JP3427113B2 - Stage accuracy evaluation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the accuracy of a stage for positioning a work piece or an object to be measured in a two-dimensional plane, and is particularly used when manufacturing a semiconductor element or a liquid crystal display element. It is suitable for application when evaluating the stepping accuracy of the wafer stage of the exposure apparatus.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device, a liquid crystal display device, or the like by a photolithography process, each shot area on a wafer (or glass plate, etc.) on which a reticle (or photomask, etc.) pattern is coated with a photosensitive material. An exposure device is used to expose to. This type of exposure apparatus is a so-called step-and-repeat method in which a wafer stage on which a wafer is placed is stepped and the operation of sequentially exposing the reticle pattern to each shot area on the wafer is repeated. Exposure equipment (steppers, etc.)
Is often used.

In general, a semiconductor element or the like is formed by stacking a large number of layers of circuit patterns on a wafer. Therefore, in an exposure apparatus, overlay accuracy is high when exposure is performed on the second and subsequent layers on the wafer. In addition, it is required to keep the stepping accuracy of the wafer stage within a predetermined allowable range. The stepping accuracy of the wafer stage means that after the exposure to a certain shot area A on the wafer is completed, the wafer stage is moved (stepped) in the X direction or the Y direction to expose the next shot area B to be exposed. It indicates a positioning error in the X and Y directions relative to the shot area A when installed in the field, a rotation error, and the like.

A so-called vernier evaluation method is known as a method of measuring the stepping accuracy in the conventional exposure apparatus. In this vernier evaluation method, a reticle on which a plurality of predetermined measurement marks are formed is used.
The plurality of measurement marks are exposed on the shot area of. Then, the wafer stage is stepped, for example, in the X direction to expose the plurality of measurement marks on the second shot area where the first shot area and the end in the X direction overlap. At this time, in the overlapping region, the measurement mark (main scale) exposed for the first time and the measurement mark (subscale) exposed for the second time are arranged close to each other. Since the positional relationship between the main scale and the vernier scale in the state where there is no stepping error is known in advance, conversely, by measuring the amount of positional deviation between the main scale and the vernier scale with respect to the design positional relationship, The principle of the vernier evaluation method is to obtain the stepping error.

Further, in the vernier evaluation method, X on the wafer
A plurality of shot areas arranged in a grid pattern so as to partially overlap each other in the Y-direction and the Y-direction are exposed with measurement marks, and after development processing, for example, several tens of points on the wafer are used, respectively, because of the design positional relationship. Measure the amount of displacement between the scale and the vernier scale. Then, the standard deviation σ (or 3σ) of the positional deviation amounts is obtained, and it is determined whether or not the standard deviation σ satisfies a predetermined standard to determine whether or not the stepping accuracy of the exposure apparatus is acceptable. It was

[0006]

As described above, in the prior art, the standard deviation σ of the amount of positional deviation between the main scale and the vernier scale is σ.
Since the pass / fail of the stepping accuracy of each exposure apparatus is determined based on (or 3σ), for example, its standard deviation σ
However, even when the stepping accuracy exceeds a predetermined standard and the stepping accuracy fails, a specific method for correcting the stepping accuracy cannot be determined. Therefore, conventionally, when the stepping accuracy is unacceptable, there is no method other than trial and error to correct the accuracy of the stage drive system or to replace it, and as a result, the time required for correction becomes long. There is an inconvenience that the throughput of the assembly adjustment process of the stage mechanism cannot be increased.

In view of the above point, the present invention provides a stage accuracy evaluation method capable of evaluating the stepping accuracy of a stage of an exposure apparatus according to various factors and suggesting a specific method for correcting the stepping accuracy. The purpose is to do.

[0008]

A first stage accuracy evaluation method according to the present invention positions a photosensitive substrate (W) in a first direction and a second direction which intersect each other in a two-dimensional plane. In the method for evaluating a stage of an exposure apparatus having a stage (14) and exposing a mask pattern (R) on the substrate, a photosensitive evaluation substrate (W) is placed on the stage (14), After the evaluation mark (26B) is exposed on the first shot area (SA ₁₁ ) on the evaluation substrate, the stage (14) is driven to move the evaluation substrate and then the evaluation substrate is moved. Second shot area (S ₁₁ ) that partially overlaps the first shot area (SA ₁₁ ) of
A ₁₂ ) has a first step of repeating the operation of exposing the evaluation mark (27H) on the A ₁₂ ).

Further, according to the present invention, the evaluation marks (26A, 27H) exposed in the overlapping portion between adjacent shot areas on the evaluation substrate are displaced in the first direction and the second direction. A second step of measuring the respective quantities (SX, BY) and a third step of obtaining a scaling error component (Rx, Ry in FIG. 9B) of the linear error component from the deviation amount measured in the second step And a fourth step of obtaining a rotation component (yawing) when the stage (14) is moved from the scaling error component obtained in the third step.

In this case, the rotational component at the time of movement of the stage (14) obtained in the fourth step is subtracted from the displacement amount (SX, BY) measured in the second step, and the stage (14) shows the difference. It is desirable to obtain the straightness error when moving in the first direction or the second direction. Also, the second
A rotation component when the stage (14) is moved, which is obtained in the fourth step from the deviation amount (SX, BY) measured in the step,
Also, it is desirable to find the positioning error of the wafer stage (14) by subtracting the straightness error when the stage (14) moves in the first direction or the second direction.

Further, according to the second stage accuracy evaluation method of the present invention, the stage (14) for positioning the photosensitive substrate (W) in the first direction and the second direction intersecting each other in the two-dimensional plane. For evaluating the photosensitivity of N (N is an integer of 2 or more) on the stage (14) in the evaluation method of the stage (14) of an exposure apparatus that exposes the mask pattern (R) on the substrate. The substrates are sequentially placed one by one, the evaluation marks are exposed on the first shot areas on each of the evaluation substrates, and then the stage (14) is driven to move the evaluation substrates, The first on the evaluation board
The first step of repeating the operation of exposing the evaluation mark on the second shot area partially overlapping the second shot area.

