 1-183928. The above-mentioned grazing incidence light type focus sensor may be a method other than the synchronous detection type, for example, a reflection slit image from the wafer surface is received by a one-dimensional photo array (CCD or the like) or a one-dimensional position sensor (PSD or the like), and The same effect can be obtained by detecting the defocus from the change in the light receiving position. Further, since the slit image of the slit 5 on the wafer surface is projected almost at the center of the shot area to be exposed, the focus of the actually exposed portion is performed in real time.

FIG. 2 is a diagram showing the structure of the leveling stage 9. The wafer W is attracted to a wafer holder (chuck) WH, and the wafer holder WH is provided integrally with the leveling stage 9. 3 drive systems 1
0, 11, and 12 are located on three virtual lines l _a , l _b , and l _c radially extending from the center of the wafer W (or the center of the wafer W mounting surface of the holder WH), and the line l _a , L _b ,
l _c is open at an angle of approximately 120 °. The distances from the center of the wafer to the points of action of the drive systems 10, 11 and 12 are substantially the same. Here, in order to simplify the following description, the drive system 10 serving as a fixed point is referred to as the C-axis, and each of the two vertically moving drive systems 11 and 12 is denoted by A.
The axes will be called the B axis. Further, the drive systems 11 and 12 are provided with potentiometers for detecting the height positions of the A axis and the B axis from a predetermined origin. The measured value from this potentiometer is used in the open control described later in detail. The leveling stage having the above structure is disclosed in, for example, Japanese Patent Laid-Open No. 62-274201.

Next, the operation of this embodiment will be described.
In this embodiment, in order to make the wafer surface, which has been measured in advance, parallel to (or coincide with) a predetermined plane (here, the best image plane) as in the conventional case, the drive system 11 is moved by the tilt of the measured wafer surface. , 12 is uniquely driven by a predetermined amount, an open control system (open drive) and a monitoring control system (close drive), which is the most characteristic feature of this embodiment, can be selectively executed. ing.

FIG. 3 is a flow chart showing the basic sequence of global leveling in which either one of the open control and the monitoring control is executed to make the entire surface of the wafer W and the best image forming plane parallel to each other. is there. The steps 100 to 128 in FIG. 3 will be described below. [Step 100] Here, when the herbing drive unit 38 controls the inclination of the herbing glass 6 in the following mode among the two modes, the following of the herbing glass 6 is stopped to return to a predetermined origin. Switch to height measurement mode. Since the inclination of the harving glass 6 is detected by the rotary encoder 17, it is extremely easy to return to the origin.

Next, the control unit 36 moves the xy stage 8 to position the wafer W so that the approximate center of the wafer W is at the optical axis position of the projection lens PL, and at that position, a focus signal (S) obtained from the focus sensor. Curve signal) is O
Move the Z stage up and down to reach V. When the vertical movement of the Z stage is stopped, the height position is maintained and the next step 102 is executed. At this time, although the surface of the central portion of the wafer is set in focus with respect to the focus sensor, it is not always in focus with respect to the best image forming plane because the tracking mode is not set. [Step 102] Next, the wafer W designated in advance
At one of the plurality of measurement points P _i (i = 1, 2, 3, ...) Above,
X so that the slit image of the focus sensor is projected
The y stage 8 is positioned. At this time, the vertical movement of the Z stage is prohibited. Then, based on the focus signal obtained from the focus sensor at the measurement point P _i , the inclination of the harping glass 6 is servo-controlled to bring the measurement point P _i into the same state as when the focus sensor is in focus. As a result, the focus signal (S curve signal) becomes O.
When the voltage reaches V, the control unit 36 reads the amount of change from the encoder 17 via the harving drive unit 38. This amount of change corresponds to the difference in the height direction between the wafer center point and the measurement point P _i .

