JPH06349706A - Alignment method - Google Patents

Abstract

PURPOSE:To minimize the influence of expansion and contraction of a chip pattern itself transferred to each shot region and overlap the chip pattern of each shot region on a sensitized substrate to the projection, image of a reticle pattern with high accuracy and throughput. CONSTITUTION:Four alignment marks 29 (n, 1)-29 (n, 4) are formed at each shot region 27-n on a wafer 8 with a reference point 28-n as a zero point. The coordinate values in the stage coordinate system (X, Y) of four alignment marks within a large number of sample shots are measured for several wafers at the top of a lot to be treated and then compensation and alignment such as chip rotation are performed according to the measurement result. The alignment mark with a large scattering in the amount of nonlinear error of past measurement result is excluded from a measurement target, thus reducing measurement targets.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a projection exposure apparatus for sequentially transferring a pattern image of a reticle to each shot area on a wafer based on array coordinates predicted by using, for example, a statistical method. The present invention relates to an alignment method suitable for application when aligning each shot area sequentially.

[0002]

2. Description of the Related Art When a semiconductor element, a liquid crystal display element, or the like is manufactured by a photolithography process, a pattern image of a photomask or reticle (hereinafter referred to as "reticle") is formed on a photosensitive substrate via a projection optical system. A projection exposure apparatus that projects onto a shot area is used. In recent years, as a projection exposure apparatus of this type, a photosensitive substrate is placed on a two-dimensionally movable stage, and the photosensitive substrate is stepped by this stage to form a pattern image of a reticle on the photosensitive substrate. A so-called step-and-repeat type exposure apparatus that repeats the operation of sequentially exposing each shot area,
For example, a reduction projection type exposure apparatus (stepper) is often used.

For example, a semiconductor element is formed by stacking a large number of layers of circuit patterns on a wafer coated with a photosensitive material as a photosensitive substrate. Therefore, when projecting and exposing the circuit patterns of the second and subsequent layers onto the wafer. Requires precise alignment between each shot area on the wafer where a circuit pattern has already been formed and the pattern image of the reticle to be exposed, that is, alignment between the wafer and reticle. A conventional wafer aligning method in a stepper or the like is roughly as follows (for example, Japanese Patent Laid-Open No. 61-61160).
-44429 gazette).

That is, a chip pattern including alignment marks (alignment marks) is formed on each of a large number of shot areas which are regularly arranged based on preset arrangement coordinates on a wafer to be processed. Are formed. However, when another pattern is overlaid on the formed pattern, even if the wafer is stepped on the basis of the set array coordinates, a satisfactory overlay accuracy is not always obtained due to the following factors.

(1) Remaining rotation error of wafer Θ (2) Orthogonality error of stage coordinate system (or shot array) W (3) Linear expansion / contraction of wafer Rx, Ry (4) Offset of wafer (center position) (parallel) Move) O
_X , _OY

Since these four error amounts can be represented by 6 parameters, a conversion matrix A of 2 rows × 2 columns consisting of elements represented by 4 parameters among them, and an offset (parallel movement) ) Consider a conversion matrix O of 2 rows × 1 column having O _X and O _Y as elements. Then, the designed array coordinate values (D _Xn , D _Yn ) of each shot area on the wafer (n = 0, 1,
2, ...) and the actual array coordinate values (F _Xn , F _Yn ) to be aligned by the step-and-repeat method are expressed by using the conversion matrices A and O as follows. And

[0007]

[Equation 1]

At this time, the array coordinate values (FM _Xn , FM _Yn ) obtained by actually measuring a plurality of shot areas (sample shots) selected on the wafer and the corresponding shot areas are calculated based on (Equation 1). The transformation matrices A and O are determined by using the least square method so that the average deviation from the calculated array coordinate values (F _Xn , F _Yn ) is minimized. And conventionally, the determined conversion matrix A, O
And the designed array coordinate values (D _Xn , D _Yn ) are used to calculate the calculated array coordinate values (F _Xn , F _Yn ) of the positions to be actually aligned from the above (Equation 1). The shot areas of the wafer are positioned based on the calculated coordinate values. A method of statistically processing the measurement results of the actual measurement of the sample shots to position each shot area is called an enhanced global alignment method (EGA method).

[0009]

However, even if the wafer alignment is performed according to the calculated array coordinate values (F _Xn , F _Yn ) calculated as described above, the chip pattern of each shot area is obtained. There is a disadvantage that satisfactory overlay accuracy may not always be obtained due to the effect of expansion and contraction or rotation of itself. This is because the reticle is rotating with respect to the moving direction of the wafer stage when the chip pattern is first printed (first layer) on each shot area on the wafer, and there is an error in the projection magnification. , Or the wafer is expanded or contracted as a whole due to a processing process or the like.

Therefore, in order to measure and correct the rotation and the like of these chip patterns as well, a plurality of alignment marks are formed in each shot area of the wafer, and the measurement results of these alignment marks are statistically processed. A method of doing is possible. However, when the number of alignment marks is increased and the number of sample shots is also increased, it takes too much time to measure the alignment marks, and the throughput of the exposure process is reduced. is there. Further, if the number of sample shots is simply reduced, the alignment accuracy will decrease.

In view of the above point, the present invention provides a method of aligning each shot area on a photosensitive substrate with a reticle based on array coordinates predicted by using a statistical method.
While suppressing the effects of expansion and contraction and rotation of the chip pattern itself transferred to each shot area, the chip pattern of each shot area on the photosensitive substrate and the projected image of the reticle pattern can be superimposed with high accuracy. , The purpose is to enable quick alignment.

[0012]

The alignment method according to the present invention is performed on a substrate (8) as shown in FIGS. 1 and 4, for example.
Each of the plurality of shot areas (27-n) arranged above and to which the pattern on the mask is transferred is set to a predetermined transfer position in the stationary coordinate system (X, Y) that defines the moving position of the substrate (8). In positioning with respect to each other, coordinate positions on a stationary coordinate system (X, Y) of a plurality of preselected sample regions among a plurality of processed regions (27-n) are measured,
By statistically calculating a plurality of coordinate positions measured in this way, a plurality of processed regions (27-
n), the coordinate position on each stationary coordinate system (X, Y) is calculated, and the plurality of processed regions (2
7-n) by controlling the moving position of the substrate (8) according to the coordinate position of each of the plurality of processed regions (27-n).
n) is aligned with its transfer position.

Further, according to the present invention, a plurality of processed regions (2) are provided on a predetermined first substrate (8) in a set of substrates to be processed.
7-n) reference positions (28-n), a plurality of alignment marks (29 (n, 1) to 29 (n, 4)) arranged in a fixed relative positional relationship by design. ) Among the (one-dimensional mark or two-dimensional mark), when converted into marks showing one-dimensional coordinates, the coordinate positions of at least seven of these positioning marks on the stationary coordinate system (X, Y) are measured. By performing the first step (step 102) and statistically calculating the plurality of coordinate positions measured in this way, the relative pattern between the mask pattern and each processed region (27-n) on the substrate (8). Error amount (chip rotation, linear expansion and contraction of the chip, etc.) of the image formation relation is calculated, and the stationary coordinate system (X, Y) of each of the plurality of processed regions (27-n) on the substrate (8) is calculated. Second step of calculating the array coordinates on the Tsu has a flop 103, 104) and.

Further, according to the present invention, the error amount of the relative image forming relationship between the pattern of the mask calculated in the second step and each processed region (27-n) on the first substrate (8). To correct the first coordinate according to the array coordinates calculated in the second step.
Third step of aligning each of the plurality of processed regions (27-n) with respect to the processing position by controlling the moving position of the substrate (8) (steps 104, 106)
And belongs to the sample area calculated in the second step when aligning the second substrate other than the first substrate (8) in the set of substrates to be processed. A coordinate position on the stationary coordinate system (X, Y) of the mark for position measurement and a coordinate position on the stationary coordinate system (X, Y) of the mark for position measurement measured in the first step. The number of alignment marks to be measured among the alignment marks belonging to each of the processed regions on the second substrate according to the difference of 8) The number is increased or decreased with respect to the number of alignment marks measured above (step 110).

In this case, within the alignment marks measured in the first step, the calculated coordinate position on the static coordinate system (X, Y) and the static coordinates measured in the first step. When there is an alignment mark having a variation in difference from the coordinate position on the system (X, Y) that is larger than a predetermined value, the alignment mark to be measured on the second substrate It is also possible to exclude the marks for alignment which have large variations in measurement.

[0016]

According to the present invention, the reference position (28-n) provided in each processing region (27-n) on the substrate (8).
Transformation parameters (parameters in transformation matrices A and O) and transformation parameters (parameters in transformation matrix B) related to magnification error and rotation error of the chip pattern (projection pattern) with respect to the reference position (28-n).
And are calculated. Then, after correcting any one of the chip rotation, the chip orthogonality, the chip scaling in one direction or the chip scaling in the other direction based on the conversion parameter related to the chip pattern, each workpiece is processed based on the conversion parameter related to the substrate (8). Area (27-
Since n) is positioned, the substrate (8)
The respective processed regions (27-n) above are properly aligned, and the chip pattern in each processed region (27-n) and the projected image of the mask are accurately overlapped.

