JPH08102438A - Alignment - Google Patents

Abstract

PURPOSE: To perform alignment with high accuracy by a method wherein irregular shots having the large non-linear component of an alignment errors are accurately eliminated from sample shots. CONSTITUTION: In respect to N sample shots the coordinate values of the N sample shots on a stage coordinate system are measured (a step 101), subsequently a conversion parameter is found using coordinate data on the (N-1) sample shots excluding the L-th sample shot and a virtical position of the L-th sample shot is found from this conversion parameter and data on a measurement of the L-th sample shot (steps 103 and 104). In the case where the deviation amount E (L) of the virtical position from the measured coordinate position of the L-th sample shot is larger than a reference value Eo, the L-th sample shot is eliminated as a missing shot (steps 109 and 110).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an exposure apparatus for sequentially exposing a pattern of a reticle on each shot area of a wafer, in which each shot area of the wafer is sequentially exposed based on the array coordinates calculated by statistical processing. The present invention relates to a positioning method suitable for application in positioning.

[0002]

2. Description of the Related Art Photomasks, reticles, etc. (hereinafter, "reticle" is used as an example) when manufacturing semiconductor devices, liquid crystal display devices, etc. by a photolithography process.
There is used a projection exposure apparatus for projecting the pattern image of (1) on each shot area on a wafer coated with a photosensitive material via a projection optical system. As a projection exposure apparatus of this type, in recent years, a wafer is placed on a two-dimensionally movable stage, and the wafer is stepped by this stage.
A so-called step-and-repeat type exposure apparatus, in particular, a reduction projection type exposure apparatus (stepper), which repeats an operation of sequentially exposing a pattern image of a reticle to each shot area on a wafer is frequently used.

For example, since a semiconductor element is formed by superposing a plurality of layers of circuit patterns on a wafer and exposing the same, when projecting and exposing the circuit patterns of the second and subsequent layers onto the wafer, the circuits on the wafer are already exposed. Aligning each shot area where the pattern is formed with the pattern image of the reticle,
That is, alignment between wafer and reticle
Need to do exactly. The wafer alignment in a conventional stepper or the like has been performed by the following enhanced global alignment (hereinafter referred to as “EGA”) system (see, for example, Japanese Patent Laid-Open No. 61-44429).

That is, a plurality of shot areas (chip patterns) to which alignment marks called wafer marks are respectively attached are formed on the wafer, and these shot areas are set in advance on the wafer. They are regularly arranged based on the arrangement coordinates. However,
Even if the wafer is stepped based on the designed array coordinate values (shot arrays) of a plurality of shot areas on the wafer, the wafer is not always accurately aligned due to the following factors. (1) Remaining rotation error (rotation) of wafer θ (2) Orthogonality error of stage coordinate system (or shot arrangement) w (3) Linear expansion and contraction (scaling) of wafer Rx, Ry (4) Wafer (center position) Offset (translation) O
x, Oy

At this time, the coordinate transformation of the wafer based on these four error amounts (six parameters) can be described by a linear transformation equation. Therefore, for a wafer in which a plurality of shot areas with wafer marks are regularly arranged, the coordinate system (x, y) on the wafer is used as a stationary coordinate system and the coordinate system (X, Y) on the stage is used. The primary conversion model to convert to
It can be expressed as follows using the individual conversion parameters a to f.

[0006]

[Equation 1]

The six conversion parameters a to f in this conversion formula can be obtained by the EGA method as follows. In this case, the coordinate system (x, y) associated with each of shot areas (hereinafter referred to as “sample shots”) selected from a plurality of shot areas (chip patterns) to be exposed on the wafer. The above design coordinates are (x ₁ , y ₁ ), (x ₂ , y ₂ ), ...
The wafer mark of (x _n , y _n ) is aligned with a predetermined reference position. And
Actual coordinate values (XM ₁ , YM ₁ ), (XM ₂ , YM ₂ ), ..., in the coordinate system (X, Y) on the stage at that time
(XM _n , YM _n ) is measured.

Also, in designing the selected wafer mark.
Array coordinates of (x_i, Y_i) (I = 1, ..., N) above
Calculated array coordinates obtained by substituting into the linear transformation model of
(X _i, Y_i) And the measured coordinates (X
M_i, YM_i) And the difference (△ x, △ y)
Think of it as an error. Also, the x component and y of the alignment error
The sum of squares of the components, that is, the difference (X_i-XM_i)
² And the difference (Y_i-YM_i)² I
Is the residual error component
You.

[0009]

[Equation 2]

Then, the residual error component is sequentially partial differentiated with the six conversion parameters a to f, an equation is set so that the value becomes 0, and these simultaneous equations are solved to obtain 6
The individual conversion parameters a to f are obtained. As described above, by the least squares method, the six conversion parameters a to
The calculation for obtaining f is called EGA calculation. After that, the alignment of each shot area of the wafer can be performed based on the array coordinates calculated by using the linear conversion equation having the conversion parameters a to f as coefficients. Alternatively, when the approximation accuracy is not good in the primary conversion formula, the wafer may be aligned by using, for example, a second or higher order formula.

In the conventional EGA type alignment method as described above, there is a so-called jump shot in which a non-linear component obtained by subtracting a linear component from an alignment error is particularly larger than other sample shots among a plurality of sample shots. It may have been included. Such a jump shot causes a measurement error due to a collapse of a wafer mark belonging to the sample shot on the wafer, a local nonlinear distortion on the wafer, or a reticle pattern of the first layer is transferred onto the wafer. Since it occurs due to the positioning error of the wafer stage at that time,
When calculating the array coordinates of other shot areas, it is desirable to exclude (reject) the alignment data (measured coordinate values) of such jump shots.