The above operation is similarly repeated for all of the plurality of measurement points P _i , and the height position of each measurement point P _i with respect to the wafer center point is measured. Generally, one plane can be specified by determining three points, so that at least three measurement points P _a , P _b , and P _c shown in FIG. 2 are selected.
Of course, more measurement points may be selected. Measuring point P _a, P _b, P _c each line l _a, l _b, and to be located above the l _c, distance measuring point P _a and A-axis, the measurement point P
_{It is} assumed that the distance between _b and the B axis and the distance between the measurement point P _c and the C axis are predetermined. [Step 104] Next, the control unit 36 controls the plurality of measurement points P.
the height position of _{i and} the position of each measurement point P _{i on} the xy coordinate system,
That is, the n-th order plane equation (current plane equation) of the wafer surface is calculated based on the three-dimensional coordinate value of the measurement point P _i . In this embodiment, the first-order plane equation is calculated using the least square method. Regarding the application of the method of least squares, Japanese Patent Laid-Open No. 58-58
Since it is described in detail in Japanese Patent Laid-Open No. -103136, the description is omitted here. [Step 106] Next, the target plane equation (assuming that it is stored in advance) corresponding to the best image plane of the projection lens PL is compared with the presently obtained first-order plane equation, Calculate how much the wafer surface is tilted with respect to the target plane. [Step 108] Next, it is determined whether or not the calculated relative inclination (deviation amount) is within an allowable range. The allowable range is set in consideration of the depth of focus of the projection lens PL, the size of the shot area, the size of the wafer W, and the like. If it is determined here that it is within the allowable range, the control unit 36 jumps to step 120, switches the harving drive unit 38 from the height measurement mode to the following mode, and ends the leveling operation. If it is outside the allowable range, step 110 is executed. [Step 110] Here, one of open drive and monitoring drive is selected in accordance with an instruction from the operator. Therefore, the case where the open drive is selected will be described first, and then the case of the monitoring drive will be described. [Step 112] First, based on the current plane equation of the wafer surface obtained in step 104, the height position T _a of the intersection of the leveling drive axes A and B with the respective current planes, Calculate T _b . The position of this intersection is known in advance from the distance of each drive system 10, 11, 12 from the wafer center. Further, the control unit 36, a difference S _a of the A-axis and the height position T _a of the B-axis ', T _b' similarly calculated, current height position when align your wafer surface target plane , S _b . Each axis A obtained by this calculation, the difference between the _{B S a = T a '-T} a, S b = T b' is a -T _b. [Step 114] Next, the control unit 36 moves the A axis up and down by servo control so that the potentiometer provided in the drive system 11 changes from the current value by S _a . [Step 116] Continuously or simultaneously with the control unit 36.
Causes the B axis to move up and down by servo control so that the current value of the potentiometer provided in the drive system 12 changes by S _b .

Through the above steps 116, the wafer W
Global leveling by the open control of is completed. [Step 118] Here, it is determined whether or not it is checked whether the wafer surface after leveling is parallel to the best image plane, and when it is checked, the process is repeated from step 102 again. Here, when the check is not necessary, the next step 120 is executed and the series of global leveling operations by the open control method is completed.

By the way, in step 110, the monitor
Open control method when ring control is selected
Executes a unique sequence unlike. Ie four
After the operation of each drive system 11 and 12 (or
Is operating) while monitoring the height position of the wafer surface,
Perform more accurate surfacing (posture control). Hereafter,
Refer to Fig. 4 (a), (b), (c)
Explain. [Step 122] First, at this point, the surface of the wafer W (currently
The present plane) is point A in Fig. 4 (a)₁, B₁, C₁3 points
It should be on the specified side. Point A₁, B₁, C₁of
Each is a point on each axis A, B, C. Target as well
The plane is point C₁, A₃, B₃Is on the surface defined by the three points
I shall. Also surface A₁B₁C₁The three set above
Point P _a1, P_b1, P_c1Each of the three
Measuring point P_a, P_b, P_cIt corresponds to. This
Measurement point P_a, P_b, P_cIs always shown in Figure 2.
You don't need to define the
The position measured by a total of 32) may be used. However,
The measurement points actually monitored during monitoring control are
P_a, P_bThere are only two points. Incidentally, surface C₁A₃B₃above
Three set points P_a3, P_b3, P_c3Is each measurement point P_a,
P_b, P_cRepresents the position on the target plane.