In this case, 1 is placed in the processed region (27-n).
If three or more alignment marks are provided when converted into marks indicating dimensional coordinates and the number of alignment marks measured on the substrate is seven or more, seven or more error parameters are set. The value of can be obtained. Therefore,
In addition to the conventional six error parameters (remaining wafer rotation error Θ, orthogonality error W, wafer linear expansion and contraction Rx, Ry, offsets O _X , O _Y ), there are 4 related chip patterns.
At least one of the linear error parameters (chip rotation rotation error θ, orthogonality error w, x-direction chip scaling rx, y-direction chip scaling ry) can be obtained.

Further, in the present invention, in order to optimize the number of alignment marks to be actually measured, the sample area and the position to be measured should be measured in advance for several substrates at the beginning of a certain lot. Set the number (and position) of alignment marks. Then, from the actual measurement result, the variation in the difference (non-linear error amount) between the calculated coordinate value of the alignment mark and the measured coordinate value is obtained. Larger ones are excluded from the measurement target from the next board,
Decrease the measurement target.

Alternatively, when there are too many variations in the non-linear error amount that are larger than a predetermined value, a new alignment mark to be measured is set to measure the sample area and / or the measurement target. Increase the number of target alignment marks. As a result, each processed area (2
Even if a plurality of alignment marks are provided in 7-n), the number of alignment marks to be measured can be optimized according to the measurement state, and throughput and alignment accuracy can be improved. .

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a positioning method according to the present invention will be described below with reference to the drawings. This example is a step
The present invention is applied to an alignment process of an exposure apparatus (stepper) that exposes a pattern of a reticle to each shot area on a wafer as a photosensitive substrate by an and repeat method.

FIG. 2 shows the exposure apparatus of this example. In FIG. 2, the exposure light IL emitted from the illumination optical system 1 illuminates the reticle 2 with a substantially uniform illuminance. The reticle 2 is held on a reticle stage 3, and the reticle stage 3 is supported so as to be movable and minutely rotatable within a two-dimensional plane on a base 4. A main control system 6 that controls the operation of the entire apparatus controls the operation of the reticle stage 3 via a drive device 5 on the base 4.

Under the exposure light IL, the pattern image of the reticle 2 is projected onto each shot area on the wafer 8 via the projection optical system 7. The wafer 8 is placed on the wafer stage 10 via the wafer holder 9. The wafer stage 10 moves the wafer 8 in a plane perpendicular to the optical axis of the projection optical system 7.
XY stage and projection optical system 7 for two-dimensionally positioning
The Z stage for positioning the wafer 8 in the direction (Z direction) parallel to the optical axis of, and the stage for minutely rotating the wafer 8 and the like.

A movable mirror 1 is provided on the upper surface of the wafer stage 10.
1 is fixed, and a laser interferometer 12 is arranged so as to face the moving mirror 11. Although shown in a simplified manner in FIG. 2, the movable mirror 11 is a plane mirror having a reflecting surface perpendicular to the X axis, where the orthogonal coordinate system in the plane perpendicular to the optical axis of the projection optical system 7 is the X axis and the Y axis. And a plane mirror having a reflecting surface perpendicular to the Y axis. Also, laser interferometer 1
Reference numeral 2 denotes two X-axis laser interferometers that irradiate the moving mirror 11 with a laser beam along the X-axis and Y-axis laser interferometers that irradiate the moving mirror 11 with a laser beam along the Y-axis. The X coordinate and the Y coordinate of the wafer stage 10 are configured by one laser interferometer for the X axis and one laser interferometer for the Y axis. Coordinate system (X, Y) consisting of X and Y coordinates measured in this way
Is hereinafter referred to as a stage coordinate system or a stationary coordinate system.

Further, the rotation angle of the wafer stage 10 is measured by the difference between the measured values of the two laser interferometers for the X axis. X coordinate, Y measured by laser interferometer 12
Information on coordinates and rotation angle is supplied to the coordinate measuring circuit 12a and the main control system 6, and the main control system 6 monitors the supplied coordinates and drives the wafer stage 10 via the drive unit 13.
Control the positioning operation of. Although not shown in FIG. 2, the reticle side is also provided with the same interferometer system as the wafer side.

The projection optical system 7 of this example is equipped with an image forming characteristic control device 14. The imaging characteristic control device 14 adjusts, for example, the distance between predetermined lens groups in the lens groups forming the projection optical system 7, or adjusts the pressure of gas in the lens chamber between the predetermined lens groups. Thus, the projection magnification and distortion of the projection optical system 7 are adjusted. The operation of the imaging characteristic control device 14 is also controlled by the main control system 6.

In this example, an off-axis alignment system 15 is arranged on the side surface of the projection optical system 7, and in this alignment system 15, the illumination light from the light source 16 is collimator lens 17, beam splitter 18, mirror 19 and objective. It is irradiated to the vicinity of the alignment mark 29 on the wafer 8 via the lens 20. In this case, the objective lens 2
The baseline amount, which is the distance between the optical axis 20a of 0 and the optical axis 7a of the projection optical system 7, is measured in advance. Then, the reflected light from the alignment mark 29 causes the objective lens 20,
Mirror 19, beam splitter 18 and condenser lens 2
It is irradiated onto the index plate 22 via 1 and an image of the alignment mark 29 is formed on the index plate 22.

The light transmitted through the index plate 22 travels through the first relay lens 23 toward the beam splitter 24, and the light transmitted through the beam splitter 24 is transmitted through the second relay lens 25X for the X axis to form an X-axis composed of a two-dimensional CCD. Is focused on the image pickup surface of the image pickup device 26X for use in the beam splitter 2
The light reflected at 4 is focused on the image pickup surface of the Y-axis image pickup device 26Y including a two-dimensional CCD by the Y-axis second relay lens 25Y. An image of the alignment mark 19 and an image of the index mark on the index plate 22 are superimposed and formed on the image pickup surfaces of the image pickup devices 26X and 26Y, respectively. The image pickup signals of the image pickup devices 26X and 26Y are both coordinate position measurement circuit 1
2a.

FIG. 3 shows the pattern on the index plate 22 of FIG. 2. In FIG. 3, an image 29P of the cross-shaped alignment mark 29 is formed in the central portion, and a linear pattern image 29XP of the image 29P intersects at right angles. And XP perpendicular to 29YP
Direction and YP direction are the wafer stage 1 of FIG.
It is conjugate with the X and Y directions of the stage coordinate system of 0. Then, two index marks 31A and 31B are formed so as to sandwich the alignment mark image 29P in the XP direction, and two index marks 32A and 32B are formed so as to sandwich the alignment mark image 29P in the YP direction.

In this case, the index marks 31A,
31B and the detection area 33 surrounding the linear pattern image 29XP
The image in X is picked up by the X-axis image pickup device 26X in FIG.
The image in the detection area 33Y surrounding the index marks 32A and 32B and the linear pattern image 29YP in the P direction is imaged by the Y-axis image sensor 26Y in FIG. Furthermore, the scanning directions when reading photoelectric conversion signals from the pixels of the image pickup devices 26X and 26Y are set to the XP direction and the YP direction, respectively, and by processing the image pickup signals of the image pickup devices 26X and 26Y,
Alignment mark image 29P and index marks 31A, 31
It is possible to obtain the amount of positional deviation between B and 32A, 32B in the XP and YP directions. Therefore, in FIG.
The coordinate measuring circuit 12a determines the stage coordinate system (X) of the alignment mark 29 based on the positional relationship between the image of the alignment mark 29 on the wafer 8 and the index mark on the index plate 22 and the measurement result of the laser interferometer 12 at that time. , Y), and the coordinate values thus measured are supplied to the main control system 6.

Next, the operation for aligning each shot area on the wafer 8 with the pattern image of the reticle 2 and exposing each shot area in this embodiment will be described. FIG. 4A shows the wafer 8 of this embodiment. In FIG. 4A, the orthogonal coordinate system (α,
A plurality of shot areas 27-n (n = 0,
, 1, ... Are arranged in a matrix, and chip patterns are formed in each shot area 27-n by exposure and development in the previous step. In FIG. 4, five shot areas 27-1 to 27-1 of the plurality of shot areas are shown.
Only 27-5 is shown as a representative.

Each shot area 27-n has a reference
The position is fixed. For example, set the reference position to each shot
Assuming that the reference point 28-n at the center of the area 27-n is
In the coordinate system (α, β) on the wafer 8 of the point 28-n
The design coordinate values are (C_Xn, C_Yn)
I shall. In addition, in each shot area 27-n,
Alignment marks 29 for alignment of four each
(N, 1), 29 (n, 2), 29 (n, 3), 29
(N, 4) is additionally provided. In this case,
In parallel with the coordinate system (α, β) on the wafer in (a), each show
Shot area 27-n as shown in FIG.
When the coordinate system (x, y) on the area is set, the alignment
29 (n, 1), 29 (n, 2), 29 (n,
3), 29 (n, 4) on the coordinate system (x, y)
The accounting coordinates are (S_1Xn, S_1Yn), (S _2Xn,
S_2Yn), (S_3Xn, S_3Yn) And (S_4Xn, S_4Yn)
It

Returning to FIG. 4A, the wafer 8 is placed on the wafer stage 10 of FIG. 2, and the reticle is projected onto each of a plurality of shot areas in which the chip pattern has already been formed by the step-and-repeat method. Exposure is performed by sequentially superimposing images. At this time, the correspondence relationship between the stage coordinate system (X, Y) that defines the moving position of the wafer stage 10 and the wafer coordinate system (α, β) is not necessarily the same as the relationship in the previous step. Therefore, from the design coordinate values (C _Xn , C _Yn ) of the reference point 28-n of each shot area 27-n with respect to the coordinate system (α, β), the stage coordinate system (X,
Even if the coordinates on Y) are obtained and the wafer is moved based on these coordinates, the shot areas 27-n may not be precisely aligned. Therefore, in the present embodiment, first, it is assumed that the positioning error is caused by the following four factors.