Therefore, conventionally, the jump shots are detected in the following manners (1) to (7) and the detected jump shots are rejected to perform the EGA type alignment. A shot area in which the alignment error is equal to or larger than a predetermined reference value is a jump shot. For example, FIG. 9A is an exaggerated view of an example of the alignment error of the sample shots distributed on the wafer 41 to be exposed.
In (a), the designed array coordinates of each shot area including a sample shot are defined on the coordinate system (x, y) on the wafer 41. On the other hand, the wafer 41
On the stage coordinate system (X, Y), which is the coordinate system of the wafer stage on which is mounted, eight sample shots SB ₁ to
The coordinate value of SB ₈ (correctly, the coordinate value of the wafer mark) is measured.

Then, eight sample shots SB ₁ ~
The alignment errors of SB ₈ are vector VB ₁ ~
It is represented by VB ₈ . For example the origin of the vector VB _1, the sample shots SB ₁ of the stage coordinate system (X,
Y) represents the designed center coordinates, and the end point of the vector VB ₁ represents the measured center coordinates of the sample shot SB _{1 on} the stage coordinate system (X, Y). In this case, the design center coordinates in the stage coordinate system (X, Y) are substituted with the approximate values of the six parameters a to f and the design value in the coordinate system on the wafer in (Equation 1). It is calculated by Further, the approximate values of the six parameters a to f are
For example, regarding the above-mentioned six parameters, linear expansion and contraction are regarded as isotropic (Rx = Ry), and the orthogonality error w is regarded as 0,
The position of the two two-dimensional alignment marks on the wafer 41 is obtained by so-called global alignment in which the position is measured on the stage coordinate system (X, Y).

FIG. 9B shows the absolute values | VB ₁ | to | VB ₈ | of the alignment error vectors of the _eight sample shots SB _{1 to} SB 8 in FIG. 9A, and these absolute values are A sample shot having a predetermined reference value VB or more, that is, the second sample shot SB ₂ is excluded. By performing the EGA calculation, the alignment error is divided into a linear component and a non-linear component, and sample shots in which the non-linear component is equal to or larger than a predetermined reference value are excluded.

[0015] FIG. 10 (a) shows another example of the alignment error vector VB ₁ through Vb ₈ 8 on the wafer 41 samples shots SB ₁ to SB _8, FIG. 10 (b)
Shows their absolute values of sample shots SB ₁ to SB ₈ each vector VB ₁ through Vb ₈ (absolute value of the alignment error). In this case, the wafer 4 of each sample shot
For the designed array coordinate values in the coordinate system on 1 and the measured coordinate values in the stage coordinate system, six conversion parameters a to satisfy (Equation 1) by the least square method by EGA calculation. The value of f is obtained, and these six conversion parameters a to f
And the designed array coordinate value are substituted into (Equation 1) to calculate a calculated array coordinate value excluding a linear error in the stage coordinate system of each of the sample shots SB _{1 to} SB ₈ . The vector from the first calculated array coordinate to the calculated array coordinate value excluding the linear error is the vector of the linear component of the alignment error.

Then, when the vector of the linear component is subtracted from the vector of the alignment error of FIG.
As shown in 1 (a), sample shots SB _{1 to} SB
Vectors of non-linear components VBN _{1 to} VBN for each ₈
You get ₈ . FIG. 11B shows a sample shot SB.
_{1 to} SB ₈ shows the absolute value of the vector of the non-linear component of the alignment error | VBN ₁ | to | VBN ₈ |, and the absolute value of this non-linear component is a sample shot larger than a predetermined reference value, for example, the eighth sample shot. SB ₈ is eliminated.

The standard deviation of the absolute value of the alignment error vector is calculated for each sample shot on the wafer, and sample shots in which the absolute value of the alignment error vector is a predetermined multiple or more of the standard deviation are excluded.

[0018]

Among the conventional techniques as described above, in the method of eliminating the sample shot in which the absolute value of the vector of the alignment error is equal to or more than the predetermined reference value, as shown in FIG. ) Is taken as an example,
Even if the vector VB ₈ has a bad balance of directions when viewed from the whole, it has a disadvantage that it cannot be excluded because its absolute value is small. Further, when the rotation, orthogonality, or linear expansion / contraction (scaling) of the entire wafer 41 is particularly large, it is almost impossible to increase the predetermined reference value (value corresponding to the reference value VB in FIG. 9B) to a large extent. The sample shots of are excluded, and high-precision alignment cannot be performed. Further, depending on the direction of the vector of the alignment error to be eliminated, the non-linear component may be emphasized, and the sample shot to be eliminated may be wrong.

Next, in the method of performing the EGA calculation to correct the linear component and comparing the absolute value of the obtained nonlinear component with a predetermined reference value as in the case of The chance of making a mistake is significantly reduced. However, the linear component calculated by the method is
Since it is calculated using the coordinate values of the jump shot that should be excluded originally, it is considered that an accurate linear component is not obtained. Therefore, the absolute value of the non-linear component of the alignment error finally obtained (corresponding to the distribution in FIG. 11B) becomes inaccurate, and, for example, in the vicinity of a predetermined reference value, a sample shot to be excluded is mistaken. There is a fear.

Further, even when the exclusion reference value is statistically changed based on the standard deviation of the absolute value of the alignment error as described above, since the linear component is not subtracted, the same as in the case of There is a case that the sample shot to be excluded is wrong. Further, it is possible to combine the method of with the method of, but since the alignment error of the sample shot to be excluded is included as the basis of the calculation, the sample to be excluded in the vicinity of the reference value is still included. It is the same as the method that there is a risk of making a mistake in the shot.