Further, the present invention is directed to the evaluation marks exposed in the overlapping portion between the adjacent shot regions of the N evaluation substrates in the first direction and the second direction. From the second step of measuring the deviation amount (SX, BY) respectively, and from the deviation amount measured in the second step, the deviation amount of the evaluation substrates for each sheet (see FIG. 20A). 3σ) is averaged over these N evaluation substrates (AV in FIG. 20C).
_W ), the total deviation of the deviation amounts of the N evaluation substrates (VR _{W in} FIG. 20C), and the deviation amounts of N deviation substrates in the same shot area on the N evaluation substrates. Variation of exposure apparatus which is variation (VR _{S in} FIG. 20C)
And a third step for obtaining.

In this case, the average variation (AV _W ) obtained in the third step and the overall variation (VR _W )
It is desirable to obtain the difference between the difference and the positioning error.

[0014]

According to such a first stage accuracy evaluation method of the present invention, first, by the vernier evaluation method, for example, as shown in FIG.
As shown in, the evaluation mark (27) exposed in the second shot area (SA ₁₂ ) partially overlaps the evaluation mark (26B) exposed in the first shot area (SA ₁₁ ).
The amount of deviation (SX, BY) from H) is measured, and the amount of deviation is similarly measured at many points. These measured deviation amounts include linear error and non-linear error in addition to the positioning error (stepping error in a narrow sense) in the original first direction (X direction) and the second direction (Y direction). The linear error includes a scaling error indicating linear expansion / contraction, an orthogonality error, and a rotation error. The non-linear error includes a rotation component due to yawing of the stage (14) and a coordinate of the stage (14). There is an error component due to bending of the moving mirror when measuring with an interferometer.

Therefore, in the present invention, first, the linear component obtained by the least-squares approximation method is subtracted from the measured displacement amount to obtain the rotational component due to the yawing of the stage (14). After that, the linear component and the rotational component due to yawing are subtracted from the measured displacement amount, and the error component due to the bending of the moving mirror (the straightness error when the stage moves)
Ask for. Then, the positioning error of the stage (14) (stepping error in a narrow sense) is obtained by subtracting the linear component, the rotational component due to yawing, and the error component due to the bending of the moving mirror from the finally measured displacement amount. Thereby, the stepping accuracy is evaluated for each factor. Therefore,
In order to improve the stepping accuracy, it is necessary to correct the factors that largely contribute to the stepping error.

Further, according to the second stage accuracy evaluation method of the present invention, the vernier evaluation method is applied to N substrates using the same exposure apparatus, and the evaluation marks for each substrate and each shot area are applied. Measure the amount of deviation. After that, the variation in the deviation amount of each of the evaluation substrates (FIG. 20).
The average variation obtained by averaging 3σ in (a) for these N evaluation substrates (A in FIG. 20C)
V _W ), the total deviation of the deviation amounts of those N evaluation substrates (VR _{W in} FIG. 20C), and the deviation amounts of N deviation substrates in the same shot area on the N evaluation substrates. Variation of the exposure apparatus, which is the variation of V (V in FIG. 20C).
R _S ) is required. In this case, the average variation (see FIG.
AV _{W of} 0 (c) indicates the average positioning ability of the exposure apparatus, and the variation of the exposure apparatus (VR in FIG. 20C).
_S ) indicates the error component characteristic of the exposure apparatus, and the overall variation (VR _{W in} FIG. 20C) indicates the error component including the offset variation of the stepping value between the substrates.

Further, the positioning error is obtained from the difference between the average variation (AV _W ) and the overall variation (VR _W ). Therefore, also in the present invention, the error factor is specified to some extent from the measured shift amount.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the stage accuracy evaluation method according to the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a projection exposure apparatus suitable for applying the evaluation method of the present embodiment. In FIG. 1, the illumination light IL generated from an ultrahigh pressure mercury lamp 1 is reflected by an elliptical mirror 2. The illumination optical system 3 including a collimator lens, an interference filter, an optical integrator (fly-eye lens), an aperture stop (σ stop), etc.
Incident on.

A shutter 11 for closing and opening the optical path of the illumination light IL by a motor 12 is arranged near the second focal point of the elliptic mirror 2. As the illumination light for exposure, laser light such as an excimer laser (KrF excimer laser, ArF excimer laser) or a harmonic wave of a metal vapor laser or a YAG laser is used in addition to the bright line of the ultra-high pressure mercury lamp 1 or the like. It doesn't matter.

In FIG. 1, illumination light (i-line or the like) IL in a wavelength range that exposes the photoresist layer emitted from the illumination optical system 3 is reflected by the mirror 4, and then the first relay lens 5 and the variable field of view. Aperture (reticle blind) 6 and second
It passes through the relay lens 7 and reaches the mirror 8. Then, the illumination light IL reflected by the mirror 8 in a substantially vertically downward direction illuminates the pattern area PA of the reticle R with substantially uniform illuminance via the main condenser lens 9. The arrangement surface of the reticle blind 6 has a conjugate relationship (imaging relationship) with the pattern forming surface of the reticle R, and the illumination field of the reticle R can be arbitrarily set by changing the size and shape of the opening of the reticle blind 6. .

The illumination light IL which has passed through the pattern area PA of the reticle R is incident on the projection optical system 13 which is telecentric on both sides (or one side), and is reduced to, for example, 1/5 by the projection optical system 13. The projected image of the pattern is projected (imaged) onto one shot area on the wafer W, which is held so that the surface thereof is coated with a photoresist layer and the surface is substantially aligned with the best image plane of the projection optical system 13. To be done. Below, Z is parallel to the optical axis AX of the projection optical system 13.
Take the axis, and in the plane perpendicular to the Z-axis parallel to the plane of the paper in Figure 1, X
The axis is taken as the Y axis perpendicular to the plane of FIG.

FIG. 3A shows the pattern of the reticle R of this embodiment. In FIG. 3A, the same evaluation marks R are provided on the peripheral portion in the pattern area of the reticle R.
A, RB, ..., RL are formed. Further, the evaluation marks RA to RC are located at positions substantially axisymmetric to the evaluation marks RG to RI with respect to the optical axis of the projection optical system 13, and the evaluation marks RD to RF are evaluated with respect to the optical axis of the projection optical system 13. The marks RJ to RL are substantially axially symmetrical. For example, the evaluation marks RA are, as shown in FIG. 3B, dot pattern rows 25Y arranged at a predetermined pitch in the X direction,
And a dot pattern row 25X arranged at a predetermined pitch in the Y direction. The evaluation mark RA may be formed as an opening pattern in the light shielding film or may be formed of the light shielding film in the transmissive portion. However, in the latter case, it is necessary to shield the mark portion formed by the second exposure from light. Further, on the reticle R, an alignment mark (not shown) composed of two cross-shaped light-shielding marks is formed in the vicinity of the outer periphery thereof so as to face each other.