Wafer rotation: This is represented by the residual rotation error Θ of the wafer coordinate system (α, β) relative to the stage coordinate system (X, Y). Orthogonality of stage coordinate system (X, Y): This occurs because the feed of the wafer stage 10 in the X-axis direction and the Y-axis direction is not exactly orthogonal, and is represented by an orthogonality error W.

Linear expansion and contraction in the α and β directions in the wafer coordinate system (α, β): This means that the wafer 8 expands and contracts as a whole due to the processing process and the like. This expansion / contraction amount is represented by Rx and Ry in the α direction and the β direction, respectively. However, Rx is represented by the ratio between the measured value and the designed value of the distance between the two points in the α direction on the wafer 8, and Ry is represented by the ratio between the measured value and the designed value between the two points in the β direction. Stage coordinate system (X,
Offset for Y): This is caused by the wafer 8 being displaced by a small amount with respect to the wafer stage 10 overall, and is represented by offset amounts O _X and O _Y.

When the error factors (1) to (3) above are added,
Coordinate values on the design of the reference point (C _Xn, C _Yn) for shot area, the stage coordinate system to be positioned when actually exposed (X, Y) on the coordinates _{(C 'Xn, C' Yn} )
Is represented as follows.

[0036]

[Equation 2]

Here, the orthogonality error W and the residual rotation error Θ
When the first-order approximation is performed assuming that is a small amount, (Equation 2) is as follows.

[0038]

[Equation 3]

Up to this point, the accurate alignment of the reference position on each shot area 27-n (in this example, the reference point at the center of each shot area) has been described. However, even if the reference points of the shot areas are accurately aligned, the entire chip pattern in each shot area and the projected image of the reticle do not necessarily exactly overlap each other.

Next, the overlay error in each shot area will be described. As already explained, FIG. 4 (b)
In any of the shot area 27-n on the coordinate system (x, y) coordinate values of the design on the _{(S 1Xn, S 1Yn) ~} (S
_4Xn , S _4Yn ) and the alignment marks 2
9 (n, 1) to 29 (n, 4) are formed. In this example, it is assumed that the overlay error in each shot area is caused by the following three factors.

Rotation of chip pattern (chip rotation): This is because, for example, when the projection image of the reticle 2 is exposed on the wafer 8, the reticle 2 is rotated with respect to the stage coordinate system (X, Y). Alternatively, it occurs when yawing is mixed in the movement of the wafer stage 10, and the coordinate system (x,
It is represented by the rotation error θ with respect to y). Orthogonality of chip: This is an error in the orthogonality of the chip pattern caused by distortion of the pattern itself on the reticle 2 or distortion of the projection optical system 7 when the projection image of the reticle 2 is exposed on the wafer 8. Yes, and is represented by an angle error w.

Linear expansion and contraction of chips (chip scaling): This is an error in the projection magnification when the projection image of the reticle 2 is exposed on the wafer 8, or the wafer 8 is wholly or partially covered by the processing process of the wafer 8. It is caused by stretching. Here, the chip scaling rx in the x direction, which is the ratio between the measured value and the design value of the distance between two points in the x direction of the coordinate system (x, y) of the shot area, and the distance between the two points in the y direction, It is assumed that the y-direction chip scaling ry, which is the ratio between the actually measured value and the design value, represents the linear expansion / contraction in two directions.

For example, FIG. 5A shows a wafer 8A in which a rotation error and a magnification error occur in the chip pattern of each shot area 27-n formed in the previous step.
In (a), an example of a shot area in the case where there is no rotation error and no magnification error is included in a shot area 34-6 surrounded by a broken line.
It is represented by 34-10. On the other hand, the shot areas 27-6 to 27-10 actually formed on the wafer 8A have different rotation angles and magnifications. These errors are
As shown in (b), the chip rotation error in which the shot area 27-n is inclined with respect to the original shot area 34-n and the magnification of the shot area 27-n as shown in FIG. Can be separated into a chip magnification error different from the original magnification of the shot area 34-n.

However, in the example of FIG. 5, there is no orthogonality error w of the chip pattern, and the chip scaling rx in the x direction.
And the chip scaling ry in the y direction are equal to each other. When the above error factors (1) to (4) are added, the designed coordinate value on the shot area 27-n becomes (S _NXn , S
_NYn ) (N = 1 to 4) alignment mark 29 (n,
N), the coordinate values (S ′ _NXn , S ′ _NYn ) on the coordinate system (x, y) of the shot area to be actually aligned.
Is represented as follows.

[0045]

[Equation 4]

Here, if the linear approximation is performed assuming that the orthogonality error w and the rotation error θ are minute amounts, (Equation 4) is expressed by the following equation.

[0047]

[Equation 5]

Now, in FIG. 4B, the array coordinate value of the reference point 28-n of the arbitrary shot area 27-n on the stage coordinate system (X, Y) is (C _Xn , C _Yn ). Therefore, the design coordinate values (D _NXn , D _NYn ) of the arbitrary alignment mark 29 (n, N) on the arbitrary shot area on the stage coordinate system (X, Y) are expressed as follows. It However, as described above, the alignment marks 29 (n, 1) to 29 (n, 4) are distinguished by the value of N (1 to 4).

[0049]

[Equation 6]

The above three errors (1) to (3) occur when the chip pattern is printed on the layer on which the alignment mark of each shot area on the wafer 8 is printed. In reality, the alignment mark 29 is further affected by the error of the above-mentioned error caused by the processing process of the wafer 8.
The coordinates (actually measured coordinate values) of the position where (n, N) should actually be on the stage coordinate system (X, Y) are (F _NXn , F _NYn ).
If (N = 1 to 4), the coordinate values (F _NXn , F _NYn ) are expressed as follows from ( _Equation 3) and ( _Equation 5).

[0051]

[Equation 7]

Next, in this embodiment, in order to facilitate the application of the least squares method, the α-direction wafer scaling Rx and the β-direction wafer scaling Ry in the equation (7) are respectively changed to new parameters Γx and It is expressed as in the following (Equation 8) using Γy. Similarly, the chip scaling rx in the x direction and the chip scaling ry in the y direction in the (Equation 7) are renewed with new parameters γx and γ, respectively.
It is expressed as in the following (Equation 8) using y.

[0053]

[Equation 8]

If the (Equation 7) is rewritten using four parameters Γx, Γy, γx, and γy indicating these new changes in linear expansion and contraction, (Equation 7) can be approximated as follows. Become.

[0055]

[Equation 9]

In this (Equation 9), if the two-dimensional vector is regarded as a matrix of 2 rows × 1 column, this (Equation 9) can be rewritten as a coordinate conversion equation using a conversion matrix as follows.

[0057]

[Equation 10]

However, each transformation matrix of (Equation 10) is defined as follows.

[0059]

[Equation 11]

The ten error parameters (θ, θ) included in the transformation matrices A, B, O in the coordinate transformation equation of (Equation 10).
W, Γx (= Rx-1 ), Γy, O X, O Y, θ, w, γx
(= Rx−1), ry) can be obtained by, for example, the method of least squares. In this example, the calculated coordinates of each shot area of the wafer 8 on the stage coordinate system (X, Y) and each error of the chip are obtained based on the coordinate conversion formula (Equation 10). Then, based on this, after correcting the chip rotation error and the chip magnification error, the calculated array coordinates (F _xn , F _yn ) of each shot area 27-n of the wafer 8 are obtained, and Each shot area 27-n and the reticle are aligned based on the array coordinates. Note that the least squares method does not necessarily have to be applied to (Equation 10), and 10 error parameters may be obtained at the stage of (Equation 7), for example.

In the above (Equation 9), four parameters (chip rotation rotation error θ, orthogonality error w, chip scaling rx (=
1 + γx), chip scaling ry (= 1 + γy))
However, (Equation 9) (or (Equation 7)) may be used by paying attention to only one of these four parameters. Specifically, when paying attention to only the rotation error θ, the orthogonality error w is regarded as 0, and the chip scalings rx and ry are regarded as 1 and the formula 9 is used. In this regard, when focusing on the chip scaling rx and ry, it is assumed that rx = ry
That is, assuming that the linear expansion and contraction is isotropic, (Equation 9) may be used.

Of the four parameters, the parameter of interest may be selected according to, for example, the type (feature) of the wafer to be exposed.

Here, it is assumed that the alignment mark is measured for a shot area (hereinafter referred to as “sample shot”) selected in advance from all the shot areas 27-n of the wafer 8. However, since the distance between the reference point 28-n of each sample shot and the alignment mark in the shot area is relatively short, four error parameters (θ, w) related to the chip pattern out of the above-mentioned 10 error parameters. , Rx, ry) has a large error due to measurement reproducibility and the like. Therefore, in order to reduce the error, it is necessary to increase the number of sample shots and the number of alignment marks to be measured, but this lowers the throughput of the exposure process. Therefore, in this example, the following sequence is used to prevent a decrease in throughput and maintain high alignment accuracy. The following method makes use of the fact that the linear error amount and the non-linear error amount that occur on the wafer and the deformation of the chip pattern in each shot area generally have the same tendency in the same lot.