In view of such a point, the present invention finds a conversion parameter by statistical processing based on the result obtained by actually measuring the position of the sample shot on the wafer to be processed in advance, and calculates this conversion parameter. In the alignment method in which each shot area on the wafer is aligned based on the calculated array coordinates (virtual coordinate system) calculated by using the jump shot that has a large non-linear component of the alignment error in the sample shot, The purpose is to eliminate and align with high accuracy.

[0022]

The alignment method according to the present invention is, for example, as shown in FIGS. 1 and 4 to 6, a first coordinate system (x, y) set on a substrate (8). Predetermined processing within the second coordinate system (X, Y) that defines the movement position of each of the plurality of processed regions (ES _i ) arranged on the substrate based on the above arrangement coordinates. In the method of aligning with respect to a position, a plurality of N (N is an integer of 4 or more) sample areas (SA ₁ , SA ₂ , ...) Of a plurality of preprocessed areas (ES _i ) are selected. First step (step 101) of measuring the coordinate position on the second coordinate system (X, Y)
And (N-1) coordinate position data excluding the L-th (L is an integer from 1 to N) sample region from the coordinate position data of those N sample regions measured in the first step. Is calculated to obtain a virtual coordinate conversion formula (conversion conversion matrix of (Equation 1)), and the virtual coordinate conversion formula and the design position of the Lth sample area The virtual position of the sample area is calculated, the virtual position thus calculated is compared with the coordinate position data of the L-th sample area measured in the first step, and the shift amount E (L) is stored. The second process (steps 102 to 107) in which the process is repeated N times while changing the value of L each time.
And.

Furthermore, the present invention provides N pieces obtained in the second step.
Deviation E (L) and a predetermined allowable value E ₀And compare respectively
And the third step (step 109)
Of these N shift amounts N (L), the Q-th (where Q is from 1 to N)
Is the predetermined tolerance E₀Greater than
If the Qth sample area was eliminated and left
(N-1) coordinate position data obtained by statistical processing
From the virtual coordinate conversion formula of
Coordinates on the second coordinate system (X, Y) of each work area
The position is calculated, and in the third step, those N deviation amounts are calculated.
All of the specified tolerance E₀N if they are
Obtained by statistically processing the coordinate position data of each sample area
From the virtual coordinate conversion formula,
Coordinates on the second coordinate system (X, Y) of each work area
Fourth step of calculating the position (steps 110 to 113)
And ,.

In this case, in the third step, when there are a plurality of N deviation amounts E (L) larger than the predetermined allowable value E _0, among these deviation amounts E (L). It is desirable to exclude one or a plurality of sample areas corresponding to the displacement amount from the largest to the predetermined limit exclusion number in the fourth step. In addition, in the fourth step, when the Q-th sample area is excluded, the number of the sample areas left in the fourth step is within the predetermined allowable number or more,
You may make it repeat the 2nd process to the 4th process about the sample area | region left in a process.

An example of the predetermined allowable value E ₀ to be compared in the third step is the second of these sample areas.
Is a value that exceeds the variation in the measurement value of the coordinate position on the coordinate system (X, Y).

[0026]

According to the present invention, N sample areas (sample shots SA ₁ and SA) selected on the substrate (8) are selected.
The coordinate position of the second coordinate system (stage coordinate system (X, Y)) of ( ₂ , ...) Is measured. After that, from these N sample areas, the L-th (where L changes from 1 to N) sample area that may be a jump shot is removed (N−
1) Statistical processing is performed on the coordinate position data measured for the sample areas.

Specifically, for example, when the EGA method is applied, the measured coordinate position data and the designed arrangement coordinates are used to perform the least squares method from the first coordinate system (x, y). Six conversion parameters a to f of (Equation 1) indicating a virtual coordinate conversion formula to the second coordinate system (X, Y).
To decide. This (Equation 1) corresponds to the linear coordinate conversion equation in which the variation of the nonlinear component is removed from the coordinate position data. The conversion parameters a to f determined in this way
The calculated array coordinate obtained by substituting the designed array coordinate into (Equation 1) using is the virtual position from which the variation of the nonlinear component is removed.

Next, by substituting the designed array coordinates of the removed L-th sample area into the (Equation 1), the virtual position of the L-th sample area (calculated array coordinates) is obtained. The amount of deviation E (L) between the virtual position and the coordinate position data measured in the first step is calculated. At this time, if the measured value of the L-th sample area has the same tendency as the measured value of the other sample areas, the value of the deviation amount E (L) should be small, but conversely If the amount E (L) is larger than the predetermined allowable value E ₀ , the L-th sample area is highly likely to be a jump shot. Therefore, jump shots are eliminated using this criterion.

Assuming that the L-th sample area is a jump shot, when a virtual coordinate conversion formula such as (Equation 1) is obtained from (N-1) coordinate position data, a jump shot is used. Since the measurement result of the L-th sample area is not included, its coordinate conversion formula is accurately determined. Therefore, by using the displacement amount E (L) of the coordinate position obtained from the virtual coordinate conversion formula as the determination reference, the jump shot can be accurately excluded, and
With the virtual coordinate conversion formula, the actual positions of almost all the processed regions (excluding jump shots) on the substrate (8) are accurately calculated, and the alignment accuracy is improved.

When the jump shots are eliminated in the third step and the fourth step, if there are a plurality of absolute values of the difference value E (L) larger than the allowable value E ₀ , a plurality of them are obtained. The sample area of may be excluded as a jump shot. Furthermore, for the remaining sample area, the first
By repeating the elimination operation of the process to the fourth process,
It is also possible to eliminate jump shots. In this case, if the number of remaining sample areas is too small, it becomes difficult to obtain the averaging effect in the subsequent statistical processing. Therefore, the lower limit (predetermined allowable number) of the number of remaining sample areas or the removal is eliminated. The averaging effect can be maintained by setting the upper limit (limit exclusion number) of the number of sample areas in advance. .