Returning to FIG. 1, these two alignment marks are used for alignment of the reticle R (positioning with respect to the optical axis AX of the projection optical system 13). The reticle R can be finely moved in the direction of the optical axis AX of the projection optical system 13,
Further, it is mounted on the reticle stage RS which can be two-dimensionally moved and finely rotated in a horizontal plane perpendicular to the optical axis AX. Above the reticle R is a reticle alignment system (R
A system) 10A and 10B are arranged, and these RA system 10
2A and 10B are formed near the outer periphery of the reticle R.
This is to detect individual cross-shaped alignment marks. By slightly moving the reticle stage RS based on the measurement signals from the RA systems 10A and 10B, the reticle R
Indicates that the center point of the pattern area PA is the optical axis A of the projection optical system 13.
Positioned to match X.

On the other hand, the wafer W is vacuum-sucked by a finely rotatable wafer holder (not shown), and is held on the wafer stage 14 via this wafer holder. The wafer stage 14 is configured to be two-dimensionally movable by a step-and-repeat method by a driving device 19, and the wafer W
When the transfer exposure of the reticle R onto one shot area above is completed, the wafer stage 14 is stepped to the next shot position.

FIG. 2 shows a coordinate measuring mechanism of the wafer stage 14 shown in FIG. 1. In FIG.
4 is a movable mirror 16 for the X axis and a movable mirror 16 for the Y axis.
The laser interferometer 17X for X axis and the laser interferometer 17 for rotation measurement are fixed so that Y is opposed to the movable mirror 16X.
A laser interferometer 17Y for the Y axis is fixed so that R is fixed and faces the movable mirror 16Y. Laser interferometer 1
The optical axis of 7X and the optical axis of the laser interferometer 17Y are set to cross the optical axis AX of the projection optical system 13, and the optical axis of the laser interferometer 17R is an off-axis system arranged on the side surface of the projection optical system 13. Alignment system 23 (omitted in FIG. 1)
It is set to cross the optical axis of. The laser beams LX and LR from the laser interferometers 17X and 17R are also included.
Is reflected by the moving mirror 16X, the laser beam LY from the laser interferometer 17Y is reflected by the moving mirror 16Y,
The measurement coordinates of the laser interferometers 17X, 17R, and 17Y are the main control system 18 and the alignment control system 1 of FIG. 1, respectively.
9 is being supplied.

The X coordinate of the wafer stage 14 is
Wafer stage 1 obtained by laser interferometer 17X
The Y coordinate of 4 is obtained from the measurement coordinate of the laser interferometer 17Y. These measurement results are constantly detected with a resolution of, for example, about 0.01 μm. The stage coordinate system (stationary coordinate system) (X, Y) of the wafer stage 14 is determined by the measurement coordinates in the X and Y directions.

On the wafer stage WS, a reference member (glass substrate) 15 having a reference mark used when measuring the baseline amount (the amount of deviation between the reference position of the alignment system and the reference position of exposure) is used. , The height of which is substantially the same as the exposed surface of the wafer W. Next, on the upper side of the projection optical system 13, is a TTL (through the lens).
Also, an alignment system 20 for the X-axis of the laser step alignment method (hereinafter, referred to as “LSA method”) is arranged, and the laser beam AL for position detection from the alignment system 20 is reflected by the mirror 21 and the mirror 22. It is guided to the projection optical system 13 via. The laser beam AL is irradiated via the projection optical system 13 as spot light 24X having a slit shape elongated in the Y direction near the evaluation mark image of the measurement target on the wafer W as shown in FIG. Figure 1
Return to the spot stage 24X through the wafer stage 14.
On the other hand, when the evaluation mark image is scanned in the X direction, when the evaluation mark image crosses the spot light 24X, the diffracted light from the evaluation mark image is projected onto the projection optical system 13 and the mirror 2.
2 and the mirror 21 to be returned to the alignment system 20. The detection signal photoelectrically converted by the alignment system 20 is supplied to the alignment control system 19. L like this
A more specific configuration of the SA type alignment system is disclosed in, for example, Japanese Patent Laid-Open No. 2-272305.

The alignment control system 19 is also supplied with the coordinates (X, Y) of the wafer stage 14 measured by the laser interferometers 17X, 17Y, 17R, and the alignment control system 19 detects, for example, from the alignment system 20. The X coordinate of the wafer stage 14 when the signal reaches a peak is detected as the X coordinate of the evaluation mark image to be measured,
The X-coordinate of each detected mark image for evaluation is sequentially determined by the main control system 18
Supply to. At this time, in this embodiment, the X coordinate is determined based on the measurement value of the laser interferometer 17X. In this case, since the spot light 24X is away from the optical axis of the laser interferometer 17X, Abbe error occurs. In this system, the Abbe error is corrected by obtaining the difference between the measurement results of the laser interferometers 17X and 17R.

Similarly, as shown in FIG. 2, the projection optical system 1
An LSA type Y-axis alignment system for irradiating a laser beam as a slit-shaped spot light 24Y long in the X direction is also arranged on the wafer W in the exposure field of No. 3. Then, the evaluation mark image is scanned with respect to the spot light 24Y, and the diffracted light from the evaluation mark image is received by the Y-axis alignment system. The detection signal from this Y-axis alignment system is also the alignment control system 1 of FIG.
9, the alignment control system 19 obtains the Y coordinate of the evaluation mark image from the detection signal and supplies it to the main control system 18. Also on this Y axis, the spot light 24Y is distant from the optical axis of the laser interferometer 17Y, and thus the Abbe error is similarly corrected.

In the main control system 18, the alignment control system 1
The coordinates of the respective evaluation mark images supplied from 9 are processed as described later to evaluate the stepping accuracy of the wafer stage 14. Note that the coordinates of each evaluation mark image may be arithmetically processed by another processing device. Next, an example of the stepping accuracy evaluation method in this embodiment will be described. First, as the reticle, a reticle R on which a large number of evaluation marks are formed as shown in FIG. 3 is used.