Referring to the flow chart of FIG.
An example of the alignment operation and the exposure operation of this example based on the coordinate conversion formula of 0) will be described. First, in step 101 of FIG. 1, loading and origin setting (pre-alignment) of the first wafer 8 in a predetermined lot, which is the current exposure target, are performed on the wafer holder 9 of FIG. A chip pattern is already formed in each shot area of the wafer 8 in the previous process. Furthermore, FIG.
, Four cross-shaped alignment marks 29 are formed in each shot area 27-n on the wafer 8.
(N, N) (N = 1 to 4) are formed. Further, the alignment of the reticle 2 is completed, and the deviation amounts of the reticle 2 in the X direction, the Y direction, and the rotation direction with respect to the orthogonal coordinate system defined by an interferometer (not shown) are almost zero.

Next, in step 102 of FIG. 1, all alignment marks 29 (n, N) of all shot areas 27-n on the wafer 8 are aligned by using the off-axis alignment system 15 of FIG. The coordinate values (FM _{NX n} , FM _NYn ) on the stage coordinate system (X, Y) of are measured. This means that all shot areas on the wafer 8 are used as sample shots and all alignment marks are measured. However, it is not always necessary to use all shot areas 27-n as sample shots, and the number may be larger than the number of normal sample shots. 1
Since each two-dimensional alignment mark has two components in the X direction and the Y direction, in order to determine the values of ten or more parameters, the coordinate values of at least five or more two-dimensional alignment marks must be determined. It is necessary to measure it.

In this case, each shot area 2 on the wafer 8
The coordinate system of the 7-n reference point 28-n on the wafer 8 (α,
β) on the designed array coordinate values (C _Xn , C _Yn ) and on the designed coordinate values (relative to each other) in the coordinate system (x, y) on each shot area 27-n of the measured alignment mark. Coordinate value)
(S _NXn , S _NYn ) is known in advance. Therefore, in step 103, on the right side of (Equation 8), the designed array coordinate values (C _Xn , C _Yn ) of the reference point of the shot area to which the measured alignment mark belongs, and the design regarding the reference point of the alignment mark Relative coordinate value (S _NXn , S
_By substituting _NYn ), the calculated coordinate value (F _NXn , F _NYn ) that the alignment mark should be on the stage coordinate system (X, Y) is _obtained .

Then, ten error parameters (Θ, W, Γx, Γy, which satisfy (Equation 10) are calculated by the method of least squares.
O _X , O _Y , θ, w, γx, γy) is obtained. In particular,
The difference (E _NXn , E _NYn ) between the actually measured coordinate value (FM _NXn , FM _NYn ) and the calculated coordinate value (F _NXn , F _NYn ) is considered as an alignment error. Therefore, E _NXn = FM _NXn −F
_NXn , E _NYn = FM _NYn- F _NYn holds. Then, the sum of squares of the alignment errors (E _NXn , E _NYn ) relating to the measured alignment mark is sequentially partial differentiated with these 10 error parameters, and an equation is set so that the value becomes 0, respectively. If 10 simultaneous equations are solved, 10 error parameters can be obtained.

Then, in step 104, (Equation 1
0) the residual rotation error (wafer rotation error) Θ of the wafer in the conversion matrix A and the rotation error θ of the chip rotation in the conversion matrix B are corrected by the reticle 2 via the reticle stage 3 in FIG. Perform appropriate rotation or rotate the wafer 8 to move the stage coordinate system (X,
Correct the rotation of the chip pattern with respect to Y). This rotates the reticle 2 or the wafer 8 in accordance with the sum (θ + θ) of the residual rotation error Θ that forms the element of the conversion matrix A of (Equation 10) and the rotation error θ that forms the element of the conversion matrix B. Means that.

However, when the wafer 8 is rotated, the offset error (O _X , O _Y ) of the wafer 8 may change. Therefore, after measuring the coordinate value of the alignment mark again, the above-mentioned minimum Calculation for finding parameters by the square method (EG
It is necessary to recalculate the error parameter by performing A calculation). That is, for example, when the wafer 8 is rotated by the angle (Θ + θ), the above steps 102 and 103 need to be repeated. This also means to confirm whether the new residual rotation error Θ after the rotation of the wafer 8 is a value corresponding to the angle rotated in step 105.

Although the orthogonality error w of the chip cannot be corrected in a strict sense, the error can be suppressed to a small value by properly rotating the reticle 2. Therefore,
It is also possible to optimize the rotation amount of the reticle 2 or the wafer 8 so that the sum of the absolute values of the rotation error Θ, the rotation error θ, and the orthogonality error w is minimized.

Next, the imaging characteristic control device 1 of FIG. 2 is arranged so as to correct the chip magnification error in the conversion matrix B of (Equation 10).
The projection magnification of the projection optical system 7 is adjusted via 4. This is the chip scaling γx (= rx-1) and γy (= ry-1) that form the elements of the conversion matrix B shown in (Equation 11).
It means that the projection magnification of the projection optical system 7 is adjusted in accordance with.

After that, using the conversion matrices A and O containing the elements consisting of the error parameters obtained in step 103,
In the following equation, the reference point 2 of each shot area 27-n on the wafer 8
By substituting the designed array coordinate values (C _Xn , C _Yn ) of 8-n, the calculated array coordinate values (G _{Xn of the} reference point 28-n on the stage coordinate system (X, Y)). , G _Yn ).

[0073]

[Equation 12]

Then, in step 105, the 10 error parameters obtained in step 103, the design coordinate value of the reference point of each shot area, and the design coordinate value of each alignment mark 29 (n, N) are set to ( Substituting into the _equation 10), the calculated coordinate value (F _NXn , F _NYn ) of each alignment mark 29 (n, N) is _obtained . Then, the actually measured coordinate values (FM _NXn ,
The _difference between FM _NYn ) and the calculated coordinate values (F _NXn , F _NYn ) is obtained as the non-linear error amount (Δ _NXn , Δ _NYn ), and this non-linear error amount is stored in the storage unit. Note that step 104
When the wafer 8 side is rotated by, the coordinate value calculated based on the measurement result again is stored.

Then, in step 106, based on the array coordinates (G _Xn , G _Yn ) obtained by the calculation and the baseline amount obtained in advance, the reference point 28- of each shot area 27-n on the wafer 8 is formed. n is sequentially aligned with a predetermined position in the exposure field of the projection optical system 7 of FIG.
The pattern image of the reticle 2 is projected and exposed on the shot area 27-n. Then, after the exposure to all the shot areas on the wafer 8 is completed, the second wafer is loaded on the wafer holder 9 in FIG.

Next, in step 107, the second sheet
From the wafer to the Qth wafer (Q is an integer of 2 or more)
Then, the reticle pattern is processed in the same process as the first wafer.
Perform turn exposure. At this time, those (Q-1)
For each wafer, each shot area on the wafer
For each alignment mark 29 (n, N) of 27-n
The measured coordinate values (FM_NXn, FM_NYn) And its calculation
Upper coordinate value (F_NXn, F _NYn) And the amount of non-linear error
(Δ_NXn, Δ_NYn). Furthermore, the 1st to Qth wafers
For all of the c, each alignment mark 29 (n,
N) non-linear error amount (Δ_NXn, Δ_NYn) Average value (A_NXn, A
_NYn) And standard deviation (σ_NXn, σ_NYn). And
In this example, as shown below, the standard deviation (σ_NXn, σ_NYn) Sum
Where the alignment mark is larger than a specified value
Area is excluded from the sample shot.
I will

Then, in step 108, the initial value of the variable q
Is set to 1 and then (Q +
q) Load the second wafer on the wafer holder 9 in FIG.
To do. Then, in step 110, the entire wafer
Of all the alignment marks in the shot area,
Standard deviation (σ_NXn, σ_NYn) Is
If the alignment mark that is larger than the specified value belongs to
For measurement area, from measurement target (sample shot)
Exclude and align marks for remaining sample shots
The coordinate values in the stage coordinate system (X, Y)
It Then, in step 111, step 103
The wafer is exposed in the same procedure as described above. This
Then, 10 error parameters corresponding to step 103
Measurement result of the alignment mark used when obtaining the data
Is the alignment measured in step 110.
This is the measurement result of the dot mark. Then, step 112
At step 110, each alignment marker measured in
(Q + q) non-linear error amounts (Δ_NXn, Δ
_NYn) Average value (A_NXn, A_NYn) And standard deviation (σ_NXn, σ
_NYn).

Then, if there are wafers to be exposed in step 113, the value of the variable q is increased by 1 in step 114 and the process returns to step 109 to expose when there are no more wafers to be exposed. To finish. In this case, in step 110, the number of sample shots measured decreases as the number of wafers exposed in the lot increases. The number of sample shots finally measured is the number of sample shots in the case of the normal EGA method (for example, about 10).
When it becomes about the same, the number and position of sample shots are fixed. This makes it possible to maintain a high alignment accuracy and prevent a large decrease in the throughput of the exposure process.

In step 110, instead of reducing the number of sample shots, the number of alignment marks to be measured in the sample shots may be reduced. In this case, as the processing progresses within the lot, the number of sample shots also decreases, and the number and arrangement of alignment marks to be measured differ depending on the sample shots. However, for example, when the alignment marks at the four corners of each sample shot are measured, only the alignment marks at a certain corner (see, for example, FIG.
In the case of 29 (n, 1) only in (b), the average value of the nonlinear error amount may be large. In such a case, the alignment mark may not be measured, but regardless of that, the marks to be measured may be reduced evenly from the alignment marks at the four corners. When reducing evenly, it is preferable to reduce from a mark having a large average value of the nonlinear error amount for each corner (for example, for each alignment mark 29 (n, 1)). There is also a method in which, with a large number of sample shots, not all alignment marks are measured from the beginning, but one or two alignment marks are evenly measured for each sample shot.