Now, based on the first-order plane equation of the current plane of the wafer surface obtained up to step 108, the control unit 36 determines only the height position of the A axis (point A ₁ ) as the height position of the target plane ( The plane equation of the first stage when it is held at the point A ₃ ) is obtained. That is, the plane C ₁ A shown in FIG. 4 (b)
₃ Obtain the first-order plane equation of B ₁ . Next, the point P on the first-stage plane C ₁ A ₃ B ₁ of the measurement point P _a closest to the A axis is
_a2 is obtained, and the height H _a of this point P _a2 is calculated. This height H _a corresponds to the amount of inclination of the harving glass 6 from the origin, that is, the amount of focus offset from the focus origin position set in step 100. [Step 124] When the height H _a of the point P _a2 on the plane C ₁ A ₃ B _{1 of the} measurement point P _a is obtained, the control unit 36 causes the focus sensor to receive a focus offset corresponding to the height H _a from the origin of harving. Harving drive 38 as given
To control. The harving drive unit 38 servo-controls the inclination drive of the harving glass 6 based on the reading value from the encoder 17. When giving this offset, the control unit 36 positions the xy stage 8 while keeping the height position of the Z stage fixed so that the focus sensor detects the measurement point P _a .

Next, the control unit 36 controls the focus sensor
Obtained measurement point P_aThe focus signal according to the height of the
Drive only the A-axis (drive system 11) vertically to reach V
Move. This is a servo signal of the drive system 11 for the focus signal.
By supplying to the road, it is possible to drive in very accurately. This
As a result, the first-order plane equation of the wafer surface is shown in Fig. 4 (b).
Surface C₁A₃B₁Matches [Step 126] Next, the control unit 36 drives only the B axis.
Then, the wafer surface is taken as plane C in FIG. 4 (b).₁A ₃B₁From first
Target plane C as shown in FIG.₁A₃B₃By all means
If it is, the measurement point P closest to the B axis_bHeight H_bCalculate
To do. Incidentally, in FIG. 4 (c), point P_b2Is the measurement point P
_bFace C₁A₃B₁The position above. This point P_b2High
It can also be calculated in advance. [Step 128] Next, the control unit 36 causes the focus sensor
Measurement point P_bTo detect the Z stage height
The xy stage 8 is positioned with the table fixed. That
And the focus sensor has a height H from the origin._bJust oh
Of the harving glass 6 so that
Adjust the amount of tilt.

Next, the control unit 36 outputs a focus signal O according to the height of the measurement point P _b obtained from the focus sensor.
Only the B axis (driving system 12) is servo-driven in the vertical direction so as to attain V. As a result, the first-order plane equation of the wafer surface agrees with the plane C ₁ A ₃ B _{3 in} FIG. 4 (c). Through the above steps 122 to 128, the global leveling by the wafer monitoring (close) control method is completed, and from the next step 118, the same operation as that described above is executed.

Next, another sequence of this embodiment will be described with reference to the flow chart of FIG. In this sequence, the flow after performing steps 100 to 108 exactly the same is different, and the characteristic step is steps 200 to 212 between steps 108 and 118. However, step 208 is a combination of the previous steps 112, 114, and 116, and step 210 is steps 122, 124, and
It is a combination of 126 and 128.