First, the wafer stage 14 of FIG.
Drive, as shown in FIG. 4 (a),
First row shot area S arranged in the X direction on stack W
A₁₁, SA₁₂・ ・ ・ Reticle R pattern is sequentially exposed on top
To do. At this time, the shot area SA₁₁, SA₁₂, ... is X
The end portions in the direction are arranged so as to overlap each other by a predetermined width.
Next, on the wafer W, the second row shots arranged in the X direction are
Area SA_{twenty one}, SA_{twenty two},, ... and the reticle R pattern
Expose the cord. At this time, the shot area SA _{twenty one}, SA
_{twenty two}, ... overlaps the edges in the X direction by a specified width and
The second shot area and the second shot area are in the Y direction.
The ends are arranged so as to overlap each other by a predetermined width. Less than,
Similarly, in the shot areas on the third and subsequent rows on the wafer W,
Shots adjacent to each other in the X and Y directions
Step the wafer stage 14 so that the edges of the regions overlap.
Ping drive to sequentially expose the pattern of the reticle R
Go.

After the exposure of all the shot areas on the wafer W is completed, the photoresist on the wafer W is developed and the evaluation mark image exposed on the wafer W is left as an uneven pattern. . The wafer W is again shown in FIG.
Mounted on the wafer stage 14 of, and using the LSA type X-axis alignment system 20 and the Y-axis alignment system, the stage coordinate system (X,
Y) Measure the coordinates on. At this time, the evaluation mark images to be measured are arranged as shown in FIG.

FIG. 4B is an enlarged view of the vicinity of the shot area SA _{11 in} FIG. 4A. In FIG. 4B, the shot area SA ₁₁ and the shot area SA ₁₂ in the X direction are shown. Evaluation mark images 26A to 26C formed by exposure to the shot area SA ₁₁ and evaluation mark images 27 formed by exposure to the shot area SA ₁₂ in the overlapping area.
I to 27G are arranged close to each other. The evaluation mark images 26A to 26C are images of the evaluation marks RA to RC in FIG. 3A, and the evaluation mark images 27I to 27C.
G is an image of the evaluation marks RI to RG in FIG. In this case, the evaluation mark images 26A, 26B, 26C
And the evaluation mark images 27I, 27H, 27G from a predetermined reference interval (alignment error)
ΔA, ΔB, and ΔC are measured by an LSA type alignment system. Each alignment error ΔA to ΔC is X
It is composed of a shift amount in the direction and a shift amount in the Y direction. Then, the evaluation mark images 26B and 27H in the central portion
The amount of deviation in the X direction from and is called SX (step X), and Y
The amount of deviation in the direction is called BY (back Y).

Specifically, the evaluation mark images 26B and 27H
In order to measure the deviation amount SX from the above, as shown in FIG. 5, a laser beam is irradiated as slit-shaped spot light 24X from the X-axis alignment system in the vicinity of the evaluation mark images 26B and 27H. Then, the wafer stage 1
4 is driven to scan the spot light 24X with the evaluation mark images 26B and 27H in the X direction. When the spot light 24X and the evaluation mark images 26 and 27H match, the spot light 24X and the evaluation mark images 26D are diffracted in predetermined directions. Since light is generated, the X-coordinates of the evaluation mark images 26 and 27H are detected, and the deviation amount of the difference between these X-coordinates from the predetermined reference interval (the reference interval is 0 in FIG. 5) is the deviation amount. It becomes SX. Similarly, the deviation amount BY between the evaluation mark images 26 and 27H in the Y direction is also detected.

The deviation amount SX (step X) does not include the Abbe error. On the other hand, the deviation amount BY includes an error due to yawing of the wafer stage 14.
An error obtained by removing an error due to yawing from the deviation amount BY becomes a stepping error in a narrow sense. Figure 4 returns (b), the Y direction in the overlap region of the shot area SA ₁₁ and a shot area SA _21, the evaluation mark image 26D~26F formed by the exposure to the shot area SA _11, the shot area SA ₂₁ Mark image 28 formed by exposure to
L to 28J are arranged close to each other. The evaluation mark images 26D to 26F are images of the evaluation marks RD to RF in FIG.
J is an image of the evaluation marks RL to RJ in FIG. Also in this case, the evaluation mark images 26D, 26E, 26
The amount of deviation (alignment error) ΔD, ΔE, ΔF from the predetermined reference distance of the distance between F and the evaluation mark images 28L, 28K, 28J is measured by the LSA alignment system. Then, the evaluation mark image 26E in the central portion
And 28K are referred to as SY (step Y), and the amount of deviation in the X direction is referred to as BX (back X). The deviation amount SY does not include the Abbe error.

In this way, in the overlapping area of all the shot areas on the wafer W shown in FIG. 4A, the deviation amount (alignment) from the reference interval of the evaluation mark images formed close to each other. Error) is measured. As a result, the deviation amounts corresponding to the alignment errors ΔA to ΔF in FIG. 4B are measured for each shot area, and these alignment errors are recorded in the data file in the storage device. From these alignment errors, an error for each factor that deteriorates the stepping accuracy is obtained as follows.

First, yawing of the wafer stage 14 is a factor that deteriorates the stepping accuracy. Generally, when the wafer stage 14 moves, yawing occurs in which the rotational state of the wafer stage 14 changes depending on the moving position 14A as shown in FIG. When such yawing occurs, the shift amounts BX (back X) and BY (back Y) are affected by the rotation and include an error in FIG. 4B.

For example, as shown in FIG. 7, the yawing of the wafer stage 14 causes the shot areas SA ₁₁ , S to be shot.
When the arrangement of A ₁₂ , ... And shot areas SA ₂₁ , SA ₂₂ , ..., Changes in the Y direction between the shot areas of the first row, BY1, BY2 ,. Between the shot areas in the X direction in the X direction BX1, BX2, ...
Will change depending on the location.

As another factor that deteriorates the stepping accuracy, moving mirrors 16X and 16Y as shown in FIG. 2 are used.
There is a bend. If the movable mirrors 16X and 16Y themselves are bent in this way, even if the wafer stage 14 is linearly stepped in the X direction or the Y direction based on the coordinates measured by the laser interferometers 17X and 17Y, the steps shown in FIG. As shown in, shot areas SA arranged in the X direction
_{, 11} and SA ₁₂ are laterally displaced in the Y direction, and the shot areas SA ₁₁ , SA ₂₁ , ... Arranged in the Y direction are laterally displaced in the X direction. That is, the actual wafer stage 1
The movement locus of 4 is bent, and the shift amount BY in the Y direction between the shot areas on the same row as in the case of FIG.
(Back Y) and the shift amount BX (Back X) in the X direction between the shot areas between adjacent rows are changed depending on the location. Therefore, even when the movable mirrors 16X and 16Y are bent, the stepping accuracy is deteriorated.