Another way of thinking about increasing or decreasing the number of alignment marks in this embodiment is to select the alignment marks to be measured so that they are always evenly distributed (with a substantially uniform density distribution) on the entire surface of the wafer. There is a method of changing the density by increasing or decreasing the alignment mark. That is, for example, the entire surface of the wafer is divided into a large number of blocks in a grid pattern, the same number of alignment marks is first selected as a measurement target in each block, and thereafter, according to the nonlinear error amount of the measurement result, A method of increasing or decreasing the number of alignment marks measured in each block by the same number can be considered. The method of changing the density of the alignment marks thus selected has an advantage that the measurement information of the alignment marks on almost the entire surface of the wafer can be obtained regardless of the number of alignment marks to be measured.

Furthermore, there are six error parameters (Θ, W, R
x, Ry, O _X , O _Y ) also in the normal EGA type alignment, by increasing or decreasing the number of alignment marks to be measured according to the nonlinear error amount of the alignment marks after measurement, as described above, The number of alignment marks to be measured can be optimized without reducing throughput and alignment accuracy.

Further, in this example, as shown in (Equation 10),
Not only the transformation matrices A and O, but also chip rotation,
Since the transformation matrix B including the parameters of the chip orthogonality error and the chip magnification is also taken into consideration, the influence of expansion and contraction or rotation of the chip pattern itself transferred to each shot area is suppressed to a small extent, and each shot area on the wafer is reduced. The chip pattern and the projected image of the reticle pattern can be superimposed with higher accuracy.

In the above-described embodiment, as shown in FIG. 4B, a cross-shaped two-dimensional alignment mark 29 (n, N) that can be simultaneously aligned in the X and Y directions on the stage coordinate system is provided. 4 on the diagonal of the shot area 27-n
There are four in the corner. However, if four alignment marks are not arranged on one straight line, for example, such an arrangement is not always necessary. Further, it is not always necessary to form an alignment mark inside each shot area 27-n, and for example, as shown in FIG. 6B, a street line area 37 between the shot area 27-n and an adjacent shot area 37. Four alignment marks 29 (n, 1) to 29 (n, 4) in the center of each upper side
May be formed.

Further, as will be described later, each shot area 27-
In some cases, the number of n alignment marks 29 (n, N) may be at least more than required. For example, as shown in FIG. 6C, two alignment marks 29 (n, n) are formed on the diagonal line of the street line area 37 surrounding the shot area 27-n.
In some cases, it may be sufficient to form 1) and 29 (n, 2). In this case, the alignment mark 29 belonging to another shot area is provided at another position of the street line area 37.
(N-1, 1) and 29 (m, 1) are formed.

Even if the one-dimensional alignment mark for the X direction and the one-dimensional alignment mark for the Y direction are separately provided, if the arrangement is taken into consideration, the same equation (10) can be obtained as in the above embodiment. The conversion matrices A, B and O can be obtained. Specifically, as shown in FIG. 6A, alignment marks 35x and 36x indicating positions in the x direction and alignment marks 35y and 36y indicating positions in the y direction are provided at four corners in the shot area 27-n. May be formed.

However, instead of the cross mark that can specify the two-dimensional position as shown in FIG. 4B, a one-dimensional alignment mark that can detect only the position in the X direction or the Y direction as shown in FIG. 6A. When using, the coordinate values of 10 or more alignment marks must be measured in order to determine the values of 10 parameters. However, in addition to the conventional six parameters (Θ, W, Rx, Ry, O _X , O _Y ),
There are four parameters (θ, w,
In some cases, it is only necessary to find at least one parameter of rx, ry), and if it is necessary to find a total of 7 parameters in this way, the coordinates of seven or more one-dimensional alignment marks All you have to do is measure the value.

In the above embodiment, in order to obtain the rotation error θ of the chip rotation, the orthogonality error w of the chip, and the linear expansion and contraction rx, ry of the chip, four shot regions 27-n of the wafer 8 are provided. Alignment mark 29
(N, N) are provided. However, the offset of the reference point of each shot area 27-n (x direction and y direction)
Considering the above, since there are six parameters to be obtained, three shot marks 27-n have three alignment marks (for example, 29 (n, 1), 29 (n, 2) and 29 (n, 1)).
(N, 3)) may be provided. Thus, when using the two-dimensional alignment mark, two alignment marks are always selected. However, if it is a one-dimensional alignment mark, each shot area 27
It is necessary to form 6 alignment marks in each −n.

In the above embodiment, the reticle (or wafer) is calculated by using the four parameters (chip rotation rotation error θ, orthogonality error w, chip scaling rx, chip scaling ry) relating to the chip pattern.
Rotation and correction of the magnification of the projection optical system. However, it is not always necessary to rotate the reticle (or wafer) and correct the magnification of the projection optical system, and each shot area may be aligned in accordance with the array coordinate values obtained in the above-described embodiment. At this time, for example, the magnification correction using the scaling parameters Rx and Ry (or Γx and Γy) relating to the wafer may or may not be performed.

Further, in the above-described embodiment, four parameters relating to the chip pattern (rotational error θ of chip rotation, orthogonality error w, chip scaling rx (= 1 +
(γx) and chip scaling ry (= 1 + γy)) are all obtained, but (Equation 7) (or (Equation 9)) may be used by paying attention to only one of these four parameters. Specifically, when focusing on only the rotation error θ,
The orthogonality error w is regarded as 0, and the chip scalings rx and ry are regarded as 1, respectively, and the formula (7) is used. In this regard, chip scaling rx and ry
When paying attention to, it is possible to use (Equation 7) assuming that rx = ry, that is, the linear expansion / contraction is isotropic.

Of the four parameters, the parameter of interest may be selected according to, for example, the type (feature) of the wafer to be exposed. Next, an example of alignment marks that can be actually used will be described with reference to FIG. First, as the alignment mark indicating the two-dimensional coordinates (two-dimensional mark), in addition to the cross-shaped alignment mark 29 used in the above-described embodiment (this is also shown in FIG. 7A), an L-shaped alignment mark is used. , T-shaped or C-shaped mark. Further, when a so-called two-beam interference type alignment system or a laser step alignment type alignment system is used, the two-dimensional lattice pattern 41 as shown in FIG. 7B also becomes a two-dimensional mark. Further, when the laser step alignment type alignment system or the image pickup type alignment system as in the above-described embodiment is used, FIG.
As shown in (c), the alignment mark 43 in which the line-and-space pattern 42X in the X direction and the line-and-space pattern 42Y in the Y direction are arranged in parallel is also a two-dimensional mark.

Selecting one such two-dimensional mark means that the data for obtaining 10 (or less than 10) parameters in (Equation 10) by the method of least squares is used as the X coordinate. This means that two data items for the Y coordinate are obtained. Therefore, when one cross-shaped alignment mark (for example, 29 (n, 1)) is selected in the above embodiment, two alignment marks (1
Equivalent to selecting (dimensional mark). However, even when the two-dimensional mark is selected, only one coordinate data of the X coordinate or the Y coordinate may be used.

As the mark showing the coordinate in the X direction among the one-dimensional marks, as shown in FIG. 8A, a line-and-space pattern (or a diffraction grating) arranged at a predetermined pitch in the X direction is used. Mark) 42X, and as a mark indicating the coordinate in the Y direction, as shown in FIG.
There is a line-and-space pattern (or diffraction grating mark) 42Y arranged at a predetermined pitch in the Y direction. Further, the two-dimensional lattice pattern 41 of FIG. 7B can be regarded as a one-dimensional mark in the X direction and can also be regarded as a one-dimensional mark in the Y direction.

Next, another example of the method of selecting the sample shot and the alignment mark to be measured will be described in detail. In this case, as a premise, the exposure apparatus executes the EGA calculation using the measurement result of the alignment mark formed in the exposure process of the previous layer. Therefore, the design position and number of alignment marks attached to each shot area on the wafer are the same in all shot areas.

First, in the conventional EGA type alignment method which does not consider the error in the conventional chip pattern, 6
Since there are error parameters (Θ, W, Rx, Ry, O _X , O _Y ), at least 6 when converted into a one-dimensional mark.
It is necessary to measure the coordinates of each alignment mark.
That is, it is sufficient to measure the X coordinate and the Y coordinate at each of at least three measurement points that are not on the same straight line on the wafer. At this time, the X coordinate and the Y coordinate of one measurement point do not need to measure the one-dimensional mark 42 in the X direction and the one-dimensional mark in the Y direction in the same shot, and are attached to one of two different shot areas. Alternatively, the one-dimensional mark in the X direction and the one-dimensional mark in the Y direction attached to the other shot area may be individually measured and the measurement result may be used.

FIG. 9 shows a method of selecting such an alignment mark. In FIG. 9, each shot area 44A, 44B, ... On the wafer 8 has a one-dimensional mark (hereinafter, referred to as "one-dimensional mark" indicating coordinates in the X direction. "X mark") 42
XA, 42XB, ... And one-dimensional marks (hereinafter referred to as “Y marks”) 42YA, 42YB, which indicate the coordinates in the Y direction.
... is attached. Therefore, for example, when measuring the coordinates of six alignment marks, first, as shown in FIG. 9A, three shot areas 44A, 44B and 4 are formed.
Y marks 42YA, 42YB and 42 attached to 4C
The Y coordinate of YC is measured, and three parameters (Θ, Ry, O _Y ) are obtained from this measurement result. After that, as shown in FIG. 9B, three shot areas 44A, 44B and 4 are formed.
X marks 42XA, 42XB and 42 attached to 4D
Measured XD Y coordinate, as a result of three parameters (W, Rx, O _X) may be calculated. In this case, the shot area 44D used in FIG. 9B is different from the shot area 44C used in FIG. 9A, but there is no problem.