The sequence shown in FIG. 5 is particularly effective when the leveling amount is large, in which open control and monitoring control are automatically selected, and both control methods are sequentially combined. The steps 200 to 212 will be described below. [Step 200] After it is determined in step 108 that the deviation amount of the inclination between the current plane of the wafer surface and the target plane is more than the allowable range, it is checked here whether the deviation amount is more than a certain value. When the displacement amount is relatively large, the open control is selected and the process proceeds to step 202. When the displacement amount is relatively small, the monitoring control is selected and the process proceeds to step 204. [Step 202] Here, the sequence flag is set to the open side. [Step 204] Here, the sequence flag is set to the monitoring side. [Step 206] Here, the flag is checked, and if the flag is open, step 208 (steps 112 to 11)
Perform 6) to perform global leveling. When monitoring, step 210 (step 122-
128) to perform global leveling. [Step 212] Here, check the flag again,
When the leveling operation is performed on the open side, the process returns to step 102 and the same operation is repeated. On the contrary, when the leveling operation is performed on the monitoring side, the process proceeds to step 118 and the same operation as that described above is executed.

According to the above sequence, step 10
Even if the deviation amount determined in 8 is extremely large, the wafer W can be leveled accurately at high speed. Although the wafer surface after leveling and the best image forming plane of the projection lens PL are exactly parallel to each other until the halving drive unit 38 is returned to the follow-up mode in step 120, they are not always in agreement. . Therefore, by returning to the follow-up mode in step 120, and thereafter, the Z stage is servo-controlled based on the focus signal detected by the focus sensor, so that the in-focus state can always be maintained regardless of the fluctuation of the best imaging plane itself. .

As described above, according to this embodiment, the target plane A ₃ B ₃ C ₁ can be arbitrarily set in step 106, so that the best image plane of the projection lens PL is the xy stage 8.
Even if the image plane is tilted with respect to the moving plane, that is, even if the image plane tilt is generated, it is only necessary to set the target plane in accordance with the image plane tilt, and therefore, there is a resolution failure within one shot to be exposed. There is an advantage that there is no portion (such as the four corners of the shot).

Further, in an exposure apparatus having a projection lens, N. A. When a lens with a large depth of focus and a shallow depth of focus is mounted, the shallow depth of focus can be effectively used by designating the target plane according to the image plane inclination of the lens. Further, in the present embodiment, the height positions of three points on the wafer are measured to specify the plane, but of course, the wafer surface set on the plane at the first stage is remeasured during the monitoring control. The same can be applied to the case. For example, the points P _a2 , P _b2, etc. in FIGS. 4 (b) and (c) are re-measured, the height of the point P _a3 from this point P _a2 is recalculated, and the height of the point P _a3 relative to the point P _{a2 is} calculated. The focus offset is further given by the amount of deviation in the vertical direction to drive the A axis for monitoring,
Similarly it is also possible to monitor driving the B-axis gives the height direction of the shift amount by further focus offset of the point P _b3 with respect to the point P _b2.

On the wafer W to be measured in step 102
Point (to be exact, the detection area by the focus sensor)
And the point of monitoring during monitoring control is this
In the example, it is supposed to be partially duplicated, but this is completely duplicated
It does not matter at any point that does not exist. Furthermore, oblique incidence type
Since the focus sensor of is used,
Extremely accurate height measurement (for example, about 0.2 μm disassembly)
It is possible to measure multiple points on the wafer surface
The accuracy of identifying the approximate plane is improved. So for example
As shown in FIG. 6, P is formed on the surface of the wafer W.₁~ P₁₅Until
Set the measurement points (measurement shots) of the
The height of the points included in the surface of the important area or the surface of the important area
Wafer table can be
An approximate plane (primary plane) that best fits a part of the surface
The equation) can be determined. Measurement points in Fig. 6
(Shot) P₁Is located almost at the center of the wafer W,
(Shot) P₂, P₃, P_Four, P_FiveIs point P₁Almost from
They are defined so that they are equidistant in four directions.
G) P₆~ P₁₅Should be located near the periphery of the wafer surface
Stipulated in. Here, due to the influence of the wafer process, etc.
Consider the case where the wafer W is warped as shown in FIG.
It FIG. 7 shows the wafer W of FIG. 6 as a point (shot) P.₁₃,
P _Four, P₉Represents a cross section when cut by a line including. We
Point P in the process₁₃The area around the left side of the wafer is warped upward
Occurs, point P₉Warpage occurs in the vicinity (on the right side of the wafer) downward
If so, each measurement point P obtained by the measurement in step 102₁~
P₁₅The current surface of the wafer obtained by the method of least squares from the height of the wafer.
Plane A₁B₁C₁Is the wafer table as shown in FIG.
Slightly inclined with respect to the flat part near the center of the surface
turn into. Therefore, the warped area around the wafer
Measurement point, eg P₇, P₈, P₉, P₁₃, P₁₄Etc.
Weighting is applied to the measured height when calculating the least squares method.
Make it smaller and point P near the center₁~ P_FiveFor height measurements at
Then, the weighting is increased. This way,
Being affected by the warp around the wafer, which originally has poor yield
The center of the wafer with high yield
Will be done.