Here, as shown in FIG. 4B, the shift amount (alignment error) measured for each shot area.
A method for obtaining the error due to the yawing of the wafer stage 14 and the error due to the bending of the movable mirrors 16X and 16Y will be described from ΔB (SX, BY) and ΔE (BX, SY). Therefore, n-th (n = 1,
(2, ...) Shot area and the shot area adjacent to the shot area are measured in the overlap area (SX, BY) as (A
_Let SB _Xn , ASB _Yn be the shift amount (BX, SY) be (ABS _Xn , ABS _Yn ).

Next, as shown in FIG. 4A, the wafer W
Let the sample coordinate system above be (x, y), and the designed (when exposed) center coordinates of the nth shot region on the sample coordinate system (x, y) be (D _xn , D _yn ). And In this case, the wafer W is placed on the wafer stage 14 after development processing and the like.
When the center coordinates of the shot area are measured by being placed on the stage coordinate system (X, Y), the center coordinates are linear with scaling Rx, Ry, orthogonality ω, rotation θ, and offsets Ox, Oy. The error and other non-linear errors are deviated from the designed coordinates (D _xn , D _yn ). The scaling Rx and Ry are
The ratio of the amount of positional deviation due to the linear expansion and contraction of the wafer W in the X direction and the Y direction is shown. The orthogonality ω has an X axis angle of Y axis +90.
The rotation θ indicates an angle [rad] between the sample coordinate system (x, y) and the stage coordinate system (X, Y).

Here, if (SX, BY), that is, (ASB _Xn , ASB _Yn ) is used as the shift amount, the measured coordinate value of the n-th shot area is (D _xn + ASB _Xn , D _yn +).
ASB _Yn ), the nonlinear error is (εASB _xn , ε
ASB _yn ), this non-linear error can be expressed as:

[0043]

[Equation 1]

In the present embodiment, the six parameters (Rx, Ry, ω, θ,
The value of Ox, Oy) is determined. For that, (Equation 1)
The sum of squares of the non-linear errors (εASB _xn , εASB _yn ) represented by is integrated over all the measured shot areas and the following residual error component is defined. It suffices to determine the values of the six parameters.

[0045]

[Equation 2]

As a result, a linear error component and a non-linear error component are obtained from the alignment error (SX, BY) in each shot area. Similarly, the shift amount is (B
X, SY), that is, (ABS _Xn , ABS _Yn ),
The measured coordinate value of the nth shot area is (D _xn + A
Since BS _Xn , D _yn + ABS _Yn ), the nonlinear error can be expressed as follows, where the nonlinear error is (εABS _xn , εABS _yn ). However, 6 parameters are (Rx ', Ry', ω ', θ', Ox ', Oy')
Is distinguished from (Equation 1).

[0047]

[Equation 3]

Also in this case, the six parameters (Rx ', Ry', ω ', θ', Ox ', O are calculated by the method of least squares.
Determine the value of y '). For that purpose, the values of these six parameters may be determined so that the residual error component of the following equation is minimized.

[0049]

[Equation 4]

As a result, the alignment error (B
(X, SY) is used to obtain the linear error component and the non-linear error component. Next, when there is yawing of the wafer stage 14 or the like, a simulation is performed in order to investigate the tendency of the above-mentioned linear error component and non-linear error component.

FIGS. 9 and 10 are simulation results when the rotation (yawing) as shown in FIG. 6 is applied so as to generate rotation of 1 μrad in the X direction and 0.5 μrad in the Y direction between the shot areas. , FIG. 9 shows the result when (SX, BY) is used as the alignment error.
Shows the result when (BX, SY) is used as the alignment error. For example, FIG. 9A shows an alignment error vector (BX, S) in each shot area on the wafer.
Y), and a vector 30 represents a vector of alignment error in the shot area. In addition, FIG.
(B) is the alignment error SX (step X), and B
The values of the average value of Y (back Y), three times the standard deviation (3σ), and the error from 1 of the scaling Rx and Ry representing the linear error, the orthogonality ω, and the rotation θ are shown. Further, FIG. 9C shows the standard deviation 3 of the linear error in the X direction and the Y direction obtained for each shot area from the parameters Rx, Ry, ω, θ and the offsets Ox, Oy.
9 (d) shows the value of 3 times (3σ), and FIG. 9 (d) shows the value of 3 times (3σ) of the standard deviation of the nonlinear error component in the X direction and the Y direction obtained from (Equation 1). The meanings of the numerical values in FIGS. 10B to 10D are the same as those in FIGS. 9B to 9D.

Focusing on the scaling Rx and Ry, the scaling error is the scaling Ry in FIG. 9B.
And the scaling Rx in FIG. 10B,
The error of the scaling Ry in FIG. 9B has the same value as the orthogonality ω in FIG. 10B. Further, the error of the scaling Rx of FIG. 10B is the same value as the orthogonality ω of FIG. 9A, and the error of the scaling Rx of FIG.
It can be seen that the sign is reversed from the rotation θ in (a). Therefore, when there is a rotation error in which the shift amounts of the shot areas are the same, the scaling R
An error value due to yawing is obtained by paying attention to x, Ry, the orthogonality ω, and the rotation θ. As an example, the scaling Ry value (0.5) of 1 in FIG.
/ 2, that is, 0.25 μrad is an error value due to yawing at the outermost periphery of the wafer.

Next, FIGS. 11 and 12 show the bending of the movable mirrors 16X and 16Y as shown in FIG. 2 so that the movable mirror 16X has a trapezoidal shape with a height in the X direction of 100 nm.
Further, the movable mirror 16Y is a result of giving a trapezoidal shape having a height in the Y direction of 50 nm. FIG. 11 shows the result when (SX, BY) is used as the alignment error, and FIG. 12 shows the alignment error. The result when (BX, SY) is used as is shown.