Note that the X mark and Y in different shot areas
It is also possible to measure the mark and calculate the X-coordinate and the Y-coordinate at a predetermined measurement point in the calculation, and use this coordinate to perform the EGA calculation. Next, in addition to the conventional 6 error parameters, from among the 4 error parameters (rotation error θ of chip rotation, orthogonality error w, chip scaling rx, chip scaling ry) introduced in the above-described embodiment, A method of selecting an alignment mark for obtaining the value of the selected predetermined error parameter will be described in the following cases with reference to FIG.

(1) When only the chip scaling ry (or γy) in the y direction is calculated: In this case, since there are seven error parameters to be obtained, at least three X marks and four Y marks are required. It is necessary to measure the coordinates. At this time, as shown in FIG. 10A, in addition to one X mark 42X and one Y mark 42Y, one Y mark 46Y having a Y coordinate different from that of the Y mark 42Y is provided in the shot area 44. Must be attached. The selection condition of the Y mark used for the EGA calculation is to select one Y mark (for example, 46Y) that is not on the straight line 45 passing through the selected one Y mark 42Y and parallel to the X axis. is there. However, it is not necessary for the two Y marks that satisfy the condition to exist on the same shot area.

Further, normally, the mark arrangement as shown in FIG. 10A is not adopted, and as shown in FIG. 10B, two two-dimensional marks are provided in each street line area adjacent to each shot area 44. 47 and 48 may be attached. In this case, the four Y marks are selected by distributing them to the Y coordinate of the two-dimensional mark 47 in the first shot area and the Y coordinate of the two-dimensional mark 48 in the same or another shot area.

(2) When calculating only the rotation error θ of the chip rotation: In this case, in addition to at least three X marks and three Y marks, the position of at least one X mark or Y mark is measured. There is a need. The last X
The mark selection condition is, as shown in FIG. 10C, a straight line 50 passing through the already selected X mark 42X and parallel to the X axis.
To select the X mark 51X that is not on the top. Also,
When the Y mark is selected instead of the X mark, a straight line 49 passing through the already selected Y mark 42Y and parallel to the Y axis is used.
It is necessary to select the Y mark 51Y that is not on the top. Even in this case, the two X marks (or Y marks) satisfying the above conditions do not have to be present in the same shot area 44.

(3) When calculating the chip scaling ry in the y direction and the rotation error θ of the chip rotation: In this case, in addition to at least three X marks and three Y marks, two Y marks ( (One can be the X mark)
Must be selected. In addition to the above conditions (1) and (2), it is necessary to select three marks that are not on the same straight line. (4) When only the chip scaling rx (or γx) in the x direction is calculated: In this case, it is necessary to measure the coordinates of at least 4 X marks and 3 Y marks. above
As in the case of (1), the selection condition for the four X marks is Y
Choose two points that are not parallel to the axis.

(5) When only the orthogonality error w is calculated: In this case, one X-mark is selected in addition to at least three X-marks and three Y-marks. Four X
The mark selection condition is to select two points that are not parallel to the X axis, as in the case of (2) above. (6) Chip scaling rx in the x direction and orthogonality error w
When calculating: In this case, in addition to at least 3 X marks and 3 Y marks, 2 X marks are selected.
The selection condition for the four X marks is to select three points that are not on the same straight line, as in the cases (3) and (4) above.

In the above description, the rotation error θ of the chip rotation may be calculated using any of the coordinates of the Y mark and the X mark, and the orthogonality error w of the X mark and the Y mark may be calculated. It may be calculated using coordinates. However, since the orthogonality error w is expressed in the format using the X mark in (Equation 7) (or (Equation 9)) of the above-described embodiment, the X mark is used in the above-described embodiment. Further, the above selection conditions for the alignment marks are not limited to selection within the same shot area.

Furthermore, if the orthogonality error w of the chip is considered to be 0, for example, the number of error parameters to be determined in (Equation 10) is nine. Therefore, the number of parameters determined in step 104 of FIG. 1 is 9, and in step 110 of FIG.
It suffices to measure the coordinate values of nine or more one-dimensional alignment marks that define the directional position.

Further, the orthogonality error w of the chip is regarded as 0, and the linear expansion / contraction of the chip is isotropic (rx
= Ry), two alignment marks (for example, 29 (n, 1) and 29 (n, 1) in each shot area 27-n.
3)) may be provided. In this case, since there are eight parameters to be determined, in step 110 in FIG. 1, the coordinate values of four or more two-dimensional alignment marks (or the coordinate values of eight or more one-dimensional alignment marks) are determined. All you have to do is measure.

Furthermore, if there is a parameter (for example, chip scaling rx and ry) that uses the average value of the measurement results for the first few wafers among the four error parameters related to the chip pattern, as described later, Since the number of unknown parameters is further reduced, step 110
The number of the minimum alignment marks to be measured at is further reduced. In summary, in the case of conversion into a one-dimensional mark, the coordinate values of at least the same number of alignment marks as the number of unknown parameters may be measured in step 110.

Conversely, more than four alignment marks may be provided in each shot area 27-n. In this case, the measurement error when actually measuring the coordinate value of the alignment mark is averaged, and the alignment mark caused by the distortion of the projection optical system when the chip pattern is first printed on the wafer (first layer). There is an advantage that the influence of the deviation from the design position is averaged.

Particularly, unlike the case where the off-axis type alignment system is used as in the above-described embodiment, the TTL (through the lens) that directly observes or detects the alignment mark through the projection optical system to perform alignment. In the case of using the)) type alignment system, it is possible to reduce the measurement error of the coordinate value due to the distortion of the projection optical system by increasing the number of alignment marks. Further, by increasing the number of alignment marks in each shot area in consideration of their arrangement, not only rotation and linear expansion / contraction of the chip pattern but also nonlinear distortion in the chip pattern can be obtained.

For example, by adding three alignment marks to each shot area along the X axis, non-linear distortion in the X direction can also be obtained. By increasing the number of alignment marks in this way, so-called distortion components of the chip pattern (parallel movement, rotation, magnification, orthogonality, trapezoidal distortion, barrel distortion, pincushion distortion, etc. of the chip pattern) are comprehensively detected. It is also possible. That is,
By increasing the number of alignment marks, the number of error parameters can be increased, and it becomes possible to more accurately grasp the error occurrence state.

Next, a second embodiment of the present invention will be described. This example is different from the first embodiment in the process of sequentially performing exposure on a large number of wafers in a lot in the projection exposure apparatus of the first embodiment. Only the operation different from that will be described. Also in this second embodiment,
In each shot area of each wafer, as shown in FIG. 4B, four alignment marks 29 (n, 1) to
29 (n, 4) are formed. Then, when the first to Qth wafers are exposed in the same manner as in the first embodiment, almost all shot areas in the shot areas on the wafer are set as sample shots, and 4 of these sample shots are used. The coordinate values of the individual alignment marks in the stage coordinate system (X, Y) are measured, and from these measurement results, according to steps 103, 104 and 106 of FIG.
Correction such as chip rotation and exposure of each wafer are performed.

At this time, in the second embodiment, instead of obtaining the nonlinear error amount of each alignment mark as in step 105, the ten error parameters (Θ, W, Γx, Γy, O _X , O _Y , θ, w, γx, γy)
4 error parameters related to the chip pattern (rotation error θ, orthogonality w, linear expansion / contraction rx (= 1 + γx)
And ry (= 1 + γy)) are stored in the storage unit. Next, in the process corresponding to step 107 in FIG.
The average value of the error parameters (θ, w, rx, ry) is calculated. After that, when performing exposure on the remaining wafers, the average value of the four error parameters (θ, w, rx, ry) obtained for the Q wafers is used in common, and the chip rotation and the chip orthogonality are used. , Correct the linear expansion and contraction of the tip.

Note that at least one error parameter (for example, only chip scaling rx) out of the average value of the four error parameters (θ, w, rx, ry) thus obtained for the Q wafers. Only the average value may be commonly used, and the other error parameters may be individually obtained for each wafer. For example, in some cases, the chip scaling rx, ry and the chip orthogonality error w have the same tendency for all wafers. In such a case, the chip scaling rx, ry and the chip orthogonality error w may occur. As for w, the average value of the measurement results of the first several sheets in the lot may be used in common. On the other hand, the rotation error θ of the chip rotation may vary from wafer to wafer even within the same lot. Therefore, it is possible to use a value measured individually for each wafer.

Therefore, when the (Q + 1) th wafer is exposed in the second embodiment, the number of the chip patterns is 4
Assuming that an average value is used for each of the six parameters, the six error parameters (Θ, W,
Rx, only Ry, O _X, may be determined a value of O _Y). That is, as in the case of the normal EGA method, about 10 shot areas are designated as sample shots, and the coordinate value of one alignment mark (for example, 29 (n, 1)) is assigned to each sample shot. The measurement is performed, and the values of these six error parameters are determined based on the measurement result. Then, the calculated array coordinates of each shot area 27-n are obtained from (Equation 10), and alignment is performed based on the array coordinates, and then each exposure may be performed.