Further, a predetermined permissible value E ₀ to be compared with the deviation amount E (L) is an alignment system for measuring the coordinate position of these sample areas on the second coordinate system (X, Y). Measurement error and the positioning error of the stage for positioning the substrate (8) at that time, that is, when the value exceeds the dispersion of the measurement values of each sample area, the measurement coordinates are displaced due to the dispersion of the measurement values. It is not necessary to mistakenly judge a sample area as a jump shot.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the alignment method according to the present invention will be described below with reference to the drawings. In this example, the present invention is applied to the alignment operation of an exposure apparatus (stepper) that exposes a pattern of a reticle to each shot area on a wafer as a photosensitive substrate by a step-and-repeat method. However, the present invention can also be applied to an exposure apparatus of a scanning exposure system such as a step-and-scan system.

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 the reticle stage 3, and the reticle stage 3 is configured to be movable and micro-rotatable within a two-dimensional plane on the reticle 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 driving device 5 on the reticle 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. Projection optical system 7
The Z axis is taken parallel to the optical axis of, and the Cartesian coordinate system of the two-dimensional plane perpendicular to the Z axis is defined as the X axis and the Y axis. Wafer stage 10
Is an XY stage for two-dimensionally positioning the wafer 8 in a plane perpendicular to the optical axis of the projection optical system 7, a Z stage for positioning the wafer 8 in the Z direction parallel to the optical axis of the projection optical system 7,
And a θ stage for rotating the wafer 8 minutely.

A movable mirror 11 is fixed on the upper surface of the wafer stage 10, and the laser interferometer 1 is arranged so as to face the movable mirror 11.
2 are arranged. Although shown in a simplified manner in FIG. 2, the movable mirror 11 is composed of a plane mirror having a reflection surface perpendicular to the X axis and a plane mirror having a reflection surface perpendicular to the Y axis. Further, the laser interferometer 12 has the movable mirror 1 along the X axis.
1. One X-axis laser interferometer that irradiates a laser beam to 1 and a Y-axis laser interferometer that irradiates 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 measured by this laser interferometer and one laser interferometer for the Y axis. The coordinate system (X, Y) composed of the X coordinate and the Y coordinate thus measured is hereinafter referred to as a stage coordinate system or a stationary coordinate system (corresponding to the "second coordinate system" of the present invention).

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. Information on the X coordinate, the Y coordinate, and the rotation angle measured by the laser interferometer 12 is used as the coordinate measuring circuit 12a and the main control system 6.
The main control system 6 controls the positioning operation of the wafer stage 10 via the driving device 13 while monitoring the supplied coordinates. Although not shown in FIG. 2, the reticle side is also provided with a triaxial interferometer system similar to 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 type image processing type 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 collimated by a collimator lens 17 and a beam splitter 18. 8 via the mirror 19, the objective lens 20
Upper X-axis wafer mark (alignment mark) Mx
Is irradiated in the vicinity of. In this case, the alignment system 1
The baseline amount, which is the distance between the reference point of the detection area 5 and the reference point of the exposure area of the projection optical system 7, is measured in advance. Then, the reflected light from the wafer mark Mx is irradiated onto the index plate 22 via the objective lens 20, the mirror 19, the beam splitter 18 and the condenser lens 21, and the image of the wafer mark Mx is formed on the index plate 22. To be done.

The light transmitted through the index plate 22 goes through the first relay lens 23 toward the beam splitter 24, and the light transmitted through the beam splitter 24 passes through the second relay lens 25X for the X axis and is transmitted from the two-dimensional CCD. The light collected on the image pickup surface of the X-axis image pickup device 26X and reflected by the beam splitter 24 passes through the Y-axis second relay lens 25Y and is formed of a two-dimensional CCD. The light is focused on the imaging surface of 26Y. Image sensor 26X and 2
An image of the wafer mark Mx and an image of the index mark on the index plate 22 are formed in an overlapping manner on the image pickup surface of 6Y. The image pickup signals of the image pickup devices 26X and 26Y are both supplied to the coordinate measuring circuit 12a.

FIG. 3 shows the pattern on the index plate 22 shown in FIG. 2. In FIG. 3, an image MxP of the wafer mark Mx consisting of three linear patterns is formed in the central portion, and the image MxP is formed in the pitch direction. 2 and the YP direction which is the longitudinal direction of the image MxP correspond to the X direction and the Y direction of the stage coordinate system of the wafer stage 10 of FIG. 2, respectively. Then, two index marks 31A and 31B are formed so as to sandwich the wafer mark image MxP in the XP direction,
Two index marks 32A and 32B are formed so as to sandwich the wafer mark image MxP in the YP direction.

In this case, the index mark 31A,
31B and a detection area 33X surrounding the wafer mark image MxP
The image inside is picked up by the X-axis image pickup device 26X in FIG.
The image in the detection area 33Y surrounding the images of the index marks 32A and 32B and the wafer mark for the Y axis (not shown, a pattern obtained by rotating the wafer mark Mx for the X axis by 90 °) in the P direction is for the Y axis in FIG. The image is picked up by the image pickup device 26Y. Further, the scanning directions when reading the 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 the image pickup signals of the image pickup devices 26X and 26Y are processed to obtain an X-axis wafer. A displacement amount of the mark image MxP and the index marks 31A and 31B in the XP direction, and Y
The amount of positional deviation in the YP direction between the image of the axis wafer mark and the index marks 32A and 32B can be obtained. Therefore, in FIG. 2, the coordinate measurement circuit 12a determines the wafer mark Mx based on the positional relationship between the image of the wafer mark Mx 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. Stage coordinate system (X,
The X coordinate on Y) is obtained, and the X coordinate thus measured is supplied to the main control system 6. Similarly, the Y coordinate of the wafer mark for the Y axis on the stage coordinate system (X, Y) is also measured and supplied to the main control system 6.