As can be seen from FIGS. 11 and 12, the bending of the movable mirrors 16X and 16Y causes the orthogonality ω, the rotation θ, and the nonlinear error, but the scaling Rx,
It is not an error of Ry. That is, as compared with FIG. 9 and FIG.
It can be seen that the error due to the yawing of 4 and the error due to the bending of the movable mirrors 16X and 16Y can be separated. Therefore,
First, after removing the error due to the yawing of the wafer stage 14 based on the scaling error (for example, after converting the values of the scaling Rx and Ry into coordinates and removing them from the alignment errors (SX, BY) and (BX, SY)). ),
In order to obtain the error due to the movable mirrors 16X and 16Y, the average value of the deviation amount BX (back X) for each shot area in the X direction is obtained, and the average value of the deviation amount BY in the Y direction is obtained.

The results of simulations using this method are shown in FIGS. 13 and 14 show simulation results when an error due to rotation of the wafer stage 14 such as yawing and an error due to bending of the movable mirrors 16X and 16Y are mixed, and FIG. 13 shows the alignment error as (SX, BY). Results when used, Figure 1
4 shows the result when (BX, SY) is used as the alignment error. From these errors, the errors due to the yawing of the wafer stage 14 are extracted by first focusing on the scaling factors Rx and Ry in correspondence with FIGS. 9 and 10. Specifically, the error of -0.42 ppm of the scaling Ry in FIG. 13B and the error of −0.42 μrad in the numerical value (−0.22 μrad) of the orthogonality ω in FIG. Is. Also, FIG. 14 (b)
The error of the scaling Rx of is almost 0, and the rotation in the X direction is negligible. As a result, it can be seen that the error due to yawing is mainly due to the rotation in the Y direction, as shown in FIG.

After removing the error due to the yawing from the results of FIGS. 13 and 14, the error due to the bending of the movable mirrors 16X and 16Y is derived as shown in FIGS. Dotted lines 34A to 34H in FIG. 15 indicate changes in the shift amount BX (back X) in each column, and a dotted line 35 is an average value of the shift amounts BX of the dotted lines 34A to 34H, that is, the movable mirror 16.
The curve of the movement trajectory of the wafer stage 14 due to the curve of X is shown. The numerical value on the right side of the dotted line 35 is a numerical value of the deviation amount when the deviation amount at the start point and the end point is regarded as 0. Similarly, the dotted lines 36A to 36H in FIG. 16 indicate changes in the deviation amount BY (back Y) in each row, and the dotted line 37 results from the average value of the deviation amount BY of the dotted lines 36A to 36H, that is, the bending of the movable mirror 16Y. The curve of the movement trajectory of the wafer stage 14 is shown. The numerical value below the dotted line 37 is a numerical value of the deviation amount when the deviation amount at the start point and the end point is regarded as 0.

Next, from the error of FIGS. 13 and 14, FIG.
18 and the error due to the bending of the movable mirror in FIGS. 15 and 16 are removed.
Deviation amount (SX, BY) and the deviation amount (BX, S) in FIG.
Y). The errors in FIGS. 18 and 19 are stepping errors in a narrow sense. In this way, by displaying the error for each factor separately, it is possible to accurately know which factor largely contributes to the error. Therefore, in order to improve the stepping accuracy, it is sufficient to remove it from the factors that greatly contribute to the error.

By various rotations including yawing
Regarding the error, random rotation for each shot area,
The difference between the X components of the deviation amounts ΔA and ΔC shown in FIG.
And the change rate of the difference between the Y components of the deviation amounts ΔD and ΔF
It is possible to make corrections by asking for it. Deviation amount ΔA and Δ
X component of C is SX_A, SX_CThen, the shift amount ΔA and
The difference of the X component of ΔC is (SX_A-SX_C), No
The Y component of the deviation amounts ΔD and ΔF is SY_D, SY_FThen,
The difference between the Y components of the deviation amounts ΔD and ΔF is (SY _D-SY
_F).

Next, another error analysis method in this embodiment will be described with reference to FIG. In this method, wafers to be measured are sequentially placed on the wafer stage 14 in FIG. 1 and the reticle pattern for evaluation is exposed as shown in FIG. Then, the exposed wafer is developed and mounted again on the wafer stage 14 of FIG. 1, and as shown in FIG. 4B, the alignment errors (SX, BY) and (BX) are set for each shot area. , SY) is measured by the LSA method.

The polygonal lines 31 and 30 in FIG. 20A are three times (3σ) [nm] the standard deviation of the alignment error (SX, BY) for each wafer measured in such a manner.
The polygonal lines 32 and 33 in FIG. 20B indicate three times (3σ) [nm] of the standard deviation of the alignment error (BX, SY) for each wafer measured in such a manner.

Further, in the present embodiment, the measurement results for all the wafers are processed, and as shown in FIG. 20C, for each of the alignment errors (SX, BY) and (BX, SY), each wafer is processed. Average value of 3σ of AV _W [n
m], 3 of standard deviation for all shot areas of all wafers
A variation VR _W [nm] that is three times (3σ) and a variation VR _S [nm] that is three times (3σ) the standard deviation of the average values of the same shot areas for all wafers are obtained. Furthermore, the measurement reproducibility for all shot areas of all wafers is 10 nm. In this case, the average value AV _W indicates the average positioning ability of the projection exposure apparatus, the variation VR _S indicates a characteristic error component of the projection exposure apparatus, and the variation VR _W includes the offset variation between wafers. Indicates an error. By analyzing these results, it is possible to determine what kind of error is large.

Further, in FIG. 20, the alignment error (S
Although the display is performed with three times the standard deviation (3σ) of (X, BY), etc., by switching the mode, for example, an analysis as shown in FIG.
It is also possible to perform an analysis as shown in FIG. 20 (c) for a more linear error component. Thereby, the cause of the error can be analyzed in more detail. Further, the variation of 3 times (3σ) of the standard deviation is determined to some extent by the numerical value of the 3σ. However, when the 3σ does not have a Gaussian distribution due to the influence of dust or the like, the variation of the 3σ is calculated and output. by doing,
It becomes easier to analyze the error factors. Similarly, the yawing of the wafer stage 14, the bending of the movable mirrors 16X and 16Y, and the other error factors may be classified, and an analysis as shown in FIG. 20C may be performed for each error of each factor. .