As described above, according to the second embodiment, when exposing a large number of wafers in a lot, the sample shots and the number of alignment marks to be measured are increased only for the first few wafers. Then, for the remaining wafers, the same number of sample shots and alignment marks as in the case of the normal EGA method are only measured. Therefore, it is possible to correct the chip rotation or the like and improve the overlay accuracy without significantly reducing the throughput of the exposure process.

The above-described embodiment is based on the EGA type alignment, and it is assumed that the error in the chip rotation and chip magnification (including distortion) for each shot area is constant within the same wafer. I was looking for an error. For this reason,
If the local array error on the wafer or the fluctuation (non-linearity) of the distortion component is large, it becomes difficult to improve the overlay accuracy in the above-described embodiment. Therefore, even with a wafer having non-linear distortion, there is a demand for an alignment method that can satisfactorily correct the chip rotation and the chip magnification error and perform highly accurate alignment. In the following, an embodiment will be described in which the above-mentioned EGA method is improved to perform positioning with higher accuracy. As this alignment method, the alignment method proposed in Japanese Patent Application No. 4-297121 is applied to the above embodiment.

FIG. 1 for such a third embodiment of the present invention.
This will be described with reference to FIG. The projection exposure apparatus shown in FIG. 2 is also used in this example, but in this example the EG used in the first embodiment is used.
A first weighted EGA method (hereinafter referred to as "W1-EGA method"), which is a further improvement of the A method alignment, is performed. This W1-EGA method alignment is effective against “regular non-linear distortion”,
It is focused on that "even if the substrate has regular nonlinear distortion, the array errors in the local region on the substrate are almost equal." Then, in this W1-EGA alignment, weighting is performed according to the distance to the sample shot, as described later.

FIG. 11 shows a wafer 8 to be exposed in this example. In FIG. 11, when the calculated coordinate position of the i-th shot area ESi on the wafer 8 is determined, the shot areas ESi and m Distances LK1 to LK between the sample shots SA1 to SA9 (m = 9 in FIG. 11)
According to 9, the weight W _in is given to each of the measured coordinate positions (alignment data) of the alignment marks in these nine sample shots. Specifically, the four alignment marks MA of the sample shot SA1
Weights W _i1 according to the distance LK1 are given to the measured coordinate positions of 1, MB1, MC1, MD1. In addition,
Strictly speaking, it is desirable to give weights according to the distance from the reference point of the shot area ESi to each alignment mark in each sample shot. Further, it is not always necessary to measure the coordinates of the four alignment marks in each sample shot.

In this W1-EGA system, the EGA system is used.
Instead of just the residual error component of the sum of squares in
The residual error component Ei defined by (Equation 13) is defined. this
In (Equation 13), the coordinate value (FM_NXn , FM_NYn )
Is the Nth alignment in the nth sample shot
Coordinate values actually measured, and coordinate values (F_NXn ，
F _NYn ) Is the calculated coordinate value.

[0118]

[Equation 13]

Then, ten error parameters (Θ, W, Γx, Γy, O _X , O _Y , θ, which satisfy (Equation 10) so that the residual error component Ei defined in this way is minimized.
w, γx, γy) is obtained. Note that here, sample shots SA1 to SA used for each shot area ESi
9 is the same, but naturally the distance to each sample shot SAn is different for each shot area ESi. Therefore,
The weight W _in given to the coordinate position (alignment data) of the sample shot SAn changes for each shot area ESi. Then, error parameters (Θ, W, Rx, Ry, O _X , O _Y , θ, w, rx, ry) for each shot area ESi.
Then, first, the wafer rotation error in the conversion matrix A of (Equation 10) and the chip rotation error in the conversion matrix B are corrected, and the chip magnification error in the conversion matrix B of (Equation 10) is also corrected.

Then, the error parameters (Θ, W, Rx
Using the conversion matrices A and O including the elements consisting of (= 1 + Γx), Ry (= 1 + Γy), O _X , O _Y , the reference point of the shot area ESi on the wafer 8 is designed in (Equation 12). By substituting the array coordinate values of the above, the calculated array coordinate values on the stage coordinate system (X, Y) of the reference point of the shot area ESi are obtained.

Thus, in the W1-EGA method, the wafer 8 is
For each shot area ESi above, each sample shot S
The weight W _in of the coordinate data of An changes. As an example, the weight W _{in is set} to the i-th shot area ESi and n.
It is expressed as follows as a function of the distance LKn from the th sample shot SAn. However, the parameter S is a parameter for changing the degree of weighting.

[0122]

[Equation 14]

As is clear from this (Equation 14), the i-th
Sample with short distance LKn to shot area ESi
Shot SAn gives more weight to the alignment data
Only W _inIs becoming larger. Also, (Equation 1
In 4), if the value of the parameter S is sufficiently large,
The result of the total calculation processing is obtained by the EGA method of the above-mentioned embodiment.
It is almost equal to the result. On the other hand, the wafer to be exposed on the wafer
All the shot areas ESi are sample shots SAn,
If the value of the parameter S is close to zero, each shot area
Position the wafer mark by measuring the position of the wafer mark for each area
Almost equal to the result obtained by the so-called die-by-die method
Become. That is, in the W1-EGA method, the parameter S is
By setting the appropriate value, EGA method and die-by
-It is possible to obtain an effect intermediate to that of the die method. example
For example, for wafers with large nonlinear components, the parameters
By setting the value of S small, the die-by-die method
It is possible to obtain the same effect (alignment accuracy) as
Satisfactorily removes alignment errors due to nonlinear components.
You can In addition, the alignment sensor measurement
If the actuality is poor, increase the value of parameter S.
By doing so, it is possible to obtain almost the same effect as the EGA method.
And reduce alignment error by averaging effect
You can

Further, the weighting function of (Equation 14) is separately prepared for the X coordinate and the Y coordinate of the alignment mark so that the weight W _in can be set independently for the X coordinate and the Y coordinate. Good. In this case, the degree of nonlinear distortion of the wafer (magnitude), regularity or step pitch,
That is, even if the center-to-center distance between two adjacent shot areas (which depends on the width of the street line on the wafer but is a value substantially corresponding to the shot size) is different in the X and Y directions, the value of the parameter S is By setting them independently, the shot arrangement error on the wafer can be corrected with high accuracy. At this time, the value of the parameter S may be different between the X coordinate and the Y coordinate as described above.
Further, whether the value of the parameter S of the X coordinate and the value of the Y coordinate are the same or different, the value of the parameter S is the magnitude of the "regular non-linear distortion", the regularity, the step pitch, or the measurement reproduction of the alignment sensor. It may be appropriately changed according to the nature.

From the above, the effect can be changed from the EGA method to the die-by-die method by appropriately changing the value of the parameter S. Therefore, for each layer, and for each component (X direction and Y direction), alignment is performed according to, for example, the characteristics of the non-linear component (for example, size, regularity, etc.), the step pitch, and the quality of the measurement reproducibility of the alignment sensor. It is possible to flexibly change and perform alignment under optimum conditions for each layer and each component.

An alignment method of the second weighted EGA method (hereinafter referred to as "W2-EGA method") will be described with reference to FIG. Here, in order to simplify the explanation, it is assumed that the wafer W is regularly and particularly point-symmetrically subjected to non-linear distortion, and the center of the point symmetry coincides with the center of the wafer W (wafer center).

FIG. 12 shows the wafer 8 to be exposed in this example. In FIG. 12, the deformation center point of the wafer 8 (the center of point symmetry of non-linear distortion), that is, the wafer center Wc,
Let LEi be the distance (radius) between the i-th shot area ESi on the wafer 8 and the wafer center Wc and m (in FIG. 12, m = 9) sample shots SA1 to SA.
The distance (radius) to each of 9 is LW1 to LW9. And even in this W2-EGA method, W1-EG
Similar to the A method, a weight W _in ′ is given to each of the measured coordinate positions (alignment data) of the alignment marks in the nine sample shots SA1 to SA9 according to the distance LEi and the distances LW1 to LW9. This W2-EG
In the A method, after detecting four alignment marks (MAi, MBi, MCi, MDi) for each sample shot, the residual error component Ei ′ is defined by the following (Equation 15) as in (Equation 13). , The error parameters (Θ, W, Γx, Γy,
O _X , O _Y , θ, w, γx, γy) are determined.

[0128]

[Equation 15]

In the W2-EGA method as well, as in the W1-EGA method, the weight W _in ′ given to the alignment data changes for each shot area ESi.
A statistical calculation is performed for each Si to obtain error parameters (Θ, W, Γ
x, Γy, O _X , O _Y , θ, w, γx, γy),
The chip rotation, the chip orthogonality, the chip magnification error, and the calculated array coordinate value will be determined.

Then, each shot area ES on the wafer W is
for each i, 'to change the weights W _in the equation (15)' weight W _in for each sample shots, i th shot area ESi and the wafer center W on the wafer 8
It is expressed as a function of the distance (radius) LEi from c as follows. However, the parameter S is a parameter for changing the degree of weighting.

[0131]

[Equation 16]

As is clear from (Equation 16), the sample shot SAn has a distance LWn to the wafer center Wc close to the distance LEi between the wafer center Wc and the i-th shot area ESi on the wafer W. The more the weight W _in ′ given to the alignment data increases. In other words, the largest weight W _in ′ is given to the alignment data of the sample shot located on the circle having the radius LEi centered on the wafer enter Wc, and the weight W to the alignment data is increased as the distance from the circle in the radial direction increases. _in ′
Is getting smaller.