Next, with reference to the flowchart of FIG. 1, the operation of positioning each shot area of the wafer to be exposed in this example and exposing the pattern image of the reticle 2 to each shot area will be described. To do. First, the wafer 8 to be exposed is loaded on the wafer holder 9 shown in FIG. FIG. 4 shows an example of an array of shot areas on the wafer 8. In FIG. 4, the coordinate system (x, y) set on the wafer 8 is set on the wafer 8 (the "first coordinate system of the present invention". Shot area E regularly along with
S ₁ , ES ₂ , ..., ES _M (M is an integer of 4 or more) are formed, and a chip pattern is formed in each shot area ES _i (i = 1 to M) by the steps up to that point.
Further, each shot area ES _i is separated by a street line of a predetermined width in each of the x direction and the y direction, and a wafer mark for the X axis is formed at the center of the street line extending in the x direction in contact with each shot area ES _i. Mx _i is formed, and the Y-axis wafer mark My _i is formed at the center of the street line extending in the y direction in contact with each shot area ES _i .

Wafer mark Mx for X axis_iAnd for the Y axis
Wafer mark My_iAre specified in the x and y directions respectively
It is an array of three straight line patterns at a pitch.
These patterns are patterns of concave or convex parts on the base of the wafer 8.
Are formed as Coordinate system on wafer 8 (x,
wafer mark Mx in y)_iX coordinate x_i(Design seat
Standard value) and wafer mark My_iY coordinate of_i(By design
(Coordinate values of) are known, and the storage unit in the main control system 6 of
Remembered in. In this case, the wafer mark Mx _iX
Coordinates and wafer mark My_iY coordinate of
Hot area ES_iX coordinate and y coordinate of

Further, two wafers 2 for performing rough alignment (global alignment) are formed on the wafer 8.
Dimensional global alignment marks (not shown) are formed, and the coordinate values of these two global alignment marks in the coordinate system (x, y) on the wafer 8 are known. Therefore, the linear expansion / contraction is regarded as isotropic (that is, Rx = Ry holds for the scaling parameters Rx and Ry in the X and Y directions), and the orthogonality error w of the stage coordinate system is regarded as 0, The number of unknown conversion parameters in Equation 1 is set to four, and then the main control system 6 in FIG. 2 causes the stage coordinate system (X) of the two two-dimensional global alignment marks on the wafer 8 via the alignment system 15 (X , Y)
Measure the coordinate values at. Based on this measurement result, the values of the four simplified conversion parameters of (Equation 1) are determined.

Further, N pieces of M shot areas ES ₁ ~ES _M in FIG. 4 in this example (N is M an integer 4 or more)
, SAN are selected, and the coordinate values of these N sample shots in the stage coordinate system (X, Y) are measured in step 101 of FIG. In FIG. 4, the number M of shot areas is 86.
In this case, the number N of sample shots is 10.

In order to perform the measurement, the main control system 6 is
4 conversion parameters obtained by global alignment,
And wafer mark Mx_iDesign x-coordinate and
Hammark My_iSubstituting the design y-coordinates into (Equation 1) sequentially
By doing so, the wafer on the stage coordinate system (X, Y)
Hammark Mx_iInitial value of X coordinate in calculation of wafer and wafer
Mark My_iThe initial value of the calculated Y coordinate is calculated. Well
Wafer mark Mx _iThe initial Y coordinate of the center of
Value and wafer mark My_iOf the calculated X coordinate of the center of
The initial value is also calculated at the same time. These stage coordinate systems (X,
Y) Based on the initial design coordinate values on the wafer
By driving the tage 10, the wafer mark Mx_i
And wafer mark My_iOf the alignment system 15
Drive into the visual field and measure accurate coordinate values.

Next, in step 102, the initial value of the variable L is set to 1, and the steps 103 to 106 are repeated N times. First, in step 103, the design coordinates of (N-1) sample shots obtained by removing the L-th sample shot from the N sample shots,
Based on the measured coordinate values, EGA calculation (or other statistical processing may be performed) is performed so as to minimize the residual error component of (Equation 2), and the six conversion parameters a of (Equation 1) are calculated. Determine the value of ~ f. The coordinate conversion formula of (Equation 1) obtained by substituting the conversion parameters a to f determined in this way corresponds to the virtual coordinate conversion formula of the present invention. The coordinate system obtained by the coordinate conversion formula of (Equation 1) can also be regarded as a linear virtual coordinate system in which nonlinear variations are removed from the measured values.

Next, in step 104, the conversion parameters a to f obtained in step 103 and the design position of the L-th sample shot are substituted into (Equation 1), and the L-th sample shot A virtual position, that is, a calculated array coordinate in the stage coordinate system (X, Y) is obtained. This means that the virtual position of the L-th sample shot is calculated from the virtual coordinate conversion formula calculated in step 103 and the designed position.

Further, in step 105, a deviation amount E (L) between the virtual position of the L-th sample shot and the coordinate position of the L-th sample shot measured in step 101 is obtained. The virtual position is ( _XL ,
Y _L), the measured coordinates (XM _L, when a YM _L), displacement amount E (L) is expressed by the following equation.