Next, an example of the operation for collectively executing the above-described alignment error analysis methods will be described with reference to FIG. First, in step 101 of FIG. 21, the X and Y components of the alignment errors ΔA to ΔF shown in FIG. 4B are measured. Let this measurement result be A. next,
In step 102, if the rotation such as yawing of the wafer stage 14 is to be corrected, the process proceeds to step 103, and if the rotation is not corrected, the process proceeds to step 106. In step 103, as shown in FIGS. 13 and 14, the alignment error A is calculated by the least square approximation calculation.
The shift amounts (SX, BY) and (BX, SY) of the above are separated into a linear component and a non-linear component. Then, step 104
In the linear component, scaling Rx, Ry
, And the orthogonality ω and rotation θ equivalent to
Error B is calculated, and in step 105, the error B is subtracted from the original error A to obtain the error C.

Then, in step 106, if the bends of the movable mirrors 16X and 16Y are to be corrected, the process proceeds to step 107, and if the bends are not to be corrected, the process proceeds to step 109. In step 107, FIG.
As shown in FIG. 16, the integrated value ΣBX in the row direction and the integrated value ΣBY in the column direction of the components of the deviation amount (BX, BY) in the error C calculated in step 105 are calculated, and further averaged. A value X _BOW (corresponding to the polygonal line 35 in FIG. 15) and an average value Y _BOW (corresponding to the bend destination 37 in FIG. 16) are calculated. Then, in step 108, the error D is calculated by subtracting the differential value (difference value) of the average value X _BOW and the average value Y _BOW from each row and each column from the error A or the error C.

Next, in step 109, the above is completed.
From the errors A, B, C and D obtained in this way, FIG.
As shown in (c), the average value A of 3σ for each wafer
V_W, Standard deviation 3 for all shot areas on all wafers
Double (3σ) value VR_W, And the same for all wafers
A value that is three times (3σ) the standard deviation of the average value for each shot area
VR _SAsk for. Then in step 110, the error
From A, B, C, D, average for each wafer and each shot area
Value, and minimum in 3 ways of all shot areas in all wafers
Calculated linear and nonlinear components by squared approximation
After that, the process proceeds to step 111 and the alignment error ΔA
X component of (ΔA + ΔB + ΔC) / 3 using ~ ΔF
And the sum of squares a of the Y component of (ΔD + ΔE + ΔF) / 3
Ask. Then, from the sum of squares a, SX of the error ΔB
And the square sum b of the error ΔE and SY
Measurement, that is, measurement of the LSA type alignment system 20, etc.
Seeking reality.

Next, the process proceeds to step 112, the display contents are selected, and the process proceeds to any of steps 113-119. In step 113, the above-mentioned respective errors A, B, C, D are displayed, in step 114 the error due to the yawing or the like indicated by the error B is displayed, and in step 115 the average value X _BOW and the average value Y _BOW are displayed. Then, in step 116, 3σ of each error ΔA to ΔF is displayed by the method of FIG. 20C, and in step 117, the offset fluctuation of the stepping value in the linear error component is displayed by the method of FIG. 20C, and At 118, an error other than the offset in the linear error component is displayed by the method of FIG. 20C, and at step 119, a factor (item) that exceeds a predetermined standard among the errors.
Is automatically selected and displayed. Then, step 120
At, the factors that cause the error to exceed the standard are summarized, and an error correction method is instructed.

In the above-described embodiment, the data of the alignment errors ΔA to ΔF at 6 positions are obtained as shown in FIG. 4B, but only the BY of the alignment error ΔB and the BX of ΔE are measured as the minimum condition. You can just do it. If the alignment errors BY and BX are obtained, information on yawing and bending of the moving mirror can be obtained. Moreover,
In this case, the measurement time is shortened.

Further, although the LSA type alignment system is used as the alignment system in the above embodiment, an image processing type alignment system or a so-called two-beam interference type alignment system may be used. Furthermore, TTL
Not only (through-the-lens) method alignment but also TTR (through-the-reticle) method or off
The present invention can also be applied to the case where an axis type alignment system is used.

The present invention is not limited to the above embodiment,
Of course, various configurations can be adopted without departing from the scope of the present invention.

[0070]

According to the first stage accuracy evaluation method of the present invention, from the deviation amount measured by the vernier evaluation method,
Since a predetermined linear error component is obtained and the rotation component when the swage moves is obtained based on this linear error component, the error component caused by the yawing of the stage can be evaluated. Therefore, when the error component is large, the yawing of the stage may be corrected, whereby the stepping accuracy can be improved easily and quickly.

Further, by subtracting the rotational component during the movement of the stage obtained in the fourth step from the deviation amount measured in the second step, the straightness when the stage moves in the first direction or the second direction is calculated. When calculating the degree error, the error component due to the bending of the movable mirror can be further calculated. Further, subtracting the rotation component when the stage is moved, which is obtained in the fourth step, and the straightness error when the stage is moving in the first direction or the second direction, from the deviation amount measured in the second step. When obtaining the positioning error of the stage, the stepping error in a narrow sense can be obtained.

Further, according to the second stage accuracy evaluation method of the present invention, based on the deviation amount measured by the vernier evaluation method for a plurality of substrates, the average variation for all the substrates and the variation in the same shot area are obtained. Therefore, it is possible to evaluate the average positioning ability of the exposure apparatus, the variation in the positioning accuracy for each shot area, and the like.
Therefore, for example, when the variation in a specific shot area is large, the stepping accuracy can be easily and quickly improved by adjusting the stage or the like correspondingly.

Further, when the difference between the average variation obtained in the third step and the overall variation is obtained and the positioning error is obtained from this difference, the tendency of the positioning error can be accurately evaluated.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a projection exposure apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a plan view showing the configuration of the wafer stage 14 of FIG.

3A is a plan view showing a pattern of the reticle R in FIG. 1, and FIG. 3B is an enlarged plan view showing an evaluation mark RA in FIG. 3A.

FIG. 4A is a plan view showing a shot array on a wafer W to be exposed in the embodiment, and FIG. 4B is an enlarged plan view showing a part of the shot area of FIG. 4A.

FIG. 5 is an enlarged plan view showing the positional relationship between the measurement laser beam and the evaluation mark image when measuring the position of the evaluation mark image by the vernier evaluation method.

FIG. 6 is an explanatory diagram when yawing occurs when the wafer stage 14 moves.