Depending on the wafer, as shown in FIG.
In some cases, the central part is generally bulging. First
Figure 8 shows point P in Figure 6.₁, P₂, P_Four, P₆, P₁₁Including
A cross section of the wafer is shown by a dashed line. Such a wafer
In case of, it is approximated by the first-order plane equation by the method of least squares
Wafer surface is plane A₁, B₁, C₁Partly like
Although parallel to the wafer surface, it is not
The sushi is not parallel either. So in this situation
In addition to global leveling, to block
A sequence for leveling should also be provided. Bu
Lock leveling is the process of making a number of blocks on the wafer surface.
To the first-order plane equation approximated for each block
Leveling is applied based on this. For example
In Figure 6, point P₁, P₂, P₃, P₆, P₇, P
₈The first block containing ₁, P₃, P_Four,
P₉, P_Ten, P₁₁A second block containing₁, P
_Four, P _Five, P₁₁, P₁₂, P₁₃A third block containing
Point P₁, P₂, P_Five, P₆, P ₁₄, P₁₅A fourth boo including
Divide into 4 blocks with rock. And first, each block
The heights of the measuring points inside are sequentially measured in step 102.
After that, a first-order plane equation for each block is obtained. This conclusion
As a result, for example, the first block is as shown in FIG.
Primary plane RP₁Is determined, and for the second block,
Primary plane RP₂Is determined.

After the primary plane for each block is determined,
When each shot is exposed by the step-and-repeat method, it is determined which block the shot belongs to, and the primary plane of the block is parallel to the best image plane (target plane). You can do leveling. It is desirable that the block leveling be similarly performed in the alignment operation before the exposure operation when the sample alignment for detecting the positions of the alignment marks associated with the plurality of shot areas on the wafer is executed.

It is also possible to measure three points on the wafer and perform global leveling by open control, and then measure a large number of measurement points again to perform block leveling during exposure or sample alignment. Further, although the throughput is slightly lowered, for example, a sequence as shown in the flowchart of FIG. 9 may be provided in order to perform the block leveling with higher accuracy. FIG. 9 schematically shows a sequence in which the precision of the monitoring control system and the high speed of the open control system are efficiently combined at the time of block leveling.

First, in step 220, a first-order plane equation for each block is obtained, and in step 222, the A-axis and the B-axis of one block are monitored and controlled, and the current plane and the target plane of the one block are accurately matched. Let At this time, it is preferable to use at least two points included in the block as points to be monitored by the focus sensor. When the leveling of the block is completed by the monitoring control, the height positions of the A-axis and the B-axis (driving system 11, 12) at that time are read from the potentiometer and stored in step 224. This operation is executed for all blocks on the wafer (step 226), and the leveling amount (potentiometer value) for each block is stored in advance. This leveling amount is extremely precise because it is determined by monitoring control. Next, when the operation of sample alignment or exposure is started, the wafer may be tilted by open control for each block based on the stored leveling amount as in step 228.