[0050]

Equation 3] E (L) = {(X L -XM L) 2 + (Y L -YM L) 2} 1/2 Then, in step 106, if the variable L is equal to N (repeated N times the line If the variable L is smaller than N, 1 is added to the variable L and the process returns to step 103. On the other hand, if the variable L is equal to N in step 106, for all N sample shots,
Since the step of calculating the virtual position by using the virtual coordinate conversion formula in the case of excluding each is performed, the operation proceeds to step 108.

Step 108 includes steps 109 to 1
This is a step for performing initialization for repeating the operations up to 12, in which the value of the number N of sample shots is stored as a variable N ′, and the variable L is initialized to 1. In the following step 109, the deviation amount E (L) calculated in step 105 is compared with a preset allowable value E _{0. If} the deviation amount E (L) is larger than E _{0, the process} proceeds to step 110. Then, the L-th sample shot is regarded as a jump shot and is deleted, and at the same time, the variable N ′ is decremented by one. In step 103 described above, (N-
1) When calculating the virtual coordinate conversion formula from the coordinate position data, since the measurement result of the L-th sample area as the jump shot is not included, the virtual coordinate conversion formula is accurately calculated. Has been. Therefore, the array coordinate in the stage coordinate system (X, Y) of almost all shot areas (excluding jump shots) on the wafer 8 is accurately calculated by this virtual coordinate conversion formula, and the coordinate conversion formula is used. By using the amount of deviation E (L) between the calculated virtual coordinates and the measured coordinates of the L-th sample shot as a criterion, jump shots can be accurately excluded.

In step 111 following step 110, similarly to step 106, it is determined whether or not the repeating operation has been performed N times. When the repetition of N times is completed, the routine proceeds to step 113. On the other hand, step 109
If the deviation amount E (L) is less than or equal to the allowable value E ₀ , the process proceeds to step 111. Then, in step 111,
When the variable L has not reached N, 1 is added to the variable L in step 112, and then the process returns to step 109 to compare the next deviation amount E (L) with the allowable value E ₀ . In this way, the deviation amount E (L) in N sample shots
Those that are larger than the allowable value E ₀ are excluded as jump shots. Therefore, in this example, the number of sample shots excluded as jump shots may be plural.

However, if the number of sample shots left after the jump shots are eliminated is too small, the averaging effect becomes small. Therefore, in order to prevent this, a predetermined upper limit value is set for the number of sample shots eliminated as the jump shots. (Limit exclusion number) may be provided, or a predetermined lower limit (allowable number) may be provided for the number of sample shots left. This will be described later.

Then, in step 113, based on the design coordinates of the N'sample shots left after the jump shots are removed and the measured coordinate values, EG is again determined.
A calculation (or other statistical processing may be performed), and (Equation 1)
The linear and virtual coordinate conversion formula shown in is obtained. And
Using this coordinate conversion formula, the array coordinates of each shot area ES _{i in} the stage coordinate system (X, Y) are obtained, and the wafer stage 10 of FIG. 2 is driven based on this to set the reference point of each shot area ES _i . Are sequentially positioned at the reference points of the exposure area by the projection optical system 7, and the pattern of the reticle 2 is projected and exposed. Then, in step 114, processing such as exposure to the next wafer is performed.

Next, the steps 103 to 105 of FIG. 1 and the step 110 will be described in detail with reference to FIGS. In the following, a case where the number N of sample shots is 10 will be described as an example. FIG. 5 shows ten (N = 10) sample shots SA1 to SA10 measured in step 101. In FIG. 5, the deviation of the measured coordinates from the designed coordinates in each sample shot (alignment error). Are represented by error vectors E1 to E10. Also, of the 10 sample shots, sample shot S
A4 is a jump shot. In this case, in step 103 of FIG. 1, EGA is performed based on 9 measured values obtained by sequentially removing the data of the L-th sample shot from these 10 measured positions and the corresponding 9 designed values.
Calculate. Then, using the obtained six conversion parameters of (Equation 1), the virtual position of the L-th sample shot is obtained in step 104 and compared with the above measured value.

FIG. 6A shows Step 1 when the sample shot SA4 (L = 4) which is a jump shot is removed.
The result of 04 is shown. That is, the EGA calculation is performed on the measurement results of 9 sample shots excluding the sample shot SA4 and the design coordinates to obtain 6 conversion parameters, and the conversion parameters and the design coordinates of the sample shot SA4 are ( Substituting into equation 1) sample shot S
Obtain the virtual coordinates of A4. Then, a vector indicating the deviation between the virtual coordinates thus obtained and the measured coordinates of the sample shot SA4 is shown as an error vector δE ₄ . This error vector δE ₄ consists of an X component and a Y component, and its absolute value (magnitude) | δE ₄ | is {(X component) ² + (Y component) ² } ^1/2 . In step 105, the absolute value | δE ₄ | is calculated, and this is calculated as the shift amount E (4)
Memorize as.

[0057] Then, as shown in FIG. 6 (b), the stored displacement amount E (4) (= | δE 4 |) is compared with the allowable value E ₀ at step 109, the deviation amount than the allowable value E ₀ If E (4) is large, the sample shot SA4 is deleted from the sample shot as a jump shot. Note that FIG. 6 (a)
For the sample shots other than the sample shot SA4 (L = 4), the error vectors E1, E2 and the deviations between the respective virtual positions calculated on the basis of the coordinate data of the nine sample shots and the measurement position are included. , But the error vectors E1, E2, ... In FIG. 6 (a) are different from the error vectors E1, E2 ,. Further, in the case of FIG. 6A, it is determined whether the sample shot SA4 is a jump shot by the shift amount |
Since only δE ₄ | is used, other error vectors E1,
It is not always necessary to obtain this for E2, ....