The value of the parameter S in (Equation 16) is the same as that required in the W1-EGA method, such as the alignment accuracy, the characteristic of the non-linear distortion (for example, size, regularity, etc.),
It may be appropriately determined depending on the step pitch, the quality of measurement reproducibility of the alignment sensor, and the like. That is, when the non-linear component is relatively large, the value of the parameter S is set to be smaller so that the distance LWn from the wafer center Wc is reduced.
It is possible to reduce the influence of the sample shots that greatly differ from each other. On the other hand, when the non-linear component is relatively small, by setting the value of the parameter S larger, it is possible to prevent the alignment accuracy of the alignment sensor (or layer) having poor measurement reproducibility from being degraded.

Further, in the W2-EGA method, a plurality of shot areas located substantially equidistant from the center of point symmetry on the wafer W, that is, a plurality of shot areas located on the same circle centered on the center of point symmetry. In each case, naturally, the weight W _in ′ given to the alignment data of the sample shot is the same. For this reason, when a plurality of shot areas are located on the same circle centered on the point symmetry center, the above-mentioned weighting and statistical calculation are performed only on any one of the shot areas, and the error parameters (Θ, W , Rx, R
y, O _X , O _Y , θ, w, rx, ry), for the remaining shot areas, the previously calculated error parameters are used as they are for the chip rotation, the chip orthogonality, the chip magnification error, and the coordinates. The position can be determined. This has the advantage of reducing the amount of calculation.

By the way, it is desirable to specify the sample shot arrangement suitable for the W2-EGA method so as to be symmetric with respect to the point symmetry center of the nonlinear distortion, that is, the wafer center Wc. For example, X based on the wafer center Wc. It may be specified as a character shape or a cross shape. Besides that,
The arrangement may be similar to that of the W1-EGA method. If the point-symmetric center of the non-linear distortion is other than the wafer center Wc, the X-shaped or cross-shaped arrangement may be used with the point-symmetric center as a reference. When determining the value of the error parameter, the weighting function shown in (Equation 16) may be set independently in each of the X direction and the Y direction.
Needless to say, the weighting function may be set independently for each alignment mark.

The W1-EGA method and the W2-EGA method
In the method, when correcting the rotation error and the magnification error based on the four error parameters (θ, w, rx, ry) related to the chip pattern, the parameters obtained for each shot region are used for each shot region. Correction may be performed. Alternatively, one set of parameters obtained for each shot area may be averaged to obtain one set of parameters, and based on this parameter, the entire wafer may be corrected only once. Further, the wafer may be divided into a plurality of blocks and the correction may be performed for each block. Further, in the W2-EGA method, it is not necessary to obtain a parameter for each shot region in a shot region located concentrically with respect to the center of point symmetry, and the parameter obtained for any one shot region is used. May be.

The method of gradually increasing or decreasing the number of alignment marks to be measured according to the present invention is a conventional ordinary E method.
It can also be applied to GA type alignment.

Further, the present invention is not limited to the step-and-repeat type exposure apparatus (for example, the reduction projection type stepper or the equal-magnification projection type stepper), but also a so-called step-and-scan exposure type exposure apparatus or proxy. The present invention can be widely applied to a mitty type stepper (X-ray exposure device, etc.). In addition to the exposure equipment, it is an equipment (defect inspection equipment, prober, etc.) that inspects semiconductor wafers and reticles with multiple chip patterns, and uses a step-and-repeat method for each chip as a standard for inspection fields and probe needles. The present invention can be similarly applied to a device for aligning with respect to a position.

When the above-mentioned alignment method is applied to a scanning type exposure apparatus such as a step-and-scan exposure type exposure apparatus, a predetermined offset ( The scanning exposure is performed after the wafer is positioned at a position to which a value that is uniquely determined according to the pattern size, the reticle, the run-up section of the wafer, etc. is added.

As described above, the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0141]

According to the present invention, with respect to all the reference positions of the plurality of processed regions on the substrate to be processed, the alignment error becomes smaller on average, and at the same time, all the chip patterns on the processed regions are processed. On the other hand, the error of superimposition with the pattern image of the mask becomes small on average. Therefore, it is possible to suppress the influence of expansion and contraction or rotation of the chip pattern itself transferred to each processing area, and to superimpose the projected image of the mask pattern with the chip pattern of each processing area on the substrate with higher accuracy. There is an advantage that can be.

In addition, since the number of alignment marks is increased as a whole, the sample area and / or the alignment mark to be measured should be adjusted according to variations in the measurement results of the alignment mark. Since the number of marks is increased or decreased, the number of alignment marks to be finally measured can be optimized. Therefore, it is possible to maintain the alignment accuracy at a predetermined level and minimize the decrease in the throughput of the alignment process.

The positions of the alignment marks belonging to some shot areas on the substrate to be processed are actually measured, that is, the position measurement using the alignment marks of the same shape is repeated a plurality of times. Therefore, there is also an advantage that a mechanical or electrical random error of the detection system is reduced. Further, a mark whose variation in difference between the calculated coordinate position of the alignment mark and the measured coordinate position is larger than a predetermined value is excluded from the alignment marks to be measured on the second substrate. In such a case, it is possible to perform positioning with higher accuracy and speed by excluding the positioning marks having poor measurement reproducibility.

[Brief description of drawings]

FIG. 1 is a flowchart showing an alignment operation and an exposure operation to which a first embodiment of a positioning method according to the present invention is applied.

FIG. 2 is a configuration diagram showing an example of a projection exposure apparatus in which an alignment operation and an exposure operation of the embodiment are performed.

FIG. 3 is an enlarged view showing an image of an alignment mark on the index plate of FIG.

4A is a plan view showing an example of an arrangement of shot areas on a wafer according to an embodiment, and FIG. 4B is an enlarged plan view showing the shot areas in FIG. 4A.

5A is a plan view showing an example of a wafer including a rotation error of a chip pattern and an error of a chip magnification, FIG.
FIG. 6 is an explanatory diagram of a chip rotation error, and FIG. 7C is an explanatory diagram of a chip magnification error.

6A to 6C are enlarged plan views showing another example of a plurality of alignment marks belonging to each shot area.

FIG. 7 is a diagram showing an example of alignment marks indicating two-dimensional coordinates.

FIG. 8 is a diagram showing an example of alignment marks indicating one-dimensional coordinates.

FIG. 9 is an explanatory diagram showing an example of selection of alignment marks when alignment is performed by a normal EGA method.

FIG. 10 is an explanatory diagram showing an example of selection of alignment marks when alignment is performed by the method of the embodiment.

FIG. 11 is a plan view showing a shot array on a wafer on which W1-EGA alignment is performed in the third embodiment of the present invention.

FIG. 12 is a plan view showing a shot array on a wafer on which W2-EGA alignment is performed in the third embodiment of the present invention.

[Explanation of symbols]

 1 Illumination Optical System 2 Reticle 6 Main Control System 7 Projection Optical System 8 Wafer 10 Wafer Stage 12 Laser Interferometer 14 Imaging Characteristic Control Device 15 Off-Axis Alignment System 27-1 to 27-5, 27-n Shot Area 28 -1 to 28-5, 28-n Reference point 29 (n, 1) to 29 (n, 4) Alignment mark

Claims (2)

[Claims] 1. A plurality of processed regions arranged on the substrate based on arrangement coordinates on a sample coordinate system set on the substrate are defined in a stationary coordinate system that defines a moving position of the substrate. When aligning with the predetermined processing position,
A plurality of sample areas on the substrate are measured by measuring coordinate positions on the stationary coordinate system of a plurality of preselected sample areas among the plurality of processed areas and statistically calculating the plurality of measured coordinate positions. By calculating array coordinates of each of the processed regions on the stationary coordinate system and controlling the moving position of the substrate according to the calculated array coordinates, each of the plurality of processed regions is set to the processing position. In the method of aligning with respect to each other, a plurality of processed regions on a predetermined first substrate in a set of substrates to be processed are arranged in a fixed relative positional relationship by design with respect to each reference position. When converting to a mark showing one-dimensional coordinates among a plurality of alignment marks,
A first step of measuring the coordinate positions of at least seven alignment marks on the stationary coordinate system; and statistically calculating the plurality of measured coordinate positions to determine the pattern of the mask and the substrate. While calculating the error amount of the relative imaging relationship with each of the processed regions of
A second step of calculating array coordinates on the stationary coordinate system of each of the plurality of processed regions on the substrate; the mask pattern calculated in the second step; and the mask on the first substrate. By correcting the error amount of the relative image formation relationship with each processing area and controlling the moving position of the first substrate according to the array coordinates calculated in the second step, a plurality of processing objects are processed. A third step of aligning each of the regions with respect to the processing position, and aligning a second substrate other than the first substrate in the set of substrates to be processed. And the calculated coordinate position on the stationary coordinate system of the position measuring mark belonging to the sample area calculated in the second step, and the position measuring mark measured in the first step. Depending on the difference with the coordinate position on the stationary coordinate system A position on the first substrate where the number of alignment marks to be measured among the plurality of alignment marks belonging to each processing region on the second substrate is measured. An alignment method characterized in that the number of marks for alignment is increased or decreased. 2. The calculated coordinate position on the stationary coordinate system and the coordinate on the stationary coordinate system measured in the first step among the alignment marks measured in the first step. When there is an alignment mark having a variation in a difference from the position larger than a predetermined value, the alignment mark having a large variation in the measurement from the alignment mark to be measured on the second substrate. The alignment method according to claim 1, wherein the mark is excluded.