When performing block leveling, if the number of blocks to be divided is increased, leveling for each shot area on the wafer, so-called each leveling (or Di
e by Die leveling) is also possible. Further, in the present embodiment, since the approximate plane equation of the wafer surface can be handled by a quadratic or higher equation, if the wafer surface is wavy like the wafer W shown in FIG. ), The higher plane A ₁ B ₁ C ₁ ′ may be determined based on the height value of the measurement point P _i . In this case, surface A ₁ B
Although it takes some time to calculate ₁ C ₁ ',
After the surface A ₁ B ₁ C ₁ ′ is specified, the most approximate tilt amount for an arbitrary shot area SA on the wafer surface is immediately obtained, so that leveling can be performed for each shot. This also applies to the wafers shown in FIGS. 7 and 8.

Although the position of the xy stage 8 is measured by the interferometer 32, the lateral displacement amount of the wafer W due to the leveling operation is generally not detected by the interferometer 32. This is because the moving mirror for receiving the laser beam from the interferometer 32 is not provided on the leveling stage 9. Therefore, if the position of the wafer W in the xy direction is deviated by a small amount before and after the leveling operation, correct overlay exposure cannot be performed. Of course, such a problem does not occur if the position of the alignment mark on the wafer is measured after performing the global leveling or the block leveling. However, depending on the sequence, the leveling amount may differ when the shot position on the wafer is determined by performing sample alignment and when the shot is actually exposed. Therefore, in this case, the lateral shift amount of the shot may be calculated from the difference in the leveling amount, or a lateral shift amount detection sensor may be provided between the leveling stage 9 and the movable mirror on the xy stage 8.

In the global leveling described above,
The operation for one wafer was described, but when multiple wafers in the same lot are processed consecutively, global leveling (or block leveling) is performed only for the first wafer in the lot, and subsequent wafers are processed. About A axis, B
It can also be used with the shaft fixed. Furthermore, it is also possible to perform the leveling operation for the first and second wafers in the lot, process the average value of the leveling amount of each wafer, and process the subsequent wafers with the average constant leveling amount. Is.

In the embodiment described above, step 10
When the number of measurement points on the wafer is 3 in the operations 2 and 104,
Identify the current plane A ₁ B ₁ C ₁ represented by the three points,
When there are four or more measurement points, the current plane A ₁ B ₁ C ₁ may be automatically specified by the least squares method. Further, when the control unit 36 determines the measurement point on the wafer, the focus sensor normally works to detect the center of the shot area. It also has an automatic addressing function that checks whether or not it protrudes from the outer shape, and if it protrudes, resets the shot area to be the measurement point inside the wafer.

Further, in the present invention, as a method for determining the best image plane to be the target plane, a test reticle is used to carry out trial baking on a wafer, and the resolving power of the four corners in one shot area is examined. A method of obtaining the height position in the Z direction (focus direction) that maximizes the resolution (best focus) for each of the four corners can be used. For example, as shown in FIG. 11, since the test chart is used, the best focus position (height) at the four corners of the shot is Z due to baking.
_{It is} assumed that it is calculated as ₁ , Z ₂ , Z ₃ , Z ₄ . In this case, the first-order plane equation that determines the target plane A ₃ B ₃ C ₁ is Z = ax + by + γ (where a, b and γ are constants)
When the constants a, b is _{b = (Z 1 + Z 2} ) - represented by _{(Z 1 + Z 3) /} 2L - (Z 3 + Z 4) / 2L a = (Z 2 + Z 4). Here, L corresponds to the length of the shot area in the x and y directions.

Of course, it is also possible to obtain the best focus positions at a larger number of points in the shot area by trial firing and determine the n-th order plane equation of the target plane by the least square method or the like.