Next, in FIG. 7A, in step 103, a sample shot SA3 (L =
With the exception of 3), the error vector δE ₃ indicating the deviation between the virtual coordinates of the sample shot SA3 obtained from steps 104 and 105 and the measured coordinates is plotted.
As shown in FIG. 7B, since the absolute value of the error vector | δE ₃ | (deviation amount E (3)) at this time is smaller than the allowable value E ₀ , the sample shot SA3 is not judged to be a jump shot. , It is not deleted in step 110. This is another sample shot SAL (L = 1, 2, 5,
6, 7, 8, 9, 10) is exactly the same.

However, at this time, the sample shot SA3
The adjacent sample shot SA4 is a jump shot
Therefore, under the influence of it (determined by EGA calculation
Absolute value of error vector |
δE₃| Is the tolerance E₀It is a large value close to. So
Absolute value | δE₃| Is the tolerance E₀Smaller than
Sample Shot SA₃Misidentify as a jump shot
However, in order to prevent misidentification even more reliably,
Sample shot near the sample shot SA3 (Fig.
For sample shots SA2 and SA4 in 7 (a),
However, the absolute value of the error vector | δE₂'|, | Δ
E_FourAsk for '| And the absolute value | δE ₂'|, | ΔE_Four'
| Is above a certain level, for example E₀When / 2 or more
Is the absolute value | δE₃Is the allowable value E₀Larger sump
Leshot SA₃Do not judge as a jump shot
May be.

The allowable value E₀Is the projection exposure equipment used
Wafer stage 10 stage stop accuracy (stepping
Accuracy) and the detection accuracy of the alignment system 15 used
Determined by the synthesis accuracy of. For example, the stage accuracy is σ value
(Standard deviation) is α, and the detection accuracy of the sensor is the σ value
If β is, then the allowable value E is obtained by using a predetermined coefficient γ. ₀
Should be set as follows. The coefficient γ is, for example,
It is a real number greater than 1.

[0061]

## EQU4 ## E ₀ = γ (α ² + β ³ ) ^{1/2 In} the above example, the number N of sample shots is 10
However, the value of N is not limited to this, and N may be a natural number of 4 or more. In addition, as described above, if the number of sample shots deleted in step 110 is too large, the averaging effect is insufficient, and the data of N ′ sample shots remaining is used in step 1
There is a possibility that the accuracy of the EGA calculation performed in 13 may deteriorate.
For this reason, an upper limit (limit exclusion number) may be set for the number of sample shots to be deleted in step 110 so that a larger number of sample shots than that number may not be deleted. Of course, the upper limit of the number of sample shots to be deleted is not set, but the lower limit N'of the number of sample shots to be left.
_This is exactly the same even if the _Lim (allowable number) is set. Generally, the EGA calculation cannot be performed unless there are three or more sample shots. Therefore, the lower limit of the number of remaining sample shots N ′ is 3, but in order to obtain a certain averaging effect, the lower limit N ' _{Set Lim} to around 6, for example. Of course, this value is not limited to 6.

In this case, it is necessary to prevent the value of the number N ′ from falling below the lower limit N ′ _Lim when deleting the sample shot in step 110. Therefore, for example, the processing in steps 109 and 110 is made different from that in FIG. 1, and in step 109, the value of the variable L such that E (L)> E ₀ and the magnitude of the deviation amount E (L) are stored, At the stage when step 109 is completed for all variables L, for each variable L for which E (L)> E ₀ , only a maximum of (NN ′ _Lim ) samples in descending order of displacement amount E (L) The shot should be deleted as a jump shot.

Prior to step 113 in FIG. 1, the number N ′ of remaining sample shots is set to N, the process proceeds to step 102 again, and the series of processes from step 103 to 112 is performed. Good. That is, the jump shot deleting operation in steps 102 to 112 can be performed in two steps. Here, in order to compare the above-described embodiment with the conventional technique, the result of applying the method of the conventional technique to the sample shot of the array of FIG. 5 is shown in FIG.
Shown in The method of the prior art is shown in FIG.
EGA calculation is performed using all the measurement coordinates of the sample shots SA1 to SA10 at 0 points, and the virtual position of each sample shot is obtained from the conversion parameters and design coordinates obtained thereby, and these virtual positions are measured. The error vector indicating the deviation from the coordinate is calculated. The error vector thus obtained for each of the sample shots SA1 to SA10 is exaggerated by an arrow in the sample shots SA1 to SA10 of FIG. Specifically, the error vectors obtained for the sample shots SA3 and SA4 are the vectors δE ₃ ′ and δE ₄ ′, but the vector δE
_The size of 3'and δE ₄ 'is almost the same. Therefore, the jump shot is the sample shot SA4 as described above, but it is difficult to accurately determine whether the jump shot is the sample shot SA3 or the sample shot SA4 from the result of FIG. I understand.

In the above embodiment, the positions of the X-axis wafer mark and the Y-axis wafer mark are measured in each sample shot SA1, SA2, ... As shown in FIG. It is not always necessary to measure the positions of the X-axis wafer mark and the Y-axis wafer mark in the shot. For example, by doubling the number of sample shots, odd-numbered sample shots SA1,
At SA3, ..., Only the X-axis wafer mark is measured, and even-numbered sample shots SA2, SA4 ,.
In the above, only the wafer mark for the Y axis may be measured. In this case, E
The virtual position of the excluded wafer mark is obtained by the coordinate conversion formula obtained by performing the GA calculation, and the wafer mark having a large amount of deviation between the virtual position and the designed position may be eliminated as the jump mark.

In the above embodiment, the EGA calculation that minimizes (Equation 2) is used. However, for each sample shot, a weight is given according to the distance from the center of the wafer, and Instead, the present invention can be applied to the case where a weighted EGA method is used in which a residual error component is defined by weighted addition using the weights and a conversion parameter is determined so that this residual error component is minimized.