FIG. 7 is a diagram showing a change in shot arrangement on a wafer when yawing occurs.

FIG. 8 is a diagram showing a change in shot arrangement on a wafer when a movable mirror is bent.

FIG. 9 is a diagram showing a simulation result of an alignment error (SX, BY) when yawing occurs.

FIG. 10 is a diagram showing a simulation result of alignment errors (BX, SY) when yawing occurs.

FIG. 11 is a diagram showing a simulation result of alignment error (SX, BY) when the movable mirror is bent.

FIG. 12 is a diagram showing a simulation result of alignment error (BX, SY) when the movable mirror is bent.

FIG. 13 is a diagram showing a simulation result of alignment error (SX, BY) when there are various error factors.

FIG. 14 is a diagram showing simulation results of alignment errors (BX, SY) when various error factors are present.

FIG. 15 is a diagram showing a straightness error in the Y direction due to the bending of the movable mirror, which is calculated based on the errors of FIGS. 13 and 14;

16 is a diagram showing a straightness error in the X direction due to the bending of the movable mirror, which is calculated based on the errors of FIGS. 13 and 14. FIG.

FIG. 17 is a diagram showing an error in the shot arrangement due to yawing calculated based on the errors in FIGS. 13 and 14;

FIG. 18 is a diagram showing a simulation result of alignment errors (SX, BY) after removing errors due to bending of the yawing and the moving mirror from the errors of FIGS. 13 and 14;

FIG. 19 is a diagram showing simulation results of alignment errors (BX, SY) after removing errors due to yawing and bending of the moving mirror from the errors of FIGS. 13 and 14;

FIG. 20 is an explanatory diagram of another error analysis method in the example.

FIG. 21 is a flowchart showing an example of an operation when collectively performing various error analysis methods according to the embodiment.

[Explanation of symbols]

R reticle 13 Projection optical system W Wafer 14 Wafer stages 16X, 16Y Moving mirrors 17X, 17Y Laser interferometer 18 Main control system 19 Alignment control system 20 LSA alignment system SA ₁₁ , SA ₁₂ , ... Shot areas 26A to 26F For evaluation Mark images 27G to 27I, 28L to 28J Evaluation mark images ΔA to ΔF Alignment error

Continuation of the front page (56) Reference JP-A-2-174110 (JP, A) JP-A-62-171126 (JP, A) JP-A-59-161815 (JP, A) JP-A-2-56920 (JP , A) JP 57-210626 (JP, A) JP 6-84753 (JP, A) JP 62-32614 (JP, A) JP 60-120360 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 B23Q 17/24 G01B 11/00 H01L 21/68

Claims (9)

(57) [Claims] 1. A stage of an exposure apparatus, comprising a stage for positioning a photosensitive substrate in a first direction and a second direction intersecting each other in a two-dimensional plane, and exposing a mask pattern on the substrate. In the evaluation method, the photosensitive evaluation substrate is placed on the stage, the evaluation mark is exposed on the first shot area on the evaluation substrate, and then the stage is driven to perform the evaluation. A first step of repeating the operation of moving the substrate and then exposing the evaluation mark onto a second shot region that partially overlaps the first shot region on the evaluation substrate; Second measuring the deviation amounts of the evaluation mark exposed in the overlapping portion between adjacent shot areas of the evaluation marks in the first direction and the second direction, respectively.
A third step of obtaining a scaling error component of a linear error component from the shift amount measured in the second step; and a rotation of the stage during movement from the scaling error component obtained in the third step. A fourth step of determining the components;
A stage accuracy evaluation method comprising: 2. The stage is deviated from the displacement amount measured in the second step by subtracting the rotational component at the time of movement of the stage obtained in the fourth step, so that the stage moves in the first direction or the second direction. The stage accuracy evaluation method according to claim 1, wherein a straightness error when moving to a position is obtained. 3. A rotation component at the time of movement of the stage, which is obtained in the fourth step from the amount of displacement measured in the second step, and the stage moves in the first direction or the second direction. 3. The stage accuracy evaluation method according to claim 2, wherein a positioning error of the stage is obtained by subtracting a straightness error when performing. 4. A stage of an exposure apparatus, comprising a stage for positioning a photosensitive substrate in a first direction and a second direction intersecting each other in a two-dimensional plane, and exposing a mask pattern on the substrate. In the evaluation method, the N (N is an integer of 2 or more) photosensitive evaluation substrates are sequentially placed one by one on the stage, and the evaluation is performed on the first shot area on each evaluation substrate. After exposing the evaluation mark, the stage is driven to move the evaluation substrate, and then the evaluation mark is formed on a second shot region that partially overlaps the first shot region on the evaluation substrate. A first step of repeating the operation of exposing the substrate, and the first direction of the evaluation marks exposed in the overlapping portion between the shot areas adjacent to each other of the evaluation substrates of the N evaluation substrates, and Amount of deviation in the second direction A second step of measuring each; an average variation obtained by averaging variations in the deviation amount of each of the evaluation substrates for each of the N evaluation substrates from the deviation amount measured in the second step A third step of obtaining a variation in the deviation amount of the N evaluation substrates as a whole and a variation of the exposure apparatus that is a deviation amount of the deviation amount in the same shot area on the N evaluation substrates in the N sheets. And a stage accuracy evaluation method comprising: 5. The stage accuracy evaluation method according to claim 4, wherein a difference between the average variation obtained in the third step and the overall variation is obtained, and a positioning error is obtained from the difference. The method according to claim 6, wherein the shift amount obtained in the second step, the linear error component comprising scaling error component obtained in the third step, during the movement of the stage obtained by the fourth step The stage accuracy evaluation method according to claim 1, wherein the non-linear error component including a rotation component is displayed separately. 7. The linear error component includes an orthogonality error component, a rotation error component, and an offset error component in addition to the scaling error component, and the non-linear error component is a rotation component when the stage is moved. 7. The stage accuracy evaluation method according to claim 6, further comprising an error component due to bending of a movable mirror provided on the stage. As 8. A display of the linear error component, the scaling error component, the orthogonality error component, and displays the rotation error components, as an indication of the non-linear error component, displaying a variation of the nonlinear error component The stage accuracy evaluation method according to claim 7, wherein. 9. The stage accuracy evaluation method according to claim 3, wherein a positioning error of the stage is displayed.