[0037]

As described above, according to the present invention, even when the amount of deviation between the desired target plane and the current plane state is large, the posture of the substrate can be controlled accurately at high speed. In addition, if the planar state of the substrate is greatly deviated from the desired target plane,
The drive mode of the adjustment stage can be switched depending on the case where the plane state of the substrate deviates from the target plane.

Therefore, it is possible to eliminate the influence caused by the taper of the substrate such as an individual wafer (or mask), and obtain the theoretical resolution of the apparatus during exposure.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a projection exposure apparatus incorporating a substrate attitude control apparatus according to an embodiment of the present invention,

FIG. 2 is a plan view showing a planar configuration of a leveling stage unit,

FIG. 3 is a flow chart for explaining the basic operation of this embodiment.

4 (a), (b), and (c) are perspective views showing a modeled state of performing wafer leveling by a monitoring control method;

FIG. 5 is a flowchart of a sequence in which open control and monitoring control are combined,

FIG. 6 is a plan view showing arrangement of measurement points on a wafer,

FIG. 7 is a diagram showing an example of a cross-sectional shape of a wafer,

FIG. 8 is a diagram showing an example of a cross-sectional shape of a wafer,

FIG. 9 is a flowchart of a sequence suitable for block leveling,

FIG. 10 is a diagram showing an example of a cross-sectional shape of a wafer,

FIG. 11 is a plan view showing a method for determining a target plane.

[Explanation of symbols]

 PL ... Projection lens, W ... Wafer, 6 ... Harving glass, 7 ... Projection objective lens, 8 ... XY stage, 9 ... Leveling stage, 10, 11, 12 ... Leveling drive system, 13 ... Light receiving objective lens, 16 ... Focus Photoelectric device of sensor, 34 ... Leveling drive unit, 38 ... Harving drive unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G03F 9/00 H 9122-2H

Claims (6)

[Claims] 1. A projection optical system for projecting a mask pattern onto one of a plurality of shot areas on a photosensitive substrate, and a detection point is set at a specific position in the best imaging plane of the projection optical system and the detection is performed. A focus sensor that measures the amount of focus deviation of the surface of the photosensitive substrate at a point, an XY stage that moves the photosensitive substrate two-dimensionally along the best image plane, and the focus position or leveling of the photosensitive substrate with respect to the best image plane. In a projection exposure apparatus including an adjustment stage for adjusting the position, the focus sensor is used to detect the focus shift amount at each of a plurality of points on the photosensitive substrate, and the current planar state of the photosensitive substrate surface is measured. Measuring means; first computing means for calculating a drive amount of the adjustment stage necessary to bring the measured plane state to a desired target plane; and the calculation First control means for driving the adjustment stage based on the driven amount and the output of a drive amount detector provided in the drive section of the adjustment stage; Second computing means for calculating an offset amount in the focus direction of an arbitrary point of interest on the photosensitive substrate, which occurs when the photosensitive substrate is shifted to the state; While detecting the amount of focus shift at the point of interest above,
Second control means for driving the adjustment stage so that the position of the point of interest is corrected by the calculated offset amount; one of the first control means and the second control means A projection exposure apparatus comprising: a designation unit that designates use. 2. The determining means determines whether or not predetermined positions in the plurality of shot areas corresponding to the detection points are off the photosensitive substrate, and the detecting means uses the determining means. The projection exposure apparatus according to claim 1, further comprising a control unit that controls the XY stage so that a point is located on the photosensitive substrate. 3. The projection exposure apparatus according to claim 1, wherein the measuring means detects the focus shift for each of a plurality of partial areas of the photosensitive substrate. 4. The projection exposure apparatus according to claim 3, wherein the plurality of partial areas are the plurality of shot areas. 5. The projection exposure apparatus according to claim 1, further comprising detection means for detecting a lateral shift amount of the plurality of shot areas based on an inclination of the photosensitive substrate. 6. The projection exposure apparatus according to claim 1, wherein the measuring means measures the current plane state by weighting the focus shift amount with a predetermined weight.