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.

[0067]

According to the alignment method of the present invention, the first N sample areas (sample shots) selected.
From the L-th sample area, virtual coordinate conversion formulas are calculated for each of the (N-1) sample regions, and the L-th virtual position is calculated based on this coordinate conversion formula. When the deviation amount from the measured coordinate position exceeds a predetermined allowable value, the jump shot is excluded. At this time, since data for jumping shots is not included in the data when the coordinate conversion formula is obtained, there is an advantage that jumping shots can be accurately excluded and alignment can be performed with high accuracy.

Further, in the third step, when there are a plurality of deviation amounts larger than the predetermined allowable value among the N deviation amounts, the predetermined maximum number of exclusions in order from the largest deviation amount among the plural deviation amounts. If one or more sample areas corresponding to the shift amount up to are excluded in the fourth step, even if there are a plurality of jump shots, the jump shots can be accurately and within a range not exceeding the limit exclusion number, and There is an advantage that it can be eliminated quickly.

Further, in the fourth step, when the Q-th sample area is excluded, the number of sample areas left in the fourth step is within a predetermined allowable number or more. Even when the second to fourth steps are repeated for the remaining sample area,
There is an advantage that a plurality of jump shots can be accurately excluded.

If the predetermined allowable value to be compared in the third step exceeds the variation in the coordinate position measurement values of the sample areas on the second coordinate system, the measurement value is If there are variations, it will no longer be mistaken for a jump shot.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing a projection exposure apparatus to which the exposure method of FIG. 1 is applied.

3 is an enlarged view showing an example of an image on an index plate of an off-axis type alignment system 15 in FIG.

FIG. 4 is a plan view showing an example of an array of sample shots on a wafer 8 to be exposed in an example.

FIG. 5 is a plan view showing an example of an array of sample shots including 10 jump shots and an alignment error.

6 is the same as FIG. 1 except that sample shot SA4 is omitted.
FIG. 10 is a diagram showing the amount of deviation between the virtual position of the sample shot SA4 and the measured position and the linear component of the alignment error of other sample shots, which is obtained by executing the process of step 104 of FIG.

FIG. 7 is a diagram of FIG. 1 except for sample shot SA3.
FIG. 8 is a diagram showing the amount of deviation between the virtual position of the sample shot SA3 and the measured position and the linear component of the alignment error of another sample shot, which is obtained by executing the process of step 104 of FIG.

8 is a plan view showing a deviation between a virtual position and a measurement position obtained by applying a conventional technique to the sample shot of FIG.

FIG. 9 is an explanatory diagram of an example of a conventional jump shot elimination method.

FIG. 10 is a diagram showing an alignment error of a sample shot on a wafer to which another example of the conventional jump shot elimination method is applied.

11 is an explanatory diagram when another example of the conventional jump shot elimination method is applied to the wafer of FIG.

[Explanation of symbols]

1 illumination optical system 2 reticle 6 main control system 7 projection optical system 8 wafer 9 wafer holder 10 the wafer stage 15 off-axis type of alignment system 22 index plate 26X, 26Y imaging element ES ₁ ~ES _M shot areas SA1~SA10 sample shots Mx _i X-axis wafer mark My _i Y-axis wafer mark

Claims (4)

[Claims] 1. A second area defining a moving position of the substrate, wherein each of a plurality of processed regions arrayed on the substrate based on array coordinates on a first coordinate system set on the substrate defines a moving position of the substrate. In a method of aligning with a predetermined processing position in a coordinate system, a preselected N (N
Is an integer greater than or equal to 4); a first step of measuring the coordinate position of the sample area on the second coordinate system; and L from the coordinate position data of the N sample areas measured in the first step. The (N-1) coordinate position data excluding the sample region (L is an integer from 1 to N) is statistically processed to obtain a virtual coordinate conversion formula, and the virtual coordinate conversion formula and the virtual coordinate conversion formula A virtual position of the L-th sample area is calculated from the design position of the L-th sample area, and the calculated virtual position and coordinate position data of the L-th sample area measured in the first step. And a process of storing the deviation amount, and repeating the process N times while changing the value of L each time; and the N deviation amounts obtained in the second step and a predetermined allowable value. And a third step of comparing each of the above; and the N deviation amounts in the third step. The Q-th (Q is an integer from 1 to N) shift amount of, if greater than said predetermined tolerance,
The Q-th sample area was excluded and left (N-
1) The coordinate position on the second coordinate system of each of the plurality of processed regions on the substrate, based on the virtual coordinate conversion formula obtained by statistically processing the coordinate position data of the sample areas. And in the third step, when all the N shift amounts are equal to or less than the predetermined allowable value, the virtual coordinate obtained by statistically processing the coordinate position data of the N sample areas. A fourth step of calculating a coordinate position on the second coordinate system of each of the plurality of processed regions on the substrate from a conversion formula; and the alignment method. 2. In the third step, when there are a plurality of displacement amounts larger than the predetermined allowable value among the N displacement amounts, a predetermined displacement is determined in order from the largest displacement amount among the displacement amounts. 2. The alignment method according to claim 1, wherein one or a plurality of sample areas corresponding to the shift amount up to the limit exclusion number are excluded in the fourth step. 3. In the fourth step, when the Q-th sample area is excluded, the number of sample areas remaining in the fourth step is equal to or more than a predetermined allowable number, and The alignment method according to claim 1 or 2, wherein the steps from the second step to the fourth step are repeated for the sample region left in the four steps. 4. The predetermined allowable value to be compared in the third step is a value that exceeds a variation in measured values of coordinate positions of the sample area on the second coordinate system. The alignment method according to claim 1, 2 or 3.